Context. There is some disagreement about the abundance of faint galaxies in high-redshift clusters, with contradictory results in the literature arising from studies of the optical galaxy luminosity ...function (GLF) for small cluster samples. Aims. We compute GLFs for one of the largest medium-to-high-redshift (0.4 ≤ z < 0.9) cluster samples to date in order to probe the abundance of faint galaxies in clusters. We also study how the GLF depends on cluster redshift, mass, and substructure and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. Methods. We calculated the GLFs for 31 clusters taken from the DAFT/FADA survey in the B,V,R, and I rest-frame bands. We used photometric redshifts computed from BVRIZJ images to constrain galaxy cluster membership. We carried out a detailed estimate of the completeness of our data. We distinguished the red-sequence and blue galaxies using a V − I versus I colour−magnitude diagram. We studied the evolution of these two populations with redshift. We fitted Schechter functions to our stacked GLFs to determine average cluster characteristics. Results. We find that the shapes of our GLFs are similar for the B,V,R, and I bands with a drop at the red GLF faint ends that is more pronounced at high redshift: αred ~ −0.5 at 0.40 ≤ z < 0.65 and αred > 0.1 at 0.65 ≤ z < 0.90. The blue GLFs have a steeper faint end (αblue ~ −1.6) than the red GLFs, which appears to be independent of redshift. For the full cluster sample, blue and red GLFs meet at MV = −20, MR = −20.5, and MI = −20.3. A study of how galaxy types evolve with redshift shows that late-type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Conclusions. Our results indicate that these clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late-type galaxies then appear to evolve into early types, enriching the red sequence between this redshift and today. This effect is consistent with the evolution of the faint-end slope of the red sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late-type galaxies that converted into early types, explaining the lack of evolution in the faint-end slopes of the blue GLFs.
The XXL Survey Farahi, Arya; Guglielmo, Valentina; Evrard, August E. ...
Astronomy & astrophysics,
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context. An X-ray survey with the XMM-Newton telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg2 fields. Combining spectroscopic and X-ray observations in one ...field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature. Aims. Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature, T300 kpc, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨lnM200 | T300 kpc, z⟩. Methods. We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts z < 0.6 to model, ⟨lnσgal | T300 kpc, z⟩, where σgal is the velocity dispersion of XXL cluster member galaxies and T300 kpc is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by N-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter. Results. For the XXL-N cluster sample, we find σgal ∝ T300 kpc0.63±0.05 $\sigma_{\textrm{gal}} \propto {{T_{\textrm{300~kpc}}}^{0.63\pm0.05}$ σgal∝T300 kpc0.63±0.05, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift, 〈ln(E(z)M200/1014 M⊙)|T300 kpc, z〉 = πT + αT ln (T300 kpc/Tp) + βT ln (E(z)/E(zp)) $\langle \ln (E(z) M_{200}/10^{14} {{\, M_{\odot}}})|{{T_{\textrm{300~kpc}}},z\rangle=\pi_{T}+\alpha_{T}\ln\left({{T_{\textrm{300~kpc}}}/T_{\textrm{p}}\right)+\beta_{T}\ln\left(E(z)/E(z_{\textrm{p}})\right)$ 〈ln(E(z)M200/1014 M⊙)|T300 kpc,z〉=πT+αTln(T300 kpc/Tp)+βTln(E(z)/E(zp)) using pivot values kTp = 2.2 keV and zp = 0.25, with normalization πT = 0.45 ± 0.24 and slope αT = 1.89 ± 0.15. We obtain only weak constraints on redshift evolution, βT = −1.29 ± 1.14. Conclusions. The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.
The XXL Survey Farahi, Arya; Guglielmo, Valentina; Evrard, August E. ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context.
An X-ray survey with the
XMM-Newton
telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg
2
fields. Combining spectroscopic and X-ray observations in one ...field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature.
Aims.
Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature,
T
300 kpc
, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨ln
M
200
|
T
300 kpc
,
z
⟩.
Methods.
We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts
z
< 0.6 to model, ⟨ln
σ
gal
|
T
300 kpc
,
z
⟩, where
σ
gal
is the velocity dispersion of XXL cluster member galaxies and
T
300 kpc
is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by
N
-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter.
Results.
