Description |
One of the biggest challenges in galaxy evolution is to understand how star formation is powered in high-redshift star-forming galaxies. Recent discovery of unusually strong (EW > 500A) Halpha emission in majority of z>4 star-forming galaxies has provided indirect evidence that significant fraction of high-redshift star formation is fueled by mechanisms other than gas-rich merger, suggesting that cold gas accretion is an important source of cold, neutral gas in high-redshift galaxies. FIR cooling lines such as CII 158 micron line, produced by the UV stellar radiation like Halpha, afford an efficient probe to study physical properties of the interstellar medium in star-forming galaxies. Therefore, we propose to observe CII emission line from local counterparts of high-redshift strong Halpha Emitters to investigate the properties of cold neutral gas in these galaxies and understand how star formation is powered. We request total 11.1 hours of Herschel/PACS observation using Line Spectroscopy AOT for 20 targets, detecting the expected CII line with line S/N of >3. Unlike the IR-luminous galaxies or QSOs, HAEs are typical star-forming galaxies at high redshifts thus CII observation of local HAEs would provide the first measurement of CII and CII/FIR ratio of typical high-redshift star-forming galaxies. Thanks to the existing data including spectroscopy, the relationship between the observed CII and Halpha, FIR luminosity can be investigated as a function of metallicity, stellar population, extinction, etc. Such relationship would be able to tell whether CII/FIR ratio can be used as an indicator that discriminates merger-driven star formation and cold-flow driven star formation. Using the last opportunity of Herschel to access rest-frame FIR cooling lines of local galaxies, this observing program would provide a detailed physical framework for interpretation of future large CII surveys in galaxies at higher redshifts using existing or planned submm to radio facilities. |