A 1200 micron MAMBO Survey of ELAIS N2 and the Lockman Hole I. Maps, sources and number cou
a r X i v :a s t r o -p h /0405361v 1 18 M a y 2004
Mon.Not.R.Astron.Soc.000,000–000(0000)Printed 2February 2008
(MN L A T E X style ?le v2.2)
A 1200μm MAMBO survey of ELAIS N2and the Lockman Hole:I.
Maps,sources and number counts
T.R.Greve 1,R.J.Ivison 1,2,F.Bertoldi 3,J.A.Stevens 2,J.S.Dunlop 1,D.Lutz 4&C.L.Carilli 5
1Institute for Astronomy,University of Edinburgh,Blackford Hill,Edinburgh EH93HJ,UK 2Astronomy Technology Centre,Royal Observatory,Blackford Hill,Edinburgh EH93HJ,UK 3Max-Planck-Institut f¨u r Radioastronomie(MPIfR),Auf dem H¨u gel 69,53121Bonn,Germany 4Max-Planck-Institut f¨u r extraterrestrische Physik,Postfach 1312,85741,Garching,Germany 5
National Radio Astronomy Observatory,P .O.Box O,Socorro,NM 87801,USA
2February 2008
ABSTRACT
We present a deep,new 1200μm survey of the ELAIS N2and Lockman Hole ?elds using the Max Planck Millimeter Bolometer array (MAMBO).The areas surveyed are 160arcmin 2in ELAIS N2and 197arcmin 2in the Lockman Hole,covering the entire SCUBA ‘8mJy Sur-vey’.In total,27(44)sources have been detected at a signi?cance ≥4.0σ(≥3.5σ).The pri-mary goals of the survey were to investigate the reliability of (sub)millimetre galaxy (SMG)samples,to analyse SMGs using ?ux ratios sensitive to redshift at z >3,and to search for ‘SCUBA drop-outs’,i.e.galaxies at z >>3.We present the 1200μm number counts and ?nd evidence of a fall at bright ?ux levels.Employing parametric models for the evolution of the local 60μm IRAS luminosity function (LF),we are able to account simultaneously for the 1200and 850μm counts,suggesting that the MAMBO and SCUBA sources trace the same underlying population of high-redshift,dust-enshrouded galaxies.From a nearest-neighbour clustering analysis we ?nd tentative evidence that the most signi?cant MAMBO sources come in pairs,typically separated by ～23′′.Our MAMBO observations unambiguously con?rm around half of the SCUBA sources.In a robust sub-sample of 13SMGs detected by both MAMBO and SCUBA at a signi?cance ≥3.5σ,only one has no radio counterpart.Further-more,the distribution of 850/1200μm ?ux density ratios for this sub-sample is consistent with the spectroscopic redshift distribution of radio-detected SMGs (Chapman et al.2003).Finally,we have searched for evidence of a high-redshift tail of SMGs amongst the 18MAMBO sources which are not detected by SCUBA.While we cannot rule out that some of them are SCUBA drop-outs at z >>3,their overall 850-to-1200μm ?ux distribution is statistically indistinguishable from that of the 13SMGS which were robustly identi?ed by both MAMBO and SCUBA.
Key words:cosmology:early Universe –cosmology:observations –galaxies:evolution –galaxies:formation –galaxies:starburst
1INTRODUCTION
In a time of ‘high-precision cosmology’one of the fundamental questions about which we remain largely ignorant is the forma-tion and evolution of galaxies and clusters of galaxies.One of the most important breakthroughs in this ?eld was the discovery of a signi?cant population of far-IR-luminous,high-redshift sources in surveys at submillimetre (submm)and millimetre (mm)wave-lengths using SCUBA and MAMBO (Smail,Ivison &Blain 1997;Hughes et al.1998;Barger et al.1999;Eales et al.2000;Bertoldi et al.2000),resolving at least half of the far-IR/submm background detected by the DIRBE and FIRAS experiments (e.g.Hauser et al.1998).
It is widely believed that the large far-IR luminosities (>～10
12
L ⊙)of these sources is caused by intense UV light from starbursts and/or active galactic nuclei (AGN)being absorbed
by dust and re-radiated longwards of 100μm .The negative k -correction at λ≥400μm allows submm/mm observations to select
star-forming galaxies at z >1in an almost distance-independent manner,providing an ef?cient method of ?nding obscured,star-forming galaxies at 1 The large star-formation rates (～1000M ⊙yr ?1)found for (sub)mm galaxies (hereafter SMGs)are suf?cient to construct a gi-ant elliptical (～1011M ⊙)in less than a Gyr,providing that the starburst is continuously fueled.This has led people to speculate that SMGs could be the progenitors of such galaxies (e.g.Dunlop 2001),a scenario which is further strengthened by the fact that the co-moving number density of SMGs appears to be consistent with that of today’s massive ellipticals (Scott et al.2002;Dunne,Eales &Edmunds 2003).However,the nature of SMGs,and in particu-lar their relationship with possible present-day counterparts,is not c 0000RAS 2Greve et al. known,just as their relation to other high-redshift populations such as Lyman-break galaxies(LBGs)and extremely red objects(EROs) is not well understood. Progress has been hampered by the large positional uncertain-ties of the SMGs.The relatively large beams of(sub)mm telescopes (11–14′′,FWHM)makes it impossible to reliably tie an SMG to an optical or near-IR counterpart,unless additional data at a com-plementary wavelength are available.Since a characteristic feature of both starburst galaxies and AGN is radio emission,deep radio imaging has proven to be a highly ef?cient way of accurately iden-tifying optical/near-IR counterparts to SMGs(Ivison et al.1998, 2000,2002;Smail et al.2000). Use of the radio-to-submm spectral index as an redshift indi-cator(Hughes et al.1998;Carilli&Yun1999,2000)has shown that the SMGs lie at high redshift,with an estimated median red-shift of≥2(Ivison et al.2002).Recently,Chapman et al.(2003, 2004)have obtained spectroscopic redshifts for～90SMGs and found they span0.8 In a very deep radio survey of the Lockman Hole and ELAIS N2?elds,Ivison et al.(2002)found that about one third of SMGs did not have radio counterparts.One plausible explana-tion was that some of these radio-blank SMGs lie at very high red-shifts.Such a population of SMGs—the so-called‘high-redshift tail’—would ask dif?cult questions of popular hierarchical mod-els.The high-redshift SMGs would have low S850μm/S1200μm?ux ratios(see Eales et al.2003)and would be readily detectable with MAMBO. Blain,Barnard&Chapman(2003),amongst others,have pointed out the limitations of photometric redshift techniques:the redshift is degenerate with the far-IR luminosity as parametrised by the dust temperature,T d.In principle,however,a comparison be-tween the850,1200μm and1.4-GHz?ux densities allows us,in some cases at least,to break this degeneracy,assuming that SMGs follow the radio/far-IR correlation.For example,an SMG which has a’warm’S850μm/S1200μm ratio but has no radio counterpart is likely to be at high redshift.The S850μm/S1200μm redshift es-timator is particular sensitive at z>3and is currently the most effective way to assess whether there is a signi?cant high-redshift tail of SMGs. The primary advantage of a mapping survey,rather than pointed photometry(on–off)observations of known sources (e.g.Eales et al.2003),is that one obtains an unbiased view of the sky.Data are not skewed by the choice of targets,by possible errors in coordinates,or by potentially spurious assumptions about how the sky is expected to appear.A key goal of our new survey was to determine unbiased?ux densities for the radio-blank SCUBA sources using MAMBO,and to search for new populations of mm-bright sources,in particular a sign of a dusty,star-forming z>>5 population—‘SCUBA drop-outs’—that would be expected to be below the typical SCUBA detection threshold at850μm but de-tectable by MAMBO at1200μm. In this paper we present a new,unbiased1200μm survey, using MAMBO on the IRAM30m telescope,of the Lockman Hole and ELAIS N2,the two regions observed by the SCUBA 8mJy survey(Scott et al.2002;Fox et al.2002).A plethora of multi-wavelength observations exist for both?elds,including very deep X-ray,optical,near-IR,mid-IR and radio imaging(Hasinger et al.2001;Manners et al.2002;Ivison et al.2002;Almaini et al.2002).Our observations,data reduction and maps are described in§2and3.The source extraction technique and the source cata-logues for each?eld are presented in§4,as are the results of Monte Carlo simulations to assess completeness,positional accuracy,?ux boosting,etc.In§5and6we present our measurements of the source counts and the clustering properties of MAMBO sources. Finally,§7describes our joint analysis of the850and1200μm sam-ples,and implications for ongoing(sub)mm surveys and for the redshift distribution of SMGs. Throughout,we have adopted a?at cosmology,with?m= 0.3,?Λ=0.7and H0=70km s?1Mpc?1. 2OBSERV ATIONS The survey was carried out with the37-and117-channel MPIfR Max Planck Millimeter Bolometer arrays(MAMBO-I and MAMBO-II;Kreysa et al.1998)at the IRAM30m telescope on Pico Veleta near Granada in Spain.Both MAMBO-I and MAMBO-II are He3-cooled arrays operating at an effective frequency of 250GHz or1200μm with a half-power spectral bandwidth of 80GHz.At1200μm,the30m telescope has an effective beam of 10.7′′(FWHM).The arrays are background limited and the perfor-mance of the array routinely gives noise equivalent?ux densities (NEFDs)of30–45mJy Hz?1/2.The bolometer feedhorns are ar-ranged in a compact hexagonal pattern each with a diameter of2Fλwhich ensures an optimal coupling to the incoming radiation from a point source.MAMBO-II is amongst the largest(sub)mm bolome-ter arrays currently in use.In combination with the IRAM30m dish which has a surface accuracy of75μm rms,it is the most powerful tool for large blank-?eld surveys at(sub)mm wavelengths,and will remain so until the advent of APEX/LABOCA,JCMT/SCUBA2 and LMT/Bolocam. Scan-mapping along the azimuthal direction is the only method available at the30m to map large areas of the sky.The signal from the sky is modulated by the secondary mirror(the wobbler)which is wobbling in the the scan direction(azimuth). The wobbler frequency is2Hz which re?ects a compromise be-tween wanting to eliminate changes in the atmosphere on as short a timescale as possible and the challenges involved in moving a 2m secondary at this frequency and keeping it mechanically sta-ble.We used a standard on-the-?y MAMBO scan-map,typically 300′′×320′′in size,scanned at a velocity of5′′s?1,and with an elevation spacing between each subscan of8′′.Hence,a map con-sists of41subscans of60s each.This results in a fully-sampled map over a300′′×320′′region in～43min(this includes～3s of overhead per subscan).In order to obtain uniform coverage,a reg-ular grid with a grid-spacing of2′was de?ned across each of the two?elds.Each grid position was observed once which in prac-tice means that,in the?nal map,each point on the sky has been observed at least two times.In principle,this ensures that an rms of～0.8mJy beam?1is reached across most of the?eld.In prac-tice,however,scans were taken in slightly different weather condi-tions which means that the noise is not entirely uniform.In order to eliminate any possible systematics and any residual effects from the double