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Register a new userThe Fundamental Plane of Galaxy Group Mergers
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We present a series of hundreds of collisionless simulations of galaxy group mergers. These simulations are designed to test whether the properties of elliptical galaxies - including the key fundamental plane scaling relation, morphology and kinematics - can be simultaneously reproduced by dry multiple mergers in galaxy groups. Preliminary results indicate that galaxy group mergers can produce elliptical remnants lying on a tilted fundamental plane, even without a central dissipational component from a starburst. This suggests that multiple mergers in groups are an alternate avenue for the formation of elliptical galaxies which could well dominate for luminous ellipticals.
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We determine the near-infrared Fundamental Plane (FP) for $sim10^4$ early-type galaxies in the 6dF Galaxy Survey (6dFGS). We fit the distribution of central velocity dispersion, near-infrared surface brightness and half-light radius with a three-dimensional Gaussian model using a maximum likelihood method. For the 6dFGS $J$ band sample we find a FP with $R_{e}$,$propto$,$sigma_0^{1.52pm0.03}I_{e}^{-0.89pm0.01}$, similar to previous near-IR determinations and consistent with the $H$ and $K$ band Fundamental Planes once allowance is made for differences in mean colour. The overall scatter in $R_e$ about the FP is $sigma_r$,=,29%, and is the quadrature sum of an 18% scatter due to observational errors and a 23% intrinsic scatter. Because of the distribution of galaxies in FP space, $sigma_r$ is not the distance error, which we find to be $sigma_d$,=,23%. Using group richness and local density as measures of environment, and morphologies based on visual classifications, we find that the FP slopes do not vary with environment or morphology. However, for fixed velocity dispersion and surface brightness, field galaxies are on average 5% larger than galaxies in higher-density environments, and the bulges of early-type spirals are on average 10% larger than ellipticals and lenticulars. The residuals about the FP show significant trends with environment, morphology and stellar population. The strongest trend is with age, and we speculate that age is the most important systematic source of offsets from the FP, and may drive the other trends through its correlations with environment, morphology and metallicity.
Diffuse radio emission in galaxy clusters is known to be related to cluster mass and cluster dynamical state. We collect the observed fluxes of radio halos, relics, and mini-halos for a sample of galaxy clusters from the literature, and calculate their radio powers. We then obtain the values of cluster mass or mass proxies from previous observations, and also obtain the various dynamical parameters of these galaxy clusters from optical and X-ray data. The radio powers of relics, halos, and mini-halos are correlated with the cluster masses or mass proxies, as found by previous authors, with the correlations concerning giant radio halos being, in general, the strongest ones. We found that the inclusion of dynamical parameters as the third dimension can significantly reduce the data scatter for the scaling relations, especially for radio halos. We therefore conclude that the substructures in X-ray images of galaxy clusters and the irregular distributions of optical brightness of member galaxies can be used to quantitatively characterize the shock waves and turbulence in the intracluster medium responsible for re-accelerating particles to generate the observed diffuse radio emission. The power of radio halos and relics is correlated with cluster mass proxies and dynamical parameters in the form of a fundamental plane.
We carry out a systematic study of the recently discovered fundamental plane of galaxy clusters (CFP) using a sample of ~250 simulated clusters from the 300th project, focusing on the stability of the plane against different temperature definitions and its dependence on the dynamical relaxation state of clusters. The CFP is characterised in the form of $T propto M_s^alpha r_s^beta$, defined with the gas temperature ($T$) and the characteristic halo scale radius and mass ($r_s$ and $M_s$) assuming an NFW halo description. We explore two definitions of weighted temperatures, namely mass-weighted and spectroscopic-like temperatures, in three radial ranges: [0.1, 1.0]$r_{200}$, [0.15,1.0]$r_{500}$, and [50,500]$h^{-1}$ kpc. We find that 300th clusters at $z=0$ lie on a thin plane whose parameters ($alpha, beta$) and dispersion (0.015--0.030 dex) depend on the gas temperature definition. The CFP for mass-weighted temperatures is closer to the virial equilibrium expectation ($alpha=1, beta=-1$) with a smaller dispersion. When gas temperatures are measured inside 500$h^{-1}$ kpc, which is close to the median value of $r_s$, the resulting CFP deviates the most from the virial expectation and shifts towards the similarity solution for a secondary infall model ($alpha=1.5, beta=-2$). Independently of the temperature definition, we find that clusters at $z=1$ form a CFP similar to the virial expectation. At all epochs, the CFP remains well defined throughout the evolution of the cluster population. The CFP of relaxed clusters is always close to the virial expectation, with a milder evolution than for the unrelaxed case. We find that only systems formed over the last 4 Gyr have a CFP that is closer to the self-similar solution. All these findings are compatible with the CFP obtained for a CLASH subsample excluding the hottest clusters with $T_X>12$ keV.
By exploiting the database of early-type galaxies (ETGs) members of the WINGS survey of nearby clusters, we address here the long debated question of the origin and shape of the Fundamental Plane (FP). Our data suggest that different physical mechanisms concur in shaping and tilting the FP with respect to the virial plane (VP) expectation. In particular, an hybrid solution in which the structure of galaxies and their stellar population are the main contributors to the FP tilt seems to be favoured. We find that the bulk of the tilt should be attributed to structural non-homology, while stellar population effects play an important but less crucial role. Our data indicate that the differential FP tilt between the V and K-band is due to a sort of entanglement between structural and stellar population effects, for which the inward steepening of color profiles (V-K) tends to increase at increasing the stellar mass of ETGs. The same analysis applied to the ATLAS3D and SDSS data in common with WINGS (WSDSS throughout the paper) confirms our results, the only remarkable difference being the less important role of the stellar mass-to-light-ratio in determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as well on the dark matter (DM) fraction and on the rotational contribution to the kinetic energy (Vrot/sigma). We show that the global properties of the FP can be understood in terms of the underlying correlation among mass, structure and stellar population of ETGs, for which, at increasing the stellar mass, ETGs become (on average) older and more centrally concentrated. Finally, we show that a Malmquist-like selection effect may mimic a differential evolution of the mass-to-light ratio for galaxies of different masses. This should be taken into account in the studies investigating the amount of the so called downsizing phenomenon.
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