Integrated properties of mass segregated star clusters

In this contribution we study integrated properties of dynamically segregated star clusters. The observed core radii of segregated clusters can be 50% smaller than the ``true'' core radius. In addition, the measured radius in the red filters is smaller than those measured in blue filters. However, these difference are small ($\lesssim10$), making it observationally challenging to detect mass segregation in extra-galactic clusters based on such a comparison. Our results follow naturally from the fact that in nearly all filters most of the light comes from the most massive stars. Therefore, the observed surface brightness profile is dominated by stars of similar mass, which are centrally concentrated and have a similar spatial distribution.Comment: 2 pages, 2 figures. To appear in proceedings of the 246th IAU symposium on "Dynamical evolution of dense stellar systems"; acknowledgements include

Comment on "Spin-1 aggregation model in one dimension"

M. Girardi and W. Figueiredo have proposed a simple model of aggregation in one dimension to mimic the self-assembly of amphiphiles in aqueous solution [Phys. Rev. E 62, 8344 (2000)]. We point out that interesting results can be obtained if a different set of interactions is considered, instead of their choice (the s=1 Ising model).Comment: Accepted for publication in Phys. Rev.

The WIYN Open Cluster Study Photometric Binary Survey: Initial Findings for NGC 188

The WIYN open cluster study (WOCS) has been working to yield precise magnitudes in the Johnson-Kron-Cousins UBVRI system for all stars in the field of a selection of ``prototypical'' open clusters. Additionally, WOCS is using radial velocities to obtain orbit solutions for all cluster binary stars with periods of less than 1000 days. Recently, WOCS is being expanded to include the near-infrared JHK_s (deep ground-based plus 2MASS) and mid-infrared ([3.6], [4.5], [5.8], [8.0]) photometry from Spitzer/IRAC observations. This multi-wavelength data (0.3--8.0 microns) allows us photometrically to identify binaries, with mass ratios from 1.0--0.3, across a wide range of primary masses. The spectral energy distribution (SED) fitter by Robitaille et al. (2007) is used to fit the fluxes of 10--12 bands, converted from the observed magnitudes, to Kurucz stellar models. Using this photometric technique, we find that NGC 188 has a binary fraction of 36--49% and provide a star-by-star comparison to the WOCS radial velocity-based binary study.Comment: 2 pages, 2 figures, Conference Proceedings from "Dynamical Evolution of Dense Stellar Systems'', IAU Symposium 246, Eds. E. Vesperini, M. Giersz, & A. Sill

The dynamical status of ZwCl 2341.1+0000: a very elongated galaxy structure with a complex radio emission

We study the dynamical status of the galaxy system ZwCl 2341.1+0000, a filamentary multi-Mpc galaxy structure associated with a complex diffuse radio emission. Our analysis is mainly based on new spectroscopic data for 128 galaxies acquired at the TNG telescope. We also use optical data available in the SDSS and X-ray data from the Chandra archive. We select 101 cluster member galaxies and compute the cluster redshift ~0.2693 and the global LOS velocity dispersion ~1000 km/s. Our optical analysis agrees with the presence of at least three, likely four or more, optical subclusters causing the SSE-NNW elongation of the galaxy distribution and a significant velocity gradient in the S-N direction. In particular, we detect an important low-velocity subclump in the southern region, roughly coincident with the brightest peak of the diffuse radio emission but with a clear offset between the optical and radio peaks. We also detect one (or two) optical subcluster(s) at north, in correspondence with the second brightest radio emission, and another one in the central cluster region, where a third diffuse radio source has been recently detected. A more refined analysis involving the study of the 2D galaxy distribution suggests an even more complex structure. As for the X-ray analysis, we confirm the SSE-NNW elongation of the intracluster medium and detect four significant peaks. The X-ray emission is strongly asymmetric and offsetted with respect to the galaxy distribution, thus suggesting a merger caught in the phase of post-core-core passage. Our findings support two possible hypotheses for the nature of the diffuse radio emission of ZwCl 2341.1+0000: a 2 relics+halo scenario or diffuse emission associated with the infall and merging of several galaxy groups during the first phase of the cluster formation.Comment: 14 pages, 14 figures, 4 tables; MNRAS in pres

Internal dynamics of the galaxy cluster Abell 959

The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still being debated. In this paper we aim to obtain new insights into the internal dynamics of Abell 959, showing evidence of a diffuse radio source, analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 107 galaxies in the cluster field acquired at the Telescopio Nazionale Galileo. We also use photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine galaxy velocities and positions to select 81 galaxies recognized as cluster members and determine global dynamical properties. We analyze the cluster searching for substructures by using several statistical methods. We also study the 2D galaxy distribution in the field of the cluster. We compare our results with those from X-ray and gravitational lensing analyses. We estimate a cluster redshift of z=0.2883 +/- 0.0004. We detect an NE high velocity group at 5' from the cluster center with a relative line--of--sight (LOS) velocity of ~ +1900 km/s with respect to the main system. We also detect a central, dense structure elongated along the SE--NW direction likely connected with the two dominant galaxies and their surrounding cores. This elongated central structure is probably the trace of an old cluster merger. The LOS velocity dispersion of galaxies is very high (1025 (-75/+104) km/s). The virial mass is M(<R=1.48 Mpc)= 1.15 (-0.19/+0.25) Msun. Our results suggest that this cluster is forming along two main directions of mass accretion and show the typical characteristics of radio clusters; i.e., it is very massive and shows a young dynamical state. However, deeper radio observations are needed to clarify the nature of the diffuse radio emission in Abell 959.Comment: 12 pages, 13 figures, 3 tables. Accepted for publication on Astronomy and Astrophysic

