The Radio Spectral Energy Distribution and Star-formation Rate Calibration in Galaxies
- Instituto de Astrofísica de Canarias, Vía Láctea S/N, E-38205 La Laguna (Spain)
- Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
- Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)
- Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
- Department of Astronomy and Joint Space Institute, University of Maryland, MD 20642 (United States)
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
- European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)
- Center for Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States)
- Unidad de Astronomía, Fac. Cs. Básicas, Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta (Chile)
- Department of Astronomy, University of MassachusettsAmherst, Amherst, MA 01003 (United States)
We study the spectral energy distribution (SED) of the radio continuum (RC) emission from the Key Insight in Nearby Galaxies Emitting in Radio (KINGFISHER) sample of nearby galaxies to understand the energetics and origin of this emission. Effelsberg multi-wavelength observations at 1.4, 4.8, 8.4, and 10.5 GHz combined with archive data allow us, for the first time, to determine the mid-RC (1–10 GHz, MRC) bolometric luminosities and further present calibration relations versus the monochromatic radio luminosities. The 1–10 GHz radio SED is fitted using a Bayesian Markov Chain Monte Carlo technique leading to measurements for the nonthermal spectral index (S{sub ν}∼ν{sup −α{sub n}{sub t}}) and the thermal fraction (f{sub th}) with mean values of α{sub nt}=0.97 ± 0.16(0.79 ± 0.15 for the total spectral index) and f{sub th} = (10 ± 9)% at 1.4 GHz. The MRC luminosity changes over ∼3 orders of magnitude in the sample, 4.3× 10{sup 2} L{sub ⊙} < MRC < 3.9× 10{sup 5} L{sub ⊙}. The thermal emission is responsible for ∼23% of the MRC on average. We also compare the extinction-corrected diagnostics of the star-formation rate (SFR) with the thermal and nonthermal radio tracers and derive the first star-formation calibration relations using the MRC radio luminosity. The nonthermal spectral index flattens with increasing SFR surface density, indicating the effect of the star-formation feedback on the cosmic-ray electron population in galaxies. Comparing the radio and IR SEDs, we find that the FIR-to-MRC ratio could decrease with SFR, due to the amplification of the magnetic fields in star-forming regions. This particularly implies a decrease in the ratio at high redshifts, where mostly luminous/star-forming galaxies are detected.
- OSTI ID:
- 22869317
- Journal Information:
- Astrophysical Journal, Vol. 836, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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