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1.
We present velocity dispersion measurements for 69 faint early-type galaxies in the core of the Coma cluster, spanning  −22.0 ≲ MR ≲−17.5 mag  . We examine the   L –σ  relation for our sample and compare it to that of bright elliptical galaxies (Es) from the literature. The distribution of the the faint early-type galaxies in the   L –σ  plane follows the relation   L ∝σ2.01±0.36  , which is significantly shallower from   L ∝σ4  as defined for the bright Es. While increased rotational support for fainter early-type galaxies could account for some of the difference in slope, we show that it cannot explain it. We also investigate the colour–σ relation for our Coma galaxies. Using the scatter in this relation, we constrain the range of galaxy ages as a function of their formation epoch for different formation scenarios. Assuming a strong coordination in the formation epoch of faint early-type systems in Coma, we find that most had to be formed at least 6 Gyr ago and over a short 1-Gyr period.  相似文献   

2.
We have constructed an analytical model of active galactic nuclei (AGN) feedback and studied its implications for elliptical galaxies and galaxy clusters. The results show that momentum injection above a critical value will eject material from low-mass elliptical galaxies, and leads to an X-ray luminosity, L X, that is  ∝σ8−10  , depending on the AGN fuelling mechanism, where σ is the velocity dispersion of the hot gas. This result agrees well with both observations and semi-analytic models. In more massive ellipticals and clusters, AGN outflows quickly become buoyancy dominated. This necessarily means that heating by a central cluster AGN redistributes the intracluster medium (ICM) such that the mass of hot gas, within the cooling radius, should be  ∝ L X(< r cool)/[ g ( r cool)σ]  , where   g ( r cool)  is the gravitational acceleration at the cooling radius. This prediction is confirmed using observations of seven clusters. The same mechanism also defines a critical ICM cooling time of  ∼0.5 Gyr  , which is in reasonable agreement with recent observations showing that star formation and AGN activity are triggered below a universal cooling time threshold.  相似文献   

3.
We present a search for  CO(1 → 0)  emission in three Local Group dwarf irregular galaxies: IC 5152, the Phoenix dwarf and UGCA 438, using the ATNF Mopra radio telescope. Our scans largely cover the optical extent of the galaxies and the stripped H  i cloud west of the Phoenix dwarf. Apart from a tentative but non-significant emission peak at one position in the Phoenix dwarf, no significant emission was detected in the CO spectra of these galaxies. For a velocity width of 6 km s−1, we derive 4σ upper limits of 0.03, 0.04 and 0.06 K km s−1 for IC 5152, the Phoenix dwarf and UGCA 438, respectively. This is an improvement of over a factor of 10 compared with previous observations of IC 5152; the other two galaxies had not yet been observed at millimetre wavelengths. Assuming a Galactic CO-to-H2 conversion factor, we derive upper limits on the molecular gas mass of  6.2 × 104, 3.7 × 103  and  1.4 × 105 M⊙  for IC 5152, the Phoenix dwarf and UGCA 438, respectively. We investigate two possible causes for the lack of CO emission in these galaxies. On the one hand, there may be a genuine lack of molecular gas in these systems, in spite of the presence of large amounts of neutral gas. However, in the case of IC 5152 which is actively forming stars, molecular gas is at least expected to be present in the star-forming regions. On the other hand, there may be a large increase in the CO-to-H2 conversion factor in very low-metallicity dwarfs  (−2 ≤[Fe/H]≤−1)  , making CO a poor tracer of the molecular gas content in dwarf galaxies.  相似文献   

4.
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   

5.
Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of     and a line-of-sight velocity dispersion σ z =599 (+230,−110) km s−1. The velocity dispersion and previously measured X-ray gas temperature of kT ≃1.9 keV are consistent with the cluster σ z kT relation, and NGC 326 is seen to be a slowly moving member of the cluster.  相似文献   

6.
We present the luminosity function and measurements of the scalelengths, colours and radial distribution of dwarf galaxies in the Coma cluster down to R =24. Our survey area is 674 arcmin2; this is the deepest and most detailed survey covering such a large area.
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ L α that is steep (α∼−1.7) for −15< MR <−11, and is shallower brighter than this. The curvature in the luminosity function at MR ∼−15 is statistically significant.
(2) The galaxies that contribute most strongly to the luminosity function at −14< MR <−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma.
(3) These galaxies with −14< MR <−12 have a colour distribution that is very strongly peaked at B − R =1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities.
(4) These galaxies with −14< MR <−12 also appear to be more confined to the cluster core ( r ∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities.  相似文献   

