| Description |
We propose to use Herschel/PACS spectroscopy of the C II 158 micron
and O I 63 micron lines to observe a sample of 16 low-redshift
infrared-luminous galaxies, at log L_IR = 11.8 to 12.3 Lsolar, that are
distinguished by large size and non-merger structure. These galaxies
are interesting because they have high star formation rate activity
spread over a large physical area, rather than concentrated into
extremely dense regions as in the nucleus of a major merger, as in most
local ULIRGs. They are potentially good analogs for high-redshift
IR-luminous galaxies, which appear to have far-IR spectral shapes
different from local ULIRGs. C II is a major cooling line in
photo-dissociation regions and O I and C II probe the physical
conditions and UV intensity in IR-emitting regions. In a few extreme
lensed high-z ULIRGs where C II can be measured, the high-z objects
have L(C II)/L(FIR) ratios that are high, more like those of local
starbursts than local ULIRGs. At z>1, much of the star formation in
massive galaxies is occurring at LIRG and ULIRG levels, and U/LIRGs
dominate the IR luminosity density. Understanding star forming regions
in high-z IR-luminous galaxies is necessary to understand the conditions
in which most of the stars in massive galaxies formed. The proposed
measurements of C II and O I in this local sample of high-z analogs
will test the hypothesis that redshift evolution in the IR SED shape and
the C II/FIR ratio are due to different physical conditions in high-z
IR-luminous galaxies, because of the larger physical extent of the star
forming area. |
