8184( 7) - 01/17/00 14:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8184 Version: 7 Check-in Date: 17-Jan-2000 14:58:36 1.Proposal Title: The Origin of cD Envelopes ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Patrick Cote California Institute of Technology CoI: Dr. Ronald Marzke Observatories of the Carnegie Institution N of Washington CoI: Prof. Michael West Saint Mary's University N ------------------------------------------------------------------------------------ 5. Abstract Approximately 20 percent of all galaxy clusters are known to contain cD galaxies. Located at the dynamical centers of their host cluster or subcluster, these supergiant elliptical galaxies show extended, diffuse stellar envelopes which trace the gravitational potential of the surrounding cluster. A leading model for their formation involves the growth of cD envelopes through mergers and/or tidal stripping of other cluster galaxies. Unfortunately, the envelopes have extremely low surface brightness, making direct observational tests of this model using either spectroscopy or broadband colors virtually impossible. On the other hand, globular clusters (GCs) are ideal tracers of the underlying stellar populations of cD envelopes. Since the mean metallicity of GCs is known to depend strongly on the total luminosity of the galaxy in which they form, an inescapable implication of cD envelope formation through mergers or tidal stripping is that the total luminosity of the envelope progenitor galaxies must be imprinted in the metallicities of the GCs now associated with these galaxies. We propose to use the superb imaging capabilities of HST to measure colors, and hence metallicities, for several hundred GCs surrounding six nearby cD galaxies. Our short program will triple the number of cDs having accurate GC metallicity distributions, and will provide the first strong constraints on the luminosities of the progenitors of cD envelopes. ------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 2] Observations Description ------------------------ The principal scientific objective of this program is to determine the luminosities of the progenitors of cD envelopes. To do so, we require accurate colors for the embedded populations of GCs. Since our targets are luminous galaxies residing at the dynamical centers of rich clusters, they are likely to have rich GC systems (i.e., 10 <~e S_N <~e 20; Forbes et al. 1997). In order to achieve a statistically significant sample of several hundred GCs, we require limiting magnitudes which are 1.4 mag brighter than the GCLF peak. This represents the standard deviation of the Gaussian which is often chosen to parameterize the GCLF. The total number of GCs in each galaxy which are brighter than this limit is given in column (6) of Table 1, assuming conservatively that S_N = 10. The GCs have a surface density profile sigma_ GC \propto R^-1.5 so that for each galaxy, a single WFPC2 field centered ~ 1^ interior to the break radius will contain several hundred GCs, minimize crowding problems, and give an acceptably faint background from underlying galaxy light. At this location we expect roughly equal numbers of GCs belonging to the core and envelope (see Figure 3). Note that metallicities can be determined on a cluster-by-cluster basis, so there is no reason to observe the envelopes directly. Total exposure times have been calculated using the WFPC2 Exposure Time Calculator and assuming: (1) an integrated spectral type of G5 for the target GCs; (2) a stellar background having a gE spectral type and a mean B-band surface brightness of 23 mag acrsec^- 2. These exposure times correspond to a signal-to-noise ratio of S/N ~eq 10. The exposures have been CR -SPLIT as described in columns (11) and (12) of Table 1. This procedure ensures that less than 0.01 percent of the WPFC2 pixels are rendered unuseable due to cosmic ray events. For all galaxies, the telescope roll angle will be adjusted so that the PC field is located closest to the cD center in order to reduce crowding problems. Since our goal is the derivation of GC metallicities, we require a color index having the highest possible metallicity sensitivity. Although the F336W-F814W index has a higher metallicity sensitivity, the requisite exposure times in the F336W filter are prohibitively long. As a compromise, we opt to use the F450W-F814W index. We emphasize that observations using F555W or F606W filters, though slightly less expensive in telescope time, lack the required metallicity sensitivity (i.e., B-I has twice the sensitivity as either B-V or V-I; Couture et al. 1990). The required amount of ``on-source" integration time is 61, 900 seconds in F450W and 24, 394 seconds in F814W. Including the appropriate amount of overhead for readout, target acquisition and telescope occulation (from Table 5 in Cycle 8 Call for Proposals), we estimate that 29 orbits are required to complete the program. Real Time Justification ----------------------- None. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 3] Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: CalTech*Mail-Stop 105-24*Pasadena, CA*91125 Ship Via: Email: pc@astro.caltech.edu ------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC541 Galaxy, Elliptical RA=01H25M43.68S +/- 0.1S, DEC=- J2000.0 V=+5417 V = 25.49 01D22'55.1" +/- 1.0", PLATE- B = 26.19 ID=00WT I = 24.49 B-V = 0.7 B-I = 1.7 Comments: Above fluxes and colors refer to those of the faintest globular clusters in this galaxy which we wish to detect in F450W and F814W. 2 NGC2832 Galaxy, Elliptical RA=09H19M46.31S +/- 0.1S, J2000.0 V=+6869 V = 26.00 DEC=+33D45'10.0" +/- 1.0", PLATE B = 26.70 -ID=01RX I = 25.00 B-V = 0.7 B-I = 1.7 Comments: Above fluxes and colors refer to those of the faintest globular clusters in this galaxy which we wish to detect in F450W and F814W. 3 NGC4839 Galaxy, Elliptical RA=12H57M25.07S +/- 0.1S, J2000.0 V=+7387 V = 26.17 DEC=+27D30'00.7" +/- 1.0", PLATE B = 26.87 -ID=002K I = 25.17 B-V = 0.7 B-I = 1.7 Comments: Above fluxes and colors refer to those of the faintest globular clusters in this galaxy which we wish to detect in F450W and F814W. 4 NGC7768 Galaxy, Elliptical RA=23H50M59.26S +/- 0.1S, J2000.0 V=+8191 V = 26.39 DEC=+27D08'59.1" +/- 1.0", PLATE B = 27.09 -ID=02CZ I = 25.39 B-V = 0.7 B-I = 1.7 Comments: Above fluxes and colors refer to those of the faintest globular clusters in this galaxy which we wish to detect in F450W and F814W. 8184( 7) - 01/17/00 14:59 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 35.0D TO 55.0D 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 NGC541 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2400 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC541 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=NO 1 1000 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC541 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=NO 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC541 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=NO 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 140.0D TO 160.0D 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 NGC2832 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2832 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2832 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 185.0D TO 198.0D 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 NGC4839 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4839 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4839 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4839 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 8] Visit: 04 Visit Priority: Visit Requirements: ORIENT 215.0D TO 235.0D 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 NGC7768 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC7768 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC7768 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC7768 WFPC2 IMAGE PC1-FIX F450W 4519 CR-SPLIT=NO 1 1200 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC7768 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=NO 1 1200 S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC7768 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=0.5 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 8184( 7) - 01/17/00 14:59 - [ 9] Summary Form for Proposal 8184 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 35.0D TO 55.0D ORIENT 140.0D TO 160.0D ORIENT 185.0D TO 198.0D ORIENT 215.0D TO 235.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F450W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC541 NGC2832 NGC4839 NGC7768 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4519 7921 ------------------------------------------------------------------------------------------------------------------------------------