6653( 14) - 12/03/96 18:04 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6653 Version: 14 Check-in Date: 03-Dec-1996 18:01:20 1.Proposal Title: Kinematics of Ionized Gas in the Dusty Nuclear Disk in NGC 6251; An Excellent Candidate for a Massive Black Hole ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Holland Ford THE JOHNS HOPKINS UNIVERSITY CoI: Laura Ferrarese Space Telescope Science Institute N CoI: Walter Jaffe Leiden Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose to use narrow-band WFPC2 images and FOS spectra to study the morphology and dynamics of the ionized gas in the nuclear disk of the elliptical galaxy NGC 6251. Our aim is to study the disk around the active nucleus, and to establish the presence and mass of a central, massive black hole, following the same procedure that led to a successful detection of black holes in M87 and NGC 4261 (Ford et al. 1994, Harmes et al. 1994, Ferrarese et al. 1996). NGC 6251 is ideal for this type of study; as in M87 and NGC 4261 (Ford et al. 1994, Jaffe et al. 1994), NGC 6251 harbors a small nuclear dust disk (O'Neil and Lynds, 1994), and is a very powerful radio galaxy. The minor axis of the dust disk is aligned with the spectacular 100 kpc radio jet and the axis of the Mpc scale radio lobes (Waggett, Warner, and Baldwin, 1977), an alignment also found in M87 and NGC 4261, suggesting that the NGC 6251 disk is causally related to the nuclear activity. Nuclear disks of ionized gas and dust provide a powerful way to measure the central potential. Indeed, HST/FOS spectra of M87 and NGC 4261 (Harms et al. 1994, Ferrarese et al. 1996) allowed us to study the orbital motion of the ionized gas in the nuclear disks, and enabled measurement of central masses of 2.4X10^9 solar masses and 1.2X10^9 solar masses in the two galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ WFPC2 Observations. In order to obtain the highest possible spatial resolution, NGC 6251 will be centered in the PC1. At a radial velocity of 6900 km/s, the redshifted Halpha emission is expected at 6713 Angstrom, wavelength region which is covered by the F673N narrow band filter. The filter transmission is highest at the wavelength at which the Halpha emission is expected. It is vital that two off-band images will be taken in regions not contaminated by line emission and on either side of the Halpha emission. There are two compelling reasons for having two off-band images: first, it will allow us to estimate color corrections between the off-band and the on-band images, allowing a more accurate subtraction of the stellar continuum than would be possible with the use of only one off-band image; second, we will use the off-band images to obtain a color map of the nuclear region and to identify dust structures. We will use the F547M and F814W filters to obtain an off-band image on the blue and red sides of the H alpha emission respectively. In order to facilitate cosmic ray removal, the images in each filter will be split into two exposures. Keeping into account the time needed for Guide Star acquisition and the overhead associated with each observation, three full orbits are necessary to complete the proposed WFPC2 observations. FOS Observations. In planning the FOS observations of NGC 6251, we followed closely the procedure adopted for our observations of NGC 4261, which proved successful in the detection of a ~ 10^9 solar masses black hole. Our models of the light and mass distribution show that the definitive signature of a massive black hole will be a transition to a rising Keplerian rotation curve for r < 0."3. We propose to use the FOS 0."09 aperture with the G780H grating, covering the redshifted Halpha+[NII] spectral region, to map the rotation curve in the disk in the crucial region r < 0."3. The final position of the FOS apertures will be defined after the exact morphology of the Halpha emission is determined using the WFPC2 images proposed here. If the emission is uniformly distributed, the pattern adopted will include a 3X3 grid centered on the nucleus and with axes aligned with the major and minor axes of the disk, plus 4 additional positions along the major and minor axes of the disk, on either side of the nucleus, placed just outside the 3X3 grid. The same pattern was used successfully for the FOS observations of NGC 4261. Since no optical spectra or emission line images of NGC 6251 are available, an accurate calculation of the exposure time needed for the spectroscopy will have to wait until the WFPC2 images proposed here will be taken and properly analyzed. Until then, we are forced to base our calculations on our past experience with M87 and NGC 4261. The most optimistic assumption we can make is that the H Alpha flux in the NGC 6251 disk is the same as observed in NGC 4261. This is likely to be an upper limit to the flux, since NGC 6251 is at least 3 times further than NGC 4261; however, the radio emission and the radio jet in NGC 6251 are stronger than in NGC 4261, leading us to expect an intrinsically higher Halpha luminosity. Our experience with NGC 4261 shows that a S/N of 10 at the peak of the [NII]6584+Halpha emission line, is necessary to resolve a Keplerian rise in the rotation curve due to a nuclear black hole with mass larger than 5X10^8 solar masses in the nucleus of NGC 6251. NGC 4261 was