beam pro?le,wobbler throws in the range36′′?45′′were used.Furthermore,maps were taken with different scan-directions, just as care was taken to map each grid position once while the ?eld was rising and once while it was setting.All this served the purpose of minimising any systematic effects from the atmosphere and/or instrument which may otherwise had arisen from observ-ing the same grid-position in two consecutive maps using identical wobbler-and scan-con?guration. c 0000RAS,MNRAS000,000–000 A1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 3 Figure1.The MAMBO survey regions(outlined in black)of the ELAIS N2and Lockman Hole?elds.The mapped areas are160and197sq.arcmin in ELAIS N2and Lockman Hole,respectively.For comparison,the coverage of the SCUBA UK8mJy Survey(Scott et al.2002)is also shown(grey curve).The boxes are21′.7×21′.7. The two?elds were only observed when above30o and below 70o in elevation.The latter constraint,which avoids distorted scan-maps,was particularly troublesome for the ELAIS N2?eld which reaches a maximum elevation of85o at Pico Veleta. Since observations were pooled,they were done only under good weather conditions,i.e.when the atmospheric zenith opacity at1200μm was less than0.3,with low sky-background variations. After each map,i.e.every hour,the telescope was pointed and fo-cused.The opacity of the atmosphere was measured every other hour by doing a skydip but was also continuously monitored with a radiometer located next to the telescope.Variations in the sky-background were monitored from the pointings by on-line mea-surements of the correlation of the horns across the array.Also quick on-offs of the pointing sources were done throughout the night in order to check the sky noise and calibration.In order to tie down the absolute?ux calibration,primary?ux calibrators(in-cluding planets when available)were observed at the beginning and end of each run,and resulted in an absolute?ux calibration of better than20per cent. In total,34scan-maps,corresponding to26hrs,went into the ?nal map of ELAIS N2,all of which were obtained with MAMBO-II as part of the pooled observing mode during the winter period of the2001-2002and2002-2003seasons.The bulk of the obser-vations of the Lockman Hole were also obtained during that time using MAMBO-II,although,early observations of the Lockman Hole during the winter of2000–01,and to some extent also2001–02,were obtained with the37-channel MAMBO-I array.For the Lockman Hole,19and51scan-maps taken with MAMBO-I and MAMBO-II,respectively,were used for the?nal map,equivalent to a total integration time of53hr. The areas surveyed were160arcmin2in the ELAIS N2?eld and197arcmin2in the Lockman Hole.In the case of ELAIS N2 the MAMBO observations were designed to cover the region ob-served at850μm as part of the SCUBA UK8mJy Survey(Scott et al.2002).The small fraction of the SCUBA map which is not covered by our observations(Fig.1)is also the most noisy,and no 850μm sources were detected in that region.However,in the Lock-man Hole the overlap between MAMBO and SCUBA observations is complete,as is seen from Fig.1.The Lockman Hole MAMBO data presented in this paper are part of the larger area MAMBO Deep Field Survey(Bertoldi et al.2000;Dannerbauer et al.2002; Bertoldi et al.2004,in prep.).In addition,the Lockman Hole is being targeted by SCUBA as part of the SCUBA Half Degree Ex-tragalactic Survey(SHADES—https://www.wendangku.net/doc/087746564.html,/ifa/shades/), and the data presented here constitute only a small part of the area surveyed at(sub)mm wavelengths in that part of the sky. 3DATA REDUCTION The data were reduced using the MOPSI software package(Zylka 1998).Bolometers which were either dead or very noisy were ?agged from the data reduction,and the remaining data streams were de-spiked,?at-?elded and corrected for atmospheric opacity. Since all bolometers look through the same region of the at-mosphere at any given time,there will be a correlated signal across the array which will have to be removed in order to recover the (uncorrelated)astronomical signal.In MOPSI the removal of this correlated sky background is done in an iterative way.For each bolometer an inner and outer radius from the channel is speci?ed, and the correlation with every bolometer lying within this annulus is computed.In our case,we chose an inner and outer radius of1′′and60′′,respectively,which is suitable for compact weak sources. The correlated signals of the surrounding6channels with the best correlation were then chosen and the average correlated noise sub-tracted from the bolometer in question.This procedure is then re-peated until the sky background has been removed satisfactorily across the array. Up until this point in the data reduction,the signal from each chopping position(called the on and off phase)was processed sep- c 0000RAS,MNRAS000,000–000 4Greve et al. arately,the reason being that in a single phase the bolometers cor-relate much better which results in a much more reliable subtrac- tion of the background.MOPSI then calculated the phase difference, thereby effectively removing any electronic systematics between the data obtained in one wobbler position and the other.Additional de-spiking and baseline-?tting was then done on the phase differ- ences,from which the weights for each bolometer were calculated. Finally,the data were restored and rebinned using a shift-and- add technique which for each map produces a positive image brack- eted by two negative images of half the intensity located one wob-bler throw away.The rebinning was done onto a grid of1square arcsec pixels,with the?ux in each pixel being a noise-weighted average of the bolometers hitting that position.MOPSI also out- puts a weight image,W,which at pixel position(i,j)is given by W(i,j)= k1/σ2k,i.e.the error on the noise-weighted aver-age,where k denotes summing over the bolometers’seen’by pixel (i,j). The noise maps are shown in Figure2.The rms noise in the deepest parts of the maps is～0.6mJy beam?1,increasing towards the edges.The Lockman Hole received more integration time than the ELAIS N2?eld and as a result it is slightly deeper and has more uniform noise properties than the latter. 4SOURCE EXTRACTION AND MONTE CARLO SIMULATIONS 4.1Source extraction Scan-mapping is the only option for large area mapping at the IRAM30m telescope,and as a result the chopping direction is not ?xed on the sky but varies with time which means that the chops are smeared out in the?nal map.Hence,unlike SCUBA jiggle maps, one cannot utilise the extra information contained in the position of the negative side-lobes for source extraction.Instead,a simple matched-?ltering technique was adopted,using a Gaussian as the ?lter.However,as is seen from the noise images shown in Figure 2,the noise is not entirely uniform across the two?elds and any attempt at extracting sources has to take this into account.This was done by adopting a noise-weighted convolution technique similar to that of Serjeant et al.(2003).In order to account for the10.7′′beam and the typical pointing error of3′′rms,a Gaussian PSF, P(x,y),with a FWHM of x,y W(i?x,j?y)P(x,y)2.(2) The error on the?ux can then be shown to be: ?F(i,j)= 1 x,y W(i?x,y?j)P(x,y)2.(3) The signal-to-noise images,F/?F,obtained in this way are shown in Figure3and4for the ELAIS N2?eld and Lockman Hole,re-spectively.The?nal source catalogues for ELAIS N2and the Lock-man Hole are listed in Table1and2.We?nd a total of13sources at signi?cance≥4.0σ,and21sources with≥3.5σin the ELAIS N2 region while the number of sources in the Lockman Hole are14 and23at≥4.0σand≥3.5σ,respectively. 4.2Monte Carlo Simulations Extensive Monte Carlo simulations were performed in order to de-termine the reliability of the source extraction technique,i.e.how large a fraction of the extracted sources are due to spurious noise peaks,and how well does the extraction reproduce?uxes and posi-tions as a function of signal-to-noise?Due to the slight difference in survey depth and also geometry between the ELAIS N2and Lock-man Hole maps,we decided to perform separate Monte Carlo sim-ulations for each of the two?elds. In order to assess the contamination from spurious noise peaks to the source catalogues,we produced maps based on the real data but with the astrometry corrupted.This was done by randomising the array parameters of each scan and then producing?nal maps using the same MOPSI data reduction pipeline as for the real map. The advantage of this method is that the correlated noise in the raw data is preserved,and is taken out during the data reduction process in the same manner as for the real map.As a result,this method should give a realistic picture of the number of spurious noise peaks expected in our maps.We produced100such astromet-rically corrupted maps and counted the number of positive spurious sources as a function of detection threshold.The results are shown in Figure5with empty and?lled circles referring to the ELAIS N2 and Lockman Hole maps,respectively.As expected,the number of spurious detections drops off exponentially as a function of signal-to-noise threshold.From Figure5we?nd that a threshold of4.0σresults in less than one spurious source expected at random,while a cut-off at3.5σyields less than2spurious sources per?eld.We adopt3.5σas the detection cut-off for sources in both?elds since it provides a good compromise between catalogue size and source reliability. Monte Carlo simulations were also used to test the complete-ness and reliability of the?ux and position estimates.Sources in the?ux range1–12mJy were added to the map in steps of0.5mJy, one at a time and each at a random position,with50sources in each ?ux bin.We used a scaled beam pattern as the template for the arti-?cial sources.However,due to sky-rotation,the double-beam pro-?le varies across the map and as a result a separate multi-beam PSF had to be constructed for each source,depending on its position in the map.To accomplish this,the source—with its correct intensity and position—was added to the data stream and then the data were reduced in the same manner as the real data.Thus,each arti?cial source added to the map had exactly the right multi-beam pro?le corresponding to its position in the map.Finally,sources were ex-tracted using the same detection threshold as used for the real map. If a simulated source happened to fall within half a beam width of a real source in the map,it was discarded from the analysis.The results from these Monte Carlo simulations are shown in Figure6, again with open and?lled circles representing results based on the ELAIS N2and Lockman Hole?elds,respectively. Figures6a and b show the completeness of the survey,i.e.the percentage of recovered sources in our Monte Carlo simulations as a function of input?ux density.As expected the source extraction does well in extracting all of the brighter