Far-Infrared Fine-Structure Line Diagnostics of Ultraluminous Infrared Galaxies

Abstract

We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z < 0.27. The lines, [O III]52µm, [N III]57µm, [O I]63µm, [N II]122µm, [O I]145µm, and [C II]158µm, are mostly single gaussians with widths <600 km s −1 and luminosities of 10 7 − 10 9 L ⊙ . There are deficits in the [O I]63/L IR , [N II]/L IR , [O I]145/L IR , and [C II]/L IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10 1 < n < 10 2.5 and 10 2.2 < G 0 < 10 3.6 , respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

Dusty star-forming galaxies at high redshift

“…Luhman et al, 1998;Abel et al, 2009;Papadopoulos et al, 2010;Sargsyan et al, 2012). Based on the existence of a deficit in [NII] (among other lines, such as [OI], Farrah et al (2013) proposed a combination of a harsher interstellar radiation field in HII regions with increased dust grain charging in the ISM as a potential origin of the line deficits. In Figure 48, we plot the current state of CII-FIR measurements for low and high-z galaxies.…”

“…These authors further suggest that the [CII]-FIR deficit therefore owes to increased contribution to the infrared luminosity by embedded AGN. Farrah et al (2013) report an empirical calibration of the [CII]-SFR relation as well.…”

“…Some of this scatter may owe to the fact that [CII] can arise from both neutral and ionized gas. Sargsyan et al (2012) and Farrah et al (2013) show a ∼ 1 dex scatter in their SFR-[CII] relations.…”

“…The local data is compiled by Brauher et al (2008), with new data by Díaz-Santos et al (2013) from the GOALS survey included as well. The data at moderate redshifts is from Farrah et al (2013) and Rigopoulou et al (2014). The high-z data is subdivided into quasars and SMGs, and comes from Cox et al (2011) Willott et al (2013) A number of studies have used extremely high resolution [CII] observations to constrain the size of the emitting region of high-z quasar host galaxies.…”

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

“…The only low-z [CII] samples have been observed with airborne (Crawford et al 1986;Stacey et al 1991a) or space based observatories (Malhotra et al 2001;Brauher et al 2008;Díaz-Santos et al 2013;Farrah et al 2013;Sargsyan et al 2014;De Looze et al 2014). Submillimetre atmospheric windows provide some access to the line from the ground at z > 1, with atmospheric transparency continuing to improve towards higher redshifts (longer wavelengths).…”