arXiv subjects

Michael S. Brotherton

Publications and source records attributed to Michael S. Brotherton.

At least 55 records · Page 3Linked to original sources

arXiv2019

Optical/NIR stellar absorption and emission-line indices from luminous infrared galaxies

We analyze a set of optical-to-near-infrared long-slit nuclear spectra of 16 infrared-luminous spiral galaxies. All of the studied sources present H$_2$ emission, which reflects the star-forming nature of our sample, and they clearly display H I emission lines in the optical. Their continua contain many strong stellar absorption lines, with the most common features due to Ca I, Ca II, Fe I, Na I, Mg I, in addition to prominent absorption bands of TiO, VO, ZrO, CN and CO. We report a homogeneous set of equivalent width (EW) measurements for 45 indices, from optical to NIR species for the 16 star-forming galaxies as well as for 19 early type galaxies where we collected the data from the literature. This selected set of emission and absorption-feature measurements can be used to test predictions of the forthcoming generations of stellar population models. We find correlations among the different absorption features and propose here correlations between optical and NIR indices, as well as among different NIR indices, and compare them with model predictions. While for the optical absorption features the models consistently agree with the observations,the NIR indices are much harder to interpret. For early-type spirals the measurements agree roughly with the models, while for star-forming objects they fail to predict the strengths of these indices.

astro-ph.GA↗

arXiv2018

Monitoring AGNs with Hβ Asymmetry. I. First Results: Velocity-resolved Reverberation Mapping

We have started a long-term reverberation mapping project using the Wyoming Infrared Observatory 2.3 meter telescope titled "Monitoring AGNs with Hβ Asymmetry" (MAHA). The motivations of the project are to explore the geometry and kinematics of the gas responsible for complex Hβ emission-line profiles, ideally leading to an understanding of the structures and origins of the broad-line region (BLR). Furthermore, such a project provides the opportunity to search for evidence of close binary supermassive black holes. We describe MAHA and report initial results from our first campaign, from December 2016 to May 2017, highlighting velocity-resolved time lags for four AGNs with asymmetric Hβ lines. We find that 3C 120, Ark 120, and Mrk 6 display complex features different from the simple signatures expected for pure outflow, inflow, or a Keplerian disk. While three of the objects have been previously reverberation mapped, including velocity-resolved time lags in the cases of 3C 120 and Mrk 6, we report a time lag and corresponding black hole mass measurement for SBS 1518+593 for the first time. Furthermore, SBS 1518+593, the least asymmetric of the four, does show velocity-resolved time lags characteristic of a Keplerian disk or virialized motion more generally. Also, the velocity-resolved time lags of 3C 120 have significantly changed since previously observed, indicating an evolution of its BLR structure. Future analyses of the data for these objects and others in MAHA will explore the full diversity of Hβ lines and the physics of AGN BLRs.

astro-ph.GA↗

arXiv2017

Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei

Type 1 active galactic nuclei display broad emission lines, regarded as arising from photoionized gas moving in the gravitational potential of a supermassive black hole. The origin of this broad-line region gas is unresolved so far, however. Another component is the dusty torus beyond the broad-line region, likely an assembly of discrete clumps that can hide the region from some viewing angles and make them observationally appear as Type 2 objects. Here we report that these clumps moving within the dust sublimation radius, like the molecular cloud G2 discovered in the Galactic center, will be tidally disrupted by the hole, resulting in some gas becoming bound at smaller radii while other gas is ejected and returns to the torus. The clumps fulfill necessary conditions to be photoionized. Specific dynamical components of tidally disrupted clumps include spiral-in gas as inflow, circularized gas, and ejecta as outflow. We calculate various profiles of emission lines from these clouds, and find they generally agree with H$β$ profiles of Palomar-Green quasars. We find that asymmetry, shape and shift of the profiles strongly depend on [O III], luminosity, which we interpret as a proxy of dusty torus angles. Tidally disrupted clumps from the torus may represent the source of the broad-line region gas.

