8690( 6) - 05/06/02 10:01 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8690 Version: 6 Check-in Date: 06-May-2002 10:00:30 1.Proposal Title: The Central Region of NGC4696: Manifestation of the Physics of Mergers? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: William Sparks Space Telescope Science Institute CoI: Dr. Marcella Carollo Columbia University N CoI: Dr. Ferdinando Macchetto Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract Massive, dominant ellipticals with attendant emission-line gas, dust and hot, heavy X--ray emitting coronae lie at the very centers of galaxy clusters. The physics of these complex, high pressure regions remains controversial: Are cooling flows responsible? Do mergers dominate, with massive accretion events triggering an array of phenomena? Is the AGN crucial? A major impetus to understanding the physics of these regions will come with Chandra. NGC4696 in the Centaurus galaxy cluster is archetypal. WFPC2 images have shown a dramatic bifurcation between gas and dust. The nucleus itself is seen to be a compact triple, with two blue components straddling a third red one. We propose to obtain STIS long- slit spectra (\romannumeral1) along a line-emission filament and (\romannumeral2) along a dust filament: are we witnessing physical separation of gas and dust, as in comet ion/dust tails, due to late stage merger physics; or are very high velocities, due to powerful AGN influences, shifting emission lines out of filters? Is the HAlpha+NII filament a shock, responsible for the known off-center X--ray peak? (\romannumeral3) A third spectrum will be across the compact 0.26'' triple nucleus: is it a multiple nucleus confirming the merger scenario; or a disk around a black-hole, allowing mass determination; or the first double optical synchrotron jet; or a gravitational lens? A wealth of vital physical and kinematical data will result from these carefully selected spectra. ------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 2] Observations Description ------------------------ sectionOverview On board target acquisitions of ``diffuse'' type will suffice for all observations, hence a minimal overhead of order 6 min will be incurred for target acquisition. (There will be an additional 6 min needed for an ACQ/PEAK on the first of the five orbits of the nucleus visit.) Together with guide star acquisition overheads, we have approximately 2500 sec of visibility remaining for science observation per orbit. We will group our observations into three visits, focussing on features illustrated in the corresponding three panels in Fig. 2. We will obtain low and intermediate resolution spectra of the continuum sources and intermediate resolution spectra of the gaseous emission sources. We request five orbits for observations of the nucleus and two each for the radial filaments. sectionThe Multiple Nucleus The multiple nuclei, central panel of Fig. 2, are primarily continuum features, although there is some line emission throughout the whole region. The separation of the nuclei is only 0.26 arcsec and so HST spatial resolution is essential to obtain spectra of the nuclei separately. With a long slit width 52* 0.1 arcsec we will optimize resolution and simultaneously acquire all three components. The flux of the two outer components is relatively constant in f_Lambda, with measurements from 3700Angstrom\ (FOC) to 7000Angstrom (WFPC2) yielding a flux f_Lambda ~ 8* 10^-18erg s^-1 cm^-2 Angstrom ^-1. The central component is much redder, visible only to any degree in the red WFPC2 image shown. We propose to obtain a low resolution spectrum covering the entire spectrum from 2900Angstrom\ to 10270Angstrom\ with observations using the G430L and G750L gratings in turn, two orbits each for a total of 5000 sec per spectrum. This will yield a continuum S/N per resolution element of ~ 6---11 depending on wavelength. With such high quality data it will be straightforward to ascertain the nature of the three components. We propose to supplement the low resolution spectrum with a one-orbit intermediate resolution spectrum using the G750M grating and 52* 0.1 arcsec slit, to cover the region 6482---7054Angstrom . This will enable us to derive emission line velocites with a velocity resolution of ~ 50 km.s^-1, and excitation character and diagnostics across the nuclear emission peak seen in Fig. 2 (right hand panel). This will include the lines of HAlpha\ 6563Angstrom , NII\ 6548, 6584Angstrom\ and the density sensitive diagnostic SII\ 6717, 6731Angstrom . The line emission surface brightness is ~ 1.4---0.2 * 10^-14erg s^-1 cm^-2 arcsec^-2 in HAlpha+NII, across the region, and NII\ 6584Angstrom\ is typically three times HAlpha from our ground-based spectra (Sparks, Carollo and Macchetto 1997). The diameter of the nuclear emission region seen in Fig. 2 (right hand panel) is ~ 0.6 arcsec. Thus with a single one-orbit 2500 sec exposure (CR-SPLIT) we would be able to achieve a S/N of ~ 9 per resolution element in the strong emission lines, allowing for line broadening, with useable signal over the