Novel insights on the Coma Cluster kinematics with DESI. I. Linking mass profile, orbital anisotropy and galaxy populations

Abstract

We investigate the kinematic properties of the Coma galaxy cluster using a new, large spectroscopic sample of member galaxies, from the Dark Energy Spectroscopic Instrument (DESI). By means of the MG-MAMPOSSt code, based on the Jeans equation, we jointly reconstruct the total cluster mass profile and the velocity anisotropy profile. Assuming a Navarro-Frenk-White model, we estimate a virial mass $M_{200}=1.08_{-0.09}^{+0.08}~({\rm stat})\pm 0.09~({\rm syst})\times 10^{15}\,\mathrm{M}_\odot $, corresponding to $r_{200}=2.12 \pm 0.06\,\mathrm{Mpc}$ and a scale radius for the mass profile $r_{\rm s}=0.48^{+0.27}_{-0.13}\,\mathrm{Mpc}$, which provides the tightest robust kinematic mass profile constraint to date. By considering separately the mass of the hot gas and the galaxy stellar mass, we determine the dark matter mass profile, with $M_{200}^{\rm DM}=8.6^{+1.2}_{-0.8}\times 10^{14}\,\text{M}_\odot$. We discuss the impact of the mass and number density parametrisations, the effect of different choices of the cluster's rest frame and of the radial range of the kinematic analysis, further comparing our results with previous estimates from the literature. The cluster dynamical state has also been assessed, using the spatial and line-of-sight velocity distributions of the members. We perform a kinematic study of different subsamples of galaxy populations, based on their colour (red sequence, green valley, and blue cloud), focusing on the anisotropy profiles and line-of-sight velocity distributions. The orbits of green valley and blue cloud galaxies appear to be more radial in the centre and in the outskirts, respectively, with the latter predicting a higher cluster virial mass. This study provides new insights on the interplay between dynamical and intrinsic properties of galaxies in massive structures, fundamental to verify the tight connection between galaxy evolution and environment.

Figures (14)

• Figure 1: Projected positions of galaxies in the Coma Cluster. The point marked with a black star indicates the cluster centre, whose coordinates (RA=194.90 deg, DEC=27.96 deg) have been taken from Malavasi20 as the position of NGC 4874, while the grey circle encloses the region within $r_{200} = 2.19 \, \mathrm{Mpc}$, quoted in Boselli_2006.
• Figure 2: Projected phase-space distribution of member galaxies in the Coma Cluster (grey dots) and interlopers removed by Clean (grey crosses). The black dashed line indicates the average velocity of the cluster (Hubble + bulk motion), while coloured curves highlight iso-density contours (dashed and solid lines correspond to 90th and 97th percentiles, respectively) for RS (red), GV (green) and BC (blue) galaxies. The projected distance from the centre is normalized to $r_{200}$, taken equal to the value quoted in Boselli_2006, $2.19 \, \mathrm{Mpc}$
• Figure 3: $(m_g-m_r)$ vs stellar mass diagram. The colour of the markers highlights the three colour classes: blue cloud (BC) in blue, red sequence (RS) in red and green valley (GV) in green. The solid line represents the best fit for RS galaxies, the dashed and dotted lines indicate the $2\,\sigma$ and $5\,\sigma$ limit, respectively.
• Figure 4: Projected surface density profile of the Coma Cluster fitted with NFW (solid line) and Hernquist (dashed line) models. The error bars correspond to the Poisson uncertainties.
• Figure 5: LoS velocity distributions of RS (upper panel), GV (middle panel) and BC (lower panel) galaxies. The vertical dashed line indicates the average velocity of the cluster.