4,434 research outputs found
Where are compact groups in the local Universe?
The purpose of this work is to perform a statistical analysis of the location
of compact groups in the Universe from observational and semi-analytical points
of view. We used the velocity-filtered compact group sample extracted from the
Two Micron All Sky Survey for our analysis. We also used a new sample of galaxy
groups identified in the 2M++ galaxy redshift catalogue as tracers of the
large-scale structure. We defined a procedure to search in redshift space for
compact groups that can be considered embedded in other overdense systems and
applied this criterion to several possible combinations of different compact
and galaxy group subsamples. We also performed similar analyses for simulated
compact and galaxy groups identified in a 2M++ mock galaxy catalogue
constructed from the Millennium Run Simulation I plus a semi-analytical model
of galaxy formation. We observed that only of the compact groups can
be considered to be embedded in larger overdense systems, that is, most of the
compact groups are more likely to be isolated systems. The embedded compact
groups show statistically smaller sizes and brighter surface brightnesses than
non-embedded systems. No evidence was found that embedded compact groups are
more likely to inhabit galaxy groups with a given virial mass or with a
particular dynamical state. We found very similar results when the analysis was
performed using mock compact and galaxy groups. Based on the semi-analytical
studies, we predict that of the embedded compact groups probably are 3D
physically dense systems. Finally, real space information allowed us to reveal
the bimodal behaviour of the distribution of 3D minimum distances between
compact and galaxy groups. The location of compact groups should be carefully
taken into account when comparing properties of galaxies in environments that
are a priori different.Comment: 14 pages, 5 figures, 8 tables. Accepted for publication in Astronomy
& Astrophysics. Tables B1 and B2 will only be available in electronic form at
the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A
Improving Hickson-like compact group finders in redshift surveys: an implementation in the SDSS
In this work we present an algorithm to identify compact groups (CGs) that
closely follows Hickson's original aim and that improves the completeness of
the samples of compact groups obtained from redshift surveys. Instead of
identifying CGs in projection first and then checking a velocity concordance
criterion, we identify them directly in redshift space using Hickson-like
criteria. The methodology was tested on a mock lightcone of galaxies built from
the outputs of a recent semi-analytic model of galaxy formation run on top of
the Millennium Simulation I after scaling to represent the first-year Planck
cosmology. The new algorithm identifies nearly twice as many CGs, no longer
missing CGs that failed the isolation criterion because of velocity outliers
lying in the isolation annulus. The new CG sample picks up lower surface
brightness groups, which are both looser and with fainter brightest galaxies,
missed by the classic method. A new catalogue of compact groups from the Sloan
Digital Sky Survey is the natural corollary of this study. The publicly
available sample comprises observational groups with four or more galaxy
members, of which clearly fulfil all the compact group requirements:
compactness, isolation, and velocity concordance of all of their members. The
remaining groups need further redshift information of potentially
contaminating sources. This constitutes the largest sample of groups that
strictly satisfy all the Hickson's criteria in a survey with available
spectroscopic information.Comment: 17 pages, 8 figures, 8 tables. Accepted for publication in Astronomy
& Astrophysics. Tables D1 and D2 will be available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/ or
https://iate.oac.uncor.edu/index.php/alcance-publico/catalogos
Fossil groups in the Millennium simulation. From the brightest to the faintest galaxies during the past 8 Gyr
We investigate the evolution of bright and faint galaxies in fossil and
non-fossil groups. We used mock galaxies constructed based on the Millennium
run simulation II. We identified fossil groups at redshift zero according to
two different selection criteria, and then built reliable control samples of
non-fossil groups that reproduce the fossil virial mass and assembly time
distributions. The faint galaxies were defined as having r-band absolute
magnitudes in the range [-16,-11]. We analysed the properties of the bright and
faint galaxies in fossil and non-fossil groups during the past 8 Gyr. We
observed that the brightest galaxy in fossil groups is typically brighter and
more massive than their counterparts in control groups. Fossil groups developed
their large magnitude gap between the brightest galaxies around 3.5 Gyr ago.
The brightest galaxy stellar masses of all groups show a notorious increment at
that time. By analysing the behaviour of the magnitude gap between the first
and the second, third, and fourth ranked galaxies, we found that at earlier
times, fossil groups comprised two large brightest galaxies with similar
magnitudes surrounded by much fainter galaxies, while in control groups these
magnitude gaps were never as large as in fossils. At early times, fossil groups
in the faint population were denser than non-fossil groups, then this trend
reversed, and finally they became similar at the present day. The mean number
of faint galaxies in non-fossil systems increases in an almost constant rate
towards later times, while this number in fossil groups reaches a plateau at
that lasts Gyr, and then starts growing again more rapidly.
The formation of fossil groups is defined at the very beginning of the groups
according to their galaxy luminosity sampling, which could be determined by
their merging rate at early times.Comment: 10 pages, 6 figures, 1 table. Accepted for publication in Astronomy &
Astrophysic
Evaluation of recipient and EMBRYO factors on success of inter-breed EMBRYO transfer in sheep
Studies on multiple ovulation and embryo transfer (MOET) showed that this technique is widely acknowledged as the best available option to a low cost route of exporting genetic material across international boundaries along with control disease transmission during imports. In addition to that MOET have been used so much to proliferate genes of reputedly superior stock. An appreciation of the potential benefit of MOET was perhaps best demonstrated in dairy cows, however, the application of MOET techniques to sheep has been much more slower. The success of this technique is very unpredictable due to many factors are contributing to the overall results.
