755 research outputs found
Vlinderbloemigen brengen bemesting in evenwicht
Vlinderbloemigen vormen de stikstofbron voor de biologische landbouw. Dit omdat ze in staat zijn stikstof uit de lucht te binden. Voor een duurzame biologische akkerbouw en de groenteteelt zijn ze daarom onontbeerlijk, evenals voor de veehouderij. Uiteindelijk is ook de stikstof uit dierlijke mest in eerste instantie via vlinderbloemigen gebonden
The Evolution of Rest-Frame K-band Properties of Early-Type Galaxies from z=1 to the Present
We measure the evolution of the rest-frame K-band Fundamental Plane from z=1
to the present by using IRAC imaging of a sample of early-type galaxies in the
Chandra Deep Field-South at z~1 with accurately measured dynamical masses. We
find that evolves as , which is
slower than in the B-band (). In the B-band
the evolution has been demonstrated to be strongly mass dependent. In the
K-band we find a weaker trend: galaxies more massive than
evolve as ;
less massive galaxies evolve as . As
expected from stellar population models the evolution in is slower than
the evolution in . However, when we make a quantitative comparison, we
find that the single burst Bruzual-Charlot models do not fit the results well,
unless large dust opacities are allowed at z=1. Models with a flat IMF fit
better, Maraston models with a different treatment of AGB stars fit best. These
results show that the interpretation of rest-frame near-IR photometry is
severely hampered by model uncertainties and therefore that the determination
of galaxy masses from rest-frame near-IR photometry may be harder than was
thought before.Comment: 5 pages, 3 figures, Accepted for publication in ApJ
Symptomatic and functional remission in young adults with a psychotic disorder in a rehabilitation focused team
The aim of this study is to assess symptomatic remission (SR) and functional remission (FR) in a rehabilitation focused program for young adults with a psychotic disorder in the Netherlands, and to investigate which individual and mental health care (MHC) factors are associated with SR and/or FR, by using Routine Outcome Monitoring data and data on met needs and unmet needs for care. Data of 287 young adults were collected. Almost 40% achieved or maintained SR, 34% FR, and 26% achieved or maintained both. In addition to sociodemographic factors, living independently, paid employment, higher levels of compliance with treatment, and better fulfillment of unmet needs for care in relation to psychological distress, company and daytime activities were associated with better outcomes on SR and/or FR. Our findings underscore that to successfully improve and sustain remission in young adults with a psychotic disorder, it is needed to conduct specific research into the relationship between SR and FR
Mass-to-Light Ratios of Field Early-Type Galaxies at z~1 from Ultra-Deep Spectroscopy: Evidence for Mass-dependent Evolution
We present an analysis of the Fundamental Plane for a sample of 27 field
early-type galaxies in the redshift range 0.6<z<1.15. The galaxies in this
sample have high S/N spectra obtained at the VLT and high resolution imaging
from the ACS. We find that the mean evolution in M/L of our sample is , with a large galaxy-to-galaxy scatter. This value can
be too low by 0.3 due to selection effects, resulting in . The strong correlation between M/L and rest-frame color
indicates that the observed scatter is not due to measurement errors, but due
to intrinsic differences between the stellar populations of the galaxies. This
pace of evolution is much faster than the evolution of cluster galaxies.
However, we find that the measured M/L evolution strongly depends on galaxy
mass. For galaxies with masses , we find no significant
difference between the evolution of field and cluster galaxies: Delta ln (M/L_B) =
-1.12+/-0.06z$ for cluster galaxies. The relation between the measured M/L
evolution and mass is partially due to selection effects. However, even when
taking selection effects into account, we still find a relation between M/L
evolution and mass, which is most likely caused by a lower mean age and a
larger intrinsic scatter for low mass galaxies. Results from lensing early-type
galaxies, which are mass-selected, show a very similar trend with mass. This,
combined with our findings, provides evidence for down-sizing. Previous studies
of the rate of evolution of field early-type galaxies found a large range of
mutually exclusive values. We show that these differences are largely caused by
the differences between fitting methods. (Abridged)Comment: figures 3 and 4 available at
http://www.strw.leidenuniv.nl/~vdwel/private/FPpaper
Structure of Protocluster Galaxies: Accelerated Structural Evolution in Overdense Environments?
We present a high spatial-resolution HST/NICMOS imaging survey in the field
of a known protocluster surrounding the powerful radio galaxy MRC1138-262 at
z=2.16. Previously, we have shown that this field exhibits a substantial
surface overdensity of red J-H galaxies. Here we focus on the stellar masses
and galaxy effective radii in an effort to compare and contrast the properties
of likely protocluster galaxies with their field counterparts and to look for
correlations between galaxy structure and (projected) distance relative to the
radio galaxy.
We find a hint that quiescent, cluster galaxies are on average less dense
than quiescent field galaxies of similar stellar mass and redshift. In fact, we
find only two (of nine) quiescent protocluster galaxies are of simliar density
to the majority of the massive, quiescent compact galaxies (SEEDs) found in
several field surveys. Furthermore, there is some indication that the
structural Sersic n parameter is higher (n ~ 3-4) on average for cluster
galaxies compared to the field SEEDs (n ~ 1-2) This result may imply that the
accelerated galaxy evolution expected (and observed) in overdense regions also
extends to structural evolution presuming that massive galaxies began as dense
(low n) SEEDs and have already evolved to be more in line with local galaxies
of the same stellar mass.Comment: 11 pages, 7 figures, 1 table, Accepted for publication in Ap
Can dry merging explain the size evolution of early-type galaxies?
