The growth of supermassive black holes in pseudo-bulges, classical bulges and elliptical galaxies     

Dimitri A. Gadotti  Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》2009,399(2):621-627

Using results from structural analysis of a sample of nearly 1000 local galaxies from the Sloan Digital Sky Survey, we estimate how the mass in central black holes is distributed amongst elliptical galaxies, classical bulges and pseudo-bulges, and investigate the relation between their stellar masses and central stellar velocity dispersion σ. Assuming a single relation between elliptical galaxy/bulge mass, M _Bulge, and central black hole mass, M _BH, we find that  55⁺⁸₋₄  per cent of the mass in black holes in the local universe is in the centres of elliptical galaxies,  41⁺⁴₋₂  per cent in classical bulges and  4^+0.9_−0.4  per cent in pseudo-bulges. We find that ellipticals, classical bulges and pseudo-bulges follow different relations between their stellar masses and σ, and the most significant offset occurs for pseudo-bulges in barred galaxies. This structural dissimilarity leads to discrepant black hole masses if single   M _BH– M _Bulge  and   M _BH–σ  relations are used. Adopting relations from the literature, we find that the   M _BH–σ  relation yields an estimate of the total mass density in black holes that is roughly 55 per cent larger than if the   M _BH– M _Bulge  relation is used.  相似文献   

Elliptical galaxies from mergers of discs     

Antonio César González-García  Marc Balcells 《Monthly notices of the Royal Astronomical Society》2005,357(2):753-772

We analyse N -body galaxy merger experiments involving disc galaxies. Mergers of disc–bulge–halo models are compared to those of bulgeless, disc–halo models to quantify the effects of the central bulge on merger dynamics and the structure of the remnant. Our models explore galaxy mass ratios 1:1 through 3:1, and use higher bulge mass fractions than previous studies. A full comparison of the structural and dynamical properties with our observations is carried out. The presence of central bulges results in longer tidal tails, oblate final intrinsic shapes, surface brightness profiles with a higher Sérsic index, steeper rotation curves and oblate-rotator internal dynamics. Mergers of bulgeless galaxies do not generate long-lasting tidal tails, and their strong triaxiality seems inconsistent with observations; these remnants show shells, which we do not find in models including central bulges. Giant ellipticals with boxy isophotes and anisotropic dynamics cannot be produced by the mergers modelled here; they could be the result of mergers between lower luminosity ellipticals, themselves plausibly formed in disc-disc mergers.  相似文献   

Triaxial stellar systems following the  r^1/n  luminosity law: an analytical mass–density expression, gravitational torques and the bulge/disc interplay     

I. Trujillo  A. Asensio Ramos  J. A. Rubiño-Martín  Alister W. Graham  J. A. L. Aguerri  J. Cepa  C. M. Gutiérrez 《Monthly notices of the Royal Astronomical Society》2002,333(3):510-516

We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the   r ^{1/ n}   luminosity law – extending the analysis by Ciotti, who explored the properties of spherical   r ^{1/ n}   systems. A new analytical expression that accurately reproduces the spatial (i.e., deprojected) luminosity density profiles (error less than 0.1 per cent) is presented for detailed modelling of the Sérsic family of luminosity profiles. We evaluate both the symmetric and the non-axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component . We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n ) is found to greatly reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for non-symmetric structures in the disc.
Using seeing-convolved   r ^{1/ n}   -bulge plus exponential-disc fits to the K -band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sérsic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, though not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker.  相似文献   

Restrictions to the galaxy evolutionary models from the Hawaiian Deep Fields SSA13 and SSA22     

J. A. L. Aguerri  I. Trujillo 《Monthly notices of the Royal Astronomical Society》2002,333(3):633-641

Quantitative structural analysis of the galaxies present in the Hawaiian Deep Fields SSA13 and SSA22 is reported. The structural parameters of the galaxies have been obtained automatically by fitting a two-component model (Sérsic r ^{1/ n} bulge and exponential disc) to the surface brightness of the galaxies. The galaxies were classified on the basis of the bulge-to-total luminosity ratio  ( B / T )  . The magnitude selection criteria and the reliability of our method have been checked by using Monte Carlo simulations. A complete sample of objects up to redshift 0.8 has been achieved. Spheroidal objects (E/S0) represent ≈33 per cent and spirals ≈41 per cent of the total number of galaxies, while mergers and unclassified objects represent ≈26 per cent. We have computed the comoving space density of the different kinds of object. In an Einstein–de Sitter universe, a decrease in the comoving density of E/S0 galaxies is observed as redshift increases (≈30 per cent less at   z =0.8)  , while for spiral galaxies a relatively quiet evolution is reported. The framework of hierarchical clustering evolution models of galaxies seems to be the most appropriate to explain our results.  相似文献   

