37 research outputs found
Inter-vehicle Communication: Quo Vadis. Report from Dagstuhl Seminar 13392
"Inter-Vehicular Communication - Quo Vadis?". With this question in mind, leading experts in the field of vehicular networking met in Dagstuhl to discuss the current state of the art and, most importantly, the open challenges in R&D from both an scientific and an industry point of view. After more than a decade of research on vehicular networks, the experts very seriously asked the question whether all of the initial research issues had been solved so far. It turned out that the perspective changed in the last few years, mainly thanks to the ongoing field operational tests in Europe and the U.S. The results point to new research directions and new challenges that need to be solved for a second generation of vehicular networking applications and protocols. In four working groups, the experts studied these new challenges and derived recommendations that are also very helpful for the respective funding organizations
The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters
AIMS: We present in this work low and intermediate resolution spectroscopic
data collected for 152 early type galaxies in 8 nearby clusters with z
0.10.
METHODS: We use low resolution data to produce the redshift and the
K-correction for every individual galaxy, as well as to give their overall
spectral energy distribution, and some spectral indicators, including the
4000\AA break, the Mg strength, and the NaD equivalent width.We have also
obtained higher resolution data for early type galaxies in three of the
clusters, to determine their central velocity dispersion.
RESULTS: The effect of the resolution on the measured parameters is
discussed.
CONCLUSIONS: New accurate systemic redshift and velocity dispersion is
presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39.
We have found that the K-correction values for E/S0 bright galaxies in a given
nearby clusters are very similar. We also find that the distribution of the
line indicators significantly differ from cluster to cluster.Comment: 16 pages, 9 figures, Accepted in A&
PMN J1838-3427: A new gravitationally lensed quasar
We report the discovery of a new double-image quasar that was found during a
search for gravitational lenses in the southern sky. Radio source PMN
J1838-3427 is composed of two flat-spectrum components with separation 1", flux
density ratio 14:1 and matching spectral indices, in VLA and VLBA images.
Ground-based BRI images show the optical counterpart (total I=18.6) is also
double with the same separation and position angle as the radio components. An
HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is
higher than the radio value probably due to differential extinction of the
components by the lens galaxy. An optical spectrum of the bright component
contains quasar emission lines at z=2.78 and several absorption features,
including prominent Ly-alpha absorption. The lens galaxy redshift could not be
measured but is estimated to be z=0.36 +/- 0.08. The image configuration is
consistent with the simplest plausible models for the lens potential. The flat
radio spectrum and observed variability of PMN J1838-3427 suggest the time
delay between flux variations of the components is measurable, and could thus
provide an independent measurement of H_0.Comment: 23 pages, incl. 6 figures, to appear in A.J.; replaced with accepted
version; minor changes to text, improved figure
Quantifying the Importance of Ram Pressure Stripping in a Galaxy Group at 100 Mpc
We examine two members of the NGC 4065 group of galaxies: a bent-double
(a.k.a. wide angle tail) radio source and an HI deficient spiral galaxy. Models
of the X-ray emitting intragroup gas and the bent-double radio source, NGC
4061, are used to probe the density of intergalactic gas in this group. HI
observations reveal an asymmetric, truncated distribution of neutral gas in
spiral galaxy, UGC 07049, and the accompanying radio continuum emission reveals
strong star formation. We examine the effectiveness of ram pressure stripping
as a gas removal mechanism and find that it alone cannot account for the HI
deficiency that is observed in UGC 07049 unless this galaxy has passed through
the core of the group with a velocity of ~800 km/s. A combination of tidal and
ram pressure stripping are necessary to produce the HI deficiency and asymmetry
in this galaxy.Comment: 8 pages, 6 figures, MNRAS accepte
The isolated elliptical NGC 4555 observed with Chandra
We present analysis of a Chandra observation of the elliptical galaxy NGC
4555. The galaxy lies in a very low density environment, either isolated from
all galaxies of similar mass or on the outskirts of a group. Despite this, NGC
4555 has a large gaseous halo, extending to ~60 kpc. We find the mean gas
temperature to be ~0.95 keV and the Iron abundance to be ~0.5 solar. We model
the surface brightness, temperature and abundance distribution of the halo and
use these results to estimate parameters such as the entropy and cooling time
of the gas, and the total gravitational mass of the galaxy. In contrast to
recent results showing that moderate luminosity ellipticals contain relatively
small quantities of dark matter, our results show that NGC 4555 has a massive
dark halo and large mass-to-light ratio (56.8 [+34.2,-35.8] solar at 50 kpc,
42.7 [+14.6,-21.2] solar at 5 effective radii, 1 sigma errors). We discuss this
disparity and consider possible mechanisms by which galaxies might reduce their
