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We present the results of a re-examination of a [Ne II] line emission data cube (λ 12.8μm) and discuss the kinematic structure of the inner 3×4 pc of the Galaxy. The quality of [Ne II] as a tracer of ionized gas is examined by comparing it to radio data. A three-dimensional representation of the data cube allows us to disentangle features which are projected onto the same location on the sky. A model of gas streams in different planes is fitted to the data. We find that most of the material is located in a main plane which itself is defined by the inner edge of the Circum-Nuclear Disk in the Galactic Center. Finally, we present a possible three-dimensional model of the gas streams. 相似文献
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Many observations indicate the occurrence of ionized gas in the distant haloes of galaxies (including our own). Since photoionization by stars (mainly O stars, young stars or evolved low-mass stars depending on the kind of galaxy) does not seem to be exclusively responsible for the ionization of the hydrogen filaments that should otherwise cool fast and recombine quickly, the question arises which extra energy source can produce the quasi-stationary ionization. We show that stationary localized magnetic reconnection in current filaments may contribute to the ionization of the extraplanar halo gas. In these filaments magnetic energy is dissipated. Consequently, the ionized as well as the neutral component is heated and re-ionized on a time-scale significantly shorter than the recombination time-scale. The amount of energy required for efficient re-ionization can in principle easily be provided by the free magnetic energy. We present quasi-static models that are characterized by plasma temperatures and densities that agree well with the observed values for the diffuse ionized gas component of the interstellar medium. Plasma–neutral gas fluid simulations are made to show that the recombination-induced dynamical reconnection process indeed works in a self-regulatory way. 相似文献
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Physical conditions and relative abundance ratios of the ionized medium of NGC 4945 are discussed. The spectral characteristics indicate forT
e=104 K a relatively low electron density (N
e1250 cm–3) decreasing outwards. N(N)/N(H) and N(S)/N(H) diminish with the distance from the nucleus while N(N)/N(S) is nearly constant. These abundance gradients, the lack of kinematical evidences of a bar and the observational difficulties to grasp its morphology, make it improbable that NGC 4945 could be classified as a barred galaxy. 相似文献
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Marc Elmouttie Bärbel Koribalski Scott Gordon Keith Taylor Sally Houghton Tracy Lavezzi Raymond Haynes & Keith Jones 《Monthly notices of the Royal Astronomical Society》1998,297(1):49-68
The TAURUS-2 Fabry–Perot interferometer, mounted on the 3.9-m Anglo-Australian Telescope, has been used to observe the Circinus galaxy. We have mapped the intensity and velocity distribution of the ionized hydrogen in the galaxy using the Balmer series Hα spectral line.
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s−1 (assuming circular motions) surrounds the core. The inclination angle of this feature, i =40°±10°, is less than that of the previously observed radio continuum disc. The velocity channel maps obtained for the Hα ring show that the kinematics resemble those of a rotating ring and the intensity displays a complex structure indicative of several, unresolved, H II regions. We believe the ring to represent a circumnuclear starburst.
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s−1 for gas above the core of Circinus. We also present evidence for inflowing ionized gas at the centre of Circinus.
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
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Peter G. Mezger Wolfgang J. Duschl Robert Zylka 《Astronomy and Astrophysics Review》1996,7(4):289-388
Summary. This paper reviews the physical state of stars and Interstellar Matter in the Galactic Bulge (radius kpc from the dynamical center of the Galaxy), in the Nuclear Bulge (kpc) and in the Sgr A Radio and GMC Complex, i.e. the central \,pc of our Galaxy. The Galactic Bulge is devoid of cold Interstellar Matter and consists mainly of old stars, while the Nuclear
Bulge accounts for of the mass of all of the Interstellar Matter in the Galaxy. A similar ratio holds for the formation rate of medium and high
mass stars in Bulge and Disk. The metal abundance of the Interstellar Matter in the Galactic Bulge is found to be . The H-to-CO conversion factors to be applied to molecular gas in the Central Region are by factors 3 (Arimoto et al. 1996) to 10 (Sodroski
et al. 1995) lower than in the solar vicinity. Hence, most H masses derived for the Central Region appear to be considerably overestimated. The Nuclear Bulge is pervaded by a thermal
plasma (K) which is responsible for the diffuse free-free emission. Lyman continuum photon and dust IR luminosity of the Nuclear Bulge
again account for of the respective total luminosities of the Galaxy. Magnetic fields in the Nuclear Bulge are strong (up to mG) as compared with the Galactic Disk (a few tens of G). The field lines are oriented parallel to the galactic plane inside giant molecular clouds and perpendicular to the plane
in the intercloud medium. The compact source Sgr A* is close to or at the dynamical center of the Galaxy. Its radio spectrum
with a high frequency cut-off at GHz, a low frequency turnover at GHz and a flux density dependence in between can be explained by synchrotron emission from quasi-monoenergetic relativistic electrons.