sources,but fares less well for sources close to the detection threshold.In both?elds the completeness is seen to be～50per cent at a?ux level of?2.5mJy, increasing to about95per cent at3mJy.The solid curves are best ?ts of the function f(S in)=1?exp(A(S in?B)C). c 0000RAS,MNRAS000,000–000 A 1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 5 Figure 2.Noise maps of the ELAIS N2and Lockman Hole East ?elds.Contours are at 0.7,0.8...1.5mJy beam ?1.The axes denote the offset (arcsec)from the map centre,and the intensity scale is in units of mJy beam ?1. Table 1.1200μm MAMBO source catalogue in the ELAIS N2?eld.The rms noise in the centre of the map is ～0.65mJy beam ?1and increases towards the edges.The area surveyed in the ELAIS N2?eld is 160arcmin 2. ID MAMBO ID RA (J2000)Dec (J2000)S 1200μm ±σ1200μm S/N MM J163647+4054N21200.116:36:47.9+40:54:464.0±0.8 5.00MM J163639+4053N21200.216:36:39.1+40:53:265.0±1.0 5.00MM J163635+4055N21200.316:36:35.7+40:55:593.9±0.8 4.87MM J163639+4056N21200.416:36:39.1+40:56:363.4±0.7 4.85MM J163632+4059N21200.516:36:32.1+40:59:465.7±1.2 4.75MM J163708+4054N21200.616:37:08.3+40:54:184.2±0.9 4.66MM J163640+4056N21200.716:36:40.7+40:56:463.2±0.7 4.57MM J163710+4055N21200.816:37:10.5+40:55:024.0±0.9 4.44MM J163705+4054N21200.916:37:05.8+40:54:264.0±0.9 4.44MM J163650+4057N21200.1016:36:50.3+40:57:363.1±0.7 4.42MM J163656+4058N21200.1116:36:56.3+40:58:142.5±0.6 4.16MM J163713+4054N21200.1216:37:13.8+40:54:034.9±1.2 4.08MM J163619+4054N21200.1316:36:19.5+40:54:005.7±1.4 4.07 MM J163640+4058N21200.1416:36:40.4+40:58:443.1±0.8 3.87MM J163636+4057N21200.1516:36:36.2+40:57:193.1±0.8 3.87MM J163644+4102N21200.1616:36:44.8+41:02:012.7±0.7 3.85MM J163706+4053N21200.1716:37:06.7+40:53:154.2±1.1 3.81MM J163655+4059N21200.1816:36:55.9+40:59:122.2±0.6 3.66MM J163658+4104N21200.1916:36:58.3+41:04:372.9±0.8 3.62MM J163647+4055N21200.2016:36:47.9+40:55:392.5±0.7 3.57MM J163715+4055N21200.2116:37:15.6+40:55:403.9±1.1 3.54 6Greve et al. Table2.1200μm MAMBO source catalogue in the Lockman Hole?eld.The rms noise is～0.6mJy beam?1at the centre where the map is deepest,and increases towards the edges.The total area surveyed is197arcmin2. ID MAMBO ID RA(J2000)Dec(J2000)S1200μm±σ1200μm S/N MM J105238+5724LE1200.110:52:38.3+57:24:374.8±0.68.00 MM J105238+5723LE1200.210:52:38.8+57:23:224.1±0.6 6.83 MM J105204+5726LE1200.310:52:04.1+57:26:583.6±0.6 6.00 MM J105257+5721LE1200.410:52:57.0+57:21:075.7±1.0 5.70 MM J105201+5724LE1200.510:52:01.3+57:24:483.4±0.6 5.66 MM J105227+5725LE1200.610:52:27.5+57:25:152.8±0.5 5.60 MM J105204+5718LE1200.710:52:04.7+57:18:123.2±0.7 4.57 MM J105142+5719LE1200.810:51:42.0+57:19:514.1±0.9 4.55 MM J105227+5722LE1200.910:52:27.6+57:22:203.1±0.7 4.42 MM J105229+5722LE1200.1010:52:29.9+57:22:052.9±0.7 4.14 MM J105158+5717LE1200.1110:51:58.3+57:17:532.9±0.7 4.14 MM J105155+5723LE1200.1210:51:55.5+57:23:103.3±0.8 4.12 MM J105246+5724LE1200.1310:52:46.9+57:24:472.4±0.6 4.00 MM J105200+5724LE1200.1410:52:00.0+57:24:252.4±0.6 4.00 MM J105245+5716LE1200.1510:52:45.1+57:16:053.1±0.8 3.87 MM J105244+5728LE1200.1610:52:44.8+57:28:125.0±1.3 3.84 MM J105121+5718LE1200.1710:51:21.5+57:18:404.8±1.3 3.69 MM J105157+5728LE1200.1810:51:57.7+57:28:002.2±0.6 3.66 MM J105128+5719LE1200.1910:51:28.4+57:19:474.0±1.1 3.63 MM J105224+5724LE1200.2010:52:24.4+57:24:201.8±0.5 3.60 MM J105131+5720LE1200.2110:51:31.3+57:20:063.6±1.0 3.60 MM J105203+5715LE1200.2210:52:03.0+57:15:462.8±0.8 3.50 MM J105223+5715LE1200.2310:52:23.4+57:15:272.8±0.8 3.50 A1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 7 Figure3.1200μm MAMBO signal-to-noise map of the ELAIS N2?eld.Sources detected at≥3.5σare circled in white,and are numbered in order of signi?cance.The axes denote the offset(arcsec)from the map centre. The boost-corrected number counts obtained in this way were then corrected for completeness using the?tted completeness curves in Figures6a and b. The?nal integrated number counts in?ux bins2.75,3.25, 3.75,4.25,4.75,and5.25mJy are given in Table3along with the raw number counts.The table shows the counts derived for the ELAIS N2and Lockman Hole separately,as well as the com-bined number counts.The quoted errors correspond to the95per cent two-sided con?dence level of a Poissonian distribution.The number counts derived from the two?elds separately are seen to agree well within the error.In Figure7we have plotted the cor-rected accumulative1200μm number counts as derived from the MAMBO survey presented in this paper.While the surface density of SCUBA sources detected at850μm has been fairly well con-strained over a large range in?ux density thanks to a number of large submm surveys(Smail et al.1997;Scott et al.2002),only one other published MAMBO survey has so far attempted to con-strain the1200μm number counts(Bertoldi et al.2000). For comparison we have also plotted the850μm source counts as derived from a number of SCUBA surveys.It is seen that the1200μm counts are lower than those at850μm.This is ex-pected if one assumes that the MAMBO and SCUBA sources trace the same population of dust-enshrouded galaxies:the lower MAMBO counts are due to the fact that one is sampling further down the Rayleigh-Jeans tail than at850μm.Thus,if one scales the MAMBO?uxes by a factor of～2.5,which roughly corresponds to the850/1200μm?ux ratio for a starburst at z～2.5,the MAMBO counts are found to coincide with the SCUBA counts.The over-all similarity between the shape of the1200and850μm number counts lends support to the view that the MAMBO and SCUBA sources are the same population viewed at slightly different wave-lengths. c 0000RAS,MNRAS000,000–000 8Greve et al. Figure 4.1200μm MAMBO signal-to-noise map of the Lockman Hole ?eld.Sources detected at ≥3.5σare circled in white,and are numbered in order of signi?cance.The axes denote the offset (arcsec)from the map centre. At ?ux levels fainter than ～4mJy the MAMBO counts dis-play a power-law slope of α??2.2,similar to that of the SCUBA counts in the ?ux range 2–9mJy.The 1200μm source counts ap-pears to show a break at ～4mJy beyond which the slope of the counts steepens to α～?4.7.The dot-dashed curve in Figure 7represents a Schechter-type function of the form dN/dS ∝(S/4mJy)?2.3exp(?S /4mJy).The Schechter function has a nat-ural break at 4mJy and appears to provide a somewhat better match than a power law,although the data do not allow for a statisti-cally signi?cant distinction between a power law and a Schechter function.At the bright end of the 850μm counts there is some dis-agreement between the SCUBA surveys,with the Scott et al.(2002)counts dropping off more steeply than found by Borys et al.(2003).The 1200μm counts show tentative evidence for a break at a ?ux level which corresponds to the 850μm ?ux at which the SCUBA counts by Scott et al.(2002)appear to turn over,suggesting that this feature is real.In order to better constrain the bright end of the num-ber counts,larger surveys such as the one square degree MAMBO Deep Field Survey (Bertoldi et al.,in preparation)and SHADES are needed.Con?rmation of our tentative ?ndings would be impor-tant —the bright (and very faint)ends of the number counts hold the biggest potential in terms of discriminating between models. At 1200μm the extragalactic background amounts to I νν～0.16nW m 2sr ?1(Fixsen et al,1998).By integrating up SdN/dS over the ?ux range 2.25–5.75mJy using the above Schechter func-tion,we estimate that our survey has resolved about 10per cent of the background light at 1200μm.This is comparable to the UK 8mJy Survey which also resolved ～10per cent of the extragalac-tic background at 850μm. If indeed MAMBO and SCUBA sources are the same,then it should be possible to construct models which can simultaneously reproduce the 850and 1200μm counts. c 0000RAS,MNRAS 000,000–000 A 1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 9 C o m p l e t e n e s s [%] S o u t /S i n S in [mJy] P o s i t i o n a l O f f s e t ["] S in [mJy] Figure 6.Results from Monte Carlo simulations.The solid lines in all three panels represent best ?ts to the points,see text for details.As in Figure 5,empty and ?lled circles refer to results from the ELAIS N2and Lockman Hole maps.Top:Percentage of added sources recovered against input ?ux in the range 1to 12mJy.Middle:The ’boosting’factor,i.e.the factor by which the input ?ux is scattered upwards due to instrumental and confusion noise (Eddington bias),plotted against input ?ux.Bottom:Deviations between true (input)positions and the positions derived from the source extraction technique as a function of input ?ux. In order to do so,we considered a simple parametric model which is based on the local 60μm LF,Φo (L 60),as derived from IRAS data (Saunders et al.1990).The latter provides the best esti-mate of the far-IR LF of dusty galaxies in the local Universe to date,and is thus a useful template to try and model the number counts of dusty high-redshift galaxies.While a local 850μm LF has been established by Dunne et al.(2000),who used SCUBA to observe a large number of galaxies from the IRAS Bright Galaxy Sample,the bright end of this function is still highly uncertain.Furthermore,if the majority of the MAMBO sources are at redshifts z >2and have similar dust temperatures to the IRAS galaxies (30–40K ),then the 60μm LF will be a better approximation to the rest-frame c 0000RAS,MNRAS 000,000–000 10Greve et al. Table3.1200μm source counts as derived from the ELAIS N2?eld(columns2–4),Lockman Hole(columns5–7),and the combined?elds(columns8–10). Only the≥3.5σcatalogue is used.The area surveyed in the three cases are160,197,and357arcmin2,respectively.The errors corresponds to95per cent two-sided con?dence levels of a Poissonian distribution. ELAIS N2LOCKMAN TOTAL S N raw(>S)N(>S)N(>S)N raw(>S)N(>S)N(>S)N raw(>S)N(>S)N(>S) corrected corrected corrected corrected corrected corrected [mJy][deg?2][deg?2][deg?2] Figure7.Cumulative number counts at1200μm(solid circles)based on the≥3.5σMAMBO source catalogue presented in this paper.The error bars represent 95per cent two-sided con?dence levels on a Poissonian distribution.Also shown are850μm cumulative number counts from a number of recent SCUBA surveys.The dashed black and grey lines show the number counts at1200and850μm,respectively,as predicted by a pure luminosity scenario in which g(z)=(1+z)3out to z=2,beyond which no further evolution occurs.The solid black and grey curves represent predicted number counts at1200and 850μm,respectively,based on the galaxy evolution model by Jameson et al.(1999),see text for details.The thin dotted line corresponds to a simple power law with slopeα=?2.2,while the dark solid curve represents the Schechter function dN/dS∝(S/S o)?