Herschel Observations of Far-infrared Cooling Lines in Intermediate Redshift (Ultra)-luminous Infrared Galaxies
Valtchanov, I.; Bock, J. J.; Scott, D.; Magdis, G. E.; Wang, L.; Cooray, A.; Farrah, D.; Rigopoulou, D.; Vaccari, M.; Huang, J. -S.; Hopwood, R.; Griffin, M. J.; Riechers, D.; Pearson, C.; Alonso-Herrero, A.; Swinyard, B. M.; Oliver, S.; Smith, A.; Clements, D.; Thatte, N.
United Kingdom, United States, China, Chile, Spain, Canada, South Africa
Abstract
We report the first results from a spectroscopic survey of the [C II] 158 μm line from a sample of intermediate redshift (0.2 <z < 0.8) (ultra)-luminous infrared galaxies, (U)LIRGs (L IR > 1011.5 L ⊙), using the Spectral and Photometric Imaging REceiver-Fourier Transform Spectrometer on board the Herschel Space Observatory. This is the first survey of [C II] emission, an important tracer of star formation, at a redshift range where the star formation rate density of the universe increases rapidly. We detect strong [C II] 158 μm line emission from over 80% of the sample. We find that the [C II] line is luminous, in the range (0.8-4) × 10-3 of the far-infrared continuum luminosity of our sources, and appears to arise from photodissociation regions on the surface of molecular clouds. The L [C II]/L IR ratio in our intermediate redshift (U)LIRGs is on average ~10 times larger than that of local ULIRGs. Furthermore, we find that the L [C II]/L IR and L [C II]/L CO(1-0) ratios in our sample are similar to those of local normal galaxies and high-z star-forming galaxies. ULIRGs at z ~ 0.5 show many similarities to the properties of local normal and high-z star-forming galaxies. Our findings strongly suggest that rapid evolution in the properties of the star-forming regions of (U)LIRGs is likely to have occurred in the last 5 billion years.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.