The parallelism between galaxy clusters and early-type galaxies

Abstract

Context. This is the second work dedicated to the observed parallelism between galaxy clusters (GCs) and early-type galaxies (ETGs). The focus is on the distribution of these systems in the scaling relations (SRs) observed when effective radii, effective surface brightness, total luminosities, and velocity dispersions are mutually correlated. Aims. Using the data of the Illustris simulation we speculate on the origin of the observed SRs. Methods. We compare the observational SRs extracted from the database of the WIde-field Nearby Galaxy-cluster Survey with the relevant parameters coming from the Illustris simulations. Then we use the simulated data at different redshift to infer the evolution of the SRs. Results. The comparison demonstrate that GCs at z ∼ 0 follow the same log(L)−​log(σ) relation of ETGs and that both in the log(⟨I⟩e)−​log(Re) and log(Re)−​log(M*) planes the distribution of GCs is along the sequence defined by the brightest and massive early-type galaxies (BCGs). The Illustris simulation reproduces the tails of the massive galaxies visible both in the log(⟨I⟩e)−​log(Re) and log(Re)−​log(M*) planes, but fails to give the correct estimate of the effective radii of the dwarf galaxies that appear too large and those of GCs that are too small. The evolution of the SRs up to z = 4 permits to reveal the complex evolutionary paths of galaxies in the SRs and indicate that the line marking the zone of exclusion, visible in the log(⟨I⟩e)−​log(Re) and the log(Re)−​log(M*) planes, is the trend followed by virialized and passively evolving systems. Conclusions. We speculate that the observed SRs originate from the intersection of the virial theorem and a relation L = L0′σβ where the luminosities depend on the star formation history.

Compact Groups of Galaxies in Sloan Digital Sky Survey and LAMOST Spectral Survey. I. The Catalogs

“…This result indicates that the compactness (size) of groups might play an important role in describing the dynamics of groups of galaxies. Indeed, the galaxy groups are known to be distributed on a fundamental plane (FP) in the logarithm space of L − σ − R parameters (e.g., Adami et al 1998;Fritsch & Buchert 1999;Díaz & Muriel 2005;D'Onofrio et al 2020). We will make a more detailed discussion on FP of isolated groups in Section 3.2.…”

Tomography of the Ie-Re and L-Sigma Planes

“…The distribution of galaxies appears limited in the maximum surface intensity at each R e . The slope of this line of avoidance is close to −1 (when I e is L pc −2 units), i.e., the slope predicted by the Virial Theorem (VT) [5]. The existence of the ZoE was first noted by [28,29] using the k-space version of the FP.…”

“…More details on the WINGS data and the procedures we have followed to select the sample in use can be found in the aforementioned studies and in [5,50,51] to which the reader should refer.…”

“…It is often claimed that Illustris models are in conflict with real data on velocity dispersions, radii or masses. However, the careful comparison of the Illustris models with the data by [29] and those of WINGS made by [5,56] shows that they nicely reproduce the tail of the I e − R e plane, the tail of the R e − M s relation of ETGs and also the location of dwarf galaxies (masses in the interval 10 8 to 10 10 M ) on the R e − M s plane [56]. The relative larger radii of these latter galaxies can be easily explained as an indirect effect of recent mergers and galactic winds (see [56] for more details).…”

“…The 'bright' family is mono-parametric (I e depends only on R e ), as it hosts only the brightest cluster galaxies (BCGs), and their members have radii larger than R e = 3 kpc. The spiral galaxies and their bulges belong to the 'ordinary' family and are not visible in the 'bright' sequence (see [4,5]).…”