Stellar populations of classical and pseudo-bulges for a sample of isolated spiral galaxies     

Yinghe Zhao 《Astrophysics and Space Science》2012,337(2):719-728

In this paper we present the stellar population synthesis results for a sample of 75 bulges in isolated spiral Sb-Sc galaxies, using the spectroscopic data from the Sloan Digital Sky Survey and the STARLIGHT code. We find that both pseudo-bulges and classical bulges in our sample are predominantly composed of old stellar populations, with mean mass-weighted stellar age around 10 Gyr. While the stellar population of pseudo-bulges is, in general, younger than that of classical bulges, the difference is not significant, which indicates that it is hard to distinguish pseudo-bulges from classical bulges, at least for these isolated galaxies, only based on their stellar populations. Pseudo-bulges have star formation activities with relatively longer timescale than classical bulges, indicating that secular evolution is more important in this kind of systems. Our results also show that pseudo-bulges have a lower stellar velocity dispersion than their classical counterparts, which suggests that classical bulges are more dispersion-supported than pseudo-bulges.  相似文献   

Inclination- and dust-corrected galaxy parameters: bulge-to-disc ratios and size–luminosity relations     

Alister W. Graham  C. Clare Worley 《Monthly notices of the Royal Astronomical Society》2008,388(4):1708-1728

While galactic bulges may contain no significant dust of their own, the dust within galaxy discs can strongly attenuate the light from their embedded bulges. Furthermore, such dust inhibits the ability of observationally determined inclination corrections to recover intrinsic (i.e. dust-free) galaxy parameters. Using the sophisticated 3D radiative transfer model of Popescu et al. and Tuffs et al., together with the recent determination of the average face-on opacity by Driver et al. in nearby disc galaxies, we provide simple equations to correct (observed) disc central surface brightness and scalelengths for the effects of both inclination and dust in the B , V , I , J and K passbands. We then collate and homogenize various literature data sets and determine the typical intrinsic scalelengths, central surface brightness and magnitudes of galaxy discs as a function of morphological type. All galaxies have been carefully modelled in their respective papers with a Sérsic   R ^{1/ n}   bulge plus an exponential disc. Using the bulge magnitude corrections from Driver et al., we additionally derive the average, dust-corrected, bulge-to-disc flux ratio as a function of galaxy type. With values typically less than 1/3, this places somewhat uncomfortable constraints on some current semi-analytic simulations. Typical bulge sizes, profile shapes, surface brightness and deprojected densities are provided. Finally, given the two-component nature of disc galaxies, we present luminosity–size and (surface brightness)–size diagrams for discs and bulges. We also show that the distribution of elliptical galaxies in the luminosity–size diagram is not linear but strongly curved.  相似文献   

The rotation curves of flattened Sérsic bulges     

Edo Noordermeer 《Monthly notices of the Royal Astronomical Society》2008,385(3):1359-1364

I present a method to deproject the observed intensity profile of an axisymmetric bulge with arbitrary flattening to derive the three-dimensional luminosity density profile, and to calculate the contribution of the bulge to the rotation curve. I show the rotation curves for a family of fiducial bulges with Sérsic surface brightness profiles and with various concentrations and intrinsic axis ratios. Both parameters have a profound impact on the shape of the rotation curve. In particular, I show how the peak rotation velocity, as well as the radius where it is reached, depends on both parameters.
I also discuss the implications of the flattening of a bulge for the decomposition of a rotation curve and use the case of NGC 5533 to show the errors that result from neglecting it. For NGC 5533, neglecting the flattening of the bulge leads to an overestimate of its mass-to-light ratio by approximately 30 per cent and an underestimate of the contributions from the stellar disc and dark matter halo in the regions outside the bulge-dominated area.  相似文献   

Phase-space density constraints on the formation of bulges from discs     

Rosemary F. G. Wyse 《Monthly notices of the Royal Astronomical Society》1998,293(4):429-433