astro-ph.GA↗

arXiv2015

Orientation and quasar black hole mass estimation

We have constructed a sample of 386 radio-loud quasars with z < 0.75 from the Sloan Digital Sky Survey in order to investigate orientation effects on black hole mass estimates. Orientation is estimated using radio core dominance measurements based on FIRST survey maps. Black hole masses are estimated from virial-based scaling relationships using H-beta, and compared to the stellar velocity dispersion (sigma_*), predicted using the Full Width at Half Maximum (FWHM) of [O III] 5007, which tracks mass via the M-sigma_* relation. We find that the FWHM of Hbeta correlates significantly with radio core dominance and biases black hole mass determinations that use it, but that this is not the case for sigma_* based on [O III] 5007. The ratio of black hole masses predicted using orientation-biased and unbiased estimates, which can be determined for radio-quiet as well as radio-loud quasars, is significantly correlated with radio core dominance. Although there is significant scatter, this mass ratio calculated in this way may in fact serve as an orientation estimator. We additionally note the existence of a small population radio core-dominated quasars with extremely broad H-beta emission lines that we hypothesise may represent recent black hole mergers.

astro-ph.GA↗

arXiv2015

Bias in C IV-based quasar black hole mass scaling relationships from reverberation mapped samples

The masses of the black holes powering quasars represent a fundamental parameter of active galaxies. Estimates of quasar black hole masses using single-epoch spectra are quite uncertain, and require quantitative improvement. We recently identified a correction for C IV $λ$1549-based scaling relationships used to estimate quasar black hole masses that relies on the continuum-subtracted peak flux ratio of the ultraviolet emission-line blend Si IV + OIV] (the $λ$1400 feature) to that of C IV. This parameter correlates with the suite of associated quasar spectral properties collectively known as "Eigenvector 1" (EV1). Here we use a sample of 85 quasars with quasi-simultaneous optical-ultraviolet spectrophotometry to demonstrate how biases in the average EV1 properties can create systematic biases in C IV-based black hole mass scaling relationships. This effect results in nearly an order of magnitude moving from objects with small $<$ peak $λ$1400/C IV $>$, which have overestimated black hole masses, to objects with large $<$ peak $\lambda1400$/C IV $>$, which have underestimated values. We show that existing reverberation-mapped samples of quasars with ultraviolet spectra -- used to calibrate C IV-based scaling relationships -- have significant EV1 biases that result in predictions of black hole masses nearly 50\% too high for the average quasar. We offer corrections and suggestions to account for this bias.

astro-ph.GA↗

arXiv2015

Post-Starburst Quasars: Bridging the Gap Between Post-Starburst Galaxies and Quasars

In order to better understand the nature of post-starburst quasars (PSQs) in the context of galaxy evolution, we compare their properties to those of post-starburst galaxies and quasars from appropriately selected samples possessing similar redshift ($z \sim 0.3$), luminosity ($M_r \sim -$23), and data quality. We consider morphologies, spectral features, and derived physical properties of the stellar populations and central supermassive black hole. PSQs themselves come in two types: the more luminous AGNs with more luminous post-starburst stellar populations hosted by elliptical galaxies, some which are clearly merger products, and the less luminous systems existing within relatively undisturbed spiral galaxies and possessing signs of a more extended period of star formation. Post-starburst galaxies (PSQs) have elliptical and disturbed/post-merger morphologies similar to those of the more luminous PSQs, display similar spectral properties, but also can have younger stellar populations for a given starburst mass. Quasars at similar redshifts and luminosities around the Seyfert/quasar transition possess similar AGN characteristics, in terms of black hole mass and accretion rate, compared with those of PSQs, but do not appear to be hosted by galaxies with significant post-starburst populations. Recent studies of more luminous quasars find hosts consistent with those of our luminous PSQs, suggesting that these PSQs may be in transition between post-starburst galaxies and a more luminous quasar stage when the post-starburst stellar population remains dominant. The lower luminosity PSQs appear to differ from lower luminosity quasars (Seyfert galaxies) in terms of more significant star formation in their past.

