Extreme Variability Quasars in Their Various States. I: The sample selection and composite SDSS spectra

Abstract

Extremely variable quasars (EVQs) are a population of sources showing large optical photometric variability revealed by time-domain surveys. The physical origin of such extreme variability is yet unclear. In this first paper of a series, we construct the largest-ever sample of 14,012 EVQs using photometric data spanning over $>$ 15 years from SDSS and Pan-STARRS1. We divide them into five sub-samples according to the relative brightness of an EVQ during SDSS spectroscopic observation compared to the mean brightness from photometric observations. Corresponding control samples of normal quasars are built with matched redshift, bolometric luminosity and supermassive black hole mass. We obtain the composite SDSS spectra of EVQs in various states and their corresponding control samples. We find EVQs exhibit clearly bluer (redder) SDSS spectra during bright (dim) states, consistent with the "bluer-when-brighter" trend widely seen in normal quasars. We further find the line EWs of broad MgII, CIV and OIII (but not broad Hb which is yet puzzling) gradually decrease from dim state to bright state, similar to the so-called intrinsic Baldwin effect commonly seen in normal AGNs. Meanwhile, EVQs have systematically larger line EWs compared with the control samples. We also see that EVQs exhibit subtle excess in the very broad line component compared with control samples. Possible explanations for the discoveries are discussed. Our findings support the hypothesis that EVQs are in the tail of a broad distribution of quasar properties, but not a distinct population.

