9396( 5) - 04/24/02 15:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9396 Version: 5 Check-in Date: 24-Apr-2002 15:46:54 1.Proposal Title: Young Cluster Systems in Two Super-Gas- Rich Mergers: Arp 220 and Arp 299 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Christine Wilson McMaster University CoI: Dr. William Harris McMaster University N CoI: Dr. Nick Scoville California Institute of Technology N CoI: Mr. Scott Brooks McMaster University N ------------------------------------------------------------------------------------ 5. Abstract Massive young star clusters are found in large numbers within the mergers of massive, gas-rich disk galaxies. The most outstanding and well studied case is in the nearby merging Antennae pair (Whitmore and colleagues). These systems may give us our best hope to see directly the way in which globular clusters formed in the uniquely gas-rich protogalactic era of the universe. But, even in the Antennae, the many hundreds of young clusters have a median mass which is still 5 to 10 times smaller than the characteristic mass ~ 3 * 10^5 M_\odot that characterizes normal, old-halo globular clusters. To find objects closer to the mass range of ``true'' protoglobular clusters, we need mergers which are still more gas-rich than the Antennae and in which the gas has been collected into more massive GMCs. Two excellent candidates are Arp 220 and Arp 299, both of which are undergoing extremely high star formation rates and have > 10^10 M_\odot of molecular hydrogen compressed into their central few kpc. With the ACS High Resolution Camera we will obtain deep UBVI imaging of the active central regions of these galaxies, allowing us to trace the luminosities, colors, masses, and ages of the young star clusters within them. ------------------------------------------------------------------------------------ 9396( 5) - 04/24/02 15:47 - [ 2] Observations Description ------------------------ NOTE: Arp 299 (IC 694 + NGC 3690) has been removed from the program due to duplication issues as of 04/24/02. - RAL Filters and Exposure Times: The appropriate choice of camera for this program is ACS in its High Resolution mode (HRC), with a 26'' * 29'' field of view and 0.025 arcsec pixel scale. For Arp 220 (at d = 77 Mpc) a single field will cover 10 kpc, sufficient to take in the entire central region of high gas content and star formation (for comparison, the WFPC2 field of view corresponded to 14 kpc diameter for the more extended Antennae system). For Arp 299, each ACS/HRC field will correspond to ~ 5.3 kpc diameter, similar to the separation between the nuclei of the two progenitor galaxies, so we will use two fields centered on the nuclei. The standard UBVI filter set will be used (F330W, F435W, F555W, F814W). For Arp 299 our target limiting magnitude will be V = 24.8 (M_V ~eq -8) at high detection completeness. For a typical A-type spectrum, exposure times of: U 4 * 1400 sec giving S/N ~eq 10 at V=25 , B 4 * 350 sec giving S/N ~eq 22 at V=25, V 4 * 400 sec giving S/N ~eq 22 at V=25 , I 4 * 400 sec giving S/N ~eq 13 at V=25$ , will be used. Adding time for filter changes and other overheads, and allowing for the location of Arp 299 in the CVZ, 2 orbits per field will be needed. For Arp 220, somewhat more distant, exposure times of: U 4 * 1365 sec giving S/N ~eq 5 at V=25.6 , B 4 * 310 sec giving S/N ~eq 9 at V=24.6 , V 4* 300 sec giving S/N ~eq 9 at V=24.6, I 4 * 600 sec giving S/N ~eq 9 at V=24.6 , will give >50\ ~eq -8.5) and high completeness brighter than V=25. Since the brightest clusters are expected to reach M_V ~eq -12, we will still cover more than a factor of 20 in cluster mass range. Cluster Sizes: Whitmore et al. (1999) found that the young Antennae star clusters were partially resolved and could measure their effective radii for comparison with Milky Way globular clusters. The median effective radii were R_eff ~eq 4 pc or 0.11 arcsec, with the largest clusters typically reaching R_eff ~ 10 pc. For Arp 299 (2.2 times more distant) and Arp 220 (4 times more distant) only the largest clusters will be clearly resolved as nonstellar, so we will not be able to make extensive size comparisons with standard globular clusters. Nevertheless, the main thrust of our program is through the UBVI color indices, with the effective size information being an interesting but not essential sidelight. Fluxes: V and B-V are given for brightest star cluster. Assumes 10 times more luminous than brightest cluster in NGC 4038/39 (M_V = -13.9) and 1 mag extra visual extinction. E(B-V) is Galactic foreground reddening from RC3 Surface brightness of Arp 220 from RC3 is also given; surface brightness is mean within the effective aperture m'_e Real Time Justification ----------------------- NOTE: Arp 299 (IC 694 + NGC 3690) has been removed from the program due to duplication issues as of 04/24/02. - RAL Arp 299: This galaxy is in the Northern CVZ and will provide the opportunity for longer exposure strings. We have reduced the number of orbits by a factor of two on each field to take advantage of this. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9396( 5) - 04/24/02 15:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 3 IRAS15327+23 GALAXY, ULTRALUMINOUS RA=15H 34M 57.31S +/- 1", J2000 E(B-V) = 0.051 40 IR GAL DEC=23D 30' 11.4" +/- 1" B-V = 0.3+/-0.2 SURF(B) = 13.23+/-0.05 V = 19+/-1 Coordinate Source: OTHER_SOURCE 9396( 5) - 04/24/02 15:47 - [ 4] Visit: 02 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 IRAS15327+2 ACS/HR ACCUM HRC F330W CR-SPLIT=NO 2 1330 S 340 C ------------------------------------------------------------------------------------------------------------------------------------ 11 IRAS15327+2 ACS/HR ACCUM HRC F330W CR-SPLIT=NO 2 1400 S SAME POS AS 10 340 C ------------------------------------------------------------------------------------------------------------------------------------ 20 IRAS15327+2 ACS/HR ACCUM HRC F435W CR-SPLIT=NO 4 310 S SAME POS AS 10 340 C ------------------------------------------------------------------------------------------------------------------------------------ 30 IRAS15327+2 ACS/HR ACCUM HRC F555W CR-SPLIT=NO 4 300 S SAME POS AS 10 340 C ------------------------------------------------------------------------------------------------------------------------------------ 40 IRAS15327+2 ACS/HR ACCUM HRC F814W CR-SPLIT=NO 4 660 S SAME POS AS 10 340 C ------------------------------------------------------------------------------------------------------------------------------------ 9396( 5) - 04/24/02 15:47 - [ 5] Summary Form for Proposal 9396 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F330W F435W F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names IRAS15327+2340 ------------------------------------------------------------------------------------------------------------------------------------