7448( 4) - 06/25/97 15:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7448 Version: 4 Check-in Date: 25-Jun-1997 15:02:31 1.Proposal Title: Star Formation in a Protogalaxy Candidate at z=2.72 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Erica Ellingson UNIVERSITY OF COLORADO CoI: Howard Yee University of Toronto N CoI: Jill Bechtold Steward Observatory N ------------------------------------------------------------------------------------ 6. Abstract Recently a new population of galaxies at high redshift has been identified by ultraviolet absorption lines which most likely arise from very young stellar populations. The galaxy MS1512-cB58 at z=2.72, discovered serendipitously by the CNOC1 redshift survey, is by far the brightest object of this class (V=20.5). We propose to use the NICMOS camera to obtain spectral and imaging information in the rest optical band to study in detail the physical conditions of a high-redshift young galaxy with definitive signatures of young stars. We will obtain grism spectra covering the 1--2 Mum region (2650 to 5350Angstrom rest) which will allow us to estimate the age of the star formation using the size of the Balmer and HK breaks. This will mostly avoid the problem of the age- reddening degeneracy which complicates the interpretation of broad band ground-based data. Furthermore, we will measure the fluxes of emission lines such as OIILambda3727, HBeta, and OIIILambdaLambda4959,5007, which will provide important estimates of the star formation rate, reddening, and metallicity. These data may allow us to resolve the factor of 17 discrepancy that currently exists between the star- formation rates measured by 1500Angstrom UV flux and HAlpha luminosity. We also propose to obtain a high signal-to-noise ratio image in the F165M filter, which, with our approved Cycle 6 WFPC2 images in the optical, will allow us to study color gradients and possible non-uniformity of dust and star formation regions using spatially resolved rest UV- optical color maps. ------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 2] Observations Description ------------------------ We require grism spectroscopy for two purposes: an accurate measurement of the continuum, and the detection and measurement of the OIILambda3727, and HBeta emission lines. Grism B provides the wavelength coverage required. cB58 is elongated EW with axes of 2.2''*0.2'' ( R. Bender, private communication). The position of the cD galaxy of the foreground cluster is such that any dispersion in the direction of the minor axis will be contaminated by the outer low- surface brightness edge of the cD galaxy, which may make the precise measurement of the continuum shape unreliable. However, because the cD galaxy is large, the spectral contribution will be smeared out, and will not affect line flux measurements. Hence, we propose two orientations for the grism observation. We also request an imaging observation to allow us to study, in combination with our cycle 6 WFPC2 images, the morphology and color gradients of the object We computed orbits including instrumental overheads, based on the instructions in the Cycle 7 call for proposals. The orbital visibility of our target is 54 minutes, and we assume 9 minutes for acquisition for the first orbit, and 6 thereafter. A 9 minute re-acquisition will take place after the first 8 orbits. The requested obserations are: 1. Grism B, Camera 3, dispersion orientation EW. This provides a spectrum dispersed in the major axis direction. In this direction, there is no contaminating object. However, the smearing from the extension of the object itself will produce a resolution of 11 pixels, or 210Angstrom in the rest frame, which will be adequate for measuring the continuum shape. cB58 has an H magnitude of 18.4, equivalent to 4.4 * 10^-5 Jy. Although the light is spread over 11 pixels or so, it is along the line of the dispersion, and hence is equivalent to a point source of similar brightness. We estimate that a 3000 s exposure will provide us with a S/N ratio 15 per pixel spectrum for precision measurement of the continuum breaks. We will also require an IR image (100 sec F160W) for the identification of objects in the grism image. Hence we request 2 orbits. 2. Grism B, Camera 3, dispersion orientation NS. This spectrum will give us almost the full resolution for grism B, as the object's minor axis is about 0.2'' (1 pixel) wide. We expect the HBeta line to have an equivalent width of about 20Angstrom (estimate based on our HAlpha measurement). Hence with a spectral resolution of about 30A (rest) and a S/N of 15 per resolution element, we will obtain a line measurement accurate to about 10\\ Spreading the object onto 11 pixels gives each pixel a flux of 4* 10^-6 Jy. For this flux, in a 24000 sec exposure, we can obtain a S/N of 4.5 per pixel (120,000 s is required for S/N=10, according to the NICMOS exposure calculator). Summing 11 columns produces a S/N 15 spectrum. We will also require a short direct (100 sec F160W) image. Hence we request 10 orbits. 