! Proposal 6499, submission 1 ! PI: Limin Lu ! Received Thu Feb 8 12:56:05 EST 1996 ! From: tripp@stout.astro.wisc.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Alice Berman ! Phone: 410-338-4462 , E-mail: aberman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. Proposal_Information ! Section 4 Title: THE RELATIONSHIP BETWEEN LYMAN-ALPHA CLOUDS AND GALAXIES AT z<0.3 Proposal_Category: GO Scientific_Category: QSO ABSORPTION LINES Cycle: 6 Investigators PI_name: Limin Lu PI_Institution: Caltech CoI_Name: Blair Savage CoI_Institution: University of Wisconsin Contact: ! Y or N (designate at most one contact) CoI_Name: Todd Tripp CoI_Institution: University of Wisconsin Contact: Y ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) Recent studies suggest that most strong (rest equivalent width w_r>300mAngstrom), low redshift (z<1) Ly-alpha\ absorbing clouds in quasar spectra are associated with luminous galaxies, but the relationship between the weaker Ly- alpha\ absorbers (w_r<300mAngstrom) and galaxies is still unclear. There is some evidence that the weaker Ly-alpha\ absorbers may form a distinct population from the stronger ones, but such a proposition cannot be rigorously tested at the present because of the very small number of known Ly- alpha\ absorbers with w_r<300 mAngstrom. We propose to obtain very high S/N (90:1 per diode) observations of the LyAlpha forest region of two low-redshift quasars PG0953+414 (z_em=0.234) and PG1116+215 (z_em=0.177) with the GHRS G140L grating. This will allow us to detect LyAlpha absorption lines as weak as 50 mAngstrom\ in rest equivalent width. These new measurements, when combined with similar observations of H1821+643 (z_em=0.297) which we will obtain in Cycle 5, will increase the sample size of low redshift weak LyAlpha absorbers (w_r<300 mAngstrom) from the existing number of 20 to ~ 70. The combination of these HST observations with ground -based imagery and multi-object spectroscopic observations of galaxies in the quasar fields will allow us to investigate the relationship between weak LyAlpha absorbers and galaxies at z<0.3 on a much firmer statistical ground than previously possible. The study is essential for understanding the nature of LyAlpha clouds which has important implications for galaxy formation and evolution in the universe. Questions ! Free format text (please update) Observing_Description: GHRS Large Science Aperture observations of two low-redshift quasars (PG0953+414 and PG1116+215) will be made with the G140L grating. S/N of 90:1 per diode is required in order to achieve the desired 4Sigma detection limit of 50 mAngstrom\ for Ly-alpha\ absorption. We will use both comb-addition and FP-split to greatly reduce the effects of fixed pattern noise. In fact, we will do FP-split at two slightly offset wavelengths in order to derive an accurate noise template, which will then be used to remove the fixed pattern noise in the data. This procedure has been demonstrated to work extremely well, achieving S/N as high as 300-1000 (Cardelli & Ebbets 1993, in Calibrating Hubble Space Telescope, eds. J.C.Blades and S.J.Osmer, p322). The spectra will be sampled with 2 sub-steps per diode (Step Pattern 4). The GHRS/G140L combination is chosen over the FOS/G130H combination because (1) the overall sensitivity of GHRS/G140L combination is ~2X higher than FOS/G130H in the relevant wavelength region; (2) the spectral resolution of the GHRS G140L grating is almost twice as high as that of the FOS G130H grating, (3) the fixed pattern noise in the GHRS G140L grating/detector system can be effectively removed through the comb-addition and FP-split processes, while the FOS grating/detector systems are known to suffer from residual flatfielding features. This fact is extremely important for our observations because we are requesting very high S/N (90:1) data in order to detect very weak absorption features. The slightly larger spectral coverage of FOS/G130H is not an issue here because with GHRS G140L we are already covering the entire Lyman-alpha forest region of the two quasars. The GHRS G140L is also much more favorable than the medium resolution gratings (GHRS G140M or G160M) because the G140L is faster and offers a much larger spectral coverage (by a factor of 7) than the medium resolution gratings. Since the key here is to detect weak Ly -alpha\ lines rather than to resolve the line profiles, the lower resolution of GHRS G140L (as compared to G140M or G160M) is not a problem. The chance for any of the Ly-alpha\ lines to fall on top of the Galactic ISM lines is negligibly small. In any case, we are quite familiar with the wavelength and expected strengths of these ``interfering'' ISM lines from our own studies of Milky Way disk and halo gas absorption. For PG0953+414, f(1400Angstrom)=3.0* 10^-14 ergs s^-1 cm^-2 AA^-1. Thus a total of 320 minutes exposure time is needed in order to reach the desired S/N. This translates into 9 spacecraft orbits including overhead. For PG1116+215, f(1400Angstrom)=5.0* 10^-14 ergs s^-1 cm^-2 AA^-1. The total required exposure time is 190 minutes, which translates into 6 spacecraft orbits including overhead. All flux values are from the IUE spectra of Lanzetta, Turnshek, & Sandoval (1993, ApJS, 84, 109). Estimates of exposure time and number of spacecraft orbits are based on the Instrument Handbook for the Goddard High Resolution Spectrograph (v6.0, June 1995). Real_Time_Justification: None The main goal of this program is to investigate the relationship between low redshift weak Ly-alpha\ absorbers and galaxies/clusters of galaxies. The HST observations proposed here will provide us with the sample of Ly-alpha\ lines. We have already secured observing time on the Wisconsin-Indiana-Yale-NOAO 3.5-m telescope (to which the proposers have guaranteed access) to carry out the required ground-based imagery and spectroscopic observations of galaxies in the fields of the target quasars. The latter observations will yield redshifts for galaxies in the quasar fields. We will then examine the relationship between the samples of Ly-alpha\ clouds and galaxies. Calibration_Justification: ! Move appropriate text from Real_Time_Justification We request Pt wavelength calibration lamp exposures be taken at the beginning of the science integration in order to obtain accurate wavelength calibrations. Accurate wavelength scales are important to our scientific analyses because we will try to match redshifts of the lyman-alpha absorbing clouds with those of galaxies in the quasar field. Additional_Comments: No additional comments. Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: PG0953+415 Alternate_Names: Description: GALAXY, QSO, QUASAR Position: RA=9H 56M 52.4S +/-1",DEC=+41D 15' 22" +/-1",PLATE-ID=00XW ! PLATE-ID=? Equinox: 2000 RV_or_Z: Z=0.234 RA_PM: 0.0 ! Units are seconds of time per year Dec_PM: 0.0 ! Units are seconds of arc per year Epoch: Annual_Parallax: 0.0 Flux: V=14.5 ! Include at least V and B-V F(1400)=3.0+/-0.3E-14 Comments: Target_Number: 2 Target_Name: PG1116+215 Alternate_Names: Description: GALAXY, QSO, QUASAR Position: RA=11H 19M 08.7S +/-1",DEC=+21D 19' 18" +/-1",PLATE-ID=01TL ! PLATE-ID=? Equinox: 2000 RV_or_Z: Z=0.177 RA_PM: 0.0 ! Units are seconds of time per year Dec_PM: 0.0 ! Units are seconds of arc per year Epoch: Annual_Parallax: 0.0 Flux: V=15.2 ! Include at least V and B-V F(1400)=5.0+/-0.5E-14 Comments: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN