17 research outputs found
Quasar Black Hole Masses from Velocity Dispersions
Much progress has been made in measuring black hole (BH) masses in
(non-active) galactic nuclei using the tight correlation between stellar
velocity dispersions (sigma) in galaxies and the mass of their central BH. The
use of this correlation in quasars, however, is hampered by the difficulty in
measuring sigma in host galaxies that tend to be overpowered by their bright
nuclei. We discuss results from a project that focuses on z~0.3 quasars
suffering from heavy extinction at shorter wavelengths. This makes it possible
to obtain clean spectra of the hosts in the spectral regions of interest, while
broad lines (like H-alpha) are still visible at longer wavelengths. We compare
BH masses obtained from velocity dispersions to those obtained from the broad
line region and thus probe the evolution of this relation and BH growth with
redshift and luminosity. Our preliminary results show an offset between the
position of our objects and the local relation, in the sense that red quasars
have, on average, lower velocity dispersions than local galaxies. We discuss
possible biases and systematic errors that may affect our results.Comment: 4 pages, to appear in the proceedings of the 2nd Kolkata conference
on Observational Evidence for Black Holes in the Universe, ed. S. Chakrabarti
(AIP
The Nature of LoBAL QSOs. II. HST/WFC3 Observations Reveal Host Galaxies Dominated by Mergers
Low-ionization broad absorption line QSOs (LoBALs) are suspected to be merging systems in which extreme, active galactic nucleus-driven outflows have been triggered. Whether or not LoBALs are uniquely associated with mergers, however, has yet to be established. To characterize the morphologies of LoBALs, we present the first high-resolution morphological analysis of a volume-limited sample of 22 Sloan Digital Sky Survey (SDSS)-selected LoBALs at 0.5 \u3c z \u3c 0.6 from Hubble Space Telescope Wide Field Camera 3 observations. Host galaxies are resolved in 86% of the systems in F125W, which is sensitive to old stellar populations, while only 18% are detected in F475W, which traces young, unobscured stellar populations. Signs of recent or ongoing tidal interaction are present in 45%–64% of the hosts, including double nuclei, tidal tails, bridges, plumes, shells, and extended debris. Ongoing interaction with a companion is apparent in 27%−41% of the LoBALs, with as much as 1/3 of the sample representing late-stage mergers at projected nuclear separations \u3c10 kpc. Detailed surface brightness modeling indicates that 41% of the hosts are bulge dominated while only 18% are disks. We discuss trends in various properties as a function of merger stage and parametric morphology. Notably, mergers are associated with slower, dustier winds than those seen in undisturbed/unresolved hosts. Our results favor an evolutionary scenario in which quasar-level accretion during various merger stages is associated with the observed outflows in low-z LoBALs. We discuss differences between LoBALs and FeLoBALs and show that selection via the traditional balnicity index would have excluded all but one of the mergers
Broad H\u3cem\u3eβ\u3c/em\u3e emission-line variability in a sample of 102 local active galaxies
A sample of 102 local (0.02 ≤ z ≤ 0.1) Seyfert galaxies with black hole masses MBH \u3e 107M⊙ was selected from the Sloan Digital Sky Survey (SDSS) and observed using the Keck 10 m telescope to study the scaling relations between MBH and host galaxy properties. We study profile changes of the broad Hβ emission line within the three to nine year time frame between the two sets of spectra. The variability of the broad Hβ emission line is of particular interest, not only because it is used to estimate MBH, but also because its strength and width are used to classify Seyfert galaxies into different types. At least some form of broad-line variability (in either width or flux) is observed in the majority (~66%) of the objects, resulting in a Seyfert-type change for ~38% of the objects, likely driven by variable accretion and/or obscuration. The broad Hβ line virtually disappears in 3/102 (~3%) extreme cases. We discuss potential causes for these changing look active galactic nuclei. While similar dramatic transitions have previously been reported in the literature, either on a case-by-case basis or in larger samples focusing on quasars at higher redshifts, our study provides statistical information on the frequency of Hβ line variability in a sample of low-redshift Seyfert galaxies
Studying the [OIII]5007A emission-line width in a sample of 80 local active galaxies: A surrogate for ?
