Mid-Infrared Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width

By H. Spoon, J. Marshall, J. Houck, M. Elitzur, L. Hao, Lee Armus, B. Brandl, Vassilis Charmandaris. 2006

323 citations recorded by the source corpus.

We present a new diagnostic diagram for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 μm PAH emission feature and the strength of the 9.7 μm silicate feature. Based on the positions in this diagram, we classify galaxies into nine classes ranging from continuum-dominated AGN hot dust spectra and PAH-dominated starburst spectra to absorption-dominated spectra of deeply obscured galactic nuclei. We find that galaxies are systematically distributed along two distinct branches: one of AGN and starburst-dominated spectra and one of deeply obscured nuclei and starburst-dominated spectra. The separation into two branches likely reflects a fundamental difference in the dust geometry in the two sets of sources: clumpy versus nonclumpy obscuration. Spectra of ULIRGs are found along the full length of both branches, reflecting the diverse nature of the ULIRG family.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0377fb906766a238e4471435c8418f3ff2129756

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In Astronomy and Astrophysics

1. H. Netzer
2. D. M. Alexander
3. Sylvain Veilleux
4. D. Rupke
5. R. Maiolino
6. P. Hopkins
7. L. Hernquist
8. D. Lutz

Citations in the corpus

• CASSIS: THE CORNELL ATLAS OF SPITZER/INFRARED SPECTROGRAPH SOURCES (2011, methodology): “The silicate absorption optical depth was measured according to Spoon et al. (2007), assuming the method usually applicable to PAH-dominated spectra.”
• A Spitzer IRS Low-Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies: A Constraint on Geometry between Energy Sources and Dust (2007, methodology): “The trend in Figure 10a (see also Spoon et al. 2007) supports the scenario B for ULIRGs with 09:7 > 2.”
• The Distribution of Silicate Strength in Spitzer Spectra of AGNs and ULIRGs (2006, methodology): “The ULIRG sample is drawn from the GTO program (program 105; Armus et al. 2007; Spoon et al. 2007).”
• EXPLAINING THE [C ii]157.7 μm DEFICIT IN LUMINOUS INFRARED GALAXIES—FIRST RESULTS FROM A HERSCHEL/PACS STUDY OF THE GOALS SAMPLE (2013, methodology): “…been widely used for the detection of AGN activity in galaxies at low and high redshifts (Genzel et al. 1998; Armus et al. 2007; Desai et al. 2007; Spoon et al. 2007; Pope et al. 2008; Murphy et al. 2009; MenéndezDelmestre et al. 2009; Veilleux et al. 2009; Petric et al. 2011; Stierwalt et al.…”
• STRUCTURE AND FORMATION OF ELLIPTICAL AND SPHEROIDAL GALAXIES (2008, unknown): “1998; Downes & Solomon 1998; Joseph 1999; Rigopoulou et al. 1999; Genzel et al. 2000; Tran et al. 2001; Spoon et al. 2007; Netzer et al. 2007; Vega et al. 2008; Nardini et al. 2008).”
• Dust covering factor, silicate emission, and star formation in luminous QSOs (2007, background): “…QSOs (Schweitzer et al., 2006), the first detection of the Silicate feature in emission (Siebenmorgen et al., 2005; Hao et al., 2005), as well as detailed studies of the silicate strength in variouscla ses of sources (Spoon et al., 2007; Hao et al., 2007; Shi et al., 2006; Imanishi et al., 2007).”
• A TWO-PARAMETER MODEL FOR THE INFRARED/SUBMILLIMETER/RADIO SPECTRAL ENERGY DISTRIBUTIONS OF GALAXIES AND ACTIVE GALACTIC NUCLEI (2014, methodology): “…PAH features have been widely used to diagnose the main power source of a galaxy (e.g., Genzel et al. 1998; Laurent et al. 2000; Armus et al. 2007; Smith et al. 2007; Spoon et al. 2007; Dale et al. 2009; Hernán-Caballero et al. 2009; Diamond-Stanic & Rieke 2010; Wu et al. 2010; Shang et al. 2011).”
• C-GOALS: Chandra observations of a complete sample of luminous infrared galaxies from the IRAS Revised Bright Galaxy Survey (2011, background): “IRAS F08572+3915 : The northwest nucleus of this double system is suspected to have an heavily obscured AGN, as the Spitzer IRS spectrum shows a very deep silicate absorption and little PAH emission (e.g., Spoon et al. 2007).”
• AGN Dusty Tori. I. Handling of Clumpy Media (2008, background): “As noted by Levenson et al. (2007), the different behavior of the 10µm absorption in ULIRGs and AGN indicates that the dust distribution is smooth in the former and clumpy in the latter (see also Spoon et al. 2007).”
• SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, methodology): “7 than Seyfert ULIRGs on average, in general agreement with Spoon et al. (2007) and Sirocky et al. (2008).”
• MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES. I. SPITZER INFRARED SPECTROGRAPH SPECTRA FOR THE GOALS SAMPLE (2013, methodology): “…with the larger samples from Spoon et al. (2007) (104 ULIRGs) and Veilleux et al. (2009) (QUEST; 50 ULIRGs), we find that the larger numbers of ULIRGs in these samples result in a larger spread in MIR properties (i.e. 6.2µm PAH EQWs up to 0.8µm and silicate depths up to 0.2; Spoon et al. (2007)).”