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The Hubble Deep Field South - STIS Imaging

a r X i v :a s t r o -p h /9912167v 1 8 D e c 1999

Accepted for publication in the Astronomical Journal,February 2000

The Hubble Deep Field South –STIS Imaging 1.

Jonathan P.Gardner 2,Ste?A.Baum 3,Thomas M.Brown 2,7,C.Marcella Carollo 4,8,9,Jennifer Christensen 3,Ilana Dashevsky 3,Mark E.Dickinson 3,Brian R.Espey 3,10,Henry C.Ferguson 3,Andrew S.Fruchter 3,Anne M.Gonnella 3,Rosa A.Gonzalez-Lopezlira 3,Richard

N.Hook 5,Mary Elizabeth Kaiser 2,4,Crystal L.Martin 3,8,Kailash C.Sahu 3,Sandra Savaglio 3,10,T.Ed Smith 3,Harry I.Teplitz 2,7,Robert E.Williams 3,Jennifer Wilson 3,11

ABSTRACT

We present the imaging observations made with the Space Telescope Imaging Spectrograph of the Hubble Deep Field –South.The ?eld was imaged in 4bandpasses:a clear CCD bandpass for 156ksec,a long-pass ?lter for 22–25ksec per pixel typical exposure,a near-UV bandpass for 23ksec,and a far-UV bandpass for 52ksec.The clear visible image is the deepest observation ever made in the UV-optical wavelength region,reaching a 10σAB magnitude of 29.4for an object of area 0.2square arcseconds.The ?eld contains QSO J2233-606,the target of the STIS spectroscopy,and extends 50′′×50′′for the visible images,and 25′′×25′′for the ultraviolet images.We present the images,catalog of objects,and galaxy counts obtained in the ?eld.

1.Introduction

The Space Telescope Imaging Spectrograph(STIS)(Kimble et al.1997;Woodgate et al.1998;Walborn&Baum1998)was used during the Hubble Deep Field–South(HDF–S) (Williams et al.1999)observations for ultraviolet spectroscopy(Ferguson et al.1999)and ultraviolet and optical imaging.In this paper we present the imaging data.

The Hubble Deep Field–North(HDF–N)(Williams et al.1996)is the best studied ?eld on the sky,with>1Msec of Hubble Space Telescope(HST)observing time(including follow-up observations by Thompson et al.1999and Dickinson et al.1999),and countless observations with ground-based telescopes(e.g.,Cohen et al.1996;Connolly et al.1997). Results obtained to date include a measurement of the ultraviolet luminosity density of the universe at z>2(Madau et al.1996),the morphological distribution of faint galaxies (Abraham et al.1996),galaxy-galaxy lensing(Hudson et al.1998),and halo star counts (Elson,Santiago&Gilmore1996).See Ferguson(1998)and Livio,Fall&Madau(1998) for reviews and further references.The HDF–S di?ers from the HDF–N in several ways. First,the installation of STIS and NICMOS on HST in1997February has enabled parallel observations with three cameras.In addition to the STIS data,the HDF–S dataset includes deep WFPC2imaging(Casertano et al.1999),deep near-infrared imaging(Fruchter et al. 1999),and wider-area?anking?eld observations(Lucas et al.1999).Second,the STIS observations were centered on QSO J2233-606,at z≈2.24,to obtain spectroscopy.Finally, the?eld was chosen in the southern HST continuous viewing zone in order to enable follow-up observations with ground-based telescopes in the southern hemisphere.

In section2we describe the observations.In section3we describe the techniques we used to reduce the CCD images.In section4we describe the reduction of the MAMA images.In section5we describe the procedures used to catalog the images.In section6we present some statistics of the data,including galaxy number counts and color distributions. Our purpose in this paper is to produce a useful reference for detailed analysis of the STIS images.Thus for the most part we refrain from model comparisons and speculation on the signi?cance of the results.We expect the STIS images to be useful for addressing a wide variety of astronomical topics,including the sizes of the faintest galaxies,the ultraviolet-optical color evolution of galaxies,the number of faint stars and white dwarfs in the galactic halo,and the relation between absorption line systems seen in the QSO spectrum and galaxies near to the line of sight.We also expect the observations to be useful for studying sources very close to the quasar,and perhaps for detecting the host galaxy of the quasar.However,this may require a re-reduction of the images,as the quasar is saturated in all of the CCD exposures,and there are signi?cant problems with scattered light and re?ections.

2.Description of the observations

The images presented here were taken in4di?erent modes,50CCD(Figure1),

F28X50LP(Figure2),NUVQTZ(Figure3),and FUVQTZ(Figure4).The50CCD and F28X50LP modes used the Charge Coupled Device(CCD)detector.The50CCD is a clear,?lterless mode,while the F28X50LP mode uses a long-pass?lter beginning at about 5500?A.The FUVQTZ and NUVQTZ used the Multi-Anode Microchannel Array(MAMA) detectors as imagers with the quartz?lter.The quartz?lter was selected to reduce the sky noise due to airglow to levels below the dark noise.The e?ective areas of the4modes are plotted in Figure5,along with a pseudo-B430bandpass constructed from the50CCD and F28X50LP?uxes.The MAMA?eld of view is a square,25′′on a side,and was dithered so that the observations include data on a?eld approximately30′′square.The50CCD mode is ?lterless imaging with a CCD.The?eld of view is a square50′′on a side,and the dithering extends to a square60′′on a side.The F28X50LP is a long-pass?lter that vignettes the ?eld of view of the CCD to a rectangle28×50′′.The observations were dithered to image the entire?eld of view of the50CCD observations,although the exposure time per point on the sky is thus approximately half the total exposure time spent in this mode.The original pixel scale is0.0244′′pix?1for the MAMA images,and0.05071′′pix?1for the CCD images. The?nal combined images have a scale of0.025′′pix?1in all cases.Table1describes the observations.The?lterless50CCD observations correspond roughly to V+I,and reach

a depth of29.4AB magnitudes at10σin a0.2square arcsecond aperture(320drizzled pixels).This is the deepest exposure ever made in the UV-optical wavelength region.

