A MUSE view of cd galaxy NGC 3311

A MUSE view of cd galaxy NGC 3311 C. E. Barbosa 1, M. Arnaboldi 2, L. Coccato 2, O. Gerhard 3, C. Mendes de Oliveira 1, M. Hilker 2, T. Richtler 4 1 Universidade de São Paulo, São Paulo, Brazil 2 European Southern Observatory, Garching, Germany 3 Max-Planck-Institut fur Extraterrestrische Physik, Garching, Germany 4 Universidad Concepción, Concepción, Chile Galaxy Groups and Clusters II: Laboratories to study galaxy evolution October 23-26, 2017 La Serena, Chile Credit: Gemini Observatory/AURA

That s a familiar system...

Introduction: cd galaxies Type-cD galaxies (cd galaxies) is a subtype of giant elliptical galaxies (D) in the Bautz-Morgan classification. Quoting Morgan and Lesh (1965) (a) they are located in clusters, of which they are outstandingly the brightest and largest members; (b) they are centrally located in their clusters; (c) they are never highly flattened in shape; (d) they are of a characteristic appearance, having bright, elliptical-like [centers], surrounded by an extended amorphous envelope.

cd envelopes SB profiles of cd galaxies deviate from the R 1/4 law (de Vaucouleurs 1953) Envelopes have shallow surface brightness profiles NGC 3311 at the Hydra I cluster Figure from Sarazin (1986). :

Formation of cd galaxies. Massive, passive evolving galaxies are identified at z 2.5 (Cimatti et al. 2004). Red nuggets population are believed to be precursor of the nearby early-type galaxies (van Dokkum et al. 2009; Cassata et al. 2010) Among different models, the two-phase formation scenario (Oser et al. 2010) is among the most promising to explain the formation of galaxies. Central region is formed in a fast dissipative process early (z 3) Stellar halo is accreted at later epochs stochastically This model is able to explain the growth of massive galaxies since z = 2 (van Dokkum et al. 2010) Can we identify the in situ and accreted populations?

The case of NGC 3311 Central galaxy of the cluster Abell 1060 (Hydra cluster) D 50 Mpc. NGC 3311 NGC 3309

The case of NGC 3311 Central galaxy of the cluster Abell 1060 (Hydra cluster) D 50 Mpc. Rising, asymmetric velocity dispersion profile (Loubser et al. 2008; Richtler et al. 2011). NGC 3309 NGC 3311 Loubser et al. 2008

The case of NGC 3311 Central galaxy of the cluster Abell 1060 (Hydra cluster) D 50 Mpc. Rising, asymmetric velocity dispersion profile (Loubser et al. 2008; Richtler et al. 2011). Unmixed populations of PNe (Ventimiglia et al. 2011). NGC 3309 NGC 3311 Loubser et al. 2008 Ventimiglia et al. 2011

In situ (central galaxy) vs accreted populations (ICL / cd envelope) I VLT MXU spectroscopic study of stellar populations (Barbosa et al. 2016) Radial gradients indicate different populations separated at R Re = 8.4 kpc / µv 22.5 mag arcsec2

Offset structure I Maximum symmetric modeling of V-band imaging indicate excess of light in the NE region (Arnaboldi et al. 2012). I Off-centered structure also observed in X-ray imaging (Hayakawa et al. 2004, 2006). I Next step: kinematics of different structures in the Hydra core!

Results from Barbosa et al. (2017) New results today on arxiv: 1710.08941

New observations of NGC 3311 with MUSE@VLT Observations carried out at 8m telescope UT4 at the VLT, Paranal (Chile). MUSE integral field spectrograph. New observations with MUSE Wide Field Mode (1 arcmin 2 ), 0.2 arcsec / pixel 4650 λ(å) 9300 Data reduced with ESO Reflex pipeline. UT1 telescope at Paranal.

