Evidence for a large undetected population of dust-reddened quasars

Webster, R. L.; Francis, Paul; Petersont, Bruce A.; Drinkwater, Michael J.; Masci, Frank J.

doi:10.1038/375469a0

Cited by 251 publications

(323 citation statements)

References 19 publications

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“…Most high-luminosity AGNs (quasars) have been selected using their rest-frame ultraviolet through optical colors in optically magnitudelimited samples. It is therefore almost certain that dust obscuration has masked some portion of the AGN population from detection and that AGNs found by their ultraviolet-optical colors are less dusty than the truly typical AGNs (Webster et al 1995 ;Baker 1997 ;Wills & Hines 1997). This bias against dust-obscured objects can a †ect our understanding of AGNs, in particular their connection to their host galaxies and nuclear environments.…”

Section: Introductionmentioning

confidence: 99%

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Quasars in the 2MASS Second Incremental Data Release

Barkhouse

Hall

2001

The Astronomical Journal

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Using the 2MASS Second Incremental Data Release, we have searched for near-infrared counterparts to 13214 quasars from the Veron-Cetty & Veron catalog. We have detected counterparts within 4A for 2277 of the approximately 6320 quasars within the area covered by the 2MASS Second Incremental Data Release. Only 1.6% of these are expected to be chance coincidences. Though this sample is heterogeneous, we Ðnd that known radio-loud quasars are more likely to have large near-infrared-to-optical luminosity ratios than radio-quiet quasars are, at a statistically signiÐcant level. This is consistent with dust-reddened quasars being more common in radio-selected samples than in optically selected samples, due to stronger selection e †ects against dust-reddened quasars in the latter. We also Ðnd a statistically signiÐcant dearth of optically luminous quasars with large near-infrared-to-optical luminosity ratios. This can be explained in a dust obscuration model but not in a model where synchrotron emission extends from the radio into the near-infrared and creates such large ratios. We also Ðnd that selection of quasar candidates from the B[J/J[K color-color diagram, modeled on the V [J/J[K selection method of Warren, Hewett, & Foltz, is likely to be more sensitive to dust-obscured quasars than selection using only infrared-infrared colors.

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Section: Introductionmentioning

confidence: 99%

“…Dust obscuration seems the simplest explanation for Figure 4, although we note that Francis, Whiting, & Webster (2000) concluded that synchrotron emission was the best explanation for the red colors of the many RLQs in the Parkes Half-Jansky sample of Webster et al (1995).…”

Section: Catalog Cross-correlationmentioning

confidence: 99%

Quasars in the 2MASS Second Incremental Data Release

Barkhouse

Hall

2001

The Astronomical Journal

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“…However, they have been found to be systematically biased against It it therefore important to understand to what extent various quasar samples suffer from biases against dust-reddened systems and quasars at high redshifts so that we can build more complete and representative samples. A large number of studies targeting reddened quasars have been executed in the past two decades (see, e.g., Webster et al 1995;Warren et al 2000;Gregg et al 2002;Richards et al 2003;Hopkins et al 2004;Glikman et al 2007Glikman et al , 2012Glikman et al , 2013Maddox et al 2008Maddox et al , 2012Urrutia et al 2009;Banerji et al 2012;Fynbo et al 2013;Krogager et al 2015), all trying to probe this underrepresented subset of quasars using a range of selection techniques that are less sensitive to dust obscuration. With the advent of large-area near-and mid-infrared surveys such as UKIDSS, WISE, and Spitzer (Wright et al 2010;Cutri & et al 2013;Lawrence et al 2007;Warren et al 2007;Werner et al 2004;Fazio et al 2004), the selection of quasars based on infrared (IR) photometry alone has been made possible as well (Donley et al 2008(Donley et al , 2012Peth et al 2011;Stern et al 2012;Mateos et al 2012;Secrest et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

Heintz

Fynbo

Møller

et al. 2016

A&A

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The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high A V quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21% +9 −5 of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39% +9 −8 reddened quasars defined by having A V > 0.1, and 21% +9 −5 of the sample having E(B − V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g − r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J < 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.

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“…Carilli et al 1993), 3-all mm-strong radio-source with a known gravitational lens (VLBI) (Webster et al 1995, Stickel & Kühr 1993, Jackson & Browne 2007. This survey led to mostly negative results, meaning that a much larger sample of radio-sources, and much more sensitivity is required to find more molecular absorption systems.…”

Section: Higher Redshift Absorptionsmentioning

confidence: 99%

Molecular absorptions in high-z objects

Combes¹

2007

Astrophys Space Sci

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Summary. Molecular absorption lines measured along the line of sight of distant quasars are important probes of the gas evolution in galaxies as a function of redshift. A review is made of the handful of molecular absorbing systems studied so far, with the present sensitivity of mm instruments. They produce information on the chemistry of the ISM at z ∼ 1, the physical state of the gas, in terms of clumpiness, density and temperature. The CMB temperature can be derived as a function of z, and also any possible variations of fundamental constants can be constrained. With the sensitivity of ALMA, many more absorbing systems can be studied, for which some predictions and perspectives are described.

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Evidence for a large undetected population of dust-reddened quasars

Cited by 251 publications

References 19 publications

Quasars in the 2MASS Second Incremental Data Release

Quasars in the 2MASS Second Incremental Data Release

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

Molecular absorptions in high-z objects

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