Reddening-independent quasar selection from a wide-field optical and near-infrared imaging survey

Sharp, Robert; Sabbey, C. N.; Vivas, A. Katherina; Oemler, Augustus; McMahon, R. G.; Hodgkin, S. T.; Coppi, P.

doi:10.1046/j.1365-8711.2002.05961.x

Cited by 22 publications

(17 citation statements)

References 36 publications

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“…There have been a number of studies employing KX selection of quasar candidates over small (<1 deg 2 ) areas (e.g. Sharp et al , or more recently, Smail et al ) but our primary goal is to utilize the technique to examine the properties of intrinsically luminous quasars where a large survey area is required due to their low surface density on the sky (tens of objects per square degree).…”

Section: Quasar Candidate Selectionmentioning

confidence: 99%

The large area KX quasar catalogue - I. Analysis of the photometric redshift selection and the complete quasar catalogue

Maddox¹,

Hewett

Péroux

et al. 2012

Monthly Notices of the Royal Astronomical Society

111

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International audienceThe results of a large area, 600?deg2, K-band flux-limited spectroscopic survey for luminous quasars are presented. The survey utilizes the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) in regions of sky within the Sloan Digital Sky Survey (SDSS) footprint. The K-band excess (KX) of all quasars with respect to Galactic stars is exploited in combination with a photometric redshift/classification scheme to identify quasar candidates for spectroscopic follow-up observations. The data contained within this investigation will be able to provide new constraints on the fraction of luminous quasars reddened by dust with E(B - V) = 0.5?mag. The spectroscopic sample is defined using the K-band, 14.0 \textless= K \textless= 16.6, and SDSS i-band limits of i = 19.5, 19.7 and 22.0 over sky areas of 287, 150 and 196?deg2, respectively. The survey includes \textgreater3200 known quasars from the SDSS and more than 250 additional confirmed quasars from the KX selection. A well-defined subsample of quasars in the redshift interval 1.0 \textless= z \textless= 3.5 includes 1152 objects from the SDSS and 172 additional KX-selected quasars. The quasar selection is \textgreater95?per cent complete with respect to known SDSS quasars and \textgreater95?per cent efficient, largely independent of redshift and i-band magnitude. The properties of the new KX-selected quasars confirm the known redshift-dependent effectiveness of the SDSS quasar selection and provide a sample of luminous quasars experiencing intermediate levels of extinction by dust. The catalogue represents an important step towards the assembly of a well-defined sample of luminous quasars that may be used to investigate the properties of quasars experiencing intermediate levels of dust extinction within their host galaxies or due intervening absorption line systems

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Section: Quasar Candidate Selectionmentioning

confidence: 99%

The large area KX quasar catalogue - I. Analysis of the photometric redshift selection and the complete quasar catalogue

Maddox¹,

Hewett

Péroux

et al. 2012

Monthly Notices of the Royal Astronomical Society

111

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“…Any quasar selection based on rest‐frame UV colour indicies is subject to bias against objects suffering moderate dust extinction either along the line of sight (Fall & Pei 1993) or intrinsic to the quasar (Sharp et al 2002). In order to draw a comparison with the luminosity function of Fan et al (2001a) no attempt is made to account for possible selection effects from dust reddening in the current work.…”

Section: Colour Selection Of Candidatesmentioning

confidence: 99%

“…Both the Big Throughput Camera 40 deg 2 survey (BTC40) of Monier et al (2002) and the Wide Field Survey of the Isaac Newton Telescope (INTWFS) (Sharp et al 2001; Sharp 2002) probe the high‐redshift ( z > 4.6) quasar luminosity function to greater depths than those reached by SDSS. These surveys cover sufficient area to recover five quasars with z > 4.6 to date.…”

