397 research outputs found
Atomic Hydrogen Properties of AGN Host Galaxies: HI in 16 NUclei of GAlaxies (NUGA) Sources
We present a comprehensive spectroscopic imaging survey of the distribution
and kinematics of atomic hydrogen (HI) in 16 nearby spiral galaxies hosting low
luminosity AGN, observed with high spectral and spatial resolution (resolution:
~20 arcsec, 5 km/s) using the NRAO Very Large Array (VLA). The sample contains
a range of nuclear types, ranging from Seyfert to star-forming nuclei and was
originally selected for the NUclei of GAlaxies project (NUGA) - a spectrally
and spatially resolved interferometric survey of gas dynamics in nearby
galaxies designed to identify the fueling mechanisms of AGN and the relation to
host galaxy evolution. Here we investigate the relationship between the HI
properties of these galaxies, their environment, their stellar distribution and
their AGN type. The large-scale HI morphology of each galaxy is classified as
ringed, spiral, or centrally concentrated; comparison of the resulting
morphological classification with AGN type reveals that ring structures are
significantly more common in LINER than in Seyfert host galaxies, suggesting a
time evolution of the AGN activity together with the redistribution of the
neutral gas. Dynamically disturbed HI disks are also more prevalent in LINER
host galaxies than in Seyfert host galaxies. While several galaxies are
surrounded by companions (some with associated HI emission), there is no
correlation between the presence of companions and the AGN type
(Seyfert/LINER).Comment: 54 pages, 7 figures, accepted for publication in AJ. The
full-resolution version is available at
http://www.mpia.de/homes/haan/research.htm
Atomic Carbon in Galaxies
We present new measurements of the ground state fine-structure line of atomic
carbon at 492 GHz in a variety of nearby external galaxies, ranging from spiral
to irregular, interacting and merging types. In comparison with CO(1-0), the
CI(1-0) intensity stays fairly comparable in the different environments, with
an average value of the ratio of the line integrated areas in Kkm/s of
CI(1-0)/CO(1-0) = 0.2 +/- 0.2. However, some variations can be found within
galaxies, or between galaxies. Relative to CO lines, CI(1-0) is weaker in
galactic nuclei, but stronger in disks, particularly outside star forming
regions. Also, in NGC 891, the CI(1-0) emission follows the dust continuum at
1.3mm extremely well along the full length of the major axis where molecular
gas is more abundant than atomic gas. Atomic carbon therefore appears to be a
good tracer of molecular gas in external galaxies, possibly more reliable than
CO. Atomic carbon can contribute significantly to the thermal budget of
interstellar gas. Cooling due to C and CO amounts typically to 2 x 10^{-5} of
the FIR continuum or 5% of the CII line. However, C and CO cooling reaches 30%
of the gas total, in Ultra Luminous InfraRed Galaxies, where CII is abnormally
faint. Together with CII/FIR, the emissivity ratio CI(1-0)/FIR can be used as a
measure of the non-ionizing UV radiation field in galaxies.Comment: 26 pages, 8 figure
SiO chimneys and supershells in M82
In this Letter we present the first images of the emission of SiO and H13CO+
in the nucleus of the starburst galaxy M82. Contrary to other molecular species
that mainly trace the distribution of the star-forming molecular gas within the
disk, the SiO emission extends noticeably out of the galaxy plane. The bulk of
the SiO emission is restricted to two major features. The first feature,
referred to as the SiO supershell, is an open shell of 150 pc diameter, located
120 pc west from the galaxy center.
The SiO supershell represents the inner front of a molecular shell expanding
at 40 km/s, produced by mass ejection around a supercluster of young stars
containing supernova remnant SNR 41.95+57.5. The second feature is a vertical
filament, referred to as the SiO chimney, emanating from the disk at 200 pc
east from the galaxy center. The SiO chimney reaches a 500 pc vertical height,
and it is associated with the most prominent chimney identified in radio
continuum maps. The kinematics, morphology, and fractional abundances of the
SiO gas features in M82 can be explained in the framework of shocked chemistry
driven by local episodes of gas ejection from the starburst disk.Comment: 10 pages, 2 figures, published in ApJLetters, 200
CO Distribution and Kinematics Along the Bar in the Strongly Barred Spiral NGC 7479
We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations
covering the whole length of the bar in the strongly barred late-type spiral
galaxy NGC 7479. CO emission is detected only along a dust lane that traverses
the whole length of the bar, including the nucleus. The emission is strongest
in the nucleus. The distribution of emission is clumpy along the bar outside
the nucleus, and consists of gas complexes that are unlikely to be
gravitationally bound. The CO kinematics within the bar consist of two separate
components. A kinematically distinct circumnuclear disk, < 500 pc in diameter,
is undergoing predominantly circular motion with a maximum rotational velocity
of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar
outside the circumnuclear disk has substantial noncircular motions which are
consistent with a large radial velocity component, directed inwards. The CO
emission has a large velocity gradient across the bar dust lane, ranging from
0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity
change across the dust lane is as high as 200 km/s. This sharp velocity
gradient is consistent with a shock front at the location of the bar dust lane.
