7,295 research outputs found
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
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
Large-to small-scale dynamo in domains of large aspect ratio: kinematic regime
The Sun’s magnetic field exhibits coherence in space and time on much larger scales than
the turbulent convection that ultimately powers the dynamo. In this work, we look for numerical
evidence of a large-scale magnetic field as the magnetic Reynolds number, Rm, is
increased. The investigation is based on the simulations of the induction equation in elongated
periodic boxes. The imposed flows considered are the standard ABC flow (named after
Arnold, Beltrami & Childress) with wavenumber ku = 1 (small-scale) and a modulated ABC
flow with wavenumbers ku = m, 1, 1 ± m, where m is the wavenumber corresponding to
the long-wavelength perturbation on the scale of the box. The critical magnetic Reynolds
number Rcrit
m decreases as the permitted scale separation in the system increases, such that
Rcrit
m ∝ [Lx /Lz]
−1/2. The results show that the α-effect derived from the mean-field theory
ansatz is valid for a small range of Rm after which small scale dynamo instability occurs and the
mean-field approximation is no longer valid. The transition from large- to small-scale dynamo
is smooth and takes place in two stages: a fast transition into a predominantly small-scale
magnetic energy state and a slower transition into even smaller scales. In the range of Rm
considered, the most energetic Fourier component corresponding to the structure in the long
x-direction has twice the length-scale of the forcing scale. The long-wavelength perturbation
imposed on the ABC flow in the modulated case is not preserved in the eigenmodes of the
magnetic field
Relevance of the purity level in a MetalOrganic Vapour Phase Epitaxy reactor environment for the growth of high quality pyramidal sitecontrolled Quantum Dots
We report in this work on the spectral purity of pyramidal site-controlled
InGaAs/AlGaAs Quantum Dots grown by metalorganic vapour phase epitaxy on(111)B
oriented GaAs substrates. Extremely sharp emission peaks were found, showing
linewidths surprisingly narrow (~27{\mu}eV) and comparable to those which can
be obtained by Molecular Beam Epitaxy in an ultra-high vacuum environment. A
careful reactor handling is regarded as a crucial step toward the fabrication
of high optical quality systems.Comment: ICMOVPE 2010 Proceedin
Multiport VNA Measurements
This article presents some of the most recent multiport VNA measurement methodologies used to characterize these highspeed digital networks for signal integrity. There will be a discussion of the trends and measurement challenges of high-speed digital systems, followed by a presentation of the multiport VNA measurement system details, calibration, and measurement techniques, as well as some examples of interconnect device measurements. The intent here is to present some general concepts and trends for multiport VNA measurements as applied to computer system board-level interconnect structures, and not to promote any particular brand or produc
Clarifying spherical collapse in coupled dark energy cosmologies
The spherical collapse model is often used to follow the evolution of
overdensities into the nonlinear regime. We describe the correct approach to be
used in coupled dark energy cosmologies, where a fifth force, different from
gravity and mediated by the dark energy scalar field, influences the collapse.
We reformulate the spherical collapse description by deriving it directly from
the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with
the corresponding relativistic equations, we show how the fifth force should be
taken into account within the spherical collapse picture and clarify the
problems arising when an inhomogeneous scalar field is considered within a
spherical collapse picture. We then apply our method to the case of coupled
quintessence, where the fifth force acts among cold dark matter particles, and
to growing neutrino quintessence, where the fifth force acts between neutrinos.
Furthermore, we review this method when applied to standard cosmologies and
apply our analysis to minimally coupled quintessence and check past results for
early dark energy parametrizations.Comment: 16 pages, 13 figures, published in Physical Review D, minor changes
and correction
Testing coupled dark energy with next-generation large-scale observations
Coupling dark energy to dark matter provides one of the simplest way to
effectively modify gravity at large scales without strong constraints from
local (i.e. solar system) observations. Models of coupled dark energy have been
studied several times in the past and are already significantly constrained by
cosmic microwave background experiments. In this paper we estimate the
constraints that future large-scale observations will be able to put on the
coupling and in general on all the parameters of the model. We combine cosmic
microwave background, tomographic weak lensing, redshift distortions and power
spectrum probes. We show that next-generation observations can improve the
current constraint on the coupling to dark matter by two orders of magnitude;
this constraint is complementary to the current solar-system bounds on a
coupling to baryons.Comment: 18 pages, 12 figs, 8 table
An assessment of the genus Columbella Lamarck, 1799 (Gastropoda: Columbellidae) from eastern Atlantic
Three species of the neogastropod genus Columbella Lamarck, 1799 are recognised from the northeastern Atlantic and the Mediterranean. One is the common Mediterranean C. rustica (Linnaeus, 1758), with
paucispiral protoconch, extending its range in the Atlantic South to Senegal and North to Portugal. Columbella adansoni Menke, 1853, with multispiral protoconch is restricted to the Macaronesian archipelagoes. A third species, also with multispiral protoconch, from West Africa is recognised through molecular methods, and the name C. xiphitella Duclos, 1840 is employed by correcting the original erroneous locality (“Californie”) to Gabon. Except for protoconch features, no major morphological characters are available to separate the three species; however diagnostic species-level differences in specific positions in the cytochrome c oxidase I (COI) sequences are present between all three species
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