Search

We present observations of pulsed radio emission from the transient anomalous X-ray pulsar XTE J1810-197. Data were obtained over a period of 100 days beginning in 2006 May using a baseband recording system at the 26 m Mount Pleasant radio telescope operated by the University of Tasmania. Pulsed emission was detected in three frequency bands centered on 1.4, 4.8, and 8.4 GHz. The mean flux density varied significantly within all bands, but we obtained fewer detections toward the end of the observing period, and the monitoring program was eventually abandoned. Most interestingly, we observed changes in the pulse-to-pulse emission characteristics. The variance of the flux in 10 s integrations changed significantly during the span of our observations, but we did not have sufficient data to identify a clear secular trend. In addition, timing measurements confirmed that the neutron star's spin period derivative changed significantly on or around MJD 53935.

Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975–1985 period of strong recurrent flaring activity.We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the λ2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system.

A set of diffuse interstellar clouds in the inner Galaxy within a few hundred parsecs of the Galactic plane has been observed at an angular resolution of ≈1′. 0 combining data from the NRAO Green Bank Telescope and the Very Large Array. At the distance of the clouds, the linear resolution ranges from ∼1.9 to ∼2.8 pc. These clouds have been selected to be somewhat outside of the Galactic plane, and thus are not confused with unrelated emission, but in other respects they are a Galactic population. They are located near the tangent points in the inner Galaxy, and thus at a quantifiable distance: 2.3 ⩽ R ⩽ 6.0 kpc from the Galactic Center and -1000 ⩽ z ⩽ +610 pc from the Galactic plane. These are the first images of the diffuse neutral H I clouds that may constitute a considerable fraction of the interstellar medium (ISM). Peak H I column densities lie in the range NH ɪ = 0.8–2.9 × 1020 cm−2. Cloud diameters vary between about 10 and 100 pc, and their H ɪ mass spans the range from less than a hundred to a few thousands M☉. The clouds show no morphological consistency of any kind, except that their shapes are highly irregular. One cloud may lie within the hot wind from the nucleus of the Galaxy, and some clouds show evidence of two distinct thermal phases as would be expected from equilibrium models of the ISM.

As we strive to understand how galaxies evolve it is crucial that we resolve physical processes and test emerging theories in nearby systems that we can observe in great detail. Our own Galaxy, the Milky Way, and the nearby Magellanic Clouds provide unique windows into the evolution of galaxies, each with its own metallicity and star formation rate. These laboratories allow us to study with more detail than anywhere else in the Universe how galaxies acquire fresh gas to fuel their continuing star formation, how they exchange gas with the surrounding intergalactic medium, and turn warm, diffuse gas into molecular clouds and ultimately stars. The $\lambda$21-cm line of atomic hydrogen (HI) is an excellent tracer of these physical processes. With the SKA we will finally have the combination of surface brightness sensitivity, point source sensitivity and angular resolution to transform our understanding of the evolution of gas in the Milky Way, all the way from the halo down to the formation of individual molecular clouds., Comment: 25 pages, from "Advancing Astrophysics with the Square Kilometre Array", to appear in Proceedings of Science

We present the first detection of HCO$^+$ absorption in the Magellanic System. Using the Australia Telescope Compact Array (ATCA), we observed 9 extragalactic radio continuum sources behind the Magellanic System and detected HCO$^+$ absorption towards one source located behind the leading edge of the Magellanic Bridge. The detection is located at LSR velocity of $v=214.0 \pm 0.4\rm\,km\,s^{-1}$, with a full width at half maximum of $\Delta v=4.5\pm 1.0\rm\,km\,s^{-1}$ and optical depth of $\tau(\rm HCO^+)=0.10\pm 0.02$. Although there is abundant neutral hydrogen (HI) surrounding the sightline in position-velocity space, at the exact location of the absorber the HI column density is low, $, Comment: Accepted for publication in ApJ. 6 pages, 2 figures, 2 tables

We present new high resolution (100 arcsec) neutral hydrogen (H I) self-absorption images of the Riegel-Crutcher cloud obtained with the Australia Telescope Compact Array and the Parkes Radio Telescope. The Riegel-Crutcher cloud lies in the direction of the Galactic center at a distance of 125 +/- 25 pc. Our observations resolve the very large, nearby sheet of cold hydrogen into a spectacular network of dozens of hair-like filaments. Individual filaments are remarkably elongated, being up to 17 pc long with widths of less than ~0.1 pc. The strands are reasonably cold, with spin temperatures of 40 K and in many places appearing to have optical depths larger than one. Comparing the H I images with observations of stellar polarization we show that the filaments are very well aligned with the ambient magnetic field. We argue that the structure of the cloud has been determined by its magnetic field. In order for the cloud to be magnetically dominated the magnetic field strength must be > 30 microGauss., To appear in the Astrophysical Journal. 26 pages, 6 figures. Full resolution version available at ftp://ftp.atnf.csiro.au/pub/people/nmcclure/papers/rc_cloud.pdf

The warm neutral medium, warm ionized medium, and cool neutral medium all show strong evidence for turbulence as a process dominating their structure and motions on a wide range of scales. The spatial power spectra of density fluctuations in all three phases are consistent with a Kolmogorov slope. Turbulence in the magnetic field in the diffuse medium can also be measured through the structure function of the Faraday rotation measure. With new surveys, new analysis techniques, and new telescopes, in the next few years it will be possible to measure the structure function of the magnetic field over a similarly wide range of scales. This will give a complete picture of the turbulence as a magneto-acoustic process.

