The Effect of Abundance Variations on Estimates of the Densities of Broad-Line Region Clouds in Quasars (original) (raw)
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Metallicities and Abundance Ratios from Quasar Broad Emission Lines
The Astrophysical Journal, 2002
The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs) are important diagnostics of the relative abundances and overall metallicity in the gas. Here we present new theoretical predictions for several UV BELs. We focus specifically on the relative nitrogen abundance as a metallicity indicator, based on the expected secondary enrichment of nitrogen at metallicities Z 0.2 Z ⊙ . Among the lines we consider, N III] λ1750/O III] λ1664, N V λ1240/(C IV λ1549 + O VI λ1034) and N V/He II λ1640 are the most robust diagnostics. We argue, in particular, that the average N V BEL is not dominated by scattered Lyα photons from a broad absorption line wind. We then compare our calculated line ratios with observations from the literature. The results support earlier claims that the gas-phase metallicities near quasars are typically near or several times above the solar value. We conclude that quasar activity is preceded by, or coeval with, an episode of rapid and extensive star formation in the surrounding galactic (or proto-galactic) nuclei. Chemical evolution models of these environments suggest that, to reach Z Z ⊙ in well-mixed interstellar gas, the star formation must have begun 10 8 yr before the observed quasar activity.
The Mass of Quasar Broad Emission Line Regions
2008
We show that the mass of ionized gas in the Broad Line Regions (BLRs) of luminous QSOs is at least several hundred M sun , and probably of order 10 3 -10 4 M sun . BLR mass estimates in several existing textbooks suggest lower values, but pertain to much less luminous Seyfert galaxies or include only a small fraction of the ionized/emitting volume of the BLR. The previous estimates also fail to include the large amounts of BLR gas that emit at low efficiency (in a given line), but that must be present based on reverberation and other studies. Very highly ionized gas, as well as partially ionized and neutral gas lying behind the ionization zones, are likely additional sources of mass within the BLR. The high masses found here imply that the chemical enrichment of the BLR cannot be controlled by mass ejection from one or a few stars. A significant stellar population in the host galaxies must be contributing. Simple scaling arguments based on normal galactic chemical enrichment and solar or higher BLR metallicities show that the minimum mass of the enriching stellar population is of order 10 times the BLR mass, or > 10 4 -10 5 M sun. More realistic models of the chemical and dynamical evolution in galactic nuclei suggest that much larger, bulge-size stellar populations are involved.
New Constraints on the Quasar Broad Emission Line Region
The Astrophysical Journal, 2012
We demonstrate a new technique for determining the physical conditions of the broad-line-emitting gas in quasars, using near-infrared hydrogen emission lines. Unlike higher ionization species, hydrogen is an efficient line emitter for a very wide range of photoionization conditions, and the observed line ratios depend strongly on the density and photoionization state of the gas present. A locally optimally emitting cloud model of the broad emission line region was compared to measured emission lines of four nearby (z ≈ 0.2) quasars that have optical and NIR spectra of sufficient signal to noise to measure their Paschen lines. The model provides a good fit to three of the objects, and a fair fit to the fourth object, an ultraluminous infrared galaxy. We find that low-incident-ionizing fluxes (Φ H < 10 18 cm −2 s −1 ) and high gas densities (n H > 10 12 cm −3 ) are required to reproduce the observed hydrogen emission line ratios. This analysis demonstrates that the use of composite spectra in photoionization modeling is inappropriate; models must be fitted to the individual spectra of quasars.
Revisited Abundance Diagnostics in Quasars: Fe ii /Mg ii Ratios
The Astrophysical Journal, 2003
Both the Fe II UV emission in the 2000−3000Å region (Fe II(UV)) and resonance emission line complex of Mg II at 2800Å are prominent features in quasar spectra. The observed Fe II(UV)/Mg II emission ratios have been proposed as means to measure the buildup of the Fe abundance relative to that of the α-elements C, N, O, Ne and Mg as a function of redshift. The current observed ratios show large scatter and no obvious dependence on redshift. Thus, it remains unresolved whether a dependence on redshift exists and whether the observed Fe II(UV)/Mg II ratios represent a real nucleosynthesis diagnostic. We have used our new 830-level model atom for Fe + in photoionization calculations, reproducing the physical conditions in the broad line regions of quasars. This modeling reveals that interpretations of high values of Fe II(UV)/Mg II are sensitive not only to Fe and Mg abundance, but also to other factors such as microturbulence, density, and properties of the radiation field. We find that the Fe II(UV)/Mg II ratio combined with Fe II (UV)/Fe II (Optical) emission ratio,
Quasars with Super-Metal-rich Emission-Line Regions
Astrophysical Journal, 2007
We study the degree of chemical enrichment in the broad emission line regions (BELRs) of two QSOs with unusually strong nitrogen emission lines. The N V λ1240/C IV λ1549 intensity ratio is often used as a metallicity indicator for QSOs. The validity of this approach can be tested by studying objects in which the N IV] and N III] lines, in addition to N V, are unusually strong and easily measurable. If all of these ionization states of nitrogen point to the same metallicity, it implies that the large N V strengths observed in most QSOs are not due to some peculiarity of the N V λ1240 line. This test had previously been applied to Q0353-383, a QSO long known to have extremely strong N III] and N IV] lines, with the result supporting high metallicity in that object. Here we make the same check in two other QSOs with very strong nitrogen lines, as a step toward using such QSOs to better probe the early chemical enrichment histories of their host galaxies. J1254+0241 has a metallicity of about 10 times solar, with good agreement between the abundance results from different line ratios. J1546+5253 has a more moderate metallicity, about 5 times solar, but the abundances determined from different line ratios show a much wider scatter than they do for J1254+0241 or Q0353-383. This QSO also has an unusual low-ionization emission line spectrum similar to some low-ionization BAL QSOs and to the unusual AGN I Zw 1. We attribute the peculiarities in its spectrum to some combination of unusual structure and/or unusual physical conditions in its BELR. Our results further affirm the validity of the N V/C IV ratio as an abundance indicator in QSOs.
