1,597 research outputs found
Molecular properties of (U)LIRGs: CO, HCN, HNC and HCO+
The observed molecular properties of a sample of FIR-luminous and OH
megamaser (OH-MM) galaxies have been investigated. The ratio of high and
low-density tracer lines is found to be determined by the progression of the
star formation in the system. The HCO+/HCN and HCO+/HNC line ratios are good
proxies for the density of the gas, and PDR and XDR sources can be
distinguished using the HNC/HCN line ratio. The properties of the OH-MM sources
in the sample can be explained by PDR chemistry in gas with densities higher
than 10^5.5 cm^-3, confirming the classical OH-MM model of IR pumped
amplification with (variable) low gains.Comment: 5 pages, 2 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
Arp 220 - IC 4553/4: understanding the system and diagnosing the ISM
Arp220 is a nearby system in final stages of galaxy merger with powerful
ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected
in HI absorption and OH Megamaser emission and later recognized as the nearest
ultra-luminous infrared galaxy also showing powerful molecular and X-ray
emissions. In this paper we review the available radio and mm-wave
observational data of Arp 220 in order to obtain an integrated picture of the
dense interstellar medium that forms the location of the powerful
star-formation at the two nuclei.Comment: 9 pages, 4 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
Recognition and reconstruction of coherent energy with application to deep seismic reflection data
Reflections in deep seismic reflection data tend to be
visible on only a limited number of traces in a common
midpoint gather. To prevent stack degeneration,
any noncoherent reflection energy has to be removed.
In this paper, a standard classification technique in
remote sensing is presented to enhance data quality. It
consists of a recognition technique to detect and extract
coherent energy in both common shot gathers and fi-
nal stacks. This technique uses the statistics of a picked
seismic phase to obtain the likelihood distribution of its
presence. Multiplication of this likelihood distribution
with the original data results in a “cleaned up” section.
Application of the technique to data from a deep seismic
reflection experiment enhanced the visibility of all
reflectors considerably.
Because the recognition technique cannot produce an
estimate of “missing” data, it is extended with a reconstruction
method. Two methods are proposed: application
of semblance weighted local slant stacks after recognition,
and direct recognition in the linear tau-p domain.
In both cases, the power of the stacking process to increase the signal-to-noise ratio is combined with the direct selection of only specific seismic phases. The joint
application of recognition and reconstruction resulted in
data images which showed reflectors more clearly than
application of a single technique
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
Muscle force is determined also by muscle relative position: isolated effects
Effects on force of changes of the position of extensor digitorum longus muscle (EDL) relative to surrounding tissues were investigated in rat. Connective tissue at the muscle bellies of tibialis anterior (TA), extensor hallucis longus (EHL) and EDL was left intact, to allow myofascial force transmission. The position of EDL muscle was altered, without changing EDL muscle–tendon complex length, and force exerted at proximal and distal tendons of EDL as well as summed force exerted at the distal tendons of TA and EHL muscles (TA+EHL) were measured. Proximal and distal EDL forces as well as distal TA+EHL force changed significantly on repositioning EDL muscle.\ud
\ud
These muscle position–force characteristics were assessed at two EDL lengths and two TA+EHL lengths. It was shown that changes of muscle force with length changes of a muscle is the result of the length changes per se, as well as of changes of relative position of parts of the muscle. It is concluded that in addition to length, muscle position relative to its surroundings co-determines isometric muscle force.\ud
\ud
Keywords: Intermuscular and extramuscular connective tissue; Myofascial force transmission; Rat m. extensor digitorum longus (EDL); Sarcomere length; Muscle relative positio
RadioAstron space-VLBI project: studies of masers in star forming regions of our Galaxy and megamasers in external galaxies
Observations of the masers in the course of RadioAstron mission yielded
detections of fringes for a number of sources in both water and hydroxyl maser
transitions. Several sources display numerous ultra-compact details. This
proves that implementation of the space VLBI technique for maser studies is
possible technically and is not always prevented by the interstellar
scattering, maser beaming and other effects related to formation, transfer, and
detection of the cosmic maser emission. For the first time, cosmic water maser
emission was detected with projected baselines exceeding Earth Diameter. It was
detected in a number of star-forming regions in the Galaxy and megamaser
galaxies NGC 4258 and NGC 3079. RadioAstron observations provided the absolute
record of the angular resolution in astronomy. Fringes from the NGC 4258
megamaser were detected on baseline exceeding 25 Earth Diameters. This means
that the angular resolution sufficient to measure the parallax of the water
maser source in the nearby galaxy LMC was directly achieved in the cosmic maser
observations. Very compact features with angular sizes about 20 microarcsec
have been detected in star-forming regions of our Galaxy. Corresponding linear
sizes are about 5-10 million kilometers. So, the major step from milli- to
micro-arcsecond resolution in maser studies is done in the RadioAstron mission.
The existence of the features with extremely small angular sizes is
established. Further implementations of the space-VLBI maser instrument for
studies of the nature of cosmic objects, studies of the interaction of
extremely high radiation field with molecular material and studies of the
matter on the line of sight are planned.Comment: To be published in Astrophysical Masers: Unlocking the Mysteries of
the Universe, IAU Symposium 336, 201
The Emission Structure of Formaldehyde MegaMasers
The formaldehyde MegaMaser emission has been mapped for the three host
galaxies IC\,860. IRAS\,151070724, and Arp\,220. Elongated emission
components are found at the nuclear centres of all galaxies with an extent
ranging between 30 to 100 pc. These components are superposed on the peaks of
the nuclear continuum. Additional isolated emission components are found
superposed in the outskirts of the radio continuum structure. The brightness
temperatures of the detected features ranges from 0.6 to 13.4
K, which confirms their masering nature. The masering scenario is interpreted
as amplification of the radio continuum by foreground molecular gas that is
pumped by far-infrared radiation fields in these starburst environments of the
host galaxies.Comment: Accepted MNRA
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
Opportunities for maser studies with the Square Kilometre Array
The Square Kilometre Array (SKA) is the radio telescope of the next
generation, providing an increase in sensitivity and angular resolution of two
orders of magnitude over existing telescopes. Currently, the SKA is expected to
span the frequency range 0.1-25 GHz with capabilities including a wide
field-of-view and measurement of polarised emission. Such a telescope has
enormous potential for testing fundamental physical laws and producing
transformational discoveries. Important science goals include using H2O
megamasers to make precise estimates of H0, which will anchor the extragalactic
distance scale, and to probe the central structures of accretion disks around
supermassive black holes in AGNs, to study OH megamasers associated with
extreme starburst activity in distant galaxies and to study with unprecedented
precision molecular gas and star formation in our Galaxy.Comment: 5 pages, to appear in: IAU Symposium 242 Astrophysical Masers and
their Environment
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