Chemical evolution of the Universe at 0.7 < z < 1.6 derived from abundance diagnostics of the broad-line region of quasars

Abstract

We present an analysis of Mg II $\lambda 2798$ and Fe II UV emission lines for archival Sloan Digital Sky Survey (SDSS) quasars to explore diagnostics of the magnesium-to-iron abundance ratio in a broad-line region cloud. Our sample consists of 17,432 quasars selected from the SDSS Data Release 7 with a redshift range of $0.72<z<1.63$. A strong anticorrelation between Mg II equivalent width (EW) and the Eddington ratio is found, while only a weak positive correlation is found between Fe II EW and the Eddington ratio. To investigate the origin of these differing behaviors of Mg II and Fe II emission lines, we have performed photoionization calculations using the Cloudy code, where constraints from recent reverberation mapping studies are considered. We find from calculations that (i) Mg II and Fe II emission lines are created at different regions in a photoionized cloud, and (ii) their EW correlations with the Eddington ratio can be explained by just changing the cloud gas density. These results indicate that the Mg II/Fe II flux ratio, which has been used as a first-order proxy for the Mg/Fe abundance ratio in chemical evolution studies with quasar emission lines, depends largely on the cloud gas density. By correcting this density dependence, we propose new diagnostics of the Mg/Fe abundance ratio for a broad line region cloud. Comparing the derived Mg/Fe abundance ratios with chemical evolution models, we suggest that $\alpha$-enrichment by mass loss from metal-poor intermediate-mass stars occurred at $z\sim 2$ or earlier.

arXiv comment18 pages, 17 figures, accepted for publication in The Astrophysical Journal

References in corpus (56)

• The Sloan Digital Sky Survey: Technical Summary
• The chemical composition of the Sun
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• 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
• A luminous quasar at a redshift of z = 7.085
• Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
• The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
• The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei
• The Relationship Between Luminosity and Broad-Line Region Size in Active Galactic Nuclei
• Linear Regression for Astronomical Data with Measurement Errors and Intrinsic Scatter
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements II. The Full Sample of Reverberation-Mapped AGNs
• An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1
• A Close Look at Star Formation around Active Galactic Nuclei
• Elemental Abundances in QSOs: Star Formation and Galactic Nuclear Evolution at High Redshifts
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
• Mass Functions of the Active Black Holes in Distant Quasars from the Large Bright Quasar Survey, the Bright Quasar Survey, and the Color-Selected Sample of the SDSS Fall Equatorial Stripe
• Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines
• Metallicity Evolution of Damped Lyman-alpha Systems out to z~5
• Nucleosynthesis in Type Ia Supernovae
• The delay-time distribution of type-Ia supernovae from Sloan II
• Nucleosynthesis in Type II Supernovae
• Delay Time Distribution Measurement of Type Ia Supernovae by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor
• Gemini Near-infrared Spectroscopy of Luminous z~6 Quasars: Chemical Abundances, Black Hole Masses, and MgII Absorption
• Fe II Emission in 14 Low-Redshift Quasars: I - Observations
• Black hole masses and enrichment of z ~ 6 SDSS quasars
• Evidence for non-evolving FeII/MgII ratios in rapidly accreting z~6 QSOs
• An Atlas of Computed Equivalent Widths of Quasar Broad Emission Lines
• Near Infrared Spectroscopy of High Redshift Active Galactic Nuclei. I. A Metallicity-Accretion Rate Relationship
• Black hole mass estimates and emission-line properties of a sample of redshift z>6.5 quasars
• The Evolution of the Broad-Line Region among SDSS Quasars
• Metallicities and Abundance Ratios from Quasar Broad Emission Lines
• Iron Emission in the z=6.4 Quasar SDSS J114816.64+525150.3
• The Lick AGN Monitoring Project 2011: Fe II Reverberation from the Outer Broad-Line Region
• The Origin of Fe II Emission in AGN
• The Sloan Digital Sky Survey Reverberation Mapping Project: First Broad-line Hbeta and MgII Lags at z>~0.3 from six-Month Spectroscopy
• FeII/MgII Emission Line Ratio in High Redshift Quasars
• Iron Emission in z~6 QSOs
• The Mass of the Central Black Hole in the Seyfert Galaxy NGC 4151
• Implications of infalling Fe II - emitting clouds in active galactic nuclei: anisotropic properties
• High Redshift Quasars and Star Formation in the Early Universe
• Early star formation traced by the highest redshift quasars
• Radiation pressure confinement - II. Application to the broad line region in active galactic nuclei
• What controls the Fe II strength in active galactic nuclei?
• FeII/MgII Emission Line Ratios of QSOs. II. z>6 Objects
• Observations of OI and CaII Emission Lines in Quasars: Implications for the Site of FeII Line Emission
• The mass-metallicity relation of SDSS quasars
• Age Dating of a High-Redshift QSO B1422+231 at Z=3.62 and its Cosmological Implications
• Hubble Space Telescope Observations of Sub-Damped Lyman-alpha Absorbers at z < 0.5, and Implications for Galaxy Chemical Evolution
• Revisited abundance diagnostics in quasars: Fe II/Mg II ratios
• Low-Ionization Emission Regions in Quasars: Gas Properties Probed with Broad O I and Ca II Lines
• Magnetic Confinement, MHD Waves, and Smooth Line Profiles in AGN
• Fe II Emission in AGN: The Role of Total and Gas-Phase Iron Abundance
• Implications from the optical to UV flux ratio of FeII emission in quasars
• A Tentative Size-Luminosity Relation for the Iron Emission-Line Region in Quasars
• Ultraviolet Fe II emission in z ~ 2 quasars

Cited by in corpus (17)

• The X-SHOOTER/ALMA sample of Quasars in the Epoch of Reionization. I. NIR spectral modeling, iron enrichment and broad emission line properties
• The Evolution of Chemical Abundance in Quasar Broad Line Region
• No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928
• Metallicity in Quasar Broad Line Regions at Redshift $\sim$ 6
• The FeII/MgII flux ratio of low-luminosity quasars at z~3
• Chemical Abundance of z~6 Quasar Broad-Line Regions in the XQR-30 Sample
• Semi-empirical metallicity calibrations based on ultraviolet emission lines of type-2 AGNs
• High-ionization emission line ratios from quasar broad line regions: metallicity or density?
• In-situ star formation in accretion disk and explanation for correlation between black hole mass and metallicity in AGNs
• Potential signature of Population III pair-instability supernova ejecta in the BLR gas of the most distant quasar at z = 7.54
• Mg II and Fe II fluxes of luminous quasars at z ~ 2.7 and evaluation of the Baldwin effect in the flux-to-abundance conversion method for quasars
• Comparison of The UV and Optical Fe II Emission in Type 1 AGNs
• The Influence of Disk Composition on the Evolution of Stars in the Disks of Active Galactic Nuclei
• The CaFe Project: Optical FeII and Near-Infrared Ca II triplet emission in active galaxies. II. The driver(s) of the Ca II and Fe II and its potential use as a chemical clock
• Top-heavy stellar mass distribution in galactic nuclei inferred from the universally high abundance ratio of [Fe/Mg]
• Radiative feedback on supermassive star formation: the massive end of the Population III initial mass function
• Strong correlation between FeII/MgII ratio and Eddington ratio of type 1 Active galactic nuclei