140 research outputs found
RXCJ1111.6+4050 galaxy cluster: the observational evidence of a transitional fossil group
We present a detailed kinematical and dynamical study of the galaxy cluster
RXCJ1111.6+4050 (RXCJ1111), at z = 0.0756 using 104 new spectroscopic redshifts
of galaxies observed at the TNG 3.5m telescope and SDSS DR16 public archive.
Our analysis is performed in a multiwavelength context in order to study and
compare mainly optical and X-ray properties using XMM-Newton data. We find that
RXCJ1111 is a galaxy cluster showing a velocity distribution with clear
deviations from Gaussianity, that we are able to explain by the presence of a
substructure within the cluster. The two cluster components show velocity
dispersions of km/s and km/s, which yield dynamical
masses of M= M and M for the main system and substructure, respectively.
RXCJ1111 presents an elongation in the North-South direction and a gradient of
250-350 km/s/Mpc in the velocity field, suggest that the merger axis between
the main system and substructure is slightly tilted with respect to the
line-of-sight. The substructure is characterized by a magnitude gap , so it fits the "fossil-like" definition of a galaxy group.
Mass estimates derived from X-ray and optical are in good agreement when two
galaxy components are considered separately. We propose a 3D merging model and
find that the fossil group is in an early phase of collision with the RXCJ1111
main cluster and almost aligned with the line-of-sight. This merging model
would explain the slight increase found in the T with respect to what we
would expect for relaxed clusters. Due to the presence of several brightest
galaxies, after this collision, the substructure would presumably lose its
fossil condition. Therefore, RXCJ1111 represents the observational evidence
that the fossil stage of a system can be temporary and transitional.Comment: 16 pages, 11 figures, 3 tables and 1 appendi
Biases in galaxy cluster velocity dispersion and mass estimates in the small number of galaxies regime
We present a study of the statistical properties of three velocity dispersion
and mass estimators, namely biweight, gapper and standard deviation, in the
small number of galaxies regime ().
Using a set of 73 numerically simulated galaxy clusters, we characterise the
statistical bias and the variance for the three estimators, both in the
determination of the velocity dispersion and the dynamical mass of the clusters
via the relation. The results are used to define a new set of
unbiased estimators, that are able to correct for those statistical biases with
a minimal increase of the associated variance. The numerical simulations are
also used to characterise the impact of velocity segregation in the selection
of cluster members, and the impact of using cluster members within different
physical radii from the cluster centre.
The standard deviation is found to be the lowest variance estimator. The
selection of galaxies within the sub-sample of the most massive galaxies in the
cluster introduces a \% bias in the velocity dispersion estimate when
calculated using a quarter of the most massive cluster members. We also find a
dependence of the velocity dispersion estimate on the aperture radius as a
fraction of , consistent with previous results.
The proposed set of unbiased estimators effectively provides a correction of
the velocity dispersion and mass estimates from all those effects in the small
number of cluster members regime. This is tested by applying the new estimators
to a subset of simulated observations. Although for a single galaxy cluster the
statistical and physical effects discussed here are comparable or slightly
smaller than the bias introduced by interlopers, they will be of relevance when
dealing with ensemble properties and scaling relations for large cluster
samples (Abridged).Comment: accepted for publication in A&
The Three Hundred : contrasting clusters galaxy density in hydrodynamical and dark matter simulations
Cluster number counts will be a key cosmological probe in the next decade
thanks to the Euclid satellite mission. For this purpose, cluster detection
algorithm performance, which are sensitive to the spatial distribution of the
cluster galaxy members and their luminosity function, need to be accurately
characterized. Using The Three Hundred hydrodynamical and dark matter only
simulations we study a complete sample of massive clusters beyond 7 (5)
10 M at redshift 0 (1) on a
volume. We find that the mass resolution of the current hydrodynamical
simulations (1.5 10 M) is not enough to characterize the
luminosity function of the sample in the perspective of Euclid data.
