Abstract
The Groth field is one of the sky regions that will be targeted by the OSIRIS Tunable Filter Emission Line Object survey in the optical 820 nm and 920 nm atmospheric windows. In the present paper, public Chandra X-ray data with total exposure time of 200 ks are analyzed and combined with optical broadband data of the Groth field, in order to study a set of optical structural parameters of the X-ray emitters and its relation with X-ray properties. To this aim, we processed the raw, public X-ray data using the Chandra Interactive Analysis of Observations, and determined and analyzed different structural parameters, in order to produce a morphological classification of X-ray sources. We present the morphology of 340 X-ray emitters with optical counterpart detected. Objects have been classified by X-ray type using a diagnostic diagram relating X-ray-to-optical ratio (X/O) to hardness ratio. We did not find any clear correlation between X-ray and morphological types. We analyzed the angular clustering of X-ray sources with optical counterpart using two-point correlation functions. A significant positive angular clustering was obtained from a preliminary analysis of four subsamples of the X-ray sources catalog. The clustering signal of the optically extended counterparts is similar to that of strongly clustered populations like red and very red galaxies, suggesting that the environment plays an important role in active galactic nuclei phenomena. Finally, we combined optical structural parameters with other X-ray and optical properties, and we confirmed an anticorrelation between the X/O ratio and the Abraham concentration index, which might suggest that early-type galaxies have lower Eddington rates than those of late-type galaxies.
Highlights
Optical broadband data combined with X-ray data provide a powerful tool to study active galactic nuclei (AGNs) properties (Georgakakis et al 2006; Steffen et al 2006; Barcons et al 2007)
We present the analysis of public, deep (200 ks) Chandra/ ACIS observations of three fields comprising the original Groth–Westphal strip (GWS), gathered from the Chandra Data Archive, and combined with optical BVRI data from our broadband survey carried out with the 4.2 m William-Herschel Telescope (WHT) at La Palma
We represented the X-ray-tooptical ratio (X/O) ratio with respect to HR1, yielding a basically identical distribution as that described above, and with respect to HR2 and HR2, observing that in these two cases it is more difficult to get a clear separation between different X-ray/morphological types; this behavior is expected since hardness ratios computed from the hard and vhard bands are less sensitive to absorption than those involving the soft band, which is one of the main criteria for the separation between X-ray type 1 and type 2 AGNs
Summary
Optical broadband data combined with X-ray data provide a powerful tool to study active galactic nuclei (AGNs) properties (Georgakakis et al 2006; Steffen et al 2006; Barcons et al 2007). While the analysis of optical data provides valuable information on the host galaxy, deep X-ray extragalactic surveys allow for an extremely efficient detection of the population of AGNs, to investigate their time evolution, and to shed light on their triggering mechanisms. X-ray emitters include a mix of different types of objects such as galaxy clusters and stars These powerful observatories make it possible to access the hard (2–10 keV) range, allowing to directly probe the AGN activity not contaminated by star formation processes. We have performed a deep BVRI broadband survey (Cepa et al 2008) in one of the fields of the Groth strip selected for the OTELO survey We combine these optical data with X-ray information, in order to tackle the study of the AGN population, one of the objectives of the OTELO project. A complete X-ray public catalog can be found in the All-wavelength Extended Groth strip International Survey (AEGIS; Laird et al 2009)
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