共查询到20条相似文献，搜索用时 31 毫秒
1.
E. G. Körding S. Jester R. Fender 《Monthly notices of the Royal Astronomical Society》2008,383(1):277-288
We derive accretion rate functions (ARFs) and kinetic luminosity functions (KLFs) for jet-launching supermassive black holes. The accretion rate as well as the kinetic power of an active galaxy is estimated from the radio emission of the jet. For compact low-power jets, we use the core radio emission while the jet power of high-power radio-loud quasars is estimated using the extended low-frequency emission to avoid beaming effects. We find that at low luminosities the ARF derived from the radio emission is in agreement with the measured bolometric luminosity function (BLF) of active galactic nucleus (AGN), i.e. all low-luminosity AGN launch strong jets. We present a simple model, inspired by the analogy between X-ray binaries (XRBs) and AGN, that can reproduce both the measured ARF of jet-emitting sources as well as the BLF. The model suggests that the break in power-law slope of the BLF is due to the inefficient accretion of strongly sub-Eddington sources. As our accretion measure is based on the jet power it also allows us to calculate the KLF and therefore the total kinetic power injected by jets into the ambient medium. We compare this with the kinetic power output from supernova remnants (SNRs) and XRBs, and determine its cosmological evolution. 相似文献
2.
We find a significant anticorrelation between the hard X-ray photon index Γ and the Eddington ratio L bol / L Edd for a sample of low-ionization nuclear emission-line regions and local Seyfert galaxies, compiled from literature with Chandra or XMM–Newton observations. This result is in contrast with the positive correlation found in luminous active galactic nuclei (AGN), while it is similar to that of X-ray binaries (XRBs) in the low/hard state. Our result is qualitatively consistent with the spectra produced from advection-dominated accretion flows (ADAFs). It implies that the X-ray emission of low-luminosity active galactic nuclei (LLAGN) may originate from the Comptonization process in ADAF, and the accretion process in LLAGN may be similar to that of XRBs in the low/hard state, which is different from that in luminous AGN. 相似文献
3.
In recent years, significant evidence for the similar nature of active galactic nuclei (AGN) and X-ray binaries (XRBs) has
been gathered. We describe a unification scheme for accreting black holes following the idea that weakly accreting systems
may be jet dominated. This is tested with the radio/X-ray correlation of XRBs and AGN. The established correlation is further
used to diagnose ultra-luminous X-ray sources. For higher accretion rates, we explore high-power jets and the effect of Compton
cooling of the jet by the accretion disk. 相似文献
4.
Elmar G. Körding 《Astrophysics and Space Science》2007,311(1-3):143-147
The “fundamental plane of accreting black holes” and an empirical connection between X-ray binaries (XRBs) and active galactic nuclei (AGN) based on variability properties is presented. Following these connections we construct disc-fraction luminosity diagrams (DFLD), a generalisation of hardness-intensity diagrams used for XRBs. We show that the radio-loudness of AGN depends on the position in the DFLD similar to what is observed in XRBs. For those XRBs and AGN on the right side of the diagram (hard state XRBs, LLAGN and many radio-loud quasars) we show that the jet power and accretion rate can be estimated from the core radio emission. This accretion measure is used to explore the dependence of the bolometric luminosity on the accretion rate. 相似文献
5.
We study, through 2D hydrodynamical simulations, the feedback of a starburst on the ISM of typical gas-rich dwarf galaxies. The main goal is to address the circulation of the ISM and metals following the starburst. We assume a single-phase rotating ISM in equilibrium in the galactic potential generated by a stellar disc and a spherical dark halo. The starburst is assumed to occur in a small volume in the centre of the galaxy, and it generates a mechanical power of 3.8×1039 or 3.8×1040 erg s−1 for 30 Myr. We find, in accordance with previous investigations, that the galactic wind is not very effective in removing the ISM. The metal-rich stellar ejecta, however, can be efficiently expelled from the galaxy and dispersed in the intergalactic medium.
Moreover, we find that the central region of the galaxy is always replenished with cold and dense gas a few 100 million years after the starburst, achieving the requisite for a new star formation event in ≈0.5–1 Gyr. The hydrodynamical evolution of galactic winds is thus consistent with the episodic star formation regime suggested by many chemical evolution studies.
We also discuss the X-ray emission of these galaxies and find that the observable (emission-averaged) abundance of the hot gas underestimates the real one if thermal conduction is effective. This could explain the very low hot-gas metallicities estimated in starburst galaxies. 相似文献
Moreover, we find that the central region of the galaxy is always replenished with cold and dense gas a few 100 million years after the starburst, achieving the requisite for a new star formation event in ≈0.5–1 Gyr. The hydrodynamical evolution of galactic winds is thus consistent with the episodic star formation regime suggested by many chemical evolution studies.
We also discuss the X-ray emission of these galaxies and find that the observable (emission-averaged) abundance of the hot gas underestimates the real one if thermal conduction is effective. This could explain the very low hot-gas metallicities estimated in starburst galaxies. 相似文献
6.
