6296( 3) - 02/01/96 17:27 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6296 Version: 3 Check-in Date: 01-Feb-1996 17:20:24 1.Proposal Title: Deep Narrow-Band Imaging of M87: A Close Look at the Disk of Ionized Gas Fueling a Massive Black Hole ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GTO/FOS 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Holland Ford Johns Hopkins University CoI: Zlatan Tsvetanov Johns Hopkins University Y CoI: Gerard Kriss Johns Hopkins University N CoI: Richard Harms RCH Scientific N CoI: Linda Dressel RCH Scientific N CoI: Bruce Margon University of Washington N CoI: Margaret Burbidge University of California San Diego N CoI: Edward Beaver University of California San Diego N CoI: Roger Angel University of Arozona N CoI: Frank Bartko University of Colorado N CoI: Ralph Bohlin Space Telescope Science Institute N CoI: Arthur Davidsen Johns Hopkins University N CoI: Rchard Allen University of Arizona N CoI: George Hartig Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract M87 provides a unique example of a 100 pc scale disk of ionized gas fueling a massive black hole (Ford et al. 1994, Harms et al. 1994). The disk shows tantalizing evidence for spiral structure and a possible connection to large scale, wrapped filaments. Sparks, Ford, and Kinney (1993) used observations of dust absorption in the filaments and blueshifted velocities with respect to M87 to conclude that the filaments are an outflow from the nucleus. If the wrapped filaments are in fact an outflow, we are witnessing the solution to an outstanding problem in astrophysics, that of removing angular momentum from a disk to allow the gas to flow onto the central massive black hole. We propose to use 6 orbits to take deep, half-pixel stepped, Halpha+[Nii] on-band images to study the morphology in the disk and filaments. The images will be one magnitude deeper than previous images and will reach the 0.06'' diffraction limit of the telescope at Halpha. Our goals are to use the deep, high resolution images to: 1) Investigate and understand the apparent connection between the filaments and the disk. 2) Delineate the apparent spiral structure in the disk. 3) Confirm the presence of faint Halpha+[Nii] emission associated with the jet, which could be gas which has been entrained by the jet. ------------------------------------------------------------------------------------ 6296( 3) - 02/01/96 17:27 - [ 2] Observations Description ------------------------ To achieve our goal of getting a much better look at the unique (to date) disk in the center of M87, we aim to significantly improve the spatial resolution and simultaneously push the limiting magnitude one magnitude deeper than in the previous WFPC2 narrow band observations of M87 (F94). We will improve the spatial resolution by increasing the signal-to-noise ratio (SNR) by a factor of more than 2, and by progressively off-setting the HST $1/2$ PC pixel (0.023~arcsec) in x and in y. HST can make accurate offsets which are this small. We will group our proposed 12 F658N exposures into four groups of 3 exposures. Each group of 3 will be taken at a position on a 2 x 2 grid where the grid points are separated by $1/2$ PC pixel in x and in y. Because the WFPC2 CCDs have significant charge diffusion from the pixels, the half-stepping will improve the resolution to around 60 mas FWHM. The effectively fully sampled, high SNR PC images will have significantly improved resolution compared to the partially sampled, non half-stepped, lower SNR PC images already obtained. Finally, based on discussions with Leon Lucy's group, we plan to use software for the image reconstruction currently being developed at the ST-ECF. The M87 exposures discussed in F94 were 2 x 400s through the F547M filter and 1300s plus 1400s through the F658N \\HaNii\\ filter. The counts/pixel in the on-band minus off-band image vary from 20 near the edge of the disk to $\\sim 300$ near the position of the central unresolved nonthermal source (which peaks at 900 counts/pixel). Because of the shot noise from the underlying stellar continuum in the on-band and off-band images, the SNR varies from a few per pixel to $\\sim 20$ per pixel in the brightest part of the disk. To maximize the SNR and limiting magnitude in 6 orbits, we plan to devote the entire observing time to narrow-band imaging with the filter that includes $H\\alpha+[NII]$, F658N. Continuum subtraction will be carried out by extracting and using