The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population

The variation of the mass-to-light ratios M/L of early type galaxies as function of their luminosities L is investigated. It is shown that the tilt beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can be understood as a combination of two effects: about one-quarter (i.e. dbeta =0.07) is a result of systematic variations of the stellar population properties with increasing luminosity. The remaining three-quarters (i.e. dbeta =0.2) can be completely attributed to nonhomology effects that lead to a systematic change of the surface brightness profiles with increasing luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where stellar population effects are negligible, is explained by nonhomology effects alone. After correcting for nonhomology, the mean value of the mass-to-light ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the published versio

The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit

The structural properties of the low surface brightness stellar host in blue compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer regions of their radial profiles. The limitations imposed by the presence of a large starburst emission overlapping the underlying component makes this kind of analysis a difficult task. We propose a two-dimensional fitting methodology in order to improve the extraction of the structural parameters of the LSB host. We discuss its advantages and weaknesses by using a set of simulated galaxies and compare the results for a sample of eight objects with those already obtained using a one-dimensional technique. We fit a PSF convolved Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R filters. We restrict the fit to the stellar host by masking out the starburst region and take special care to minimize the sky-subtraction uncertainties. In order to test the robustness and flexibility of the method, we carry out a set of fits with synthetic galaxies. Furthermore consistency checks are performed to assess the reliability and accuracy of the derived structural parameters. The more accurate isolation of the starburst emission is the most important advantage and strength of the method. Thus, we fit the host galaxy in a range of surface brightness and in a portion of area larger than in previous published 1D fits with the same dataset. We obtain robust fits for all the sample galaxies, all of which, except one, show Sersic indices n very close to 1, with good agreement in the three bands. These findings suggest that the stellar hosts in BCDs have near-exponential profiles, a result that will help us to understand the mechanisms that form and shape BCD galaxies, and how they relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in A&A. A higher resolution version of the figures can be provided upon reques

A photometric and kinematic study of the stars and interstellar medium in the central two kpc of NGC 3379

HST images of NGC 3379 show that the V and I luminosity profiles in the inner 13 arcsec of this E1 galaxy are represented by two different components: a stellar bulge following a Sersic Law with exponent n = 2.36, and a central core (r < 0.7 arcsec) with a characteristic "cuspy" profile. Subtraction of the underlying stellar component represented by the fitted Sersic profile revealed the presence of a small (r ~ 105 pc) dust disk of about 150 solar masses, oriented at PA = 125 degrees and inclined ~ 77 degrees with respect to the line of sight. The same absorption structure is detected in the color-index (V-I) image. The stellar rotation in the inner 20 arcsec is well represented by a parametric planar disk model, inclined ~ 26 degrees relative to the plane of the sky, and apparent major axis along PA ~ 67 degrees. The gas velocity curves in the inner 5 arcsec show a steep gradient, indicating that the gas rotates much faster than the stars, although in the same direction. The velocity field of the gaseous system, however, is not consistent with the simple model of Keplerian rotation sustained by the large (7 x 10E9 solar masses within a radius of ~ 90 pc) central mass implied by the maximum velocity observed, but the available data precludes a more detailed analysis.Comment: 23 pages, LaTeX(aaspp4.sty), 9 figures included. Figs. 1 and 5 are colour plates. Accepted for publication in The Astrophysical Journal (part 1

A New Approach to the Study of Stellar Populations in Early-Type Galaxies: K-band Spectral Indices and an Application to the Fornax Cluster

New measurements of K-band spectral features are presented for eleven early-type galaxies in the nearby Fornax galaxy cluster. Based on these measurements, the following conclusions have been reached: (1) in galaxies with no signatures of a young stellar component, the K-band Na I index is highly correlated with both the optical metallicity indicator [MgFe]' and central velocity dispersion; (2) in the same galaxies, the K-band Fe features saturate in galaxies with sigma > 150 km/s while Na I (and [MgFe]') continues to increase; (3) [Si/Fe] (and possibly [Na/Fe]) is larger in all observed Fornax galaxies than in Galactic open clusters with near-solar metallicity; (4) in various near-IR diagnostic diagrams, galaxies with signatures of a young stellar component (strong Hbeta, weak [MgFe]') are clearly separated from galaxies with purely old stellar populations; furthermore, this separation is consistent with the presence of an increased number of M-giant stars (most likely to be thermally pulsating AGB stars); (5) the near-IR diagrams discussed here seem as efficient for detecting putatively young stellar components in early-type galaxies as the more commonly used age/metallicity diagnostic plots using optical indices (e.g Hbeta vs. [MgFe]').Comment: 47 pages, 16 figures, ApJ accepte

A Correlation between Light Concentration and Cluster Local Density for Elliptical Galaxies

