The far-infrared emitting region in local galaxies and QSOs: Size and scaling relations

Abstract

We use Herschel 70 to 160 µm images to study the size of the far-infrared emitting region in about 400 local galaxies and quasar (QSO) hosts. The sample includes normal 'main-sequence' star-forming galaxies, as well as infrared luminous galaxies and Palomar-Green QSOs, with different levels and structures of star formation. Assuming Gaussian spatial distribution of the far-infrared (FIR) emission, the excellent stability of the Herschel point spread function (PSF) enables us to measure sizes well below the PSF width, by subtracting widths in quadrature. We derive scalings of FIR size and surface brightness of local galaxies with FIR luminosity, with distance from the star-forming main-sequence, and with FIR color. Luminosities L FIR ∼10 11 L ⊙ can be reached with a variety of structures spanning 2 dex in size. Ultraluminous L FIR 10 12 L ⊙ galaxies far above the main-sequence inevitably have small R e,70 ∼0.5 kpc FIR emitting regions with large surface brightness, and can be close to optically thick in the FIR on average over these regions. Compared to these local relations, first ALMA sizes for the dust emission regions in high redshift galaxies, measured at somewhat longer rest wavelengths, suggest larger sizes at the same IR luminosity. We report a remarkably tight relation with 0.15 dex scatter between FIR surface brightness and the ratio of [Cii] 158 µm emission and FIR emission -the so-called [Cii]-deficit is more tightly linked to surface brightness than to FIR luminosity or FIR color. Among 33 z≤0.1 PG QSOs with typical L FIR /L Bol,AGN ≈0.1, 19 have a measured 70 µm half light radius, with median R e,70 =1.1 kpc. This is consistent with the FIR size for galaxies with similar L FIR but lacking a QSO, in accordance with a scenario where the rest FIR emission of these types of QSOs is, in most cases, due to host star formation.

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

“…The fits have been set to the maximum value of the respective quadratic equation below the wavelength at which the maximum is reached, such that the ratio remains constant. For reference, in the panel showing the C II 158 [ ] deficit we also plot the best fit found by Lutz et al (2016) using the same parameterization (dashed line; within the errors of our fit) and the best fit originally found by Díaz-Santos et al (2013) using galaxy sizes measured in the MIR with Spitzer and assuming a linear log-log relation (dot-dashed line). (Ferland et al 1998) by increasing the ionization parameter from log(U )∼−2.5 to −1.5 (Voit 1992;Abel et al 2009;Graciá-Carpio et al 2011;Fischer et al 2014 The total luminosity of an optically thin modified blackbody (mBB) increases as a function of its temperature as T 4 b + , where β is the emissivity index of the emitting material.…”

Kiloparsec-Scale Dust Disks in High-Redshift Luminous Submillimeter Galaxies

“…Sérsic profile fits reveal that the galaxies have a median effective radius of R e =0 24±0 02at a rest wavelength of l m 250 m (for a typical source redshift ofz 2.5), corresponding to a typical physical size of =  R 1.8 e 0.2 kpc. In contrast, Herschel 70-160 μm imaging of 400 local galaxies and QSO hosts suggests that ULIRGs are exclusively found with very compact (R 0.5 e kpc) morphologies (albeit at shorter rest wavelengths of l m 70 m; Lutz et al 2016). This confirms earlier suggestions from CO observations and marginally resolved radio and submillimeter data (e.g., Chapman et al 2004;Carilli et al 2010;Ivison et al 2010Ivison et al , 2011Hodge et al 2013a;De Breuck et al 2014;Gilli et al 2014;Simpson et al 2015b;Ikarashi et al 2015;Miettinen et al 2015) that high-redshift dusty star-forming galaxies are indeed larger than similarly luminous local galaxies.…”

The Dust and [C ii] Morphologies of Redshift ∼4.5 Sub-millimeter Galaxies at ∼200 pc Resolution: The Absence of Large Clumps in the Interstellar Medium at High-redshift

“…This follows the relation seen by Smith et al (2017) for local star-forming galaxies. A higher star formation rate surface density in the L C II to L FIR ratio as a function of the star formation rate density for local galaxies in the KINGFISH and GOALS (Armus et al 2009;Lutz et al 2016;Díaz-Santos et al 2017), a sample of high-redshift galaxies (Wang et al 2013;Capak et al 2015;Gullberg et al 2015;Kimball et al 2015;Lutz et al 2016;Nesvadba et al 2016;Díaz-Santos et al 2017;Jones et al 2017;Umehata et al 2017;Venemans et al 2017), and our sample of four z∼4.5 SMGs. We note that the sizes used to achieve the star formation rate densities for the GOALS sample are the 70 μm effective radii under the assumption of a uniform dust temperature.…”

“…Figure 6 shows [ ] L C II /L FIR as function of star formation rate surface density for the low-redshift KINGFISH sample (Kennicutt et al 2011;Dale et al 2016;Croxall et al 2017), the GOALS sample (Díaz-Santos et al 2013;Lutz et al 2016), and a high-redshift sample of SMGs (Gullberg et al 2015;Lutz et al 2016, typically lensed). example of a simulated 345 GHz continuum map of a smooth exponential disk observed with the same observational parameters as the data shown in the map to the left.…”

“…For galaxies with L FIR <10 11 L e , the [ ] L C II /L FIR ratio is constant at ∼1%; however, at L FIR >10 11 L e , the [ ] L C II /L FIR ratio decreases to ∼0.1%-0.01%. This decrease is known as the "[C II] deficit," and many attempts have been made over the past two decades to investigate its origin (e.g., Hailey-Dunsheath et al 2010;Ivison et al 2010;Stacey et al 2010;Graciá-Carpio et al 2011;Valtchanov et al 2011;Farrah et al 2013;Gullberg et al 2015;Lutz et al 2016;Díaz-Santos et al 2017).…”