共查询到20条相似文献,搜索用时 588 毫秒
1.
R. Decarli G. Gavazzi I. Arosio L. Cortese A. Boselli C. Bonfanti M. Colpi 《Monthly notices of the Royal Astronomical Society》2007,381(1):136-150
The first spectroscopic census of active galactic nuclei (AGNs) associated with late-type galaxies in the Virgo cluster was carried out by observing 213 out of a complete set of 237 galaxies more massive than M dyn > 108.5 M⊙ . Among them, 77 are classified as AGNs [including 21 transition objects, 47 low-ionization nuclear emission regions (LINERs) and nine Seyferts] and comprise 32 per cent of the late-type galaxies in Virgo. Due to spectroscopic incompleteness, at most 21 AGNs are missed in the survey, so that the fraction would increase up to 41 per cent. Using corollary near-infrared observations that enable us to estimate galaxy dynamical masses, it is found that AGNs are hosted exclusively in massive galaxies, i.e. M dyn ≳ 1010 M⊙ . Their frequency increases steeply with the dynamical mass from zero at M dyn ≈ 109.5 M⊙ to virtually 1 at M dyn > 1011.5 M⊙ . These frequencies are consistent with those of low-luminosity AGNs found in the general field by the Sloan Digital Sky Survey. Massive galaxies that harbour AGNs commonly show conspicuous r -band star-like nuclear enhancements. Conversely, they often, but not necessarily, contain massive bulges. A few well-known AGNs (e.g. M61, M100, NGC 4535) are found in massive Sc galaxies with little or no bulge. The AGN fraction seems to be only marginally sensitive to galaxy environment. We infer the black hole masses using the known scaling relations of quiescent black holes. No black holes lighter than ∼106 M⊙ are found active in our sample. 相似文献
2.
Raul Jimenez Benjamin Panter Alan F. Heavens Licia Verde 《Monthly notices of the Royal Astronomical Society》2005,356(2):495-501
Using the spectroscopic sample of the Sloan Digital Sky Survey Data Release 1 (SDSS DR1), we measure how gas was transformed into stars as a function of time and stellar mass: the baryonic conversion tree (BCT). There is a clear correlation between early star formation activity and present-day stellar mass: the more massive galaxies have formed approximately 80 per cent of their stars at z > 1 , while for the less massive ones the value is only approximately 20 per cent. By comparing the BCT with the dark matter merger tree, we find indications that star formation efficiency at z > 1 had to be approximately a factor of two higher than today (∼10 per cent) in galaxies with present-day stellar mass larger than 2 × 1011 M⊙ , if this early star formation occurred in the main progenitor. Therefore, the λ cold dark matter (LCDM) paradigm can accommodate a large number of red objects. On the other hand, in galaxies with present-day stellar mass less than 1011 M⊙ , efficient star formation seems to have been triggered at z ∼ 0.2 . We show that there is a characteristic mass ( M * ∼ 1010 M⊙ ) for feedback efficiency (or lack of star formation). For galaxies with masses lower than this, feedback (or star formation suppression) is very efficient while for higher masses it is not. The BCT, determined here for the first time, should be an important observable with which to confront theoretical models of galaxy formation. 相似文献
3.
Luca Tornatore rea Ferrara Raffaella Schneider 《Monthly notices of the Royal Astronomical Society》2007,382(3):945-950
A Population III/Population II transition from massive to normal stars is predicted to occur when the metallicity of the star-forming gas crosses the critical range Z cr = 10−5±1 Z⊙ . To investigate the cosmic implications of such a process, we use numerical simulations which follow the evolution, metal enrichment and energy deposition of both Population II and Population III stars. We find that: (i) due to inefficient heavy element transport by outflows and slow 'genetic' transmission during hierarchical growth, large fluctuations around the average metallicity arise; as a result, Population III star formation continues down to z = 2.5 , but at a low peak rate of 10−5 M⊙ yr−1 Mpc−3 occurring at z ≈ 6 (about 10−4 of the Population II one); and (ii) Population III star formation proceeds in an 'inside–out' mode in which formation sites are progressively confined to the periphery of collapsed structures, where the low gas density and correspondingly long free-fall time-scales result in a very inefficient astration. These conclusions strongly encourage deep searches for pristine star formation sites at moderate (2 < z < 5) redshifts where metal-free stars are likely to be hidden. 相似文献
4.
