CHILES VERDES: Radio variability at an unprecedented depth and cadence in the COSMOS field

Abstract

Although it is well-established that some extragalactic radio sources are time-variable, the properties of this radio variability, and its connection with host galaxy properties, remain to be explored---particularly for faint sources. Here we present an analysis of radio variable sources from the CHILES Variable and Explosive Radio Dynamic Evolution Survey (CHILES VERDES)---a partner project of the 1.4 GHz COSMOS \ion{H}{1} Large Extragalactic Survey (CHILES). CHILES VERDES provides an unprecedented combination of survey depth, duration, and cadence, with 960 hrs of 1--2 GHz continuum VLA data obtained over 209 epochs between 2013 and 2019 in a 0.44 deg${}^2$ section of the well-studied extragalactic deep field, COSMOS. We identified 18 moderate-variability sources (showing $10-30\%$ flux density variation) and 40 lower variability sources (2-10$\%$ flux density variation). They are mainly active galactic nuclei (AGN) with radio luminosities in the range of $10^{22}-10^{27}$ W Hz${}^{-1}$ based on cross-matching with COSMOS multi-wavelength catalogs. The moderate-variability sources span redshifts $z=0.22-1.56$, have mostly flat radio spectra ($\alpha >-0.5$), and vary on timescales ranging from days to years. Lower-variability sources have similar properties, but have generally higher radio luminosities than the moderate-variability sources, extend to $z=2.8$, and have steeper radio spectra ($\alpha <-0.5$). No star-forming galaxy showed statistically significant variability in our analysis. The observed variability likely originates from scintillation on short ($\sim$week) timescales, and Doppler-boosted intrinsic AGN variability on long (month--year) timescales.

