6888( 4) - 03/13/96 09:00 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6888 Version: 4 Check-in Date: 13-Mar-1996 08:56:56 1.Proposal Title: Scattered Emission from the Active Nucleus Buried in NGC 4258 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Gary D. Schmidt Steward Observatory, University of Arizona CoI: Paul S. Smith Steward Observatory, University of Arizona N CoI: H.S. Stockman Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract The recent detection of H_2O masers in an edge-on disk orbiting a massive black hole in the nearby spiral galaxy NGC 4258 (Miyoshi et al. 1995) represents a fundamental step forward in our understanding of the structure of active galactic nuclei. Ground -based imaging- and spectro- polarimetry obtained by us during the past year have extended this result with the discovery of a featureless nuclear continuum and 1000 km s^-1-wide emission lines, polarized presumably by scattering in a toroidal geometry. The polarization position angle is identical to the elongation of the maser disk on the sky, establishing a direct link between the geometry of an obscuring torus in an active galaxy and material orbiting a compact object of high mass. We propose to obtain small-aperture UV spectroscopy and spectropolarimetry of the nucleus of NGC 4258 to isolate this scattered AGN spectrum from the surrounding starlight. This will be used to measure the nonthermal spectral shape and luminosity, and search for scattered UV emission lines. In addition, ultraviolet images obtained with WFPC2 will be compared with existing Cycle 4 optical continuum and emission- line images to search for the ionizing cones which are expected to be produced by radiation escaping along the axis of the torus. Unfortunately, high- resolution imaging polarimetry must await the installation of the Advanced Camera in 1999. ------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 2] Observations Description ------------------------ Because of the likelihood that the scattering region in NGC 4258 may be resolved, we have chosen the "s0.5\\ aperture of FOS despite the increase in admitted starlight over the "s0.3\\ option. The only UV spectrum available (Kinney et al. 1993) measures a total flux of 1.5times10^-14 ergs cm^-2 s^-1 Angstrom^-1 at 2500 Angstrom\\ in a 10"\\by20"\\ aperture, dominated by starlight. Our optical CCD images suggest that 3 --5\\ would be detected in a "s0.5\\ aperture. From extrapolation of our optical spectropolarimetry on p. 3, the polarized component would be expected to account for ~1/4 of this total -- the remainder being starlight. If we require a polarimetric uncertainty Sigma_P~1\\ polarized emission lines above such a continuum, the FOS/polarimeter sensitivity figures in the Instrument Handbook indicate a total observing time with the G270H,POL0-B grating of ~10 hrs. The spectropolarimetry using FOS/BL and G270H,POL0-B requires 16 orbits. Two of these orbits will have to be devoted to target acquisition (4-stage ACQ/PEAKs) since a maximum of 8 orbits can scheduled without interference from the South Atlantic Anomaly (SAA). In order to obtain similar polarimetric accuracy using FOS/BL and G190H, nearly 30 hrs would be needed. Therefore, only spectroscopy using this grating, 0arcs5 aperture, and FOS/RD will be obtained. However, this observation will yield the first UV spectrum that isolates the nucleus and allows for the measurement of important emission lines expected from the AGN in this spectral region (such as HeII Lambda1640 and CIII Lambda1909). A separate target acquisition (same as above) will be necessary for the G190H observation because of the constraints imposed by the SAA. The RED detector offers a factor of 2--3 increased sensitivity over FOS/BL for most of the spectrum sampled by the G190H grating, and we estimate that 3 orbits in this configuration will yield a SNR of sim20 diode^-1. Our WFPC2 observation will require 1 orbit and consist of two 1200 s Planetary Camera exposures using the F300W filter. >From our estimate that ~4\\ flux will be admitted by the 0arcs5 aperture of FOS, there will be a flux of roughly 2.4 * 10^-15 ergs cm^-2 s^-1 AA^-1 within the inner arcsec^2. This translates into sim650 electrons pixel^-1 in a 1200 s exposure assuming that the flux is uniformly distributed within this region. The UV background is negligible (< 1 e^- pix^-1), read noise = 5.2 e^- pix^-1, and dark count = sim6 e^- pix^-1 in a 1200 s exposure. Real Time Justification ----------------------- None. Ground-based polarimetry of NGC 4258 spanning a period of 6 months have shown no indication of variability. Thus, coordinated observations are not expected to be necessary. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4258 GALAXY,Seyfert RA=12H 18M 57.51S +/- 1.0", 2000 V=+472 F(5500)=1.4+/-0.1e-14 DEC=47D 18' 14.50" +/- 1.0", F(4400)=1.4+/-0.1e-14 PLATE-ID=024D Comments: Nucleus of a giant SABbc galaxy. 6888( 4) - 03/13/96 09:00 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4258 WFPC2 IMAGE PC1 F300W 2943 1 1800S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC4258 WFPC2 IMAGE PC1 F300W 2943 CR-SPLIT=NO 1 600S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 6] 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4258 FOS/BL ACQ/PEA 4.3 MIRROR SCAN-STEP- 1 5.0S ONBOARD ACQuisition FOR 21 K Y=1.23,SEARCH- SIZE-X=1,SEARCH -SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC4258 FOS/BL ACQ/PEA 1.0 MIRROR SCAN-STEP- 1 5.5S ONBOARD ACQuisition FOR 22 K X=0.61,SCAN- STEP- Y=0.61,SEARCH- SIZE-X=6,SEARCH Comments: -SIZE-Y=2 ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC4258 FOS/BL ACQ/PEA 0.5 MIRROR SCAN-STEP- 1 6.0S ONBOARD ACQuisition FOR 23 K X=0.29,SCAN- STEP- Y=0.29,SEARCH- SIZE-X=3,SEARCH Comments: -SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC4258 FOS/BL ACQ/PEA 0.3 MIRROR SCAN-STEP- 1 6.3S ONBOARD ACQuisition FOR 30-90 K X=0.11,SCAN- STEP- Y=0.11,SEARCH- SIZE-X=4,SEARCH Comments: -SIZE-Y=4 ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4258 FOS/BL ACCUM 0.5 G270H 2750 POLSCAN=4B 1 2300S NO SPLIT Comments: POLSCAN AT POL0-B, POL22.5-B, POL45-B, AND POL67.5-B ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC4258 FOS/BL ACCUM 0.5 G270H,POL2750 POLSCAN=4B 1 2300S NO SPLIT 90-B Comments: POLSCAN AT POL90-B, POL112.5-B, POL135-B, AND POL157.5-B ------------------------------------------------------------------------------------------------------------------------------------ 50 NGC4258 FOS/BL ACCUM 0.5 G270H,POL2750 POLSCAN=4B 1 2300S NO SPLIT 180-B Comments: POLSCAN AT POL180-B, POL202.5-B, POL225-B, AND POL247.5-B ------------------------------------------------------------------------------------------------------------------------------------ 60 NGC4258 FOS/BL ACCUM 0.5 G270H,POL2750 POLSCAN=4B 1 2300S NO SPLIT 270-B Comments: POLSCAN AT POL270-B, POL292.5-B, POL315-B, AND POL337.5-B ------------------------------------------------------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 70 NGC4258 FOS/BL ACCUM 0.5 G270H 2750 POLSCAN=4B 1 2300S NO SPLIT Comments: POLSCAN AT POL0-B, POL22.5-B, POL45-B, AND POL67.5-B ------------------------------------------------------------------------------------------------------------------------------------ 80 NGC4258 FOS/BL ACCUM 0.5 G270H,POL2750 POLSCAN=4B 1 2300S NO SPLIT 90-B Comments: POLSCAN AT POL90-B, POL112.5-B, POL135-B, AND POL157.5-B ------------------------------------------------------------------------------------------------------------------------------------ 90 NGC4258 FOS/BL ACCUM 0.5 G270H,POL2750 POLSCAN=8B 1 2000S NO SPLIT 180-B Comments: POLSCAN AT POL180-B, POL202.5-B, POL225-B, POL247.5-B, POL270-B, POL292.5-B, POL315-B, AND POL337.5-B ------------------------------------------------------------------------------------------------------------------------------------ 6888( 4) - 03/13/96 09:00 - [ 8] Summary Form for Proposal 6888 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO SEARCH-SIZE-Y=3 SEARCH-SIZE-Y=2 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=4 POLSCAN=4B POLSCAN=8B ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements NO SPLIT ONBOARD ACQuisition FOR 21 ONBOARD ACQuisition FOR 22 ONBOARD ACQuisition FOR 23 ONBOARD ACQuisition FOR 30-90 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F300W MIRROR G270H G270H,POL90-B G270H,POL180-B G270H,POL270-B ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4258 ------------------------------------------------------------------------------------------------------------------------------------