Herschel-ATLAS/GAMA: What determines the far-infrared properties of radio-galaxies?

TL;DR

This study uses stacking analysis of Herschel and GAMA data to explore how the far-infrared properties of radio galaxies relate to their radio luminosity, size, and environment, revealing that massive radio galaxies tend to have lower FIR luminosities and that compact sources show higher dust temperatures.

Contribution

It provides new insights into the FIR properties of radio galaxies, showing no direct relation with radio luminosity and highlighting environmental effects and source size on dust temperature and luminosity.

Findings

No correlation between L250 and L_1.4GHz after mass and redshift correction.

Massive radio galaxies (>1.5 L_{K}^{*}) have lower FIR luminosities than non-radio counterparts.

Compact radio sources have higher dust temperatures and FIR luminosities than extended sources.

Abstract

We perform a stacking analysis of H-ATLAS data in order to obtain isothermal dust temperatures and rest-frame luminosities at 250um (L250), for 1599 radio sources over the H-ATLAS P1 GAMA area. The radio sample is generated using a combination of NVSS data and K-band UKIDSS-LAS data, over 0.01<z<0.8. The FIR properties of the sample are investigated as a function of L_1.4 GHz, z, projected radio-source size and radio spectral index. In order to search for stellar-mass dependent relations, we split the parent sample into those sources which are below and above 1.5 L_{K}^{*}. Correcting for stellar mass and redshift, we find no relation between the L250 and L_1.4GHz of radio AGN. This implies that a galaxy's nominal radio luminosity has little or no bearing on the SFR and/or dust mass content of the host system. The L250 of both the radio detected and non radio-detected galaxies (defined as those sources not detected at 1.4GHz but detected in the SDSS with r'<22) rises with increasing z. For mass and colour matched samples, sub-1.5 L_{K}^{*} and super-1.5 L_{K}^{*} radio-detected galaxies have 0.89\pm0.18 and 0.49\pm0.12 times the L250 of their non radio-detected counterparts. We explain these results in terms of the hotter, denser and richer halo environments massive radio-galaxies maintain and are embedded in. These results indicate that all massive radio galaxies (>1.5 L_{K}^{*}) may have systematically lower FIR luminosities (~25%) than their colour-matched non radio-detected counterparts. Compact radio sources (<30kpc) are associated with higher L250s and dust temperatures than their more extended (>30kpc) counterparts. The higher dust temperature suggests that this may be attributed to enhanced SFRs, but whether this is directly or indirectly due to radio activity (e.g. jet induced or merger-driven SF) is as yet unknown.