Extragalactic abstracts - IRSA - California Institute of Technology

Mar 25, 10 16:24 Spitzer_Approved_Extragalactic Page 19/742
Abstract:
The observable properties of galaxy evolution are largely driven by the
life−cycle of baryonic matter: stars precipitate out of a complex, multi−phase
interstellar medium; and eventually, evolved stellar populations return enriched
material back to the ISM via stellar winds or supernova explosions. As
demonstrated by the SAGE−LMC survey, comprehensive Spitzer imaging of a nearby
galaxy provides an incredibly rich view of this baryonic lifecycle, allowing for
an unprecedented understanding of the physical processes which drive galaxy
evolution. This proposal will extend the SAGE analysis to the whole SMC (Bar,
Wing, and high−density portion of the Magellanic Bridge), a galaxy whose
properties are uniquely similar to those of star−forming galaxies at high
redshift. Specifically, the SMC’s metallicity is below the critical threshold
(1/3−1/4 Z_sun) where interstellar medium properties are observed to change
dramatically (sharp reduction in the PAH dust mass fraction, reduced dust−to−gas
ratio, and extreme ultraviolet extinction curve variations). In addition, the
SMC has been profoundly influenced by past interactions with the LMC and Milky
Way, allowing us to study the impact of periodic interactions on the structure
of the ISM and the physical processes of star formation. We will gain crucial
insight into the ISM and star formation in a known tidal debris structure
(Bridge portion of SMC), which has a metallicity 4 times lower than the rest of
the SMC. When combined with observations of the Milky Way (GLIMPSE, MIPSGAL) and
the LMC (SAGE−LMC), our survey of the SMC (SAGE−SMC) will provide a complete and
detailed picture of the life−cycle of baryons in galactic environments spanning
orders of magnitude in metallicity, and wide ranges in star formation history.
This understanding will equip us to properly interpret the infrared properties
of more distant galaxies, both in the local (e.g., SINGS) and high−redshift
(e.g., GOODS and SWIRE) universe.
Spitzer_Approved_Extragalactic
Printed_by_SSC
Mar 25, 10 16:24 Page 20/742
Spitzer Space Telescope − Guaranteed Time Observer Proposal #50816
A complete Survey of the SDSS metal−poor BCDs
Principal Investigator: Lei Hao
Institution: Cornell University
Technical Contact: Lei Hao, Cornell University
Co−Investigators:
Vianney Lebouteiller, Cornell University
Yanling Wu, Cornell University
Jim Houck, Cornell University
Science Category: local group galaxies
Observing Modes: IrsStare
Hours Approved: 33.3
Abstract:
Extremely low−metallicity galaxies represent key objects to understand the
chemical evolution of galaxies throughout the ages of the Universe. Spitzer
observed so far an incomplete sample for which the metallicity distribution may
not be representative of the actual situation in the Universe. We selected a
complete sample of very metal−poor galaxies ($leq 1/10 Zodot$) from the SDSS DR5
survey. This sample will allow doubling the present sample of Spitzer
observations of BCDs with comparable metallicities. The main goal of the
proposal is to view the sample as a whole, and study the variation and
distributions of their infrared properties. We will explore the effect of
metallicity on the variation of these properties, particularly examine the
possibility of a metallicity threshold for the formation of polycyclic aromatic
hydrocarbons. We are also interested in the general properties and variations in
the SED of these BCDs. The wealthy information from the SDSS survey will be
implemented to the sample to understand the influence of the large−scale
environment on the star−formation properties inferred from their infrared
observations. The resulted dataset we can obtain will constitute a long−lasting
resource for studies of metal−deficient galaxies. The whole observations are
divided into one GO and one GTO proposals. The GTO proposal is focused on
obtaining the IRS spectra of the sample, while the GO one is focused on the
photometry of the sample. Thus they are each complete in its own.
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