Jorge Peñarrubia

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, and surface gravity) of up to one million stars using the Six Degree Field multiobject spectrograph on the 1.2 m UK Schmidt Telescope of the Anglo-Australian Observatory. The RAVE program started in 2003, obtaining medium-resolution spectra (median R 1⁄4 7500) in the Ca-triplet region (8410–8795 8) 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 reobservations). Those data were obtained on 67 nights between 2003 April 11 and 2004 April 3. The total sky coverage within this data release is 4760 deg. 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 ratio. 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 the TwoMicron All Sky Survey). The data release can be accessed via the RAVE Web site.

The Radial Velocity Experiment (RAVE)

We present the second data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity, and rotational velocity) 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 specUniversity of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia Astrophysikalisches Institut Potsdam, Potsdam, Germany Observatoire de Strasbourg, Strasbourg, France INAF, Osservatorio Astronomico di Padova, Sede di Asiago, Italy RSAA, Australian national University, Canberra, Australia Anglo Australian Observatory, Sydney, Australia Johns Hopkins University, Baltimore MD, USA Macquarie University, Sydney, Australia Institute of Astronomy, University of Cambridge, UK e2v Centre for Electronic Imaging, School of Engineering and Design, Brunel University, Uxbridge, UK Astronomisches Rechen-Institut, Center for Astronomy of the University of Heidelberg, Heidelberg, Germany Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands University of Victoria, Victoria, Canada Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Australia Rudolf Pierls Center for Theoretical Physics, University of Oxford, UK Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia Sterrewacht Leiden, University of Leiden, Leiden, the Netherlands University of Leicester, Leicester, UK MPI fuer extraterrestrische Physik, Garching, Germany University of Central Lancashire, Preston, UK University of Rochester, Rochester NY, USA University of Edinburgh, Edinburgh, UK

A Comprehensive model for the Monoceros tidal stream

We have compiled an extensive data set on potential parts of the Monoceros tidal stream and performed an exhaustive survey of dwarf galaxy semianalytic 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 ? 0.05 and i = 25? ? 5?. Ten new estimates of proper motions from the Sloan Digital Sky Survey 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.; Newberg et al.) and 12-18 kpc (the Tri/And stream; Rocha-Pinto et al.) from the Sun. We have attempted to predict the present location of the Monoceros stream progenitor using different information: (1) the kinematical and spatial distribution of detections, and (2) the different mean metallicity in the inner and the outer rings. Because of the lack of observational data in the whole range of Galactic latitudes, the geometrical/kinematical constraints lead to a wide range of possible locations. By associating older parts of the model stream with lower metallicity parts of the observed data, we argue in favor of a current location of l ~ 245?, b ~ -18?, with a distance to the Sun rs 15 kpc. The mass of the progenitor has been poorly constrained because of the slow orbital decay. Similar fits have been obtained for masses (3-9) ? 108 M?. We have analyzed the possible common origin of the Canis Major dwarf and the Monoceros stream. The Canis Major dwarf moves on a prograde, nearly circular orbit (e 0.16) in the Milky Way disk (i 4 deg). This orbital inclination is too low to account for the large vertical dispersion of stream stars. However, the bimodal distribution of radial velocities in the central region found by Martin et al. probably indicates that their selection criteria for identifying dwarf stars lead to a contamination of background stars. In that case, the kinematical data outlined above might result in an underestimate of the orbital inclination. Finally, the distance estimation to Canis Major dwarf is around a factor of 2 smaller than that obtained from our model. Unfortunately, the possible identification of the Monoceros stream progenitor in Canis Major remains unclear.