dark matter content.Comment: 10 pages, 7 postscript figures, accepted for publication in MNRA
Intragroup diffuse light in compact groups of galaxies II. HCG 15, 35 and 51
This continuing study of intragroup light in compact groups of galaxies aims
to establish new constraints to models of formation and evolution of galaxy
groups, specially of compact groups, which are a key part in the evolution of
larger structures, such as clusters. In this paper we present three additional
groups (HCG 15, 35 and 51) using deep wide field and band images
observed with the LAICA camera at the 3.5m telescope at the Calar Alto
observatory (CAHA). This instrument provides us with very stable flatfielding,
a mandatory condition for reliably measuring intragroup diffuse light. The
images were analyzed with the OV\_WAV package, a wavelet technique that allows
us to uncover the intragroup component in an unprecedented way. We have
detected that 19, 15 and 26% of the total light of HCG 15, 35 and 51,
respectively, is in the diffuse component, with colours that are compatible
with old stellar populations and with mean surface brightness that can be as
low as . Dynamical masses, crossing times and
mass to light ratios were recalculated using the new group parameters. Also
tidal features were analyzed using the wavelet technique.Comment: 12 pages, 5 figures. Accepted for publication in MNRAS. See
http://www.eso.org/~cdarocha/publications/DaRochaetal2008_IGL_HCG.pdf for
full resolution version. Complementary reference adde
Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxy
catalogue (Falco 1999) we have identified 291 compact groups (CGs) with
redshifts between 1000 and 10000 km/s. The sample is analysed to investigate
whether Triplets display kinematical and morphological characteristics similar
to higher order CGs (Multiplets). It is found that Triplets constitute low
velocity dispersion structures, have a gas-rich galaxy population and are
typically retrieved in sparse environments. Conversely Multiplets show higher
velocity dispersion, include few gas-rich members and are generally embedded
structures. Evidence hence emerges indicating that Triplets and Multiplets,
though sharing a common scale, correspond to different galaxy systems. Triplets
are typically field structures whilst Multiplets are mainly subclumps (either
temporarily projected or collapsing) within larger structures. Simulations show
that selection effects can only partially account for differences, but
significant contamination of Triplets by field galaxy interlopers could
eventually induce the observed dependences on multiplicity.Comment: 13 pages, 12 figures. The file is in latex (A & A style) format. The
figures are in postscript. A & A accepte
The Dynamical Status of the Cluster of Galaxies 1E0657-56
We present the results of a new spectroscopic and photometric survey of the
hot X-ray cluster 1E0657-56, at z=0.296. We determine the presence of a low
velocity dispersion subcluster, which is offset from the main cluster position
by 0.7 Mpc and about 600 km/s. We determine the virial masses and total
luminosities of the cluster and its subcluster, and solve for the two-body
dynamical model. With additional constraints from the results of the analysis
of the cluster X-ray emission by Markevitch et al. (2001), we find that the
subcluster passed through the cluster centre about 0.15 Gyr ago. Taken at face
value the mass of the subcluster is typical of a loose group. It is however
difficult to establish the pre-merger mass of the colliding system. We provide
tentative evidence that the subcluster is in fact the remnant core of a
moderately massive cluster, stripped by the collision with 1E0657-56. The main
cluster dynamics does not seem to have suffered from this collision. On the
contrary, the cluster X-ray properties seem to have been significantly
affected. We also discuss the effect of the subcluster collision in relation to
starburst events and the cluster radio halo.Comment: Accepted for publication on A&
The architecture of Abell 1386 and its relationship to the Sloan Great Wall
We present new radial velocities from AAOmega on the Anglo-Australian
Telescope for 307 galaxies (b_J < 19.5) in the region of the rich cluster Abell
1386. Consistent with other studies of galaxy clusters that constitute
sub-units of superstructures, we find that the velocity distribution of A1386
is very broad (21,000--42,000 kms^-1, or z=0.08--0.14) and complex. The mean
redshift of the cluster that Abell designated as number 1386 is found to be
~0.104. However, we find that it consists of various superpositions of
line-of-sight components. We investigate the reality of each component by
testing for substructure and searching for giant elliptical galaxies in each
and show that A1386 is made up of at least four significant clusters or groups
along the line of sight whose global parameters we detail. Peculiar velocities
of brightest galaxies for each of the groups are computed and found to be
different from previous works, largely due to the complexity of the sky area
and the depth of analysis performed in the present work. We also analyse A1386
in the context of its parent superclusters: Leo A, and especially the Sloan
Great Wall. Although the new clusters may be moving toward mass concentrations
in the Sloan Great Wall or beyond, many are most likely not yet physically
bound to it.Comment: 21 pages, 9 figures, includes the full appendix table. Accepted for
publication in MNRA