A Herschel Space Observatory Spectral Line Survey of Local Luminous Infrared Galaxies from 194 to 671 Microns^∗

Abstract

We describe a Herschel Space Observatory 194-671 μm spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO J to J-1 rotational transitions for   J 4 13, the [N II] 205 μm line, the [C I] lines at 609 and 370 μm, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at J4 and likely represents the same gas phase traced by CO (1−0), and (ii) a warm component, which dominates over the mid-J regime (4<J10) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at J>10. The flux ratios of the two [C I] lines imply modest excitation temperatures of 15-30 K; the [C I] 370 μm line scales more linearly in flux with CO (4−3) than with CO (7−6). These findings suggest that the [C I] emission is predominantly associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of H O 2 vapor as a function of the FIR color in a direction consistent with infrared photon pumping.

A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies

“…We note that we do not apply the correction factors to the [N II] 205 μm emission based on the FIR color of galaxies provided in Lu et al (2017). We use instead the original, point-source calibrated fluxes since we do not use those corrections in our Herschel/PACS data.…”

The ‘Red Radio Ring’: ionized and molecular gas in a starburst/active galactic nucleus at z ∼ 2.55

“…Its molecular gas excitation hints at the ex- istence of a strong heating source. To account for the strong mid-J CO lines observed in NGC 253 and NGC 891, both Hailey-Dunsheath et al (2008); Nikola et al (2011) both invoke the need for strong mechanical heating/shocks from a turbulent star-forming environment (see also Kamenetzky et al 2016;Lu et al 2017). The high-J turnover (at Jup ≥ 5) and tail of the CO SLED indicates that the CO excitation is, however, not as extreme as in the highly excited QSO systems (Weiß et al 2007;Salomé et al 2012).…”

“…Using the SPIFI spectrometer on the AST/RO telescope at South Pole, Oberst et al (2006Oberst et al ( , 2011 (Goldsmith et al 2015), and demonstrated that most of the [Nii] line arises from extended, low density (n e − ∼ 10 to 50 cm −3 ) Hii regions. Other efforts to use [Nii] to derive average electron densities have been made in a range of local galaxies (n e − ∼ 20-100 cm −3 ), for instance: M51 and Centaurs A, (Parkin et al 2013), Ultra-luminous Infrared Galaxies ULIRGs (HERUS sample;Farrah et al 2013), Dwarf galaxies (Cormier et al 2015), KINGFISH galaxies (Herrera-Camus et al 2016) and other SFGs (Lu et al 2017).…”

Central molecular zones in galaxies:12CO-to-13CO ratios, carbon budget, andXfactors

“…The newly determined multi-transition 12 COto-13 CO isotopologue ratios allow us to determine more accurately the CO gas column densities and their relation to the much more abundant H 2 gas, including the values of X in a large number of galaxy central regions. The analysis of the 12 CO and 13 CO spectral lines is of particular importance in the interpretation of the Herschel Space Observatory (2009-2013) observations of galaxies in the two submillimeter [CI] lines and the farinfrared [CII] line (Israel et al 2015;Kamenetzky et al 2016;Fernández-Ontiveros et al 2016;Lu et al 2017;Croxall et al 2017;Díaz-Santos et al 2017;and Herrera-Camus et al 2018). With it, we will place significant constraints on the relation between molecular and atomic carbon and determine the carbon budget in the observed galaxy centers.…”

“…Figure 13CO fraction of all C6.2. Neutral atomic carbon fractionWe took central[CI] line data from the compilations byIsrael et al (2015),Kamenetzky et al (2016), andLu et al (2017).…”