The Closest View of a Dwarf Galaxy: New Evidence on the Nature of the Canis Major Overdensity

We present the first deep color-magnitude diagram of the putative central region (05 × 05) of the Canis Major stellar overdensity (l, b) = (240, - 8) found recently by Martin and coworkers, which has been proposed as the remnant of a dwarf satellite accreted onto the Milky Way on a near-equatorial orbit. We find a narrow (in apparent magnitude) main sequence extending 6 mag below the turnoff to our limiting magnitude of B ~ 24.5 mag. This main sequence has very high contrast (>3) with respect to the thin/thick disk/halo background; its narrowness at brighter magnitudes clearly implies the presence of a distinct and possibly still bound stellar system. We derived the line-of-sight size (r1/2) of this system based on the B-band width of the lower main sequence, obtaining 0.94 ± 0.18 (random) ± 0.18 (systematic) kpc. That size matches a model prediction for the main body of the parent galaxy of the Monoceros tidal stream. The high-density contrast and limited spatial extent in the radial direction are very hard to reconcile with the alternative explanation put forward to explain the Canis Major stellar overdensity: a flared or warped Galactic disk viewed in projection, as found in the recent work of Momany and coworkers. We also derived a central surface brightness of μV,0 = 23.3 ± 0.1 mag arcsec-2 and an absolute magnitude of MV = -14.5 ± 0.1 mag. These values place the Canis Major object in the category of dwarf galaxy, considering the LV-size and MV - μV planes for such objects. However, like the Sagittarius dwarf, it is an outlier in the [Fe/H] - MV plane in the sense that it is too metal-rich for its estimated absolute magnitude. This suggests that the main mechanism driving its recent and current star formation history (possibly tidal stripping) is different from that of isolated dwarfs.

Effects of dynamical evolution on the distribution of substructures

We develop a semi-analytical model that determines the evolution of the mass and position 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. 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 per cent) in the number of substructures at r 0.25r 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 significantly altered by dynamical evolution.

Absolute Proper Motion of the Canis Major Dwarf Galaxy Candidate

We have measured the absolute proper motion of the candidate Canis Major dwarf galaxy (CMa), at (l, b) =(240°, -8°). Likely main-sequence stars in CMa have been selected from a region in the color-magnitude diagram that has very little contamination from known Milky Way components. We obtain μl cos b = -1.47 ± 0.37 and μb = -1.07 ± 0.38 mas yr-1, on the International Celestial Reference System by means of Hipparcos stars. Together with the radial velocity of 109 km s-1 and the assumed distance of 8 kpc, these results imply a space motion of (Π, Θ, W) = (-5 ± 12, 188 ± 10, -49 ± 15) km s-1. While CMa has in-plane rotation similar to the mean of thick-disk stars, it shows significant (3 σ) motion perpendicular to the disk and differs even more (7 σ) from that expected for the Galactic warp. The W-velocity lends support to the argument that the CMa overdensity is part of a satellite-galaxy remnant.

A THEORETICAL STUDY OF THE LUMINOSITY-TEMPERATURE RELATION FOR CLUSTERS OF GALAXIES

A luminosity-temperature relation is derived for clusters of galaxies. The two models used take into account the angular momentum acquisition by the protostructures during their expansion and collapse. The first model is a modification of the self-similar model, while the second is a modification of the punctuated equilibria model of Cavaliere et al. In both models the mass-temperature relation (M-T) used is based on previous calculations of Del Popolo. We show that the above models lead, in X-rays, to a luminosity-temperature relation that scales as L ∝ T5 at the scale of groups, flattening to L ∝ T3 for rich clusters and converging to L ∝ T2 at higher temperatures. However, a fundamental result of our paper is that the nonsimilarity in the L-T relation can be explained by a simple model that takes into account the amount of angular momentum of a protostructure. This result is in disagreement with the widely accepted idea that the nonsimilarity is due to nongravitating processes, such as heating and/or cooling.

The Canis Major dwarf galaxy as the progenitor of the Monoceros tidal stream

The Sloan Digital Sky Survey has recently discovered a coherent ring of stars at low galactic latitude that is believed to be the tidal stream of a merging dwarf galaxy in the Galactic plane (named the Monoceros tidal stream). The existence and location of the core of its progenitor galaxy is still controversial. The best candidate is the Canis Major dwarf galaxy, a distinct overdensity of red stars discovered in the 2MASS survey, but also interpreted as the signature of the Galactic warp viewed in projection. In this paper, we report a variety of new observational evidence that supports the notion that CMa is the remnant of a partially disrupted core of a dwarf satellite. The comparison of the orbit derived from our theoretical model for the parent galaxy of this ring-like structure with an accurate determination of CMa orbit leads to the conclusion that this satellite is the best candidate for the progenitor of the Monoceros tidal stream.