The properties of galaxies in supercluster filaments (original) (raw)
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Star formation in galaxies along the Pisces-Cetus Supercluster filaments
Monthly Notices of the Royal Astronomical Society, 2007
We investigate the variation of current star formation in galaxies as a function of distance along three supercluster filaments, each joining pairs of rich clusters, in the Pisces-Cetus supercluster, which is part of the two-degree Field Galaxy Redshift Survey (2dFGRS). We find that even though there is a steady decline in the rate of star formation, as well as in the fraction of star forming galaxies, as one approaches the core of a cluster at an extremity of such a filament, there is an increased activity of star formation in a narrow distance range between 3-4 h −1 70 Mpc, which is 1.5-2 times the virial radius of the clusters involved. This peak in star formation is seen to be entirely due to the dwarf galaxies (−20 < M B −17.5). The position of the peak does not seem to depend on the velocity dispersion of the nearest cluster, undermining the importance of the gravitational effect of the clusters involved. We find that this enhancement in star formation occurs at the same place for galaxies which belong to groups within these filaments, while group members elsewhere in the 2dFGRS do not show this effect. We conclude that the most likely mechanism for this enhanced star formation is galaxy-galaxy harassment, in the crowded infall region of rich clusters at the extremities of filaments, which induces a burst of star formation in galaxies, before they have been stripped of their gas in the denser cores of clusters. The effects of strangulation in the cores of clusters, as well as excess star formation in the infall regions along the filaments, are more pronounced in dwarfs since they more vulnerable to the effects of strangulation and harassment than giant galaxies.
Star formation in galaxies falling into clusters along supercluster-scale filaments
Monthly Notices of the Royal Astronomical Society, 2008
With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within the two-degree Field Redshift Survey region, we find a significant enhancement of star formation, within a narrow range between ∼2-3 h −1 70 Mpc of the centre of the cluster into which the galaxy is falling. This burst of star formation is almost exclusively seen in the fainter dwarf galaxies (M B −20). The relative position of the peak does not depend on whether the galaxy is a member of a group or not, but non-group galaxies have on average a higher rate of star formation immediately before falling into a cluster. From the various trends, we conclude that the predominant process responsible for this rapid burst is the close interaction with other galaxies falling into the cluster along the same filament, if the interaction occurs before the gas reservoir of the galaxy gets stripped off due to the interaction with the intracluster medium.
Monthly Notices of the Royal Astronomical Society, 2005
The Pisces-Cetus supercluster (redshift z ∼ 0.06) is one of the richest nearby (z < 0.1) superclusters of galaxies, and emerges as a remarkable filament of galaxies at the edges of the two-degree Field Galaxy Redshift Survey (2dFGRS) and the ongoing Sloan Digital Sky Survey (SDSS). We explore the extent of the supercluster on the sky and in redshift space, and map the distribution of its constituent clusters and groups. We find evidence of enhanced star formation in galaxies belonging to groups in the supercluster compared to those in the field. This effect appears to be higher among the poorer groups than in the richer ones. In contrast, star formation is suppressed in the galaxies in rich clusters, which is consistent with previous studies. We identify two major filaments in this supercluster, consisting of 11 and 5 Abell clusters, including Abell 133 and Abell 85, respectively, and estimate the virial masses of the clusters from their velocity dispersions and optical surface brightness profiles. The lower limit to the masses of these filaments, amounting to the total virial mass of the constituent clusters, turns out to be 5.2 × 10 15 h −1 70 M and 6.0 × 10 15 h −1 70 M over volumes of almost 6750 h −3 70 Mpc 3 and 19 600 h −3 70 Mpc 3 , respectively. This corresponds to mass overdensities of / crit ≡ δ M > 4.7 and δ M > 1.3 for the two filaments making up the supercluster.
Superclusters of galaxies in the 2dF redshift survey. 3. The properties of galaxies in superclusters
2006
Context. Superclusters are the largest systems in the Universe to give us information about the very early Universe. Our present series of papers is devoted to the study of the properties of superclusters of galaxies from the 2dF Galaxy Redshift survey. Aims. We use catalogues of superclusters of galaxies from the 2dF Galaxy Redshift Survey to compare the properties of rich and poor superclusters. In particular, we study the properties of galaxies (spectral types, colours, and luminosities) in superclusters. Methods. We compare the distribution of densities in rich and poor superclusters, and the properties of galaxies in high and lowdensity regions of rich superclusters, in poor superclusters, and in the field. In superclusters and in the field, we also compare the properties of galaxies in groups, and the properties of those galaxies which do not belong to any group. Results. We show that in rich superclusters the values of the luminosity density smoothed on a scale of 8 h −1 Mpc are higher than in poor superclusters: the median density in rich superclusters is δ ≈ 7.5 and in poor superclusters δ ≈ 6.0. Rich superclusters contain high-density cores with densities δ > 10, while in poor superclusters such high-density cores are absent. The properties of galaxies in rich and poor superclusters and in the field are different: the fraction of early type, passive galaxies in rich superclusters is slightly higher than in poor superclusters, and is the lowest among the field galaxies. Most importantly, in high-density cores of rich superclusters (δ > 10), there is an excess of early type, passive galaxies in groups and clusters, as well as among those which do not belong to any group. The main galaxies of superclusters have a rather limited range of absolute magnitudes. The main galaxies of rich superclusters have higher luminosities than those of poor superclusters and of groups in the field. Conclusions. Our results show that both the local (group/cluster) environments and global (supercluster) environments influence galaxy morphologies and their star formation activity.
