共查询到20条相似文献，搜索用时 640 毫秒
1.
2.
Using the Berlind et al. algorithm and the Davis et al. algorithm, we find that the mean velocity dispersion, virial radius,
and virial mass of the group catalogs identified in the volume-limited sample are much smaller than those identified in the
flux-limited sample. Our study shows that these properties of groups are heavily influenced by the relative values of the
linking parameters and that there may be no values for the linking lengths that will work perfectly for every sample. In addition,
we note that the luminosity distribution of member galaxies of groups identified by different algorithms is nearly the same,
but member galaxies of groups identified using the linking lengths b⊥ = 0.14, b∥ = 0.75 have a higher proportion of blue galaxies and a lower proportion of red galaxies than member galaxies of groups identified
using the linking length b = 0.2, and the early-type fraction of member galaxies of groups identified using the linking length
b = 0.2 is higher than that of member galaxies of groups identified using the linking lengths b⊥ = 0.14, b∥ = 0.75.
Published in Astrofizika, Vol. 51, No. 4, pp. 555–566 (August 2008). 相似文献
3.
We review here the interplay of cluster and galaxy evolution. As a case study, we consider the Butcher-Oemler effect and propose
that it is the result of the changing rate of cluster merger events in a hierarchical universe. This case study highlights
the need for new catalogs of clusters and groups that possess quantified morphologies. We present such a sample here, namely
the Sloan Digital Sky Survey (SDSS) C4 Catalog, which has been objectively-selected from the SDSS spectroscopic galaxy sample.
We outline here the C4algorithm and present first results based on the SDSS Early Data Release, including an X-ray luminosity-velocity
dispersion (Lx-σv) scaling relationship (as a function of cluster morphology) and the density-SFR relation of galaxies within C4 clusters (Gomez et al., 2003). We also discuss the merger of Coma and the NGC4839 group and
its effect on the galaxy populations in these systems. We finish with a brief discussion of a new sample ofHΔ-selected galaxies
(i.e., k+a, post-starburst galaxies) obtained from the SDSS spectroscopic survey.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Darren J. Croton Peder Norberg Enrique Gaztañaga Carlton M. Baugh 《Monthly notices of the Royal Astronomical Society》2007,379(4):1562-1570
We present measurements of the higher order clustering of red and blue galaxies as a function of scale and luminosity made from the two-degree field galaxy redshift survey (2dFGRS). We use a counts-in-cells analysis to estimate the volume-averaged correlation functions, , as a function of scale up to the order of p = 5 , and also the reduced void probability function. Hierarchical amplitudes are constructed using the estimates of the correlation functions: . We find that (i) red galaxies display stronger clustering than blue galaxies at all orders measured; (ii) red galaxies show values of S p that are strongly dependent on luminosity whereas blue galaxies show no segregation in S p within the errors; this is remarkable given the segregation in the variance; (iii) the linear relative bias shows the opposite trend to the hierarchical amplitudes, with little segregation for the red sequence and some segregation for the blue; (iv) faint red galaxies deviate significantly from the 'universal' negative binomial reduced void probabilities followed by all other galaxy populations. Our results show that the characteristic colour of a galaxy population reveals a unique signature in its spatial distribution. Such signatures will hopefully further elucidate the physics responsible for shaping the cosmological evolution of galaxies. 相似文献
5.
We have obtained Hα fluxes and luminosities for a sample of 95 galaxies from observations of 31 Hickson Compact Groups (HCGs) in the northern
hemisphere. This sample is the largest Hα selected catalogue of galaxies having Hα calibrated fluxes so far. The results obtained from a preliminary analysis of a subsample of66 galaxies show that the Hα luminosity of the galaxies is correlated with velocity dispersion and compactness of groups. These correlations would point
towards a scenario in which the brightest Hα galaxies reside in compact groups having higher probability of galaxy interaction, i.e. lower values of velocity dispersion.
Moreover, such relations seem to depend on the environment in which HCGs themselves are embedded.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine central
velocity dispersions (σo) for 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 brightbona fide ellipticals located in the field or very loose groups. Several tests are carried out to avoid systematic effects in σ measurements.
We use these velocity dispersions to compare the position of 11 compact group galaxies in the Fundamental Plane to that of
a large and homogeneous sample of elliptical galaxies (Burstein et al., 1987).We find that little or no significant difference
exists, as far as the Fundamental Plane is concerned, between ellipticals in compact groups and their counterparts in other
environments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
E. H. Nikogossian 《Astrophysics》2000,43(1):32-39
The hierarchical structure of the clusters of galaxies A 999, A 1016, and A 1142, which are part of one supercluster, is investigated.
