Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5396 Report Date: 18-Jul-95:17:17 Version: ********** Check-in Date: ********** 1.Proposal Title: THE FORMATION OF GLOBULAR CLUSTERS DURING MERGERS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID GALAXIES & CLUSTERS GO Sub Category PECULIAR/INTERACTING ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Stephen E Zepf UNIVERSITY OF CALIFORNIA, BE USA 510-642-5275 ------------------------------------------------------------------------------------ 7. Abstract Both theoretical and observational studies have demonstrated that elliptical galaxies can form through the merger of spirals. However, if most ellipticals formed in this way, new globular clusters must be formed during mergers. This is required to reconcile the merger hypothesis with the higher specific frequency of globular clusters around ellipticals relative to spirals. We have previously proposed that the formation of new globular clusters is a natural outcome of the merger process. Ground-based data provide some evidence for the existence of young globulars in mergers, but do not have sufficient resolution to distinguish globulars from more extended star formation regions. Results from the two relevant galaxies which have been imaged by the WFPC1 demonstrate the promise of space-based resolution, but are somewhat limited by the broad wings of the psf. Therefore, we propose to obtain images with the WFPC2 of a sample of four merging systems, carefully chosen from our ground-based survey to represent a range of merging states. Since the formation of new globular clusters is required if ellipticals are the products of spiral mergers, this program is a very economical way to test the merger hypothesis. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 7.20 par: 0 10. Num targs pri: 4 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5396 PI: Stephen E Zepf Proposal Title: THE FORMATION OF GLOBULAR CLUSTERS DURING MERGERS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Stephen E Zepf 1500 USA Keith M Ashman 2400 USA Jayanne English 4140 AUSTRALIA Kenneth C Freeman 4140 AUSTRALIA Ray M Sharples 8018 UNITED KING ------------------------------------------------------------------------------------ 3. Description of proposed observations. The WFPC2 will be used with the F450W and F814W filters to image four galaxies which are commonly believed to be recent mergers (NGC 1487, NGC 3256, NGC 3597, and Arp 230). For each galaxy the exposures will be 25M in the F450W filter and 20M in the F814W filter. We will divide these into two paired exposures in order to facilitate cosmic ray removal and to allow for reality checks on phenomena seen in individual frames. For the two cases in which the field of view of the PC2 adequately covers the main body of the galaxy (NGC 3597 and Arp 230), we will center the galaxy in the PC2 and observe in this position. For the two galaxies for which more spatial coverage is required (NGC 1487 and NGC 3256), we will use two separate exposures, shifting slightly (30 arcseconds) between locations. This procedure gives sufficient spatial coverage. For NGC 1487, we are also able to keep the orientation the same, so the only one guide star acquisition is required. This may not be true for NGC 3256, in which we are also changing the orientation. NOTE: Due to duplication issues versus GTOs, the following two targets and their corresponding observations have been removed from the program on the instructions of the Director of STScI: Arp 230 and NGC 3597. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The high resolution imaging capabilities of the HST and WFPC2 are essential for distinguishing between young globular clusters which have high spatial densities and are truly equivalent to old globular clusters in all respects except age, and more extended star-forming complexes which should not be compared to globular clusters. This distinction is central to determining whether the specific frequency of globular clusters rules out a merger origin for elliptical galaxies or if the problem is solved by the formation of new globulars during mergers We have recently completed a program of deep imaging of merging galaxies with 4m class telescopes. From these data, we have identified candidate young globular clusters. However, at a typical distance of the galaxies in our sample (about 30 Mpc), the half-mass radius of globular clusters is about 0.05 arcseconds. Therefore, the spatial resolution of the Planetary Camera 2 is critical for addressing the question of the size of the candidate young clusters. Moreover, even with exposure times of only 1200s, the PC2 images will detect young globulars clusters over the whole range of expected luminosities, thereby allowing a much more detailed study of the properties of the young cluster system. We request exposure times totalling 1500s in the F450W and 1200s in the F814W filter. We estimate that this will give a S/N of 10 within a radius of 0.1'' for globular clusters of B = 25 and I = 24. This calculation assumes the clusters have the color of an F0 star and lie on a galaxy background of B = 20 magnitudes/arcsec^2 and I = 18.5 magnitudes/arcsec^2. We expect nearly all of the young globulars and about half of the old ones to be brighter than this limit for the typical galaxy in our sample. This S/N will be clearly sufficient to determine if the candidate young globular clusters have the high central stellar density characteristic of true globular clusters. Moreover, since we will also detect old globular clusters in our images, we can compare the sizes of the two populations directly. We will also be able to study the shapes of the brighter young globulars in more detail. Furthermore, we will obtain precise B-I colors which form the basis for a determination of the age of the young globular clusters. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. None. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None ------------------------------------------------------------------------------------ 8. Additional comments or special requests. None. ------------------------------------------------------------------------------------ 9. Description of previous HST work. Cycle 3 No. 4423 "The Formation of Globular Clusters during Mergers" (same team as this proposal). Chosen for Supplemental Pool. Cycle 2 No. 3647 "The Star Forming Histories of Elliptical Galaxies" (Zepf co-I). Cycle 1 No. 2147 "Disk and Halo Globular Clusters in the Edge-On Spiral Galaxy 5170" (Freeman co-I) No. 2269 "Galaxy Populations in Intermediate Redshift Clusters" (Sharples co-I). Only the Supplemental Cycle 3 program is related to this proposal. No data has yet been obtained for that program. `Deep Wide Field Camera Images of a z=0.3 Cluster' Couch, W.J., Ellis, R.S., & Sharples, R. 1992, ST-ECF Newsletter, No. 17, p. 13. `Deep WFC Imaging of the z=0.3 Cluster AC114' Sharples, R.M., Smail, I.R., Ellis, R.S., Couch, W.J., Fitchett, M.J. & Jorgensen, `Morphological Studies of Galaxy Populations in Distant BO Custers' Couch, W.J., Ellis, R.S., Sharples, R.M., & Smail, I.R. 1993, in `Observational Cosmology', ed. G. Chincarini, ASP Conference Series, in press. Page 4 ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). UC Berkeley, Durham University, and Mount Stromlo and Siding Spring Observatory provide excellent computing facilities based on UNIX workstations running the IRAF/STSDAS software package. The national observatory facilities of both the UK and Australia have already generously supported the ground-based aspects of this program. ------------------------------------------------------------------------------------ 11. Address Information Name: Stephen E Zepf Category: PI Institution: 1500 Address: University of California Department of Astronomy Campbell Hall City: Berkeley State: CA Zip Code: 94720 Country: USA Telephone: 510-642-2359 Telex (or e-mail): 510-642-3411 ------------------------------------------------------------------------------------ Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5396 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1487-POS1 E,320,318,918 RA = 03H 55M 45.3S +/- 1.0", J2000 V=856 1 V=23. DEC = -42D 22' 10.0" +/- 2 V-I=0.5+/-0.3 1.0" 3 SURF-BKG(V)=20+/-0.5 4 SURF-BKG(I)=19+/-0.5 Comments: FLUX VALUES ARE FOR CANDIDATE YOUNG GLOBULAR CLUSTERS WITHIN THE TARGET GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1487-POS2 E,320,318,918 RA = 03H 55M 45.3S +/- 1.0", J2000 V=856 1 V=23. DEC = -42D 22' 30.0" +/- 2 V-I=0.5+/-0.3 1.0" 3 SURF-BKG(V)=20+/-0.5 4 SURF-BKG(I)=19+/-0.5 Comments: FLUX VALUES ARE FOR CANDIDATE YOUNG GLOBULAR CLUSTERS WITHIN THE TARGET GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC3256-POS1 E,320,318,918 RA=10H 27M 51.0S +/- 1.0", J2000 V=2821 1 V=23. DEC=-43D 54' 15.0" +/- 1.0" 2 V-I=0.5+/-0.3 3 SURF-BKG(V) = 20 +/- 0.5 4 SURF-BKG(I) = 19 +/- 0.5 Comments: FLUX VALUES ARE FOR CANDIDATE YOUNG GLOBULAR CLUSTERS WITHIN