2.1.Selection of the Field

Selection of the?eld is described by Williams et al.(1999).The QSO is at

RA=22h33m37.5883s,Dec=?60?33′29.128′′(J2000).The errors on this position are estimated to be less than40milli-arcseconds(Zacharias et al.1998).The position of the QSO on the50CCD and F28X50LP images is x=1206.61,y=1206.32,and on the MAMA images is x=806.61,y=806.32.

2.2.Test Data

Test observations of the?eld were made in1997October.These data are not used in the present analysis.While the test exposures do not add signi?cantly to the exposure time, they would provide a one-year baseline for proper motion studies of the brighter objects.

2.3.Observing Plan

The STIS observations were scheduled so that the CCD was used in the orbits that were impacted by the South Atlantic Anomaly,and the MAMAs were used in the clear orbits.The observations were made in the continuous viewing zone,and therefore were all made close to the limb of the Earth.The G430M spectroscopy,all of which was read-noise limited,was done during the day or bright part of the orbit,while the CCD imaging was all done during the night or dark part of the orbit.The MAMA imaging,done with the quartz ?lter,is insensitive to scattered Earth light,and was therefore done during bright time.A more detailed discussion of the scheduling issues is given by Williams et al.(1999).The sky levels in the50CCD images were approximately twice the square of the read noise,so these data are marginally sky noise limited.The MAMA images are limited by the dark noise.

2.4.Dithering and Rotation

The images were dithered in right ascension(RA)and declination(Dec)in order to sample the sky at the sub-pixel level.In addition,variations in rotation of about±1degree were used to provide additional dithering for the WFPC2and NICMOS?elds during the STIS spectroscopic observations.The STIS imaging observations were interspersed with the STIS spectroscopic observations;therefore,all of the images were dithered in rotation as well as RA and Dec.

2.5.CR-SPLIT and pointing strategy

The CCD exposures were split into2or3cr-split s that each have the same RA, Dec,and rotation.This facilitates cosmic ray removal,although as discussed below,this was only used in the?rst iteration of the data reduction.The?nal50CCD image is the combination of193exposures making up67cr-split pointings.After standard pipeline processing,(including bias and dark subtraction,and?at?elding),each exposure is given a flt?le extension,and the cosmic-ray rejected combinations of each cr-split is given a crj?le extension.The?nal F28X50LP image is the combination of66exposures making up23cr-split pointings.The F28X50LP image included12pointings at the northern part of the?eld,one pointing at the middle of the?eld,and10pointings at the southern half of the?eld.

2.6.PSF observations

In order to allow for PSF subtraction of the QSO present in the center of the STIS 50CCD image,two SAO stars of about10mag were observed in the?lterless50CCD mode before and after the main HDF-S campaign.The stars are SAO255267,a G2star,and SAO255271,an F8star,respectively.These targets have spectral energy distributions in the STIS CCD sensitivity range similar to that of the QSO.For each star,32di?erent

cr-split exposures were taken.The following strategy was used:(i)four di?erent exposure times between0.1s and5s for each cr-split frame,to ensure high signal-to-noise in the wings while not saturating the center;(ii)a four-position dither pattern with quarter-pixel sampling and cr-split at each pointing with each exposure time;(iii)use of gain=4,to insure no saturation in the A-to-D conversion.During the observations for SAO255267, a failure in the guide star acquisition procedure caused the loss of its long-exposure(5s) images.Gain=4has a well-documented large scale pattern noise that must be removed,e.g., by Fourier?ltering,before a reliable PSF can be produced.These data are not discussed further in this paper,but are available from the HST archive for further analysis.

3.Reduction of the CCD Images

3.1.Bias,Darks,Flats and Masks

Standard processing of CCD images involves bias and dark subtraction,?at?elding,and masking of detector defects.The bias calibration?le used for the HDF-S was constructed from285individual exposures,combined together with cosmic-ray and hot-pixel trail rejection.

The dark?le was constructed from a“superdark”frame and a“delta”dark frame. The superdark is the cosmic-ray rejected combination of over100individual1200s dark exposures taken over the several months preceding the HDF-S campaign.The delta dark adds into this high S/N dark frame the pixels that are more than5σfrom the mean in the superdark-subtracted combination of14dark exposures taken during the HDF-S campaign. Calibration of the images with this dark frame removes most of the hot pixels but still leaves several hundred in each image.

An image mask was constructed to remove the remaining hot pixels and detector features.The individual cosmic-ray rejected HDF-S50CCD exposures were averaged

together without registration.The remaining hot pixels were identi?ed with the IRAF12 cosmicrays task.These pixels were included in a mask that was used to reject pixels during the drizzle phase.Pixels that were more than5σbelow the mean sky background were also masked,as were the30worst hot pixel trails,and the unilluminated portions of the detector around the edges.Hot pixel trails run along columns and are caused by high dark current in a single pixel along the column.

Flat?elding was carried out by the IRAF/STSDAS calstis pipeline using two reference ?les.The?rst,the pflat corrects for small-scale pixel-to-pixel sensitivity variations,but is smooth on large scales.This?le was created from ground-test data but comparisons to a preliminary version of the on-orbit?at revealed only a few places where the di?erence was more than1%.The CCD also shows a5-10%decrease in sensitivity near the edges due to vignetting.This illumination pattern was corrected by a low-order?t to a sky?at constructed from the?anking?eld observations.

