Extragalactic abstracts - IRSA - California Institute of Technology

Spitzer_Approved_Extragalactic
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Spitzer Space Telescope − General Observer Proposal #50783
Interstellar Dust in Distant Galaxies: A Spitzer Study of Dusty Damped
Lyman−alpha Absorbers
Principal Investigator: Varsha Kulkarni
Institution: Univ. of South Carolina
Technical Contact: Varsha Kulkarni, Univ. of South Carolina
Co−Investigators:
Daniel E. Welty, University of Chicago
Donald G. York, University of Chicago
Giovanni Vladilo, Osservatorio Astronomico di Trieste
Science Category: high−z galaxies (z>0.5)
Observing Modes: IrsStare
Hours Approved: 36.3
Abstract:
Understanding the nature of interstellar dust grains in distant galaxies is
crucial for investigating the chemical evolution of galaxies and for correcting
observations of high−redshift objects used for cosmological studies. However,
very little is known about the nature of dust in the distant Universe.
Absorption line systems in quasar spectra, especially the damped Lyman−alpha
(DLA) absorbers, provide excellent venues for directly studying dust in distant
galaxies, selected independently of the galaxy luminosities. A subset of dusty
metal−rich absorption systems has been discovered using the Sloan Digital Sky
Survey and radio surveys. These absorbers appear to be more massive and
chemically more evolved than the general DLA population, and may contribute
significantly to the global metal content. Here we propose IR spectroscopy of 10
quasars with intervening dusty DLAs to study the 9.7 micron silicate absorption
feature, and in a few cases also the 18 micron silicate feature. In a recent
exploratory study, we have made the first identifications of the silicate
features in a few DLAs with Spitzer IRS spectra, and developed the techniques
for analyzing them. Although relatively shallow, the features can be detected at
a statistical level of > 10−15 sigma. The profile of the detected features
resembles those seen in diffuse interstellar clouds, and in laboratory amorphous
olivine. The features appear to be somewhat deeper than expected from the
tau_{9.7} vs. E(B−V) relation for Galactic diffuse interstellar clouds,
suggesting different dust extinction properties. We now wish to examine whether
these properties are common in other DLAs and study trends with redshift,
metallicity, and depletions, by studying the silicate features in other DLAs.
Our sample contains both diffuse and molecular clouds spanning look−back times
of 2−9 Gyr. Spitzer IRS is the only instrument available to further explore the
new window on the dust in the distant Universe opened up by our exploratory
study.
Spitzer_Approved_Extragalactic
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Spitzer Space Telescope − General Observer Proposal #30873
The ages and star formation rates of massive galaxies at z=2−3
Principal Investigator: Ivo Labbe
Institution: Carnegie Instition of Washington
Technical Contact: Ivo Labbe, Carnegie Instition of Washington
Co−Investigators:
Eric Gawiser, Yale
Pieter van Dokkum, Yale
Pauline Lira, U. Chile
Jiasheng Huang, CfA
Garth Illingworth, UC Santa Cruz
Marijn Franx, Leiden Observatory
Danilom Marchesini, Yale
Ryan Quadri, Yale
Tracy Webb, McGill
Mariska Kriek, Leiden Observatory
Greg Rudnick, NOAO
Science Category: high−z galaxies (z>0.5)
Observing Modes: IracMap MipsPhot
Hours Approved: 27.4
Abstract:
Using deep multiwavelength surveys from MUSYC, GOODS, and FIRES, and IR
selection techniques we are now able to select galaxies at z>2 by stellar mass.
Detailed optical−to−infrared photometry has recently revealed that massive M >
10^11 Msun galaxies at z=2−3 are on average already surprisingly red (J_ab −
K_ab ~ 1.5). Studies in FIRES and GOODS have demonstrated that IRAC and MIPS are
critical to determine the origin of these red colors. Thanks to Spitzer we can
now distinguish galaxies that are ‘‘red and dead’’ from those that are actively
forming stars and enshrouded by dust. Nevertheless, inferences for galaxy
formation scenarios are severely limited by field−to−field variance. Strong
clustering causes density fluctuations by more than a factor of 3 on fields the
size of GOODS. Worse, current estimates of the space densities of dead galaxies
differ by a factor of 10. It is imperative to extend to new and larger fields.
Unfortunately, the fundamental obstacle is the lack of sufficiently deep J and
K−band imaging in available IRAC fields. Because deep wide area NIR imaging is
excessively time−consuming to obtain, we face delays of years before we can
improve on current results. Therefore, to immediately enhance the scientific
return of IRAC and MIPS, we propose to observe the *only* substantial fields
with deep NIR imaging in the J,H, and K−band that are available *now*: the MUSYC
survey, comprising 4 fields of 100 arcmin^2 each. These fields are very
compelling for follow−up with Spitzer, as they are also the main focus of our
Gemini/GNIRS ‘‘Key Science Program’’ obtaining very deep NIR spectra on massive
distant galaxies. This unique program is producing dozens of direct measurements
of the Balmer/4000 A break and Balmer decrement in z=2−3 massive galaxies,
providing independent estimates of the ages, star formation rates, and
extinctions. Ultimately, such NIR spectra will be crucial to calibrate the
constraints that IRAC and MIPS place on the stellar populations of high redshift
galaxies.
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