331 research outputs found
The abundance of Bullet-groups in LCDM
We estimate the expected distribution of displacements between the two
dominant dark matter (DM) peaks (DM-DM displacements) and between DM and
gaseous baryon peak (DM-gas displacements) in dark matter halos with masses
larger than Msun/h. We use as a benchmark the observation of SL2S
J08544-0121, which is the lowest mass system ( Msun/h)
observed so far featuring a bi-modal dark matter distribution with a dislocated
gas component. We find that % of the dark matter halos with
circular velocities in the range 300 km/s to 700 km/s (groups) show DM-DM
displacements equal or larger than kpc/h as observed in SL2S
J08544-0121. For dark matter halos with circular velocities larger than 700
km/s (clusters) this fraction rises to 70 10%. Using the same simulation
we estimate the DM-gas displacements and find that 0.1 to 1.0% of the groups
should present separations equal or larger than kpc/h corresponding
to our observational benchmark; for clusters this fraction rises to (7
3)%, consistent with previous studies of dark matter to baryon separations.
Considering both constraints on the DM-DM and DM-gas displacements we find that
the number density of groups similar to SL2S J08544-0121 is Mpc, three times larger than the estimated value for clusters.
These results open up the possibility for a new statistical test of LCDM by
looking for DM-gas displacements in low mass clusters and groups.Comment: 6 pages, 3 figures, accepted for publication in ApJ Letter
Its moderately extended low-density halo and its accretion history
We present results based on Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relatively small size and mass, there is not yet a general consensus on the existence of extra-tidal structures surrounding it. While some previous results suggest the absence of such features, others show that the cluster is under the effects of tidal stripping. We have built a cluster stellar density map from DECaLS g, r magnitudes-previously corrected for interstellar reddening-of stars placed along the cluster main sequence in the color-magnitude diagram. The resulting density map shows nearly smooth contours around Pal 13 out to approximately 1.6 t the most recent estimate of its Jacobi radius, which was derived whilst taking into account the variation along its orbital motion. This outcome favors the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disk a comparably large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of lost cluster mass.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de AstronomÃa Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de AstronomÃa Teórica y Experimental; ArgentinaFil: Fernández Trincado, José G.. Universidad de Atacama; Chil
Close encounters involving RAVE stars beyond the 47 Tucanae tidal radius
The most accurate 6D phase-space information from the Radial Velocity
Experiment (RAVE) was used to integrate the orbits of 105 stars around the
galactic globular cluster 47 Tucanae, to look for close encounters between them
in the past, with a minimum distance approach less than the cluster tidal
radius. The stars are currently over the distance range 3.0 kpc d 5.5
kpc. Using the uncertainties in the current position and velocity vector for
both, star and cluster, 105 pairs of star-cluster orbits were generated in a
Monte Carlo numerical scheme, integrated over 2 Gyr and considering an
axisymmetric and non-axisymmetric Milky-Way-like Galactic potential,
respectively. In this scheme, we identified 20 potential cluster members that
had close encounters with the globular cluster 47 Tucanae, all of which have a
relative velocity distribution (V) less than 200 km s at the
minimum distance approach. Among these potential members, 9 had close
encounters with the cluster with velocities less than the escape velocity of 47
Tucanae, therefore a scenario of tidal stripping seems likely. These stars have
been classified with a 93\% confidence level, leading to the identification of
extratidal cluster stars. For the other 11 stars, V exceeds the escape
velocity of the cluster, therefore they were likely ejected or are unassociated
interlopers.Comment: 10 pages, 6 figures, 2 table, Accepted for publication in MNRA
Searching for tidal tails around Centauri using RR Lyrae Stars
We present a survey for RR Lyrae stars in an area of 50 deg around the
globular cluster Centauri, aimed to detect debris material from the
alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars of
which only 11 have been previously reported. Ten among the eleven previously
known stars were found inside the tidal radius of the cluster. The rest were
located outside the tidal radius up to distances of degrees from the
center of the cluster. Several of those stars are located at distances similar
to that of Centauri. We investigated the probability that those stars
may have been stripped off the cluster by studying their properties (mean
periods), calculating the expected halo/thick disk population of RR Lyrae stars
in this part of the sky, analyzing the radial velocity of a sub-sample of the
RR Lyrae stars, and finally, studying the probable orbits of this sub-sample
around the Galaxy. None of these investigations support the scenario that there
is significant tidal debris around Centauri, confirming previous
studies in the region. It is puzzling that tidal debris have been found
elsewhere but not near the cluster itself.Comment: 11 pages, 11 figures, Accepte
Characterizing SL2S galaxy groups using the Einstein radius
We analyzed the Einstein radius, , in our sample of SL2S galaxy
groups, and compared it with (the distance from the arcs to the center of
the lens), using three different approaches: 1.- the velocity dispersion
obtained from weak lensing assuming a Singular Isothermal Sphere profile
(), 2.- a strong lensing analytical method ()
combined with a velocity dispersion-concentration relation derived from
numerical simulations designed to mimic our group sample, 3.- strong lensing
modeling () of eleven groups (with four new models presented in
this work) using HST and CFHT images. Finally, was analyzed as a function
of redshift to investigate possible correlations with L, N, and the
richness-to-luminosity ratio (N/L). We found a correlation between
and , but with large scatter. We estimate = (2.2 0.9)
+ (0.7 0.2), = (0.4 1.5) + (1.1
0.4), and = (0.4 1.5) + (0.9 0.3) for
each method respectively. We found a weak evidence of anti-correlation between
and , with Log = (0.580.06) - (0.040.1), suggesting
a possible evolution of the Einstein radius with , as reported previously by
other authors. Our results also show that is correlated with L and N
(more luminous and richer groups have greater ), and a possible
correlation between and the N/L ratio. Our analysis indicates that
is correlated with in our sample, making useful to
characterize properties like L and N (and possible N/L) in galaxy groups.
Additionally, we present evidence suggesting that the Einstein radius evolves
with .Comment: Accepted for publication in Astronomy & Astrophysics. Typos correcte
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