275 research outputs found
The A&A Experience With Impact Factors
There is a widespread impression that the scientific journal "Astronomy &
Astrophysics" (A&A) has a smaller impact, as measured by citations to articles,
than some of the other major astronomy journals. This impression was apparently
supported - and probably created - by the Journal Citation Report (JCR), which
is prepared annually by the Institute of Scientific Information (ISI) Web of
Knowledge. The published poor impact factor of A&A was in fact wrong and was
due to a serious flaw in the method used by ISI Web of Knowledge to determine
it. The resulting damage inflicted upon A&A by the JCR is incalculable.Comment: 4 pages, to be published in A. Heck (ed.) "Organizations and
Strategies in Astronomy, Vol. 5" (Kluwer, 2004
Psychosocial Factors’ Influence on Work Ability of People Experiencing Sick Leave Resulting From Common Mental Disorders
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
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
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
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
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 Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies
We use the difference (delta) between the position angles of the nuclear
radio emission and the host galaxy major axis to investigate the distribution
of the angle (beta) between the axes of the nuclear accretion disk and the host
galaxy disk in Seyfert galaxies. We provide a critical appraisal of the quality
of all measurements, and find that the data are limited by observational
uncertainties and biases, such as the well known deficiency of Seyfert galaxies
of high inclination. There is weak evidence that the distribution of delta for
Seyfert 2 galaxies may be different (at the 90% confidence level) from a
uniform distribution, while the Seyfert 1 delta distribution is not
significantly different from a uniform distribution or from the Seyfert 2 delta
distribution. The cause of the possible non-uniformity in the distribution of
delta for Seyfert 2 galaxies is discussed. Seyfert nuclei in late-type spiral
galaxies may favor large values of delta (at the ~96% confidence level), while
those in early-type galaxies show a more or less random distribution of delta.
This may imply that the nuclear accretion disk in non-interacting late-type
spirals tends to align with the stellar disk, while that in early-type galaxies
is more randomly oriented, perhaps as a result of accretion following a galaxy
merger.
We point out that biases in the distribution of inclination translate to
biased estimates of beta in the context of the unified scheme. When this effect
is taken into account, the distributions of beta for all Seyferts together, and
of Seyfert 1's and 2's separately, agree with the hypothesis that the radio
jets are randomly oriented with respect to the galaxy disk. The data are
consistent with the expectations of the unified scheme, but do not demand it.Comment: To appear in the Astrophysical Journal, Vol 516 #1, May 1, 1999.
Corrected figure placement within pape
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