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Title:
A detailed study of the radio-FIR correlation in NGC 6946 with Herschel-PACS/SPIRE from KINGFISH
Authors:
Tabatabaei, F. S.; Schinnerer, E.; Murphy, E. J.; Beck, R.; Groves, B.; Meidt, S.; Krause, M.; Rix, H.-W.; Sandstrom, K.; Crocker, A. F.; Galametz, M.; Helou, G.; Wilson, C. D.; Kennicutt, R.; Calzetti, D.; Draine, B.; Aniano, G.; Dale, D.; Dumas, G.; Engelbracht, C. W.; Gordon, K. D.; Hinz, J.; Kreckel, K.; Montiel, E.; Roussel, H.
Affiliation:
AA(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany ), AB(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AC(Observatories of the Carnegie Institution for Science, Pasadena, CA, 91101, USA), AD(Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany), AE(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AF(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AG(Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany), AH(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AI(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AJ(Department of Astronomy, University of Massachusetts, Amherst, MA, 01003, USA), AK(Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK), AL(Infrared Processing and Analysis Center, MS 100-22, Pasadena, CA, 91125, USA), AM(Department of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada), AN(Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK), AO(Department of Astronomy, University of Massachusetts, Amherst, MA, 01003, USA), AP(Princeton University Observatory, Peyton Hall, Princeton, NJ, 08544-1001, USA), AQ(Princeton University Observatory, Peyton Hall, Princeton, NJ, 08544-1001, USA), AR(Department of Physics & Astronomy, University of Wyoming, Laramie, WY, 82071, USA), AS(Institut de RadioAstronomie Millimétrique, 38406, Grenoble, France), AT(Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ, 85721, USA; Raytheon Company, 1151 E. Hermans Road, Tucson, AZ, 85756, USA), AU(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA), AV(Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ, 85721, USA), AW(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany), AX(Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ, 85721, USA), AY(Institut d'Astrophysique de Paris, Université Pierre et Marie Curie (UPMC), CNRS (UMR 7095), 75014, Paris, France)
Publication:
Astronomy & Astrophysics, Volume 552, id.A19, 18 pp. (A&A Homepage)
Publication Date:
04/2013
Origin:
EDP Sciences
Astronomy Keywords:
galaxies: individual: NGC 6946, radio continuum: ISM, ISM: magnetic fields, infrared: ISM, galaxies: star formation
DOI:
10.1051/0004-6361/201220249
Bibliographic Code:
2013A&A...552A..19T

Abstract

We derive the distribution of the synchrotron spectral index across NGC 6946 and investigate the correlation between the radio continuum (synchrotron) and far-infrared (FIR) emission using the KINGFISH Herschel-PACS and SPIRE data. The radio-FIR correlation is studied as a function of star formation rate, magnetic field strength, radiation field strength, and the total gas surface density. The synchrotron emission follows both star-forming regions and the so-called magnetic arms present in the inter-arm regions. The synchrotron spectral index is steepest along the magnetic arms (alphan ~ 1), while it is flat in places of giant Hii regions and in the center of the galaxy (alphan ~ 0.6-0.7). The map of alphan provides observational evidence for aging and energy loss of cosmic ray electrons (CREs) propagating in the disk of the galaxy. Variations in the synchrotron-FIR correlation across the galaxy are shown to be a function of both star formation and magnetic field strength. We find that the synchrotron emission correlates better with cold rather than with warm dust emission, when the diffuse interstellar radiation field is the main heating source of dust. The synchrotron-FIR correlation suggests a coupling between the magnetic field and the gas density. NGC 6946 shows a power-law behavior between the total (turbulent) magnetic field strength B and the star formation rate surface density SigmaSFR with an index of 0.14 (0.16) ± 0.01. This indicates an efficient production of the turbulent magnetic field with the increasing gas turbulence expected in actively star forming regions. Moreover, it is suggested that the B-SigmaSFR power law index is similar for the turbulent and the total fields in normal galaxies. On the other hand, for galaxies interacting with the cluster environment this index is steeper for turbulent magnetic fields than it is for the total magnetic fields. The scale-by-scale analysis of the synchrotron-FIR correlation indicates that the ISM affects the propagation of old/diffused CREs, resulting in a diffusion coefficient of D0 = 4.6 × 1028 cm2 s-1 for 2.2 GeV CREs.

Maps as FITS files are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A19


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