Observations of [OI]63 µm line emission in main-sequence galaxies at z 1.5
Daddi, E.; Valtchanov, I.; Walter, F.; Dannerbauer, H.; Sargent, M.; Riechers, D.; Aravena, M.; Díaz-Santos, T.; Decarli, R.; Wagg, J.; Brisbin, D.; Carilli, C.
United Kingdom, Chile, Spain, United States, France, Italy, China, Germany
Abstract
We present Herschel-PACS spectroscopy of four main-sequence star-forming galaxies at z ~ 1.5. We detect [OI]63 μm line emission in BzK-21000 at z = 1.5213, and measure a line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (3.9\pm 0.7)\times 10^9$ L⊙. Our PDR modelling of the interstellar medium in BzK-21000 suggests a UV radiation field strength, G ~ 320G0, and gas density, n ~ 1800 cm-3, consistent with previous LVG modelling of the molecular CO line excitation. The other three targets in our sample are individually undetected in these data, and we perform a spectral stacking analysis which yields a detection of their average emission and an [O I]63 μm line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (1.1\pm 0.2)\times 10^9$ L⊙. We find that the implied luminosity ratio, $L_{\rm [O\, {\small I}]63\, \mu m}/L_{\rm IR}$, of the undetected BzK-selected star-forming galaxies broadly agrees with that of low-redshift star-forming galaxies, while BzK-21000 has a similar ratio to that of a dusty star-forming galaxy at z ~ 6. The high [O I]63 μm line luminosities observed in BzK-21000 and the z ~ 1-3 dusty and sub-mm luminous star-forming galaxies may be associated with extended reservoirs of low density, cool neutral gas.