For the XXL-N cluster sample, we find σ
gal
∝ T
300 kpc
0.63±0.05
, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift,
〈ln(
E
(
z
)
M
200
/10
14
M
⊙
)|T
300
kpc,
z
〉 = π
T
+ α
T
ln (
T
300
kpc/
T
p
) +
β
T
ln (
E
(
z
)/
E
(
z
p
)) using pivot values
kT
p
= 2.2 keV and
z
p
= 0.25, with normalization
π
T
= 0.45 ± 0.24 and slope
α
T
= 1.89 ± 0.15. We obtain only weak constraints on redshift evolution,
β
T
= −1.29 ± 1.14.
Conclusions.
The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.
While our current cosmological model places galaxy clusters at the nodes of a filament network (the cosmic web), we still struggle to detect these filaments at high redshifts. We perform a weak ...lensing study for a sample of 16 massive, medium-high redshift (0.4 <z< 0.9) galaxy clusters from the DAFT/FADA survey, which are imaged in at least three optical bands with Subaru/Suprime-Cam or CFHT/MegaCam. We estimate the cluster masses using an NFW fit to the shear profile measured in a KSB-like method, adding our contribution to the calibration of the observable-mass relation required for cluster abundance cosmological studies. We compute convergence maps and select structures within these maps, securing their detection with noise resampling techniques. Taking advantage of the large field of view of our data, we study cluster environment, adding information from galaxy density maps at the cluster redshift and from X-ray images when available. We find that clusters show a large variety of weak lensing maps at large scales and that they may all be embedded in filamentary structures at megaparsec scale. We classify these clusters in three categories according to the smoothness of their weak lensing contours and to the amount of substructures: relaxed (~7%), past mergers (~21.5%), and recent or present mergers (~71.5%). The fraction of clusters undergoing merging events observationally supports the hierarchical scenario of cluster growth, and implies that massive clusters are strongly evolving at the studied redshifts. Finally, we report the detection of unusually elongated structures in CLJ0152, MACSJ0454, MACSJ0717, A851, BMW1226, MACSJ1621, and MS1621.
ACO2163 is one of the hottest (mean \(kT=12-15.5\) keV) and extremely X-ray overluminous merging galaxy clusters which is located at \(z=0.203\). The cluster hosts one of the largest giant radio ...halos which are observed in most of the merging clusters, and a candidate radio relic. Recently, three merger shock fronts were detected in this cluster, explaining its extreme temperature and complex structure. Furthermore, previous XMM-Newton and Chandra observations hinted at the presence of a shock front that is associated with the gas `bullet' crossing the main cluster in the west-ward direction, and which heated the intra-cluster medium, leading to adiabatic compression of the gas behind the 'bullet'. The goal of this paper is to report on the detection of this shock front as revealed by the temperature discontinuity in the X-ray XMM-Newton image, and the edge in the Very Large Array (VLA) radio image. We also report on the detection of a relic source in the north-eastern region of the radio halo in the KAT-7 data, confirming the presence of an extended relic in this cluster. The brightness edge in the X-rays corresponds to a shock front with a Mach number \(M= 2.2\pm0.3\), at a distance of 0.2 Mpc from the cluster centre. An estimate from the luminosity jump gives \(M=1.9\pm0.4\). We consider a simple explanation for the electrons at the shock front, and for the observed discrepancy between the average spectral index of the radio halo emission and that predicted by the \(M=2.2\) shock which precedes the 'bullet'.
Je présente dans cette thèse les résultats obtenus à partir de la collaboration Franco Américaine appelée le Dark energy American French Team/ French American DArk energy Team (DAFT/FADA). Le but de ...la collaboration DAFT/FADA est de mener à bien un sondage sur la tomographie par lentilles faibles de riches amas de galaxies compris entre les redshifts z=0.4 et z=0.9. Contrairement aux autres méthodes comme les supernovae ou les comptages d'amas de galaxies, la tomographie par lentilles faibles est purement basée sur la géométrie et ne dépend pas de la connaissance sur la physique des objets utilisés comme indicateurs de distance. De plus, la raison pour analyser les observations dans la direction des amas est que le signal de cisaillement est augmenté d'un facteur 10 par rapport aux galaxies de champs. Notre travail contiendra les résultats de 91 riches amas de galaxies provenant du HST combiné avec le travail sur des données sol pour obtenir des redshifts photométriques. Cette combinaison de redshifts photométriques et de tomographie avec lentilles minces nous permettra de contraindre les équations d'état avec l'énergie noire, ainsi que l'évolution des propriétés des amas avec le redshift. C'est dans ce cadre que, durant ma thèse, j'ai étudié le comportement et des composants des amas DAFT/FADAS eux-mêmes. Cela s'est traduit par une étude de la lumière diffuse contenue dans 10 amas ainsi qu'une étude dynamique sur une gamme de redshifts allant de z=0.4 _a z=0.8.
