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ATNF Science Highlights 2014

Enjoy our new ATNF Daily Astronomy Picture - contributions welcome.

A new 1.4 GHz radio continuum map of the sky south of declination +25 degr (01/2014)

Calabretta, Staveley-Smith & Barnes (2014, PASA 31, 7) carefully reprocessed archival data from the HI Parkes All-Sky Survey (HIPASS) and the HI Zone of Avoidance (HIZOA) survey into a new 1.4 GHz continuum map of the sky. The wide sky coverage (Dec < +25 degr), high sensitivity of 40 mK (limited by confusion), resolution of 14.4 arcmin and low level of artefacts make this map ideal for numerous studies, including: merging into interferometer maps to complete large-scale structures; decomposition of thermal and non-thermal emission components from Galactic and extragalactic sources; and comparison of emission regions with other frequencies. The new map is available for download.

Evidence of an asteroid encountering a pulsar (01/2014)

Brook et al. (2014, ApJ 780, L31) present the results of long-term monitoring of PSR J0738-4042 with the Parkes telescope. They found that its pulse shape changed multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead them to postulate that we are witnessing an asteroid falling into the magnetosphere of the pulsar. - Paul Brook is a student at Oxford University in the UK and a co-supervised student at CSIRO Astronomy and Space Science (CASS).

The kinematics and orbital dynamics of the PSR B1259-63/LS 2883 system from 23 yr of pulsar timing (02/2014)

Shannon, Johnston & Manchester (2014, MNRAS 437, 3255) present an analysis of 23 yr of pulse arrival times for PSR B1259-63. The pulsar is in a binary orbit about its approximately 20 Msun companion LS 2883. Their best-fitting timing solution has none of the pulse-number ambiguities that have plagued previous attempts to model the binary orbit. By combining proper motion of the pulsar with radial velocity measurements of the companion, they measure the 3D velocity of the system, which is then used to constrain the masses of the stars prior to the supernova explosion and the kick the pulsar received at or immediately after the explosion.

Spatially-resolved dust properties of the GRB 980425 host galaxy (02/2014)

Michalowski et al. (2014, A&A 562, 70) present spatially resolved maps of dust emission of the host galaxy of the closest known GRB 980425 at z = 0.0085 using our new high-resolution observations from Herschel, Atacama Pathfinder Experiment (APEX), Atacama Large Millimeter Array (ALMA) and Australia Telescope Compact Array (ATCA). Gamma-ray bursts (GRBs) have been proposed as a tool for studying star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way special compared with other star-forming galaxies. - The R-band image to the right is overlaid with radio continuum ATCA contours at 1.324 and 2.348 GHz; fits files provided on-line, with thanks to Michalowski et al. (2014).

The Jet and Arc Molecular Clouds toward Westerlund 2 (02/2014)

Furukawa et al. (2014, ApJ 781, 70) present new 12CO and 13CO (J=2-1 and J=1-0) observations of two molecular clouds made with NANTEN2 and the Mopra Telescope. The so-called "jet" and "arc" clouds are loacted toward the stellar cluster Westerlund 2, RCW49, and the TeV gamma-ray source HESS J1023-575. Furukawa et al. suggest that neither are physically linked with Westerlund 2 but are located at a greater distance around 7.5 kpc.

CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources (03/2014)

Emonts et al. (2014, MNRAS 438, 2898) present a CO(1-0) survey for cold molecular gas in a representative sample of 13 high-z radio galaxies (HzRGs) at 1.4 < z < 2.8, using the Australia Telescope Compact Array (ATCA). They detect CO(1-0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 (Spiderweb Galaxy) and MRC 2048-272. Intriguingly, in all five sources the CO(1-0) emission is found up to tens of kpc from the host galaxy. In several cases the CO(1-0) traces a large reservoir of cold gas at the tip of the radio source, which suggests that jet-induced feedback can trigger the formation of cold molecular gas in the halo environment of high-z radio galaxies. These results show that the compact hybrid array configurations of the ATCA are sensitive to tracing the most widespread and possibly diffuse molecular gas in the Early Universe, something that cannot be efficiently done by any other radio telescope. - The image shows CO(1-0) emission (in blue) spread across the inter-galactic medium of the massive Spiderweb Galaxy at z=2.16 (high-resolution follow-up, as shown by the line-profile on the top-right, is in progress).

