5,864 research outputs found
Galaxy populations in the Antlia cluster - III. Properties of faint early-type galaxies
(Abridge) We present a new analysis of the early-type galaxy population in
the central region of the Antlia cluster, focusing on the faint systems like
dwarf ellipticals (dE) and dwarf spheroidals (dSph). We confirm 22 early-type
galaxies as Antlia members, using GEMINI-GMOS and MAGELLAN-MIKE spectra. Among
them, 2 belong to the rare type of compact ellipticals (cE), and 5 are new
faint dwarfs that had never been catalogued before. In addition, we present 16
newly identified low surface brightness galaxy candidates, almost half of them
displaying morphologies consistent with being Antlia's counterparts of Local
Group dSphs, that extend the faint luminosity limit of our study down to MB =
-10.1 (BT = 22.6) mag. We built an improved CMR in the Washington photometric
system, i.e. integrated T1 magnitudes versus (C - T1) colours, which extends
\sim 4 mag faintwards the limit of spectroscopically confirmed Antlia members.
When only confirmed early-type members are considered, this relation extends
over 10 mag in luminosity with no apparent change in slope or increase in
colour dispersion towards its faint end. The intrinsic colour scatter of the
relation is compared with those reported for other clusters of galaxies; we
argue that it is likely that the large scatter of the CMR, usually reported at
faint magnitudes, is mostly due to photometric errors along with an improper
membership/morphological classification. The distinct behaviour of the
luminosity versus mean effective surface brightness relation at the bright and
faint ends is analyzed, while it is confirmed that dE galaxies on the same
relation present a very similar effective radius, regardless of their colour.
The projected spatial distribution of the member sample confirms the existence
of two groups in Antlia, each one dominated by a giant elliptical galaxy and
with one cE located close to each giant.Comment: 19 pages, 9 figures, 5 tables. Accepted for publication in MNRA
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Longitudinal Spin Transfer to and Hyperons in Polarized Proton-Proton Collisions at = 200 GeV
The longitudinal spin transfer, , from high energy polarized protons
to and hyperons has been measured for the first time
in proton-proton collisions at with the STAR
detector at RHIC. The measurements cover pseudorapidity, , in the range
and transverse momenta, , up to . The longitudinal spin transfer is found to be for inclusive
and for
inclusive hyperons with and . The dependence on and is presented.Comment: 5 pages, 4 figure
Studies of di-jet survival and surface emission bias in Au+Au collisions via angular correlations with respect to back-to-back leading hadrons
We report first results from an analysis based on a new multi-hadron
correlation technique, exploring jet-medium interactions and di-jet surface
emission bias at RHIC. Pairs of back-to-back high transverse momentum hadrons
are used for triggers to study associated hadron distributions. In contrast
with two- and three-particle correlations with a single trigger with similar
kinematic selections, the associated hadron distribution of both trigger sides
reveals no modification in either relative pseudo-rapidity or relative
azimuthal angle from d+Au to central Au+Au collisions. We determine associated
hadron yields and spectra as well as production rates for such correlated
back-to-back triggers to gain additional insights on medium properties.Comment: By the STAR Collaboration. 6 pages, 2 figure
Observation of the antimatter helium-4 nucleus
High-energy nuclear collisions create an energy density similar to that of
the universe microseconds after the Big Bang, and in both cases, matter and
antimatter are formed with comparable abundance. However, the relatively
short-lived expansion in nuclear collisions allows antimatter to decouple
quickly from matter, and avoid annihilation. Thus, a high energy accelerator of
heavy nuclei is an efficient means of producing and studying antimatter. The
antimatter helium-4 nucleus (), also known as the anti-{\alpha}
(), consists of two antiprotons and two antineutrons (baryon
number B=-4). It has not been observed previously, although the {\alpha}
particle was identified a century ago by Rutherford and is present in cosmic
radiation at the 10% level. Antimatter nuclei with B < -1 have been observed
only as rare products of interactions at particle accelerators, where the rate
of antinucleus production in high-energy collisions decreases by about 1000
with each additional antinucleon. We present the observation of the antimatter