3. F165M image, Camera 2: Although the average surface brightness of cB58 is about 0.0001Jy per sq arc sec; we wish to obtain a reasonable S/N ratio (~5/pix) image for the lower surface brightness (outskirts) part of the object as well, at about 3 mag below the average surface brightness. This will sample down to approximately the same depth as the WFPC2 images. This requires ~7000 sec, and hence we request 3 orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 3] Data Distribution Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MS1512+36- GALAXY,PROTOGALAXY RA=15H 12M 25.70S +/- 0.05S, B1950 Z=2.72 H = 18.4+/-0.3 CB58 DEC=36D 47' 31.1" +/- 0.5", PLATE-ID=01R7 2 MS1512+36- GALAXY,PROTOGALAXY RA=15H 12M 25.90S +/- 0.05S, B1950 Z=2.72 H = 18.4+/-0.3 CENTER DEC=36D 47' 26.7" +/- 0.5", PLATE-ID=01R7 7448( 4) - 06/25/97 15:03 - [ 5] Visit: 01 Visit Requirements: ORIENT 214D TO 224D On Hold Comments: Additional Comments: An alternate ORIENT 34D to 44D is also valid for this visit Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MS1512+36-C NIC3 MULTIAC NIC3 F160W SAMP-SEQ=SPARS64,NSAMP=8 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 MS1512+36-C NIC3 MULTIAC NIC3 G141 PATTERN=SPIRAL-DITH,DITH-SIZE=.5, 1 DEF PAR 3-4 WITH 2 B58 CUM NUM-POS=9,SAMP-SEQ=MIF512, NSAMP=25 ------------------------------------------------------------------------------------------------------------------------------------ 3 MS1512+36-C NIC1 MULTIAC NIC1 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 MS1512+36-C NIC2 MULTIAC NIC2 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 6] Visit: 02 Visit Requirements: ORIENT 124D TO 134D On Hold Comments: Additional Comments: An alternate ORIENT 304D to 314D is also valid for this visit Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MS1512+36-C NIC3 MULTIAC NIC3 F160W SAMP-SEQ=SPARS64,NSAMP=8 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 MS1512+36-C NIC3 MULTIAC NIC3 G141 PATTERN=SPIRAL-DITH,DITH-SIZE=.50 1 DEF PAR 3-4 with 2 B58 CUM ,NUM-POS=24,SAMP-SEQ=MIF512, NSAMP=25 ------------------------------------------------------------------------------------------------------------------------------------ 3 MS1512+36-C NIC1 MULTIAC NIC1 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 MS1512+36-C NIC2 MULTIAC NIC2 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 7] Visit: 03 Visit Requirements: ORIENT 124D TO 134D On Hold Comments: Additional Comments: An alternate ORIENT 304D to 314D is also valid for this visit Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MS1512+36-C NIC3 MULTIAC NIC3 F160W SAMP-SEQ=SPARS64,NSAMP=8 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 MS1512+36-C NIC3 MULTIAC NIC3 G141 PATTERN=SPIRAL-DITH,DITH-SIZE=.3, 1 DEF PAR 3-4 WITH 2 B58 CUM NUM-POS=24,SAMP-SEQ=MIF512, NSAMP=25 ------------------------------------------------------------------------------------------------------------------------------------ 3 MS1512+36-C NIC1 MULTIAC NIC1 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 MS1512+36-C NIC2 MULTIAC NIC2 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF B58 CUM ------------------------------------------------------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 8] Visit: 04 Visit Requirements: ORIENT 1D TO 359D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MS1512+36-C NIC2 MULTIAC NIC2 F165M PATTERN=SPIRAL-DITH,DITH-SIZE=.25 1 DEF PAR 2-3 WITH 1 ENTER CUM ,NUM-POS=15,SAMP-SEQ=MIF512, NSAMP=25 ------------------------------------------------------------------------------------------------------------------------------------ 2 MS1512+36-C NIC1 MULTIAC NIC1 F165M SAMP-SEQ=SPARS256,NSAMP=4 1 DEF ENTER CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 MS1512+36-C NIC3 MULTIAC NIC3 F160W SAMP-SEQ=SPARS256,NSAMP=4 1 DEF ENTER CUM ------------------------------------------------------------------------------------------------------------------------------------ 7448( 4) - 06/25/97 15:03 - [ 9] Summary Form for Proposal 7448 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC3 NIC1 NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMP-SEQ=SPARS64 NSAMP=8 NSAMP=25 NSAMP=4 SAMP-SEQ=SPARS256 SAMP-SEQ=MIF512 NUM-POS=24 NUM-POS=15 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 214D TO 224D PAR 3-4 WITH 2 ORIENT 124D TO 134D ORIENT 1D TO 359D PAR 2-3 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W G141 F165M ------------------------------------------------------------------------------------------------------------------------------------ Target Names MS1512+36-CB58 MS1512+36-CENTER ------------------------------------------------------------------------------------------------------------------------------------