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1.
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.
We present the results of a study which uses the 3C RR sample of radio-loud active galactic nuclei to investigate the evolution of the black hole:spheroid mass ratio in the most massive early-type galaxies from  0 < z < 2  . Radio-loud unification is exploited to obtain virial (linewidth) black hole mass estimates from the 3C RR quasars, and stellar mass estimates from the 3C RR radio galaxies, thereby providing black hole and stellar mass estimates for a single population of early-type galaxies. At low redshift  ( z ≲ 1)  , the 3C RR sample is consistent with a black hole:spheroid mass ratio of   M bh/ M sph≃ 0.002  , in good agreement with that observed locally for quiescent galaxies of similar stellar mass  ( M sph≃ 5 × 1011 M⊙)  . However, over the redshift interval  0 < z < 2  the 3C RR black hole:spheroid mass ratio is found to evolve as   M bh/ M sph∝ (1 + z )2.07±0.76  , reaching   M bh/ M sph≃ 0.008  by redshift   z ≃ 2  . This evolution is found to be inconsistent with the local black hole:spheroid mass ratio remaining constant at a moderately significant level (98 per cent). If confirmed, the detection of evolution in the 3C RR black hole:spheroid mass ratio further strengthens the evidence that, at least for massive early-type galaxies, the growth of the central supermassive black hole may be completed before that of the host spheroid.  相似文献   

3.
We use the very large Millennium Simulation of the concordance Λ cold dark matter cosmogony to calibrate the bias and error distribution of Timing Argument estimators of the masses of the Local Group and of the Milky Way. From a large number of isolated spiral–spiral pairs similar to the Milky Way/Andromeda system, we find the interquartile range of the ratio of timing mass to true mass to be a factor of 1.8, while the 5 and 95 per cent points of the distribution of this ratio are separated by a factor of 5.7. Here, we define true mass as the sum of the 'virial' masses, M 200, of the two dominant galaxies. For present best values of the distance and approach velocity of Andromeda, this leads to a median likelihood estimate of the true mass of the Local Group of  5.27 × 1012 M⊙  or  log  M LG/M⊙= 12.72  , with an interquartile range of [12.58, 12.83] and a 5–95 per cent range of [12.26, 13.01]. Thus, a 95 per cent lower confidence limit on the true mass of the Local Group is  1.81 × 1012 M⊙  . A timing estimate of the Milky Way's mass based on the large recession velocity observed for the distant satellite Leo I works equally well, although with larger systematic uncertainties. It gives an estimated virial mass for the Milky Way of  2.43 × 1012 M⊙  with a 95 per cent lower confidence limit of  0.80 × 1012 M⊙  .  相似文献   

4.
The Sc galaxy M 99 in the Virgo Cluster has been strongly affected by tidal interactions and recent close encounters, responsible for an asymmetric spiral pattern and a high star formation rate. Our XMM–Newton study shows that the inner disc is dominated by hot plasma at kT ≈ 0.30 keV, with a total X-ray luminosity of ≈1041 erg s−1 in the 0.3–12 keV band. At the outskirts of the galaxy, away from the main star-forming regions, there is an ultraluminous X-ray source (ULX) with an X-ray luminosity of ≈2 × 1040 erg s−1 and a hard spectrum well fitted by a power law of photon index Γ≈ 1.7. This source is close to the location where a massive H  i cloud appears to be falling on to the M 99 disc at a relative speed of >100 km s−1. We suggest that there may be a direct physical link between fast cloud collisions and the formation of bright ULXs, which may be powered by accreting black holes with masses ∼100 M⊙. External collisions may trigger large-scale dynamical collapses of protoclusters, leading to the formation of very massive (≳200 M⊙) stellar progenitors; we argue that such stars may later collapse into massive black holes if their metal abundance is sufficiently low.  相似文献   

5.
We report further UKIRT spectroscopic observations of Sakurai's object (V4334 Sgr) made in 1999 April/May in the 1–4.75 μm range, and find that the emission is dominated by amorphous carbon at T d~600 K. The estimated maximum grain size is 0.6 μm, and the mass lower limit is 1.7±0.2×10−8 M⊙ to 8.9±0.6×10−7 M⊙ for distances of 1.1–8 kpc. For 3.8 kpc the mass is 2.0±0.1×10−7 M⊙.
We also report strong He  i emission at 1.083 μm, in contrast to the strong absorption in this line in 1998. We conclude that the excitation is collisional, and is probably caused by a wind, consistent with the P Cygni profile observed by Eyres et al. in 1998.  相似文献   

6.
Active galactic nuclei can produce extremely powerful jets. While tightly collimated, the scale of these jets and the stellar density at galactic centres implies that there will be many jet/star interactions, which can mass load the jet through stellar winds. Previous work employed modest wind mass outflow rates, but this does not apply when mass loading is provided by a small number of high mass-loss stars. We construct a framework for jet mass loading by stellar winds for a broader spectrum of wind mass-loss rates than has previously been considered. Given the observed stellar mass distributions in galactic centres, we find that even highly efficient (0.1 Eddington luminosity) jets from supermassive black holes of masses M BH≲ 104 M⊙ are rapidly mass loaded and quenched by stellar winds. For  104 M⊙ < M BH < 108 M⊙  , the quenching length of highly efficient jets is independent of the jet's mechanical luminosity. Stellar wind mass loading is unable to quench efficient jets from more massive engines, but can account for the observed truncation of the inefficient M87 jet, and implies a baryon-dominated composition on scales ≳2 kpc therein even if the jet is initially pair plasma dominated.  相似文献   

7.
We present J , H and K -band spectroscopy of Cygnus A, spanning 1.0–2.4 μm in the rest-frame and hence several rovibrational H2, H recombination and [Fe  ii ] emission lines. The lines are spatially extended by up to 6 kpc from the nucleus, but their distinct kinematics indicate that the three groups (H, H2 and [Fe  ii ]) are not wholly produced in the same gas. The broadest line, [Fe  ii ] λ 1.644, exhibits a non-Gaussian profile with a broad base (FWHM≃1040 km s−1), perhaps because of the interaction with the radio source. Extinctions to the line-emitting regions substantially exceed earlier measurements based on optical H recombination lines.
Hard X-rays from the quasar nucleus are likely to dominate the excitation of the H2 emission. The results of Maloney, Hollenbach & Tielens are thus used to infer the total mass of gas in H2 v=1–0 S(1)-emitting clouds as a function of radius, for gas densities of 103 and 105 cm−3, and stopping column densities N H=1022–1024 cm−2. Assuming azimuthal symmetry, at least 2.3×108 M⊙ of such material is present within 5 kpc of the nucleus, if the line-emitting clouds see an unobscured quasar spectrum. Alternatively, if the bulk of the X-ray absorption to the nucleus inferred by Ueno et al. actually arises in a circumnuclear torus, the implied gas mass rises to ∼1010 M⊙. The latter plausibly accounts for 109 yr of mass deposition from the cluster cooling flow, for which within this radius.  相似文献   

8.
A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 μm has been carried out to map the regions around several 850-μm-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-μm flux densities for 24 850-μm sources, seven of which are detected at ≥2.5σ within a 10 arcsec search radius of the 850-μm positions. When results from the literature are included the total number of 350-μm flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich  ( M dust≃ 9 × 108 M⊙)  , luminous  ( L FIR≃ 2 × 1012 L⊙)  star-forming galaxies with intrinsic dust temperatures of ≃35 K and star formation rates of  ≃400 M⊙ yr−1  . We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-μm source counts, N 350(>25 mJy) ∼ 200–500 deg−2.  相似文献   

