HERUS: The Far-IR/Submm Spectral Energy Distributions of Local ULIRGs & Photometric Atlas

TL;DR

This paper presents Herschel-SPIRE photometry for 43 local ULIRGs, analyzes their far-IR spectral energy distributions, and compares their dust properties with other galaxy samples, revealing warmer dust temperatures in ULIRGs.

Contribution

The study provides the first comprehensive Herschel-SPIRE photometric atlas for a complete flux-limited sample of local ULIRGs, analyzing their dust properties and comparing them with other galaxy populations.

Findings

ULIRGs have warmer dust (median T = 37.9 K) than non-ULIRG galaxies.

Dust masses in ULIRGs are significantly higher (10^7.5 to 10^9 Msun).

Differences with high-redshift samples may be due to selection effects.

Abstract

We present the Herschel-SPIRE photometric atlas for a complete flux limited sample of 43 local Ultraluminous Infrared Galaxies (ULIRGs), selected at 60${\mu}$m by IRAS, as part of the HERschel ULIRG Survey (HERUS). Photometry observations were obtained using the SPIRE instrument at 250, 350 and 500${\mu}$m. We describe these observations, present the results, and combine the new observations with data from IRAS to examine the far-IR spectral energy distributions (SEDs) of these sources. We fit the observed SEDs of HERUS objects with a simple parameterised modified black body model where temperature and emissivity $\beta$ are free parameters. We compare the fitted values to those of non-ULIRG local galaxies, and find, in agreement with earlier results, that HERUS ULIRGs have warmer dust (median temperature T = 37.9+/-4.7 K compared to 21.3+/-3.4 K) but a similar $\beta$ distribution (median $\beta$ = 1.7 compared to 1.8) to the Herschel reference sample (HRS, Cortese et al., 2014) galaxies. Dust masses are found to be in the range of 10^7.5 to 10^9 Msun significantly higher than that of Herschel Reference Sample (HRS) sources. We compare our results for local ULIRGs with higher redshift samples selected at 250 and 850${\mu}$m. These latter sources generally have cooler dust and/or redder 100-to-250 ${\mu}$m colours than our 60${\mu}$m-selected ULIRGs. We show that this difference may in part be the result of the sources being selected at different wavelengths rather than being a simple indication of rapid evolution in the properties of the population.