A large 12C/13C isotopic ratio in M82 and NGC253

J. Martin-Pintado; R. Aladro; R. Mauersberger; Sergio Martin

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A large 12C/13C isotopic ratio in M82 and NGC253

Sergio Martin, R. Aladro, J. Martin-Pintado, R. Mauersberger

Cosmology and Nongalactic Astrophysics · Submitted 28 Jun 2010

abstract compiled · 2026-09-23 · no language-model review

The authors' main claim The large 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.

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What the abstract itself states, as probabilities: claims first 0.65 · states limitation 0.77 · human participants 0.01 · controlled comparison 0.13 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.96 · mentions code or data availability 0.02.

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To derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M82 and NGC253. We present high sensitivity observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well as the optically thin emission from C18O and 13C18O. We assume the column density ratio between isotopologues is representative of the 12C13C isotopic ratio. From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M82, and 81 in NGC253, are derived. Lower limits to the 12C/13C ratios from CO isotopologues support these. 13C18O is tentatively detected in NGC253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16O/18O>350 and >300 in M82 and NGC253, respectively, and 32S/34S>16 in NGC253. and the H2 column density determination through the optically thin tracers 13CO and C18O. The derived CCH fractional abundances toward these galaxies of <~1.1\times10^-8 are in good agreement with those of molecular clouds in the Galactic disk. Our lower limits to the 12C/13C ratio from CCH are a factor of 2-3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The large 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.

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What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	To derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M82 and NGC253.	contribution 0.76	0.69	0.03	unclear 0.84
s1	We present high sensitivity observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well as the optically thin emission from C18O and 13C18O.	method 0.77	0.96	0.02	asserted 1.00
s2	We assume the column density ratio between isotopologues is representative of the 12C13C isotopic ratio.	method 0.99	0.32	0.04	asserted 0.84
s3	From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M82, and 81 in NGC253, are derived.	result 1.00	0.96	0.45	asserted 1.00
s4	Lower limits to the 12C/13C ratios from CO isotopologues support these. 13C18O is tentatively detected in NGC253, which is the first reported detection in the extragalactic ISM.	result 1.00	0.94	0.09	asserted 0.74
s5	Based on these limits, we infer ratios of 16O/18O>350 and >300 in M82 and NGC253, respectively, and 32S/34S>16 in NGC253. and the H2 column density determination through the optically thin tracers 13CO and C18O.	result 0.98	0.91	0.11	asserted 0.86
s6	The derived CCH fractional abundances toward these galaxies of <~1.1\times10^-8 are in good agreement with those of molecular clouds in the Galactic disk.	result 0.93	0.94	0.04	asserted 0.91
s7	Our lower limits to the 12C/13C ratio from CCH are a factor of 2-3 larger than previous limits.	result 0.93	0.89	0.11	asserted 1.00
s8	The results are discussed in the context of molecular and nucleo-chemical evolution.	interpretation 0.90	0.31	0.04	unclear 0.72
s9	The large 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.	interpretation 1.00	0.74	0.80	hedged possibility 0.99

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 1.00.

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Original abstract

To derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M82 and NGC253. We present high sensitivity observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well as the optically thin emission from C18O and 13C18O. We assume the column density ratio between isotopologues is representative of the 12C13C isotopic ratio. From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M82, and 81 in NGC253, are derived. Lower limits to the 12C/13C ratios from CO isotopologues support these. 13C18O is tentatively detected in NGC253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16O/18O>350 and >300 in M82 and NGC253, respectively, and 32S/34S>16 in NGC253. and the H2 column density determination through the optically thin tracers 13CO and C18O. The derived CCH fractional abundances toward these galaxies of <~1.1\times10^-8 are in good agreement with those of molecular clouds in the Galactic disk. Our lower limits to the 12C/13C ratio from CCH are a factor of 2-3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The large 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.

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Assumptions used here are that the lines are optically thin and from gas in LTE at 50 K and that the molecular abundances are [/]=$10^-4$, [/]$≈$80, and [/]$≈$300; the latter two are from the lower limits in the center of NGC 253 obtained by [ref] .

Star-forming Cloud Complexes in the Central Molecular Zone of NGC 253 · Gas Column Density, Mass, and CO Opacity · 0.96

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