Experiments were initiated to determine effects of factors related to recipient and embryo on MOET success in inter-breed embryo transfer in sheep. Three experiments were conducted to compare recipient and embryo genotypes, cryopreservation techniques, and pregnancy rates obtained with fresh and frozen embryo transfers. Further investigations were conducted on such as number of corpus luteum, site of ovulation and transfer in recipients and number of embryos used as single or in pairs, stage of embryo development and quality grades
Nominal Debt as a Burden on Monetary Policy
We characterize the optimal sequential choice of monetary policy in economies with either nominal or indexed debt. In a model where nominal debt is the only source of time inconsistency, the Markov-perfect equilibrium policy implies the progressive depletion of the outstanding stock of debt, until the time inconsistency disappears. There is a resulting welfare loss if debt is nominal rather than indexed. We also analyze the case where monetary policy is time inconsistent even when debt is indexed. In this case, with nominal debt, the sequential optimal policy converges to a time-consistent steady state with positive -- or negative -- debt, depending on the value of the intertemporal elasticity of substitution. Welfare can be higher if debt is nominal rather than indexed and the level of debt is not too high.nominal debt; indexed debt; optimal monetary policy; time consistency; Markov-perfect equilibrium
Are compact groups hostile towards faint galaxies?
The goal of this work is to understand whether the extreme environment of
compact groups can affect the distribution and abundance of faint galaxies
around them. We performed an analysis of the faint galaxy population in the
vicinity of compact groups and normal groups. We built a light-cone mock galaxy
catalogue constructed from the Millennium Run Simulation II plus a
semi-analytical model of galaxy formation. We identified a sample of compact
groups in the mock catalogue as well as a control sample of normal galaxy
groups and computed the projected number density profiles of faint galaxies
around the first- and the second-ranked galaxies. We also compared the profiles
obtained from the semi-analytical galaxies in compact groups with those
obtained from observational data. In addition, we investigated whether the
ranking or the luminosity of a galaxy is the most important parameter in the
determination of the centre around which the clustering of faint galaxies
occurs. There is no particular influence of the extreme compact group
environment on the number of faint galaxies in such groups compared to control
groups. When selecting normal groups with separations between the 1st and 2nd
ranked galaxies similar to what is observed in compact groups, the faint galaxy
projected number density profiles in compact groups and normal groups are
similar in shape and height. We observed a similar behaviour of the population
of faint galaxies in observations and simulations in the regions closer to the
1st and 2nd ranked galaxies. Finally, we find that the projected density of
faint galaxies is higher around luminous galaxies,regardless of the ranking in
the compact group. The semi-analytical approach shows that compact groups and
their surroundings do not represent a hostile enough environment to make faint
galaxies to behave differently than in normal groups.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy &
Astrophysic
On the properties of compact groups identified in different photometric bands
Historically, compact group catalogues vary not only in their identification
algorithms and selection functions, but also in their photometric bands.
Differences between compact group catalogues have been reported. However, it is
difficult to assess the impact of the photometric band in these differences
given the variety of identification algorithms. We used the mock lightcone
built by Henriques et al. (2012) to identify and compare compact groups in
three different photometric bands: , , and . We applied the same
selection functions in the three bands, and found that compact groups in the
u-band look the smallest in projection, the difference between the two
brightest galaxies is the largest in the K-band, while compact groups in the
r-band present the lowest compactness. We also investigated the differences
between samples when galaxies are selected only in one particular band (pure
compact groups) and those that exist regardless the band in which galaxies were
observed (common compact groups). We found that the differences between the
total samples are magnified, but also some others arise: pure-r compact groups
are the largest in projection; pure-u compact groups have the brightest first
ranked galaxies, and the most similar two first ranked galaxies; pure-K compact
groups have the highest compactness and the most different two first ranked
galaxies; and common compact groups show the largest percentage of physically
dense groups. Therefore, without a careful selection and identification of the
samples, the characteristic features of group properties in a particular
photometric band could be overshadowed.Comment: 9 pages, 3 figures, 5 tables. Accepted for publication in MNRA
Updated facts on the U.S. distributions of earnings, income, and wealth
Wealth ; Income distribution
Compact groups from semi-analytical models of galaxy formation -- II: Different assembly channels
We study the formation of over 6000 compact groups (CGs) of galaxies
identified in mock redshift-space galaxy catalogues built from semi-analytical
models of galaxy formation (SAMs) run on the Millennium Simulations. We select
CGs of 4 members in our mock SDSS galaxy catalogues and, for each CG, we trace
back in time the real-space positions of the most massive progenitors of their
4 galaxies. By analysing the evolution of the distance of the galaxy members to
the centre of mass of the group, we identify 4 channels of CG formation. The
classification of these assembly channels is performed with an automatic recipe
inferred from a preliminary visual inspection and based on the orbit of the
galaxy with the fewest number of orbits. Most CGs show late assembly, with the
last galaxy arriving on its first or second passage, while only 10-20 per cent
form by the gradual contraction of their orbits by dynamical friction, and only
a few per cent forming early with little subsequent contraction. However, a SAM
from a higher resolution simulation leads to earlier assembly. Assembly
histories of CGs also depend on cosmological parameters. At similar resolution,
CGs assemble later in SAMs built on parent cosmological simulations of high
density parameter. Several observed properties of mock CGs correlate with their
assembly history: early-assembling CGs are smaller, with shorter crossing
times, and greater magnitude gaps between their brightest two members, and
their brightest galaxies have smaller spatial offsets and are more passive.Comment: 14 pages, 11 figures, 3 tables, accepted for publication in MNRA
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