The VLA Galactic Plane Survey (VGPS) of the first Galactic quadrant was searched for HI emission with velocities well above the maximum velocity allowed by Galactic rotation. A sample of 17 small fast-moving clouds was identified. The distribution of the ensemble of clouds in longitude and velocity indicates that the clouds are part of the Galactic disk, despite their large forbidden velocity. The median angular diameter of the clouds detected in the VGPS is 3.4 arcminutes. These clouds would not be noticed in previous low resolution surveys because of strong beam dilution. Assuming each cloud is located at the tangent point, a median cloud has a diameter of 10 pc, HI mass of 60 M_sun, and a velocity more than 25 km/s beyond the local terminal velocity derived from 12CO observations. Three clouds in the sample have a velocity between 50 and 60 km/s in excess of the local terminal velocity. The longitude distribution of the sample peaks near l = 30 degrees, while the latitude distribution of the clouds is nearly flat. The observed longitude and latitude distributions are compared with simulated distributions taking into account the selection criteria of the cloud search. It is found that the number of clouds declines with distance from the Galactic center, with an exponential scale length 2.8 - 8 kpc at the 99% confidence level. We find a lower limit to the scale height of the clouds of 180 pc (HWHM), but the true value is likely significantly higher., Comment: Accepted for publication in The Astrophysical Journal. 28 pages, 10 figures of which 3 as separate jpg files

A systematic and automated search of the extensive GLIMPSE mid-infrared survey data of the inner Galaxy was carried out to uncover new star clusters. This search has yielded 59 new clusters. Using our automated search algorithm, these clusters were identified as significant localized overdensities in the GLIMPSE point-source catalog (GLMC) and archive (GLMA). Subsequent visual inspection of the GLIMPSE image mosaics confirmed the existence of these clusters plus an additional 33 heavily embedded clusters missed by our detection algorithm, for a total of 92 newly discovered clusters. These previously uncataloged clusters range in type from heavily embedded to fully exposed clusters. More than half of the clusters have memberships exceeding 35 stars, and nearly all the clusters have diameters of 3' or less. The Galactic latitude distribution of the clusters reveals that the majority are concentrated toward the Galactic midplane. There is an asymmetry in the number of clusters located above and below the midplane, with more clusters detected below the midplane. We also observe an asymmetry in the number of clusters detected in the northern and southern halves of the Galaxy, with more than twice as many clusters detected in the south.

Spitzer IRAC 3.6-8 micron photometry obtained as part of the GLIMPSE survey has revealed mid-infrared excesses for 33 field stars with known spectral types in a 1.2 sq. degree field centered on the southern Galactic HII region RCW49. These stars comprise a subset of 184 stars with known spectral classification, most of which were pre-selected to have unusually red IR colors. We propose that the mid-IR excesses are caused by circumstellar dust disks that are either very late remnants of stellar formation or debris disks generated by planet formation. Of these 33 stars, 29 appear to be main-sequence stars based on optical spectral classifications. Five of the 29 main-sequence stars are O or B stars with excesses that can be plausibly explained by thermal bremsstrahlung emission, and four are post main-sequence stars. The lone O star is an O4V((f)) at a spectrophotometric distance of 3233+ 540- 535 pc and may be the earliest member of the Westerlund 2 cluster. Of the remaining 24 main-sequence stars, 18 have SEDs that are consistent with hot dusty debris disks, a possible signature of planet formation. Modeling the excesses as blackbodies demonstrates that the blackbody components have fractional bolometric disk-to-star luminosity ratios, LIR/L*, ranging from 10^-3 to 10^-2 with temperatures ranging from 220 to 820 K. The inferred temperatures are more consistent with asteroid belts rather than the cooler temperatures expected for Kuiper belts. Mid-IR excesses are found in all spectral types from late B to early K.

The λ21-cm line is an excellent tracer of the neutral interstellar medium (ISM). Atomic hydrogen (H I ) is found in a variety of environments, from dense clouds to the diffuse galactic halo, and its filling factor is often high, so structures with sizes over a wide range of scales can be mapped with this line. Galactic H I surveys show small scale structure that is consistent with a spectrum of interstellar turbulence similar to what is measured in the ionized component of the ISM. But our sampling of the spectrum of this turbulence is limited to a few size ranges, based on the sensitivities of existing telescopes for emission and absorption studies. The Square Kilometer Array (SKA) will provide the sensitivity and resolution to give continuous coverage of the turbulence spectrum from hundreds of parsecs to a few tens of Astronomical Units. By showing us the full spectrum of interstellar turbulence in the neutral medium, the physical processes driving hydrodynamic and magneto-hydrodynamic instabilities will be illuminated. Ultimately the turbulence governs the passage of the gas from the warm phases of the medium to the cold phases where gravitational collapse can initiate star formation. The SKA is needed to fill in this missing link in the cycle of star formation and chemical enrichment that drives the evolution of galaxies. In the Milky Way halo, SKA mapping of H I high velocity clouds will trace the structure and motion of both the warm phase gas and the hot medium. The interaction between these two phases of halo gas is a great unsolved problem in Galactic astrophysics.