αexp(?S/S o),whereα=2.3and S o=4mJy. Finally,the thick dotted line represent a no-evolution scenario. c 0000RAS,MNRAS000,000–000 A 1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 11 S/N threshold # s p u r i o u s d e t e c t i o n s Figure 5.Expected average number of spurious positive sources in ELAIS N2(empty circles)and the Lockman Hole (?lled circles)as a func-tion of signal-to-noise ratio.The solid and dashed lines are the expected number of positive spurious sources in the ELAIS N2and Lockman Hole,assuming the noise is purely Gaussian and the MAMBO beam is a Gaussian with a FWHM of 10.7′′. far-IR LF of the MAMBO sources.We have therefore adopted the 60μm LF as the reference LF at z =0.In order to assess the evo-lution in the far-IR LF,we used a simple approach in which the LF at redshift z is given by a simple scaling and/or translation of the local LF,i.e.Φ(L,z )=f (z )Φo (L/g (z )),where f (z )and g (z )are parametric models of the evolution in number density and luminosity,respectively.It is then straightforward to compute the cumulative source counts per unit solid angle brighter than a given ?ux density,S ν,as N (≥S ν)= z max ∞ L min (S ν,z ) f (z )Φo L dz dz,(4) where dV C /dz is the co-moving volume element per redshift in-crement,and L min (S ν,z )=4πD 2 L S ν(1+z )?1L ν/L ν(1+z )is the minimum luminosity observable for a source at redshift z and a survey ?ux limit of S ν.The evolution functions f (z )and g (z )are constrained by the fact that their predictions of the extragalactic background,the observed number counts and redshift distribution has to be consistent with observations. In Figure 7we have plotted the predicted 1200and 850μm number counts from a model with a luminosity evolution of g (z )=(1+z )3out to z =2,beyond which the evolution is un-changed out to z =10,which marks the high-redshift cut-off of the model.The model assumes the same SED for all sources —here we have adopted T d =44K ,β=+1.2,and a critical frequency of νc =2THz.While this pure-luminosity evolution model does an excellent job at reproducing the number counts at 1200μm it fares less well at 850μm,where it tends to slightly underpredict the number counts at bright ?ux levels. Another parametric model is that of Jameson (1999)which employs a pure luminosity evolution of the form g (z )=(1+z )3/2sech 2(b ln(1+z )?c )cosh 2c, (5) where b =2.2±0.1and c =1.84±0.1,see also Smail et al.(2002).This model is arguably the most realistic of the parametric models,since it is motivated by semi-analytical models,i.e.mod-els based on dark matter halo merging trees and assumptions about the astrophysics of the gas in halos.Furthermore,the model is not only in agreement with predictions of the chemical enrichment as a function of cosmic time but it also naturally includes a peak in the evolution at z ?2which is in agreement with the recently de-termined redshift distribution of radio-identi?ed SMGs (Chapman et al.2003).In Figure 7we have plotted the predicted 1200and 850μm number counts for this model,under the assumption that the SEDs of all MAMBO and SCUBA sources are well matched by modi?ed blackbody law with T d =37K ,β=+1.5,and a crit-ical frequency of νc =2THz.It is seen that this physically more realistic model is able to reproduce both the MAMBO and SCUBA number counts extremely well,suggesting that the MAMBO and SCUBA sources trace the same population of high-redshift,far-IR-luminous,starburst galaxies. While the mm number counts at faint as well as bright ?ux levels is still too poorly determined to warrant a detailed test of models of galaxy evolution,it is clear from the comparison with simple analytical model made above,that a scenario in which no evolution takes place at all,as illustrated by the thick dotted line in Figure 7,can be ruled out. 6CLUSTERING OF MAMBO SOURCES The next big step forward in our understanding of SMGs is likely to come from determining how they are clustered.Their clustering properties may then provide a link to a present-day population of galaxies.If SMGs are the progenitors of massive elliptical galax-ies,as suggested by their star-formation rates,molecular/dynamical masses and co-moving space densities,then they are expected to be strongly clustered.This follows from the way peaks in the den-sity ?eld in the early Universe are biased in mass (e.g.Benson et al.2001).Giant ellipticals,being the most luminous objects in the local Universe,are often found residing in the centres of galaxy clusters;as such they pin-point the most overdense and therefore mass-biased regions in the Universe. Submm surveys of various depths and sizes have searched for clustering among SMGs and have all failed to detect a signi?cant signal (Scott et al.2002;Webb et al.2003;Borys et al.2003).This has been due largely to the limited size of the survey regions,though efforts are further hampered by the fact the (sub)mm pop-ulation spans a broad range in redshift —the quartile range is z =1.9–2.8(Chapman et al.2003,2004)with a possible high-redshift tail extending to z >～4—and any clustering signal will thus,when projected onto the sky,become heavily diluted.Any detection of angular clustering will therefore be a lower limit on the real 3D clustering.One lesson learned from these surveys was that very large (～1square degree)areas containing several hundred sources with strong redshift constraints are required in order to determine the clustering properties of SMGs.Here,we present the results for the the MAMBO population using two independent clustering statistics. The ?rst test calculates the angular two-point correlation func-tion,w (θ),which quanti?es the excess probability of ?nding a source within an angle,θ,of a randomly selected source,over that of a random distribution,i.e. c 0000RAS,MNRAS 000,000–000 12Greve et al. δP(θ)=N2(1+w(θ))δ?1δ?2,(6) whereδP(θ)is the probability of?nding a source within a solid angleδ?1,and another source in another solid angleδ?2within a angular distanceθof each other(see e.g.Coles&Lucchin2002). N is the mean surface density of objects on the sky. Several estimators of w(θ)have been suggested in the liter- ature,and here we shall use the one?rst proposed by Landy& Szalay(1993): DD ?2 DR + RR w(θ)= DD 1/2. structure.A more detailed analysis of this will be presented in a future paper(Greve et al.,in preparation). An alternative test for clustering is the so-called nearest- neighbour analysis(Scott&Tout1989).This considers the distri- bution of nearest neighbour separations,θ,of sources on a sphere. For a random distribution of sources,the probability density func- tion can be shown to be: N?1 P(θ)dθ= A1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 13 Figure9.Distributions of nearest-neighbours in the ELAIS N2(left col- umn)and the Lockman Hole(right column).The black curves represent the actual data(the≥4.0σsource catalogues),while the red curves are the en- semble averaged distributions obtained from500simulated maps of the two ?elds. distributions being drawn from the same underlying distribution is about10per cent.In other words,there is a10per cent chance of a random distribution yielding a more paired distribution than that observed for the MAMBO sources.A similar analysis on the ≥3.5σsample shows a similar signi?cant peak at～15–30′′. Thus,while we haven’t found a signi?cant clustering signal from the two-point correlation function,there is tentative evidence from the nearest-neighbour analysis that MAMBO sources are not randomly distributed but tend to come in pairs.This is qualitatively in agreement with a recent study which utilises the results from the spectroscopic survey of radio-bright SMGs to search for pairs and/or triplets of sources in redshift space.This has yielded a sig- ni?cant detection of the clustering of SMGs and has constrained the correlation length to r0?6.1±2.1h?1Mpc(Blain et al.2004; Smail et al.2003). 7COMPARISON WITH THE SCUBA UK8MJY SURVEY While a detailed analysis of the properties of the MAMBO sources at radio and optical/near-IR wavelengths shall be presented in Paper II(Greve et al.,in preparation),it is appropriate here to compare the MAMBO and SCUBA maps.Such a comparison is meaningful since as we saw in section5both surveys reach very similar integral counts,and a’typical’z～2.5starburst SED will hit the?ux limit in both surveys almost simultaneously. 7.1The reliability of(sub)mm surveys First of all,such a cross-check between the MAMBO and SCUBA catalogues will allow us to assess the reliability of(sub)mm sur- veys.As already mentioned,(sub)mm surveys in general have adopted detection thresholds at low signal-to-noise ratios(typically 3.0–3.5σ-see e.g.Eales et al.2000;Scott et al.2002;Webb et al.2003;this work),and confusion has been a major issue for these surveys.In addition,different surveys have used different data- reduction software,and widely differing source extraction tech- niques have been adopted. The comparison between the MAMBO and SCUBA≥3.5σ source catalogues is shown in Figure10,which shows the outline of the MAMBO and SCUBA maps with the≥3.5σ850μm sample as given by Scott et al.(2002)and the≥3.5σ1200μm sources presented in this paper overplotted.It is seen immediately that four SCUBA sources in ELAIS N2are unambiguously detected at 1200μm,while in the Lockman Hole eight SCUBA sources have been con?rmed with MAMBO. It is interesting to see how these MAMBO identi?cations are distributed in terms of signal-to-noise and whether the identi?- cation rate increases if we lower the source detection threshold to3.0σ.In order to do so,we have compared the4.0,3.5,and 3.0σSCUBA source lists of Scott et al.with our corresponding MAMBO source catalogues,and for each SCUBA source we com- puted the distance to the nearest MAMBO source.The resulting distributions are shown in Figure11.For both?elds the distribution is seen to peak at offsets smaller than10′′.In fact,both distributions seem to show that a cutoff in positional offset of<10′′is a natu- ral selection criterion as to whether a MAMBO source is a genuine counterpart to a SCUBA source or not.This is in line with what we would expect given the FWHM s of the MAMBO and SCUBA beams.Adopting this criterion and using the≥3.0/3.5/4.0σcata- logues from both surveys,we con?rm6/4/3out of36/17/7SCUBA sources in the ELAIS N2?eld and9/8/5out of36/21/12SCUBA sources in the Lockman Hole,respectively.Thus,the identi?cation rate clearly increases with signal-to-noise,from17–25per cent for the3.0σ-catalogues to43per cent in ELAIS N2and42per cent in the Lockman Hole for the4.0σ-catalogues.At face value,our MAMBO survey thus con?rms about half of the most signi?cant SCUBA sources. An additional24hr of850μm data—not used in the original 8mJy Survey—resulted in a slightly different source catalogue than that given in Scott et al.