arXiv subjects

G. Surcis

Publications and source records attributed to G. Surcis.

39 records · Page 3Linked to original sources

arXiv2010

Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2

We present polarization observations of the 6.7-GHz methanol masers around the massive protostar Cepheus A HW2 and its associated disc. The data were taken with the Multi-Element Radio Linked Interferometer Network. The maser polarization is used to determine the full three-dimensional magnetic field structure around Cepheus A HW2. The observations suggest that the masers probe the large scale magnetic field and not isolated pockets of a compressed field. We find that the magnetic field is predominantly aligned along the protostellar outflow and perpendicular to the molecular and dust disc. From the three-dimensional magnetic field orientation and measurements of the magnetic field strength along the line of sight, we are able to determine that the high density material, in which the masers occurs, is threaded by a large scale magnetic field of ~23 mG. This indicates that the protostellar environment at ~1000 AU from Cepheus A HW2 is slightly supercritical (lambda approximately 1.7) and the relation between density and magnetic field is consistent with collapse along the magnetic field lines. Thus, the observations indicate that the magnetic field likely regulates accretion onto the disc. The magnetic field dominates the turbulent energies by approximately a factor of three and is sufficiently strong to be the crucial component stabilizing the massive accretion disc and sustaining the high accretion rates needed during massive star-formation.

astro-ph.GA↗

arXiv2009

Methanol masers probing the ordered magnetic field of W75N

The role of magnetic fields during the protostellar phase of high-mass star-formation is a debated topic. In particular, it is still unclear how magnetic fields influence the formation and dynamic of disks and outflows. Most current information on magnetic fields close to high-mass protostars comes from H2O and OH maser observations. Recently, the first 6.7 GHz methanol maser polarization observations were made, and they reveal strong and ordered magnetic fields. The morphology of the magnetic field during high-mass star-formation needs to be investigated on small scales, which can only be done using very long baseline interferometry observations. The massive star-forming regionW75N contains three radio sources and associated masers, while a large-scale molecular bipolar outflow is also present. Polarization observations of the 6.7 GHz methanol masers at high angular resolution probe the strength and structure of the magnetic field and determine its relation to the outflow. Eight of the European VLBI network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7 GHz methanol masers in the star-forming region W75N. We detected 10 methanol maser features, 4 of which were undetected in previous work. All arise near the source VLA1 of W75N. The linear polarization of the masers reveals a tightly ordered magnetic field over more than 2000 AU around VLA1 that is exactly aligned with the large-scale molecular outflow. This is consistent with the twisted magnetic field model proposed for explaining dust polarization observations. The Zeeman-splitting measured on 3 of the maser features indicates a dynamically important magnetic field in the maser region of the order of 50mG. We suggest VLA1 is the powering sources of the bipolar outflow.

astro-ph.SR↗

arXiv2009

New H2O masers in Seyfert and FIR bright galaxies. III. The Southern Sample

Recently, a relationship between the water maser detection rate and far infrared (FIR) flux densities has been established as a result of two 22 GHz maser surveys in a complete sample of galaxies (Dec>-30 degree) with 100 micron flux densities of > 50 Jy and > 30 Jy. This survey has been extended to the southern galaxies in order to discover new maser sources and to investigate the galaxies hosting the maser spots with particular emphasis on their nuclear regions. A sample of 12 galaxies with Dec<-30 degree and S(100 micron)>50 Jy was observed with the 70-m telescope of the Canberra Deep Space Communication Complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3 sigma noise level of the survey is 15 mJy for a 0.42 km/s channel, corresponding to a detection threshold of ~0.1 solar luminosities for the isotropic maser luminosity at a distance of 25 Mpc. Two new detections are reported: a kilomaser with an isotropic luminosity L_H2O ~5 solar luminosities in NGC3620 and a maser with about twice this luminosity in the merger system NGC3256. The detections have been followed-up through continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC3256, a fraction (about a third) of the maser emission arises from two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may arise from weaker centers of maser activity distributed over the central 50 arcsec. [abridged]

astro-ph.CO↗