arXiv subjects

J. Penarrubia

Publications and source records attributed to J. Penarrubia.

23 records · Page 2Linked to original sources

arXiv2006

The Radial Velocity Experiment (RAVE): first data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R=7,500) in the Ca-triplet region ($λλ$ 8,410--8,795 Å) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9<I<12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including re-observations). Those data were obtained on 67 nights between 11 April 2003 to 03 April 2004. The total sky coverage within this data release is $\sim$4,760 square degrees. The average signal to noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km/s. Combining internal errors and zero-point errors, the mode is found to be 2 km/s. Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km/s. We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal to noise. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2 and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS and 2MASS). The data release can be accessed via the RAVE webpage: http://www.rave-survey.org.

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arXiv2005

A theoretical study of the luminosity temperature relation for clusters of galaxies

A luminosity-temperature relation for clusters of galaxies is derived. The two models used, take into account the angular momentum acquisition by the proto-structures during their expansion and collapse. The first one is a modification of the self-similar model (SSM) while the second one is a modification of the Punctuated Equilibria Model (Cavaliere et al. 1999). In both models the mass-temperature relation (M-T) used is based on the calculations of Del Popolo (2002b). We show that the above models lead, in X-rays, to a luminosity-temperature relation that scales as L \propto T^5, at scale of groups, flattening to L \propto T^3 for rich clusters and converging to L \propto T^2 at higher temperatures. However a fundamental result of our paper is that the non-similarity in the L-T relation, can be explained by a simple model that takes into account the amount of the angular momentum of a proto-structure. This result is in disagreement with the widely accepted idea that the above non-similarity is due to non-gravitating processes as those of heating/cooling.

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arXiv2004

Effects of dynamical evolution on the distribution of substructures

We develop a semi-analytical model that determines the evolution of the mass, position and internal structure of dark matter substructures orbiting in dark matter haloes. We apply this model to the case of the Milky Way. We focus in particular on the effects of mass loss, dynamical friction and substructure--substructure interactions, the last of which has previously been ignored in analytic models of substructure evolution. Our semi-analytical treatment reproduces both the spatial distribution of substructures and their mass function as obtained from the most recent N-body cosmological calculations of Gao et al. (2004). We find that, if mass loss is taken into account, the present distribution of substructures is practically insensitive to dynamical friction and scatterings from other substructures. Implementing these phenomena leads to a slight increase (~5%) in the number of substructures at r<0.35 r_vir, whereas their effects on the mass function are negligible. We find that mass loss processes lead to the disruption of substructures before dynamical friction and gravitational scattering can significantly alter their orbits. Our results suggest that the present substructure distribution at r>0.35 r_vir reflects the orbital properties at infall and is, therefore, purely determined by the dark matter environment around the host halo and has not been altered by dynamical evolution.

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arXiv2004

Large scale inhomogeneity and local dynamical friction

We investigate the effect of a density gradient on Chandrasekhar's dynamical friction formula based on the method of 2-body encounters in the local approximation. We apply these generalizations to the orbit evolution of satellite galaxies in Dark Matter haloes. We find from the analysis that the main influence occurs through a position-dependent maximum impact parameter in the Coulomb logarithm, which is determined by the local scale-length of the density distribution. We also show that for eccentric orbits the explicit dependence of the Coulomb logarithm on position yields significant differences for the standard homogeneous force. Including the velocity dependence of the Coulomb logarithm yields ambigous results. The orbital fits in the first few periods are further improved, but the deviations at later times are much larger. The additional force induced by the density gradient, the inhomogeneous force, is not antiparallel to the satellite motion and can exceed 10% of the homogeneous friction force in magnitude. However, due to the symmetry properties of the inhomogeneous force, there is a deformation and no secular effect on the orbit at the first order. Therefore the inhomogeneous force can be safely neglected for the orbital evolution of satellite galaxies. For the homogeneous force we compare numerical N-body calculations with semi-analytical orbits to determine quantitatively the accuracy of the generalized formulae of the Coulomb logarithm in the Chandresekhar approach. With the local scale-length as the maximum impact parameter we find a significant improvement of the orbital fits and a better interpretation of the quantitative value of the Coulomb logarithm.

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arXiv2004

A comprehensive model for the Monoceros tidal stream

We have compiled an extensive dataset on potential parts of the Monoceros tidal stream and performed an exhaustive survey of dwarf galaxy semi-analytic orbits in order to constrain its orbital properties. The best-fit orbits are subsequently realized as self-consistent N-body simulations in order to reproduce the spatial and velocity distribution of satellite debris. We find that all kinematic and geometric constraints can be fit by a single stream allowing for multiple wraps. The orbital eccentricity and inclination of the progenitor are strongly constrained to be e = 0.10 \pm 0.05 and i = 25 \pm 5 deg. Ten new estimates of proper motions from the Sloan Digital Sky Survey (SDSS) clearly exclude all retrograde orbits. Particles lost by the satellite populate two, nearly concentric rings naturally explaining the detection of stream stars at both 6--8 kpc (Ibata et al. 2003, Newberg et al. 2003) and 12--18 kpc (the Tri/And stream; Rocha-Pinto et al. 2003) from the Sun. We have attempted to predict the present location of the Monoceros stream progenitor using different information: (i) the kinematical and spatial distribution of detections and (ii) the different mean metallicity in the innner and the outer rings. A current location at l ~ 245, b ~ -18., with a distance to the Sun r_s~15 kpc, reproduces the available constraints. The mass of the progenitor has been poorly determined due to the slow orbital decay. Similar fits have been obtained for masses (3-9)10^8 M_sun. Additionally, we have analyzed to possible common origin of the Canis Major dwarf and the Monoceros stream, unfortunately, without a conclusive result.

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