The spectral energy distributions, host galaxies and environments of variability-selected active galactic nuclei in GOODS-South

Villforth, C.; Sarajedini, Vicki L.; Koekemoer, Anton M.

doi:10.1111/j.1365-2966.2012.21732.x

Cited by 31 publications

(33 citation statements)

References 102 publications

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“…For the magnitude bins in the bright end, the fraction reaches values of about ∼70%, while at fainter magnitude bins there are no X-ray detections. Villforth et al (2012) and Trevese et al (2008) found similar results, while Sarajedini et al (2011) had a higher rate of variable sources with X-ray detections. Out of the variable sample of Falocco et al (2015), less than 10% had X-ray counterparts, and in the COSMOS field, De Cicco et al (2015) reached a high percentage, up to ∼75%.…”

Section: X-ray Mid-ir and Optical Variability Selected Agnssupporting

confidence: 54%

“…Villforth et al (2010) identified 88 variable sources (out of ∼6,000 sources) using the C-statistic (the ratio of the measured standard deviation, σ, to the expected one σ exp , in this case scaled from the estimated photometric errors; de Diego 2010) on z -band data with the same epochs and time baseline as in Sarajedini et al (2011). The authors, after removing the false positive detections and the stellar population, validated the AGN nature of 55/88 variable sources through spectral energy distribution fitting, the identification of X-ray counterparts in the CDF-S 4Ms catalogue and auxiliary radio and IR data (Villforth et al 2012).…”

Section: Introductionmentioning

confidence: 96%

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Robust identification of active galactic nuclei through HST optical variability in GOODS-S: comparison with the X-ray and mid-IR-selected samples★

Pouliasis

Georgantopoulos

Bonanos

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Identifying Active Galactic Nuclei (AGNs) through their X-ray emission is efficient, but necessarily biased against X-ray-faint objects. We aim to characterize this bias by comparing X-ray-selected AGNs to the ones identified through optical variability and mid-IR colours. We present a catalogue of AGNs selected through optical variability using all publicly available z-band Hubble Space Telescope images in the GOODS-South field. For all objects in the catalogue, we compute X-ray upper limits or discuss detections in the deepest available ∼7 Ms Chandra Deep Field South images and present the Spitzer/IRAC mid-IR colours. For the variability study, we consider only sources observed over at least five epochs and over a time baseline of up to ten years. We adopt the elevated median absolute deviation as a variability indicator robust against individual outlier measurements and identify 113 variability-selected AGN candidates. Among these, 26 have an X-ray counterpart and lie within the conventional AGN area in the F X /F opt diagram. The candidates with X-ray upper limits are on average optically fainter, have higher redshifts compared to the X-ray detected ones and are consistent with low luminosity AGNs. Out of 41 variable optical sources with IR detections, 13 fulfill the IR AGN colour selection criteria. Our work emphasizes the importance of optical variability surveys for constructing complete samples of AGNs including the ones that remain undetected even by the deepest X-ray and IR surveys.

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Section: X-ray Mid-ir and Optical Variability Selected Agnssupporting

confidence: 54%

Section: Introductionmentioning

confidence: 96%

Robust identification of active galactic nuclei through HST optical variability in GOODS-S: comparison with the X-ray and mid-IR-selected samples★

Pouliasis

Georgantopoulos

Bonanos

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Many also believe that the same mechanism could give birth to an active nucleus (e.g. Umemura 1998; Kawakatu et al 2006;Ellison et al 2011;Silverman et al 2011;Villforth et al 2012). Even though the exact mechanism is still unknown, in the local Universe a minimum accretion rate of ∼10 −6±1 M /yr is needed to fuel the black hole (Ho 2008).…”

