29 research outputs found
Unveiling the Dynamical State of Massive Clusters through the ICL Fraction
We have selected a sample of 11 massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the intracluster light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs ICL estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between ~7% and 23%, compared with the ~2%–11% found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, so are their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/younger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event
Unveiling the Dynamical State of Massive Clusters through the ICL Fraction
We have selected a sample of 11 massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the intracluster light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs ICL estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between ~7% and 23%, compared with the ~2%–11% found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, so are their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/younger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event
J-PLUS : analysis of the intracluster light in the Coma cluster
Context. The intracluster light (ICL) is a luminous component of galaxy clusters composed of stars that are gravitationally bound to the cluster potential, but do not belong to the individual galaxies. Previous studies of the ICL have shown that its formation and evolution are intimately linked to the evolutionary stage of the cluster. Thus, the analysis of the ICL in the Coma cluster will give insights into the main processes driving the dynamics in this highly complex system. Aims. Using a recently developed technique, we measure the ICL fraction in Coma at several wavelengths, using the J-PLUS unique filter system. The combination of narrow- and broadband filters provides valuable information on the dynamical state of the cluster, the ICL stellar types, and the morphology of the diffuse light. Methods. We used the Chebyshev-Fourier intracluster light estimator (CICLE) to distinguish the ICL from the light of the galaxies, and to robustly measure the ICL fraction in seven J-PLUS filters. Results. We obtain the ICL fraction distribution of the Coma cluster at different optical wavelengths, which varies from ∼7%−21%, showing the highest values in the narrowband filters J0395, J0410, and J0430. This ICL fraction excess is a distinctive pattern that has recently been observed in dynamically active clusters (mergers), indicating a higher amount of bluer stars in the ICL than in cluster galaxies. Conclusions. The high ICL fractions and the excess in the bluer filters are indicative of a merging state. The presence of younger stars or stars with lower metallicity in the ICL suggests that the main mechanism of ICL formation for the Coma cluster is the stripping of the stars in the outskirts of infalling galaxies and possibly the disruption of dwarf galaxies during past or ongoing mergers
Evidence for a redshifted excess in the intracluster light fractions of merging clusters at
The intracluster light (ICL) fraction is a well-known indicator of the
dynamical activity in intermediate-redshift clusters. Merging clusters in the
redshift interval have a distinctive peak in the ICL fractions
measured between \AA. In this work, we analyze two
higher-redshift, clearly merging clusters, ACT-CLJ0102-49151 and CL
J0152.7-1357, at , using the HST optical and infrared images obtained by
the RELICS survey. We report the presence of a similar peak in the ICL
fractions, although wider and redshifted to the wavelength interval \AA. The fact that this excess in the ICL fractions is found at
longer wavelengths can be explained by an assorted mixture of stellar
populations in the ICL, direct inheritance of an ICL that was mainly formed by
major galaxy mergers with the BCG at and whose production is
instantaneously burst by the merging event. The ubiquity of the ICL fraction
merging signature across cosmic time enhances the ICL as a highly reliable and
powerful probe to determine the dynamical stage of galaxy clusters, which is
crucial for cluster-based cosmological inferences that require relaxation of
the sample.Comment: 11 pages, 3 figures, accepted for publication in ApJ
Preparing for low surface brightness science with the Vera C. Rubin Observatory: a comparison of observable and simulated intracluster light fractions