7.
The modified Newtonian dynamics (MOND), suggested by Milgrom as an alternative to dark matter, implies that isothermal spheres with a fixed anisotropy parameter should exhibit a near-perfect relation between the mass and velocity dispersion of the form M ∝ σ  4. This is consistent with the observed Faber–Jackson relation for elliptical galaxies: a luminosity–velocity dispersion relation with large scatter. However, the observable global properties of elliptical galaxies comprise a three-parameter family; they lie on a 'fundamental plane' in a logarithmic space consisting of central velocity dispersion, effective radius ( r e) and luminosity. The scatter perpendicular to this plane is significantly less than that about the Faber–Jackson relation. I show here that, in order to match the observed properties of elliptical galaxies with MOND, models must deviate from being strictly isothermal and isotropic; such objects can be approximated by high-order polytropic spheres with a radial orbit anisotropy in the outer regions. MOND imposes boundary conditions on the inner Newtonian regions which restrict these models to a dynamical fundamental plane of the form where the exponents may differ from the Newtonian expectations ( α =2, γ =1). Scatter about this plane is relatively insensitive to the necessary deviations from homology.  相似文献   

8.
Understanding the origin and evolution of dwarf early-type galaxies remains an important open issue in modern astrophysics. Internal kinematics of a galaxy contains signatures of violent phenomena which may have occurred, e.g. mergers or tidal interactions, while stellar population keeps a fossil record of the star formation history; therefore studying connection between them becomes crucial for understanding galaxy evolution. Here, in the first paper of the series, we present the data on spatially resolved stellar populations and internal kinematics for a large sample of dwarf elliptical (dE) and lenticular (dS0) galaxies in the Virgo cluster. We obtained radial velocities, velocity dispersions, stellar ages and metallicities out to 1–2 half-light radii by reanalysing already published long-slit and integral-field spectroscopic data sets using the nbursts full spectral fitting technique. Surprisingly, bright representatives of the dE/dS0 class (   MB =−18.0  to −16.0 mag) look very similar to intermediate-mass and giant lenticulars and ellipticals: (1) their nuclear regions often harbour young metal-rich stellar populations always associated with the drops in the velocity dispersion profiles; (2) metallicity gradients in the main discs/spheroids vary significantly from nearly flat profiles to −0.9 dex   r −1e  , i.e. somewhat three times steeper than for typical bulges; (3) kinematically decoupled cores were discovered in four galaxies, including two with very little, if any, large-scale rotation. These results suggest similarities in the evolutionary paths of dwarf and giant early-type galaxies and call for reconsidering the role of major mergers in the dE/dS0 evolution.  相似文献   

9.
Cosmological N -body simulations were performed to study the evolution of the phase-space density   Q =ρ/σ3  of dark matter haloes. No significant differences in the scale relations   Q ∝σ−2.1  or   Q ∝ M −0.82  are seen for the 'cold' or 'warm' dark matter models. The follow-up of individual haloes from   z = 10  up to the present time indicate the existence of two main evolutionary phases: an early and fast one  (10 > z > 6.5)  , in which Q decreases on the average by a factor of 40 as a consequence of the randomization of bulk motions, and a late and long one  (6.5 > z ≥ 0)  , in which Q decreases by a factor of 20 because of mixing induced by merger events. The study of these haloes has also evidenced that rapid and positive variations of the velocity dispersion, induced by merger episodes, are related to a fast decrease of the phase-space density Q .  相似文献   

10.
The recent detection by Limousin et al. of five new strong lensing events dominated by galaxy cluster members in Abell 1689, and outside the critical regime of the cluster itself, offers a way to obtain constraints on the cluster mass distribution in a region inaccessible to standard lensing analysis. In addition, modelling such systems will provide another window on the dark matter haloes of galaxies in very dense environments. Here, it is shown that the boost in image separation due to the external shear and convergence from a smooth cluster component means that more numerous, less massive galaxies have the potential to create multiple images with detectable separations, relative to isolated field galaxies. This comes in addition to a potential increase in their lensing (source plane) cross-section. To gain insight into the factors involved and as a precursor to a numerical study using N -body simulations, a simple analytic model of a cluster at   z = 0.3  lensing background galaxies at   z = 2  is considered here. The fiducial model has cluster members with isothermal density profiles and luminosities L , distributed in a Schechter function (faint-end slope  ν=−1.25  ), related to their velocity dispersions σ via the Faber–Jackson scaling L ∝σ4. Just outside the critical regime of the cluster, the scale of galaxy-dominated image separations is significantly increased. Folding in the fact that less massive galaxies present a lower lensing cross-section, and that the cross-section can itself be enhanced in an external field leads to a factor of a few times more detected events relative to field galaxies. These values will be higher closer to the critical curve. Given that the events in Abell 1689 were detected over a very small region of the cluster where ACS data were available, this motivates the search for such events in other clusters.  相似文献   

11.
We show that the luminosity functions of the distant rich clusters Abell 665 ( z =0.182) and Abell 963 ( z =0.206) are flat or gradually rising down to MR =−14, with α≈−1.2±0.4 [here α is the logarithmic slope of the luminosity function: φ( L )∝ L α at the faint end]. We do not confirm the steep luminosity functions (α≤−1.8) that have been recently proposed for these two clusters.
Several technical points are discussed in detail. In particular, we compute the corrections to the background contamination caused by gravitational lensing from the cluster dark matter, and show that the corrections are small unless we wish to determine variations in the luminosity function on small scales.
Recent observations have also shown that the field galaxy luminosity function at z ≈0.2 is also shallow between MB =−19 and MB =−13. Abell 665 and 963 are two of the richest clusters known at that redshift. We therefore propose that the galaxy luminosity function might be universal in this magnitude range at z =0.2.
The dwarf galaxies that we see in Abell 665 have a colour distribution that is strongly peaked at B − R =1.9. We compute K -corrections based on the spectral energy distributions of local galaxies, and show that these are probably dwarf spheroidal galaxies. This might suggest that the dwarf spheroidal population observed in Virgo already existed at z =0.2.  相似文献   

12.
We have used far-infrared data from IRAS , Infrared Space Observatory ( ISO ), Spitzer Wide-Area Infrared Extragalactic (SWIRE), Submillimetre Common User Bolometer Array (SCUBA) and Max-Planck Millimetre Bolometer (MAMBO) to constrain statistically the mean far-infrared luminosities of quasars. Our quasar compilation at redshifts  0 < z < 6.5  and I -band luminosities  −20 < I AB < −32  is the first to distinguish evolution from quasar luminosity dependence in such a study. We carefully cross-calibrate IRAS against Spitzer and ISO , finding evidence that IRAS 100-μm fluxes at <1 Jy are overestimated by ∼30 per cent. We find evidence for a correlation between star formation in quasar hosts and the quasar optical luminosities, varying as star formation rate (SFR)  ∝ L 0.44±0.07opt  at any fixed redshift below   z = 2  . We also find evidence for evolution of the mean SFR in quasar host galaxies, scaling as  (1 + z )1.6±0.3  at   z < 2  for any fixed quasar I -band absolute magnitude fainter than −28. We find no evidence for any correlation between SFR and black hole mass at  0.5 < z < 4  . Our data are consistent with feedback from black hole accretion regulating stellar mass assembly at all redshifts.  相似文献   

13.
We perform a series of comparisons between distance-independent photometric and spectroscopic properties used in the surface brightness fluctuation (SBF) and fundamental plane (FP) methods of early-type galaxy distance estimation. The data are taken from two recent surveys: the SBF Survey of Galaxy Distances and the Streaming Motions of Abell Clusters (SMAC) FP survey. We derive a relation between     colour and Mg2 index using nearly 200 galaxies and discuss implications for Galactic extinction estimates and early-type galaxy stellar populations. We find that the reddenings from Schlegel et al. for galaxies with     appear to be overestimated by     per cent, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison with stellar population models having solar elemental abundance ratios, the galaxies in our sample are generally too blue at a given Mg2; we ascribe this to the well-known enhancement of the α -elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion σ and the SBF 'fluctuation count' parameter N¯ , which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between N¯ and σ is even tighter than that between Mg2 and σ . Finally, we derive FP photometric parameters for 280 galaxies from the SBF survey data set. Comparisons with external sources allow us to estimate the errors on these parameters and derive the correction necessary to bring them on to the SMAC system. The data are used in a forthcoming paper, which compares the distances derived from the FP and SBF methods.  相似文献   

14.
We examine the effects of cooling flows on the T X– L Bol relation for a sample of the most X-ray luminous ( L Bol > 1045 erg s−1) clusters of galaxies known. Using high-quality ASCA X-ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X-ray properties of the clusters and show that this reduces the previously noted dispersion in the T X– L Bol relationship. More importantly, the slope of the relationship is flattened from L Bol ∝  T 3X to approximately L Bol ∝  T 2X, in agreement with recent theoretical models which include the effects of shocks and pre-heating on the X-ray gas. We find no evidence for evolution in the T X– L Bol relation within z  ∼ 0.3. Our results demonstrate that the effects of cooling flows must be accounted for before cosmological parameters can be determined from X-ray observations of clusters. The results presented here should provide a reliable basis for modelling the T X– L Bol relation at high X-ray luminosities.  相似文献   

