Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 3507c Report Date: 09-May-96:18:39 Version: ********** Check-in Date: ********** 1.Proposal Title: ULTRAVIOLET SPECTROSCOPY AND HIGH-RESOLUTION IMAGING OF NGC 4395, THE LEAST LUMINOUS AND NEAREST KNOWN SEYFERT 1 NUCLEUS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID QUASARS & AGN GO Sub Category SEYFERTS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Alexei V Filippenko UNIVERSITY OF CALIFORNIA AT USA 510-642-1813 ------------------------------------------------------------------------------------ 7. Abstract We have discovered the least luminous known Seyfert 1 nucleus, in the very nearby (d = 2.6 Mpc), Sd III-IV galaxy NGC 4395. Seyfert 1 nuclei have never before been seen in galaxies of such late Hubble type, and so nearby. The luminosity of the broad H- alpha emission line is a factor of 10 lower than in M81, the previous champion. The blue continuum magnitude of the nucleus is -10, no brighter than a cluster of luminous stars; thus, it is remotely possible that the object itself can be explained by purely stellar phenomena, rather than by accretion onto a black hole. In order to test this hypothesis, and to further explore the unique properties of the active nucleus in NGC 4395, we propose to obtain UV spectra as part of an ongoing multi-wavelength study of this object. Detailed comparisons will be made with the spectra of typical luminous Seyfert 1 nuclei. A search will be made for absorption features produced by hot stars. We will determine whether the continuum has a "big blue bump" (like other type 1 Seyferts), and we will examine various emission-line intensity ratios to see whether a nonstellar photoionizing continuum is required. Since the active nucleus is in a spatially well-resolved galaxy, the spectra will not be contaminated by starlight from a galactic bulge. A direct image of NGC 4395, obtained with the PC, will show whether the active nucleus is a true point source less than 1 pc in size, rather than an extended source (such as a collection of very hot stars). ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 7.01 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 3507c PI: Alexei V Filippenko Proposal Title: ULTRAVIOLET SPECTROSCOPY AND HIGH-RESOLUTION IMAGING OF NGC 4395, THE LEAST LUMINOUS AND NEAREST KNOWN SEYFERT 1 NUCLEUS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Alexei V Filippenko UNIVERSITY OF CALIFORNIA AT USA BERKELEY Wallace W Sargent CALIFORNIA INSTITUTE OF USA TECHNOLOGY ------------------------------------------------------------------------------------ 3. Description of proposed observations. SPECTROSCOPY. To detect faint features, and to study the profiles of emission lines and absorption lines, we require spectra having good S/N ratio and moderately high resolution over most of the UV wavelength range. We will connect the red end of the UV spectrum with our optical/IR spectrum, obtained at ground- based observatories. The resulting spectrum covering a broad range will allow us to measure accurate emission-line intensity ratios and continuum colors. 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 4.3" X 4.3" aperture. This yields the best throughput, and the resulting resolution will be adequate for our purposes. We can use such a large aperture without worrying about contamination from circumnuclear stars because the bulge of NGC 4395 is almost nonexistent. IMAGING. To see if the nucleus of NGC 4395 is spatially extended, we will obtain images with the PC. We will take one exposure in each of the F336W, F547M, and F785LP filters. Emission lines are weak or absent in all cases, and the different exposures can be used to eliminate cosmic rays. We agree with the assessment of the TAC that a narrow-band [O III] image would also be useful, and we now plan to obtain one. To eliminate cosmic rays and test for image stability, a second narrow-band image will be obtained, but at H-beta. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The nucleus of NGC 4395 is very faint at UV wavelengths. If a power law of index -1.5 is used to extrapolate the observed optical flux to the UV range, we find that the nuclear continuum flux density at 2000 A is about 0.1 mJy. This may be compared with 0.2 mJy for the faintest Seyfert nuclei successfully observed by IUE. (The resulting IUE spectra had low S/N ratios.) Nevertheless, in 1989 we applied for, and received, some time with IUE, in order to get a rough indication of the UV properties of NGC 4395. Unfortunately, it turned out that there were no suitable guide stars in the restricted field available to the IUE FES. However, the IUE data probably would not have given us much information; the review panel concluded that "[our proposed study] looks like one of those excellent projects which should be reserved for ST." The necessity of HST is also obvious for imaging NGC 4395. We are trying to see whether the nucleus is spatially resolved. The best ground-based image we have been able to obtain has stellar seeing disks of 1.0", or about 13 pc at the distance of NGC 4395. Even with 0.5" seeing, rarely available from ground-based observatories, the upper limit to the volume of an unresolved nucleus is at least 100 times larger than is currently achievable with HST. Constraints on the nature of the activity in the nucleus of NGC 4395 become progressively more severe as we increase the spatial resolution. Page 3 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The data will be reduced with standard programs (IRAF, etc.). Special care will be taken to use the best image reconstruction techniques when analyzing the PC images; we want to achieve the highest possible