248 research outputs found
Odin observations of ammonia in the Sgr A +50 km/s Cloud and Circumnuclear Disk
Context. The Odin satellite is now into its sixteenth year of operation, much
surpassing its design life of two years. One of the sources which Odin has
observed in great detail is the Sgr A Complex in the centre of the Milky Way.
Aims. To study the presence of NH3 in the Galactic Centre and spiral arms.
Methods. Recently, Odin has made complementary observations of the 572 GHz NH3
line towards the Sgr A +50 km/s Cloud and Circumnuclear Disk (CND). Results.
Significant NH3 emission has been observed in both the +50 km/s Cloud and the
CND. Clear NH3 absorption has also been detected in many of the spiral arm
features along the line of sight from the Sun to the core of our Galaxy.
Conclusions. The very large velocity width (80 km/s) of the NH3 emission
associated with the shock region in the southwestern part of the CND may
suggest a formation/desorption scenario similar to that of gas-phase H2O in
shocks/outflows.Comment: 5 pages, 3 figures, 3 table
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
Searching for O in the SMC:Constraints on Oxygen Chemistry at Low Metallicities
We present a 39 h integration with the Odin satellite on the ground-state
118.75 GHz line of O2 towards the region of strongest molecular emission in the
Small Magellanic Cloud. Our 3sigma upper limit to the O2 integrated intensity
of <0.049 K km/s in a 9'(160 pc) diameter beam corresponds to an upper limit on
the O2/H2 abundance ratio of <1.3E-6. Although a factor of 20 above the best
limit on the O2 abundance obtained for a Galactic source, our result has
interesting implications for understanding oxygen chemistry at sub-solar metal
abundances. We compare our abundance limit to a variety of astrochemical models
and find that, at low metallicities, the low O2 abundance is most likely
produced by the effects of photo-dissociation on molecular cloud structure.
Freeze-out of molecules onto dust grains may also be consistent with the
observed abundance limit, although such models have not yet been run at
sub-solar initial metallicities.Comment: 4 pages, accepted to A&A Letter
Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy)
The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in
March-April 2013 and January 2015, combined with the improved observational
capabilities of submillimeter facilities, offered an opportunity to carry out
sensitive compositional and isotopic studies of the volatiles in their coma. We
observed comet Lovejoy with the IRAM 30m telescope between 13 and 26 January
2015, and with the Odin submillimeter space observatory on 29 January - 3
February 2015. We detected 22 molecules and several isotopologues. The
HO and HO production rates measured with Odin follow a
periodic pattern with a period of 0.94 days and an amplitude of ~25%. The
inferred isotope ratios in comet Lovejoy are O/O = 499 24
and D/H = 1.4 0.4 in water, S/S = 24.7
3.5 in CS, all compatible with terrestrial values. The ratio
C/C = 109 14 in HCN is marginally higher than terrestrial
and N/N = 145 12 in HCN is half the Earth ratio. Several
upper limits for D/H or 12C/13C in other molecules are reported. From our
observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio
in an Oort Cloud comet that is not larger than the terrestrial value. On the
other hand, the observation of the same HDO line in the other Oort-cloud comet,
C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous
measurements of D/H in cometary water, this illustrates that a diversity in the
D/H ratio and in the chemical composition, is present even within the same
dynamical group of comets, suggesting that current dynamical groups contain
comets formed at very different places or times in the early solar system.Comment: Accepted for publication in Astronomy and Astrophysic
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite I. The observational data
Spectral line surveys are useful since they allow identification of new
molecules and new lines in uniformly calibrated data sets. Nonetheless, large
portions of the sub-millimetre spectral regime remain unexplored due to severe
absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the
measurements presented here is to cover wavelength regions at and around 0.55
mm -- regions largely unobservable from the ground. Using the Odin
astronomy/aeronomy satellite, we performed the first spectral survey of the
Orion KL molecular cloud core in the bands 486--492 and 541--576 GHz with
rather uniform sensitivity (22--25 mK baseline noise). Odin's 1.1 m size
telescope, equipped with four cryo-cooled tuneable mixers connected to broad
band spectrometers, was used in a satellite position-switching mode. Two mixers
simultaneously observed different 1.1 GHz bands using frequency steps of 0.5
GHz (25 hours each). An on-source integration time of 20 hours was achieved for
most bands. The entire campaign consumed ~1100 orbits, each containing one hour
of serviceable astro-observation. We identified 280 spectral lines from 38
known interstellar molecules (including isotopologues) having intensities in
the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart
from the ground state rotational 1(1,0)--1(0,1) transitions of ortho-H2O, H218O
and H217O, the high energy 6(2,4)--7(1,7) line of para-H2O and the
HDO(2,0,2--1,1,1) line have been observed, as well as the 1,0--0,1 lines from
NH3 and its rare isotopologue 15NH3. We suggest assignments for some
unidentified features, notably the new interstellar molecules ND and SH-.
