1,394 research outputs found
Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy
Simultaneous modeling of the line and continuum emission from the nuclear
region of the Circinus galaxy is presented. Composite models which include the
combined effect of shocks and photoionization from the active center and from
the circumnuclear star forming region are considered. The effects of dust
reradiation, bremsstrahlung from the gas and synchrotron radiation are treated
consistently. The proposed model accounts for two important observational
features. First, the high obscuration of Circinus central source is produced by
high velocity and dense clouds with characteristic high dust-to-gas ratios.
Their large velocities, up to 1500 km\s, place them very close to the active
center. Second, the derived size of the line emitting region is well in
agreement with the observed limits for the coronal and narrow line region of
Circinus.Comment: 36 pages, LaTex (including 4 Tables and 9 figures), removed from
Abstract To appear in "The Astrophysical Journal
The Distribution of H2O Maser Emission in the Nucleus of NGC 4945
We present the first interferometer map of the water maser emission in the
active nucleus of NGC 4945. Although the declination of the galaxy is about -49
degrees, we were able to make the observations with the southernmost antennas
of the Very Long Baseline Array. Strong maser emission is present in three
velocity ranges, one near the systemic velocity and two shifted roughly
symmetrically by +/-(100-150) km/s. This is the first detection of highly
blue-shifted water emission in NGC 4945. We determined the position of the
maser to be RA(B1950)= 13 02 32.28 +/- 0.02 ; Dec(B1950)= -49 12 01.9 +/- 0.1.
The uncertainties in earlier estimates are at least several arcseconds. The
maser lies within 2'' (36 pc at a distance of 3.7 Mpc) of the peaks in 1.4 GHz
continuum and 1.6 micron emission from the nucleus. The mappable maser emission
is distributed roughly linearly over about 40 milliarcseconds (0.7 pc) at a
position angle of about 45 degrees, which is close to the 43 +/- 2 degree
position angle of the galactic disk. The red and blue-shifted emission
symmetrically stradle the systemic emission on the sky, which suggests material
in edge-on circular motion around a central object. The position-velocity
structure indicates a binding mass of about one million Suns, within a volume
of radius about 0.3 pc. This implies that the central engine radiates on the
order of 10% of its Eddington luminosity.Comment: 18 pages, including 5 Postscript figures. Accepted for publication in
ApJ Letter
PKS 1018-42: A Powerful Kinetically Dominated Quasar
We have identified PKS 1018-42 as a radio galaxy with extraordinarily
powerful jets, over twice as powerful as any 3CR source of equal or lesser
redshift except for one (3C196). It is perhaps the most intrinsically powerful
extragalactic radio source in the, still poorly explored, Southern Hemisphere.
PKS 1018-42 belongs to the class of FR II objects that are kinetically
dominated, the jet kinetic luminosity, (calculated at 151 MHz), is 3.4 times larger than the
total thermal luminosity (IR to X-ray) of the accretion flow, . It is the fourth most kinetically dominated
quasar that we could verify from existing radio data. From a review of the
literature, we find that kinetically dominated sources such as PKS 1018-42 are
rare, and list the 5 most kinetically dominated sources found from our review.
Our results for PKS 1018-42 are based on new observations from the Australia
Telescope Compact Array.Comment: To appear in ApJ Letter
The optical-ultraviolet continuum of Seyfert 2 galaxies
This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting
the single galaxies in the sample of Heckman et al. (1995) with composite
models (shock+ photoionization from the active center), we show that five main
components characterize the SED of the continuum. Shocks play an important role
since they produce a high temperature zone where soft X-rays are emitted.
We show that in the optical-UV range, the slope of the NLR emission
reproduces the observed values, and may be the main component of the
featureless continuum. The presence of star forming regions cannot be excluded
in the circumnuclear region of various Seyfert galaxies. An attempt is made to
find their fingerprints in the observed AGN spectra. Finally, it is
demonstrated that multi-cloud models are necessary to interpret the spectra of
single objects, even in the global investigation of a sample of galaxies.Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To
appear in "The Astrophysical Journal
The Molonglo Galactic Plane Survey: I. Overview and Images
The first epoch Molonglo Galactic Plane Survey (MGPS1) is a radio continuum
survey made using the Molonglo Observatory Synthesis Telescope (MOST) at 843
MHz with a resolution of 43" X 43" cosec |delta|. The region surveyed is 245
deg < l < 355 deg, |b| < 1.5 deg. The thirteen 9 deg X 3 deg mosaic images
presented here are the superposition of over 450 complete synthesis
observations, each taking 12 h and covering 70' X 70' cosec |delta|. The
root-mean-square sensitivity over much of the mosaiced survey is 1-2 mJy/beam
(1 sigma), and the positional accuracy is approximately 1" X 1" cosec |delta|
for sources brighter than 20 mJy. The dynamic range is no better than 250:1,
and this also constrains the sensitivity in some parts of the images. The
survey area of 330 sq deg contains well over 12,000 unresolved or barely
resolved objects, almost all of which are extra-galactic sources lying in the
Zone of Avoidance. In addition a significant fraction of this area is covered
by extended, diffuse emission associated with thermal complexes, discrete H II
regions, supernova remnants, and other structures in the Galactic interstellar
medium.Comment: Paper with 3 figures and 1 table + Table 2 + 7 jpg grayscales for Fig
4. Astrophysical Journal Supplement (in press) see also
http://www.astrop.physics.usyd.edu.au/MGP
Stringent neutron-star limits on large extra dimensions
Supernovae (SNe) are copious sources for Kaluza-Klein gravitons which are
generic for theories with large extra dimensions. These massive particles are
produced with average velocities ~0.5 c so that many of them are
gravitationally retained by the SN core. Every neutron star thus has a halo of
KK gravitons which decay into nu bar-nu, e^+e^- and gamma gamma on time scales
\~10^9 years. The EGRET gamma-flux limits (E_gamma ~ 100 MeV) for nearby
neutron stars constrain the fundamental scale for n=2 extra dimensions to M
>500 TeV, and M>30 TeV for n=3. The upcoming GLAST satellite is a factor ~30
more sensitive and thus may detect KK decays, for example at the nearby neutron
star RX J185635--3754. The requirement that neutron stars are not excessively
heated by KK decays implies M>1700 TeV for n=2, and M>60 TeV for n=3.Comment: Minor changes, matches version to appear in PR
Violent behaviour in early psychosis patients: Can we identify clinical risk profiles?
