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Riquelme D.,Institute Radioastronomia Milimetrica IRAM | Riquelme D.,Max Planck Institute for Radio Astronomy | Amo-Baladron M.A.,CSIC - National Institute of Aerospace Technology | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | And 3 more authors.
Astronomy and Astrophysics | Year: 2012

Context. It is well known that the kinetic temperatures, Tkin, of the molecular clouds in the Galactic center region are higher than in typical disk clouds. However, the Tkin of the molecular complexes found at higher latitudes towards the giant molecular loops in the central region of the Galaxy is so far unknown. The gas of these high-latitude molecular clouds (hereafter referred to as "halo clouds") is located in a region where the gas in the disk may interact with the gas in the halo in the Galactic center region. Aims. To derive Tkin in the molecular clouds at high latitude and understand the physical process responsible for the heating of the molecular gas both in the central molecular zone (the concentration of molecular gas in the inner ∼500 pc) and in the giant molecular loops. Methods. We measured the metastable inversion transitions of NH3 from (J,K)=(1,1) to (6,6) toward six positions selected throughout the Galactic central disk and halo. We used rotational diagrams and large velocity gradient (LVG) modeling to estimate the kinetic temperatures toward all the sources. We also observed other molecules like SiO, HNCO, CS, C34S, C18O, and 13CO, to derive the densities and to trace different physical processes (shocks, photodissociation, dense gas) expected to dominate the heating of the molecular gas. Results. We derive for the first time T kin of the high-latitude clouds interacting with the disk in the Galactic center region. We find high rotational temperatures in all the observed positions. We derive two kinetic temperature components (∼150 K and ∼40 K) for the positions in the central molecular zone, and only the warm kinetic temperature component for the clouds toward the giant molecular loops. The fractional abundances derived from the different molecules suggest that shocks provide the main heating mechanism throughout the Galactic center, also at high latitudes. © 2012 ESO. Source

Wang L.-Y.,National Taiwan University | Wang L.-Y.,Academia Sinica, Taiwan | Shang H.,Academia Sinica, Taiwan | Su Y.-N.,Academia Sinica, Taiwan | And 5 more authors.
Astrophysical Journal | Year: 2014

The molecular outflow from IRAS 04166+2706 was mapped with the Submillimeter Array at a 350 GHz continuum and CO J = 3-2 at an angular resolution of ∼1″. The field of view covers the central arcminute, which contains the inner four pairs of knots of the molecular jet. On the channel map, conical structures are clearly present in the low-velocity range (|V-V 0| < 10 km s-1), and the highly collimated knots appear in the extremely high velocity range (50 >|V-V 0| > 30 km s-1). The higher angular resolution of ∼1″ reveals the first blue-shifted knot (B1) that was missing in previous Plateau de Bure Interferometer observation of Santiago-García et al. at an offset of ∼6″ to the northeast of the central source. This identification completes the symmetric sequence of knots in both the blue- and red-shifted lobes of the outflow. The innermost knots R1 and B1 have the highest velocities within the sequence. Although the general features appear to be similar to previous CO J = 2-1 images in Santiago-García et al., the emission in CO J = 3-2 almost always peaks further away from the central source than that of CO J = 2-1 in the red-shifted lobe of the channel maps. This gives rise to a gradient in the line-ratio map of CO J = 3-2/J = 2-1 from head to tail within a knot. A large velocity gradient analysis suggests that the differences may reflect a higher gas kinetic temperature at the head. We also explore possible constraints imposed by the nondetection of SiO J = 8-7. © 2014. The American Astronomical Society. All rights reserved. Source

Bujarrabal V.,Observatorio Astronomico Nacional | Mikolajewska J.,pernicus Astronomical Center | Alcolea J.,Observatorio Astronomico Nacional IGN | Quintana-Lacaci G.,Institute Radioastronomia Milimetrica IRAM
Astronomy and Astrophysics | Year: 2010