SDSS superclusters: morphology and galaxy content
Astronomy & Astrophysics, 2014
Context. Understanding the formation, evolution and present-day properties of the cosmic web and objects forming it is an important task in cosmology. Aims. We compare the galaxy populations in superclusters of different morphology in the nearby Universe (180 h −1 Mpc ≤ d ≤ 270 h −1 Mpc) to see whether the inner structure and overall morphology of superclusters are important in shaping galaxy properties in superclusters. Methods. We find supercluster morphology with Minkowski functionals and analyse the probability density distributions of colours, morphological types, stellar masses, star formation rate (SFR) of galaxies, and the peculiar velocities of the main galaxies in groups in superclusters of filament and spider types, and in the field. We test the statistical significance of the results with the KS test.
Superclusters of galaxies in the 2dF redshift survey
Astronomy & Astrophysics, 2007
Context. Superclusters are the largest systems in the Universe to give us information about the very early Universe. Our present series of papers is devoted to the study of the properties of superclusters of galaxies from the 2dF Galaxy Redshift survey. Aims. We use catalogues of superclusters of galaxies from the 2dF Galaxy Redshift Survey to compare the properties of rich and poor superclusters. In particular, we study the properties of galaxies (spectral types, colours, and luminosities) in superclusters. Methods. We compare the distribution of densities in rich and poor superclusters, and the properties of galaxies in high and lowdensity regions of rich superclusters, in poor superclusters, and in the field. In superclusters and in the field, we also compare the properties of galaxies in groups, and the properties of those galaxies which do not belong to any group. Results. We show that in rich superclusters the values of the luminosity density smoothed on a scale of 8 h −1 Mpc are higher than in poor superclusters: the median density in rich superclusters is δ ≈ 7.5 and in poor superclusters δ ≈ 6.0. Rich superclusters contain high-density cores with densities δ > 10, while in poor superclusters such high-density cores are absent. The properties of galaxies in rich and poor superclusters and in the field are different: the fraction of early type, passive galaxies in rich superclusters is slightly higher than in poor superclusters, and is the lowest among the field galaxies. Most importantly, in high-density cores of rich superclusters (δ > 10), there is an excess of early type, passive galaxies in groups and clusters, as well as among those which do not belong to any group. The main galaxies of superclusters have a rather limited range of absolute magnitudes. The main galaxies of rich superclusters have higher luminosities than those of poor superclusters and of groups in the field. Conclusions. Our results show that both the local (group/cluster) environments and global (supercluster) environments influence galaxy morphologies and their star formation activity.
THE ORIENTATIONS OF GALAXY GROUPS AND FORMATION OF THE LOCAL SUPERCLUSTER
The Astrophysical Journal, 2010
We analysed the orientation of galaxy groups in the Local Supercluster (LSC). It is strongly correlated with the distribution of neighbouring groups in the scale till about 20 Mpc. The group major axis is in alignment with both the line joining the two brightest galaxies and the direction toward the centre of the LSC, i.e. Virgo cluster. These correlations suggest that two brightest galaxies were formed in filaments of matter directed towards the protosupercluster centre. Afterwards, the hierarchical clustering leads to aggregation of galaxies around these two galaxies. The groups are formed on the same or similarly oriented filaments. This picture is in agreement with the predictions of numerical simulations.
Clusters and superclusters of galaxies
Rich clusters of galaxies are the most massive virialized systems known. Even though they contain only a small fraction of all galaxies, rich clusters provide a powerful tool for the study of galaxy formation, dark matter, large-scale structure, and cosmology.
The dynamical evolution of stellar superclusters
Monthly Notices of the Royal Astronomical Society, 1998
Recent images taken with the Hubble Space Telescope (HST) of the interacting disk galaxies NGC 4038/4039 (the Antennae) reveal clusters of many dozens and possibly hundreds of young compact massive star clusters within projected regions spanning about 100 to 500 pc. It is shown here that a large fraction of the individual star clusters merge within a few tens to a hundred Myr. Bound stellar systems with radii of a few hundred pc, masses < ∼ 10 9 M ⊙ and relaxation times of 10 11 − 10 12 yr may form from these. These spheroidal dwarf galaxies contain old stars from the pre-merger galaxy and much younger stars formed in the massive star clusters, and possibly from later gas-accretion events. The possibility that star formation in the outer regions of gas-rich tidal tails may also lead to super clusters is raised. The mass-to-light ratio of these objects is small, because they contain an insignificant amount of dark matter. After many hundred Myr such systems may resemble dwarf spheroidal satellite galaxies with large apparent mass-to-light ratia, if tidal shaping is important.