5,215 research outputs found
Probing the cool ISM in galaxies via 21cm HI absorption
Recent targeted studies of associated HI absorption in radio galaxies are
starting to map out the location, and potential cosmological evolution, of the
cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21
cm absorption profiles often show two distinct spectral-line components:
narrow, deep lines arising from cold gas in the extended disc of the galaxy,
and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al.
2011). Here, we present results from a targeted search for associated HI
absorption in the youngest and most recently-triggered radio AGN in the local
universe (Allison et al. 2012b). So far, by using the recently commissioned
Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011),
we have detected two new absorbers and one previously-known system. While two
of these show both a broad, shallow component and a narrow, deep component (see
Fig. 1), one of the new detections has only a single broad, shallow component.
Interestingly, the host galaxies of the first two detections are classified as
gas-rich spirals, while the latter is an early-type galaxy. These detections
were obtained using a spectral-line finding method, based on Bayesian
inference, developed for future large-scale absorption surveys (Allison et al.
2012a).Comment: 1 page, 1 figure, published in Proceedings of IAU Symposium No. 29
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Mapping solar irradiance within Schrödinger Basin for future robotic sample return missions
The US National Research Council (NRC) identified eight scientific concepts and thirty-five prioritized investigations to be addressed with continued lunar exploration. These objectives are broadly consistent with those identified throughout the international community. the majority of these objectives require sample return from the Moon. Schrödinger basin has been highlighted as a particularly attractive location to find suitable samples
A survey for redshifted molecular and atomic absorption lines I
We are currently undertaking a large survey for redshifted atomic and
molecular absorption ... only one clear and one tentative detection were
obtained: HI absorption at z = 0.097 in PKS 1555-140 and OH absorption at z
=0.126 in PKS 2300-189, respectively... In order to determine why no clear
molecular absorption was detected in any of the 13 sources searched, we
investigate the properties of the five redshifted systems currently known to
exhibit OH absorption. In four of these, molecules were first detected via
millimetre-wave transitions and the flat radio spectra indicate compact
background continuum sources, which may suggest a high degree of coverage of
the background source by the molecular clouds in the absorber. Furthermore, for
these systems we find a relationship between the molecular line strength and
red optical--near infrared (V-K) colours, thus supporting the notion that the
reddening of these sources is due to dust, which provides an environment
conducive to the formation of molecules. Upon comparison with the V-K colours
of our sample, this relationship suggests that, presuming the reddening occurs
at the host galaxy redshift at least in some of the targets, many of our
observations still fall short of the sensitivityrequired to detect OH
absorption, although a confirmation of the ``detection'' of OH in 2300-189
could contravene this.Comment: 13 pages, loads of figures, accepted by MNRA
On the Accuracy of A.C. Flux Leakage, Eddy Current, EMAT and Ultrasonic Methods of Measuring Surface Connecting Flaws in Seamless Steel Tubing
The objective of this study was to perform a comparative experimental evaluation to determine the detection sensitivity, classification (fJaw type) and depth sizing accuracy of A.C. flux leakage, single-frequency eddy current, electromagnetic acoustic transducer (EMAT) generated surface waves, and broadband ultrasonic methods for the measurement of complex surface connecting flaws in hot rolled, seamless, ferritic tubing. Since it was of interest to invest NDE techniques over a wide range of capabilities, tubing having flaw depths far exceeding industry standards was tested and evaluated. Results of the study will be used to provide a benchmark assessment of these NDE methods, from which decisions concerning production test systems can be made
HI emission and absorption in nearby, gas-rich galaxies II. -- sample completion and detection of intervening absorption in NGC 5156
We present the results of a survey for intervening 21cm HI absorption in a
sample of 10 nearby, gas-rich galaxies selected from the HI Parkes All-Sky
Survey (HIPASS). This follows the six HIPASS galaxies searched in previous work
and completes our full sample. In this paper we searched for absorption along
17 sightlines with impact parameters between 6 and 46 kpc, making one new
detection. We also obtained simultaneous HI emission-line data, allowing us to
directly relate the absorption-line detection rate to the HI distribution. From
this we find the majority of the non-detections in the current sample are
because sightline does not intersect the HI disc of the galaxy at sufficiently
high column density, but that source structure is also an important factor.
The detected absorption-line arises in the galaxy NGC 5156 () at an
impact parameter of 19 kpc. The line is deep and narrow with an integrated
optical depth of 0.82 km s. High resolution Australia Telescope Compact
Array (ATCA) images at 5 and 8 GHz reveal that the background source is
resolved into two components with a separation of 2.6 arcsec (500 pc at the
redshift of the galaxy), with the absorption likely occurring against a single
component. We estimate that the ratio of the spin temperature and covering
factor, , is approximately 950 K in the outer disc of NGC
5156, but further observations using VLBI would allow us to accurately measure
the covering factor and spin temperature of the gas.Comment: 31 pages, 11 figure
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