Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Intracluster light (ICL) provides a record of the dynamical interactions undergone by clusters, giving clues on cluster formation and evolution. Here, we analyse the properties of ICL in the massive cluster Abell 2390 at redshift z = 0.228. Our analysis is based on the deep images obtained by the Euclid mission as part of the Early Release Observations in the near-infrared (YE, JE, HE bands), using the NISP instrument in a 0.75 deg² field. We subtracted a point–spread function (PSF) model and removed the Galactic cirrus contribution in each band after modelling it with the DAWIS software. We then applied three methods to detect, characterise, and model the ICL and the brightest cluster galaxy (BCG): the CICLE 2D multi-galaxy fitting; the DAWIS wavelet-based multiscale software; and a mask-based 1D profile fitting. We detect ICL out to 600 kpc. The ICL fractions derived by our three methods range between 18% and 36% (average of 24%), while the BCG+ICL fractions are between 21% and 41% (average of 29%), depending on the band and method. A galaxy density map based on 219 selected cluster members shows a strong cluster substructure to the south-east and a smaller feature to the north-west. Ellipticals dominate the cluster’s central region, with a centroid offset from the BCG by about 70 kpc and distribution following that of the ICL, while spirals do not trace the entire ICL but rather substructures. The comparison of the BCG+ICL, mass from gravitational lensing, and X-ray maps show that the BCG+ICL is the best tracer of substructures in the cluster. Based on colours, the ICL (out to about 400 kpc) seems to be built by the accretion of small systems (M ∼ 10^9.5 M ), or from stars coming from the outskirts of Milky Way-type galaxies (M ∼ 10¹⁰ M ). Though Abell 2390 does not seem to be undergoing a merger, it is not yet fully relaxed, since it has accreted two groups that have not fully merged with the cluster core. We estimate that the contributions to the inner 300 kpc of the ICL of the north-west and south-east subgroups are 21% and 9%, respectively.

Abstract:

The intracluster light (ICL) permeating galaxy clusters is a tracer of the cluster assembly history and potentially a tracer of their dark matter structure. In this work, we explore the capability of the Euclid Wide Survey to detect ICL using HE-band mock images. We simulated clusters across a range of redshifts (0.3-1.8) and halo masses (1013:9-1015:0 M_) using an observationally motivated model of ICL. We identified a 50- 200 kpc circular annulus around the brightest cluster galaxy (BCG) in which the signal-to-noise ratio of the ICL is maximised and used the S/N within this aperture as our figure of merit for ICL detection.We compared three state-of-the-art methods for ICL detection and found that a method that performs simple aperture photometry after high-surface brightness source masking is able to detect ICL with minimal bias for clusters more massive than 1014:2 M_. The S/N of the ICL detection is primarily limited by the redshift of the cluster, which is driven by cosmological dimming rather than the mass of the cluster. Assuming the ICL in each cluster contains 15% of the stellar light, we forecast that Euclid will be able to measure the presence of ICL in up to _80 000 clusters of >1014:2 M_ between z = 0:3 and 1.5 with an S/N > 3. Half of these clusters will reside below z = 0:75, and the majority of those below z = 0:6 will be detected with an S/N > 20. A few thousand clusters at 1:3 < z < 1:5 will have ICL detectable with an S/N > 3. The surface brightness profile of the ICL model is strongly dependent on both the mass of the cluster and the redshift at which it is observed so that the outer ICL is best observed in the most massive clusters of >1014:7 M_. Euclid will detect the ICL at a distance of more than 500 kpc from the BCG, up to z = 0:7, in several hundred of these massive clusters over its large survey volume.