Due to an extinction between Sun and Galactic Center corresponding to , an intrinsic weakness of this source in the near infrared, and a strong background emission from warm dust there are only
upper limits available for the flux density of Sgr A* in the far, mid and near infrared and X-ray regime. The size of Sgr
A* in the radio regime is cm, its dereddened K-band flux density is mJy, its luminosity has upper limits of (if radiation comes from an Accretion Disk) and (if black-body radiation from an object with a single temperature of K is assumed). If anyone of the soft X-ray sources detected by ROSAT actually coincides with Sgr A*, its X-ray luminosity
would be less than a few . With a dark mass of Sgr A* is the best candidate for a starving black hole, although there are no observational indications for the presence
of a (Standard) Accretion Disk. While the radio/IR spectrum of Sgr A* is purely nonthermal, the spectrum integrated over the
central parsec resembles that of a Seyfert galaxy. Sgr A* is embedded in the Hii region Sgr A West with part of the ionized gas forming a minispiral. Sgr A West is surrounded by the Circum Nuclear Disk,
an irregular shaped assembly of molecular gas which extends from pc and rotates around the Galactic Center with an estimated dynamical time scale of \,yr. The total luminosity of of the central parsec is due to the radiation of early-type stars of which have now been directly identified as luminous blue supergiants. It is still debated, however, if these stars can also account
for all of the ionization of Sgr A West. In addition, the central parsec contains red giants, AGB stars, and a few super giants
of which the brightest are now identified by direct imaging. These stars – together with a few million low mass main sequence stars – account for
the bulk of the 2.2\,m emission. The spatial distributions of the three stellar populations in the central pc are remarkably different. Sgr A* is – along the line-of-sight – presumably located close to the center of the Hii region Sgr A West, which in turn is located in front of the extended (pc) synchrotron source Sgr A East, which appears to be the remnant of a gigantic explosion (of the order of the energy of a single supernova explosion) which took place yr ago inside the GMC Sgr A East Core. X-ray observations show within pc a pervasive hot (keV) plasma of expansion age of yr. Both phenomena – as well as the formation of the Circum Nuclear Disk – may have the same origin. Influx of material is
observed within the Nuclear Bulge on all distance scales. In the Nuclear Bulge (pc) as well as in the Circum Nuclear Disk (pc) inflow towards the Galactic Center occurs primarily in the galactic plane and amounts to a few . The accretion rate into the central Black Hole, deduced from the luminosity of Sgr A*, however, appears to be lower by at
least five orders of magnitude (assuming standard disk accretion). But in an equilibrium state only part of the infalling
mass which is not accreted by the Black Hole can be consumed by star formation. A mass inflow rate varying with time is a
more natural explanation. Comparing the physical state of the Center of our Galaxy with that of Active Galactic Nuclei derived
from observations and modelling, we find that most of the basic characteristics of an AGN are also present in the Galactic
Center. Lacking are, however, both the evidence for a standard Accretion Disk and a hard UV spectrum with accompanying high
excitation emission lines in the Galactic Center which are characteristic for AGN. The luminosity of the central parsec, , amounts to only of the total luminosity of the Galaxy of . Seen from a distance of M31 (kpc) with an angular resolution of (corresponding to a linear size of pc) the Center of our Galaxy would appear as a mildly active nucleus with some starburst activity and would probably be classified
as a weak Seyfert galaxy. The synchrotron spectrum of Sgr A*, however, would be completely masked by reprocessed stellar light
(i.e. free-free and dust emission).
Received: October 21, 1996 相似文献
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Dejan Urošević 《Astrophysics and Space Science》2003,283(1):75-86
This paper represents the updated empirical Galactic andextragalactic Σ-D relations (relations between the surface brightness Σ and the diameter D) for supernova remnants(SNRs), with checking the connection of the main Galactic radio loops (Loop I, II, III and IV) with
these relations. We present results which suggest, once again, that the radio loops may have an SNR origin. The updated relations
for old SNRs have been measured to have slopes, β ≈ 2 in log-log space. The best Σ-D relations for M31 and M33 galaxies were derived and these relations are shown to be flatter (β ≲2) than those for Galactic
SNRs alone. A Σ-D relation with168 reliable calibrators (both Galactic and extragalactic) is derived.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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James Cordes 《Astrophysics and Space Science》2001,278(1-2):11-16
I first review the observables and optics of interstellar seeing associated with radio wave scattering in the interstellar
medium. I then describe the Galactic distribution of electron density and its fluctuations, as inferred from a number of observables,
including angular and pulse broadening, diffractive scintillations, and dispersion measures. Propects for improving the Galactic
model are outlined.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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S. C. O. Glover 《Monthly notices of the Royal Astronomical Society》2007,379(4):1352-1358
H2 formation in metal-free gas occurs via the intermediate H− or H+ 2 ions. Destruction of these ions by photodissociation therefore serves to suppress H2 formation. In this paper, I highlight the fact that several processes that occur in ionized primordial gas produce photons energetic enough to photodissociate H− or H+ 2 and outline how to compute the photodissociation rates produced by a particular distribution of ionized gas. I also show that there are circumstances of interest, such as during the growth of H ii regions around the first stars, in which this previously overlooked form of radiative feedback is of considerable importance. 相似文献
