A survey of CH2DOH towards starless and pre-stellar cores in the Taurus molecular cloud

ABSTRACT Recent observations indicate that organic molecules are prevalent towards starless and pre-stellar cores. Deuteration of these molecules has not been well studied during the starless phase. Published observations of singly deuterated methanol, CH2DOH, have only been observed in a couple of well-studied, dense, and evolved pre-stellar cores (e.g. L1544, L183). Since the formation of gas-phase methanol during this cold phase is believed to occur via desorption from the icy grain surfaces, observations of CH2DOH may be useful as a probe of the deuterium fraction in the ice mantles of dust grains. We present a systematic survey of CH2DOH towards 12 starless and pre-stellar cores in the B10 region of the Taurus molecular cloud. Nine of the 12 cores are detected with [CH2DOH]/[CH3OH] ranging from <0.04 to 0.23$^{+0.12}_{-0.06}$ with a median value of 0.11. Sources not detected tend to have larger virial parameters and larger methanol linewidths than detected sources. The results of this survey indicate that deuterium fractionation of organic molecules, such as methanol, during the starless phase may be more easily detectable than previously thought.

The relative orientation between the magnetic field and gradients of surface brightness within thin velocity slices of 12CO and 13CO emission from the Taurus molecular cloud

ABSTRACT We examine the role of the interstellar magnetic field to modulate the orientation of turbulent flows within the Taurus molecular cloud using spatial gradients of thin velocity slices of 12CO and 13CO antenna temperatures. Our analysis accounts for the random errors of the gradients that arise from the thermal noise of the spectra. The orientations of the vectors normal to the antenna temperature gradient vectors are compared to the magnetic field orientations that are calculated from Planck 353 GHz polarization data. These relative orientations are parameterized with the projected Rayleigh statistic and mean resultant vector. For 12CO, strongly parallel and strongly perpendicular relative orientations are found in 28 percent and 39 percent of the cloud area respectively. For the lower opacity 13CO emission, strongly parallel and strongly perpendicular orientations are found in 7 per cent and 43 per cent of the cloud area, respectively. For both isotopologues, strongly parallel or perpendicular alignments are restricted to localized regions with low levels of turbulence. If the relative orientations serve as an observational proxy to the Alfvénic Mach number then our results imply local variations of the Alfvénic Mach number throughout the cloud.

First clear detection of the CCS Zeeman splitting toward the pre-stellar core, Taurus Molecular Cloud 1

We report the first clear detection of the Zeeman splitting of a CCS emission line at 45 GHz toward the nearby pre-stellar dense filament, Taurus Molecular Cloud 1 (TMC-1). We observed HC$_3$N non-Zeeman lines simultaneously with the CCS line, and did not detect any significant splitting of the HC$_3$N lines. Thus, we conclude that our detection of CCS Zeeman splitting is robust. The derived line-of-sight magnetic field strength is about $117 \pm 21 \, \mu$G, which corresponds to a normalized mass-to-magnetic flux ratio of 2.2 if we adopt an inclination angle of 45$^\circ$. Thus, we conclude that the TMC-1 filament is magnetically supercritical. Recent radiative transfer calculations of the CCS and HC$_3$N lines along the line of sight suggest that the filament is collapsing with a speed of $\sim$0.6 km s$^{-1}$, which is comparable to three times the isothermal sound speed. This infall velocity appears to be consistent with the evolution of a gravitationally infalling core.

QUIJOTE scientific results – III. Microwave spectrum of intensity and polarization in the Taurus Molecular Cloud complex and L1527

We present new intensity and polarization observations of the Taurus Molecular Cloud (TMC) region in the frequency range 10–20 GHz with the multifrequency instrument (MFI) mounted on the first telescope of the Q-U-I-JOint TEnerife (QUIJOTE) experiment. From the combination of the QUIJOTE data with the WMAP 9-yr data release, the Planck second data release, the DIRBE maps, and ancillary data, we detect an anomalous microwave emission (AME) component with flux density $S_{\rm AME, peak} = 43.0 \pm 7.9\,$ Jy in the TMC and $S_{\rm AME, peak} = 10.7 \pm 2.7\,$ Jy in the dark cloud nebula L1527, which is part of the TMC. In the TMC the diffuse AME emission peaks around a frequency of 19 GHz, compared with an emission peak about a frequency of 25 GHz in L1527. In the TMC, the best constraint on the level of AME polarization is obtained at the Planck channel of 28.4 GHz, with an upper limit $\pi _{\rm AME}\lt 4.2\, {{\ \rm per\ cent}}$ (95 $\, {{\ \rm per\ cent}}$ C.L.), which reduces to $\pi _{\rm AME}\lt 3.8\, {{\ \rm per\ cent}}$ (95 $\, {{\ \rm per\ cent}}$ C.L.) if the intensity of all the free–free, synchrotron and thermal dust components are negligible at this frequency. The same analysis in L1527 leads to $\pi _{\rm AME}\lt 5.3{{\ \rm per\ cent}}$ (95 $\, {{\ \rm per\ cent}}$ C.L.) or $\pi _{\rm AME}\lt 4.5\, {{\ \rm per\ cent}}$ (95 ${{\ \rm per\ cent}}$ C.L.) under the same assumption. We find that in the TMC and L1527 on average about $80{{\ \rm per\ cent}}$ of the H ii gas should be mixed with thermal dust. Our analysis shows how the QUIJOTE-MFI 10–20 GHz data provide key information to properly separate the synchrotron, free–free, and AME components.