- ID:
- ivo://CDS.VizieR/J/A+A/625/A148
- Title:
- 12 molecular clouds of M31 spectra
- Short Name:
- J/A+A/625/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse molecular observations performed at IRAM interferometer in CO(1-0) of the circum-nuclear region (within 250pc) of Andromeda, with 2. arcsec=11pc resolution. We detect 12 molecular clumps in this region, corresponding to a total molecular mass of (8.4+/ 0.4)x10^4^M_{sun}_. They follow the Larson's mass-size relation, but lie well above the velocity-size relation. We discuss that these clumps are probably not virialised, but transient agglomerations of smaller entities that might be virialised. Three of these clumps have been detected in CO(2-1) in a previous work, and we find temperature line ratio below 0.5. With a RADEX analysis, we show that this gas is in non local thermal equilibrium with a low excitation temperature (Tex=5-9K). We find a surface beam filling factor of order 5 percent and a gas density in the range 60-650cm^-3^, well below the critical density. With a gas-to-stellar mass fraction of 4x10^-4^ and dust-to-gas ratio of 0.01, this quiescent region has exhausted his gas budget. Its spectral energy distribution is compatible with passive templates assembled from elliptical galaxies. While weak dust emission is present in the region, we show that no star formation is present and support the previous results that the dust is heated by the old and intermediate stellar population. We study that this region lies formally in the low-density part of the Kennicutt-Schmidt law, in a regime where the SFR estimators are not completely reliable. We confirm the quiescence of the inner part of this galaxy known to lie on the green valley.
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- ID:
- ivo://CDS.VizieR/J/A+A/627/A95
- Title:
- Molecular DNM in Chamaeleon CO spectra
- Short Name:
- J/A+A/627/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To determine carbon monoxide column densities along sightlines through the Chamaeleon cloud complex where molecular absorption had been observed but CO emission had not been detected. We took ^12^CO J=1-0 absorption profiles toward 6 of 8 members of a group of sightlines in Chamaeleon having abundant dark neutral matter and molecular hydrogen but no detectable CO emission. CO absorption was detected along five of the six sightlines at column densities 4x10^+13^cm^-2^<~N(CO)<~10^15^cm^-2^ that are below typical survey detection limits of 1-2K-km/s. Dark gas absent in CO emission along sightlines in the outskirts of the Chamaeleon complex where molecular gas is readily detected in HCO^+^ absorption results from small CO column densities around the onset of CO formation at the HI/H_2_ transition. Relative abundances N(CO)/H_2_<3x10^-6^ in Chamaeleon are comparable to those seen in UV absorption toward early-type stars and in a CO absorption/emission line survey toward local quasar background targets away from the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A26
- Title:
- Molecular ion abundances in diffuse ISM
- Short Name:
- J/A+A/622/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The transition between atomic and molecular hydrogen is associated with important changes in the structure of interstellar clouds, and marks the beginning of interstellar chemistry. Most molecular ions are rapidly formed (in ion-molecule reactions) and destroyed (by dissociative recombination) in the diffuse ISM. Because of the relatively simple networks controlling their abundances, molecular ions are usually good probes of the underlying physical conditions including for instance the fraction of gas in molecular form or the fractional ionization. In this paper we focus on three possible probes of the molecular hydrogen column density, HCO^+^, HOC^+^, and CF^+^. We presented high sensitivity ALMA absorption data toward a sample of compact HII regions and bright QSOs with prominent foreground absorption, in the ground state transitions of the molecular ions HCO^+^, HOC^+^, and CF^+^ and the neutral species HCN and HNC, and from the excited state transitions of C_3_H^+^(4-3) and ^13^CS(2-1). These data are compared with Herschel absorption spectra of the ground state transition of HF and p-H_2_O. We show that the