J. Dabringhausen P. Kroupa H. Baumgardt 《Monthly notices of the Royal Astronomical Society》2009,394(3):1529-1543
It has been recently shown that the dynamical V -band mass-to-light ratios of compact stellar systems with masses from 106 to 108 M⊙ are not consistent with the predictions from simple stellar population models. Top-heavy stellar initial mass functions (IMFs) in these so-called ultra-compact dwarf galaxies (UCDs) offer an attractive explanation for this finding, the stellar remnants and retained stellar envelopes providing the unseen mass. We therefore construct a model which quantifies by how much the IMFs of UCDs would have to deviate in the intermediate- and high-mass range from the canonical IMF in order to account for the enhanced M / LV ratio of the UCDs. The deduced high-mass IMF in the UCDs depends on the age of the UCDs and the number of faint products of stellar evolution retained by them. Assuming that the IMF in the UCDs is a three-part power law equal to the canonical IMF in the low-mass range and taking 20 per cent as a plausible choice for the fraction of the remnants of high-mass stars retained by UCDs, the model suggests the exponent of the high-mass IMF to be ≈1.6 if the UCDs are 13 Gyr old (i.e. almost as old as the Universe) or ≈1.0 if the UCDs are 7 Gyr old, in contrast to 2.3 for the Salpeter–Massey IMF. If the IMF was as top heavy as suggested here, the stability of the UCDs might have been threatened by heavy mass loss induced by the radiation and evolution of massive stars. The central densities of UCDs must have been in the range 106 to 107 M⊙ pc−3 when they formed with star formation rates of 10 to 100 M⊙ yr−1 . 相似文献
5.
Recent evidence of a young progenitor population for many Type Ia supernovae (SNe Ia) raises the possibility that evolved intermediate-mass progenitor stars may be detected in pre-explosion images. NGC 1316, a radio galaxy in the Fornax cluster, is a prolific producer of SNe Ia, with four detected since 1980. We analyse Hubble Space Telescope ( HST ) pre-explosion images of the sites of two of the SNe Ia that exploded in this galaxy, SN2006dd (a normal Type Ia) and SN2006mr (likely a subluminous, 1991bg-like, SN Ia). Astrometric positions are obtained from optical and near-infrared ground-based images of the events. We find no candidate point sources at either location, and set upper limits on the flux in B, V and I from any such progenitors. We also estimate the amount of extinction that could be present, based on analysis of the surface-brightness inhomogeneities in the HST images themselves. At the distance of NGC 1316, the limits correspond to absolute magnitudes of ∼−5.5, −5.4 and −6.0 mag in M B , M V and M I , respectively. Comparison to stellar evolution models argues against the presence at the supernova sites, 3 yr prior to the explosion, of normal stars with initial masses ≳6 M⊙ at the tip of their asymptotic-giant branch (AGB) evolution, young post-AGB stars that had initial masses ≳4 M⊙ and post-red giant stars of initial masses ≳9 M⊙ . 相似文献
6.
