共查询到20条相似文献，搜索用时 640 毫秒
1.
Hideyuki Kamaya 《Astrophysics and Space Science》2011,334(2):261-265
Recent observational studies have discovered very small dwarf spheroidal galaxies (dSphs) which are the faintest member of
the local group of galaxies. This paper examines their faintness because of the following reason: Comparing their M/L (mass-luminosity ratio) to that of the other normal dSphs, we find very small dSphs are faint for their dark matter mass.
This indicates their star formation is suppressed. There are two possibilities for the suppression: (1) ram pressure of IGM
(intra-group medium), (2) wind from the Milky Way (MW). Owing to the ram pressure, interstellar medium of very small dSphs
is possible to be stripped because of the shallowness of their gravitational potential. That is, star formation can be terminated
during their evolution. However, the latter is difficult at the moment since their distance is far from MW. The author suggests
star formation was terminated only when very small dSphs were beside MW whose wind was strong. 相似文献
2.
Based on two models, we investigate the molecular-to-atomic gas ratio in Virgo cluster galaxies in comparison with field galaxies.
We show that the enhanced metallicity for cluster members and the ram pressure stripping of atomic gas from the disk periphery
cannot fully explain the observed gas component ratios. The additional environmental factors affecting the interstellar medium
and leading to an increase in the molecular gas fraction should be taken into account for cluster galaxies. 相似文献
3.
With the advent of the new generation wide-field cameras it became possible to survey in an unbiased mode galaxies spanning a variety of local densities, from the core of rich clusters, to compact and loose groups, down to filaments and voids. The sensitivity reached by these instruments allowed to extend the observation to dwarf galaxies, the most “fragile” objects in the universe. At the same time models and simulations have been tailored to quantify the different effects of the environment on the evolution of galaxies. Simulations, models, and observations consistently indicate that star-forming dwarf galaxies entering high-density environments for the first time can be rapidly stripped from their interstellar medium. The lack of gas quenches the activity of star formation, producing on timescales of \({\sim }\)1 Gyr quiescent galaxies with spectro-photometric, chemical, structural, and kinematical properties similar to those observed in dwarf early-type galaxies inhabiting rich clusters and loose groups. Simulations and observations consistently identify ram pressure stripping as the major effect responsible for the quenching of the star-formation activity in rich clusters. Gravitational interactions (galaxy harassment) can also be important in groups or in clusters whenever galaxies have been members since early epochs. The observation of clusters at different redshifts combined with the present high infalling rate of galaxies onto clusters indicate that the quenching of the star-formation activity in dwarf systems and the formation of the faint end of the red sequence is a very recent phenomenon. 相似文献
4.
本文在星系有偏袒形成的冷暗物质模型框架下,假定星系都在红移～5时形成,研究了星系群和星系团的形成对星系演化的影响。由示冷暗物质模型中各种不同尺度扰动的幅度相近,星系群和星系团的维里化与星系的维里化在时间上比较接近,在星系群或星系团的维里化过程中获得巨大维里速度的星系仍然富有气体,因此,当它们因为频繁的互相碰撞,或者因为进入星系团中心区的稠密星系际介质受到巨大冲压,或者是被附近射电星系的喷流所产生的高压茧状体所包容,都可能激发活动性,造成恒星的爆发性形成.高红移星系团中观测到的B-O效应和高红移射电星系的光学像与射电喷流同轴向现象都可以据此得到解释. 相似文献
5.
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
6.
New observations show that most of the flattened diffuse elliptical (dE) galaxies are essentially isotropic rotators. This
supports the idea that dEs have evolved from fast rotating dIrr systems or late-type spirals after their gas was expelled
by SN-driven winds and stripped by ram pressure against the intergalactic medium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
We present three-dimensional (3D) hydrodynamical simulations of ram pressure stripping of massive disc galaxies in clusters. Studies of galaxies that move face-on have predicted that in such a geometry the galaxy can lose a substantial amount of its interstellar medium. But only a small fraction of galaxies is moving face-on. In this work we focus on a systematic study of the effect of the inclination angle between the direction of motion and the galaxy's rotation axis.
In agreement with some previous works, we find that the inclination angle does not play a major role for the mass loss as long as the galaxy is not moving close to edge-on (inclination angle ≲60°). We explain this behaviour by extending Gunn & Gott's estimate of the stripping radius, which is valid for face-on geometries, to moderate inclinations.
The inclination plays a role as long as the ram pressure is comparable to pressures in the galactic plane, which can span two orders of magnitude. For very strong ram pressures, the disc will be stripped completely, and for very weak ram pressures, mass loss is negligible independent of inclination. We show that in non-edge-on geometries the stripping proceeds remarkably similar. A major difference between different inclinations is the degree of asymmetry introduced in the remaining gas disc.
