Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4340c Report Date: 09-May-96:19:32 Version: ********** Check-in Date: ********** 1.Proposal Title: THE ORIGIN OF THE BLUE FEATURELESS CONTINUUM IN SEYFERT 2 NUCLEI: CYCLE3MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID QUASARS & AGN GO Sub Category SEYFERTS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Prof. Alexei V. Filippenko UC-BERKELEY USA ------------------------------------------------------------------------------------ 7. Abstract Recent spectropolarimetric studies of Seyfert 2 nuclei have shown that NGC 4922B has very low polarization, despite having a rather prominent blue featureless continuum (BFC). Broad permitted lines also appear to be absent, both in direct and reflected light. These observed characteristics conflict with the predictions of simple Seyfert unified models, which assume that the viewing angle is the only parameter that determines whether the object appears as a Seyfert 1 or a Seyfert 2 nucleus. If all Seyfert 2s behave like the prototypical NGC 1068, it is expected that the BFC should be polarized at least a few percent and that broad lines be present in polarized light. A possible explanation for NGC 4922B is that the classical broad- line region does not exist in this object. We should be able to test this by examining the line profiles of Ly-alpha, C IV, and Mg II. If this object does indeed harbor a hidden Seyfert 1 nucleus, we should also be able to detect broad Fe II emission in the UV. Another possibility is that the BFC originates from a population of hot stars. Much evidence has recently been accumulated that hot stars may play a significant role in Seyfert 2 nuclei. If so, then FOS spectra should reveal stellar absorption features (e.g., C IV, Si IV), and FOC images should appear extended. The shape of the UV continuum will also be useful in discriminating between a stellar or an AGN ionizing source. We believe that this study has important implications for the Seyfert unified model. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.45 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS FOC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4340c PI: Prof. Alexei V. Filippenko Proposal Title: THE ORIGIN OF THE BLUE FEATURELESS CONTINUUM IN SEYFERT 2 NUCLEI: CYCLE3MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Alexei V. Filippenko UC-BERKELEY USA Luis C. Ho UC-BERKELEY USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We will observe the Seyfert 2 nucleus of NGC 4922B. Our main goals for the spectroscopy are to detect faint broad wings in the profiles of permitted emission lines (C IV 1549, Mg II 2800, UV Fe II blends), and to determine whether the blue continuum in the nucleus is truly featureless. Thus, we require spectra having good S/N ratio and modest resolution over the entire accessible UV wavelength range. We will connect the red end of the UV spectrum (around 3150 A) with our optical spectra, obtained at ground-based observatories. Three HST grating settings are needed, as follows: (1) FOS, G130H grating, 1150-1608 A, 1.0 A/diode, blue digicon. (2) FOS, G190H grating, 1573-2323 A, 1.5 A/diode, red digicon. (3) FOS, G270H grating, 2227-3306 A, 2.1 A/diode, red digicon. The FOS spectra will be obtained through the 1.0" circular aperture, since the 4.3" square aperture gives rise to broad wings in narrow lines. Note that NGC 7672 is deleted from the program, due to insufficient HST time. The goal of the direct imaging is to examine the morphology of the UV continuous emission. Imaging in the UV is best accomplished with the FOC. The composite IUE spectrum of NGC 1068 published by Snijders et al. (1986), together with the FOC/96 filter transmission curves shown in Figure 12 of the FOC Handbook, suggest that the optimal filter is F210M, but there could be a significant red leak. This leak will be eliminated with the F210M + F220W combination. The UV morphology will be compared with the red morphology (F600M). We will use the FOC/96 with a 512 X 512 pixel format, a 25 X 25 micron square pixel size (0.022" X 0.022" pixels), and a 11" X 11" FOV. