! File: 4434C.PROP ! Database: PEPDB ! Date: 22-FEB-1994:11:49:07 coverpage: title_1: USING MRK 205 TO PROBE THE IONIZED ISM IN NGC 4319 sci_cat: INTERSTELLAR MEDIUM sci_subcat: ABSORPTION LINES proposal_for: GO pi_fname: DAVID pi_mi: V. pi_lname: BOWEN pi_inst: STSCI pi_country: USA hours_pri: 4.72 num_pri: 1 hrs: Y funds_length: 12 off_fname: HERVEY off_lname: STOCKMAN, JR. off_title: DEPUTY DIRECTOR off_inst: SPACE TELESCOPE SCIENCE INSTITUTE off_addr_1: 3700 SAN MARTIN DRIVE off_city: BALTIMORE off_state: MD off_zip: 21218 off_country: USA off_phone: 410-338-4973 ! end of coverpage abstract: line_1: We propose using the 160M grating of the GHRS to search for Lya line_2: absorption in the spectrum of the QSO Mrk 205, at the line_3: redshift of the intervening galaxy NGC 4319. The line-of-sight to the quasar line_4: lies only 3-5 kpc from the center of the galaxy, passing through an inter-arm line_5: region of the disk and halo. The QSO was observed in Cycle 1 as part of our line_6: programme to search for metal absorption lines in intervening galaxies, when we line_7: detected Mg II and C IV absorption from NGC 4319. The gas appears to be highly line_8: ionized, at least compared to Milky Way halo gas, and we now request line_9: further GHRS observations of Lya to line_10: explore the conditions within the gas. line_12: The sightline offers a unique opportunity to probe the interstellar medium of line_13: both a low-redshift galaxy and our own Galactic halo, and to provide important line_14: comparisons with QSO absorption systems seen at higher redshifts. ! ! end of abstract general_form_proposers: lname: BOWEN fname: DAVID mi: V. inst: STSCI country: USA esa: Y ! lname: BLADES fname: CHRIS title: PI inst: STSCI country: USA esa: Y ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: ! question: 3 section: 1 line_1: We wish to use the G160M grating to observe Ly$\alpha$ absorption from both line_2: NGC~4319 and from our own Galactic halo. Since the H~I absorption from our own line_3: galaxy will produce a damped absorption line profile, that is, a profile which line_4: depends on the column density alone, a spectrum with a S/N of 5 (per pixel, line_5: assuming half-stepped data) centered at the middle of the damped profile (i.e. line_6: zero velocity) should provide enough information for us to accurately fit the line_7: local absorption. As discussed in the Phase 1 text, such an unambiguous fit line_8: should be easily allow fitting Ly$\alpha$ absorption from NGC~4319. ! question: 4 section: 1 line_1: The study of absorption by low-redshift galactic haloes in the {\it same} ions line_2: observed at higher redshifts is arguably the most important step in line_3: understanding the nature of the absorbing galaxies in the early universe. line_4: Moreover, this sightline offers a unique opportunity to study, in detail, the line_5: inter-arm region of an extragalactic ISM. line_7: Ly$\alpha$ is only accessible at low redshifts with the {\it line_8: International Ultraviolet Explorer} (IUE). {IUE} has a small aperture line_9: which permits detection of only strong ($1-2$~\AA ) lines in the brightest line_10: quasar spectra and is unsuitable for detecting lines at the equivalent width line_11: limits (0.25~\AA ) of the higher redshift absorption line surveys. The line_12: {GHRS} plus {HST} is ideal for this study. The instrument is sensitive line_13: enough to detect weak lines in bright quasars, and, with the line_14: intermediate-dispersion gratings, data can be obtained with a resolution which line_15: discerns the large-scale velocity structure of the absorption-line profiles. line_16: This in turn permits a more accurate determination of column densities and line_17: doppler parameters, and leads to a more detailed analysis of the chemical, line_18: ionization and kinematics of the absorbing gas. For these two reasons, the line_19: GHRS is more suitable for studying the physics of galactic haloes than line_20: the FOS. Our Cycle 1 observations of Mrk~205 demonstrate these assertions. ! question: 4 section: 2 line_1: