A random forest-based selection of optically variable AGN in the VST-COSMOS field

Abstract

The survey of the COSMOS field by the VLT Survey Telescope is an appealing testing ground for variability studies of active galactic nuclei (AGN). With 54 r-band visits over 3.3 yr and a single-visit depth of 24.6 r-band mag, the dataset is also particularly interesting in the context of performance forecasting for the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). This work is the fifth in a series dedicated to the development of an automated, robust, and efficient methodology to identify optically variable AGN, aimed at deploying it on future LSST data. We test the performance of a random forest (RF) algorithm in selecting optically variable AGN candidates, investigating how the use of different AGN labeled sets (LSs) and features sets affects this performance. We define a heterogeneous AGN LS and choose a set of variability features and optical and near-infrared colors based on what can be extracted from LSST data. We find that an AGN LS that includes only Type I sources allows for the selection of a highly pure (91%) sample of AGN candidates, obtaining a completeness with respect to spectroscopically confirmed AGN of 69% (vs. 59% in our previous work). The addition of colors to variability features mildly improves the performance of the RF classifier, while colors alone prove less effective than variability in selecting AGN as they return contaminated samples of candidates and fail to identify most host-dominated AGN. We observe that a bright (r < 21 mag) AGN LS is able to retrieve candidate samples not affected by the magnitude cut, which is of great importance as faint AGN LSs for LSST-related studies will be hard to find and likely imbalanced. We estimate a sky density of 6.2 million AGN for the LSST main survey down to our current magnitude limit.

25 pages, 14 figures; accepted for publication in A&A

References in corpus (51)

• Scikit-learn: Machine Learning in Python
• Stellar population synthesis at the resolution of 2003
• The Sloan Digital Sky Survey: Technical Summary
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The Cosmic Evolution Survey (COSMOS) -- Overview
• COSMOS Photometric Redshifts with 30-bands for 2-deg2
• The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies
• Preliminary Results from NEOWISE: An Enhancement to the Wide-field Infrared Survey Explorer for Solar System Science
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• The COSMOS Survey: Hubble Space Telescope / Advanced Camera for Surveys (HST/ACS) Observations and Data Processing
• SWIRE: The SIRTF Wide-area InfraRed Extragalactic Survey
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Active Galactic Nuclei: what's in a name?
• Identifying Luminous AGN in Deep Surveys: Revised IRAC Selection Criteria
• The Chandra Deep Field-South Survey: 4 Ms Source Catalogs
• The Chandra COSMOS Legacy survey: overview and point source catalog
• COSMOS : Hubble Space Telescope Observations
• The Ensemble Photometric Variability of ~25000 Quasars in the Sloan Digital Sky Survey
• Weak Gravitational Lensing with COSMOS: Galaxy Selection and Shape Measurements
• Mid-Infrared Selection of Active Galactic Nuclei with the Wide-Field Infrared Survey Explorer. II. Properties of WISE-Selected Active Galactic Nuclei in the NDWFS Boötes Field
• Cosmic X-ray Surveys of Distant Active Galaxies: The Demographics, Physics, and Ecology of Growing Supermassive Black Holes
• The Chandra COSMOS Legacy survey: optical/IR identifications
• On Machine-Learned Classification of Variable Stars with Sparse and Noisy Time-Series Data
• The XMM-Newton Wide-Field Survey in the COSMOS field (XMM-COSMOS): demography and multiwavelength properties of obscured and unobscured luminous AGN
• The Chandra Deep Survey of the Hubble Deep Field North Area. II. Results from the Caltech Faint Field Galaxy Redshift Survey Area
• The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources
• The WISE AGN Catalog
• Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System
• The DEIMOS 10k spectroscopic survey catalog of the COSMOS field
• The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population
• The Spitzer Extragalactic Representative Volume Survey (SERVS): survey definition and goals
• Selecting Quasars by their Intrinsic Variability
• The CatWISE Preliminary Catalog: Motions from $WISE$ and $NEOWISE$ Data
• Understanding extreme quasar optical variability with CRTS: I. Major AGN flares
• The Variability of Quasars. II. Frequency Dependence
• QSO Selection Algorithm Using Time Variability and Machine Learning: Selection of 1,620 QSO Candidates from MACHO LMC Database
• The EPOCH Project: I. Periodic variable stars in the EROS-2 LMC database
• A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescale
• Measuring X-ray variability in faint/sparsely-sampled AGN
• Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE Survey of the COSMOS Field
• Wide-Field InfraRed Survey Telescope (WFIRST) Mission and Synergies with LISA and LIGO-Virgo
• Robust period estimation using mutual information for multi-band light curves in the synoptic survey era
• Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
• SUDARE-VOICE variability-selection of Active Galaxies in the Chandra Deep Field South and the SERVS/SWIRE region
• Pan-STARRS1 variability of XMM-COSMOS AGN. I. Impact on photometric redshifts
• The QUEST-La Silla AGN Variability Survey: selection of AGN candidates through optical variability
• The QUEST-La Silla AGN Variability Survey
• An irregular discrete time series model to identify residuals with autocorrelation in astronomical light curves
• Extending the variability selection of active galactic nuclei in the W-CDF-S and SERVS/SWIRE region
• A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

Cited by in corpus (17)

• A structure function analysis of VST-COSMOS AGN
• The LSST era of supermassive black holes accretion-disk reverberation mapping
• Estimating AGN Black Hole Masses via Continuum Reverberation Mapping in the Era of LSST
• Continuum optical-UV and X-ray variability of AGN: current results and future challenges
• ULISSE: A Tool for One-shot Sky Exploration and its Application to Active Galactic Nuclei Detection
• Target Detection Framework for Lobster Eye X-Ray Telescopes with Machine Learning Algorithms
• Selection of optically variable active galactic nuclei via a random forest algorithm
• Long-term variability of the composite galaxy SDSS J103911-000057: A candidate of true Type-2 AGN
• Disentangling transients and their host galaxies with Scarlet2: A framework to forward model multi-epoch imaging
• Identification of problematic epochs in astronomical time series through transfer learning
• Scalable and Robust Multiband Modeling of AGN Light Curves in Rubin-LSST
• Automated algorithms to build Active Galactic Nuclei classifiers
• Unlocking AGN Variability with Custom ZTF Photometry for High-Fidelity Light Curves and Robust Selection
• Navigating AGN variability with self-organizing maps
• AGN variability in the age of VRO
• VarIabiLity seLection of AstrophysIcal sources iN PTF (VILLAIN) I. Structure function fits to 71 million objects
• AGILE: an end-to-end Rubin-LSST simulation of AGNs, galaxies, and stars I. Software description and first data release