7265( 21) - 04/16/99 13:33 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7265 Version: 21 Check-in Date: 16-Apr-1999 13:32:59 1.Proposal Title: The Metallicity Distribution of the Globular Cluster Systems of Giant Elliptical Galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Douglas Geisler Kitt Peak National Observatory CoI: Terry Bridges Royal Greenwich Observatory N CoI: Jay Elias Kitt Peak National Observatory N ------------------------------------------------------------------------------------ 5. Abstract We propose to obtain deep F555W (V) and F160W (H) integrated broadband photometry of the globular cluster systems of two giant elliptical galaxies. This novel combination of WFPC2 and NICMOS data will provide a color index which maximizes metallicity sensitivity (tripling that of the traditional V-I index) while maintaining a low sensitivity to any age variations. Our photometry will reach or approach the turnover in the globular cluster luminosity function and allow us to measure the metallicities of over 500 globular clusters in each galaxy to a precision of 0.2 dex. This unprecedented database will allow us to definitively determine the metallicity distribution of the clusters in each galaxy and unequivocally establish whether they are uni-, bi- or multi-modal, and thus help to constrain theories of globular cluster and galaxy formation. We will also determine the mean metallicity of each cluster system and add significantly to the database for understanding the relationship between this quantity and the parent galaxy luminosity, and obtain deep luminosity functions in order to assess the metallicity dependance of the turnover and further investigate its use as a distance indicator. These observations will have a significant impact on our understanding of the origin and nature of globular cluster systems in galaxies. ------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 2] Observations Description ------------------------ Our primary requirement is to obtain sufficiently precise photometry to derive accurate metal abundances for about 500 GCs in each galaxy in order to unequivocally resolve distinct metallicity peaks. According to our adaptation of the Cohen and Matthews V-K calibration to V-H, we can derive abundances to 0.23 dex for a GC with Sigma (V) = Sigma (H) = 0.1, or S/N=10 in each filter. From their radial velocities, Ho=75, and a comparison with the very well-known GCLF in Virgo galaxies (e.g. Whitmore et. al 1995), we anticipate the turnover in the GCLFs of NGC 3842 and NGC 6166 to lie at V~ 27.5 and 28.3, respectively. Note that these galaxies are at very high galactic latitude and that the reddenings are negligible (Burstein and Heiles 1982 AJ, 87, 1165). From existing ground-based studies of the spatial distribution and total cluster populations in these galaxies, we estimate that 3 NIC3 fields will contain >~ 500 clusters if we observe to V ~ 26.5, H~ 24 mag in each galaxy. For the V data, we will use WFPC2 and the F555W filter. In order to estimate exposure times, we need to know the surface brightness of each galaxy as a function of radial distance. These are available from Schombert (1986, ApJS, 60, 603; and 1987, ApJS, 64, 643) and indicate that within ~ 20" (8kpc) of the center of NGC 3842 and 10" (6kpc) of NGC 6166, Mu _V<22 and our S/N values will be compromised. However, the vast majority of our clusters will lie in regions where the galaxy surface brightness will not be significant. We have used the WFPC2 Exposure Time Calculator for point sources plus stellar background to determine that in 4* 1200s exposures we can achieve S/N=11 for V=26.5 in each galaxy, or 2 orbits. Each orbit will be broken down as follows: 9m guide star acquisition (6m second orbit) +2* 1300s CR-SPLIT exposures (2*1200s exposures for the first orbit on NGC3842) +5m CR-SPLIT overhead. In this same exposure time, we will reach S/N~ 5 at the GCLF turnover in NGC 3842 and 0.8 mags brighter than the turnover in NGC 6166. This data will enable us to investigate the GCLF and S_N with a sample size >1000. We will also use the V mags of any WFPC2 objects that are not observed with NICMOS for these investigations. For the H data, we will