3.2.Shifts and rotations

After pipeline processing,the CCD images were reduced using the IRAF/STSDAS package dither,and test versions called xdither,and xditherii.These packages include the drizzle software(Fruchter&Hook1998;Fruchter et al.1998;Fruchter1998).We used drizzle version1.2,dated1998February.The test versions di?er from the previously released version primarily in their ability to remove cosmic rays from each individual exposure,and include tasks that have not yet been released.

The xditherii package uses an iterative process to reject cosmic rays and determine the x and y sub-pixel shifts,which we summarize here.The standard pipeline rejects cosmic rays using each cr-split of2or3images.The resulting crj?les are used as the ?rst iteration,we determine the x and y shifts,and the?les are median combined.The resulting preliminary combination is then shifted back into the frame of each of the original exposures(flt?les),and a new cosmic ray mask is made.By comparing each exposure to a high signal-to-noise combination of all of the data,we are less likely to leave cosmic ray residuals.The x and y shifts are determined at each iteration as well.

The rotations used in combining the data were determined from the roll

12IRAF is distributed by the National Optical Astronomy Observatories,which are operated by the Association of Universities for Research in Astronomy,Inc.,under cooperative agreement with the National Science Foundation.

parameter in the jitter?les,using the program bearing.We did not seek to improve on these rotations via cross-correlation or any other method.We did use cross-correlation to determine the x and y shifts.

Determination of the sub-pixel x and y shifts was done with an iterative procedure. The?rst iteration was obtained by determining the centroid of the bright point source just west of the QSO,using the pipeline cosmic-ray rejected crj?les.We could not use cross-correlation in this?rst iteration,because the very bright star on the southern edge of the?eld was present on images taken at some,but not all,dither positions,which corrupted the cross-correlation.The source we used for centroiding was clearly visible on all of the 50CCD and F28X50LP frames.

Using these shifts(which were accurate to better than1pixel),we created a preliminary combined image.After pipeline processing and cosmic ray rejection,the drizzle program was used to shift and rotate each sc crj?le onto individual outputs,without combining them.We then used the task imcombine to create a median combination of the?les.This preliminary image was then shifted and rotated back into the frame of each individual exposure using the xdither task,blot,ready for the next iteration of the cosmic-ray rejection procedure.

3.3.Cosmic ray rejection

In this iteration,we discarded the crj?les,and went back to the flt?les,in which each exposure had undergone bias and dark subtraction and?at?elding,but not cosmic-ray rejection.Each exposure was compared to the blotted image,and a cosmic-ray mask for that exposure was created from all of the pixels that di?ered(positively or negatively)by more than a given threshold from the blotted image.In the version1.0released50CCD image,this threshold was set to be5σ.However,we believe that a small error in the sky level determination,introduced by the ampli?er ringing correction discussed below,meant that our rejection was approximately at the3σlevel.The cosmic ray masks were multiplied by the hot pixel masks discussed above,and resulted in about8%of the pixels being masked as either cosmic rays or hot pixels.This is,perhaps,overly conservative.A less conservative cut(after correcting the error in the sky value)would result in slightly higher exposure time per pixel,and thus an improvement of1-2%in the signal to noise ratio.The cosmic ray mask was combined with the hot pixel and cosmetic defect mask.

This problem with the sky value was corrected in the F28X50LP image,and a3σlevel was used in the cosmic ray rejection.

3.4.Ampli?er ringing correction

Horizontal features due to ampli?er ringing,varying in pattern from image to image, were present in most of the STIS CCD frames.When a pixel saw a highly saturated signal, the bias level was depressed in the readout for the next few rows.The very high signals causing this ringing came from hot pixels and from the saturated QSO.The signal-to-noise ratio in the overscan region of the detector was not su?cient to remove these features well.We removed them with a procedure that subtracted on a row-by-row basis,from each individual image,the weighted average of the background as derived from the innermost 800columns after masking and rejecting“contaminated”pixels.The masks included all visible sources,hot pixels,and cosmic-ray hits.The source mask was determined from the initial registered median-combined image,shifted back to the reference frame of each of the individual images.For the unmasked pixels in each row,the50highest and lowest were rejected and the mean of the remaining pixels was subtracted from the each pixel in that row.

Heavily smoothing the images reveals very slight horizontal residuals that were not removed by the present choice of parameters in this process.

3.5.Drizzling it all together

The?nal image combination was done by drizzling the ampli?er-ringing corrected pipeline products together onto a single output image.The exposures were weighted

by the square of the exposure time,divided by the variance,which is(sky+rn2+dark). The rotations were corrected so that North is in the+y direction,and the scale used was0.492999original CCD pixels per output pixel so that the?nal pixel scale is exactly 0.025arcsec/pixel.For the50CCD data we used a pixfrac=0.1,which is approximately equivalent to interleaving,where each input pixel falls on a single output pixel.For the F28X50LP data we used pixfrac=0.6,as a smaller pixfrac left visible holes in the

?nal image.See Fruchter&Hook(1998)for a discussion of the meaning of the drizzle parameters.The point spread functions of bright,non-saturated point sources are shown in Figure6.The sources selected are the point source just to the west of the quasar in the 50CCD and F28X50LP images,and the QSO in the MAMA images.

The?nal image is given in counts per second,which can be converted to magnitudes on the stmag system using the photometric zeropoints given by the photflam parameter supplied in the image headers.We used the pipeline photometric zeropoints for the50CCD and MAMA images,but revised the F28X50LP zeropoint by0.1magnitude based on

a comparison of STIS photometry of the HST calibration?eld inωCentauri with the ground-based photometry of Walker(1994).The zeropoints in the AB magnitude system which we used are26.386,25.291,23.887,and21.539,for the50CCD,F28X50LP,NUVQTZ and FUVQTZ respectively.We also supply the weight image,which is the sum of the weights falling on each pixel.For the F28X50LP image,we supply an exposure-time image, which is the total exposure time contributing to each pixel.We have multiplied this image by the area of the output pixels.The world coordinate system in the headers was corrected so that North is exactly in the+y direction,and the pixel scale is exactly0.025arcsec/pixel.