(2002).With the inclusion of the new data,the signi?cance of N2850.17drops from3.5σto3.3σ,with a new?ux density of5.3±1.7mJy,while N2850.16disappears(see Ivison et al.2002).At the position of N2850.17in the MAMBO map,we detect a source at the2.7σsigni?cance level,suggesting that N2850.17is a real source,even though it is just below the formal3.5σdetection threshold of the8mJy Survey.N2850.16, however,is not detected at1200μm at greater than1σsigni?cance, con?rming that this was a spurious source in the original Scott et al.map. Based on extremely deep radio imaging of the8mJy?elds, Ivison et al.(2002)concluded that six of the original SCUBA sources in the ELAIS N2and Lockman Hole?elds were likely to be fake sources.Not only were they extracted from extremely noisy regions,but they also lacked a radio counterpart despite be- ing amongst the brightest SMGs in the sample.The sources in ques- tion were LE850.9,LE850.10,LE850.11,LE850.15,LE850.20, and N2850.14.From Figure10it is seen that none of these sources,which are denoted by grey crosses,coincide with a≥3.5σ MAMBO source.In fact,the highest signi?cance1200μm de- tection of the above sources was at the1.6-σlevel.Hence,our MAMBO maps strengthen the conclusion of Ivison et al.(2002) that these sources are spurious.If we compare the MAMBO catalogue with the re?ned SCUBA source catalogue,in which c 0000RAS,MNRAS000,000–000 14Greve et al. Figure 10.Distribution of MAMBO and SCUBA sources detected at ≥3.5σin the ELAIS N2and Lockman Hole ?elds (this paper;Scott et al.2002).The black circles are sources detected by MAMBO while grey triangles are SCUBA detections.The crosses denote the seven SCUBA sources which were deemed spurious and therefore rejected by Ivison et al.(2002)due to their lack of radio identi?cations and high associated noise levels.The MAMBO and SCUBA survey regions are outlined in black and grey,respectively,see also Figure 1.The boxes are 21′. 7×21′.7.the above mentioned SCUBA sources (including N2850.16and N2850.17)have been omitted,we ?nd that at the ≥3.0/3.5/4.0σlevel,we con?rm 6/4/3out of 33/14/7SCUBA sources in the ELAIS N2?eld and 9/8/5out of 31/16/9SCUBA sources in the Lockman Hole,respectively.Hence,the MAMBO identi?cation rate of SCUBA sources in the Lockman Hole increases to 56per cent,which is becoming comparable to fraction of SMGs detected in deep radio maps (Smail et al.2000;Ivison et al.2002). An important point to make in this context is that Figure 10clearly shows that while not all SCUBA sources are detected by MAMBO,there is a good overall spatial correspondence between SCUBA and MAMBO sources,as was also pointed out in section 6.One way to interpret this result is that the two surveys represent two different realisations of the same large-scale structure.From two independent but similar (sub)mm surveys of the same region,we would expect to ?nd the most signi?cant sources in both sur-veys,but this is not necessarily true of the fainter sources near the detection threshold. Deep radio observations provide an alternative route to reli-ably identify SMGs.About two thirds of SMGs are detected in the radio where the ratio of submm to radio ?ux detection thresholds is above ～400(Smail et al.2000;Ivison et al.2002).However,it remains an open question whether the third of the population which are radio-blank are SMGs at very high redshifts (z >>3),or cooler,less-far-IR-luminous objects at similar redshifts as the bulk of the population,or simply spurious sources.All three scenarios would explain the lack of radio counterparts. In Table 4we list all the ≥3.5σSCUBA sources with a MAMBO counterpart detected at ≥3.0σsigni?cance within 10′′,along with their positional offsets and ?ux densities at 1200and 850μm.Of the 12≥3.5σSCUBA sources in the ELAIS N2?eld which were not detected by MAMBO,only four had a radio iden-ti?cation.Of the eight radio-blank SCUBA sources,only one —N2850.3—was con?rmed by MAMBO,indicating that it could be cool,or lie at z >>3.In the Lockman Hole,none of the radio-blank SCUBA sources were detected at 1200μm,and only three of the 11radio-identi?ed SCUBA sources were not detected by MAMBO. Since the depth of the MAMBO maps at 1200μm is compara-ble to that of the SCUBA maps at 850μm it is hard to conceive of a way in which an 850μm source with no radio counterpart could fail to be detected at 1200μm .The only plausible explanations require that the sources are spurious or confused. In Table 5we have summarised the above ?ndings.They suggest strongly that the fraction of robust SCUBA sources,i.e.sources con?rmed by MAMBO,which are not detected in the radio is low:20per cent (1/5)in ELAIS N2and 0per cent in the Lockman Hole.These ?ndings suffer from small number statistics and we await a comparison between the much larger map of the Lockman Hole being obtained with MAMBO (Bertoldi et al.in prep.)and the SCUBA map of that region which is being obtained as part of SHADES (see https://www.wendangku.net/doc/087746564.html,/ifa/shades/). In the light of current and future (sub)mm surveys,our ?nd-ings underline the importance of multi-wavelength follow-up in or-der to establish the reality of (sub)mm sources,and the dependence only on the most robust samples to draw meaningful statistical con-clusions (cf.Dannerbauer et al.2004).7.2The 850/1200μm ?ux density ratio Another valuable piece of information which can be gleaned from a comparison of the MAMBO and SCUBA maps is the 850/1200μm ?ux ratios for a large sample of (sub)mm galaxies.Beyond z ≥3this ?ux ratio becomes a strong function of red-shift,and can thus be used as a crude discriminator between low-and high-redshift sources (Eales et al.2003),much in the same way that the radio-to-submm spectral index acts as a redshift estimator for sources at z <～3(Carilli &Yun 1999,2000).Thus,the two c 0000RAS,MNRAS 000,000–000 A1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I15 Table4.MAMBO and VLA radio identi?cations of the SCUBA8mJy Survey≥3.5σsource catalogue(Scott et al.2002).The850μm and1.4GHz radio ?ux densities are from Scott et al.(2002)and Ivison et al.(2002),respectively. SCUBA ID S850μm±σ850μm MAMBO ID S1200μm±σ1200μm SCUBA/MAMBO Offset RADIO S1.4GHz±σ1.4GHz mJy mJy′′μJy N2850.111.2±1.6yes45±16 N2850.210.7±2.0N21200.393.4±1.18.4yes92±16 N2850.38.5±1.6N21200.192.9±0.8 5.1no<44 N2850.48.2±1.7N21200.103.1±0.7 4.5yes221±17 N2850.58.5±2.2N21200.33.9±0.8 1.0yes77±31 N2850.69.2±2.4no38±19 N2850.79.0±2.4N21200.43.4±0.7 4.0yes159±27 N2850.85.1±1.4yes74±29 N2850.99.0±2.5yes33±12 N2850.105.4±1.5no58±24 N2850.117.1±2.0no<44 N2850.125.5±1.6no32±17 N2850.13?6.3±1.9yes99±23 N2850.14?11.2±3.3no<44 N2850.155.0±1.5no31±20 N2850.16?12.9±3.9no<44 N2850.17??5.3±1.7no<44σ≥4.0Detections 4.0>σ≥3.5Detections ?Detected with MAMBO at the2.8σlevel. ?Excluded from the re?ned8mJy sample of Ivison et al.(2002). ?This source vanished with the inclusion of an additional24hr of SCUBA data. ??This source dropped from3.5to3.3σwith the inclusion of additional SCUBA data.It is detected with MAMBO at2.7σ. c 0000RAS,MNRAS000,000–000 16 Greve et al. 01234 5 N ELAIS N2 4.0 sigma 3.5 sigma 3.0 sigma 5 1015 20 25 Offset ["] 1234 5 N LOCKMAN 4.0 sigma 3.5 sigma 3.0 sigma Figure 11.Distribution of offsets between SCUBA sources and their near-est MAMBO counterpart in the ELAIS N2(top panel)and Lockman Hole ?elds (bottom panel).The 4.0,3.5,and 3.0σMAMBO samples are com-pared with the 4.0,3.5,and 3.0σSCUBA samples of Scott et al.(2002),and the corresponding distributions are shown as solid,dashed and dotted curves,respectively. redshift estimators complement each other,and if used in combi-nation can potentially be used to probe the redshift distribution of (sub)mm sources.However,both of these redshift estimators suffer from the T d ?z degeneracy ?rst pointed out by Blain (1999),which implies that a low-redshift source with a cold dust temperature is indistinguishable from a warm source at high redshift. The distribution of 850/1200μm ?ux ratios for the 13≥3.5σSCUBA sources which were robustly identi?ed by our MAMBO survey are plotted in Figure 12a,along with the ratios for a sample of SCUBA-observed MAMBO sources by Eales et al.(2003).Us-ing SCUBA in its photometry mode,they observed 21MAMBO- Figure 12.a)The distribution of 850/1200μm ?ux ratios for the 13≥3.5σSCUBA sources identi?ed with MAMBO in this paper (light-grey shaded area),and for the sample presented by Eales et al.(2003)(dashed line).b)The dotted histogram is the ?ux ratio distribution for all the ≥3.5σMAMBO sources within the SCUBA regions,including the ones which were not detected by SCUBA.In the latter case upper ?ux limits were es-timated as the peak ?ux within an aperture of radius 10′′centered on the MAMBO position in the SCUBA map.The distribution of ?ux ratios for all the ≥3.5σSCUBA sources (dashed histogram)were obtained in a similar manner by measuring the peak ?ux in the MAMBO map within a 10′′radius of the SCUBA position.The light-grey shaded histogram represents the dis-tribution for the subset of MAMBO sources which were robustly identi?ed in the radio.c)The same as b)except more conservative upper ?ux limits (2σ+F )were adopted,see text for details. c 0000RAS,MNRAS 000,000–000 A 1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I 17 Figure 13.The 850/1200μm ?ux density ratio for SCUBA sources de-tected by MAMBO in the ELAIS N2(crosses)and Lockman Hole (tri-angles).Six of the sources have spectroscopic redshifts (see Chapman et al.2003,2004),while the remainder have been placed at z =0.5.The two encircled sources have no radio counterpart.Shown as diamonds are the 850/1200μm ?ux ratios for the sample of Eales et al.(2003).The thick solid curve represents the expected ?ux ratio for an optically thin modi?ed blackbody with T d =45K and β=+1.5,typical for a local ULIRG.This curve is enveloped by two thin solid curves which correspond to changes in the dust temperature and spectral index of ?T d =±5K and ?β=±0.2.The light-grey shaded area corresponds to a modi?ed black-body with T d =(35.6±5.0)K and β=(+1.3±0.2).The dot-dashed curves corresponds to SEDs with β=1.0and T d =20...70K in step if 10K. Table 5.The number (and percentage)of SCUBA sources identi?ed by MAMBO divided into radio and non-radio ID categories.Note,that all the number in this table are based on the comparison with the ≥3.5σ8mJy Sample of Scott et al.(2002)and the ≥3.0σMAMBO sample presented in this paper. MAMBO ID No MAMBO ID Field Radio ID No Radio ID Total Radio ID No Radio ID Total ELAIS N24154812Lockman 80831013Total 12(92%) 1(8%) 13 7(28%) 18(72%) 25 selected sources from the MAMBO Deep Field Survey (Bertoldi et al.,in preparation).While there is a considerable overlap between the two distributions,the latter has a signi?cant over-density at low values which is not reproduced by our sample.From our sample we ?nd a median value of S 850/S 1200=2.6±0.6,marginally higher than the median value of 2.1±0.7found by Eales et al.