Examination of early, in-orbit checkout (IOC) images of a portion of the Galactic plane obtained by the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope revealed the presence of an extended emission nebula with internal structure. The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) data show this nebula, located at l � 42 � and b � 0N5, contains bright point sources and two nonstellar regions. Ancillary data sets were used to help reveal the nature of this nebula and its exciting objects. In particular, 13 CO J ¼ 1 ! 0 line emission mapped by the Galactic Ring Survey (GRS) shows molecular gas associated with the infrared nebula. The 13 CO radial velocity yields a far-kinematic distance of 11.1 kpc to the nebula, since there is no evidence for H i self-absorption. At 11.1 kpc, the far-infrared luminosity of the nebula is 4:8;10 4 L� , and the mass of its molecular cloud is 1:1;10 4 M� . The spectral energy distribution rises steeply from 2.2 to 100 � m with an absorption feature at 10 � m, exhibiting the shape of a late Class 0 young stellar object (YSO). The radio continuum flux observed toward the nebula is consistent with the free-free emission from one or more massive YSOs (MYSOs) with spectral types in the range O9 to B0. This analysis demonstrates one technique the GLIMPSE team will use for revealing thousands of Galactic star formation regions.

One mechanism for spreading hot, metal enriched gas away from galaxies is through gigantic chimneys formed in the disk of a galaxy. Chimneys form when shells or bubbles blown by many massive stellar winds and supernova explosions grow large enough to exceed the neutral hydrogen (H I) scale height of the disk. The shells then become unstable at their polar regions and expand rapidly, breaking out to the galaxy's halo. If galactic fountain models are correct the hot gas liberated by these chimneys should cool into H I cloudlets high above the galaxy's disk. The Milky Way provides the nearest laboratory to search for these objects in order to study how they form and the fate of the expelled gas. While we expect tens of chimneys in the Milky Way to account for the thermal support of the halo there are only a few known chimneys. Here we present an H I study of one Galactic chimney GSH 277+00+36. GSH 277+00+36 is the the only chimney known to have blown out of both sides of a galactic disk. We discuss the development of Rayleigh-Taylor instabilities in this object and the role those may have had in the formation of the chimney.

The very local interstellar medium (LISM) has physical characteristics that are typical of the warm neutral medium throughout the disk of the Milky Way. Recent high resolution surveys of the Galactic plane in the λ21 cm line of hydrogen show that structures like the local bubble and the local clouds within it are very common. On smaller scales, observations predict that inside the local clouds there should be structure in the density and velocity field that might be detectable by direct measurements. With a time baseline of a few years or more, even an upper limit on the variation in these parameters would be useful to clarify the interpretation of controversial 21 cm VLBI observations.

Using data from the Southern Galactic Plane Survey (SGPS) we analyze an HI self-absorption cloud centered on l = 318.0 deg, b = -0.5 deg, and velocity, v = -1.1 km/s. The cloud was observed with the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope, and is at a near kinematic distance of less than 400 pc with derived dimensions of less than 5 x 11 pc. We apply two different methods to find the optical depth and spin temperature. In both methods we find upper limit spin temperatures ranging from 20 K to 25 K and lower limit optical depths ~ 1. We look into the nature of the HI emission and find that 60-70% originates behind the cloud. We analyze a second cloud at the same velocity centered on l = 319 deg and b = 0.4 deg with an upper limit spin temperature of 20 K and a lower limit optical depth of 1.6. The similarities in spin temperature, optical depth, velocity, and spatial location are evidence the clouds are associated, possibly as one large cloud consisting of smaller clumps of gas. We compare HI emission data with 12CO emission and find a physical association of the HI self-absorption cloud with molecular gas.

We present 12 CO(J= 1-0) line observations of 99 galaxies obtained with the SEST 15 m, the Kitt Peak 12 m and the IRAM 30 m telescopes. The target galaxies were selected from the catalogue of isolated galaxies of Karachentseva (1973). These data are thus representative of the CO properties of isolated late-type galaxies. All objects were observed in their central position, those with large angular sizes were mapped. These new measurements are used to estimate the molecular gas mass of the target galaxies. The molecular gas is on average18% of the atomic gas mass.

We present new high-resolution H I images of the Galactic chimney GSH 277+00+36. The chimney is at a distance of ~6.5 kpc, is more than 600 pc in diameter, and extends at least 1 kpc above and below the Galactic midplane. Using the Australia Telescope Compact Array and the Parkes Radiotelescope as part of the Southern Galactic Plane Survey, we have imaged the H I associated with this chimney, with a spatial resolution of ~6 pc. These are among the highest spatial resolution images of an H I chimney. We find very narrow well-defined shell walls, a remarkably empty interior, and complex small-scale structures. The shell walls show a very steep reduction in emission at the interior edge and a more gradual decline toward the exterior. We suggest that this structure is characteristic of compression and may be used to distinguish stellar by-product shells from shell-like structures resulting from random turbulent motions. The shell and chimney walls also exhibit a great deal of small-scale structure, which we discuss in the context of hydrodynamic instabilities. We find that these structures are primarily cold gas with narrow line widths in the range 1.5-2.5 km s-1.