Paolo Salucci Charu Ratnam Pierluigi Monaco Luigi Danese 《Monthly notices of the Royal Astronomical Society》2000,317(2):488-496
We use the innermost kinematics of spirals to investigate whether these galaxies could host the massive black hole remnants that once powered the quasi-stellar object (QSO) phenomenon. Hundreds of rotation curves of early- and late-type spirals are used to place upper limits on the central black hole (BH) masses. We find that (i) in late-type spirals, the central massive dark objects (MDOs) are about 10–100 times smaller than the MDOs detected in ellipticals, and (ii) in early-type spirals, the central bodies are likely to be in the same mass range as the elliptical MDOs. As a consequence, the contribution to the QSO/active galactic nuclei (AGN) phenomenon by the BH remnants eventually hosted in spirals is negligible: ρ BH (Sb–Im)<6×104 M⊙ Mpc−3 . We find several hints that the MDO mass versus bulge mass relationship is significantly steeper in spirals than in ellipticals, although the very issue of the existence of such a relation for late Hubble type objects remains open. The upper limits on the masses of the BHs resident in late-type spirals are stringent: M BH 106 –107 M⊙ , indicating that only low-luminosity activity could possibly have occurred in these objects . 相似文献
7.
V. Belokurov N. W. Evans P. C. Hewett A. Moiseev R. G. McMahon S. F. Sanchez L. J. King 《Monthly notices of the Royal Astronomical Society》2009,392(1):104-112
We present discovery images, together with follow-up imaging and spectroscopy, of two large-separation gravitational lenses found by our survey for wide arcs [the CAmbridge Sloan Survey Of Wide ARcs in the skY (CASSOWARY)]. The survey exploits the multicolour photometry of the Sloan Digital Sky Survey to find multiple blue components around red galaxies. CASSOWARY 2 (or 'the Cheshire Cat') is composed of two massive early-type galaxies at z = 0.426 and 0.432, respectively, lensing two background sources, the first a star-forming galaxy at z = 0.97 and the second a high -redshift galaxy ( z > 1.4) . There are at least three images of the former source and probably four or more of the latter, arranged in two giant arcs. The mass enclosed within the larger arc of radius ∼11 arcsec is ∼33 × 1012 M⊙ . CASSOWARY 3 comprises an arc of three bright images of a z = 0.725 source, lensed by a foreground elliptical at z = 0.274 . The radius of the arc is ∼4 arcsec and the enclosed mass is ∼2.5 × 1012 M⊙ . Together with earlier discoveries like the Cosmic Horseshoe and the 8 o'clock Arc, these new systems, with separations intermediate between the arcsecond-separation lenses of typical strong galaxy lensing and arcminute-separation cluster lenses, probe the very high end of the galaxy mass function. 相似文献
8.
Thomas H. Greif † Jarrett L. Johnson Ralf S. Klessen Volker Bromm 《Monthly notices of the Royal Astronomical Society》2008,387(3):1021-1036
We investigate the properties of the first galaxies at z ≳ 10 with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds ≃104 K , and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a ≃5 × 107 M⊙ system by means of a detailed merger tree and derive an upper limit on the number of Population III (Pop III) stars formed prior to its assembly. We investigate the thermal and chemical evolution of infalling gas and find that partial ionization at temperatures ≳104 K catalyses the formation of H2 and hydrogen deuteride, allowing the gas to cool to the temperature of the cosmic microwave background. Depending on the strength of radiative and chemical feedback, primordial star formation might be dominated by intermediate-mass Pop III stars formed during the assembly of the first galaxies. Accretion on to the nascent galaxy begins with hot accretion, where gas is accreted directly from the intergalactic medium and shock heated to the virial temperature, but is quickly accompanied by a phase of cold accretion, where the gas cools in filaments before flowing into the parent halo with high velocities. The latter drives supersonic turbulence at the centre of the galaxy and could lead to very efficient chemical mixing. The onset of turbulence in the first galaxies thus likely marks the transition to Pop II star formation. 相似文献
9.
