scholarly journals An ALMA and ATCA Molecular Line Survey Toward Centaurus A

2012 ◽  
Vol 8 (S292) ◽  
pp. 251-251
Author(s):  
Jürgen Ott ◽  
Mark McCoy ◽  
David Meier
Keyword(s):  
Radio Galaxy ◽  
Molecular Absorption ◽  
Physical Processes ◽  
Molecular Line ◽  
Physical Conditions ◽  
Line Survey ◽  
Molecular Abundances ◽  
Excitation Conditions ◽  
Compact Array ◽  
Centaurus A

AbstractWe present Atacama Large Millimeter/submillimeter Array (ALMA) and Australia Telescope Compact Array (ATCA) data of molecular absorption lines toward the bright central core of the prominent, nearby (d ∼ 3.8 Mpc) radio galaxy Centaurus A, at 13, 7, 3, and 1mm wavelengths. The line of sight crosses the prominent dust lane and continues through the disk and eventually through gas that may be very close to the central supermassive black hole. The goal of our survey is to determine the physical conditions of the gas via analyses of molecular line tracers including molecular abundances and excitation conditions that are sensitive to changes in temperature, density, ionization, and shocks. This study allows us to derive the physical processes that are shaping each molecular environment.

scholarly journals Signatures of turbulence in the dense interstellar medium

1991 ◽  
Vol 147 ◽  
pp. 119-136
Author(s):  
E. Falgarone ◽  
T.G. Phillips
Keyword(s):  
Interstellar Medium ◽  
Turbulent Flows ◽  
Fractal Geometry ◽  
Molecular Clouds ◽  
Large Range ◽  
Line Profiles ◽  
Physical Processes ◽  
Molecular Line ◽  
Scale Size ◽  
Excitation Conditions

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104cm—3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.

scholarly journals A molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at 3 mm with the Nobeyama 45 m radio telescope: The data

2019 ◽  
Vol 71 (Supplement_1) ◽  
Author(s):  
Shuro Takano ◽  
Taku Nakajima ◽  
Kotaro Kohno
Keyword(s):  
Radio Telescope ◽  
High Spectral Resolution ◽  
X Rays ◽  
Narrow Beam ◽  
Molecular Line ◽  
Line Intensities ◽  
Nearby Galaxies ◽  
Ngc 1068 ◽  
Line Survey ◽  
Molecular Abundances

AbstractWe present observational data of a molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at wavelengths of 3 mm (∼85–116 GHz) obtained with the Nobeyama 45 m radio telescope. Regarding IC 342, a line survey with high spectral resolution in the 3 mm region was reported for the first time. NGC 1068 is a nearby gas-rich galaxy with X-rays from an active galactic nucleus (AGN), and NGC 253 and IC 342 are nearby gas-rich galaxies with prototypical starbursts. These galaxies are useful for studying the impacts of X-rays and ultraviolet radiation on molecular abundances. The survey was carried out with a resulting rms noise level of a few mK ($T\rm {_A^*}$). As a result we could obtain almost complete data of these galaxies in the 3 mm region: we detected 19–23 molecular species, depending on the galaxies, including several new detections (e.g., cyclic-C3H2 in IC 342). We found that the intensities of HCN, CN, and HC3N relative to 13CO are significantly strong in NGC 1068 compared with those in NGC 253 and IC 342. On the other hand, CH3CCH was not detected in NGC 1068. We obtained these results with the narrow beam (${15{^{\prime\prime}_{.}}2}$–${19{^{\prime\prime}_{.}}1}$) of the 45 m telescope, among single-dish telescopes, and in particular selectively observed molecular gas close to the circumnuclear disk (CND) in NGC 1068. The present line intensities in NGC 1068 were compared with those obtained with the IRAM 30 m radio telescope already reported. As a result, the intensity ratio of each line was found to have information on the spatial distribution. Our observations revealed the line intensities and stringent constraints on the upper limit for the three galaxies with such a narrow beam; consequently, the present data will be a basis for further observations with high spatial resolution.

scholarly journals Signatures of turbulence in the dense interstellar medium

1991 ◽  
Vol 147 ◽  
pp. 119-136
Author(s):  
E. Falgarone ◽  
T.G. Phillips
Keyword(s):  
Interstellar Medium ◽  
Turbulent Flows ◽  
Fractal Geometry ◽  
Molecular Clouds ◽  
Large Range ◽  
Line Profiles ◽  
Physical Processes ◽  
Molecular Line ◽  
Scale Size ◽  
Excitation Conditions

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104cm—3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.

scholarly journals Millimetre wavelength methanol masers survey towards massive star forming regions

2007 ◽  
Vol 3 (S242) ◽  
pp. 234-235
Author(s):  
T. Umemoto ◽  
N. Mochizuki ◽  
K. M. Shibata ◽  
D.-G. Roh ◽  
H.-S. Chung
Keyword(s):  
Detection Rate ◽  
Massive Star ◽  
Molecular Line ◽  
Maser Emission ◽  
Star Forming ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Methanol Masers ◽  
Maser Sources

AbstractWe present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above −25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

Molecular Line Survey

2014 ◽  
pp. 1-6
Author(s):  
Brett A. McGuire ◽  
Anthony J. Remijan
Keyword(s):  
Molecular Line ◽  
Line Survey

scholarly journals Molecular line survey of the high-mass star-forming region NGC 6334I withHerschel/HIFI and the Submillimeter Array