The Messenger, 2015
The Messenger 160 – June 2015 of the observable baryons in the Universe (e.g, Shull et al., 2012; Noterdaeme et al., 2012). In their neutral and molecular phases, baryons are the reservoirs of gas from which stars form. The HI clouds form molecules and molecular clouds further cool, fragment, and initiate star formation in galaxies. The neutral gas mass density (Ωg) evolution over cosmological scales is a possible indicator of gas consumption as star formation proceeds. Ωg observed in high-redshift quasar absorbers is expressed as a fraction of today’s critical density. The contribution of sub-DLAs to Ωg was however poorly constrained until now (see Péroux et al., 2005). Simulations indicate that the gas in sub-DLAs is located in extended halos, whereas the gas in DLAs is located in dense and compact regions (van de Voort et al., 2012). DLAs/sub-DLAs provide the reservoir of neutral gas and serve as a barometer of recent star formation activity.
The Astrophysical Journal, 1973
The luminosity function of quasars and its evolution are discussed, based on comparison of available data on optically selected quasars and quasars found in radio catalogs. It is assumed that the redshift of quasars is cosmological and the results are expressed in the framework of the A = 0, qo = 1 cosmological model. The predictions of various density evolution laws are compared with observations of an optically selected sample of quasars and quasarsamples from radio catalogs. The differences between the optical luminosity functions, the redshift distributions and the radio to optical luminosity ratios of optically selected quasars and radio quasars rule out luminosity functions where there is complete absence of correlation between radio and optical luminosities. These differences also imply that Schmidt's (1970) luminosity function, where there exists a statistical correlation between radio and optical luminosities, although may be correct for high redshift objects, disagrees with observation at low redshifts. These differences can be accounted for by postulating existence of two classes (I and II) of objects. The class I non-evolving objects dominate the optically selected samples at low redshifts, have low optical luminosities of about 10 w/Hz (at 2500 A) and are absent from radio samples because of their relative low radio to optical luminosity ratios. The class II objects are the quasars found in radio catalogs, show strong evolution, have optical luminosities of 1023 to 10 24w/Hz and dominate the optically selected samples at large redshifts. Possible relations between the two classes are also discussed, and tests for the validity of this picture are presented.
Constraint on Quasar Number Counts from Their Contribution to the X-ray Background
Highlights of Astronomy, 1980
Observations with the Einstein X-ray telescope show that quasars, as a class, are luminous X-ray emitters. By coupling our X-ray observations with quasar optical number counts, we can show that the quasars contribute significantly to the diffuse X-ray background. In fact, the X-ray data strongly suggest that somewhat above HPthe slope of the optical counts must flatten.
The quasar mass-luminosity plane - I. A sub-Eddington limit for quasars
Monthly Notices of the Royal Astronomical Society, 2010
We use 62,185 quasars from the Sloan Digital Sky Survey DR5 sample to explore the relationship between black hole mass and luminosity. Black hole masses were estimated based on the widths of their Hβ, MgII, and CIV lines and adjacent continuum luminosities using standard virial mass estimate scaling laws. We find that, over the range 0.2 < z < 4.0, the most luminous low-mass quasars are at their Eddington luminosity, but the most luminous high-mass quasars in each redshift bin fall short of their Eddington luminosities, with the shortfall of order ten or more at 0.2 < z < 0.6. We examine several potential sources of measurement uncertainty or bias and show that none of them can account for this effect. We also show the statistical uncertainty in virial mass estimation to have an upper bound of ∼ 0.15 dex, smaller than the 0.4 dex previously reported. We also examine the highest-mass quasars in every redshift bin in an effort to learn more about quasars that are about to cease their luminous accretion. We conclude that the quasar mass-luminosity locus contains a number of new puzzles that must be explained theoretically.