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Title: | The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies | Authors: | Tisanić, K. Smolčić, V. Delhaize, J. Novak, M. Intema, H. Delvecchio, I. Schinnerer, E. Zamorani, G. BONDI, MARCO Vardoulaki, E. |
Issue Date: | 2019 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 621 | First Page: | A139 | Abstract: | We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z ∼ 4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared-radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies' (SFGs) SED. To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published Very Large Array observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (z ∈ [0.3, 4], SFR ≥ 100 M<SUB>☉</SUB> yr<SUP>-1</SUP>) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from α<SUB>1</SUB> = 0.42 ± 0.06 below a rest-frame frequency of 4.3 GHz to α<SUB>2</SUB> = 0.94 ± 0.06 above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs ( SFR > 10 M<SUB>☉</SUB> yr<SUP>-1</SUP>) that show the SED of HSFGs to differ from the SED found for normal SFGs ( SFR < 10 M<SUB>☉</SUB> yr<SUP>-1</SUP>). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free-free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q - z trend in SFGs. The table of the cross-matched fluxes is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/621/A139">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/621/A139 | URI: | http://hdl.handle.net/20.500.12386/29460 | URL: | https://www.aanda.org/articles/aa/abs/2019/01/aa34002-18/aa34002-18.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201834002 | Bibcode ADS: | 2019A&A...621A.139T | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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File | Description | Size | Format | |
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aa34002-18.pdf | Pdf editoriale | 1.99 MB | Adobe PDF | View/Open |
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