ATCA Survey of Ammonia in the Galactic Center: The Temperatures of Dense Gas Clumps between Sgr A* and Sgr B2 (04/2014)

Ott et al. (2014, ApJ 785, 55) present a large-scale, interferometric survey of ammonia toward the Galactic center observed with the Australia Telescope Compact Array (ATCA). The survey covers the region between the supermassive black hole Sgr A* and the massive star forming region Sgr B2 with a resolution of about 20 arcsec (0.8 pc). Emission at scales larger than 2 arcmin (3.2 pc) is filtered out due to missing short spacings. Consequently, the data represent the denser, compact clouds and disregard the large-scale, diffuse gas. - The RGB image shows the temperature map of the Galactic center: Tkin ~ 30 K (blue), Tkin ~ 50 K (green), lower limit of 80 K (red). Radio continuum emission at 22 GHz (1 cm; white contours) is overlaid in the bottom panel.

Southern class I methanol masers at 36 and 44 GHz (04/2014)

Voronkov et al. (2014, MNRAS 439, 2584) used the Australia Telescope Compact Array (ATCA) for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. This is the largest interferometric survey of common class I methanol masers available to date, and the first of this kind in the southern hemisphere. In addition, this is the first high angular resolution study of a large number of 36 GHz masers. The data reveal a high level of morphological and kinematical complexity, and allow them to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding HII regions, dark clouds, shocks traced by the 4.5 micron emission and 8.0 micron filaments. More than 700 maser component features were found at each of the two methanol transitions.

The molecular gas reservoir of 6 low-metallicity galaxies from the Herschel Dwarf Galaxy Survey. A ground-based follow-up survey of CO(1-0), CO(2-1), and CO(3-2) (04/2014)

Cormier et al. (2014, A&A 564, 121) present CO observations obtained at the ATNF Mopra 22-m, APEX, and IRAM 30-m telescopes in 6 nearby low-metallicity galaxies. For the first time, they detect CO(1-0) in NGC625 and get strong limits for Haro11 and UM311 thanks to Mopra. While those galaxies are forming stars, CO is faint. The molecular gas masses derived from CO and dust methods are quite discrepant and stress the large uncertainties on the true molecular mass present in these compact galaxies which may harbor a significant reservoir of ``CO-dark'' molecular gas.

The Radio Relics and Halo of El Gordo, a Massive z = 0.870 Cluster Merger (05/2014)

Lindner et al. (2014, ApJ 789, 49) present 610 MHz and 2.1 GHz imaging of the massive Sunyaev-Zel'dovich Effect selected z = 0.870 cluster merger ACT-CL J0102-4915 ("El Gordo"), obtained with the Giant Metrewave Radio Telescope and the Australia Telescope Compact Array (ATCA), respectively. They detect two complexes of radio relics separated by 3.4 arcmin (1.6 Mpc) along the system's northwest-to-southeast collision axis that have high integrated polarization fractions (33%) and steep spectral indices, consistent with creation via Fermi acceleration by shocks in the intracluster medium triggered by the cluster collision.

Deep radio observations of the radio halo of the bullet cluster 1E 0657-55.8 (06/2014)

Shimwell et al. (2014, MNRAS 440, 2901) present deep 1.1-3.1 GHz Australia Telescope Compact Array (ATCA) observations of the radio halo of the bullet cluster, 1E 0657-55.8. In comparison to existing images of this radio halo, the detection in their images is at higher significance. The radio halo is as extended as the X-ray emission in the direction of cluster merger but is significantly less extended than the X-ray emission in the perpendicular direction. These observations support the theory that shocks and turbulence influence the formation and evolution of radio halo synchrotron emission.