We study the chemical and spectrophotometric evolution of galactic discs with detailed models calibrated on the Milky Way and using simple scaling relations, based on currently popular semi-analytic models of galaxy formation. We compare our results with a large body of observational data on present-day galactic discs, including disc sizes and central surface brightness, Tully–Fisher relations in various wavelength bands, colour–colour and colour–magnitude relations, gas fractions versus magnitudes and colours and abundances versus local and integrated properties, as well as spectra for different galactic rotational velocities. Despite the extremely simple nature of our models, we find satisfactory agreement with all those observables, provided that the time-scale for star formation in low-mass discs is longer than for more massive ones. This assumption is apparently in contradiction with the standard picture of hierarchical cosmology. We find, however, that it is extremely successful in reproducing major features of present-day discs, like the change in the slope of the Tully–Fisher relation with wavelength, the fact that more massive galaxies are on average 'redder' than low-mass ones (a generic problem of standard hierarchical models) and the metallicity–luminosity relation for spirals. It is concluded that, on a purely empirical basis, this new picture is at least as successful as the standard one. Observations at high redshifts could help to distinguish between the two possibilities. 相似文献
7.
S. Boissier A. Boselli N. Prantzos G. Gavazzi 《Monthly notices of the Royal Astronomical Society》2001,321(4):733-742
We study the star formation history of normal spirals by using a large and homogeneous data sample of local galaxies. For our analysis we utilize detailed models of chemical and spectrophotometric galactic evolution, calibrated on the Milky Way disc. We find that star formation efficiency is independent of galactic mass, while massive discs have, on average, lower gas fractions and are redder than their low-mass counterparts; put together, these findings convincingly suggest that massive spirals are older than low-mass ones. We evaluate the effective ages of the galaxies of our sample and we find that massive spirals must be several Gyr older than low-mass ones. We also show that these galaxies (having rotational velocities in the 80–400 km s−1 range) cannot have suffered extensive mass losses, i.e. they cannot have lost during their lifetime an amount of mass much larger than their current content of gas+stars. 相似文献
8.
Assuming that damped Lyman- α (DLA) systems are galactic discs, we calculate the corresponding evolution of metal abundances. We use detailed multizone models of galactic chemical evolution (reproducing successfully the observed properties of disc galaxies) and appropriate statistics (including geometrical probability factors) to calculate the average metallicity as a function of redshift. The results are compatible with available observations, provided that observational biases are taken into account , as suggested by Boissé et al. In particular, high column density and high-metallicity systems are not detected because the light of backround quasars is severely extinguished, while low column density and low-metallicity systems are not detectable through their absorption lines by current surveys. We show that these observational constraints lead to a 'no-evolution' picture for the DLA metallicity, which does not allow us to draw strong conclusions about the nature of those systems or about their role in 'cosmic chemical evolution'. 相似文献
9.
Tao Hu Qiu-He Peng Hong-Shi Zong 《中国天文和天体物理学报》2007,7(4):579-589
We present disk thicknesses, some other parameters and their statistics of 108 non-edge-on spiral galaxies. The method for determining the disk thickness is based on solving Poisson's equation for a disturbance of matter density in three-dimensional spiral galaxies. From the spiral arms found we could obtain the pitch angles, the inclination of the galactic disk, and the position of the innermost point (the forbidden region with radius r 0 to the galactic center) of the spiral arm, and finally the thickness. 相似文献
10.
Agostino Martinelli Francesca Matteucci & Sergio Colafrancesco 《Monthly notices of the Royal Astronomical Society》1998,298(1):42-52
Models of chemical evolution of elliptical galaxies taking into account different escape velocities at different galactocentric radii are presented. As a consequence of this, the chemical evolution develops differently in different galactic regions; in particular, we find that the galactic wind, powered by supernovae (of Type II and I) starts, under suitable conditions, in the outer regions and successively develops in the central ones. The star formation is assumed to stop after the onset of the galactic wind in each region. The main result found in the present work is that this mechanism is able to reproduce metallicity gradients, namely the gradients in the Mg2 index, in good agreement with observational data. We also find that in order to honour the constant [〈Mg/Fe〉] ratio with galactocentric distance, as inferred from metallicity indices, a variable initial mass function as a function of galactocentric distance is required. This is only a suggestion, as trends on abundances inferred purely from metallicity indices are still uncertain. 相似文献
11.
We study the self-consistent, linear response of a galactic disc to vertical perturbations, as induced, say, by a tidal interaction. We calculate the self-gravitational potential corresponding to a non-axisymmetric, self-consistent density response of the disc using the Green's function method. The response potential is shown to oppose the perturbation potential because the self-gravity of the disc resists the imposed potential, and this resistance is stronger in the inner parts of a galactic disc. For the m = 1 azimuthal wavenumber, the disc response opposes the imposed perturbation up to a radius that spans a range of 4–6 disc scalelengths, so that the disc shows a net warp only beyond this region. This physically explains the well known but so far unexplained observation that warps typically set in beyond this range of radii. We show that the inclusion of a dark matter halo in the calculation only marginally changes (by ∼10 per cent) the radius for the onset of warps. For perturbations with higher azimuthal wavenumbers, the net signature of the vertical perturbations can only be seen at larger radii – for example, beyond 7 exponential disc scalelengths for m = 10 . Also, for the high- m cases, the magnitude of the negative disc response due to the disc self-gravity is much smaller. This is shown to result in corrugations of the mid-plane density, which explains the puzzling scalloping with m = 10 detected in H i in the outermost regions ∼30 kpc in the Galaxy. 相似文献
12.
