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Register a new userThe Fundamental Plane of Radio Galaxies
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D. Bettoni
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We collected photometrical and dynamical data for 73 low red-shift (z<0.2) Radio Galaxies (LzRG) in order to study their Fundamental Plane (FP). For 22 sources we also present new velocity dispersion data, that complement the photometric data given in our previous study of LzRG (Govoni et al. 2000a). It is found that the FP of LzRG is similar to the one defined by non-active elliptical galaxies, with LzRG representing the brightest end of the population of early type galaxies. Since the FP mainly reflects the virial equilibrium condition, our result implies that the global properties of early--type galaxies (defining the FP) are not influenced by the presence of gas accretion in the central black hole. This is fully in agreement with the recent results in black hole demography, showing that virtually all luminous spheroidal galaxies host a massive black hole and therefore may potentially become active. We confirm and extend to giant ellipticals the systematic increase of the mass-to-light ratio with galaxy luminosity.
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The photometric, structural and kinematical properties of the centers of elliptical galaxies, harbor important information of the formation history of the galaxies. In the case of non active elliptical galaxies these properties are linked in a way that surface brightness, break radius and velocity dispersion of the core lie on a fundamental plane similar to that found for their global properties. We construct the Core Fundamental Plane (CFP) for a sizeable sample of low redshift radio galaxies and compare it with that of non radio ellipticals. To pursue this aim we combine data obtained from high resolution HST images with medium resolution optical spectroscopy to derive the photometric and kinematic properties of ~40 low redshift radio galaxies. We find that the CFPs of radio galaxies is indistinguishable from that defined by non radio elliptical galaxies of similar luminosity. The characteristics of the CFP of radio galaxies are also consistent (same slope) with those of the Fundamental Plane (FP) derived from the global properties of radio (and non radio) elliptical galaxies. The similarity of CFP and FP for radio and non radio ellipticals suggests that the active phase of these galaxies has minimal effects for the structure of the galaxies.
High magnetic fields are a distinguishing feature of neutron stars and the existence of sources (the soft gamma repeaters and the anomalous X-ray pulsars) hosting an ultra-magnetized neutron star (or magnetar) has been recognized in the past few decades. Magnetars are believed to be powered by magnetic energy and not by rotation, as with normal radio pulsars. Until recently, the radio quietness and magnetic fields typically above the quantum critical value (Bq~4.4x10^{13} G), were among the characterizing properties of magnetars. The recent discovery of radio pulsed emission from a few of them, and of a low dipolar magnetic field soft gamma repeater, weakened further the idea of a clean separation between normal pulsars and magnetars. In this Letter we show that radio emission from magnetars might be powered by rotational energy, similarly to what occurs in normal radio pulsars. The peculiar characteristics of magnetars radio emission should be traced in the complex magnetic geometry of these sources. Furthermore, we propose that magnetar radio activity or inactivity can be predicted from the knowledge of the stars rotational period, its time derivative and the quiescent X-ray luminosity.
We have used the ESO Nearby Abell Cluster Survey (ENACS) in combination with the Cosmos Galaxy Catalogue, to investigate the existence of a Fundamental Plane (FP) for rich clusters of galaxies. The 20 clusters with the most regular projected galaxy distributions appear to define a quite narrow FP, which is similar to the FP found by Schaeffer et al., who used other clusters. Our cluster FP appears to be different from that of ellipticals, as well as from the virial prediction. The latter fact may have several physical explanations, or a combination thereof. If M/L varies with L this will change the FP slope away from the virial slope. Differences in dynamical structure between clusters will also produce deviations from the virial FP. In view of the long virialization time-scales in all but the very central parts of galaxy clusters, the deviation of the cluster FP from the virial expectation may also result from clusters not being totally virialized. The scatter of the observations around the cluster FP is fairly small. An important part of the observed scatter is likely to be intrinsic. If this intrinsic spread were due exclusively to deviations from the Hubble flow it would imply cluster peculiar velocities of at most about 1000 km.s-1.
Here we present new measurements of effective radii, surface brightnesses and internal velocity dispersions for 23 isolated early-type galaxies. The photometric properties are derived from new multi-colour imaging of 10 galaxies, whereas the central kinematics for 7 galaxies are taken from forthcoming work by Hau & Forbes. These are supplemented with data from the literature. We reproduce the colour-magnitude and Kormendy relations and strengthen the result of Paper I that isolated galaxies follow the same photometric relations as galaxies in high density environments. We also find that some isolated galaxies reveal fine structure indicative of a recent merger while others appear undisturbed. We examine the Fundamental Plane in both traditional R_e, mu_e and sigma space and also kappa-space. Most isolated galaxies follow the same Fundamental Plane tilt and scatter for galaxies in high density environments. However, a few galaxies notably deviate from the plane in the sense of having smaller M/L ratios. This can be understood in terms of their younger stellar populations, which are presumably induced by a gaseous merger. Overall, isolated galaxies have similar properties to those in roups and clusters with a slight enhancement in the frequency of recent mergers/interactions.
Three observables of early-type galaxies - size ($r_{e}$), surface brightness ($I_{e}$), and velocity dispersion ($sigma_{0}$) - form a tight planar correlation known as the fundamental plane (FP), which has provided great insights into the galaxy formation and the evolution processes. However, the FP has been found to be tilted against the simple virial expectation, prompting debates on its origin. In order to investigate the contribution of systematic stellar population variation to the FP tilt, we study here the FP relations of early-type galaxies in mid-infrared (MIR) which may represent the stellar mass well. We examined the wavelength dependence of the FP coefficients, $a$ and $b$ in $log r_{e}= alogsigma_{0} + blog< I >_{e} + c$, using a sample of 56 early-type galaxies for which visible (V-band), near-infrared (K-band), and MIR (Spitzer IRAC, 3.6--8.0$mu$m) data are available. We find that the coefficient $a$ increases as a function of wavelength as $da/dlambda=0.11pm0.04mu m^{-1}$, while the coefficient $b$ reaches the closest to -1 at 3.6--5.8$mu$m. When applied to the visible FP coefficients derived from a larger sample of nearby early-type galaxies, we get the FP relation with $(a,b) simeq $(1.6--1.8,-0.9) at 3.6$mu$m. Our result suggests that the stellar population effect can explain more than half of the FP tilt, closing the gap between the virial expectation and the optical FP. The reduction in the FP tilt is reflected in the dynamical mass-to-light ratio, $M_{dyn}/L$, dependence on $L$ which decreases toward 3.6--5.8$mu$m, suggesting that the MIR light better represents mass than the shorter wavelengths.
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