225 research outputs found
Modelling the Molecular Gas in NGC 6240
We present the first observations of HCN, HCO
and SiO in NGC\,6240, obtained with the IRAM PdBI. Combining a Markov
Chain Monte Carlo (MCMC) code with Large Velocity Gradient (LVG) modelling, and
with additional data from the literature, we simultaneously fit three gas
phases and six molecular species to constrain the physical condition of the
molecular gas, including massluminosity conversion factors. We find
of dense molecular gas in cold, dense clouds (\,K, \,cm) with a volume filling factor
, embedded in a shock heated molecular medium (\,K,
\,cm), both surrounded by an extended diffuse
phase (\,K, \,cm). We
derive a global with gas masses
, dominated by the
dense gas. We also find , which traces the
cold, dense gas. The [C]/[C] ratio is only slightly elevated
(), contrary to the very high [CO]/[CO] ratio (300-500)
reported in the literature. However, we find very high [HCN]/[HCN] and
[HCO]/[HCO] abundance ratios which we
attribute to isotope fractionation in the cold, dense clouds.Comment: 27 pages, 17 figures, 9 tables. Accepted in Ap
Chemically Distinct Nuclei and Outflowing Shocked Molecular Gas in Arp 220
We present the results of interferometric spectral line observations of Arp
220 at 3.5mm and 1.2mm from the Plateau de Bure Interferometer (PdBI), imaging
the two nuclear disks in HCN and , HCO and , and HNC as well as SiO and , HCN, and SO. The gas traced by SiO
has a complex and extended kinematic signature including a prominent P Cygni
profile, almost identical to previous observations of HCO. Spatial
offsets north and south of the continuum centre in the emission and
absorption of the SiO P Cygni profile in the western nucleus (WN)
imply a bipolar outflow, delineating the northern and southern edges of its
disk and suggesting a disk radius of pc, consistent with that found by
ALMA observations of Arp 220. We address the blending of SiO and
HCO by considering two limiting cases with regards to the
HCO emission throughout our analysis. Large velocity gradient (LVG)
modelling is used to constrain the physical conditions of the gas and to infer
abundance ratios in the two nuclei. Our most conservative lower limit on the
[HCN]/[HCO] abundance ratio is 11 in the WN, cf. 0.10 in the
eastern nucleus (EN). Comparing these ratios to the literature we argue on
chemical grounds for an energetically significant AGN in the WN driving either
X-ray or shock chemistry, and a dominant starburst in the EN.Comment: 28 pages, 17 figures, accepted to Ap
Widespread HCO emission in the M82's nuclear starburst
We present a high-resolution (~ 5'') image of the nucleus of M82 showing the
presence of widespread emission of the formyl radical (HCO). The HCO map, the
first obtained in an external galaxy, reveals the existence of a structured
disk of ~ 650 pc full diameter. The HCO distribution in the plane mimics the
ring morphology displayed by other molecular/ionized gas tracers in M82. More
precisely, rings traced by HCO, CO and HII regions are nested, with the HCO
ring lying in the outer edge of the molecular torus. Observations of HCO in
galactic clouds indicate that the abundance of HCO is strongly enhanced in the
interfaces between the ionized and molecular gas. The surprisingly high overall
abundance of HCO measured in M82 (X(HCO) ~ 4x10^{-10}) indicates that its
nuclear disk can be viewed as a giant Photon Dominated Region (PDR) of ~ 650 pc
size. The existence of various nested gas rings, with the highest HCO abundance
occurring at the outer ring (X(HCO) ~ 0.8x10^{-9}), suggests that PDR chemistry
is propagating in the disk. We discuss the inferred large abundances of HCO in
M82 in the context of a starburst evolutionary scenario, picturing the M82
