4,925 research outputs found

    On the shape of the light profiles of early-type galaxies

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    We have obtained the best fit to the light profiles of a luminosity limited sample of elliptical and S0 galaxies with a power law \rn, letting the exponent remain free rather than keeping it fixed at 1/n=1/41/n=1/4 as in the well known \GV formula. The introduction of a free parameter in the fitting formula (ranging from n=0.5n=0.5 for =0.3=0.3 kpc to n=16n=16 for =25=25 kpc) is justified by the existence of a good correlation between nn and the global galaxian parameters, such as total luminosity and scale-radius. This result seems to be in line with the segregation of properties between the `ordinary' and `bright' families of early-type galaxies, and has consequence for the claimed independence of the shape of galaxy profiles with respect to the Fundamental Plane parameters.Comment: 10 pages, postscript file including figures, PADOVA (archived file truncated during email transfer

    Structure and kinematics of the peculiar galaxy NGC 128

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    This is a multiband photometric and spectroscopic study of the peculiar S0 galaxy NGC128. We present results from broad (B and R) and narrow band optical CCD photometry, near (NIR) and far (FIR) infrared observations, long slit spectroscopy, and Fabry-Perot interferometry (CIGALE). The peculiar peanut shape morphology of the galaxy is observed both at optical and near-infrared wavelengths. The stellar disk is thick and distorted (arc-bended), with a color asymmetry along the major axis due to the presence of a large amount of dust, estimated through NIR and FIR data of ~6x10^6 M_sun, in the region of interaction with the companion galaxy NGC127. The color maps are nearly uniform over the whole galaxy, but for the major axis asymmetry, and a small gradient toward the center indicating the presence of a redder disk-like component. The H_alpha image indeed reveals the existence of a tilted gaseous ``disk'' around the center, oriented with the major axis toward the companion galaxy NGC127. Long slit and CIGALE data confirm the presence of gas in a disk-like component counter-rotating and inclined approximately of 50 deg. to the line of sight. The mass of the gas disk in the inner region is ~2.7x10^4 M_sun. The stellar velocity field is cylindrical up to the last measured points of the derived rotation curves, while the velocity dispersion profiles are typical for an S0 galaxy, but for an extended constant behaviour along the minor axis.Comment: accepted for pubblication in A&A Supp

    Fifty Years of Quasars: Physical Insights and Potential for Cosmology

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    Last year (2013) was more or less the 50th anniversary of the discovery of quasars. It is an interesting time to review what we know (and don't know) about them both empirically and theoretically. These compact sources involving line emitting plasma show extraordinary luminosities extending to one thousand times that of our Milky Way in emitting volumes of a few solar system diameters (bolometric luminosity log Lbol∌_{bol} \sim 44-48 [erg s−1^{-1}]: D=1-3 light months ∌\sim 10310^3 - 10410^4 gravitational radii). The advent of 8-10 meter class telescopes enables us to study them spectroscopically in ever greater detail. In 2000 we introduced a 4D Eigenvector 1 parameters space involving optical, UV and X-Ray measures designed to serve as a 4D equivalent of the 2D Hertzsprung-Russell diagram so important for depicting the diversity of stellar types and evolutionary states. This diagram has revealed a principal sequence of quasars distinguished by Eddington ratio (proportional to the accretion rate per unit mass). Thus while stellar differences are primarily driven by the mass of a star, quasar differences are apparently driven by the ratio of luminosity-to-mass. Out of this work has emerged the concept of two quasars populations A and B separated at Eddington ratio around 0.2 which maximizes quasar multispectral differences. The mysterious 8% of quasars that are radio-loud belong to population B which are the lowest accretors with the largest black hole masses. Finally we consider the most extreme population A quasars which are the highest accretors and in some cases are among the youngest quasars. We describe how these sources might be exploited as standard candles for cosmology.Comment: Accepted for publication in Journal of Physics Conference Series (10 pages, 4 figures). Invited Lecture at International Symposium on the Physics of Ionized Gas (SPIG 2014), Belgrade 26-29 August 201

    The evolution of the number density of compact galaxies

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    We compare the number density of compact (small size) massive galaxies at low and high redshift using our Padova Millennium Galaxy and Group Catalogue (PM2GC) at z=0.03-0.11 and the CANDELS results from Barro et al. (2013) at z=1-2. The number density of local compact galaxies with luminosity weighted (LW) ages compatible with being already passive at high redshift is compared with the density of compact passive galaxies observed at high-z. Our results place an upper limit of a factor ~2 to the evolution of the number density and are inconsistent with a significant size evolution for most of the compact galaxies observed at high-z. The evolution may be instead significant (up to a factor 5) for the most extreme, ultracompact galaxies. Considering all compact galaxies, regardless of LW age and star formation activity, a minority of local compact galaxies (<=1/3) might have formed at z<1. Finally, we show that the secular decrease of the galaxy stellar mass due to simple stellar evolution may in some cases be a non-negligible factor in the context of the evolution of the mass-size relation, and we caution that passive evolution in mass should be taken into account when comparing samples at different redshifts.Comment: ApJ in pres

    Bimodality in low-luminosity E and S0 galaxies

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    Stellar population characteristics are presented for a sample of low-luminosity early-type galaxies (LLEs) in order to compare them with their more luminous counterparts. Long-slit spectra of a sample of 10 LLEs were taken with the ESO New Technology Telescope, selected for their low luminosities. Line strengths were measured on the Lick standard system. Lick indices for these LLEs were correlated with velocity dispersion (σ), alongside published data for a variety of Hubble types. The LLEs were found to fall below an extrapolation of the correlation for luminous ellipticals and were consistent with the locations of spiral bulges in plots of line strengths versus σ. Luminosity weighted average ages, metallicities and abundance ratios were estimated from χ2 fitting of 19 Lick indices to predictions from simple stellar population models. The LLEs appear younger than luminous ellipticals and of comparable ages to spiral bulges. These LLEs show a bimodal metallicity distribution, consisting of a low-metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high-metallicity group (similar to spiral bulges). Finally, they have low α-element to iron peak abundance ratios indicative of slow, extended star formation

    Structure of Early-Type Galaxies: 2D Fit of the Light Distribution for a Complete Volume-Limited Sample

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    We outline the results of a two-dimensional (2D) fit of the light distribution of early-type galaxies belonging to a complete volume-limited sample, and briefly discuss the significant correlations among the structural parameters. In particular we reconfirm that the lack of structural homology is likely a characteristic of hot stellar systems.Comment: 8 pages and 4 figures. To appear in the proceedings of the Euroconference "the Evolution of Galaxies on Cosmological Timescales" Nov 30th - Dec 5th 1998 Puerto de la Cruz Tenerife, Spai