3.6.Window re?ection

A window in the STIS CCD re?ects slightly out-of-focus light from bright sources to the +x,?y direction(SW on the HDF-S images).The QSO is saturated in every50CCD and F28X50LP exposure.The window re?ection of the QSO is clearly visible in the F28X50LP image,but has been partially removed from the50CCD image by the cosmic-ray rejection procedure.We wish to emphasize that it has only been partially removed,and there are remaining residuals.These residuals should not be mistaken for galaxies near the QSO,nor should they be mistaken for the host galaxy of the QSO.There is additional re?ected light from the QSO(and from the bright star at the southern edge)evident in the images.We believe that the version1.0released images are not appropriate for searching for objects very close to or underlying the QSO,and that such a search would require re-processing the raw data with particular attention paid to the window re?ection,other re?ected light,and to the PSF of the QSO.The di?raction spikes of the QSO are smeared in the?nal images by the rotation of the individual exposures.

4.Reduction of the MAMA Images

The near-UV and far-UV images are respectively the weighted averages of12and25 registered frames,with total exposure times of22616s and52124s.The MAMAs do not su?er from read noise or cosmic rays,and the quasar is not saturated in any of the UV data.However,the MAMAs do have calibration issues that must be addressed.

4.1.Flats,Dark Counts,and Geometric Correction

Prior to combination,all frames were processed with CALSTIS,including updated high-resolution pixel-to-pixel?at?eld?les for both UV detectors.Geometric correction and rescaling were applied in the?nal combinations via the drizzle program.The quartz ?lter changes the far-UV plate scale relative to that in the far-UV clear mode,and so the relative scale between MAMA imaging modes was determined from calibration images of the globular cluster NGC6681.

Dark subtraction for the near-UV image was done by subtracting a scaled and

?at-?elded dark image from each near-UV frame.The scale for the dark image was determined by inspection of the right-hand corners of the near-UV image,because these portions of the detector are occulted by the aperture mask and thus only register dark counts.For the far-UV images,calstis removes a nearly?at dark frame,but the upper left-hand quadrant of STIS far-UV frames contains a residual glow in the dark current after nominal calibration.This glow varies from frame to frame and also appears to change shape slightly with time.To remove the residual dark current,the16far-UV frames with the highest count rates in the glow region were co-added without object registration but with individual object masks for the only two obvious objects in the far-UV frames(the quasar and bright spiral NNE of the quasar).We then?t the result with a cubic spline to produce a glow pro?le.This pro?le was then scaled to the residual glow in each processed frame and subtracted prior to the?nal drizzle.Even during observations with a strong dark glow,where the dark count rate is an order of magnitude higher than normal,it is still very low,reaching rates no higher than6×10?5cts sec?1pix?1.The glow thus appears as a higher concentration of ones in a sea of zeros,and the subtraction of a smooth glow pro?le from such quantized data over-subtracts from the zeros and under-subtracts from the ones. These e?ects are visible in the corrected data,even when smoothed out considerably in the?nal drizzled far-UV image.A low-resolution?at-?eld correction was applied to the far-UV frames after subtraction of the residual dark glow.The near-UV frames require no low-resolution?at?eld correction.

4.2.Shifts and Rotations

Currently,geometrically corrected NUVQTZ and FUVQTZ frames do not have the same plate scale.Although geometric correction,rotation,and rescaling is applied during the?nal summation of individual calibrated frames,we?rst produced a set of calibrated frames that included these corrections,in order to accurately determine the relative shifts between them;this information was then used in conjunction with these corrections in

the?nal drizzle.All near-UV and far-UV frames were geometrically corrected,rescaled to 0.025′′pix?1,and rotated to align North with the+y image axis.The roll angle speci?ed in the jitter?les was used to determine the relative roll between frames,and the mean

di?erence between the planned roll and the jitter roll determined the absolute rotation.

It is di?cult to determine accurate roll angles from the images themselves,because of the scarcity of objects in the MAMA images.All near-UV and far-UV frames were then cross-correlated against one of the far-UV frames to provide shifts in the output coordinate system.Note that centroiding on the quasar in all far-UV and near-UV frames yields the same shifts as cross-correlation,within0.1pixel.

4.3.Drizzling

The calibrated frames were drizzled to a1600×1600pixel image,including the above corrections,rescaling,rotations,and shifts.We updated the world coordinate system in the image headers to exactly re?ect the plate scale,alignment,and the astrometry of the quasar.

For both the far-UV and near-UV frames,individual pixels in each frame were weighted by the ratio of the exposure time squared to the dark count variance;this weights the exposures by(S/N)2for sources that are fainter than the background.Although the variations in the far-UV dark pro?le are smooth,the near-UV dark pro?le is an actual sum of dark frames,and so we smoothed the near-UV dark pro?le to determine the weights. With this weighting algorithm,pixels in the upper left-hand quadrant of a given far-UV image contribute less when the dark glow is high,and contribute more when it is low.The statistical errors(cts s?1)in the?nal drizzled image,for objects below the background(e.g., objects other than the quasar),are given by the square root of the?nal drizzled weights?le.

