1,488 research outputs found
Black hole masses in active galaxies
This contribution reviews two topics of current interest in the study of black hole
demographics in active galaxies: Can the stellar velocity dispersions of quasar host galaxies be
measured? And can we constrain the black hole mass function below 10^6 M_⊙
The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50
The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our data set covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of ~4 in the U-band continuum and a factor of ~2 in the Hβ line. Using standard cross-correlation techniques, we find that Hβ and Hγ lag the V-band continuum by τ_(cen) = 10.64^(+0.82)_(–0.93) and 8.43^(+1.30)_(–1.28) days, respectively, while the lag of He II λ4686 is unresolved. The Hβ line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region (BLR) dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f = 5.25, the virial estimate of the black hole mass is (3.2 ± 0.5) × 10^7 M_☉. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of BLR structure and dynamics
The Carnegie-Irvine Galaxy Survey. V. Statistical study of bars and buckled bars
Simulations have shown that bars are subject to a vertical buckling
instability that transforms thin bars into boxy or peanut-shaped structures,
but the physical conditions necessary for buckling to occur are not fully
understood. We use the large sample of local disk galaxies in the
Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars
across the Hubble sequence. Depending on the disk inclination angle (), a
buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high )
or as a barlens structure (at low ). We visually identify bars,
boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and
buckled bar fractions on host galaxy properties, including Hubble type, stellar
mass, color, and gas mass fraction. We find that the barred and unbarred disks
show similar distributions in these physical parameters. The bar fraction is
higher (70\%--80\%) in late-type disks with low stellar mass () and high gas mass ratio. In contrast, the buckled bar
fraction increases to 80\% toward massive and early-type disks (), and decreases with higher gas mass ratio. These
results suggest that bars are more difficult to grow in massive disks that are
dynamically hotter than low-mass disks. However, once a bar forms, it can
easily buckle in the massive disks, where a deeper potential can sustain the
vertical resonant orbits. We also find a probable buckling bar candidate (ESO
506G004) that could provide further clues to understand the timescale of the
buckling process.Comment: 9 pages, 7 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
On the Virialization of Disk Winds: Implications for the Black Hole Mass Estimates in AGN
Estimating the mass of a supermassive black hole (SMBH) in an active galactic
nucleus (AGN) usually relies on the assumption that the broad line region (BLR)
is virialized. However, this assumption seems invalid in BLR models that
consists of an accretion disk and its wind. The disk is likely Keplerian and
therefore virialized. However, the wind material must, beyond a certain point,
be dominated by an outward force that is stronger than gravity. Here, we
analyze hydrodynamic simulations of four different disk winds: an isothermal
wind, a thermal wind from an X-ray heated disk, and two line-driven winds, one
with and the other without X-ray heating and cooling. For each model, we check
whether gravity governs the flow properties, by computing and analyzing the
volume-integrated quantities that appear in the virial theorem: internal,
kinetic, and gravitational energies, We find that in the first two models, the
winds are non-virialized whereas the two line-driven disk winds are virialized
up to a relatively large distance. The line-driven winds are virialized because
they accelerate slowly so that the rotational velocity is dominant and the wind
base is very dense. For the two virialized winds, the so-called projected
virial factor scales with inclination angle as . Finally, we
demonstrate that an outflow from a Keplerian disk becomes unvirialized more
slowly when it conserves the gas specific angular momentum -- as in the models
considered here, than when it conserves the angular velocity -- as in the
so-called magneto-centrifugal winds.Comment: Accepted to Ap
The M87 Black Hole Mass From Gas-Dynamical Models Of Space Telescope Imaging Spectrograph Observations
The supermassive black hole of M87 is one of the most massive black holes known and has been the subject of several stellar and gas-dynamical mass measurements; however, the most recent revision to the stellar-dynamical black hole mass measurement is a factor of about two larger than the previous gas-dynamical determinations. Here, we apply comprehensive gas-dynamical models that include the propagation of emission-line profiles through the telescope and spectrograph optics to new Space Telescope Imaging Spectrograph observations from the Hubble Space Telescope. Unlike the previous gas-dynamical studies of M87, we map out the complete kinematic structure of the emission-line disk within similar to 40 pc from the nucleus, and find that a small amount of velocity dispersion internal to the gas disk is required to match the observed line widths. We examine a scenario in which the intrinsic velocity dispersion provides dynamical support to the disk, and determine that the inferred black hole mass increases by only 6%. Incorporating this effect into the error budget, we ultimately measure a mass of M-BH = (3.5(-0.7)(+0.9)) x 10(9)M circle dot (68% confidence). Our gas-dynamical black hole mass continues to differ from the most recent stellar-dynamical mass by a factor of two, underscoring the need for carrying out more cross-checks between the two main black hole mass measurement methods.NSF Astronomy and Astrophysics Postdoctoral Fellowship 1102845Space Telescope Science Institute 12162NASA NAS 5-26555NSF AST-1108835Astronom