In this paper we study 21-cm absorption spectra and the corresponding emission spectra toward bright continuum sources in the test region (326deg , is measured as a function of Galactic radius; it increases going in from the solar circle, to a peak in the molecular ring of about four times its local value. This suggests that the cool phase is more abundant there, and colder, than it is locally. The distribution of cool phase temperatures is derived in three different ways. The naive, ``spin temperature'' technique overestimates the cloud temperatures, as expected. Using two alternative approaches we get good agreement on a histogram of the cloud temperatures, T(cool), corrected for blending with warm phase gas. The median temperature is about 65 K, but there is a long tail reaching down to temperatures below 20 K. Clouds with temperatures below 40 K are common, though not as common as warmer clouds (40 to 100 K). Using these results we discuss two related quantities, the peak brightness temperature seen in emission surveys, and the incidence of clouds seen in HI self-absorption. Both phenomena match what would be expected based on our measurements of and T(cool).

21 cm HI line observations were made with the Arecibo Gregorian telescope of 9 HI clouds in the Hercules Cluster which were reported as tenative detections in a VLA HI study of the cluster (Dickey 1997) and for which our deep CCD imaging failed to find any optical counterparts. No sensitive observations could be made of one of these (sw-174) due to the presence of a close-by strong continuum source. The other 8 tentative HI detections were not reconfirmed by the Arecibo HI measurements. The CCD images did reveal faint, low surface brightness counterparts near the centres of two other VLA HI sources invisible on the Palomar Sky Survey, sw-103 and sw-194., Comment: 7 pages, accepted for Astronomy and Astrophysics on 8 Nov. 2002; new references added on 23 Dec. 2002

Kinematic distance determinations in the inner Galaxy are hampered by the near-far kinematic distance ambiguity. Here we resolve the ambiguity for 49 H II region complexes with known recombination-line velocities in the first Galactic quadrant. We measured the 21 cm H I absorption spectrum toward each source with the Very Large Array in the C array. The maximum velocity of H I absorption was used to discriminate between the near and far kinematic distances. The number ratio of far to near sources, ~3, can be entirely explained as a geometrical effect. The kinematic distances that we derive are compared with previous determinations for the same sources. Although our distance determinations are largely in agreement with previous measurements, there are 22 discrepancies that we discuss. Using our distance determinations, we create a face-on Galactic map of the H II region complexes and compare it with a kinematically derived profile of the distribution of CO-traced molecular hydrogen. The H II region complexes delineate the large-scale features seen in the molecular gas. The 5 kpc molecular ring and the Sagittarius spiral arm are clearly evident, and a few H II region complexes lie in the Perseus arm.

H I absorption spectra measured against bright extragalactic radio continuum sources offer a simple way to measure the optical depth of cold atomic gas as a function of Galactocentric radius. We have observed the 21 cm H I line in absorption toward 54 bright, compact extragalactic radio continuum sources in the first Galactic quadrant with the VLA in C array. We have determined the average radial profile of 21 cm H I optical depth in the first quadrant using the Clemens rotation curve. There is a region of high average optical depth between Galactic radii of 4 and 8 kpc where the average optical depth, , exceeds 0.8. This region also contains most of the molecular gas in the Galaxy. Furthermore, the highest peak in occurs in the region of the 5 kpc molecular ring, the Galaxy's single most prominent molecular feature. Inward of 4 kpc, drops below 0.5, and beyond 8.5 kpc, remains below 0.4. The H I optical depth measurements were used to construct the 21 cm H I velocity-averaged absorption coefficient, , as a function of Galactocentric radius. The average value of exceeds 4.5 km s-1 kpc-1 between 4 and 8 kpc and drops sharply at smaller and larger radii. The highest peak in rises above 15 km s-1 kpc-1 and again corresponds to the 5 kpc molecular ring. Two other large peaks correspond to the Sagittarius and Perseus spiral arms. We suggest that the high H I opacity in the inner Galaxy, particularly between 4 and 8 kpc, is due to the presence of cold atomic gas associated with molecular clouds.

We report the discovery of nineteen new HI shells in the Southern Galactic Plane Survey (SGPS). These shells, which range in radius from 40 pc to 1 kpc, were found in the low resolution Parkes portion of the SGPS dataset, covering Galactic longitudes l=253 deg to l=358 deg. Here we give the properties of individual shells, including positions, physical dimensions, energetics, masses, and possible associations. We also examine the distribution of these shells in the Milky Way and find that several of the shells are located between the spiral arms of the Galaxy. We offer possible explanations for this effect, in particular that the density gradient away from spiral arms, combined with the many generations of sequential star formation required to create large shells, could lead to a preferential placement of shells on the trailing edges of spiral arms. Spiral density wave theory is used in order to derive the magnitude of the density gradient behind spiral arms. We find that the density gradient away from spiral arms is comparable to that out of the Galactic plane and therefore suggest that this may lead to exaggerated shell expansion away from spiral arms and into interarm regions., 25 pages, 20 embedded EPS figures, uses emulateapj.sty, to appear in the Astrophysical Journal

We present a new algorithm, named Autonomous Gaussian Decomposition (AGD), for automatically decomposing spectra into Gaussian components. AGD uses derivative spectroscopy and machine learning to provide optimized guesses for the number of Gaussian components in the data, and also their locations, widths, and amplitudes. We test AGD and find that it produces results comparable to human-derived solutions on 21cm absorption spectra from the 21cm SPectral line Observations of Neutral Gas with the EVLA (21-SPONGE) survey. We use AGD with Monte Carlo methods to derive the HI line completeness as a function of peak optical depth and velocity width for the 21-SPONGE data, and also show that the results of AGD are stable against varying observational noise intensity. The autonomy and computational efficiency of the method over traditional manual Gaussian fits allow for truly unbiased comparisons between observations and simulations, and for the ability to scale up and interpret the very large data volumes from the upcoming Square Kilometer Array and pathfinder telescopes., 12 pages, 8 figures, submitted to AJ

