arXiv subjects

M. Capaccioli

Publications and source records attributed to M. Capaccioli.

131 records · Page 8Linked to original sources

arXiv1997

The Stellar Distribution of the Globular Cluster M55

We have used extensive V, I photometry (down to V=20.9) of 33615 stars in the direction of the globular cluster M55 to study the dynamical interaction of this cluster with the tidal fields of the Galaxy. An entire quadrant of the cluster has been covered, out to ~2.0 times the tidal radius. A CMD down to about 4 magnitudes below the turn-off is presented and analysed. A large population of BS has been identified. The BS are significantly more concentrated in the inner 300 arcsec, while they become less concentrated in the cluster envelope. We have obtained luminosity functions at various radial intervals from the center and their corresponding mass functions. Both clearly show the presence of mass segregation inside the cluster. A dynamical analysis shows that the observed mass segregation is compatible with what is predicted by multi-mass King-Michie models. The global mass function is very flat with a power-law slope of x=-1.0+/-0.4. This suggest that M55 might have suffered selective losses of stars, caused by tidal interactions with the Galactic disk and bulge. The radial density profile of M55 out to ~2.0 r_t suggests the presence of extra-tidal stars whose nature could be connected with the cluster.

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arXiv1997

The relative distances to the Virgo, Fornax, and Coma clusters of galaxies through the Dn-sigma and the Fundamental Plane relations

We derive the relative distances to the Virgo, Fornax, and Coma clusters of galaxies by applying the Dn-sigma and the Fundamental Plane (FP) relations to the data of the homogeneous samples of early--type galaxies studied by Caon etal, Lucey etal, and Jorgensen etal. The two distance indicators give consistent results, the relative distance moduli to Fornax and Coma with respect to Virgo being Dmu(FV)=0.45+-0.15 and Dmu(CV)=3.55+-0.15) respectively. The formal error on D(m-M) may be as small as 0.07 mag (~3% in distance), provided that all the sources of bias are taken into account and a correct statistical approach is used. Much of the actual uncertainty in the relative distance of the clusters (12-15%), is due to the existence of systematic departures in the measurements of the velocity dispersions among the various datasets, and to the corrections for aperture effects. The above result for the Fornax cluster is supported by the L-sigma-mu relation and, with lesser accuracy, by the log(m)-log(re) relations. Our value of Dmu(FV) is in fair agreement with the one derived using planetary nebulae and SNe-Ia, while is in open contrast with that coming from surface brightness fluctuations, globular clusters luminosity function, and infrared Tully-Fisher relation. In our data Coma appears slightly nearer than indicated by the other distance indicators, but now a better agreement with the Tully-Fisher relation seems to exist. Finally we found that there aren't correlations of the residuals of the Dn-sigma with the effective surface brightness, the total luminosity of the galaxies, with the ellipticity and the shape parameter a4. Instead a correlation seems to exists with maximum Vrot, with (V/sigma) and with the exponent m of the r^1/m fit to major axis light of galaxies.

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arXiv1994

Major axis kinematics of 15 early-type galaxies in the Fornax cluster

Major axis rotation curves and velocity dispersions profiles, extending out to about one effective radius, are presented for 15 ellipticals and S0's out of the photometric sample of Fornax cluster galaxies studied by Caon \etal\ (1994). A brief description of the spectroscopic and photometric characteristics of each galaxy is provided, together with a comparison with previous studies. Six of the nine E's are possibly misclassified S0's or ellipticals harboring a disk-like component. Two galaxies (NGC~1399 and 1404) show a hint of counter-rotation. Evidence is given that the \bright\ and the \ordinary\ families of early-type galaxies, first introduced by Capaccioli \etal\ (1992), look distinct also in term of the anisotropy parameter $(\Vm/σ)^*$.

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arXiv1993

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

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 $1/n=1/4$ as in the well known \GV formula. The introduction of a free parameter in the fitting formula (ranging from $n=0.5$ for $<\re>=0.3$ kpc to $n=16$ for $<\re>=25$ kpc) is justified by the existence of a good correlation between $n$ 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.

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arXiv1993

Deep Kinematics and Dynamics of Edge-on S0 Galaxies. I. NGC 3115

As a first step of a program aimed to the detection of dark matter (or radial variations of M/L) in early-type galaxies, we report deep spectroscopic observations of the bulge-dominated edge-on S0 galaxy NGC 3115, made at ESO, La Silla, using EFOSC at the 3.6m telescope and EMMI at NTT. Such observations allow measurements of the rotational velocity out to 1.8 a_e (effective radii) from the galaxy center, where the surface brightness is μ_B ~ 24 mag arcsec**-2. The rotation curve quickly reaches an asymptotic value, v_f ~ 260 km/s, with only marginal indication of systematic decline within the range of our observations. The line-of-sight velocity dispersion has also been measured; it decreases steeply from a rather high central value and flattens out (<σ> ~ 100 km/s) within our observing range (a ~< 1.3 a_e). Models built on these data and simple dynamical arguments show that the M/L of NGC 3115 must thus be increasing from M/L = 6 (in solar units) in the inner regions (~ 1 a_e) to at least M/L >= 10 in the outermost regions (~ 2 a_e).

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