Detection of 36 GHz Class I methanol maser emission toward NGC 253 (08/2014)

Ellingsen et al. (2014, ApJ 790, L28) have used the Australia Telescope Compact Array (ATCA) to search for emission from the 36.2 GHz transition of methanol toward the center of the nearby starburst galaxy NGC 253. Two regions of emission were detected, offset from the nucleus along the same position angle as the inner spiral arms. The 36.2 GHz methanol emission in NGC 253 has more than an order of magnitude higher isotropic luminosity than the widespread emission recently detected toward the center of the Milky Way. If emission from this transition scales with the nuclear star formation rate, then it may be detectable in the central regions of many starburst galaxies.

From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region within the Large Magellanic Cloud (09/2014)

Anderson et al. (2014, ApJ 793, 37) present parsec-scale interferometric maps of HCN(1-0) and HCO+(1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array (ATCA). This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. They detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud.

The Galactic Position Dependence of Fast Radio Bursts and the Discovery of FRB011025 (09/2014)

Burke-Spolaor & Bannister (2014, ApJ 792, 19) report the detection of a dispersed fast radio burst (FRB) in archival intermediate-latitude Parkes Radio Telescope data. The burst appears to be of the same physical origin as the four purported extragalactic FRBs reported by Thornton et al. They consider that this survey, and many other archival low-latitude pulsar surveys, have been searched for FRBs but produced fewer detections than the comparatively brief Thornton etal. search. Such a rate dependence on Galactic position could provide critical supporting evidence for an extragalactic origin for FRBs.

TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jet (09/2014)

Mueller et al. (2014, A&A 569, 115) observed the active galactic nucleus of Centaurus A (CenA) approximately every six months at 8.4 GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand, and South Africa, complemented by quasi-simultaneous 22.3 GHz observations. The first seven epochs of high-resolution TANAMI VLBI observations are presented, resolving the jet on (sub-)milliarcsecond scales.

2MTF - IV. A bulk flow measurement of the local Universe (11/2014)

Hong et al. (2014, MNRAS 445, 402) use 2MASS near-infrared photometry and high signal-to-noise HI 21-cm data from the Arecibo, Green Bank, Nancay, and Parkes telescopes to calculate the redshift-independent distances and peculiar velocities of 2018 bright inclined spiral galaxies over the whole sky. This project is part of the 2MASS Tully-Fisher survey (2MTF), aiming to map the galaxy peculiar velocity field within 100 Mpc.

The three discrete nulling time-scales of PSR J1717-4054 (11/2014)

Kerr et al. (2014, MNRAS 445, 320) studied the emission from PSR J1717-4054 over intervals from single pulses to years using the Parkes radio telescope and the Australia Telescope Compact Array (ATCA). They identified and characterized nulling at three discrete time-scales: the pulsar emits during `active states' separated by nulls lasting many thousands of rotations, while active states themselves are interrupted by nulls with a bimodal distribution of durations - one to two rotations, or tens of rotations.

What triggers a radio AGN? The intriguing case of PKS B1718-649 (11/2014)

Maccagni et al. (2014, A&A 571, 67) present new Australia Telescope Compact Array (ATCA) observations of the young radio galaxy PKS B1718-649. They study the morphology and the kinematics of the neutral hydrogen (HI) disk and focus on analyzing the cold gas in relation to the triggering of the nuclear activity. The different kinematical properties of two distinct HI absorption lines suggest that PKS B1718-649 may belong to a family of young low-excitation radio AGN where, rather than through a gas-rich merger, the active nuclei (AGN) are triggered by local mechanisms such as accretion of small gas clouds.

Spectral and Morphological Analysis of the Remnant of Supernova 1987A with ALMA and ATCA (12/2014)

Zanardo et al. (2014, ApJ 796, 82) present a comprehensive spectral and morphological analysis of the remnant of supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the emission from 94 to 672 GHz are separated with the assistance of a synchrotron template from the ATCA high-resolution observations at 44 GHz, and a dust template from ALMA observations at 672 GHz. The synchrotron/dust-subtracted images and the spectral energy distribution indicate additional emission beside the main synchrotron component (alpha = -0.73) and the thermal component originating from dust grains at T~22 K. Results from both the morphological and spectral analysis suggest the presence of a pulsar wind nebula in the remnant interior, powered by a pulsar likely located at a westward offset from the SN position.