Intracluster light (ICL) provides an important record of the interactions galaxy clusters have undergone. However, we are limited in our understanding by our measurement methods. To address this, we measure the fraction of cluster light that is held in the Brightest Cluster Galaxy and ICL (BCG+ICL fraction) and the ICL alone (ICL fraction) using observational methods (surface brightness threshold-SB, non-parametric measure-NP, composite models-CM, and multi-galaxy fitting-MGF) and new approaches under development (wavelet decomposition-WD) applied to mock images of 61 galaxy clusters (14 <log10M200c/M⊙ < 14.5) from four cosmological hydrodynamical simulations. We compare the BCG+ICL and ICL fractions from observational measures with those using simulated measures (aperture and kinematic separations). The ICL fractions measured by kinematic separation are significantly larger than observed fractions. We find the measurements are related and provide equations to estimate kinematic ICL fractions from observed fractions. The different observational techniques give consistent BCG+ICL and ICL fractions but are biased to underestimating the BCG+ICL and ICL fractions when compared with aperture simulation measures. Comparing the different methods and algorithms, we find that the MGF algorithm is most consistent with the simulations, and CM and SB methods show the smallest projection effects for the BCG+ICL and ICL fractions, respectively. The Ahad (CM), MGF, and WD algorithms are best set up to process larger samples; however, the WD algorithm in its current form is susceptible to projection effects. We recommend that new algorithms using these methods are explored to analyse the massive samples that Rubin Observatory’s Legacy Survey of Space and Time will provide
Preparing for low surface brightness science with the Vera C. Rubin Observatory: A Comparison of Observable and Simulated Intracluster Light Fractions
Intracluster Light (ICL) provides an important record of the interactions
galaxy clusters have undergone. However, we are limited in our understanding by
our measurement methods. To address this we measure the fraction of cluster
light that is held in the Brightest Cluster Galaxy and ICL (BCG+ICL fraction)
and the ICL alone (ICL fraction) using observational methods (Surface
Brightness Threshold-SB, Non-Parametric Measure-NP, Composite Models-CM,
Multi-Galaxy Fitting-MGF) and new approaches under development (Wavelet
Decomposition-WD) applied to mock images of 61 galaxy clusters (14<log10
M_200c/M_solar <14.5) from four cosmological hydrodynamical simulations. We
compare the BCG+ICL and ICL fractions from observational measures with those
using simulated measures (aperture and kinematic separations). The ICL
fractions measured by kinematic separation are significantly larger than
observed fractions. We find the measurements are related and provide equations
to estimate kinematic ICL fractions from observed fractions. The different
observational techniques give consistent BCG+ICL and ICL fractions but are
biased to underestimating the BCG+ICL and ICL fractions when compared with
aperture simulation measures. Comparing the different methods and algorithms we
find that the MGF algorithm is most consistent with the simulations, and CM and
SB methods show the smallest projection effects for the BCG+ICL and ICL
fractions respectively. The Ahad (CM), MGF and WD algorithms are best set up to
process larger samples, however, the WD algorithm in its current form is
susceptible to projection effects. We recommend that new algorithms using these
methods are explored to analyse the massive samples that Rubin Observatory's
Legacy Survey of Space and Time will provide.Comment: Submitted for publication in MNRAS, posted to arXiv after responding
to two positive rounds of referee comments. Key results in Figs 3, 5, 6 and
1
Galaxy clusters and groups in the ALHAMBRA Survey
We present a catalogue of 348 galaxy clusters and groups with
selected in the 2.78 ALHAMBRA Survey. The high precision of our
photometric redshifts, close to , and the wide spread of the seven
ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and
is less affected by cosmic variance than comparable samples.
The detection has been carried out with the Bayesian Cluster Finder (BCF),
whose performance has been checked in ALHAMBRA-like light-cone mock catalogues.
Great care has been taken to ensure that the observable properties of the mocks
photometry accurately correspond to those of real catalogues. From our
simulations, we expect to detect galaxy clusters and groups with both
completeness and purity down to dark matter halo masses of
for . Cluster redshifts are
expected to be recovered with precision for . We also expect
to measure cluster masses with
precision down to , masses which are
smaller than those reached by similar work.
