Michael S. Brotherton

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 FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later

We have used the Very Large Array (VLA) FIRST survey and the Automated Plate Measuring Facility (APM) catalog of the Palomar Observatory Sky Survey I (POSS-I) plates as the basis for constructing a new radio-selected sample of optically bright quasars. This is the first radio-selected sample that is competitive in size with current optically selected quasar surveys. Using only two basic criteria, radio-optical positional coincidence and optical morphology, quasars and BL Lac objects can be identified with 60% selection efficiency; the efficiency increases to 70% for objects fainter than 17 mag. We show that a more sophisticated selection scheme can predict with better than 85% reliability which candidates will turn out to be quasars. This paper presents the second installment of the FIRST Bright Quasar Survey (FBQS), with a catalog of 636 quasars distributed over 2682 deg2. The quasar sample is characterized and all spectra are displayed. The FBQS detects both radio-loud and radio-quiet quasars out to redshift z > 3. We find a large population of objects of intermediate radio loudness; there is no evidence in our sample for a bimodal distribution of radio characteristics. The sample includes ~29 broad absorption line quasars, both high and low ionization, and a number of new objects with remarkable optical spectra.

Properties of Radio-selected Broad Absorption Line Quasars from the First Bright Quasar Survey

In a spectroscopic follow-up to the VLA FIRST survey, the FIRST Bright Quasar Survey (FBQS) has found 29 radio-selected broad absorption line (BAL) quasars. This sample provides the first opportunity to study the properties of radio-selected BAL quasars. Contrary to most previous studies, we establish that a significant population of radio-loud BAL quasars exists. Radio-selected BAL quasars display compact radio morphologies and possess both steep and flat radio spectra. Quasars with low-ionization BALs have a color distribution redder than that of the FBQS sample as a whole. The frequency of BAL quasars in the FBQS is significantly greater, perhaps by as much as a factor of 2, than that inferred from optically selected samples. The frequency of BAL quasars appears to have a complex dependence on radio loudness. The properties of this sample appear to be inconsistent with simple unified models in which BAL quasars constitute a subset of quasars seen edge-on.

Composite Spectra from the FIRST Bright Quasar Survey

We present a very high signal-to-noise ratio composite spectrum created using 657 radio-selected quasars from the FIRST Bright Quasar Survey. The spectrum spans rest-frame wavelengths 900-7500 A. Additionally, we present composite spectra formed from subsets of the total data set in order to investigate the spectral dependence on radio loudness and the presence of broad absorption lines. In particular, radio-loud quasars are red compared to radio-quiet quasars, and quasars showing low-ionization broad absorption lines are red compared to other quasars. We compare our composites with those from the Large Bright Quasar Survey. Composite quasar spectra have proved to be valuable tools for a host of applications, and in that spirit we make these publicly available via the FIRST survey web page.

