Semi‐empirical analysis of Sloan Digital Sky Survey galaxies – III. How to distinguish AGN hosts

By G. Stasińska, R. C. Fernandes, A. Mateus, L. Sodré, N. Asari. 2006

251 citations recorded by the source corpus.

This paper considers the techniques to distinguish normal star-forming (NSF) galaxies and active galactic nuclei (AGNs) hosts using optical spectra. The observational data base is a set of 20000 galaxies extracted from the Sloan Digital Sky Survey, for which we have determined the emission-line intensities after subtracting the stellar continuum obtained from spectral synthesis. Our analysis is based on photoionization models computed using the stellar ionizing radiation predicted by population synthesis codes (essentially STARBURST99) and, for the AGNs, a broken power-law spectrum. We explain why, among the four classical emission-line diagnostic diagrams, ([O III]/Hβ versus [O II]/Hβ, [O III]/Hβ versus [N II]/Hα (the BPT diagram), [O III]/Hβ versus [S II]/Hα and [O III]/Hβ versus [O I]/Hα), the BPT one works best. We show, however, that none of these diagrams is efficient in detecting AGNs in metal-poor galaxies, should such cases exist. We propose a new divisory line between 'pure' NSF galaxies and AGN hosts: y = (-30.787 + 1.1358x + 0.27297x 2 ) tanh (5.7409x) - 31.093, where y = log([O III]/Hβ), and x = log([N II]/Hα). According to our models, the divisory line drawn empirically by Kauffmann et al. includes among NSF galaxies objects that may have an AGN contribution to Hβ of up to 3 per cent. The Kewley et al. line allows for an AGN contribution of roughly 20 per cent. About 20 per cent of the galaxies in our entire sample that can be represented in the BTP diagram are found between our divisory line and the Kauffmann et al. line, meaning that the local Universe contains a fair proportion of galaxies with a very low-level nuclear activity, in agreement with the statistics from observations of nuclei of nearby galaxies. We also show that a classification into NSF and AGN galaxies using only [N II]/Hα is feasible and useful. Finally, we propose a new classification diagram, the DEW diagram, plotting D n (4000) versus max(EW[O II], EW[Ne III]). This diagram can be used with optical spectra for galaxies with redshifts up to z = 1.3, meaning an important progress over classifications proposed up to now. Since the DEW diagram requires only a small range in wavelength, it can also be used at even larger redshifts in suitable atmospheric windows. It also has the advantage of not requiring stellar synthesis analysis to subtract the stars and of allowing one to see all the galaxies in the same diagram, including passive galaxies.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Bulge mass is king: the dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey (2014, methodology): “Here we use the Kauffmann et al. (2003) cut at a S/N > 3, but we find no significant change by moving to the Stasinska et al. (2006) definition of star forming dominated galaxies, or by varying the signalto-noise threshold modestly.”
Observational evidence for AGN feedback in early-type galaxies (2007, result): “We verified that the somewhat more restrictive separation betwe n star forming and AGN suggested by Stasińska et al. (2006) does not alter the results of this work.”
NEW STRONG-LINE ABUNDANCE DIAGNOSTICS FOR H ii REGIONS: EFFECTS OF κ-DISTRIBUTED ELECTRON ENERGIES AND NEW ATOMIC DATA (2013, result): “The models presented here represent a great improvement over the earlier work of our group, although we should note in passing that the models of Stasińska et al. (2006) provide a rather good description of the upper envelope of the H ii regionlike points on these diagrams.”
Integral field spectroscopy with SINFONI of VVDS galaxies I. Galaxy dynamics and mass assembly at 1.2 < z < 1.6 (2009, background): “The average [Nii]/Hα and [Sii]/Hα ratios are typical of star-forming galaxies (Stasińska et al. 2006), and the [Nii]/Hα 2D maps do not show a central excess of [Nii] which could indicate an AGN.”
SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, background): “…of this branch can be reproduced well by HII regions photoionisation models as the envelope of the expected line ratios for different values of metallicity and ionisation parameter for gas ionised by OB stars (Kewley et al. 2001; Nagao et al. 2006; Stasińska et al. 2006; Sánchez et al. 2015).”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, methodology): “The optical classification uses the diagnostic of Stasinska et al. (2006) which is sensitiveto ven modest contributions from an AGN.”
