Diffuse Intracluster Light Research Articles

Detection of Intracluster Globular Clusters in the First JWST Images of the Gravitational Lens Cluster SMACS J0723.3–7327 at z = 0.39

We present a survey of globular clusters (GCs) in the massive gravitational lens cluster SMACS J0723.3–7327 at z = 0.39 based on the early released JWST/NIRCam images. In the color–magnitude diagrams of the point sources, we clearly find a rich population of intracluster GCs that are spread over a wide area of the cluster. Their ages, considering the cluster redshift, are younger than 9.5 Gyr. The F200W (AB) magnitudes of these GCs, 26.5 mag < F200W0 < 29.5 mag, correspond to −15.2 mag < M F200W < −12.2 mag, showing that they belong to the brightest GCs (including ultracompact dwarfs). The spatial distributions of these GCs show a megaparsec-scale structure elongated along the major axis of the brightest cluster galaxy. In addition, they show a large number of substructures, some of which are consistent with the substructures seen in the map of diffuse intracluster light. The GC number density map is, in general, consistent with the dark matter mass density map based on the strong lensing analysis in the literature. The radial number density profile of the GCs in the outer region is steeper than the dark matter mass profile obtained from lensing models. These results are consistent with those for the GCs found in the deep HST images of A2744, another massive cluster at z = 0.308, and in simulated galaxy clusters. This shows that the intracluster GCs are an excellent independent tool to probe the dark matter distribution in galaxy clusters, as well as reveal the cluster assembly history in the JWST era.

Is diffuse intracluster light a good tracer of the galaxy cluster matter distribution?

ABSTRACT We explore the relation between diffuse intracluster light (central galaxy included) and the galaxy cluster (baryonic and dark) matter distribution using a sample of 528 clusters at 0.2 ≤ z ≤ 0.35 found in the Dark Energy Survey (DES) Year 1 data. The surface brightness of the diffuse light shows an increasing dependence on cluster total mass at larger radius, and appears to be self-similar with a universal radial dependence after scaling by cluster radius. We also compare the diffuse light radial profiles to the cluster (baryonic and dark) matter distribution measured through weak lensing and find them to be comparable. The IllustrisTNG galaxy formation simulation, TNG300, offers further insight into the connection between diffuse stellar mass and cluster matter distributions – the simulation radial profile of the diffuse stellar component does not have a similar slope with the total cluster matter content, although that of the cluster satellite galaxies does. Regardless of the radial trends, the amount of diffuse stellar mass has a low-scatter scaling relation with cluster’s total mass in the simulation, out-performing the total stellar mass of cluster satellite galaxies. We conclude that there is no consistent evidence yet on whether or not diffuse light is a faithful radial tracer of the cluster matter distribution. Nevertheless, both observational and simulation results reveal that diffuse light is an excellent indicator of the cluster’s total mass.

Dark Energy Survey Year 1 results: the effect of intracluster light on photometric redshifts for weak gravitational lensing

Abstract We study the effect of diffuse intracluster light on the critical surface mass density estimated from photometric redshifts of lensing source galaxies, and the resulting bias in a weak lensing measurement of galaxy cluster mass. Under conservative assumptions, we find the bias to be negligible for imaging surveys like the Dark Energy Survey with a recommended scale cut of ≥200 kpc distance from cluster centres. For significantly deeper lensing source galaxy catalogues from present and future surveys like the Large Synoptic Survey Telescope program, more conservative scale and source magnitude cuts or a correction of the effect may be necessary to achieve percent level lensing measurement accuracy, especially at the massive end of the cluster population.

Chandra Detection of Intracluster X-Ray Sources in Fornax

Abstract Based on archival Chandra observations with a total exposure of 1.3 Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intracluster X-ray source populations. We detect 1177 point sources out to a projected radius of ∼30 arcmin (∼180 kpc) from the cluster center and down to a limiting 0.5–8 keV luminosity of ∼3 × 1037 erg s−1. We construct the source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs, and galactic nuclei. From this profile we statistically identify ∼183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at the ≳2σ level (with a maximum of 3.6σ) outside three effective radii of the central giant elliptical, NGC 1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries (LMXBs)), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intracluster light, thus providing strong evidence for the presence of intracluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.