SPLASH (the Southern Parkes Large-Area Survey in Hydroxyl) is a sensitive, unbiased and fully-sampled survey of the Southern Galactic Plane and Galactic Centre in all four ground-state transitions of the hydroxyl (OH) radical. The survey provides a deep census of 1612-, 1665-, 1667- and 1720-MHz OH absorption and emission from the Galactic ISM, and is also an unbiased search for maser sources in these transitions. We present here first results from the SPLASH pilot region, which covers Galactic longitudes 334 to 344 degrees and latitudes of -2 to +2 degrees. Diffuse OH is widely detected in all four transitions, with optical depths that are always small (averaged over the Parkes beam), and with departures from LTE common even in the 1665- and 1667-MHz main lines. To a 3$\sigma$ sensitivity of 30 mK, we find no evidence of OH envelopes extending beyond the CO-bright regions of molecular cloud complexes, and conclude that the similarity of the OH excitation temperature and the level of the continuum background is at least partly responsible for this. We detect masers and maser candidates in all four transitions, approximately 50 per cent of which are new detections. This implies that SPLASH will produce a substantial increase in the known population of ground-state OH masers in the Southern Galactic Plane., Comment: 20 pages, 9 figures, accepted for publication in MNRAS

We use the Karl G. Jansky Very Large Array (VLA) to conduct a high-sensitivity survey of neutral hydrogen (HI) absorption in the Milky Way. In combination with corresponding HI emission spectra obtained mostly with the Arecibo Observatory, we detect a widespread warm neutral medium (WNM) component with excitation temperature = 7200 (+1800,-1200) K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Ly-{\alpha} scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that HI absorption can be used to constrain the Ly-{\alpha} radiation field, a critical quantity for studying the energy balance in the ISM and intergalactic medium yet notoriously difficult to model because of its complicated radiative transfer, in and around galaxies nearby and at high redshift., Comment: 7 pages, 3 figures, 1 table. Accepted for publication in ApJ Letters

In this project, we determine the mixture of thermal phases in the atomic medium of the Small Magellanic Cloud. The larger purpose is to study the difference in properties of the interstellar medium in a dwarf irregular galaxy compared with the Milky Way. The observations used the Australia Telescope Compact Array to measure absorption spectra of the 21 cm line through the SMC, for comparison with 21 cm emission spectra from a combination of data from the Parkes and Compact Array telescopes. Using the two together, we find the abundance of cool-phase gas to be less than 15% of the total H I. Thus, the cool-phase gas is very scarce, only about half as abundant relative to the total H I as in the solar neighborhood, a lower figure than that found in the LMC, M31, M33, or the solar neighborhood of the Milky Way. This is in qualitative agreement with the heating/cooling equilibrium calculations for conditions in a dwarf irregular galaxy. In addition, we find the temperature of the cool-phase clouds to be very low, typically 40 K or less. This is much less than the nominal diffuse cloud temperature in the Milky Way (50-100 K). This suggests that the H I may be more abundant in dense cold clouds in the SMC than in the Milky Way, where clouds of similar density and temperature are largely molecular.

As part of a survey of H I λ21 cm emission in the southern Milky Way, we have detected two large shells in the interstellar neutral hydrogen near l = 279°. The center velocities are +36 and +59 km s-1, which puts the shells at kinematic distances of 7 and 10 kpc. The larger shell is about 610 pc in diameter and very empty, with density contrast of at least 15 between the middle and the shell walls. It has expansion velocity of about 20 km s-1 and swept-up mass of several million solar masses. The energy indicated by the expansion may be as high as 2.4 × 1053 ergs. We estimate its age to be 15 to 20 million years. The smaller shell has diameter of about 400 pc, expansion velocity about 10 km s-1, and swept-up mass of about 106 M⊙. Morphologically both regions appear to be shells, with high-density regions mostly surrounding the voids, although the first appears to have channels of low density that connect with the halo above and below the H I layer. They lie on the edge of the Carina arm, which suggests that they may be expanding horizontally into the interarm region, as well as vertically out of the disk. If this interpretation is correct, this is the first detection of an H I chimney which has blown out of both sides of the disk.

We present CO (1–0) and (2–1) observations of 33 galaxies in the Coma/Abell 1367 supercluster made with the IRAM 30 m telescope. In addition, we observed four of the galaxies with the 15 m JCMT, at CO (2–1). The indicative molecular gas mass correlates strongly with the dust mass, and a stronger relationship is seen between the far-infrared and CO surface brightnesses than between the simple luminosities. Comparison of CO (2–1) spectra from IRAM and JCMT allows an estimate of the size of the CO emission region, which varies between 10% and 100% of the size of the optical disk, contrary to earlier estimates that the CO is contained within the optical half-light radius. There is a slight suggestion that starburst galaxies have a lower ratio of brightness temperatures, Tb(2–1)/Tb(1–0), than other galaxies.