mapped with the FOS/G570H at 13 different aperture position, using an exposure time of 2100 seconds for each exposure. We conclude that this is the minimum amount of time that should be spent at each aperture position for NGC 6251. If the analysis of the WFPC2 images shows that the flux in Halpha is lower than for NGC 4261, we will reduce the number of aperture positions in order to achieve the desired S/N ratio. In the most pessimistic case in which the Halpha flux is too low or the Halpha emission is not resolved, we will use all the time allocated to the FOS part of this program to obtain only one spectrum at the nuclear position. Taking into account a 6 minutes overhead associated with each exposure and the time needed for Guide Star acquisition, each of the 13 aperture positions will fill about 80% of one orbit. The ensamble of 13 spectra will therefore require 11 orbits. The nucleus of NGC 6251 is unresolved (O'Neil and Lynds 1995) and sits on a fairly homogeneous background (the dust disk), therefore the acquisition procedure will consist of a binary acquisition in the 1."0 aperture (the color of the nucleus will be derived from the WFPC2 images proposed as the first stage of this program), followed by a standard two stage peak up in the 0."3 and 0."1 apertures. The entire procedure will take two orbits (giving the overhead times tabulated at pages 30 and 31 of the FOS Instrument Handbook). A very similar procedure was executed successfully for the target acquisition of the NGC 4261's nucleus. Therefore, a total of 11 + 2 = 13 orbits are required for the spectroscopy. Real Time Justification ----------------------- None Calibration Justification ------------------------- None Additional Comments ------------------- None ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address*Bloomberg Center,*Homewood Campus*Baltimore*21218 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6653( 14) - 12/03/96 18:04 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6251-NUC GALAXY,ELLIPTICAL,RADIO RA=16H 32M 31.85S +/- 0.04S, J2000 V=+6900 SURF(R) = 19.5+/-0.5 GALAXY DEC=82D 32' 16.3" +/- 0.5", V-R = 0.6 PLATE-ID=01JN Comments: Plate-ID is the one from which the GASP finder charts are made and from which the guide stars should be taken since the only other calibrated GS plate on which the target appears is one on which the target is at an extreme edge of the plate. It is much more centrally located on 01JN which corresponds to region N009. 2 NGC6251-FOS- GALAXY,ELLIPTICAL,RADIO RA=16H 32M 32.16S +/- 0.006S, J2000 V=+6900 V = 18.72+/-0.14 NUC GALAXY DEC=82D 32' 16.59" +/- 0.1" V-I = 1.17+/-0.23 F(6725)=2.6+/-0.3e-16 Comments: Updated coords based on WFPC2 EARLY ACQ in Visit 1. 3 NGC6251-OFF1 GALAXY,ELLIPTICAL,RADIO XI-OFF=0.0897"+/-0.01", ETA-OFF= J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY -0.0078"+/-0.01", FROM 2 F(6725)=6.2+/-0.6e-17 4 NGC6251-OFF2 GALAXY,ELLIPTICAL,RADIO XI-OFF=0.1793"+/-0.01", ETA-OFF= J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY -0.0157"+/-0.01", FROM 2 F(6725)=7.5+/-0.8e-18 5 NGC6251-OFF3 GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.0897"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=0.0078"+/-0.01", FROM 2 F(6725)=6.2+/-0.6e-17 6 NGC6251-OFF4 GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.1793"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=0.0157"+/-0.01", FROM 2 F(6725)=7.5+/-0.8e-18 7 NGC6251-OFF5 GALAXY,ELLIPTICAL,RADIO XI-OFF=0.0078"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=0.0897"+/-0.01", FROM 2 F(6725)=6.2+/-0.6e-17 8 NGC6251-OFF6 GALAXY,ELLIPTICAL,RADIO XI-OFF=0.0157"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=0.1793"+/-0.01", FROM 2 F(6725)=7.5+/-0.8e-18 9 NGC6251-OFF7 GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.0078"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=-0.0897"+/-0.01", FROM 2 F(6725)=6.2+/-0.6e-17 10 NGC6251-OFF8 GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.0157"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=-0.1793"+/-0.01", FROM 2 F(6725)=7.5+/-0.8e-18 11 NGC6251-OFF9 GALAXY,ELLIPTICAL,RADIO XI-OFF=0.0975"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 GALAXY OFF=0.0818"+/-0.01", FROM 2 F(6725)=1.0+/-0.1e-17 12 NGC6251- GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.0818"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 OFF10 GALAXY OFF=0.0975"+/-0.01", FROM 2 F(6725)=1.0+/-0.1e-17 13 NGC6251- GALAXY,ELLIPTICAL,RADIO XI-OFF=-0.0975"+/-0.01", ETA- J2000 V=+6900 V-I = 1.17+/-0.23 OFF11 GALAXY OFF=-0.0818"+/-0.01", FROM 2 F(6725)=1.0+/-0.1e-17 14 NGC6251- GALAXY,ELLIPTICAL,RADIO XI-OFF=0.0818"+/-0.01", ETA-OFF= J2000 V=+6900 V-I = 1.17+/-0.23 OFF12 GALAXY -0.0975"+/-0.01", FROM 2 F(6725)=1.0+/-0.1e-17 6653( 14) - 12/03/96 18:04 - [ 2] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Early Acquisition for visit 2 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6251-NUC WFPC2 IMAGE PC1 F547M 1 1200 S Comments: Off-band exposure ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC6251-NUC WFPC2 IMAGE PC1 F814W 1 1200 S Comments: Off-band exposure ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC6251-NUC WFPC2 IMAGE PC1 F673N 1 2900 S Comments: Halpha+[NII] on-band exposure ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC6251-NUC WFPC2 IMAGE PC1 F673N 1 2900 S