arXiv subjects

Tao-Chung Ching

Publications and source records attributed to Tao-Chung Ching.

59 records · Page 4Linked to original sources

arXiv2016

Helical Magnetic Fields in the NGC1333 IRAS 4A Protostellar Outflows

We present Submillimeter Array (SMA) polarization observations of the CO $J$ = 3--2 line toward the NGC1333 IRAS 4A. The CO Stokes $I$ maps at an angular resolution of $\sim$1$\arcsec$ reveal two bipolar outflows from the binary sources of the NGC 1333 IRAS 4A. The kinematic features of the CO emission can be modeled by wind-driven outflows at $\sim$ 20$\arcdeg$ inclined from the plane of the sky. Close to the protostars the CO polarization, at an angular resolution of $\sim$$2\farcs3$, has a position angle approximately parallel to the magnetic field direction inferred from the dust polarizations. The CO polarization direction appears to vary smoothly from an hourglass field around the core to an arc-like morphology wrapping around the outflow, suggesting a helical structure of magnetic fields that inherits the poloidal fields at the launching point and consists of toroidal fields at a farther distance of outflow. The helical magnetic field is consistent with the theoretical expectations for launching and collimating outflows from a magnetized rotating disk. Considering that the CO polarized emission is mainly contributed from the low-velocity and low-resolution data, the helical magnetic field is likely a product of the wind-envelope interaction in the wind-driven outflows. The CO data reveal a PA of $\sim$ 30$\arcdeg$ deflection in the outflows. The variation in the CO polarization angle seems to correlate with the deflections. We speculate that the helical magnetic field contributes to $\sim$ 10$\arcdeg$ deflection of the outflows by means of Lorenz force.

astro-ph.SR↗

arXiv2015

Local Magnetic Field Role in Star Formation

We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions.

astro-ph.GA↗

arXiv2014

The Importance of the Magnetic Field from an SMA-CSO-Combined Sample of Star-Forming Regions

Submillimeter dust polarization measurements of a sample of 50 star-forming regions, observed with the SMA and the CSO covering pc-scale clouds to mpc-scale cores, are analyzed in order to quantify the magnetic field importance. The magnetic field misalignment $δ$ -- the local angle between magnetic field and dust emission gradient -- is found to be a prime observable, revealing distinct distributions for sources where the magnetic field is preferentially aligned with or perpendicular to the source minor axis. Source-averaged misalignment angles $\langle|δ|\rangle$ fall into systematically different ranges, reflecting the different source-magnetic field configurations. Possible bimodal $\langle|δ|\rangle$-distributions are found for the separate SMA and CSO samples. Combining both samples broadens the distribution with a wide maximum peak at small $\langle|δ|\rangle$-values. Assuming the 50 sources to be representative, the prevailing source-magnetic field configuration is one that statistically prefers small magnetic field misalignments $|δ|$. When interpreting $|δ|$ together with an MHD force equation, as developed in the framework of the polarization-intensity gradient method, a sample-based scaling fits the magnetic field tension-to-gravity force ratio $\langleΣ_B\rangle$ versus $\langle|δ|\rangle$ with $\langleΣ_B\rangle = 0.116 \cdot \exp(0.047\cdot \langle|δ|\rangle)\pm 0.20$ (mean error), providing a way to estimate the relative importance of the magnetic field, only based on measurable field misalignments $|δ|$. The force ratio $Σ_B$ discriminates systems that are collapsible on average ($\langle Σ_B\rangle <1$) from other molecular clouds where the magnetic field still provides enough resistance against gravitational collapse ($\langle Σ_B\rangle >1$) (abridged).

astro-ph.GA↗

arXiv2014

Magnetic field structure in the Flattened Envelope and Jet in the young protostellar system HH 211

HH 211 is a young Class 0 protostellar system, with a flattened envelope, a possible rotating disk, and a collimated jet. We have mapped it with the Submillimeter Array in 341.6 GHz continuum and SiO J=8-7 at ~ 0.6 resolution. The continuum traces the thermal dust emission in the flattened envelope and the possible disk. Linear polarization is detected in the continuum in the flattened envelope. The field lines implied from the polarization have different orientations, but they are not incompatible with current gravitational collapse models, which predict different orientation depending on the region/distance. Also, we might have detected for the first time polarized SiO line emission in the jet due to the Goldreich-Kylafis effect. Observations at higher sensitivity are needed to determine the field morphology in the jet.

astro-ph.GA↗

arXiv2014

Magnetic Fields and Massive Star Formation

Massive stars ($M > 8$ \msun) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 $μ$m obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of $\lsim$ 0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within $40^\circ$ of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks ($\lsim 10^3$ AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scale of 0.01 - 0.1 pc in the context of massive star and cluster star formation.

astro-ph.GA↗