9.
Using eight dark matter haloes extracted from fully self-consistent cosmological N -body simulations, we perform microlensing experiments. A hypothetical observer is placed at a distance of 8.5 kpc from the centre of the halo measuring optical depths, event durations and event rates towards the direction of the Large Magellanic Cloud. We simulate 1600 microlensing experiments for each halo. Assuming that the whole halo consists of massive astronomical compact halo objects (MACHOs),   f = 1.0  , and a single MACHO mass is   m M= 1.0 M⊙  , the simulations yield mean values of  τ= 4.7+5.0−2.2× 10−7  and  Γ= 1.6+1.3−0.6× 10−6  events star−1 yr−1. We find that triaxiality and substructure can have major effects on the measured values so that τ and Γ values of up to three times the mean can be found. If we fit our values of τ and Γ to the MACHO collaboration observations, we find   f = 0.23+0.15−0.13  and   m M= 0.44+0.24−0.16  . Five out of the eight haloes under investigation produce f and m M values mainly concentrated within these bounds.  相似文献   

10.
We have observed the   z =0.78  cluster MS 1137.5+6625 with the Ryle Telescope (RT) at 15 GHz. After subtraction of contaminating radio sources in the field, we find a Sunyaev–Zel'dovich flux decrement of  -421±60 μJy  on the ≈0.65 k λ baseline of the RT, spatially coincident with the optical and X-ray positions for the cluster core.
For a spherical King-profile cluster model, the best fit to our flux measurement has a core radius   θ C=20 arcsec  , consistent with previous X-ray observations, and a central temperature decrement  Δ T =650±92 μK  .
Using this model, we calculate that the cluster has a gas mass inside a     radius of  2.9×1013 M⊙  for an  Ω M =1  universe and  1.6×1013 M⊙  for  Ω M =0.3  ,  ΩΛ=0.7  . We compare this model with existing measurements of the total mass of the cluster, based on gravitational lensing, and estimate a gas fraction for MS 1137.5+6625 of ≈8 per cent.  相似文献   

11.
The cluster 3C 129 is classified as a rich cluster. An analysis of the properties of the cluster 3C 129 from ROSAT PSPC and HRI, Einstein IPC, and EXOSAT ME observations is presented. The mean temperature from a joint fit of the ROSAT PSPC and EXOSAT ME data is 5.5(±0.2) keV. The luminosity is 0.6×1044 erg s−1 in 0.2–2.4 keV and 2.7×1044 erg s−1 in 0.2–10 keV. We find a cooling flow with a rate of ∼84 M⊙ yr−1. The central gas density is 6×10−3 cm−3, and the ICM mass is 3.6×1013 M⊙. The total cluster mass is ∼5×1014 M⊙. The X-ray morphology shows an east–west elongation, which is evidence for a recent merger event. The radio source 3C 129.1 is located near the X-ray centre. Another cluster member galaxy (the radio galaxy 3C 129) is a prototype of head-tailed radio galaxies, and is located in the west part of the cluster. The tail points along the gradient of intracluster gas pressure. There are no significant point X-ray sources associated with the AGNs of the two radio galaxies.  相似文献   

12.
In large spheroidal stellar systems, such as elliptical galaxies, one invariably finds a  106–109 M⊙  supermassive black hole at their centre. In contrast, within dwarf elliptical galaxies one predominantly observes a  105–107 M⊙  nuclear star cluster. To date, few galaxies have been found with both types of nuclei coexisting and even less have had the masses determined for both central components. Here, we identify one dozen galaxies housing nuclear star clusters and supermassive black holes whose masses have been measured. This doubles the known number of such hermaphrodite nuclei – which are expected to be fruitful sources of gravitational radiation. Over the host spheroid (stellar) mass range  108–1011 M⊙  , we find that a galaxy's nucleus-to-spheroid (baryon) mass ratio is not a constant value but decreases from a few per cent to ∼0.3 per cent such that  log[( M BH+ M NC)/ M sph]=−(0.39 ± 0.07) log[ M sph/1010 M⊙]− (2.18 ± 0.07)  . Once dry merging commences and the nuclear star clusters disappear, this ratio is expected to become a constant value.
As a byproduct of our investigation, we have found that the projected flux from resolved nuclear star clusters is well approximated with Sérsic functions having a range of indices from ∼0.5 to ∼3, the latter index describing the Milky Way's nuclear star cluster.  相似文献   

