Extragalactic abstracts - IRSA - California Institute of Technology
Extragalactic abstracts - IRSA - California Institute of Technology
Extragalactic abstracts - IRSA - California Institute of Technology
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Spitzer_Approved_<strong>Extragalactic</strong><br />
Mar 25, 10 16:24 Page 735/742<br />
Spitzer Space Telescope − General Observer Proposal #20577<br />
Nascent starbursts: a missing link in galaxy evolution<br />
Principal Investigator: Helene Roussel<br />
Institution: <strong>California</strong> <strong>Institute</strong> <strong>of</strong> <strong>Technology</strong><br />
Technical Contact: Helene Roussel, Max−Planck−Institut fur Astronomie<br />
Co−Investigators:<br />
George Helou, IPAC/Caltech<br />
Jim Condon, National Radio Astronomy Observatory<br />
Rainer Beck, Max−Planck−Institut fur Radioastronomie<br />
John−David Smith, University <strong>of</strong> Arizona<br />
Science Category: starburst galaxies<br />
Observing Modes: IracMap IrsMap MipsPhot<br />
Hours Approved: 20.4<br />
Abstract:<br />
We have identified a rare category <strong>of</strong> galaxies characterized by an extreme<br />
deficiency in synchro− tron radiation, relative to dust emission, and very high<br />
dust temperatures. We studied in detail the most extreme such object, and<br />
concluded in favor <strong>of</strong> a starburst just breaking out, less than one megayear old,<br />
in a galaxy having undergone no major star formation episode in the last 100<br />
Myr. Such systems <strong>of</strong>fer a perfect setting to study the initial conditions and<br />
early dynamics <strong>of</strong> starbursts and understand better the regulation <strong>of</strong> the<br />
infrared−radio continuum correlation in galaxies. For the prototypical nascent<br />
starburst, the mid−infrared spectrum is quite peculiar, suggesting tran− sient<br />
dust species and high optical depth; tracers <strong>of</strong> dust and molecular gas are the<br />
only indicators <strong>of</strong> unusual activity, and the active regions are likely very<br />
compact and dust−bounded, suppressing ionization. Only Spitzer data can provide<br />
the needed physical diagnostics for such regions. A sample <strong>of</strong> 25 nascent<br />
starbursts was drawn from the cross−correlation <strong>of</strong> the IRAS Faint Source Catalog<br />
and the NVSS VLA radio survey, and carefully selected based on our<br />
multi−wavelength VLA maps to span a range <strong>of</strong> infrared to radio ratios and<br />
luminosities. This sample allows a first step beyond studying prototypes toward<br />
a statistical analysis addressing systematic physical pro− perties,<br />
classification and search for starburst development sequences. We propose<br />
imaging and spectroscopic observations from 3 to 160 microns to characterize the<br />
state <strong>of</strong> the interstellar medium and the gas and dust excitation origin. Our aim<br />
is to learn from these unique systems how a star formation burst may develop in<br />
its very earliest phases, how it affects the fueling material and the host<br />
galaxy. Acquired observations <strong>of</strong> the radio continuum, cold molecular gas and<br />
tracers <strong>of</strong> shocks and HII regions will help us interpret the rich Spitzer data<br />
set and extract a coherent picture <strong>of</strong> the interstellar medium in our targets.<br />
Spitzer_Approved_<strong>Extragalactic</strong><br />
Printed_by_SSC<br />
Mar 25, 10 16:24 Page 736/742<br />
Spitzer Space Telescope − Directors Discretionary Time Proposal #492<br />
An Extremely Metal−Poor Population <strong>of</strong> L* Galaxies at z~0.35<br />
Principal Investigator: John Salzer<br />
Institution: Indiana University<br />
Technical Contact: Rose Finn, Siena College<br />
Co−Investigators:<br />
Rose Finn, Siena College<br />
George Helou, IPAC/SSC<br />
Science Category: starburst galaxies<br />
Observing Modes: IracMap MipsPhot<br />
Hours Approved: 4.9<br />
Abstract:<br />
We propose to obtain IRAC and MIPS observations <strong>of</strong> seven prototypes <strong>of</strong> a<br />
recently discovered class <strong>of</strong> star−forming galaxies with 0.29 < z < 0.41.<br />
Originally thought to be intermediate−redshift Seyfert 2 galaxies when first<br />
discovered in the KPNO International Spectroscopic Survey (KISS), recent optical<br />
spectroscopy in the far red has revealed these objects to be very metal−poor<br />
star−forming galaxies. These galaxies follow a luminosity−metallicity (L−Z)<br />
relation that parallels the one defined by low−redshift galaxies, but is <strong>of</strong>fset<br />
by a factor <strong>of</strong> 10 to lower abundances! The amount <strong>of</strong> chemical and/or luminosity<br />
evolution required to place these galaxies on the local L−Z relation is extreme.<br />
Either they are late−forming massive systems, which would challenge the current<br />
paradigm <strong>of</strong> galaxy formation, or they represent intense starbursts in<br />
dwarf−dwarf mergers. In either case, these objects represent an extreme stage <strong>of</strong><br />
galaxy evolution taking place at relatively low redshift. In order to arrive at<br />
a more complete understanding <strong>of</strong> the nature <strong>of</strong> these objects, we are applying<br />
now to DDT in order to capture a minimum <strong>of</strong> FIR information before Spitzer runs<br />
out <strong>of</strong> He coolant. We stress that the nature <strong>of</strong> these objects has only recently<br />
been recognized, so that it was not possible to apply to observe them during the<br />
most recent call for proposals.<br />
Thursday March 25, 2010 xgal_covers.txt<br />
368/371