共查询到20条相似文献,搜索用时 388 毫秒
1.
Igor V. Chilingarian 《Monthly notices of the Royal Astronomical Society》2009,394(3):1229-1248
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 −1 e , 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
2.
Ignacio Ferreras Thorsten Lisker Anna Pasquali Sadegh Khochfar Sugata Kaviraj 《Monthly notices of the Royal Astronomical Society》2009,396(3):1573-1578
The evolution of number density, size and intrinsic colour is determined for a volume-limited sample of visually classified early-type galaxies selected from the Hubble Space Telescope /Advanced Camera for Surveys images of the Great Observatories Origins Deep Survey (GOODS) North and South fields (version 2). The sample comprises 457 galaxies over 320 arcmin2 with stellar masses above 3 × 1010 M⊙ in the redshift range 0.4 < z < 1.2 . Our data allow a simultaneous study of number density, intrinsic colour distribution and size. We find that the most massive systems (≳3 × 1011 M⊙ ) do not show any appreciable change in comoving number density or size in our data. Furthermore, when including the results from 2dF galaxy redshift survey, we find that the number density of massive early-type galaxies is consistent with no evolution between z = 1.2 and 0, i.e. over an epoch spanning more than half of the current age of the Universe. We find large discrepancies between the predictions of semi-analytic models. Massive galaxies show very homogeneous intrinsic colour distributions, with nearly flat radial colour gradients, but with a significant negative correlation between stellar mass and colour gradient, such that red cores appear predominantly in massive galaxies. The distribution of half-light radii – when compared to z ∼ 0 and z > 1 samples – is compatible with the predictions of semi-analytic models relating size evolution to the amount of dissipation during major mergers. 相似文献
3.
Radial and 2D colour properties of E+A galaxies 总被引:1,自引:0,他引:1
Chisato Yamauchi Tomotsugu Goto 《Monthly notices of the Royal Astronomical Society》2005,359(4):1557-1574
We investigated the radial colour gradient and two-dimensional (2D) colour properties of 22 E+A galaxies with 5.5 < Hδ equivalent width(EW) < 8.5 Å and 49 normal early-type galaxies as a control sample at a redshift of <0.2 in the Second Data Release of the Sloan Digital Sky Survey. We found that a substantial number of E+A galaxies exhibit positive slopes of radial colour gradient (bluer gradients toward the centre) which are seldom seen in normal early-type galaxies. We found irregular 'colour morphologies'– asymmetrical and clumpy patterns – at the centre of g − r and r − i 2D colour maps of E+A galaxies with positive slopes of colour gradient. Kolomogorov–Smirnov two-sample tests show that g − r and r − i colour gradient distributions of E+A galaxies differ from those of early-type galaxies with a more than 99.99 per cent significance level. We also found a tight correlation between radial colour gradients and colours, and between radial colour gradients and the 4000-Å break in the E+A sample; E+A galaxies which exhibit bluer colour or weaker D 4000 tend to have positive slopes of radial colour gradient. We compared the GISSEL model and E+A observational quantities, Hδ EW, D 4000 and u − g colour, and found that almost all our E+A galaxies are situated along a single evolutionary track. Therefore, these results are interpreted as E+A galaxies evolving from Hδ EW ∼ 8 Å to Hδ EW ∼ 5 Å , with colour gradients changing from positive to negative, and with the irregular 2D colour map becoming smoother, during a time-scale of ∼300 Myr. Our results favour the hypothesis that E+A galaxies are post-starburst galaxies caused by merger/interaction, having undergone a centralized violent starburst. 相似文献
4.
