Multi-spin stellar velocity maps of the most massive galaxies

Abstract

(Abridged) We present stellar kinematics of the MUSE Most Massive Galaxies (M3G) Survey, comprising 25 galaxies brighter than -25.7 mag in the Ks-band and stellar mass above ~6x10^11 Msun. Galaxies are divided between the brightest cluster galaxies (BCGs) and lower-ranked (in brightness) galaxies (non-BCGs) in three rich galaxy clusters within the core of the Shapley super cluster. We find several velocity maps with rich kinematic structure, including multiple spin reversals within the region encompassing central two effective radii, typically associated with BCGs. The majority of BCGs show rotation around the major-axis, at least in one of the visible velocity components. These kinematic structures are possible only if galaxies have non-axisymmetric shapes and contain several orbital families with both prograde and retrograde rotations. There are six fast rotators in the M3G sample, all among non-BCGs, and typically ranked below the 3rd brightest galaxy. Based on the properties of the h3 Gauss-Hermite moment, fast rotation can be linked to the dominance of prograde rotating short-axis tubes in the orbital distribution. Slow rotators are BCGs or the second and sometimes third brightest galaxies, indicating that the galaxy mass (brightness) is not the only driver of low spin, but that the location within the local environment also plays a role. Slow rotators, as evidenced from their multi-spin velocity maps, require more complex orbital structures. Furthermore, some BCGs show kinematic evidence for a secondary component at larger radii, likely not in equilibrium with the main galaxy and possibly made of stars accreted from other cluster galaxies. Multi-spin velocity maps, low angular momentum and additional kinematic components highlight the difference in the evolutionary histories of BCGs (including 2nd ranked galaxies) and non-BCGs.

Figures (16)

• Figure 1: Left top: A histogram of the distances to the BCGs (orange) and the satellites galaxies (blue). Left bottom: Richness of the host galaxy cluster vs the absolute $K_{s}$ magnitude of the corresponding BCG. BCGs in the Shapley Super Cluster are shown as pentagrams (Abell 3558, Abell 3556 and Abell 3562 in order of decreasing brightness of the BCGs). Virgo and Coma cluster (squares) are added as references for the ATLAS$^{\rm 3D}$ and the MASSIVE Surveys. Right: The size -- luminosity relation for the M3G sample galaxies, split in BCGs (red) and satellites (blue). Galaxies from two other surveys are added for comparison: ETGs from the ATLAS$^{\rm 3D}$ Survey (light green large squares), spirals from the ATLAS$^{\rm 3D}$ Survey parent sample (dark green small squares), and ETGs from the MASSIVE survey (brown triangles). ATLAS$^{\rm 3D}$ sample is a magnitude-limited sample within 42 Mpc, while the galaxies in the MASSIVE are the brightest galaxies within 100 Mpc. The solid and dashed black lines are relations for fast rotators and S0-Sa galaxies from the ATLAS$^{\rm 3D}$ survey, respectively. The red line denotes the so-called 'zone of avoidance'. All three relations are taken from 2011MNRAS.413..813C.
• Figure 2: Distribution of the VLT auto-guider seeing measurements, averaged over each exposure taken with MUSE for all M3G galaxies. Horizontal lines denote the two seeing limits imposed on the programme. Blue squares show the mean value of all observations for each galaxy. Red circles are exposures which were targeted to be done in "good seeing" conditions (FWHM<0.8$^{\prime\prime}$).
• Figure 3: Spectral fits using pPXF for three different spectra from the PGC 099188* MUSE field, which features a large interloping satellite. Panels from top to bottom show: the central spectrum of PGC 099188*, a spectrum from the midpoint between the centre of PGC 099188* and the interloping satellite, and the central spectrum of the interloping satellite. In each panel the black line shows the observed spectrum, the red line the pPXF fit, with the residual of the fit in green points at the bottom. Green shaded polygons are masked regions excluded from the fit. The middle panel has two additional spectra shown by light and dark blue colours, belonging to the main galaxy and the satellite, respectively. These are model spectra vertically shifted for an arbitrary amount, obtained from the pPXF fits highlighting the satellite and the galaxy contributions to the total spectrum.
• Figure 4: The radial profiles of the absolute $k_0$ variation for M3G galaxies ($\delta k_0 = |k_0(0) - k_0(R)|$), compared to the same from the ATLAS$^{\rm 3D}$ galaxies. M3G galaxies are divided in BCGs (red lines) and non-BCGs (blue lines), while ATLAS$^{\rm 3D}$ galaxies are divided into fast (light blue dashed lines) and slow (light red dashed lines) rotators, respectively. Purple shaded regions show the standard deviation of all ATLAS$^{\rm 3D}$ and M3G (darker shaded regions) velocity errors. Names highlight specific galaxies with the largest difference between the maximum and the minimum values of $k_0$: $\Delta k_0>20$ km/s.
• Figure 5: An example of a multi-spin galaxy: PGC 046832, which has five visible changes of the rotational orientation. Left: kinematic positions angle as a function of radius (1 kpc $\sim$ 1), with the photometric major axis shown in dashed black line and median position angles of five components highlighted with short orange lines. Middle: observed velocity map. Right: reconstructed velocity map using low-order kinemetry coefficients, highlighting only the rotational component of the velocity map. Red solid and dashed lines are the project major and minor axes of the galaxy, respectively. Along the major axis in projection, there are three reversals of the short-axis rotation (prograde, retrograde, prograde), while along the minor axis in projection, there are two (prograde and retrograde), making this galaxy a case of five multi-spin components.