whole central region (binning at the largest radii to improve S/N). For a distance to NGC 4696 of ~ 50 Mpc (H_0 = 60 km s^-1 Mpc^-1) the nuclear components lie ~ 31 pc from the center and 50 km.s^ -1 orbital motion would arise from 1.8* 10^7M_\odot interior mass. We will therefore also have a very sensitive probe of the nuclear mass distribution across quite a broad region around the nucleus. Note that the emission filament spectrum, below, will cut this region at approximately 90degrees\ position angle which will provide very valuable information in allowing us to properly interpret whatever velocity field we find. It will be deeper, and uses the 0.2 arcsec slit. sectionThe Bright Line-Emission Filament, West Fig. 2 right hand panel shows an approximately linear, bright emission filament extending slightly North of West from the nucleus. (Note that there is no corresponding enhancement in the optical depth image in the left hand panel.) The brightest knots in this filaments have a surface brightness of up to ~ 3.3 * 10^-15erg s^ -1 cm^-2 arcsec^-2 in HAlpha+NII. Typical surface brightnesses seen in low resolution ground-based work are are ~ hboxfew* 10^-16erg s^-1 cm^-2 arcsec^-2, which are seen clearly in Fig. 1 and can be made out in the LRF image, Fig. 2. In order to measure the velocities, line widths and excitation character along this important region, we propose to orient the 52* 0.2 arcsec slit from the nucleus along the feature using the G750M grating. With a two orbit exposure totalling 5000 sec we expect to obtain a S/N of ~ 12 per resolution element in the knots, with a limiting surface brightness approximately the level of the ground-based low-surface- brightness emission. Thus, the bright filament itself is a straighforward target for observation, while information on the diffuse emission will be derived, possibly requiring spatial or spectral binning in the fainter regions. (This would be carried out in post-observation data analysis.) An S/N or order 10 or more per resolution element will give excellent diagnostic and kinematic information on the feature. sectionThe Radial Dust Filament, North-East To the East of the nucleus, pointing to the North-East, there lies a narrow, possibly twisted, filament of dust shown quite well in the optical depth image of Fig. 2 (left hand panel). Previously, every occurence of dust in an elliptical galaxy has been found to be accompanied by optical line emission, e.g. Sparks (1997). This feature however does not appear to be accompanied by an enhancement in optical line emission in Fig. 2. There are several possiblities (\romannumeral1) there is no gas associated with the dust (\romannumeral2) the emission is there, but at a lower surface brightness or severely reddened (\romannumeral3) the velocity of the emission has redshifted or blueshifted it out of the filter bandpass (\romannumeral4) the excitation character has changed dramatically to either much lower or higher state. We propose to obtain a matching 5000 sec 52* 0.2 slit G750M observation equivalent in every way to the observation across the emission filament. This will enable us to identify which of the above options is the most likely. The flux limit for the 5000 sec G750M spectrum is comparable to the surface brightness seen in ground-based work, ~ hboxfew * 10^-16erg s^-1 cm^-2 arcsec^-2, depending on binning parameters, line widths, etc. (narrower lines farther out give easier detection and better limits, however the actual linewidth is not known. We assumed 300 km.s^-1 above which is likely to be conservative.) Hence we will have a sensitive set of well- matched spectra to enable velocity and emission characterization and comparison of these two apparently very different regions. Real Time Justification ----------------------- Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4696 GALAXY, ELLIPTICAL RA=12H 48M 49.17S +/- 0.02S, J2000 V = 2925 V = 10.7 DEC=-41D 18' 37.96" +/- 0.05", B-V = 1.0 PLATE-ID=0162 Coordinate Source: HST_IMAGE Comments: Coordinates measured from WFPC2 2 NGC4696-DUST GALAXY, ELLIPTICAL XI-OFF=1.548" +/- 0.02", ETA- J2000 V = 2925 SURF(V) = 20.0 OFF=0.109" +/- 0.02", FROM 1, B-V = 1.0 PLATE-ID=0162 Coordinate Source: HST_IMAGE Comments: Target is to East and North of nucleus 3 NGC4696-EM GALAXY, ELLIPTICAL XI-OFF=-1.345" +/- 0.025", ETA- J2000 V = 2925 SURF(V) = 20.0 OFF=+1.046" +/- 0.025", FROM 1, B-V = 1.0 PLATE-ID=0162 Coordinate Source: HST_IMAGE 4 NGC4696- GALAXY, ELLIPTICAL RA=12H 48M 49.21S +/- 0.02S, J2000 V = 2925 V = 10.7 UPDATED DEC=-41D 18' 40.20" +/- 0.05", B-V = 1.0 PLATE-ID=0162 Coordinate Source: HST_IMAGE Comments: Updated coordinates from Bill Sparks 8690( 6) - 05/06/02 10:01 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 74D TO 76D ORIENT 254D TO 256D On Hold Comments: Additional Comments: Nuclear triple Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4696-UPD STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE, 1 60 S SEQ 10-20 NON-INT ATED CD P DIFFUSE-CENTER=FLUX-CENTROID, CHECKBOX=11 Comments: Onboard acq for visit 1 