Morphometric analysis of brightest cluster galaxies

ABSTRACT We study the build-up of the stellar mass of brightest cluster galaxies (BCGs) at z < 0.1 as a function of their morphological type. Morphometric parameters for 1216 BCGs were obtained from the SDSS DR12 r-band images with the code morfometryka. We show that the morphometric parameters are efficient to separate BCGs into cD galaxies, conventional ellipticals, disc-dominated BCGs, and merging objects. We propose a simple classification scheme using two concentration indices, C1 and C2, and the spirality σψ. We then investigate how the stellar masses of BCGs and the velocity dispersions of their parent haloes relate to their morphological properties. We find that BCGs with larger envelope contributions are more massive than BCGs in other classes and more common in massive clusters. The stellar mass and the halo velocity dispersion correlate for all classes, suggesting that environmental effects are important for BCGs of any morphology. At fixed parent halo mass, we detect a continuous mass excess up to $\sim 60{{\ \rm per\ cent}}$ from pure E galaxies to extreme cD galaxies, while the inner regions of such cDs present only $\sim 40{{\ \rm per\ cent}}$ of the mass of an E galaxy. We interpret our findings in a scenario where different BCGs have developed their mass through an asymmetric combination of distinct processes, so that present-time cD galaxies have grown in mass mainly through minor merging and tidal stripping from satellite galaxies, while elliptical BCGs evolve mainly through processes like major merging.

Implications of the mild gas motion found with Hitomi in the core of the Perseus cluster

Based mainly on X-ray observations, we study the interactions between the intracluster medium (ICM) in clusters of galaxies and their member galaxies. Through (magneto)hydrodynamic and gravitational channels, moving galaxies are expected to drag the ICM around them, and then transfer some fraction of their dynamical energies on cosmological timescales to the ICM. This hypothesis is in line with several observations, including the possible cosmological infall of galaxies toward the cluster center, found over redshifts of z ∼ 1 to z ∼ 0. Further assuming that the energy lost by these galaxies is first converted into ICM turbulence and then dissipated, this picture can explain the subsonic and uniform ICM turbulence, measured with Hitomi in the core region of the Perseus cluster. The scenario may also explain several other unanswered problems regarding clusters of galaxies, such as what prevents the ICM from underoing the expected radiative cooling, how the various mass components in nearby clusters have attained different radial distributions, and how a thermal stability is realized between hot and cool ICM components that co-exist around cD galaxies. This view is also considered to pertain to the general scenario of galaxy evolution, including their environmental effects.

Observational Data Related to the Largest Galaxies of the Universe: What they Tell?

The physical mechanism of interaction between dark energy and ordinary baryonic matter is used to show that Ambartsumian's cosmogonic paradigm on the galaxy formation gets new support. This mechanism is considered to compare the cD galaxies observational properties with the model predictions in the framework of the suggested paradigm.

Characteristics of transonic spherical symmetric accretion flow in Schwarzschild-de Sitter and Schwarzschild anti-de Sitter backgrounds, in pseudo-general relativistic paradigm

In this paper, we present a complete work on steady state spherically symmetric Bondi type accretion flow in the presence of cosmological constant (Λ) in both Schwarzschild-de Sitter (SDS) and Schwarzschild anti-de Sitter (SADS) backgrounds considering an isolated supermassive black hole (SMBH), with the inclusion of a simple radiative transfer scheme, in the pseudo-general relativistic paradigm. We do an extensive analysis on the transonic behavior of the Bondi type accretion flow onto the cosmological BHs including a complete analysis of the global parameter space and the stability of flow, and do a complete study of the global family of solutions for a generic polytropic flow. Bondi type accretion flow in SADS background renders multiplicity in its transonic behavior with inner "saddle" type and outer "center" type sonic points, with the transonic solutions forming closed loops or contours. There is always a limiting value for ∣Λ∣ up to which we obtain valid stationary transonic solutions, which correspond to both SDS and SADS geometries; this limiting value moderately increases with the increasing radiative efficiency of the flow, especially correspond to Bondi type accretion flow in SADS background. Repulsive Λ suppresses the Bondi accretion rate by an order of magnitude for relativistic Bondi type accretion flow for a certain range in temperature, and with a marginal increase in the Bondi accretion rate if the corresponding accretion flow occurs in SADS background. However, for a strongly radiative Bondi type accretion flow with high mass accretion rate, the presence of cosmological constant do not much influence the corresponding Bondi accretion rate of the flow. Our analysis show that the relic cosmological constant has a substantial effect on Bondi type accretion flow onto isolated SMBHs and their transonic solutions beyond length-scale of kiloparsecs, especially if the Bondi type accretion occurs onto the host supergiant ellipticals or central dominant (CD) galaxies directly from ambient intercluster medium (ICM). However, for high mass accretion rate, the influence of cosmological constant on Bondi accretion dynamics, generically, diminishes. As active galactic nuclei (AGN)/ICM feedback can be advertently linked to Bondi type spherical accretion, any proper modeling of AGN feedback or megaparsecs-scale jet dynamics or accretion flow from ICM onto the central regions of host galaxies should take into account the relevant information of repulsive Λ, especially in context to supergiant elliptical galaxies or CD galaxies present in rich galaxy clusters. This could also explore the feasibility to limit the value of Λ, from the kinematics in local galactic-scales.

Photometric and spectroscopic study of cD galaxies

We have carried out photometry and spectroscopy on a sample of 10 cD galaxies. The photometry shows, in general, fairly flat and red profile colours, implying an envelope with the same stellar population as the central galaxy. This may indicate a possible primordial origin for both structures, consistent with ideas of downsizing. Preliminary spectroscopic results are generally in agreement with the photometry, with for example younger populations at large radii for A2199, but A2589 has only younger populations.