2012 ◽  
Vol 546 ◽  
pp. A87 ◽  
Author(s):  
A. Zernickel ◽  
P. Schilke ◽  
A. Schmiedeke ◽  
D. C. Lis ◽  
C. L. Brogan ◽  
...  
Keyword(s):  
High Mass ◽  
Mass Star ◽  
Molecular Line ◽  
Star Forming ◽  
Line Survey

scholarly journals A sensitive λ 3 mm line survey of L483

2019 ◽  
Vol 625 ◽  
pp. A147 ◽  
Author(s):  
M. Agúndez ◽  
N. Marcelino ◽  
J. Cernicharo ◽  
E. Roueff ◽  
M. Tafalla
Keyword(s):  
Chemical Composition ◽  
Chemical Characterization ◽  
Isotopic Ratios ◽  
Dark Cloud ◽  
Carbon Chains ◽  
Prestellar Cores ◽  
Low Mass ◽  
Line Survey ◽  
Molecular Abundances

An exhaustive chemical characterization of dense cores is mandatory to our understanding of chemical composition changes from a starless to a protostellar stage. However, only a few sources have had their molecular composition characterized in detail. Here we present a λ 3 mm line survey of L483, a dense core around a Class 0 protostar, which was observed with the IRAM 30 m telescope in the 80–116 GHz frequency range. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud according to their narrow lines (FWHM ~ 0.5 km s−1) and low rotational temperatures (≲10 K). Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH3, CH3OCH3, and C2H5OH, a wide variety of carbon chains, nitrogen oxides like N2O, and saturated molecules like CH3SH, in addition to eight new interstellar molecules (HCCO, HCS, HSC, NCCNH+, CNCN, NCO, H2NCO+, and NS+) whose detection has already been reported. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 and B1-b, and are similar to those in L1527. Apart from the overabundance of carbon chains in TMC-1, we find that L483 does not have a marked chemical differentiation with respect to starless/prestellar cores like TMC-1 and L1544, although it does chemically differentiate from Class 0 hot corino sources like IRAS 16293−2422. This fact suggests that the chemical composition of the ambient cloud of some Class 0 sources could be largely inherited from the dark cloud starless/prestellar phase. We explore the use of potential chemical evolutionary indicators, such as the HNCO/C3S, SO2/C2S, and CH3SH/C2S ratios, to trace the prestellar/protostellar transition. We also derived isotopic ratios for a variety of molecules, many of which show isotopic ratios close to the values for the local interstellar medium (remarkably all those involving 34S and 33S), while there are also several isotopic anomalies like an extreme depletion in 13C for one of the two isotopologs of c-C3H2, a drastic enrichment in 18O for SO and HNCO (SO being also largely enriched in 17O), and different abundances for the two 13C substituted species of C2H and the two 15N substituted species of N2H+. We report the first detection in space of some minor isotopologs like c-C3D. The exhaustive chemical characterization of L483 presented here, together with similar studies of other prestellar and protostellar sources, should allow us to identify the main factors that regulate the chemical composition of cores along the process of formation of low-mass protostars.

scholarly journals The molecular gas in Luminous Infrared Galaxies: a new emergent picture

2012 ◽  
Vol 8 (S292) ◽  
pp. 209-214
Author(s):  
Padelis P. Papadopoulos ◽  
Zhi-Yu Zhang ◽  
Axel Weiss ◽  
Paul van der Werf ◽  
Kate Isaak ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Molecular Gas ◽  
Infrared Galaxies ◽  
Space Observatory ◽  
Local Universe ◽  
Star Forming ◽  
Luminous Infrared Galaxies ◽  
Physical Conditions ◽  
J 13 ◽  
Line Survey

AbstractResults from a large, multi-J CO, 13CO, and HCN line survey of Luminous Infrared Galaxies (LIRGs: LIR≥ 1010 L⊙) in the local Universe (z≤0.1), complemented by CO J=4–3 up to J=13–12 observations from the Herschel Space Observatory (HSO), paints a new picture for the average conditions of the molecular gas of the most luminous of these galaxies with turbulence and/or large cosmic ray (CR) energy densities UCR rather than far-UV/optical photons from star-forming sites as the dominant heating sources. Especially in ULIRGs (LIR>1012 L⊙) the Photon Dominated Regions (PDRs) can encompass at most a few % of their molecular gas mass while the large UCR∼ 103 UCR, Galaxy, and the strong turbulence in these merger/starbursts, can volumetrically heat much of their molecular gas to Tkin∼ (100-200) K, unhindered by the high dust extinctions. Moreover the strong supersonic turbulence in ULIRGs relocates much of their molecular gas at much higher average densities (≥104 cm−3) than in isolated spirals (∼ 102–103 cm−3). This renders low-J CO lines incapable of constraining the properties of the bulk of the molecular gas in ULIRGs, with substantial and systematic underestimates of its mass possible when only such lines are used. Finally a comparative study of multi-J HCN lines and CO SLEDs from J=1–0 up to J=13–12 of NGC 6240 and Arp 193 offers a clear example of two merger/starbursts whose similar low-J CO SLEDs, and LIR/LCO,1−0 and LHCN, 1−0/LCO,1-0 ratios (proxies of the so-called SF efficiency and dense gas mass fraction), yield no indications about their strongly diverging CO SLEDs beyond J=4–3, and ultimately the different physical conditions in their molecular ISM. The much larger sensitivity of ALMA and its excellent site in the Atacama desert now allows the observations necessary to assess the dominant energy sources of the molecular gas and its mass in LIRGs without depending on the low-J CO lines.

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