The HTree method is used to determine that A 999 and A 1016 are a single, dynamically bound system consisting of two “cores”
and a common field of galaxies. The composition of the “cores” includes almost all the E and S0 galaxies, the luminosity function
of which is very nearly Gaussian. It is also established that the cluster A 1142 has a nonuniform structure, both in density
distribution and in radial velocity distribution. The location of the maxima in density and in the radial velocity distribution
correlates with the galaxies that are sources of radio and x-ray emission.
Translated from Astrofizika, Vol. 43, No. 1, pp. 45-54, January–March, 2000. 相似文献
8.
Compact groups are association of 4-8 galaxies with high spatial densities (Δρ/ρ∼10–20), but low velocity dispersion. Galaxy-galaxy
interactions (e.g. close tidal encounters or mergers) are therefore likely to dominate any environmentally-dependent evolution
of galaxies in these compact, highlocal-density, groups, unlike in the field, where galaxy densities are too low, and in clusters,
where relative velocities are too high. We present here the results from spectroscopic and photometric observations of a new
sample of compact groups in the Southern Sky, selected by an automatic detection algorithm applied to a digitized galaxy database.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
A distribution of matter up to 100 h
-1 Mpc could be obtained from the large-scale galaxy peculiar motions. The best picture of such motion is given for today by
two galaxy catalogs, namely MarkIII and RFGC. We compare their velocity fields and show they are very similar and have not
only practically the same multipole structure but also a corresponding small-scale motions . We estimate a mean radial component
of this small-scale motion as 500–700 kms. An additional comparison of distances to common galaxies is made.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
The hierarchical substructure of the core of the Perseus cluster of galaxies (A426, A262, A347, N507, and N383) is investigated
using the method of S-tree diagrams. In the main system M (100 galaxies), two substructures AM (35 galaxies) and BM (13 galaxies)
are determined. The group AM can be identified with the cluster A262 and the group N507; BM can be identified with the group
N383; A426 and A347 are in the main system. The axis of symmetry of the system M passes through the Seyfert galaxy N1275 and
is parallel to the axis of symmetry of the group AM, which is the core of increased density of the cluster of galaxies. Radial
segregation of galaxies by morphological types is observed in the systems M and AM. The distribution of galaxies by position
angles is uniform.
Translated from Astrofizika, Vol. 41, No. 1, pp. 65–72, January-March, 1998. 相似文献
11.
The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant
HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies
is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions.
It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions
are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the
hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could
have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that
tidal interaction is likely to be an effective mechanism for transforming spirals to S0s. 相似文献
12.
By means of population synthesis models with variable α/Fe ratios we derive average ages, metallicities, and [α/Fe] element
enhancements for a sample of 126 field and cluster early-type galaxies. We find a clear positive relation between [α/Fe] and
velocity dispersion. Zero-point, slope, and scatter of this correlation are the same for cluster and field galaxies. In particular,
the [α/Fe] ratios and mean ages of cluster ellipticals are positively correlated. This strongly reinforces the view that the
[α/Fe] element enhancement in ellipticals is produced by star formation timescales rather than by variations of the initial
mass function. These results indicate that the more massive the galaxy, the shorter is its star formation timescale, and the
higher is the redshift of the bulk of star formation. This finding is not compatible with the predictions from models of hierarchical
galaxy formation. The lenticular and field galaxies of the investigated sample do not follow the correlation between age and
[α/Fe], but contain a non-negligible fraction of galaxies with young average ages and high [α/Fe] ratios.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
13.
We used a sample of 20 poor groups of galaxies to study the low mass tail of the relationships among the X-ray temperature
T, the X-ray luminosity Lx and the optical velocity dispersion σ. We obtained redshifts for the fainter members of these groups. We find that X-ray
bright groups have more members and higher velocity dispersions on average. Using the fainter group members and MonteCarlo
tests, we define the number of group members required to calculate a robust velocity dispersion. There is a tendency to underestimate
the group velocity dispersion for samples of fewer than∼ 10 members that introduces systematic errors in the slope of the
relationships among Lx, T, and σ. A comparison with the data of Ponman and Mahdavi shows that our improved velocity dispersions provide better constraints
on the relationship between the kinematics of the hot gas and galaxies in these common environments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
We have started a survey of galaxies at intermediate redshifts using the HST-STIS parallel fields. Our main goal is to analyse
the morphology of faint galaxies in order to estimate the epoch of formation of the Hubble classification sequence. The high
resolution of STIS images (0.05″) is ideal for this work and enables us to perform a morphological classification and to analyse
the internal structures of galaxies. We find that 40% of the 290 galaxies are early types and that there are more irregulars
and ellipticals at the fainter magnitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
P. Amram C. Mendes de Oliveira H. Plana C. Balkowski J. Boulesteix C. Carignan 《Astrophysics and Space Science》2002,281(1-2):389-392
A long-term program based on Fabry-Perot Hα velocity field data of compact groups has been undertaken in order to analyse
the kinematics of the compact group galaxies and the extent of their dark halos. The data are taken at the ESO and the CFH
3.6 m telescopes. The main goals of our project are: • To determine the evolutionary stages of the studied groups, • To search
for tidal dwarf galaxy candidates in heavily interacting systems and • in combination with photometry available in the literature,
to determine the Tully-Fisher relation for the group galaxies. The sample contains examples of groups at a variety of dynamical
stages: from a false group that is in fact one single irregular galaxy with several star-forming blobs (e.g. H18) to a group
whose members are strongly interacting and possibly forming tidal dwarf galaxies (e.g. H92) to a group in the final process
of merging. We have so far identified five HCG classes: 1. merging groups2. strongly interacting, 3. weakly interacting, 4.
