The key diagnostic of the warm star-forming molecular clouds in galaxies is provided by their cooling radiation: [CII] and [OI] lines, but also lines of CO, the main tracer of molecular gas. While in our Galaxy cooling by CO lines is unimportant, this situation is totally different in local ULIRGs, where the CO is an important coolant, and the thermal balance is totally different from that in our Galaxy. These results demonstrate the enormous, as yet almost unexplored, diagnostic power of these lines for probing physical conditions. Since these lines are very luminous, they can be used to probe galaxies out to very high redshifts.
Here we propose a systematic study with the SPIRE-FTS and PACS of the principal neutral gas cooling lines ([CII], [OI] and the CO ladder from 5-4 to 13-12) in a 60 micron flux-limited sample of 32 galaxies: 24 LIRGs and 8 ULIRGs. Aims of this key project are: - analysis of the neutral gas cooling budget, in particular the relative importance of CO and [CII] emission; - analysis of the CO rotational ladder to derive the mass of molecular gas as a function of temperature and density; - modeling of the data using advanced PDR/XDR models with the goal of separating UV-excited (starburst) and X-ray excited (AGN) components; - analysis of the implications for molecular mass measurements based on CO lines, both at low and high redshift; - achieving statistical robustness, so that inferences can be made on the infrared galaxy population in general, and trends with other galaxy characteristics (IR luminosity, type of power source,.) can be traced.
Only Herschel can provide the necessary high-J CO and cooling line data. Combined with our extensive ground-based data (low-J CO, HCN lines) this dataset will elucidate the energy source and physical conditions in local ULIRGs, and establish the critical lin...k necessary for the interpretation of observations of high-z galaxies in mid-J CO lines and other luminous lines, which will become routine in the ALMA era.
Publication
Strong C+ Emission in Galaxies at z virgul 1-2: Evidence for Cold Flow Accretion Powered Star Formation in the Early Universe . Brisbin Drew et al. . The Astrophysical Journal, Volume 799, Issue 1, article id. 13, 18 pp. (2015). . 799 . 10.1088\/0004-637X\/799\/1\/13 . 2015ApJ...799...13B , A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies . Díaz-Santos T. et al. . The Astrophysical Journal, Volume 846, Issue 1, article id. 32, 22 pp. (2017). . 846 . 10.3847\/1538-4357\/aa81d7 . 2017ApJ...846...32D , Far-infrared Line Spectra of Active Galaxies from the Herschel/PACS Spectrometer: The Complete Database . Fernández-Ontiveros Juan Antonio et al. . The Astrophysical Journal Supplement Series, Volume 226, Issue 2, article id. 19, 26 pp. (2016). . 226 . 10.3847\/0067-0049\/226\/2\/19 . 2016ApJS..226...19F , Extended [C II] Emission in Local Luminous Infrared Galaxies . Díaz-Santos T. et al. . The Astrophysical Journal Letters, Volume 788, Issue 1, article id. L17, 5 pp. (2014). . 788 . 10.1088\/2041-8205\/788\/1\/L17 . 2014ApJ...788L..17D , Regulating Star Formation in Nearby Dusty Galaxies: Low Photoelectric Efficiencies in the Most Compact Systems . McKinney J. et al. . The Astrophysical Journal . null . null . 2021ApJ...908..238M , The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types . De Looze Ilse et al. . Astronomy & Astrophysics, Volume 568, id.A62, 34 pp. . 568 . 10.1051\/0004-6361\/201322489 . 2014A&A...568A..62D ..., Measuring Star Formation Rate and Far-infrared Color in High-redshift Galaxies Using the CO(7-6) and [N II] 205 μm Lines . Lu Nanyao et al. . The Astrophysical Journal Letters, Volume 802, Issue 1, article id. L11, 6 pp. (2015). . 802 . 10.1088\/2041-8205\/802\/1\/L11 . 2015ApJ...802L..11L , The Herschel Comprehensive (U)LIRG Emission Survey (HERCULES): CO Ladders, Fine Structure Lines, and Neutral Gas Cooling . Rosenberg M. J. F. et al. . The Astrophysical Journal, Volume 801, Issue 2, article id. 72, 18 pp. (2015). . 801 . 10.1088\/0004-637X\/801\/2\/72 . 2015ApJ...801...72R , The Local [C II] 158 μm Emission Line Luminosity Function . Hemmati Shoubaneh et al. . The Astrophysical Journal, Volume 834, Issue 1, article id. 36, 10 pp. (2017). . 834 . 10.3847\/1538-4357\/834\/1\/36 . 2017ApJ...834...36H , Neon and [C II] 158 μm Emission Line Profiles in Dusty Starbursts and Active Galactic Nuclei . Samsonyan Anahit et al. . The Astrophysical Journal Supplement Series, Volume 226, Issue 1, article id. 11, 18 pp. (2016). . 226 . 10.3847\/0067-0049\/226\/1\/11 . 2016ApJS..226...11S , Early Science with the Large Millimeter Telescope: CO and [C II] Emission in the z = 4.3 AzTEC J095942.9+022938 (COSMOS AzTEC-1) . Yun Min S. et al. . Monthly Notices of the Royal Astronomical Society, Volume 454, Issue 4, p.3485-3499 . 454 . 10.1093\/mnras\/stv1963 . 2015MNRAS.454.3485Y , Explaining the [C II]157.7 μm Deficit in Luminous Infrared Galaxies—First Results from a Herschel/PACS Study of the GOALS Sample . Díaz-Santos T. et al. . The Astrophysical Journal, Volume 774, Issue 1, article id. 68, 13 pp. (2013). . 774 . 10.1088\/0004-637X\/774\/1\/68 . 2013ApJ...774...68D ,
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.