(2003),although within the scatter. In Figure 13we have plotted the measured 850/1200μm ?ux ratios of our sample and the Eales et al.sample along with curves showing the predicted 850/1200μm ?ux density ratios against red-shift for an SED with T d =45K and β=+1.5,and an SED with T d =35.6K and β=+1.3.The former SED provides a good match to the local ULIRG,Arp 220,while the latter is based on the average T d and βvalues derived from the SCUBA Local Uni-verse Galaxy Survey (Dunne et al.2000).In addition,we have also plotted the S 850μm /S 1200μm –z relationship for a set of SEDs with β=1and T d =20,30...70K,i.e.SEDs which have very different dust properties from local ULIRGs.Note,the above dust tempera-tures are at a redshift of zero.In order to account for the increas-ing cosmic microwave background radiation (CMBR)temperature with redshift and its thermal coupling with the dust we have used T d (z )= T 4+βd,z =0+T 4+βCMBR (1+z ) 4+β ?1 1/(4+β) ,(9) where T CMBR is the present epoch CMBR temperature,(see e.g.Eales &Edmunds 1996).The effect is only signi?cant when the dust is cold relative to the CMBR temperature,and therefore be-comes more important at very high redshifts.The slight downward trend in the S 850μm /S 1200μm curves at low redshifts is due to the negative spectral slope (α=?0.7)of the radio continuum emis-sion which boosts the 1200μm ?ux relative to the ?ux at 850μm .However,this effect is completely negligible at redshifts beyond z ～0.5. The low ?ux ratios found by Eales et al.(2003)led them to conclude that a signi?cant fraction of SMGs must lie at very high redshifts (z >>3)or possess dust properties different from low-redshift starburst galaxies.In contrast,we ?nd no con?ict between our measured S 850μm /S 1200μm ratios and SEDs based on local ULIRGs.From a subset of ?ve sources which have been targeted spectroscopically by Chapman et al.(2003,2004),and thus are placed at their correct redshift in Figure 13,we can conclude that the observed ?ux ratios for at least four of the ?ve sources are con-sistent with the range of SEDs expected from local ULIRGs.The one exception is the outlying point at S 850μm /S 1200μm =3.8This data point corresponds to the source LE 850.6/LE 1200.10which has another source (LE 1200.9)close to it.This source was detected by MAMBO but not by SCUBA,and it is likely that LE 1200.9contributes to the 850μm ?ux of LE 850.6,leading to an arti?cially high ?ux ratio for this source. Our sample is taken from two unbiased surveys at slightly dif-ferent (sub)mm wavelengths and is thus independent of any radio selection bias.Furthermore,it is clear from Figure 13that the SMG without a radio counterpart (circled symbol)does not have a lower 850/1200μm ?ux ratio than the rest of the sample.This suggest that the source is blank in the radio because it is a cooler,less-far-IR-luminous object at similar redshifts to the bulk of the popula-tion,not because it lies at a very high redshift. Candidates for very-high-redshift sources,i.e.850μm dropouts,should be sought amongst sources de-tected by MAMBO but not SCUBA.From Figure 10it is seen that 9MAMBO sources in the ELAIS N2?eld and 9in the Lockman Hole fall within the regions observed by SCUBA,yet are not detected at ≥3.5σsigni?cance at 850μm.Upper limits on the ?ux densities at 850μm of these sources were measured,taking the peak ?ux in a 10′′radius aperture region of the SCUBA map coincident with the MAMBO position.These limits were then merged with the 850μm ?uxes of the robust sample,resulting in 850μm ?ux estimates (or upper limits)for all the 9+9+13=31MAMBO sources which lie within the SCUBA regions.The resulting distribution of 850-to-1200μm ?ux ratios is shown as the dotted curve in Figure 12b.The distribution appears to have two peaks,one at S 850μm /S 1200μm ～1which reproduces the low-end tail of Eales et al.(2003)rather well and is almost entirely due to the MAMBO sources not detected by SCUBA,and another at c 0000RAS,MNRAS 000,000–000 18Greve et al. ～2.5which stems from the13sources robustly identi?ed at both 1200μm and850μm. In order to make a fair comparison with the?ux ratios of the SCUBA sample,we estimated1200μm?uxes for all the SCUBA sources.This was done in an identical fashion as above,i.e.upper 1200μm?ux limits were derived for the SCUBA sources not de-tected with MAMBO using the peak?ux within a10′′radius aper-ture region of the MAMBO map centered on the SCUBA position, and concatenated with the robust sample.This distribution is shown as the dashed histogram in12b. The dotted and dashed distributions appear to be distinct, and in order to determine the probability of the two samples be-ing drawn from the same parent distribution,we have employed the standard’survival analysis’tests(Feigelson&Nelson1985), which are appropriate in the case where the samples contain up-per or lower limits(censored data).This included the Gehan,log rank,Peto-Peto,and Peto-Prentice tests,the latter being perhaps the most conservative and least sensitive to differences in the censoring patterns.However,common to all the tests is that they are unable to compare samples with mixed censor indicators,i.e.one cannot compare a sample containing upper limits with a sample containing lower limits.As a result we ran the tests where only one of the sam-ples contained censored data,assuming that the limits in the other sample were not limits but measured values,and vice versa.In both cases the tests yielded probabilities less than0.01,thereby strongly suggesting that the two distributions are signi?cantly different.This argues in favour of there being a low-end tail consisting of galaxies at either high redshifts or with cool dust temperatures.Consistent with these?ndings is the distribution of MAMBO sources with ra-dio counterparts(shaded histogram in Figure12b)which shows that few of the sources with?ux ratios<～1.5are identi?ed in the radio.This is what one would expect if they were at high redshifts or cool,not very far-IR luminous systems. In addition to the two astrophysical explanations(i.e.cold dust or high redshift)Eales et al.also suggest more mundane reasons for their low?ux ratios,the most important of which is astromet-ric errors(see discussion in Eales et al.2003).For all but?ve of their21sources,they used positions derived from radio observa-tions or mm-wave interferometry.For the remaining sources they used the MAMBO positions.With our dataset,in conjunction with the8mJy Survey images,we can reproduce the Eales et al.exper-iment in the case where only MAMBO positions are available.In order to do this we consider the sample of13sources which were detected by both MAMBO and SCUBA.However,instead of using the850μm?uxes reported by Scott et al.(2002),we measure the 850μm?ux at the MAMBO position in the SCUBA map using the peak?ux within a10′′aperture.In general,we?nd that the effects of positional errors are small,and the?ux ratios are not skewed towards lower values. Finally,it is possible that contamination by spurious or?ux-boosted MAMBO sources is responsible for at least some of the low?ux ratios observed.However,based the Monte Carlo simula-tions in section4.2we expect no more than2sources to be spurious in each of the MAMBO maps.This is an upper limit,given that the overlap between the SCUBA and MAMBO regions is only about 68per cent of the areas covered by MAMBO. While the above analysis suggests that astrometrical errors and spurious/?ux-boosted sources are unable to account for the12 MAMBO sources with S850μm/S1200μm<～1.5,we caution that the low?ux ratio could be due to the way we have estimated the up-per?ux limits.Simply adopting the peak?ux within a10′′aperture might in some cases result in too low?ux estimates and would tend to bias the MAMBO and SCUBA distributions towards lower and higher?ux ratios,respectively.In Figure12c we have adopted a more conservative approach in which the upper limits on the?uxes were estimated by adding2×σto the peak?ux,whereσis the local rms noise.Clearly,the overlap between the two distributions is now much greater,and the two distributions appear to be indistinguish-able.This is con?rmed by the’survival analysis’tests which yield probabilities in the range0.22(log rank)to0.11(Peto-Prentice)and similar for the reverse comparison,https://www.wendangku.net/doc/087746564.html,paring the SCUBA dis-tribution with the uncensored MAMBO distribution.Thus,adopt-ing what is arguably more realistic upper?ux limits we?nd no ev-idence for SMGs with unusually low850-to-1200μm?ux ratios as reported by Eales et al.(2003).If this is the case,the major impli-cation is that,beyond the few completely unrepresentative submm-loud AGN at z>4,there is no signi?cant population of SMGs at very high redshifts.The redshift distribution of radio-identi?ed SCUBA sources,as determined by Chapman et al.(2003,2004), would be applicable to virtually all of the(sub)mm population. However,while we?nd no conclusive evidence for’850μm-dropouts’a handful of MAMBO sources do seem to be good can-didates for SMGs at z>>5.In particular,LE1200.2is one of the brightest sources in our survey,yet it is not detected by SCUBA nor is it seen in the radio.Pointed SCUBA photometry observa-tions of this source would provide an accurate accurate estimate of its850μm?ux and con?rm or dismiss its status as a’850μm-dropout’. Furthermore,with the completion of the MAMBO Deep Field Survey and the SCUBA Half Degree Extragalactic Survey,which will not only provide us with much larger samples but also a mul-titude of observations at complementary wavelengths,we should be able to obtain a much better census of the high-redshift tail of (sub)mm sources. 8CONCLUSIONS In this paper we have presented results from a MAMBO 1200μm blank-?eld survey of the ELAIS N2and Lockman Hole?elds,covering a total of357arcmin2to a rms level of ～0.8mJy beam?1.We detect27sources at≥4.0σsigni?cance, and more than40sources at≥3.5σ. From the≥3.5σcatalogue we have derived accurate num-ber counts over the?ux range3–5.5mJy,and?nd evidence for a break at S1200μm?4mJy.This corresponds to a far-IR lumi-nosity of～1013L⊙for a modi?ed blackbody with T d=40K andβ=+1.5at z=2.5.The observed1200μm source counts can be successfully reproduced by a simple parametric model for the evolution the local ULIRG population.Furthermore,this model also?ts the850μm source counts which suggests that the MAMBO and SCUBA sources are drawn from the same population of dust-enshrouded starburst at high redshift. Two independent tests were carried out with the aim of de-tecting clustering in the MAMBO population.Although,the an-gular two-point correlation function showed no evidence of clus-tering,a nearest neighbour analysis suggests that the most signif-icant MAMBO sources are not randomly distributed but come in pairs,typically separated by23′′.Furthermore,the spatial distri-bution of sources appears to be non-random,with sources tend-ing to reside in clusters surrounding large voids.The reality of these structures is strengthened by the good overall spatial corre-lation between the SCUBA,MAMBO andμJy-level radio sources. This suggests that co-spatial surveys at the two slightly different c 0000RAS,MNRAS000,000–000 A1200μm MAMBO Survey of the ELAIS N2and Lockman Hole:I19 (sub)mm wavelengths skim the brightest members of a numerous but faint population,yielding two similar but low-signal-to-noise visualisations of the true(sub)mm sky. Our MAMBO survey con?rms roughly half of the re?ned ≥3.5σSCUBA8mJy Survey sample(Scott et al.2002;Ivison et al.2002).This is comparable to the radio identi?cation rate of SCUBA and MAMBO sources.As a by-product of this analysis,we have produced a extremely robust sub-sample of13SMGs detected at≥3.5σby both SCUBA and MAMBO.We?nd that only one (～8per cent)has no radio counterpart,a signi?cantly lower frac-tion than the third which the radio-blank SMGs have generally been believed to constitute.Our results thus suggest that the population of SMGs which are detected by both SCUBA and MAMBO has no signi?cant tail at z>>3.This conclusion is further strengthened by the observed distribution of850/1200μm?ux density ratios for the13sources in our sample.We?nd their?ux density ratios to be consistent with the SEDs found for local ULIRGs and in agreement with the spectroscopic redshift distribution of SMGs as determined by Chapman et al.