103 research outputs found
Formation of Large-Scale Obscuring Wall and AGN Evolution Regulated by Circumnuclear Starbursts
By considering the radiative force by a circumnuclear starburst as well as an
AGN, we analyze the equilibrium configuration and the stability of dusty gas in
the circumnuclear regions. It is found that the radiative force by an intensive
starburst can support a stable gaseous wall with a scale-height of several
hundred parsecs. Moreover, by taking the simple stellar evolution in the
starburst into account, we find that the covering factor of the wall decreases
on a time-scale of several yr. The large-scale wall, if formed, works to
obscure the nucleus due to the dust opacity. Hence, it is anticipated that the
index of AGN type tends to shift from higher to lower in several yr
according as the circumnuclear starburst becomes dimmer. On the other hand, if
the AGN itself is brighter than the circumnuclear starburst (e.g. quasar case),
no stable large-scale wall forms. In that case, the AGN is highly probably
identified as type 1. The present mechanism may provide a physical explanation
for the putative correlation between AGN type and host properties that Sy2's
are more frequently associated with circumnuclear starbursts than Sy1's,
whereas quasars are mostly observed as type 1 regardless of star-forming
activity in the host galaxies.Comment: 10 pages, 3 figures, ApJ Letters in pres
Circumnuclear Gas in Seyfert 1 Galaxies: Morphology, Kinematics, and Direct Measurement of Black Hole Masses
(Abridged) The two-dimensional distribution and kinematics of the molecular,
ionized, and highly ionized gas in the nuclear regions of Seyfert 1 galaxies
have been measured using high spatial resolution (~0''.09) near-infrared
spectroscopy from NIRSPEC with adaptive optics on the Keck telescope. Molecular
hydrogen, H2, is detected in all nine Seyfert 1 galaxies and, in the majority
of galaxies, has a spatially resolved flux distribution. In contrast, the
narrow component of the BrG emission has a distribution consistent with that of
the K-band continuum. In general, the kinematics of H2 are consistent with thin
disk rotation, with a velocity gradient of over 100 km/s measured across the
central 0''.5 in three galaxies, and across the central 1''.5 in two galaxies.
The kinematics of BrG are in agreement with the H2 rotation, except in all four
cases the central 0''.5 is either blue- or redshifted by more than 75 km/s. The
highly ionized gas, measured with the [Ca VIII] and [Si VII] coronal lines, is
spatially and kinematically consistent with BrG in the central 0''.5. Dynamical
models have been fitted to the two-dimensional H2 kinematics, taking into
account the stellar mass distribution, the emission line flux distribution, and
the point spread function. For NGC 3227 the modeling indicates a black hole
mass of Mbh = 2.0{+1.0/-0.4} x 10^7 Msun, and for NGC 4151 Mbh =
3.0{+0.75/-2.2} x 10^7 Msun. In NGC 7469 the best fit model gives Mbh < 5.0 x
10^7 Msun. In all three galaxies, modeling suggests a near face-on disk
inclination angle, which is consistent with the unification theory of active
galaxies. The direct black hole mass estimates verify that masses determined
from the technique of reverberation mapping are accurate to within a factor of
three with no additional systematic errors.Comment: 43 pages, including 47 figures; Accepted for publication in ApJ. All
2-D maps (in high resolution) are available at
http://www.astro.ucla.edu/~ehicks . Minor changes to the text and updated
reverberation mapped black hole mass estimates; the conclusions are unchange
A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei
We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035)
Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features
or multiple nuclei. The incidence of inner starburst rings is about 10% in both
classes of Sy galaxies. In contrast, galaxies with H II region emission line
spectra appear substantially more irregular because of their much higher
specific rates of star formation. An unresolved central continuum source in our
HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1
point sources are saturated in our images; we use their wings to estimate their
magnitudes. The converse is not however true, as over a third of Sy's with
direct spectroscopic evidence for broad Balmer wings show no nuclear point
source. Like the Sy2's, they have central surface brightnesses consistent with
those expected for the bulges of normal galaxies. The frequency of bars in
Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more
