152 research outputs found
Structure and kinematics of the molecular spiral arms in M51
Mapping of the CO(1-0) emission from the spiral galaxy was made with the Onsala 20 m antenna. The observations show that the emission is considerably enhanced in spiral arms which appear to originate as intense ridges of emission about 1 kpc from the nucleus. One of the main objectives for the 1986 observations was to study the variations of the tangential velocity component of molecular gas across a spiral arm. The radial velocity was found to have a velocity shift similar to that predicted by the density wave theory. The present (1986) observations of the inner southern spiral arm of M51 show that the tangential velocity component also behaves in a way which conforms with the density wave model. The molecular arms were compared with the H alpha ionized gas arms of Tully (1974) and it was found that the ionized gas appears to have its maximum intensity slightly outside the molecular arm
Physical properties of outflows: Comparing CO and H2O based parameters in Class 0 sources
Context. The observed physical properties of outflows from low-mass sources
put constraints on possible ejection mechanisms. Historically, these quantities
have been derived from CO using ground-based observations. It is thus important
to investigate whether parameters such as momentum rate (thrust) and mechanical
luminosity (power) are the same when different molecular tracers are used.
Aims. We aim at determining the outflow momentum, dynamical time-scale, thrust,
energy and power using CO and H2O as tracers of outflow activity. Methods.
Within the framework of the WISH key program, three molecular outflows from
Class 0 sources have been mapped using the HIFI instrument aboard Herschel. We
use these observations together with previously published H2 data to infer the
physical properties of the outflows. We compare the physical properties derived
here with previous estimates based on CO observations. Results. Inspection of
the spatial distribution of H2O and H2 confirms that these molecules are
co-spatial. The most prominent emission peaks in H2 coincide with strong H2O
emission peaks and the estimated widths of the flows when using the two tracers
are comparable. Conclusions. For the momentum rate and the mechanical
luminosity, inferred values are independent of which tracer that is used, i.e.,
the values agree to within a factor of 4 and 3 respectively.Comment: Accepted for publication in A&A, 5 pages, 2 figure
Molecular Gas in Elliptical Galaxies: Distribution and Kinematics
I present interferometric images (approx. 7" resolution) of CO emission in
five elliptical galaxies and nondetections in two others. These data double the
number of elliptical galaxies whose CO emission has been fully mapped. The
sample galaxies have 10^8 to 5x10^9 solar masses of molecular gas distributed
in mostly symmetric rotating disks with diameters of 2 to 12 kpc. Four out of
the five molecular disks show remarkable alignment with the optical major axes
of their host galaxies. The molecular masses are a few percent of the total
dynamical masses which are implied if the gas is on circular orbits. If the
molecular gas forms stars, it will make rotationally supported stellar disks
which will be very similar in character to the stellar disks now known to be
present in many ellipticals. Comparison of stellar kinematics to gas kinematics
in NGC 4476 implies that the molecular gas did not come from internal stellar
mass loss because the specific angular momentum of the gas is about three times
larger than that of the stars.Comment: 47 pages, 6 tables, 27 figures. Accepted by AJ, scheduled for August
200
Herschel and Odin observations of H2O, CO, CH, CH+, and NII in the barred spiral galaxy NGC 1365. Bar-induced activity in the outer and inner circumnuclear tori
The Odin satellite is now into its twentieth year of operation, much
surpassing its design life of two years. One of its major pursuits was the
search for and study of H2O in the Solar System and the Milky Way galaxy.
Herschel has observed the central region of NGC 1365 in two positions, and both
its SPIRE and PACS observations are available in the Herschel Science Archive.
Herschel PACS images have been produced of the 70 and 160 micron infrared
emission from the whole galaxy, and also of the cold dust distribution as
obtained from the ratio of the 160 to 70 micron images. The Herschel SPIRE
observations have been used to produce maps of the 557 GHz o-H2O, 752 GHz
p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH+, and the 1461
GHz NII lines; however, these observations have no effective velocity
resolution. Odin has recently observed the 557 GHz o-H2O ground state line in
the central region with high (5 km/s) spectral resolution. The emission and
absorption of H2O at 557 GHz, with a velocity resolution of 5 km/s, has been
marginally detected in NGC 1365 with Odin. The H2O is predominantly located in
a shocked 15" (1.3 kpc) region near some central compact radio sources and
hot-spot HII regions, close to the northeast component of the molecular torus
surrounding the nucleus. An analysis of the H2O line intensities and velocities
indicates that a shock-region is located here. This is corroborated by a
statistical image deconvolution of our SEST CO(3-2) observations, yielding 5"
resolution, and a study of our VLA HI absorption observations. Additionally, an
enticing 20" HI ridge is found to extend south-southeast from the nucleus,
coinciding in position with the southern edge of an OIII outflow cone,
emanating from the nucleus. The molecular chemistry of the shocked central
region is analyzed with special emphasis on the CO, H2O and CH, CH+ results.Comment: 25 pages, 11 figure
A comparison between Pa alpha and H alpha emission: The relation between HII region mean reddening, local gas density and metallicity
We measure reddenings to HII regions in NGC 2903, NGC 1512, M51, NGC 4449 and
NGC 6946 from Hubble Space Telescope Pa alpha and H alpha images. Extinctions
range from A_V ~ 5 - 0 depending upon the galaxy. For the galaxies with HST
images in both lines, NGC 2903, NGC 1512 and M51, the Pa alpha and H alpha
emission are almost identical in morphology which implies that little emission
from bright HII regions is hidden from view by regions of comparatively high
extinction. The scatter in the measured extinctions is only +- 0.5 mag.