The colours of stellar bulges and of inner stellar discs are comparable, and consistent with rather similar mean metallicities and ages. Indeed, the mean chemical abundances of the Milky Way bulge and old disc are approximately equal. Further, the scalelengths of discs and bulges are correlated. These observations imply a close relationship between discs and bulges, and may support models in which stellar bulges form from stellar discs. The present paper discusses constraints on this scenario from the stellar phase-space density of bulges and of discs. Phase-space density cannot increase in the absence of collisional processes. We show here that the maximum phase-space density of galactic bulges is higher than that of inner discs, arguing that instabilities of purely stellar discs cannot form bulges. Rather, the high densities of bulges probably reflect gaseous dissipation. Gas inflow from the disc would complicate the interpretation of the similarities in stellar colours between discs and bulges. Gas inflow from the stellar halo, if one exists, may be favoured on angular momentum grounds, but this means of formation of the bulge would provide no explanation for the relationships between disc and bulge in any one galaxy. At least in the Milky Way, the metallicity distribution of the bulge is not consistent with the bulge being built up from the dense regions of accreted satellite galaxies and/or globular clusters.  相似文献   

The black hole mass–stellar velocity dispersion correlation: bulges versus pseudo-bulges     

Jian Hu 《Monthly notices of the Royal Astronomical Society》2008,386(4):2242-2252

We investigate the correlation between the supermassive black holes (SMBHs) mass ( M _bh) and the stellar velocity dispersion  (σ_*)  in two types of host galaxies: the early-type bulges (disc galaxies with classical bulges or elliptical galaxies) and pseudo-bulges. In the form  log ( M _bh/M_⊙) =α+β log (σ_*/200 km s⁻¹)  , the best-fitting results for the 39 early-type bulges are the slope  β= 4.06 ± 0.28  and the normalization  α= 8.28 ± 0.05  ; the best-fitting results for the nine pseudo-bulges are  β= 4.5 ± 1.3  and  α= 7.50 ± 0.18  . Both relations have intrinsic scatter in  log  M _bh  of ≲0.27 dex. The   M _bh–σ_*  relation for pseudo-bulges is different from the relation in the early-type bulges over the 3σ significance level. The contrasting relations indicate the formation and growth histories of SMBHs depend on their host type. The discrepancy between the slope of the   M _bh–σ_*  relations using different definition of velocity dispersion vanishes in our sample, a uniform slope will constrain the coevolution theories of the SMBHs and their host galaxies more effectively. We also find the slope for the 'core' elliptical galaxies at the high-mass range of the relation appears steeper  (β≃ 5–6)  , which may be the imprint of their origin of dissipationless mergers.  相似文献   

Structure and dynamics of galaxies with a low surface-brightness disc – I. The stellar and ionized-gas kinematics     

A. Pizzella  E. M. Corsini  M. Sarzi  J. Magorrian  J. Méndez-Abreu  L. Coccato  L. Morelli  F. Bertola 《Monthly notices of the Royal Astronomical Society》2008,387(3):1099-1116

Photometry and long-slit spectroscopy are presented for a sample of six galaxies with a low surface-brightness stellar disc and a bulge. The characterizing parameters of the bulge and disc components were derived by means of a two-dimensional photometric decomposition of the images of the sample galaxies. Their surface-brightness distribution was assumed to be the sum of the contribution of a Sérsic bulge and an exponential disc, with each component being described by elliptical and concentric isophotes of constant ellipticity and position angle. The stellar and ionized-gas kinematics were measured along the major and minor axes in half of the sample galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level  μ _R ≈ 24  mag arcsec⁻², reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionized-gas kinematics, which often shows the presence of non-circular, off-plane and non-ordered motions. This raises the question about the reliability of the use of the ionized gas as the tracer of the circular velocity in the modelling of the mass distribution, in particular in the central regions of low surface-brightness galaxies.  相似文献   

On the nature of bulges in general and of box/peanut bulges in particular: input from N-body simulations     

E. Athanassoula 《Monthly notices of the Royal Astronomical Society》2005,358(4):1477-1488

Objects designated as bulges in disc galaxies do not form a homogeneous class. I distinguish three types: the classical bulges, the properties of which are similar to those of ellipticals and which form by collapse or merging; boxy and peanut bulges, which are seen in near-edge-on galaxies and which are in fact just a part of the bar seen edge-on; and, finally, disc-like bulges, which result from the inflow of (mainly) gas to the centre-most parts, and subsequent star formation. I make a detailed comparison of the properties of boxy and peanut bulges with those of N -body bars seen edge-on, and answer previously voiced objections about the links between the two. I also present and analyse simulations where a boxy/peanut feature is present at the same time as a classical spheroidal bulge, and compare them with observations. Finally, I propose a nomenclature that can help to distinguish between the three types of bulges and avoid considerable confusion.  相似文献   