For a sample of 80 local () Seyfert-1 galaxies
with high-quality long-slit Keck spectra and spatially-resolved
stellar-velocity dispersion () measurements, we study the
profile of the [OIII]5007A emission line to test the validity of using
its width as a surrogate for . Such an approach has often been
used in the literature, since it is difficult to measure for
type-1 active galactic nuclei (AGNs) due to the AGN continuum outshining the
stellar-absorption lines. Fitting the [OIII] line with a single Gaussian or
Gauss-Hermite polynomials overestimates by 50-100%. When line
asymmetries from non-gravitational gas motion are excluded in a double Gaussian
fit, the average ratio between the core [OIII] width () and is 1, but with individual data points
off by up to a factor of two. The resulting black-hole-mass- relation scatters around that of quiescent galaxies and
reverberation-mapped AGNs. However, a direct comparison between
and shows no close correlation, only
that both quantities have the same range, average and standard deviation,
probably because they feel the same gravitational potential. The large scatter
is likely due to the fact that line profiles are a luminosity-weighted average,
dependent on the light distribution and underlying kinematic field. Within the
range probed by our sample (80-260 km s), our results strongly caution
against the use of [OIII] width as a surrogate for on an
individual basis. Even though our sample consists of radio-quiet AGNs, FIRST
radio-detected objects have, on average, a 10% larger [OIII] core width.Comment: 15 pages, 10 figures, 6 tables. Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad-Line Region
We present models of the H-emitting broad-line region (BLR) in seven
Seyfert 1 galaxies from the Lick AGN (Active Galactic Nucleus) Monitoring
Project 2011 sample, drawing inferences on the BLR structure and dynamics as
well as the mass of the central supermassive black hole. We find that the BLR
is generally a thick disk, viewed close to face-on, with preferential emission
back toward the ionizing source. The dynamics in our sample range from
near-circular elliptical orbits to inflowing or outflowing trajectories. We
measure black hole masses of for PG 1310108, for Mrk 50,
for Mrk 141, for Mrk 279,
for Mrk 1511, for NGC 4593, and
for Zw 229015. We use these black hole mass
measurements along with cross-correlation time lags and line widths to recover
the scale factor used in traditional reverberation mapping measurements.
Combining our results with other studies that use this modeling technique,
bringing our sample size to 16, we calculate a scale factor that can be used
for measuring black hole masses in other reverberation mapping campaigns. When
using the root-mean-square (rms) spectrum and using the line dispersion to
measure the line width, we find . Finally, we search for correlations between and other AGN
and BLR parameters and find marginal evidence that is correlated with
and the BLR inclination angle, but no significant evidence of a
correlation with the AGN luminosity or Eddington ratio.Comment: 26 pages, 14 figures. Accepted for publication in Ap
The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad Line Region in Mrk 50
We present dynamical modeling of the broad line region (BLR) in the Seyfert 1
galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN
Monitoring Project (LAMP) 2011. We model the reverberation mapping data
directly, constraining the geometry and kinematics of the BLR, as well as
deriving a black hole mass estimate that does not depend on a normalizing
factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is
a nearly face-on thick disk, with a mean radius of 9.6(+1.2,-0.9) light days, a
width of the BLR of 6.9(+1.2,-1.1) light days, and a disk opening angle of
25\pm10 degrees above the plane. We also constrain the inclination angle to be
9(+7,-5) degrees, close to face-on. Finally, the black hole mass of Mrk 50 is
inferred to be log10(M(BH)/Msun) = 7.57(+0.44,-0.27). By comparison to the
virial black hole mass estimate from traditional reverberation mapping
analysis, we find the normalizing constant (virial coefficient) to be log10(f)
= 0.78(+0.44,-0.27), consistent with the commonly adopted mean value of 0.74
based on aligning the M(BH)-{\sigma}* relation for AGN and quiescent galaxies.
