9403( 2) - 02/15/02 16:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9403 Version: 2 Check-in Date: 15-Feb-2002 16:58:01 1.Proposal Title: Galaxy Formation in Nearby Voids: Reflections of the High-Redshift Universe? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Norman Grogin Space Telescope Science Institute CoI: Dr. Margaret Geller Smithsonian Astrophysical Observatory N CoI: Dr. Anton Koekemoer Space Telescope Science Institute N CoI: Dr. Ethan Schreier Space Telescope Science Institute N CoI: Dr. Brad Whitmore Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract Galaxy voids, at the opposite environmental extreme from galaxy clusters, present an ideal yet under- utilized laboratory for probing the relationship between environment and the mechanisms of galaxy formation and evolution. Mounting evidence from ground-based surveys of galaxies in voids suggests that they have formed comparatively recently (and many are still forming) from gas-rich, low velocity- dispersion surroundings: a picture in accordance with models of hierarchical structure formation. The superior resolution of HST allows us to verify this hypothesis with the first directed HST imaging survey of void galaxies (VGs). With HST/ACS deep imaging of a subset of E+S0 VGs from our earlier ground-based imaging and spectroscopic survey, we will investigate their globular cluster (GC) systems to unravel their formation history and to constrain the age of their oldest GCs. The HST resolution of their inner light profiles will reveal whether they have significantly under-massive central black holes, as might be expected if these are young systems. HST will also detect the presence of morphological fine structure indicative of recent merger activity. If the present-day VGs truly reflect the early stages of galaxy formation which occurred at higher redshift outside the voids, their proximity enables the investigation of galaxy formation processes in much greater detail than possible from observations of the high-redshift field, even with NGST. ------------------------------------------------------------------------------------ 9403( 2) - 02/15/02 16:59 - [ 2] Observations Description ------------------------ Our primary science requirement in these observations is to obtain precise V and I photometry of enough GCs in our target void galaxies to discriminate between possible heterogeneous GC populations and to place meaningful constraints on their ages. Stellar population models (e.g., Bruzual & Charlot 2000) indicate that when globular clusters first form they should be ~1.2 mag bluer in V-I and ~6 mag brighter in V than when they are 15 Gyr old. Objects with these magnitudes and colors have now been discovered in a large number of merging galaxies, the most famous being the Antennae galaxies (NGC 4038/4039; Whitmore et al. 1999). As the globular clusters age they become fainter and redder, with the crossover in color occurring at ~1 Gyr (Fig. 2). However, young globular clusters can still be identified during this stage as they are roughly 2 mags brighter than 15 Gyr clusters. We will use a similar technique to Whitmore et al. (1997), who age-date a number of young GCSs (with ages ranging from 3 Myr to 4 Gyr) by measuring the differential brightness Del(V) and differential color Del(V-I) between the GCS of interest and the fiducial 15 Gyr GCS (Fig. 2). Supporting evidence for this technique's reliability is the finding that younger clusters tend to be more centrally concentrated than the older globular clusters, as predicted by Zepf & Ashman (1993). This approach is attractive in that it only requires photometry of the luminous clusters (V<-8). Hence it is not necessary to reach beyond the peak of the GCLF (V~-7.4 for an old GC propulation), which would require substantially longer integrations for our target galaxies at ~100 Mpc. Our ACS/WFC exposures must therefore be deep enough for photometry of the brighter oldest-population GCs, with V-I uncertainty less than the typical ~0.2 mag separation in the peaks of a bimodal GCS distribution of V-I. This requires GC detections at V<-7.5 with S/N>~10 in both V and I. Because the three galaxies in this pilot study are at almost identical distance, cz~6800--7600km/s, we can use a single observing setup to obtain the same GCS magnitude limit in all cases. The ACS ETC suggests 2 orbits (4 CR-SPLITs) in F606W and F814W will provide the minimum depth for our science requirements (see table below). We favor F606W over the traditional Johnson V filter (F555W) because the large increase in S/N per exposure time outweighs the modest reduction in GCS diagnostic leverage using Del(F606W-F814W) rather than Del(F555W-F814W). Achieving comparable S/N in F555W would require 6 orbits per galaxy, doubling the size of the proposal. We summarize the ETC results in the table below, showing the expected S/N for a V=-7.5 GC with a typical V- I=1.0. Because the GCs will be superposed on the diffuse stellar background of the host galaxy, we also note the expected S/N in the presence of low, medium, and high galactic background (Mu_V=26, 23.5, and 21 mag arcsec^-2, respectively). The three galaxies selected for this study have sizes ~60--90", well-suited to the 200" ACS/WFC (and not the 33" ACS/HRC, which also suffers from PSF halos at F814W).