A comparison of H-alpha and CO kinematics across the dust lane shows that
although the H-alpha emission is often observed both upstream and downstream
from the dust lane, the CO emission is observed only where the velocity
gradient is large. We also compare the observations with hydrodynamic models
and discuss star formation along the bar.Comment: 16 pages, including 10 figures. Accepted for publication in Ap
Star formation in isolated AMIGA galaxies: dynamical influence of bars
Star formation depends strongly both on the local environment of galaxies,
and on the internal dynamics of the interstellar medium. To disentangle the two
effects, we obtained, in the framework of the AMIGA project, Ha and Gunn r
photometric data for more than 200 spiral galaxies lying in very low-density
regions of the local Universe. We characterise the Ha emission, tracing current
star formation, of the 45 largest and less inclined galaxies observed for which
we estimate the torques between the gas and the bulk of the optical matter. We
could subsequently study the Ha morphological aspect of these isolated spiral
galaxies. Using Fourier analysis, we focus on the modes of the spiral arms and
also on the strength of the bars, computing the torques between the gas and
newly formed stars (Ha) and the bulk of the optical matter (Gunn r). We
interpret the various bar/spiral morphologies observed in terms of the secular
evolution experienced by galaxies in isolation. We also classify the different
spatial distributions of star forming regions in barred galaxies. The observed
frequency of particular patterns brings constraints on the lifetime of the
various evolution phases. We propose an evolutive sequence accounting for the
transitions between the different phases we could observe. Isolated galaxies
appear not to be preferentially barred or unbarred. Through numerical
simulations, trying to fit the Ha distributions yields constraints on the star
formation law, which is likely to differ from a genuine Schmidt law. In
particular, it is probable that the relative velocity of the gas in the bar
also needs to be taken into account.Comment: 15 pages, 9 figures (low resolution), 2 tables, accepted by A&
SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?
We present high angular resolution (0.5-2.0") observations of the mm
continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1),
HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk
(r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with
the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and
improved 12CO(J=2-1) observations of NGC1068 at high angular resolution
(1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure
Interferometer. Based on the complex dynamics of the molecular gas emission
indicating non-circular motions in the central ~100pc, we propose a scenario in
which part of the molecular gas in the circumnuclear disk of NGC1068 is
radially blown outwards as a result of shocks. This shock scenario is further
supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained
from the observed molecular line ratios. The HCN abundance in the circumnuclear
disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the
abundances derived for galactic and extragalactic starforming/starbursting
regions. This results lends further support to X-ray enhanced HCN formation in
the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+
abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of
galactic and extragalactic starforming/starbursting regions. When trying to fit
the cm to mm continuum emission by different thermal and non-thermal processes,
it appears that electron-scattered synchrotron emission yields the best results
while thermal free-free emission seems to over-predict the mm continuum
emission.Comment: accepted for publication by ApJ; 35pages, 22 figures and 6 tables (at
the end of the file); 3 figures have been decreased in quality to match size
limi
Planetary boundary layer height variability over Athens, Greece, based on the synergy of Raman lidar and radiosonde data: application of the Kalman filter and other techniques (2011-2016)
The temporal evolution of the Planetary Boundary Layer height over Athens, Greece for a 5-year period (2011-2016) is presented. Using the EOLE Raman lidar system, the range-corrected lidar signals were selected around 12:00 UTC and 00:00 UTC for a total of 332 cases (165 days and 167 nights). The Kalman filter and other techniques were used to determine PBL height. The mean PBL height was found to be around 1617±324 m (12:00 UTC) and 892±130 m (00:00 UTC).Peer ReviewedPostprint (published version
The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453
We present new ALMA Band 7 ( GHz) observations of the dense gas
tracers HCN, HCO, and CS in the local, single-nucleus, ultraluminous
infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission,
relative to HCO (4-3), but do not find evidence for radiative pumping of
HCN. Considering the size of the starburst (0.5 kpc) and the estimated
supernovae rate of yr, the high HCN/HCO ratio can be
explained by an enhanced HCN abundance as a result of mechanical heating by the
supernovae, though the active galactic nucleus and winds may also contribute
additional mechanical heating. The starburst size implies a high
of kpc, slightly below predictions of
radiation-pressure limited starbursts. The HCN line profile has low-level
wings, which we tentatively interpret as evidence for outflowing dense
molecular gas. However, the dense molecular outflow seen in the HCN line wings
is unlikely to escape the galaxy and is destined to return to the nucleus and
fuel future star formation. We also present modeling of Herschel observations
of the HO lines and find a nuclear dust temperature of K. IRAS
13120-5453 has a lower dust temperature and than is inferred for
the systems termed "compact obscured nuclei" (such as Arp 220 and Mrk 231). If
IRAS 13120-5453 has undergone a compact obscured nucleus phase, we are likely
witnessing it at a time when the feedback has already inflated the nuclear ISM
and diluted star formation in the starburst/AGN core.Comment: accepted for publication in ApJ, 21 pages, 11 figure
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