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D.J.Zhou J.L.Han Jun Xu Chen Wang P.F.Wang Tao Wang Wei-Cong Jing Xue Chen Yi Yan Wei-Qi.Su Heng-Qian Gan Peng Jiang Jing-Hai Sun Hong-Guang Wang Na Wang Shuang-Qiang Wang Ren-Xin Xu Xiao-Peng You 《天文和天体物理学研究(英文版)》2023,(10):3-72
We have carried out the Galactic Plane Pulsar Snapshot(GPPS) survey by using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), the most sensitive systematic pulsar survey in the Galactic plane. In addition to more than 500 pulsars already discovered through normal periodical search, we report here the discovery of 76 new transient radio sources with sporadic strong pulses, detected by using the newly developed module for a sensitive single-pulse search. Their small DM values sugge... 相似文献
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Nine of the most important estimators known for the two-point correlation function are compared using a predetermined, rigorous criterion. The indicators were extracted from over 500 subsamples of the Virgo Hubble volume simulation cluster catalog. The "real" correlation function was determined from the full survey in a 3000 h(-1) Mpc periodic cube. The estimators were ranked by the cumulative probability of returning a value within a certain tolerance of the real correlation function. This criterion takes into account bias and variance, and it is independent of the possibly non-Gaussian nature of the error statistics. As a result, for astrophysical applications, a clear recommendation has emerged: the Landy & Szalay estimator, in its original or grid version (Szapudi & Szalay), is preferred in comparison with the other indicators examined, with a performance almost indistinguishable from the Hamilton estimator. 相似文献
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R. Paladini G. De Zotti R. D. Davies M. Giard 《Monthly notices of the Royal Astronomical Society》2005,360(4):1545-1552
We present an analysis of the thin layer of Galactic warm ionized gas at an angular resolution ∼10 arcmin. This is carried out using radio continuum data at 1.4, 2.7 and 5 GHz in the coordinate region . For this purpose, we evaluate the zero level of the 2.7- and 5-GHz surveys using auxiliary data at 2.3 GHz and 408 MHz. The derived zero-level corrections are T zero (2.7 GHz) = 0.15 ± 0.06 K and T zero (5 GHz) = 0.1 ± 0.05 K . We separate the thermal (free–free) and non-thermal (synchrotron) component by means of a spectral analysis performed adopting an antenna temperature spectral index −2.1 for the free–free emission, a realistic spatial distribution of indices for the synchrotron radiation and by fitting, pixel-by-pixel, the Galactic spectral index. We find that at 5 GHz, for | b | = 0° , the fraction of thermal emission reaches a maximum value of 82 per cent, while at 1.4 GHz, the corresponding value is 68 per cent. In addition, for the thermal emission, the analysis indicates a dominant contribution of the diffuse component relative to the source component associated with discrete H ii regions. 相似文献
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Now there are two basic observational techniques to investigate a gravitational potential at the Galactic Center, namely, (a) monitoring the orbits of bright stars near the Galactic Center to reconstruct a gravitational potential; (b) measuring the size and shape of shadows around black hole giving an alternative possibility to evaluate black hole parameters in mm-band with VLBI-technique. At the moment, one can use a small relativistic correction approach for stellar orbit analysis (however, in the future the approximation will not be precise enough due to enormous progress of observational facilities) while for smallest structure analysis in VLBI observations one really needs a strong gravitational field approximation. We discuss results of observations, their conventional interpretations, tensions between observations and models and possible hints for a new physics from the observational data and tensions between observations and interpretations. We discuss an opportunity to use a Schwarzschild metric for data interpretation or we have to use more exotic models such as Reissner–Nordstrom or Schwarzschild–de-Sitter metrics for better fits. 相似文献
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Ralf-Jürgen Dettmar 《Astrophysics and Space Science》2004,289(3-4):349-357
The presence of gaseous halos in star forming disk galaxies is reviewed inthe context of a proposed disk-halo connection of the interstellar medium (ISM). Results from a new survey for H+ halos of edge-on galaxies are presented. The data confirm that thepresence of diffuse ionized gas (DIG) in the disk-halo interface of spiral galaxies is related to star formationprocesses in the underlying disk. A discussion allows us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. By comparing some recent observational results for diagnostic emission lines with model predictions from photoionization we demonstratethat the origin and excitation of the ionized halo gas is still not completely understood and that a discussion gives important constraints formodels of the ISM. In comparison with similar findings for the Milky Way the need for an additional heating source is established. Special emphasis is given to some recent developments. In particular, newkinematical information for the DIG layer in NGC 5775 from ESO/VLT long-slitspectra is discussed in connection with the magnetic field structure in the halo of this object as deduced from VLA radio-continuum polarization data (Tüllmann et al., 2001). Finally, the rôle ofdust for the physical processes in the disk-halo interface is briefly addressed. 相似文献