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Start Over Subject molecular physics Content Level Research
1. ALMA astrochemical obs. of the merger NGC 3256
ID:
ivo://CDS.VizieR/J/ApJ/855/49
Title:
ALMA astrochemical obs. of the merger NGC 3256
Short Name:
J/ApJ/855/49
Date:
21 Oct 2021
Publisher:
CDS
Description:
In external galaxies, molecular composition may be influenced by extreme environments such as starbursts and galaxy mergers. To study such molecular chemistry, we observed the luminous infrared galaxy and merger NGC 3256 using the Atacama Large Millimeter/submillimeter Array. We covered most of the 3 and 1.3mm bands for a multispecies, multitransition analysis. We first analyzed intensity ratio maps of selected lines such as HCN/HCO^+^, which shows no enhancement at an active galactic nucleus. We then compared the chemical compositions within NGC 3256 at the two nuclei, tidal arms, and positions with influence from galactic outflows. We found the largest variation in SiO and CH_3_OH, species that are likely to be enhanced by shocks. Next, we compared the chemical compositions in the nuclei of NGC 3256, NGC 253, and Arp 220; these galactic nuclei have varying star formation efficiencies. Arp 220 shows higher abundances of SiO and HC_3_N than NGC 3256 and NGC 253. Abundances of most species do not show a strong correlation with star formation efficiencies, although the CH_3_CCH abundance seems to have a weak positive correlation with the star formation efficiency. Lastly, the chemistry of spiral arm positions in NGC 3256 is compared with that of W51, a Galactic molecular cloud complex in a spiral arm. We found higher fractional abundances of shock tracers, and possibly also a higher dense gas fraction in NGC 3256 compared with W51.
2. ALMA data for 5 luminous & ultraluminous IR gal.
ID:
ivo://CDS.VizieR/J/ApJ/882/5
Title:
ALMA data for 5 luminous & ultraluminous IR gal.
Short Name:
J/ApJ/882/5
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array for five luminous or ultraluminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to 1.74_-0.07_^+0.09^ for gas surface densities {Sigma}_mol_>10^3^M_{sun}_/pc^2^ and an assumed constant CO-to-H2 conversion factor. The velocity dispersion of the CO line, {sigma}_v_, scales approximately as the inverse square root of {Sigma}_mol_, making the empirical gas scale height determined from H~0.5{sigma}^2^/({pi}G{Sigma}_mol_) nearly constant, 150-190pc, over 1.5 orders of magnitude in {Sigma}_mol_. This constancy of H implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which in turn implies that the gas dynamical rate (the inverse of the freefall time) varies with {Sigma}_mol_^1/2^, thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per freefall time is roughly constant, 5%-7%, and the gas depletion time decreases at high {Sigma}_mol_, reaching only ~16Myr at {Sigma}_mol_~10^4^M_{sun}_/pc^2^. The variation of {sigma}_v_ with {Sigma}_mol_ and the constancy of H are in tension with some feedback-driven models, which predict {sigma}_v_ to be more constant and H to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre Q instability parameter.
3. ALMA obs. of ethyl formate toward Orion KL
ID:
ivo://CDS.VizieR/J/ApJ/871/251
Title:
ALMA obs. of ethyl formate toward Orion KL
Short Name:
J/ApJ/871/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies. We wish to explore more organic molecules with increasing complexity in this region. In particular, we have searched for one of the most complex organic molecules detected in space so far, ethyl formate (C_2_H_5_OCHO). This species is the next step in chemical complexity after the simplest member of esters (methyl formate, CH_3_OCHO). The mechanisms leading to its formation are still poorly known. We have used high angular resolution (~1.5") ALMA observations covering a large bandwidth from 214 to 247GHz. We have detected 82 unblended lines of C_2_H_5_OCHO (49 and 33 of the trans- and gauche- conformers, respectively). The line images showed that C2H5OCHO arises mainly from the compact ridge and the hot core-southwest regions. The derived rotational temperatures and column densities are 122+/-34K, (0.9+/-0.3)x10^16^cm^-2^ for the hot core-SW, and 103+/-13K, (0.6+/-0.3)x10^16^cm^-2^ for the compact ridge. The comparison of spatial distribution and abundance ratios with chemically related molecules (methyl formate, ethanol, and formic acid) indicates that C_2_H_5_OCHO is likely formed on the surface of dust grains by addition of CH_3_ to functional-group radicals (CH_2_OCHO) derived from methyl formate (CH_3_OCHO).
