J/A+A/686/A252 APEX spectra of 4 IR quiet massive clumps (Bouscasse+, 2024)
Complex organic molecules uncover deeply embedded precursors of hot cores.
An APEX unbiased spectral survey of infrared quiet massive clumps.
Bouscasse L., Csengeri T., Wyrowski F., Menten K.M., Bontemps S.
<Astron. Astrophys. 686, A252 (2024)>
=2024A&A...686A.252B 2024A&A...686A.252B (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; Interstellar medium ; Spectra, infrared
Keywords: stars: formation - stars: massive - stars: protostars -
ISM: abundances - ISM: lines and bands - ISM: molecules
Abstract:
During the process of star formation, the dense gas undergoes
significant chemical evolution leading to the emergence of a rich
variety of molecules associated with hot cores and hot corinos.
However, the physical conditions and the chemical processes involved
in this evolution are poorly constrained. In particular, the early
phases, corresponding to a stage prior to the emergence of any strong
ionising emission from the protostar, are still poorly studied.
In this work, we provide a full inventory of the emission from complex
organic molecules (COMs) to investigate the physical structure and
chemical composition of six high-mass protostellar envelopes. We aim
to investigate the conditions for the emergence of COMs in hot cores.
We performed an unbiased spectral survey towards six infrared-quiet
massive clumps between 159GHz and 374GHz with the APEX 12m telescope,
covering the entire atmospheric windows at 2mm, 1.2mm, and 0.8mm. To
identify the spectral lines, we used rotational diagrams and radiative
transfer modelling assuming local thermodynamic equilibrium.
We detect up to 11 COMs plus three isotopologues, of which at least
five COMs (CH3OH, CH3CN, CH3OCHO, CH3OCH3, and CH3CHO) are
detected towards all sources. Towards all the objects, most of the COM
emission is found to be cold, with respect to the typical temperatures
at which COMs are found, with a temperature of 30K and extended with a
size of ∼0.3pc. Although the bulk of the gas for our sample of young
massive clumps has a cold temperature, we also detect emission from
COMs originating from the immediate vicinity of the protostar. This
warm component of the envelope is best traced by methanol and methyl
cyanide, in particular methyl cyanide traces a compact (∼1") and the
hottest (T∼200K) component of the envelope. Only three out of the six
sources exhibit a robustly detected hot gas component (T>100K) traced
by several COMs. We find a gradual emergence of the warm component in
terms of size and temperature, together with an increasing molecular
complexity, allowing us to establish an evolutionary sequence for our
sample based on COMs. While they can already be well characterised by
an emerging molecular richness, gas temperatures of COMs in the hot
gas and molecular abundances suggest that COMs may become abundant in
the gas phase at temperatures below the thermal desorption
temperature.
Our findings confirm that the sources of our sample of infrared-quiet
massive clumps are in an early evolutionary stage during which the
bulk of the gas is cold. The presence of COMs is found to be
characteristic of these early evolutionary stages accompanying
high-mass star and cluster formation. While the extent of the compact
heated regions resembles that of hot cores, the molecular abundances,
except for complex cyanides, resemble those of hot corinos and are
lower than the peak COM abundances of hot cores. We suggest that the
emergence of hot cores is preceded by a phase in which mostly
O-bearing COMs appear first with similar abundances to hot corinos
albeit with larger source sizes.
Description:
We performed an unbiased spectral survey between 159GHz
and 374GHz with the APEX telescope towards six massive protostellar
objects from the SPARKS survey (Csengeri et al. 2017b) that are
associated with the ATLASGAL clumps G320.2325-0.2844 (G320.23),
G328.2551-0.5321 (G328.25), G333.4659-0.1641 (G333.46),
G335.5857-0.2906 (G335.58), G335.7896+0.1737 (G335.78),
G343.7559-0.1640 (G343.75).
We present here the final spectra of 4 sources.
Objects:
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RA (2000) DE Designation(s)
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16 21 20.09 -50 09 47.7 [CUS2014] G333.4659-0.1641 = AGAL G333.466-00.164
16 30 58.70 -48 43 53.0 [CUS2014] G335.5857-0.2906 = AGAL G335.586-00.291
16 29 47.33 -48 15 52.0 [CUS2014] G335.7896+0.1737 = AGAL G335.789+00.174
17 00 49.83 -42 26 09.3 [CUS2014] G343.7559-0.1640 = AGAL G343.756-00.164
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 134 4 List of fits spectra
fits/* . 4 Individual fits spectra
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 25 I6 --- Nx Number of pixels along X-axis
27- 49 A23 "datime" Obs.date Observation date
51- 62 E12.6 Hz bFREQ Lower value of frequency interval
64- 74 E11.6 Hz BFREQ Upper value of frequency interval
76- 81 I6 Hz dFREQ Frequency resolution
83- 86 I4 Kibyte size Size of FITS file
88-103 A16 --- FileName Name of FITS file, in subdirectory fits
105-134 A30 --- Title Title of the FITS file
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Acknowledgements:
Laure Bouscasse, bouscasse(at)iram.fr
(End) Patricia Vannier [CDS] 12-Jun-2024