Physical Properties of the Narrow-Line Region of Low-Mass Active Galaxies
We present spectroscopic observations of 27 active galactic nuclei (AGN) with
some of the lowest black hole (BH) masses known. We use the high spectral
resolution and small aperture of our Keck data, taken with the Echellette
Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these
low-mass BHs. We investigate their emission-line properties and compare them
with those of AGN with higher-mass black holes. While we are unable to
determine absolute metallicities, some of our objects plausibly represent
examples of the low-metallicity AGN described by Groves et al. (2006), based on
their [N II]/H_alpha ratios and their consistency with the Kewley & Ellison
(2008) mass-metallicity relation. We find tentative evidence for steeper far-UV
spectral slopes in lower-mass systems. Overall, NLR emission lines in these
low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs,
such as increasing blueshifts and broadening with increasing ionization
potential. Additionally, we see evidence of an intermediate line region whose
intensity correlates with L/L_Edd, as seen in higher-mass AGN. We highlight the
interesting trend that, at least in these low-mass AGN, the [O III] equivalent
width (EW) is highest in symmetric NLR lines with no blue wing. This trend of
increasing [O III] EW with line symmetry could be explained by a high covering
factor of lower ionization gas in the NLR. In general, low-mass AGN preserve
many well-known trends in the structure of the NLR, while exhibiting steeper
ionizing continuum slopes and somewhat lower gas-phase metallicities.Comment: 46 pages, 14 figures, 7 table
Feedback In Luminous Obscured Quasars
We use spatially resolved long-slit spectroscopy from Magellan to investigate the extent, kinematics, and ionization structure in the narrow-line regions of 15 luminous, obscured quasars with z < 0.5. Increasing the dynamic range in luminosity by an order of magnitude, as well as improving the depth of existing observations by a similar factor, we revisit relations between narrow-line region size and the luminosity and linewidth of the narrow emission lines. We find a slope of 0.22 +/- 0.04 for the power-law relationship between size and luminosity, suggesting that the nebulae are limited by availability of gas to ionize at these luminosities. In fact, we find that the active galactic nucleus is effectively ionizing the interstellar medium over the full extent of the host galaxy. Broad (similar to 300-1000 km s(-1)) linewidths across the galaxies reveal that the gas is kinematically disturbed. Furthermore, the rotation curves and velocity dispersions of the ionized gas remain constant out to large distances, in striking contrast to normal and starburst galaxies. We argue that the gas in the entire host galaxy is significantly disturbed by the central active galactic nucleus. While only similar to 10(7)-10(8) M-circle dot worth of gas are directly observed to be leaving the host galaxies at or above their escape velocities, these estimates are likely lower limits because of the biases in both mass and outflow velocity measurements and may in fact be in accord with expectations of recent feedback models. Additionally, we report the discovery of two dual obscured quasars, one of which is blowing a large-scale (similar to 10 kpc) bubble of ionized gas into the intergalactic medium.NSF AST-0548198Astronom
The Extremely High Dark Matter Halo Concentration of the Relic Compact Elliptical Galaxy Mrk 1216
Compact elliptical galaxies (CEGs) are candidates for local analogs of the
high-redshift "red nuggets" thought to represent the progenitors of today's
early-type galaxies (ETGs). To address whether the structure of the dark matter
(DM) halo in a CEG also reflects the extremely quiescent and isolated evolution
of its stars, we use a new ks Chandra observation together with a
shallow ks archival observation of the CEG Mrk 1216 to perform a
hydrostatic equilibrium analysis of the luminous and relaxed X-ray plasma
emission extending out to a radius . We examine several DM model
profiles and in every case obtain a halo concentration that is a
large positive outlier in the theoretical CDM
relation; i.e., ranging from above the median
CDM relation in terms of the intrinsic scatter. The high value of
we measure implies an unusually early formation time that firmly
establishes the relic nature of the DM halo in Mrk 1216. The highly
concentrated DM halo leads to a higher DM fraction and smaller total mass slope
at compared to nearby normal ETGs. In addition, the highly concentrated
total mass profile of Mrk 1216 cannot be described by MOND without adding DM,
and it deviates substantially from the Radial Acceleration Relation. Mrk 1216
contains of the cosmic baryon fraction within . The
radial profile of the ratio of cooling time to free-fall time varies within a
narrow range over a large central region ( kpc) suggesting "precipitation-regulated AGN feedback" for a multiphase
plasma, though presently there is little evidence for cool gas in Mrk 1216. The
properties of Mrk 1216 are remarkably similar to those of the nearby fossil
group NGC 6482.Comment: 29 pages, 12 figures; Accepted for publication in The Astrophysical
Journal; Added new section 8.4 discussing the radial range fitted; Several
other minor changes; Conclusions unchange
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