M. Tamura — Page 9 | Searcharxiv

arXiv2002

The Magnetic Field Structure in W51A

We present 850 micron imaging polarimetry of the W51A massive star forming region performed with SCUBA on the JCMT. From the polarimetry we infer the column-averaged magnetic field direction, projected onto the plane of the sky. We find that the magnetic field geometry in the region is complicated. We compare the field geometry with 6 cm and CS J=7-6 emission and determine that the magnetic field must be relatively weak and plays a passive role, allowing itself to be shaped by pressure forces and dynamics in the ionised and neutral gases. Comparisons are drawn between our data and 1.3 mm BIMA interferometric polarimetry data, from which we conclude that the magnetic field must increase in importance as we move to smaller scales and closer to sites of active star formation.

astro-ph↗

arXiv2001

Submillimeter Imaging Polarimetry of the NGC 7538 Region

Imaging polarimetry of the 0.85mm continuum emission in the NGC 7538 region, obtained with the SCUBA Polarimeter, is presented. The polarization map is interpreted in terms of thermal radiation by magnetically aligned dust grains. Two prominent cores associated with IRS 1 and IRS 11, IRS 1(SMM) and IRS 11(SMM), are found in the surface brightness map. Although these cores look similar in surface brightness, their polarization shows striking differences. In IRS 11(SMM), the polarization vectors are extremely well ordered, and the degrees of polarization are quite high with an average of ~3.9 %. In IRS 1(SMM), on the other hand, the directions of polarization vectors are locally disturbed, and the degrees of polarization are much lower than those of IRS 11(SMM). These differences suggest that small scale fluctuations of the magnetic field are more prominent in IRS 1(SMM). This can be interpreted in terms of the difference in evolutionary stage of the cores. Inside IRS 1(SMM), which seems to be at a later evolutionary stage than IRS 11(SMM), substructures such as subclumps or a cluster of infrared sources have already formed. Small scale fluctuations in the magnetic field could have developed during the formation of these substructures. The distribution of magnetic field directions derived from our polarization map agrees well with those of molecular outflows associated with IRS 1(SMM) and IRS 11(SMM). Comparisons of energy densities between the magnetic field and the outflows show that the magnetic field probably plays an important role in guiding the directions of the outflows.

astro-ph↗

arXiv2000

Infrared Star Count Models and Their Application to the Subaru Deep Field

We construct infrared star count models of the Galaxy applicable at faint magnitudes. In addition to dwarfs and subdwarfs, we also take into account L dwarfs, T dwarfs, and white dwarfs of both disk and halo. As a test case of the models, we analyze the infrared imaging data at J and K' obtained during the Subaru Deep Field Survey to study stellar objects. Infrared star count models we have obtained predict that the Next Generation Space Telescope will primarily see T dwarfs, M subdwarfs, and old halo white dwarfs at faint magnitudes.

astro-ph↗