Section: Introductionmentioning

confidence: 99%

A survey for low-luminosity quasars at redshiftz∼ 5

Sharp¹,

Crampton²,

Hook³

et al. 2004

Monthly Notices of the Royal Astronomical Society

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We present the results of a multicolour (VIZ) survey for low‐luminosity (MB < − 23.5) quasars with z∼ 5 using the 12K CCD mosaic camera on the Canada–France–Hawaii Telescope (CFHT). The survey covers 1.8 deg2 to a limiting magnitude of mz= 22.5(Vega), about two magnitudes fainter than the SDSS (Sloan Digital Sky Survey) quasar survey. Twenty candidates were selected by their VIZ colours, and spectra for 15 of these were obtained with GMOS on the Gemini North telescope. A single quasar with z= 4.99 was recovered; the remaining candidates are all M stars. The detection of only a single quasar in the redshift range 4.8 < z < 5.2 accessible to the survey is indicative of a possible turnover in the luminosity function at faint quasar magnitudes, and a departure from the form observed at higher luminosities (in agreement with quasar lensing observations by Richards et al.). However, the derived space densities of quasars more luminous than MB (Vega) < − 23.5, of 2.96 × 10−7 Mpc−3 is consistent at the 65 per cent confidence level with extrapolation of the quasar luminosity function as derived by Fan et al. at mi < 19.6(Vega).

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“…There have been two studies to date employing KX selection of quasars: the first by Croom, Warren & Glazebrook (2001) and the second by Sharp et al (2002). Although pioneering in nature, the limited areal coverage, 48 arcmin 2 and 0.7 deg 2 , respectively, restricts the effectiveness in constraining the fraction of reddened quasars.…”

Section: Introductionmentioning

confidence: 99%

Luminous K-band selected quasars from UKIDSS

Maddox

Hewett

Warren

et al. 2008

Monthly Notices of the Royal Astronomical Society

103

141

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The largest K-band flux-limited sample of luminous quasars to date has been constructed from the UKIRT (UK Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release, covering an effective area of 12.8 deg 2 . Exploiting the K-band excess (KX) of all quasars with respect to foreground stars, including quasars experiencing dust reddening and objects with non-standard spectral energy distributions (SEDs), a list of targets suitable for spectroscopic follow-up observations with the AAOmega multi-object spectrograph is constructed, resulting in more than 200 confirmed active galactic nuclei (AGN). KX selection successfully identifies as quasar candidates objects that are excluded from the Sloan Digital Sky Survey (SDSS) quasar selection algorithm due to their colours being consistent with the stellar locus in optical colour space (with the space density of the excluded objects agreeing well with results from existing completeness analyses). Nearly half of the KX-selected quasars with K 17.0 at z < 3 are too faint in the i band to have been targeted by the SDSS quasar selection algorithm, revealing a large population of quasars with red i − K colours. The majority of these objects have significant amounts of host galaxy light contributing to their K-band magnitudes, consistent with previous predictions. The remaining objects are morphologically stellar and have colours consistent with quasars experiencing Small Magellanic Cloud (SMC)type reddening with 0.10 < E(B − V) < 0.25. The i − K colour distribution indicates that <10 per cent of the quasar population is missing from this K-band selected sample due to dust reddening, and comparisons with simulations strongly favour an obscured fraction of <20 per cent. Photometric redshifts and classifications are computed for the candidates that were not observed spectroscopically. For the extended objects whose colours are consistent with those of a reddened quasar, models of galaxy surface brightness profiles appropriate for each object are used to eliminate the possibility of the presence of a nuclear source bright enough for inclusion in a K 17.0 quasar sample. The effectiveness of near-infrared colour selection of quasars has been demonstrated by this modest-sized sample, and it will only become more apparent as the amount of available data increases.

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Reddening-independent quasar selection from a wide-field optical and near-infrared imaging survey

Cited by 22 publications

References 36 publications

The large area KX quasar catalogue - I. Analysis of the photometric redshift selection and the complete quasar catalogue

The large area KX quasar catalogue - I. Analysis of the photometric redshift selection and the complete quasar catalogue

A survey for low-luminosity quasars at redshiftz∼ 5

Luminous K-band selected quasars from UKIDSS

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