Showing papers by "Maxim Voronkov published in 2015"

The 6-GHz methanol multibeam maser catalogue - V. Galactic longitudes 20 ◦ -60 ◦

Abstract: WepresentthefifthportionofanunbiasedsurveyoftheGalacticplane, |b |≤ 2 ◦ ,for6668-MHz methanol masers This section of the survey completes the Galactic longitude range visible to the Parkes radio telescope, incorporating the longitude range 20 ◦ –60 ◦ Within this section of the survey we find 265 methanol masers, 64 new to the survey, bringing the total number of methanol masers detected across the full longitude coverage (186 ◦ , through 0 ◦ ,t o 60 ◦ ) to 972

Discovery of H i gas in a young radio galaxy at z = 0.44 using the Australian Square Kilometre Array Pathfinder

Abstract: We report the discovery of a new 21-cm H I absorption system using commissioning data from the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5-1015.5 MHz band of ASKAP we were able to conduct a blind search for the 21-cm line in a continuous redshift range between z = 0.4 and 1.0, which has, until now, remained largely unexplored. The absorption line is detected at z = 0.44 towards the GHz-peaked spectrum radio source PKS B1740-517 and demonstrates ASKAP's excellent capability for performing a future wide-field survey for H I absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the H I gas is intrinsic to the host galaxy of the radio source. The narrow [O III] emission lines show clear double-peaked structure, indicating either large-scale outflow or rotation of the ionized gas. Archival data from the XMM-Newton satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the active galactic nucleus. The H I absorption profile is complex, with four distinct components ranging in width from 5 to 300 km s-1 and fractional depths from 0.2 to 20 per cent. In addition to systemic H I gas, in a circumnuclear disc or ring structure aligned with the radio jet, we find evidence for a possible broad outflow of neutral gas moving at a radial velocity of v ˜ 300 km s-1. We infer that the expanding young radio source (tage ≈ 2500 yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of ˜1 M⊙ yr-1.

ASKAP HI imaging of the galaxy group IC 1459

Abstract: We present HI imaging of the galaxy group IC 1459 carried out with six antennas of the Australian SKA Pathfinder equipped with phased-array feeds. We detect and resolve HI in eleven galaxies down to a column density of $\sim10^{20}$ cm$^{-2}$ inside a ~6 deg$^2$ field and with a resolution of ~1 arcmin on the sky and ~8 km/s in velocity. We present HI images, velocity fields and integrated spectra of all detections, and highlight the discovery of three HI clouds -- two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an HI mass of $10^9$ M$_\odot$ and accounts for ~15% of the HI associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data we find evidence of additional extended, low-column-density HI emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intra-group gas within the IC 1459 group. Altogether, the HI found outside galaxies in this group amounts to several times $10^9$ M$_\odot$, at least 10% of the HI contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.

FIRST PARALLAX MEASUREMENTS TOWARD A 6.7 GHz METHANOL MASER WITH THE AUSTRALIAN LONG BASELINE ARRAY-DISTANCE TO G 339.884-1.259

Abstract: We have conducted the first parallax and proper motion measurements of 6.7 GHz methanol maser emission using the Australian Long Baseline Array. The parallax of G 339.884-1.259 measured from five epochs of observations is 0.48 +/- 0.08 mas, corresponding to a distance of 2.1(-0.3)(+0.4) kpc, placing it in the Scutum spiral arm. This is consistent (within the combined uncertainty) with the kinematic distance estimate for this source at 2.5 +/- 0.5 kpc using the latest Solar and Galactic rotation parameters. We find from the Lyman continuum photon flux that the embedded core of the young star is of spectral type B1, demonstrating that luminous 6.7 GHz methanol masers can be associated with high-mass stars toward the lower end of the mass range.

MALT-45: a 7 mm survey of the southern Galaxy - I. Techniques and spectral line data

Abstract: We present the first results from the MALT-45 (Millimetre Astronomer's Legacy Team - 45 GHz) Galactic Plane survey. We have observed 5 square-degrees (l=330−335, b=±0.5) for spectral lines in the 7 mm band (42-44 and 48-49 GHz), including CS (1−0), class I CH3OH masers in the 7(0,7)−6(1,6) A+ transition and SiO (1−0) v=0,1,2,3. MALT-45 is the first unbiased, large-scale, sensitive spectral line survey in this frequency range. In this paper, we present data from the survey as well as a few intriguing results; rigorous analyses of these science cases are reserved for future publications. Across the survey region, we detected 77 class I CH3OH masers, of which 58 are new detections, along with many sites of thermal and maser SiO emission and thermal CS. We found that 35 class I CH3OH masers were associated with the published locations of class II CH3OH, H2O and OH masers but 42 have no known masers within 60 arcsec. We compared the MALT-45 CS with NH3 (1,1) to reveal regions of CS depletion and high opacity, as well as evolved star-forming regions with a high ratio of CS to NH3. All SiO masers are new detections, and appear to be associated with evolved stars from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Generally, within SiO regions of multiple vibrational modes, the intensity decreases as v=1,2,3, but there are a few exceptions where v=2 is stronger than v=1.

6.7-GHz methanol maser associated outflows: an evolutionary sequence

Abstract: We present a continuing study of a sample 44 molecular outflows, observed in 13CO lines, closely associated with 6.7-GHz methanol masers, hence called methanol maser associated outflows (MMAOs). We compare MMAO properties with those of outflows from other surveys in the literature. In general, MMAOs follow similar trends, but show a deficit in number at low masses and momenta, with a corresponding higher fraction at the high end of the distributions. A similar trend is seen for the dynamical time-scales of MMAOs. We argue that the lack of relatively low mass and young flows in MMAOs is due to the inherent selection-bias in the sample, i.e. its direct association with 6.7-GHz methanol masers. This implies that methanol masers must switch on after the onset of outflows (hence accretion), and not before a sufficient abundance of methanol is liberated from icy dust mantles. Consequently the average dynamical age of MMAOs is older than for the general population of molecular outflows. We propose an adjusted evolutionary sequence of outflow and maser occurrence in the hot core phase, where methanol masers turn on after the onset of the outflow phase.

ASKAP data processing

Abstract: Wide instantaneous field of view is a new dimension of parameter space explored by the next generation radio telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP), an array of 36 antennas equipped with phased array feeds (PAFs) located in the Western Australian outback. Processing data from such an instrument presents new challenges. With the data rate from the correlator to central processor in excess of 2 GB/s and the requirement for non-trivial and poorly scaling algorithms to achieve good quality images, ASKAP is fundamentally a real-time telescope - the processing pipelines have to keep up with observations. We will review the software architecture and hardware design decisions aimed at reducing the cost of processing. In particular, the parallel software design using the master-worker approach, where a single processing rank orchestrates parallel computations and performs parts of the algorithm which are naturally serial, was found grossly inadequate to perform efficiently given the memory constraints of the ASKAP's central processor. A new framework has been suggested which enables a more flexible parallelization and allows us to process different PAF beams in parallel.