Iskren Y. Georgiev Thomas H. Puzia Michael Hilker Paul Goudfrooij 《Monthly notices of the Royal Astronomical Society》2009,392(2):879-893
We investigate the old globular cluster (GC) population of 68 faint ( M V > −16 mag) dwarf galaxies located in the halo regions of nearby (≲12 Mpc) loose galaxy groups and in the field environment based on archival Hubble Space Telescope ( HST )/Advanced Camera for Surveys (ACS) images in F606W and F814W filters. The combined colour distribution of 175 GC candidates peaks at ( V − I ) = 0.96 ± 0.07 mag and the GC luminosity function turnover for the entire sample is found at M V ,TO =−7.6 ± 0.11 mag , similar to the old metal-poor Large Magellanic Cloud (LMC) GC population. Our data reveal a tentative trend of M V ,TO becoming fainter from late- to early-type galaxies. The luminosity and colour distributions of GCs in dIrrs show a lack of faint blue GCs (bGCs). Our analysis reveals that this might reflect a relatively younger GC system than typically found in luminous early-type galaxies. If verified by spectroscopy, this would suggest a later formation epoch of the first metal-poor star clusters in dwarf galaxies. We find several bright (massive) GCs which reside in the nuclear regions of their host galaxies. These nuclear clusters have similar luminosities and structural parameters as the peculiar Galactic clusters suspected of being the remnant nuclei of accreted dwarf galaxies, such as M54 and ωCen. Except for these nuclear clusters, the distribution of GCs in dIrrs in the half-light radius versus cluster mass plane is very similar to that of Galactic young halo clusters, which suggests comparable formation and dynamical evolution histories. A comparison with theoretical models of cluster disruption indicates that GCs in low-mass galaxies evolve dynamically as self-gravitating systems in a benign tidal environment. 相似文献
5.
Gerhardt R. Meurer Lister Staveley-Smith & N. E. B. Killeen 《Monthly notices of the Royal Astronomical Society》1998,300(3):705-717
We present 21-cm H i line observations of the blue compact dwarf galaxy NGC 1705. Previous optical observations show a strong outflow powered by an ongoing starburst dominating the H ii morphology and kinematics. In contrast, most of the H i lies in a rotating disc. An extraplanar H i spur accounts for ∼8 per cent of the total H i mass, and is possibly associated with the H ii outflow. The inferred mass loss rate out of the core of the galaxy is significant, ∼0.2 − 2 M⊙ yr−1 , but does not dominate the H i dynamics. Mass model fits to the rotation curve show that the dark matter (DM) halo is dominant at nearly all radii and has a central density ρ0 ≈ 0.1 M⊙ pc−3 : ten times higher than typically found in dwarf irregular galaxies, but similar to the only other mass-modelled blue compact dwarf, NGC 2915. This large difference strongly indicates that there is little evolution between dwarf irregular and blue compact dwarf types. Instead, dominant DM haloes may regulate the morphology of dwarf galaxies by setting the critical surface density for disc star formation. Neither our data nor catalogue searches reveal any likely external trigger to the starburst in NGC 1705. 相似文献
6.
R. E. Skelton P. A. Woudt R. C. Kraan-Korteweg 《Monthly notices of the Royal Astronomical Society》2009,396(4):2367-2378
A deep K s -band photometric catalogue of galaxies at the core of the rich, nearby Norma cluster (ACO3627) is presented. The survey covers about 45 × 45 arcmin2 (slightly less than 1/3 Abell radius), which corresponds to ∼0.8 h −2 70 Mpc2 at the adopted distance ( v CMB / H 0 ) of 70 h −1 70 Mpc of this cluster. The survey is estimated to be complete to a magnitude of . This extends into the dwarf regime, 6 mag below . The catalogue contains 390 objects, 235 of which are classified as likely or definite galaxies and 155 as candidate galaxies. The K s -band luminosity function (LF) is constructed from the photometric sample, using a spectroscopic subsample to correct for fore and background contamination. We fit a Schechter function with a characteristic magnitude of and faint-end slope of α=−1.26 ± 0.10 to the data. The shape of the LF is similar to those found in previous determinations of the cluster LF, in both optical and near-infrared. The Schechter parameters agree well with those of recent field LFs, suggesting that the shape of both the bright-end and the faint-end slopes are relatively insensitive to environment. 相似文献
7.
