818 research outputs found
Overlapping functions of the cell adhesion molecules Nr-CAM and L1 in cerebellar granule cell development
The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patterns in cerebellar granule cells. Here we analyzed their involvement in granule cell development using mutant mice. Nr-CAM–deficient cerebellar granule cells failed to extend neurites in vitro on contactin, a known ligand for Nr-CAM expressed in the cerebellum, confirming that these mice are functionally null for Nr-CAM. In vivo, Nr-CAM–null cerebella did not exhibit obvious histological defects, although a mild size reduction of several lobes was observed, most notably lobes IV and V in the vermis. Mice deficient for both L1 and Nr-CAM exhibited severe cerebellar folial defects and a reduction in the thickness of the inner granule cell layer. Additionally, anti-L1 antibodies specifically disrupted survival and maintenance of Nr-CAM–deficient granule cells in cerebellar cultures treated with antibodies. The combined results indicate that Nr-CAM and L1 play a role in cerebellar granule cell development, and suggest that closely related molecules in the L1 family have overlapping functions
Witnessing the active assembly phase of massive galaxies since z = 1
We present an analysis of ~60 000 massive (stellar mass M_star > 10^{11}
M_sun) galaxies out to z = 1 drawn from 55.2 deg2 of the United Kingdom
Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) and the Sloan
Digital Sky Survey (SDSS) II Supernova Survey. This is by far the largest
survey of massive galaxies with robust mass estimates, based on infrared
(K-band) photometry, reaching to the Universe at about half its present age. We
find that the most massive (M_star > 10^{11.5} M_sun) galaxies have experienced
rapid growth in number since z = 1, while the number densities of the less
massive systems show rather mild evolution. Such a hierarchical trend of
evolution is consistent with the predictions of the current semi-analytic
galaxy formation model based on Lambda CDM theory. While the majority of
massive galaxies are red-sequence populations, we find that a considerable
fraction of galaxies are blue star-forming galaxies. The blue fraction is
smaller in more massive systems and decreases toward the local Universe,
leaving the red, most massive galaxies at low redshifts, which would support
the idea of active 'bottom-up' formation of these populations during 0 < z < 1.Comment: Accepted for publication in MNRAS; replaced with revised version
(minor changes in results and wordings); MNRAS online early version availabl
Autocorrelations of stellar light and mass at z~0 and ~1: From SDSS to DEEP2
We present measurements of projected autocorrelation functions w_p(r_p) for
the stellar mass of galaxies and for their light in the U, B and V bands, using
data from the third data release of the DEEP2 Galaxy Redshift Survey and the
final data release of the Sloan Digital Sky Survey (SDSS). We investigate the
clustering bias of stellar mass and light by comparing these to projected
autocorrelations of dark matter estimated from the Millennium Simulations (MS)
at z=1 and 0.07, the median redshifts of our galaxy samples. All of the
autocorrelation and bias functions show systematic trends with spatial scale
and waveband which are impressively similar at the two redshifts. This shows
that the well-established environmental dependence of stellar populations in
the local Universe is already in place at z=1. The recent MS-based galaxy
formation simulation of Guo et al. (2011) reproduces the scale-dependent
clustering of luminosity to an accuracy better than 30% in all bands and at
both redshifts, but substantially overpredicts mass autocorrelations at
separations below about 2 Mpc. Further comparison of the shapes of our stellar
mass bias functions with those predicted by the model suggests that both the
SDSS and DEEP2 data prefer a fluctuation amplitude of sigma_8 0.8 rather than
the sigma_8=0.9 assumed by the MS.Comment: 10 pages, 4 figures, accepted for publication in Monthly Notices,
minor revisions in tex
The VIMOS VLT Deep Survey. The Assembly History of the Stellar Mass in Galaxies: from the Young to the Old Universe
We present a detailed analysis of the Galaxy Stellar Mass Function of
galaxies up to z=2.5 as obtained from the VVDS. We estimate the stellar mass
from broad-band photometry using 2 different assumptions on the galaxy star
formation history and show that the addition of secondary bursts to a
continuous star formation history produces systematically higher (up to 40%)
stellar masses. At low redshift (z=0.2) we find a substantial population of
low-mass galaxies (<10^9 Msun) composed by faint blue galaxies (M_I-M_K=0.3).
In general the stellar mass function evolves slowly up to z=0.9 and more
significantly above this redshift. Conversely, a massive tail is present up to
z=2.5 and have extremely red colours (M_I-M_K=0.7-0.8). We find a decline with
redshift of the overall number density of galaxies for all masses (59+-5% for
M>10^8 Msun at z=1), and a mild mass-dependent average evolution
(`mass-downsizing'). In particular our data are consistent with mild/negligible
(6x10^10 Msun). For less
massive systems the no-evolution scenario is excluded. A large fraction (>=50%)
of massive galaxies have been already assembled and converted most of their gas
into stars at z=1, ruling out the `dry mergers' as the major mechanism of their
assembly history below z=1. This fraction decreases to 33% at z=2. Low-mass
systems have decreased continuously in number and mass density (by a factor up
to 4) from the present age to z=2, consistently with a prolonged mass assembly
also at z<1.Comment: 20 pages with 12 encapsulated figures. Version accepted by A&
Measurement of the branching fraction for the decay KS --> pi e nu
We present a measurement of the branching ratio BR(KS --> pi e nu) performed
using the KLOE detector. KS mesons are produced in the reaction e+ e- --> phi
--> KS KL at the DAFNE collider. In a sample of about 5 million KS-tagged
events we find 624 +- 30 semileptonic KS decays. Normalizing to the KS --> pi+
pi- count in the same data sample, we obtain BR(KS --> pi e nu) = (6.91 +-
0.37) 10^-4, in agreement with the Standard Model expectation.Comment: 9 pages, 5 Encapsulated Postscript figures. Submitted to Phys. Lett.