nucleus as an evolved starburst.Comment: 13 pages, 3 figures, to appear in ApJ Letters; corrected list of
author
Detection of CO+ in the nucleus of M82
We present the detection of the reactive ion CO+ towards the prototypical
starburst galaxy M82. This is the first secure detection of this short-lived
ion in an external galaxy. Values of [CO+]/[HCO+]>0.04 are measured across the
inner 650pc of the nuclear disk of M82. Such high values of the [CO+]/[HCO+]
ratio had only been previously measured towards the atomic peak in the
reflection nebula NGC7023. This detection corroborates that the molecular gas
reservoir in the M82 disk is heavily affected by the UV radiation from the
recently formed stars. Comparing the column densities measured in M82 with
those found in prototypical Galactic photon-dominated regions (PDRs), we need
\~20 clouds along the line of sight to explain our observations. We have
completed our model of the molecular gas chemistry in the M82 nucleus. Our PDR
chemical model successfully explains the [CO+]/[HCO+] ratios measured in the
M~82 nucleus but fails by one order of magnitude to explain the large measured
CO+ column densities (~1--4x10^{13} cm^{-2}). We explore possible routes to
reconcile the chemical model and the observations.Comment: 12 pages, 2 figure
Draft genome sequence of multidrug-resistant vibrio parahaemolyticus strain PH698, infecting penaeid shrimp in the Philippines
The emergence of multidrug-resistant bacterial strains in diverse settings has been reported globally. In the Philippine shrimp aquaculture industry, antibiotics are used for the treatment of bacterial diseases during the production cycle. We report the draft genome of Vibrio parahaemolyticus PH698, a multidrug-resistant strain isolated from a Philippine shrimp farm
High-resolution imaging of the molecular outflows in two mergers: IRAS17208-0014 and NGC1614
Galaxy evolution scenarios predict that the feedback of star formation and
nuclear activity (AGN) can drive the transformation of gas-rich spiral mergers
into ULIRGs, and, eventually, lead to the build-up of QSO/elliptical hosts. We
study the role that star formation and AGN feedback have in launching and
maintaining the molecular outflows in two starburst-dominated advanced mergers,
NGC1614 and IRAS17208-0014, by analyzing the distribution and kinematics of
their molecular gas reservoirs. We have used the PdBI array to image with high
spatial resolution (0.5"-1.2") the CO(1-0) and CO(2-1) line emissions in
NGC1614 and IRAS17208-0014, respectively. The velocity fields of the gas are
analyzed and modeled to find the evidence of molecular outflows in these
sources and characterize the mass, momentum and energy of these components.
While most (>95%) of the CO emission stems from spatially-resolved
(~2-3kpc-diameter) rotating disks, we also detect in both mergers the emission
from high-velocity line wings that extend up to +-500-700km/s, well beyond the
estimated virial range associated with rotation and turbulence. The kinematic
major axis of the line wing emission is tilted by ~90deg in NGC1614 and by
~180deg in IRAS17208-0014 relative to their respective rotating disk major
axes. These results can be explained by the existence of non-coplanar molecular
outflows in both systems. In stark contrast with NGC1614, where star formation
alone can drive its molecular outflow, the mass, energy and momentum budget
requirements of the molecular outflow in IRAS17208-0014 can be best accounted
for by the existence of a so far undetected (hidden) AGN of L_AGN~7x10^11
L_sun. The geometry of the molecular outflow in IRAS17208-0014 suggests that
the outflow is launched by a non-coplanar disk that may be associated with a
buried AGN in the western nucleus.Comment: Final version in press, accepted by A&A. Reference list updated.
