! Proposal 6791, submission 1 ! PI: Jeffrey Kenney ! Received Fri Feb 9 14:22:57 EST 1996 ! From: kenney@psycho.astro.yale.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! Id: 6791 ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! Anything after a "!" is ignored, and may be deleted ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Alice Berman ! Phone: 410-338-4462 , E-mail: aberman@stsci.edu ! Proposal_Information ! Section 4 Title: THE COLLISIONAL DEBRIS OF NGC 4438 Proposal_Category: GO Scientific_Category: GALAXIES & CLUSTERS Cycle: 6 Investigators PI_name: Jeffrey Kenney PI_Institution: Yale University Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: NGC4438 Alternate_Names: Description: GALAXY,SPIRAL,INTERACTING GALAXY,LINER Position: RA=12H 27M 45.65S +/- 0.6S,DEC=13D 00' 30.5" +/- 1",PLATE-ID=00IY ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V=+71 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: 0.0 Flux: SURF(V)=16.7+/-0.5 ! Include at least V and B-V SURF(R)=16.3+/-0.3 B-V=0.76+/-0.1 SURF(6563)=4+/-2 E-15 SURF(6583)=7+/-3 E-15 Comments: Fixed_Targets ! Section 5.1 Target_Number: 2 Target_Name: NGC4435 Alternate_Names: Description: GALAXY,LENTICULAR,INTERACTING GALAXY Position: RA=12H 27M 40.58S +/- 0.6S,DEC=13D 04' 43.9" +/- 1",PLATE-ID=00IY ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V=+800 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: 0.0 Flux: SURF(V)=15.6+/-0.5 ! Include at least V and B-V B-V=0.90+/-0.1 Comments: Solar_System_Targets ! Section 5.2 Generic_Targets ! Section 5.3 Scan_Data ! Appendix B ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 01 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ORIENTation 254D TO 270D ! ORIENTation 240D TO 297D ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN