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Register a new userSpectral Line Survey toward Spiral Arm of M51 in the 3 mm and 2 mm Bands
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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.
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Spectral line survey observations are conducted toward the high-mass protostar candidate NGC 2264 CMM3 in the 4 mm, 3 mm, and 0.8 mm bands with the Nobeyama 45 m telescope and the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope. In total, 265 emission lines are detected in the 4 mm and 3 mm bands, and 74 emission lines in the 0.8 mm band. As a result, 36 molecular species and 30 isotopologues are identified. In addition to the fundamental molecular species, many emission lines of carbon-chain molecules such as HC5N, C4H, CCS, and C3S are detected in the 4 mm and 3 mm bands. Deuterated molecular species are also detected with relatively strong intensities. On the other hand, emission lines of complex organic molecules such as HCOOCH3, and CH3OCH3 are found to be weak. For the molecules for which multiple transitions are detected, rotation temperatures are derived to be 7-33 K except for CH3OH. Emission lines with high upper-state energies (Eu > 150 K) are detected for CH3OH, indicating existence of a hot core. In comparison with the chemical composition of the Orion KL, carbon-chain molecules and deuterated molecules are found to be abundant in NGC 2264 CMM3, while sulfur-bearing species and complex organic molecules are deficient. These characteristics indicate chemical youth of NGC 2264 CMM3 in spite of its location at the center of the cluster forming core, NGC 2264 C.
We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star-formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a LINER/Seyfert 2 type nucleus. In spite of these physical differences, the chemical composition shows impressive similarities among the three regions. This result means that the characteristic chemical composition associated with these regions is insensitive to the local physical conditions such as star formation rate, because such local effects are smeared out by extended quiescent molecular gas on scales of 1 kpc. Moreover, the observed chemical compositions are also found to be similar to those of molecular clouds in our Galaxy and the spiral arm of M51, whose elemental abundances are close to those in NGC 3627. Therefore, this study provides us with a standard template of the chemical composition of extended molecular clouds with the solar metalicity in nearby galaxies.
We have conducted a mapping spectral line survey toward the Galactic giant molecular cloud W51 in the 3 mm band with the Mopra 22 m telescope in order to study an averaged chemical composition of the gas extended over a molecular cloud scale in our Galaxy. We have observed the area of $25 times 30$, which corresponds to 39 pc $times$ 47 pc. The frequency ranges of the observation are 85.1 - 101.1 GHz and 107.0 - 114.9 GHz. In the spectrum spatially averaged over the observed area, spectral lines of 12 molecular species and 4 additional isotopologues are identified. An intensity pattern of the spatially-averaged spectrum is found to be similar to that of the spiral arm in the external galaxy M51, indicating that these two sources have similar chemical compositions. The observed area has been classified into 5 sub-regions according to the integrated intensity of $^{13}$CO($J=1-0$) ($I_{rm ^{13}CO}$), and contributions of the fluxes of 11 molecular lines from each sub-region to the averaged spectrum have been evaluated. For most of molecular species, 50 % or more of the flux come from the sub-regions with $I_{rm ^{13}CO}$ from 25 K km s$^{-1}$ to 100 K km s$^{-1}$, which does not involve active star forming regions. Therefore, the molecular-cloud-scale spectrum observed in the 3 mm band hardly represents the chemical composition of star forming cores, but mainly represents the chemical composition of an extended quiescent molecular gas. The present result constitutes a sound base for interpreting the spectra of external galaxies at a resolution of a molecular cloud scale ($sim10$ pc) or larger.
We present the results of our spectral line surveys in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216. Totally 377 lines are detected, among which 360 lines are assigned to 57 known molecules (including 29 rare isotopomers and 2 cyclic isomers). Only 17 weak lines remain unidentified. Rotational lines of isotopomers 13CCH and HN13C are detected for the first time in IRC +10216. The detection of the formaldehyde lines in this star is also confirmed. Possible abundance difference among the three 13C substituted isotopic isomers of HC3N is reported. Isotopic ratios of C and O are confirmed to be non-solar while those of S and Si to be nearly solar. Column densities have been estimated for 15 molecular species. Modified spectroscopic parameters have been calculated for NaCN, Na13CN, KCN and SiC2. Transition frequencies from the present observations were used to improve the spectroscopic parameters of Si13CC, 29SiC2 and 30SiC2.
In order to study a molecular-cloud-scale chemical composition, we have conducted a mapping spectral line survey toward the Galactic molecular cloud W3(OH), which is one of the most active star forming regions in the Perseus arm, with the NRO 45 m telescope. We have observed the area of 16 $times$ 16, which corresponds to 9.0 pc $times$ 9.0 pc. The observed frequency ranges are 87--91, 96--103, and 108--112 GHz. We have prepared the spectrum averaged over the observed area, in which 8 molecular species CCH, HCN, HCO$^+$, HNC, CS, SO, C$^{18}$O, and $^{13}$CO are identified. On the other hand, the spectrum of the W3(OH) hot core observed at a 0.17 pc resolution shows the lines of various molecules such as OCS, H$_2$CS CH$_3$CCH, and CH$_3$CN, in addition to the above species. In the spatially averaged spectrum, emission of the species concentrated just around the star-forming core such as CH$_3$OH and HC$_3$N is fainter than in the hot core spectrum, whereas emission of the species widely extended over the cloud such as CCH is relatively brighter. We have classified the observed area into 5 subregions according to the integrated intensity of $^{13}$CO, and have evaluated the contribution to the averaged spectrum from each subregion. The CCH, HCN, HCO$^+$, and CS lines can be seen even in the spectrum of the subregion with the lowest $^{13}$CO integrated intensity range ($< 10$ K km s$^{-1}$). Thus, the contributions of the spatially extended emission is confirmed to be dominant in the spatially averaged spectrum.
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