A chemical study of carbon fractionation in external galaxies

Viti, S.; Fontani, F.; Jiménez-Serra, Izaskun

doi:10.1093/mnras/staa2215

Cited by 14 publications

(14 citation statements)

References 54 publications

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“…The 12 C/ 13 C ratios obtained in NGC 253 in the literature are 21 ± 6 (Martín et al 2019b) from C 18 O/ 13 C 18 O, which is close to our obtained values. However, note that the 12 C/ 13 C ratio can also depend on the species because of fractionation (Colzi et al 2020;Viti et al 2020).…”

Section: Column Densities and Ratiosmentioning

confidence: 99%

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Harada

Martín

Mangum

et al. 2021

ApJ

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Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1−0) integrated intensity shows its association with “superbubbles,” cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10–150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10−11–6 × 10−10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ≳ 103 if the maximum visual extinction is ≳5, or a cosmic-ray ionization rate of ζ ≳ 10−14 s−1 (3–4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.

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Section: Column Densities and Ratiosmentioning

confidence: 99%

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Harada

Martín

Mangum

et al. 2021

ApJ

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“…In particular, Viti et al (2011), and later Benedettini et al (2013), found that at least some of the species observed in B1 were likely the product of a non-dissociative, C-type shock with pre-shock density n(H) ≥ 10 5 cm −3 and shock velocity V s ∼ 40 km s −1 . In this section, we use their same (updated) chemical and shock time dependent gas-grain model, UCLCHEM (Holdship et al 2017), augmented with the nitrogen and carbon isotopologues chemistry (Viti et al 2019(Viti et al , 2020, to determine whether, theoretically, we should expect the passage of a shock to affect the nitrogen fractionation in L1157-B1. Full details of the chemical and shock model UCLCHEM can be found in the references above.…”

Section: Models Of Nitrogen Fractionation In Shocksmentioning

confidence: 99%

Seeds of Life in Space (SOLIS)

Benedettini

Viti

Codella

et al. 2021

A&A

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Context. The isotopic ratio of nitrogen presents a wide range of values in the Solar System: from ~140 in meteorites and comets to 441 in the solar wind. In star-forming systems, we observe even a higher spread of ~150–1000. The origin of these differences is still unclear. Aims. Chemical reactions in the gas phase are one of the possible processes that could modify the 14N/15N ratio. We aim to investigate if and how the passage of a shock wave in the interstellar medium, which activates a rich chemistry, can affect the relative fraction of nitrogen isotopes. The ideal place for such a study is the chemically rich outflow powered by the L1157-mm protostar, where several shocked clumps are present. Methods. We present the first measurement of the 14N/15N ratio in the two shocked clumps, B1 and B0, of the protostellar outflow L1157. The measurement is derived from the interferometeric maps of the H13CN (1–0) and the HC15N (1–0) lines obtained with the NOrthern Extended Millimeter Array (NOEMA) interferometer as part of the Seeds of Life in Space (SOLIS) programme. Results. In B1, we find that the H13CN (1–0) and HC15N (1–0) emission traces the front of the clump, that is the apex of the shocked region, where the fast jet impacts the lower velocity medium with an averaged column density of N(H13CN) ~ 7 × 1012 cm−2 and N(HC15N) ~ 2 × 1012 cm−2. In this region, the ratio H13CN (1–0)/HC15N (1–0) is almost uniform with an average value of ~5 ± 1. The same average value is also measured in the smaller clump B0e. Assuming the standard 12C/13C = 68, we obtain 14N/15N = 340 ± 70. This ratio is similar to those usually found with the same species in prestellar cores and protostars. We analysed the prediction of a chemical shock model for several shock conditions and we found that the nitrogen and carbon fractionations do not vary much for the first period after the shock. The observed H13CN/HC15N can be reproduced by a non-dissociative, C-type shock with pre-shock density n(H) = 105 cm−3, shock velocity Vs between 20 and 40 km s−1, and cosmic-ray ionization rate of 3 × 10−16 s−1; this agrees with previous modelling of other chemical species in L1157-B1. Conclusions. Both observations and chemical models indicate that the rich chemistry activated by the shock propagation does not affect the nitrogen isotopic ratio, which remains similar to that measured in lower temperature gas in prestellar cores and protostellar envelopes.

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“…We further note that the center of NGC 7465 does not exhibit particularly unusual levels of photodissociation in general, as its [C II]/CO line ratio is typical for nearby spiral galaxies (Figure 14). Finally, Viti et al (2020) argue that fractionation is unlikely to be a significant effect for the CO isotopologues in typical conditions, though it may be more important for other molecular species.…”

Section: Csmentioning

confidence: 94%

The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

Young

Meier

Bureau

et al. 2021

ApJ

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We present ALMA observations of CO isotopologues and high-density molecular tracers (HCN, HCO+, CN, etc.) in NGC 7465, an unusually gas-rich early-type galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular gas kinematics are misaligned with respect to all other galaxy components; as the gas works its way inward, it is torqued into polar orbits about the stellar kinematically decoupled core (KDC), indicating that the stellar KDC is not related to the current gas accretion event. The galaxy also exhibits unusually high 12CO/13CO line ratios in its nucleus but typical 13CO/C18O ratios. Our calculations show that this result does not necessarily indicate an unusual [12CO/13CO] abundance ratio but rather that 12CO (1–0) is optically thin due to high temperatures and/or large line widths associated with the inner decoupled, misaligned molecular structure. Line ratios of the higher-density tracers suggest that the densest phase of molecular gas in NGC 7465 has a lower density than is typical for nearby galaxies, possibly as a result of the recent gas accretion. All of the observed molecular properties of NGC 7465 are consistent with it having acquired its molecular (and atomic) gas from a spiral galaxy. Further detailed studies of the CO isotopologues in other early-type galaxies would be valuable for investigating the histories of those that may have acquired their gas from dwarfs. Finally, these ALMA data also show an unidentified line source that is probably a background galaxy similar to those found at z = 1–3 in blind CO surveys.

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A chemical study of carbon fractionation in external galaxies

Cited by 14 publications

References 54 publications

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Seeds of Life in Space (SOLIS)

The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

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A chemical study of carbon fractionation in external galaxies

Cited by 14 publications

References 54 publications

Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI

Seeds of Life in Space (SOLIS)

The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

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Product

Resources

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Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI