296 research outputs found
Mylk3 null C57BL/6N mice develop cardiomyopathy, whereas Nnt null C57BL/6J mice do not.
The C57BL/6J and C57BL/6N mice have well-documented phenotypic and genotypic differences, including the infamous nicotinamide nucleotide transhydrogenase (Nnt) null mutation in the C57BL/6J substrain, which has been linked to cardiovascular traits in mice and cardiomyopathy in humans. To assess whether Nnt loss alone causes a cardiovascular phenotype, we investigated the C57BL/6N, C57BL/6J mice and a C57BL/6J-BAC transgenic rescuing NNT expression, at 3, 12, and 18 mo. We identified a modest dilated cardiomyopathy in the C57BL/6N mice, absent in the two B6J substrains. Immunofluorescent staining of cardiomyocytes revealed eccentric hypertrophy in these mice, with defects in sarcomere organisation. RNAseq analysis identified differential expression of a number of cardiac remodelling genes commonly associated with cardiac disease segregating with the phenotype. Variant calling from RNAseq data identified a myosin light chain kinase 3 (Mylk3) mutation in C57BL/6N mice, which abolishes MYLK3 protein expression. These results indicate the C57BL/6J Nnt-null mice do not develop cardiomyopathy; however, we identified a null mutation in Mylk3 as a credible cause of the cardiomyopathy phenotype in the C57BL/6N
Evolved stars hint to an external origin of enhanced metallicity in planet-hosting stars
Exo-planets are preferentially found around high metallicity main sequence
stars. We aim at investigating whether evolved stars share this property, and
what this tells about planet formation. Statistical tools and the basic
concepts of stellar evolution theory are applied to published results as well
as our own radial velocity and chemical analyses of evolved stars. We show that
the metal distributions of planet-hosting (P-H) dwarfs and giants are
different, and that the latter do not favor metal-rich systems. Rather, these
stars follow the same age-metallicity relation as the giants without planets in
our sample. The straightforward explanation is to attribute the difference
between dwarfs and giants to the much larger masses of giants' convective
envelopes. If the metal excess on the main sequence is due to pollution, the
effects of dilution naturally explains why it is not observed among evolved
stars. Although we cannot exclude other explanations, the lack of any
preference for metal-rich systems among P-H giants could be a strong indication
of the accretion of metal-rich material. We discuss further tests, as well as
some predictions and consequences of this hypothesis.Comment: A&A, in pres
The Spatial Clustering of ROSAT All-Sky Survey AGNs II. Halo Occupation Distribution Modeling of the Cross Correlation Function
This is the second paper of a series that reports on our investigation of the
clustering properties of AGNs in the ROSAT All-Sky Survey (RASS) through
cross-correlation functions (CCFs) with Sloan Digital Sky Survey (SDSS)
galaxies. In this paper, we apply the Halo Occupation Distribution (HOD) model
to the CCFs between the RASS Broad-line AGNs with SDSS Luminous Red Galaxies
(LRGs) in the redshift range 0.16<z<0.36 that was calculated in paper I. In our
HOD modeling approach, we use the known HOD of LRGs and constrain the HOD of
the AGNs by a model fit to the CCF. For the first time, we are able to go
beyond quoting merely a `typical' AGN host halo mass, M_h, and model the full
distribution function of AGN host dark matter halos. In addition, we are able
to determine the large-scale bias and the mean M_h more accurately. We explore
the behavior of three simple HOD models. Our first model (Model A) is a
truncated power-law HOD model in which all AGNs are satellites. With this
model, we find an upper limit to the slope (\alpha) of the AGN HOD that is far
below unity. The other two models have a central component, which has a step
function form, where the HOD is constant above a minimum mass, without (Model
B) or with (Model C) an upper mass cutoff, in addition to the truncated
power-law satellite component, similar to the HOD that is found for galaxies.