We have compared these detections with previous optical, spectroscopic and
X-rays work, finding an excellent agreement with the rates reported from the
simulations. We have also explored the overall properties of these detections
such as the presence of a colour-magnitude relation, the evolution of the
photometric blue fraction and the clustering of these sources in the different
ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that,
for a fixed stellar mass, the environment is playing a crucial role at lower
redshifts (z0.5).Comment: Accepted for publication in MNRAS. Catalogues and figures available
online and under the following link:
http://bascaso.net46.net/ALHAMBRA_clusters.htm
CLASH: Precise New Constraints on the Mass Profile of Abell 2261
We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the
first time and determine this cluster is not "over-concentrated" as found
previously, implying a formation time in agreement with {\Lambda}CDM
expectations. These results are based on strong lensing analyses of new 16-band
HST imaging obtained as part of the Cluster Lensing and Supernova survey with
Hubble (CLASH). Combining this with revised weak lensing analyses of Subaru
wide field imaging with 5-band Subaru + KPNO photometry, we place tight new
constraints on the halo virial mass M_vir = 2.2\pm0.2\times10^15 M\odot/h70
(within r \approx 3 Mpc/h70) and concentration c = 6.2 \pm 0.3 when assuming a
spherical halo. This agrees broadly with average c(M,z) predictions from recent
{\Lambda}CDM simulations which span 5 <~ 8. Our most significant
systematic uncertainty is halo elongation along the line of sight. To estimate
this, we also derive a mass profile based on archival Chandra X-ray
observations and find it to be ~35% lower than our lensing-derived profile at
r2500 ~ 600 kpc. Agreement can be achieved by a halo elongated with a ~2:1 axis
ratio along our line of sight. For this elongated halo model, we find M_vir =
1.7\pm0.2\times10^15 M\odot/h70 and c_vir = 4.6\pm0.2, placing rough lower
limits on these values. The need for halo elongation can be partially obviated
by non-thermal pressure support and, perhaps entirely, by systematic errors in
the X-ray mass measurements. We estimate the effect of background structures
based on MMT/Hectospec spectroscopic redshifts and find these tend to lower
Mvir further by ~7% and increase cvir by ~5%.Comment: Submitted to the Astrophysical Journal. 19 pages, 14 figure
Full Lensing Analysis of Abell 1703: Comparison of Independent Lens-Modelling Techniques
The inner mass-profile of the relaxed cluster Abell 1703 is analysed by two
very different strong-lensing techniques applied to deep ACS and WFC3 imaging.
Our parametric method has the accuracy required to reproduce the many sets of
multiple images, based on the assumption that mass approximately traces light.
We test this assumption with a fully non-parametric, adaptive grid method, with
no knowledge of the galaxy distribution. Differences between the methods are
seen on fine scales due to member galaxies which must be included in models
designed to search for lensed images, but on the larger scale the general
distribution of dark matter is in good agreement, with very similar radial mass
profiles. We add undiluted weak-lensing measurements from deep multi-colour
Subaru imaging to obtain a fully model-independent mass profile out to the
virial radius and beyond. Consistency is found in the region of overlap between
the weak and strong lensing, and the full mass profile is well-described by an
NFW model of a concentration parameter, (and
). Abell 1703 lies above
the standard -- relation predicted for the standard CDM model,
similar to other massive relaxed clusters with accurately determined
lensing-based profiles.Comment: 12 pages, 17 figures, 1 table, accepted for publication in MNRAS. V2
includes minor changes and revised figure
Two lensed star candidates at behind the galaxy cluster MACS J0647.7+7015
We report the discovery of two extremely magnified lensed star candidates
behind the galaxy cluster MACS J0647.7+7015, in recent multi-band James Webb
Space Telescope (JWST) NIRCam observations. The candidates are seen in a
previously known, dropout giant arc that straddles the
critical curve. The candidates lie near the expected critical curve position
but lack clear counter images on the other side of it, suggesting these are
possibly stars undergoing caustic crossings. We present revised lensing models
for the cluster, including multiply imaged galaxies newly identified in the
JWST data, and use them to estimate a background macro-magnification of at
least and at the positions of the two candidates,
respectively. With these values, we expect effective, caustic-crossing
magnifications of for the two star candidates. The Spectral Energy
Distributions (SEDs) of the two candidates match well spectra of B-type stars
with best-fit surface temperatures of K, and K,
respectively, and we show that such stars with masses M
and M, respectively, can become sufficiently magnified to
be observed. We briefly discuss other alternative explanations and conclude
these are likely lensed stars, but also acknowledge that the less magnified
candidate may instead be or reside in a star cluster. These star candidates
constitute the second highest-redshift examples to date after Earendel at
, establishing further the potential of studying extremely
magnified stars to high redshifts with the JWST. Planned visits including
NIRSpec observations will enable a more detailed view of the candidates already
in the near future.Comment: 12 pages, 5 figures, 2 tables. Fixed Fig 3. comments are welcom