The DEEP Groth Strip Survey. VI. Spectroscopic, Variability, and X‐Ray Detection of Active Galactic Nuclei

Sarajedini, Vicki L.; Koo, David C.; Phillips, Andrew C.; Kobulnicky, Henry A.; Gebhardt, Karl; Willmer, Christopher N. A.; Vogt, Nicole P.; Laird, E. S.; Im, Myungshin; Iverson, Sarah; Mattos, Wanessa

doi:10.1086/505909

Cited by 33 publications

(28 citation statements)

References 59 publications

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“…Subsequent work by Sarajedini et al (2003Sarajedini et al ( , 2006 and Klesman & Sarajedini (2007), thanks to the high spatial a NLAGN = Narrow Line AGN, reported by Szokoly et al (2004) as high excitation line sources (HEX) and by Treister et al (2008) as obscured AGN (OAGN).…”

Section: Resultsmentioning

confidence: 99%

“…For this reason Bershady et al (1998) applied for the first time a detection criterion based on variability to objects with extended images, creating a sample of candidates in the Selected Area 57, which was subsequently studied in X-rays (Trevese et al 2007) and follow-up optical spectroscopy (Trevese et al 2008b). Variability-selected samples were created on the basis of high spatial resolution Hubble Space Telescope Images by Sarajedini et al (2003Sarajedini et al ( , 2006, to minimise the dilution effect of the (constant) galaxy light. These studies discovered a number of AGN candidates not detected in X-rays.…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

Boutsia

Leibundgut

Trèvese³

et al. 2009

A&A

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Context. Supermassive black holes with masses of 10 5 -10 9 M are believed to inhabit most, if not all, nuclear regions of galaxies, and both observational evidence and theoretical models suggest a scenario where galaxy and black hole evolution are tightly related. Luminous AGNs are usually selected by their non-stellar colours or their X-ray emission. Colour selection cannot be used to select low-luminosity AGNs, since their emission is dominated by the host galaxy. Objects with low X-ray to optical ratio escape even the deepest X-ray surveys performed so far. In a previous study we presented a sample of candidates selected through optical variability in the Chandra Deep Field South, where repeated optical observations were performed in the framework of the STRESS supernova survey. Aims. The analysis is devoted to breaking down the sample in AGNs, starburst galaxies, and low-ionisation narrow-emission line objects, to providing new information about the possible dependence of the emission mechanisms on nuclear luminosity and blackhole mass, and eventually studying the evolution in cosmic time of the different populations. Methods. We obtained new optical spectroscopy for a sample of variability selected candidates with the ESO NTT telescope. We analysed the new spectra, together with those existing in the literature and studied the distribution of the objects in U − B and B − V colours, optical and X-ray luminosity, and variability amplitude. Results. A large fraction (17/27) of the observed candidates are broad-line luminous AGNs, confirming the efficiency of variability in detecting quasars. We detect: i) extended objects which would have escaped the colour selection and ii) objects of very low X-ray to optical ratio, in a few cases without any X-ray detection at all. Several objects resulted to be narrow-emission line galaxies where variability indicates nuclear activity, while no emission lines were detected in others. Some of these galaxies have variability and X-ray to optical ratio close to active galactic nuclei, while others have much lower variability and X-ray to optical ratio. This result can be explained by the dilution of the nuclear light due to the host galaxy.Conclusions. Our results demonstrate the effectiveness of supernova search programmes to detect large samples of low-luminosity AGNs. A sizable fraction of the AGN in our variability sample had escaped X-ray detection (5/47) and/or colour selection (9/48). Spectroscopic follow-up to fainter flux limits is strongly encouraged.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

Boutsia

Leibundgut

Trèvese³

et al. 2009

A&A

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“…By cadencing the IRAC observations over multiple visibility windows, SDWFS has opened the largely unexplored territory of mid-IR variability. Dramatic AGN variations have been seen at X-ray, optical, near-infrared, and radio wavelengths (e.g., Hovatta et al 2008;Papadakis et al 2008;Sarajedini et al 2006). Monitoring campaigns are an efficient method to identify AGN and provide information on the size scales, geometries, and physics of the nuclear regions, providing fundamental tests of unified AGN models.…”

Section: Introductionmentioning

confidence: 99%

THESPITZERDEEP, WIDE-FIELD SURVEY

Ashby

Stern

Brodwin

et al. 2009

ApJ

207

263

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The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of 10 deg 2 in the Boötes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Spitzer Cycle 4 Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit-for the first time-the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z ∼ 3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS data sets will thus be especially useful for characterizing galaxy evolution beyond z ∼ 1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 × 10 5 distinct sources detected to the average 5σ , 4 -diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 μm, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 minute integration time of the SDWFS IRAC imaging, > 50% of isolated Faint Images of the Radio Sky at Twenty cm radio sources and > 80% of on-axis XBoötes sources are detected out to 8.0 μm. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.

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“…Selection by variability has enabled us to identify objects of intrinsically low X-ray to optical ratio, which would be otherwise missed by X-ray surveys (Sarajedini et al 2003(Sarajedini et al , 2006Trevese et al 2007). These objects, in addition to their contribution to the LF evolution, provide information on accretion and/or on star-burst activity.…”

Section: Introductionmentioning

confidence: 99%

Variability-selected active galactic nuclei from supernova search in the Chandra deep field south

Trèvese¹,

Boutsia

Vagnetti

et al. 2008

A&A

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Context. Variability is a property shared by virtually all active galactic nuclei (AGNs), and was adopted as a criterion for their selection using data from multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light of their host galaxies, and cannot therefore be detected by the usual colour techniques. For this reason, their evolution in cosmic time is poorly known. Consistency with the evolution derived from X-ray detected samples has not been clearly established so far, also because the low luminosity population consists of a mixture of different object types. LLAGNs can be detected by the nuclear optical variability of extended objects. Aims. Several variability surveys have been, or are being, conducted for the detection of supernovae (SNe). We propose to re-analyse these SNe data using a variability criterion optimised for AGN detection, to select a new AGN sample and study its properties. Methods. We analysed images acquired with the wide field imager at the 2.2 m ESO/MPI telescope, in the framework of the STRESS supernova survey. We selected the AXAF field centred on the Chandra Deep Field South where, besides the deep X-ray survey, various optical data exist, originating in the EIS and COMBO-17 photometric surveys and the spectroscopic database of GOODS. Results. We obtained a catalogue of 132 variable AGN candidates. Several of the candidates are X-ray sources. We compare our results with an HST variability study of X-ray and IR detected AGNs, finding consistent results. The relatively high fraction of confirmed AGNs in our sample (60%) allowed us to extract a list of reliable AGN candidates for spectroscopic follow-up observations.

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The DEEP Groth Strip Survey. VI. Spectroscopic, Variability, and X‐Ray Detection of Active Galactic Nuclei

Cited by 33 publications

References 59 publications

Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

THESPITZERDEEP, WIDE-FIELD SURVEY

Variability-selected active galactic nuclei from supernova search in the Chandra deep field south

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