6810( 5) - 03/04/96 13:45 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6810 Version: 5 Check-in Date: 04-Mar-1996 13:39:43 1.Proposal Title: The Globular Cluster Systems of Distant Giant Ellipticals ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Doug Geisler Kitt Peak National Observatory CoI: Myung Gyung Lee Seoul National University N CoI: Keith Ashman University of Kansas N CoI: Terry Bridges Royal Greenwich Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose a definitive test of two competing scenarios for the origin of the rare high specific frequency (S) globular cluster systems (GCS) -- the empirical result that such systems are only found in cD galaxies and the recent suggestion by West et al. (1995) that such systems are instead due to the presence of a large number of intracluster globular clusters (IGCs). We will observe the GCSs of two galaxies in order to unambiguously discriminate between these two alternatives. NGC 1129 is situated at the center of a massive cluster yet it is not a cD. UGC 9799 has the highest S value known; however, this determination is based on only the brightest magnitude of the luminosity function (GCLF). This is one of the key galaxies in the West et al. scenario but the derived S value is very uncertain. Our observations will also improve our knowledge of the mean GCS metallicity: parent galaxy luminosity relation at the very bright end where current data are very sparse. How much scatter does this relation have and does its nature change at very high luminosity? Both of these galaxies are among the most luminous known. We will also obtain metallicities for a large number of clusters per galaxy in order to search for bimodality as predicted by merger models. The GCLF turnover in NGC 1129 will be observed and will be used to check the metallicity dependance of this feature and further investigate its use as a distance indicator. ------------------------------------------------------------------------------------ 6810( 5) - 03/04/96 13:45 - [ 2] Observations Description ------------------------ For NGC 1129, we wish to reach the turnover of the GCLF with a S/N between 5-- 10. This will allow us to accurately determine the total number of globular clusters in this galaxy. From its radial velocity and a reddening of E(B-V)~ 0.09 (Burstein and Heiles 1982), we anticipate the turnover to lie at V ~ 27.3, I ~ 26.3. Using the information in the WFPC2 Handbook (Version 3.0), we calculate that exposures of 6500 sec in V and I will allow us to reach V=27.3, I=26.3 with a S/N of ~ 6. These calculations assume a total background surface brightness of 22 mag/arcsec^2 in V (23 mag/arcsec^2 from the sky, and 22.5 mag/arcsec^2 average surface brightness from the galaxy itself as determined from Peletier et al (1990)), and the WF chip. Thus 13,000 sec total science exposure is required. 5 orbits will allow us to achieve the necessary exposures, with overheads (7.5 min for GS acquistion 6 min for reacquistion on subsequent orbits, plus 5 min for WFPC2 overheads CR-SPLIT; the Orbital Visibility is 54 minutes for NGC 1129). For each orbit, we will obtain two (CR- SPLIT) exposures, thus obtaining 5 total for each filter, which will allow good removal of cosmic rays. At V=25.3 and I=24.3, the S/N is 35--40 in 6500 sec. This S/N will allow us to obtain V-I colours good to +/- 0.04, or Fe/H values precise to +/- 0.2 dex (Couture et al 1990). Here we are two magnitudes brightwards of the GCLF peak, and for a GCLF dispersion of 1.4 mag, we expect to see ~ 8\\% of the total number of clusters over all magnitudes if the GCLF is similar in shape and (absolute) turnover mag to those of the Milky Way and M31. Accounting also for our incomplete spatial coverage (since we will place the galaxy near one edge of one of the WF chips; see below), this means that we should get Fe/H values to +/- 0.2 dex for 200 (600) clusters for a globular cluster specific frequency S_N of 4 (12) and M_V = -23.5 for NGC 1129. NGC 1129 is at low Galactic latitude (-15 deg), and contamination from field stars is an important consideration. Thus, we will place NGC 1129 at the center of the WF4 chip, which will mean the other corner will be a radial distance of 2.6 arcmin (~ 56 kpc for H_0 = 75) from the galaxy center. This should be far enough away to obtain a clean background (ie. free from NGC 1129 globulars), so that we may correct for the field star contamination. This placement will also allow us to determine the total extent of the NGC 1129 cluster system, as well as to search for intracluster globulars (West et al 1995). Since these fields will be uncrowded, there is no reason for us to center the galaxy on the PC chip. Most contaminating background galaxies will be resolved; (V-I) colors will remove many of the rest. For UGC 9799 is ~ 1.5 mag more distant than NGC 1129 (twice the redshift). We will obtain integrations of 6200 sec in V and 6500s in I in 5 orbits. We will CR-split all exposures. This should be sufficient to eliminate most CRs. We will center UGC 9799 on the PC chip, since UGC 9799 is at much higher Galactic latitude (50 deg), and field star contamination will be much less severe. This placement will allow us to maximize our spatial coverage of the cluster system, which is important given that UGC 9799 is more distant than NGC 1129. Real Time Justification ----------------------- None None Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6810( 5) - 03/04/96 13:45 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6810( 5) - 03/04/96 13:45 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1129 GALAXY,ELLIPTICAL,BCM RA=2H 54M 27.4S +/- 0.25S, J2000 Z=0.0182 V = 13.0 DEC=+41D 34' 46" +/- 2", PLATE- B-V = 1.0 ID=02RZ E(B-V) = 0.09+/-0.03 SURF(V) = 22.5 2 UGC9799 GALAXY,ELLIPTICAL,BCM RA=15H 16M 44.6S +/- 0.2S, J2000 Z=0.0342 V = 13.5 DEC=+7D 01' 18" +/- 2", PLATE- B-V = 1.0 ID=0292 E(B-V) = 0.03+/-0.03 SURF(V) = 22.5 6810( 5) - 03/04/96 13:45 - [ 5] Visit: 01 Visit Requirements: ORIENT 90D TO 325D 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 NGC1129 WFPC2 IMAGE WF4-FIX F555W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1129 WFPC2 IMAGE WF4-FIX F555W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1129 WFPC2 IMAGE WF4-FIX F555W CR-SPLIT=NO 1 1300S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1129 WFPC2 IMAGE WF4-FIX F814W CR-SPLIT=NO 1 1300S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1129 WFPC2 IMAGE WF4-FIX F814W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1129 WFPC2 IMAGE WF4-FIX F814W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 6810( 5) - 03/04/96 13:45 - [ 6] Visit: 02 Visit Requirements: ORIENT 110D TO 215D 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 UGC9799 WFPC2 IMAGE PC1-FIX F555W CR- 1 2400S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 UGC9799 WFPC2 IMAGE PC1-FIX F555W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 UGC9799 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 1200S ------------------------------------------------------------------------------------------------------------------------------------ 4 UGC9799 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1300S ------------------------------------------------------------------------------------------------------------------------------------ 5 UGC9799 WFPC2 IMAGE PC1-FIX F814W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 6 UGC9799 WFPC2 IMAGE PC1-FIX F814W CR- 1 2600S TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 6810( 5) - 03/04/96 13:45 - [ 7] Summary Form for Proposal 6810 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-TOLERANCE=0.0 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 90D TO 325D ORIENT 110D TO 215D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1129 UGC9799 ------------------------------------------------------------------------------------------------------------------------------------