arXiv comment25 pages and 21 figures; Accepted for publication in ApJ

References in corpus (100)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• Unified Schemes for Radio-Loud Active Galactic Nuclei
• Correcting for the Effects of Interstellar Extinction
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Baryon Oscillation Spectroscopic Survey of SDSS-III
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• A Catalog of Quasar Properties from SDSS DR7
• Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample
• Dynamics of line-driven disk winds in Active Galactic Nuclei
• Estimating Black Hole Masses in Active Galaxies Using the Halpha Emission Line
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• The Rest-Frame Extreme Ultraviolet Spectral Properties of QSOs
• An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1
• Biases in Virial Black Hole Masses: An SDSS Perspective
• The Ensemble Photometric Variability of ~25000 Quasars in the Sloan Digital Sky Survey
• The Sloan Digital Sky Survey Quasar Catalog: Fourteenth Data Release
• Unification of Luminous Type 1 Quasars through CIV Emission
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• A Catalog of Broad Absorption Line Quasars in Sloan Digital Sky Survey Data Release 5
• Broad Emission Line Shifts in Quasars: An Orientation Measure for Radio-Quiet Quasars?
• A Systematic Search for Changing-Look Quasars in SDSS
• X-CIGALE: fitting AGN/galaxy SEDs from X-ray to infrared
• Long-term optical variability properties of the Palomar-Green quasars
• Comparing Single-Epoch Virial Black Hole Mass Estimators for Luminous Quasars
• Spectral Classification of Quasars in the Sloan Digital Sky Survey: Eigenspectra; Redshift and Luminosity Effects
• What controls the C IV line profile in active galactic nuclei?
• The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity
• CIV 1549 as an Eigenvector 1 Parameter for Active Galactic Nuclei
• The Black Hole Mass - Galaxy Bulge Relationship for QSOs in the SDSS DR3
• Discovery of 21 New Changing-look AGNs in Northern Sky
• Spectral properties of quasars from Sloan Digital Sky Survey data release 14: The catalog
• Quasar Accretion Disks Are Strongly Inhomogeneous
• Analysis of optical Fe II emission in a sample of AGN spectra
• The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
• The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Correcting CIV-Based Virial Black Hole Masses
• 1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months
• Continuum and Emission Line Strength Relations for a large Active Galactic Nuclei Sample
• A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN Fading
• Changing-Look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
• Towards an Understanding of Changing-Look Quasars: An Archival Spectroscopic Search in SDSS
• Systematic Uncertainties in Black Hole Masses Determined from Single Epoch Spectra
• Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence
• The Lick AGN Monitoring Project: Recalibrating Single-Epoch Virial Black Hole Mass Estimates
• The Close AGN Reference Survey (CARS) - Mrk 1018 returns to the shadows after 30 years as a Seyfert 1
• A new physical interpretation of optical and infrared variability in quasars
• CIV Emission Line Properties and Systematic Trends in Quasar Black Hole Mass Estimates
• Are Outflows Biasing Single-Epoch CIV Black Hole Mass Estimates?
• The correlation of line strength with luminosity and redshift from composite QSO spectra
• On the origin of the C IV Baldwin effect in AGN
• The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82
• The Color Variability of Quasars
• Quasar Spectral Slope Variability in the Optical Band
• Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82
• Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
• Evidence for Large Temperature Fluctuations in Quasar Accretion Disks From Spectral Variability
• Broad Hbeta Emission-Line Variability in a Sample of 102 Local Active Galaxies
• The Discovery of Timescale-Dependent Color Variability of Quasars
• The Demise of the Classical BLR in the Luminous Quasar PG1416-129
• The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines
• Understanding Broad Mg II Variability in Quasars with Photoionization: Implications for Reverberation Mapping and Changing-Look Quasars
• Accretion Disk Temperatures and Continuum Colors in QSOs
• Eddington ratio governs the equivalent width of MgII emission line in active galactic nuclei
• EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing
• Coexistence of Gravitationally Bound and Radiation Driven CIV Emission Line Regions in Active Galactic Nuclei
• The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes
• Testing broad line region models with Reverberation Mapping
• Initial results from a systematic search for changing-look active galactic nuclei selected via mid-infrared variability
• Rehabilitating CIV-based black hole mass estimates in quasars
• Identification of SDSSJ141324.27+530527.0 as A New "Changing-Look" Quasar with a "Turn-on" Transition
• Time-delay measurement of MgII broad line response for the highly-accreting quasar HE 0413-4031: Implications for the MgII-based radius-luminosity relation
• The first high-redshift changing-look quasars
• Simulating the timescale dependent color variation in quasars with a revised inhomogeneous disk model
• The Sloan Digital Sky Survey Reverberation Mapping Project: the CIV Blueshift, Its Variability, and Its Dependence Upon Quasar Properties
• Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129
• Spectral Variability of Quasars in the Sloan Digital Sky Survey. II: The C IV Line
• Is the slope of the intrinsic Baldwin effect constant?
• High-redshift Extreme Variability Quasars from Sloan Digital Sky Survey Multi-Epoch Spectroscopy
• The optical variability of SDSS quasars from multi-epoch spectroscopy. II. color variation
• Ultraviolet Continuum Color Variability of Luminous Sloan Digital Sky Survey QSOs
• EUCLIA. II. On the puzzling large UV to X-ray lags in Seyfert galaxies
• Spectral Variability of a Sample of Extreme Variability Quasars and Implications for the MgII Broad-line Region
• Colour changes in quasar light curves
• The Redshifted Excess in Quasar C IV Broad Emission Lines
• The intrinsic Baldwin effect in broad Balmer lines of six long-term monitored AGNs
• Optical emission line properties of a sample of the broad-line AGNs: the Baldwin effect and eigenvector 1
• The Timescale-Dependent Color Variability of Quasars Viewed with GALEX
• Spectral variability of FIRST bright QSOs with SDSS observations
• The Extreme Red Excess in Blazar Ultraviolet Broad Emission Lines
• Characterization of Optical Light Curves of Extreme Variability Quasars Over a ~16-yr Baseline
• The non-constant slope of the CIV Baldwin effect in NGC 4151
• Behaviour of the MgII 2798AA Line Over the Full Range of AGN Variability
• New Clues to Jet Launching: The inner disks in radio loud quasars may be more stable
• More variable quasars have stronger emission lines
• A Sample Bias in Quasar Variability Studies
• Exploring the Variable Sky with the Sloan Digital Sky Survey

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