M. Elmouttie M. Krause R. F. Haynes & K. L. Jones 《Monthly notices of the Royal Astronomical Society》1998,300(4):1119-1126
We have used the Swedish ESO Submillimeter Telescope to observe the molecular gas in the Circinus galaxy using the CO(1 → 0) transition as a tracer. The central region and major axis have been mapped and several other points were also observed. The gas in the galaxy is concentrated towards the nucleus, the peak being coincident with the radio/optical core. The inclination of the molecular galactic disc is more comparable to that of the radio continuum than to that of the large-scale H i emission. Evidence for an anomalous spur structure pointing radially away from the galactic centre is presented, and may indicate a causal link between it and similar features seen in optical lines and radio continuum. Our data suggest the presence of a central molecular ring or disc with radius 300 ± 50 pc and a rotation velocity of about 200 km s−1 (assuming i = 73°). The dynamical mass of the nucleus is estimated to be no greater than 3.9 × 109 M⊙ . Assuming that the distribution of gas varies smoothly in the outer regions, we calculate the mass of molecular gas in the galaxy to be at least M mol = 1.1 × 109 M⊙ , and the star-forming efficiency to be 11 ± 2 L⊙ M⊙ −1 . These results imply that Circinus is undergoing a massive central starburst which may be, at least partially, responsible for its extended minor axis emission seen in several wavebands. 相似文献
10.
Richard J. Stancliffe John J. Eldridge 《Monthly notices of the Royal Astronomical Society》2009,396(3):1699-1708
We have developed a detailed stellar evolution code capable of following the simultaneous evolution of both stars in a binary system, together with their orbital properties. To demonstrate the capabilities of the code, we investigate potential progenitors for the Type IIb Supernova 1993J, which is believed to have been an interacting binary system prior to its primary exploding. We use our detailed binary stellar evolution code to model this system to determine the possible range of primary and secondary masses that could have produced the observed characteristics of this system, with particular reference to the secondary. Using the luminosities and temperatures for both stars (as determined by Maund et al.) and the remaining mass of the hydrogen envelope of the primary at the time of explosion, we find that if mass transfer is 100 per cent efficient, the observations can be reproduced by a system consisting of a 15 M⊙ primary and a 14 M⊙ secondary in an orbit with an initial period of 2100 days. With a mass transfer efficiency of 50 per cent, a more massive system consisting of a 17 M⊙ primary and a 16 M⊙ secondary in an initial orbit of 2360 days is needed. We also investigate some of the uncertainties in the evolution, including the effects of tidal interaction, convective overshooting and thermohaline mixing. 相似文献
11.
12.
Vimal Simha David H. Weinberg Romeel Davé Oleg Y. Gnedin Neal Katz Duan Kere 《Monthly notices of the Royal Astronomical Society》2009,399(2):650-662
We examine the accretion and merger histories of central and satellite galaxies in a smoothed particle hydrodynamics (SPH) cosmological simulation that resolves galaxies down to 7 × 109 M⊙ . Most friends-of-friends haloes in the simulation have a distinct central galaxy, typically 2–5 times more massive than the most massive satellite. As expected, satellites have systematically higher assembly redshifts than central galaxies of the same baryonic mass, and satellites in more massive haloes form earlier. However, contrary to the simplest expectations, satellite galaxies continue to accrete gas and convert it to stars; the gas accretion declines steadily over a period of 0.5–1 Gyr after the satellite halo merges with a larger parent halo. Satellites in a cluster mass halo eventually begin to lose baryonic mass. Typically, satellites in our simulation are 0.1–0.2 mag bluer than in models that assume no gas accretion on to satellites after a halo merger. Since z = 1 , 27 per cent of central galaxies (above 3 × 1010 M⊙ ) and 22 per cent of present-day satellite galaxies have merged with a smaller system above a 1:4 mass ratio; about half of the satellite mergers occurred after the galaxy became a satellite and half before. In effect, satellite galaxies can remain 'central' objects of halo substructures, with continuing accretion and mergers, making the transition in assembly histories and physical properties a gradual one. Implementing such a gradual transformation in semi-analytic models would improve their agreement with observed colour distributions of satellite galaxies in groups and with the observed colour dependence of galaxy clustering. 相似文献
13.
