Observations of 170 local (z 0.08) galaxy clusters in the northern hemisphere have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). We correct for systematic effects such as PSF broadening, foreground stars contamination, relative bias offsets and charge persistence. Scattered light induced background inhomogeneities are reduced down to ∆SB > 31 g' mag arcsec −2 by large dithering and subtraction of night-sky flats. Residual background inhomogeneities brighter than SB σ < 27.6 g' mag arcsec −2 caused by galactic cirrus are detected in front of 23% of the clusters. However, the large field of view allows to discriminate between accretion signatures and galactic cirrus. We detect accretion signatures in form of tidal streams in 22%, shells in 9.4%, multiple nuclei in 47% and two Brightest Cluster Galaxies (BCGs) in 7% of the clusters / BCGs.We measure semi-major axis surface brightness profiles of the BCGs and their surrounding Intracluster Light (ICL) down to a limiting surface brightness of SB = 30 g' mag arcsec −2 . The spatial resolution in the inner regions is increased by combining the WWFI light profiles with those that we measured from archival Hubble Space Telescope images or deconvolved WWFI images. We find that 71% of the BCG+ICL systems have SB profiles that are well described by a single Sérsic (SS) function whereas 29% require a double Sérsic (DS) function to obtain a good fit. SS BCGs, having more symmetric isophotal shapes and fewer detected accretion signatures than DS BCGs, appear to have slightly more relaxed morphology than their DS counterparts. Members of the latter type encompass S2 = 52 ± 21% of their total light in the outer Sérsic component. There is a wide scatter in transition radii r × between the two Sérsic components and surface brightnesses at the transition radii SB(r × ). The integrated brightnesses of the BCG+ICL systems correlate only weakly with S2, r × and SB(r × ). That indicates that the outer Sérsic component is unlikely to trace the dynamically hot ICL since BCG+ICL systems grow at present epoch predominantly in their outskirts.We find that BCGs have scaling relations that differ markedly from those of normal ellipticals, likely due to their indistinguishable embedding in the ICL. The most extended BCG+ICL systems have luminosities and radii comparable to whole clusters. We use different plausible estimates for the ICL component (based on an integrated brightness threshold, SB thresholds and profile decompositions) and find that they do not affect our conclusions about the properties of the ICL. On average, the ICL seems to be better aligned than the BCG with the host cluster in terms of position angle and centering. That makes it a potential Dark Matter tracer. We find positive correlations between BCG+ICL brightness and cluster mass, cluster radius, cluster richness and integrated satellite brightness, confirming that BCG/ICL growth is indeed coupled with cluster growth.

We present SMART, a new 3D implementation of the Schwarzschild Method and its application to a triaxial N-body merger simulation. SMART fits full line-of-sight velocity distributions (LOSVDs) to determine the viewing angles, black hole, stellar and dark matter (DM) masses and the stellar orbit distribution of galaxies. Our model uses a 5D orbital starting space to ensure a representative set of stellar trajectories adaptable to the integrals-of-motion space and it is designed to deal with non-parametric stellar and DM densities. SMART’s efficiency is demonstrated by application to a realistic N-body merger simulation including supermassive black holes which we model from five different projections. When providing the true viewing angles, 3D stellar luminosity profile and normalized DM halo, we can (i) reproduce the intrinsic velocity moments and anisotropy profile with a precision of $\sim 1\%$ and (ii) recover the black hole mass, stellar mass-to-light ratio and DM normalization to better than a few percent accuracy. This precision is smaller than the currently discussed differences between initial-stellar-mass functions and scatter in black hole scaling relations. Further tests with toy models suggest that the recovery of the anisotropy in triaxial galaxies is almost unique when the potential is known and full LOSVDs are fitted. We show that orbit models even allow the reconstruction of full intrinsic velocity distributions, which contain more information than the classical anisotropy parameter. Surprisingly, the orbit library for the analysed N-body simulation’s gravitational potential contains orbits with net rotation around the intermediate axis that is stable over some Gyrs.

We investigate the accuracy and precision of triaxial dynamical orbit models by fitting two dimensional mock observations of a realistic N-body merger simulation resembling a massive early-type galaxy with a supermassive black hole (SMBH). We show that we can reproduce the triaxial N-body merger remnant’s correct black hole mass, stellar mass-to-light ratio and total enclosed mass (inside the half-light radius) for several different tested orientations with an unprecedented accuracy of 5-10 per cent. Our dynamical models use the entire non-parametric line-of-sight velocity distribution (LOSVD) rather than parametric LOSVDs or velocity moments as constraints. Our results strongly suggest that state-of-the-art integral-field projected kinematic data contain only minor degeneracies with respect to the mass and anisotropy recovery. Moroever, this also demonstrates the strength of the Schwarzschild method in general. We achieve the proven high recovery accuracy and precision with our newly developed modeling machinery by combining several advancements: (i) our new semi-parametric deprojection code probes degeneracies and allows to constrain the viewing angles of a triaxial galaxy; (ii) our new orbit modeling code SMART uses a 5-dim orbital starting space to representatively sample in particular near-Keplerian orbits in galaxy centers; (iii) we use a generalised information criterion AICp to optimise the smoothing and to compare different mass models to avoid biases that occur in χ2-based models with varying model flexibilities.

We explore the potential of our novel triaxial modeling machinery in recovering the viewing angles, the shape and the orbit distribution of galaxies by using a high-resolution N-body merger simulation. Our modelling technique includes several recent advancements. (i) Our new triaxial deprojection algorithm SHAPE3D is able to significantly shrink the range of possible orientations of a triaxial galaxy and therefore to constrain its shape relying only on photometric information. It also allows to probe degeneracies, i.e. to recover different deprojections at the same assumed orientation. With this method we can constrain the intrinsic shape of the N-body simulation, i.e. the axis ratios p = b/a and q = c/a, with Δp and Δq ≲ 0.1 using only photometric information. The typical accuracy of the viewing angles reconstruction is 15-20○. (ii) Our new triaxial Schwarzschild code SMART exploits the full kinematic information contained in the entire non-parametric line-of-sight velocity distributions (LOSVDs) along with a 5D orbital sampling in phase space. (iii) We use a new generalised information criterion AICp to optimise the smoothing and to select the best-fit model, avoiding potential biases in purely χ2-based approaches. With our deprojected densities, we recover the correct orbital structure and anisotropy parameter β with Δβ≲ 0.1. These results are valid regardless of the tested orientation of the simulation and suggest that even despite the known intrinsic photometric and kinematic degeneracies the above described advanced methods make it possible to recover the shape and the orbital structure of triaxial bodies with unprecedented accuracy.