astro-ph.GA↗

arXiv2014

Radio-Loud and Radio-Quiet BAL Quasars: A Detailed Ultraviolet Comparison

Studies of radio-loud (RL) broad absorption line (BAL) quasars indicate that popular orientation-based BAL models fail to account for all observations. Are these results extendable to radio-quiet (RQ) BAL quasars? Comparisons of RL and RQ BAL quasars show that many of their properties are quite similar. Here we extend these analyses to the rest-frame ultraviolet (UV) spectral properties, using a sample of 73 RL and 473 RQ BAL quasars selected from the Sloan Digital Sky Survey (SDSS). Each RQ quasar is individually matched to a RL quasar in both redshift (over the range $1.5 < z < 3.5$) and continuum luminosity. We compare several continuum, emission line, and absorption line properties, as well as physical properties derived from these measurements. Most properties in the samples are statistically identical, though we find slight differences in the velocity structure of the BALs that cause apparent differences in CIV emission line properties. Differences in the velocities may indicate an interaction between the radio jets and the absorbing material. We also find that UV FeII emission is marginally stronger in RL BAL quasars. All of these differences are subtle, so in general we conclude that RL and RQ BAL QSOs are not fundamentally different objects, except in their radio properties. They are therefore likely to be driven by similar physical phenomena, suggesting that results from samples of RL BAL quasars can be extended to their RQ counterparts.

astro-ph.GA↗

arXiv2014

2D stellar population and gas kinematics of the inner kiloparsec of the post-starburst quasar SDSS J0330-0532

We have used optical Integral Field Spectroscopy in order to map the star formation history of the inner kiloparsec of the Post-Starburst Quasar (PSQ) J0330--0532 and to map its gas and stellar kinematics as well as the gas excitation. PSQs are hypothesized to represent a stage in the evolution of galaxies in which the star formation has been recently quenched due to the feedback of the nuclear activity, as suggested by the presence of the post-starburst population at the nucleus. We have found that the old stellar population (age $\ge$ 2.5 Gyr) dominates the flux at 5100 Å in the inner 0.26 kpc, while both the post-starburst (100 Myr $\le$ age $<$ 2.5 Gyr) and starburst (age $<$ 100 Myr) components dominate the flux in a circumnuclear ring at $\approx$0.5 kpc from the nucleus. With our spatially resolved study we do not have found any post-starburst stellar population in the inner 0.26\,kpc. On the other hand, we do see the signature of AGN feedback in this region, which does not reach the circumnuclear ring where the post-starburst population is observed. We thus do not support the quenching scenario for the J0330-0532. In addition, we have concluded that the strong signature of the post-starburst population in larger aperture spectra (e.g. from Sloan Digital Sky Survey) is partially due to the combination of the young and old age components. Based on the M$_{\rm BH}-σ_{\rm star}$ relationship and the stellar kinematics we have estimated a mass for the supermassive black hole of 1.48 $\pm$ 0.66 $\times$10$^7$ M$_\odot$.

astro-ph.GA↗

arXiv2013

The X-ray Spectrum and Spectral Energy Distribution of FIRST J155633.8+351758: a LoBAL Quasar with a Probable Polar Outflow