Bahram Mobasher & Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,293(3):315-324
We present K -band observations of the low-luminosity galaxies in the Coma cluster, which are responsible for the steep upturn in the optical luminosity function at M R ∼−16, discovered recently. The main results of this study are as follows.
(i) The optical–near-infrared colours of these galaxies imply that they are dwarf spheroidal galaxies. The median B − K colour for galaxies with −19.3< MK <−16.3 is 3.6 mag.
(ii) The K -band luminosity function in the Coma cluster is not well constrained, because of the uncertainties due to the field-to-field variance of the background. However, within the estimated large errors, this is consistent with the R -band luminosity function, shifted by ∼3 mag.
(iii) Many of the cluster dwarfs lie in a region of the B − K versus B − R colour–colour diagram where background galaxies are rare ( B − K <5; 1.2< B − R <1.6). Local dwarf spheroidal galaxies lie in this region too. This suggests that a better measurement of the K -band cluster luminosity can be made if the field-to-field variance of the background can be measured as a function of colour, even if it is large.
(iv) If we assume that none of the galaxies in the region of the B − K versus B − R plane given in (iii) in our cluster fields are background, and that all the cluster galaxies with 15.5< K <18.5 lie in this region of the plane, then we measure α=−1.41+0.34 −0.37 for −19.3< MK −16.3, where α is the logarithmic slope of the luminosity function. The uncertainties in this number come from counting statistics. 相似文献
(i) The optical–near-infrared colours of these galaxies imply that they are dwarf spheroidal galaxies. The median B − K colour for galaxies with −19.3< M
(ii) The K -band luminosity function in the Coma cluster is not well constrained, because of the uncertainties due to the field-to-field variance of the background. However, within the estimated large errors, this is consistent with the R -band luminosity function, shifted by ∼3 mag.
(iii) Many of the cluster dwarfs lie in a region of the B − K versus B − R colour–colour diagram where background galaxies are rare ( B − K <5; 1.2< B − R <1.6). Local dwarf spheroidal galaxies lie in this region too. This suggests that a better measurement of the K -band cluster luminosity can be made if the field-to-field variance of the background can be measured as a function of colour, even if it is large.
(iv) If we assume that none of the galaxies in the region of the B − K versus B − R plane given in (iii) in our cluster fields are background, and that all the cluster galaxies with 15.5< K <18.5 lie in this region of the plane, then we measure α=−1.41
8.
Shannon Whitlock Duncan A. Forbes Michael A. Beasley 《Monthly notices of the Royal Astronomical Society》2003,345(3):949-959
We present wide-area UBRI photometry for globular clusters around the Leo group galaxy NGC 3379. Globular cluster candidates are selected from their B -band magnitudes and their ( U − B ) o versus ( B − I ) o colours. A colour–colour selection region was defined from photometry of the Milky Way and M31 globular cluster systems. We detect 133 globular cluster candidates, which supports previous claims of a low specific frequency for NGC 3379.
The Milky Way and M31 reveal blue and red subpopulations, with ( U − B ) o and ( B − I ) o colours indicating mean metallicities similar to those expected based on previous spectroscopic work. The stellar population models of Maraston and Brocato et al. are consistent with both subpopulations being old, and with metallicities of [Fe/H]∼−1.5 and −0.6 for the blue and red subpopulations, respectively. The models of Worthey do not reproduce the ( U − B ) o colours of the red (metal-rich) subpopulation for any modelled age.
For NGC 3379 we detect a blue subpopulation with similar colours, and presumably age/metallicity, to that of the Milky Way and M31 globular cluster systems. The red subpopulation is less well defined, perhaps due to increased photometric errors, but indicates a mean metallicity of [Fe/H]∼−0.6. 相似文献
The Milky Way and M31 reveal blue and red subpopulations, with ( U − B )
For NGC 3379 we detect a blue subpopulation with similar colours, and presumably age/metallicity, to that of the Milky Way and M31 globular cluster systems. The red subpopulation is less well defined, perhaps due to increased photometric errors, but indicates a mean metallicity of [Fe/H]∼−0.6. 相似文献
9.