The drizzle“dropsize”(pixfrac)was0.6,thus improving the resolution over a pixfrac of1.0(which would be equivalent to simple shift-and-add).The1600×1600pixel format contains all dither positions,and pixels outside of the dither pattern are at a count rate of zero.The pixel mask for each near-UV input frame included the occulted corners of the detector,a small number of hot pixels,and pixels with relatively low response(those with values≤0.75in the high-resolution?at?eld).The pixel mask for each far-UV frame included hot pixels and all pixels?agged in the data quality?le for that frame.When every input pixel drizzled onto a given output pixel was masked,that pixel was set to zero.

4.4.Window Re?ection

As with the CCD,a window re?ection of the QSO appears in the near-UV image. This re?ection appears≈0.2′′east of the QSO itself,and should not be considered an astronomical object.

5.Cataloging

5.1.Cataloging the Optical Images

The catalog was created using the SExtractor package(Bertin&Arnouts1996), revision of1998November19,with some minor modi?cations that were done for this application.We used two separate runs of SExtractor,and manually merged the resulting output catalogs.The?rst run used a set of parameters selected to optimize the detection of faint sources while not splitting what appeared to the eye to be substructure in a single object.We varied the parameters detect mincont, back filtersize.We decided to use a detection threshold corresponding to an isophote of0.65σ.Sources were required a minimum area of16connected pixels above this threshold.Deblending was done when the?ux in the fainter object was a minimum of 0.03times the?ux in the brighter object.The background map was constructed on a grid of60pixels,and subsequently?ltered with a3×3median?lter.Prior to cataloging,the image was convolved with a Gaussian kernel with full width half maximum of3.4pixels.As discussed in Fruchter&Hook(1998),the e?ects of drizzling on the photometry is no more than2%,and in our well-sampled50CCD?eld,the e?ects should be much less than this. This e?ect is smaller than other uncertainties in the photometry of extended objects.

The second run of SExtractor was optimized to detect objects that lay near the QSO and the bright star at the southern edge of the image.These objects tend to be blended in with the point source at the lower detection threshold.Although our catalog might include galaxies that are associated with absorption lines in the quasar spectrum, we did not attempt to subtract the quasar light from the image,and so the catalog does not include objects within3′′of the quasar.The parameters used for the second run were the same as for the?rst run,with the exception of the detect

detected in the second run were added to the catalog generated by the?rst run,and?agged accordingly.Objects from the second run that were not confused with the quasar or the bright star were not included.The isophotal photometry of objects from the second run will not be consistent with the photometry of objects from the?rst run,because a di?erent isophote was used.Eight objects were added to the catalog in this way.

In addition,26objects from the?rst SExtractor run were clearly spurious due to the di?raction spikes of the QSO and the bright star.These were manually deleted from the catalog.

Photometry of the F28X50LP image was done with SExtractor run in two-image mode,in which the objects were detected and identi?ed on the50CCD image,but the photometry was done in the other band.Isophotes and elliptical apertures are thus determined by the extent of the objects on the50CCD images.Objects detected in

the F28X50LP image but not on the50CCD image are impossible,since it has a lower throughput and shorter exposure time.

5.2.Cataloging the Ultraviolet Images

Fluxes in the UV were calculated outside of SExtractor because it had some problems handling quantized low-signal data.To determine the gross?ux,we summed the countrate within the area for each object appearing in the SExtractor50CCD segmentation map.We then created an object mask by“growing”each object in the segmentation map,using the IDL routine dilate,until it subtended an area three times its original size.The resulting mask excludes faint emission outside of the SExtractor isophotes for all known objects in the?eld.The sky was calculated from those exposed pixels within a151×151pixel box centered on each object,excluding pixels from the mask. The mean countrate per pixel in this sky region was used to determine the background for each object(the median is not a useful quantity when dealing with very low quantized signals),and thus the net?ux.Statistical errors per pixel for objects at or below the background are determined from the drizzle weight image raised to the?1/2power.The statistical errors for the gross?ux and sky?ux were calculated using this pixel map of statistical errors,and thus underestimate the errors for bright objects such as the quasar.

Some objects that are fully-exposed in the CCD image do not fall entirely within the exposed area of the MAMA images;for these objects,we calculated the UV?ux in the exposed area only,without correcting for the incomplete exposure,and?agged such objects accordingly.Objects were also?agged if the sky-box described above did not contain at

least100pixels(e.g.,the quasar).For these objects,we calculated a global sky value from a larger685×670pixel box,roughly centered in each MAMA image,that only includes areas fully exposed in the dither pattern,and excludes pixels in the object mask.When the net?ux incorporates this global sky value,they have been?agged accordingly.We do not expect or see any evidence for objects in the ultraviolet images that do not appear on the 50CCD image.

5.3.The Catalog

The catalog is presented in Table2,which contains a subset of the photometry.The full catalogs are available on the World Wide Web.For each object we report the following parameters:

ID:The SExtractor identi?cation number.The objects in the list have been sorted by right ascension(?rst)and declination(second),and thus are no longer in catalog order. In addition,the numbers are no longer continuous,as some of the object identi?cations from the?rst SExtractor run have been removed.Objects from the second SExtractor run have had10000added to their identi?cation numbers.These identi?cation numbers provide a cross-reference to the segmentation maps.

