We have conducted a spectral line survey in the 3 mm and 2 mm bands toward two positions in a spiral arm of M51 (NGC 5194) with the IRAM 30 m telescope. In this survey, we have identified 13 molecular species, including CN, CCH, N2H+, HNCO, and CH3OH
. Furthermore, 6 isotopologues of the major species have been detected. On the other hand, SiO, HC3N, CH3CN, and the deuterated species such as DCN and DCO+ are not detected. The deuterium fractionation ratios are evaluated to be less than 0.8 % and 1.2 % for DCN/HCN and DCO+/HCO+, respectively. By comparing the results of the two positions with different star formation activities, we have found that the observed chemical compositions do not strongly depend on star formation activities. They seem to reflect a chemical composition averaged over the 1-kpc scale region including many giant molecular clouds. Among the detected molecules CN, CCH, and CH3OH are found to be abundant. High abundances of CN, and CCH are consistent with the above picture of a wide spread distribution of molecules, because they can be produced by photodissociation. On the other hand, it seems likely that CH3OH is liberated into the gas phase by shocks associated with large scale phenomena such as cloud-cloud collisions and/or by non-thermal desorption processes such as photoevaporation due to cosmic-ray induced UV photons. The present result demonstrates a characteristic chemical composition of a giant molecular cloud complex in the spiral arm, which can be used as a standard reference for studying chemistry in AGNs and starbursts.
We report the first detection of a radio-continuum and molecular jet associated with a dominant blue-shifted maser source, G353.273+0.641. A radio jet is extended 3000 au along NW-SE direction. H$_{2}$O masers are found to be clustered in the root of
a bipolar radio jet. A molecular jet is detected by thermal SiO ($upsilon$ = 0, $J$ = 2-1) emission. The SiO spectrum is extremely wide (-120 -- +87 km s$^{-1}$) and significantly blue-shift dominated, similar to the maser emission. The observed geometry and remarkable spectral similarity between H$_{2}$O maser and SiO strongly suggests the existence of a maser-scale ($sim$ 340 au) molecular jet that is enclosed by the extended radio jet. We propose a disc-masking scenario as the origin of the strong blue-shift dominance, where an optically thick disc obscures a red-shifted lobe of a compact jet.
We report on the astrometric observations of the 22 GHz H2O masers in the high mass star-forming region G5.89-0.39 with VERA (VLBI Exploration of Radio Astrometry). Newly derived distance of 1.28^{+0.09}_{-0.08} kpc is the most precise and significan
tly nearer than previous values. We revised physical parameters and reconsidered nature of G5.89-0.39 based on the new distance as follows. (1) The ionizing star of the ultra compact (UC) HII region is a late O-type (O8 - 8.5) zero age main sequence (ZAMS) star, consistent with previously established limits based on its infrared spectral line emission. (2) Crescent-like maser alignment at the position of the O type ZAMS star may trace accretion disk (or its remnant), which suggests that the star is still young and before complete evaporation of circumstellar materials. (3) Although the revised mass for the east-west outflow has been reduced, it still quite large (100 Msun) which indicates that a significant fraction of the mass is entrained material and that the dynamical age significantly underestimates the actual outflow age. Our newly-derived distance emphasizes that G5.89-0.39 is one of the nearest targets to investigate ongoing high-mass star formation and evolution in a compact cluster containing a young O-type star.