4. ALMA obs. of star-forming regions toward NGC6334I
ID:
ivo://CDS.VizieR/J/ApJ/883/129
Title:
ALMA obs. of star-forming regions toward NGC6334I
Short Name:
J/ApJ/883/129
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relative column densities of the structural isomers methyl formate, glycolaldehyde, and acetic acid are derived for a dozen positions toward the massive star-forming regions MM1 and MM2 in the NGC 6334I complex, which are separated by ~4000au. Relative column densities of these molecules are also gathered from the literature for 13 other star-forming regions. In this combined data set, a clear bimodal distribution is observed in the relative column densities of glycolaldehyde and methyl formate. No such distribution is evident with acetic acid. The two trends are comprised of star-forming regions with a variety of masses, suggesting that there must be some other common parameter that is heavily impacting the formation of glycolaldehyde. This is indicative of some demonstrable differentiation in these cores; studying the abundances of these isomers may provide a clue as to the integral chemical processes ongoing in a variety of protostellar environments.
5. A^1^{Pi}-X^1^{Sigma}^+^ transitions of CO study
ID:
ivo://CDS.VizieR/J/ApJ/859/19
Title:
A^1^{Pi}-X^1^{Sigma}^+^ transitions of CO study
Short Name:
J/ApJ/859/19
Date:
21 Oct 2021
Publisher:
CDS
Description:
Highly correlated ab initio calculations were performed for an accurate determination of the A^1^{Pi}-X^1^{Sigma}^+^ system of the CO molecule. A highly accurate multi-reference configuration interaction approach was used to investigate the potential energy curves (PECs) and the transition dipole moment curve (TDMC). The resultant PECs and TDMC found by using the aug-cc-pV5Z (aV5Z) basis set and 5330 active spaces are in good agreement with the experimental data. Moreover, the Einstein A coefficients, lifetimes, ro-vibrational intensities, absorption oscillator strengths, and integrated cross sections are calculated so that the vibrational bands include v"=0-39 -> v'=0-23. For applications in the atmosphere and interstellar clouds, we studied the transition lineshapes to Gaussian and Lorentzian profiles at different temperatures and pressures. The intensities were calculated at high temperature that was used to satisfy some astrophysical applications, such as in planetary atmospheres. The results are potentially useful for important SAO/NASA Astrophysics Data System and databases such as HITRAN, HITEMP, and the National Institute of Standards and Technology. Because the results from many laboratory techniques and our calculations now agree, analyses of interstellar CO based on absorption from A^1^{Pi}-X^1^{Sigma}^+^ are no longer hindered by present spectral parameters.
6. Astrochemical study along M83 circumnuclear ring
ID:
ivo://CDS.VizieR/J/ApJ/884/100
Title:
Astrochemical study along M83 circumnuclear ring
Short Name:
J/ApJ/884/100
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report an astrochemical study on the evolution of interstellar molecular clouds and consequent star formation in the center of the barred spiral galaxy M83. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to image molecular species indicative of shocks (SiO and CH_3_OH), dense cores (N_2_H^+^), and photodissociation regions (CN and CCH), as well as a radio recombination line (H41{alpha}) tracing active star-forming regions. M83 has a circumnuclear gas ring that is joined at two intersections by gas streams from the leading- edge gas lanes on the bar. We found elevated abundances of the shock and dense-core tracers in one of the orbit-intersecting areas, and found peaks of CN and H41{alpha} downstream. In the other orbit-intersection area, we found a similar enhancement of the shock tracers, but less variation of other tracers, and no sign of active star formation in the stream. We propose that the observed chemical variation or lack of it is due to the presence or absence of collision-induced evolution of molecular clouds and induced star formation. This work presents the clearest case of the chemical evolution in the circumnuclear rings of barred galaxies thanks to the ALMA resolution and sensitivity.
7. ATLASGAL dense clumps Molecular parameters
ID:
ivo://CDS.VizieR/J/MNRAS/484/4444
Title:
ATLASGAL dense clumps Molecular parameters
Short Name:
J/MNRAS/484/4444
Date:
10 Dec 2021 00:02:11
Publisher:
CDS
Description:
We have conducted a 3-mm molecular-line survey towards 570 high-mass star-forming clumps, using the Mopra telescope. The sample is selected from the 10000 clumps identified by the ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey and includes all of the most important embedded evolutionary stages associated with massive star formation, classified into five distinct categories (quiescent, protostellar, young stellar objects, HII regions, and photon-dominated regions). The observations were performed in broad-band mode with frequency coverage of 85.2-93.4GHz and a velocity resolution of ~0.9km/s, detecting emission from 26 different transitions. We find significant evolutionary trends in the detection rates, integrated line intensities, and abundances of many of the transitions and also identify a couple of molecules that appear to be invariant to changes in the dust temperature and evolutionary stage [N_2_H^+^ (1-0) and HN^13^C (1-0)]. We use the K-ladders for CH_3_C_2_H (5-4) and CH_3_CH (5-4) to calculate the rotation temperatures and find around one-third of the quiescent clumps have rotation temperatures that suggest the presence of an internal heating source. These sources may constitute a population of very young protostellar objects that are still dark at 70um and suggest that the fraction of truly quiescent clumps may only be a few per cent. We also identify a number of line ratios that show a strong correlation with the evolutionary stage of the embedded objects and discuss their utility as diagnostic probes of evolution.
