Optical Variability of Infrared Power Law-Selected Galaxies & X-ray Sources in the GOODS-South Field

Abstract

We investigate the use of optical variability to identify and study Active Galactic Nuclei (AGN) in the GOODS-South field. A sample of 22 mid-infrared power law sources and 102 X-ray sources with optical counterparts in the HST ACS images were selected. Each object is classified with a variability significance value related to the standard deviation of its magnitude in five epochs separated by 45-day intervals. The variability significance is compared to the optical, mid-IR, and X-ray properties of the sources. We find that 26% of all AGN candidates (either X-ray- or mid-IR-selected) are optical variables. The fraction of optical variables increases to 51% when considering sources with soft X-ray band ratios. For the mid-IR AGN candidates which have multiwavelength SEDs, we find optical variability for 64% of those classified with SEDs like Broad Line AGNs. While mostly unobscured AGN appear to have the most significant optical variability, some of the more obscured AGNs are also observed as variables. In particular, we find two mid-IR power law-selected AGN candidates without X-ray emission that display optical variability, confirming their AGN nature.

arXiv comment11 pages, 4 figures, 1 table, accepted for publication in ApJ

References in corpus (15)

• The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs
• The Chandra Deep Field South: the 1 Million Second
• The Chandra Deep Field South: Optical Spectroscopy I
• Deep Extragalactic X-ray Surveys
• Infrared power-law galaxies in the Chandra Deep Field South: AGN and ULIRGs
• Rapid Growth of Black Holes in Massive Star-Forming Galaxies
• Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model
• Spitzer Detection of PAH and Silicate Dust Features in the Mid-Infrared Spectra of z~2 Ultraluminous Infrared Galaxies
• Variability of Active Galactic Nuclei
• Mid-infrared properties of X-ray sources in the Extended Groth Strip
• Why X-ray--Selected AGN Appear Optically Dull
• Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
• A V-Band Survey for Variable Galactic Nuclei in the Hubble Deep Field
• Variable Extended Objects in SA 57
• The DEEP Groth Strip Survey VI. Spectroscopic, Variability, and X-ray Detection of AGN

Cited by in corpus (19)

• Spitzer's Contribution to the AGN Population
• A new extensive catalog of optically variable AGN in the GOODS Fields and a new statistical approach to variability selection
• Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE Survey of the COSMOS Field
• Variability-selected active galactic nuclei from supernova search in the Chandra deep field south
• Lyman continuum leaking AGN in the SSA22 field
• Variability-based AGN selection using image subtraction in the SDSS and LSST era
• Variability and Multiwavelength Detected AGN in the GOODS Fields
• Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
• Searching for candidates of Lyman continuum sources - revisiting the SSA22 field
• A photometric search for transients in galaxy clusters
• Genuine Retrieval of the AGN Host Stellar Population (GRAHSP)
• A Multi-wavelength Survey of AGN in Massive Clusters: AGN Detection and Cluster AGN Fraction
• Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South
• Continuum optical-UV and X-ray variability of AGN: current results and future challenges
• Active Galactic Nuclei Discovered in the Kepler Mission
• Selection of optically variable active galactic nuclei via a random forest algorithm
• Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 $\mu$m variability
• A Multi-wavelength Survey of AGN in Massive Clusters: AGN Distribution and Host Galaxy Properties
• Optical Spectroscopy of Active Galactic Nuclei in SA57