MeerKAT uncovers the physics of an odd radio circle

Odd radio circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift (z ∼0.2-0.6). Here, we present detailed new MeerKAT radio images at 1284 MHz of the first ORC, originally discovered with the Australian Square Kilometre Array Pathfinder, with higher resolution (6 arcsec) and sensitivity (∼2.4 μJy/beam). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarization and spectral index maps. Based on these new data, we consider potential mechanisms that may generate the ORCs

The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy

The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm emission line survey covering the whole southern sky from declination -90 to +25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from the region south of declination +2, is presented in Meyer et al. (2004a, Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width, and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure.Comment: Accepted for publication in MNRAS. 12 pages, 11 figures. Paper with higher resolution figures can be downloaded from http://hipass.aus-vo.or

The Northern HIPASS catalogue - Data presentation, completeness and reliability measures

The Northern HIPASS catalogue (NHICAT) is the northern extension of the HIPASS catalogue, HICAT (Meyer et al. 2004). This extension adds the sky area between the declination range of +2 deg < dec. < +25.5 deg to HICAT's declination range of -90 deg < dec. < +2 deg. HIPASS is a blind HI survey using the Parkes Radio Telescope covering 71% of the sky (including this northern extension) and a heliocentric velocity range of -1,280 km/s to 12,700 km/s . The entire Virgo Cluster region has been observed in the Northern HIPASS. The galaxy catalogue, NHICAT, contains 1002 sources with v_hel > 300 km/s . Sources with -300 km/s < v_hel < 300 km/s were excluded to avoid contamination by Galactic emission. In total, the entire HIPASS survey has found 5317 galaxies identified purely by their HI content. The full galaxy catalogue is publicly-available at .Comment: 12 pages, accepted for publication by MNRA

Open astronomy and big data science

Open Astronomy is an important and valuable goal, including the availability of refereed science papers and user-friendly public astronomy data archives. The latter allow and encourage interested researchers from around the world to visualise, analyse and possibly download data from many different science and frequency domains. With the enormous growth of data volumes and complexity, open archives are essential to explore ideas and make discoveries. Open source software is equally important for many reasons, including reproducibility and collaboration. I will present examples of open archive and software tools, including the CSIRO ASKAP Science Data Archive (CASDA), the Local Volume HI Survey (LVHIS), the 3D Source Finding Application (SoFiA) and the Busy Function (BF). Astronomy is international and includes or links to an incredibly wide range of sciences, computing, engineering, and education. Its open nature can serve as an example for world-wide interdisciplinary collaborations

H I mapping of galaxies in six Group Evolution Multiwavelength Study groups

Here, we present Australia Telescope Compact Array (ATCA) H i maps of 16 H i sources in six Group Evolution Multiwavelength Study groups that were previously observed with the Parkes telescope. The higher spatial resolution of the ATCA allows us to clearly identify the optical counterparts for the first time---most being associated with low surface brightness late-type galaxies. New integrated H i maps and velocity fields for each source are presented. We find several interacting systems; one of which contains three galaxies within a common H i envelope. Extended H i structures in the sample are more consistent with tidal effects than ram pressure stripping. We identify two H i detections with previously uncatalogued optical galaxies, and add a total of six newly identified group members to the NGC 3923, 5044 and 7144 groups

The Ursa Major cluster redefined as a 'supergroup'

We identify gravitationally bound structures in the UrsaMajor region using positions, velocities and photometry from the Sloan Digital Sky Survey (SDSS DR7) and the Third Reference Catalogue of Bright Galaxies (RC3). A friends-of-friends algorithm is extensively tested on mock galaxy lightcones and then implemented on the real data to determine galaxy groups whose members are likely to be physically and dynamically associated with one another. We find several galaxy groups within the region that are likely bound to one another and in the process of merging. We classify 6 galaxy groups as the Ursa Major ‘supergroup’, which are likely to merge and form a poor cluster with a mass of ∼8 × 1013 M . Furthermore, the Ursa Major supergroup as a whole is likely bound to the Virgo cluster, which will eventually form an even larger system in the context of hierarchical structure formation. We investigate the evolutionary state of the galaxy groups in the Ursa Major region and conclude that these groups are in an early evolutionary state and the properties of their member galaxies are similar to those in the field

The galaxy morphology-density relation in the EAGLE simulation

The optical morphology of galaxies is strongly related to galactic environment, with the fraction of early-type galaxies increasing with local galaxy density. In this work, we present the first analysis of the galaxy morphology-density relation in a cosmological hydrodynamical simulation. We use a convolutional neural network, trained on observed galaxies, to perform visual morphological classification of galaxies with stellar masses M* > 1010 M⊙ in the EAGLE simulation into elliptical, lenticular and late-type (spiral/irregular) classes. We find that EAGLE reproduces both the galaxy morphology-density and morphology-mass relations. Using the simulations, we find three key processes that result in the observed morphology-density relation: (i) transformation of disc-dominated galaxies from late-type (spiral) to lenticular galaxies through gas stripping in high-density environments, (ii) formation of lenticular galaxies by merger-induced black hole feedback in low-density environments, and (iii) an increasing fraction of high-mass galaxies, which are more often elliptical galaxies, at higher galactic densities

Peekaboo : the extremely metal poor dwarf galaxy HIPASS J1131-31

The dwarf irregular galaxy HIPASS J1131-31 was discovered as a source of HI emission at low redshift in such close proximity of a bright star that we call it Peekaboo. The galaxy resolves into stars in images with Hubble Space Telescope, leading to a distance estimate of 6.8 ± 0.7 Mpc. Spectral optical observations with the Southern African Large Telescope reveal HIPASS J1131-31 to be one of the most extremely metal-poor galaxies known with the gas-phase oxygen abundance 12 + log(O/H) = 6.99 ± 0.16 dex via the direct [O III] 4363 line method and 6.87 ± 0.07 dex from the two strong line empirical methods. The red giant branch of the system is tenuous compared with the prominence of the features of young populations in the colour-magnitude diagram, inviting speculation that star formation in the galaxy only began in the last few Gyr

Zur Geschichte des Tourismus: e. Skizze d. Entwicklung d tourist. Reisen in d. Moderne

SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 150959 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Radio monitoring of protoplanetary discs

Protoplanetary disc systems observed at radio wavelengths often show excess emission above that expected from a simple extrapolation of thermal dust emission observed at short millimetre wavelengths. Monitoring the emission at radio wavelengths can be used to help disentangle the physical mechanisms responsible for this excess, including free-free emission from a wind or jet, and chromospheric emission associated with stellar activity. We present new results from a radio monitoring survey conducted with Australia Telescope Compact Array over the course of several years with observation intervals spanning days, months and years, where the flux variability of 11 T Tauri stars in the Chamaeleon and Lupus star forming regions was measured at 7 and 15 mm and 3 and 6 cm. Results show that for most sources are variable to some degree at 7 mm, indicating the presence of emission mechanisms other than thermal dust in some sources. Additionally, evidence of grain growth to cm-sized pebbles was found for some sources that also have signs of variable flux at 7 mm. We conclude that multiple processes contributing to the emission are common in T Tauri stars at 7 mm and beyond, and that a detection at a single epoch at radio wavelengths should not be used to determine all processes contributing to the emission.Comment: Accepted 2017 January 4, Monthly Notices of the Royal Astronomical Societ