Aims. We have studied the molecular content of the circumstellar environs of symbiotic stellar systems, in particular of the well know objects R Aqr and CH Cyg. The study of molecules in these stars will help for understanding the properties of the very inner shells around the cool stellar component from which molecular emission is expected to come. Methods. We performed mm-wave observations with the IRAM 30 m telescope of the 12CO= J = 1-0= and J = 2-1, 13CO= J = 1-0= and J = 2-1, and SiO J = 5-4= transitions in the symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a simple analytical description of the general properties of molecular emission from the inner shells around the cool star. Numerical calculations of the expected line profiles were also performed that took the level population and radiative transfer under such conditions into account. Results. Weak emission of 12CO= J = 1-0= and J = 2-1= was detected in R Aqr and CH Cyg and a good line profile of 12CO J = 2-1= in R Aqr was obtained. The intensities and profile shapes of the detected lines are compatible with emission coming from a very small shell around the Mira-type star, with a radius comparable to or slightly smaller than the distance to the hot dwarf companion, 1014-2×1014 cm. We argue that other possible explanations are improbable. This region probably shows properties similar to those characteristic of the inner shells around standard AGB stars: outwards expansion at about 5-25 km s-1, with a significant acceleration of the gas, temperatures decreasing with radius between about 1000 and 500 K, and densities ∼109-3×108 cm-3. Our model calculations are able to explain the asymmetric line shape observed in 12CO= J = 2-1= from R Aqr, in which the relatively weaker blue part of the profile would result from selfabsorption by the outer layers (in the presence of a velocity increase and a temperature decrease with radius). The mass-loss rates are somewhat higher than in standard AGB stars, as often happens for symbiotic systems. In R Aqr, we find that the total mass of the CO emitting region is ∼2-3×10-5 M, corresponding to M= ∼ 5×10-6-10-5 M yr-1= and compatible with results obtained from dust emission. Considering other existing data on molecular emission, we suggest that the limited extent of the molecule-rich gas in symbiotic systems is mainly due to molecule photodissociation by the radiation of the hot dwarf star. © 2010 ESO. Source

Martin S.,European Southern Observatory | Aladro R.,Institute Radioastronomia Milimetrica IRAM | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | Mauersberger R.,Joint Alma Observatory
Astronomy and Astrophysics | Year: 2010

Aims. Our aim is to derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M 82 and NGC 253. Methods. We present high-sensitivity observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well as the optically thin emission from C18O and 13C 18O. We assume the column density ratio between isotopologues is representative of the 12C/13C isotopic ratio. Results. From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M 82, and 81 in NGC 253, are derived. Lower limits to the 12C/13C ratios from CO isotopologues support these. 13C18O is tentatively detected in NGC 253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16O/18O>350 and >300 in M 82 and NGC 253, respectively, and 32S/34S > 16 in NGC 253. The derived CCH fractional abundances toward these galaxies of ≤≲ 1.1 × 10-8 agree well with those of molecular clouds in the Galactic disk. Conclusions. Our lower limits to the 12C/13C ratio from CCH are a factor of 2-3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The high 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions. © 2010 ESO. Source

Tafalla M.,Observatorio Astronomico Nacional IGN | Santiago-Garcia J.,Observatorio Astronomico Nacional IGN | Santiago-Garcia J.,Institute Radioastronomia Milimetrica IRAM | Hacar A.,Observatorio Astronomico Nacional IGN | Bachiller R.,Observatorio Astronomico Nacional IGN
Astronomy and Astrophysics | Year: 2010

Context. Bipolar outflows from Class 0 protostars often present two components in their CO spectra that have different kinematic behaviors: a smooth outflow wing and a discrete, extremely high-velocity (EHV) peak. Aims. To better understand the origin of these two outflow components, we have studied and compared their molecular composition. Methods. We carried out a molecular survey of the outflows powered by L1448-mm and IRAS 04166+2706, two sources with prominent wing and EHV components. For each source, we observed a number of molecular lines towards the brightest outflow position and used them to determine column densities for 12 different molecular species. Results. The molecular composition of the two outflows is very similar. It presents systematic changes with velocity that we analyze by dividing the outflow in three chemical regimes, two of them associated with the wing component and the other the EHV gas. The analysis of the two wing regimes shows that species like H2CO and CH3OH favor the low-velocity gas, while SiO and HCN are more abundant in the fastest gas. This fastest wing gas presents strong similarities with the composition of the "chemically active" L1157 outflow (whose abundances we re-evaluate in an appendix). We find that the EHV regime is relatively rich in O-bearing species compared to the wing regime. The EHV gas is not only detected in CO and SiO (already reported elsewhere), but also in SO, CH3OH, and H2CO (newly reported here), with a tentative detection in HCO+. At the same time, the EHV regime is relatively poor in C-bearing molecules like CS and HCN, for which we only obtain weak detections or upper limits despite deep integrations. We suggest that this difference in composition arises from a lower C/O ratio in the EHV gas. Conclusions. The different chemical compositions of the wing and EHV regimes suggest that these two outflow components have different physical origins. The wing component is better explained by shocked ambient gas, although none of the existing shock models explains all observed features. We hypothesize that the peculiar composition of the EHV gas reflects its origin as a dense wind from the protostar or its surrounding disk. © 2010 ESO. Source

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