31 research outputs found
Environments of Active Galaxies
This dissertation presents studies on the environments of active galaxies.
Paper I is a case study of a cluster of galaxies containing BL Lac object RGB
1745+398. We measured the velocity dispersion, mass, and richness of the cluster. This
was one of the most thorough studies of the environments of a BL Lac object. Methods
used in the paper could be used in the future for studying other clusters as well.
In Paper II we studied the environments of nearby quasars in the Sloan Digital Sky
Survey (SDSS). We found that quasars have less neighboring galaxies than luminous
inactive galaxies. In the large-scale structure, quasars are usually located at the edges
of superclusters or even in void regions. We concluded that these low-redshift quasars
may have become active only recently because the galaxies in low-density environments
evolve later to the phase where quasar activity can be triggered.
In Paper III we extended the analysis of Paper II to other types of AGN besides
quasars. We found that different types of AGN have different large-scale environments.
Radio galaxies are more concentrated in superclusters, while quasars and Seyfert galaxies
prefer low-density environments. Different environments indicate that AGN have
different roles in galaxy evolution. Our results suggest that activity of galaxies may
depend on their environment on the large scale.
Our results in Paper III raised questions of the cause of the environment-dependency
in the evolution of galaxies. Because high-density large-scale environments contain
richer groups and clusters than the underdense environments, our results could reflect
smaller-scale effects. In Paper IV we addressed this problem by studying the group and
supercluster scale environments of galaxies together. We compared the galaxy populations
in groups of different richnesses in different large-scale environments. We found
that the large-scale environment affects the galaxies independently of the group richness.
Galaxies in low-density environments on the large scale are more likely to be
star-forming than those in superclusters even if they are in groups with the same richness.
Based on these studies, the conclusion of this dissertation is that the large-scale environment
affects the evolution of galaxies. This may be caused by different âspeedâ of
galaxy evolution in low and high-density environments: galaxies in dense environments
reach certain phases of evolution earlier than galaxies in underdense environments. As a
result, the low-density regions at low redshifts are populated by galaxies in earlier phases
of evolution than galaxies in high-density regions.Siirretty Doriast
Tracing high redshift cosmic web with quasar systems
We trace the cosmic web at redshifts 1.0 <= z <= 1.8 using the quasar data
from the SDSS DR7 QSO catalogue (Schneider et al. 2010). We apply a
friend-of-friend (FoF) algorithm to the quasar and random catalogues to
determine systems at a series of linking lengths, and analyse richness and
sizes of these systems. At the linking lengths l <= 30 Mpc/h the number of
quasar systems is larger than the number of systems detected in random
catalogues, and systems themselves have smaller diameters than random systems.
The diameters of quasar systems are comparable to the sizes of poor galaxy
superclusters in the local Universe, the richest quasar systems have four
members. The mean space density of quasar systems is close to the mean space
density of local rich superclusters. At intermediate linking lengths (40 <= l
<= 70 Mpc/h) the richness and length of quasar systems are similar to those
derived from random catalogues. Quasar system diameters are similar to the
sizes of rich superclusters and supercluster chains in the local Universe. At
the linking length 70 Mpc/h the richest systems of quasars have diameters
exceeding 500 Mpc/h. The percolating system which penetrate the whole sample
volume appears in quasar sample at smaller linking length than in random
samples (85 Mpc/h). Quasar luminosities in systems are not correlated with the
system richness. Quasar system catalogues at our web pages
http://www.aai.ee/~maret/QSOsystems.html serve as a database to search for
superclusters of galaxies and to trace the cosmic web at high redshifts.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Infalling groups and galaxy transformations in the cluster A2142
We study galaxy populations and search for possible merging substructures in
the rich galaxy cluster A2142. Normal mixture modelling revealed in A2142
several infalling galaxy groups and subclusters. The projected phase space
diagram was used to analyse the dynamics of the cluster and study the
distribution of various galaxy populations in the cluster and subclusters. The
cluster, supercluster, BCGs, and one infalling subcluster are aligned. Their
orientation is correlated with the alignment of the radio and X-ray haloes of
the cluster. Galaxies in the centre of the main cluster at the clustercentric
distances have older stellar populations (with the median age
of ~Gyrs) than galaxies at larger clustercentric distances.
Star-forming and recently quenched galaxies are located mostly in the infall
region at the clustercentric distances ,
where the median age of stellar populations of galaxies is about ~Gyrs.
Galaxies in A2142 have higher stellar masses, lower star formation rates, and
redder colours than galaxies in other rich groups. The total mass in infalling
groups and subclusters is ,
approximately half of the mass of the cluster, sufficient for the mass growth
of the cluster from redshift (half-mass epoch) to the present. The
cluster A2142 may have formed as a result of past and present mergers and
infallen groups, predominantly along the supercluster axis. Mergers cause
complex radio and X-ray structure of the cluster and affect the properties of
galaxies in the cluster, especially in the infall region. Explaining the
differences between galaxy populations, mass, and richness of A2142, and other
groups and clusters may lead to better insight about the formation and
evolution of rich galaxy clusters.Comment: 16 pages, 13 figures, A&A, in pres
Properties of brightest group galaxies in cosmic web filaments
Context. The cosmic web, a complex network of galaxy groups and clusters
connected by filaments, is a dynamical environment in which galaxies form and
evolve. However, the impact of cosmic filaments on the properties of galaxies
is difficult to study because of the much more influential local (galaxy-group
scale) environment.