Mass-to-light ratio gradients in early-type galaxy haloes 总被引:1,自引:0,他引:1
N. R. Napolitano M. Capaccioli A. J. Romanowsky N. G. Douglas M. R. Merrifield K. Kuijken M. Arnaboldi O. Gerhard K. C. Freeman 《Monthly notices of the Royal Astronomical Society》2005,357(2):691-706
Owing to the fact that the near future should see a rapidly expanding set of probes of the halo masses of individual early-type galaxies, we introduce a convenient parameter for characterizing the halo masses from both observational and theoretical results: ∇ℓ ϒ , the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Λ-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies εSF . As a pilot study, we assemble the available ∇ℓ ϒ data from kinematics in early-type galaxies – representing the first unbiased study of halo masses in a wide range of early-type galaxy luminosities – and find a correlation between luminosity and ∇ℓ ϒ , such that the brightest galaxies appear the most dark-matter dominated. We find that the gradients in most of the brightest galaxies may fit in well with the ΛCDM predictions, but that there is also a population of fainter galaxies whose gradients are so low as to imply an unreasonably high star formation efficiency εSF > 1 . This difficulty is eased if dark haloes are not assumed to have the standard ΛCDM profiles, but lower central concentrations. 相似文献
10.
S. Santra J. S. Sanders A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2007,382(2):895-902
We present a study of the X-ray emission from the nuclei of galaxies observed in the core of the Perseus cluster in a deep exposure with Chandra . Point sources are found coincident with the nuclei of 13 early-type galaxies, as well as the central galaxy NGC 1275. This corresponds to all galaxies brighter than M B > −18 in the Chandra field. All of these sources have a steep power-law spectral component and four have an additional thermal component. The unabsorbed power-law luminosities in the 0.5–7.0 keV band range from 8 × 1038 to 5 × 1040 erg s−1 . We find no simple correlations between the K -band luminosity, or the FUV and NUV AB magnitudes of these galaxies and their X-ray properties. We have estimated the black hole masses of the nuclei using the K -band M BH – L K bol relation and again find no correlation between black hole mass and the X-ray luminosity. Bondi accretion on to the black holes in the galaxies with minihaloes should make them much more luminous than observed. 相似文献
11.
Matthew Prescott Ivan K. Baldry Phil A. James 《Monthly notices of the Royal Astronomical Society》2009,397(1):90-102
We produce and analyse u -band ( λ≈ 355 nm) luminosity functions (LFs) for the red and blue populations of galaxies using data from the Sloan Digital Sky Survey (SDSS) u -band Galaxy Survey ( u GS) and Deep Evolutionary Exploratory Probe 2 (DEEP2) survey. From a spectroscopic sample of 41 575 SDSS u GS galaxies and 24 561 DEEP2 galaxies, we produce colour magnitude diagrams and make use of the colour bimodality of galaxies to separate red and blue populations. LFs for eight redshift slices in the range 0.01 < z < 1.2 are determined using the 1/ V max method and fitted with Schechter functions showing that there is significant evolution in M * , with a brightening of 1.4 mag for the combined population. The integration of the Schechter functions yields the evolution in the u -band luminosity density (LD) out to z ∼ 1 . By parametrizing the evolution as ρ∝ (1 + z )β , we find that β= 1.36 ± 0.2 for the combined populations and β= 2.09 ± 0.2 for the blue population. By removing the contribution of the old stellar population to the u -band LD and correcting for dust attenuation, we estimate the evolution in the star formation rate (SFR) of the Universe to be βSFR = 2.5 ± 0.3 . Discrepancies between our result and higher evolution rates measured using the infrared and far-UV can be reconciled by considering possibilities such as an underestimated dust correction at high redshifts or evolution in the stellar initial mass function. 相似文献
12.
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
13.