The Euro changeover and price adjustments in Italy

By estimating a staggered price model over the period 1980q1-2010q2, this paper documents that, after the euro changeover, Italian retailers have increased the number of price adjustments, which has translated into a higher inflation rate, with a detrimental effect on the competitiveness of the Italian economy

The puzzling merging cluster Abell 1914: new insights from the kinematics of member galaxies

We analyze the dynamical state of Abell 1914, a merging cluster hosting a radio halo, quite unusual for its structure. Our study considers spectroscopic data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo. We select 89 cluster members from spatial and velocity distributions. We also use photometry Canada-France-Hawaii Telescope archives. We compute the mean cluster redshift, =0.168, and the velocity dispersion which shows a high value, sigma_v=1210_{-110}^{+125} km/s. From the 2D analysis we find that Abell 1914 has a NE-SW elongated structure with two galaxy clumps, that mostly merge in the plane of the sky. Our best, but very uncertain estimate of the velocity dispersion of the main system is sigma_v~1000 km/s. We estimate a virial mass M_sys=1.4--2.6 10^{15} h_{70}^{-1} Msun for the whole system. We study the merger through a simple two-body model and find that data are consistent with a bound, outgoing substructure observed just after the core crossing. By studying the 2D distribution of the red galaxies, photometrically selected, we show that Abell 1914 is contained in a rich large scale structure, with two close companion galaxy systems, known to be at z~0.17. The system at SW supports the idea that the cluster is accreting groups from a filament aligned in the NE-SW direction, while that at NW suggests a second direction of the accretion NW-SE. We conclude that Abell 1914 well fits among typical clusters with radio halos. We argue that the unusual radio emission is connected to the complex cluster accretion and suggest that Abell 1914 resembles the well-known nearby merging cluster Abell 754 for its particular observed phenomenology.Comment: 14 pages, 10 figures, 2 table

Stellar populations in the Galactic bulge

AIMS:The aim of this paper is to study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge. We study the entire stellar population, but also retrieve information using only the red clump stars. METHODS: To study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge, we compared the output of the galaxy model TRILEGAL, which implements the Binney et al. (1997) bulge model, with observations from 2MASS and OGLE-II. A minimisation procedure has been set up to retrieve the best fitting model with different stellar populations and metallicity distributions. RESULTS: Using the TRILEGAL code we find that the best model resembling the characteristics of the Galactic bulge is a model with the distance to the Galactic centre $R_0 = 8.7\pm^{0.57}_{0.43}$ kpc, the major axis ratios of the bar $1:\eta:\zeta = 1 : 0.68\pm_{0.19}^{0.05} : 0.31\pm_{0.04}^{0.06}$, and the angle between the Sun-centre line and the bar $\phi = 15\deg\pm_{12.7}^{13.3}$. Using these parameters the best model is found for a burst of 8 Gyr, although it is almost indistinguishable from models with ages of 9 and 10 Gyr. The metallicity distribution found is consistent with metallicity distributions in the literature based on spectroscopic results.Comment: A&A accepte

Galaxies in group and field environments: a comparison of optical-NIR luminosities and colors

We compare properties of galaxies in loose groups with those in field environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy systems. We consider as group galaxies, objects belonging to systems with at least five members identified by means of the "friends of friends method", and, as field galaxies, all galaxies with no companions. We analyze both a magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies, respectively, B<14 mag, and 2000<cz<6000 km/s) and a volume-limited sample (M_B <-19.01 mag, 2000<cz<4000 km/s 369 group and 548 field galaxies). For all these galaxies, blue corrected magnitudes and morphological types are available. The cross-correlation of NOG with the 2MASS second release allow us to assign K magnitudes and obtain B-K colors for about half of the galaxies in our samples. We analyze luminosity and color segregation-effects in relation with the morphological segregation. For both B and K bands, we find that group galaxies are, on average, more luminous than field galaxies and this effect is not entirely a consequence of the morphological segregation. After taking into account the morphological segregation, the luminosity difference between group and field galaxies is about 10%. When considering only very early-type galaxies (T<-2) the difference is larger than 30%. We also find that group galaxies are redder than field galaxies, Delta(B-K) about 0.4 mag. However, after taking into account the morphological segregation, we find a smaller B-K difference, poorly significant (only at the c.l. of about 80%).Comment: 11 pages, 10 eps figures, A&A in pres