(2003,2004). Finally,we have identi?ed18MAMBO sources within the SCUBA UK8-mJy regions which are not detected at850μm at greater than3.0σsigni?cance.Any high-redshift SMGs should be sought amongst this population of’850μm-dropouts’.However, using conservative upper?ux limits we?nd that the distribution of850-to-1200μm?ux ratios for these sources is statistically in-distinguishable from that of the sources identi?ed robustly in both wavelengths. ACKNOWLEDGEMENTS TRG acknowledges support from the Danish Research Council and from the European Union RTN Network,POE.We are grateful to Robert Zylka for providing us with the MOPSI package and for use-ful discussions concerning MOPSI.We are also grateful to Ian Smail for helpful comments on the paper.Finally,we thank Ernst Kreysa and his team for providing MAMBO. REFERENCES Barger,A.J.,Cowie,L.L.,&Sanders,D.B.1999,ApJ,518,5L. Benson, A.J.,Frenk,C.S.,Baugh, C.M.,Cole,S.,&Lacey, C.G.2001,MNRAS,327,1041. 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Zylka,R.1998,Pocket Cookbook for the MOPSI Software. http://www.iram.es/IRAMES/otherDocuments/manuals/Datared/pockcoo.ps This paper has been typeset from a T E X/L A T E X?le prepared by the author. c 0000RAS,MNRAS000,000–000 从实践的角度探讨在日语教学中多媒体课件的应用 在今天中国的许多大学，为适应现代化，信息化的要求，建立了设备完善的适应多媒体教学的教室。许多学科的研究者及现场教员也积极致力于多媒体软件的开发和利用。在大学日语专业的教学工作中，教科书、磁带、粉笔为主流的传统教学方式差不多悄然向先进的教学手段而进展。 一、多媒体课件和精品课程的进展现状 然而，目前在专业日语教学中能够利用的教学软件并不多见。比如在中国大学日语的专业、第二外語用教科书常见的有《新编日语》（上海外语教育出版社）、《中日交流标准日本語》（初级、中级）（人民教育出版社）、《新编基础日语（初級、高級）》（上海译文出版社）、《大学日本语》（四川大学出版社）、《初级日语》《中级日语》（北京大学出版社）、《新世纪大学日语》（外语教学与研究出版社）、《综合日语》（北京大学出版社）、《新编日语教程》（华东理工大学出版社）《新编初级（中级）日本语》（吉林教育出版社）、《新大学日本语》（大连理工大学出版社）、《新大学日语》（高等教育出版社）、《现代日本语》（上海外语教育出版社）、《基础日语》（复旦大学出版社）等等。配套教材以录音磁带、教学参考、习题集为主。只有《中日交流標準日本語（初級上）》、《初級日语》、《新编日语教程》等少数教科书配备了多媒体DVD视听教材。 然而这些试听教材，有的内容为日语普及读物，并不适合专业外语课堂教学。比如《新版中日交流标准日本语（初级上）》，有的尽管DVD视听教材中有丰富的动画画面和语音练习。然而，课堂操作则花费时刻长，不利于教师重点指导，更加适合学生的课余练习。比如北京大学的《初级日语》等。在这种情形下，许多大学的日语专业致力于教材的自主开发。 其中，有些大学的还推出精品课程，取得了专门大成绩。比如天津外国语学院的《新编日语》多媒体精品课程为2007年被评为“国家级精品课”。目前已被南开大学外国语学院、成都理工大学日语系等全国40余所大学推广使用。 Unit1 Americans believe no one stands still. If you are not moving ahead, you are falling behind. This attitude results in a nation of people committed to researching, experimenting and exploring. Time is one of the two elements that Americans save carefully, the other being labor. "We are slaves to nothing but the clock,” it has been said. Time is treated as if it were something almost real. We budget it, save it, waste it, steal it, kill it, cut it, account for it; we also charge for it. It is a precious resource. Many people have a rather acute sense of the shortness of each lifetime. Once the sands have run out of a person’s hourglass, they cannot be replaced. We want every minute to count. A foreigner’s first impression of the U.S. is li kely to be that everyone is in a rush -- often under pressure. City people always appear to be hurrying to get where they are going, restlessly seeking attention in a store, or elbowing others as they try to complete their shopping. Racing through daytime meals is part of the pace 新视野三版读写B2U4Text A College sweethearts 1I smile at my two lovely daughters and they seem so much more mature than we,their parents,when we were college sweethearts.Linda,who's21,had a boyfriend in her freshman year she thought she would marry,but they're not together anymore.Melissa,who's19,hasn't had a steady boyfriend yet.My daughters wonder when they will meet"The One",their great love.They think their father and I had a classic fairy-tale romance heading for marriage from the outset.Perhaps,they're right but it didn't seem so at the time.In a way, love just happens when you least expect it.Who would have thought that Butch and I would end up getting married to each other?He became my boyfriend because of my shallow agenda:I wanted a cute boyfriend! 2We met through my college roommate at the university cafeteria.That fateful night,I was merely curious,but for him I think it was love at first sight."You have beautiful eyes",he said as he gazed at my face.He kept staring at me all night long.I really wasn't that interested for two reasons.First,he looked like he was a really wild boy,maybe even dangerous.Second,although he was very cute,he seemed a little weird. 3Riding on his bicycle,he'd ride past my dorm as if"by accident"and pretend to be surprised to see me.I liked the attention but was cautious about his wild,dynamic personality.He had a charming way with words which would charm any girl.Fear came over me when I started to fall in love.His exciting"bad boy image"was just too tempting to resist.What was it that attracted me?I always had an excellent reputation.My concentration was solely on my studies to get superior grades.But for what?College is supposed to be a time of great learning and also some fun.I had nearly achieved a great education,and graduation was just one semester away.But I hadn't had any fun;my life was stale with no component of fun!I needed a boyfriend.Not just any boyfriend.He had to be cute.My goal that semester became: Be ambitious and grab the cutest boyfriend I can find. 4I worried what he'd think of me.True,we lived in a time when a dramatic shift in sexual attitudes was taking place,but I was a traditional girl who wasn't ready for the new ways that seemed common on campus.Butch looked superb!I was not immune to his personality,but I was scared.The night when he announced to the world that I was his girlfriend,I went along Unit 1 1学习外语是我一生中最艰苦也是最有意义的经历之一。虽然时常遭遇挫折，但却非常有价值。 2我学外语的经历始于初中的第一堂英语课。老师很慈祥耐心，时常表扬学生。由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。两年中，我的成绩一直名列前茅。 3到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！”没有多久，我便不再渴望回答问题了。我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 4好在这种情况没持续多久。到了大学，我了解到所有学生必须上英语课。与高中老师不。大学英语老师非常耐心和蔼，而且从来不带教鞭！不过情况却远不尽如人意。由于班大，每堂课能轮到我回答的问题寥寥无几。上了几周课后，我还发现许多同学的英语说得比我要好得多。我开始产生一种畏惧感。虽然原因与高中时不同，但我却又一次不敢开口了。看来我的英语水平要永远停步不前了。 5直到几年后我有机会参加远程英语课程，情况才有所改善。这种课程的媒介是一台电脑、一条电话线和一个调制解调器。我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 6网上学习并不比普通的课堂学习容易。它需要花许多的时间，需要学习者专心自律，以跟上课程进度。我尽力达到课程的最低要求，并按时完成作业。 7我随时随地都在学习。不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。我学习中出过许多错，有时是令人尴尬的错误。有时我会因挫折而哭泣，有时甚至想放弃。但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 8学习外语对我来说是非常艰辛的经历，但它又无比珍贵。它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。学习一门外语最令人兴奋的收获是我能与更多的人交流。与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。由于我已能说英语，别人讲英语时我不再茫然不解了。我能够参与其中，并结交朋友。我能与人交流，并能够弥合我所说的语言和所处的文化与他们的语言和文化之间的鸿沟。 III. 1. rewarding 2. communicate 3. access 4. embarrassing 5. positive 6. commitment 7. virtual 8. benefits 9. minimum 10. opportunities IV. 1. up 2. into 3. from 4. with 5. to 6. up 7. of 8. in 9. for 10.with V. 1.G 2.B 3.E 4.I 5.H 6.K 7.M 8.O 9.F 10.C Sentence Structure VI. 1. Universities in the east are better equipped, while those in the west are relatively poor. 2. Allan Clark kept talking the price up, while Wilkinson kept knocking it down. 3. The husband spent all his money drinking, while his wife saved all hers for the family. 4. Some guests spoke pleasantly and behaved politely, while others wee insulting and impolite. 5. Outwardly Sara was friendly towards all those concerned, while inwardly she was angry. VII. 1. Not only did Mr. Smith learn the Chinese language, but he also bridged the gap between his culture and ours. 2. Not only did we learn the technology through the online course, but we also learned to communicate with friends in English. 3. Not only did we lose all our money, but we also came close to losing our lives. 新大学日语简明教程课文翻译 第21课 一、我的留学生活 我从去年12月开始学习日语。已经3个月了。每天大约学30个新单词。每天学15个左右的新汉字，但总记不住。假名已经基本记住了。 简单的会话还可以，但较难的还说不了。还不能用日语发表自己的意见。既不能很好地回答老师的提问，也看不懂日语的文章。短小、简单的信写得了，但长的信写不了。 来日本不久就迎来了新年。新年时，日本的少女们穿着美丽的和服，看上去就像新娘。非常冷的时候，还是有女孩子穿着裙子和袜子走在大街上。 我在日本的第一个新年过得很愉快，因此很开心。 现在学习忙，没什么时间玩，但周末常常运动，或骑车去公园玩。有时也邀朋友一起去。虽然我有国际驾照，但没钱，买不起车。没办法，需要的时候就向朋友借车。有几个朋友愿意借车给我。 二、一个房间变成三个 从前一直认为睡在褥子上的是日本人，美国人都睡床铺，可是听说近来纽约等大都市的年轻人不睡床铺，而是睡在褥子上，是不是突然讨厌起床铺了？ 日本人自古以来就睡在褥子上，那自有它的原因。人们都说日本人的房子小，从前，很少有人在自己的房间，一家人住在一个小房间里是常有的是，今天仍然有人过着这样的生活。 在仅有的一个房间哩，如果要摆下全家人的床铺，就不能在那里吃饭了。这一点，褥子很方便。早晨，不需要褥子的时候，可以收起来。在没有了褥子的房间放上桌子，当作饭厅吃早饭。来客人的话，就在那里喝茶；孩子放学回到家里，那房间就成了书房。而后，傍晚又成为饭厅。然后收起桌子，铺上褥子，又成为了全家人睡觉的地方。 如果是床铺的话，除了睡觉的房间，还需要吃饭的房间和书房等，但如果使用褥子，一个房间就可以有各种用途。 据说从前，在纽约等大都市的大学学习的学生也租得起很大的房间。但现在房租太贵，租不起了。只能住更便宜、更小的房间。因此，似乎开始使用睡觉时作床，白天折小能成为椅子的、方便的褥子。 新视野大学英语第一册Unit 1课文翻译 学习外语是我一生中最艰苦也是最有意义的经历之一。 虽然时常遭遇挫折，但却非常有价值。 我学外语的经历始于初中的第一堂英语课。 老师很慈祥耐心，时常表扬学生。 由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。 两年中，我的成绩一直名列前茅。 到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。 以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。 每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！” 没有多久，我便不再渴望回答问题了。 我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 好在这种情况没持续多久。 到了大学，我了解到所有学生必须上英语课。 与高中老师不同，大学英语老师非常耐心和蔼，而且从来不带教鞭！ 不过情况却远不尽如人意。 由于班大，每堂课能轮到我回答的问题寥寥无几。 上了几周课后，我还发现许多同学的英语说得比我要好得多。 我开始产生一种畏惧感。 虽然原因与高中时不同，但我却又一次不敢开口了。 看来我的英语水平要永远停步不前了。 直到几年后我有机会参加远程英语课程，情况才有所改善。 这种课程的媒介是一台电脑、一条电话线和一个调制解调器。 我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 网上学习并不比普通的课堂学习容易。 它需要花许多的时间，需要学习者专心自律，以跟上课程进度。 我尽力达到课程的最低要求，并按时完成作业。 我随时随地都在学习。 不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。 我学习中出过许多错，有时是令人尴尬的错误。 有时我会因挫折而哭泣，有时甚至想放弃。 但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。 突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。 尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 学习外语对我来说是非常艰辛的经历，但它又无比珍贵。 它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。 学习一门外语最令人兴奋的收获是我能与更多的人交流。 与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。 