Hot Molecular Clouds Research Articles

The Way of Water: ALMA Resolves H2O Emission Lines in a Strongly Lensed Dusty Star-forming Galaxy at z ∼ 3.1

We report Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution (≲0.3″) observations of water emission lines p-H2O(202 − 111), o-H2O(321 − 312), p-H2O(422 − 413), in the strongly lensed galaxy HATLASJ113526.2-01460 at redshift z ∼3.1. From the lensing-reconstructed maps of water emission and line profiles, we infer the general physical properties of the interstellar medium (ISM) in the molecular clouds where the lines arise. We find that the water vapor lines o-H2O(321 − 312), p-H2O(422 − 413) are mainly excited by far-infrared (FIR) pumping from dust radiation in a warm and dense environment, with dust temperatures ranging from 70 to ∼100 K, as suggested by the line ratios. The p-H2O(202 − 111) line, instead, is excited by a complex interplay between FIR pumping and collisional excitation in the dense core of the star-forming region. This scenario is also supported by the detection of the medium-level excitation of CO resulting in the line emission CO (J = 8–7). Thanks to the unprecedented high resolution offered by the combination of ALMA capabilities and gravitational lensing, we discern the different phases of the ISM and locate the hot molecular clouds into a physical scale of ∼500 pc. We discuss the possibility of J1135 hosting an active galactic nucleus in its accretion phase. Finally, we determine the relation between the water emission lines and the total IR luminosity of J1135, as well as the star formation rate as a function of water emission intensities, comparing the outcomes to local and high-z galactic samples from the literature.

NEAR-INFRARED SPECTROSCOPY OF CO RO-VIBRATIONAL ABSORPTION TOWARD HEAVILY OBSCURED AGNs

We provide a new physical insight on the hot molecular clouds near the nucleus of the obscured AGNs. We performed near-infrared spectroscopic observations of heavily obscured AGNs in order to reveal physical characteristics of molecular clouds, especially focused on the CO fundamental ro-vibrational absorption around <TEX>$4.7{\mu}m$</TEX>. We have made systematic moderate-resolution spectroscopic observations toward 30 representative (U)LIRGs using the AKARI/IRC, and some of the ULIRGs showed the strong CO absorption feature. For three bright (U)LIRGs that show a steep red continuum with the deep CO absorption feature, IRAS 08572+3915, UGC 05101, and IRAS 01250+2832, we have also made high-resolution spectroscopic observations using the Subaru/IRCS. We have successfully detected many absorption lines up to highly excited rotational levels, and these lines are very deep and extremely broad. The derived physical conditions of molecular clouds are extreme; the gas temperature is as high as several 100 to a 1000 K, the <TEX>$H_2$</TEX> column density is larger than <TEX>$10^{22}cm^{-2}$</TEX>, and the gas density is greater than <TEX>$10^7cm^{-3}$</TEX>. Such hot and dense molecular clouds must exist around the central engine of the AGN.

Aldehydes and sugars from evolved precometary ice analogs: Importance of ices in astrochemical and prebiotic evolution

Evolved interstellar ices observed in dense protostellar molecular clouds may arguably be considered as part of precometary materials that will later fall on primitive telluric planets, bringing a wealth of complex organic compounds. In our laboratory, experiments reproducing the photo/thermochemical evolution of these ices are routinely performed. Following previous amino acid identifications in the resulting room temperature organic residues, we have searched for a different family of molecules of potential prebiotic interest. Using multidimensional gas chromatography coupled to time-of-flight mass spectrometry, we have detected 10 aldehydes, including the sugar-related glycolaldehyde and glyceraldehyde--two species considered as key prebiotic intermediates in the first steps toward the synthesis of ribonucleotides in a planetary environment. The presence of ammonia in water and methanol ice mixtures appears essential for the recovery of these aldehydes in the refractory organic residue at room temperature, although these products are free of nitrogen. We finally point out the importance of detecting aldehydes and sugars in extraterrestrial environments, in the gas phase of hot molecular clouds, and, more importantly, in comets and in primitive meteorites that have most probably seeded the Earth with organic material as early as 4.2 billion years ago.

NEAR-INFRARED HIGH-RESOLUTION SPECTROSCOPY OF THE OBSCURED AGN IRAS 01250+2832

We provide a new physical insight on the hot molecular clouds near the nucleus of the heavily obscured AGN IRAS 01250+2832, based on the results of near-infrared high-resolution spectroscopy of gaseous CO ro-vibrational absorption lines with Subaru/IRCS. The detected CO absorption lines up to highly excited rotational levels reveal that hot dense molecular clouds exist around the AGN under the peculiar physical conditions.

