Nitrogen fractionation in external galaxies

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

doi:10.1093/mnras/stz1172

Cited by 12 publications

(5 citation statements)

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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%

“…In the gas phase, isotope exchange reactions at low temperatures (Roueff et al 2015) and/or isotope-selective photodissociation of N 2 (Heays et al 2014;Furuya & Aikawa 2018) seem to be the more promising processes. A recent paper by Viti et al (2019), which includes up-to-date chemical networks for 14 N and 15 N isotopic species, found that 14 N/ 15 N in HCN, HNC, and CN can vary by about an order of magnitude with time causing a possible spread in the range from ∼100 to ∼1000. In addition, an increase in the nitrogen fractionation in the ISM can be obtained in high gas densities aided by high fluxes of cosmic rays.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Models Of Nitrogen Fractionation In Shocksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seeds of Life in Space (SOLIS)

Benedettini

Viti

Codella

et al. 2021

A&A

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“…For the abundance ratios 12/13 C = [ 12 C]/[ 13 C], 14/15 N = [ 14 N]/[ 15 N] and 16/18 O = [ 16 O]/[ 18 O] we turn to the literature to break the degeneracy of optical depth and abundance ratio. We adopt 12/13 C = 40 ± 20 (among nearby galaxies including NGC 253, Henkel et al 2014;Martin et al 2010Martin et al , 2019Tang et al 2019), 14/15 N = 200 ± 1 dex (Viti et al 2019, and references therein, see table 1 for an overview) and 16/18 O = 130 ± 40 (NGC 253; Martin et al 2019).…”

Section: Isotopic Ratios and Optical Depthmentioning

confidence: 99%

The Molecular ISM in the Super Star Clusters of the Starburst NGC 253

Krieger,

Bolatto,

Leroy

et al. 2020

Preprint

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We present submillimeter spectra of the (proto-)super star cluster (SSC) candidates in the starbursting center of the nearby galaxy NGC 253 identified by Leroy et al. (2018). The 2.5 pc resolution of our ALMA cycle 3 observations approach the size of the SSCs and allows the study of physical and chemical properties of the molecular gas in these sources. In the 14 SSC sources and in the frequency ranges 342.0 − 345.8 GHz and 353.9 − 357.7 GHz we detect 55 lines belonging to 19 different chemical species. The SSCs differ significantly in chemical complexity, with the richest clusters showing 19 species and the least complex showing 4 species. We detect HCN isotopologues and isomers (H 13 CN, HC 15 N, H 15 NC), abundant HC 3 N, SO and S 18 O, SO 2 , and H 2 CS. The gas ratios CO/HCN, CO/HCO + are low, ∼ 1 − 10, implying high dense gas fractions in the SSCs. Line ratio analyses suggests chemistry consistent with photon-dominated regions and mechanical heating. None of the SSCs near the galaxy center show line ratios that imply an X-ray dominated region, suggesting that heating by any (still unknown) AGN does not play a major role. The gas temperatures are high in most sources, with an average rotational temperature of ∼ 130 K in SO 2 . The widespread existence of vibrationally excited HCN and HC 3 N transitions implies strong IR radiation fields, potentially trapped by a greenhouse effect due to high continuum opacities.

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“…The new models also rule out significant nitrogen fractionation processes in the most abundant molecules during the chemical evolution of a star-forming core. In fact, significant variations in nitrogen fractionation are theoretically predicted only in extragalactic environments strongly affected by very high fluxes of cosmic rays (Viti et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Solis

Evans

Fontani

Vastel

et al. 2022

A&A

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Context. Isotopic fractionation is an important tool for investigating the chemical history of our Solar System. In particular, the isotopic fraction of nitrogen (14N/15N) is lower in comets and other pristine Solar System bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of 15N during the formation of the Solar System. Therefore, interferometric studies of nitrogen fractionation in Solar System precursors are needed for us to obtain clues about our astrochemical origins. Aims. In this work we have investigated the variation in the 14N/15N ratio in one of the closest analogues of the environment in which the Solar System was born: the protocluster OMC-2 FIR4. We present the first comparison at high angular resolution between HCN and N2H+ using interferometric data. Methods. We analysed observations of the HCN isotopologues H13CN and HC15N in the OMC-2 FIR4 protocluster. Specifically, we observed the transitions H13CN (1−0) and HC15N (1−0) with the NOrthern Extended Millimeter Array (NOEMA) within the context of the IRAM Seeds Of Life In Space (SOLIS) Large Program. We combined our results with analysis of archival data obtained with the Atacama Large Millimeter Array of N2H+ and its 15N isotopologues. Results. Our results show a small regional variation in the 14N/15N ratio for HCN, from ~250 to 500. The ratios in the central regions of FIR4, where the candidate protostars are located, are largely consistent with one another and within that range (~300). They also show little variation from the part of the protocluster known to harbour a high cosmic-ray ionisation rate to the portion with a lower rate. We also found a small variation in the 14N/15N ratio of N2H+ across different regions, from ~200 to ~400. Conclusions. These results suggest that local changes in the physical parameters occurring on the small linear scales probed by our observations in the protocluster do not seem to affect the 14N/15N ratio in either HCN or N2H+ and hence that this is independent of the molecule used. Moreover, the high level of irradiation due to cosmic rays does not affect the N fractionation either.

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Nitrogen fractionation in external galaxies

Cited by 12 publications

References 50 publications

Seeds of Life in Space (SOLIS)

Seeds of Life in Space (SOLIS)

The Molecular ISM in the Super Star Clusters of the Starburst NGC 253

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