We investigate the viability and precision of using 12CO (J = 1 → 0) emission lines from galaxies in lieu of 21 cm emission in the Tully-Fisher distance indicator (TF). Here we combine CO data gathered specifically for Tully-Fisher analysis with I-band photometry (both new and from the literature) for cluster galaxies between 3500 and 8000 km s-1 and compare the luminosity–line width relation using CO with the results of recent, large TF surveys using H I and Hα. We cull some CO data as suggested by previously published numerical simulations and find that CO line widths, with corrections for turbulence and noise-broadening on the order of 35 km s-1, behave identically to H I and Hα in luminosity–line width analyses. We also examine the relation between CO line shapes and other parameters of the galaxies. Key words: distance scale — galaxies: distances and redshifts — galaxies: spiral

We present 12CO (J = 1–0) (2.6 mm, 115 GHz) spectra from 44 galaxies in clusters between 3500 and 8000 km s-1. The data were obtained using the NRAO 12 m telescope at Kitt Peak. Forty galaxies are detected. We deduce molecular gas masses from the line integrated intensities and upper limits for the four nondetections. Although the sample's first inclusion criterion is that a source have 60 μm flux greater than 350 mJy, the galaxies in this survey are found to be neither ultraluminous in the far-IR nor particularly rich in molecular gas, nor do they exhibit evidence of interactions. Neither the molecular gas mass nor the far-IR luminosity shows variations as functions of the galaxies' proximity to the cluster cores. Because the CO line widths and central velocities agree overall with the 21 cm widths and redshifts for these galaxies, we argue that CO spectra could be used in lieu of H I spectra for Tully-Fisher calculations.

We present the results of a continuum snap- shot survey of a 3 4 region of the Large Magellanic Cloud including the area of the giant molecular cloud and the 30 Doradus nebula. The observations have been carried out with the Australia Telescope Compact Array (ATCA) 1 at 1.4 and 2.4 GHz. Most elds are complete to about 6 mJy peak flux density at 1.4 GHz and to about 3 mJy at 2.4 GHz. The positions, peak and integral flux densities of 113 compact (< 54 00 ) sources detected at 1.4 GHz and of 70 sources (< 34 00 ) detected at 2.4 GHz are presented. Positions are accurate to about 3 00 and peak flux densities are accurate to about 10% or better, depend- ing on the source position relative to the pointing centers. 32 of the sources detected at 1.4 GHz are coincident with H objects in the catalogue of Davies et al.; these are pos- sibly intrinsic to the LMC. However, we suppose that most are background objects, since the number vs. flux agrees with predictions of extragalactic source counts from other surveys.

This Letter presents spin temperatures of neutral atomic hydrogen clouds in the vicinity of 30 Doradus in the Large Magellanic Cloud (LMC). Using emission and absorption spectra obtained by combining the Australia Telescope Compact Array and the Parkes Telescope, we have minimized errors due to beam blending. We have developed a new technique to disentangle blending of emission components in the velocity domain. The results show much cooler temperatures for the diffuse interstellar clouds than obtained with other techniques: typical values are 30-40 K. Whether or not H I clouds in the LMC are actually cooler than the ones in our Galaxy or other galaxies cannot be concluded from the data currently available.

Absorption lines at $\lambda$ 21-cm are detected in the Stokes Q and U components of the Galactic synchrotron background. The lower limit distance implied for the emission region is 2 kpc in the direction (l,b) = (329.5$^{\circ}$,+1.15$^{\circ}$). The Australia Telescope Compact Array has the capability of mapping this absorption over large areas of the Galactic plane. Observations like these have the potential to reveal the three dimensional structure of the Galactic synchrotron emission throughout the Milky Way disk.

We report a search for the NH3 (J,K) = (1,1) inversion line in the Large Magellanic Cloud (LMC) using the Parkes 64–m telescope. Candidate positions were chosen with the help of recent H i data from the Australia Telescope Compact Array and published 12CO data from the Swedish–ESO Submillimetre Telescope. No detections of NH3 in emission were found at the positions surveyed. Upper limits are approximately 25 to 74 mK.

We have measured the Faraday rotation toward a large sample of polarized radio sources behind the Large Magellanic Cloud (LMC), to determine the structure of this galaxy's magnetic field. The magnetic field of the LMC consists of a coherent axisymmetric spiral of field strength ~1 microgauss. Strong fluctuations in the magnetic field are also seen, on small (, 15 pages, including 3 embedded EPS figures (1 color, 2 b/w) plus supporting on-line material; uses scicite.sty. To appear in Science, vol 307, number 5715 (11 March 2005)

The new Australian geodetic VLBI network operated by the University of Tasmania (UTAS) started regular observations in June, 2011. Three 12-m “Patriot” radio telescopes (Hobart in Tasmania, Yarragadee in Western Australia and Katherine in the Northern Territory) are dedicated to the improvement of the celestial and terrestrial reference frames in the southern hemisphere. We present first results from the analysis of a 16-month set of geodetic VLBI data. The data were processed within a VLBI solution for 78 sessions in 2011–2012 by the least squares collocation method using the OCCAM software. The geodetic positions of the AuScope radio telescopes were estimated with accuracy less than 10 mm, and the first sign of their motion due to tectonic plate movement was indicated. Results of independent verification using GPS and geodetic local tie for Hobart12 showed consistency within 20 mm for all three components. Positions of Hobart12 in the ITRF2005 system are presented for the 2012.0 epoch.

The Space Geodesy Project (SGP) development by NASA is an effort to co-locate the four international geodetic techniques Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR), Very Long Baseline Interferometry (VLBI), Global Navigation Satellite System (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) into one tightly referenced campus and coordinated reference frame analysis. The SGP requirement locates these stations within a small area to maintain line-of-sight and frequent automated survey known as the vector tie system. This causes a direct conflict with the new broadband VLBI technique. Broadband means 2-14 GHz, and RFI susceptibility at -80 dBW or higher due to sensitive RF components in the front end of the radio receiver., IGARSS 2013 : IEEE International Geoscience and Remote Sensing Symposium, July 21-27, 2013, Melbourne, Australia

The AuScope geodetic Very Long Baseline Interferometry array consists of three new 12 m radio telescopes and a correlation facility in Australia. The telescopes at Hobart (Tasmania), Katherine (Northern Territory) and Yarragadee (Western Australia) are co-located with other space geodetic techniques including Global Navigation Satellite Systems (GNSS) and gravity infrastructure, and in the case of Yarragadee, Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) facilities. The correlation facility is based in Perth (Western Australia). This new facility will make significant contributions to improving the densification of the International Celestial Reference Frame in the Southern Hemisphere, and subsequently enhance the International Terrestrial Reference Frame through the ability to detect and mitigate systematic error. This, combined with the simultaneous densification of the GNSS network across Australia will enable the improved measurement of intraplate deformation across the Australian tectonic plate. In this paper we present a description of this new infrastructure and present some initial results, including telescope performance measurements and positions of the telescopes in the International Terrestrial Reference Frame. We show that this array is already capable of achieving centimetre precision over typical long-baselines and that network and reference source systematic effects must be further improved to reach the ambitious goals of VLBI2010., Journal of Geodesy, March 2013

A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of HI emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg, spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream., 45 pages, 8 figures, Pub. Astron. Soc. Australia (in press)

The neutral atomic hydrogen in the Milky Way constitutes two different thermal phases of the interstellar gas: the warm neutral medium and the cool neutral medium. The best way to trace these phases on the scale of the entire Galactic disk is by using the λ21-cm line at radio frequencies. This chapter explains with examples how observations of the 21-cm line are interpreted, with emission and absorption spectra leading to estimates of the column density and the excitation- or spin-temperature of the gas. The structure of the H I disk has both a thin component, with half-width ∼100 pc that includes both warm and cool gas, plus a thick disk, ∼400 pc half-width, that is mostly all warm. In the inner Galaxy the distribution of brightness in longitude-velocity coordinates is largely determined by the velocity gradient along the line of sight, with self-absorption by cool clouds competing with irregularities in the density and velocity field to modulate the intensity of the 21-cm emission. In the outer Galaxy the disk becomes more and more H I dominated, with an increase in the scale height and a strong warp that becomes very one-sided at Galactic radius greater than ∼20 kpc. The thermal balance in the two atomic phases is set by heating and cooling equilibrium, but the system does not have time to reach hydrostatic balance before supernova remnants disrupt the gas and broaden the pressure distribution function. Pressure variations can drive the gas either way between warm and cool phases, but the net flux must be from warm to cool, and on to molecular clouds, in order to explain the continuous cycle of star formation and chemical enrichment of the Galaxy. The small-scale structure of the H I shows a power-law spectrum of velocity and density fluctuations similar to that of a turbulent fluid. In some cases, the structure is enhanced in the cool neutral medium on scales of a few hundred astronomical units. The magnetic field may be important dynamically, particularly on the smaller scales. These and other issues about the H I disk will be better answered when the next generation of telescopes becomes available for Galactic survey projects. Keywords: 21-cm line, cloud random velocities, column density, cool neutral medium, cooling rate, galactic plane surveys, galactic structure, galactic warp, gas scale height, heating rate, H I column density, HISA, interstellar clouds, interstellar magnetic field, interstellar medium, interstellar turbulence, radio astronomy, radio interferometers, radio spectroscopy, rotation curve, spatial power spectrum, spectral lines, spin temperature, square kilometer array, thermal balance, warm neutral medium

We present a catalog of 1268 galxies, essentially complete to B(is less than or equal to)17.0, found by scanning glass copies of several fields of the original Palomar Sky Survey using the Minnesota Automated Plate Scanner in its isodensitometricmode(as opposed to the threshold densitometric mode used in the APS Catalog of the POSS I).

We present observations of the 12 CO(J=1 0) line at 2.6 mm of 65 galaxies located in the Coma supercluster region: 33 actually belong to the Coma supercluster while 32 are either foreground or background objects. These data have been obtained using the NRAO 12 m telescope at Kitt Peak (United States), and for four galaxies, using the IRAM 30 m telescope at Pico Veleta (Spain). Out of these 65 galaxies, 54 had never been observed in the CO(1 0) line; 49 have been detected by us, of which 37 are new detections. We give molecular gas masses deduced from the CO line integrated intensities, and upper limits for the 16 undetected objects, computed with a Galactic conversion factor N (H2 )=2 .3 10 20 I(CO) and H0 = 75 km/s/Mpc. ??