T. M. Lawlor T. R. Young T. A. Johnson J. MacDonald 《Monthly notices of the Royal Astronomical Society》2008,384(4):1533-1543
We present stellar evolution calculations for Population III stars for both single- and binary-star evolutions. Our models include 10- and 16.5-M⊙ single stars and a 10-M⊙ model star that undergoes an episode of accretion resulting in a final mass of 16.1 M⊙ . For comparison, we present the evolution of a solar heavy element abundance model. We use the structure from late-stage evolution models to calculate simulated supernova light curves. Light curve comparisons are made between accretion and non-accretion progenitor models, and models for single-star evolution of comparable masses. Where possible, we make comparisons to previous works. Similar investigations have been carried out, but primarily for solar or near-solar heavy metal abundance stars and not including both the evolution and the supernova explosions in one work. 相似文献
14.
A. Elyiv O. Melnyk I. Vavilova 《Monthly notices of the Royal Astronomical Society》2009,394(3):1409-1418
A geometric method based on the high-order 3D Voronoi tessellation is proposed for identifying single galaxies, pairs and triplets. This approach allows us to select small galaxy groups and isolated galaxies in different environments and to find the isolated systems. The volume-limited sample of galaxies from the Sloan Digital Sky Survey Data Release 5 spectroscopic survey was used. We conclude that in such small groups as pairs and triplets, segregation by luminosity is clearly observed: galaxies in isolated pairs and triplets are on average two times more luminous than isolated galaxies. We consider the dark matter content in different systems. The median values of mass-to-luminosity ratio are 12 M⊙ /L⊙ for the isolated pairs and 44 M⊙ /L⊙ for the isolated triplets, and 7 (8) M⊙ /L⊙ for the most compact pairs (triplets). We also found that systems in denser environments have greater rms velocity and mass-to-luminosity ratio. 相似文献
15.
Jun'ichi Sato † Masayuki Umemura Keisuke Sawada 《Monthly notices of the Royal Astronomical Society》2008,387(4):1517-1524
We consider the effect of a supernova (SN) explosion in a very massive binary that is expected to form in a portion of Population III stars with the mass higher than 100 M⊙ . In a Population III binary system, a more massive star can result in the formation of a black hole (BH) and a surrounding accretion disc. Such BH accretion could be a significant source of the cosmic reionization in the early Universe. However, a less massive companion star evolves belatedly and eventually undergoes a SN explosion, so that the accretion disc around a BH might be blown off in a lifetime of companion star. In this paper, we explore the dynamical impact of a SN explosion on an accretion disc around a massive BH, and elucidate whether the BH accretion disc is totally demolished or not. For the purpose, we perform three-dimensional hydrodynamic simulations of a very massive binary system, where we assume a BH of 103 M⊙ that results from a direct collapse of a very massive star and a companion star of 100 M⊙ that undergoes a SN explosion. We calculate the remaining mass of a BH accretion disc as a function of time. As a result, it is found that a significant portion of gas disc can survive through three-dimensional geometrical effects even after the SN explosion of a companion star. Even if the SN explosion energy is higher by two orders of magnitude than the binding energy of gas disc, about a half of disc can be left over. The results imply that the Population III BH accretion disc can be a long-lived luminous source, and therefore could be an important ionizing source in the early Universe. 相似文献
16.
We investigate the role that dry mergers play in the build-up of massive galaxies within the cold dark matter paradigm. Implementing an empirical shut-off mass scale for star formation, we find a nearly constant dry merger rate of ∼6 × 10−5 Mpc−3 Gyr−1 at z ≤ 1 and a steep decline at larger z . Less than half of these mergers are between two galaxies that are morphologically classified as early-types, and the other half is mostly between an early- and late-type galaxy. Latter are prime candidates for the origin of tidal features around red elliptical galaxies. The introduction of a transition mass scale for star formation has a strong impact on the evolution of galaxies, allowing them to grow above a characteristic mass scale of M *, c ∼ 6.3 × 1010 M⊙ by mergers only. As a consequence of this transition, we find that around M *, c , the fraction of 1:1 mergers is enhanced with respect to unequal mass major mergers. This suggests that it is possible to detect the existence of a transition mass scale by measuring the relative contribution of equal mass mergers to unequal mass mergers as a function of galaxy mass. The evolution of the high-mass end of the luminosity function is mainly driven by dry mergers at low z . We however find that only 10–20 per cent of galaxies more massive than M *, c experience dry major mergers within their last Gyr at any given redshift z ≤ 1 . 相似文献
17.