While our dynamical model includes the possibility of a net inflow or outflow
in the BLR, we cannot distinguish between these two scenarios.Comment: Accepted for publication in ApJ. 8 pages, 6 figure
The Nature of LoBAL QSOs: I. SEDs and mid-infrared spectral properties
We have obtained Spitzer IRS spectra and MIPS 24, 70, and 160 micron
photometry for a volume-limited sample of 22 SDSS-selected Low-ionization Broad
Absorption Line QSOs (LoBALs) at 0.5 < z < 0.6. By comparing their mid-IR
spectral properties and far-IR SEDs with those of a control sample of 35
non-LoBALs matched in M_i, we investigate the differences between the two
populations in terms of their infrared emission and star formation activity.
Twenty five percent of the LoBALs show PAH features and 45% have weak 9.7
micron silicate dust emission. We model the SEDs and decouple the AGN and
starburst contributions to the far-infrared luminosity in LoBALs and in
non-LoBALs. Their median total, starburst, and AGN infrared luminosities are
comparable. Twenty percent (but no more than 60%) of the LoBALs and 26% of the
non-LoBALs are ultra-luminous infrared galaxies (ULIRGs; L_IR>10^12*L_sun). We
estimate star formation rates (SFRs) corrected for the AGN contribution to the
FIR flux and find that LoBALs have comparable levels of star formation activity
to non-LoBALs when considering the entire samples. However, the SFRs of the
IR-luminous LoBALs are 80% higher than those of their counterparts in the
control sample. The median contribution of star formation to the total
far-infrared flux in LoBALs and in non-LoBALs is estimated to be 40-50%, in
agreement with previous results for PG QSOs. Overall, our results show that
there is no strong evidence from the mid- and far-IR properties that LoBALs are
drawn from a different parent population than non-LoBALs.Comment: 28 pages, 8 figures, 7 tables; Accepted for publication in Ap
Recommended from our members
BROAD H beta EMISSION-LINE VARIABILITY IN A SAMPLE OF 102 LOCAL ACTIVE GALAXIES
A sample of 102 local (0.02 < z < 0.1) Seyfert galaxies with black hole
masses MBH > 10^7 M_sun was selected from the Sloan Digital Sky Survey (SDSS)
and observed using the Keck 10-m telescope to study the scaling relations
between MBH and host galaxy properties. We study profile changes of the broad
Hbeta emission line within the ~3-9 year time-frame between the two sets of
spectra. The variability of the broad Hbeta emission line is of particular
interest, not only since it is used to estimate MBH, but also since its
strength and width is used to classify Seyfert galaxies into different types.
At least some form of broad-line variability (in either width or flux) is
observed in the majority (~66%) of the objects, resulting in a Seyfert-type
change for ~38% of the objects, likely driven by variable accretion and/or
obscuration. The broad Hbeta line virtually disappears in 3/102 (~3%) extreme
cases. We discuss potential causes for these changing-look AGNs. While similar
dramatic transitions have previously been reported in the literature, either on
a case-by-case basis or in larger samples focusing on quasars at higher
redshifts, our study provides statistical information on the frequency of
H line variability in a sample of low-redshift Seyfert galaxies
Recommended from our members
BROAD H beta EMISSION-LINE VARIABILITY IN A SAMPLE OF 102 LOCAL ACTIVE GALAXIES
A sample of 102 local (0.02 < z < 0.1) Seyfert galaxies with black hole
masses MBH > 10^7 M_sun was selected from the Sloan Digital Sky Survey (SDSS)
and observed using the Keck 10-m telescope to study the scaling relations
between MBH and host galaxy properties. We study profile changes of the broad
Hbeta emission line within the ~3-9 year time-frame between the two sets of
spectra. The variability of the broad Hbeta emission line is of particular
interest, not only since it is used to estimate MBH, but also since its
strength and width is used to classify Seyfert galaxies into different types.
At least some form of broad-line variability (in either width or flux) is
observed in the majority (~66%) of the objects, resulting in a Seyfert-type
change for ~38% of the objects, likely driven by variable accretion and/or
obscuration. The broad Hbeta line virtually disappears in 3/102 (~3%) extreme
cases. We discuss potential causes for these changing-look AGNs. While similar
dramatic transitions have previously been reported in the literature, either on
a case-by-case basis or in larger samples focusing on quasars at higher
redshifts, our study provides statistical information on the frequency of
H line variability in a sample of low-redshift Seyfert galaxies