I present in this thesis the results obtained from the American French collaboration called the Dark energy American French Team/French American DArk energy Team (DAFT/FADA). The goal of the DAFT/FADA collaboration is to carry out a weak lensing tomography survey of z = 0.4-0.9 rich clusters of galaxies. Unlike supernovae or other methods such as cluster of galaxy counts, weak lensing tomography is purely based on geometry and does not depend on knowledge of the physics of the objects used as distance indicators. In addition, the reason for analyzing observations in the direction of clusters is that the shear signal is enhanced by about 10 over the feld. Our work will contain results obtained on 91 rich clusters from the HST archive combined with ground based work to obtain photo-zs. This combination of photo-z and weak lensing tomography will enable us to constrain the equation of state of dark energy, and the cluster properties evolution with redshift. In this framework, during my PhD, I studied the behaviour and the comnents of the DAFT/FADAS clusters themselves. More precisely, I studied the difuse light contained within 10 clusters of the syrvey as well as their dynamical behaviour on a range of redshifts between z=0.4 and 0.8. indeed, The galaxy clusters themselves are still an important feld of study nowadays, mainly due to the fact they are the largest, at least partially virialized, structures we can observe, allowing us to better understand the history and evolution of our Universe. I present here the latest results obtained so far in my work on the DAFT/FADAS survey.
While our current cosmological model places galaxy clusters at the nodes of a filament network (the cosmic web), we still struggle to detect these filaments at high redshifts. We perform a weak ...lensing study for a sample of 16 massive, medium-high redshift (0.4<z<0.9) galaxy clusters from the DAFT/FADA survey, that are imaged in at least three optical bands with Subaru/Suprime-Cam or CFHT/MegaCam. We estimate the cluster masses using an NFW fit to the shear profile measured in a KSB-like method, adding our contribution to the calibration of the observable-mass relation required for cluster abundance cosmological studies. We compute convergence maps and select structures within, securing their detection with noise re-sampling techniques. Taking advantage of the large field of view of our data, we study cluster environment, adding information from galaxy density maps at the cluster redshift and from X-ray images when available. We find that clusters show a large variety of weak lensing maps at large scales and that they may all be embedded in filamentary structures at megaparsec scale. We classify them in three categories according to the smoothness of their weak lensing contours and to the amount of substructures: relaxed (~7%), past mergers (~21.5%), recent or present mergers (~71.5%). The fraction of clusters undergoing merging events observationally supports the hierarchical scenario of cluster growth, and implies that massive clusters are strongly evolving at the studied redshifts. Finally, we report the detection of unusually elongated structures in CLJ0152, MACSJ0454, MACSJ0717, A851, BMW1226, MACSJ1621, and MS1621.
We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9) cluster samples to date in order to probe ...the abundance of faint galaxies in clusters. We also study how the GLFs depend on cluster redshift, mass, and substructure, and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. We find that the shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5 at 0.40 < z < 0.65 and alpha(red) > 0.1 at 0.65 < z < 0.90. The blue GLFs have a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be independent of redshift. For the full cluster sample, blue and red GLFs intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy types evolve with redshift shows that late type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Our results indicate that our clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late type galaxies then appear to evolve into early types, enriching the red-sequence between this redshift and today. This effect is consistent with the evolution of the faint end slope of the red-sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late type galaxies that converted into early types, explaining the lack of evolution in the faint end slopes of the blue GLFs.
Cluster faint low surface brightness galaxies (fLSBs) are difficult to observe. Consequently, their origin, physical properties and number density are not well known. After a first search for fLSBs ...in the highly substructured Coma cluster, we present here a search for fLSBs in Abell 496. This cluster appears to be much more relaxed than Coma, but is embedded in a large scale filament of galaxies. Our aim is to compare the properties of fLSBs in these two very different clusters, to search for environmental effects. Based on deep CFHT/Megacam images in the u*, g', r' and i' bands, we selected galaxies with r'>21 and surface brightness > 24 mag/arcsec-2. We estimated photometric redshifts for all these galaxies and kept the 142 fLSBs with photo-z<0.2. In a g'-i' versus i' color-magnitude diagram, we find that a large part of these fLSBs follow the red sequence (RS) of brighter galaxies. The fLSBs within +-1sigma of the RS show a homogeneous spatial distribution, while those above the RS appear to be concentrated along the large scale filament of galaxies. These properties are interpreted as agreeing with the idea that RS fLSBs are formed in groups prior to cluster assembly. The formation of red fLSBs could be related to infalling galaxies.
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