| 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. |
