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Bujarrabal V.,Observatorio Astronomico Nacional. Ap 112 | 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, 10 14-2×1014 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 Ṁ ∼ 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. © ESO 2010.

Tafalla M.,Observatorio Astronomico Nacional IGN | Liseau R.,Chalmers University of Technology | Nisini B.,National institute for astrophysics | Bachiller R.,Observatorio Astronomico Nacional IGN | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Water is a potential tracer of outflow activity because it is heavily depleted in cold ambient gas and is copiously produced in shocks. Aims. We present a survey of the water emission in a sample of more than 20 outflows from low-mass young stellar objects with the goal of characterizing the physical and chemical conditions of the emitting gas. Methods. We used the HIFI and PACS instruments on board the Herschel Space Observatory to observe the two fundamental lines of ortho-water at 557 and 1670 GHz. These observations were part of the "Water In Star-forming regions with Herschel" (WISH) key program, and have been complemented with CO and H2 data. Results. The emission of water has a different spatial and velocity distribution from that of the J = 1-0 and 2-1 transitions of CO. On the other hand, it has a similar spatial distribution to H2, and its intensity follows the H 2 intensity derived from IRAC images. This suggests that water traces the outflow gas at hundreds of kelvins that is responsible for the H 2 emission, and not the component at tens of kelvins typical of low-J CO emission. A warm origin of the water emission is confirmed by a remarkable correlation between the intensities of the 557 and 1670 GHz lines, which also indicates that the emitting gas has a narrow range of excitations. A radiative transfer analysis shows that while there is some ambiguity in the exact combination of density and temperature values, the gas thermal pressure nT is constrained within less than a factor of 2. The typical nT over the sample is 4 × 109 cm-3K, which represents an increase of 10 4 with respect to the ambient value. The data also constrain the water column density within a factor of 2 and indicate values in the sample between 2 × 1012 and 1014 cm-2. When these values are combined with estimates of the H2 column density, the typical water abundance is only 3 × 10-7, with an uncertainty of a factor of 3. Conclusions. Our data challenge current C-shock models of water production through the combination of wing-line profiles, high gas compressions, and low abundances. © ESO, 2013.

Xia X.Y.,Tianjin Normal University | Gao Y.,Chinese Academy of Sciences | Hao C.-N.,Tianjin Normal University | Tan Q.H.,Chinese Academy of Sciences | And 8 more authors.
Astrophysical Journal | Year: 2012

We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30 m telescope. The cold molecular gas reservoir in these objects is in a range of (0.2-2.1) × 1010 M ⊙ (adopting a CO-to-H2 conversion factor αCO = 0.8 M ⊙ (K km s-1 pc 2)-1). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency (L FIR/L′CO), and CO (1-0) line widths, are indistinguishable from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of low- and high-redshift CO-detected QSOs reveals a tight correlation between L FIR and L′CO(1-0) for all QSOs. This suggests that, similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust heated by star formation rather than by active galactic nuclei (AGNs), confirming similar findings from mid-infrared spectroscopic observations by Spitzer. A correlation between the AGN-associated bolometric luminosities and the CO line luminosities suggests that star formation and AGNs draw from the same reservoir of gas and there is a link between star formation on kpc scale and the central black hole accretion process on much smaller scales. © 2012. The American Astronomical Society. All rights reserved.

Riquelme D.,Institute Radioastronomia Milimetrica IRAM | Riquelme D.,University of Chile | Bronfman L.,University of Chile | Mauersberger R.,Institute Radioastronomia Milimetrica IRAM | And 3 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. A large-scale survey of the Galactic center region in the 3 mm rotational transitions of SiO, HCO+ and H13CO+ (beamsize ∼3′.6) was conducted to provide an estimate of cloud conditions, heating mechanisms, chemistry, and other properties. Methods. Using the NANTEN 4 m telescope from Nagoya University, a region between -5°75 < l < 5°6 and -0°68 < b < 1°3 was mapped in the J = 1 →0 lines of HCO+ and H13CO+ and in the J = 2 → 1 line of SiO with a spacing of 3°75 (HCO+) and 1→875 (SiO and H13CO+). Results. Velocity channel maps, longitude-velocity maps, and latitude-velocity maps are presented. We identify 51 molecular clouds; 33 of them belong to the Galactic center and 18 to disk gas. We derive an average of the luminosity ratio of SiO(J = 2 → 1)/CO(J = 1 →0) in clouds belonging to the Galactic center of 4.9 × 10-3 and for disk clouds of 3.4 × 10-3. The luminosity ratio of HCO+(J = 1 →0)/CO(J = 1 →0) in the Galactic center is 3.5 × 10-2, and for disk clouds it is 1.5 × 10-2. We can distinguish clearly between regions where the SiO or HCO+ dominate. © 2010 ESO.