use NIC3 and the F160W filter. A typical GC should have V- H~ 2.5, so we require S/N~ 10 for a limiting H magnitude of 24. The above V surface brightness limits also approximately correspond to the limiting surface brightness for the H photometry. We have used the NICMOS Exposure Time Calculator for point sources to determine that in 4* 832s exposures we can achieve our desired precision. We will use MULTIACCUM and 16 reads per exposure (15 for the first of the 3 different Nic3 fields in each galaxy). At these magnitude levels, the objects' peak signal level is roughly 10% of background, or less, so that both statistical and systematic effects in the background removal need to be held below 1%. This is best done by limited use of the ``dither'' observing mode, so we will take a series of 4 dithered exposures, using 2 arcsec steps. For exposures this long in the F160W filter, shot noise is greater than read noise, but not completely dominant. MULTIACCUM therefore helps to improve signal-to-noise (by about 15%) as well as minimizing effects of cosmic rays. Each orbit will be broken down as follows: 9m guide star acquisition (6m subsequent orbits) +12s setup time +3* 832s exposures (3*896s on subsequent orbits) +3* 12s MULTIACCUM readout time +2* 12s dither time +90s data management time. On the second orbit, we will obtain the 4th and final 832s exposure on our first field and slew to a second field and obtain 2* 896s exposures on it. We will center each of the NIC3 fields in the center of each of the 3 WF chips, and the galaxy will be centered at the WFALL position. This slew will then only require 90s. Thus, it will take us 1 and 1/3 orbits to observe each of the 3 required fields, or 4 orbits total per galaxy. Thus, at the faint limit of the sample used to derive our metallicity distribution, a cluster will have S/N=11 in V and 10 in H, or Sigma (V-H)=0.13. This translates to a random metallicity error of only 0.22 dex. The rest of our MD sample will have even smaller metallicity errors. Real Time Justification ----------------------- Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 3] Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3842- GALAXY, ELLIPTICAL, BCM RA=11H 44M 2.14S +/- 0.25S, J2000 Z=0.021 V = 12.5 CENTER DEC=19D 56' 59.8" +/- 1.5", B-V = 0.95 PLATE-ID=019N E(B-V) = 0.0 SURF(V) = 24.0 2 NGC3842-WF2 GALAXY, ELLIPTICAL, BCM RA=11H 44M 1.73S +/- 0.25S, J2000 Z=0.021 V = 12.5 DEC=19D 56' 5.1" +/- 1.5", PLATE B-V = 0.95 -ID=019N E(B-V) = 0.0 SURF(V) = 24.0 3 NGC3842-WF3 GALAXY, ELLIPTICAL, BCM RA=11H 43M 59.56S +/- 0.25S, J2000 Z=0.021 V = 12.5 DEC=19D 57' 13.8" +/- 1.5", B-V = 0.95 PLATE-ID=019N E(B-V) = 0.0 SURF(V) = 24.0 4 NGC3842-WF4 GALAXY, ELLIPTICAL, BCM RA=11H 44M 4.43S +/- 0.25S, J2000 Z=0.021 V = 12.5 DEC=19D 57' 44.3" +/- 1.5", B-V = 0.95 PLATE-ID=019N E(B-V) = 0.0 SURF(V) = 24.0 5 NGC6166- GALAXY, ELLIPTICAL, BCM RA=16H 28M 38.33S +/- 0.25S, J2000 Z=0.0315 V = 12.3 CENTER DEC=39D 33' 4.9" +/- 1.5", PLATE B-V = 1.0 -ID=00CL E(B-V) = 0.0 SURF(V) = 23.0 6 NGC6166-WF2 GALAXY, ELLIPTICAL, BCM RA=16H 28M 34.80S +/- 0.25S, J2000 Z=0.0315 V = 12.3 DEC=39D 32' 28.1" +/- 1.5", B-V = 1.0 PLATE-ID=00CL E(B-V) = 0.0 SURF(V) = 23.0 7 NGC6166-WF3 GALAXY, ELLIPTICAL, BCM RA=16H 28M 36.80S +/- 0.25S, J2000 Z=0.0315 V = 12.3 DEC=39D 33' 39.7" +/- 1.5", B-V = 1.0 PLATE-ID=00CL E(B-V) = 0.0 SURF(V) = 23.0 8 NGC6166-WF4 GALAXY, ELLIPTICAL, BCM RA=16H 28M 42.98S +/- 0.25S, J2000 Z=0.0315 V = 12.3 DEC=39D 33' 16.3" +/- 1.5", B-V = 1.0 PLATE-ID=00CL E(B-V) = 0.0 SURF(V) = 23.0 7265( 21) - 04/16/99 13:33 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 101D TO 121D On Hold Comments: Additional Comments: We are specifying a very tight orient because we were told this is the best way to ensure that the Nic3 fields will be centered in each of the 3 WF fields, which is one of our prime science requirements. However, the exact value of the orient is immaterial to us - we simply need to specify SOME value in order to know where the WF fields are so we can center Nic3 in them. Obviously, the proper value is one that maximizes schedulability and guide stars. We have made a rough first pass at finding this value with the help of our PC, Alice Berman, but we would like to try to optimize this value. We assume that, during a given visit with a specified Orient that the orientation will be the same even though different guide stars will most likely be used for the WF and Nic3 observations. