\citet{JIMMY13} measured the stellar kinematics and photometry of the galaxies in our sample, we summarise their method and results in this section.
First a signal-to-noise ratio (SNR) cut of 5 across all the spaxels (spatial pixels) was applied. The spaxels were then re-binned to a minimum SNR of 10, using the spatial binning Voronoi code of \citet{CAPPELLARI03}. The velocity and line-of-sight velocity dispersion were computed using the penalised fitting scheme of \citet[pPXF;][]{PPXF}, and the MILES \citep[Medium-resolution Isaac Newton Telescope Library of Empirical Spectra; ][]{MILES} library stellar templates. pPXF fits the stellar library templates to the absorption line features of the BCG spectra, giving the redshifts and the broadening of the spectral lines.
The angular momentum was characterised by the \(\lambda_{\rm R}\) parameter defined by \citet{EMSELLEM07}. It is calculated as follows:
\[\lambda_{\rm R} \sim \frac{\langle R |V| \rangle}{\langle R\sqrt{V^2+\sigma^2 \rangle}},\]
where \(R\) represents the radius of the galaxy, V is the stellar velocity and \(\sigma\) the velocity dispersion. The numerator and denominator are luminosity weighted. A higher \(\lambda_{\rm R}\) represents a higher angular momentum. The ellipticity (\(\epsilon\)) at the effective radius of each galaxy was measured using the publicly available IDL routine \(find\_galaxy.pro\) developed by Michele Cappellari1. Following \citet{EMSELLEM11}, the values of \(\lambda_{\rm R}\) and \(\epsilon\) can be used to distinguish fast and slow rotators (FR and SR respectively) by using the threshold:
\[\lambda_{\rm R} \geq (0.31 \pm 0.01)\times \sqrt{\epsilon},\]
where FRs lie above this threshold and SRs lie below.
The dynamical mass was measured using the standard equation given in \citet{CAPPELLARI06}.
\[M_{dyn}=\frac{5R_e \sigma_e^2}{G},\]
where \(\sigma_e\) is the aperture corrected velocity dispersion of the integrated spectrum within the effective radius; G is the gravitational constant. In Table \ref{tab:kin} we summarise the relevant kinematic results. 7 of the BCGs are SR and 2 are FR. For \(\sigma_{e}, \epsilon_e\) and \(\lambda_{R_e}\) we refer the reader to Table 2 of \citet{JIMMY13}.
\citet{JIMMY13} analysed the photometry of this sample using images from SDSS Data Release 3. They measured the effective radius by fitting a 2D de Vaucouleurs profile. They also analysed the presence of recent mergers using the Gini, and M\(_{\rm 20}\) coefficients \citep{LOTZ08}. This method studies the distribution of light looking for irregularities that could indicate morphological signatures of mergers. A galaxy is a merger candidate if it crosses the threshold: \[G \geq -0.14M_{20} + 0.33\] Where M\(_{\rm 20}\) is the 2nd order moment of the brightest 20 per cent of pixels, and G is the Gini coefficient. In the case of gas-poor galaxies like our sample, a galaxy will be above the threshold if it is currently merging or has merged in the last 0.2 Gyr \citep{LOTZ11}. 4 of the BCGs in the sample are merging. The relevant kinematic and photometric results of \citet{JIMMY13} are presented in Table \ref{tab:kin}.
Kinematic properties of BCGs and their companions from \citet{JIMMY13}. Seven of the BCGs are slow rotating (SR) and two are fast rotating (FR). Four of the BCGs show photometric signs of merging.
| \label{tab:kin} Galaxy | \(z\) | log M\(_{\rm dyn}\) M\(_{\odot}\) | R\(_e\)(arcsec) | Merging | SR/FR |
| \(\pm0.01\) | \(\pm 0.01\) | \(G-M_{20}\) | |||
| BCGs | |||||
| 1027A | 0.090 | 11.79 | 6.98 | y | SR |
| 1042 | 0.094 | 11.83 | 7.22 | n | SR |
| 1050 | 0.072 | 11.78 | 8.43 | n | SR |
| 1066 | 0.083 | 11.62 | 5.07 | y | SR |
| 2001 | 0.041 | 11.38 | 5.84 | n | SR |
| 2039 | 0.082 | 11.86 | 8.82 | n | SR |
| 2086 | 0.083 | 11.60 | 4.83 | y | SR |
| 1048A | 0.077 | 11.59 | 5.17 | y | FR |
| 1261 | 0.037 | 11.32 | 5.76 | n | FR |
| Comp | |||||
| 1027B | 0.090 | 11.17 | 4.39 | y | FR |
| 1048B | 0.080 | 10.51 | 1.08 | y | FR |
| 1048C | 0.074 | 10.54 | 1.24 | y | FR |
\label{sec:sauron} Throughout the paper we compare our observations to those of early-type galaxies of similar mass observed by ATLAS\(^{3D}\) (which includes the SAURON galaxy sample). The ATLAS\(^{3D}\) sample is composed of 260 field and cluster early-type galaxies and it only contains one BCG, M87. The spatially-resolved stellar populations (central values and gradients) of the SAURON sample were presented in \citet{KUNTSCHNER10}. The central stellar populations of the ATLAS\(^{3D}\) sample were presented in \citet{ATLAS3D}. We therefore compare our central stellar populations with the whole ATLAS\(^{3D}\) sample and the stellar population gradients only with the SAURON sample.
\citet{KUNTSCHNER10} and \citet{ATLAS3D} use the stellar models of \citet{SCHIAVON07} in the Lick/IDS system \citep{WORTHEY97} to measure the stellar population parameters of age, total metallicity [Z/H] and abundance of alpha elements [\(\alpha\)/Fe]. For our spectral fitting, we use models with only solar abundances, i.e. \([\alpha\)/Fe\(]=0\). In this case [Fe/H] is effectively a measure of the total metallicity2. Therefore, we directly compare the ATLAS\(^{3D}\) total metallicities to our measured metallicities throughout the paper. The central stellar populations in the ATLAS\(^{3D}\) sample correspond to an aperture of 0.125 R\(_e\).
We compare the median, and standard deviation for the two samples in the same mass range (M\(_{dyn}>10^{11.3}\)M\(_{\odot}\)). In order to compare our BCGs with a non-BCG early-type galaxy sample, we do not include the BCG M87. This gives a comparison sample of 20 massive early-type galaxies from the ATLAS\(^{3D}\) sample. We highlight M87 as a blue-filled circle in the figures.