We have developed a method to make a spectral-line-based survey of hot cores,
which represent an important stage of high-mass star formation, and applied the
method to the data of the FUGIN (FOREST ...Unbiased Galactic plane Imaging survey
with the Nobeyama 45-m telescope) survey. First, we select hot core candidates
by searching the FUGIN data for the weak hot core tracer lines (HNCO and
CH$_3$CN) by stacking, and then we conduct follow-up pointed observations on
these candidates in C$^{34}$S, SO, OCS, HC$_3$N, HNCO, CH$_3$CN, and CH$_3$OH
$J=2-1$ and $J=8-7$ lines to confirm and characterize them. We applied this
method to the $l = 10^\circ-20^\circ$ portion of the FUGIN data and identified
22 "Hot Cores" (compact sources with more than two significant detection of the
hot core tracer lines, i.e., SO, OCS, HC$_3$N, HNCO, CH$_3$CN, or CH$_3$OH
$J=8-7$ lines) and 14 "Dense Clumps" (sources with more than two significant
detection of C$^{34}$S, CH$_3$OH $J=2-1$, or the hot core tracer lines). The
identified Hot Cores are found associated with signposts of high-mass star
formation such as ATLASGAL clumps, WISE HII regions, and Class II methanol
masers. For those associated with ATLASGAL clumps, their bolometric luminosity
to clump mass ratios are consistent with the star formation stages centered at
the hot core phase. The catalog of FUGIN Hot Cores provides a useful starting
point for further statistical studies and detailed observations of high-mass
star forming regions.
We have developed a method to make a spectral-line-based survey of hot cores, which represent an important stage of high-mass star formation, and applied the method to the data of the FUGIN (FOREST ...Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope) survey. First, we select hot core candidates by searching the FUGIN data for the weak hot core tracer lines (HNCO and CH\(_3\)CN) by stacking, and then we conduct follow-up pointed observations on these candidates in C\(^{34}\)S, SO, OCS, HC\(_3\)N, HNCO, CH\(_3\)CN, and CH\(_3\)OH \(J=2-1\) and \(J=8-7\) lines to confirm and characterize them. We applied this method to the \(l = 10^\circ-20^\circ\) portion of the FUGIN data and identified 22 "Hot Cores" (compact sources with more than two significant detection of the hot core tracer lines, i.e., SO, OCS, HC\(_3\)N, HNCO, CH\(_3\)CN, or CH\(_3\)OH \(J=8-7\) lines) and 14 "Dense Clumps" (sources with more than two significant detection of C\(^{34}\)S, CH\(_3\)OH \(J=2-1\), or the hot core tracer lines). The identified Hot Cores are found associated with signposts of high-mass star formation such as ATLASGAL clumps, WISE HII regions, and Class II methanol masers. For those associated with ATLASGAL clumps, their bolometric luminosity to clump mass ratios are consistent with the star formation stages centered at the hot core phase. The catalog of FUGIN Hot Cores provides a useful starting point for further statistical studies and detailed observations of high-mass star forming regions.
We report 850~$\mu$m dust polarization observations of a low-mass ($\sim$12
$M_{\odot}$) starless core in the $\rho$ Ophiuchus cloud, Ophiuchus C, made
with the POL-2 instrument on the James Clerk ...Maxwell Telescope (JCMT) as part
of the JCMT B-fields In STar-forming Region Observations (BISTRO) survey. We
detect an ordered magnetic field projected on the plane of sky in the starless
core. The magnetic field across the $\sim$0.1~pc core shows a predominant
northeast-southwest orientation centering between $\sim$40$^\circ$ to
$\sim$100$^\circ$, indicating that the field in the core is well aligned with
the magnetic field in lower-density regions of the cloud probed by
near-infrared observations and also the cloud-scale magnetic field traced by
Planck observations. The polarization percentage ($P$) decreases with an
increasing total intensity ($I$) with a power-law index of $-$1.03 $\pm$ 0.05.
We estimate the plane-of-sky field strength ($B_{\mathrm{pos}}$) using modified
Davis-Chandrasekhar-Fermi (DCF) methods based on structure function (SF),
auto-correlation (ACF), and unsharp masking (UM) analyses. We find that the
estimates from the SF, ACF, and UM methods yield strengths of 103 $\pm$ 46
$\mu$G, 136 $\pm$ 69 $\mu$G, and 213 $\pm$ 115 $\mu$G, respectively. Our
calculations suggest that the Ophiuchus C core is near magnetically critical or
slightly magnetically supercritical (i.e. unstable to collapse). The total
magnetic energy calculated from the SF method is comparable to the turbulent
energy in Ophiuchus C, while the ACF method and the UM method only set upper
limits for the total magnetic energy because of large uncertainties.
