Understanding Broad Mg II Variability in Quasars with Photoionization: Implications for Reverberation Mapping and Changing-Look Quasars

Abstract

The broad Mg II line in quasars has distinct variability properties compared with broad Balmer lines: it is less variable, and usually does not display a "breathing" mode, the increase in the average cloud distance when luminosity increases. We demonstrate that these variability properties of Mg II can be reasonably well explained by simple Locally Optimally Emitting Cloud (LOC) photoionization models, confirming earlier photoionization results. In the fiducial LOC model, the Mg II-emitting gas is on average more distant from the ionizing source than the H$\alpha$/H$\beta$ gas, and responds with a lower amplitude to continuum variations. If the broad-line region (BLR) is truncated at a physical radius of $\sim 0.3$ pc (for a $10^{8.5}{M}_{\odot }$ BH accreting at Eddington ratio of 0.1), most of the Mg II flux will always be emitted near this outer boundary and hence will not display breathing. These results indicate that reverberation mapping results on broad Mg II, while generally more difficult to obtain due to the lower line responsivity, can still be used to infer the Mg II BLR size and hence black hole mass. But it is possible that Mg II does not have a well defined intrinsic BLR size-luminosity relation for individual quasars, even though a global one for the general population may still exist. The dramatic changes in broad H$\alpha$/H$\beta$ emission in the observationally-rare changing-look quasars are fully consistent with photoionization responses to extreme continuum variability, and the LOC model provides natural explanations for the persistence of broad Mg II in changing-look quasars defined on H$\alpha$/H$\beta$, and the rare population of broad Mg II emitters in the spectra of massive inactive galaxies.

arXiv comment15 pages, 10 figures, accepted for publication in ApJ

References in corpus (54)

• Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• A Catalog of Quasar Properties from SDSS DR7
• Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
• AGN Dusty Tori: II. Observational Implications of Clumpiness
• Biases in Virial Black Hole Masses: An SDSS Perspective
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
• Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
• The AGN Black Hole Mass Database
• Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines
• A Systematic Search for Changing-Look Quasars in SDSS
• What the Optical Recombination Lines Can Tell Us About the Broad Line Regions of Active Galactic Nuclei
• The Sloan Digital Sky Survey Reverberation Mapping Project: H$\alpha$ and H$\beta$ Reverberation Measurements From First-year Spectroscopy and Photometry
• Discovery of 21 New Changing-look AGNs in Northern Sky
• Quasar Accretion Disks Are Strongly Inhomogeneous
• The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
• The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
• Quasar Outflows and AGN Feedback in the Far UV: HST/COS Observations of QSO HE0238-1904
• Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. V. A New Size-Luminosity Scaling Relation for the Broad-Line Region
• Changing-Look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
• Mid-infrared variability of changing-look AGN
• Systematic Uncertainties in Black Hole Masses Determined from Single Epoch Spectra
• The Lick AGN Monitoring Project: Recalibrating Single-Epoch Virial Black Hole Mass Estimates
• The Sloan Digital Sky Survey Reverberation Mapping Project: First Broad-line Hbeta and MgII Lags at z>~0.3 from six-Month Spectroscopy
• Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-Line Analysis for NGC 5548
• The broad emission-line region: the confluence of the outer accretion disc with the inner edge of the dusty torus
• Locally Optimally-Emitting Clouds and the Variable Broad Emission Line Spectrum of NGC 5548
• Quantifying the impact of variable BLR diffuse continuum contributions on measured continuum inter-band delays
• The Mass of the Central Black Hole in the Seyfert Galaxy NGC 4151
• Broad Hbeta Emission-Line Variability in a Sample of 102 Local Active Galaxies
• An accretion disc model for quasar optical variability
• The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines
• Interpreting broad emission-line variations I : Factors influencing the emission-line response
• Eddington ratio governs the equivalent width of MgII emission line in active galactic nuclei
• Photoionized HBeta Emission in NGC 5548: It Breathes!
• The structure of the Mg II broad line emitting region in Type 1 AGNs
• Time delay measurement of Mg II line in CTS C30.10 with SALT
• An Intrinsic Baldwin Effect in the H-beta Broad Emission Line in the Spectrum of NGC 5548
• Discovery of A Mg II Changing-look AGN and its Implications for a Unification Sequence of Changing-look AGNs
• The Sloan Digital Sky Survey Reverberation Mapping Project: Accretion and Broad Emission Line Physics from a Hypervariable Quasar
• Statistical Properties of Multi-epoch Spectral Variability of SDSS Stripe82 Quasars
• Swift/UVOT grism monitoring of NGC 5548 in 2013: an attempt at MgII reverberation mapping
• Simultaneous Ultraviolet and Optical Emission-line Profiles of Quasars: Implications for Black Hole Mass Determination
• Simulating the timescale dependent color variation in quasars with a revised inhomogeneous disk model
• Line and continuum variability of two intermediate-redshift, high-luminosity quasars
• MgII Line Variability of High Luminosity Quasars
• The first spectroscopic dust reverberation programme on active galactic nuclei: the torus in NGC 5548
• Is the slope of the intrinsic Baldwin effect constant?
• On the absence of broad MgII emission-line variability in NGC 3516 during 1996
• The intrinsic Baldwin effect in broad Balmer lines of six long-term monitored AGNs
• SALT long-slit spectroscopy of LBQS 2113-4538: variability of the Mg II and Fe II component
• SALT long-slit spectroscopy of CTS C30.10: two-component Mg II line