HCO^+^, HOC^+^, and CF^+^ column densities are well correlated with each other. HCO^+^ and HOC^+^ are tightly correlated with p-H_2_O, while they exhibit a different correlation pattern with HF depending on whether the absorbing matter is located in the Galactic disk or in the central molecular zone. We report new detections of C_3_H^+^ confirming that this ion is ubiquitous in the diffuse matter, with an abundance relative to H_2_ of ~7x10^-11^. We confirm that the CF^+^ abundance is lower than predicted by simple chemical models and propose that the rate of the main formation reaction is lower by a factor of about 3 than usually assumed. In the absence of CH or HF data, we recommend to use the ground state transitions of HCO^+^, CCH, and HOC^+^ to trace diffuse molecular hydrogen, with mean abundances relative to H_2_ of 3x10^-9^, 4x10^-8^ and 4x10^-11^ respectively, leading to sensitivity N(H_2_)/{int}{tau}dv of 4x10^20^, 1.5x10^21^, and 6x10^22^cm^-2^/km/s, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/661/250
- Title:
- Molecular line survey of CRL 618
- Short Name:
- J/ApJ/661/250
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the complete data set, model, and line identification of a survey of the emission from the C-rich proto-planetary nebula CRL 618 performed with the IRAM 30m telescope in the frequency ranges 80.25-115.75GHz, 131.25-179.25GHz, and 204.25-275.250GHz. A selection of lines from different species has been used in previous works to derive the structure of the source, its physical conditions, and the chemical abundances in the different gas regions. In this work, we have used this information to run a global simulation of the spectrum in order to check the consistency of the model and to ease the task of line identification. The total number of lines that have a correspondence in both data and model is ~3100, although quite often in this object many lines blend into complex features, so that the model, which takes into account line blending, is a key tool at this stage of the analysis. Of all the lines that we have been able to label, ~55% of them belong to the different forms of HC3N, and ~18% to HC5N. The density of remaining unidentified features above the 3sigma limit is only 1 per ~2.1GHz (74 features), which is unprecedented in the analysis of this type of large millimeter-wave line surveys.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A46
- Title:
- Mono-^13^C acetaldehydes mm/submm wave spectra
- Short Name:
- J/A+A/579/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The acetaldehyde molecule is ubiquitous in the interstellar medium of our galaxy, and due to its dense and complex spectrum, large dipole moment, and several low-lying torsional states, acetaldehyde is considered to be a "weed" molecule for radio astronomy observations. Mono-^13^C acetaldehydes ^13^CH_3_CHO and CH_3_^13^CHO are likely to be identified in astronomical surveys, such as those available with the very sensitive ALMA telescope. Laboratory measurements and analysis of the millimeter and submillimeter-wave spectra are the prerequisites for the successful radioastronomical search for the new interstellar molecular species, as well as for new isotopologs of already detected interstellar molecules. In this context, to provide reliable predictions of ^13^CH_3_CHO and CH_3_^13^CHO spectra in millimeter and submillimeter wave ranges, we study rotational spectra of these species in the frequency range from 50 to 945GHz. The spectra of mono-^13^C acetaldehydes were recorded using the spectrometer based on Schottky-diode frequency-multiplication chains in the Lille laboratory. The rotational spectra of ^13^CH_3_CHO and CH_3_^13^CHO molecules were analyzed using the Rho axis method.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A40
- Title:
- MSX high-contrast IRDCs with NH_3_
- Short Name:
- J/A+A/552/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 220 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15K, are turbulent (with line width FWHMs around 2km/s), have ammonia column densities on the order of 10^14^cm^-2^ and molecular hydrogen column densities on the order of 10^22^cm^-2^. Their virial masses are between 100 and a few 1000M_{sun}_. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.