Section: Introductionmentioning

confidence: 99%

Activity of the Seyfert galaxy neighbours

Koulouridis

Plionis

Chavushyan

et al. 2013

A&A

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We present a follow-up study of a series of papers concerning the role of close interactions as a possible triggering mechanism of AGN activity. We have already studied the close (≤100 h −1 kpc) and the large-scale (≤1 h −1 Mpc) environment of a local sample of Sy1, Sy2, and bright IRAS galaxies (BIRG) and of their respective control samples. The results led us to the conclusion that a close encounter appears capable of activating a sequence where an absorption line galaxy (ALG) galaxy first becomes a starburst, then a Sy2, and finally a Sy1. Here we investigate the activity of neighbouring galaxies of different types of AGN, since both galaxies of an interacting pair should be affected. To this end we present the optical spectroscopy and X-ray imaging of 30 neighbouring galaxies around two local (z 0.034) samples of 10 Sy1 and 13 Sy2 galaxies. Although this is a pilot study of a small sample, various interesting trends have been discovered that imply physical mechanisms that may lead to different Seyfert types. Based on the optical spectroscopy, we find that more than 70% of all neighbouring galaxies exhibit star forming and/or nuclear activity (namely recent star formation and/or AGN), while an additional X-ray analysis showed that this percentage might be significantly higher. Furthermore, we find a statistically significant correlation, at a 99.9% level, between the value of the neighbour's [OIII]/Hβ ratio and the activity type of the central active galaxy, i.e. the neighbours of Sy2 galaxies are systematically more ionized than the neighbours of Sy1s. This result, in combination with trends found using the Equivalent Width of the Hα emission line and the stellar population synthesis code STARLIGHT, indicate differences in the stellar mass, metallicity, and star formation history between the samples. Our results point towards a link between close galaxy interactions and activity and also provide more clues regarding the possible evolutionary sequence inferred by our previous studies.

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“…This kind of perturbation can be provided by interactions and merging between two galaxies, and the result of the inflow is the feeding of the black hole and activation of the AGN phase (e.g., Umemura 1998; Kawakatu et al 2006; Koulouridis et al 2006aKoulouridis et al ,b, 2013Ellison et al 2011;Silverman et al 2011;Villforth et al 2012;Hopkins & Quataert 2011). Thus, the cluster environment, where the concentration of galaxies is very high relative to the field, would also seem favorable to AGN.…”

Section: Introductionmentioning

confidence: 99%

X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression

Koulouridis

Plionis

Мelnyk

et al. 2014

A&A

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We present a study of the overdensity of X-ray-selected active galactic nuclei (AGN) in 33 galaxy clusters in the XMM-LSS field (The XMM-Newton Large Scale Structure Survey), up to redshift z = 1.05 and further divided into a lower (0.14 ≤ z ≤ 0.35) and a higher redshift (0.43 ≤ z ≤ 1.05) subsample. Previous studies have shown that the presence of X-ray-selected AGN in rich galaxy clusters is suppressed, since their number is significantly lower than what is expected from the high galaxy overdensities in the area. In the current study we have investigated the occurrence of X-ray-selected AGN in low ( L x , bol = 2.7 × 10 43 erg/s) and moderate ( L x , bol = 2.4 × 10 44 erg/s) X-ray luminosity galaxy clusters in an attempt to trace back the relation between high-density environments and nuclear activity. Owing to the wide contiguous XMM-LSS survey area, we were able to extend the study to the cluster outskirts. We therefore determined the projected overdensity of X-ray point-like sources around each cluster out to 6r 500 radius, within δr 500 = 1 annulus, with respect to the field expectations based on the X-ray source log N − log S of the XMM-LSS field. To provide robust statistical results we also conducted a consistent stacking analysis separately for the two z ranges. We investigated whether the observed X-ray overdensities are to be expected thanks to the obvious enhancement of galaxy numbers in the cluster environment by also estimating the corresponding optical galaxy overdensities, and we assessed the possible enhancement or suppression of AGN activity in clusters. We find a positive X-ray projected overdensity in both redshift ranges at the first radial bins, which however has the same amplitude as that of optical galaxies. Therefore, no suppression (or enhancement) of X-ray AGN activity with respect to the field is found, in sharp contrast to previous results based on rich galaxy clusters, implying that the mechanisms responsible for the suppression are not as effective in lower density environments. After a drop to roughly the background level between 2 and 3r 500 , the X-ray overdensity exhibits a rise at larger radii, significantly greater than the corresponding optical overdensity. The radial distance of this overdensity "bump", corresponding to ∼1.5−3 Mpc, depends on the richness of the clusters, as well as on the overall X-ray overdensity profile. Finally, using the redshift information, photometric or spectroscopic, of the optical counterparts, we derive the spatial overdensity profile of the clusters. We find that the agreement between X-ray and optical overdensities in the first radial bins is also suggested in the 3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at larger radial distance is at least partially a result of flux boosting by gravitational lensing of background quasi-stellar objects, confirming previous results. For high-redshift clusters, the enhancement of X-ray AGN activity in their outskirts appears to be intrinsic. We argue that a spatial ana...

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The spectral energy distributions, host galaxies and environments of variability-selected active galactic nuclei in GOODS-South

Cited by 31 publications

References 102 publications

Robust identification of active galactic nuclei through HST optical variability in GOODS-S: comparison with the X-ray and mid-IR-selected samples★

Robust identification of active galactic nuclei through HST optical variability in GOODS-S: comparison with the X-ray and mid-IR-selected samples★

Activity of the Seyfert galaxy neighbours

X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression

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