220 research outputs found
Odin observations of the Galactic centre in the 118-GHz band. Upper limit to the O2 abundance
The Odin satellite has been used to search for the 118.75-GHz line of
molecular oxygen (O2)in the Galactic centre. Odin observations were performed
towards the Sgr A* circumnuclear disk (CND), and the Sgr A +20 km/s and +50
km/s molecular clouds using the position-switching mode. Supplementary
ground-based observations were carried out in the 2-mm band using the ARO Kitt
Peak 12-m telescope to examine suspected SiC features. A strong emission line
was found at 118.27 GHz, attributable to the J=13-12 HC3N line. Upper limits
are presented for the 118.75-GHz O2 (1,1-1,0) ground transition line and for
the 118.11-GHz 3Pi2, J=3-2 ground state SiC line at the Galactic centre. Upper
limits are also presented for the 487-GHz O2 line in the Sgr A +50 km/s cloud
and for the 157-GHz, J=4-3, SiC line in the Sgr A +20 and +50 km/s clouds, as
well as the CND. The CH3OH line complex at 157.2 - 157.3 GHz has been detected
in the +20 and +50 km/s clouds but not towards Sgr A*/CND. A 3-sigma upper
limit for the fractional abundance ratio of [O2]/[H2] is found to be X(O2) <
1.2 x 10exp(-7) towards the Sgr A molecular belt region.Comment: Accepted for publication in A&A. 6 journal pages, 5 figure
Psychosocial Factors’ Influence on Work Ability of People Experiencing Sick Leave Resulting From Common Mental Disorders
HNC, HCN and CN in Seyfert galaxies
Bright HNC 1--0 emission has been found towards several Seyfert galaxies.
This is unexpected since traditionally HNC is a tracer of cold (10 K) gas, and
the molecular gas of luminous galaxies like Seyferts is thought to have bulk
kinetic temperatures surpassing 50 K. In this work we aim to distinguish the
cause of the bright HNC and to model the physical conditions of the HNC and HCN
emitting gas. We have used SEST, JCMT and IRAM 30m telescopes to observe HNC
3-2 and HCN 3-2 line emission in a selection of 5 HNC-luminous Seyfert
galaxies. We estimate and discuss the excitation conditions of HCN and HNC in
NGC 1068, NGC 3079, NGC 2623 and NGC 7469, based on the observed 3-2/1-0 line
intensity ratios. We also observed CN 1-0 and 2-1 emission and discuss its role
in photon and X-ray dominated regions. HNC 3-2 was detected in 3 galaxies (NGC
3079, NGC 1068 and NGC 2623). HCN 3-2 was detected in NGC 3079, NGC 1068 and
NGC 1365. The HCN 3-2/1-0 ratio is lower than 0.3 only in NGC 3079, whereas the
HNC 3-2/1-0 ratio is larger than 0.3 only in NGC 2623. The HCN/HNC 1-0 and 3-2
line ratios are larger than unity in all the galaxies. The HCN/HNC 3-2 line
ratio is lower than unity only in NGC 2623, similar to Arp 220, Mrk 231 and NGC
4418. In three of the galaxies the HNC emissions emerge from gas of densities
n<10^5 cm^3, where the chemistry is dominated by ion-neutral reactions. In NGC
1068 the emission of HNC emerges from lower (<10^5 cm^3) density gas than HCN
(>10^5 cm^3). Instead, the emissions of HNC and HCN emerge from the same gas in
NGC 3079. The observed HCN/HNC and CN/HCN line ratios favor a PDR scenario,
rather than an XDR one. However, the N(HNC)/N(HCN) column density ratios
obtained for NGC 3079 can be found only in XDR environments.Comment: Accepted for publication in A&A. A selection of this paper will be
presented as a poster in the FIR workshop 2007, held at Bad Honnef, Germany.