First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies

The IllustrisTNG project is a new suite of cosmological magneto-hydrodynamical simulations of galaxy formation performed with the Arepo code and updated models for feedback physics. Here we introduce the first two simulations of the series, TNG100 and TNG300, and quantify the stellar mass content of about 4000 massive galaxy groups and clusters ($10^{13} \leq M_{\rm 200c}/M_{\rm sun} \leq 10^{15}$) at recent times ($z \leq 1$). The richest clusters have half of their total stellar mass bound to satellite galaxies, with the other half being associated with the central galaxy and the diffuse intra-cluster light. The exact ICL fraction depends sensitively on the definition of a central galaxy's mass and varies in our most massive clusters between 20 to 40% of the total stellar mass. Haloes of $5\times 10^{14}M_{\rm sun}$ and above have more diffuse stellar mass outside 100 kpc than within 100 kpc, with power-law slopes of the radial mass density distribution as shallow as the dark matter's ( $-3.5 < \alpha_{\rm 3D} < -3$). Total halo mass is a very good predictor of stellar mass, and vice versa: at $z=0$, the 3D stellar mass measured within 30 kpc scales as $\propto (M_{\rm 500c})^{0.49}$ with a $\sim 0.12$ dex scatter. This is possibly too steep in comparison to the available observational constraints, even though the abundance of TNG less massive galaxies ($< 10^{11}M_{\rm sun}$ in stars) is in good agreement with the measured galaxy stellar mass functions at recent epochs. The 3D sizes of massive galaxies fall too on a tight ($\sim$0.16 dex scatter) power-law relation with halo mass, with $r^{\rm stars}_{\rm 0.5} \propto (M_{\rm 500c})^{0.53}$. Even more fundamentally, halo mass alone is a good predictor for the whole stellar mass profiles beyond the inner few kpc, and we show how on average these can be precisely recovered given a single mass measurement of the galaxy or its halo.

Chandra Detection of Intracluster X-Ray sources in Virgo

Abstract We present a survey of X-ray point sources in the nearest and dynamically young galaxy cluster, Virgo, using archival Chandra observations that sample the vicinity of 80 early-type member galaxies. The X-ray source populations at the outskirts of these galaxies are of particular interest. We detect a total of 1046 point sources (excluding galactic nuclei) out to a projected galactocentric radius of ∼40 kpc and down to a limiting 0.5–8 keV luminosity of ∼ 2 × 10 38 erg s − 1 . Based on the cumulative spatial and flux distributions of these sources, we statistically identify ∼120 excess sources that are not associated with the main stellar content of the individual galaxies, nor with the cosmic X-ray background. This excess is significant at a 3.5σ level, when Poisson error and cosmic variance are taken into account. On the other hand, no significant excess sources are found at the outskirts of a control sample of field galaxies, suggesting that at least some fraction of the excess sources around the Virgo galaxies are truly intracluster X-ray sources. Assisted with ground-based and HST optical imaging of Virgo, we discuss the origins of these intracluster X-ray sources, in terms of supernova-kicked low-mass X-ray binaries (LMXBs), globular clusters, LMXBs associated with the diffuse intracluster light, stripped nucleated dwarf galaxies and free-floating massive black holes.

THE BURRELL SCHMIDT DEEP VIRGO SURVEY: TIDAL DEBRIS, GALAXY HALOS, AND DIFFUSE INTRACLUSTER LIGHT IN THE VIRGO CLUSTER

ABSTRACT We present the results of a deep imaging survey of the Virgo cluster of galaxies, concentrated around the cores of Virgo subclusters A and B. The goal of this survey was to detect and study very low surface brightness features present in Virgo, including discrete tidal features, the faint halos of luminous galaxies, and the diffuse intracluster light (ICL). Our observations span roughly 16 degrees2 in two filters, reaching a 3σ limiting depth of = 29.5 and = 28.5 mag arcsec−2. At these depths, our limiting systematic uncertainties are astrophysical: variations in faint background sources as well as scattered light from galactic dust. We show that this dust-scattered light is well traced by deep far-infrared imaging, making it possible to separate it from true diffuse light in Virgo. We use our imaging to trace and measure the color of the diffuse tidal streams and ICL in the Virgo core near M87, in fields adjacent to the core including the M86/M84 region, and to the south of the core around M49 and subcluster B, along with the more distant W cloud around NGC 4365. Overall, the bulk of the projected ICL is found in the Virgo core and within the W cloud; we find little evidence for an extensive ICL component in the field around M49. The bulk of the ICL we detect is fairly red in color (B − V = 0.7–0.9), indicative of old, evolved stellar populations. Based on the luminosity of the observed ICL features in the cluster, we estimate a total Virgo ICL fraction of 7%–15%. This value is somewhat smaller than that expected for massive, evolved clusters, suggesting that Virgo is still in the process of growing its extended ICL component. We also trace the shape of M87's extremely boxy outer halo out to ∼150 kpc, and show that the current tidal stripping rate from low luminosity galaxies is insufficient to have built M87's outer halo over a Hubble time. We identify a number of previously unknown low surface brightness structures around galaxies projected close to M86 and M84. The extensive diffuse light seen in the infalling W cloud around NGC 4365 is likely to be subsumed in the general Virgo ICL component once the group enters the cluster, illustrating the importance of group infall in generating ICL. Finally, we also identify another large and extremely low surface brightness ultradiffuse galaxy, likely in the process of being shredded by the cluster tidal field. With the survey complete, the full imaging data set is now available for public release.