Cited by in corpus (32)

• Improving Damped Random Walk parameters for SDSS Stripe 82 Quasars with Pan-STARRS1
• The Sloan Digital Sky Survey Reverberation Mapping Project: MgII Lag Results from Four Years of Monitoring
• The Time Domain Spectroscopic Survey: Changing-Look Quasar Candidates from Multi-Epoch Spectroscopy in SDSS-IV
• The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes
• Initial results from a systematic search for changing-look active galactic nuclei selected via mid-infrared variability
• Exploring Changing-look Active Galactic Nuclei with the Sloan Digital Sky Survey V: First Year Results
• Time Delay of MgII Emission Response for the Luminous Quasar HE 0435-4312: Towards Application of High-Accretor Radius-Luminosity Relation in Cosmology
• Time-delay measurement of MgII broad line response for the highly-accreting quasar HE 0413-4031: Implications for the MgII-based radius-luminosity relation
• OzDES Reverberation Mapping Program: The first Mg II lags from five years of monitoring
• Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 3516
• Velocity-resolved Reverberation Mapping of Changing-look AGN NGC 2617
• Extreme Variability and Episodic Lifetime of Quasars
• High-redshift Extreme Variability Quasars from Sloan Digital Sky Survey Multi-Epoch Spectroscopy
• Flare-like Variability of the Mg~II $\lambda$2798 Å Emission Line and UV Fe~II band in the Blazar CTA~102
• A Systematic Analysis of Stellar Populations in the Host Galaxies of Changing-look AGNs
• Do reverberation-measured H$\beta$ quasars provide a useful test of cosmology?
• Consistency study of high- and low-accreting Mg ii quasars: No significant effect of the Fe ii to Mg ii flux ratio on the radius-luminosity relation dispersion
• Extreme Variability Quasars in Their Various States. I: The sample selection and composite SDSS spectra
• Caltech-NRAO Stripe 82 Survey (CNSS). IV. The Birth of Radio-loud Quasar 013815+00
• Long-term optical spectral monitoring of a changing-look active galactic nucleus NGC 3516 -- II. Broad-line profile variability
• Characterization of Optical Light Curves of Extreme Variability Quasars Over a ~16-yr Baseline
• Behaviour of the MgII 2798AA Line Over the Full Range of AGN Variability
• The SOUX AGN Sample: SDSS-XMM-Newton Optical, Ultraviolet and X-ray selected active galactic nuclei spanning a wide range of parameter space -- Sample definition
• Dark Energy Survey Identification of A Low-Mass Active Galactic Nucleus at Redshift 0.823 from Optical Variability
• Discovery of a new extreme changing-state quasar with 4 mag variation, SDSS J125809.31+351943.0
• Optical Continuum Reverberation Mapping of a Candidate IMBH in a Nearby Seyfert 1 Galaxy
• Velocity-Resolved Ionization Mapping of Broad Line Region. I. Insights into Diverse Geometry and Kinematics
• Extreme Variability Quasars in Their Various States. II: Spectral Variation Revealed with Multi-epoch Spectra
• The Deviation of the Broad-line Region Size Between Reverberation Mapping and Spectroastrometry
• Standardizing reverberation-measured Mg II time-lag quasars, by using the radius-luminosity relation, and constraining cosmological model parameters
• Rarefied Broad-Line Regions in Active Galactic Nuclei: Anomalous Responses in Reverberation Mapping and Implications for Weak Emission-Line Quasars
• Association of Optical, Ultraviolet and Soft X-ray excess Emissions in AGNs