Sarah Salviander

The Black Hole-Bulge Relationship in Quasars

We use quasi-stellar object (QSO) emission-line widths to examine the MBH-σ* relationship as a function of redshift and to extend the relationship to larger masses. Supermassive black holes in galactic nuclei are closely related to the bulge of the host galaxy. The mass of the black hole MBH increases with the bulge luminosity and with the velocity dispersion of the bulge stars, σ*. An important clue to the origin of this correlation would be an observational determination of the evolution, if any, in the MBH-σ* relationship as a function of cosmic time. The high luminosity of QSOs affords the potential for studies at large redshifts. We derive black hole masses from the continuum luminosity and the width of the broad Hβ line and σ* from the width of the narrow [O III] lines. We find that radio-quiet QSOs conform to the established MBH-σ* relationship up to values of MBH ≈ 1010 M☉, with no discernible change in the relationship out to redshifts of z ≈ 3. These results are consistent with the idea that the growth of supermassive black holes and massive bulges occurred simultaneously.

The Black Hole Mass-Galaxy Bulge Relationship for QSOs in the Sloan Digital Sky Survey Data Release 3

We investigate the relationship between black hole mass, MBH, and host galaxy velocity dispersion, σ*, for QSOs in Data Release 3 of the Sloan Digital Sky Survey. We derive MBH from the broad Hβ line width and continuum luminosity and the bulge stellar velocity dispersion from the narrow [O III] line width (σ[O III]). At higher redshifts, we use Mg II and [O II] in place of Hβ and [O III]. For redshifts z < 0.5, our results agree with the MBH-σ* relationship for nearby galaxies. For 0.5 < z < 1.2, the MBH-σ* relationship appears to show evolution with redshift in the sense that the bulges are too small for their black holes. However, we find that part of this apparent trend can be attributed to observational biases, including a Malmquist bias involving the QSO luminosity. Accounting for these biases, we find ~0.2 dex evolution in the MBH-σ* relationship between now and redshift z ≈ 1.We investigate the relationship between black hole mass, MBH, and host galaxy velocity dispersion, σ∗, for QSOs in Data Release 3 of the Sloan Digital Sky Survey. We derive MBH from the broad Hβ line width and continuum luminosity, and the bulge stellar velocity dispersion from the [O iii] narrow line width (σ[O III]). At higher redshifts, we use Mg ii and [O ii] in place of Hβ and [O iii]. For redshifts z < 0.5, our results agree with the MBH − σ∗ relationship for nearby galaxies. For 0.5 < z < 1.2, the MBH − σ∗ relationship appears to show evolution with redshift in the sense that the bulges are too small for their black holes. However, we find that part of this apparent trend can be attributed to observational biases, including a Malmquist bias involving the QSO luminosity. Accounting for these biases, we find ∼ 0.2 dex evolution in the MBH − σ∗ relationship between now and redshift z ≈ 1. Subject headings: galaxies: active — quasars: general — black hole physics

A SEARCH FOR BINARY ACTIVE GALACTIC NUCLEI: DOUBLE-PEAKED [O III] AGNs IN THE SLOAN DIGITAL SKY SURVEY

We present active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) having double-peaked profiles of [O III]λλ5007, 4959 and other narrow emission lines, motivated by the prospect of finding candidate binary AGNs. These objects were identified by means of a visual examination of 21,592 quasars at z < 0.7 in SDSS Data Release 7 (DR7). Of the spectra with adequate signal-to-noise, 148 spectra exhibit a double-peaked [O III] profile. Of these, 86 are Type 1 AGNs and 62 are Type 2 AGNs. Only two give the appearance of possibly being optically resolved double AGNs in the SDSS images, but many show close companions or signs of recent interaction. Radio-detected quasars are three times more likely to exhibit a double-peaked [O III] profile than quasars with no detected radio flux, suggesting a role for jet interactions in producing the double-peaked profiles. Of the 66 broad-line (Type 1) AGNs that are undetected in the FIRST survey, 0.9% show double-peaked [O III] profiles. We discuss statistical tests of the nature of the double-peaked objects. Further study is needed to determine which of them are binary AGNs rather than disturbed narrow line regions, and how many additional binaries may remain undetected because of insufficient line-of-sight velocity splitting. Previous studies indicate that 0.1% of SDSS quasars are spatially resolved binaries, with typical spacings of ~10-100 kpc. If a substantial fraction of the double-peaked objects are indeed binaries, then our results imply that binaries occur more frequently at smaller separations (<10 kpc). This suggests that simultaneous fueling of both black holes is more common as the binary orbit decays through these spacings.

Recoiling Black Holes in Quasars

Recent simulations of merging black holes with spin give recoil velocities from gravitational radiation up to several thousand kilometers per second. A recoiling supermassive black hole can retain the inner part of its accretion disk, providing fuel for a continuing QSO phase lasting millions of years as the hole moves away from the galactic nucleus. One possible observational manifestation of a recoiling accretion disk is in QSO emission lines shifted in velocity from the host galaxy. We have examined broad-line QSOs with measurable Hβ and [O III] from the Sloan Digital Sky Survey that have broad emission lines substantially shifted relative to the narrow lines. We find no convincing evidence for recoiling black holes carrying accretion disks. We place upper limits on the incidence of recoiling black holes in QSOs of 0.2% for kicks greater than 800 km s-1, 0.08% for kicks greater than 2000 km s-1, and 0.04% for kicks greater than 2500 km s-1 line-of-sight velocity.