Intragroup and Intracluster Light

AbstractThe largest stellar halos in the universe are found in massive galaxy clusters, where interactions and mergers of galaxies, along with the cluster tidal field, all act to strip stars from their host galaxies and feed the diffuse intracluster light (ICL) and extended halos of brightest cluster galaxies (BCGs). Studies of the nearby Virgo Cluster reveal a variety of accretion signatures imprinted in the morphology and stellar populations of its ICL. While simulations suggest the ICL should grow with time, attempts to track this evolution across clusters spanning a range of mass and redshift have proved difficult due to a variety of observational and definitional issues. Meanwhile, studies of nearby galaxy groups reveal the earliest stages of ICL formation: the extremely diffuse tidal streams formed during interactions in the group environment.

Probing cluster environments of blazars throughγγabsorption

Most blazars are known to be hosted in giant elliptic galaxies, but their cluster environments have not been thoroughly investigated. Cluster environments may contain radiation fields of low-energy photons created by nearby galaxies and/or stars in the intracluster medium that produce diffuse intracluster light. These radiation fields may absorb very high energy gamma rays ($E\gtrsim100$ GeV; VHE) and trigger pair cascades with further production of subsequent generations of gamma rays with lower energies via inverse Compton scattering on surrounding radiation fields leaving a characteristic imprint in the observed spectral shape. The change of the spectral shape of the blazar reflects the properties of its ambient medium. We show, however, that neither intracluster light nor the radiation field of an individual nearby galaxy can cause substantial gamma-gamma absorption. Substantial gamma-gamma absorption is possible only in the case of multiple, $\gtrsim5$, luminous nearby galaxies. This situation is not found in the local Universe, but may be possible at larger redshifts ($z\gtrsim2$). Since VHE gamma rays from such distances are expected to be strongly absorbed by the extragalactic background light, we consider possible signatures of gamma-ray induced pair cascades by calculating the expected GeV flux which appears to be below the Fermi sensitivity even for $\sim10$ nearby galaxies.

THE NEXT GENERATION VIRGO CLUSTER SURVEY. VIII. THE SPATIAL DISTRIBUTION OF GLOBULAR CLUSTERS IN THE VIRGO CLUSTER

We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey, a large imaging survey covering Virgo's primary subclusters to their virial radii. Using the g', (g'-i') color-magnitude diagram of unresolved and marginally-resolved sources, we constructed 2-D maps of the GC distribution. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the extent of the cluster, where the red (metal-rich) GCs are largely located around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a more extended spatial distribution, with significant populations present beyond 83' (215 kpc) along the major axes of M49 and M87. The GC distribution around M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness of the diffuse light surrounding both galaxies. We find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to the locations of Virgo galaxies and the intracluster X-ray gas, and find good agreement between these baryonic structures. The Virgo cluster contains a total population of 67300$\pm$14400 GCs, of which 35% are located in M87 and M49 alone. We compute a cluster-wide specific frequency S_N,CL=$2.8\pm0.7$, including Virgo's diffuse light. The GC-to-baryonic mass fraction is e_b=$5.7\pm1.1\times10^{-4} $and the GC-to-total cluster mass formation efficiency is e_t=$2.9\pm0.5\times10^{-5}$, values slightly lower than, but consistent with, those derived for individual galactic halos. Our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the diffuse intracluster light) is an ongoing process.(abridged)

