Extragalactic abstracts - IRSA - California Institute of Technology

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Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 735/742 Spitzer Space Telescope − General Observer Proposal #20577 Nascent starbursts: a missing link in galaxy evolution Principal Investigator: Helene Roussel Institution: California Institute of Technology Technical Contact: Helene Roussel, Max−Planck−Institut fur Astronomie Co−Investigators: George Helou, IPAC/Caltech Jim Condon, National Radio Astronomy Observatory Rainer Beck, Max−Planck−Institut fur Radioastronomie John−David Smith, University of Arizona Science Category: starburst galaxies Observing Modes: IracMap IrsMap MipsPhot Hours Approved: 20.4 Abstract: We have identified a rare category of galaxies characterized by an extreme deficiency in synchro− tron radiation, relative to dust emission, and very high dust temperatures. We studied in detail the most extreme such object, and concluded in favor of a starburst just breaking out, less than one megayear old, in a galaxy having undergone no major star formation episode in the last 100 Myr. Such systems offer a perfect setting to study the initial conditions and early dynamics of starbursts and understand better the regulation of the infrared−radio continuum correlation in galaxies. For the prototypical nascent starburst, the mid−infrared spectrum is quite peculiar, suggesting tran− sient dust species and high optical depth; tracers of dust and molecular gas are the only indicators of unusual activity, and the active regions are likely very compact and dust−bounded, suppressing ionization. Only Spitzer data can provide the needed physical diagnostics for such regions. A sample of 25 nascent starbursts was drawn from the cross−correlation of the IRAS Faint Source Catalog and the NVSS VLA radio survey, and carefully selected based on our multi−wavelength VLA maps to span a range of infrared to radio ratios and luminosities. This sample allows a first step beyond studying prototypes toward a statistical analysis addressing systematic physical pro− perties, classification and search for starburst development sequences. We propose imaging and spectroscopic observations from 3 to 160 microns to characterize the state of the interstellar medium and the gas and dust excitation origin. Our aim is to learn from these unique systems how a star formation burst may develop in its very earliest phases, how it affects the fueling material and the host galaxy. Acquired observations of the radio continuum, cold molecular gas and tracers of shocks and HII regions will help us interpret the rich Spitzer data set and extract a coherent picture of the interstellar medium in our targets. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 736/742 Spitzer Space Telescope − Directors Discretionary Time Proposal #492 An Extremely Metal−Poor Population of L* Galaxies at z~0.35 Principal Investigator: John Salzer Institution: Indiana University Technical Contact: Rose Finn, Siena College Co−Investigators: Rose Finn, Siena College George Helou, IPAC/SSC Science Category: starburst galaxies Observing Modes: IracMap MipsPhot Hours Approved: 4.9 Abstract: We propose to obtain IRAC and MIPS observations of seven prototypes of a recently discovered class of star−forming galaxies with 0.29 < z < 0.41. Originally thought to be intermediate−redshift Seyfert 2 galaxies when first discovered in the KPNO International Spectroscopic Survey (KISS), recent optical spectroscopy in the far red has revealed these objects to be very metal−poor star−forming galaxies. These galaxies follow a luminosity−metallicity (L−Z) relation that parallels the one defined by low−redshift galaxies, but is offset by a factor of 10 to lower abundances! The amount of chemical and/or luminosity evolution required to place these galaxies on the local L−Z relation is extreme. Either they are late−forming massive systems, which would challenge the current paradigm of galaxy formation, or they represent intense starbursts in dwarf−dwarf mergers. In either case, these objects represent an extreme stage of galaxy evolution taking place at relatively low redshift. In order to arrive at a more complete understanding of the nature of these objects, we are applying now to DDT in order to capture a minimum of FIR information before Spitzer runs out of He coolant. We stress that the nature of these objects has only recently been recognized, so that it was not possible to apply to observe them during the most recent call for proposals. Thursday March 25, 2010 xgal_covers.txt 368/371
Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 737/742 Spitzer Space Telescope − General Observer Proposal #3177 Probing the Neutral to Molecular Transition in the Dwarf Starburst Galaxy NGC 4214 Principal Investigator: Evan Skillman Institution: University of Minnesota Technical Contact: Evan Skillman, University of Minnesota Co−Investigators: John Cannon, University of Minnesota Fabian Walter, National Radio Astronomy Observatory Science Category: starburst galaxies Observing Modes: IrsMap Hours Approved: 24.8 Abstract: We propose to perform an in−depth study of the molecular ISM in the nearby low−metallicity dwarf galaxy NGC 4214. The goal is to study the transition from neutral to molecular gas in a metal−poor environment − a fundamental process that drives star formation in galaxies. NGC 4214 is one of the few nearby dwarf galaxies where high−quality CO and HI observations exist and where drastically different star formation environments are located in close proximity. Using IRS in spectral mapping mode, we propose to carry out a detailed study of the S(0), S(1) and S(2) pure rotational lines of H2 at 28.2, 17.0, and 12.3 microns in NGC 4214. We will accurately map the individual molecular clouds and HI peaks to empirically test models of star formation where low−metallicity molecular clouds are predicted to have dense CO cores, surrounded by diffuse neutral carbon envelopes with co−spatial H2. The results of this investigation will offer the first empirical insight into the behavior of the neutral−to−molecular transition at comparatively low metallicities, a typical environment expected to prevail at large lookback times. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 738/742 Spitzer Space Telescope − Guaranteed Time Observer Proposal #40018 Mapping the frosty exotic ISM around the deeply buried AGN in the nearby starburst galaxy NGC4945 Principal Investigator: Henrik Spoon Institution: Cornell University Technical Contact: Henrik Spoon, Cornell University Co−Investigators: Vassilis Charmandaris, University of Crete Jeronimo Bernard−Salas, Cornell University John−David Smith, Steward Observatory Helene Roussel, MPIA Daniel Devost, Cornell University Duncan Farrah, Cornell University Science Category: starburst galaxies Observing Modes: IrsMap IrsStare Hours Approved: 10.8 Abstract: The nearly edge−on galaxy NGC4945 is one of the closest galaxies where an AGN and starburst coexist. Hard X−ray observations have shown the central black hole in this galaxy to be obscured by a Compton−thick hydrogen column of N_H=5 x 10^24 cm^−2. Despite this huge column, the AGN in NGC4945 is one of the brightest extragalactic sources in the sky at 100keV. In contrast, at optical and infrared wavelengths the AGN has remained undetected until very recently. Instead, at these wavelengths the central region is dominated by a starburst responsible for a spectacular starburst wind−blown, conical shaped cavity aligned with the galaxy’s minor axis. Near and mid−infrared spectroscopy of the nucleus have shown the central region to be dominated by very strong obscuration, rivaled only in strength by some of the most deeply obscured UltraLuminous Infrared Galaxies (ULIRGs). This obscuring medium is littered with cold molecular clouds, as evidenced by the presence of strong absorption bands of water ice and volatile ice species such as CO2, CO and ‘XCN’ in the 3−5 micron range, as well as by a very deep 10 micron silicate absorption feature. Other similarly inclined nearby starburst galaxies such as M82 and NGC253 do not show similar spectral properties on these scales. This makes NGC4945 a unique laboratory to study an environment otherwise only found in distant ULIRGs and, likely, their higher redshift counterparts. We therefore propose to map the bright central region of NGC4945 in SL, LL and SH to obtain the spatial distribution of ISM emission and absorption features, which will allow a characterization of the physical conditions in the frosty exotic ISM exposed to the hostile radiation from the circumnuclear starburst which coexists with a deeply buried AGN. Thursday March 25, 2010 xgal_covers.txt 369/371
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Extragalactic abstracts - IRSA - California Institute of Technology

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