Density–potential pairs for spherical stellar systems with Sérsic light profiles and (optional) power-law cores     

Bal&#;a Terzi&#;  Alister W. Graham 《Monthly notices of the Royal Astronomical Society》2005,362(1):197-212

Popular models for describing the luminosity-density profiles of dynamically hot stellar systems (e.g. Jaffe, Hernquist, Dehnen) were constructed with the desire to match the deprojected form of an   R ^1/4  light profile. Real galaxies, however, are now known to have a range of different light-profile shapes that scale with mass. Consequently, although highly useful, the above models have implicit limitations, and this is illustrated here through their application to a number of real galaxy density profiles. On the other hand, the analytical density profile given by Prugniel & Simien closely matches the deprojected form of Sérsic   R ^{1/ n}   light profiles – including deprojected exponential light profiles. It is thus applicable for describing bulges in spiral galaxies, dwarf elliptical galaxies, and both ordinary and giant elliptical galaxies. Moreover, the observed Sérsic quantities define the parameters of the density model. Here we provide simple equations, in terms of elementary and special functions, for the gravitational potential and force associated with this density profile. Furthermore, to match galaxies with partially depleted cores, and better explore the supermassive black hole/galaxy connection, we have added a power-law core to this density profile and derived similar expressions for the potential and force of this hybrid profile. Expressions for the mass and velocity dispersion, assuming isotropy, are also given. These spherical models may also prove appropriate for describing the dark matter distribution in haloes formed from ΛCDM cosmological simulations.  相似文献   

Galactic bulges from Hubble Space Telescope NICMOS observations: ages and dust     

Reynier F. Peletier  Marc Balcells  Roger L. Davies  Y. Andredakis  A. Vazdekis  A. Burkert  F. Prada 《Monthly notices of the Royal Astronomical Society》1999,310(3):703-716

We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the Hubble Space Telescope ( HST ). By combined use of HST and ground-based data, the colour information spans a region from a few tens of pc to a few kpc. In almost all galaxies, the colour profiles in the central 100–200 pc become more rapidly redder. We attribute the high central colour indices to a central concentration of dust. We infer an average extinction at the centre of A _V =0.6–1.0 mag. Several objects show central dust rings or discs at subkpc scales similar to those found by others in giant ellipticals. For galactic bulges of types S0 to Sb, the tightness of the B − I versus I − H relation suggests that the age spread among bulges of early-type galaxies is small, at most 2 Gyr. Colours at 1 R _eff, where we expect extinction to be negligible, are similar to those of elliptical galaxies in the Coma cluster, suggesting that these bulges formed at the same time as the bright galaxies in Coma. Furthermore, the galaxy ages are found to be independent of their environment. As it is likely that Coma was formed at redshift z >3, our bulges, which are in groups and in the field, must also have been formed at this epoch. Bulges of early-type spirals cannot be formed by secular evolution of bars at recent epochs, because such bulges would be much younger. There are three galaxies of type Sbc and later; their bulges are younger and could perhaps arise from secular evolution of transient bars. Our results are in good agreement with semi-analytic predictions, which also predict that bulges, in clusters and in the field, are as old as giant ellipticals in clusters.  相似文献   

Strong size evolution of the most massive galaxies since z∼ 2     

Ignacio Trujillo †  C. J. Conselice  Kevin Bundy  M. C. Cooper  P. Eisenhardt  Richard S. Ellis 《Monthly notices of the Royal Astronomical Society》2007,382(1):109-120

Using the combined capabilities of the large near-infrared Palomar/DEEP-2 survey, and the superb resolution of the Advanced Camera for Surveys HST camera, we explore the size evolution of 831 very massive galaxies  ( M _⋆≥ 10¹¹ h ⁻²₇₀ M_⊙)  since   z ∼ 2  . We split our sample according to their light concentration using the Sérsic index n . At a given stellar mass, both low  ( n < 2.5)  and high  ( n > 2.5)  concentrated objects were much smaller in the past than their local massive counterparts. This evolution is particularly strong for the highly concentrated (spheroid like) objects. At   z ∼ 1.5  , massive spheroid-like objects were a factor of 4 (±0.4) smaller (i.e. almost two orders of magnitudes denser) than those we see today. These small sized, high-mass galaxies do not exist in the nearby Universe, suggesting that this population merged with other galaxies over several billion years to form the largest galaxies we see today.  相似文献   