Comment On The Black Hole Recoil Candidate Quasar SDSS J092712.65+294344.0

The Sloan Digital Sky Survey (SDSS) quasar J092712.65+294344.0 has been proposed as a candidate for a supermassive black hole (~108.8 M ?) ejected at high speed from the host galactic nucleus by gravitational radiation recoil, or alternatively for a supermassive black hole binary. This is based on a blueshift of 2650 km s?1 of the broad emission lines (b-system) relative to the narrow emission lines (r-system) presumed to reflect the galaxy velocity. New observations with the Hobby-Eberly Telescope (HET) confirm the essential features of the spectrum. We note a third redshift system, characterized by weak, narrow emission lines of [O III] and [O II] at an intermediate velocity 900 km s?1 redward of the broad-line velocity (i-system). A composite spectrum of SDSS QSOs similar to J0927+2943 illustrates the feasibility of detecting the calcium K absorption line in spectra of sufficient quality. The i-system may represent the QSO host galaxy or a companion. Photoionization requires the black hole to be ~3?kpc from the r-system emitting gas, implying that we are observing the system only 106 yr after the recoil event and contributing to the low probability of observing such a system. The HET observations give an upper limit of 10 km s?1 per year on the rate of change of the velocity difference between the r- and b-systems, constraining the orbital phase in the binary model. These considerations and the presence of a cluster of galaxies apparently containing J0927+2943 favor the idea that this system represents a superposition of two active galactic nuclei.

Accretion disk temperatures and continuum colors in QSOs

Accretion disks around supermassive black holes are widely believed to be the dominant source of the optical-ultraviolet continuum in many classes of active galactic nuclei (AGN). We study here the relationship between the continuum colors of AGN and the characteristic accretion disk temperature (Tmax). Based on non-LTE (NLTE) models of accretion disks in AGN computed as described by Hubeny and coworkers, we find that continuum intensity ratios for several pairs of wavelengths between 1350 and 5100 A should show a trend of bluer colors for higher Tmax, notwithstanding random disk inclinations. We compare this theoretical expectation with observed colors of QSOs in the Sloan Digital Sky Survey (SDSS), deriving black hole mass and thence Tmax from the width of the Mg II broad emission line. The observed colors generally do not show the expected trend, and in some cases show a reverse trend of redder colors with increasing Tmax. The cause of this discrepancy does not appear to be dust reddening or galaxy contamination, but may relate to the accretion rate, as the offset objects are accreting above ~30% of the Eddington limit. The derived disk temperature depends primarily on line width, with little or no dependence on luminosity.

QSO NARROW [O III] LINE WIDTH AND HOST GALAXY LUMINOSITY

Galaxy bulge luminosity L, black hole mass MBH, and stellar velocity dispersion ?* increase together in a way suggesting a close evolutionary relationship. Measurements of the MBH-?* relationship as a function of cosmic time may shed light on the origin of this relationship. Direct measurements of ?* at high redshift are difficult, and the width of the narrow emission lines of active galactic nuclei (AGN) has been proposed as a surrogate for ?*. We investigate the utility of using ? for ?* by examining host galaxy magnitudes and [O III] line widths for low-redshift QSOs. For radio-quiet QSOs, ? is consistent in the mean with the value of ?* predicted by the Faber-Jackson relation. For our limited range of Lhost, scatter obscures the expected increase of ? with Lhost. However, for a sample of AGN covering a wide range of measured or inferred ?*, there is a clear increase of ? with ?*. Radio-loud QSOs on average have ? smaller by 0.1 dex than radio-quiet QSOs of similar Lhost, at least for luminosities typical of PG QSOs. Star formation rates in our low-redshift QSOs are smaller than required in order to maintain the typical observed ratio of bulge mass to black hole mass.

The Black Hole Mass-Stellar Velocity Dispersion Relationship for Quasars in the Sloan Digital Sky Survey Data Release 7

We assess evolution in the M BH-σ* relationship for quasars in the Sloan Digital Sky Survey Data Release 7 for the redshift range 0.1 109.0 M ☉) and lowest-mass (M BH < 107.5 M ☉) black holes appears to evolve significantly; however, most or all of this apparent evolution can be accounted for by various observational biases due to intrinsic scatter in the relationship and to uncertainties in observed quantities. The M BH-σ* relationship for black holes in the middle mass range (107.5 < M BH < 109.0 M ☉) shows minimal change with redshift. The overall results suggest a limit of ±0.2 dex on any evolution in the M BH-σ* relationship for quasars out to z ≈ 1 compared with the relationship observed in the local universe. Intrinsic scatter may also provide a plausible way to reconcile the wide range of results of several different studies of the black hole-galaxy relationships.

Accretion Disk Temperatures Of QSOs: Constraints From The Emission Lines

We compare QSO emission-line spectra to predictions based on theoretical ionizing continua of accretion disks. The observed line intensities do not show the expected trend of higher ionization with theoretical accretion disk temperature as predicted from the black hole mass and accretion rate. Consistent with earlier studies, this suggests that the inner disk does not reach temperatures as high as expected from standard disk theory. Modified radial temperature profiles, taking account of winds or advection in the inner disk, achieve better agreement with observation. The emission lines of radio-detected and radio-undetected sources show different trends as a function of the theoretically predicted disk temperature.

In Search of the Largest Velocity Dispersion Galaxies

We present Hobby-Eberly Telescope (HET) observations for galaxies at redshift z 500 km s−1 by the local M•-σ* relationship. This suggests either that QSO black hole masses are overestimated or that the black hole-bulge relationship changes at high black hole mass. The latter option is consistent with evidence that the increase in σ* with luminosity levels off for the brightest elliptical galaxies.