13.
We present a ROSAT and ASCA study of the Einstein source X-9 and its relation to a shock-heated shell-like optical nebula in a tidal arm of the M81 group of interacting galaxies. Our ASCA observation of the source shows a flat and featureless X-ray spectrum well described by a multicolour disc blackbody model. The source most likely represents an optically thick accretion disc around an intermediate-mass black hole  ( M ∼102 M⊙)  in its high/soft state, similar to other variable ultraluminous X-ray sources observed in nearby disc galaxies. Using constraints derived from both the innermost stable orbit around a black hole and the Eddington luminosity, we find that the black hole is fast-rotating and that its mass is between ∼80 M⊙–1.5×102 M⊙. The inferred bolometric luminosity of the accretion disc is ∼(1.1×1040 erg s−1)/(cos  i ). Furthermore, we find that the optical nebula is very energetic and may contain large amounts of hot gas, accounting for a soft X-ray component as indicated by archival ROSAT PSPC data. The nebula is apparently associated with X-9; the latter may be powering the former and/or they could be formed in the same event (e.g. a hypernova). Such a connection, if confirmed, could have strong implications for understanding both the birth of intermediate-mass black holes and the formation of energetic interstellar structures.  相似文献   

14.
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15.
Possible orbital histories of the Sgr dwarf galaxy are explored. A special-purpose N -body code is used to construct the first models of the Milky Way–Sgr dwarf system in which both the Milky Way and the Sgr dwarf are represented by full N -body systems and followed for a Hubble time. These models are used to calibrate a semi-analytic model of the Sgr dwarf's orbit that enables us to explore a wider parameter space than is accessible to the N -body models. We conclude that the extant data on the Sgr dwarf are compatible with a wide range of orbital histories. At one extreme the Sgr dwarf initially possesses ∼1011 M⊙ and starts from a Galactocentric distance R D(0)≳200 kpc. At the other extreme the Sgr dwarf starts with ∼109 M⊙ and R D(0)∼60 kpc, similar to its present apocentric distance. In all cases the Sgr dwarf is initially dark matter dominated and the current velocity dispersion of the Sgr dwarf's dark matter is tightly constrained to be 21±2 km s−1. This number is probably compatible with the smaller measured dispersion of the Sgr dwarf's stars because of (i) the dynamical difference between dark and luminous matter, and (ii) velocity anisotropy.  相似文献   

16.
The analysis of hard X-ray INTEGRAL observations (2003–2008) of superaccreting Galactic microquasar SS433 at precessional phases of the source with the maximum disc opening angle is carried out. It is found that the shape and width of the primary X-ray eclipse are strongly variable, suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I component and the wind–wind collision region. The independence of the observed hard X-ray spectrum on the accretion disc precessional phase suggests that hard X-ray emission (20–100 keV) is formed in an extended, hot, quasi-isothermal corona, probably heated by interaction of relativistic jet with inhomogeneous wind outflow from the precessing supercritical accretion disc. A joint modelling of X-ray eclipsing and precessional hard X-ray variability of SS433 revealed by INTEGRAL by a geometrical model suggests the binary mass ratio   q = mx / m v ≃  0.25–0.5. The absolute minimum of joint orbital and precessional  χ2  residuals is reached at   q ≃ 0.3  . The found binary mass ratio range allows us to explain the substantial precessional variability of the minimum brightness at the middle of the primary optical eclipse. For the mass function of the optical star   f v = 0.268 M⊙  as derived from Hillwig & Gies data, the obtained value of   q ≃ 0.3  yields the masses of the components   mx ≃ 5.3 M⊙, m v ≃ 17.7 M⊙  , confirming the black hole nature of the compact object in SS433.  相似文献   

