The far-infrared/radio correlation as probed by Herschel
Berta, S.; Magnelli, B.; Nordon, R.; Lutz, D.; Altieri, B.; Andreani, P.; Aussel, H.; Cepa, J.; Cimatti, A.; Daddi, E.; Elbaz, D.; Genzel, R.; Maiolino, R.; Pérez-Fournon, I.; Poglitsch, A.; Popesso, P.; Pozzi, F.; Riguccini, L.; Rodighiero, G.; Sturm, E.; Valtchanov, I.; Ivison, R. J.; Omont, A.; Clements, D. L.; Lagache, G.; Scott, D.; Buat, V.; Burgarella, D.; Dwek, E.; Wang, L.; Hatziminaoglou, E.; Franceschini, A.; Bock, J.; Cooray, A.; Farrah, D.; Ibar, E.; Marchetti, L.; Oliver, S. J.; Page, M. J.; Rigopoulou, D.; Roseboom, I. G.; Symeonidis, M.; Vaccari, M.; Saintonge, A.; Conley, A.; Santini, P.; Auld, R.; Cava, A.; Eales, S.; Vieira, J.; Panuzzo, P.; Boselli, A.; Amblard, A.; Arumugam, V.; Babbedge, T.; Blain, A.; Bongiovanni, A.; Castro-Rodríguez, N.; Chanial, P.; Cirasuolo, M.; Conversi, L.; Dominguez, H.; Dowell, C. D.; Förster Schreiber, N.; Fox, M.; Gear, W.; Glenn, J.; Griffin, M.; Gruppioni, C.; Halpern, M.; Isaak, K.; Levenson, L.; Lu, N.; Madden, S.; Maffei, B.; Magdis, G.; Mainetti, G.; Morrison, G. E.; Mortier, A. M. J.; Nguyen, H. T.; O'Halloran, B.; Owen, F. N.; Papageorgiou, A.; Pearson, C. P.; Pérez García, A. M.; Pohlen, M.; Rawlings, J. I.; Raymond, G.; Rizzo, D.; Rowan-Robinson, M.; Sanchez Portal, M.; Schulz, B.; Seymour, N.; Shao, L.; Shupe, D. L.; Smith, A. J.; Stevens, J. A.; Tacconi, L.; Trichas, M.; Tugwell, K. E.; Vigroux, L.; Ward, R.; Wright, G.; Xu, C. K.; Zemcov, M.
United Kingdom, Germany, Italy, France, Spain, United States, Canada
Abstract
We set out to determine the ratio, qIR, of rest-frame 8-1000-μm flux, SIR, to monochromatic radio flux, S1.4 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 LIR-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, qIR, 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.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.