likely to show nuclear dust absorption, especially in lanes and patches which
are irregular or reach close to the nucleus. The difference cannot be explained
by different average redshifts or selection techniques. This is confirmed by
our morphology classifications, which show that Sy1 nuclei reside in earlier
type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy
properties may undermine the strong unification hypothesis for Sy galaxies that
they appear different due to the orientation of their central engine. The
excess galactic dust we see in Sy2's may cause substantial absorption which
obscures their hypothesized broad emission-line regions and central nonstellar
continua. This galactic dust could produce much of the absorption in Sy2 nuclei
which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9
figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT
included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as
anonymous and give your e-mail address as the password. The images are in the
/pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included
here and can be printed using the lpr command in unix system
Quality control of CarboEurope flux data ? Part II: Inter-comparison of eddy-covariance software
International audienceAs part of the quality assurance and quality control activities within the CarboEurope-IP network, a comparison of eddy-covariance software was conducted. For four five-day datasets, CO2 flux estimates were calculated by seven commonly used software packages to assess the uncertainty of CO2 flux estimates due to differences in post-processing. The datasets originated from different sites representing different commonly applied instrumentation and different canopy structures to cover a wide range of realistic conditions. Data preparation, coordinate rotation and the implementation of the correction for high frequency spectral losses were identified as crucial processing steps leading to significant discrepancies in the CO2 flux results. The overall comparison indicated a good although not yet perfect agreement among the different software within 5?10% difference for 30-min CO2 flux values. Conceptually different ideas about the selection and application of processing steps were a main reason for the differences in the CO2 flux estimates observed. A balance should be aspired between scientific freedom on the one hand, in order to advance methodical issues, and standardisation of procedures on the other hand, in order to obtain comparable fluxes for multi-site synthesis studies
The Nuclear Gas Dynamics and Star Formation of NGC 7469
We report interferometric radio CO2-1 observations at a resolution of 0.7",
and 0.085" resolution adaptive optics K-band spectroscopy of the inner few
arcseconds of NGC7469. The CO2-1 map shows a ring of molecular clouds and a
bright extended nucleus, with a bar or pair of spiral arms between them. The
dynamical structure of both the radio CO2-1 and the K-band H2 1-0S(1) lines can
be reproduced using an axisymmetric mass model comprising 3 components: a broad
disk, a ring 4-5" across, and an inner nuclear ring about 0.5" across. No
non-circular motions faster than the velocity residuals of 25 km/s are seen,
although this may be because in some cases a secondary bar is not expected to
cause gas inflow. From the dynamical mass and estimates of the stellar mass we
find that the CO-to-H_2 conversion is 0.4-0.8 times that for the Milky Way. The
H2 1-0S(1) morphology peaks at the nucleus, although there is no strong nuclear
mass concentration. The 1-0S(1) is likely to originate in X-ray of gas by the
AGN rather than via star formation. Using the 2.3um stellar CO2-0 absorption
and the continuum slope we have directly resolved the nuclear star cluster to
be 0.15-0.20" across, and find that it is asymmetric. This cluster has an age
of less than about 60Myr and contributes 20-30% of the nuclear K-band light,
and about 10% of the nuclear bolometric luminosity. Within a radius of ~4" gas
contributes more than half the total mass; but in the nucleus, within a radius
of 0.1", it is likely that most of the mass is due to starsComment: accepted for publication in ApJ (see their pages for a version with
higher quality figures
Montane ecosystem productivity responds more to global circulation patterns than climatic trends