Comments: Halpha+[NII] on-band exposure ------------------------------------------------------------------------------------------------------------------------------------ 6653( 14) - 12/03/96 18:04 - [ 3] Visit: 02 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 ------------------------------------------------------------------------------------------------------------------------------------ 100 NGC6251-FOS FOS/RD ACQ/PEA 1.0-PAI G780H 6650-68 SCAN-STEP-X=0.70,SCAN-STEP-Y=0.70 1 65 S ONBOARD ACQ FOR 110 -NUC K R-B 30 ,SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5 ------------------------------------------------------------------------------------------------------------------------------------ 110 NGC6251-FOS FOS/RD ACQ/PEA 0.5-PAI G780H 6650-68 SCAN-STEP-X=0.30,SCAN-STEP-Y=0.30 1 100 S ONBOARD ACQ FOR 120 -NUC K R-B 30 ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 120 NGC6251-FOS FOS/RD ACQ/PEA 0.25-PA G780H 6650-68 SCAN-STEP-X=0.17,SCAN-STEP-Y=0.17 1 90 S ONBOARD ACQ FOR 130 -NUC K IR-B 30 ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 130 NGC6251-FOS FOS/RD ACQ/PEA 0.1-PAI G780H 6650-68 SCAN-STEP-X=0.052, 1 75 S ONBOARD ACQ FOR 200-320 -NUC K R-B 30 SCAN-STEP-Y=0.052,SEARCH-SIZE-X=5 ,SEARCH-SIZE-Y=5 ------------------------------------------------------------------------------------------------------------------------------------ 150 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 200 NGC6251-FOS FOS/RD ACCUM 0.1-PAI G780H 1 2050 S -NUC R-B ------------------------------------------------------------------------------------------------------------------------------------ 210 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 1 R-B ------------------------------------------------------------------------------------------------------------------------------------ 215 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 220 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 2 R-B ------------------------------------------------------------------------------------------------------------------------------------ 230 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 3 R-B ------------------------------------------------------------------------------------------------------------------------------------ 235 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 240 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 4 R-B ------------------------------------------------------------------------------------------------------------------------------------ 250 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 5 R-B ------------------------------------------------------------------------------------------------------------------------------------ 255 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 260 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 6 R-B ------------------------------------------------------------------------------------------------------------------------------------ 6653( 14) - 12/03/96 18:04 - [ 4] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 270 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 7 R-B ------------------------------------------------------------------------------------------------------------------------------------ 275 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 280 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 8 R-B ------------------------------------------------------------------------------------------------------------------------------------ 290 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 9 R-B ------------------------------------------------------------------------------------------------------------------------------------ 295 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 300 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 10 R-B ------------------------------------------------------------------------------------------------------------------------------------ 310 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 11 R-B ------------------------------------------------------------------------------------------------------------------------------------ 320 NGC6251-OFF FOS/RD ACCUM 0.1-PAI G780H 1 2050 S 12 R-B ------------------------------------------------------------------------------------------------------------------------------------ 325 WAVE FOS/RD ACCUM 0.1-PAI G780H 1 DEF R-B ------------------------------------------------------------------------------------------------------------------------------------ 6653( 14) - 12/03/96 18:04 - [ 5] Summary Form for Proposal 6653 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-X=0.70 SCAN-STEP-Y=0.70 SEARCH-SIZE-X=5 SEARCH-SIZE-Y=5 SEARCH-SIZE-Y=3 SEARCH-SIZE-X=3 SCAN-STEP-Y=0.052 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 110 ONBOARD ACQ FOR 120 ONBOARD ACQ FOR 130 ONBOARD ACQ FOR 200-320 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F547M F814W F673N G780H ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6251-NUC NGC6251-FOS-NUC WAVE NGC6251-OFF1 NGC6251-OFF2 NGC6251-OFF3 NGC6251-OFF4 NGC6251-OFF5 NGC6251-OFF6 NGC6251-OFF7 NGC6251-OFF8 NGC6251-OFF9 NGC6251-OFF10 NGC6251-OFF11 NGC6251-OFF12 ------------------------------------------------------------------------------------------------------------------------------------