Physics of the Galaxy and Interstellar Matter

Scheffler, Helmut; Elsässer, H.

doi:10.1007/978-3-642-71721-5

Cited by 75 publications

(44 citation statements)

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“…We note here that both the studies of distribution of matter in the Galaxy as well as the measurements of radial velocities of H ii regions in the range l ≈ 300 • -340 • indicate the presence of a spiral arm at a distance of ∼ 4 kpc (Scheffler & Elsasser 1987 and references therein). Our derived kinematic distance and the relatively large EB−V of GX 339-4 are consistent with its location in that arm.…”

Section: Distancementioning

confidence: 68%

Broad-band X-ray/γ-ray spectra and binary parameters of GX 339–4 and their astrophysical implications

Zdziarski¹,

Poutanen²,

Mikołajewska³

et al. 1998

Monthly Notices of the Royal Astronomical Society

197

217

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We present X-ray/γ-ray spectra of the binary GX 339-4 observed in the hard state simultaneously by Ginga and CGRO OSSE during an outburst in 1991 September. The Ginga X-ray spectra are well represented by a power law with a photon spectral index of Γ ≃ 1.75 and a Compton reflection component with a fluorescent Fe Kα line corresponding to a solid angle of an optically-thick, ionized, medium of ∼ 0.4×2π. The OSSE data ( 50 keV) require a sharp high-energy cutoff in the power-law spectrum. The broad-band spectra are very well modelled by repeated Compton scattering in a thermal plasma with an optical depth of τ ∼ 1 and kT ≃ 50 keV. We also study the distance to the system and find it to be > ∼ 3 kpc, ruling out earlier determinations of ∼ 1 kpc. Using this limit, the observed reddening and the orbital period, we find the allowed range of the mass of the primary is consistent with it being a black hole.We find the data are incosistent with models of either homogenous or patchy coronae above the surface of an accretion disc. Rather, they are consistent with the presence of a hot inner hot disc with the viscosity parameter of α ∼ 1 accreting at a rate close to the maximum set by advection. The hot disc is surrounded by a cold outer disc, which gives rise to the reflection component and a soft X-ray excess, also present in the data. The seed photons for Comptonization are unlikely to be due to thermal synchrotron radiation. Rather, they are supplied by the outer cold disc and/or cold clouds within the hot disc. e ± pair production is negligible if electrons are thermal. The hot disc model, which scaled parameters are independent of the blackhole mass, is supported by the similarity of the spectrum of GX 339-4 to those of other black-hole binaries and Seyfert 1s. On the other hand, their spectra in the soft γ-ray regime are significantly harder than those of weakly-magnetized neutron stars. Based on this difference, we propose that the presence of broad-band spectra corresponding to thermal Comptonization with kT > ∼ 50 keV represents a black-hole signature.

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Section: Distancementioning

confidence: 68%

Broad-band X-ray/γ-ray spectra and binary parameters of GX 339–4 and their astrophysical implications

Zdziarski¹,

Poutanen²,

Mikołajewska³

et al. 1998

Monthly Notices of the Royal Astronomical Society

197

217

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“…(42) and the standard dispersion [37] are confronted in order to see the difference between f (R) and Newtonian gravity. (42) in which we imposed the value for α given by (43). The thin line indicates the plot of the standard dispersion equation [37].…”

Section: Jeans Criterion For Gravitational Instability In F (R) Gmentioning

confidence: 99%

“…Using very general conditions [40][41][42][43][44][45][46][47][48], we want to show the difference in the Jeans mass value between standard and f (R)-gravity. Let us take into account Eq.…”

Section: V1 the Mj -T Relationmentioning

confidence: 99%

Jeans analysis of self-gravitating systems inf(R)gravity

et al. 2012

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Dynamics and collapse of collisionless self-gravitating systems is described by the coupled collisionless Boltzmann and Poisson equations derived from f (R) gravity in the weak field approximation. Specifically, we describe a system at equilibrium by a time-independent distribution function f0(x, v) and two potentials Φ0(x) and Ψ0(x) solutions of the modified Poisson and collisionless Boltzmann equations. Considering a small perturbation from the equilibrium and linearizing the field equations, it can be obtained a dispersion relation. A dispersion equation is achieved for neutral dust-particle systems where a generalized Jeans wave-number is obtained. This analysis gives rise to unstable modes not present in the standard Jeans analysis (derived assuming Newtonian gravity as weak filed limit of f (R) = R). In this perspective, we discuss several self-gravitating astrophysical systems whose dynamics could be fully addressed in the framework of f (R)-gravity.

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“…The ratio of -values can be expressed as a function of J, , CO-specific constants, and the Boltzmann equation (see, e.g., Scheffler & Elsaesser 1987). 3.…”

Section: Lte Analysismentioning

confidence: 99%

Molecular Gas in Candidate Double‐barred Galaxies. II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations

Petitpas

Wilson

2003

ApJ

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We have performed a multitransition CO study of the centers of seven double-barred galaxies that exhibit a variety of molecular gas morphologies to determine if the molecular gas properties are correlated with the nuclear morphology and star-forming activity. Near-infrared galaxy surveys have revealed the existence of nuclear stellar bars in a large number of barred or lenticular galaxies. High-resolution CO maps of these galaxies exhibit a wide range of morphologies. Recent simulations of double-barred galaxies suggest that variations in the gas properties may allow it to respond differently to similar gravitational potentials. We find that the 12 CO J ¼ 3 2/J ¼ 2 1 line ratio is lower in galaxies with centrally concentrated gas distributions and higher in galaxies with CO emission dispersed around the galactic center in rings and peaks. The 13 CO/ 12 CO J ¼ 2 1 line ratios are similar for all galaxies, which indicates that the J ¼ 3 2/J ¼ 2 1 line ratio is tracing variations in gas temperature and density, rather than variations in optical depth. There is evidence that the galaxies which contain more centralized CO distributions are composed of molecular gas that is cooler and less dense. Observations suggest that the star formation rates are higher in the galaxies containing the warmer, denser, less centrally concentrated gas. It is possible that either the bar dynamics are responsible for the variety of gas distributions and densities (and hence the star formation rates) or that the star formation alone is responsible for modifying the gas properties.

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Physics of the Galaxy and Interstellar Matter

Cited by 75 publications

References 0 publications

Broad-band X-ray/γ-ray spectra and binary parameters of GX 339–4 and their astrophysical implications

Broad-band X-ray/γ-ray spectra and binary parameters of GX 339–4 and their astrophysical implications

Jeans analysis of self-gravitating systems inf(R)gravity

Molecular Gas in Candidate Double‐barred Galaxies. II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations

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