BLAST: the far-infrared/radio correlation in distant galaxies (original) (raw)

2010, Monthly Notices of the Royal Astronomical Society

We investigate the correlation between far-infrared (FIR) and radio luminosities in distant galaxies, a lynchpin of modern astronomy. We use data from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), Spitzer, the Large Apex BOlometer Cam-erA (LABOCA), the Very Large Array (VLA) and the Giant Metre-wave Radio Telescope (GMRT) in the Extended Chandra Deep Field South (ECDFS). For a catalogue of BLAST 250-µm-selected galaxies, we re-measure the 70-870-µm flux densities at the positions of their most likely 24-µm counterparts, which have a median [interquartile] redshift of 0.74 [0.25, 1.57]. From these, we determine the monochromatic flux density ratio, q 250 (= log 10 [S 250µm /S 1,400MHz ]), and the bolometric equivalent, q IR . At z ≈ 0.6, where our 250-µm filter probes rest-frame 160-µm emission, we find no evolution relative to q 160 for local galaxies. We also stack the FIR and submm images at the positions of 24-µm-and radio-selected galaxies. The difference between q IR seen for 250-µm-and radio-selected galaxies suggests star formation provides most of the IR luminosity in < ∼ 100-µJy radio galaxies, but rather less for those in the mJy regime. For the 24-µm sample, the radio spectral index is constant across 0 < z < 3, but q IR exhibits tentative evidence of a steady decline such that q IR ∝ (1 + z) −0.15±0.03 -significant evolution, spanning the epoch of galaxy formation, with major implications for techniques that rely on the FIR/radio correlation. We compare with model predictions and speculate that we may be seeing the increase in radio activity that gives rise to the radio background.