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4696-UPD STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=2 1 36 M PAR 25 WITH 20 ATED CD ------------------------------------------------------------------------------------------------------------------------------------ 25 ANY WFPC2 IMAGE WFALL F555W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4696-UPD STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 44 M PAR 35 WITH 30 ATED CD ------------------------------------------------------------------------------------------------------------------------------------ 35 ANY WFPC2 IMAGE WFALL F814W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC4696-UPD STIS/C ACCUM 52X0.2 G750L 7751 CR-SPLIT=3 1 42 M PAR 45 WITH 40 ATED CD ------------------------------------------------------------------------------------------------------------------------------------ 45 ANY WFPC2 IMAGE WFALL F555W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 80 CCDFLAT STIS/C ACCUM 52X0.2 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 90 NGC4696-UPD STIS/C ACCUM 52X0.2 G750M 6768 CR-SPLIT=3 1 42 M PAR 95 WITH 90 ATED CD ------------------------------------------------------------------------------------------------------------------------------------ 95 ANY WFPC2 IMAGE WFALL F814W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 160D TO 162D ORIENT 340D TO 342D On Hold Comments: Additional Comments: Nuclear triple orthogonal Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4696 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE, 1 60 S CD P DIFFUSE-CENTER=FLUX-CENTROID, CHECKBOX=11 Comments: ONBOARD ACQ FOR 20 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4696 STIS/C ACCUM 52X0.1 G750M 6768 CR-SPLIT=2 1 35 M PAR 25-26 WITH 20 CD ------------------------------------------------------------------------------------------------------------------------------------ 25 ANY WFPC2 IMAGE WFALL F555W 1 14 M ------------------------------------------------------------------------------------------------------------------------------------ 26 ANY WFPC2 IMAGE WFALL F814W 1 14 M ------------------------------------------------------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 83D TO 87D ORIENT 263D TO 267D On Hold Comments: Additional Comments: Dust filament Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4696 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE, 1 60 S CD P DIFFUSE-CENTER=FLUX-CENTROID, CHECKBOX=11 Comments: ONBOARD ACQ FOR VISIT 3 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4696-DUS STIS/C ACCUM 52X0.2 G750M 6768 CR-SPLIT=2 1 35 M PAR 25 WITH 20 T CD ------------------------------------------------------------------------------------------------------------------------------------ 25 ANY WFPC2 IMAGE WFALL F555W 2 12 M ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4696-DUS STIS/C ACCUM 52X0.2 G750M 6768 CR-SPLIT=3 1 44 M PAR 35 WITH 30 T CD ------------------------------------------------------------------------------------------------------------------------------------ 35 ANY WFPC2 IMAGE WFALL F814W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 7] Visit: 04 Visit Priority: Visit Requirements: ORIENT 140D TO 141D ORIENT 320D TO 321D 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 NGC4696 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE, 1 60 S CD P DIFFUSE-CENTER=FLUX-CENTROID, CHECKBOX=11 Comments: ONBOARD ACQ FOR VISIT 4 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4696-EM STIS/C ACCUM 52X0.2 G750M 6768 CR-SPLIT=2 1 35 M PAR 25 WITH 20 CD ------------------------------------------------------------------------------------------------------------------------------------ 25 ANY WFPC2 IMAGE WFALL F555W 2 12 M ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4696-EM STIS/C ACCUM 52X0.2 G750M 6768 CR-SPLIT=3 1 44 M PAR 35 WITH 30 CD ------------------------------------------------------------------------------------------------------------------------------------ 35 ANY WFPC2 IMAGE WFALL F814W 2 14 M ------------------------------------------------------------------------------------------------------------------------------------ 8690( 6) - 05/06/02 10:01 - [ 8] Summary Form for Proposal 8690 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 WFALL 52X0.1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE DIFFUSE-CENTER=FLUX-CENTROID CHECKBOX=11 CR-SPLIT=2 CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 74D TO 76D ORIENT 254D TO 256D SEQ 10-20 NON-INT PAR 25 WITH 20 PAR 35 WITH 30 PAR 45 WITH 40 PAR 95 WITH 90 ORIENT 160D TO 162D ORIENT 340D TO 342D PAR 25-26 WITH 20 ORIENT 83D TO 87D ORIENT 263D TO 267D ORIENT 140D TO 141D ORIENT 320D TO 321D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L F555W F814W G750L G750M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4696-UPDATED ANY CCDFLAT NGC4696 NGC4696-DUST NGC4696-EM ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 7751 6768 ------------------------------------------------------------------------------------------------------------------------------------