THE TARGET GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC3256-POS2 E,320,318,918 RA=10H 27M 49.0S +/- 1.0", J2000 V=2821 1 V=23. DEC=-43D 54' 27.0" +/- 1.0" 2 V-I=0.5+/-0.3 3 SURF-BKG(V) = 20 +/- 0.5 4 SURF-BKG(I) = 19 +/- 0.5 Comments: FLUX VALUES ARE FOR CANDIDATE YOUNG GLOBULAR CLUSTERS WITHIN THE TARGET GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5396 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1487- WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5 1 1600S 10 1 1 CYCLE 4 POS1 CR- 2 ORIENT 150D +/- TOLERANCE=0.0 4 30D Comments: CR-TOLERANCE OF 0.0 IS NOT ABSOLUTELY REQUIRED. IT CAN BE RELAXED TO 0.1 IF NECESSARY. REQUESTED ORIENTATION ON SKY IS WF CCDS ROUGHLY NORTHWEST OF PC2 THIS CAN BE FLEXIBLE IF NECESSARY ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1487- WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=0.5 1 1800S 10 1 1 CYCLE 4 / 3-4 POS1 CR- 2 SEQ 3-4 NO GAP TOLERANCE=0.0 3 SAME POS FOR 4 AS 3 Comments: REQUIREMENTS 2 AND 3 (GROUP 3-4 WITHIN 7D) AND SAME ORIENT FOR 4 AS 3 CAN BE REPLACED BY GROUP 3-4 NO GAP IF THAT MAKES SCHEDULING EASIER. ORIENTATION MUST STILL BE VERY CLOSE (1D) TO PREVIOUS EXPOSURE ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1487- WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5 1 1600S 10 1 1 CYCLE 4 POS2 CR- 2 ORIENT 150D +/- TOLERANCE=0.0 4 30D Comments: CR-TOLERANCE OF 0.0 IS NOT ABSOLUTELY REQUIRED. IT CAN BE RELAXED TO 0.1 IF NECESSARY. REQUESTED ORIENTATION ON SKY IS WF CCDS ROUGHLY NORTHWEST OF PC2 THIS CAN BE FLEXIBLE IF NECESSARY ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1487- WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=0.5 1 1800S 10 1 1 CYCLE 4 / 5-6 POS2 CR- 2 SEQ 5-6 NO GAP TOLERANCE=0.0 3 SAME POS FOR 6 AS 5 Comments: REQUIREMENTS 2 AND 3 (GROUP 5-6 WITHIN 7D) AND SAME ORIENT FOR 6 AS 5 CAN BE REPLACED BY GROUP 5-6 NO GAP IF THAT MAKES SCHEDULING EASIER. ORIENTATION MUST STILL BE VERY CLOSE (1D) TO PREVIOUS EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5396 [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC3256- WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5 1 1600S 10 1 1 CYCLE 4 POS1 CR- 2 ORIENT 217D +/- TOLERANCE=0.0 4 40D Comments: CR-TOLERANCE OF 0.0 IS NOT ABSOLUTELY REQUIRED. IT CAN BE RELAXED TO 0.1 IF NECESSARY. REQUESTED ORIENTATION ON SKY IS WF CCDS ROUGHLY NORTHEAST OF PC2 THIS CAN BE FLEXIBLE IF NECESSARY ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC3256- WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=0.5 1 1800S 10 1 1 CYCLE 4 / 7-8 POS1 CR- 2 SEQ 7-8 NO GAP TOLERANCE=0.0 3 SAME POS FOR 8 AS 7 Comments: REQUIREMENTS 2 AND 3 (GROUP 7-8 WITHIN 7D) AND SAME ORIENT FOR 8 AS 7 CAN BE REPLACED BY GROUP 7-8 NO GAP IF THAT MAKES SCHEDULING EASIER. ORIENTATION MUST STILL BE VERY CLOSE (1D) TO PREVIOUS EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC3256- WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5 1 1600S 10 1 1 CYCLE 4 POS2 CR- 2 ORIENT 145D +/- TOLERANCE=0.0 4 50D Comments: CR-TOLERANCE OF 0.0 IS NOT ABSOLUTELY REQUIRED. IT CAN BE RELAXED TO 0.1 IF NECESSARY. REQUESTED ORIENTATION ON SKY IS WF CCDS ROUGHLY NORTHWEST OF PC2 THIS CAN BE FLEXIBLE IF NECESSARY ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC3256- WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=0.5 1 1800S 10 1 1 CYCLE 4 / 9-10 POS2 CR- 2 SEQ 9-10 NO GAP TOLERANCE=0.0 3 SAME POS FOR 10 AS 9 Comments: REQUIREMENTS 2 AND 3 (GROUP 9- 10 WITHIN 7D) AND SAME ORIENT FOR 10 AS 9 CAN BE REPLACED BY GROUP 9-10 NO GAP IF THAT MAKES SCHEDULING EASIER. ORIENTATION MUST STILL BE VERY CLOSE (1D) TO PREVIOUS EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5396 [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT CR-TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 7.20 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category PECULIAR/INTERACTING ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; ORIENT 150D +/- 30D CYCLE 4 / 3-4; SEQ 3-4 NO GAP; SAME POS FOR 4 AS 3 CYCLE 4 / 5-6; SEQ 5-6 NO GAP; SAME POS FOR 6 AS 5 ORIENT 217D +/- 40D CYCLE 4 / 7-8; SEQ 7-8 NO GAP; SAME POS FOR 8 AS 7 ORIENT 145D +/- 50D CYCLE 4 / 9-10; SEQ 9-10 NO GAP; SAME POS FOR 10 AS 9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F450W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1487-POS1 NGC1487-POS2 NGC3256-POS1 NGC3256-POS2 ------------------------------------------------------------------------------------------------------------------------------------