HDFS

J223333.69?603346.0, at RA22h33m33.69s,Dec60deg33′46.0′′,epoch J2000.

x,y:The x and y pixel positions of the object on the50CCD and F28X50LP images. To get the x and y pixel positions on the MAMA images,subtract400from each.

m i,m a:The isophotal(m i)and“mag

auto”is an elliptical Kron(1980)magnitude,determined from the sum of the counts in an elliptical aperture.The semi-major axis of this aperture is de?ned by2.5times the?rst moments of the?ux distribution within an ellipse roughly twice the isophotal radius.However if the aperture de?ned this way would have a semi-major axis smaller than than3.5pixels,a3.5pixel value is used.

clr-lp:Isophotal color,50CCD?F28X50LP,in the AB magnitude system,as determined in the50CCD isophote.SExtractor was run in two-image mode to determine

the photometry in the F28X50LP image,using the50CCD image as the detection image. When the measured F28X50LP?ux is less than2σ,we determine an upper limit to the color using the?ux plus2σwhen the measured?ux is positive,and2σwhen the measured ?ux is negative.We did not clip the50CCD photometry.

nuv-clr,fuv-clr:Isophotal colors,NUVQTZ-50CCD and FUVQTZ-50CCD,in the AB magnitude system.Photometry in the MAMA images are discussed above.Photometry of objects falling partially outside the MAMA image are?agged and should not be considered reliable.When the measured?ux is less than2σ,we give lower limits to the color as discussed above.

r h:The half-light radius of the object in the50CCD image,given in milli-arcseconds. The half-light radius was determined by SExtractor to be the radius at which a circular aperture contains half of the?ux in the“mag

30mag.The turnover fainter than this is due to incompleteness;the counts do not turn over for astrophysical or cosmological reasons.

6.2.Colors and Dropouts

The50CCD-F28X50LP colors of objects in the STIS images are plotted as points

in Figure8.Flagged objects have been removed from the sample.For comparison,we plot K–corrected(no-evolution)colors of the template galaxies in the Kinney et al.(1996) sample as a function of redshift on the left of the?gure.The LP?lter is able to distinguish blue galaxies at z<2.5,but becomes dominated by the noise for blue galaxies fainter than 28mag,and loses color resolution at z>3,where the Lyαforest dominates the color in these bandpasses.

Because the F28X50LP bandpass is entirely contained within the50CCD bandpass, it is possible,by subtracting an appropriately scaled version of the measured F28X50LP ?ux from the50CCD?ux,to construct a pseudo-B430measurement(see Figure5).This pseudo-B430is combined with the NUVQTZ and the F28X50LP measurements in a color-color diagram in Figure9.NUV drop-outs,indicated on this?gure by the dashed line,are those objects with blue colors in the visible,but red colors in the UV,indicative of galaxies at z>～1.5.These galaxies show blue colors characteristic of rapid star formation, while the red NUV to optical color is due to the Lyman break and absorption by the Lyαforest.The selection criteria were determined using the models of Madau et al.(1996).In an inset to Figure9,we plot the e?ciency of these criteria for selecting galaxies of high redshift.The solid line is the fraction of all of the models that meet these criteria,while the dotted line is the fraction of those models with ages<108years and foreground-screen extinction less than A B=2.These criteria are very e?cient at?nding young,star-forming galaxies at1.5

In Figure10we give a FUV-NUV vs NUV-50CCD color-color plot showing FUV dropouts,where the Lyman break is passing through the FUV bandpass at z>0.6.Of the 17galaxies in the MAMA?eld with NUV magnitudes brighter than28.4,only3have a clear signature of a Lyman break at0.60.6.

7.Conclusions

We have presented the STIS imaging observations that were done as part of the Hubble Deep Field–South campaign.The50CCD image is the deepest image ever made in the UV-optical wavelength region,and achieves a point source resolution near the di?raction limit of the HST.We have presented the catalog,and some statistics of the data.These data will be useful for the study of the number and sizes of faint galaxies,the UV-optical color evolution of galaxies,the number of faint stars and white dwarfs in the galactic halo, and the relation between absorption line systems seen in the QSO spectrum and galaxies near to the line of sight.Follow-up observations of the HDF-South?elds by southern hemisphere ground-based telescopes,by HST,and by other space missions will also greatly increase our understanding of the processes of galaxy formation and evolution.

The images and catalog presented here are available on the World Wide Web at:

We would like to thank all of the people who contributed to making the HDF-South campaign a success,including those who helped to identify a target quasar in the southern CVZ,and those who helped in planning and scheduling the observations.JPG,TMB, and HIT wish to acknowledge funding by the Space Telescope Imaging Spectrograph Investigation De?nition Team through the National Optical Astronomical Observatories, and by the Goddard Space Flight Center.CLM and CMC wish to acknowledge support by NASA through Hubble Fellowship grants awarded by STScI.

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如何写先进个人事迹

如何写先进个人事迹篇一：如何写先进事迹材料如何写先进事迹材料一般有两种情况：一是先进个人，如先进工作者、优秀党员、劳动模范等；一是先进集体或先进单位，如先进党支部、先进车间或科室，抗洪抢险先进集体等。无论是先进个人还是先进集体，他们的先进事迹，内容各不相同，因此要整理材料，不可能固定一个模式。一般来说，可大体从以下方面进行整理。 (1)要拟定恰当的标题。先进事迹材料的标题，有两部分内容必不可少，一是要写明先进个人姓名和先进集体的名称，使人一眼便看出是哪个人或哪个集体、哪个单位的先进事迹。二是要概括标明先进事迹的主要内容或材料的用途。例如《王鬃同志端正党风的先进事迹》、《关于评选张鬃同志为全国新长征突击手的材料》、《关于评选鬃处党支部为省直机关先进党支部的材料》等。 (2)正文。正文的开头，要写明先进个人的简要情况，包括：姓名、性别、年龄、工作单位、职务、是否党团员等。此外，还要写明有关单位准备授予他(她)什么荣誉称号，或给予哪种形式的奖励。对先进集体、先进单位，要根据其先进事迹的主要内容，寥寥数语即应写明，不须用更多的文字。然后，要写先进人物或先进集体的主要事迹。这部分内容是全篇材料