Severe blends have been detected in the line wings of the H218O, H217O and 13CO
lines changing the true linewidths of the outflow emission.Comment: 21 pages, 10 figures, 7 tables, accepeted for publication in
Astronomy and Astrophysics 30 August 200
Water and ammonia abundances in S140 with the Odin satellite
We have used the Odin satellite to obtain strip maps of the ground-state
rotational transitions of ortho-water and ortho-ammonia, as well as CO(5-4) and
13CO(5-4) across the PDR, and H218O in the central position. A physi-chemical
inhomogeneous PDR model was used to compute the temperature and abundance
distributions for water, ammonia and CO. A multi-zone escape probability method
then calculated the level populations and intensity distributions. These
results are compared to a homogeneous model computed with an enhanced version
of the RADEX code. H2O, NH3 and 13CO show emission from an extended PDR with a
narrow line width of ~3 kms. Like CO, the water line profile is dominated by
outflow emission, however, mainly in the red wing. The PDR model suggests that
the water emission mainly arises from the surfaces of optically thick, high
density clumps with n(H2)>10^6 cm^-3 and a clump water abundance, with respect
to H2, of 5x10^-8. The mean water abundance in the PDR is 5x10^-9, and between
~2x10^-8 -- 2x10^-7 in the outflow derived from a simple two-level
approximation. Ammonia is also observed in the extended clumpy PDR, likely from
the same high density and warm clumps as water. The average ammonia abundance
is about the same as for water: 4x10^-9 and 8x10^-9 given by the PDR model and
RADEX, respectively. The similarity of water and ammonia PDR emission is also
seen in the almost identical line profiles observed close to the bright rim.
Around the central position, ammonia also shows some outflow emission although
weaker than water in the red wing. Predictions of the H2O(110-101) and
(111-000) antenna temperatures across the PDR are estimated with our PDR model
for the forthcoming observations with the Herschel Space Observatory.Comment: 13 pages, 14 figures, 10 tables. Accepted for publication in
Astronomy & Astrophysics 14 November 200
Ground-state ammonia and water in absorption towards Sgr B2
We have used the Odin submillimetre-wave satellite telescope to observe the
ground state transitions of ortho-ammonia and ortho-water, including their 15N,
18O, and 17O isotopologues, towards Sgr B2. The extensive simultaneous velocity
coverage of the observations, >500 km/s, ensures that we can probe the
conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the
Galactic centre, and the more diffuse gas in the Galactic disk clouds along the
line-of-sight. We present ground-state NH3 absorption in seven distinct
velocity features along the line-of-sight towards Sgr B2. We find a nearly
linear correlation between the column densities of NH3 and CS, and a
square-root relation to N2H+. The ammonia abundance in these diffuse Galactic
disk clouds is estimated to be about (0.5-1)e-8, similar to that observed for
diffuse clouds in the outer Galaxy. On the basis of the detection of H218O
absorption in the 3 kpc arm, and the absence of such a feature in the H217O
spectrum, we conclude that the water abundance is around 1e-7, compared to
~1e-8 for NH3. The Sgr B2 molecular cloud itself is seen in absorption in NH3,
15NH3, H2O, H218O, and H217O, with emission superimposed on the absorption in
the main isotopologues. The non-LTE excitation of NH3 in the environment of Sgr
B2 can be explained without invoking an unusually hot (500 K) molecular layer.
A hot layer is similarly not required to explain the line profiles of the
1_{1,0}-1_{0,1} transition from H2O and its isotopologues. The relatively weak
15NH3 absorption in the Sgr B2 molecular cloud indicates a high [14N/15N]
isotopic ratio >600. The abundance ratio of H218O and H217O is found to be
relatively low, 2.5--3. These results together indicate that the dominant
nucleosynthesis process in the Galactic centre is CNO hydrogen burning.Comment: 10 pages, 5 figure
Submillimeter Emission from Water in the W3 Region
We have mapped the submillimeter emission from the 1(10)-1(01) transition of
ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3
IRS5 region reveals strong water lines at half the positions in the map. The
relative strength of the Odin lines compared to previous observations by SWAS
suggests that we are seeing water emission from an extended region. Across much
of the map the lines are double-peaked, with an absorption feature at -39 km/s;
however, some positions in the map show a single strong line at -43 km/s. We
interpret the double-peaked lines as arising from optically thick,
self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted
lines originate in emission near W3 IRS4. In this model, the unusual appearance
of the spectral lines across the map results from a coincidental agreement in
velocity between the emission near W3 IRS4 and the blue peak of the more
complex lines near W3 IRS5. The strength of the water lines near W3 IRS4
suggests we may be seeing water emission enhanced in a photon-dominated region.Comment: Accepted to A&A Letters as part of the special Odin issue; 4 page
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