We report the results of a new 60 ks Chandra X-ray Observatory Advanced CCD Imaging Spectrometer S-array (ACIS-S) observation of the reddened, radio-selected, highly polarized `FeLoBAL' quasar FIRST J1556+3517. We investigated a number of models of varied sophistication to fit the 531-photon spectrum. These models ranged from simple power laws to power laws absorbed by hydrogen gas in differing ionization states and degrees of partial covering. Preferred fits indicate that the intrinsic X-ray flux is consistent with that expected for quasars of similarly high luminosity, i.e., an intrinsic, dereddened and unabsorbed optical to X-ray spectral index of -1.7. We cannot tightly constrain the intrinsic X-ray power-law slope, but find indications that it is flat (photon index Gamma = 1.7 or flatter at a >99% confidence for a neutral hydrogen absorber model). Absorption is present, with a column density a few times 10^23 cm^-2, with both partially ionized models and partially covering neutral hydrogen models providing good fits. We present several lines of argument that suggest the fraction of X-ray emissions associated with the radio jet is not large. We combine our Chandra data with observations from the literature to construct the spectral energy distribution of FIRST J1556+3517 from radio to X-ray energies. We make corrections for Doppler beaming for the pole-on radio jet, optical dust reddening, and X-ray absorption, in order to recover a probable intrinsic spectrum. The quasar FIRST J1556+3517 seems to be an intrinsically normal radio-quiet quasar with a reddened optical/UV spectrum, a Doppler-boosted but intrinsically weak radio jet, and an X-ray absorber not dissimilar from that of other broad absorption line quasars.

astro-ph.HE↗

arXiv2013

Mid-infrared Spectral Properties of Post-Starburst Quasars

We present Spitzer InfraRed Spectrograph (IRS) low-resolution spectra of 16 spectroscopically selected post-starburst quasars (PSQs) at z ~ 0.3. The optical spectra of these broad-lined active galactic nuclei (AGNs) simultaneously show spectral signatures of massive intermediate-aged stellar populations making them good candidates for studying the connections between AGNs and their hosts. The resulting spectra show relatively strong polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 and 11.3\micron and a very weak silicate feature, indicative of ongoing star formation and low dust obscuration levels for the AGNs. We find that the mid-infrared composite spectrum of PSQs has spectral properties between ULIRGs and QSOs, suggesting that PSQs are hybrid AGN and starburst systems as also seen in their optical spectra. We also find that PSQs in early-type host galaxies tend to have relatively strong AGN activities, while those in spiral hosts have stronger PAH emission, indicating more star formation.

astro-ph.CO↗

arXiv2012

The Properties of Post-Starburst Quasars Based on Optical Spectroscopy

We present optical spectroscopy of a sample of 38 post-starburst quasars (PSQs) at z ~ 0.3, 29 of which have morphological classifications based on Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs) possess the spectral signatures of massive intermediate-aged stellar populations making them potentially useful for studying connections between nuclear activity and host galaxy evolution. We model the spectra in order to determine the ages and masses of the host stellar populations, and the black hole masses and Eddington fractions of the AGNs. Our model components include an instantaneous starburst, a power-law, and emission lines. We find the PSQs have MBH ~ 10^8 Msun accreting at a few percent of Eddington luminosity and host ~ 10^10.5 Msun stellar populations which are several hundred Myr to a few Gyr old. We investigate relationships among these derived properties, spectral properties, and morphologies. We find that PSQs hosted in spiral galaxies have significantly weaker AGN luminosities, older starburst ages, and narrow emission-line ratios diagnostic of ongoing star-formation when compared to their early-type counterparts. We conclude that the early-type PSQs are likely the result of major mergers and were likely luminous infrared galaxies in the past, while spiral PSQs with more complex star-formation histories are triggered by less dramatic events (e.g., harassment, bars). We provide diagnostics to distinguish the early-type and spiral hosts when high spatial resolution imaging is not available.

astro-ph.CO↗

arXiv2012

2D stellar population and gas kinematics of the inner 1.5 kpc of the post-starburst quasar SDSS J0210-0903

