740 research outputs found
The irradiated ISM of ULIRGs
The nuclei of ULIRGs harbor massive young stars, an accreting central black
hole, or both. Results are presented for molecular gas that is exposed to
X-rays (1-100 keV, XDRs) and far-ultraviolet radiation (6-13.6 eV, PDRs).
Attention is paid to species like HCO+, HCN, HNC, OH, H2O and CO. Line ratios
of HCN/HCO+ and HNC/HCN discriminate between PDRs and XDRs. Very high J (>10)
CO lines, observable with HIFI/Herschel, discriminate very well between XDRs
and PDRs. In XDRs, it is easy to produce large abundances of warm (T>100 K) H2O
and OH. In PDRs, only OH is produced similarly well.Comment: 5 pages, 6 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
WSRT 1.4 GHz Observations of the Hubble Deep Field
We present WSRT 1.38 GHz observations of the Hubble Deep Field (and flanking
fields). 72 hours of data were combined to produce the WSRT's deepest image
yet, achieving an r.m.s. noise level of 8 microJy per beam. We detect radio
emission from galaxies both in the HDF and HFF which have not been previously
detected by recent MERLIN or VLA studies of the field.Comment: 2 pages, 1 figure, to appear in "The Universe at Low Radio
Frequencies", IAU Symposium 199. For colour figures, see
http://www.nfra.nl/~mag/hdf_wsrt.htm
Short-time homomorphic wavelet estimation
Successful wavelet estimation is an essential step for seismic methods like
impedance inversion, analysis of amplitude variations with offset and full
waveform inversion. Homomorphic deconvolution has long intrigued as a
potentially elegant solution to the wavelet estimation problem. Yet a
successful implementation has proven difficult. Associated disadvantages like
phase unwrapping and restrictions of sparsity in the reflectivity function
limit its application. We explore short-time homomorphic wavelet estimation as
a combination of the classical homomorphic analysis and log-spectral averaging.
The introduced method of log-spectral averaging using a short-term Fourier
transform increases the number of sample points, thus reducing estimation
variances. We apply the developed method on synthetic and real data examples
and demonstrate good performance.Comment: 13 pages, 5 figures. 2012 J. Geophys. Eng. 9 67
Dense circum-nuclear molecular gas in starburst galaxies
We present results from a study of the dense circum-nuclear molecular gas of
starburst galaxies. The study aims to investigate the interplay between
starbursts, active galactic nuclei and molecular gas. We characterise the dense
gas traced by HCN, HCO and HNC and examine its kinematics in the
circum-nuclear regions of nine starburst galaxies observed with the Australia
Telescope Compact Array. We detect HCN (10) and HCO (10) in seven
of the nine galaxies and HNC (10) in four. Approximately 7 arcsec resolution
maps of the circum-nuclear molecular gas are presented. The velocity integrated
intensity ratios, HCO (10)/HCN (10) and HNC (10)/HCN (10),
are calculated. Using these integrated intensity ratios and spatial intensity
ratio maps we identify photon dominated regions (PDRs) in NGC 1097, NGC 1365
and NGC 1808. We find no galaxy which shows the PDR signature in only one part
of the observed nuclear region. We also observe unusually strong HNC emission
in NGC 5236, but it is not strong enough to be consistent with X-ray dominated
region (XDR) chemistry. Rotation curves are derived for five of the galaxies
and dynamical mass estimates of the inner regions of three of the galaxies are
made.Comment: Accepted for publication in MNRAS, 22 December 2015. Main manuscript
is 13 pages, containing 3 figures. Also has 4 appendices of 13 pages total
containing numerous figures and details of calculation
A morphological algorithm for improving radio-frequency interference detection
A technique is described that is used to improve the detection of
radio-frequency interference in astronomical radio observatories. It is applied
on a two-dimensional interference mask after regular detection in the
time-frequency domain with existing techniques. The scale-invariant rank (SIR)
operator is defined, which is a one-dimensional mathematical morphology
technique that can be used to find adjacent intervals in the time or frequency
domain that are likely to be affected by RFI. The technique might also be
applicable in other areas in which morphological scale-invariant behaviour is
desired, such as source detection. A new algorithm is described, that is shown
to perform quite well, has linear time complexity and is fast enough to be
applied in modern high resolution observatories. It is used in the default
pipeline of the LOFAR observatory.Comment: Accepted for publication in A&
The OH Megamaser Emission in Arp\,220: the rest of the story