DIFFUSE OPTICAL INTRACLUSTER LIGHT AS A MEASURE OF STELLAR TIDAL STRIPPING: THE CLUSTER CL0024+17 ATz∼ 0.4 OBSERVED AT THE LARGE BINOCULAR TELESCOPE

We have evaluated the diffuse intracluster light (ICL) in the central core of the galaxy cluster CL0024+17 at $z\sim 0.4$ observed with the prime focus camera (LBC) at LBT. The measure required an accurate removal of the galaxies light within $\sim 200$ kpc from the center. The residual background intensity has then been integrated in circular apertures to derive the average ICL intensity profile. The latter shows an approximate exponential decline as expected from theoretical cold dark matter models. The radial profile of the ICL over the galaxies intensity ratio (ICL fraction) is increasing with decreasing radius but near the cluster center it starts to bend and then decreases where the overlap of the halos of the brightest cluster galaxies becomes dominant. Theoretical expectations in a simplified CDM scenario show that the ICL fraction profile can be estimated from the stripped over galaxy stellar mass ratio in the cluster. It is possible to show that the latter quantity is almost independent of the properties of the individual host galaxies but mainly depends on the average cluster properties. The predicted ICL fraction profile is thus very sensitive to the assumed CDM profile, total mass and concentration parameter of the cluster. Adopting values very similar to those derived from the most recent lensing analysis in CL0024+17 we find a good agreement with the observed ICL fraction profile. The galaxy counts in the cluster core have then been compared with that derived from composite cluster samples in larger volumes, up to the clusters virial radius. The galaxy counts in the CL0024+17 core appear flatter and the amount of bending respect to the average cluster galaxy counts imply a loss of total emissivity in broad agreement with the measured ICL fraction.

Growth of brightest cluster galaxies via mergers since z=1

Hierarchical assembly within clusters of galaxies is tied directly to the evolution of the Brightest Cluster Galaxies (BCGs), which dominate the stellar light in the centres of rich clusters. In this paper we investigate the number of mergers onto BCGs in 14 X-ray selected clusters over the redshift range 0.8 < z < 1.4 using HST imaging data. We find significant differences in the numbers of companion galaxies to BCGs between the clusters in our sample indicating that BCGs in similar mass clusters can have very different merging histories. Within a 50 kpc radius around the BCGs we find an average of 6.45 \pm 1.15 companion galaxies with mass ratios (companion:BCG) between 1:1 and 1:20. The infalling companions show a 50/50 split between major (1:1 - 1:2) and minor (1:3 - 1:20) mergers. When compared to similar work using lower redshift clusters, these results demonstrate that both major and minor merging was more common in the past. Since the dynamical timescales for merging onto the BCG are relatively short compared with the look-back time to z ~ 1 our results suggest that the BCG stellar mass may increase by as much as 1.8 times since z = 1. However the growth rate of BCGs will be substantially less if stripped material from nearby companions ends up in the diffuse intracluster light.

Measurement of the intracluster light at z∼1

A significant fraction of the total photospheric light in nearby galaxy clusters is thought to be contained within the diffuse intracluster light (ICL), which extends 100s of kpc from cluster cores. The study of the ICL can reveal details of the evolutionary histories and processes occurring within galaxy clusters, however since it has a very low surface brightness it is often difficult to detect. We present here the first measurements of the ICL as a fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m) imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) = 22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius R500. This is broadly consistent with simulations of the ICL at a similar redshift and when compared to nearby observations suggests that the fraction of the total cluster light that is in the ICL has increased by a factor 2 - 4 since z\sim1. We also find the fraction of the total cluster light contained within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts, which in 5 out of 6 cases is larger than the fraction of the ICL component, in contrast to results from nearby clusters. This suggests that the evolution in cluster cores involves substantial stripping activity at late times, in addition to the early build up of the BCG stellar mass through merging. The presence of significant amounts of stellar light at large radii from these BCGs may help towards solving the recent disagreement between the semi-analytic model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the observed large masses and scale sizes reported for BCGs at high redshift.

