33 research outputs found
Compact groups from semi-analytical models of galaxy formation -- V: their assembly channels as a function of the environment
We delved into the assembly pathways and environments of compact groups (CGs)
of galaxies using mock catalogues generated from semi-analytical models (SAMs)
on the Millennium simulation. We investigate the ability of SAMs to replicate
the observed CG environments and whether CGs with different assembly histories
tend to inhabit specific cosmic environments. We also analyse whether the
environment or the assembly history is more important in tailoring CG
properties. We find that about half of the CGs in SAMs are non-embedded
systems, 40% are inhabiting loose groups or nodes of filaments, while the rest
distribute evenly in filaments and voids, in agreement with observations. We
observe that early-assembled CGs preferentially inhabit large galaxy systems (~
60%), while around 30% remain non-embedded. Conversely, lately-formed CGs
exhibit the opposite trend. We also obtain that lately-formed CGs have lower
velocity dispersions and larger crossing times than early-formed CGs, but
mainly because they are preferentially non-embedded. Those lately-formed CGs
that inhabit large systems do not show the same features. Therefore, the
environment plays a strong role in these properties for lately-formed CGs.
Early-formed CGs are more evolved, displaying larger velocity dispersions,
shorter crossing times, and more dominant first-ranked galaxies, regardless of
the environment. Finally, the difference in brightness between the two
brightest members of CGs is dependent only on the assembly history and not on
the environment. CGs residing in diverse environments have undergone varied
assembly processes, making them suitable for studying their evolution and the
interplay of nature and nurture on their traits.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
Galaxy groups in the 2dF galaxy redshift survey: A Compactness Analysis of Groups
A comprehensive study on compactness has been carried out on the 2dF Galaxy
Group Catalogue constructed by Merch\'an & Zandivarez. The compactness indexes
defined in this work take into account different geometrical constraints in
order to explore a wide range of possibilities. Our results show that there is
no clear distinction between groups with high and low level of compactness when
considering particular properties as the radial velocity dispersion, the
relative fraction of galaxies per spectral type and luminosity functions of
their galaxy members.
Studying the trend of the fraction of galaxies per spectral type as a
function of the dimensionless crossing time some signs of dynamical evolution
are observed. From the comparison with previous works on compactness we realize
that special care should be taken into account for some compactness criteria
definitions in order to avoid possible biases in the identification.Comment: 11 pages, 14 figures, resubmitted to MNRAS after minor revisio
Compact groups from semi-analytical models of galaxy formation-III: Purity and completeness of Hickson-like catalogues
Many catalogues of isolated compact groups of galaxies (CGs) have been extracted using Hickson's criteria to identify isolated, dense systems of galaxies, with at least three or four galaxies concordant in magnitude and redshift. But is not clear to what extent the catalogues of CGs are complete and reliable, relative to 3D truly isolated, dense groups. Using five different semi-analytical models of galaxy formation (SAMs), we identify isolated dense groups in 3D real space, containing at least three galaxies. We then build mock redshift space galaxy catalogues and run a Hickson-like CG finder. We find that the Hickson-like algorithm in redshift space is poor at recovering 3D CGs of at least three galaxies, with a purity of ∼ 10 per cent and a completeness of ∼ 22 per cent. Among the ∼ 90 per cent of spurious systems, typically 60 per cent are dense structures that failed the 3D isolation criteria, while the remaining 40 per cent are chance alignments of galaxies along the line of sight, nearly all of which are within regular groups, with some variation with the SAM used for the analysis. In other words, while only 10 per cent of CGs are isolated dense groups, as intended, half are dense structures embedded within larger groups, and one-third are chance alignments within larger groups. The low completeness of the extracted CG sample is mainly due to the flux limits of the selection criteria. Our results suggest that a new observational algorithm to identify compact groups in redshift space is required to obtain dense isolated galaxy systems.Fil: Taverna, Maria Antonela. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Díaz Giménez, Eugenia. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Zandivarez, Arnaldo Ariel. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Mamon, G. A.. Sorbonne University; Franci
Galaxy groups in the 2dF redshift survey: Galaxy Spectral Type Segregation in Groups
The behaviour of the relative fraction of galaxies with different spectral
types in groups is analysed as a function of projected local galaxy density and
the group-centric distance. The group sample was taken from the 2dF Group
Galaxy Calatogue constructed by Merch\'an & Zandivarez. Our group sample was
constrained to have a homogeneous virial mass distribution with redshift.
Galaxies belonging to this group sample were selected in order to minimize
possible biases such as preferential selection of high luminosity objects. We
find a clear distinction between high virial mass groups (M_V\gsim 10^{13.5}
M_{\odot}) and the less massive ones. While the massive groups show a
significant dependence of the relative fraction of low star formation galaxies
on local galaxy density and group-centric radius,groups with lower masses show
no significant trends. We also cross-correlate our group subsample with the
previously identified clusters finding that this sample shows a very similar
behaviour as observed in the high virial mass group subsample.Comment: 3 figures replaced, accepted for publication in MNRA
Hickson-like compact groups inhabiting different environments
Although Compact Groups of galaxies (CGs) have been envisioned as isolated
extremely dense structures in the Universe, it is accepted today that many of
them could be not as isolated as thought. In this work, we study Hickson-like
CGs identified in the Sloan Digital Sky Survey Data Release 16 to analyse these
systems and their galaxies when embedded in different cosmological structures.
