5,085 research outputs found
Galaxies infalling into groups: filaments vs. isotropic infall
We perform a comparative analysis of the properties of galaxies infalling
into groups classifying them accordingly to whether they are: falling along
filamentary structures; or they are falling isotropically. For this purpose, we
identify filamentary structures connecting massive groups of galaxies in the
SDSS. We perform a comparative analysis of some properties of galaxies in
filaments, in the isotropic infall region, in the field, and in groups. We
study the luminosity functions (LF) and the dependence of the specific star
formation rate (SSFR) on stellar mass, galaxy type, and projected distance to
the groups that define the filaments. We find that the LF of galaxies in
filaments and in the isotropic infalling region are basically indistinguishable
between them, with the possible exception of late-type galaxies. On the other
hard, regardless of galaxy type, their LFs are clearly different from that of
field or group galaxies. Both of them have characteristic absolute magnitudes
and faint end slopes in between the field and group values. More significant
differences between galaxies in filaments and in the isotropic infall region
are observed when we analyse the SSFR. We find that galaxies in filaments have
a systematically higher fraction of galaxies with low SSFR as a function of
both, stellar mass and distance to the groups, indicating a stronger quenching
of the star formation in the filaments compared to both, the isotropic
infalling region, and the field. Our results suggest that some physical
mechanisms that determine the differences observed between field galaxies and
galaxies in systems, affect galaxies even when they are not yet within the
systems.Comment: Accepted in MNRAS, 10 pages, 8 figure
Comparing galaxy populations in compact and loose groups of galaxies II: brightest group galaxies
The properties of the brightest galaxies (BCGs) are studied in both compact
and loose groups of galaxies in order to better understand the physical
mechanisms influencing galaxy evolution in different environments. Samples of
BCGs are selected in the compact groups identified by McConnachie et al.
(2009), and in loose groups taken from Zandivarez & Mart\'inez (2011). The
following physical properties of the BCGs in compact groups and in subsamples
of loose groups are compared, defined by their mass and total luminosity. The
fraction of BCGs classified as red and/or early-type as a function of galaxy
luminosity are studied. The fraction of the group's total luminosity contained
in the BCG and the difference in luminosity between the BCG and the
second-ranked galaxy, are also analysed. Some properties of BCGs in compact and
loose groups are comparable. However, BCGs in compact groups are systematically
more concentrated and have larger surface brightness than their counterparts in
both, high- and low-mass loose groups. The fractions of red and early-type BCGs
in compact groups are consistent with those of high-mass loose groups.
Comparing BCGs in subsamples of compact and loose groups selected for their
similar luminosities, BCGs in compact groups are found to be, on average,
brighter, more massive, larger, redder and more frequently classified as
elliptical. In compact groups, the BCG contains a larger fraction of the
system's total luminosity and differs more in absolute magnitude from the
second-ranked galaxy. BCGs in compact and loose groups are found to be
different. Some mechanisms responsible for transforming late-type galaxies into
early types, such as mergers, may be more effective within compact groups due
to their high densities and small velocity dispersion, which would lead their
BCGs along somewhat different evolutionary paths.Comment: Accepted for publication in Astronomy & Astrophysics (A&A
On source and channel codes for multiple inputs and outputs: does multiple description beat space time?
We compare two strategies for lossy source description across a pair of unreliable channels. In the first strategy, we use a broadcast channel code to achieve a different rate for each possible channel realization, and then use a multiresolution source code to describe the source at the resulting rates. In the second strategy, we use a channel coding strategy for two independent channels coupled with a multiple description source code. In each case, we choose the coding parameters to minimize the expected end-to-end distortion in the source reconstruction. We demonstrate that in point-to-point communication across a pair of non-ergodic channels, multiple description coding can provide substantial gains relative to multiresolution and broadcast coding. We then investigate this comparison in a simple MIMO channel. We demonstrate the inferior performance of space time coding with multiresolution source coding and broadcast channel coding relative to multiple description codes and a time sharing channel coding strategy. These results indicate that for non-ergodic channels, the traditional definition of channel capacity does not necessarily lead to the best channel code from the perspective of end-to-end source distortion
On the geometry of lambda-symmetries, and PDEs reduction
We give a geometrical characterization of -prolongations of vector
fields, and hence of -symmetries of ODEs. This allows an extension to
the case of PDEs and systems of PDEs; in this context the central object is a
horizontal one-form , and we speak of -prolongations of vector fields
and -symmetries of PDEs. We show that these are as good as standard
symmetries in providing symmetry reduction of PDEs and systems, and explicit
invariant solutions
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