The velocity dispersion of the interstellar gas measured perpendicular to the disk in face-on spiral galaxies shows a remarkable consistency. Typically the width of the velocity distribution decreases monotonically with increasing galactic radius through the luminous, stellar disk; but in the outer disk where there is gas but no stars the velocity dispersion is συ ≃ 7 km s−1 with a scatter of 2 km s–1 at most from one position to another and from one galaxy to another. Trying to understand this number raises questions about the thermal state of the H I in outer, gaseous disks. The most important issue is to understand the dominant heating and cooling processes for the atomic gas.

We present a study of the magnetic field of the Large Magellanic Cloud (LMC), carried out using diffuse polarized synchrotron emission data at 1.4 GHz acquired at the Parkes Radio Telescope and the Australia Telescope Compact Array. The observed diffuse polarized emission is likely to originate above the LMC disk on the near side of the galaxy. Consistent negative rotation measures (RMs) derived from the diffuse emission indicate that the line-of-sight magnetic field in the LMC's near-side halo is directed coherently away from us. In combination with RMs of extragalactic sources that lie behind the galaxy, we show that the LMC's large scale magnetic field is likely to be of quadrupolar geometry, consistent with the prediction of dynamo theory. On smaller scales, we identify two brightly polarized filaments southeast of the LMC, associated with neutral hydrogen arms. The filaments' magnetic field potentially aligns with the direction towards the Small Magellanic Cloud. We suggest that tidal interactions between the Small and the Large Magellanic Clouds in the past 10^9 years is likely to have shaped the magnetic field in these filaments., Comment: 42 pages, 22 figures, 2 tables. Accepted for publication in ApJ. Electronic version of Table 2 is available via email from the first author

Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of -30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at {\gamma}-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 15%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI., Comment: 6 pages, 6 figures, 1 table. Accepted for publication in A&A

We present new 21-cm observations of faint (15.7pg−1 Mpc. We calculate the global dynamical mass of Hercules using 3 different but related methods: two versions of the virial theorem and the projected mass estimator. These masses lie in the range 3–6×1014 M⊙. We investigate the importance of subclustering in A2151 using the statistical test of Dressler and Shectman1 and the effects of the detected substructure on the dynamical mass determination. The clumpy distribution of galaxies is interpreted as a sign that the galaxies in the cluster have not reached dynamical equilibrium in the gravitational potential, which means that dynamical mass estimates are prone to significant errors. In spite of this uncertainty, we estimate that the virial theorem errors due to the presence of substructure are not larger than 30% in A2151. Finally, we use the 21-cm linewidths to estimate the minimum total mass in the cluster which is contained within the HI radii of the cluster galaxies is about 3×1014 M⊙. This number may be compared with the dynamical mass and used to separate the contribution of dark matter inside and outside the HI envelopes of galaxies, and the fraction of DM which cannot be associated with individual galaxies, about 90–95%.

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the world's first spacecraft to successfully demonstrate solar-sail technology in interplanetary space. The spacecraft is made of square shape of very thin membrane, whose diagonal dimension is 20m. By changing its attitude toward Sun, radiation pressure of solar photons can be used as propulsive force of the spacecraft. To determine the orbit under the continuous big influence of the nongravitational perturbative force (i.e. solar radiation pressure), Very Long Baseline Interferometry (VLBI) observation is effective because sky plane position of the spacecraft can be directly and instantaneously measured by VLBI observables without (or with less dependence on) a priori assumption for solar radiation pressure model. In order to effectively perform VLBI measurements, a signal generator of Differential One-way Range (DOR) tones, which consist of multiple tones whose spanning bandwidth is about 28MHz, was developed and installed to the spacecraft. A digital backend system for the ground stations which has maximum output performance of 4-Gbps had also developed to sample wideband DOR tones. A total number of 24 international VLBI experiments were carried out by using totally 15 antennas among 8 agencies during July and August in 2010. As a result of initial analysis, measurement accuracy of VLBI delay was confirmed to be 50 pico second level, which is 20 times improved precision compared to the JAXA's conventional deep space spacecraft such as Hayabusa and Akatsuki.

We have studied the archetypal Gigahertz Peaked Spectrum radio galaxy, PKS 1934-638, using the Australian Long Baseline Array, augmented with two new telescopes that greatly improve the angular resolution of the array. These VLBI observations represent the first scientific results from a new antenna in NZ and the first antenna of the Australian SKA Pathfinder (ASKAP). A compact double radio source, PKS 1934-638, has been monitored over a period of 40 years, and the observation described here provides the latest datum, eight years after the previous observation, to aid in the study of the long-term evolution of the source structure. We take advantage of these new long baselines to probe PKS 1934-638 at the relatively low frequency of 1.4 GHz, in order to examine the effects of optical depth on the structure of the radio source. Optical depth effects, resulting in the observation of frequency dependent structure, may have previously been interpreted in terms of an expansion of the source as a function of time. Expansion and frequency dependent effects are important to disentangle in order to estimate the age of PKS 1934-638. We show that frequency dependent structure effects are likely to be important in PKS 1934-638 and present a simple two-dimensional synchrotron source model in which opacity effects due to synchrotron self-absorption are taken into account. Evidence for expansion of the radio source over 40 years is therefore weak, with consequences for the estimated age of the radio source., Comment: 18 pages, 5 figures. Accepted for publication in AJ

We use the spatial power spectrum for a statistical study of HI in the SMC in order to probe the intrinsic topology of the ISM. A remarkable power-law fit to the spatial power spectrum was found, supporting an alternative ISM model having a fractal nature resulting from interstellar turbulence.