High resolution figures in original paper. 16 pages, 8 figure
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
Very Large Array Observations of Galactic Center OH 1720 MHz Masers in Sagittarius A East and in the Circumnuclear Disk
We present Very Large Array (VLA) radio interferometry observations of the
1720 MHz OH masers in the Galactic Center (GC). Most 1720 MHz OH masers arise
in regions where the supernova remnant Sgr A East is interacting with the
interstellar medium. The majority of the newly found 1720 MHz OH masers are
located to the northeast, independently indicating and confirming an area of
shock interaction with the +50 km/s molecular cloud (M-0.02-0.07) on the far
side of Sgr A East. The previously known bright masers in the southeast are
suggested to be the result of the interaction between two supernova remnants,
instead of between Sgr A East and the surrounding molecular clouds as generally
found elsewhere in the Galaxy. Together with masers north of the circumnuclear
disk (CND) they outline an interaction on the near side of Sgr A East. In
contrast to the interaction between the +50 km/s cloud and Sgr A East, OH
absorption data do not support a direct interaction between the CND material
and Sgr A East. We also present three new high-negative velocity masers,
supporting a previous single detection. The location and velocities of the
high-negative and high-positive velocity masers are consistent with being near
the tangent points of, and physically located in the CND. We argue that the
high velocity masers in the CND are pumped by dissipation between density
clumps in the CND instead of a shock generated by the supernova remnant. That
is, the CND masers are not coupled to the supernova remnant and are sustained
independently.Comment: accepted to ApJ, 9 pages 3 figure
The Starburst Contribution to the Extra-Galactic Gamma-Ray Background
Cosmic ray protons interacting with gas at the mean density of the
interstellar medium in starburst galaxies lose energy rapidly via inelastic
collisions with ambient nuclei. The resulting pions produce secondary electrons
and positrons, high-energy neutrinos, and gamma-ray photons. We estimate the
cumulative gamma-ray emission from starburst galaxies. We find a total
integrated background above 100 MeV of F_gamma ~ 10^{-6} GeV/cm^2/s/sr and a
corresponding specific intensity at GeV energies of nuI_nu ~ 10^{-7}
GeV/cm^2/s/sr. Starbursts may thus account for a significant fraction of the
extra-galactic -ray background. We show that the FIR-radio correlation
provides a strong constraint on the gamma-ray emission from starburst galaxies
because pions decay into both gamma-rays and radio-emitting electron/positron
pairs. We identify several nearby systems where the potential for observing
gamma-ray emission is the most favorable (M82, NGC 253, and IC 342), predict
their fluxes, and predict a linear FIR-gamma-ray correlation for the densest
starbursts. If established, the FIR-gamma-ray correlation would provide strong
evidence for the ``calorimeter'' theory of the FIR-radio correlation and would
imply that cosmic rays in starburst galaxies interact with gas at approximately
the mean density of the interstellar medium (ISM), thereby providing an
important constraint on the physics of the ISM in starbursts.Comment: text revised and updated in response to referee's comments, 7 pages,
1 table, 1 figure, emulateap
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
The Suaineadh Project : a stepping stone towards the deployment of large flexible structures in space
The Suaineadh project aims at testing the controlled deployment and stabilization of space web. The deployment system is based on a simple yet ingenious control of the centrifugal force that will pull each of the four daughters sections apart. The four daughters are attached onto the four corners of a square web, and will be released from their initial stowed configuration attached to a central hub. Enclosed in the central hub is a specifically designed spinning reaction wheel that controls the rotational speed with a closed loop control fed by measurements from an onboard inertial measurement sensor. Five other such sensors located within the web and central hub provide information on the surface curvature of the web, and progression of the deployment. Suaineadh is currently at an advanced stage of development: all the components are manufactured with the subsystems integrated and are presently awaiting full integration and testing. This paper will present the current status of the Suaineadh project and the results of the most recent set of tests. In particular, the paper will cover the overall mechanical design of the system, the electrical and sensor assemblies, the communication and power systems and the spinning wheel with its control system
Modeling the Gas Flow in the Bar of NGC 1365
We present new observations of the strongly-barred galaxy NGC 1365, including
new photometric images and Fabry-Perot spectroscopy, as well as a detailed
re-analysis of the neutral hydrogen observations from the VLA archive. We find
the galaxy to be at once remarkably bi-symmetric in its I-band light
distribution and strongly asymmetric in the distribution of dust and in the
kinematics of the gas in the bar region. The velocity field mapped in the
H-alpha line reveals bright HII regions with velocities that differ by 60 to 80
km/s from that of the surrounding gas, which may be due to remnants of
infalling material. We have attempted hydrodynamic simulations of the bar flow
to estimate the separate disk and halo masses, using two different dark matter
halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar
pattern speeds (Omega_p). None of our models provides a compelling fit to the
data, but they seem most nearly consistent with a fast bar, corotation at sim
1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully
maximal, disk. The fitted dark halos are unusually concentrated, a requirement
driven by the declining outer rotation curve.Comment: 43 pages, 15 figures, accepted to appear in Ap
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