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Radio continuum properties of luminous infrared galaxies Identifying the presence of an AGN in the radio

Vardoulaki, E. and Charmandaris, V. and Murphy, E. J. and Díaz-Santos, T. and Armus, L. and Evans, A. S. and Mazzarella, J. M. and Privon, G. C. and Stierwalt, S. and Barcos-Muñoz, L. (2015) Radio continuum properties of luminous infrared galaxies Identifying the presence of an AGN in the radio. Astronomy and Astrophysics, 574 . Art. No. A4. ISSN 0004-6361.

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Context. Luminous infrared galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. Aims. The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z< 0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of active galactic nuclei (AGN). Methods. We used the archival data at 1.49 and 8.44 GHz to create radio-spectral-index maps using the standard relation between flux density S_ν and frequency ν, S_ν ~ ν^(−α), where α is the radio spectral index. By studying the spatial variations in α, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2 μm PAH feature) and optical (BPT diagram) AGN diagnostics. Results. We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on the mid-infrared and optical AGN diagnostics presented in this study.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Vardoulaki, E.0000-0002-4437-1773
Charmandaris, V.0000-0002-2688-1956
Murphy, E. J.0000-0001-7089-7325
Díaz-Santos, T.0000-0003-0699-6083
Armus, L.0000-0003-3498-2973
Evans, A. S.0000-0003-2638-1334
Mazzarella, J. M.0000-0002-8204-8619
Privon, G. C.0000-0003-3474-1125
Stierwalt, S.0000-0002-2596-8531
Barcos-Muñoz, L.0000-0003-0057-8892
Additional Information:© 2015 ESO. Received 3 May 2014. Accepted 11 August 2014. Published online 15 January 2015. We would like to thank the anonymous referee whose careful reading and detailed comments greatly improved the manuscript. E.V. is funded by the Action “Supporting Postdoctoral Researchers” of the Operational Program ”Education and Lifelong Learning” (Action’s Beneficiary: General Secretariat for Research and Technology), and is co-financed by the European Social Fund (ESF) and the Greek State. E.V. would like to acknowledge Hanae Inami and Jim Condon for most useful conversations, and Grigoris Maravelias, Thomas Robitaille and Laure Ciesla for their most helpful assistance in Python. V.C. would like to acknowledge partial support from the EU FP7 Grant PIRSES-GA-2012-316788.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
General Secretariat for Research and Technology (GSRT)UNSPECIFIED
European Research Council (ERC)PIRSES-GA-20120316788
European Social FundUNSPECIFIED
Subject Keywords:galaxies: active, galaxies: starburst, galaxies: nuclei, radio continuum: galaxies, infrared: galaxies
Record Number:CaltechAUTHORS:20150326-132504832
Persistent URL:
Official Citation:Radio continuum properties of luminous infrared galaxies - Identifying the presence of an AGN in the radio E. Vardoulaki, V. Charmandaris, E. J. Murphy, T. Diaz-Santos, L. Armus, A. S. Evans, J. M. Mazzarella, G. C. Privon, S. Stierwalt and L. Barcos-Muñoz A&A 574 A4 (2015) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56141
Deposited By: Ruth Sustaita
Deposited On:26 Mar 2015 21:08
Last Modified:05 Nov 2019 05:51

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