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. A substantial fraction of the light in Seyfert 2 nuclei comes from old stars of the host galaxy (Koski 1978). Thus, the near-UV to optical spectral region is heavily contaminated by starlight. The two main objectives of our proposed study of NGC 4922B are (1) to search for broad permitted lines in the emission-line spectrum, and (2) to try to identify a hot star population by searching for stellar absorption lines, studying the continuum shape, and looking for extended emission in two-dimensional images. While searching for broad H-alpha in low- luminosity AGNs by subtraction of "template" galaxies is sometimes feasible (Filippenko and Sargent 1985), it becomes increasingly difficult for objects whose active nuclei are very faint relative to the underlying starlight. Since the contamination from old stars is much smaller in the UV than in the optical, we expect the weak, broad permitted lines, if they are present, to be much more easily discernible. For the same reason, the UV is a more suitable region to study the shape of the ionizing continuum. Furthermore, the UV Fe II multiplets are expected to be 10 to 15 times stronger than their optical counterparts. Probably the most important reason to look in the UV, however, is that this region contains distinctive absorption features of hot stars (e.g., C IV 1549, Si IV 1400), unlike the optical or near-infrared region. The necessity for HST's imaging capabilities is also obvious. We want to see whether the blue featureless continuum is spatially resolved on scales smaller than 1", and we would like to determine the morphology of any resolved continuous emission; comparisons with the red image will be made. At optical wavelengths, the continuum can be represented roughly as a power law: f_nu proportional to nu**-1.5). Extrapolating the observed continuum at 5500 A (f_nu = 1.5 mJy) down to UV wavelengths, we predict that at 1400 A, 1700 A, and 2300 A the flux density is 0.19 mJy, 0.26 mJy, and 0.41 mJy, respectively. However, E(B-V) = 0.026 mag, so the UV extinction is about 0.2 mag; the revised flux densities are 0.16 mJy, 0.22 mJy, and 0.34 mJy, respectively. These values are used in the following calculations. FOS, G130H grating, blue digicon: At 1400 A, the efficiency is 0.007. The throughput of the 1" circular aperture is 0.27 for point sources, and we have 1.0 A/diode. Using equation (5) of Table 1.2.1 in the FOS Instrument Handbook, we find a count rate of 0.015 per second per diode. Zodiacal light, airglow, diffuse Galactic light, and the dark current are all significantly less than this. For S/N = 8, we require an exposure time of about 75 minutes. Similarly, for the G190H grating + red digicon, at 1700 A the efficiency is 0.02 and the throughput is 0.30; there are 1.47 A/diode. The derived count rate is 0.078 per second per diode in the continuum. For S/N = 13, the exposure time is about 36 minutes. Finally, for the G270H grating + red digicon, at 2300 A the continuum count rate is 0.44 per second per diode, so the exposure time is 18 minutes for S/N = 22. For the FOC and the F210M + F220W filter combination, 750 sec are required for S/N = 8 per pixel. The F600M filter requires 270 sec. This will allow us to carefully examine the UV continuum morphology, and to make comparisons with the red continuum morphology. Page 4 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Originally I had assumed that ACQ/BINARY would be used to acquire the target. However, during a visit to STScI I was told this would be quite risky for a galaxy, even though it has a star-like nucleus (it is an active galaxy). The reason is that the background is uneven, and also the apparent brightness depends on how much of the "fuzz" is integrated. Moreover, the nucleus itself might even be resolved on the 0.3" scale. So, I reluctantly decided to play it safe and use ACQ/PEAK instead. Since the total spacecraft time does not exceed 6 hours, the peak-up can be done for only the red (or blue) side (i.e., side-switching IS allowed). I have put relatively long integration times for the dwells, in order to be certain of getting enough counts for successful acquisition. The first spatial scan will be 3 X 1 with the 4.3" aperture; each dwell should be 1 s on the red side (or 7 s on the blue side). The second spatial scan will be 2 X 6 with the 1" circular aperture; each dwell should be 2 s on the red side (or 11 s on the blue side). The third peak-up will be 3 X 3 with the 0.5" circular aperture; each dwell should be 3 s on the red side (or 18 s on the blue side). The science observations will be conducted with the 1.0" circular aperture. If it turns out that the extra time for peak-up acquisitions is NOT charged to the GO, please ADD 23M (total = 98M) to the FOS/BL G130H science integration (exposure line 6). This will make the total time equal to the allocated spacecraft time, if ACQ/BINARY had been used. Thank you. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The calibrated one-dimensional FOS spectra will be measured and analyzed with an extensive program written by the PI. All absorption and emission lines will be measured, and the continuum spectral energy distribution will be quantified. The profiles of the emission lines will be carefully examined in order to search for broad wings (as in a Seyfert 1 nucleus). We will also try to detect the presence of broad Fe II blends in the range 1900-3000 A. If stellar absorption lines are visible, the stellar population responsible for the observed continuum will be estimated using spectral synthesis techniques. The method will follow, with a few modifications, that described by Fanelli, O'Connell, & Thuan (1988, ApJ, 334, 665). Initial input parameters for the dominant luminous constituents will be based on comparisons of our spectrum with reference spectra of stars in Wu et al. (1983, The IUE Ultraviolet Spectral Atlas) and in the library of far-UV spectra developed by Fanelli, O'Connell, & Thuan (1987, ApJ, 321, 768). The FOC images will be reduced and analyzed with standard image processing software. It should be possible to run image deconvolution algorithms in order to improve the effective spatial resolution of the data (e.g., King et al. 1991, AJ, 102, 1553; Macchetto et al. 1991, ApJL, 369, L55). Some algorithms achieve superior spatial resolution at the expense of less reliable photometry, whereas others preserve the photometric integrity of the data while giving only moderate resolution. We will use a variety of techniques to obtain the maximum amount of information from the data. The morphology of any extended component to the continuous emission will be determined. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. When our HST observing dates become known, we will request nearly simultaneous time at Lick Observatory to obtain optical spectra and images, IR images, and (if possible) IR spectra. These data will be combined with the UV spectra to construct an overall continuum spanning a large wavelength range. A complete analysis of the data will subsequently be done. No funds are being requested here to support the ground-based observations. Page 5 ------------------------------------------------------------------------------------ 9. Description of previous HST work. A. V. Filippenko, PI: GO 2590, "Deep Imaging of the Site of SN 1961V, a Possible Extragalactic Eta Carinae Analogue." Not related to this project. A. V. Filippenko, Co-I: GO 3484, "Probing the Nuclear Regions of the Seyfert Galaxy NGC 5548." (PI: B. M. Peterson). Not related to this project. A. V. Filippenko, PI: GO 3507, "UV Spectroscopy and High-Resolution Imaging of NGC 4395, the Least Luminous and Nearest Known Seyfert 1 Nucleus." Not related to this project, but shows that the data quality for NGC 4922B should be adequate. (NGC 4395 is somewhat fainter than NGC 4922B in the UV.) A. V. Filippenko, Co-I: GO 3519, "UV Imaging of Nearby Galaxies." (PI: D. Maoz.) Not related to this project. A. V. Filippenko, Co-I: GO 3810, "The Stellar Content of Wolf-Rayet Galaxies." (PI: P. Conti.) Not related to this project. In addition, Filippenko was involved in one of the discoveries made by the QSO Snapshot Survey (PI: J. N. Bahcall.) GO 2590: Data were received a few months ago, and are currently being analyzed. An object has been detected at the position of SN 1961V; color information is being used to determine whether this is the supernova remnant, the surviving "progenitor," or an unrelated object. GO 3507: We recently received the data. Preliminary analysis reveals strong emission lines similar to those of luminous Seyfert 1 nuclei (e.g., C IV 1549, C III] 1909, Mg II 2800) superposed on a weak continuum. The nucleus seems unresolved on a scale of 1 pc (0.1"). Thus, NGC 4395 appears to contain a bona fide Seyfert 1 nucleus, but with an absolute blue magnitude of only -10 --- comparable to very luminous stars Other proposals: Data not obtained yet. "A Gravitational Lens Candidate Discovered with the Hubble Space Telescope." D. Maoz, J. N. Bahcall, D. P. Schneider, R. Doxsey, N. A. Bahcall, A. V. Filippenko, W. M. Goss, O. Lahav, and B. Yanny; Astrophysical Journal (Letters), 386, L1, 1992. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The U. C. Berkeley Astronomy Department has extensive computing facilities (VMS and UNIX). Image-processing workstations, graphics terminals, laser printers, large disks, and tape drives are all available. Numerous computer programs exist for analysis of data. Co-I Luis Ho, an outstanding graduate student whose doctoral thesis is on AGNs, will do a substantial fraction of the analysis. Additional ground-based complementary observations may readily be obtained at Lick Observatory; we hope to also use the Keck telescope this year. The usual secretarial and technical support is available at U.C. Berkeley. ------------------------------------------------------------------------------------ 11. Address Information Name: ALEXEI V. FILIPPENKO Category: PI Institution: UC-Berkeley Address: DEPARTMENT OF ASTRONOMY 601 CAMPBELL HALL UNIVERSITY OF CALIFORNIA City: BERKELEY State: CA Zip Code: 94720 Country: USA Telephone: 510-642-1813 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4340c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4922B E,312,320,910 RA = 12H 59M 01.32S +/- 1950.0 Z = 1 V = 16.0 +/- 0.4 0.06S, 0.024 2 B-V = 0.5 +/- 0.3 DEC = +29D 34' 55.7" +/- 3 F-CONT(1400) = 2.4 +/- 0.7 E-15 0.6" 4 F-CONT(1700) = 2.3 +/- 0.7 E-15 5 F-CONT(2300) = 1.9 +/- 0.6 E-15 Comments: MAGNITUDES AND FLUXES REFER TO NUCLEUS ONLY. BRIGHT NUCLEUS SUPERPOSED ON FAINTER GALAXY BACKGROUND. PI HAS COMPARED THESE COORDS TO GASP, AND PREFERS THESE. - 2/11/93 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4340c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4922B FOS/RD ACQ/ 4.3 MIRROR 1 1S 1 1 ONBOARD ACQ FOR 2 PEAK 2 SPATIAL SCAN CYCLE 3 / 1-8 GROUP 1-6 NO GAP Comments: BLUE SIDE ACQ/PEAK: SP- ELEMENT=MIRROR, EXP = 7S IF BLUE SIDE NEEDED. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4922B FOS/RD ACQ/ 1.0 MIRROR 1 2S 1 1 ONBOARD ACQ FOR 3 PEAK 2 SPATIAL SCAN Comments: BLUE SIDE ACQ/PEAK: SP- ELEMENT=MIRROR, EXP = 11S IF BLUE SIDE NEEDED. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4922B FOS/RD ACQ/ 0.5 MIRROR SCAN-STEP=0.35 1 3S 1 1 ONBOARD ACQ FOR 4- PEAK SEARCH-SIZE=3 2 6 Comments: BLUE SIDE ACQ/PEAK: SP- ELEMENT=MIRROR, EXP = 18S IF BLUE SIDE NEEDED. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4922B FOS/RD ACCUM 1.0 G270H 2760 1 18M 22 5 1 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4922B FOS/RD ACCUM 1.0 G190H 1950 1 36M 13 4 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC4922B FOS/BL ACCUM 1.0 G130H 1380 1 75M 8 3 3 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC4922B FOC/96 IMAGE 512X512 F210M, 2150 1 750S 8 4 4 GROUP 7-8 NO GAP F220W 5 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC4922B FOC/96 IMAGE 512X512 F600M 5800 1 270S 8 1 5 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ Scan Paramters Form Proposal ID: 4340c [ 8] ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 1 Exposure Logsheet lines: 1 FGS Scan: DWELL Dwell Only: dwell points/line: 3 Seconds per dwell: 1.00 Scan width (arc-secs): 0.0000 Scan length (arc-secs): 2.8000 Angle between sides (degrees) 90.00 Number of lines: 1 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 0.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.4000 Width Offset (arc-sec): 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 2 Exposure Logsheet lines: 2 FGS Scan: DWELL Dwell Only: dwell points/line: 6 Seconds per dwell: 1.00 Scan width (arc-secs): 0.7000 Scan length (arc-secs): 3.5000 Angle between sides (degrees) 90.00 Number of lines: 2 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 90.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.7500 Width Offset (arc-sec): 0.3500 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4340c [ 9] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD FOS/BL FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP=0.35 SEARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.45 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASARS & AGN ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SEYFERTS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2; SPATIAL SCAN; CYCLE 3 / 1-8; GROUP 1-6 NO GAP; ONBOARD ACQ FOR 3; ONBOARD ACQ FOR 4-6; GROUP 7-8 NO GAP; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G270H G190H G130H F210M,F220W F600M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4922B 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