The objective of this study is to explore, within a sample of early psychosis patients (EPP), if subgroups regarding rate of violent behaviour (VB) against others can be identified on the basis of dynamic risk factors (treatment modifiable characteristics).
In a sample of 265 EPP, treated at the Treatment and Early Intervention in Psychosis Program in Lausanne, we conducted a latent-class analysis on the basis of the main dynamic VB risk factors (substance use disorder [SUD], positive symptoms, insight, and impulsivity). VB were restricted to "serious violence" and were assessed through patients self-report, interview with relatives or forensic services and with a standardized instrument.
The analysis confirmed the heterogeneity of the sample regarding rate of VB. Patients could be stratified within 4 subgroups, 3 of which were at increased risk of VB. The two groups with the highest rates of VB displayed specific clinical profiles. The first one was characterized by high levels of impulsivity, hostility, positive symptoms and SUD, and the second, by low level of insight and low social functioning. These patterns suggest that significant difficulties in social interaction may contribute to the emergence of aggressive reactions against others.
Identification of EPP at increased risk of VB seems possible on the basis of dynamic risk factors. If confirmed prospectively, this could pave the way to the development of preventive strategies and specific interventions
Resolving the timescales of magmatic and hydrothermal processes associated with porphyry deposit formation using zircon UâPb petrochronology
Understanding the formation of economically important porphyry CuâAu
deposits requires knowledge of the magmatic-to-hydrothermal processes
that act within the much larger magmatic system and the timescales on which
they occur. We apply high-precision zircon geochronology (chemical abrasionâisotope dilutionâthermal ionisation mass spectrometry; CAâIDâTIMS) and
spatially resolved zircon geochemistry (laser ablation inductively coupled plasma mass
spectrometry; LA-ICP-MS) to constrain the magmatic
evolution of the underlying magma reservoir at the Pliocene Batu Hijau
porphyry CuâAu deposit. We then use this extensive dataset to assess the
accuracy and precision of different UâPb dating methods of the same zircon
crystals.
Emplacement of the oldest pre- to syn-ore tonalite (3.736±0.023 Ma)
and the youngest tonalite porphyry to cross-cut economic CuâAu mineralisation
(3.646±0.022 Ma) is determined by the youngest zircon grain from
each sample, which constrains the duration of metal precipitation to fewer
than 90±32 kyr. Overlapping spectra of single zircon crystallisation
ages and their trace element distributions from the pre-, syn and post-ore
tonalite porphyries reveal protracted zircon crystallisation together with
apatite and plagioclase within the same magma reservoir over >300 kyr. The presented petrochronological data constrain a protracted early
>200 kyr interval of melt differentiation and cooling within a
large heterogeneous magma reservoir, followed by magma storage in a highly
crystalline state and chemical and thermal stability over several tens of thousands of years
during which fluid expulsion formed the ore deposit. Irregular trace element
systematics suggest magma recharge or underplating during this final short
time interval.
The comparison of high-precision CAâIDâTIMS results with in situ LA-ICP-MS
and a sensitive high-resolution ion microprobe (SHRIMP) UâPb geochronology data from the same zircon grains allows a
comparison of the applicability of each technique as a tool to constrain
dates and rates on different geological timescales. All techniques provide
accurate dates but with different precision. Highly precise dates derived by
the calculation of the weighted mean and standard error of the mean of
the zircon dates obtained by in situ techniques can lead to ages of unclear
geological significance that are older than the maximum ages of emplacement
given by the CAâIDâTIMS ages of the youngest zircons in each sample. This
lack of accuracy of the weighted means is due to the protracted nature of
zircon crystallisation in upper crustal magma reservoirs, suggesting that
standard errors should not be used as a means to describe the uncertainty in
those circumstances. We conclude from this and similar published studies
that the succession of magma and fluid pulses forming a single porphyry
deposit and similarly rapid geological events are too fast to be reliably
resolved by in situ UâPb geochronology and that assessing the tempo of ore
formation requires CAâIDâTIMS geochronology.</p
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