Galaxy and Mass Assembly (GAMA): A WISE Study of the Activity of Emission-line Systems in G23

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 2σ 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.Unified Astronomy Thesaurus concepts: Galaxy evolution (594); AGN host galaxies (2017); Infrared galaxies (790)

GAMA/XXL: X-ray point sources in low-luminosity galaxies in the GAMA G02/XXL-N field

“…This gives 806 galaxies with secure redshifts and with X-ray detections, about 4% of the GAMA galaxies in the overlap region, consistent with the fraction of AGN seen elsewhere in GAMA (e.g. Yao et al 2020). Restricting our sample to sources with at least 10 counts in the soft X-ray band (0.5 to 2 keV), in order to allow moderately good estimates of the X-ray fluxes, reduces this to 712.…”

“…In other words, a 19 m galaxy, for instance, should have the same X-ray flux, and therefore be equally detectable, regardless of whether it is a nearby dwarf or a distant giant. As we detect about 800 GAMA galaxies in X-rays, or 4% of the 20000 galaxies in the overlap region, then all other things being equal, and assuming most of the sources in massive galaxies are AGN (Yao et al 2020), we should also expect 4% of the 1200 low mass galaxies to be X-ray detectable AGN, i.e. about 50.…”

“…Another useful discriminant between AGN and star-forming galaxies is the mid-infrared colour. Specifically looking at the WISE 3.4 micron (W1) and 4.6 micron (W2) bands, Stern et al (2012) suggest a simple division at W1-W2 = 0.8 6 , with 80% of AGN having redder colours (see also Jarrett et al 2011;Yao et al 2020), though see the caveat in Hainline et al (2016) regarding dwarf galaxy colours. Passive galaxies typically have 0 < ∼ W1-W2 < ∼ 0.3 and star-forming galaxies 0 < ∼ W1-W2 < ∼ 0.6 (Cluver et al Kewley (thick, upper) and Kauffmann (thin, lower) demarcation lines between AGN and star forming galaxies.…”

Central X-ray point-sources found to be abundant in low-mass, late-type galaxies predicted to contain an intermediate-mass black hole

“…Thanks to facilities like the Wide-field Infrared Survey Explorer (WISE: Wright et al 2010) and the Spitzer Space Telescope (Werner et al 2004), one can use midinfrared diagnostics to separate AGN from star formation. The presence of mid-IR high-ionization lines, combined with the strength of polycyclic aromatic hydrocarbon (PAH) emission features, can provide a means to discriminate between the dominant energy source within one's aperture (e.g., Dale et al 2006;Satyapal et al 2009;Stern et al 2012;Yao et al 2020). The presence of high-ionization optical emission lines can also support the presence of a black hole (Baldwin et al 1981;Veilleux & Osterbrock 1987;Kewley et al 2006;Martínez-Palomera et al 2020;Mezcua & Domínguez Sánchez 2020).…”

Connecting MeerKAT Radio Continuum Properties to GAMA Optical Emission-line and WISE Mid-infrared Activity

“…At optical wavelengths, emission lines from the accretion disk are detected and specific combinations of these lines (known as BPT diagrams; Baldwin et al 1981) have proven to be very useful for the separation of AGNs and SF galaxies (see Baldwin et al 1981;Veilleux & Osterbrock 1987;Kewley et al 2001;Kauffmann et al 2003;Kewley et al 2006;Yao et al 2020). It does demand the presence of emission lines, which may typically be faint to observe for most galaxies (e.g., the H-β recombination line).…”