We explore the implications of a possible cosmic-ray (CR) background generated during the first supernova explosions that end the brief lives of massive Population III stars. We show that such a CR background could have significantly influenced the cooling and collapse of primordial gas clouds in minihaloes around redshifts of z ∼ 15–20 , provided the CR flux was sufficient to yield an ionization rate greater than about 10−19 s−1 near the centre of the minihalo. The presence of CRs with energies ≲107 eV would indirectly enhance the molecular cooling in these regions, and we estimate that the resulting lower temperatures in these minihaloes would yield a characteristic stellar mass as low as ∼10 M⊙ . CRs have a less-pronounced effect on the cooling and collapse of primordial gas clouds inside more massive dark matter haloes with virial masses ≳108 M⊙ at the later stages of cosmological structure formation around z ∼ 10–15 . In these clouds, even without CR flux the molecular abundance is already sufficient to allow cooling to the floor set by the temperature of the cosmic microwave background. 相似文献
18.
Vasilii V. Gvaramadze Alessia Gualandris Simon Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2009,396(1):570-578
We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50–100 M⊙ star or a more massive one, formed through runaway mergers of ordinary stars in the core of a young massive star cluster). In this process, one of the binary components becomes gravitationally bound to the very massive star, while the second one is ejected, sometimes with a high speed. We performed three-body scattering experiments and found that early B-type stars (the progenitors of the majority of neutron stars) can be ejected with velocities of ≳200–400 km s−1 (typical of pulsars), while 3–4 M⊙ stars can attain velocities of ≳300–400 km s−1 (typical of the bound population of halo late B-type stars). We also found that the ejected stars can occasionally attain velocities exceeding the Milky Ways's escape velocity. 相似文献
19.
Andrew J. Davis Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2009,393(4):1498-1502
In this paper, we study the angular momentum properties of simulated dark matter haloes at high redshifts that likely host the first stars in the Universe. Calculating the spin distributions of these 106 – 107 M⊙ haloes in redshift slices from z = 15 to 6, we find that they are well fit by a lognormal distribution as is found for lower redshift and more massive haloes in earlier work. We find that both the mean value of the spin and dispersion are largely unchanged with redshift for all haloes. Our key result is that subsamples of low- and high-spin, 106 and 107 M⊙ , haloes show difference in clustering strength. In both mass bins, higher spin haloes are more strongly clustered in concordance with a tidal torquing picture for the growth of angular momentum in dark matter haloes in the cold dark matter paradigm. 相似文献
20.
F. Donato G. Gentile P. Salucci C. Frigerio Martins M. I. Wilkinson G. Gilmore E. K. Grebel A. Koch R. Wyse 《Monthly notices of the Royal Astronomical Society》2009,397(3):1169-1176
We confirm and extend the recent finding that the central surface density μ0D ≡ r 0 ρ0 of galaxy dark matter haloes, where r 0 and ρ0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves (RCs) of ∼1000 spiral galaxies, the mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality RCs, and the galaxy–galaxy weak-lensing signals from a sample of spiral and elliptical galaxies, we find that log μ0D = 2.15 ± 0.2 in units of log(M⊙ pc−2 ) . We also show that the observed kinematics of Local Group dwarf spheroidal galaxies are consistent with this value. Our results are obtained for galactic systems spanning over 14 mag, belonging to different Hubble types and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of μ0D is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including ρ0 and central stellar surface density. 相似文献