Optical thickness, spin temperature and correction factor for the density of Galactic H i gas

Sofue, Yoshiaki

doi:10.1093/mnras/stx672

Cited by 8 publications

(6 citation statements)

References 29 publications

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“…In this case, for the conversion factor we use the value from [28]: X HI = 1.83 × 10 18 cm −2 K −1 km −1 s. This conversion factor is derived from the assumption of optically thin emission and must be corrected for possible absorption caused by cooler components. Following for example [42], the corrected column density is calculated as:…”

Section: Appendix A: Mass Determinationmentioning

confidence: 99%

Probing the sea of galactic cosmic rays with Fermi-LAT

et al. 2020

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High energy γ rays from Giant Molecular Clouds (GMCs) carry direct information about the spatial and energy distributions of Galactic Cosmic Rays (CRs). The recently released catalogs of GMCs contain sufficiently massive clouds to be used as barometers for probing, through their γ-ray emission, the density of CRs throughout the Galactic Disk. Based on the data of Fermi-LAT , we report the discovery of γ-ray signals from nineteen GMCs located at distances up to 12.5 kpc. The galactocentric radial distribution of the CR density derived from the γ-ray and CO observations of these objects, as well as from some nearby clouds that belong to the Gould Belt complex, unveil a homogeneous "sea" of CRs with a constant density and spectral shape close to the flux of directly (locally) measured CRs. We found noticeable deviations from the "sea level" only in some locations characterized by enhanced CR density in the galactocentric 4-6 kpc ring. Furthermore, we found a hint for fluctuations of the CR density in different locations within the same 4-6 kpc ring. The confirmation of this result with the next-generation γ-ray detectors based on the higher quality data and denser coverage of galactocentric distances, would have dramatic implications for the understanding of the origin of Galactic CRs.PACS numbers: 95.85.Ry; 98.70.Sa

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Section: Appendix A: Mass Determinationmentioning

confidence: 99%

Probing the sea of galactic cosmic rays with Fermi-LAT

et al. 2020

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“…which is assumed to be x e ∼ 0.1 after Foster et al (2013), who obtained x e ∼ 0.08. Local HI gas is considered to be in cold phase from recent measurement of spin temperature (Sofue 2017(Sofue , 2018.…”

Section: Thermal Electron Densitymentioning

confidence: 99%

Magnetic field and ISM in the local Galactic disc

Sofue

Nakanishi

Ichiki

2019

Monthly Notices of the Royal Astronomical Society

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Correlation analysis is obtained among Faraday rotation measure, HI column density, thermal and synchrotron radio brightness using archival all-sky maps of the Galaxy. A method is presented to calculate the magnetic strength and its line-of-sight (LOS) component, volume gas densities, effective LOS depth, effective scale height of the disk from these data in a hybrid way. Applying the method to archival data, all-sky maps of the local magnetic field strength and its parallel component are obtained, which reveal details of local field orientation.

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“…Our temperature threshold is somewhat higher than the CNM temperature estimated in real galaxies ( 300 K, e.g., Wolfire et al 2003) because, in our simulation, we do not resolve the transition between warm and cold neutral gas phases, which results in intermediate gas temperatures on the resolution scale. The particular value of the temperature threshold was chosen to select ∼ 40% of the neutral hydrogen mass, which is close to the CNM mass fractions estimated in the Milky Way and nearby galaxies (e.g., Heiles & Troland 2003;Braun 2012;Pineda et al 2013;Sofue 2017).…”

Section: Introductionmentioning

confidence: 99%

The Physical Origin of Long Gas Depletion Times in Galaxies

Semenov

Kravtsov

Gnedin

2017

ApJ

123

106

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We present a model that explains why galaxies form stars on a time scale significantly longer than the time scales of processes governing the evolution of interstellar gas. We show that gas evolves from a nonstar-forming to a star-forming state on a relatively short time scale and thus the rate of this evolution does not limit the star formation rate. Instead, the star formation rate is limited because only a small fraction of star-forming gas is converted into stars before star-forming regions are dispersed by feedback and dynamical processes. Thus, gas cycles into and out of star-forming state multiple times, which results in a long time scale on which galaxies convert gas into stars. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in simulations. In particular, the model explains how feedback selfregulates the star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated L * -sized galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is almost linear on kiloparsec scales, although a nonlinear relation is adopted in simulation cells. We discuss how a linear relation emerges from non-self-similar scaling of the gas density PDF with the average gas surface density.

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Optical thickness, spin temperature and correction factor for the density of Galactic H i gas

Cited by 8 publications

References 29 publications

Probing the sea of galactic cosmic rays with Fermi-LAT

Probing the sea of galactic cosmic rays with Fermi-LAT

Magnetic field and ISM in the local Galactic disc

The Physical Origin of Long Gas Depletion Times in Galaxies

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