The characteristic size of early-type galaxies (ETGs) of given stellar mass
is observed to increase significantly with cosmic time, from redshift z>2 to
the present. A popular explanation for this size evolution is that ETGs grow
through dissipationless ("dry") mergers, thus becoming less compact. Combining
N-body simulations with up-to-date scaling relations of local ETGs, we show
that such an explanation is problematic, because dry mergers do not decrease
the galaxy stellar-mass surface-density enough to explain the observed size
evolution, and also introduce substantial scatter in the scaling relations.
Based on our set of simulations, we estimate that major and minor dry mergers
increase half-light radius and projected velocity dispersion with stellar mass
(M) as M^(1.09+/-0.29) and M^(0.07+/-0.11), respectively. This implies that: 1)
if the high-z ETGs are indeed as dense as estimated, they cannot evolve into
present-day ETGs via dry mergers; 2) present-day ETGs cannot have assembled
more than ~45% of their stellar mass via dry mergers. Alternatively, dry
mergers could be reconciled with the observations if there was extreme fine
tuning between merger history and galaxy properties, at variance with our
assumptions. Full cosmological simulations will be needed to evaluate whether
this fine-tuned solution is acceptable.Comment: 5 pages, 2 figures. Accepted for publication in ApJ Letter
The pair faction of massive galaxies at 0 †z †3
Using a mass-selected (M-star >= 10(11) M-circle dot) sample of 198 galaxies at 0 <= z <= 3.0 with Hubble Space Telescope/NICMOS H-160-band images from the COSMOS survey, we find evidence for the evolution of the pair fraction above z similar to 2, an epoch in which massive galaxies are believed to undergo significant structural and mass evolution. We observe that the pair fraction of massive galaxies is 0.15 +/- 0.08 at 1.7 <= z <= 3.0, where galaxy pairs are defined as massive galaxies having a companion of flux ratio from 1:1 to 1:4 within a projected separation of 30 kpc. This is slightly lower but still consistent with the pair fraction measured previously in other studies, and the merger fraction predicted in halo-occupation modeling. The redshift evolution of the pair fraction is described by a power law F(z) = (0.07 +/- 0.04) x (1 + z)(0.6 +/- 0.5). The merger rate is consistent with no redshift evolution; however it is difficult to constrain due to the limited sample size and the high uncertainties in the merging timescale. Based on the merger rate calculation, we estimate that a massive galaxy undergoes on average 1.1 +/- 0.5 major mergers from z = 3 to 0. The observed merger fraction is sufficient to explain the number density evolution of massive galaxies, but insufficient to explain the size evolution. This is a hint that mechanism(s) other than major merging may be required to increase the sizes of the massive, compact quiescent galaxies from z similar to 2 to 0
The Nascent Red Sequence at z~2
We present new constraints on the evolution of the early-type galaxy
color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy
protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space
Telescope. This field contains a spectroscopically confirmed space-overdensity
of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio
galaxy MRC 1138-262. Using these NICMOS data we identify a significant
surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram
(when compared with deep NICMOS imaging from the HDF-N and UDF). The
optical-NIR colors of these prospective red-sequence galaxies indicate the
presence of on-going dust-obscured star-formation or recently formed (<~ 1.5
Gyr)stellar populations in a majority of the red galaxies. We measure the slope
and intrinsic scatter of the CMR for three different red galaxy samples
selected by a wide color cut, and using photometric redshifts both with and
without restrictions on rest-frame optical morphology. In all three cases both
the rest-frame slope and intrinsic color scatter are considerably higher
than corresponding values for lower redshift galaxy clusters. These results
suggest that while some relatively quiescent galaxies do exist in this
protocluster both the majority of the galaxy population and hence the
color-magnitude relation are still in the process of forming, as expected.Comment: 8 pages, 7 figures, accepted for publication in ApJ (to appear June
1, 2008, v679n2
The Fundamental Plane of Field Early Type Galaxies at z=1
We present deep VLT spectra of early type galaxies at z~1 in the Chandra Deep
Field South, from which we derive velocity dispersions. Together with
structural parameters from Hubble Space Telescope imaging, we can study the
Fundamental Plane for field early type galaxies at that epoch. We determine
accurate mass-to-light ratios and colors for four field early type galaxies in
the redshift range 0.96<z<1.14, and two with 0.65<z<0.70.
The galaxies were selected by color and morphology, and have generally red
colors. Their velocity dispersions show, however, that they have a considerable
spread in mass-to-light ratios (factor of 3). We find that the colors and
directly measured mass-to-light ratios correlate well, demonstrating that the
spread in mass-to-light ratios is real and reflects variations in stellar
populations.
The most massive galaxies have mass-to-light ratios comparable to massive
cluster galaxies at similar redshift, and therefore have stellar populations
which formed at high redshift (z>2). The lower mass galaxies at z~1 have a
lower average mass-to-light ratio, and one is a genuine 'E+A' galaxy. The
mass-to-light ratios indicate that their luminosity weighted ages are a factor
of three younger at the epoch of observation, due to either a late formation
redshift, or due to late bursts of star formation contributing 20-30% of the
mass.Comment: 4 pages incl. 4 figures, Accepted for publication in ApJ Letter
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