Alternative diagnostic diagrams and the 'forgotten' population of weak line galaxies in the SDSS

By R. C. Fernandes, G. Stasińska, M. Schlickmann, A. Mateus, N. Asari, William Schoenell, L. S. J. Ufsc, Brazil, Luth, O. Paris and 2 more. 2009

331 citations recorded by the source corpus.

A numerous population of weak line galaxies (WLGs) is often left out of statistical studies on emission-line galaxies (ELGs) due to the absence of an adequate classification scheme, since classical diagnostic diagrams, such as [O III]/Hβ versus [N II]/Hα (the BPT diagram), require the measurement of at least four emission lines. This paper aims to remedy this situation by transposing the usual divisory lines between star-forming (SF) galaxies and active galactic nuclei (AGN) hosts and between Seyferts and LINERs to diagrams that are more economical in terms of line quality requirements. By doing this, we rescue from the classification limbo a substantial number of sources and modify the global census of ELGs. More specifically, (1) we use the Sloan Digital Sky Survey Data Release 7 to constitute a suitable sample of 280 000 ELGs, one-third of which are WLGs. (2) Galaxies with strong emission lines are classified using the widely applied criteria of Kewley et al., Kauffmann et al. and Stasinska et al. to distinguish SF galaxies and AGN hosts and Kewley et al. to distinguish Seyferts from LINERs. (3) We transpose these classification schemes to alternative diagrams keeping [N II]/Hα as a horizontal axis, but replacing Hβ by a stronger line (Hα or [O II]), or substituting the ionization-level sensitive [O III]/Hβ ratio with the equivalent width of Hα (W Hα ). Optimized equations for the transposed divisory lines are provided. (4) We show that nothing significant is lost in the translation, but that the new diagrams allow one to classify up to 50 per cent more ELGs. (5) Introducing WLGs in the census of galaxies in the local Universe increases the proportion of metal-rich SF galaxies and especially LINERs. In the course of this analysis, we were led to make the following points. (i) The Kewley et al. BPT line for galaxy classification is generally ill-used. (ii) Replacing [O III]/Hβ by W Hα in the classification introduces a change in the philosophy of the distinction between LINERs and Seyferts, but not in its results. Because the W Hα versus [N II]/Hα diagram can be applied to the largest sample of ELGs without loss of discriminating power between Seyferts and LINERs, we recommend its use in further studies. (iii) The dichotomy between Seyferts and LINERs is washed out by WLGs in the BPT plane, but it subsists in other diagnostic diagrams. This suggests that the right wing in the BPT diagram is indeed populated by at least two classes, tentatively identified with bona fide AGN and 'retired' galaxies that have stopped forming stars and are ionized by their old stellar populations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/65a68ed762fbf8c0abd1b17c7fc4006ed0e7f029

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

Citations in the corpus

Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger AGN (2011, background): “Indeed, there is an observational link between enhanced central star formation rates and black hole activity that extends beyondmergers to the general galaxy population (Cid-Fernandes et al. 2001; Kauffmann et al. 2003a; Silverman et al. 2009; Reichard et al. 2009).”
CALIFA, the Calar Alto Legacy Integral Field Area survey - III. Second public data release (2012, unknown): “…of individual galaxies according to such a scheme can be complicated, i.e., in border-line cases or due to systematic uncertainties in the emission-line measurements, as well as adopting other types of diagnostic diagrams (e.g. Cid Fernandes et al. 2010), or a di ﬀ erent classiﬁcation scheme.”
CALIFA : a diameter-selected sample for an integral field spectroscopy galaxy survey (2014, methodology): “We use the demarcation lines of Kauffmann et al. (2003b), Kewley et al. (2001) and Cid Fernandes et al. (2010) to classify the objects into star forming (SF), Seyferts, SF/AGN intermediate, and LINER-like galaxies.”
A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA (2013, methodology): “For example, Cid Fernandes et al. (2011) propose using EW(Hα) to distinguish between retired (non star-forming) galaxies, weak AGNs, and star-forming galaxies.”
On the fundamental dichotomy in the local radio-AGN population (2012, methodology): “(v) If [NII] and Hα emission line measurements were available for the source, then the [NII]/Hα vs [OIII]/Hα emission line diagnostic of Cid Fernandes et al. (2010) was used, using either a detection or a limit (if definitive) for the [OIII] emission line [769 LERG; 24 HERG] To illustrate the consis”
GALAXY ZOO: THE FUNDAMENTALLY DIFFERENT CO-EVOLUTION OF SUPERMASSIVE BLACK HOLES AND THEIR EARLY- AND LATE-TYPE HOST GALAXIES (2010, background): “Cid Fernandes et al. (2009) have recently similarly argued that many of the SDSS objects in the LINER box are “retired” galaxies powered by old stellar populations.”
Characterizing the Fast Radio Burst Host Galaxy Population and its Connection to Transients in the Local and Extragalactic Universe (2021, background): “For comparison, we show the distribution of nearby (0.02< z< 0.4) emission-line (>5σ significance) galaxies from the Sloan Digital Sky Survey (SDSS) including the standard demarcation lines between SF, AGN, and LINER galaxies (Kauffmann et al. 2003; Cid Fernandes et al. 2010).”
Near infrared spectroscopy and star-formation histories of 3 ≤ z ≤ 4 quiescent galaxies (2018, background): “In fact, given that our galaxies have (a priori) low sSFR, both emission lines may be significantly contaminated by energy sources other than star-formation; an AGN, or low-ionization emission from old/intermediate-age stars (see, e.g., Cid Fernandes et al. 2010, 2011 for Balmer lines, and Yan et al”
Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies (2013, background): “Cid-Fernandes et al. (2010) have made a thorough investigation of the impact of S/N requirements on the selection of galaxies within the BPT diagram.”
Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for Their Progenitors (2020, unknown): “We also include the standard demarcation lines between SF, AGN, and LINER galaxies (Kauffmann et al. 2003; Cid Fernandes et al. 2010).”