Spatial distribution of interstellar gas in the innermost 3 kpc of our galaxy

Ferrière, K.; Gillard, W.; Jean, P.

doi:10.1051/0004-6361:20066992

Cited by 246 publications

(437 citation statements)

References 63 publications

(186 reference statements)

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“…These average values for the hydrogen and helium densities are of course approximations based on local estimates, but we do not expect significant changes in the averaging within the kpc scale (Ferrière et al 2007), which, as we show in the subsequent sections, is the relevant scale for the secondary positron propagation. Cross-sections for heavy nuclei were dealt with in the same way as in Norbury & Townsend (2007).…”

Section: Incident Proton Fluxmentioning

confidence: 75%

Galactic secondary positron flux at the Earth

Delahaye

Lineros²,

Donato³

et al. 2009

A&A

218

308

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Context. Secondary positrons are produced by spallation of cosmic rays within the interstellar gas. Measurements have been typically expressed in terms of the positron fraction, which exhibits an increase above 10 GeV. Many scenarios have been proposed to explain this feature, among them some additional primary positrons originating from dark matter annihilation in the Galaxy. Aims. The PAMELA satellite has provided high quality data that has enabled high accuracy statistical analyses to be made, showing that the increase in the positron fraction extends up to about 100 GeV. It is therefore of paramount importance to constrain theoretically the expected secondary positron flux to interpret the observations in an accurate way. Methods. We focus on calculating the secondary positron flux by using and comparing different up-to-date nuclear cross-sections and by considering an independent model of cosmic ray propagation. We carefully study the origins of the theoretical uncertainties in the positron flux. Results. We find the secondary positron flux to be reproduced well by the available observations, and to have theoretical uncertainties that we quantify to be as large as about one order of magnitude. We also discuss the positron fraction issue and find that our predictions may be consistent with the data taken before PAMELA. For PAMELA data, we find that an excess is probably present after considering uncertainties in the positron flux, although its amplitude depends strongly on the assumptions made in relation to the electron flux. By fitting the current electron data, we show that when considering a soft electron spectrum, the amplitude of the excess might be far lower than usually claimed. Conclusions. We provide fresh insights that may help to explain the positron data with or without new physical model ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow stronger constraints to be aplaced on the cosmic-ray transport parameters, and are likely to reduce drastically the theoretical uncertainties.

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Section: Incident Proton Fluxmentioning

confidence: 75%

Galactic secondary positron flux at the Earth

Delahaye

Lineros²,

Donato³

et al. 2009

A&A

218

308

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“…Characteristic cloud line widths are ≥20 km s −1 , compared to a few km s −1 for GMCs in the disk (e.g. Morris & Serabyn 1996;Oka et al 1998;Ferrière et al 2007). In addition, GMCs in the CMZ have higher kinetic temperatures, T k ∼ 30 to 200 K (Ao et al 2013;Mills & Morris 2013), and densities, n(H 2 ) ≥ 10 4−5 cm −3 (e.g.…”

Section: Introductionmentioning

confidence: 93%

“…Jackson et al 1996;Oka et al 1998;Dame et al 2001;Martin et al 2004), than GMCs in the disk. The gas distribution within the inner Galaxy and across the edge of the CMZ is thought to be due to the gravitational potential and dynamics of the gas there (see overview by Ferrière et al 2007). While the atomic and molecular hydrogen distributions in the CMZ have been mapped with spectrally resolved H i and CO, respectively, less is known about the distribution and properties of the ionized gas in this region.…”

Section: Introductionmentioning

confidence: 99%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims. We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N + and C + .Methods. We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H 2 .Results. We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at −207 km s −1 associated with Sgr E and the other at −174 km s −1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ∼5 to 21 cm −3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H 2 layer in the −207 km s −1 cloud is ∼1−2× 10 21 cm −2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ∼7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N + and high electron density require an intense EUV field with a photon flux of order 10 6 to 10 7 photons cm −2 s −1 , and/or efficient proton charge exchange with nitrogen, at temperatures of order 10 4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

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“…• 7 in the CMZ as traced by CO (Oka et al 1998) and a scale height z = 30 pc (disk thickness of 60 pc) slightly larger than the scale height of the dense WIM (Ferrière et al 2007) 3 . We adopt the following densities and temperatures for the key ISM components that contribute to the [C ii] emission from galactic nuclei: 1) the low density WIM is assumed to have T kin = 8000 K and an average density n(e) ∼ 10 cm −3 (Cordes & Lazio 2003;Roy 2013); 2) diffuse atomic hydrogen clouds with n(H) = 100 cm −3 and T kin = 100 K, 3) dense PDRs with n(H 2 ) = 10 3 cm −3 and T kin = 100 K, and for the dense ionized skins we adopt n(e) = 20 cm −3 from the study of two clouds at the edge of the CMZ (Langer et al 2015).…”

Section: Galactic Nucleus With Cmz Model Parametersmentioning

confidence: 98%

“…The black hole assumed associated with Sgr A at the Galactic Center has a current luminosity ∼10 33 erg s −1 (Baganoff et al 2001), but may have To calculate the [C ii] luminosity for the CMZ we use the CMZ physical dimensions adopted in Sect. 4.2 and ISM parameters in Table 4 for the atomic clouds, PDRs, and DIS components, but modify the WIM model to fit with the WIM electron profile (Ferrière et al 2007), as discussed below. The atomic, molecular, and ionized gas in the CMZ is concentrated at the center and decreases with radius and distance above and below the plane.…”

Section: Central Molecular Zone [C Ii] Luminositymentioning

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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Spatial distribution of interstellar gas in the innermost 3 kpc of our galaxy

Cited by 246 publications

References 63 publications

Galactic secondary positron flux at the Earth

Galactic secondary positron flux at the Earth

Ionized gas at the edge of the central molecular zone

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

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