We present an analysis of O I 63 [ ] , [O III] 88 , [N II] 122 , and C II 158 [ ] far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ∼240 local luminous infrared galaxies (LIRGs) in the Great Observatories Allsky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for [ ] is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, n H , and intensity of the interstellar radiation field, G, in units of G 0 and find G/n H ratios of ∼0.1-50 G 0 cm 3 , with ULIRGs populating the upper end of the distribution. There is a relation between G/n H and IR

We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These new images have both the angular resolution to study the detailed morphologies of the two nuclei that power the galaxy merger and sensitivity to a wide range of spatial scales. At 33 GHz, we achieve a resolution of 0. 081 × 0. 063 (29.9 × 23.3 pc) and resolve the radio emission surrounding both nuclei. We conclude from the decomposition of the radio spectral energy distribution that a majority of the 33 GHz emission is synchrotron radiation. The spatial distributions of radio emission in both nuclei are well-described by exponential profiles. These have deconvolved half-light radii (R 50d ) of 51 and 35 pc for the eastern and western nuclei, respectively, and they match the number density profile of radio supernovae observed with very long baseline interferometry. This similarity might be due to the fast cooling of cosmic rays electrons caused by the presence of a strong (∼ mG) magnetic field in this system. We estimate extremely high molecular gas surface densities of 2.2 +2.1 −1.0 × 10 5 (east) and 4.5 +4.5 −1.9 × 10 5 (west) M pc −2 , corresponding to total hydrogen column densities of N H = 2.7 +2.7 −1.2 × 10 25 (east) and 5.6 +5.5 −2.4 × 10 25 cm −2 (west). The implied gas volume densities are similarly high, n H 2 ∼ 3.8 +3.8 −1.6 10 4 (east) and ∼ 11 +12 −4.5 × 10 4 cm −3 (west). We also estimate very high luminosity surface densities of Σ IR ∼ 4.2 +1.6 −0.7 × 10 13 (east) and Σ IR ∼ 9.7 +3.7 −2.4 × 10 13 (west) L kpc −2 , and star formation rate surface densities of Σ SFR ∼ 10 3.7±0.1 (east) and Σ SFR ∼ 10 4.1±0.1 (west) M yr −1 kpc −2 . These values, especially for the western nucleus are, to our knowledge, the highest luminosity surface densities and star formation rate surface densities measured for any star-forming system. Despite these high values, the nuclei appear to lie below the dusty Eddington limit in which radiation pressure is balanced only by self-gravity. The small measured sizes also imply that at wavelengths shorter than λ = 1 mm, dust absorption effects must play an important role in the observed light distribution while below 5 GHz free-free absorption contributes substantial opacity. According to these calculations, the nuclei of Arp 220 are only transparent in the frequency range ∼ 5 to 350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.14 Lonsdale et al. (2006) report offsets from the center of Arp 220, which we take to be α 2000 = 15 h 34 m 57.259 s , δ 2000 = 23 • 30 11 .409.

For L IR - The best-fit lines in Figure 6 of the original article are correct and the conclusions of the paper are not affected. We thank Iván Oteo for bringing the discrepancy in the original paper to our attention. , and J HNC 1 0 ( ) =  , for a sample of 58 local luminous and ultraluminous infrared galaxies from the Great Observatories All-sky LIRG Survey (GOALS). By combining our new IRAM data with literature data and Spitzer/IRS spectroscopy, we study the correspondence between these putative tracers of dense gas and the relative contribution of active galactic nuclei (AGNs) and star formation to the mid-infrared luminosity of each system. We find the HCN (1-0) emission to be enhanced in AGN-dominated systems (áL HCN 1 0 ¢ + emission do not appear to have a simple interpretation in terms of the AGN dominance or the star formation rate, and are likely determined by multiple processes, including density and radiative effects.