In these two models we find the upper limits of \alpha < 0.95 and \alpha < 0.84
for Model B and C respectively. Our analysis suggests that the satellite AGN
occupation increases slower than, or may even decrease with, M_h, in contrast
to the satellite's HODs of luminosity-threshold samples of galaxies, which, in
contrast, grow approximately as \propto M_h^\alpha with \alpha\approx 1. These
results are consistent with observations that the AGN fraction in groups and
clusters decreases with richness.Comment: 15 pages, 9 figures. ApJ in pres
From Galaxy Clusters to Ultra-Faint Dwarf Spheroidals: A Fundamental Curve Connecting Dispersion-supported Galaxies to Their Dark Matter Halos
We examine scaling relations of dispersion-supported galaxies over more than
eight orders of magnitude in luminosity by transforming standard fundamental
plane parameters into a space of mass (M1/2), radius (r1/2), and luminosity
(L1/2). We find that from ultra-faint dwarf spheroidals to giant cluster
spheroids, dispersion-supported galaxies scatter about a one-dimensional
"fundamental curve" through this MRL space. The weakness of the M1/2-L1/2 slope
on the faint end may imply that potential well depth limits galaxy formation in
small galaxies, while the stronger dependence on L1/2 on the bright end
suggests that baryonic physics limits galaxy formation in massive galaxies. The
mass-radius projection of this curve can be compared to median dark matter halo
mass profiles of LCDM halos in order to construct a virial mass-luminosity
relationship (Mvir-L) for galaxies that spans seven orders of magnitude in
Mvir. Independent of any global abundance or clustering information, we find
that (spheroidal) galaxy formation needs to be most efficient in halos of Mvir
~ 10^12 Msun and to become inefficient above and below this scale. Moreover,
this profile matching technique is most accurate at the high and low luminosity
extremes (where dark matter fractions are highest) and is therefore quite
complementary to statistical approaches that rely on having a well-sampled
luminosity function. We also consider the significance and utility of the
scatter about this relation, and find that in the dSph regime observational
errors are almost at the point where we can explore the intrinsic scatter in
the luminosity-virial mass relation. Finally, we note that purely stellar
systems like Globular Clusters and Ultra Compact Dwarfs do not follow the
fundamental curve relation. This allows them to be easily distinguished from
dark-matter dominated dSph galaxies in MRL space. (abridged)Comment: 27 pages, 18 figures, ApJ accepted. High-res movies of 3D figures are
available at http://www.physics.uci.edu/~bullock/fcurve/movies.htm
Modelling non-linear redshift-space distortions in the galaxy clustering pattern: systematic errors on the growth rate parameter
We investigate the ability of state-of-the-art redshift-space distortions
models for the galaxy anisotropic two-point correlation function \xi(r_p, \pi),
to recover precise and unbiased estimates of the linear growth rate of
structure f, when applied to catalogues of galaxies characterised by a
realistic bias relation. To this aim, we make use of a set of simulated
catalogues at z = 0.1 and z = 1 with different luminosity thresholds, obtained
by populating dark-matter haloes from a large N-body simulation using halo
occupation prescriptions. We examine the most recent developments in
redshift-space distortions modelling, which account for non-linearities on both
small and intermediate scales produced respectively by randomised motions in
virialised structures and non-linear coupling between the density and velocity
fields. We consider the possibility of including the linear component of galaxy
bias as a free parameter and directly estimate the growth rate of structure f.
Results are compared to those obtained using the standard dispersion model,
over different ranges of scales.We find that the model of Taruya et al. (2010),
the most sophisticated one considered in this analysis, provides in general the
most unbiased estimates of the growth rate of structure, with systematic errors
within 4% over a wide range of galaxy populations spanning luminosities between
L > L* and L > 3L*. The scale-dependence of galaxy bias plays a role on
recovering unbiased estimates of f when fitting quasi non-linear scales. Its
effect is particularly severe for most luminous galaxies, for which systematic
effects in the modelling might be more difficult to mitigate and have to be
further investigated. [...]Comment: 17 pages, 16 figures, Accepted for publication in MNRA
A group-galaxy cross-correlation function analysis in zCOSMOS
We present a group-galaxy cross-correlation analysis using a group catalog
produced from the 16,500 spectra from the optical zCOSMOS galaxy survey. Our
aim is to perform a consistency test in the redshift range 0.2 < z < 0.8
between the clustering strength of the groups and mass estimates that are based
on the richness of the groups. We measure the linear bias of the groups by
means of a group-galaxy cross-correlation analysis and convert it into mass
using the bias-mass relation for a given cosmology, checking the systematic
errors using realistic group and galaxy mock catalogs. The measured bias for
the zCOSMOS groups increases with group richness as expected by the theory of
cosmic structure formation and yields masses that are reasonably consistent
with the masses estimated from the richness directly, considering the scatter
that is obtained from the 24 mock catalogs. An exception are the richest groups
at high redshift (estimated to be more massive than 10^13.5 M_sun), for which
the measured bias is significantly larger than for any of the 24 mock catalogs
(corresponding to a 3-sigma effect), which is attributed to the extremely large
structure that is present in the COSMOS field at z ~ 0.7. Our results are in
general agreement with previous studies that reported unusually strong
clustering in the COSMOS field.Comment: 13 pages, 9 figures, published in Ap
Connecting stellar mass and star-formation rate to dark matter halo mass out to z ~ 2
We have constructed an extended halo model (EHM) which relates the total
stellar mass and star-formation rate (SFR) to halo mass (M_h). An empirical
relation between the distribution functions of total stellar mass of galaxies
and host halo mass, tuned to match the spatial density of galaxies over 0<z<2
and the clustering properties at z~0, is extended to include two different
scenarios describing the variation of SFR on M_h. We also present new
measurements of the redshift evolution of the average SFR for star-forming
galaxies of different stellar mass up to z=2, using data from the Herschel
Multi-tiered Extragalactic Survey (HerMES) for infrared-bright galaxies.
