Origin and<i>z</i>-distribution of Galactic diffuse [C II] emission

Velusamy, T.; Langer, W. D.

doi:10.1051/0004-6361/201424350

Cited by 34 publications

(23 citation statements)

References 57 publications

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“…We measure the II] are observed at lower metallicity is consistent with observations of dwarf galaxies (Cormier et al 2015). Similarly, these results are also consistent with recent investigations into the origin of Galactic plane emission carried out in [C II] (Pineda et al 2013;Velusamy & Langer 2014) and [N II] (Goldsmith et al 2015) that find 1/3-1/2 of Galactic [C II] emission is associated with ionized gas.…”

Section: Summary and Discussionsupporting

confidence: 92%

“…The difficulty of disentangling the origins of [C II] emission were recently highlighted by Velusamy & Langer (2014) emission primarily originates in molecular gas (∼62%) with the remainder coming from H I gas and the warm ionized medium. Unfortunately, applying this multi-tracer approach to study the origin of C II in distant galaxies is complicated as the spatial resolution of observations is limited, preventing the separation of different spatial components.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Summary and Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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

Croxall

Smith

Pellegrini

et al. 2017

ApJ

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“…However, because [C ii] traces many different gas components, to get the scale heights of the different ISM components it is necessary to separate out the different scale heights by associating the emission coming from CO, H i, and WIM regions. Velusamy & Langer (2014) analyzed the distribution of all the [C ii] emission detected by the GOT C+ survey as a function of z and found that the average scale height for [C ii] (all gas components) is ∼ 170 pc, larger than that for CO, but smaller than that for H i, as might be expected. They found that [C ii] from the WIM and H i combined had a scale height ∼330 pc, larger than H i alone.…”

Section: Z-distributionmentioning

confidence: 63%

“…However, because [C ii] traces many different gas components it is necessary to separate out the different scale heights by determining the C + emission coming from CO, H i, and WIM regions. To separate out the different [C ii] sources, Velusamy & Langer (2014) correlated the intensities in 3 km s −1 wide velocity bins, "spaxels", in each [C ii] velocity profile with the corresponding spaxel intensities in the 12 CO, 13 CO and H i velocity profiles, and found that the [C ii] gaussian scale height for z in the Scutum tangency is smaller than the average value for [C ii] for the disk as a whole. There are a number of possible reasons for the difference.…”

Section: Z-distributionmentioning

confidence: 99%

Ionized gas in the Scutum spiral arm as traced in [N ii] and [C ii]

Langer

Velusamy

Goldsmith

et al. 2017

A&A

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Context. The warm ionized medium (WIM) occupies a significant fraction of the Galactic disk. Determining the WIM properties at the leading edge of spiral arms is important for understanding its dynamics and cloud formation. Aims. To derive the properties of the WIM at the inner edge of the Scutum arm tangency, which is a unique location in which to disentangle the WIM from other components, using the ionized gas tracers C + and N + . Methods. We use high spectral resolution [C ii] 158 µm and [N ii] 205 µm fine structure line observations taken with the upGREAT and GREAT instruments, respectively, on SOFIA, along with auxiliary H i and 13 CO observations. The observations consist of samples in and out of the Galactic plane along 18 lines of sight (LOS) between longitude 30• and 32• . Results. We detect strong [N ii] emission throughout the Scutum tangency. At V LS R = 110 to 125 km s −1 where there is little, if any, 13 CO, we are able to disentangle the [N ii] and [C ii] emission that arises from the WIM at the arm's inner edge. We find an average electron density ∼0.9 cm −3 in the plane, and ∼0.4 cm −3 just above the plane. The [N ii] emission decreases exponentially with latitude with a scale height ∼55 pc. For V LS R <110 km s −1 there is [N ii] emission tracing highly ionized gas throughout the arm's molecular layer. This ionized gas has a high density, n(e) ∼30 cm −3 , and a few percent filling factor. We also find evidence for [C ii] absorption by foreground gas. Conclusions. [N ii] and [C ii]observations at the Scutum arm tangency reveal a highly ionized gas with average electron density about 10 to 20 times those of the interarm WIM, and is best explained by a model in which the interarm WIM is compressed as it falls into the potential well of the arm. The widespread distribution of [N ii] in the molecular layers shows that high density ionized gas is distributed throughout the Scutum arm. The electron densities derived from [N ii] for these molecular cloud regions are ∼30 cm −3 , and probably arise in the ionized boundary layers of clouds. The [N ii] detected in the molecular portion of the spiral arm arises from several cloud components with a combined total depth ∼8 pc. This [N ii] emission most likely arises from ionized boundary layers, probably the result of the shock compression of the WIM as it impacts the arm's neutral gas, as well as from extended H ii regions.