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.

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.

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.

Aladro R.,Institute Radioastronomia Milimetrica IRAM | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | Martin S.,European Southern Observatory | Martin S.,Harvard - Smithsonian Center for Astrophysics | And 2 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. We aim to study the properties of the dense molecular gas towards the inner few 100 pc of four nearby starburst galaxies dominated both by photo dissociation regions (M  82) and large-scale shocks (NGC  253, IC  342, and Maffei  2), and to connect the chemical and physical properties of the molecular clouds with the evolutionary stage of the nuclear starbursts. Methods. We have carried out multi-transitional observations and analyses of three dense gas molecular tracers, CS, HC3N (cyanoacetylene), and CH3CCH (methyl acetylene), using Boltzmann diagrams in order to determine the rotational temperatures and column densities of the dense gas, and using a large velocity gradients model to calculate the H2 density structure in the molecular clouds. Results. The CS and HC3N data indicate the presence of density gradients in the molecular clouds. These two molecules show similar excitation conditions, suggesting that they arise from the same gas components. In M 82, CH3CCH has the highest fractional abundance determined in an extragalactic source (1.1 × 10-8). Conclusions. The density and the chemical gradients we found in all galaxies can be explained in the framework of the starburst evolution, which affects the chemistry and the structure of molecular clouds around the galactic nuclei. The young shock-dominated starburst galaxies, like presumably Maffei 2, show a cloud structure with a fairly uniform density and chemical composition that suggests low star formation activity. Molecular clouds in galaxies with starburst in an intermediate stage of evolution, such as NGC 253 and IC 342, show clouds with a high density contrast (two orders of magnitude) between the denser regions (cores) and the less dense regions (halos) of the molecular clouds and relatively constant chemical abundance. Finally, the galaxy with the most evolved starburst, M 82, has clouds with a fairly uniform density structure, large envelopes of atomic/molecular gas subjected to UV photodissociating radiation from young star clusters, and very different chemical abundances of HC3N and CH3CCH. © 2010 ESO.

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.

Aladro R.,Institute Radioastronomia Milimetrica IRAM | Aladro R.,University College London | Martin S.,European Southern Observatory | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | And 6 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. We study the chemical complexity towards the central parts of the starburst galaxy M 82, and investigate the role of certain molecules as tracers of the physical processes in the galaxy circumnuclear region. Methods. We carried out a spectral line survey with the IRAM-30 m telescope towards the northeastern molecular lobe of M 82. It covers the frequency range between 129.8 GHz and 175.0 GHz in the 2 mm atmospheric window, and between 241.0 GHz and 260.0 GHz in the 1.3 mm atmospheric window. Results. Sixty-nine spectral features corresponding to 18 different molecular species are identified. In addition, three hydrogen recombination lines are detected. The species NO, H2S, H2CS, NH2CN, and CH3CN are detected for the first time in this galaxy. Assuming local thermodynamic equilibrium, we determine the column densities of all the detected molecules. We also calculate upper limits to the column densities of fourteen other important, but undetected, molecules, such as SiO, HNCO, or OCS. We compare the chemical composition of the two starburst galaxies M 82 and NGC 253. This comparison enables us to establish the chemical differences between the products of the strong photon-dominated regions driving the heating in M 82, and the large-scale shocks that influence the properties of the molecular clouds in the nucleus of NGC 253. Conclusions. Overall, both sources have different chemical compositions. Some key molecules highlight the different physical processes dominating both central regions. Examples include CH3CCH, c-C 3H2, or CO+, the abundances of which are clearly higher in M 82 than in NGC 253, pointing at photodissociating regions. On the other hand, species such as CH2NH, NS, SiO, and HOCO + have abundances of up to one order of magnitude higher in NGC 253 than in M 82. © 2011 ESO.

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