Ajuts: we thank the support of KIT IMK-IFU, the University of Wisconsin sabbatical leave program, and the Helmholtz Society/MICMOR fellowship program. We also thank the DWD for German weather data. Phenology data were provided by the members of the PEP725 project. We are indebted to the providers and funders of the eddy covariance flux tower observations, the FLUXNET program, and its database. The sites in Graswang, Rottenbuch and Fendt belong to the TERENO and ICOS-ecosystems networks, funded by Bundesministerium für Bildung und Forschung(BMBF)and the Helmholtz Association. The modeling study of SOLVEG was partially supported by Grant-in-Aid for Scientific Research, no. 21120512, provided by the Japan Society for the Promotion of Science(JSPS). This study was financially supported by the Austrian National Science Fund(FWF) under contract P26425 to GW.Regional ecosystem productivity is highly sensitive to inter-annual climate variability, both within and outside the primary carbon uptake period. However, Earth system models lack sufficient spatial scales and ecosystem processes to resolve how these processes may change in a warming climate. Here, we show, how for the European Alps, mid-latitude Atlantic ocean winter circulation anomalies drive high-altitude summer forest and grassland productivity, through feedbacks among orographic wind circulation patterns, snowfall, winter and spring temperatures, and vegetation activity. Therefore, to understand future global climate change influence to regional ecosystem productivity, Earth systems models need to focus on improvements towards topographic downscaling of changes in regional atmospheric circulation patterns and to lagged responses in vegetation dynamics to non-growing season climate anomalies
Radial Velocity Studies of Close Binary Stars.III
Radial velocity measurements and simple sine-curve fits to the orbital
velocity variations are presented for the third set of ten contact binary
systems: CN And, HV Aqr, AO Cam, YY CrB, FU Dra, RZ Dra, UX Eri, RT LMi, V753
Mon, OU Ser. All systems but two are contact, double-line spectroscopic
binaries with four of them (YY CrB, FU Dra, V753 Mon, OU Ser) being the recent
discoveries of the Hipparcos satellite project. The most interesting object is
V753 Mon with the mass-ratio closest to unity among all contact systems (q =
0.970 pm 0.003) and large total mass ((M1+M2)sin^3i = 2.93 pm 0.06). Several of
the studied systems are prime candidates for combined light and radial-velocity
synthesis solutions.Comment: submitted for publication in Astronomical Journal; 3 figures, 2
table
Obscuration of Active Galactic Nuclei by Circumnuclear Starbursts
We examine the possibility of the active galactic nucleus (AGN) obscuration
by dusty gas clouds that spurt out from circumnuclear starburst regions. For
the purpose, the dynamical evolution of gas clouds is pursued, including the
effects of radiation forces by an AGN as well as a starburst. Here, we solve
the radiative transfer equations for clouds, taking into consideration the
growth of clouds by inelastic cloud-cloud collisions and the resultant change
in optical depth. As a result, it is shown that if the starburst is more
luminous than the AGN, gas clouds are distributed extensively above a galactic
disk with the assistance of radiation pressure from the starburst. The total
covering factor of gas clouds reaches a maximum of around 20%. After several
yr, gas clouds with larger optical depth form by cloud-cloud collisions
and thereafter the clouds fall back due to weakened radiation pressure. The
larger clouds undergo runaway growth and are eventually distributed around the
equatorial plane on the inner sides of circumnuclear starburst regions. These
clouds have an optical depth of several tens. The result is qualitatively
consistent with the putative tendency that Seyfert 2 galaxies appear more
frequently associated with starbursts than Seyfert 1s. On the other hand, if
the AGN luminosity overwhelms that of the starburst, almost all clouds are
ejected from the galaxy due to the radiation pressure from the AGN, resulting
in the formation of a quasar-like object. The origin of obscuration of AGNs is
discussed with relevant observations.Comment: 10 pages, 8 figure, accepted for publication in ApJ; Fig. 3 and Fig .
7 are available at http://www.rccp.tsukuba.ac.jp/Astro/watabe
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
Eddy-covariance flux measurements with a weight-shift microlight aircraft
The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (&sigma;<sub><i>u,v</i></sub> &le; 0.09 m s<sup>&minus;1</sup>, &sigma;<sub><i>w</i></sub> = 0.04 m s<sup>&minus;1</sup>), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s<sup>&minus;1</sup>), and sensible- (5 W m<sup>&minus;2</sup>) and latent (3 W m<sup>&minus;2</sup>) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform
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