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“…We will show that the X-ray flux can reduce the abundance of C + primarily in highly ionized regions and that, under the right conditions, will reduce the [C ii] emission significantly in galactic nuclei. In the Galactic disk the WIM contributes about 20% to 30% of the [C ii] luminosity (Pineda et al 2013;Velusamy & Langer 2014) using the scale heights derived from [C ii] (Langer et al 2014a;Velusamy & Langer 2014). In the Galactic central molecular zone (CMZ) the WIM densities are much higher and may contribute an even larger percentage of the [C ii] luminosity.…”

Section: Introductionmentioning

confidence: 99%

[C ii] emission from galactic nuclei in the presence of X-rays

Langer

Pineda

2015

A&A

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Context. The luminosity of [C ii] is used as a probe of the star formation rate in galaxies, but the correlation breaks down in some active galactic nuclei (AGNs). Models of the [C ii] emission from galactic nuclei do not include the influence of X-rays on the carbon ionization balance, which may be a factor in reducing the [C ii] luminosity.Aims. We aim to determine the properties of the ionized carbon and its distribution among highly ionized states in the interstellar gas in galactic nuclei under the influence of X-ray sources. We calculate the [C ii] luminosity in galactic nuclei under the influence of bright sources of soft X-rays. Methods. We solve the balance equation of the ionization states of carbon as a function of X-ray flux, electron, atomic hydrogen, and molecular hydrogen density. These are input to models of [C ii] emission from the interstellar medium (ISM) in galactic nuclei representing conditions in the Galactic central molecular zone and a higher density AGN model. The behavior of the [C ii] luminosity is calculated as a function of the X-ray luminosity. We also solve the distribution of the ionization states of oxygen and nitrogen in highly ionized regions. Results. We find that the dense warm ionized medium (WIM) and dense photon dominated regions (PDRs) dominate the [C ii]emission when no X-rays are present. The X-rays in galactic nuclei can affect strongly the C + abundance in the WIM, converting some fraction to C 2+ and higher ionization states and thus reducing its [C ii] luminosity. For an X-ray luminosity L(X-ray) 10 43 erg s −1 the [C ii] luminosity can be suppressed by a factor of a few, and for very strong sources, L(X-ray) >10 44 erg s −1 such as found for many AGNs, the [C ii] luminosity is significantly depressed. Comparison of the model with several extragalactic sources shows that the [C ii] to far-infrared ratio declines for L(X-ray) 10 43 erg s −1 , in reasonable agreement with our model. Conclusions. We conclude that X-rays can suppress the C + abundance and, therefore, the [C ii] luminosity of the ISM in active galactic nuclei with a large X-ray flux. The X-ray flux can arise from a central massive accreting black hole and/or from many smaller discrete sources distributed throughout the nuclei. We also find that the lower ionization states of nitrogen and oxygen are also suppressed at high X-ray fluxes in warm ionized gas.

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Origin andz-distribution of Galactic diffuse [C II] emission

Cited by 34 publications

References 57 publications

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

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

Ionized gas in the Scutum spiral arm as traced in [N ii] and [C ii]

[C ii] emission from galactic nuclei in the presence of X-rays

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