A Composite Extreme-Ultraviolet QSO Spectrum from FUSE

The Far Ultraviolet Spectroscopic Explorer (FUSE) has surveyed a large sample (>100) of active galactic nuclei (AGNs) in the low-redshift universe (z 0.33 formed from archival Hubble Space Telescope (HST) spectra, α = -1.76 ± 0.12. We identify several prominent emission lines in the FUSE composite and find that the high-ionization O VI and Ne VIII emission lines are enhanced relative to the HST composite. Power-law continuum fits to the individual FUSE AGN spectra reveal a correlation between EUV spectral slope and AGN luminosity in the FUSE and FUSE+HST samples, in the sense that lower luminosity AGNs show harder spectral slopes. We find an anticorrelation between the hardness of the EUV spectral slope and AGN black hole mass, using estimates of this quantity found in the literature. We interpret these results in the context of the well-known anticorrelation between AGN luminosity and emission-line strength, the Baldwin effect, given that the median luminosity of the FUSE AGN sample is an order of magnitude lower than that of the HST sample.The Far Ultraviolet Spectroscopic Explorer (FUSE) has surveyed a large sample (>100) of active galactic nuclei in the low-redshift universe (z<1). Its response at short wavelengths makes it possible to measure directly the far ultraviolet spectral properties of quasistellar objects (QSOs) and Seyfert 1 galaxies at z<0.3. Using archival FUSE spectra, we form a composite extreme ultraviolet (EUV) spectrum of QSOs at z<0.67. After consideration of many possible sources of systematic error in our analysis, we find that the spectral slope of the FUSE composite spectrum, \alpha= -0.56^+0.38_-0.28 for F_\nu \propto \nu^\alpha, is significantly harder than the EUV (\lambda \lesssim 1200 A) portion of the composite spectrum of QSOs with z>0.33 formed from archival Hubble Space Telescope spectra, \alpha=-1.76 \pm 0.12. We identify several prominent emission lines in the \fuse composite and find that the high-ionization O VI and Ne VIII emission lines are enhanced relative to the HST composite. Power law continuum fits to the individual FUSE AGN spectra reveal a correlation between EUV spectral slope and AGN luminosity in the FUSE and FUSE + HST samples in the sense that lower luminosity AGNs show harder spectral slopes. We find an anticorrelation between the hardness of the EUV spectral slope and AGN black hole mass, using estimates of this quantity found in the literature. We interpret these results in the context of the well-known anticorrelation between AGN luminosity and emission line strength, the Baldwin effect, given that the median luminosity of the FUSE AGN sample is an order of magnitude lower than that of the HST sample.

On the Fraction of Quasars with Outflows

Outflows from active galactic nuclei (AGNs) seem to be common and are thought to be important from a variety of perspectives: as an agent of chemical enhancement of the interstellar and intergalactic media, as an agent of angular momentum removal from the accreting central engine, and as an agent limiting star formation in starbursting systems by blowing out gas and dust from the host galaxy. To understand these processes, we must determine what fraction of AGNs feature outflows and understand what forms they take. We examine recent surveys of quasar absorption lines, reviewing the best means to determine if systems are intrinsic and result from outflowing material, and the limitations of approaches taken to date. The surveys reveal that, while the fraction of specific forms of outflows depends on AGN properties, the overall fraction displaying outflows is fairly constant, approximately 60%, over many orders of magnitude in luminosity. We emphasize some issues concerning classification of outflows driven by data type rather than necessarily the physical nature of outflows and illustrate how understanding outflows probably requires a more comprehensive approach than has usually been taken in the past.

The Reddest Quasars

In a survey of quasar candidates selected by matching the Faint Images of the Radio Sky at Twenty cm (FIRST) and Two Micron All-Sky Survey catalogs, we have found two extraordinarily red quasars. FIRST J013435.7-093102 is a 1 Jy source at z = 2.216 and has B-K 10, while FIRST J073820.1+275045 is a 2.5 mJy source at z = 1.985 with B-K ≈ 8.4. FIRST J073820.1+275045 has strong absorption lines of Mg II and C IV in the rest frame of the quasar and is highly polarized in the rest-frame ultraviolet, strongly favoring the interpretation that its red spectral energy distribution is caused by dust reddening local to the quasar. FIRST J073820.1+275045 is thus one of the few low radio luminosity, highly dust-reddened quasars known. The available observational evidence for FIRST J013435.7-093102 leads us to conclude that it too is reddened by dust. We show that FIRST J013435.7-093102 is gravitationally lensed, increasing the number of known lensed, extremely dust-reddened quasars to at least three, including MG 0414-0534 and PKS 1830-211. We discuss the implications of whether these objects are reddened by dust in the host or lensing galaxies. If reddened by their local environment, then we estimate that between 10% and 20% of the radio-loud quasar population is reddened by dust in the host galaxy. The discovery of FIRST J073820.1+275045 and objects now emerging from X-ray surveys suggests the existence of an analogous radio-quiet red quasar population. Such objects would be entirely missed by standard radio or optical quasar surveys. If dust in the lensing galaxies is primarily responsible for the extreme redness of the lensed quasars, then an untold number of gravitationally lensed quasars are being overlooked.

