Galaxy and Mass Assembly (GAMA)

A WISE study of the activity of emission-line systems in G23

H. F.M. Yao*, T. H. Jarrett, M. E. Cluver, L. Marchetti, Edward N. Taylor, M. G. Santos, Matt S. Owers, Angel R. Lopez-Sanchez, Y. A. Gordon, M. J. I. Brown, S. Brough, S. Phillipps, B. W. Holwerda, A. M. Hopkins, L. Wang

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

We present a detailed study of emission-line systems in the Galaxy And Mass Assembly (GAMA) G23 region, making use of Wide-field Infrared Survey Explorer (WISE) photometry that includes carefully measured resolved sources. After applying several cuts to the initial catalog of. 41,000 galaxies, we extract a sample of 9809 galaxies. We then compare the spectral diagnostic Baldwin, Philips & Terlevich (BPT) classification of 1154 emission-line galaxies (38% resolved in W1) to their location in the WISE color-color diagram, leading to the creation of a new zone for mid-infrared "warm"galaxies located 2μm above the star-forming sequence, below the standard WISE active galactic nucleus (AGN) region. We find that the BPT and WISE diagrams agree on the classification for 85% and 8% of the galaxies as non-AGN (star-forming = SF) and AGN, respectively, and disagree on. 7% of the entire classified sample. Thirty-nine percent of the AGNs (all types) are broad-line systems for which the [N II] and [Hα] fluxes can barely be disentangled, giving in most cases spurious [N II]/[Hα] flux ratios. However, several optical AGNs appear to be completely consistent with SF in WISE. We argue that these could be low-power AGNs, or systems whose hosts dominate the IR emission. Alternatively, given the sometimes high [O III] luminosity in these galaxies, the emission lines may be generated by shocks coming from super-winds associated with SF rather than AGN activity. Based on our findings, we have created a new diagnostic: [W1 - W2] versus [N II]/[Hα], which has the virtue of separating SF from AGNs and high-excitation sources. It classifies 3 to ∼5 times more galaxies than the classic BPT.

Original languageEnglish
Article number91
Pages (from-to)1-31
Number of pages31
JournalAstrophysical Journal
Volume903
Issue number2
DOIs
Publication statusPublished - 10 Nov 2020

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