Minor typos correcte
Photon-Dominated Chemistry in the Nucleus of M82: Widespread HOC+ emission in the inner 650 pc disk
The nucleus of M82 has been mapped in several 3mm and 1mm lines of CN, HCN,
C2H, c-C3H2, CH3C2H, HC3N and HOC+ using the IRAM 30m telescope. These species
have been purposely selected as good tracers of photon-dominated chemistry. We
have measured [CN]/[HCN] ~ 5 in the inner 650 pc galaxy disk. Furthermore, we
have detected the HOC+ 1--0 line with an intensity similar to that of the
H13CO+ 1--0 line. This implies a [HCO+]/[HOC+] ratio of ~40. These results
corroborate the existence of a giant photo-dissociation region (PDR) in the
nucleus of M82. In fact, the low [HCO+]/[HOC+] ratio can only be explained if
the nucleus of M82 is formed by small (r<0.02-0.2 pc) and dense (n ~ a few
10^4--10^5 cm^{-3}) clouds immersed in an intense UV field (G_0 ~ 10^4 in units
of the Habing field). The detection of the hydrocarbons c-C3H2 and CH3C2H in
the nucleus of M82 suggests that a complex carbon chemistry is developing in
this giant PDR.Comment: 4 pages, 2 fig
Full-disc CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H conversion factor
Carbon monoxide (CO) provides crucial information about the molecular gas
properties of galaxies. While CO has been targeted extensively,
isotopologues such as CO have the advantage of being less optically
thick and observations have recently become accessible across full galaxy
discs. We present a comprehensive new dataset of CO(1-0) observations
with the IRAM 30-m telescope of the full discs of 9 nearby spiral galaxies from
the EMPIRE survey at a spatial resolution of 1.5kpc. CO(1-0) is
mapped out to and detected at high signal-to-noise throughout our
maps. We analyse the CO(1-0)-to-CO(1-0) ratio () as a
function of galactocentric radius and other parameters such as the
CO(2-1)-to-CO(1-0) intensity ratio, the 70-to-160m flux
density ratio, the star-formation rate surface density, the star-formation
efficiency, and the CO-to-H conversion factor. We find that varies by
a factor of 2 at most within and amongst galaxies, with a median value of 11
and larger variations in the galaxy centres than in the discs. We argue that
optical depth effects, most likely due to changes in the mixture of
diffuse/dense gas, are favored explanations for the observed variations,
while abundance changes may also be at play. We calculate a spatially-resolved
CO(1-0)-to-H conversion factor and find an average value of
cm (K.km/s) over our sample with a standard
deviation of a factor of 2. We find that CO(1-0) does not appear to be a
good predictor of the bulk molecular gas mass in normal galaxy discs due to the
presence of a large diffuse phase, but it may be a better tracer of the mass
than CO(1-0) in the galaxy centres where the fraction of dense gas is
larger.Comment: accepted for publication in MNRA
Molecular gas chemistry in AGN. II. High-resolution imaging of SiO emission in NGC1068: shocks or XDR?
This paper is part of a multi-species survey of line emission from the
molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC1068.
Single-dish observations have provided evidence that the abundance of silicon
monoxide(SiO) in the CND of NGC1068 is enhanced by 3-4 orders of magnitude with
respect to the values typically measured in quiescent molecular gas in the
Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. We
have imaged with the IRAM Plateau de Bure interferometer the emission of the
SiO(2-1) and CN(2--1) lines in NGC1068 at 150pc and 60pc spatial resolution,
respectively. We have also obtained complementary IRAM 30m observations of HNCO
and methanol (CH3OH) lines. SiO is detected in a disk of 400pc size around the
AGN. SiO abundances in the CND of (1-5)xE-09 are about 1-2 orders of magnitude
above those measured in the starburst ring. The overall abundance of CN in the
CND is high: (0.2-1)xE-07. The abundances of SiO and CN are enhanced at the
extreme velocities of gas associated with non-circular motions close to the AGN
(r<70pc). Abundances measured for CN and SiO, and the correlation of CN/CO and
SiO/CO ratios with hard X-ray irradiation, suggest that the CND of NGC1068 has
become a giant X-ray dominated region (XDR). The extreme properties of
molecular gas in the circum-nuclear molecular disk of NGC1068 result from the
interplay between different processes directly linked to nuclear activity.
Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC1068,
the relevance of shocks deserves further scrutiny. The inclusion of dust grain
chemistry would help solve the controversy regarding the abundances of other
molecular species, like HCN, which are under-predicted by XDR models.Comment: 18 pages, 13 figures, 2 tables; accepted for publication in A&
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