6789( 17) - 12/05/96 12:52 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6789 Version: 17 Check-in Date: 05-Dec-1996 12:50:16 1.Proposal Title: A Search for Intermediate-Age Globular Clusters in the Nearby Giant Elliptical Galaxy NGC 5128 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: PATRICK COTE DOMINION ASTROPHYSICAL OBSERVATORY CoI: James E. Hesser Dominion Astrophysical Observatory N CoI: Stephen Holland University of British Columbia N ------------------------------------------------------------------------------------ 6. Abstract NGC 5128 is the nearest giant elliptical galaxy. An enormous body of evidence now suggests that most of its major features (e.g. a wide central dust lane, an optical- , radio- and X-ray- luminous jet, numerous bright shells, filaments and star-forming regions) are the result of a 1 Gyr-old merger with a gas-rich system. We propose to use the superb spatial resolution of the WFPC2 to survey (in V and I) the central 4.5 * 6.7 arcminutes of the galaxy to search for the expected population of intermediate-age globular clusters (GCs) formed in this merger event. At a distance of 3.1 Mpc, even the most compact GCs in NGC 5128 are resolved with the HST. All new clusters discovered with the HST will be added to our ongoing spectroscopic survey of the brightest, ancient clusters with the CTIO 4m telescope. By extending our spectroscopic survey to the intermediate-age clusters found here, we will be able to probe the processes of GC formation and evolution in a level of detail not possible with the young ``globular'' clusters currently forming in distant systems like NGC 1275, NGC 3921 and NGC 7252. ------------------------------------------------------------------------------------ Observations Description ------------------------ In order to sample adequately the inner regions of the galaxy, we request a total of six fields across the central dust lane of NGC 5128. Our survey spans an area of approximately 4.5 * 6.7 arcminutes centred on the nucleus of the galaxy at alpha(2000) = 13:25:27.57 and delta(2000) = -43:01:08.7. We have a retained an overlap between adjacent fields of approximately 0.5 arcminutes for calibration purposes. The effective area of the survey is approximately 25 square arcminutes. We request exposures in F555W (broadband V) and F814W (broadband I) to efficiently identify GCs as well as to provide crude metallicities/ages for all objects in the survey. Since the exact choice of color index is not critical, we have requested the F555W and F814W filters to minimize our exposure times. We have estimated our exposure times based on simulated WFPC2 images generated with STSDAS and our own software, which convolves GC surface brightness profiles with the WFPC2 PSF (see Holland et al. 1996 for details). Our model assumptions include: (1) King-model GC surface brightness profiles with concentration parameter c = 1.26; (2) a GC spectral energy distribution characteristic of a K0III star; (3) the underlying galaxy light has a uniform surface brightness of mu_V = 19 magnitudes per square arcsecond (van den Bergh 1976; Hesser et al. 1984) and a uniform color of (V-I) = 2. At a distance of 3.1 Mpc, the luminosity function of the old GCS turns over at V = 20.1 and the brightest clusters appear at approximately V = 16.5. For the putative population of 1 Gyr- old clusters, these values are approximately 2 magnitudes brighter (Schweizer and Seitzer 1993). With exposure times of 3 *60 seconds, we will be able to derive magnitudes and colors for not only the brightest, intermediate-age objects (V ~= 14; S/N ~= 150), but also for old clusters near the apparent turnover of the NGC 5128 GC luminosity function (V ~= 20; S/N ~= 5). Due to the short exposure times (and to the fact that the essential aspect of this program is high spatial resolution, not ultra -precise photometry), CR-SPLITing is not required. Including overhead, we estimate that V and I images for two fields can be acquired in one orbit; the entire survey can therefore be completed in three orbits. Real Time Justification ----------------------- None. As mentioned above, some of us (G. Harris, P. Cote, J. Hesser, & G. Worthey) are conducting a spectroscopic survey of approximately 50 of the confirmed GCs in NGC 5128 using Argus on the CTIO 4m telescope. These data will be used to disentangle age and metallicity effects in the NGC 5128 GC system. All new clusters discovered in our proposed HST survey (especially those candidate approximately 1 Gyr old objects) will be included in our spectroscopic survey to give unprecedented insights into the formation and evolution of the GC system surrounding this giant elliptical. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 6789( 17) - 12/05/96 12:52 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 32.98S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD1 CLUSTER,STAR FORMING 43D 0' 8.56" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located slightly NE of the the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 2 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 27.55S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD2 CLUSTER,STAR FORMING 43D 0' 8.70" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located directly N of the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 3 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 22.13S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD3 CLUSTER,STAR FORMING 43D 0' 8.84" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located slightly NW of the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 4 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 33.00S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD4 CLUSTER,STAR FORMING 43D 2' 8.56" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located slightly SE of the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 6789( 17) - 12/05/96 12:52 - [ 2] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 27.58S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD5 CLUSTER,STAR FORMING 43D 2' 8.70" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located slightly S of the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 6 NGC5128- EXT-CLUSTER,GLOBULAR RA=13H 25M 22.16S +/- 1.0S,DEC=- J2000 V = 547 SURF-BKG(V) = 19+/-0.5 FIELD6 CLUSTER,STAR FORMING 43D 2' 8.84" +/- 1.0" SURF-BKG(I) = 17.8+/-0.5 REGION,GALAXY,ELLIPTICA SURF(V) = 14.5+/-0.5 L,DUST LANE SURF(I) = 13.2+/-0.5 E(B-V) = 0.15+/-0.1 V-I = 1.2+/-0.5 A(V) = 0.48+/-0.32 Comments: This field is located slightly SW of the centre of NGC 5128 on the dust lane. The quoted surface brightnesses are for the brightest star clusters. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0 0 0 6789( 17) - 12/05/96 12:52 - [ 3] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: The objects of interest have central surface brightnesses of between approximately V = 14.5 and V = 20.5. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD1 IX ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD1 IX ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD2 IX ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 4 60 S LD2 IX Comments: The extra exposure is simply to make use of all avaliable observing time in this orbit. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD3 IX ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD3 IX ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD6 IX ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD6 IX ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 3 40 S LD4 IX ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 40 S LD4 IX ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC5128-FIE WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7,CR-SPLIT=NO 3 50 S LD5 IX ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC5128-FIE WFPC2 IMAGE WFALL-F F555W ATD-GAIN=7,CR-SPLIT=NO 3 60 S LD5 IX ------------------------------------------------------------------------------------------------------------------------------------ 6789( 17) - 12/05/96 12:52 - [ 4] Summary Form for Proposal 6789 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5128-FIELD1 NGC5128-FIELD2 NGC5128-FIELD3 NGC5128-FIELD6 NGC5128-FIELD4 NGC5128-FIELD5 ------------------------------------------------------------------------------------------------------------------------------------