non-groups, 5. single irregular galaxies. The ones which can be used in the TF studies are those in classes (2) and (3), for
which comprehensive rotation curves can be derived.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
16.
We have studied the pitch angles of spiral arms for 31 distant galaxies at z ∼ 0.7 from three Hubble Deep Fields (HDF-N, HDF-S, HUDF). Using the pitch angle-rotation velocity relation calibrated from
nearby galaxies, we have estimated the rotation velocities of galaxies from the deep fields. These estimates have a low accuracy
(∼50 km s−1), but they allow low-mass and giant galaxies to be distinguished. The Tully-Fisher relation constructed using our velocity
estimates shows satisfactory agreement with the actually observed relations for distant galaxies and provides evidence for
the luminosity evolution of spiral galaxies. 相似文献
17.
We present an analysis of the chiral property of 667 spiral and barred spiral galaxies in the Local Supercluster (radial velocity
<3 000 km s−1). The arms of a galaxy (spiral or barred spiral) can be distinguished according to their orientation (leading or trailing)
relative to the direction of the rotation. We use environment of each galaxy as a subsample in order to study the chiral property
of galaxies. In addition, equatorial position angle distributions of leading and trailing arm galaxies are studied. We classify
our database according as their morphology, diameters, radial velocities, axial ratios and magnitudes. The distribution of
trailing and leading arm galaxies in the Local Supercluster is found homogeneous. A significant dominance of either trailing
or leading structures is noticed within the Virgo cluster region, suggesting that the aggregation of these structures might
have already started there. The rotation axes of the galaxies in the Virgo cluster is found to lie in the equatorial plane.
Chirality of galaxies is found strong for the subsamples that showed a random alignment in the equatorial position angle distribution.
Possible explanations of the results will be presented. 相似文献
18.
We have collected the observational data accumulated before the Swift experiment to check the possible connection of short
gamma-ray bursts (GRBs) with low-redshift galaxies. The BATSE/IPN experimental data on well-localized short GRBs and the SDSS
DR5 and PSCz catalogs of galaxies are used. The PSCz sky coverage has allowed us to search for host galaxies for a sample
of 34 short GRBs. One or more galaxies have been found in the error boxes of six bursts, but the probability of a chance coincidence
for each of them is high. No excess of nearby galaxies in the total sample has been detected. The 90% confidence limit corresponds
to the fact that no more than 7%of the short GRBs could originate in nearby galaxies of the PSCz sample. The estimated upper
limit of several percent may be considered to be valid in the volume z = 0.015–0.025. Based on the results of our search, we have estimated the lower limits for the isotropic energies E
γiso of 31 short bursts from our sample. Their values lie within the range 1.0 × 1047–2.7 × 1049 erg. The possible fraction of the flares from magnetars in our sample of short GRBs is discussed. The SDSS sky coverage is
currently insufficient to perform a similar analysis. 相似文献
19.
The widely varying dwarf galaxy counts in different environments provide a strong challenge to standard hierarchical clustering
models. The luminosity function is not universal, but seems to be strongly dependent upon environment. In this paper we describe
an automated procedure for detecting and measuring very Low Surface Brightness (LSB) features in deep CCD data. We apply this
procedure to large area CCD survey fields of the Virgo cluster and find 105 dwarf LSB galaxies previously uncatalogued over
an area of ∼14 sq deg. We show that there are many more faint (14≤MB≤–10) LSB galaxies than would be predicted from extrapolation of the Virgo cluster catalogue luminosity function. Over our
limited range of measurement the faint end slope of the luminosity function becomesα=–1.6. Although these galaxies contribute
a small fraction of the total stellar light of the cluster, they may contribute significantly to the mass in galaxies if they
have large mass-to-light ratios similar to those recently measured for Local Group dwarf galaxies. By a comparison with different
environments, the Virgo Cluster seems to be highly `dwarf rich' if considering the dwarf to giant ratio or it's luminosity
function faint end slope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is
a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies
in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp
+ Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from
31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈
1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation
curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies.
These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos,
and the kinematical and HI lopsidedness in galaxies. 相似文献