Rotational spectrum of deuterated and $\mathsf{^{15}}$N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C$\mathsf{^{15}}$N

Context. Ethyl cyanide is an abundant molecule in hot molecular clouds. Its rotational spectrum is very dense and several hundreds of rotational transitions within the ground state have been identified in molecular clouds in the 40−900 GHz frequency range. Lines from 13 C isotopically substituted ethyl cyanide were identified in Orion. Aims. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of 15 N substituted ethyl cyanide CH3CH2C 15 N. Using these experimental data, we have searched for these species in Orion. Methods. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier Transform spectrometer (8−17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150−260 and 580−660 GHz). More than 300 lines were identified for each species, for J values in the range 71−80 and Ka values in the range 28−31 depending on the isotopologues. The experimental spectra were analyzed using a Watson’s Hamiltonian in the A-reduction. Results. From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4−1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15 N substituted ethyl cyanide CH3CH2C 15 N for the first time in Orion. The derived column density and rotational temperature are 10 13 cm −2 and 150 K for the plateau and 3 × 10 14 cm −2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10 14 cm −2 .

Isotopic ethyl cyanide $^{\mathsf{13}}$CH$_\mathsf{3}$CH$_\mathsf{2}$CN, CH$_\mathsf{3}$$^{\mathsf{13}}$CH$_\mathsf{2}$CN, and CH$_\mathsf{3}$CH$_\mathsf{2}$$^{\mathsf{13}}$CN: laboratory rotational spectrum and detection in Orion

Context. Astronomical spectra of hot molecular clouds in the wavelength range from centimeter to submillimeter show a huge number of rotational lines due to the emission of complex organic molecules, and a large fraction of these lines are unidentified. The assignment of these lines to new molecules, to known molecules in excited states, or to their isotopologues requires a good knowledge of the spectroscopic parameters of these molecules. Aims. We present the experimental study of the spectroscopic properties of 13 C-substituted ethyl cyanide 13 CH 3 CH 2 CN, CH 3 13 CH 2 CN, and CH 3 CH 2 13 CN. Methods. The rotational spectra of the three species in the ground state have been measured in the frequency ranges from 5 to 26 GHz using waveguide Fourier transform spectrometers and from 160 to 360 GHz using a source-modulated spectrometer employing backward-wave oscillators (BWOs). Results. A new accurate set of spectroscopic constants has been determined for each isotopic species. This permits prediction of the position of rotational lines that are best suited for detection with an accuracy of a few hundreds of kHz. The three isotopologues have been detected in an Orion IRc2 IRAM survey via several hundred of lines, illustrating that many unidentified bands are definitely due to isotopologues of known molecules.

Prebiologically Important Interstellar Molecules

Understanding the organic chemistry of molecular clouds, particularly the formation of biologically important molecules, is fundamental to the study of the processes which lead to the origin, evolution and distribution of life in the Galaxy. Determining the level of molecular complexity attainable in the clouds, and the nature of the complex organic material available to protostellar disks and the planetary systems that form from them, requires an understanding of the possible chemical pathways and is therefore a central question in astrochemistry. We have thus searched for prebiologically important molecules in the hot molecular cloud cores: Sgr B2(N-LMH), W51 e1/e2 and Orion-KL. Among the molecules searched: Pyrimidine is the unsubstituted ring analogue for three of the DNA and RNA bases. 2H-Azirine and Aziridine are azaheterocyclic compounds. And Glycine is the simplest amino acid. Detections of these interstellar organic molecular species will thus have important implications for Astrobiology. Our preliminary results indicate a tentative detection of interstellar glycine. If confirmed, this will be the first detection of an amino acid in interstellar space and will greatly strengthen the thesis that interstellar organic molecules could have played a pivotal role in the prebiotic chemistry of the early Earth.

Oxirane: An Exotic Oxygenated Organic Compound on Titan?