Strategy Observation of four fields fields I-III observe central galaxy + offset halo field IV allocated in the tidal tail of HCC 007 Masking of dwarf galaxies and UCDs from the halo with SExtractor (Bertin and Arnouts 1996) Voronoi binning (Cappellari and Copin 2003) to achieve S/N 70 / bin.

Methods Calculation of LOS Velocity distribution (LOSVD) with ppxf (Cappellari and Emsellem 2004). Fitting of Gaussian-Hermite profile with four moments: V, σ, h 3, h 4 Use of two components: SSPs + emission lines Emission lines re-analyzed individually after subtraction of stellar continuum to improve accuracy

Systemic velocity Velocity offset of 50 km s 1 between the systemic velocity of the central region and the outer halo The central galaxy has a 2D velocity field that does not satisfy point-symmetry. Analysis of velocity field with kinemetry (Krajnović et al. 2006) indicates that the system is not supported by rotation May be classified as slow rotator (SR) according to ATLAS 3D criteria

Velocity dispersion Velocity dispersion increases with the radius, from 180 km s 1 to 400 km s 1 in the outermost data points. Stars in the halo are bound to the cluster s gravitational potential. σ reach the velocity dispersion of the cluster of 647 km s 1 (Struble and Rood 1999).

Skewness (γ 3 ) and kurtosis (γ 4 ) h 3 γ3 4 3 Measures the asymmetry of the LOSVD h 4 γ4 3 8 6 Probe radial (h 4 > 0) and tangencial (h 4 < 0) anisotropies.

Photometry (A) V-band FORS2/VLT imaging from Arnaboldi et al. (2012) (B) galfitm (Vika et al. 2013) modelling of three main galaxies (C) Using non-photometric component to produce mostly positive residuals

Photometry Surface brightness profile at 55 degrees. NGC 3311 is modeled with 4 Sérsic components A-C are almost concentrical D component is offset by 8 kpc Residuals indicate substructures

Finite mixture modeling of kinematics Multiple non-rotating components in the LOS LOSVD is given by superposition weighted by the luminosity Finite mixture modeling of N components, i = 1,.., N, with individual LOSVD L i (v), the expected value is given by E i [g(v)] = + Considering an arbitrary function g(v) for the mean, g(v) = µ i = v for the velocity dispersion, g(v) = σ 2 i In a finite mixture model g(v)l i (v)dv = (v µ)2 E[g(v)] = N i=1 w ie i [g(v)] E[(v µ) m ] = N i=1 m j=0 ( m j ) wi (µ i µ) m j E[(v µ i ) j ] Weights (w i ) in the model are given by the photometric components

Results Parameters for the kinematics of each component in the finite mixture model. Component V (km / s) σ (km / s) h 3 h 4 A+B 3856.7 ± 1.5 152.8 ± 2.6 0.056 ± 0.008 0.076 ± 0.019 C 3836 ± 6 188 ± 7 0.000 ± 0.020 0.010 ± 0.027 D 3978 ± 13 327 ± 9 0.097 ± 0.011 0.036 ± 0.012

Model + results of FMD modeling

Scaling relations Each modeled component follow the values predicted from scaling relations Clear separation of galaxy and cd envelope. Natural explanation for large central h 4 in massive galaxies as a superposition effect of populations.

Radial profiles of kinematic properties Good description of variations of all moments Does not require large anisotropies Allows inference of velocity offset between galaxy and cd halo V 120km s 1. BCG has a velocity bias of 30% in relation to the mean velocity of galaxies: supports Non-relaxed Halo hypothesis

Summary Mapping of the LOSVD of NGC 3311 and its surrounding stellar halo Revisited photometry indicates the existence of an offset component with much larger size which matches the definition of a cd halo. Finite mixture model was developed to describe the LOSVD as a superposition of nearly isothermal spheres. Results indicate good agreement with observations. We obtained an explanation for the observed large h 4 found in massive galaxies (e.g. MASSIVE survey) New tool to aid the analysis of the LOSVD of overlapping systems.