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

Trèvese, D.; Boutsia, K.; Vagnetti, F.; Cappellaro, E.; Puccetti, S.

doi:10.1051/0004-6361:200809884

Cited by 42 publications

(80 citation statements)

References 67 publications

(97 reference statements)

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“…This source is pointlike in HST ACS F180LP image from CANDELS (Grogin et al 2011, Koekemoer et al 2011, Skelton et al 2014) (see Figure 6, bottom left). This source was also identified as an optical variable by Trevese et al (2008) and potentially the radio and optical variability are intrinsically linked e.g. see Breedt et al (2010).…”

Section: Atcdfs J033208-274734mentioning

confidence: 98%

A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

Bell

Huynh

Hancock

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We present a three epoch survey for transient and variables in the extended Chandra Deep Field South at 5.5 GHz with the Australia Telescope Compact Array. A region covering ∼0.3 deg 2 was observed on timescales of 2.5 months and 2.5 years and typical sensitivities 12.1 − 17.1 µJy beam −1 (1σ) were achieved. This survey represents the deepest search for transient and variable radio sources at 5.5 GHz. In total 124 sources were detected above the 5.5σ level. One highly variable radio source was found with ∆S > 50% implying a surface density of ∼3 deg −2 . A further three radio sources were found with lower levels of variability equating to a surface density of ∼13 deg −2 above a detection threshold of 82.3 µJy. All of the variable sources have inverted radio spectra (between 1.4 and 5.5 GHz) and are associated with active galactic nuclei. We conclude that these variables are young gigahertz peaked-spectrum sources with active and self-absorbed radio jets. We explore the variability completeness of this sample and conclude that the fairly low levels of variability would only be detectable in 3−25% of all sources within the field. No radio transients were detected in this survey and we place an upper limit on the surface density of transient events < 7.5 deg −2 above a detection threshold of 68.8 µJy.

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Section: Atcdfs J033208-274734mentioning

confidence: 98%

A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

Bell

Huynh

Hancock

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…where s(V) and Σ σ (V) are the ensemble average and standard deviation of σ, as a function of the magnitude V. Details about the selection criteria, the complete catalogue of the variability selected candidates in the AXAF field, and a comparison of our sample with the already existing ones in the same field have been presented in Trevese et al (2008a). In the present followup campaign we simply started from the catalogue of variable objects selected in Paper I, we excluded all those objects whose redshift was already known from the literature, then we sorted the remaining objects according to increasing V magnitude and prepared a list to observe as many as possible, starting with the brightest ones.…”

Section: Selection Of Candidates and Observationsmentioning

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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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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“…Optical variability has been widely used to identify unobscured AGNs in multiepoch surveys (e.g., Bershady et al 1998;Klesman & Sarajedini 2007;Trevese et al 2008;Villforth et al 2010); the techniques based on optical variability allow the surveying of extended areas by means of ground-based telescopes and do not miss those sources that are characterized by an unusually low X-ray to optical flux ratio (X/O) and hence are not detected by X-rays surveys; furthermore, as several studies (e.g., Barr & Mushotzky 1986;Lawrence & Papadakis 1993;Cristiani et al 1996) support the existence of an anti-correlation between AGN luminosity and the amplitude of variability, lowluminosity AGNs (LLAGNs) can be identified more effectively.…”

Section: Introductionmentioning

confidence: 99%

Variability-selected active galactic nuclei in the VST-SUDARE/VOICE survey of the COSMOS field

Cicco

Paolillo²,

Covone

et al. 2015

A&A

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Context. Active galaxies are characterized by variability at every wavelength, with timescales from hours to years depending on the observing window. Optical variability has proven to be an effective way of detecting AGNs in imaging surveys, lasting from weeks to years. Aims. In the present work we test the use of optical variability as a tool to identify active galactic nuclei in the VST multiepoch survey of the COSMOS field, originally tailored to detect supernova events. Methods. We make use of the multiwavelength data provided by other COSMOS surveys to discuss the reliability of the method and the nature of our AGN candidates. Results. The selection on the basis of optical variability returns a sample of 83 AGN candidates; based on a number of diagnostics, we conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as supernovae, while the nature of the remaining 4 is unknown. For the subsample of AGNs with some spectroscopic classification, we find that Type 1 are prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to retrieve on average 15% of all AGNs in the field identified by means of spectroscopic or X-ray classification, with a strong dependence on the source apparent magnitude (completeness ranging from 26% to 5%). In particular, the completeness for Type 1 AGNs is 25%, while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN population presents on average a larger rms variability than the bulk of non-variable sources, indicating that variability detection for at least some of these objects is prevented only by the photometric accuracy of the data. The low completeness is in part due to the short observing span: we show that increasing the temporal baseline results in larger samples as expected for sources with a red-noise power spectrum. Our results allow us to assess the usefulness of this AGN selection technique in view of future wide-field surveys.

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

Cited by 42 publications

References 67 publications

A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

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

Variability-selected active galactic nuclei in the VST-SUDARE/VOICE survey of the COSMOS field

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