17.
We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N -body code n-mody , which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 104 to  109 M⊙  and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime  ( a i, a e≪ a 0)  , where the motion of stars is either dominated by internal accelerations  ( a i≫ a e)  or constant external accelerations  ( a e≫ a i)  . In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime  ( a i∼ a e∼ a 0)  . This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal 14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.  相似文献   

18.
We present a detailed calculation of the evolution of low-mass (<0.25 M⊙) helium white dwarfs. These white dwarfs (the optical companions to binary millisecond pulsars) are formed via long-term, low-mass binary evolution. After detachment from the Roche lobe, the hot helium cores have a rather thick hydrogen layer with mass between 0.01 and 0.06 M⊙. As a result of mixing between the core and outer envelope, the surface hydrogen content ( X surf) is 0.5–0.35 , depending on the initial value of the heavy element Z and the initial secondary mass. We found that the majority of our computed models experience one or two hydrogen shell flashes. We found that the mass of the helium dwarf in which the hydrogen shell flash occurs depends on the chemical composition. The minimum helium white dwarf mass in which a hydrogen flash takes place is 0.213 M⊙ ( Z =0.003), 0.198 M⊙ ( Z =0.01), 0.192 M⊙ ( Z =0.02) or 0.183 M⊙ ( Z =0.03). The duration of the flashes (independent of chemical composition) is between a few ×106 and a few ×107 yr. In several flashes the white dwarf radius will increase so much that it forces the model to fill its Roche lobe again. Our calculations show that the cooling history of the helium white dwarf depends dramatically on the thickness of the hydrogen layer. We show that the transition from a cooling white dwarf with a temporarily stable hydrogen-burning shell to a cooling white dwarf in which almost all residual hydrogen is lost in a few thermal flashes (via Roche lobe overflow) occurs between 0.183 and 0.213 M⊙ (depending on the heavy element value).  相似文献   

19.
We report the first detection of CO in the bulge of M31. The 12CO (1–0) and (2–1) lines are both detected in the dust complex D395A/393/384, at 1.3 arcmin (∼0.35 kpc) from the centre. From these data and from visual extinction data, we derive a CO luminosity to reddening ratio (and a CO luminosity to H2 column density ratio) quite similar to that observed in the local Galactic clouds. The (2–1) to (1–0) line intensity ratio points to a CO rotational temperature and a gas kinetic temperature of >10 K. The molecular mass of the complex, inside a 25-arcsec (100 pc) region, is 1.5×104 M⊙.  相似文献   

20.
The 'Carina Flare' supershell, GSH 287+04−17, is a molecular supershell originally discovered in  12CO( J = 1–0)  with the NANTEN 4 m telescope. We present the first study of the shell's atomic ISM, using H  i 21-cm line data from the Parkes 64-m telescope Southern Galactic Plane Survey. The data reveal a gently expanding,  ∼230 × 360  pc H  i supershell that shows strong evidence of Galactic Plane blowout, with a break in its main body at   z ∼ 280  pc and a capped high-latitude extension reaching   z ∼ 450  pc. The molecular clouds form comoving parts of the atomic shell, and the morphology of the two phases reflects the supershell's influence on the structure of the ISM. We also report the first discovery of an ionized component of the supershell, in the form of delicate, streamer-like filaments aligned with the proposed direction of blowout. The distance estimate to the shell is re-examined, and we find strong evidence to support the original suggestion that it is located in the Carina Arm at a distance of  2.6 ± 0.4 kpc  . Associated H  i and H2 masses are estimated as   M H I≈ 7 ± 3 × 105 M⊙  and     , and the kinetic energy of the expanding shell as   E K ∼ 1 × 1051  erg. We examine the results of analytical and numerical models to estimate a required formation energy of several 1051 to  ∼1052  erg, and an age of  ∼107 yr  . This age is compatible with molecular cloud formation time-scales, and we briefly consider the viability of a supershell-triggered origin for the molecular component.  相似文献   

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