20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues

We present a series of new high-sensitivity and high-resolution radio-continuum images of M31 at \lambda=20 cm (\nu=1.4 GHz). These new images were produced by merging archived 20 cm radio-continuum observations from the Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60 \mu Jy and feature high angular resolution (<10"). A complete sample of discrete radio sources have been catalogued and analysed across 17 individual VLA projects. We identified a total of 864 unique discrete radio sources across the field of M31. One of the most prominent regions in M31 is the ring feature for which we estimated total integrated flux of 706 mJy at \lambda=20 cm. We compare here, detected sources to those listed in Gelfand et al. (2004) at \lambda=92 cm and find 118 sources in common to both surveys. The majority (61%) of these sources exhibit a spectral index of \alpha <-0.6 indicating that their emission is predominantly non-thermal in nature. That is more typical for background objects.Comment: 28 pages, 25 figures, accepted for publication in the Serbian Astronomical Journa

Multi-frequency study of Local Group Supernova Remnants The curious case of the Large Magellanic Cloud SNR J0528-6714

Aims. Recent ATCA, XMM-Newton and MCELS observations of the Magellanic Clouds (MCs) cover a number of new and known SNRs which are poorly studied, such as SNR J0528-6714 . This particular SNR exhibits luminous radio-continuum emission, but is one of the unusual and rare cases without detectable optical and very faint X-ray emission (initially detected by ROSAT and listed as object [HP99] 498). We used new multi-frequency radio-continuum surveys and new optical observations at H{\alpha}, [S ii] and [O iii] wavelengths, in combination with XMM-Newton X-ray data, to investigate the SNR properties and to search for a physical explanation for the unusual appearance of this SNR. Methods. We analysed the X-ray and Radio-Continuum spectra and present multi-wavelength morphological studies of this SNR. Results. We present the results of new moderate resolution ATCA observations of SNR J0528-6714. We found that this object is a typical older SNR with a radio spectral index of {\alpha}=-0.36 \pm 0.09 and a diameter of D=52.4 \pm 1.0 pc. Regions of moderate and somewhat irregular polarisation were detected which are also indicative of an older SNR. Using a non-equilibrium ionisation collisional plasma model to describe the X-ray spectrum, we find temperatures kT of 0.26 keV for the remnant. The low temperature, low surface brightness, and large extent of the remnant all indicate a relatively advanced age. The near circular morphology indicates a Type Ia event. Conclusions. Our study revealed one of the most unusual cases of SNRs in the Local Group of galaxies - a luminous radio SNR without optical counterpart and, at the same time, very faint X-ray emission. While it is not unusual to not detect an SNR in the optical, the combination of faint X-ray and no optical detection makes this SNR very unique.Comment: 6 pages, 5 figures, Accepted for publication in A&

Seasonal and depth-driven changes in rhodolith bed structure and associated macroalgae off Arvoredo island (southeastern Brazil)

Rhodoliths are formed by coralline red algae and can form heterogeneous substrata with high biodiversity. Here we describe a rhodolith bed at the southern limit of the known distribution of this habitat in the western Atlantic. We characterized rhodolith and macroalgal assemblages at 5, 10 and 15. m depth during summer and winter. Lithothamnion crispatum was dominant amongst the six rhodolith-forming species present. Most rhodoliths were spheroidal in shape indicating high mobility due to water movement. Rhodolith density decreased with increasing depth and during winter. Turf-forming seaweeds accounted for 60% of the biomass growing on rhodoliths. Macroalgae increased abundance and richness in the summer, but was similar between 5 and 15. m depth. They were less abundant and diverse than that recorded in rhodolith beds further north in Brazil. Both, season and depth, affected the structure of the macroalgae assemblages. We conclude that Lithothamniom is the most representative genus of Brazilian rhodolith beds. Summer is responsible for increasing the diversity and richness of macroalgae, as well as increasing rhodolith density. © 2013 Elsevier B.V

AGN behind the SMC selected from radio and X-ray surveys

The XMM-Newton survey of the Small Magellanic Cloud (SMC) revealed 3053 X-ray sources with the majority expected to be active galactic nuclei (AGN) behind the SMC. However, the high stellar density in this field often does not allow assigning unique optical counterparts and hinders source classification. On the other hand, the association of X-ray point sources with radio emission can be used to select background AGN with high confidence, and to constrain other object classes like pulsar wind nebula. To classify X-ray and radio sources, we use clear correlations of X-ray sources found in the XMM-Newton survey with radio-continuum sources detected with ATCA and MOST. Deep radio-continuum images were searched for correlations with X-ray sources of the XMM-Newton SMC-survey point-source catalogue as well as galaxy clusters seen with extended X-ray emission. Eighty eight discrete radio sources were found in common with the X-ray point-source catalogue in addition to six correlations with extended X-ray sources. One source is identified as a Galactic star and eight as galaxies. Eight radio sources likely originate in AGN that are associated with clusters of galaxies seen in X-rays. One source is a PWN candidate. We obtain 43 new candidates for background sources located behind the SMC. A total of 24 X-ray sources show jet-like radio structures.Comment: 9 pages, 6 figures, accepted for publication in A&