Electron Excitation Collision Strengths for Singly Ionized Nitrogen

Tayal, S. S.

doi:10.1088/0067-0049/195/2/12

Cited by 116 publications

(61 citation statements)

References 17 publications

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“…As it has been proven by Mesa-Delgado et al (2008, 2009, 2011) the presence of localized high-velocity flows and/or high density gas -with higher surface brightness -in the line of sight of the observed aperture can produce higher values of the ADF(O 2+ ). In any case, although the local effects may be affecting the position of some Galactic objects in Fig.…”

Section: Adf(o 2+mentioning

confidence: 61%

Carbon and oxygen in H ii regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

Cipriano

Domínguez-Guzmán

Esteban

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present C and O abundances in the Magellanic Clouds derived from deep spectra of H ii regions. The data have been taken with the Ultraviolet-Visual Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 H ii regions in the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We measure pure recombination lines (RLs) of C ii and O ii in all the objects, permitting to derive the abundance discrepancy factors (ADFs) for O 2+ , as well as their O/H, C/H and C/O ratios. We compare the ADFs with those of other H ii regions in different galaxies. The results suggest a possible metallicity dependence of the ADF for the low-metallicity objects; but more uncertain for high-metallicity objects. We compare nebular and Btype stellar abundances and we find that the stellar abundances agree better with the nebular ones derived from collisionally excited lines (CELs). Comparing these results with other galaxies we observe that stellar abundances seem to agree better with the nebular ones derived from CELs in low-metallicity environments and from RLs in high-metallicity environments. The C/H, O/H and C/O ratios show almost flat radial gradients, in contrast with the spiral galaxies where such gradients are negative. We explore the chemical evolution analysing C/O vs. O/H and comparing with the results of H ii regions in other galaxies. The LMC seems to show a similar chemical evolution to the external zones of small spiral galaxies and the SMC behaves as a typical star-forming dwarf galaxy.

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Section: Adf(o 2+mentioning

confidence: 61%

Carbon and oxygen in H ii regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

Cipriano

Domínguez-Guzmán

Esteban

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Nevertheless, the observed scatter is insufficient to explain the significant observed trend of [C II]/[N II] with metallicity. We combine the C/N ratio as a function of O/H with the collision strengths of Tayal (2011) Figure 4. The expected evolution of the C/N ratio with changing oxygen abundance produces a much flatter correlation than is observed.…”

Section: Resultsmentioning

confidence: 99%

The Origins of [C ii] Emission in Local Star-forming Galaxies

Croxall

Smith

Pellegrini

et al. 2017

ApJ

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The [C II] 158 μm fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C II] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C II] emission remains unclear because C + can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C II] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N II] 205 μm fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of emission originates from neutral gas. We find that the fraction of [C II] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C II] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.

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“…Tayal (2011), this translates to an upper limit to the electron density of n 20 e  cm −3 since this is approximately the [N II] 122 μm/205 μm ratio diagnostic lower density limit. In other words, our measurements are consistent with a relatively low density for the ionized material, somewhat lower than the mean ionized gas density observed in the KINGFISH sample of galaxy disks of n 30 .2, mostly independent of density owing to the similarity in the critical densities (Tayal 2008(Tayal , 2011. Because the [N II] emission can only arise from ionized gas, the fact that we measure over ∼20 times fainter [N II] relative to [C II] suggests that the contribution of ionized gas to [C II] is at most 5%.…”

Section: [N Ii] and Contribution From Ionized Gasmentioning

confidence: 99%

First Results from the Herschel and ALMA Spectroscopic Surveys of the SMC: The Relationship between [C ii]-bright Gas and CO-bright Gas at Low Metallicity*

Jameson

Bolatto

Wolfire

et al. 2018

ApJ

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The Small Magellanic Cloud (SMC) provides the only laboratory to study the structure of molecular gas at high resolution and low metallicity. We present results from the Herschel Spectroscopic Survey of the SMC (HS   ( 3 < pc) scales. We estimate A V using far-IR thermal continuum emission from dust and find that the CO/[C II] ratios reach the Milky Way value at high A V in the centers of the clouds and fall to 1 5 1 10-the Milky Way value in the outskirts, indicating the presence of translucent molecular gas not traced by bright CO 12 emission. We estimate the amount of molecular gas traced by bright [C II] emission at low A V and bright CO 12 emission at high A V . We find that most of the molecular gas is at low A V and traced by bright [C II] emission, but that faint CO 12 emission appears to extend to where we estimate that the H 2 -to-H I transition occurs. By converting our H 2 gas estimates to a CO-to-H 2 conversion factor (X CO ), we show that X CO is primarily a function of A V , consistent with simulations and models of low-metallicity molecular clouds.

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Electron Excitation Collision Strengths for Singly Ionized Nitrogen

Cited by 116 publications

References 17 publications

Carbon and oxygen in H ii regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

Carbon and oxygen in H ii regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

The Origins of [C ii] Emission in Local Star-forming Galaxies

First Results from the Herschel and ALMA Spectroscopic Surveys of the SMC: The Relationship between [C ii]-bright Gas and CO-bright Gas at Low Metallicity*

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