Dense gas in nearby galaxies : XI. Interstellar 12C/13C ratios in the central regions of M 82 and IC 342

[[abstract]](12) C / (13) C line intensity ratios have been derived from several carbon-bearing molecules to confine the range of carbon and oxygen isotope abundance ratios toward the nuclear regions of two infrared bright galaxies. The most stringent limits are obtained from CN mm-wave emission lines. Supplementary measurements toward the Galactic center region indicate that overall I(twCN)/I(thCN) line intensity ratios are giving lower limits to the corresponding ISOC abundance ratio. Toward M82 and IC342, we find ISOC > 40 and > 30. Therefore the smaller ISOC ratio of our own Galactic center region (25) may not be typical for central regions of galaxies which are more luminous in the infrared. The ISOC limits and data from various isotopic species of CO also infer ISOA abundance ratios of > 90 and > 125 for M82 and IC342, respectively. From the I(HCfoN) / I(HCfiN) line intensity ratio, ISON > 100 is derived for M82. Based on observations with the IRAM 30-m telescope, Pico Veleta, Spain and the Swedish-ESO Submillimetre Telescope (SEST) at the European Southern Observatory (ESO), La Silla, Chile[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]FR

Dense gas in nearby galaxies: VIII. The detection of OCS

[[abstract]]The detection of extragalactic OCS, the heaviest molecule identified outside the Galaxy, is reported in three rotational transitions toward the bulge of NGC253. Toward M82, OCS has been tentatively detected. Abundances are consistent with models for warm, dense clouds which have not yet reached chemical equilibrium or with the frequent erosion of grain mantles by C-shocks. This can also explain the large abundances of complex molecules in NGC253. Densities and temperatures of the OCS emitting gas are compared with results from other molecular tracers. From model computations, OCS in the center of NGC253 is emitted by a moderately dense molecular component with n(H2) ~ 103.4 /cm3. This component makes up the bulk of the molecular gas mass. Other molecules also reveal the presence of a much denser component with 10(5-5.5) /cm3. A molecular gas mass of ~ 2 × 108 solar masses is estimated for a 180pc sized molecular cloud toward the center of NGC253; the mean H2 density is ~ 2000 /cm3; and the mean H2 column density, 7 × 1023 /cm2, corresponds to a visual extinction of 700m. The relative OCS abundance is X(OCS) ~ 10-8.9. From detections of the J=2-1 and 3-2 transitions of C34S, the density of the dense molecular gas toward the nuclear region of IC342 is n(H2) ~ 104.6 /cm3. Also presented are a possible detection of the HC3N J=16-15 line toward IC342 and upper limits for the emission of the DCN J=2-1 line toward NGC253 and IC342. For NGC253, [DCN]/[HCN] <= 4 × 10-3.[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子版[[countrycodes]]FR

Cool gas in southern galaxies

[[notice]]本書目待補

Molecular abundances in the Magellanic Clouds .2. Deuterated species in the LMC

The first definite discoveries of extragalactic deuterium are reported. DCO^+ has been detected in three and DCN has been measured in one star-forming region of the Large Magellanic Cloud (LMC). While the HCO^+/DCO^+ abundance ratios are found to be 19 \pm 3, 24 \pm 4 and 67 \pm 18 for N113, N44BC and N159HW, respectively, a HCN/DCN abundance ratio of 23 \pm 5 is obtained for N113. These results are consistent with a gas temperature of about 20\,K and a D/H ratio of about 1.5 \times 10^{-5}, consistent with that observed in the Galaxy. If the cloud temperature is closer to 30\,K, then a D/H ratio is required to be up to an order of magnitude larger. Because this ratio provides a lower limit to the primordial D/H ratio, it indicates that the baryon mass density alone is unable to close the universe

Molecular abundances in the magellanic clouds .1. A multiline study of five cloud cores

Nine HII regions of the LMC were mapped in 13CO(1--0) and three in 12CO(1--0) to study the physical properties of the interstellar medium in the Magellanic Clouds. For N113 the molecular core is found to have a peak position which differs from that of the associated HII region by 20 arcsec. Toward this molecular core the 12CO and 13CO peak Tmb line temperatures of 7.3\,K and 1.2\,K are the highest so far found in the Magellanic Clouds. The molecular concentrations associated with N113, N44BC, N159HW, and N214DE in the LMC and LIRS\,36 in the SMC were investigated in a variety of molecular species to study the chemical properties of the interstellar medium. I(HCO+)/I(HCN) and I(HCN)/I(HNC) intensity ratios as well as lower limits to the I(13CO)/I(C18O) ratio were derived for the rotational 1--0 transitions. Generally, HCO+ is stronger than HCN, and HCN is stronger than HNC. The high relative HCO+ intensities are consistent with a high ionization flux from supernovae remnants and young stars, possibly coupled with a large extent of the HCO+ emission region. The bulk of the HCN arises from relatively compact dense cloud cores. Warm or shocked gas enhances HCN relative to HNC. From chemical model calculations it is predicted that I(HCN)/I(HNC) close to one should be obtained with higher angular resolution (> 30 arcsec) toward the cloud cores. Comparing virial masses with those obtained from the integrated CO intensity provides an H2 mass-to-CO luminosity conversion factor of 1.8 \times 10^{20}\,mol\,cm^{-2}\,(Kkms)^{-1} for N113 and 2.4 \times 10^{20}\,mol\,cm^{-2}\,(Kkms)^{-1} for N44BC. This is consistent with values derived for the Galactic disk

A case study on the application of Fuzzy QFD in TRIZ for service quality improvement

Fuzzy QFD, TRIZ, Contradiction Matrix, E-Commerce,