|Hydrogen Fluoride Absorption Toward Luminous Infrared Galaxies
|We propose to carry out a HIFI survey of the fundamental transition of HF at 1.232 THz toward 24 relatively nearby IR-bright galaxies to probe their ISM physical conditions. HF is a very new tracer of the diffuse and dense ISM, with its use originating with the ISO detection of the J=2-1 transition in absorption toward Sgr B2. Widespread HF J=1-0 absorption toward galactic starforming regions has been recently detected by HIFI and HF emission in an extragalactic nucleus has been detected at low spectral resolution by SPIRE. We intend to make use of this unique probe by conducting a high spectral resolution (10-20 km-s) HIFI absorption survey toward continuum-bright external galactic nuclei exhibiting a wide range of physical properties (AGN, starbursts, mergers). HF is chemically very strongly bound and therefore resistant to photodissociation. Our study is facilitated by this resistance of HF molecules to destruction, which will occur in the extreme environments in the galactic nuclei. HF will thus be a very useful probe in regions of the ISM where more traditional gas probes, such as CO, are more prone to error (e.g., the use of the X-factor). With the simplifying assumption that all fluorine is likely to be locked up in HF, and that the HF molecules will reside in the ground rotational state, we can measure the hydrogen column density and mass of the nearby IR-bright galaxies. Observations of the local galaxies proposed here are the first step toward using HF as a tracer of the gas in high-redshift galaxies. By looking at extragalactic continuum-bright nuclei, we will also be able, through the use of the HIFI Wide Band Spectrometer, to simultaneously search for absorption through the Milky Way halo cloud population. Here, the rapid formation rate of HF and its strong molecular bond will allow us to detect HF absorption toward the tenuous and quiescent mostly HI clouds making up the galactic halo. These diffuse, co...ld regions may not otherwise be detectable in CO emission or other commonly uses tracers.
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT1_tphill01_1, SPG v14.1.0. https://doi.org/10.5270/esa-mceff0j