--- S/N Calculations with the ETC: V=-7.5, V-I=1.0 GC at 100 Mpc Add'l bkgnd. F606W F814W (mag arcsec^-2) (5ks) (5ks)---------------- ------------- None 11.7 10.0 Mu_V=26 11.6 9.9 Mu_V=23.5 10.7 8.9 Mu_V=21 6.6 5.1 Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9403( 2) - 02/15/02 16:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CGCG-- GALAXY, LENTICULAR RA=00H 30M 28.72S +/- 1.0", J2000 V = 7087 SURF(R) = 22.45+/-3.45 0027.9+0536 DEC=05D 51' 39.74" +/- 1.0" SURF(B) = 23.8+/-3.2 Coordinate Source: OTHER_SOURCE 2 CGCG-- GALAXY, LENTICULAR RA=14H 40M 5.77S +/- 1.0", J2000 V = 6740 SURF(R) = 22.8+/-3.4 1437.9+3143 DEC=31D 30' 5.85" +/- 1.0" SURF(B) = 23.75+/-3.35 Coordinate Source: OTHER_SOURCE Comments: VTT Generated target from local image 3 CGCG-- GALAXY, ELLIPTICAL RA=16H 2M 16.64S +/- 1.0", J2000 V = 7357 SURF(R) = 22.25+/-3.35 1600.6+4302 DEC=42D 55' 1.65" +/- 1.0" SURF(B) = 23.65+/-3.35 Coordinate Source: OTHER_SOURCE Comments: VTT Generated target from local image 9403( 2) - 02/15/02 16:59 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 35.0D TO 45.0D ORIENT 215.0D TO 225.0D 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 CGCG--0027. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1210 S 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 2 CGCG--0027. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1210 S POS TARG 0.248, 0.094 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 3 CGCG--0027. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1290 S POS TARG 0.124, 0.233 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 4 CGCG--0027. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1290 S POS TARG -0.124, 0.140 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 5 CGCG--0027. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1260 S 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 6 CGCG--0027. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1260 S POS TARG 0.248, 0.094 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 7 CGCG--0027. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1290 S POS TARG 0.124, 0.233 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 8 CGCG--0027. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1290 S POS TARG -0.124, 0.140 9+0536 C ------------------------------------------------------------------------------------------------------------------------------------ 9403( 2) - 02/15/02 16:59 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 105.0D TO 115.0D ORIENT 285.0D TO 295.0D 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 CGCG--1437. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1240 S 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 2 CGCG--1437. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1240 S POS TARG 0.248, 0.094 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 3 CGCG--1437. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1310 S POS TARG 0.124, 0.233 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 4 CGCG--1437. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1310 S POS TARG -0.124, 0.140 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 5 CGCG--1437. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1280 S 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 6 CGCG--1437. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1280 S POS TARG 0.248, 0.094 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 7 CGCG--1437. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1310 S POS TARG 0.124, 0.233 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 8 CGCG--1437. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1310 S POS TARG -0.124, 0.140 9+3143 C ------------------------------------------------------------------------------------------------------------------------------------ 9403( 2) - 02/15/02 16:59 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 250.0D TO 260.0D ORIENT 70.0D TO 80.0D 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 CGCG--1600. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1280 S 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 2 CGCG--1600. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1280 S POS TARG 0.248, 0.094 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 3 CGCG--1600. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1350 S POS TARG 0.124, 0.233 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 4 CGCG--1600. ACS/WF ACCUM WFC1 F814W CR-SPLIT=NO 1 1350 S POS TARG -0.124, 0.140 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 5 CGCG--1600. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1320 S 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 6 CGCG--1600. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1320 S POS TARG 0.248, 0.094 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 7 CGCG--1600. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1350 S POS TARG 0.124, 0.233 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 8 CGCG--1600. ACS/WF ACCUM WFC1 F606W CR-SPLIT=NO 1 1350 S POS TARG -0.124, 0.140 6+4302 C ------------------------------------------------------------------------------------------------------------------------------------ 9403( 2) - 02/15/02 16:59 - [ 7] Summary Form for Proposal 9403 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 35.0D TO 45.0D ORIENT 215.0D TO 225.0D POS TARG 0.248, 0.094 POS TARG 0.124, 0.233 POS TARG -0.124, 0.140 ORIENT 105.0D TO 115.0D ORIENT 285.0D TO 295.0D ORIENT 250.0D TO 260.0D ORIENT 70.0D TO 80.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names CGCG--0027.9+0536 CGCG--1437.9+3143 CGCG--1600.6+4302 ------------------------------------------------------------------------------------------------------------------------------------