的主体，要下功夫写好，关键是要写得既具体，又不繁琐；既概括，又不抽象；既生动形象，又很实在。总之，就是要写得很有说服力，让人一看便可得出够得上先进的结论。比如，写一位端正党风先进人物的事迹材料，就应当着重写这位同志在发扬党的优良传统和作风方面都有哪些突出的先进事迹，在同不正之风作斗争中有哪些突出的表现。又如，写一位搞改革的先进人物的事迹材料，就应当着力写这位同志是从哪些方面进行改革的，已经取得了哪些突出的成果，特别是改革前后的．经济效益或社会效益都有了哪些明显的变化。在写这些先进事迹时，无论是先进个人还是先进集体的，都应选取那些具有代表性的具体事实来说明。必要时还可运用一些数字，以增强先进事迹材料的说服力。为了使先进事迹的内容眉目清晰、更加条理化，在文字表述上还可分成若干自然段来写，特别是对那些涉及较多方面的先进事迹材料，采取这种写法尤为必要。如果将各方面内容材料都混在一起，是不易写明的。在分段写时，最好在每段之前根据内容标出小标题，或以明确的观点加以概括，使标题或观点与内容浑然一体。最后，是先进事迹材料的署名。一般说，整理先进个人和先进集体的材料，都是以本级组织或上级组织的名义；是代表组织意见的。因此，材料整理完后，应经有关领导同志审定，以相应一级组织正式署名上报。这类材料不宜以个人名义署名。写作典型经验材料-般包括以下几部分： (1)标题。有多种写法，通常是把典型经验高度集中地概括出来，一

浅析语义场理论对英语词汇教学的启发

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个人先进事迹简介

个人先进事迹简介 01 在思想政治方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.利用课余时间和党课机会认真学习政治理论,积极向党组织靠拢. 在学习上,xxxx同学认为只有把学习成绩确实提高才能为将来的实践打下扎实的基础,成为社会有用人才.学习努力、成绩优良. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意识和良好的心理素质和从容、坦诚、乐观、快乐的生活态度,乐于帮助身边的同学,受到师生的好评. 02 xxx同学认真学习政治理论,积极上进,在校期间获得原院级三好生,和校级三好生,优秀团员称号,并获得三等奖学金. 在学习上遇到不理解的地方也常常向老师请教,还勇于向老师提出质疑.在完成自己学业的同时,能主动帮助其他同学解决学习上的难题,和其他同学共同探讨,共同进步. 在社会实践方面,xxxx同学参与了中国儿童文学精品“悦”读书系,插画绘制工作,xxxx同学在班中担任宣传委员,工作积极主动,认真负责,有较强的组织能力.能够在老师、班主任的指导下独立完成学院、班级布置的各项工作. 03 xxx同学在政治思想方面积极进取,严格要求自己.在学习方面刻苦努力,不断钻研,学习成绩优异,连续两年荣获国家励志奖学金；作

为一名学生干部,她总是充满激情的迎接并完成各项工作,荣获优秀团干部称号.在社会实践和志愿者活动中起到模范带头作用. 04 xxxx同学在思想方面,积极要求进步,为人诚实,尊敬师长.严格要求自己.在大一期间就积极参加了党课初、高级班的学习,拥护中国共产党的领导,并积极向党组织靠拢. 在工作上,作为班中的学习委员,对待工作兢兢业业、尽职尽责的完成班集体的各项工作任务.并在班级和系里能够起骨干带头作用.热心为同学服务,工作责任心强. 在学习上,学习目的明确、态度端正、刻苦努力,连续两学年在班级的综合测评排名中获得第1.并荣获院级二等奖学金、三好生、优秀班干部、优秀团员等奖项. 在社会实践方面,积极参加学校和班级组织的各项政治活动,并在志愿者活动中起到模范带头作用.积极锻炼身体.能够处理好学习与工作的关系,乐于助人,团结班中每一位同学,谦虚好学,受到师生的好评. 05 在思想方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.作为一名共产党员时刻起到积极的带头作用,利用课余时间和党课机会认真学习政治理论. 在工作上,作为班中的团支部书记,xxxx同学积极策划组织各类团活动,具有良好的组织能力. 在学习上,xxxx同学学习努力、成绩优良、并热心帮助在学习上有困难的同学,连续两年获得二等奖学金. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意识和良好的心理素质.