We present 850 $\mu$m imaging polarimetry data of the $\rho$ Oph-A core taken
with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its
polarimeter (POL-2), as part of our ongoing survey ...project, BISTRO (B-fields In
STar forming RegiOns). The polarization vectors are used to identify the
orientation of the magnetic field projected on the plane of the sky at a
resolution of 0.01 pc. We identify 10 subregions with distinct polarization
fractions and angles in the 0.2 pc $\rho$ Oph A core; some of them can be part
of a coherent magnetic field structure in the $\rho$ Oph region. The results
are consistent with previous observations of the brightest regions of $\rho$
Oph-A, where the degrees of polarization are at a level of a few percents, but
our data reveal for the first time the magnetic field structures in the fainter
regions surrounding the core where the degree of polarization is much higher
($> 5 \%$). A comparison with previous near-infrared polarimetric data shows
that there are several magnetic field components which are consistent at
near-infrared and submillimeter wavelengths. Using the
Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in
several sub-core regions, which range from approximately 0.2 to 5 mG. We also
find a correlation between the magnetic field orientations projected on the sky
with the core centroid velocity components.
We report the first high spatial resolution measurement of magnetic fields surrounding LkH\(\alpha\) 101, a part of the Auriga-California molecular cloud. The observations were taken with the POL-2 ...polarimeter on the James Clerk Maxwell Telescope within the framework of the B-fields In Star-forming Region Observations (BISTRO) survey. Observed polarization of thermal dust emission at 850 \(\mu\)m is found to be mostly associated with the red-shifted gas component of the cloud. The magnetic field displays a relatively complex morphology. Two variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure function, are used to calculate the strength of magnetic fields in the plane of the sky, yielding a similar result of \(B_{\rm POS}\sim 115\) \(\mathrm{\mu}\)G. The mass-to-magnetic-flux ratio in critical value units, \(\lambda\sim0.3\), is the smallest among the values obtained for other regions surveyed by POL-2. This implies that the LkH\(\alpha\) 101 region is sub-critical and the magnetic field is strong enough to prevent gravitational collapse. The inferred \(\delta B/B_0\sim 0.3\) implies that the large scale component of the magnetic field dominates the turbulent one. The variation of the polarization fraction with total emission intensity can be fitted by a power-law with an index of \(\alpha=0.82\pm0.03\), which lies in the range previously reported for molecular clouds. We find that the polarization fraction decreases rapidly with proximity to the only early B star (LkH\(\alpha\) 101) in the region. The magnetic field tangling and the joint effect of grain alignment and rotational disruption by radiative torques are potential of explaining such a decreasing trend.
We report 850~\(\mu\)m dust polarization observations of a low-mass (\(\sim\)12 \(M_{\odot}\)) starless core in the \(\rho\) Ophiuchus cloud, Ophiuchus C, made with the POL-2 instrument on the James ...Clerk Maxwell Telescope (JCMT) as part of the JCMT B-fields In STar-forming Region Observations (BISTRO) survey. We detect an ordered magnetic field projected on the plane of sky in the starless core. The magnetic field across the \(\sim\)0.1~pc core shows a predominant northeast-southwest orientation centering between \(\sim\)40\(^\circ\) to \(\sim\)100\(^\circ\), indicating that the field in the core is well aligned with the magnetic field in lower-density regions of the cloud probed by near-infrared observations and also the cloud-scale magnetic field traced by Planck observations. The polarization percentage (\(P\)) decreases with an increasing total intensity (\(I\)) with a power-law index of \(-\)1.03 \(\pm\) 0.05. We estimate the plane-of-sky field strength (\(B_{\mathrm{pos}}\)) using modified Davis-Chandrasekhar-Fermi (DCF) methods based on structure function (SF), auto-correlation (ACF), and unsharp masking (UM) analyses. We find that the estimates from the SF, ACF, and UM methods yield strengths of 103 \(\pm\) 46 \(\mu\)G, 136 \(\pm\) 69 \(\mu\)G, and 213 \(\pm\) 115 \(\mu\)G, respectively. Our calculations suggest that the Ophiuchus C core is near magnetically critical or slightly magnetically supercritical (i.e. unstable to collapse). The total magnetic energy calculated from the SF method is comparable to the turbulent energy in Ophiuchus C, while the ACF method and the UM method only set upper limits for the total magnetic energy because of large uncertainties.
We present 850 \(\mu\)m imaging polarimetry data of the \(\rho\) Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2), as part of our ongoing ...survey project, BISTRO (B-fields In STar forming RegiOns). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01 pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2 pc \(\rho\) Oph A core; some of them can be part of a coherent magnetic field structure in the \(\rho\) Oph region. The results are consistent with previous observations of the brightest regions of \(\rho\) Oph-A, where the degrees of polarization are at a level of a few percents, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (\(> 5 \%\)). A comparison with previous near-infrared polarimetric data shows that there are several magnetic field components which are consistent at near-infrared and submillimeter wavelengths. Using the Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in several sub-core regions, which range from approximately 0.2 to 5 mG. We also find a correlation between the magnetic field orientations projected on the sky with the core centroid velocity components.