helium-4 nucleus, the heaviest observed antinucleus. In total 18
counts were detected at the STAR experiment at RHIC in 10 recorded Au+Au
collisions at center-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon
pair. The yield is consistent with expectations from thermodynamic and
coalescent nucleosynthesis models, which has implications beyond nuclear
physics.Comment: 19 pages, 4 figures. Submitted to Nature. Under media embarg
Charged and strange hadron elliptic flow in Cu+Cu collisions at = 62.4 and 200 GeV
We present the results of an elliptic flow analysis of Cu+Cu collisions
recorded with the STAR detector at 62.4 and 200GeV. Elliptic flow as a function
of transverse momentum is reported for different collision centralities for
charged hadrons and strangeness containing hadrons , ,
, in the midrapidity region . Significant reduction in
systematic uncertainty of the measurement due to non-flow effects has been
achieved by correlating particles at midrapidity, , with those at
forward rapidity, . We also present azimuthal correlations in
p+p collisions at 200 GeV to help estimating non-flow effects. To study the
system-size dependence of elliptic flow, we present a detailed comparison with
previously published results from Au+Au collisions at 200 GeV. We observe that
() of strange hadrons has similar scaling properties as were
first observed in Au+Au collisions, i.e.: (i) at low transverse momenta,
, scales with transverse kinetic energy, , and
(ii) at intermediate , , it scales with the number of
constituent quarks, . We have found that ideal hydrodynamic calculations
fail to reproduce the centrality dependence of () for
and . Eccentricity scaled values, , are larger
in more central collisions, suggesting stronger collective flow develops in
more central collisions. The comparison with Au+Au collisions which go further
in density shows depend on the system size, number of
participants . This indicates that the ideal hydrodynamic limit is
not reached in Cu+Cu collisions, presumably because the assumption of
thermalization is not attained.Comment: 18 pages, 14 figure
Identified high- spectra in Cu+Cu collisions at =200 GeV
We report new results on identified (anti)proton and charged pion spectra at
large transverse momenta (3<<10 GeV/c) from Cu+Cu collisions at
=200 GeV using the STAR detector at the Relativistic Heavy Ion
Collider (RHIC). This study explores the system size dependence of two novel
features observed at RHIC with heavy ions: the hadron suppression at
high- and the anomalous baryon to meson enhancement at intermediate
transverse momenta. Both phenomena could be attributed to the creation of a new
form of QCD matter. The results presented here bridge the system size gap
between the available pp and Au+Au data, and allow the detailed exploration for
the on-set of the novel features. Comparative analysis of all available 200 GeV
data indicates that the system size is a major factor determining both the
magnitude of the hadron spectra suppression at large transverse momenta and the
relative baryon to meson enhancement.Comment: Submitted to Phys. Rev. C, 9 pages, 5 figure
Strangeness Enhancement in Cu+Cu and Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV
We report new STAR measurements of mid-rapidity yields for the ,
, , , , ,
particles in Cu+Cu collisions at \sNN{200}, and mid-rapidity
yields for the , , particles in Au+Au at
\sNN{200}. We show that at a given number of participating nucleons, the
production of strange hadrons is higher in Cu+Cu collisions than in Au+Au
collisions at the same center-of-mass energy. We find that aspects of the
enhancement factors for all particles can be described by a parameterization
based on the fraction of participants that undergo multiple collisions
Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at = 200 GeV
Forward-backward multiplicity correlation strengths have been measured with
the STAR detector for Au+Au and collisions at =
200 GeV. Strong short and long range correlations (LRC) are seen in central
Au+Au collisions. The magnitude of these correlations decrease with decreasing
centrality until only short range correlations are observed in peripheral Au+Au
collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate
(CGC) predict the existence of the long range correlations. In the DPM the
fluctuation in the number of elementary (parton) inelastic collisions produces
the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is
in qualitative agreement with the predictions from the DPM and indicates the
presence of multiple parton interactions.Comment: 6 pages, 3 figures The abstract has been slightly modifie
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