Study of the Decay phi --> eta pi0 gamma with the KLOE detector
In a sample of 5.3x10^7 phi-decays observed with the KLOE detector at the
Frascati phi-factory Dafne we find 605 eta pi0 gamma events with eta -->
gamma\gamma and 197 eta pi0 gamma events with eta --> pi+ pi- pi0. The decay
phi --> eta pi0 gamma is dominated by the process phi --> a0 gamma. From a fit
to the eta pi0 mass spectrum we find BR(phi --> ao(980) gamma)= (7.4 +-
0.7)x10^-5.Comment: 12 pages, 6 figures, submitted to Phys.Lett.
The VIMOS VLT Deep Survey: Tracing the galaxy stellar mass assembly history over the last 8Gyr
We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep
Survey in the redshift interval 0.5<z<1.3. We used the amplitude of the 4000
Balmer break (Dn4000) to separate the galaxy population and the EW[OII]3727
line as proxy for the star formation activity. We discuss to what extent
stellar mass drives galaxy evolution, showing for the first time the interplay
between stellar ages and stellar masses over the past 8Gyr. Low-mass galaxies
have small Dn4000 and at increasing stellar mass, the galaxy distribution moves
to higher Dn4000 values as observed in the local Universe. As cosmic time goes
by, we witness an increasing abundance of massive spectroscopically ET systems
at the expense of the LT systems. This spectral transformation is a process
started at early epochs and continuing efficiently down to the local Universe.
This is confirmed by the evolution of our type-dependent stellar mass function.
The underlying stellar ages of LT galaxies apparently do not show evolution,
likely as a result of a continuous formation of new stars. All star formation
activity indicators consistently point towards a star formation history peaked
in the past for massive galaxies, with little or no residual star formation
taking place in the most recent epochs. The activity and efficiency of forming
stars are mechanisms that depend on stellar mass, and the mass assembly becomes
progressively less efficient in massive systems as time elapses. The concepts
of star formation downsizing and mass assembly downsizing describe a single
scenario that has a top-down evolutionary pattern. The role of (dry) merging
events seems to be only marginal at z<1.3, as our estimated efficiency in
stellar mass assembly can possibly account for the progressive accumulation of
passively evolving galaxies.Comment: Accepted for pubblication in A&A, 14 pages, 5 figure
The zCOSMOS Survey. The dependence of clustering on luminosity and stellar mass at z=0.2-1
We study the dependence of galaxy clustering on luminosity and stellar mass
at redshifts z ~ [0.2-1] using the first zCOSMOS 10K sample.
We measure the redshift-space correlation functions xi(rp,pi) and its
projection wp(rp) for sub-samples covering different luminosity, mass and
redshift ranges. We quantify in detail the observational selection biases and
we check our covariance and error estimate techniques using ensembles of
semi-analytic mock catalogues. We finally compare our measurements to the
cosmological model predictions from the mock surveys.
At odds with other measurements, we find a weak dependence of galaxy
clustering on luminosity in all redshift bins explored. A mild dependence on
stellar mass is instead observed. At z~0.7, wp(rp) shows strong excess power on
large scales. We interpret this as produced by large-scale structure dominating
the survey volume and extending preferentially in direction perpendicular to
the line-of-sight. We do not see any significant evolution with redshift of the
amplitude of clustering for bright and/or massive galaxies.
The clustering measured in the zCOSMOS data at 0.5<z<1 for galaxies with
log(M/M_\odot)>=10 is only marginally consistent with predictions from the mock
surveys. On scales larger than ~2 h^-1 Mpc, the observed clustering amplitude
is compatible only with ~1% of the mocks. Thus, if the power spectrum of matter
is LCDM with standard normalization and the bias has no unnatural
scale-dependence, this result indicates that COSMOS has picked up a
particularly rare, ~2-3 sigma positive fluctuation in a volume of ~10^6 h^-1
Mpc^3. These findings underline the need for larger surveys of the z~1 Universe
to appropriately characterize the level of structure at this epoch.Comment: 18 pages, 21 figures, accepted for publication in Astronomy and
Astrophysic
Lipid Profile and Serum Characteristics of the Blind Subterranean Mole Rat, Spalax
to underground life resulted in structural and molecular-genetic differences comparing to above-ground mammals. These differences include higher myocardial maximal oxygen consumption, increased lung diffusion capacity, increased blood vessels density, and unique expression patterns of cancer and angiogenesis related genes such as heparanase, vascular endothelial growth factor, and P53. revealed special features in this mammal. pursue underground, dietary components, and evolutionary genetic adaptations. Unfolding the genetic basis of these differences will probably result in unique treatments for a variety of human diseases such as dyslipedemias, inflammation and cancer
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
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