8. BAT AGN Spectroscopic Survey. XX. Molecular gas
ID:
ivo://CDS.VizieR/J/ApJS/252/29
Title:
BAT AGN Spectroscopic Survey. XX. Molecular gas
Short Name:
J/ApJS/252/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the host-galaxy molecular gas properties of a sample of 213 nearby (0.01<z<0.05) hard-X-ray-selected active galactic nucleus (AGN) galaxies, drawn from the 70-month catalog of Swift's Burst Alert Telescope (BAT), with 200 new CO(2-1) line measurements obtained with the James Clerk Maxwell Telescope and the Atacama Pathfinder Experiment telescope. We find that AGN in massive galaxies (log(M_*_/M_{sun}_)>10.5) tend to have more molecular gas and higher gas fractions than inactive galaxies matched in stellar mass. When matched in star formation, we find AGN galaxies show no difference from inactive galaxies, with no evidence that AGN feedback affects the molecular gas. The higher molecular gas content is related to AGN galaxies hosting a population of gas-rich early types with an order of magnitude more molecular gas and a smaller fraction of quenched, passive galaxies (~5% versus 49%) compared to inactive galaxies. The likelihood of a given galaxy hosting an AGN (L_bol_>10^44^erg/s) increases by ~10-100 between a molecular gas mass of 10^8.7^M_{sun}_ and 10^10.2^M_{sun}_. AGN galaxies with a higher Eddington ratio (log(L/L_Edd_)>-1.3) tend to have higher molecular gas masses and gas fractions. The log(NH/cm^-2^)>23.4) of AGN galaxies with higher column densities are associated with lower depletion timescales and may prefer hosts with more gas centrally concentrated in the bulge that may be more prone to quenching than galaxy-wide molecular gas. The significant average link of host-galaxy molecular gas supply to supermassive black hole (SMBH) growth may naturally lead to the general correlations found between SMBHs and their host galaxies, such as the correlations between SMBH mass and bulge properties, and the redshift evolution of star formation and SMBH growth.
9. CH_3_OCH_2_OH ALMA detection in NGC 6334I
ID:
ivo://CDS.VizieR/J/ApJ/851/L46
Title:
CH_3_OCH_2_OH ALMA detection in NGC 6334I
Short Name:
J/ApJ/851/L46
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the detection of interstellar methoxymethanol (CH_3_OCH_2_OH) in Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ~0.1-1" spatial resolution. A column density of 4(2)x10^18^cm^-2^ at T_ex_=200K is derived toward MM1, ~34 times less abundant than methanol (CH_3_OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH_3_OH photodissociation products, the methoxy (CH_3_O) and hydroxymethyl (CH_2_OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase versus grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH3OH rather than photodissociation.
10. Cloud-scale molecular gas properties in 15 galaxies
ID:
ivo://CDS.VizieR/J/ApJ/860/172
Title:
Cloud-scale molecular gas properties in 15 galaxies
Short Name:
J/ApJ/860/172
Date:
21 Oct 2021
Publisher:
CDS
Description:
We measure the velocity dispersion, {sigma}, and surface density, {Sigma}, of the molecular gas in nearby galaxies from CO spectral line cubes with spatial resolution 45-120pc, matched to the size of individual giant molecular clouds. Combining 11 galaxies from the PHANGS-ALMA survey with four targets from the literature, we characterize ~30000 independent sightlines where CO is detected at good significance. {Sigma} and {sigma} show a strong positive correlation, with the best-fit power-law slope close to the expected value for resolved, self-gravitating clouds. This indicates only a weak variation in the virial parameter {alpha}_vir_{propto}{sigma}^2^/{Sigma}, which is ~1.5-3.0 for most galaxies. We do, however, observe enormous variation in the internal turbulent pressure P_turb_{propto}{Sigma}{sigma}^2^, which spans ~5dex across our sample. We find {Sigma}, {sigma}, and P_turb_ to be systematically larger in more massive galaxies. The same quantities appear enhanced in the central kiloparsec of strongly barred galaxies relative to their disks. Based on sensitive maps of M31 and M33, the slope of the {sigma}-{Sigma} relation flattens at {Sigma}<~10M_{sun}_/pc^2^, leading to high {sigma} for a given {Sigma} and high apparent {alpha}_vir_. This echoes results found in the Milky Way and likely originates from a combination of lower beam-filling factors and a stronger influence of local environment on the dynamical state of molecular gas in the low-density regime.

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