We demonstrate that the tail of gas stripped from the galaxy does not necessarily point in a direction opposite to the galaxy's direction of motion. Therefore, the observation of a galaxy's gas tail may be misleading about the galaxy's direction of motion. 相似文献
In agreement with some previous works, we find that the inclination angle does not play a major role for the mass loss as long as the galaxy is not moving close to edge-on (inclination angle ≲60°). We explain this behaviour by extending Gunn & Gott's estimate of the stripping radius, which is valid for face-on geometries, to moderate inclinations.
The inclination plays a role as long as the ram pressure is comparable to pressures in the galactic plane, which can span two orders of magnitude. For very strong ram pressures, the disc will be stripped completely, and for very weak ram pressures, mass loss is negligible independent of inclination. We show that in non-edge-on geometries the stripping proceeds remarkably similar. A major difference between different inclinations is the degree of asymmetry introduced in the remaining gas disc.
We demonstrate that the tail of gas stripped from the galaxy does not necessarily point in a direction opposite to the galaxy's direction of motion. Therefore, the observation of a galaxy's gas tail may be misleading about the galaxy's direction of motion. 相似文献
8.
The sample of galaxies within 7 Mpc has been compared with that of the Virgo cluster in order to find new and confirm already known differences which may be caused by the environment. The well-known morphology-density relation is found to be valid not only for luminous galaxies but also for faint objects. The differences in the global luminosity functions are mainly caused by the different composition of the samples, whereas the luminosity functions of narrow morphological subgroups, with the exception of the irregulars, probably are not dependent on the density or on other quantities. The already observed HI-deficiency of the interstellar medium of the Virgo cluster spirals has been confirmed. There is a steep drop of this quantity with increasing distance from the dominant galaxies M 87 and M 49. The interstellar dust masses of Virgo cluster spirals and irregulars have been estimated from far-infrared fluxes. These data have been combined with the HI masses in order to obtain the gas-to-dust ratios, which come out to be smaller by a factor of 4 for the Virgo cluster spiral galaxies than for the nearby systems, on the average. The gas-to-dust ratio is strongly correlated with the HI-deficiency. These results support the concept of the ram pressure of the intracluster medium on the spiral galaxies in the core of the Virgo cluster. 相似文献
9.
The gas-to-dust ratio in the interstellar medium of nearby spiral systems and dwarf irregular galaxies has been obtained by using mainly the compiled data by Schmidt and Boller (1992a). The gas-to-dust ratio of dwarf irregulars is larger by about one order of magnitude than for spiral galaxies, on the average. A relation between the gas-to-dust ratio and the metallicity, represented by the abundance of oxygen, has been detected. 相似文献
10.
We propose an evolutionary model for dwarf galaxies in which initially metal-poor gas-rich dwarf irregular (dI) galaxies evolve through bursting Blue Compact Dwarf (BCD) stages and eventually fade from the BCD phase to become dwarf ellipticals (dE). During the bursting phase the surface brightness of the galaxy increases rapidly due to enhanced OB star formation. The source of fuel for the intermittent bursts of star formation is assumed to be primordial gas which continues to collapse onto the already formed central structure. The dE galaxies form as a result of eventual gas depletion through star formation.With this proposed dIBCDdE evolutionary sequence we can explain the similar photometric structure of the different dwarf types and the differences in their star formation rates, surface brightnesses,Hi contents and metallicities. A final central BCD burst can account for the nucleation in brighter dEs and their residual star formation, while earlier more widespread star formation bursts would fade to give an irregular dI. Inflow of gas may allow dEs to be less flattened than dIs.Using galaxy fading and metallicity models we can reproduce the observed number ratiosN(dI)N(BCD) andN(dI)N(dE) and also the observed metallicity magnitude relation of local dwarf spheroidal galaxies. 相似文献
11.
A. M. Karick M. J. Drinkwater M. D. Gregg 《Monthly notices of the Royal Astronomical Society》2003,344(1):188-200
We present BVI photometry of 190 galaxies in the central 4 ×3 deg2 region of the Fornax cluster observed with the Michigan Curtis Schmidt Telescope. Results from the Fornax Cluster Spectroscopic Survey (FCSS) and the Flair-II Fornax Surveys have been used to confirm the membership status of galaxies in the Fornax Cluster Catalogue (FCC). In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmed radial velocities.
In this paper, we investigate the surface brightness–magnitude relation for Fornax cluster galaxies. Particular attention is given to the sample of cluster dwarfs and the newly discovered ultracompact dwarf galaxies (UCDs) from the FCSS. We examine the reliability of the surface brightness–magnitude relation as a method for determining cluster membership and find that at surface brightnesses fainter than 22 mag arcsec−2 , it fails in its ability to distinguish between cluster members and barely resolved background galaxies. Cluster members exhibit a strong surface brightness–magnitude relation. Both elliptical (E) galaxies and dwarf elliptical (dE) galaxies increase in surface brightness as luminosity decreases. The UCDs lie off the locus of the relation.
