Extragalactic abstracts - IRSA - California Institute of Technology

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Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 43/742 Spitzer Space Telescope − General Observer Proposal #50804 Leo T: Probing Star Formation and Dust in the Most Metal−Poor Galaxy Known Principal Investigator: Joshua Simon Institution: California Institute of Technology Technical Contact: Joshua Simon, California Institute of Technology Co−Investigators: Alberto Bolatto, Maryland Marla Geha, Yale Science Category: local group galaxies Observing Modes: IracMap MipsPhot Hours Approved: 8.5 Abstract: We propose IRAC and MIPS imaging of Leo T, the most metal−poor galaxy ever discovered. This new denizen of the Local Group is located just 420 kpc from the Milky Way and has a metallicity of less than 1/100 Zsun. However, it also contains significant amounts of cold gas, as well as a population of young massive stars. We will use very deep IRAC imaging of this unique system to search for YSOs, with techniques that we have perfected in the Small Magellanic Cloud. We will be sensitive to protostars with masses down to 4 Msun. We will also create a deep 160 um map of Leo T to constrain the dust associated with the cold gas, with the sensitivity to detect dust masses of as little as 10 Msun. Because of the combination of its unprecedently low metallicity and nearby location, Leo T is by far the best target for studying star formation and the dust content of the ISM at extremely low metallicities. With a small investment of Spitzer time, these observations offer the possibility of a very large scientific payoff: learning about stars similar to the theoretical Population III, but in the local universe. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 44/742 Spitzer Space Telescope − General Observer Proposal #20425 Dust at Low Metallicity: MIPS Observations of Local Group Dwarfs Principal Investigator: Evan Skillman Institution: University of Minnesota Technical Contact: Evan Skillman, University of Minnesota Co−Investigators: John Cannon, Max Planck Institute for Astronomy Robert Gehrz, University of Minnesota Dale Jackson, University of Minnesota Henry Lee, University of Minnesota Elisha Polomski, University of Minnesota Soo−Chang Rey, Yonsei University, Korea Fabian Walter, Max Planck Institue for Astronomy Charles Woodward, University of Minnesota Ted Wyder, Califonia Institute of Technology Science Category: local group galaxies Observing Modes: MipsScan Hours Approved: 16.4 Abstract: Characterizing the ISM and the star formation process at low metallicity is vital to our understanding of galaxy formation and evolution. Nearby dwarf galaxies represent our best opportunity to obtain observational constraints on our theoretical models of the low metallicity environment. Prior to Spitzer, even the closest dwarf galaxies were practically invisible at mid− and far− infrared wavelengths due to their intrinsically low surface brightnesses. However, the unprecedented sensitivity of MIPS on Spitzer allows us to make high resolution observations of the nearest low metallicity dwarf star forming galaxies for the first time. We will map the dust distributions, fluxes, and temperatures in these galaxies and, in combination with a nearly ideal set of ancillary observations, study the dependence of the physical properties of the ISM as a function of metallicity. We will also determine the metallicity dependence of three independent measurements of the star formation rate. The proposed modest number of requested observing hours will allow important strides forward in our understanding of the nature of the ISM and star formation at very low metallicities. Thursday March 25, 2010 xgal_covers.txt 22/371
Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 45/742 Spitzer Space Telescope − General Observer Proposal #40457 Spatially Resolved PAH Emission in Nearby Low−Metallicity Galaxies Principal Investigator: Evan Skillman Institution: University of Minnesota Technical Contact: Evan Skillman, University of Minnesota Co−Investigators: Dale Jackson, University of Minnesota John Cannon, Wesleyan University Robert Gehrz, University of Minnesota Science Category: local group galaxies Observing Modes: IrsMap IrsStare MipsScan Hours Approved: 18.5 Abstract: Significant progress has recently been made in measuring the mid−IR luminosity of galaxies over an impressive range of parameter space. An empirical trend of decreasing mid−IR luminosity with decreasing metallicity has now been well established. Further, a ‘transition metallicity’ has been identified where a drastic shift occurs in the relative mid−infrared contributions from hot dust continuum and polycyclic aromatic hydrocarbons (PAHs). However, we have not yet pinpointed the physical processes responsible for this shift. We know that the strength of mid−IR emission is dependent on a galaxy’s underlying dust and PAH content, as well as the ability of these components to be individually stimulated into emission, destroyed, and regrown through different physical processes in the ISM. However, the conditions regulating these processes remain highly unconstrained. To place strict constraints on the conditions regulating both hot dust and PAH emission we propose Spitzer/IRS spectral mapping of three nearby star−forming irregular galaxies. We will measure the relative strengths of hot dust and PAH emission with resolution on unprecidented spatial scales (70 pc). Our sample of metal−poor targets are the closest systems in which we can investigate the empirical transition where PAHs go from dominating the mid−IR flux to being completely absent, providing the conditions required to understand the physical processes responsible for this transition. In combination with a comprehensive set of ancillary data, we will compare our spectral maps with highly resolved stellar population data to precisely quantify the effects that radiation field strength and hardness and history of supernova activity have on dust and PAHs. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 46/742 Spitzer Space Telescope − General Observer Proposal #40524 The AGB Star Census of Local Group Irregular Galaxies Principal Investigator: Evan Skillman Institution: University of Minnesota Technical Contact: Evan Skillman, University of Minnesota Co−Investigators: Dale Jackson, University of Minnesota Robert Gehrz, University of Minnesota Science Category: local group galaxies Observing Modes: IracMap Hours Approved: 2.2 Abstract: Studies of the resolved stellar populations of nearby galaxies provide very strong constraints on their evolutionary histories. Because these are the most secure of all galaxy evolution studies, they represent a calibration of high−redshift investigations where the stellar populations are not resolvable. This work has typically been done at optical wavelengths, and therefore, is biased against very red and highly extincted objects. For example, AGB stars, which are important tracers of the intermediate age evolution of galaxies and are also important contributors to their chemical evolution, are incompletely sampled in typical optical studies, due to extinguishing material expelled by winds late in their evolution. Prior to Spitzer, infrared observations of low surface brightness galaxies were virtually impossible, but our Spitzer/IRAC pilot program imaging Local Group dwarf irregular galaxies has demonstrated that infrared studies of the resolved stellar populations in these galaxies are now available. These observations, in combination with ground based and HST optical imaging, confirm that optical studies do present a highly biased view of the stellar populations in nearby galaxies. These observations also provide the first direct measurement of AGB mass−loss in environments very different from the Milky Way, placing strict constraints on the role metal abundance plays on the physics governing the late stages of stellar evolution. Here we propose to extend our pilot study to a much broader range of parameter space, completing our IRAC investigation of the evolved stellar populations in Local Group star forming dwarf galaxies. Thursday March 25, 2010 xgal_covers.txt 23/371
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Extragalactic abstracts - IRSA - California Institute of Technology

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