Aims. The aim of this paper is to investigate the dependence of intrinsic
galaxy properties on distance to the nearest cosmic web filament, using a
sample of galaxies for which the local environment is easily assessable.}
Methods. Our study is based on a volume-limited galaxy sample with
mag, drawn from the SDSS DR12. We chose brightest
group galaxies (BGGs) in groups with two to six members as our probes of the
impact of filamentary environment because their local environment can be
determined more accurately. We use the Bisous marked point process method to
detect cosmic-web filaments with radii of Mpc and measure the
perpendicular filament spine distance () for the BGGs. We
limit our study to values up to 4 Mpc. We use the luminosity
density field as a tracer of the local environment. To achieve uniformity of
the sample and to reduce potential biases we only consider filaments longer
than 5 Mpc. Our final sample contains 1427 BGGs.
Results. We note slight deviations between the galaxy populations inside and
outside the filament radius in terms of stellar mass, colour, the 4000AA break,
specific star formation rates, and morphologies. However, all these differences
remain below 95% confidence and are negligible compared to the effects arising
from local environment density.
Conclusions. Within a 4 Mpc radius of the filament axes, the effect of
filaments on BGGs is marginal. The local environment is the main factor in
determining BGG properties.Comment: 11 pages, 9 figures, Accepted for publication in A&
BOSS Great Wall: morphology, luminosity, and mass
We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift . We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with .
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than . This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional for the richer BGW superclusters (
and ) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of , and masses in the range of . Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.Comment: Comments: 10 pages, 2 figures, A&A, in pres
The evolution of high-density cores of the BOSS Great Wall superclusters
Context. High-density cores (HDCs) of galaxy superclusters that embed rich clusters and groups of galaxies are the earliest large objects to form in the cosmic web, and the largest objects that may collapse in the present or future.Aims. We aim to study the dynamical state and possible evolution of the HDCs in the BOSS Great Wall (BGW) superclusters at redshift z approximate to 0.5 from the CMASS (constant mass) galaxy sample, based on the Baryon Oscillation Spectroscopic Survey (BOSS) in order to understand the growth and evolution of structures in the Universe.Methods. We analysed the luminosity density distribution in the BGW superclusters to determine the HDCs in them. We derived the density contrast values for the spherical collapse model in a wide range of redshifts and used these values to study the dynamical state and possible evolution of the HDCs of the BGW superclusters. The masses of the HDCs were calculated using stellar masses of galaxies in them. We found the masses and radii of the turnaround and future collapse regions in the HDCs of the BGW superclusters and compared them with those of local superclusters.Results. We determined eight HDCs in the BGW superclusters. The masses of their turnaround regions are in the range of M-T approximate to 0.4-3.3 x 10(15) h(-1) M-circle dot, and radii are in the range of R-T approximate to 3.5-7 h(-1) Mpc. The radii of their future collapse regions are in the range of R-FC approximate to 4-8h(-1) Mpc. Distances between individual cores in superclusters are much larger: of the order of 25-35h(-)(1) Mpc. The richness and sizes of the HDCs are comparable with those of the HDCs of the richest superclusters in the local Universe.Conclusions. The BGW superclusters will probably evolve to several poorer superclusters with masses similar to those of the local superclusters. This may weaken the tension with the ACDM model, which does not predict a large number of very rich and large superclusters in our local cosmic neighbourhood, and explains why there are no superclusters as elongated as those in the BGW in the local Universe.Peer reviewe
The Corona Borealis supercluster: connectivity, collapse, and evolution
We present a study of the Corona Borealis (CB) supercluster. We determined
the high-density cores of the CB and the richest galaxy clusters in them, and
studied their dynamical state and galaxy content. We determined filaments in
the supercluster to analyse the connectivity of clusters. We compared the mass
distribution in the CB with predictions from the spherical collapse model and
analysed the acceleration field in the CB. We found that at a radius
around clusters in the CB (A2065, A2061, A2089, and Gr2064)
(corresponding to the density contrast ), the galaxy
distribution shows a minimum. The values for individual clusters lie
in the range of Mpc. The radii of the clusters (splashback
radii) lie in the range of .
The projected phase space diagrams and the comparison with the spherical
collapse model suggest that regions have passed turnaround
and are collapsing. Galaxy content in clusters varies strongly. The cluster
A2061 has the highest fraction of galaxies with old stellar populations, and
A2065 has the highest fraction of galaxies with young stellar populations. The
number of long filaments near clusters vary from one at A2089 to five at A2061.
During the future evolution, the clusters in the main part of the CB may merge
and form one of the largest bound systems in the nearby Universe. Another part
of the CB, with the cluster Gr2064, will form a separate system. The structures
with a current density contrast have passed turnaround
and started to collapse at redshifts . The comparison of
the number and properties of the most massive collapsing supercluster cores
from observations and simulations may serve as a test for cosmological models.Comment: 24 pages, 17 figures, accepted for publication in A&