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Rao R.,Institute of Astronomy and Astrophysics | Girart J.M.,Institute Of Ciencies Of Lespai Csic Ieec | Lai S.-P.,National Tsing Hua University | Lai S.-P.,Academia Sinica, Taiwan | Marrone D.P.,University of Arizona
Astrophysical Journal Letters | Year: 2014

We present subarcsecond resolution polarimetric observations of the 878 μm thermal dust continuum emission obtained with the Submillimeter Array toward the IRAS 16293-2422 protostellar binary system. We report the detection of linearly polarized dust emission arising from the circumstellar disk associated with the IRAS 16293-2422 B protostar. The fractional polarization of ≃ 1.4% is only slightly lower than that expected from theoretical calculations in such disks. The magnetic field structure on the plane of the sky derived from the dust polarization suggests a complex magnetic field geometry in the disk, possibly associated with a rotating disk that is wrapping the field lines as expected from the simulations. The polarization around IRAS 16293-2422 A at subarcsecond angular resolution is only marginally detected. © 2014. The American Astronomical Society. All rights reserved.. Source

Girart J.M.,Institute Of Ciencies Of Lespai | Estalella R.,University of Barcelona | Palau A.,Institute Of Ciencies Of Lespai | Torrelles J.M.,Institute Of Ciencies Of Lespai | And 2 more authors.
Astrophysical Journal Letters | Year: 2014

We present CO 3-2, SiO 8-7, C34S 7-6, and 878 μm dust continuum subarcsecond angular resolution observations with the Submillimeter Array (SMA) toward the IRAS 16293-2422 (I16293) multiple low-mass protostellar system. The C34S emission traces the 878 μm dust continuum well, and in addition clearly shows a smooth velocity gradient along the major axis of component I16293A. CO shows emission at moderate high velocities arising from two bipolar outflows, which appear to be perpendicular with respect to each other. The high sensitivity and higher angular resolution of these observations allows us to pinpoint well the origin of these two outflows at the center of component I16293A. Interestingly, the most compact outflow appears to point toward I16293B. Our data show that the previously reported monopolar blueshifted CO outflow associated with component I16293B seems to be part of the compact outflow arising from component I16293A. In addition, the SiO emission is also tracing this compact outflow: on the one hand, the SiO emission appears to have a jet-like morphology along the southern redshifted lobe; on the other hand, the SiO emission associated with the blueshifted northern lobe traces a well-defined arc on the border of component I16293B facing I16293A. The blueshifted CO lobe of the compact outflow splits into two lobes around the position of this SiO arc. All these results lead us to propose that the compact outflow from component I16293A is impacting on the circumstellar gas around component I16293B, possibly being diverged as a consequence of the interaction. © 2014. The American Astronomical Society. All rights reserved. Source

Frau P.,CSIC - Institute of Materials Science | Girart J.M.,Institute Of Ciencies Of Lespai | Zhang Q.,Harvard - Smithsonian Center for Astrophysics | Rao R.,Institute of Astronomy and Astrophysics
Astronomy and Astrophysics | Year: 2014

Context. NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact HII regions, molecular outflows, and masers. In such a complex environment, interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. Aims. We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces in the formation and evolution of high-mass star-forming clusters. Methods. We performed SMA high angular resolution observations at 880 μm with the compact configuration. We developed the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. To quantify the stability against gravitational collapse we developed the "mass balance" analysis that accounts for all the energetics on core scales. Results. We detect 14 dust cores from 3.5 M to 37 M arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large-scale velocity gradients in H13CO+ 4-3 and C17O 3-2, and magnetic field segments aligned well to the dust main axis. The velocity gradient is reproduced well by a spiral arm expanding at 9 km s-1 with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable to the spiral-arm kinetic energy, which dominates gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. On core scales, those embedded in the central bar seem to be unstable against gravitational collapse and prone to forming high-mass stars, while those in the spiral arm have lower masses that seem to be supported by non-thermal motions and magnetic fields. Conclusions. The NGC 7538 IRS 1-3 cluster seems to be dominated by protostellar feedback. The dusty spiral arm appears to be formed in a snowplow fashion owing to the outflow from the MM1 core. We speculate that the external pressure from the redshifted lobe of the outflow could trigger star formation in the spiral arm cores. This scenario would form a small cluster with a few central high-mass stars, surrounded by a number of low-mass stars formed through protostellar feedback. © ESO, 2014. Source

Bisbas T.G.,University College London | Bisbas T.G.,Max Planck Institute for Extraterrestrial Physics | Bisbas T.G.,University of Florida | Haworth T.J.,University of Cambridge | And 22 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

STARBENCH is a project focused on benchmarking and validating different star formation and stellar feedback codes. In this first STARBENCH paper we perform a comparison study of the D-type expansion of an HII region. The aim of this work is to understand the differences observed between the 12 participating numerical codes against the various analytical expressions examining the D-type phase of HII region expansion. To do this, we propose two well-defined tests which are tackled by 1D and 3D grid- and smoothed particle hydrodynamics-based codes. The first test examines the 'early phase' D-type scenario during which the mechanical pressure driving the expansion is significantly larger than the thermal pressure of the neutral medium. The second test examines the 'late phase' D-type scenario during which the system relaxes to pressure equilibrium with the external medium. Although they are mutually in excellent agreement, all 12 participating codes follow a modified expansion law that deviates significantly from the classical Spitzer solution in both scenarios. We present a semi-empirical formula combining the two different solutions appropriate to both early and late phases that agrees with high-resolution simulations to ≲ 2 per cent. This formula provides a much better benchmark solution for code validation than the Spitzer solution. The present comparison has validated the participating codes and through this project we provide a data set for calibrating the treatment of ionizing radiation hydrodynamics codes. © 2015 The Authors. Source

Basilakos S.,Academy of Athens | Basilakos S.,University of Barcelona | Plionis M.,Institute of Astronomy and Astrophysics | Plionis M.,National Institute of Astrophysics, Optics and Electronics | And 2 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We derive an exact analytical solution for the redshift evolution of linear and scale-independent bias, by solving a second-order differential equation based on linear perturbation theory. This bias evolution model is applicable to all different types of dark energy and modified gravity models. We propose that the combination of the current bias evolution model with data on the bias of extragalactic mass tracers could provide an efficient way to discriminate between geometrical dark energy models and dark energy models that adhere to general relativity. © 2011 American Physical Society. Source

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