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（一）什么是词义客观事物（这里指人脑以外的所有事物，包括一切生物、非生物、事件以及它们的行动、状态、性质等等）反映在人脑中，产生感觉（sensation），知觉（perception），表象（representation）;人脑把感觉、知觉、表象加以概括和抽象，形成概念（concept）。人们用语言形式把概念固定下来，成为人们交流思想的符号（sign），这就是有一定意义的词。也就是说，词的意义的"人"赋予它的，难怪英国语言学家帕特里奇（Eric Partridge）说过，"Words have no meaning; peope have meaning for them"（词本无义，人赋予之）。传统语义学家通常用三角图形来说明词义，称"词义三角"（triangle of significance）：意义（概念）Meaning (Concept) 词Word 形式Form……所指对象Referent 这个图形表示：第一，词有两个方向--"形式"和"意义（概念）"。"形式"首先是指词的语音形式，也就是平常所说的发音，其次是指词的书面形式，也就是平常的说的拼写；与此相对的是词的意义（其核心部分是概念），也就是词的内容。每个词都有一定的形式和意义；这两方面缺一不可，统一在每个词中。第二，词义与所指对象联接在一起--一方面，词义在客观世界中是有所指的，另一方面，词义又是客观世界的某一（或某些）事物在语言中的反映。客观世界是无穷无尽、无限丰富的，客观世界的事物之间存在着细微的千差万别。人类语言无法完完全全地准确表达客观世界。一种语言无论词汇多么浩瀚、词义多么丰富，都不足以完完全全地准确反映客观世界。现代语义学家对"词义三角"提出很多批评，涉及哲学、心理学等各个领域。但是如果我们从学习语言的实用目的出发，粗浅地分析词义、解释有关词义的种种现象，传统语义学提出的"词义三角"还是能说明一些问题的。（三）词义分析和语义场前面已经提到，词义是词的内容，每个词有一个或几个意义，每个词义又可以进一步分析成若干个语义成分（semantic compo-nents）或语义特征（semantic features）作为区别性特征（distinctive features）。叶姆斯列夫（Hjelmslev）在本世纪四十年代出版的《语言理论导论》中应用于语义成分分析了"公羊、母羊、男人、女人、男孩、女孩、公马、母马"这组词。至于语义成分分析法（componential analysis）则是美国的人类学家威廉·古迪纳夫（W. H. Doodenough）于1956年提出来的。此后，美国语言学家奈达（Nida）、卡兹（Katz）和福德（Fodor）等人进一步发展了这种方法。举个最简单的例子：man, woman, boy, girl都属于"人"（human）这个语义范围（即语义场，semantic field），以"人"（human）这一共同的语义成分为核心，以男性（male）女性（female），成年（adult 每个词的语义又可以分别通过区别性特征表示为： man: +人+ 成年+ 男性 woman: +人+ 成年-男性 boy: +人- 成年+ 男性 girl: +人- 成年- 男性把每个词义分析成若干语义成分可以帮助我们比较完整地了解词义，以及词与词之间的关系。例如：adult和grown-up这一对同义词就可以表示为：+ 人+成年，另外再表明它们的文体区别，前者是正式用语，后者是非正式用语。又如man这个词的多义性可以表示为：它有两个词义，第一个词义是+ 人+ 成年+ 男性，第二个词义是+ 人。词义研究的另一种理论是所谓的"语义场"（semantic field），这个理论最早是由德语言学家特里尔（Jost Trier）在本世纪三十年代初提出来的。他认为，每个词都身居其亲属概念之间，这些词相互之间以及它们特指的那个词一起构成了一个自成系统的整体，这种结构可称为"词场"（das Wortfeld）或语言符号场（das Spraches Zeichenfeld）。其实，语义场就是同一词类的词由于它们之间紧密的联系而形成的一个词汇小体系，这些词具有它们的共有语义成分，体现了它们的概念核心。属于同一个语义场的词除了具有共同的语义成分以外，还具有各种非共同语义成分作为区别性特征。按照区别性特征的不同，语义场可以分为同义、近义类义、反义等几种。同义语义场里的词的概念意义相同，关联意义有差别；近义语义场里的词的共同语义成分的含义在程度上有细微的差别；类义语义场里的词在非共同语义成分的种别上有差异；反义语义场里的词的非共同语义成分的含义截然相反或者相对。各个语义场之间也呈现着包含、并列、部分覆盖等错综复杂的关系。用语义场的概念

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个人事迹简介

个人事迹简介我是来自计算机与与软件学院的学生，现在为青年志愿者协会的干事，在班级担任生活委员。在过去的一年里，我注重个人能力的培养积极向上，热心公益，服务群众，奉献社会，热忱的投身于青年支援者的行动中！一年时间虽短，但在这一年的时间里，作为一名志愿者，我确信我成长了很多，成熟了很多。“奉献、友爱、互助、进步”这是我们志愿者的精神，在献出爱心的同时，得到的是帮助他人的满足和幸福，得到的是无限的快乐与感动。路虽漫漫，吾将上下而求索！在以后的日子里，我会在志愿者事业上做的更好。在思想上，我积极进取,关心国家大事，并多次与同学们一起学习志愿者精神,希望我们会在新的世纪里继续努力,发扬我国青年的光传统,不懈奋斗,不断创造,奋勇前进,为实现中华民族的伟大复兴做出了更大的贡献。在学习上刻苦认真，抓紧时间，不仅学习好学科基础知识，更加学好专业课知识，在课堂上积极配合老师的教学，乐意帮助其它同学，有什么好的学习资料，学习心得也与他们交流，希望大家能共同进步。在上一个年度总成绩在班级排名第四，综合考评在班级排名第二。在工作中，我认真负责，出色的完成老师、同学交给的各项任务，所以班级人际关系良好。

此外参加了学院组织的活动，并踊跃地参加，发挥自己的特长，为班级争得荣誉。例如：参加校举办的大合唱比赛并获得良好成绩；参加了计算机与软件学院党校学习并顺利结业；此外,参加了计算机与软件进行的“计算机机房义务打扫与系统维护”的活动。在这些活动中体验到了大学生生活的乐趣。现将多次参与各项志愿活动汇报如下：2013年10月26日，参加计算机与软件学院团总支实践部、计算机与软件学院青年志愿者协会组织“志愿者在五福家园的健身公园开展义务家教招新活动”；2013年11月7日，参加组成计算机与软件学院运动员方阵在田径场参加学院举办的学校运动会；2013年12月5日，参与学校学院组织的”一二．五“大合唱比赛；2014年3月12日，参加由宿舍站长组织义务植树并参与植树活动；2014年3月23日，在计算机与软件学院团总支书记茅老师的带领下，民俗文化传承协会、计算机与软件学院青年志愿者协会以及学生会的同学们参观了“计算机软件学院的文化素质教育共建基地--南京市民俗博物馆”的活动；2014年3月26日，参加有宿舍站长组织的“清扫宿舍公寓周围死角垃圾”的活动；2014年4月5日，参加由校青年志愿者协会、校实践部组织的“南京市雨花台扫墓”活动，2014年4月9日，作为班级代表参加计算机软件学院组织部组织的“计算机应用office操作大赛”的活动。在参与各项志愿活动的同时，我的学习、工作、生活能力得到了提高和认可，丰富生活体验，提供学习的机会，提供学习的机会。