After the discovery of CO, CO2, and more recently H2O in Titan's atmosphere, the chemistry of oxygenated organic compounds in this environment has been limited to theoretical studies only. Both kinetic and thermochemical models predict the formation of methanol and formaldehyde as the main O-organic products. Here we show that oxirane (also named ethylene oxide) is the main product in experiments designed to simulate the upper atmosphere of Titan; methanol and formaldehyde are not produced in detectable amounts. Oxirane has been previously detected in the interstellar medium and hot molecular cloud cores. The first opportunity to detect it in Titan will occur in 2005 January during the entry of the Huygens probe into the satellite's atmosphere. Therefore, oxirane becomes a molecule of wide astrophysical interest.

Einstein A-coefficients for vib-rotational transitions in CO

Einstein A-coefficients for the electric-dipole transitions between the rotational levels up to 400 cm−1 in the ground vibrational state of methylene (CH2) are calculated. The coefficients are used to compute the mean-radiative-life-times of the levels. It is concluded that in hot molecular clouds, CH2 may be detected through the stimulated emission of the radiation at 69.36 GHz.

Molecular abundances and low-mass star formation. 1: Si- and S-bearing species toward IRAS 16293-2422

Results from millimeter and submillimeter spectral line surveys of the protobinary source IRAS 16293-2422 are presented. Here we outline the abundances of silicon- and sulfur-containing species. A combination of rotation diagram and full statistical equilibrium/radiative transfer calculations is used to constrain the physical conditions toward IRAS 16293 and to construct its beam-averaged chemical composition over a 10-20 (1600-3200 AU) scale. The chemical complexity as judged by species such as SiO, OCS, and H_2S, is mtermedtate between that of dark molecular clouds such as Ll34N and hot molecular cloud cores such as Orion KL. From the richness of the spectra compared to other young stellar objects of similar luminosity, it is clear that molecular abundances do not scale simply with mass; rather, the chemistry is a strong function of evolutionary state, i.e., age.

The detection of acetaldehyde in cold dust clouds.

Observations of the 1(01) --> 0(00) rotational transitions of A and E state acetaldehyde are reported. The transitions were detected, for the first time in interstellar space, in the cold dust clouds TMC-1 and L134N, and in Sgr B2. This is also the first time acetaldehyde has been found in a dust cloud and is the most complex oxygen-bearing molecule yet known in this environment. We find a column density of 6 x 10(12) cm-2 in TMC-1, comparable to many other species detected there, and an approximately equal column density in L134N. In the direction of Sgr B2, the CH3CHO profile appears to consist of broad emission features from the hot molecular cloud core, together with absorption features resulting from intervening colder material. We also report the possible detection of HC9N toward IRC +10 degrees 216 through its J = 33 --> 32 transition. Implications for cold dust cloud chemistry and excitation are discussed.

Einstein A-coefficients for rotational transitions in CH2

Einstein A-coefficients for the electric-dipole transitions between the rotational levels up to 400 cm−1 in the ground vibrational state of methylene (CH2) are calculated. The coefficients are used to compute the mean-radiative-life-times of the levels. It is concluded that in hot molecular clouds, CH2 may be detected through the stimulated emission of the radiation at 69.36 GHz.

The M17 SW molecular cloud

view Abstract Citations (58) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The M17 SW molecular cloud. Thronson, H. A., Jr. ; Lada, C. J. Abstract The H II region M17 is one of the best known objects in the sky. The H II region abuts a dense, relatively hot molecular cloud known as M17 SW, which is itself embedded within the edge of one of the largest giant molecular cloud complexes in the Galaxy. Carbon monoxide observations (J = 1 to 0) were obtained during two observing runs at an 11 m telescope during the time of 1981 January 26-29 and 1981 September 22-27. New, moderate-resolution maps of the massive M17 SW molecular cloud are presented and discussed. It is found that the strongest molecular emission lies in a ridge parallel and adjacent to an apparent ionization and molecular dissociation front. M17 SW is a massive dense molecular condensation. The visual extinction through the center of the cloud is around 200 mag. The present data are consistent with the views that the M17 SW cloud is largely heated externally, by the ionizing stars of the H II region. Publication: The Astrophysical Journal Pub Date: June 1983 DOI: 10.1086/161028 Bibcode: 1983ApJ...269..175T Keywords: Abundance; Infrared Astronomy; Molecular Clouds; Radio Sources (Astronomy); Stellar Evolution; Carbon Monoxide; Gas Dissociation; Gas Temperature; H Ii Regions; Infrared Spectra; Interstellar Extinction; Ionized Gases; Millimeter Waves; Optical Thickness; Astrophysics full text sources ADS | data products SIMBAD (2)