Paper detail

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

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.