Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4434c Report Date: 09-May-96:19:36 Version: ********** Check-in Date: ********** 1.Proposal Title: USING MRK 205 TO PROBE THE IONIZED ISM IN NGC 4319 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID INTERSTELLAR MEDIUM GO Sub Category ABSORPTION LINES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone David V. Bowen STSCI USA ------------------------------------------------------------------------------------ 7. Abstract We propose using the 160M grating of the GHRS to search for Lya absorption in the spectrum of the QSO Mrk 205, at the redshift of the intervening galaxy NGC 4319. The line-of-sight to the quasar lies only 3-5 kpc from the center of the galaxy, passing through an inter-arm region of the disk and halo. The QSO was observed in Cycle 1 as part of our programme to search for metal absorption lines in intervening galaxies, when we detected Mg II and C IV absorption from NGC 4319. The gas appears to be highly ionized, at least compared to Milky Way halo gas, and we now request further GHRS observations of Lya to explore the conditions within the gas. The sightline offers a unique opportunity to probe the interstellar medium of both a low-redshift galaxy and our own Galactic halo, and to provide important comparisons with QSO absorption systems seen at higher redshifts. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 4.72 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4434c PI: David V. Bowen Proposal Title: USING MRK 205 TO PROBE THE IONIZED ISM IN NGC 4319 ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ David V. Bowen STSCI USA X Pi Chris Blades STSCI USA X ------------------------------------------------------------------------------------ 2. Scientific Justification. ------------------------------------------------------------------------------------ 3. Description of proposed observations. We wish to use the G160M grating to observe Ly$\alpha$ absorption from both NGC~4319 and from our own Galactic halo. Since the H~I absorption from our own galaxy will produce a damped absorption line profile, that is, a profile which depends on the column density alone, a spectrum with a S/N of 5 (per pixel, assuming half-stepped data) centered at the middle of the damped profile (i.e. zero velocity) should provide enough information for us to accurately fit the local absorption. As discussed in the Phase 1 text, such an unambiguous fit should be easily allow fitting Ly$\alpha$ absorption from NGC~4319. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The study of absorption by low-redshift galactic haloes in the {\it same} ions observed at higher redshifts is arguably the most important step in understanding the nature of the absorbing galaxies in the early universe. Moreover, this sightline offers a unique opportunity to study, in detail, the inter-arm region of an extragalactic ISM. Ly$\alpha$ is only accessible at low redshifts with the {\it International Ultraviolet Explorer} (IUE). {IUE} has a small aperture which permits detection of only strong ($1-2$~\AA ) lines in the brightest quasar spectra and is unsuitable for detecting lines at the equivalent width limits (0.25~\AA ) of the higher redshift absorption line surveys. The {GHRS} plus {HST} is ideal for this study. The instrument is sensitive enough to detect weak lines in bright quasars, and, with the intermediate-dispersion gratings, data can be obtained with a resolution which discerns the large-scale velocity structure of the absorption-line profiles. This in turn permits a more accurate determination of column densities and doppler parameters, and leads to a more detailed analysis of the chemical, ionization and kinematics of the absorbing gas. For these two reasons, the GHRS is more suitable for studying the physics of galactic haloes than the FOS. Our Cycle 1 observations of Mrk~205 demonstrate these assertions. All our exposure times are chosen to ensure that sufficient signal-to-noise is reached to allow the fitting of theoretical absorption line profiles. From our experience with the Cycle 1 observations, we find that the S/N needs to be $\apg\:5$ per pixel to fit weak lines, a value we aim for in this proposal. If, however, the Ly alpha from NGC 4319 is strong, simulations suggest that fitting the absorption line profile seen in data with a S/N of 5 should be quite easy. A second problem is that we expect the count rate at 1216A to be dominated by geocoronal Lyalpha emission. Comparisons between the width of the damped profile and the width of the geocoronal emission seen in G160M/LSA observations of the dMe star AU Mic suggest that the local absorption will still be well enough defined to allow theoretical line fits. There is some ambiguity in the exact value of the flux at the wavelength regions of interest: comparison between the fluxes obtained during our Cycle 1 observations of Mg~II and C~IV and those given by Kinney~\etal\ (1991) of a composite IUE spectrum reveals that the flux was 1.7 times brighter during our HST observations. This increase is important in that it allows good S/N spectra to be obtained in short exposure times. However, since it is impossible to predict whether the flux will stay at the same level during Cycle 3, we have increased the flux measured by Kinney~\etal\ by only 1.35, half the difference found. With these fluxes, we base our exposure times on the sensitivity curves in v3.0 of the GHRS Instrument Handbook. We have adopted a background count of 0.012~\cds\ for Detector 2, and assumed half-stepped data. Wave- Line Flux Count Rate Exposure Time S/N length ergs/cm**2/ c/pix/hr hrs /pix (A) s/A 1216 Ly$\alpha$ 2.0e-14 27 5.0 5.4 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. None ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. All the data should be reducible using standard IRAF and STSDAS reduction packages. For absorption lines in which we resolve components, we have profile fitting routines available for subjective fits to the data, plus automatic routines which produce a best fit based on minimizing chi-squared. One of us (DVB) will work full time on the data reduction and analysis. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Page 4 ------------------------------------------------------------------------------------ 9. Description of previous HST work. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). ------------------------------------------------------------------------------------ 11. Address Information Name: DAVID V BOWEN Category: PI Institution: STScI Address: 3700 SAN MARTIN DRIVE City: BALTIMORE State: MD Zip Code: 21218 Country: USA Telephone: 410-516-4889 Telex (or e-mail): bowen@stsci.edu ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4434c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 1219+755 E,313,314 RA= 12H 21M 44.04S +/- 0.3", 2000 Z=0.07 1 V=14.5 (MRK 205) DEC= +75D 18' 38.2" +/- 2 F-CONT(1216) = 2E-14 0.3", PLATE-ID=01G5 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4434c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 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 1219+755 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3 1 9S 2 1 CYCLE 3 BRIGHT=RETURN ONBOARD ACQ FOR 2 DARK TIME ------------------------------------------------------------------------------------------------------------------------------------ 2 1219+755 HRS ACCUM 2.0 G160M 1221.3 COMB=FOUR 11 1545S 5.2 2 1 CYCLE 3 FP-SPLIT=FOUR 17000S STEP-PATT=4 Comments: REQUIRE DARK TIME TO AVOID SEVERE CONTAMINATION FROM GEOCORONAL LYMAN ALPHA. IF DIFFICULT TO SCHEDULE, OR DEEMED UNECCESSARY, RELAX DARK TIME CONSTRAINT (EXCEPT FOR ACQ) ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4434c [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 BRIGHT=RETURN COMB=FOUR FP-SPLIT=FOUR STEP-PATT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 4.72 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category ABSORPTION LINES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 3; ONBOARD ACQ FOR 2; DARK TIME CYCLE 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names 1219+755 (MRK 205) ------------------------------------------------------------------------------------------------------------------------------------