Post-Starburst Quasars (PSQs) are hypothesized to represent a stage in the evolution of massive galaxies in which the star formation has been recently quenched due to the feedback of the nuclear activity. In this paper our goal is to test this scenario with a resolved stellar population study of the PSQ J0210-0903, as well as of its emitting gas kinematics and excitation. We have used optical Integral Field Spectroscopy obtained with the Gemini GMOS instrument at a velocity resolution of ~120 km/s and spatial resolution of ~0.5 kpc. We find that old stars dominate the luminosity (at 4700 Å) in the inner 0.3 kpc (radius), while beyond this region (at ~0.8 kpc) the stellar population is dominated by both intermediate age and young ionizing stars. The gas emission-line ratios are typical of Seyfert nuclei in the inner 0.3 kpc, where an outflow is observed. Beyond this region the line ratios are typical of LINERs and may result from the combination of diluted radiation from the nucleus and ionization from young stars. The gas kinematics show a combination of rotation in the plane of the galaxy and outflows, observed with a maximum blueshift of -670 km/s. We have estimated a mass outflow rate in ionized gas in the range 0.3--1.1 M_sun/yr and a kinetic power for the outflow of dE/dt ~ 1.4--5.0 x 10^40 erg/s ~0.03% - 0.1% x L_bol. This outflow rate is two orders of magnitude higher than the nuclear accretion rate of ~8.7 x 10^-3 M_sun/yr, thus being the result of mass loading of the nuclear outflow by circumnuclear galactic gas. Our observations support an evolutionary scenario in which the feeding of gas to the nuclear region has triggered a circumnuclear starburst 100's Myr ago, followed by the triggering of the nuclear activity, producing the observed gas outflow which may have quenched further star formation in the inner 0.3 kpc.

astro-ph.CO↗

arXiv2012

Black Hole - Bulge Relationship of Post-Starburst Quasars at z \sim 0.3

The MBH - σ\ast relation has been studied extensively for local galaxies, but to date there have been scarce few direct measurements of stellar velocity dispersions for systems beyond the local universe. We investigate black hole and host galaxy properties of six "post-starburst quasars" at z \sim 0.3. Spectra of these objects simultaneously display features from the active nucleus including broad emission lines and a host galaxy Balmer absorption series indicative of the post-starburst stellar population. These are the first measurements of σ\ast in such objects, and we significantly increase the number of directly-measured non-local objects on the MBH - σ\ast diagram. The "post-starburst quasars" of our sample fall on or above the locally defined MBH - σ\ast relation, a result that is consistent with previous MBH - σ\ast studies of samples at z > 0.1. However, they are generally consistent with the MBH-Lbulge relation. Futhermore, their location on the Faber-Jackson relation suggests that some of the bulges may be dynamically peculiar.

astro-ph.CO↗

arXiv2012

The Optical and Ultraviolet Emission-Line Properties of Bright Quasars with Detailed Spectral Energy Distributions

We present measurements and statistical properties of the optical and ultraviolet emission lines present in the spectra of 85 bright quasars which have detailed spectral energy distributions. This heterogeneous sample has redshifts up to z=1.5 and is comprised of three subsamples that may be of particular utility: ultraviolet excess Palomar-Green quasars, quasars with far-ultraviolet coverage from FUSE, and radio-loud quasars selected to have similar extended radio luminosity originally selected for orientation studies. Most of the objects have quasi-simultaneous optical-ultraviolet spectra, with significant coverage in the radio-to-X-ray wavebands. The parameters of all strong emission lines are measured by detailed spectral fitting. Many significant correlations previously found among quasar emission-line properties are also present in this sample, e.g., the Baldwin effect, the optical correlations collectively known as eigenvector 1, and others. Finally, we use our measurements plus scaling relationships to estimate black hole masses and Eddington fractions. We show the mass estimates from different emission lines are usually in agreement within a factor of 2, but nearly a third show larger differences. We suggest using multiple mass scaling relationships to estimate black hole masses when possible, and adopting a median of the estimates as the black hole mass for individual objects. Line measurements and derived AGN properties will be used for future studies examining the relationships among quasar emission lines and their spectral energy distributions.

astro-ph.CO↗

arXiv2012

Updating quasar bolometric luminosity corrections. II. Infrared bolometric corrections

