964 research outputs found
Keck Deep Fields. II. The UV Galaxy Luminosity Function at z~4, 3, and 2
We use very deep UGRI multi-field imaging obtained at the Keck telescope to
study the evolution of the rest-frame 1700A galaxy luminosity function as the
Universe doubles its age from z~4 to z~2. The depth of our imaging allows us to
constrain the faint end of the luminosity function reaching M_1700A ~ -18.5 at
z~3 (equivalent to ~1M_sun/yr) accounting for both N^1/2 uncertainty in the
number of galaxies and for cosmic variance. We carefully examine many potential
sources of systematic bias in our LF measurements before drawing the following
conclusions. We find that the luminosity function of Lyman Break Galaxies
evolves with time and that this evolution is likely differential with
luminosity. The result is best constrained between the epochs at z~4 and z~3,
where we find that the number density of sub-L* galaxies increases with time by
at least a factor of 2.3 (11sigma statistical confidence); while the faint end
of the LF evolves, the bright end appears to remain virtually unchanged,
indicating that there may be differential, luminosity-dependent evolution
significant at the 97% level. Potential systematic biases restric our ability
to draw strong conclusions about continued evolution of the luminosity function
to lower redshifts, z~2.2 and z~1.7, but, nevertheless, it appears certain that
the number density of z~2.2 galaxies at all luminosities we studied,
-22<M_1700A<-18, is at least as high as that of their counterparts at z~3.
While it is not yet clear what mechanism underlies the observed evolution, the
fact that this evolution is differential with luminosity opens up new avenues
of improving our understanding of how galaxies form and evolve at high
redshift.Comment: Accepted for publication in ApJ. Updated preprint to reflect this
final versio
Keck Deep Fields. III. Luminosity-dependent Evolution of the Ultraviolet Luminosity and Star Formation Rate Densities at z~4, 3, and 2
We use the Keck Deep Fields UGRI catalog of z~4, 3, and 2 UV-selected
galaxies to study the evolution of the rest-frame 1700A luminosity density at
high redshift. The ability to reliably constrain the contribution of faint
galaxies is critical and our data do so as they reach to M*+2 even at z~4 and
deeper still at lower redshifts. We find that the luminosity density at high
redshift is dominated by the hitherto poorly studied galaxies fainter than L*,
and, indeed, the the bulk of the UV light in the high-z Universe comes from
galaxies in the luminosity range L=0.1-1L*. It is these faint galaxies that
govern the behavior of the total UV luminosity density. Overall, there is a
gradual rise in luminosity density starting at z~4 or earlier, followed by a
shallow peak or a plateau within z~3--1, and then followed by the well-know
plunge at lower redshifts. Within this total picture, luminosity density in
sub-L* galaxies evolves more rapidly at high redshift, z>~2, than that in more
luminous objects. However, this is reversed at lower redshifts, z<~1, a
reversal that is reminiscent of galaxy downsizing. Within the context of the
models commonly used in the observational literature, there seemingly aren't
enough faint or bright LBGs to maintain ionization of intergalactic gas even as
late as z~4. This is particularly true at earlier epochs and even more so if
the faint-end evolutionary trends we observe at z~3 and 4 continue to higher
redshifts. Apparently the Universe must be easier to reionize than some recent
studies have assumed. Nevertheless, sub-L* galaxies do dominate the total UV
luminosity density at z>~2 and this dominance further highlights the need for
follow-up studies that will teach us more about these very numerous but thus
far largely unexplored systems.Comment: Accepted for publication in the Astrophysical Journal. Abstract
abridge
Immunohistochemical and electron-microscopical identification of neuroendocrine cells in the respiratory tract of rats with experimental uraemia
The aim of the present study was to characterise immunohistochemically and
ultrastructurally the neuroendocrine cells in the pulmonary systems of uraemic
rats. Pieces of lung and trachea were collected 1, 2 and 4 weeks after nephrectomy.
Paraffin-embedded sections were stained with H+E and by silver impregnation.
For the identification of neuroendocrine cells immunohistochemical reactions
were performed with the use of specific antibodies against calcitonin
(CT), somatostatin (SOM), synaptophysin (SYN), neuron-specific enolase (NSE)
and calcitonin gene-related peptide (CGRP). For electron microscopy, ultrathin
sections were used. The analysis showed an increased number of both the solitary
neuroendocrine cells and of neuroepithelial bodies in uraemic rats when
compared to control animals
Large-Scale Tests of the DGP Model
The self-accelerating braneworld model (DGP) can be tested from measurements
of the expansion history of the universe and the formation of structure.
Current constraints on the expansion history from supernova luminosity
distances, the CMB, and the Hubble constant exclude the simplest flat DGP model
at about 3sigma. The best-fit open DGP model is, however, only a marginally
poorer fit to the data than flat LCDM. Its substantially different expansion
history raises structure formation challenges for the model. A dark-energy
model with the same expansion history would predict a highly significant
discrepancy with the baryon oscillation measurement due the high Hubble
constant required and a large enhancement of CMB anisotropies at the lowest
multipoles due to the ISW effect. For the DGP model to satisfy these
constraints new gravitational phenomena would have to appear at the non-linear
and cross-over scales respectively. A prediction of the DGP expansion history
in a region where the phenomenology is well understood is that high-redshift
galaxies should be substantially correlated with the CMB through the ISW
effect. This correlation should provide a sharp test of the DGP model in the
future.Comment: 8 pages, 5 figures, added and updated references, version reflects
that accepted by PRD, v3 fixes bibliography issue
Seeding supermassive black holes with a nonvortical dark-matter subcomponent
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Luminosity Dependent Evolution of Lyman Break Galaxies from redshift 5 to 3
In this contribution we briefly describe our recent results on the properties
of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys
using Subaru telescope, and through the comparison with samples at lower
redshift ranges we discuss the evolution of star-forming galaxies in the early
universe.Comment: 2 pages, 1 figure, for the proceedings of the IAU Symposium 235,
Galaxies Across the Hubble Time, J. Palous & F. Combes, ed
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