- ID:
- ivo://CDS.VizieR/J/ApJS/156/127
- Title:
- 350{mu}m molecular line survey of Orion KL
- Short Name:
- J/ApJS/156/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the Caltech Submillimeter Observatory, we have carried out an unbiased spectral line survey of Orion KL throughout the 350{mu}m band (from 795 to 903GHz). This is the first systematic study of molecular radiation in this frequency range. A total of 541 features, resulting from 929 transitions from a total of 26 species, have been detected. High-excitation transitions from CH_3_OH, CH_3_CN, H_2_CO, HNCO, and C_2_H_5_CN indicate the presence of a very hot (~250K) component at the systemic velocity characteristic of the Hot Core. Physical parameters (column density and rotational temperature) relative to a number of species have been estimated by fitting, in the LTE (Local Thermodynamic Equilibrium) approximation, the whole 100GHz spectrum at once, thus taking line blending and optical depth effects properly into account. We also report the tentative detection, for the first time outside the Galactic center region, of the radical NH2, one of the building blocks of the chemistry of ammonia.
- ID:
- ivo://CDS.VizieR/J/ApJS/233/15
- Title:
- ND_2_ rotational spectrum
- Short Name:
- J/ApJS/233/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The deuteration mechanism of molecules in the interstellar medium is still being debated. Observations of deuterium-bearing species in several astronomical sources represent a powerful tool to improve our understanding of the interstellar chemistry. The doubly deuterated form of the astrophysically interesting amidogen radical could be a target of detection in space. In this work, the rotational spectrum of the ND_2_ radical in its ground vibrational and electronic X^2^B_1_ state has been investigated between 588 and 1131GHz using a frequency modulation millimeter/submillimeter-wave spectrometer. The ND_2_ molecule has been produced in a free-space glass absorption cell by discharging a mixture of ND_3_ and Ar. Sixty-four new transition frequencies involving J values from 2 to 5 and K_a_ values from 0 to 4 have been measured. A global analysis including all the previous field-free pure rotational data has been performed, allowing for a more precise determination of a very large number of spectroscopic parameters. Accurate predictions of rotational transition frequencies of ND_2_ are now available from a few gigahertz up to several terahertz.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A133
- Title:
- New APEX-SEPIA660 observations in OMC-1
- Short Name:
- J/A+A/644/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The star-formation rates and stellar densities found in young massive clusters suggest that these stellar systems originate from gas at densities of n(H_2_)>10^6^cm^-3^. Until today, however, the physical characterization of this ultra high density material remains largely unconstrained in observations. We investigate the density properties of the star-forming gas in the OMC-1 region located in the vicinity of the Orion Nebula Cluster (ONC). Methods. We mapped the molecular emission at 652GHz in OMC-1 as part of the APEX-SEPIA660 Early Science. We detect bright and extended N_2_H^+^ (J=7-6) line emission along the entire OMC-1 region. Comparisons with previous ALMA data of the (J=1-0) transition and radiative transfer models indicate that the line intensities observed in this N_2_H^+^ (7-6) line are produced by large mass reservoirs of gas at densities n(H_2_)>10^7^cm^-3^. The first detection of this N_2_H^+^ (7-6) line at parsec-scales demonstrates the extreme density conditions of the star-forming gas in young massive clusters such as the ONC. Our results highlight the unique combination of sensitivity and mapping capabilities of the new SEPIA660 receiver for the study of the ISM properties at high frequencies.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A151
- Title:
- NGC 7213 central region molecular gas
- Short Name:
- J/A+A/641/A151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multi-wavelength study (from X-ray to mm) of the nearby low-luminosity active galactic nucleus (LLAGN) NGC 7213. We combine the information from the different bands to characterise the source in terms of contribution from the AGN and the host-galaxy interstellar medium (ISM). This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2-1) emission line has been used as a tracer of the molecular gas. Using the 3DBarolo code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2-1) emission, finding a rotationally dominated pattern. The molecular gas mass of the host galaxy was estimated from the integrated CO(2-1) emission line obtained with APEX data, assuming an alpha_co conversion factor. Had we used the ALMA data, we would have underestimated the gas masses by a factor ~3, given the filtering out of the large-scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN proved to be too faint to significantly affect the properties of the host galaxy, such as star formation activity and molecular gas kinematics and distribution.