resolution. When our HST observing dates become known, we will request nearly simultaneous time at Lick and Palomar Observatories to obtain optical spectra and images, IR images, and IR spectra. These data will be combined with the UV spectra to construct an overall continuum spanning a large wavelength range. We will also schedule VLA observations on, or near, the appropriate dates. A complete analysis of the data will subsequently be done. Measurement and analysis of the calibrated one- dimensional spectra will be done with an extensive program written by the PI for his studies of optical spectra. All emission lines will be measured (wavelengths, fluxes, equivalent widths, velocity widths), and the continuum shape will be determined. A search will be made for absorption lines, which might reveal the presence of very hot stars. The continuum flux will be extrapolated beyond the Lyman limit, to see whether it can indeed account for the emission lines. A photoionization code (CLOUDY) will then be used to analyze the overall emission- line spectrum using the observed continuum, together with the derived density and temperature, as input parameters. The possibility of stellar versus nonstellar photoionization will be examined. Comparisons with shock models will also be made. ------------------------------------------------------------------------------------ 9. Description of previous HST work. Alexei V. Filippenko, PI: GO 2590, "Deep Imaging of the Site of SN 1961V, a Possible Extragalactic Eta Carinae Analogue". Not related to this project. Wallace W. Sargent, Co-I: GO 2078, "A Search for Primordial Gas: is I Zw 18 a Young Galaxy?" (PI: James Lequeux). Not related to this project. Wallace W. Sargent, Co-I: GO 2424, "Quasar Absorption Line Survey" (PI: John N. Bahcall). Not related to this project. Some HST data have been obtained for the above programs; analysis is in progress. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Both Caltech and U. C. Berkeley have extensive computing facilities (VMS and UNIX) in their Astronomy Departments. Image-processing workstations, graphics terminals, laser printers, large disks, and tape drives are all available. Many computer programs exist for analysis of data. Both institutions also have many extremely capable graduate students, one of whom will participate in various aspects of this project. Ground-based complementary observations may readily be obtained at both Palomar and Lick Observatories. The usual secretarial and technical support is available at Caltech and Berkeley. ------------------------------------------------------------------------------------ 11. Address Information Name: ALEXEI V FILIPPENKO Category: PI Institution: UNIVERSITY OF CALIFORNIA AT BERKE 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 = 3507c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 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 NGC4395 E,301,312,910 RA = 12H 23M 19.84S +/- 1950.0 V = +317 BKG 1 V = 17.0 +/- 0.5 0.1S, 2 B-V = 0.36 +/- 0.2 DEC = +33D 49' 24.3" +/- 1" 3 F-LINE(5007) = 6 +/- 1 E-16 4 W-LINE(5007) = 310 +/- 50 5 F-LINE(4861) = 6 +/- 1 E-16 6 W-LINE(4861) = 60 +/- 10 Comments: MAGNITUDES AND FLUXES REFER TO NUCLEUS ONLY. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3507c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 NGC4395 FOS/BL ACQ/ 4.3 MIRROR 1 69S 1 2 ONBOARD ACQ FOR 2 BINARY CYCLE 2 / 1-10 GROUP 1-2 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4395 FOS/BL ACCUM 4.3 G130H 1380 1 260M 14 1 2 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULATATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4395 FOS/RD ACQ/ 4.3 MIRROR 1 26S 1 1 ONBOARD ACQ FOR 4- BINARY 5 GROUP 3-5 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4395 FOS/RD ACCUM 4.3 G190H 1950 1 97M 16 1 1 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULATATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4395 FOS/RD ACCUM 4.3 G270H 2760 1 32.2M 20 1 1 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULATATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC4395 PC IMAGE PC6 F547M 5470 CR-SPLIT=NO 1 2M 100 1 3 GROUP 6-10 NO GAP PRE-FLASH=YES Comments: WANT DATA FROM ALL 4 CCDS ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC4395 PC IMAGE PC6 F336W 3350 CR-SPLIT=NO 1 400S 50 1 3 PRE-FLASH=YES 2 Comments: WANT DATA FROM ALL 4 CCDS ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC4395 PC IMAGE PC6 F785LP 8960 CR-SPLIT=NO 1 1M 60 1 3 PRE-FLASH=YES 2 Comments: WANT DATA FROM ALL 4 CCDS ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC4395 PC IMAGE PC6 F502N 5016 CR-SPLIT=NO 1 5M 50 3 3 PRE-FLASH=YES 4 Comments: WANT DATA FROM ALL 4 CCDS ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4395 PC IMAGE PC6 F487N 4867 CR-SPLIT=NO 1 15M 50 5 3 PRE-FLASH=YES 6 Comments: WANT DATA FROM ALL 4 CCDS ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 3507c [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL FOS/RD PC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACCUM IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO PRE-FLASH=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 7.01 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASARS & AGN ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SEYFERTS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2; CYCLE 2 / 1-10; GROUP 1-2 NO GAP ONBOARD ACQ FOR 4-5; GROUP 3-5 NO GAP GROUP 6-10 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G130H G190H G270H F547M F336W F785LP F502N F487N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4395 ------------------------------------------------------------------------------------------------------------------------------------