Combining the EHM with the halo accretion histories from numerical
simulations, we trace the stellar mass growth and star-formation history in
halos spanning a range of masses. We find that: (1) The intensity of the
star-forming activity in halos in the probed mass range has steadily decreased
from z~2 to 0; (2) At a given epoch, halos in the mass range between a few
times 10^{11} M_Sun and a few times 10^{12} M_Sun are the most efficient at
hosting star formation; (3) The peak of SFR density shifts to lower mass halos
over time; (4) Galaxies that are forming stars most actively at z~2 evolve into
quiescent galaxies in today's group environments, strongly supporting previous
claims that the most powerful starbursts at z~2 are progenitors of today's
elliptical galaxies.Comment: 15 pages, 12 figures, accepted for publication in MNRA
The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z 1
We model the evolution of the mean galaxy occupation of dark-matter halos
over the range , using the data from the VIMOS-VLT Deep Survey
(VVDS). The galaxy projected correlation function was computed for a
set of luminosity-limited subsamples and fits to its shape were obtained using
two variants of Halo Occupation Distribution models. These provide us with a
set of best-fitting parameters, from which we obtain the average mass of a halo
and average number of galaxies per halo. We find that after accounting for the
evolution in luminosity and assuming that we are largely following the same
population, the underlying dark matter halo shows a growth in mass with
decreasing redshift as expected in a hierarchical structure formation scenario.
Using two different HOD models, we see that the halo mass grows by 90% over the
redshift interval z=[0.5,1.0]. This is the first time the evolution in halo
mass at high redshifts has been obtained from a single data survey and it
follows the simple form seen in N-body simulations with , and . This provides evidence for a rapid accretion
phase of massive halos having a present-day mass , with a merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z 1.0 to z
0.5, with a sharp increase by a factor 3 from z 0.5 to z 0.1,
likely due to the dynamical friction of subhalos within their host halos.Comment: 14 pages, 6 figures, 5 tables. MNRAS accepted
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
Control of ventricular excitability by neurons of the dorsal motor nucleus of the vagus nerve
Background The central nervous origins of functional parasympathetic innervation of cardiac ventricles remain controversial. Objective This study aimed to identify a population of vagal preganglionic neurons that contribute to the control of ventricular excitability. An animal model of synuclein pathology relevant to Parkinson’s disease was used to determine whether age-related loss of the activity of the identified group of neurons is associated with changes in ventricular electrophysiology. Methods In vivo cardiac electrophysiology was performed in anesthetized rats in conditions of selective inhibition of the dorsal vagal motor nucleus (DVMN) neurons by pharmacogenetic approach and in mice with global genetic deletion of all family members of the synuclein protein. Results In rats anesthetized with urethane (in conditions of systemic beta-adrenoceptor blockade), muscarinic and neuronal nitric oxide synthase blockade confirmed the existence of a tonic parasympathetic control of cardiac excitability mediated by the actions of acetylcholine and nitric oxide. Acute DVMN silencing led to shortening of the ventricular effective refractory period (vERP), a lowering of the threshold for triggered ventricular tachycardia, and prolongation of the corrected QT (QTc) interval. Lower resting activity of the DVMN neurons in aging synuclein-deficient mice was found to be associated with vERP shortening and QTc interval prolongation. Conclusion Activity of the DVMN vagal preganglionic neurons is responsible for tonic parasympathetic control of ventricular excitability, likely to be mediated by nitric oxide. These findings provide the first insight into the central nervous substrate that underlies functional parasympathetic innervation of the ventricles and highlight its vulnerability in neurodegenerative diseases
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