8164( 20) - 05/04/00 10:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8164 Version: 20 Check-in Date: 04-May-2000 10:18:53 1.Proposal Title: A Search for Intergalactic Globular Clusters in A1185 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Michael West University of Hawaii CoI: Dr. Patrick C\^ot\'e California Institute of Technology N CoI: Dr. Ronald Marzke Observatories of the Carnegie Institution N of Washington CoI: Rene Tanaja Saint Mary's University N ------------------------------------------------------------------------------------ 5. Abstract The origin of the anomalously rich globular cluster populations surrounding many supergiant elliptical galaxies remains one of the great unsolved problems in the study of extragalactic globular cluster systems. A number of authors have suggested that the intrinsic globular cluster populations of such galaxies may have been augmented by large numbers of intergalactic globular clusters which are not bound to individual galaxies but, instead, roam freely throughout the cores of clusters of galaxies. Although there is now considerable circumstantial evidence in support of this view, efforts to detect intergalactic globular clusters directly have thus far been thwarted by the complication that most galaxy clusters have a supergiant elliptical galaxy residing at their dynamical centre, which makes it impossible to separate bona fide intergalactic globulars from the galaxy's own intrinsic population. To avoid this difficulty, we propose to search for intergalactic globulars in th e rich, nearby cluster Abell 1185, since its brightest member galaxy is offset from the X-ray centroid by ~eq 4 arcmin (150 kpc). A series of deep WFPC2 images centered on the peak of the X-ray distribution in Abell 1185 should reveal a population of intergalactic globular cluster if it exists. The detection (or non- detection) of such globular clusters will provide important new constraints on galaxy interactions and evolution in clusters. ------------------------------------------------------------------------------------ 8164( 20) - 05/04/00 10:19 - [ 2] Observations Description ------------------------ The essential element of this program is high-resolution imaging of very faint objects. We will image the X-ray centroid of Abell 1185 with WFPC2 in IMAGE mode using the F814W filter. Based on calculations with the WFPC2 Exposure Time Calculator, we require a total integration time of 11, 514 seconds in order to detect faint GCs at I=26.48 with a signal-to-noise ratio S/N=10, adequate for reliable star/globular cluster/galaxy separation (see, e.g., Elson et al. 1996 who found that a detection threshold of at least 6 sigma was required to distinguish between resolved and unresolved objects in the Hubble Deep Field). This amount of integration time requires five orbits, after allowing for CR- SPLITTING, telescope occultation and target acquisition. Note that this program involves minimal overhead since we are proposing single-filter observations of a single target. We choose to observe in F814W rather than F555W or F450W because of the red colors (i.e., V-I ~eq 1.0) of the GCs; t his will also allow a more direct comparison with our wide-field CFHT I-band images. Real Time Justification ----------------------- The lone supporting observations for this program (i.e., deep, wide-field images from CFHT needed for an accurate determination of the background) are already in hand. Reductions are underway. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8164( 20) - 05/04/00 10:19 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1185 CLUSTER OF GALAXIES, RA=11H 10M 42.00S +/- 0.0", J2000 Z = I = 26.5+/-1.0 RICH CLUSTER DEC=28D 43' 55.00" +/- 0.0", 0.033 V-I = 1.0+/-0.4 PLATE-ID=019K E(B-V) = 0.0 Coordinate Source: Comments: Our target is a relatively "blank" region in the heart of a rich cluster of galaxies, Abell 1185, and hence there are no pre-selected targets. Our goal is to detect a population of faint intergalactic globular clusters which may be present in this field. The broad band magnitude I=26.5 is the expected magnitude of globular clusters at this distance. 8164( 20) - 05/04/00 10:19 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 295D TO 305D On Hold Comments: Additional Comments: Orientation constraints are tight, as this allows us to position the PC closest to the X-ray centroid of Abell 1185 (where the density of intergalactic globulars is expected to be highest) while at the same time preventing contaminating stars and galaxies from falling into the field of view. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1185 WFPC2 IMAGE PC1-FIX F814W 1 2600 S ------------------------------------------------------------------------------------------------------------------------------------ 2 ABELL1185 WFPC2 IMAGE PC1-FIX F814W 1 2600 S POS TARG 0.5, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 ABELL1185 WFPC2 IMAGE PC1-FIX F814W 1 2600 S POS TARG 0.0, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 ABELL1185 WFPC2 IMAGE PC1-FIX F814W 1 2600 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 ABELL1185 WFPC2 IMAGE PC1-FIX F814W 1 2600 S POS TARG 0.35, 0.35 ------------------------------------------------------------------------------------------------------------------------------------ 8164( 20) - 05/04/00 10:19 - [ 5] Summary Form for Proposal 8164 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 295D TO 305D POS TARG 0.5, 0.0 POS TARG 0.0, 0.5 POS TARG 0.5, 0.5 POS TARG 0.35, 0.35 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ABELL1185 ------------------------------------------------------------------------------------------------------------------------------------