2,057 research outputs found
Star Formation and Dynamics in the nuclei of AGN
Using adaptive optics on Keck and the VLT in the H- and K-bands, we have
begun a project to probe the dynamics and star formation around AGN on scales
of 0.1arcsec. The stellar content of the nucleus is traced through the
2.29micron CO2-0 and 1.62micron CO6-3 absorption bandheads. These features are
directly spatially resolved, allowing us to measure the extent and distribution
of the nuclear star forming region. The dynamics are traced through the
2.12micron H_2 1-0S(1) and 1.64micron [FeII] emission lines, as well as stellar
absorption features. Matching disk models to the rotation curves at various
position angles allows us to determine the mass of the stellar and gas
components, and constrain the mass of the central black hole. In this
contribution we summarise results for the two type~1 AGN Mkn231 and NGC7469.Comment: contribution to "The interplay among Black Holes, Stars and ISM in
Galactic Nuclei", March 200
Ultra-Luminous Infrared Mergers: Elliptical Galaxies in Formation?
We report high quality near-infrared spectroscopy of 12 ultra-luminous
infrared galaxy mergers (ULIRGs). Our new VLT and Keck data provide ~0.5"
resolution, stellar and gas kinematics of these galaxies most of which are
compact systems in the last merger stages.
We confirm that ULIRG mergers are 'ellipticals-in-formation'. Random motions
dominate their stellar dynamics, but significant rotation is common. Gas and
stellar dynamics are decoupled in most systems. ULIRGs fall on or near the
fundamental plane of hot stellar systems, and especially on its less evolution
sensitive, r(eff)-sigma projection. The ULIRG velocity dispersion distribution,
their location in the fundamental plane and their distribution of
v(rot)*sin(i)/sigma closely resemble those of intermediate mass (~L*),
elliptical galaxies with moderate rotation. As a group ULIRGs do not resemble
giant ellipticals with large cores and little rotation. Our results are in good
agreement with other recent studies indicating that disky ellipticals with
compact cores or cusps can form through dissipative mergers of gas rich, disk
galaxies while giant ellipticals with large cores have a different formation
history.Comment: submitted to Ap
Eddington limited starbursts in the central 10pc of AGN, and the Torus in NGC1068
We present results from a survey of nearby AGN using the near infrared
adaptive optics integral field spectrograph SINFONI. These data enable us to
probe the distribution and kinematics of the gas and stars at spatial
resolutions as small as 0.085arcsec. We find strong evidence for recent but
short lived starbursts residing in very dense nuclear disks. On scales of less
than 10pc these would have reached Eddington-limited luminosities when active,
perhaps accounting for their short duration. In addition, for NGC1068 at a
resolution of 6pc, we present direct observations of molecular gas close around
the AGN which we identify with the obscuring torus.Comment: Conference proceedings to appear in "The Central Engine of Active
Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP
Stellar and Molecular Gas Kinematics of NGC1097: Inflow Driven by a Nuclear Spiral
We present spatially resolved distributions and kinematics of the stars and
molecular gas in the central 320pc of NGC1097. The stellar continuum confirms
the previously reported 3-arm spiral pattern extending into the central 100pc.
The stellar kinematics and the gas distribution imply this is a shadowing
effect due to extinction by gas and dust in the molecular spiral arms. The
molecular gas kinematics show a strong residual (i.e. non-circular) velocity,
which is manifested as a 2-arm kinematic spiral. Linear models indicate that
this is the line-of-sight velocity pattern expected for a density wave in gas
that generates a 3-arm spiral morphology. We estimate the inflow rate along the
arms. Using hydrodynamical models of nuclear spirals, we show that when
deriving the accretion rate into the central region, outflow in the disk plane
between the arms has to be taken into account. For NGC1097, despite the inflow
rate along the arms being ~1.2Msun/yr, the net gas accretion rate to the
central few tens of parsecs is much smaller. The numerical models indicate that
the inflow rate could be as little as ~0.06Msun/yr. This is sufficient to
generate recurring starbursts, similar in scale to that observed, every
20-150Myr. The nuclear spiral represents a mechanism that can feed gas into the
central parsecs of the galaxy, with the gas flow sustainable for timescales of
a Gigayear.Comment: accepted by Ap
The Discovery of Water Maser Emission from Eight Nearby Galaxies
Using the Green Bank Telescope, we conducted a ``snapshot'' survey for water
maser emission toward the nuclei of 611 galaxies and detected eight new
sources. The sample consisted of nearby (v < 5000 km/s) and luminous (M_B <
-19.5) galaxies, some with known nuclear activity but most not previously known
to host AGNs. Our detections include both megamasers associated with AGNs and
relatively low luminosity masers probably associated with star formation. The
detection in UGC 3789 is particularly intriguing because the spectrum shows
both systemic and high-velocity lines indicative of emission from an AGN
accretion disk seen edge-on. Based on six months of monitoring, we detected
accelerations among the systemic features ranging from 2 to 8 km/s/yr, the
larger values belonging to the most redshifted systemic components.