The OH Megamaser emission in the merging galaxy Arp220 has been re-observed
with the Multi-Element Radio Linked Interferometer Network (MERLIN) and the
European VLBI Network (EVN). Imaging results of the OH line emission at the two
nuclei are found to be consistent with earlier observations and confirm
additional extended emission structures surrounding the nuclei. Detailed
information about the distributed emission components around the two nuclei has
been obtained using a concatenated MERLIN and EVN database with intermediate
(40 mas) spatial resolution. Continuum imaging shows a relatively compact West
nucleus and a more extended East nucleus in addition to an extended continuum
ridge stretching below and beyond the two nuclei. Spectral line imaging show
extended emission regions at both nuclei together with compact components and
additional weaker components north and south of the West nucleus. Spectral line
analysis indicates that the dominant OH line emission originates in foreground
molecular material that is part of a large-scale molecular structure that
engulfs the whole nuclear region. Compact OH components are representative of
star formation regions within the two nearly edge-on nuclei and define the
systemic velocities of East and West as 5425 km/s and 5360 km/s.
The foreground material at East and West has a 100 km/s lower velocity at
5314 and 5254 km/s. These emission results confirm a maser amplification
scenario where the background continuum and the line emission of the star
formation regions are amplified by foreground masering material that is excited
by the FIR radiation field originating in the two nuclear regions.Comment: 17 pages, 18 figure
Mechanical feedback in the molecular ISM of luminous IR galaxies
Aims: Molecular emission lines originating in the nuclei of luminous
infra-red galaxies are used to determine the physical properties of the nuclear
ISM in these systems.
Methods: A large observational database of molecular emission lines is
compared with model predictions that include heating by UV and X-ray radiation,
mechanical heating, and the effects of cosmic rays.
Results: The observed line ratios and model predictions imply a separation of
the observedsystems into three groups: XDRs, UV-dominated high-density (n>=10^5
cm-3) PDRs, and lower-density (n=10^4.5 cm-3) PDRs that are dominated by
mechanical feedback.
Conclusions: The division of the two types of PDRs follows naturally from the
evolution of the star formation cycle of these sources, which evolves from
deeply embedded young stars, resulting in high-density (n>=10^5 cm-3) PDRs, to
a stage where the gas density has decreased (n=10^4.5 cm-3) and mechanical
feedback from supernova shocks dominates the heating budget.Comment: 4 pages, 3 figures, published as Letter to the Editor in A&A (see
http://www.aanda.org/articles/aa/abs/2008/34/aa10327-08/aa10327-08.html
Safety risks among frail older people living at home in the Netherlands:A cross‐sectional study in a routine primary care sample
Frail older people face a range of problems and risks that could undermine their ability to live safely at home. A comprehensive overview of these risks, from a multidimensional perspective, is currently lacking. This study aims to examine the prevalence of risks in multiple domains of life among frail older people living at home. We used cross‐sectional data from 824 people aged 65 years and older, who received a comprehensive geriatric assessment (the interRAI Home Care [interRAI‐HC]) between 2014 and 2018, as part of routine care from 25 general practices in the region of West‐Friesland, the Netherlands. The interRAI‐HC identifies amenable risks related to people's clinical conditions, functioning, lifestyle and behaviour, and social and physical environment. Descriptive statistics were used to examine population characteristics (age, gender, marital status, living arrangements and presence of chronic conditions) and prevalence of risks. Most common risks were related to people's clinical conditions (i.e cardio‐respiratory health, urinary incontinence, pain), functioning (i.e. limitations in instrumental activities of daily living and mood) and social environment (i.e. limitations in informal care and social functioning). More than 80% of frail older people faced multiple risks, and often on multiple domains of life simultaneously. People experiencing multiple risks per person, and on multiple domains simultaneously, were more often widowed and living alone. The multidimensional character of risks among frail older people living at home implies that an integrated approach to care, comprising both health and social care, is necessary. Insight in the prevalence of these risks can give direction to care allocation decisions
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