Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40244s&link_type=abstract
Spitzer Proposal ID #40244
Physics
Scientific paper
Ultraluminous infrared galaxies (ULIRGs) have the power output of quasars, yet emit nearly all their energy in the mid and far-infrared part of the spectrum. Over the last 10 years, much effort has focussed on identifying tracers of AGN and star formation activity in the infrared in order to quantify the origin of the infrared luminosity in these systems. Recently, we discovered the presence of warm (200-600K) dense (~10^6 cm-3) molecular gas through acetylene, hydrogen cyanide, and carbon dioxide gas-phase absorption lines in the IRS spectra of (U)LIRGs. In the Galaxy these lines are characteristic for the 'Hot Core' phase of deeply embedded protostars. Consequently, we attribute these lines to a phase of deeply embedded star formation. While these features are most readily recognized in the spectra of highly dust enshrouded (U)LIRGs, they are also seen in ULIRGs with unambiguous evidence for an AGN. Hence, such deeply embedded star formation seems to be a general characteristic of (U)LIRG nuclei. Here we propose to use the IRS on Spitzer to search for these molecular absorption lines in a wider sample of ULIRG nuclei to determine the frequency and importance of this hitherto unrecognized phase of hidden star formation and characterize the physical conditions of the absorbing dense gas. These spectra, combined with existing high signal-to-noise observations of (U)LIRGs will allow us to place our observations of hidden star formation in ULIRGs in the context of evolution of infrared galaxies as a whole.
Armus Lee
Imanishi Masatoshi
Lahuis Fred
Spaans Marco
Spoon Henrick
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