To achieve this goal, we identify several cosmological structures where CGs can
reside: Nodes of filaments, Loose Groups, Filaments and cosmic Voids. Our
results indicate that 45 per cent of CGs do not reside in any of these
structures, i.e., they can be considered non-embedded or isolated systems. Most
of the embedded CGs are found inhabiting Loose Groups and Nodes, while there
are almost no CGs residing well inside cosmic Voids. Some physical properties
of CGs vary depending on the environment they inhabit. CGs in Nodes show the
largest velocity dispersions, the brightest absolute magnitude of the
first-ranked galaxy, and the smallest crossing times, while the opposite occurs
in Non-Embedded CGs. When comparing galaxies in all the environments and
galaxies in CGs, CGs show the highest fractions of red/early-type galaxy
members in most of the absolute magnitudes ranges. The variation between
galaxies in CGs inhabiting one or another environment is not as significant as
the differences caused by belonging or not to a CG. Our results suggest a
plausible scenario for galaxy evolution in CGs in which both, large-scale and
local environments play essential roles.Comment: 16 pages, 9 figures, 1 table, accepted for publication in MNRA
Properties of groups of galaxies in the vicinity of massive clusters
This work analyses the properties of groups of galaxies in the surroundings
of clusters. On the basis of a very large public Virgo Consortium Simulation,
we identified systems of galaxies in a wide range of masses. Systems with
masses greater than are
considered "host", whereas smaller systems are taken as groups. Our results
show that groups properties are affected by the proximity of massive hosts.
Physical properties such as velocity dispersion, internal energy () and
virial radius, show an increment, whereas the mean density decreases as the
host-group distance is smaller. By analysing groups with different properties,
we find that the low mass and the weakly bounded () subsamples, are
strongly affected by the presence of the host; on the other hand, massive
groups and groups with do not show dependence on the host-group
distance. Using a sample of groups identified in the final version of the 2dF
Galaxy Redshift Survey, we find a very similar velocity dispersion behaviour in
the observational data compared to results in the simulation. We also study the
dependence of the groups velocity dispersion on the host masses in both,
observations and simulation; finding that the larger is the host mass the
higher is the effect on its vicinity.Comment: 6 pages, 7 figures, accepted for publication in MNRA
Photometric redshifts as a tool to study the Coma cluster galaxy populations
We investigate the Coma cluster galaxy luminosity function (GLF) at faint
magnitudes, in particular in the u* band by applying photometric redshift
techniques applied to deep u*, B, V, R, I images covering a region of ~1deg2 (R
24). Global and local GLFs in the B, V, R and I bands obtained with photometric
redshift selection are consistent with our previous results based on a
statistical background subtraction.
In the area covered only by the u* image, the GLF was also derived after
applying a statistical background subtraction. The GLF in the u* band shows an
increase of the faint end slope towards the outer regions of the cluster (from
alpha~1 in the cluster center to alpha~2 in the cluster periphery). This could
be explained assuming a short burst of star formation in these galaxies when
entering the cluster.
The analysis of the multicolor type spatial distribution reveals that late
type galaxies are distributed in clumps in the cluster outskirts, where X-ray
substructures are also detected and where the GLF in the u* band is steeper.Comment: 14 pages, 2 figures in jpeg format, accepted in A&
X-ray selected AGN in groups at redshifts z~1
We explore the role of the group environment in the evolution of AGN at the
redshift interval 0.7<z<1.4, by combining deep Chandra observations with
extensive optical spectroscopy from the All-wavelength Extended Groth strip
International Survey (AEGIS). The sample consists of 3902 optical sources and
71 X-ray AGN. Compared to the overall optically selected galaxy population,
X-ray AGN are more frequently found in groups at the 99% confidence level. This
is partly because AGN are hosted by red luminous galaxies, which are known to
reside, on average, in dense environments. Relative to these sources, the
excess of X-ray AGN in groups is significant at the 91% level only. Restricting
the sample to 0.7<z<0.9 and M_B<-20mag in order to control systematics we find
that X-ray AGN represent (4.7\pm1.6) and (4.5\pm1.0)% of the optical galaxy
population in groups and in the field respectively. These numbers are
consistent with the AGN fraction in low redshift clusters, groups and the
field. The results above, although affected by small number statistics, suggest
that X-ray AGN are spread over a range of environments, from groups to the
field, once the properties of their hosts (e.g. colour, luminosity) are
accounted for. There is also tentative evidence, significant at the 98% level,
that the field produces more X-ray luminous AGN compared to groups, extending
similar results at low redshift to z~1. This trend may be because of either
cold gas availability or the nature of the interactions occurring in the denser
group environment (i.e. prolonged tidal encounters).Comment: To appear in MNRA