arXiv comment28 pages, 17 figures. Submitted to ApJ

References in corpus (92)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• Cosmic Star Formation History
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• LOFAR: The LOw-Frequency ARray
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• The Cosmic Evolution Survey (COSMOS) -- Overview
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies
• The First Release COSMOS Optical and Near-IR Data and Catalog
• The Herschel Multi-tiered Extragalactic Survey: HerMES
• Studies in Astronomical Time Series Analysis. VI. Bayesian Block Representations
• Identifying Luminous AGN in Deep Surveys: Revised IRAC Selection Criteria
• The Spitzer Legacy Survey of the HST-ACS 2 sq. deg. COSMOS Field: survey strategy and first analysis
• The Chandra Deep Field South: Optical Spectroscopy I
• A multi-scale multi-frequency deconvolution algorithm for synthesis imaging in radio interferometry
• Self-Consistent Models of the AGN and Black Hole Populations: Duty Cycles, Accretion Rates, and the Mean Radiative Efficiency
• The Chandra COSMOS Legacy survey: overview and point source catalog
• The Expanded Very Large Array -- a New Telescope for New Science
• Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
• An Accurate Flux Density Scale from 1 to 50 GHz
• The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release
• An Accurate Flux Density Scale from 50 MHz to 50 GHz
• The Chandra COSMOS Legacy survey: optical/IR identifications
• The VLA-COSMOS Survey. IV. Deep Data and Joint Catalog
• AzTEC Millimetre Survey of the COSMOS Field: I. Data Reduction and Source Catalogue
• VLA-COSMOS 3GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to $z\lesssim 6$
• The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population
• Characterisation of SCUBA-2 450um and 850um-selected Galaxies in the COSMOS Field
• The VLA-COSMOS 3~GHz Large Project: AGN and host-galaxy properties out to z$\lesssim$6
• The Far-Infrared--Radio Correlation at High Redshifts: Physical Considerations and Prospects for the Square Kilometer Array
• On the use of structure functions to study blazar variability: caveats and problems
• AzTEC millimeter survey of the COSMOS field - III. Source catalog over 0.72 sq. deg. and plausible boosting by large-scale structure
• Orphan GRB radio afterglows: Candidates and constraints on beaming
• MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. XI. Spectral distributions
• Integrated Polarization Properties of 3C48, 3C138, 3C147, and 3C286
• The VLA-COSMOS 3~GHz Large Project: Cosmic evolution of radio AGN and implications for radio-mode feedback since z~5
• Millimeter imaging of submillimeter galaxies in the COSMOS field: Redshift distribution
• The Caltech-NRAO Stripe 82 Survey (CNSS) Paper I: The Pilot Radio Transient Survey In 50 deg${}^2$
• The Parameter Space of Galaxy Formation
• A Complete Survey of the Transient Radio Sky and Implications for Gamma-Ray Bursts, Supernovae, and other Relativistic Explosions
• First Results from MASIV: The Micro-Arcsecond Scintillation-Induced Variability Survey
• Highest Redshift Image of Neutral Hydrogen in Emission: A CHILES Detection of a Starbursting Galaxy at z=0.376
• Thermal and non-thermal emission from circumstellar interaction
• VAST: An ASKAP Survey for Variables and Slow Transients
• SubmilliJansky Transients in Archival Radio Observations
• No precise localization for FRB 150418: claimed radio transient is AGN variability
• The radio AGN population dichotomy: Green valley Seyferts versus red sequence low-excitation AGN
• A Revised View of the Transient Radio Sky
• Limits on Fast Radio Bursts and other transient sources at 182 MHz using the Murchison Widefield Array
• A VLA search for 5 GHz radio transients and variables at low Galactic latitudes
• A 22-year Southern Sky Survey for Transient and Variable Radio Sources using the Molonglo Observatory Synthesis Telescope
• Variable and Transient Radio Sources in the FIRST Survey
• The variability timescales and brightness temperatures of radio flares from stars to supermassive black holes
• Galaxy And Mass Assembly (GAMA): Curation and reanalysis of 16.6k redshifts in the G10/COSMOS region
• LOFAR MSSS: Detection of a low-frequency radio transient in 400 hrs of monitoring of the North Celestial Pole
• A Pilot for a VLA HI Deep Field
• A survey for transients and variables with the Murchison Widefield Array 32-tile prototype at 154 MHz
• Variability of sub-mJy radio sources
• Sample variance, source clustering and their influence on the counts of faint radio sources
• Late Time Observations of the Afterglow and Environment of GRB 030329
• The faint radio sky: VLBA observations of the COSMOS field
• Sensitive Search For Radio Variables And Transients In The Extended Chandra Deep-Field South
• The Allen Telescope Array Twenty-centimeter Survey - A 690-Square-Degree, 12-Epoch Radio Dataset - I: Catalog and Long-Duration Transient Statistics
• Doppler Boosting, Superluminal Motion, and the Kinematics of AGN Jets
• CHILES VI: HI and H$\alpha$ Observations for z < 0.1 Galaxies; Probing HI Spin Alignment with Filaments in the Cosmic Web
• G10/COSMOS: 38 band (far-UV to far-IR) panchromatic photometry using LAMBDAR
• Optical Properties of faint FIRST Variable Radio Sources
• (Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies - I. Multiwavelength identifications and redshift distribution
• Discovery of a bright radio transient in M82: a new radio supernova?
• An automated archival VLA transients survey
• Surveying the Dynamic Radio Sky with the Long Wavelength Demonstrator Array
• CHILES: HI morphology and galaxy environment at z=0.12 and z=0.17
• MKT J170456.2-482100: the first transient discovered by MeerKAT
• The Allen Telescope Array Twenty-centimeter Survey -- A 700-Square-Degree, Multi-Epoch Radio Dataset -- II: Individual Epoch Transient Statistics
• Discovery of a Meter-Wavelength Radio Transient in the SWIRE Deep Field: 1046+59
• Large Scale Structure in CHILES
• The Allen Telescope Array Pi GHz Sky Survey II. Daily and Monthly Monitoring for Transients and Variability in the Bootes Field
• ThunderKAT: The MeerKAT Large Survey Project for Image-Plane Radio Transients
• Coefficients of variation for detecting solar-like oscillations
• A pilot ASKAP survey of radio transient events in the region around the intermittent pulsar PSR J1107-5907
• Radio Variability from a Quiescent Stellar Mass Black Hole Jet
• Using the Intensity Modulation Index to Test Pulsar Radio Emission Models
• The Allen Telescope Array Pi GHz Sky Survey - III: The ELAIS-N1, Coma, and Lockman Hole Fields
• Radio variability in the Phoenix Deep Survey at 1.4GHz
• An insight into the extragalactic transient and variable microJy radio sky across multiple decades
• Millijansky Radio Variability in SDSS Stripe 82
• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
• A pilot survey for transients and variables with the Australian Square Kilometre Array Pathfinder
• The Murchison Widefield Array Transients Survey (MWATS). A search for low frequency variability in a bright Southern hemisphere sample

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