TomasDahlén ClaesFransson MagnusNäslund 《Monthly notices of the Royal Astronomical Society》2002,330(1):167-183
Photometric redshifts are used to determine the rest-frame luminosity function (LF) of both early- and late-type galaxies to MB ∼−17.6 for the cluster Cl 1601+42 at z=0.54 . The total LF shows a steep faint-end slope α ∼−1.4 , indicating the existence of a population of numerous dwarf galaxies. Luminous galaxies, with MB ≲−19.5 are mostly red, early-type galaxies, with a LF best described by a Gaussian. Faint galaxies are predominantly blue, late-type galaxies, well fitted by a Schechter function with α ∼−1.7 . Compared with clusters at lower redshift, the steepening of the faint end starts at brighter magnitudes for Cl 1601+42, which may indicate a brightening of the present-day dwarf population relative to the giant population with increasing redshift. Early-type galaxies are centrally concentrated, and dominate the core region, implying that the radial gradient of early-type galaxies seen in local clusters is already established at z∼0.5 . Bright, late-type galaxies are rare, consistent with a decrease in star formation in field galaxies as they are accreted on to the cluster, while faint, blue galaxies are evenly distributed across the cluster, except for a depletion in the core region. The blue fraction is fB ∼0.15 , which is somewhat lower than the Butcher–Oemler average at z∼0.5 . The value of f B is found to increase with limiting magnitude and with radius from the centre. 相似文献
14.
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
15.
Nelson D. Padilla Michael A. Strauss 《Monthly notices of the Royal Astronomical Society》2008,388(3):1321-1334
We determine the underlying shapes of spiral and elliptical galaxies in the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) from the observed distribution of projected galaxy shapes, taking into account the effects of dust extinction and reddening. We assume that the underlying shapes of spirals and ellipticals are well approximated by triaxial ellipsoids. The elliptical galaxy data are consistent with oblate spheroids, with a correlation between luminosity and ellipticity: the mean values of minor to middle axis ratios are 0.41 ± 0.03 for M r ≈−18 ellipticals and 0.76 ± 0.04 for M r ≈−22.5 ellipticals. Ellipticals show almost no dependence of axial ratio on galaxy colour, implying a negligible dust optical depth.
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E0 in spiral galaxies is E 0 ≃ 0.45 mag for galaxies of median colours, increasing to E 0 = 1 mag for g − r > 0.9 and E 0 = 1.9 for the luminous and most compact galaxies, with half-light radii <2 h −1 kpc . 相似文献
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E
16.
J. Ma R. de Grijs D. Chen S. van den Bergh Z. Fan Z. Wu H. Wu X. Zhou J. Wu Z. Jiang J. Chen 《Monthly notices of the Royal Astronomical Society》2007,376(4):1621-1629
Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, r c = 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc) , a tidal radius, r t = 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc) , and a concentration index c = log ( r t / r c ) = 2.01 ± 0.02 . The central surface brightness is 13.510 mag arcsec−2 . We also calculate the half-light radius, at r h = 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc) . The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log R h diagram as ω Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log R h plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. 相似文献
17.