High-velocity maser lines in UGC 3789 show no detectable drift over the same
period. Although UGC 3789 was not known to be an AGN prior to this survey, the
presence of a disk maser is strong evidence for nuclear activity, and an
optical spectrum obtained later has confirmed it. With follow up observations,
it may be possible to measure a geometric distance to UGC 3789.Comment: to appear in Astrophysical Journal, 1 May 200
Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA
(Abridged) Combining the deepest Herschel extragalactic surveys (PEP,
GOODS-H, HerMES), and Monte Carlo mock catalogs, we explore the robustness of
dust mass estimates based on modeling of broad band spectral energy
distributions (SEDs) with two popular approaches: Draine & Li (2007, DL07) and
a modified black body (MBB). As long as the observed SED extends to at least
160-200 micron in the rest frame, M(dust) can be recovered with a >3 sigma
significance and without the occurrence of systematics. An average offset of a
factor ~1.5 exists between DL07- and MBB-based dust masses, based on consistent
dust properties. At the depth of the deepest Herschel surveys (in the GOODS-S
field) it is possible to retrieve dust masses with a S/N>=3 for galaxies on the
main sequence of star formation (MS) down to M(stars)~1e10 [M(sun)] up to z~1.
At higher redshift (z<=2) the same result is achieved only for objects at the
tip of the MS or lying above it. Molecular gas masses, obtained converting
M(dust) through the metallicity-dependent gas-to-dust ratio delta(GDR), are
consistent with those based on the scaling of depletion time, and on CO
spectroscopy. Focusing on CO-detected galaxies at z>1, the delta(GDR)
dependence on metallicity is consistent with the local relation. We combine
far-IR Herschel data and sub-mm ALMA expected fluxes to study the advantages of
a full SED coverage.Comment: Accepted for publication in Astronomy and Astrophysics. Some figures
have degraded quality for filesize reason
Rapid Formation of Supermassive Black Hole Binaries in Galaxy Mergers with Gas
Supermassive black holes (SMBHs) are a ubiquitous component of the nuclei of
galaxies. It is normally assumed that, following the merger of two massive
galaxies, a SMBH binary will form, shrink due to stellar or gas dynamical
processes and ultimately coalesce by emitting a burst of gravitational waves.
However, so far it has not been possible to show how two SMBHs bind during a
galaxy merger with gas due to the difficulty of modeling a wide range of
spatial scales. Here we report hydrodynamical simulations that track the
formation of a SMBH binary down to scales of a few light years following the
collision between two spiral galaxies. A massive, turbulent nuclear gaseous
disk arises as a result of the galaxy merger. The black holes form an eccentric
binary in the disk in less than a million years as a result of the
gravitational drag from the gas rather than from the stars.Comment: Accepted for publication in Science, 40 pages, 7 figures,
Supplementary Information include
A far-infrared study of N/O abundance ratio in galactic H 2 regions
Far-infrared lines of N++ and O++ in several galactic H II regions were measured in an effort to probe the abundance ratio N/O. New measurements are presented for W32 (630.8-0.0), Orion A, and G75.84+0.4. The combination of (N III) 57.3 millimicrons and (O III) 88.4 and 51.8 millimicrons yields measurements of N++/O++ that are largely insensitive to electron temperature, density uncertainties, and to clumping of the ionized gas, due to the similarity of the critical densities for these transitions. In the observed nebulae, N++/O++ should be indicative of N/O, a ratio that is of special importance in nucleosynthesis theory. Measurements are compared with previous measurements of M17 and W51. For nebulae in the solar circle, N++/O++ is greater than the N/O values derived from optical studies of N+/O+ in low ionization zones of the same nebulae. We find that N++/O++ in W43 is significantly higher than for the other H II regions in the sample. Since W43 is located at R = 5 kpc, which is the smallest galactocentric distance in our sample, our data appear consistent with the presence of a negative abundance gradient d(N/O)dR
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