Extragalactic abstracts - IRSA - California Institute of Technology

Spitzer_Approved_Extragalactic
Mar 25, 10 16:24 Page 483/742
Spitzer Space Telescope − General Observer Proposal #20757
Spectroscopy of Dusty Quasar Absorption Line Systems
Principal Investigator: Varsha Kulkarni
Institution: Univ. of South Carolina
Technical Contact: Varsha Kulkarni, Univ. of South Carolina
Co−Investigators:
Donald York, University of Chicago
Bruce Woodgate, NASA Goddard Space Flight Center
Science Category: AGN/quasars/radio galaxies
Observing Modes: IrsStare
Hours Approved: 1.4
Abstract:
Damped Lyman−alpha absorbers (DLAs) in quasar spectra contain a large fraction
of the neutral gas in galaxies and offer the most comprehensive information
about chemical composition of distant galaxies. Recent observations, including
our HST and MMT spectroscopy, are suggesting that the global mean metallicity of
DLAs is relatively low at all redshifts, contrary to the predictions of cosmic
chemical evolution models. Furthermore, imaging observations of most DLAs are
suggesting star formation rates (SFRs) far below the global mean SFR. These
"missing−metals" and "missing−stars" problems could be dust selection effects,
since the more metal−rich and more star−forming DLAs may obscure background
quasars more. As a first step toward characterizing the properties and
distribution of dust in DLAs and their environments, here we propose a search
for the IR emission and absorption signatures of the dust in a pilot sample of 5
DLAs at 0.3 < z < 2.8. All of these DLAs show signs of large amounts of dust,
(e.g., detections of the 2175 A dust feature or H2 or large depletions).
Furthermore, each field shows several spectroscopically identified galaxies with
Ly−alpha, H−alpha, [O II] or [O III] emission. We propose to obtain IRAC and
MIPS images to detect the dust emission from the DLAs and their companion
galaxies. We also propose to obtain IRS spectra of one of the background quasars
to search for the redshifted 9.7 micron silicate absorption feature in this
dusty DLA. The proposed observations will constrain (a) the rest−frame IR
luminosities, (b) the nature of the stellar populations, (c) the extinction
curve and dust composition, and (d) the unattenuated SFRs in the DLAs and their
environments. These observations will provide the first detailed IR look at
DLAs, and will help to quantify the role of dust in observations of DLAs and
high−z galaxies in general. Spitzer is essential because it is the only existing
facility with the necessary wavelength coverage and sensitivity.
Spitzer_Approved_Extragalactic
Printed_by_SSC
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Spitzer Space Telescope − General Observer Proposal #20083
A direct comparison of the infared SEDs of type−1 and type−2 quasars
Principal Investigator: Mark Lacy
Institution: Spitzer Science Center
Technical Contact: Mark Lacy, Spitzer Science Center
Co−Investigators:
Lee Armus, Spitzer Science Center, Caltech
Gabriela Canalizo, University of California, Riverside
Susan Ridgway, Johns Hopkins University
Anna Sajina, University of British Columbia
Lisa Storrie−Lombardi, Spitzer Science Center, Caltech
Science Category: AGN/quasars/radio galaxies
Observing Modes: IrsStare MipsPhot
Hours Approved: 21.9
Abstract:
We have used the Spitzer First Look Survey, in conjunction with the Sloan
Digital Sky Survey, to select the first sample of type−1 (unobscured) and type−2
(obscured) quasars matched in mid−infrared luminosity. We wish to study the
infrared SEDs of these objects using low resolution IRS spectroscopy and MIPS
photometry. The results of this study will help us understand the relationship
between the well−studied type−1 and the much less well−studied type−2 quasar
populations. We will search for evidence of higher star formation activity in
the type−2 objects though enhanced PAH and far−IR emission which may indicate
that type−2 quasars evolve into type−1s. If, on the other hand, the only
difference between type−1 and type−2 quasars is orientation, we expect the PAH
emission and far−infrared SEDs to be similar. We will also compare our
mid−infrared SEDs to models of emission from the dusty torus around the quasars,
and use our observations of the SED shape and depth of the silicate absorption
feature to constrain the clumpiness and optical depth of the dust.
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