Using photometric and redshift data for the Virgo and Coma clusters, we present evidence for a correlation between the light concentration of elliptical galaxies (including dwarf ellipticals) and the local 3-D (i.e. non-projected) density of the clusters: more concentrated ellipticals are located in denser regions. The null hypothesis (i.e. the absence of any relation) is rejected at a significance level better than 99.9%. In order to explain the observed relation, a power law relating the galaxy light concentration and the cluster 3-D density is proposed. We study how the projection effects affect the form and dispersion of the data-points in the light concentration-projected density diagram. The agreement between our model and the observed data suggests that there is a paucity of dwarf elliptical galaxies in the cluster central regions.Comment: 7 pages, 2 figures, ApJL accepte

Weak homology of elliptical galaxies

We start by studying a small set of objects characterized by photometric profiles that have been pointed out to deviate significantly from the standard R^{1/4} law. For these objects we confirm that a generic R^{1/n} law, with n a free parameter, can provide superior fits (the best-fit value of n can be lower than 2.5 or higher than 10), better than those that can be obtained by a pure R^{1/4} law, by an R^{1/4}+exponential model, and by other dynamically justified self--consistent models. Therefore, strictly speaking, elliptical galaxies should not be considered homologous dynamical systems. Still, a case for "weak homology", useful for the interpretation of the Fundamental Plane of elliptical galaxies, could be made if the best-fit parameter n, as often reported, correlates with galaxy luminosity L, provided the underlying dynamical structure also follows a systematic trend with luminosity. We demonstrate that this statement may be true even in the presence of significant scatter in the correlation n(L). Preliminary indications provided by a set of "data points" associated with a sample of 14 galaxies suggest that neither the strict homology nor the constant stellar mass--to--light solution are a satisfactory explanation of the observed Fundamental Plane (abridged).Comment: 34 pages, 11 figures, accepted by Astronomy and Astrophysic

A log-quadratic relation for predicting supermassive black hole masses from the host bulge Sersic index

We reinvestigate the correlation between black hole mass and bulge concentration. With an increased galaxy sample, updated estimates of galaxy distances, black hole masses, and Sersic indices `n' - a measure of concentration - we perform a least-squares regression analysis to obtain a relation suitable for the purpose of predicting black hole masses in other galaxies. In addition to the linear relation, log(M_bh) = 7.81(+/-0.08) + 2.69(+/-0.28)[log(n/3)] with epsilon_(intrin)=0.31 dex, we investigated the possibility of a higher order M_bh-n relation, finding the second order term in the best-fitting quadratic relation to be inconsistent with a value of zero at greater than the 99.99% confidence level. The optimal relation is given by log(M_bh) = 7.98(+/-0.09) + 3.70(+/-0.46)[log(n/3)] - 3.10(+/-0.84)[log(n/3)]^2, with epsilon_(intrin)=0.18 dex and a total absolute scatter of 0.31 dex. Extrapolating the quadratic relation, it predicts black holes with masses of ~10^3 M_sun in n=0.5 dwarf elliptical galaxies, compared to ~10^5 M_sun from the linear relation, and an upper bound on the largest black hole masses in the local universe, equal to 1.2^{+2.6}_{-0.4}x10^9 M_sun}. In addition, we show that the nuclear star clusters at the centers of low-luminosity elliptical galaxies follow an extrapolation of the same quadratic relation. Moreover, we speculate that the merger of two such nucleated galaxies, accompanied by the merger and runaway collision of their central star clusters, may result in the late-time formation of some supermassive black holes. Finally, we predict the existence of, and provide equations for, a relation between M_bh and the central surface brightness of the host bulge

Third workshop on full-body and multisensory experience

The workshop on "Full-Body and Multisensory Experience" aims at discussing the rich possibilities that the body offers to experience the external world and the prospects that arise for interaction designers when these often-neglected abilities are taken into account. In particular, the workshop will focus on the rediscovery of the human senses, either alone or in a multimodal combination, and of the perceptual-motor abilities of our body. The one-day workshop is divided in three steps: first phase is for the generation of ideas on multisensory interfaces, in the second phase, participants will have the possibilities to explore and rediscover their sensorimotor abilities through several exercises and games; in the third and last phase, there will be a further creative session in order to evaluate how the full body and multisensory activities have fostered people's creative processes. The aim of the whole experience is twofold: first, inspiring participants in designing novel concepts for multisensory interfaces; second, providing a preliminary study on the effect of these exercises in fostering creativity and supporting the design process of multisensory interfaces

Detection of Radial Surface Brightness Fluctuation and Color Gradients in elliptical galaxies with ACS

We study surface brightness fluctuations (SBF) in a sample of 8 elliptical galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when available -- are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF--broadband color calibration for the ACS/WFC F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies. We detect and study in detail the SBF variations within individual galaxies as a probe of possible changes in the underlying stellar populations. Inspecting both the SBF and color gradients in comparison to model predictions, we argue that SBF, and SBF-gradients, can in principle be used for unraveling the different evolutionary paths taken by galaxies, though a more comprehensive study of this issue would be required. We confirm that the radial variation of galaxy stellar population properties should be mainly connected to the presence of radial chemical abundance gradients, with the outer galaxy regions being more metal poor than the inner ones.Comment: 47 pages, 13 figures, ApJ, accepte