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3842-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2400 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3842-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2600 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 110D TO 112D 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 NGC3842-WF2 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 2-3 WITH 1-1 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC3842-WF3 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 5-6 WITH 4-4 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC3842-WF4 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 8-9 WITH 7-7 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 143D TO 163D On Hold Comments: Additional Comments: We are specifying a very tight orient because we were told this is the best way to ensure that the Nic3 fields will be centered in each of the 3 WF fields, which is one of our prime science requirements. However, the exact value of the orient is immaterial to us - we simply need to specify SOME value in order to know where the WF fields are so we can center Nic3 in them. Obviously, the proper value is one that maximizes schedulability and guide stars. We have made a rough first pass at finding this value with the help of our PC, Alice Berman, but we would like to try to optimize this value. We assume that, during a given visit with a specified Orient that the orientation will be the same even though different guide stars will most likely be used for the WF and Nic3 observations. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6166-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2600 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6166-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2600 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 8] Visit: 04 Visit Priority: Visit Requirements: ORIENT 152D TO 154D 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 NGC6166-WF2 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 2-3 WITH 1-1 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6166-WF3 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 5-6 WITH 4-4 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6166-WF4 NIC3 MULTIAC NIC3 F160W PATTERN=SQUARE-WAVE-DITH, 1 DEF PAR 8-9 WITH 7-7 CUM NUM-POS=4,DITH-SIZE=2, SAMP-SEQ=SPARS64,NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC1 MULTIAC NIC1 F160W SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY NIC2 MULTIAC NIC2 F237M SAMP-SEQ=SPARS64,NSAMP=16 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 9] Visit: 11 Visit Priority: Visit Requirements: ORIENT 101D TO 121D On Hold Comments: Additional Comments: This visit repeats failed visit 1. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3842-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2400 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3842-CEN WFPC2 IMAGE WFALL-F F555W CR-TOLERANCE=0.0 1 2600 S TER IX ------------------------------------------------------------------------------------------------------------------------------------ 7265( 21) - 04/16/99 13:33 - [ 10] Summary Form for Proposal 7265 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX NIC3 NIC1 NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 NIC3 NIC1 NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-TOLERANCE=0.0 NSAMP=16 SAMP-SEQ=SPARS64 DITH-SIZE=2 NUM-POS=4 PATTERN=SQUARE-WAVE-DITH ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 101D TO 121D ORIENT 110D TO 112D PAR 2-3 WITH 1-1 PAR 5-6 WITH 4-4 PAR 8-9 WITH 7-7 ORIENT 143D TO 163D ORIENT 152D TO 154D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F160W F237M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3842-CENTER NGC3842-WF2 ANY NGC3842-WF3 NGC3842-WF4 NGC6166-CENTER NGC6166-WF2 NGC6166-WF3 NGC6166-WF4 ------------------------------------------------------------------------------------------------------------------------------------