Nuclear Activity in Nearby Galaxies (2008, methodology): “…relatively 2The classification criteria adopted here differ slightly from those proposed by Kewley et al. (2001), Kauffmann et al. (2003), or Stasińska et al. (2006), but this difference has little effect on the general conclusions. uniform, is by no means invariant (Ho, Filippenko &…”
A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA (2013, methodology): “…for each of the selected ∼5000 H ii regions, we adopted the empirical calibrator based on the O3N2 ratio (Alloin et al. 1979; Pettini & Pagel 2004; Stasińska et al. 2006): O3N2 = log10 [ I([O iii] λ5007)/I(Hβ) I([N ii] λ6584)/I(Hα) ] · (1) This ratio is basically not affected by the effects of…”
A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, methodology): “…for AGN classification such as Hα and [N ii]λ6584 are shifted into the near-infrared, preventing the application of well-calibrated, traditional diagnostics (Baldwin et al. 1981; Veilleux & Osterbrock 1987; Kewley et al. 2001; Kauffmann et al. 2003; Kewley et al. 2006; Stasińska et al. 2006).”
The history of star-forming galaxies in the Sloan Digital Sky Survey (2007, methodology): “From our sequence of photoionization models (SEAGal III) and Zneb, we derive a new estimate for (Hα/Hβ)int, and hence A neb V (eq.”
Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger AGN (2011, methodology): “In this paper, we will investigate all three of the common BPT classification schemes: Kewley et al (2001), Kauffmann et al. (2003a) and Stasinska et al. (2006).”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “In Figure 4, we plot the [N ii] λ6584/Hα versus [O iii] λ5007/Hβ emission-line diagnostic diagram (Baldwin et al. 1981; Veilleux & Osterbrock 1987), which has been shown to be a sensitive diagnostic of AGN activity (Kewley et al. 2000, 2001b; Kauffmann et al. 2003; Stasińska et al. 2006).”
Strongly star forming galaxies in the local Universe with nebular He iiλ4686 emission (2012, methodology): “…discussed extensively (e.g. Terlevich et al. 1991; Kewley et al. 2001, hereafter Ke01; Kauffmann et al. 2003, hereafter Ka03; Kewley et al. 2006; Stasińska et al. 2006), this diagram allows a separation of AGN and SF galaxies because of their significantly different ionizing spectra, typically…”
Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies (2013, methodology): “To select galaxies that are dominated by star-formation we use the criteria of Kauffmann et al. (2003b)3 and to select galaxies with some contribution from AGN we use the criteria of Stasinska et al. (2006).”
ONGOING AND CO-EVOLVING STAR FORMATION IN zCOSMOS GALAXIES HOSTING ACTIVE GALACTIC NUCLEI (2008, background): “The SDSS has generated an unprecedented sample of galaxies to select large numbers of low redshift (z < 0.3) narrowline AGN (Kauffmann et al. 2003b; Kewley et al. 2006; Stasińska et al. 2006; Heckman et al. 2006; Wild et al. 2007) to cleanly study their host properties.”
Alternative diagnostic diagrams and the 'forgotten' population of weak line galaxies in the SDSS (2009, methodology): “Empirical and model-based frontiers have been drawn in the [O III]/Hβ–[N II]/Hα space to delineate the SF territory from the rest (Kewley et al. 2001, hereafter K01; K03; Stasińska et al. 2006, hereafter S06).”
GALAXY ZOO: THE FUNDAMENTALLY DIFFERENT CO-EVOLUTION OF SUPERMASSIVE BLACK HOLES AND THEIR EARLY- AND LATE-TYPE HOST GALAXIES (2010, background): “…Stasińska 1990; Leitherer & Heckman 1995; Leitherer et al. 1999; Kewley et al. 2001, 2006; Groves et al. 2004a,b) and by observational work (e.g., Veilleux & Osterbrock 1987; Ho et al. 1995, 1997a,b,c; Kauffmann et al. 2003a; Stasińska et al. 2006; Sarzi et al. 2006; Stasińska et al. 2008).”
De re metallica: the cosmic chemical evolution of galaxies (2018, background): “Even more indicators, based a different combinations of several lines or on other elements such as Argon, have been proposed, among others, by Pérez-Montero & Dı́az (2005), Stasińska (2006), Pérez-Montero et al. (2007), Kobulnicky et al. (1999), Dopita et al. (2016), and Pilyugin & Grebel (2016).”
The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe (2014, background): “Other authors have proposed further refinements of this division (e.g. Stasinska et al. 2006, Kewley et al. 2006, Cid Fernandes et al. 2011).”