Internal dynamics of the galaxy cluster Abell 545

Diffuse radio emission in galaxy clusters, and their connection with cluster mergers, are still debated. We seek to explore the internal dynamics of the radio halo cluster Abell 545. This cluster is also peculiar for hosting in its center a very bright, red, diffuse intracluster light due to an old, stellar population, so bright to be named as "star pile". Our analysis is based on redshift data for 110 galaxies. We identify 95 cluster members and analyze the cluster internal dynamics by combining galaxy velocities and positions. We also use both photometric and X-ray data. We estimate the cluster redshift, z=0.1580, a velocity dispersion of 1200 km/s, and ICM temperature kT_X~8 keV. Our optical and X-ray analyses detect substructures. Optical data reveal three main galaxy clumps (center, NNW, and NE), and possibly a fourth clump at South. There is not a dominant galaxy and the four brightest galaxies avoid the cluster core (>~0.4h distant from the cluster center) and are >~1500 km/s far from the mean cluster velocity. The analysis of the X-ray surface brightness distribution provides us evidence of a disturbed dynamical phase. Located in the star pile region there is the brightest galaxies of the cluster core (CBCG) and a very compact elliptical galaxy. We show that the star pile has a similar redshift to that of the CBCG. Both the star pile and the CBCG are at rest in the cluster rest frame. The emerging picture of Abell 545 is that of a massive, M(R<1.6 h_70^-1 Mpc)=1.1-1.8x10^15 h_70^-1 Msun, very complex cluster with merging occurring along two directions. A545 gives another proof in the favor of the connection between cluster merger and extended, diffuse radio emission. The star pile, likely due to the process of a brightest galaxy forming in the cluster core. A545 represents a textbook cluster where to study the simultaneous formation of a galaxy system and its brightest galaxy.

Diffuse intracluster light at intermediate redshifts: intracluster light observations in an X-ray cluster at z= 0.29★

The diffuse intracluster light (ICL) contains a significant fraction of the total stellar mass in clusters of galaxies, and contributes in roughly equal proportion as the hot intracluster medium to the total baryon content of clusters. Because of the potential importance of understanding the origin of the ICL in the context of the formation and evolution of structure in the Universe, the field has recently undergone a revival both in the quality and quantity of observational and theoretical investigations. Because of cosmological dimming, the observational work has mostly concentrated on low-redshift clusters, but clearly observations at higher redshifts can provide interesting clues about the evolution of the diffuse component. In this paper we present the first results of a programme to characterize the ICL of intermediate-redshift clusters. We find that at z∼ 0.3, the X-ray cluster RX J0054.0−2823 already has a significant ICL and that the fraction of the total light in the ICL and the brightest cluster galaxy (BCG) is comparable to that of similar clusters at lower redshift. We also find that the kinematics of the ICL is consistent with it being the remnant of tidally destroyed galaxies streaming in the central regions of the cluster, which has three central giant elliptical galaxies acting as an efficient ‘galaxy grinding machine’. Our cluster has a bi-modal radial velocity distribution and thus two possible values for the velocity dispersion. We find that the cluster fits well in the correlation between BCG+ICL fraction and cluster mass for a range of velocity dispersions, leading us to question the validity of a relevant correlation between these two quantities.

The unmixed kinematics and origins of diffuse stellar light in the core of the Hydra I cluster (Abell 1060)

Diffuse intracluster light (ICL) and cD galaxy halos are believed to originate from galaxy evolution and disruption. We present a kinematic study of the ICL in the Hydra I cluster core, using planetary nebulas (PNs) as tracers. We used multi-slit imaging spectroscopy with FORS2 on VLT-UT1 to detect 56 PNs associated with diffuse light in the central 100 x 100 kpc^2 of Hydra I. We measured their [OIII] magnitudes, sky positions, and velocity distribution (LOSVD), and compared with the phase-space distribution of nearby galaxies. The luminosity function of the detected PNs is consistent with that expected at a distance of ~50 Mpc. Their number density is ~4 times lower for the light seen than expected, and we discuss ram pressure stripping of the PNs by the hot ICM as one of the possible explanations. The LOSVD histogram of the PNs is highly non-Gaussian and multipeaked: it is dominated by a broad central component with sigma~500 km/s at around the average velocity of the cluster, and shows two additional narrower peaks at 1800 km/s and 5000 km/s. The main component is broadly consistent with the outward continuation of the intracluster halo of NGC 3311, which was earlier shown to have a velocity dispersion of ~470 km/s at radii of >50". Galaxies with velocities in this range are absent in the central 100 x 100 kpc^2 and may have been disrupted earlier to build this component. The PNs in the second peak in the LOSVD at 5000 km/s are coincident spatially and in velocities with a group of dwarf galaxies in the MSIS field. They may trace the debris from the ongoing tidal disruption of these galaxies. Most of the diffuse light in the core of Hydra is still not phase-mixed. The build-up of ICL and the dynamically hot cD halo around NGC 3311 are ongoing, through the accretion of material from galaxies falling into the cluster core and tidally interacting with its potential well.