15.
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   

16.
We present the result of a photometric and Keck low-resolution imaging spectrometer (LRIS) spectroscopic study of dwarf galaxies in the core of the Perseus Cluster, down to a magnitude of   M B =−12.5  . Spectra were obtained for 23 dwarf-galaxy candidates, from which we measure radial velocities and stellar population characteristics from absorption line indices. From radial velocities obtained using these spectra, we confirm 12 systems as cluster members, with the remaining 11 as non-members. Using these newly confirmed cluster members, we are able to extend the confirmed colour–magnitude relation for the Perseus Cluster down to   M B =−12.5  . We confirm an increase in the scatter about the colour–magnitude relationship below   M B =−15.5  , but reject the hypothesis that very red dwarfs are cluster members. We measure the faint-end slope of the luminosity function between   M B =−18  and −12.5, finding  α=−1.26 ± 0.06  , which is similar to that of the field. This implies that an overabundance of dwarf galaxies does not exist in the core of the Perseus Cluster. By comparing metal and Balmer absorption line indices with α-enhanced single stellar population models, we derive ages and metallicities for these newly confirmed cluster members. We find two distinct dwarf elliptical populations: an old, metal-poor population with ages ∼8 Gyr and metallicities  [Fe/H] < −0.33  , and a young, metal-rich population with ages <5 Gyr and metallicities  [Fe/H] > −0.33  . Dwarf galaxies in the Perseus Cluster are therefore not a simple homogeneous population, but rather exhibit a range in age and metallicity.  相似文献   

17.
One of the predictions of the standard cold dark matter model is that dark haloes have centrally divergent density profiles. An extensive body of rotation curve observations of dwarf and low surface brightness galaxies shows the dark haloes of those systems to be characterized by soft constant-density central cores. Several physical processes have been proposed to produce soft cores in dark haloes, each one with different scaling properties. With the aim of discriminating among them we have examined the rotation curves of dark-matter-dominated dwarf and low surface brightness galaxies and the inner mass profiles of two clusters of galaxies lacking a central cD galaxy and with evidence of soft cores in the centre. The core radii and central densities of these haloes scale in a well-defined manner with the depth of their potential wells, as measured through the maximum circular velocity. As a result of our analysis we identify self-interacting cold dark matter as a viable solution to the core problem, where a non-singular isothermal core is formed in the halo centre surrounded by a Navarro, Frenk & White profile in the outer parts. We show that this particular physical situation predicts core radii in agreement with observations. Furthermore, using the observed scalings, we derive an expression for the minimum cross-section ( σ ) which has an explicit dependence with the halo dispersion velocity ( v ). If m x is the mass of the dark matter particle: σ m x ≈4×10−25 (100 km s−1  v −1) cm2 GeV−1.  相似文献   

18.
We propose a model for the source of the X-ray background (XRB) in which low-luminosity active nuclei ( L  ∼ 1043 erg s−1) are obscured ( N  ∼ 1023 cm−2) by nuclear starbursts within the inner ∼ 100 pc. The obscuring material covers most of the sky as seen from the central source, rather than being distributed in a toroidal structure, and hardens the averaged X-ray spectrum by photoelectric absorption. The gas is turbulent with velocity dispersion ∼ few × 100 km s−1 and cloud–cloud collisions lead to copious star formation. Although supernovae tend to produce outflows, most of the gas is trapped in the gravity field of the star-forming cluster itself and the central black hole. A hot ( T  ∼ 106 − 107 K) virialized phase of this gas, comprising a few per cent of the total obscuring material, feeds the central engine of ∼ 107 M⊙ through Bondi accretion, at a sub-Eddington rate appropriate for the luminosity of these objects. If starburst-obscured objects give rise to the residual XRB, then only 10 per cent of the accretion in active galaxies occurs close to the Eddington limit in unabsorbed objects.  相似文献   

19.
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   

20.
The differing   M bh– L   relations presented in McLure & Dunlop, Marconi & Hunt and Erwin et al. have been investigated. A number of issues have been identified and addressed in each of these studies, including but not limited to the removal of a dependency on the Hubble constant, a correction for dust attenuation in the bulges of disc galaxies, the identification of lenticular galaxies previously treated as elliptical galaxies and the application of the same ( Y ∣ X ) regression analysis. These adjustments result in relations which now predict similar black hole masses. The optimal K -band relation is  log( M bh/M⊙) =−0.37(±0.04)( M K + 24) + 8.29(±0.08)  , with a total (not intrinsic) scatter in log M bh equal to 0.33 dex. This level of scatter is similar to the value of 0.34 dex from the     relation of Tremaine et al. and compares favourably with the value of 0.31 dex from the   M bh– n   relation of Graham & Driver. Using different photometric data, consistent relations in the B and R band are also provided, although we do note that the small  ( N = 13)  R -band sample used by Erwin et al. is found here to have a slope of −0.30 ± 0.06. Performing a symmetrical regression on the larger K -band sample gives a slope of ∼−0.40, implying M bh∝ L 1.00. Implications for galaxy–black hole co-evolution, in terms of dry mergers, are briefly discussed, as are the predictions for intermediate mass black holes. Finally, as noted by others, a potential bias in the galaxy sample used to define the   M bh– L   relations is shown and a corrective formula provided.  相似文献   

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