B − V and V − I colours are determined for a sample of 113 cluster galaxies and the colour–magnitude relation is explored for each morphological type. The UCDs lie off the locus of the colour–magnitude relation. Their mean V − I colours (∼1.09) are similar to those of globular clusters associated with NGC 1399. The location of the UCDs on both surface brightness and colour–magnitude plots supports the 'galaxy threshing' model for infalling nucleated dwarf elliptical (dE, N) galaxies. 相似文献
In this paper, we investigate the surface brightness–magnitude relation for Fornax cluster galaxies. Particular attention is given to the sample of cluster dwarfs and the newly discovered ultracompact dwarf galaxies (UCDs) from the FCSS. We examine the reliability of the surface brightness–magnitude relation as a method for determining cluster membership and find that at surface brightnesses fainter than 22 mag arcsec
B − V and V − I colours are determined for a sample of 113 cluster galaxies and the colour–magnitude relation is explored for each morphological type. The UCDs lie off the locus of the colour–magnitude relation. Their mean V − I colours (∼1.09) are similar to those of globular clusters associated with NGC 1399. The location of the UCDs on both surface brightness and colour–magnitude plots supports the 'galaxy threshing' model for infalling nucleated dwarf elliptical (dE, N) galaxies. 相似文献
12.
Peter J. Boyce Steven Phillipps J. Bryn Jones Simon P. Driver Rodney M. Smith Warrick J. Couch 《Monthly notices of the Royal Astronomical Society》2001,328(1):277-282
We present the results of a study of the morphology of the dwarf galaxy population in Abell 868, a rich, intermediate-redshift cluster which has a galaxy luminosity function (LF) with a steep faint-end slope . A statistical background subtraction method is employed to study the colour distribution of the cluster galaxies. This distribution suggests that the galaxies contributing to the faint-end of the measured cluster LF can be split into three populations: dwarf irregular galaxies (dIrrs) with dwarf elliptical galaxies (dEs) with and contaminating background giant ellipticals (gEs) with . The removal of the contribution of the background gEs from the counts only marginally lessens the faint-end slope . However, the removal of the contribution of the dIrrs from the counts produces a flat LF . The dEs and the dIrrs have similar spatial distributions within the cluster, except that the dIrrs appear to be totally absent within a central projected radius of about 0.2 Mpc . The number densities of both dEs and dIrrs appear to fall off beyond a projected radius of ≃ 0.35 Mpc. We suggest that the dE and dIrr populations of A868 have been associated with the cluster for similar time-scales, but evolutionary processes such as 'galaxy harassment' tend to fade the dIrr galaxies while having a much smaller effect on the dE galaxies. The harassment would be expected to have the greatest effect on dwarfs residing in the central parts of the cluster. 相似文献
13.
14.
I. V. Chilingarian P. Prugniel O. K. Sil'chenko V. L. Afanasiev 《Monthly notices of the Royal Astronomical Society》2007,376(3):1033-1046
We present the first 3D observations of a diffuse elliptical galaxy (dE). The good quality data (S/N up to 40) reveal the kinematical signature of an embedded stellar disc, reminiscent of what is commonly observed in elliptical galaxies, though similarity of their origins is questionable. Colour map built from Hubble Space Telescope Advanced Camera for Surveys (ACS) images confirms the presence of this disc. Its characteristic scale (about 3 arcsec =250 pc) is about a half of galaxy's effective radius, and its metallicity is 0.1–0.2 dex larger than the underlying population. Fitting the spectra with synthetic single stellar populations (SSP), we found an SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H] =−0.06 dex. We checked that these determinations are consistent with those based on Lick indices, but have smaller error bars. The kinematical discovery of a stellar disc in dE gives additional support to an evolutionary link from dwarf irregular galaxies due to stripping of the gas against the intracluster medium. 相似文献
15.
《New Astronomy》2013
A multivariate classification has been performed for a large sample of dynamically hot stellar systems comprising globular clusters to giant ellipticals, in quest of the formation theory of ultra compact dwarf galaxies (UCDs). For this K means cluster analysis is carried out together with the optimum criterion (Sugar et al., 2003) with respect to three parameters, logarithm of stellar mass, logarithm of effective radius and stellar mass to light ratio. The present data set has been taken from Misgeld and Hilker (2011). We found five groups MK1–MK5. These are predominated by giant ellipticals (gEs), faint dwarf ellipticals (dEs), globular clusters (GCs), massive compact objects (UCDs and nuclei of dE,Ns) and bright dwarf ellipticals respectively. Almost all UCDs are found either in MK3 or MK4. The fraction is roughly 50%–50% between MK3 and MK4. Comparable fraction of UCDs share properties either with normal GCs or with nuclei of dE,N. This adds a quantitative constraint to the long discussed hypothesis that UCDs may be formed either as massive globular clusters or have an origin similar to nuclei of dwarf galaxies. We finally find that for our clustering test in mass-size-stellar M/L ratios, ultra faint dwarf galaxies are attributed to globular cluster group (MK3) and not to the dwarf galaxy group (MK2). This highlights that there is no clear cut morphological distinction between extended star clusters and ultra faint dwarfs. These groups are highly consistent with the groups found in a previous classification for a smaller sample and completely different set of parameters. 相似文献
16.
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
17.
I. V. Chilingarian O. K. Sil’chenko V. L. Afanasiev Ph. Prugniel 《Astronomy Letters》2007,33(5):292-298
We report the discovery of young embedded structures in three diffuse elliptical galaxies (dE) in the Virgo cluster: IC 783,
IC 3468, and IC 3509. We performed 3D spectroscopic observations of these galaxies with the MPFS spectrograph at the 6-m Special
Astrophysical Observatory telescope and obtained spatially resolved distributions of kinematic and stellar population parameters
by fitting high-resolution PEGASE. HR synthetic single stellar populations (SSP) in pixel space. In all three galaxies, the
luminosity-weighted age of the nuclei (∼4 Gyr) is considerably younger than that of the population in the outer regions of
the galaxies. We discuss two possibilities for the formation of such structures—a dissipative merger event and a different
ram pressure stripping efficiency during two consecutive crossings of the Virgo cluster centre.
The article was translated by the authors. 相似文献
18.
It is difficult to detect X-ray emission associated with galaxies in rich clusters, because the X-ray images of the clusters are dominated by the emission from their hot intracluster media (ICM). Only the nearby Virgo cluster provides us with information about the X-ray properties of galaxies in clusters. Here we report on the analysis of a deep ROSAT HRI image of the moderately rich cluster Abell 2634, by which we have been able to detect the X-ray emission from the galaxies in the cluster. The ICM of Abell 2634 is an order of magnitude denser than that of the Virgo cluster, and so this analysis allows us to explore the X-ray properties of individual galaxies in the richest environment yet explored.
By stacking the X-ray images of the galaxies together, we show that the emission from the galaxies appears to be marginally resolved by the HRI. This extent is smaller than for galaxies in poorer environments, and is comparable to the size of the galaxies in optical light. These facts suggest that the detected X-ray emission originates from the stellar populations of the galaxies, rather than from extended hot interstellar media. Support for this hypothesis comes from placing the optical and X-ray luminosities of these galaxies in the LB –LX plane: the galaxies of Abell 2634 lie in the region of this plane where models indicate that all the X-ray emission can be explained by the usual population of X-ray binaries. It is therefore probable that ram pressure stripping has removed the hot gas component from these galaxies. 相似文献
By stacking the X-ray images of the galaxies together, we show that the emission from the galaxies appears to be marginally resolved by the HRI. This extent is smaller than for galaxies in poorer environments, and is comparable to the size of the galaxies in optical light. These facts suggest that the detected X-ray emission originates from the stellar populations of the galaxies, rather than from extended hot interstellar media. Support for this hypothesis comes from placing the optical and X-ray luminosities of these galaxies in the L
19.
Vanessa Doublier 《Astrophysics and Space Science》2002,281(1-2):211-212
Planetary Nebulae have proven to be an essential key to understand the long term chemical enrichment of the interstellar medium
due to low mass stars. They allow to study the original abundances of the star, and the effect of the star on the interstellar
medium. Blue compact dwarf galaxies are known to host violent star formation in very heavy element depleted environments.
They also show traces of past star formation (Doublier et al., 1999; 2001), including AGB starsand red giants which are responsible
for long term enrichment. However, models fails to reproduce the low metallicities observed if those stars are taken into
account. We observed PNe in BCDGs, and made a comparative study of the abundances in the HII regions and of the PNe.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
20.
Hideyuki Kamaya 《Astrophysics and Space Science》2008,317(3-4):235-238
In this paper, the author proposes a formation scenario of dwarf spheroidal galaxies (dSphs); part of dSphs form as a result of collision of dark matter (DM) halos which retain ISM (interstellar medium). First of all, a primordial dSph forms compact when collision of DM halos occurs. After the collision, the primordial dSph leaves a mass-radius relation among old stellar systems. This intermediate evolutionary phase finishes when the galactic wind occurs. Finally, it is re-virialized. Once this scenario is adopted, we explain the reason why large M/L (mass-to-light ratio) is a result of galactic wind. Then, we conclude it is possible for part of dSphs to be remnants of DM halo collisions. 相似文献