line_2: All our exposure times are chosen to ensure that sufficient signal-to-noise is line_3: reached to allow the fitting of theoretical absorption line profiles. From our line_4: experience with the Cycle 1 observations, we find that the S/N needs to be line_5: $\apg\:5$ per pixel to fit weak lines, a value we aim for in this proposal. line_6: If, however, the Ly alpha from NGC 4319 is strong, simulations suggest that line_7: fitting the absorption line profile seen in data with a S/N of 5 should be line_8: quite easy. line_10: A second problem is that we expect the count rate at 1216A to be dominated by line_11: geocoronal Lyalpha emission. Comparisons between the width of the damped line_12: profile and the width of the geocoronal emission seen in G160M/LSA observations line_13: of the dMe star AU Mic suggest that the local absorption will still be well line_14: enough defined to allow theoretical line fits. ! question: 4 section: 3 line_1: There is some ambiguity in the exact value of the flux at the wavelength line_2: regions of interest: comparison between the fluxes obtained during our Cycle 1 line_3: observations of Mg~II and C~IV and those given by Kinney~\etal\ (1991) of a line_4: composite IUE spectrum reveals that the flux was 1.7 times brighter during our line_5: HST observations. This increase is important in that it allows good S/N line_6: spectra to be obtained in short exposure times. However, since it is line_7: impossible to predict whether the flux will stay at the same level during line_8: Cycle 3, we have increased the flux measured by Kinney~\etal\ by only 1.35, line_9: half the difference found. line_11: With these fluxes, we base our exposure times on the sensitivity curves in line_12: v3.0 of the GHRS Instrument Handbook. We have adopted a background count of line_13: 0.012~\cds\ for Detector 2, and assumed half-stepped data. line_15: Wave- Line Flux Count Rate Exposure Time S/N line_16: length ergs/cm**2/ c/pix/hr hrs /pix line_17: (A) s/A line_19: 1216 Ly$\alpha$ 2.0e-14 27 5.0 5.4 ! question: 5 section: 1 line_1: None ! question: 6 section: 1 line_1: None ! question: 7 section: 1 line_1: All the data should be reducible using standard IRAF and STSDAS reduction line_2: packages. For absorption lines in which we resolve components, we line_3: have profile fitting routines available for subjective fits to the data, plus line_4: automatic routines which produce a best fit based on minimizing chi-squared. line_5: One of us (DVB) will work full time on the data reduction and analysis. ! question: 8 section: 1 line_1: ! question: 9 section: 1 line_1: ! question: 10 section: 1 line_1: ! !end of general form text general_form_address: lname: BOWEN fname: DAVID mi: V category: PI inst: STScI addr_1: 3700 SAN MARTIN DRIVE city: BALTIMORE state: MD zip: 21218 country: USA phone: 410-516-4889 telex: bowen@stsci.edu ! ! end of general_form_address records fixed_targets: targnum: 1 name_1: 1219+755 name_2: (MRK 205) descr_1: E,313,314 pos_1: RA= 12H 21M 44.04S +/- 0.3", pos_2: DEC= +75D 18' 38.2" +/- 0.3", pos_3: PLATE-ID=01G5 equinox: 2000 rv_or_z: Z=0.07 fluxnum_1: 1 fluxval_1: V=14.5 fluxnum_2: 2 fluxval_2: F-CONT(1216) = 2E-14 ! ! end of fixed targets ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 1.000 targname: 1219+755 config: HRS opmode: ACQ aperture: 2.0 sp_element: MIRROR-N2 num_exp: 1 time_per_exp: 9S fluxnum_1: 2 priority: 1 param_1: SEARCH-SIZE=3 param_2: BRIGHT=RETURN req_1: CYCLE 3; req_2: ONBOARD ACQ FOR 2; req_3: DARK TIME ! linenum: 2.000 targname: 1219+755 config: HRS opmode: ACCUM aperture: 2.0 sp_element: G160M wavelength: 1221.3 num_exp: 11 time_per_exp: 1545S s_to_n: 5.2 s_to_n_time: 17000S fluxnum_1: 2 priority: 1 param_1: COMB=FOUR param_2: FP-SPLIT=FOUR param_3: STEP-PATT=4 req_1: CYCLE 3 comment_1: REQUIRE DARK TIME TO AVOID SEVERE comment_2: CONTAMINATION FROM GEOCORONAL comment_3: LYMAN ALPHA. IF DIFFICULT TO comment_4: SCHEDULE, OR DEEMED UNECCESSARY, comment_5: RELAX DARK TIME CONSTRAINT comment_6: (EXCEPT FOR ACQ) ! ! end of exposure logsheet ! No scan data records found