由于我已能说英语，别人讲英语时我不再茫然不解了。 我能够参与其中，并结交朋友。 习惯与礼仪 我是个漫画家，对旁人细微的动作、不起眼的举止等抱有好奇。所以，我在国外只要做错一点什么，立刻会比旁人更为敏锐地感觉到那个国家的人们对此作出的反应。 譬如我多次看到过，欧美人和中国人见到我们日本人吸溜吸溜地出声喝汤而面露厌恶之色。过去，日本人坐在塌塌米上，在一张低矮的食案上用餐，餐具离嘴较远。所以，养成了把碗端至嘴边吸食的习惯。喝羹匙里的东西也象吸似的，声声作响。这并非哪一方文化高或低，只是各国的习惯、礼仪不同而已。 日本人坐在椅子上围桌用餐是1960年之后的事情。当时，还没有礼仪规矩，甚至有人盘着腿吃饭。外国人看见此景大概会一脸厌恶吧。 韩国女性就座时，单腿翘起。我认为这种姿势很美，但习惯于双膝跪坐的日本女性大概不以为然，而韩国女性恐怕也不认为跪坐为好。 日本等多数亚洲国家，常有人习惯在路上蹲着。欧美人会联想起狗排便的姿势而一脸厌恶。 日本人常常把手放在小孩的头上说“好可爱啊！”，而大部分外国人会不愿意。 如果向回教国家的人们劝食猪肉和酒，或用左手握手、递东西，会不受欢迎的。当然，饭菜也用右手抓着吃。只有从公用大盘往自己的小盘里分食用的公勺是用左手拿。一旦搞错，用黏糊糊的右手去拿， 会遭人厌恶。 在欧美，对不受欢迎的客人不说“请脱下外套”，所以电视剧中的侦探哥隆波总是穿着外套。访问日本家庭时，要在门厅外脱掉外套后进屋。穿到屋里会不受欢迎的。 这些习惯只要了解就不会出问题，如果因为不知道而遭厌恶、憎恨，实在心里难受。 过去，我曾用色彩图画和简短的文字画了一本《关键时刻的礼仪》（新潮文库）。如今越发希望用各国语言翻译这本书。以便能对在日本的外国人有所帮助。同时希望有朝一日以漫画的形式画一本“世界各国的习惯与礼仪”。 练习答案 ５、 （１）止める並んでいる見ているなる着色した （２）拾った入っていた行ったしまった始まっていた 新视野大学英语第三版第二册读写课文翻译 Unit 1 Text A 一堂难忘的英语课 1 如果我是唯一一个还在纠正小孩英语的家长，那么我儿子也许是对的。对他而言，我是一个乏味的怪物：一个他不得不听其教诲的父亲，一个还沉湎于语法规则的人，对此我儿子似乎颇为反感。 2 我觉得我是在最近偶遇我以前的一位学生时，才开始对这个问题认真起来的。这个学生刚从欧洲旅游回来。我满怀着诚挚期待问她：“欧洲之行如何？” 3 她点了三四下头，绞尽脑汁，苦苦寻找恰当的词语，然后惊呼：“真是，哇！” 4 没了。所有希腊文明和罗马建筑的辉煌居然囊括于一个浓缩的、不完整的语句之中！我的学生以“哇！”来表示她的惊叹，我只能以摇头表达比之更强烈的忧虑。 5 关于正确使用英语能力下降的问题，有许多不同的故事。学生的确本应该能够区分诸如their/there/they're之间的不同，或区别complimentary 跟complementary之间显而易见的差异。由于这些知识缺陷，他们承受着大部分不该承受的批评和指责，因为舆论认为他们应该学得更好。 6 学生并不笨，他们只是被周围所看到和听到的语言误导了。举例来说，杂货店的指示牌会把他们引向stationary（静止处），虽然便笺本、相册、和笔记本等真正的stationery（文具用品）并没有被钉在那儿。朋友和亲人常宣称They've just ate。实际上，他们应该说They've just eaten。因此，批评学生不合乎情理。 7 对这种缺乏语言功底而引起的负面指责应归咎于我们的学校。学校应对英语熟练程度制定出更高的标准。可相反，学校只教零星的语法，高级词汇更是少之又少。还有就是，学校的年轻教师显然缺乏这些重要的语言结构方面的知识，因为他们过去也没接触过。学校有责任教会年轻人进行有效的语言沟通，可他们并没把语言的基本框架——准确的语法和恰当的词汇——充分地传授给学生。 新视野大学英语1课文翻译 1下午好！作为校长，我非常自豪地欢迎你们来到这所大学。你们所取得的成就是你们自己多年努力的结果，也是你们的父母和老师们多年努力的结果。在这所大学里，我们承诺将使你们学有所成。 2在欢迎你们到来的这一刻，我想起自己高中毕业时的情景，还有妈妈为我和爸爸拍的合影。妈妈吩咐我们：“姿势自然点。”“等一等,”爸爸说，“把我递给他闹钟的情景拍下来。”在大学期间，那个闹钟每天早晨叫醒我。至今它还放在我办公室的桌子上。 3让我来告诉你们一些你们未必预料得到的事情。你们将会怀念以前的生活习惯，怀念父母曾经提醒你们要刻苦学习、取得佳绩。你们可能因为高中生活终于结束而喜极而泣，你们的父母也可能因为终于不用再给你们洗衣服而喜极而泣！但是要记住：未来是建立在过去扎实的基础上的。 4对你们而言，接下来的四年将会是无与伦比的一段时光。在这里，你们拥有丰富的资源：有来自全国各地的有趣的学生，有学识渊博又充满爱心的老师，有综合性图书馆，有完备的运动设施，还有针对不同兴趣的学生社团——从文科社团到理科社团、到社区服务等等。你们将自由地探索、学习新科目。你们要学着习惯点灯熬油，学着结交充满魅力的人，学着去追求新的爱好。我想鼓励你们充分利用这一特殊的经历，并用你们的干劲和热情去收获这一机会所带来的丰硕成果。 5有这么多课程可供选择，你可能会不知所措。你不可能选修所有的课程，但是要尽可能体验更多的课程！大学里有很多事情可做可学，每件事情都会为你提供不同视角来审视世界。如果我只能给你们一条选课建议的话，那就是：挑战自己！不要认为你早就了解自己对什么样的领域最感兴趣。选择一些你从未接触过的领域的课程。这样，你不仅会变得更加博学，而且更有可能发现一个你未曾想到的、能成就你未来的爱好。一个绝佳的例子就是时装设计师王薇薇，她最初学的是艺术史。随着时间的推移，王薇薇把艺术史研究和对时装的热爱结合起来，并将其转化为对设计的热情，从而使她成为全球闻名的设计师。 6在大学里，一下子拥有这么多新鲜体验可能不会总是令人愉快的。在你的宿舍楼里，住在你隔壁寝室的同学可能会反复播放同一首歌，令你头痛欲裂！你可能喜欢早起，而你的室友却是个夜猫子！尽管如此，你和你的室友仍然可能成 新视野大学英语2课文翻译（Unit1-Unit7） Unit 1 Section A 时间观念强的美国人 Para. 1 美国人认为没有人能停止不前。如果你不求进取，你就会落伍。这种态度造就了一个投身于研究、实验和探索的民族。时间是美国人注意节约的两个要素之一，另一个是劳力。 Para. 2 人们一直说：“只有时间才能支配我们。”人们似乎是把时间当作一个差不多是实实在在的东西来对待的。我们安排时间、节约时间、浪费时间、挤抢时间、消磨时间、缩减时间、对时间的利用作出解释；我们还要因付出时间而收取费用。时间是一种宝贵的资源，许多人都深感人生的短暂。时光一去不复返。我们应当让每一分钟都过得有意义。 Para. 3 外国人对美国的第一印象很可能是：每个人都匆匆忙忙——常常处于压力之下。城里人看上去总是在匆匆地赶往他们要去的地方，在商店里他们焦躁不安地指望店员能马上来为他们服务，或者为了赶快买完东西，用肘来推搡他人。白天吃饭时人们也都匆匆忙忙，这部分地反映出这个国家的生活节奏。工作时间被认为是宝贵的。Para. 3b 在公共用餐场所，人们都等着别人吃完后用餐，以便按时赶回去工作。你还会发现司机开车很鲁莽，人们推搡着在你身边过去。你会怀念微笑、简短的交谈以及与陌生人的随意闲聊。不要觉得这是针对你个人的，这是因为人们非常珍惜时间，而且也不喜欢他人“浪费”时间到不恰当的地步。 Para. 4 许多刚到美国的人会怀念诸如商务拜访等场合开始时的寒暄。他们也会怀念那种一边喝茶或咖啡一边进行的礼节性交流，这也许是他们自己国家的一种习俗。他们也许还会怀念在饭店或咖啡馆里谈生意时的那种轻松悠闲的交谈。一般说来，美国人是不会在如此轻松的环境里通过长时间的闲聊来评价他们的客人的，更不用说会在增进相互间信任的过程中带他们出去吃饭，或带他们去打高尔夫球。既然我们通常是通过工作而不是社交来评估和了解他人，我们就开门见山地谈正事。因此，时间老是在我们心中的耳朵里滴滴答答地响着。 Para. 5 因此，我们千方百计地节约时间。我们发明了一系列节省劳力的装置；我们通过发传真、打电话或发电子邮件与他人迅速地进行交流，而不是通过直接接触。虽然面对面接触令人愉快，但却要花更多的时间, 尤其是在马路上交通拥挤的时候。因此，我们把大多数个人拜访安排在下班以后的时间里或周末的社交聚会上。 Para. 6 就我们而言，电子交流的缺乏人情味与我们手头上事情的重要性之间很少有或完全没有关系。在有些国家, 如果没有目光接触，就做不成大生意，这需要面对面的交谈。在美国，最后协议通常也需要本人签字。然而现在人们越来越多地在电视屏幕上见面，开远程会议不仅能解决本国的问题，而且还能通过卫星解决国际问题。 新视野大学英语3第三版课文翻译 Unit 1 The Way to Success 课文A Never, ever give up! 永不言弃！ As a young boy, Britain's great Prime Minister, Sir Winston Churchill, attended a public school called Harrow. He was not a good student, and had he not been from a famous family, he probably would have been removed from the school for deviating from the rules. Thankfully, he did finish at Harrow and his errors there did not preclude him from going on to the university. He eventually had a premier army career whereby he was later elected prime minister. He achieved fame for his wit, wisdom, civic duty, and abundant courage in his refusal to surrender during the miserable dark days of World War II. His amazing determination helped motivate his entire nation and was an inspiration worldwide. Toward the end of his period as prime minister, he was invited to address the patriotic young boys at his old school, Harrow. The headmaster said, "Young gentlemen, the greatest speaker of our time, will be here in a few days to address you, and you should obey whatever sound advice he may give you." The great day arrived. Sir Winston stood up, all five feet, five inches and 107 kilos of him, and gave this short, clear-cut speech: "Young men, never give up. Never give up! Never give up! Never, never, never, never!" 英国的伟大首相温斯顿·丘吉尔爵士，小时候在哈罗公学上学。当时他可不是个好学生，要不是出身名门，他可能早就因为违反纪律被开除了。谢天谢地，他总算从哈罗毕业了，在那里犯下的错误并没影响到他上大学。后来，他凭着军旅生涯中的杰出表现当选为英国首相。他的才思、智慧、公民责任感以及在二战痛苦而黑暗的时期拒绝投降的无畏勇气，为他赢得了美名。他非凡的决心，不仅激励了整个民族，还鼓舞了全世界。 在他首相任期即将结束时，他应邀前往母校哈罗公学，为满怀报国之志的同学们作演讲。校长说：“年轻的先生们，当代最伟大的演说家过几天就会来为你们演讲，他提出的任何中肯的建议，你们都要听从。”那个激动人心的日子终于到了。温斯顿爵士站了起来——他只有5 英尺5 英寸高，体重却有107 公斤。他作了言简意赅的讲话：“年轻人，要永不放弃。永不放弃！永不放弃！永不，永不，永不，永不！” Personal history, educational opportunity, individual dilemmas - none of these can inhibit a strong spirit committed to success. No task is too hard. No amount of preparation is too long or too difficult. Take the example of two of the most scholarly scientists of our age, Albert Einstein and Thomas Edison. Both faced immense obstacles and extreme criticism. Both were called "slow to learn" and written off as idiots by their teachers. Thomas Edison ran away from school because his teacher whipped him repeatedly for asking too many questions. Einstein didn't speak fluently until he was almost nine years old and was such a poor student that some thought he was unable to learn. Yet both boys' parents believed in them. They worked intensely each day with their sons, and the boys learned to never bypass the long hours of hard work that they needed to succeed. In the end, both Einstein and Edison overcame their childhood persecution and went on to achieve magnificent discoveries that benefit the entire world today. Consider also the heroic example of Abraham Lincoln, who faced substantial hardships, failures and repeated misfortunes in his lifetime. His background was certainly not glamorous. He was raised in a very poor family with only one year of formal education. He failed in business twice, suffered a nervous breakdown when his first love died suddenly and lost eight political Text A 课文 A The humanities: Out of date? 人文学科：过时了吗？ When the going gets tough, the tough takeaccounting. When the job market worsens, manystudents calculate they can't major in English orhistory. They have to study something that booststheir prospects of landing a job. 当形势变得困难时，强者会去选学会计。当就业市场恶化时，许多学生估算着他们不能再主修英语或历史。他们得学一些能改善他们就业前景的东西。 The data show that as students have increasingly shouldered the ever-rising c ost of tuition,they have defected from the study of the humanities and toward applied science and "hard"skills that they bet will lead to employment. In oth er words, a college education is more andmore seen as a means for economic betterment rather than a means for human betterment.This is a trend that i s likely to persist and even accelerate. 数据显示，随着学生肩负的学费不断增加，他们已从学习人文学科转向他们相信有益于将来就业的应用科学和“硬”技能。换言之，大学教育越来越被看成是改善经济而不是提升人类自身的手段。这种趋势可能会持续，甚至有加快之势。 Over the next few years, as labor markets struggle, the humanities will proba bly continue theirlong slide in succession. There already has been a nearly 50 percent decline in the portion of liberal arts majors over the past generatio n, and it is logical to think that the trend is boundto continue or even accel erate. Once the dominant pillars of university life, the humanities nowplay li ttle roles when students take their college tours. These days, labs are more vi vid and compelling than libraries. 在未来几年内，由于劳动力市场的不景气，人文学科可能会继续其长期低迷的态势。在上一代大学生中，主修文科的学生数跌幅已近50%。这种趋势会持续、甚至加速的想法是合情合理的。人文学科曾是大学生活的重要支柱，而今在学生们参观校园的时候，却只是一个小点缀。现在，实验室要比图书馆更栩栩如生、受人青睐。 Here, please allow me to stand up for and promote the true value that the h umanities add topeople's lives. 在这儿，请允许我为人文学科给人们的生活所增添的真实价值进行支持和宣传。 第10课 日本的季节 日本的一年有春、夏、秋、冬四个季节。 3月、4月和5月这三个月是春季。春季是个暖和的好季节。桃花、樱花等花儿开得很美。人们在4月去赏花。 6月到8月是夏季。夏季非常闷热。人们去北海道旅游。7月和8月是暑假，年轻人去海边或山上。也有很多人去攀登富士山。富士山是日本最高的山。 9月、10月和11月这3个月是秋季。秋季很凉爽，晴朗的日子较多。苹果、桔子等许多水果在这个季节成熟。 12月到2月是冬季。日本的南部冬天不太冷。北部非常冷，下很多雪。去年冬天东京也很冷。今年大概不会那么冷吧。如果冷的话，人们就使用暖气炉。 第12课 乡下 我爷爷住哎乡下。今天，我要去爷爷家。早上天很阴，但中午天空开始变亮，天转好了。我急急忙忙吃完午饭，坐上了电车。 现在，电车正行驶在原野上。窗外，水田、旱地连成一片。汽车在公路上奔驰。 这时，电车正行驶在大桥上。下面河水在流动。河水很清澈，可以清澈地看见河底。可以看见鱼在游动。远处，一个小孩在挥手。他身旁，牛、马在吃草。 到了爷爷居住的村子。爷爷和奶奶来到门口等着我。爷爷的房子是旧房子，但是很大。登上二楼，大海就在眼前。海岸上，很多人正在全力拉缆绳。渐渐地可以看见网了。网里有很多鱼。和城市不同，乡下的大自然真是很美。 第13课 暑假 大概没有什么比暑假更令学生感到高兴的了。大学在7月初，其他学校在二十四日左右进入暑假。暑假大约1个半月。 很多人利用这个假期去海边、山上，或者去旅行。学生中，也有人去打工。学生由于路费等只要半价，所以在学期间去各地旅行。因此，临近暑假时，去北海道的列车上就挤满了这样的人。从炎热的地方逃避到凉爽的地方去，这是很自然的事。一般在1月、最迟在2月底之前就要预定旅馆。不然的话可能会没有地方住。 暑假里，山上、海边、湖里、河里会出现死人的事，这种事故都是由于不注意引起的。大概只能每个人自己多加注意了。 在东京附近，镰仓等地的海面不起浪，因此挤满了游泳的人。也有人家只在夏季把海边的房子租下来。 暑假里，学校的老师给学生布置作业，但是有的学生叫哥哥或姐姐帮忙。 第14课 各式各样的学生 我就读的大学都有各种各样的学生入学。学生有的是中国人，有的是美国人，有的是英国人。既有年轻的，也有不年轻的。有胖的学生，也有瘦的学生。学生大多边工作边学习。因此，大家看上去都很忙。经常有人边听课边打盹。 我为了学习日本先进的科学技术和日本文化来到日本。预定在这所大学学习3年。既然特意来了日本，所以每天都很努力学习。即便如此，考试之前还是很紧张。其他学生也是这 教育界的科技革命 如果让生活在年的人来到我们这个时代，他会辨认出我们当前课堂里发生的许多事情——那盛行的讲座、对操练的强调、从基础读本到每周的拼写测试在内的教学材料和教学活动。可能除了教堂以外，很少有机构像主管下一代正规教育的学校那样缺乏变化了。 让我们把上述一贯性与校园外孩子们的经历作一番比较吧。在现代社会，孩子们有机会接触广泛的媒体，而在早些年代这些媒体简直就是奇迹。来自过去的参观者一眼就能辨认出现在的课堂，但很难适应现今一个岁孩子的校外世界。 学校——如果不是一般意义上的教育界——天生是保守的机构。我会在很大程度上为这种保守的趋势辩护。但变化在我们的世界中是如此迅速而明确，学校不可能维持现状或仅仅做一些表面的改善而生存下去。的确，如果学校不迅速、彻底地变革，就有可能被其他较灵活的机构取代。 计算机的变革力 当今时代最重要的科技事件要数计算机的崛起。计算机已渗透到我们生活的诸多方面，从交通、电讯到娱乐等等。许多学校当然不能漠视这种趋势，于是也配备了计算机和网络。在某种程度上，这些科技辅助设施已被吸纳到校园生活中，尽管他们往往只是用一种更方便、更有效的模式教授旧课程。 然而，未来将以计算机为基础组织教学。计算机将在一定程度上允许针对个人的授课，这种授课形式以往只向有钱人提供。所有的学生都会得到符合自身需要的、适合自己学习方法和进度的课程设置，以及对先前所学材料、课程的成绩记录。 毫不夸张地说，计算机科技可将世界上所有的信息置于人们的指尖。这既是幸事又是灾难。我们再也无须花费很长时间查找某个出处或某个人——现在，信息的传递是瞬时的。不久，我们甚至无须键入指令，只需大声提出问题，计算机就会打印或说出答案，这样，人们就可实现即时的"文化脱盲"。 美中不足的是，因特网没有质量控制手段；"任何人都可以拨弄"。信息和虚假信息往往混杂在一起，现在还没有将网上十分普遍的被歪曲的事实和一派胡言与真实含义区分开来的可靠手段。要识别出真的、美的、好的信息，并挑出其中那些值得知晓的, 这对人们构成巨大的挑战。 对此也许有人会说，这个世界一直充斥着错误的信息。的确如此，但以前教育当局至少能选择他们中意的课本。而今天的形势则是每个人都拥有瞬时可得的数以百万计的信息源，这种情况是史无前例的。 教育的客户化 与以往的趋势不同，从授权机构获取证书可能会变得不再重要。每个人都能在模拟的环境中自学并展示个人才能。如果一个人能像早些时候那样"读法律"，然后通过计算机模拟的实践考试展现自己的全部法律技能，为什么还要花万美元去上法学院呢？用类似的方法学开飞机或学做外科手术不同样可行吗？ 在过去，大部分教育基本是职业性的：目的是确保个人在其年富力强的整个成人阶段能可靠地从事某项工作。现在，这种设想有了缺陷。很少有人会一生只从事一种职业；许多人都会频繁地从一个职位、公司或经济部门跳到另一个。 在经济中，这些新的、迅速变换的角色的激增使教育变得大为复杂。大部分老成持重的教师和家长对帮助青年一代应对这个会经常变换工作的世界缺乏经验。由于没有先例，青少年们只有自己为快速变化的"事业之路"和生活状况作准备。从实践的角度探讨在日语教学中多媒体课件的应用
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