3,895 research outputs found
Galaxy properties in clusters. II. Backsplash Galaxies
We explore the properties of galaxies on the outskirts of clusters and their
dependence on recent dynamical history in order to understand the real impact
that the cluster core has on the evolution of galaxies. We analyse the
properties of more than 1000 galaxies brighter than =-19.6 on the
outskirts of 90 clusters () in the redshift range .
Using the line of sight velocity, we selected high and low velocity subsamples.
Theoretical predictions indicate that a significant fraction of the first
subsample should be backsplash galaxies, that is, objects that have already
orbited near the cluster centre. A significant proportion of the sample of high
relative velocity HV galaxies seems to be composed of infalling objects. Our
results suggest that, at fixed stellar mass, late type galaxies in the low
velocity LV sample are systematically older, redder and have formed fewer stars
during the last 3 Gyrs than galaxies in the HV sample. This result is
consistent with models that assume that the central regions of clusters are
effective in quenching the star formation by means of processes such as ram
pressure stripping or strangulation. At fixed stellar mass, LV galaxies show
some evidence of having higher surface brightness and smaller size than HV
galaxies. These results are consistent with the scenario where galaxies that
have orbited the central regions of clusters are more likely to suffer tidal
effects, producing loss of mass as well as a redistribution of matter towards
more compact configurations. Finally, we found a higher fraction of ET galaxies
in the LV sample, supporting the idea that the central region of clusters of
galaxies may contribute to the transformation of morphological types towards
earlier types.Comment: Accepted for publication in Astronomy & Astrophysics (A&A
The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z=0.343
The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources
that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE
gamma-rays, which allowed constraining the redshift of PKS 0447-439 by
considering the attenuation caused by gamma-ray interactions with ambient
photons in the extragalactic background light (EBL). This constraint agreed
with color-magnitude and spectroscopic redshift constraints (0.179 < z < 0.56),
Recently, however, a much higher redshift was proposed for this blazar (z >
1.2). This value was debated because if true, it would imply either that the
relevant absorption processes of gamma-rays are not well understood or that the
EBL is dramatically different from what is believed today. This high redshift
was not confirmed by three independent new spectroscopic observations at high
signal-to-noise ratios.
Given that BL-Lac are typically hosted by elliptical galaxies, which in turn
are associated with groups, we aim to find the host group of galaxies of PKS
0447-439. The ultimate goal is to estimate a redshift for this blazar.
Spectra of twenty-one objects in the field of view of PKS 0447-439 were
obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and
coordinates of these galaxies, we searched for groups of galaxies. Using a deep
catalog of groups, we studied the probability of finding by chance a group of
galaxies in the line of sight of PKS 0447-439.
We identified a group of galaxies that was not previously cataloged at z =
0.343 with seven members, a virial radius of 0.42 Mpc, and a velocity
dispersion of 622 km s^-1. We found that the probability of the host galaxy of
PKS 0447-439 to be a member of the new group is >= 97%. Therefore, we propose
to adopt z = 0.343 +- 0.002 as the most likely redshift for PKS 0447-439.Comment: Accepted for publication in A&
On some new approaches to practical Slepian-Wolf compression inspired by channel coding
This paper considers the problem, first introduced by Ahlswede and Körner in 1975, of lossless source coding with coded side information. Specifically, let X and Y be two random variables such that X is desired losslessly at the decoder while Y serves as side information. The random variables are encoded independently, and both descriptions are used by the decoder to reconstruct X. Ahlswede and Körner describe the achievable rate region in terms of an auxiliary random variable. This paper gives a partial solution for the optimal auxiliary random variable, thereby describing part of the rate region explicitly in terms of the distribution of X and Y
Bolivian sub-national revenues: A review
This papers reviews main topics concerning sub-national revenues (intergovernmental transfers and taxes) and discusses some policy options to develop own sub-national revenues. The review covers the political-legal framework and the fiscal outcomes, finding that: i) intergovernmental transfers policies have expanded over time, generating inequity problems, principally at the departmental level; ii) sub-national revenues depend mostly on intergovernmental transfers; this has generated high levels of vertical imbalances, mainly for department governments whose revenues rely mostly on the hydrocarbons sector; and iii) lack of adequate tax policies that promote fiscal effort and equity led to large horizontal imbalances in municipal per capita tax collection, unrelated to poverty or human development differences. In this regard, policy options were discussed to increase own sub-national revenues, taking into account political and social discussions, the economic, fiscal and legal base, and relevant tax principles. The main recommendations are: i) to promote in-kind contributions (materials and labour) at the municipal level, especially in poor rural municipalities; ii) to improve municipal tax administration supporting the continuation of the RUAT's work and improving the registry with the new census; and iii) to evaluate the possibility of redefining the RC-IVA as a personal income tax shared between the central government and the departments
- …