THE CONNECTION BETWEEN DIFFUSE LIGHT AND INTRACLUSTER PLANETARY NEBULAE IN THE VIRGO CLUSTER

We compare the distribution of diffuse intracluster light detected in the Virgo Cluster via broadband imaging with that inferred from searches for intracluster planetary nebulae (IPNe). We find a rough correspondence on large scales (~ 100 kpc) between the two, but with very large scatter (~ 1.3 mag/arcsec^2). On smaller scales (1 -- 10 kpc), the presence or absence of correlation is clearly dependent on the underlying surface brightness. On these scales, we find a correlation in regions of higher surface brightness (mu_V < ~27) which are dominated by the halos of large galaxies such as M87, M86, and M84. In those cases, we are likely tracing PNe associated with galaxies rather than true IPNe. In true intracluster fields, at lower surface brightness, the correlation between luminosity and IPN candidates is much weaker. While a correlation between broadband light and IPNe is expected based on stellar populations, a variety of statistical, physical, and methodological effects can act to wash out this correlation and explain the lack of a strong correlation at lower surface brightness found here. [abridged]

Diffuse Optical Light in Galaxy Clusters. II. Correlations with Cluster Properties

We have measured the flux, profile, color, and substructure in the diffuse intracluster light (ICL) in a sample of ten galaxy clusters with a range of mass, morphology, redshift, and density. Deep, wide-field observations for this project were made in two bands at the one meter Swope and 2.5 meter du Pont telescope at Las Campanas Observatory. Careful attention in reduction and analysis was paid to the illumination correction, background subtraction, point spread function determination, and galaxy subtraction. ICL flux is detected in both bands in all ten clusters ranging from 7.6 x 10^{10} to 7.0 x 10^{11} h^{-1} solar luminosities in r and 1.4 x 10^{10} to 1.2 x 10^{11} h^{-1} solar luminosities in the B-band. These fluxes account for 6 to 22% of the total cluster light within one quarter of the virial radius in r and 4 to 21% in the B-band. Average ICL B-r colors range from 1.5 to 2.8 mags when k and evolution corrected to the present epoch. In several clusters we also detect ICL in group environments near the cluster center and up to ~1 h^{-1} Mpc distant from the cluster center. Our sample, having been selected from the Abell sample, is incomplete in that it does not include high redshift clusters with low density, low flux, or low mass, and it does not include low redshift clusters with high flux, mass, or density. This bias makes it difficult to interpret correlations between ICL flux and cluster properties. Despite this selection bias, we do find that the presence of a cD galaxy corresponds to both centrally concentrated galaxy profiles and centrally concentrated ICL profiles. This is consistent with ICL either forming from galaxy interactions at the center, or forming at earlier times in groups and later combining in the center.

Diffuse light and building history of the galaxy cluster Abell 2667

We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or are part of the very elliptical external envelope of the central galaxy remains unclear. VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow to compute a redshift. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south and hotter regions towards the north east, south west and north west. This possibly suggests shock fronts along these directions produced by infalling material. These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions.

Diffuse Light in the Virgo Cluster

We present deep optical imaging of the inner 1.5 x1.5 of the Virgo cluster to search for diffuse intracluster light (ICL). Our image reaches a 1 depth of µv=28.5 mag/arcsec 2 — 1.5 mag/arcsec 2 deeper than previous surveys — and reveals an intricate web of diffuse intracluster light. We see several long (>100 kpc) tidal streamers, as well as a myriad of smaller-scale tidal tails and bridges between galaxies. The diffuse halo of M87 is traced out to nearly 200 kpc, appearing very irregular on these scales, while significant diffuse light is also detected around the M84/M86 pair. Several galaxies in the core are embedded in common envelopes, suggesting they are true physical subgroups. The complex substructure of Virgo’s diffuse ICL reflects the hierarchical nature of cluster assembly, rather than being the product of smooth accretion around a central galaxy. Subject headings:galaxies: clusters: individual (Virgo) — galaxies: interactions