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_o. Among the lines we consider, N III] 1750/O III] 1664, N V 1240/(C IV 1549 + O VI 1034) and N V/He II 1640 are the most robust diagnostics. We argue, in particular, that the average N V BEL is not dominated by scattered Ly-alpha 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_o in well-mixed interstellar gas, the star formation must have begun > 10^8 yr before the observed quasar activity.Comment: 15 pages, 5 figures in 6 files, in press with ApJ. This version fixes some minor glitches and includes previously omitted reference

We analyze UV spectra for a large sample of 578 type 1 active galactic nuclei and derive Eddington ratios, L=L Edd , from the bolometric luminosities and emission-line widths for each object in the sample. The sample spans 5 orders of magnitude in supermassive black hole (SMBH) mass, 7 orders of magnitude in luminosity, and a redshift range 0 z 5. We include a sample of 26 low-redshift narrow-line Seyfert 1 galaxies (NLS1's) for comparative analysis. The NLS1's have slightly larger than average L=L Edd ratios (and smaller SMBH masses) for their luminosities, but those L=L Edd values are still substantially below the average for luminous quasars. A large fraction (27%) of the objects overall have L=L Edd > 1, which might be explained by nonspherically symmetric accretion. We find no trend between L=L Edd and either redshift or SMBH mass. Composite spectra sorted by L=L Edd show an unusual emission-line behavior: nearly constant peak heights and decreasing FWHMs with increasing L=L Edd . This is in marked contrast to the emission-line behaviors with luminosity, SMBH mass, and FWHM(C iv), which clearly show trends analogous to the Baldwin effect: decreasing line peaks and equivalent widths with increasing luminosity, SMBH mass, and FWHM. The origins of the unusual behavior with L=L Edd are not understood, but one implication is that metallicity estimates based on emission-line ratios involving nitrogen show no trend with L=L Edd in the composite spectra created from different ranges in L=L Edd . The NLS1 composite, however, shows a slightly high metallicity for its SMBH mass and luminosity. Our earlier work suggests that host galaxy mass, correlated with SMBH mass and AGN luminosity, is the fundamental parameter affecting broad emission line region metallicities. Some secondary effect, not related to L=L Edd , must be enhancing the metallicities in NLS1's.

We analyze spectra for a large sample of 578 active galactic nuclei to examine the relationships between broad emission line properties and central supermassive black hole (SMBH) mass. We estimate SMBH masses by applying the virial theorem to the C iv 1549 broad emission line. Although the FWHMs of C iv and H appear nearly unrelated in individual objects, these FWHMs are well correlated when averaged over subsamples in our database. Therefore, the lines are equally valid indicators of the average SMBH mass in quasar samples. Our sample spans 5 orders of magnitude in SMBH mass, 6 orders of magnitude in luminosity, and a redshift range of 0 z 5. Most lines diminish in equivalent width with increasing black hole mass (the usual '' Baldwin effect ''), and there are no trends with redshift. Recent studies indicate that there is a relationship between SMBH mass and the overall bulge/spheroidal component mass of the surrounding galaxy. This relation, together with the well-known mass-metallicity relationship among galaxies, predicts a relationship between SMBH mass and quasar metallicity. We estimate the metallicity in the broad emission line region by comparing several line ratios involving nitrogen to theoretical predictions. We find that the data are consistent with a trend between SMBH mass and metallicity, with some line ratios indicating a very strong trend, but the uncertainties in several other important line ratios are too large to confirm or test this correlation.

The intensity of the strong N v 1240 line relative to C iv 1549 or to He ii 1640 has been proposed as an indicator of the metallicity of quasi-stellar object (QSO) broad emission line regions, allowing abundance measurements in a large number of QSOs out to the highest redshifts. Previously, it had been shown that the (normally) much weaker lines N iii] 1750 and N iv] 1486 could be used in the same way. The redshift 1.96 QSO 0353À383 has long been known to have N iii] and N iv] lines that are far stronger relative to Ly or C iv than in any other QSO. Because in this particular case these intercombination lines can be easily measured, this unusual object provides an ideal opportunity for testing whether the N v line is a valid abundance indicator. Using new observations of Q0353À383 made both with the Hubble Space Telescope in the ultraviolet and from the ground in the visible passband, we have carefully remeasured the emission lines and reanalyzed their strengths using the latest models of the QSO broad emission line region. We find that intensity ratios involving the strengths of N v, N iv], and N iii] relative to lines of He, C, and O all indicate that nitrogen is overabundant relative to oxygen in Q0353À383 by a factor of $15 compared to solar ratios. This agreement among the diagnostics supports the use of these lines for measuring broad emission line region chemical abundances. If nitrogen behaves like a secondary element, such that N=O / O=H, then the extreme nitrogen enhancement in Q0353À383 implies a metallicity of $15 times the solar value. Even if Q0353À383 represents an extreme outlier in the N=O / O=H relation, the overall metallicity should still be at least 5 times solar. Unusually high metallicities in Q0353À383 might imply that we caught this object just as the gas-phase metallicity in the central part of its host galaxy has peaked, at a time when the interstellar gas supply is nearly exhausted and hence the fuel source for the central QSO is ready to shut off.

Conditions in a black hole outburst The binary system V404 Cygni consists of a red giant star orbiting a black hole. In 2015, a surge of accretion by the black hole caused the surrounding plasma to brighten suddenly for the first time since 1989, briefly becoming the brightest x-ray source in the sky. Dallilar et al. combined observations from radio, infrared, optical, and x-ray telescopes taken during the outburst. They compared how fast the flux decayed at each wavelength, which allowed them to constrain the size of the emitting region, determine that the plasma within it cooled through synchrotron radiation, and measure the magnetic field around the black hole. Science , this issue p. 1299