Nevertheless, these simulations are still useful to characterize the spatial
distribution of the cluster substructures assuming a common relative mass
threshold for the different flavours and resolutions. By comparing with the
dark matter only version of these simulations, we demonstrate that baryonic
physics preserves significantly low mass subhalos (galaxies) as have also been
observed in previous studies with less statistics. Furthermore, by comparing
the hydro simulations with higher resolution dark matter only simulations of
the same objects and taking the same limit in subhalo mass we find
significantly more cuspy galaxy density profiles towards the center of the
clusters, where the low mass substructures would tend to concentrate. We
conclude that using dark matter only simulation may lead to some biases on the
spatial distribution and density of galaxy cluster members. Based on the
preliminary analysis of few high resolution hydro simulations we conclude that
a mass resolution of 1.8 10 h M will be needed
for The Three Hundred simulations to approach the expected magnitude limits for
the Euclid survey
Prospects for high-z cluster detections with Planck, based on a follow-up of 28 candidates using MegaCam@CFHT
The Planck catalogue of SZ sources limits itself to a significance threshold
of 4.5 to ensure a low contamination rate by false cluster candidates. This
means that only the most massive clusters at redshift z>0.5, and in particular
z>0.7, are expected to enter into the catalogue, with a large number of systems
in that redshift regime being expected around and just below that threshold. In
this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues
from 2013 and 2015. In the latter maps, we consider detections around and at
lower significance than the threshold adopted by the Planck Collaboration. To
keep the contamination rate low, our 28 candidates are chosen to have
significant WISE detections, in combination with non-detections in SDSS/DSS,
which effectively selects galaxy cluster candidates at redshifts .
By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A
rest-frame break over a significant redshift range, thus allowing accurate
redshift estimates of red-sequence cluster galaxies up to z~0.8. After
discussing the possibility that an overdensity of galaxies coincides -by
chance- with a Planck SZ detection, we confirm that 16 of the candidates have
likely optical counterparts to their SZ signals, 13 (6) of which have an
estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally
lower than expected given the halo masses estimated from the Planck maps.
However, when we follow a simplistic model to correct for Eddington bias in the
SZ halo mass proxy, the richnesses are consistent with a reference
mass-richness relation established for clusters detected at higher
significance. This illustrates the benefit of an optical follow-up, not only to
obtain redshift estimates, but also to provide an independent mass proxy that
is not based on the same data the clusters are detected with, and thus not
subject to Eddington bias.Comment: 13 pages, 7 figures. Accepted for publication in A&
Impact of filaments on galaxy cluster properties in The Three Hundred simulation
Galaxy clusters and their filamentary outskirts reveal useful laboratories to test cosmological models and investigate Universe composition and evolution. Their environment, in particular the filaments of the Cosmic Web to which they are connected, plays an important role in shaping the properties of galaxy clusters. In this project, we analyse the gas filamentary structures present in 324 regions of The Three Hundred hydrodynamical simulation extracted with the DisPerSE filament finder. We estimate the number of gas filaments globally connected to several galaxy clusters, i.e. the connectivity k, with a mass range of 1013 †M200 hâ1 Mâ †1015 at redshift z = 0. We study the positive correlation between the connectivity and mass of galaxy clusters. Moreover, we explore the impact of filaments on the dynamical state of clusters, quantified by the degree of relaxation parameter Ï
The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features
The black hole transient V404 Cygni exhibited a bright outburst in June 2015
that was intensively followed over a wide range of wavelengths. Our team
obtained high time resolution optical spectroscopy (~90 s), which included a
detailed coverage of the most active phase of the event. We present a database
consisting of 651 optical spectra obtained during this event, that we combine
with 58 spectra gathered during the fainter December 2015 sequel outburst, as
well as with 57 spectra from the 1989 event. We previously reported the
discovery of wind-related features (P-Cygni and broad-wing line profiles)
during both 2015 outbursts. Here, we build diagnostic diagrams that enable us
to study the evolution of typical emission line parameters, such as line fluxes
and equivalent widths, and develop a technique to systematically detect outflow
signatures. We find that these are present throughout the outburst, even at
very low optical fluxes, and that both types of outflow features are observed
simultaneously in some spectra, confirming the idea of a common origin. We also
show that the nebular phases depict loop patterns in many diagnostic diagrams,
while P-Cygni profiles are highly variable on time-scales of minutes. The
comparison between the three outbursts reveals that the spectra obtained during