We compare the reddenings we measure in five galaxies using the Pa alpha to H
alpha ratios to those measured previously from the Balmer decrement in the LMC
and as a function of radius in M101 and M51. We find that luminosity weighted
mean extinctions of these ensembles of HI regions are correlated with gas
surface density and metallicity. The correlation is consistent with the mean
extinction depending on dust density where the dust to gas mass ratio scales
with the metallicity. This trend is expected if HII regions tend to be located
near the mid-plane of a gas disk and emerge from their parent molecular clouds
soon after birth. In environments with gas densities below a few hundred
Msol/pc^2 star formation rates estimated from integrated line fluxes and mean
extinctions are likely to be fairly accurate.Comment: accepted for publication in A
Obscuration in the Host Galaxies of Soft X-ray Selected Seyferts
We define a new sample of 96 low-redshift (z<0.1), soft X-ray selected
Seyferts from the catalog of the Einstein Slew Survey (Elvis etal. 1992,
Plummer et al. 1994). We probe the geometry and column depth of obscuring
material in the host-galaxy disks using galaxian axial ratios determined mainly
from the Digitized Sky Survey. The distribution of host-galaxy axial ratios
clearly shows a bias against edge-on spirals, confirming the existence of a
geometrically thick layer of obscuring material in the host-galaxy planes. Soft
X-ray selection recovers some of the edge-on objects missed in UV and visible
surveys but still results in 30% incompleteness for Type 1's. We speculate that
thick rings of obscuring material like the ones we infer for these Seyferts
might be commonly present in early type spirals, sitting at the Inner Lindblad
Resonances of the nonaxisymmetric potentials of the host galaxies.Comment: 14 pages including 2 tables and 3 eps figures, aas2pp4.sty, to appear
in Ap
A New High Resolution CO Map of the inner 2.'5 of M51 I. Streaming Motions and Spiral Structure
[Abridged] The Owens Valley mm-Array has been used to map the CO 1--0
emission in the inner 2'.5 of the grand design spiral galaxy M51 at 2''-3''
resolution. The molecular spiral arms are revealed with unprecedented clarity:
supermassive cloud complexes, Giant Molecular Associations, are for the first
time resolved both along and perpendicular to the arms. Major complexes occur
symmetrically opposite each other in the two major arms. Streaming motions can
be studied in detail along the major and minor axes of M51. The streaming
velocities are very large, 60-150 km/s. For the first time, sufficient
resolution to resolve the structure in the molecular streaming motions is
obtained. Our data support the presence of galactic shocks in the arms of M51.
In general, velocity gradients across arms are higher by a factor of 2-10 than
previously found. They vary in steepness along the spiral arms, becoming
particularly steep in between GMAs. The steep gradients cause conditions of
strong reverse shear in several regions in the arms, and thus the notion that
shear is generally reduced by streaming motions in spiral arms will have to be
modified. Of the three GMAs studied on the SW arm, only one shows reduced
shear. We find an expansion in the NE molecular arm at 25'' radius SE of the
center. This broadening occurs right after the end of the NE arm at the Inner
Lindblad Resonance. Bifurcations in the molecular spiral arm structure, at a
radius of 73'', may be evidence of a secondary compression of the gas caused by
the 4/1 ultraharmonic resonance. Inside the radius of the ILR, we detect narrow
(~ 5'') molecular spiral arms possibly related to the K-band arms found in the
same region. We find evidence of non-circular motions in the inner 20'' which
are consistent with gas on elliptical orbits in a bar.Comment: 29 pages, 15 figures, uses latex macros for ApJ; accepted for
publication in Ap
H2O line mapping at high spatial and spectral resolution - Herschel observations of the VLA1623 outflow
Apart from being an important coolant, H2O is known to be a tracer of
high-velocity molecular gas. Recent models predict relatively high abundances
behind interstellar shockwaves. The dynamical and physical conditions of the
H2O emitting gas, however, are not fully understood yet. We aim to determine
the abundance and distribution of H2O, its kinematics and the physical
conditions of the gas responsible for the H2O emission. The observed line
profile shapes help us understand the dynamics in molecular outflows. We mapped
the VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFI
and PACS instruments. We also present observations of higher energy transitions
of o-H2O and p-H2O obtained with HIFI and PACS towards selected outflow
positions. From comparison with non-LTE radiative transfer calculations, we
estimate the physical parameters of the water emitting regions. The observed
water emission line profiles vary over the mapped area. Spectral features and
components, tracing gas in different excitation conditions, allow us to
constrain the density and temperature of the gas. The H2O emission originates
in a region where temperatures are comparable to that of the warm H2 gas
(T\gtrsim200K). Thus, the H2O emission traces a gas component significantly
warmer than the gas responsible for the low-J CO emission. The H2O column
densities at the CO peak positions are low, i.e. N(H2O) \simeq (0.03-10)x10e14
cm-2. The H2O abundance with respect to H2 in the extended outflow is estimated
at X(H2O)<1x10e-6, significantly lower than what would be expected from most
recent shock models. The H2O emission traces a gas component moving at
relatively high velocity compared to the low-J CO emitting gas. However, other
dynamical quantities such as the momentum rate, energy and mechanical
luminosity are estimated to be the same, independent of the molecular tracer
used, CO or H2O.Comment: 14 pages, 13 figures, 4 table
Gas and dust in the star-forming region ρ Oph A ∗, ∗∗, ∗∗∗: The dust opacity exponent β and the gas-to-dust mass ratio g2d
© ESO, 2015. Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N<inf>2</inf>H<sup>+</sup>, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N<inf>2</inf>H<sup>+</sup> (J = 3-2) and (J = 6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H<inf>2</inf>), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, = 88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C<sup>18</sup>O, also N<inf>2</inf>H<sup>+</sup> is frozen onto the grains
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