A MUSE view of cD galaxy NGC 3311
C. E. Barbosa1, M. Arnaboldi2, L. Coccato2, O. Gerhard3, C. Mendes de Oliveira1, M. Hilker2, T. Richtler4
1Universidade de S˜aoPaulo, S˜aoPaulo, Brazil 2European Southern Observatory, Garching, Germany 3Max-Planck-Institut fur Extraterrestrische Physik, Garching, Germany 4Universidad Concepci´on,Concepci´on,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
I 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
I SB profiles of cD galaxies deviate from the R1/4 law (de Vaucouleurs 1953)
I Envelopes have shallow surface brightness profiles
: NGC 3311 at the Hydra I cluster Figure from Sarazin (1986). Formation of cD galaxies
I Massive, passive evolving galaxies are identified at z ∼ 2.5 (Cimatti et al. 2004).
I ”Red nuggets” population are believed to be precursor of the nearby early-type galaxies (van Dokkum et al. 2009; Cassata et al. 2010)
I Among different models, the two-phase formation scenario (Oser et al. 2010) is among the most promising to explain the formation of galaxies. I Central region is formed in a fast dissipative process early (z & 3) I Stellar halo is accreted at later epochs stochastically I This model is able to explain the growth of massive galaxies since z = 2 (van Dokkum et al. 2010)
I Can we identify the in situ and accreted populations? . I Rising, asymmetric velocity dispersion profile (Loubser et al. 2008; Richtler et al. 2011). I Unmixed populations of PNe (Ventimiglia et al. 2011).
The case of NGC 3311
I Central galaxy of the cluster Abell 1060 (Hydra cluster) I D ≈ 50 Mpc.
NGC 3309 NGC 3311 I Unmixed populations of PNe (Ventimiglia et al. 2011).
The case of NGC 3311
I Central galaxy of the cluster Abell 1060 (Hydra cluster) I D ≈ 50 Mpc. I 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
I Central galaxy of the cluster Abell 1060 (Hydra cluster) I D ≈ 50 Mpc. I Rising, asymmetric velocity dispersion profile (Loubser et al. 2008; Richtler et al. 2011). I 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 Radial gradients indicate different populations separated at R ∼ R = 8.4 kpc / VLT MXU spectroscopic study of stellar populations (Barbosa et al. e µ ∼ 22.5 mag arcsec2 2016) V 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)
I 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.
I New observations with MUSE I Wide Field Mode (1 arcmin2), 0.2 arcsec / pixel I 4650 & λ(A˚) & 9300 I Data reduced with ESO Reflex pipeline.
UT1 telescope at Paranal. Strategy
I Masking of dwarf galaxies and UCDs I Observation of four fields from the halo with SExtractor (Bertin and Arnouts 1996) I fields I-III observe central galaxy + offset halo I Voronoi binning (Cappellari and I field IV allocated in the tidal Copin 2003) to achieve S/N≈ 70 / tail of HCC 007 bin. Methods
I Calculation of LOS Velocity distribution (LOSVD) with pPXF (Cappellari and Emsellem 2004).
I Fitting of Gaussian-Hermite profile with four moments: V , σ, h3, h4 I Use of two components: SSPs + emission lines
I Emission lines re-analyzed individually after subtraction of stellar continuum to improve accuracy Systemic velocity
−1 I Velocity offset of ∼50 km s between the systemic velocity of the central region and the outer halo
I The central galaxy has a 2D velocity field that does not satisfy point-symmetry.
I Analysis of velocity field with kinemetry (Krajnovi´cet al. 2006) indicates that the system is not supported by rotation
I May be classified as slow rotator (SR) according to ATLAS3D criteria Velocity dispersion
I Velocity dispersion increases with the radius, from ∼180 km s−1 to ∼400 km s−1 in the outermost data points.
I Stars in the halo are bound to the cluster’s gravitational potential. I σ reach the velocity dispersion of the cluster of 647 km s−1 (Struble and Rood 1999). Skewness (γ3) and kurtosis (γ4)
γ3 I h3 ≈ √ h ≈ γ4√−3 4 3 I 4 8 6 I Measures the asymmetry of the I Probe radial (h4 > 0) and LOSVD tangencial (h4 < 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. I NGC 3311 is modeled with 4 S´ersiccomponents I A-C are almost concentrical I Residuals indicate substructures I D component is offset by 8 kpc Finite mixture modeling of kinematics
I Multiple non-rotating components in the LOS
I LOSVD is given by superposition weighted by the luminosity
I Finite mixture modeling of N components, i = 1, .., N, with individual LOSVD Li(v), the expected value is given by
Z +∞ Ei[g(v)] = g(v)Li(v)dv −∞
I Considering an arbitrary function g(v)
I for the mean, g(v) = µi = v 2 2 I for the velocity dispersion, g(v) = σi = (v − µ)
I In a finite mixture model PN I E[g(v)] = i=1 wiEi[g(v)] m PN Pm m m−j j I E[(v − µ) ] = i=1 j=0 j wi(µi − µ) E[(v − µi) ]
I Weights (wi) in the model are given by the photometric components Results
I Parameters for the kinematics of each component in the finite mixture model.
Component V (km / s) σ (km / s) h3 h4 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
I Each modeled component follow the values predicted from scaling relations
I Clear separation of galaxy and cD envelope.
I Natural explanation for large central h4 in massive galaxies as a superposition effect of populations. Radial profiles of kinematic properties
I Good description of variations of all moments
I Does not require large anisotropies
I Allows inference of velocity offset between galaxy and cD halo ∆V ∼ 120km s−1.
I BCG has a velocity bias of 30% in relation to the mean velocity of galaxies: supports “Non-relaxed Halo” hypothesis Summary
I Mapping of the LOSVD of NGC 3311 and its surrounding stellar halo
I Revisited photometry indicates the existence of an offset component with much larger size which matches the definition of a cD halo.
I Finite mixture model was developed to describe the LOSVD as a superposition of nearly isothermal spheres.
I Results indicate good agreement with observations.
I We obtained an explanation for the observed large h4 found in massive galaxies (e.g. MASSIVE survey) I New tool to aid the analysis of the LOSVD of overlapping systems.