Antonio Pipino Joseph Silk Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2009,392(1):475-482
The overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass, poses a serious problem for all current models of galaxy formation. Here, we improve on the one-zone chemical evolution models for elliptical galaxies by taking into account positive feedback produced in the early stages of supermassive central black hole growth. We can account for both the observed correlation and the scatter if the observed anti-hierarchical behaviour of the AGN population couples to galaxy assembly and results in an enhancement of the star formation efficiency which is proportional to galactic mass. At low and intermediate galactic masses, however, a slower mode for star formation suffices to account for the observational properties. 相似文献
13.
14.
Chemo-spectrophotometric evolution of spiral galaxies – III. Abundance and colour gradients in discs
We study the relations between luminosity and chemical-abundance profiles of spiral galaxies, using detailed models for the chemical and spectrophotometric evolution of galactic discs. The models are 'calibrated' on the Milky Way disc and are successfully extended to other discs with the help of simple 'scaling' relations, obtained in the framework of semi-analytic models of galaxy formation. We find that our models exhibit oxygen abundance gradients that increase in absolute value with decreasing disc luminosity (when expressed in dex kpc−1 ) and are independent of disc luminosity (when expressed in dex scalelength−1 ), both in agreement with observations. We notice an important strong correlation between abundance gradient and disc scalelength. These results support the idea of 'homologous evolution' of galactic discs. 相似文献
15.
16.
M. Ideta S. Hozumi T. Tsuchiya M. Takizawa 《Monthly notices of the Royal Astronomical Society》2000,311(4):733-740
A recent observation with the Hipparcos satellite and some numerical simulations imply that the interaction between an oblate halo and a disc is inappropriate for the persistence of galactic warps. Following on from this , we have compared the time evolution of galactic warps in a prolate halo with that in an oblate halo. The haloes were approximated as fixed potentials, while the discs were represented by N -body particles. We have found that the warping in the oblate halo continues to wind up, and finally disappears. On the other hand, for the prolate halo model, the precession rate of the outer disc increases when the precession of the outer disc recedes from that of the inner disc, and vice versa. Consequently, the warping in the prolate halo persisted to the end of the simulation by retaining the alignment of the line of nodes of the warped disc. Therefore, our results suggest that prolate haloes could sustain galactic warps. The physical mechanism of the persistence of warp is discussed on the basis of the torque between a halo and a disc and that between the inner and outer regions of the disc. 相似文献
17.
V. M. Muñoz Marín T. Storchi-Bergmann R. M. González Delgado H. R. Schmitt P. F. Spinelli E. Pérez R. Cid Fernandes 《Monthly notices of the Royal Astronomical Society》2009,399(2):842-860
We study the nature of the extended near-UV emission in the inner kiloparsec of a sample of 15 Seyfert (Sy) galaxies which have both near-UV (F330W) and narrow-band [O iii ] high-resolution Hubble images. For the majority of the objects, we find a very similar morphology in both bands. From the [O iii ] images, we construct synthetic images of the nebular continuum plus the emission-line contribution expected through the F330W filter, which can be subtracted from the F330W images. We find that the emission of the ionized gas dominates the near-UV extended emission in half of the objects. A further broad-band photometric study, in the bands F330W ( U ), F547M ( V ) and F160W ( H ), shows that the remaining emission is dominated by the underlying galactic bulge contribution. We also find a blue component whose nature is not clear in four out of 15 objects. This component may be attributed to scattered light from the active galactic nuclei, to a young stellar population in unresolved star clusters, or to early disrupted clusters. Star-forming regions and/or bright off nuclear star clusters are observed in 4/15 galaxies of the sample. 相似文献
18.
S. A. Sim K. S. Long L. Miller T. J. Turner 《Monthly notices of the Royal Astronomical Society》2008,388(2):611-624
We use a multidimensional Monte Carlo code to compute X-ray spectra for a variety of active galactic nucleus (AGN) disc–wind outflow geometries. We focus on the formation of blueshifted absorption features in the Fe K band and show that line features similar to those which have been reported in observations are often produced for lines of sight through disc–wind geometries. We also discuss the formation of other spectral features in highly ionized outflows. In particular, we show that, for sufficiently high wind densities, moderately strong Fe K emission lines can form and that electron scattering in the flow may cause these lines to develop extended red wings. We illustrate the potential relevance of such models to the interpretation of real X-ray data by comparison with observations of a well-known AGN, Mrk 766. 相似文献
19.
X. Hernandez B. Cervantes-Sodi 《Monthly notices of the Royal Astronomical Society》2006,368(1):351-360
We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies. 相似文献
20.