June and December 2015 share many similarities, while those from 1989 exhibit
narrower emission lines and lower wind terminal velocities. The diagnostic
diagrams presented in this work have been produced using standard measurement
techniques and thus may be applied to other active low-mass X-ray binaries.Comment: Accepted for publication in MNRAS. 23 pages paper, plus a 9 pages
appendix with extra tables and figures. 18 figures are included in the paper
and 8 in the appendi
The three hundred project. A machine learning method to infer clusters of galaxy mass radial profiles from mock SunyaevâZelâdovich maps
We develop a machine learning algorithm to infer the three-dimensional cumulative radial profiles of total and gas masses in galaxy clusters from thermal SunyaevâZelâdovich effect maps. We generate around 73 000 mock images along various lines of sight using 2522 simulated clusters from THE THREE HUNDRED project at redshift z < 0.12 and train a model that combines an auto-encoder and a random forest. Without making any prior assumptions about the hydrostatic equilibrium of the clusters, the model is capable of reconstructing the total mass profile as well as the gas mass profile, which is responsible for the SunyaevâZelâdovich effect. We show that the recovered profiles are unbiased with a scatter of about 10 per cent, slightly increasing towards the core and the outskirts of the cluster. We selected clusters in the mass range of 1013.5 †M200/(hâ1 M) †1015.5, spanning different dynamical states, from relaxed to disturbed haloes. We verify that both the accuracy and precision of this method show a slight dependence on the dynamical state, but not on the cluster mass. To further verify the consistency of our model, we fit the inferred total mass profiles with a NavarroâFrenkâWhite model and contrast the concentration values with those of the true profiles. We note that the inferred profiles are unbiased for higher concentration values, reproducing a trustworthy massâconcentration relation. The comparison with a widely used mass estimation technique, such as hydrostatic equilibrium, demonstrates that our method recovers the total mass that is not biased by non-thermal motions of the gas
The hydrostatic-to-lensing mass bias from resolved X-ray and optical-IR data
An accurate reconstruction of galaxy cluster masses is key to use this
population of objects as a cosmological probe. In this work we present a study
on the hydrostatic-to-lensing mass scaling relation for a sample of 53 clusters
whose masses were reconstructed homogeneously in a redshift range between and . The mass for each cluster was indeed inferred from
the mass profiles extracted from the X-ray and lensing data, without using a
priori observable-mass scaling relations. We assessed the systematic dispersion
of the masses estimated with our reference analyses with respect to other
published mass estimates. Accounting for this systematic scatter does not
change our main results, but enables the propagation of the uncertainties
related to the mass reconstruction method or used dataset. Our analysis gives a
hydrostatic-to-lensing mass bias of and no
evidence of evolution with redshift. These results are robust against possible
subsample differences
The Three Hundred project: Contrasting clusters optical and IR properties in hydrodynamical and dark matter only simulations
Cluster number count is a major cosmological probe for the next generation of cosmological large scale-structure surveys like the one expected from the Euclid satellite mission. Cosmological constraints will be mainly limited by the understanding of the selection function (SF), which characterize the probability of detecting a cluster of a given mass and redshift. The SF can be estimated by injecting realistic simulated clusters into the survey and re-applying the detection procedure. In this paper, we use the galaxy clusters from The Three Hundred project to study this effect with their member galaxies. We further study possible resolution effects by comparing low and high resolution simulations. Finally, we present the density profiles of the member galaxies and discuss their evolution with cluster mass and redshift
Galaxy cluster mass bias from projected mass maps: The Three Hundred-NIKA2 LPSZ twin samples
The determination of the mass of galaxy clusters from observations is subject
to systematic uncertainties. Beyond the errors due to instrumental and
observational systematic effects, in this work we investigate the bias
introduced by modelling assumptions. In particular, we consider the
reconstruction of the mass of galaxy clusters from convergence maps employing
spherical mass density models. We make use of The Three Hundred simulations,
selecting clusters in the same redshift and mass range as the NIKA2
Sunyaev-Zel'dovich Large Program sample: and . We study different
modelling and intrinsic uncertainties that should be accounted for when using
the single cluster mass estimates for scaling relations. We confirm that the
orientation of clusters and the radial ranges considered for the fit have an
important impact on the mass bias. The effect of the projection adds
uncertainties to the order of to to the mass estimates. We also
find that the scatter from cluster to cluster in the mass bias when using
spherical mass models is less than of the true mass of the clusters
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