A statistical study of properties of Seyfert and starburst galaxies

Dahari, O.; Robertis, M. M. De

doi:10.1086/191273

Cited by 132 publications

(110 citation statements)

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“…Several independent measurements have suggested that this is indeed the case (Netzer et al 2006, and references therein). Reddening estimates from Balmer decrements suggest that the narrow-line regions of type 2 sources are more heavily reddened than those of type 1 sources (De Zotti & Gaskell 1985;Dahari & De Robertis 1988). Recent IR observations strongly indicate that the narrow-line regions of type 2 quasars are significantly more obscured than those of type 1 quasars, by up to a factor of 10 (Haas et al 2005).…”

Section: Reddening and Extinctionmentioning

confidence: 99%

Space Density of Optically Selected Type 2 Quasars

Reyes¹,

Zakamska²,

Strauss³

et al. 2008

The Astronomical Journal

270

167

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Type 2 quasars are luminous active galactic nuclei whose central regions are obscured by large amounts of gas and dust. In this paper, we present a catalog of type 2 quasars from the Sloan Digital Sky Survey, selected based on their optical emission lines. The catalog contains 887 objects with redshifts z < 0.83; this is 6 times larger than the previous version and is by far the largest sample of type 2 quasars in the literature. We derive the [O iii]5007 luminosity function (LF) for 10 8.3 L < L [O iii] < 10 10 L (corresponding to intrinsic luminosities up to M[2500 Å] −28 mag or bolometric luminosities up to 4 × 10 47 erg s −1 ). This LF provides robust lower limits to the actual space density of obscured quasars due to our selection criteria, the details of the spectroscopic target selection, and other effects. We derive the equivalent LF for the complete sample of type 1 (unobscured) quasars and determine the ratio of type 2 to type 1 quasar number densities. Our data constrain this ratio to be at least ∼ 1.5:1 for 10 8.3 L < L [O iii] < 10 9.5 L at z < 0.3, and at least ∼ 1.2:1 for L [O iii] ∼ 10 10 L at 0.3 < z < 0.83. Type 2 quasars are at least as abundant as type 1 quasars in the relatively nearby universe (z 0.8) for the highest luminosities.

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Section: Reddening and Extinctionmentioning

confidence: 99%

Space Density of Optically Selected Type 2 Quasars

Reyes¹,

Zakamska²,

Strauss³

et al. 2008

The Astronomical Journal

270

167

View full text Add to dashboard Cite

show abstract

“…Zakamska et al (2003) used the Balmer decrement, f Hα /f Hβ , measured from a composite spectrum of their SDSS non-BLAGNs as a proxy for the volumeaveraged narrow emission-line reddening and found a similar result of E(B − V ) = 0.27 mag (though see Netzer et al 2006 for a discussion of possible selection effects). Dahari & De Robertis (1988) and Bassani et al (1999) found significantly larger median reddening in their non-BLAGNs of E(B − V ) = 0.48 mag and E(B − V ) = 0.65 mag, respectively. The Dahari & De Robertis (1988) sample represented the largest available uniform database of optical spectra at that time, including most of the known Markarian Seyferts and a majority of the classical Seyferts listed in Weedman (1977Weedman ( , 1978.…”

Section: Emission-line Reddeningmentioning

confidence: 90%

“…Dahari & De Robertis (1988) and Bassani et al (1999) found significantly larger median reddening in their non-BLAGNs of E(B − V ) = 0.48 mag and E(B − V ) = 0.65 mag, respectively. The Dahari & De Robertis (1988) sample represented the largest available uniform database of optical spectra at that time, including most of the known Markarian Seyferts and a majority of the classical Seyferts listed in Weedman (1977Weedman ( , 1978. The median reddening quoted above is for the 20 Seyfert 1s in their sample with z < 0.03 and axial ratios b/a > 0.5.…”

Section: Emission-line Reddeningmentioning

confidence: 90%

The Optx Project. Iv. How Reliable Is [O Iii] as a Measure of Agn Activity?

Trouille

Barger

2010

ApJ

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We compare optical and hard X-ray identifications of active galactic nuclei (AGNs) using a uniformly selected (above a flux limit of f 2-8 keV = 3.5 × 10 −15 erg cm −2 s −1 ) and highly optically spectroscopically complete (>80% for f 2-8 keV > 10 −14 erg cm −2 s −1 and >60% below) 2-8 keV sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N). We find that empirical emission-line ratio diagnostic diagrams misidentify 50% of the X-ray-selected AGNs that can be put on these diagrams as star formers. We confirm that there is a large (two orders of magnitude) dispersion in the ratio of the [O iii]λ5007 (hereafter [O iii]) to hard X-ray luminosities for the non-broad-line AGNs, even after applying reddening corrections to the [O iii] luminosities. We find that the dispersion is similar for the broad-line AGNs, where there is not expected to be much X-ray absorption from an obscuring torus around the AGN nor much obscuration from the galaxy along the line of sight if the AGN is aligned with the galaxy. We postulate that the X-ray-selected AGNs that are misidentified by the diagnostic diagrams have low [O iii] luminosities due to the complexity of the structure of the narrow-line region, which causes many ionizing photons from the AGN not to be absorbed. This would mean that the [O iii] luminosity can only be used to predict the X-ray luminosity to within a factor of ∼3 (1σ ). Despite selection effects, we show that the shapes and normalizations of the [O iii] and transformed hard X-ray luminosity functions show reasonable agreement, suggesting that the [O iii] samples are not finding substantially more AGNs at low redshifts than hard X-ray samples.

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“…Other methods, based on the observed Balmer decrement, can be used to obtain the volume averaged narrow line reddening. For example, the median reddening found by Dahari & De-Robertis (1988) in type-II sources is E(B − V) ∼ 0.54 mag. These authors also mention that the (less certain) line reddening in type-I sources is smaller, by about 0.1-0.2 mag.…”

Section: Emission Line Reddeningmentioning

confidence: 97%

The correlation of narrow line emission and X-ray luminosity in active galactic nuclei

Netzer

Mainieri

Rosati

et al. 2006

A&A

109

146

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Aims. We combine emission line and X-ray luminosities for 45 sources from the Chandra Deep Field South (CDF-S), and seven HELLAS sources, to obtain a new sample of 52 X-ray selected type-II active galactic nuclei (AGNs). Eighteen of our sources are very luminous with a typical, absorption-corrected 2-10 keV luminosity of f ew × 10 44 erg s −1 (type-II QSOs). Methods. We compare the emission line properties of the new sources with emission line and X-ray luminosities of known low redshift, mostly lower luminosity AGNs by using a composite spectrum.

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A statistical study of properties of Seyfert and starburst galaxies

Cited by 132 publications

References 0 publications

Space Density of Optically Selected Type 2 Quasars

Space Density of Optically Selected Type 2 Quasars

The Optx Project. Iv. How Reliable Is [O Iii] as a Measure of Agn Activity?

The correlation of narrow line emission and X-ray luminosity in active galactic nuclei

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