We present infrared bolometric luminosity corrections derived from the detailed spectral energy distributions of 62 bright quasars of low- to moderate-redshift (z=0.03-1.4). At 1.5, 2, 3, 7, 12, 15, and 24 microns we provide bolometric corrections of the mathematical forms L_iso=ζλL_λand log(L_iso)=A+B log(λL_λ). Bolometric corrections for radio-loud and radio-quiet objects are consistent within 95% confidence intervals, so we do not separate them. Bolometric luminosities estimated using these corrections are typically smaller than those derived from some commonly used in the literature. We investigate the possibility of a luminosity dependent bolometric correction and find that, while the data are consistent with such a correction, the dispersion is too large and the luminosity range too small to warrant such a detailed interpretation. Bolometric corrections at 1.5 $μ$m are appropriate for objects with properties that fall in the range log(L_bol)=45.4-47.3 and bolometric corrections at all other wavelengths are appropriate for objects with properties that fall in the range log(L_bol)=45.1-47.0.

astro-ph.CO↗

arXiv2012

The Viewing Angles of Broad Absorption Line Versus Unabsorbed Quasars

It was recently shown that there is a significant difference in the radio spectral index distributions of broad absorption line (BAL) quasars and unabsorbed quasars, with an overabundance of BAL quasars with steeper radio spectra. This result suggests that source orientation does play into the presence or absence of BAL features. In this paper we provide more quantitative analysis of this result based on Monte-Carlo simulations. While the relationship between viewing angle and spectral index does indeed contain a lot of scatter, the spectral index distributions are different enough to overcome that intrinsic variation. Utilizing two different models of the relationship between spectral index and viewing angle, the simulations indicate that the difference in spectral index distributions can be explained by allowing BAL quasar viewing angles to extend about 10 degrees farther from the radio jet axis than non-BAL sources, though both can be seen at small angles. These results show that orientation cannot be the only factor determining whether BAL features are present, but it does play a role.

astro-ph.CO↗

arXiv2012

Updating quasar bolometric luminosity corrections

Bolometric corrections are used in quasar studies to quantify total energy output based on a measurement of a monochromatic luminosity. First, we enumerate and discuss the practical difficulties of determining such corrections, then we present bolometric luminosities between 1 μm and 8 keV rest frame and corrections derived from the detailed spectral energy distributions of 63 bright quasars of low to moderate redshift (z = 0.03-1.4). Exploring several mathematical fittings, we provide practical bolometric corrections of the forms L_iso=ζλL_λ and log(L_iso)=A+B log(λL_λ) for λ= 1450, 3000, and 5100 Å, where L_iso is the bolometric luminosity calculated under the assumption of isotropy. The significant scatter in the 5100 Å bolometric correction can be reduced by adding a first order correction using the optical slope, α_λ,opt. We recommend an adjustment to the bolometric correction to account for viewing angle and the anisotropic emission expected from accretion discs. For optical/UV monochromatic luminosities, radio-loud and radio-quiet bolometric corrections are consistent within 95% confidence intervals so we do not make separate radio-loud and radio-quiet corrections. In addition, we provide several bolometric corrections to the 2-10 keV X-ray luminosity, which are shown to have very large scatter. Separate radio-loud and radio-quiet corrections are warranted by the X-ray data.

astro-ph.CO↗

arXiv2012

Reorienting Our Perspective of Broad Absorption Line Quasars

New multi-frequency radio observations of a large sample of radio-selected BAL quasars, along with a very well matched sample of normal quasars, are presented. The observations were made one immediately after the other at 4.9 and 8.4 GHz with the goal of measuring the radio spectral index of each source. We have identified, for the first time, a significant difference in the spectral index distributions of BAL versus non-BAL quasars, with BAL sources showing an overabundance of steep-spectrum sources. This is the first direct observation suggesting that BAL quasars are more likely to be seen farther from the radio jet axis, although a range of orientations is needed to explain the width of the distribution. Utilizing a few different relationships between spectral index and viewing angle, we have also performed Monte-Carlo simulations to quantify the viewing angle to these sources. We find that the difference in the distributions of spectral index can be explained by allowing the BAL sources to have viewing angles extending about 10 degrees farther from the jet axis than non-BAL quasars.

astro-ph.CO↗