The far-infrared/radio correlation as probed by Herschel
Astronomy and Astrophysics 518:4 (2010)
Authors:
RJ Ivison, B Magnelli, E Ibar, P Andreani, D Elbaz, B Altieri, A Amblard, V Arumugam, R Auld, H Aussel, T Babbedge, S Berta, A Blain, J Bock, A Bongiovanni, A Boselli, V Buat, D Burgarella, N Castro-RodrÃguez, A Cava, J Cepa, P Chanial, A Cimatti, M Cirasuolo, DL Clements, A Conley, L Conversi, A Cooray, E Daddi, H Dominguez, CD Dowell, E Dwek, S Eales, D Farrah, N FörsterSchreiber, M Fox, A Franceschini, W Gear, R Genzel, J Glenn, M Griffin, C Gruppioni, M Halpern, E Hatziminaoglou, K Isaak, G Lagache, L Levenson, N Lu, D Lutz, S Madden, B Maffei, G Magdis, G Mainetti, R Maiolino, L Marchetti, GE Morrison, AMJ Mortier, HT Nguyen, R Nordon, B O'Halloran, SJ Oliver, A Omont, FN Owen, MJ Page, P Panuzzo, A Papageorgiou, CP Pearson, I Pérez-Fournon, AMP GarcÃa, A Poglitsch, M Pohlen, P Popesso, F Pozzi, JI Rawlings, G Raymond, D Rigopoulou, L Riguccini, D Rizzo, G Rodighiero, IG Roseboom, M Rowan-Robinson, A Saintonge, M SanchezPorta, P Santini, B Schulz, D Scott, N Seymour, L Shao, DL Shupe, AJ Smith, JA Stevens, E Sturm, M Symeonidis, L Tacconi, M Trichas, KE Tugwell, M Vaccari, I Valtchanov, J Vieira, L Vigroux
Abstract:
We set out to determine the ratio, qIR, of rest-frame 8-1000-μm flux, SIR, to monochromatic radio flux, S 1.4 GHz, for galaxies selected at far-infrared (IR) and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, Td, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation (FIRRC) is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-μm and 1.4-GHz samples, obtained using Herschel and the Very Large Array (VLA) in GOODS-North (-N). We determine bolometric IR output using ten bands spanning λobs = 24-1250 μm, exploiting data from PACS and SPIRE (PEP; HerMES), as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L IR-matched sample, designed to reveal evolution of qIR with redshift, spanning log LIR = 11-12 L⊙ and z = 0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies in GOODS-N, we see tentative evidence of a break in the flux ratio, q IR, at L1.4 GHz ∼ 1022.7 W Hz-1, where active galactic nuclei (AGN) are starting to dominate the radio power density, and of weaker correlations with redshift and Td. From our 250-μm-selected sample we identify a small number of far-IR-bright outliers, and see trends of qIR with L1.4 GHz, LIR, Td and redshift, noting that some of these are inter-related. For our LIR-matched sample, there is no evidence that qIR changes significantly as we move back into the epoch of galaxy formation: we find qIR (1+z)γ, where γ = -0.04±0.03 at z = 0-2; however, discounting the least reliable data at z < 0.5 we find γ = -0.26±0.07, modest evolution which may be related to the radio background seen by ARCADE 2, perhaps driven by <10-μJy radio activity amongst ordinary star-forming galaxies at z>1. © ESO 2010.