Quasars and the Big Blue Bump

We investigate the ultraviolet-to-optical spectral energy distributions of 17 active galactic nuclei (AGNs) using quasi-simultaneous spectrophotometry spanning 900-9000 A (rest frame). We employ data from the Far Ultraviolet Spectroscopic Explorer, the Hubble Space Telescope, and the 2.1 m telescope at Kitt Peak National Observatory. Taking advantage of the short-wavelength coverage, we are able to study the so-called big blue bump, the region in which the energy output peaks, in detail. Most objects exhibit a spectral break around 1100 A. Although this result is formally associated with large uncertainty for some objects, there is strong evidence in the data that the far-ultraviolet spectral region is below the extrapolation of the near-ultraviolet-optical slope, indicating a spectral break around 1100 A. We compare the behavior of our sample to those of non-LTE thin-disk models covering a range in black hole mass, Eddington ratio, disk inclination, and other parameters. The distribution of ultraviolet-optical spectral indices redward of the break and far-ultraviolet indices shortward of the break are in rough agreement with the models. However, we do not see a correlation between the far-ultraviolet spectral index and the black hole mass, as seen in some accretion disk models. We argue that the observed spectral break is intrinsic to AGNs, although intrinsic reddening as well as Comptonization can strongly affect the far-ultraviolet spectral index. We make our data available online in digital format.

The Next Generation Atlas of Quasar Spectral Energy Distributions from Radio To X-Rays

We have produced the next generation of quasar spectral energy distributions (SEDs), essentially updating the work of Elvis et al. by using high-quality data obtained with several space- and ground-based telescopes, including NASAs Great Observatories. We present an atlas of SEDs of 85 optically bright, non-blazar quasars over the electromagnetic spectrum from radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58 radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical spectroscopic data, supplemented with some far-ultraviolet spectra, and more than half also have Spitzer mid-infrared Infrared Spectrograph spectra. The X-ray spectral parameters are collected from the literature where available. The radio, far-infrared, and near-infrared photometric data are also obtained from either the literature or new observations. We construct composite SEDs for radio-loud and radio-quiet objects and compare these to those of Elvis et al., finding that ours have similar overall shapes, but our improved spectral resolution reveals more detailed features, especially in the mid- and near-infrared.

Is It Round? Spectropolarimetry of the Type II-p Supernova 1999em

We present the first multiepoch spectropolarimetry of a Type II plateau supernova (SN II-P), with optical observations of SN 1999em on days 7, 40, 49, 159, and 163 after discovery. These data are used to probe the geometry of the electron scattering atmosphere before, during, and after the plateau phase, which ended roughly 90 days after discovery. Weak continuum polarization with an unchanging polarization angle (θ ≈ 160°) is detected at all epochs, with p ≈ 0.2% on day 7, p ≈ 0.3% on days 40 and 49, and p ≈ 0.5% in the final observations. Distinct polarization modulations across strong line features are present on days 40, 49, 159, and 163. Uncorrected for interstellar polarization (which is believed to be quite small), polarization peaks are associated with strong P Cygni absorption troughs, and nearly complete depolarization is seen across the Hα emission profile. The temporal evolution of the continuum polarization and sharp changes across lines indicate polarization intrinsic to SN 1999em. When modeled in terms of the oblate, electron scattering atmospheres of Hoflich, the observed polarization suggests an asphericity of at least 7% during the period studied. The temporal polarization increase may indicate greater asphericity deeper into the ejecta. We discuss the implications of asphericity on the use of Type II-P supernovae as primary extragalactic distance indicators through the expanding photosphere method (EPM). If asphericity produces directionally dependent flux and peculiar galaxy motions are characterized by σ = 300 km s-1, it is shown that the agreement between previous EPM measurements of SNe II and distances to the host galaxies predicted by a linear Hubble law restricts mean SN II asphericity to values less than 30% (3 σ) during the photospheric phase.