The early-type galaxies NGC 1407 and NGC 1400 – II. Star formation and chemical evolutionary history
Max Spolaor Duncan A. Forbes Robert N. Proctor George K. T. Hau Sarah Brough 《Monthly notices of the Royal Astronomical Society》2008,385(2):675-686
We present a possible star formation and chemical evolutionary history for two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Our analysis is based on new high signal-to-noise ratio spatially resolved integrated spectra obtained at the ESO 3.6-m telescope, out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. Using Lick/IDS indices, we estimate luminosity-weighted ages, metallicities and α-element abundance ratios. Colour radial distributions from HST /ACS and Subaru Suprime-Cam multiband wide-field imaging are compared to colours predicted from spectroscopically determined ages and metallicities using single stellar population (SSP) models. The galaxies formed over half of their mass in a single short-lived burst of star formation (≥100 M⊙ yr−1 ) at redshift z ≥ 5. This likely involved an outside–in mechanism with supernova-driven galactic winds, as suggested by the flatness of the α-element radial profiles and the strong negative metallicity gradients. Our results support the predictions of the revised version of the monolithic collapse model for galaxy formation and evolution. We speculate that, since formation, the galaxies have evolved quiescently and that we are witnessing the first infall of NGC 1400 in the group. 相似文献
Our analysis is based on new high signal-to-noise ratio spatially resolved integrated spectra obtained at the ESO 3.6-m telescope, out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. Using Lick/IDS indices, we estimate luminosity-weighted ages, metallicities and α-element abundance ratios. Colour radial distributions from HST /ACS and Subaru Suprime-Cam multiband wide-field imaging are compared to colours predicted from spectroscopically determined ages and metallicities using single stellar population (SSP) models. The galaxies formed over half of their mass in a single short-lived burst of star formation (≥100 M
18.
N. I. Grant J. A. Kuipers S. Phillipps 《Monthly notices of the Royal Astronomical Society》2005,363(3):1019-1030
Using images from a charge-coupled device survey with the Wide Field Camera on the Isaac Newton Telescope, we performed B - and I -band photometry on 156 Virgo cluster dwarf elliptical (dE) galaxies, 25 candidate new cluster dwarfs, and nine candidate field dwarfs. Galaxies were modelled with Sérsic profiles, using both 1D χ2 and 2D cross-correlation methods, with nuclei modelled as point sources. The intensity profiles of 50 galaxies previously classified as dE, dE?, or ? are more accurately fitted if a nucleus is included, and this results in the majority of dwarfs now being classified as nucleated dwarf ellipticals (dE,N). Some faint galaxies with B magnitudes of 18–21 have particularly large relative nuclei, while a small number have apparent central dimmings. For cluster dE,N galaxies the nucleus magnitude is correlated with the magnitude of the host galaxy. The profile parameters of dE and dE,N galaxies are not significantly different, and there is no evident discontinuity in relative nucleus size between non-nucleated and nucleated dwarfs, suggesting that they may form a continuum. Nuclei are on average redder than their underlying galaxies, though a spread of relative colours was found, and two-fifths of nuclei are bluer. Formation mechanisms of nuclei are discussed: at least some appear to have formed in an already existing non-nucleated galaxy, though others may have formed simultaneously with their galaxies and subsequently evolved within them. 相似文献
19.
Neil Trentham R. Brent Tully Marc A. W. Verheijen 《Monthly notices of the Royal Astronomical Society》2001,325(3):1275-1280
We present and discuss optical, near-infrared and H i measurements of the galaxy Markarian 1460 at a distance of 19 Mpc in the Ursa Major Cluster. This low-luminosity ( M B =−14) galaxy is unusual because (i) it is blue ( B − R =0.8) and has the spectrum of an H ii galaxy, (ii) it has a light profile that is smooth and well fitted by an r 1/4 and not an exponential function at all radii larger than the seeing, and (iii) it has an observed central brightness of about μ B =20 mag arcsec−2 , intermediate between those of elliptical galaxies (on the bright μ B side) and normal low-luminosity dwarf irregular (on the low μ B side) galaxies. No other known galaxy exhibits all these properties in conjunction. On morphological grounds this galaxy looks like a normal distant luminous elliptical galaxy, since the Fundamental Plane tells us that higher luminosity normal elliptical galaxies tend to have lower surface-brightnesses. Markarian 1460 has 2×107 M⊙ of H i and a ratio M (H i )/ L B of 0.2, which is low compared to the typical values for star-forming dwarf galaxies. From the high surface-brightness and r 1/4 profile, we infer that the baryonic component of Markarian 1460 has become self-gravitating through dissipative processes. From the colours, radio continuum, H i and optical emission line properties, and yet smooth texture, we infer that Markarian 1460 has had significant star formation as recently as ∼1 Gyr ago but not today. 相似文献
20.
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