Nuclear stellar discs in early-type galaxies — II. Photometric properties     

Cecilia Scorza  & Frank C. van den Bosch 《Monthly notices of the Royal Astronomical Society》1998,300(2):469-478

Hubble Space Telescope images of two early-type galaxies harbouring both nuclear and outer stellar discs are studied in detail. By means of a photometric decomposition, the images of NGC 4342 and 4570 are analysed and the photometric properties of the nuclear discs investigated. We find a continuity of properties in the parameter space defined by the central surface brightness μ₀ and the scalelength R _d of discs in spirals, S0s and embedded discs in ellipticals, in the sense that the nuclear discs extend the observed disc properties even further towards smaller scalelengths and brighter central surface brightnesses. When including the nuclear discs, disc properties span more than four orders of magnitude in both scalelength and central surface brightness. The nuclear discs studied here are the smallest and brightest stellar discs known, and as such, they are as extreme in their photometric properties as Malin I, when compared with typical galactic discs that obey Freeman's law. We discuss a possible formation scenario in which the double-disc structure observed in these galaxies has been shaped by now dissolved bars. Based on the fact that the black holes known to exist in some of these galaxies have masses comparable to those of the nuclear discs, we explore a possible link between the black holes and the nuclear discs.  相似文献   

The flattening and the orbital structure of early-type galaxies and collisionless N-body binary disc mergers     

J. Thomas  R. Jesseit  R. P. Saglia  R. Bender  A. Burkert  E. M. Corsini  K. Gebhardt  J. Magorrian  T. Naab  D. Thomas  G. Wegner 《Monthly notices of the Royal Astronomical Society》2009,393(2):641-652

We use oblate axisymmetric dynamical models including dark haloes to determine the orbital structure of intermediate mass to massive early-type galaxies in the Coma galaxy cluster. We find a large variety of orbital compositions. Averaged over all sample galaxies the unordered stellar kinetic energy in the azimuthal and the radial direction are of the same order, but they can differ by up to 40 per cent in individual systems. In contrast, both for rotating and non-rotating galaxies the vertical kinetic energy is on average smaller than in the other two directions. This implies that even most of the rotating ellipticals are flattened by an anisotropy in the stellar velocity dispersions. Using three-integral axisymmetric toy models, we show that flattening by stellar anisotropy maximizes the entropy for a given density distribution. Collisionless disc merger remnants are radially anisotropic. The apparent lack of strong radial anisotropy in observed early-type galaxies implies that they may not have formed from mergers of discs unless the influence of dissipational processes was significant.  相似文献   

Numerical modelling of the vertical structure and dark halo parameters in disc galaxies     

A. Khoperskov  D. Bizyaev  N. Tiurina  M. Butenko 《Astronomische Nachrichten》2010,331(7):731-745

The non‐linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N‐body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo‐to‐disc mass ratio is predicted from the simulations. The method of assessment of the spherical‐to‐disc mass ratio for edge‐on spiral galaxies with a small bulge is considered. Modelling of eight edge‐on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark‐to‐luminous mass ratio in our galaxies is of the order of one within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Bulge–disc decompositions and structural bimodality of Ursa Major cluster spiral galaxies     

Michael McDonald †  Stéphane Courteau  R. Brent Tully 《Monthly notices of the Royal Astronomical Society》2009,393(2):628-640

We present bulge and disc (B/D) decompositions of existing   K '  surface brightness profiles for 65 Ursa Major (UMa) cluster spiral galaxies. This improves upon the disc-only fits of Tully et al. The 1996 disc fits were used by Tully & Verheijen for their discovery of the bimodality of structural parameters in the UMa cluster galaxies. It is shown that our new one-dimensional B/D decompositions yield disc structural parameters that differ only slightly from the basic fits of Tully et al. and evidence for structural bimodality of UMa galaxies is maintained. Our B/D software for the decomposition of one-dimensional surface brightness profiles of galaxies uses a non-linear minimization scheme to recover the best-fitting Sérsic bulge and the exponential disc while accounting for the possible presence of a compact nucleus and spiral arms and for the effects of seeing and disc truncations. In agreement with Tully & Verheijen, we find that the distribution of near-infrared disc central surface brightnesses is bimodal with an F-test confidence of 80 per cent. There is also strong evidence for a local minimum in the luminosity function at     . A connection between the brightness bimodality and a dynamical bimodality, based on new H  i linewidths, is identified. The B/D parameters are presented in Table 1 .