archival data to be obtained by various groups during Cycle 4. For example, Macchetto, Sparks and Biretta in GO proposal 5477 will be obtaining deep F555W and F814W continuum images with the PC. These data will serve two purposes: firstly, following the now standard procedure, a model galaxy whose isophotes are pure ellipses will be constructed at both wavelengths, (e.g. Sparks et~al. 1985 and SFK), and secondly, in conjunction with the model, images of the distribution of dust absorption optical depth will be made at both wavelengths. For the latter, the image data are divided by the model to get an image of the effective optical depth, and as a check, lower SNR ``color'' images are used in which the F555W image is divided by the F814W image directly. The $2 \\times 400$ sec intermediate band F547M images obtained by Ford et~al. (1994) will be used to assess the relevance of emission line contamination in the broad-band images, which is generally small. With this information, accurate continuum subtraction is straightforward for the F658N observations. In the event that dust absorption is not significant, we will use the model galaxies to maximize SNR, since there is no shot-noise component to the model. On larger scales SFK found typical optical depths only of order 0.02 (i.e. only 2\\%\\ of the emission is extinguished), so this situation is quite likely. If we find that dust absorption features are significant in the higher resolution images, we can construct a simple correction to the model, since we will have images of the dust optical depth at two separate wavelengths that bracket the F658N observations. Because of the large overhead penalty for short off-band exposures, omitting the off-band exposures allows us to increase the total F658N on-band exposure time in 6 orbits from 150 minutes to 240 minutes. The latter is 5.3 times longer than the 45 minute on-band exposure in F94, and will give at least one magnitude fainter limiting magnitude in the bright center of M87 where we are shot noise limited. The proposed exposures, which require six orbits, are: first orbit; F658N (17.5 min) F658N (17.5 min), and, in orbits two through six; F658N (20.5 min) F658N (20.5 min). Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6296( 3) - 02/01/96 17:27 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6296( 3) - 02/01/96 17:27 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4486 GALAXY RA=12H 30M 49.4286S +/- 0.3", 2000 V=1200 V = 16.7 DEC=+12D 23' 27.985" +/- 0.3", E(B-V) = 0.01 PLATE-ID=00IY 6296( 3) - 02/01/96 17:27 - [ 5] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1100S POS TARG 0.0,0.0 Comments: POS-1 for dithering ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1000S SAME POS AS 1 Comments: POS-1 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1100S SAME POS AS 1 Comments: POS-1 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S POS TARG 0.250586,0.0 Comments: POS-2: move 5.5,0 pixels in X,Y from POS-1 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S SAME POS AS 4 Comments: POS-2 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S SAME POS AS 4 Comments: POS-2 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S POS TARG 0.250586,0.250476 Comments: POS-3: move 5.5,5.5 pixels in X,Y from POS-1 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S SAME POS AS 7 Comments: POS-3 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1100S SAME POS AS 7 Comments: POS-3 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S POS TARG 0.0,0.250476 Comments: POS-4: move 0,5.5 pixels in X,Y from POS-1 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S SAME POS AS 10 Comments: POS-4 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC4486 WFPC2 IMAGE PC1 F658N CR-SPLIT=NO 1 1200S SAME POS AS 10 Comments: POS-4 ------------------------------------------------------------------------------------------------------------------------------------ 6296( 3) - 02/01/96 17:27 - [ 6] Summary Form for Proposal 6296 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GTO/FOS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 0.0,0.0 SAME POS AS 1 POS TARG 0.250586,0.0 SAME POS AS 4 POS TARG 0.250586,0.250476 SAME POS AS 7 POS TARG 0.0,0.250476 SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F658N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4486 ------------------------------------------------------------------------------------------------------------------------------------