6791( 14) - 09/04/98 14:22 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6791 Version: 14 Check-in Date: 04-Sep-1998 14:21:48 1.Proposal Title: THE COLLISIONAL DEBRIS OF NGC 4438 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 6 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Jeffrey Kenney Yale University ------------------------------------------------------------------------------------ 5. Abstract We propose to image the center of the peculiar Virgo cluster galaxy NGC 4438 with WFPC2 in 3 broadband (B, R, I) and 2 narrowband (HAlpha, NII) filters, and the central field of NGC 4435 in 3 broadband (B, R, I) filters. NGC 4438 and NGC 4435 have experienced a recent high-velocity (900 km s^-1) collision, and NGC 4438 has a strongly disturbed ISM attributable to a high-velocity ISM-ISM collision. In order to assess how the collision has changed NGC 4438, we wish to search for evidence of recent and ongoing star and cluster formation in the collisional debris. Ground- based images reveal features suggesting that collisionally-induced star formation may be widespread in NGC 4438: 1.) Unresolved continuum sources peppered throughout the debris, suggesting that high-velocity collisions produce halo globular clusters. 2.) A highly disturbed central ISM with strong CO, HAlpha, and x-ray emission, and LINER line ratios. 3.) Ionized gas filaments which extend outwards from one side of the disk, which may be cooling gas resettling into NGC 4438 in the aftermath of the collision. High resolution HST HAlpha, NII line and B, R, I images are required to resolve star clusters, and to identify compact HII regions within a disturbed ISM which is predominantly shock-excited. This system is the nearest example of a recent and close high-velocity collision between 2 large galaxies, and offers a unique opportunity to learn about the physical processes in high-velocity collisions which can transform cluster galaxies. ------------------------------------------------------------------------------------ 6791( 14) - 09/04/98 14:22 - [ 2] Observations Description ------------------------ % 12. DESCRIPTION OF THE OBSERVATIONS % % Provide a short DESCRIPTION of the proposed observations --- by % cycle for Long-Term projects. Explain the amount of exposure % time and number of orbits requested (e.g., number of objects, % examples of exposure-time calculations and orbit estimations for % some typical observations, etc.). Explicitly describe any cali- % bration requirements for your observations, and for FOS % observations, your target acquisition strategy. SNAPshot proposals % should identify the requested guiding mode and the requested % proprietary data-rights period for the exposures. % \describeobservations % Do not delete this command. % Enter your description here. (updated 23may97) With the pointing and position angle selected for NGC~4438, the WF CCDs can cover most of the region of interest, including the entire bulge-dominated region with strong line emission, most of the optical filaments, and many of the small ``halo'' knots. The nucleus will be centered in WF3. I had originally planned to observe 2 adjacent fields and mosaic them together, but a lack of guide stars for one of the fields caused me to revise the planned observations. I will now observe one field, and spend twice as long on it. We wish to image NGC~4438 in three broadband filters F450W="Wide B", F675W="R", and F814W="Wide I", and in two narrowband filters F656N=Halpha and F658N=[NII]. The B-I color will give an indication of the age of star clusters and other stellar features. The R image will be used to subtract the continuum emission from the line images. The brightest of the small ``halo'' knots have magnitudes of R=21, corresponding to M_R= -10. We wish to reach a limiting magnitude of M_R= -6 (R=25), in order to measure the cluster luminosity function over a range of several magnitudes. Our Cycle 4 observations of the Virgo galaxy NGC~4526 reached a limiting magnitude of V=24 (S/N=10) for cluster candidates in 460s. Based on this, and accounting for the expected red colors of the clusters, we request 480s in F814W="Wide I", 540s in F675W="R", and 720s in F450W="Wide B". We wish to image both the Halpha and [NII] lines in NGC~4438. Since NGC~4438 has a radial velocity close to zero (71 km s^-1), the galaxy emission from these lines will be well separated by the F656N (Halpha) and F658N ([NII]) filters. The morphology of the line emitting regions, the map of line ratios, and the comparison with the continuum should clarify the origin of the line emission, and allow identification of HII regions and regions of shock excitation. Our 3000s Halpha HST image of NGC~4536 reached a sensitivity of 10^{-15} erg cm^{-2} s^{-1} arcsec^{-2} in the PC 0.045'' pixels. Exposure times of 2400 sec with the WF chips should therefore allow us to detect all of the line emission in the central 1', as well as HII regions and other bright peaks within the extended filaments. The surface brightness of the line emission shown in Fig. 2 ranges from 10^{-14}-10^{-16} erg cm^{-2} s^{-1} arcsec^{-2}. NGC~4435 requires one pointing centered on the nucleus. NGC~4435 and NGC~4438 are only 5' apart, so that both galaxies can be observed within one visit, but don't need to be. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6791( 14) - 09/04/98 14:22 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6791( 14) - 09/04/98 14:22 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4438 GALAXY, SPIRAL, RA=12H 27M 45.65S +/- 0.6S, J2000 V=+71 SURF(V) = 16.7+/-0.5 INTERACTING GALAXY, DEC=13D 00' 30.5" +/- 1", PLATE- SURF(R) = 16.3+/-0.3 LINER ID=00IY B-V = 0.76+/-0.1 SURF(6563)=4+/-2e-15 SURF(6583)=7+/-3e-15 2 NGC4435 GALAXY, LENTICULAR, RA=12H 27M 40.58S +/- 0.6S, J2000 V=+800 SURF(V) = 15.6+/-0.5 INTERACTING GALAXY DEC=13D 04' 43.9" +/- 1", PLATE- B-V = 0.90+/-0.1 ID=00IY 6791( 14) - 09/04/98 14:22 - [ 5] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC4438 WFPC2 IMAGE WF3-FIX F814W 3 350 S POS TARG -20, -20 GS ACQ SCENARIO SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC4438 WFPC2 IMAGE WF3-FIX F675W 1 400 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC4438 WFPC2 IMAGE WF3-FIX F675W 3 350 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC4438 WFPC2 IMAGE WF3-FIX F450W 2 400 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC4438 WFPC2 IMAGE WF3-FIX F450W 1 500 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 16 NGC4438 WFPC2 IMAGE WF3-FIX F656N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 17 NGC4438 WFPC2 IMAGE WF3-FIX F656N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 18 NGC4438 WFPC2 IMAGE WF3-FIX F656N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 19 NGC4438 WFPC2 IMAGE WF3-FIX F656N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4438 WFPC2 IMAGE WF3-FIX F658N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC4438 WFPC2 IMAGE WF3-FIX F658N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC4438 WFPC2 IMAGE WF3-FIX F658N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC4438 WFPC2 IMAGE WF3-FIX F658N CR-SPLIT=NO 1 1300 S SAME POSition AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 6791( 14) - 09/04/98 14:22 - [ 6] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: NGC4435 and NGC4438 are 5' apart and can be observed within the same visit if convenient Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 31 NGC4435 WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=NO 2 300 S ------------------------------------------------------------------------------------------------------------------------------------ 32 NGC4435 WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=NO 2 260 S SAME POSition AS 31 ------------------------------------------------------------------------------------------------------------------------------------ 33 NGC4435 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 2 260 S SAME POSition AS 31 ------------------------------------------------------------------------------------------------------------------------------------ 6791( 14) - 09/04/98 14:22 - [ 7] Summary Form for Proposal 6791 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF3-FIX PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG -20, -20 GS ACQ SCENARIO SINGLE SAME POSition AS 11 SAME POSition AS 31 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F675W F450W F656N F658N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4438 NGC4435 ------------------------------------------------------------------------------------------------------------------------------------