565 research outputs found
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
The Calar Alto Deep Imaging Survey: K-band Galaxy Number Counts
We present K-band number counts for the faint galaxies in the Calar Alto Deep
Imaging Survey (CADIS). We covered 4 CADIS fields, a total area of 0.2deg^2, in
the broad band filters B, R and K. We detect about 4000 galaxies in the K-band
images, with a completeness limit of K=19.75mag, and derive the K-band galaxy
number counts in the range of 14.25 < K < 19.75mag. This is the largest medium
deep K-band survey to date in this magnitude range. The B- and R-band number
counts are also derived, down to completeness limits of B=24.75mag and
R=23.25mag. The K-selected galaxies in this magnitude range are of particular
interest, since some medium deep near-infrared surveys have identified breaks
of both the slope of the K-band number counts and the mean B-K color at
K=17\sim18mag. There is, however, a significant disagreement in the K-band
number counts among the existing surveys. Our large near-infrared selected
galaxy sample allows us to establish the presence of a clear break in the slope
at K=17.0mag from dlogN/dm = 0.64 at brighter magnitudes to dlogN/dm = 0.36 at
the fainter end. We construct no-evolution and passive evolution models, and
find that the passive evolution model can simultaneously fit the B-, R- and
K-band number counts well. The B-K colors show a clear trend to bluer colors
for K > 18mag. We also find that most of the K=18-20mag galaxies have a B-K
color bluer than the prediction of a no-evolution model for an L_* Sbc galaxy,
implying either significant evolution, even for massive galaxies, or the
existence of an extra population of small galaxies.Comment: Accepted for A&A, 10 pages, 7 figure
Constraints to the evolution of Ly-Alpha bright galaxies between z=3 and z=6
Galaxies at high redshift with a strong Ly-Alpha emission line trace massive
star formation in the absence of dust, and can therefore be regarded as a prime
signature of the first major starburst in galaxies. We report results of the
Ly-Alpha search within the Calar Alto Deep Imaging Survey (CADIS). With imaging
Fabry-Perot interferometer CADIS can detect emission lines in three waveband
windows free of night-sky emission lines at 700nm, 820nm, and 920nm. The
typical flux detection limit for Ly-Alpha emission redshifted into these
windows, Flim > 3X10^(-20) Wm^(-2), corresponds to (unobscured) star formation
rates of >10Msun/yr at z=6. Candidate Ly-Alpha-emitting galaxies are selected
from the total emission line sample, which contains more than 97% of objects at
z<1.2, by the absence of flux below the Lyman limit (B-band "dropouts"), and
the non-detection of secondary emission lines in narrow band filters. We have
detected 5 bright Ly-Alpha-emitting galaxy candidates at z ~ 4.8, and 11
candidates at z ~ 5.7. For two of four observed Ly-Alpha candidates, one
candidate at z ~ 4.8, and the other at z ~ 5.7, the emission line detected with
the Fabry-Perot has been verified spectroscopically at the VLT. When compared
to Ly-Alpha surveys at z<3.5 even the upper limits set by our list of
candidates show that bright Ly-Alpha galaxies are significantly rarer at z>5
than the assumption of a non-evolving population would predict. Therefore we
conclude that the Ly-Alpha bright phase of primeval star formation episodes
reached its peak at redshifts between 3 and 6.Comment: Accepted for publication in A&A; 15 pages, 4 figure
Multi-color Classification in the Calar Alto Deep Imaging Survey
We use a multi-color classification method introduced by Wolf, Meisenheimer &
Roeser (2000) to reliably identify stars, galaxies and quasars in the up to
16-dimensional color space provided by the filter set of the Calar Alto Deep
Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained
this way have been used for dedicated studies published in separate papers. The
classification is good enough to detect quasars rather completely and
efficiently without confirmative spectroscopy. The multi-color redshifts are
accurate enough for most statistical applications, e.g. evolutionary studies of
the galaxy luminosity function. We characterize our current dataset on the
CADIS 1h-, 9h- and 16h-fields. Using Monte-Carlo simulations we model the
classification performance expected for CADIS. We present a summary of the
classification results and discuss unclassified objects. More than 99% of the
whole catalog sample at R<22 (more than 95% at R<23) are successfully
classified matching the expectations derived from the simulations. A small
number of peculiar objects challenging the classification are discussed in
detail. Spectroscopic observations are used to check the reliability of the
multi-color classification (6 mistakes among 151 objects with R<24). We also
determine the accuracy of the multi-color redshifts which are rather good for
galaxies (sigma_z = 0.03) and useful for quasars. We find the classification
performance derived from the simulations to compare well with results from the
real survey. Finally, we locate areas for potential improvement of the
classification.Comment: 18 pages, 13 figures included, accepted for publication in Astronomy
& Astrophysic
Sub 15 fs X ray pump and X ray probe experiment for the study of ultrafast magnetization dynamics in ferromagnetic alloys
In this paper, we present a new setup for the measurement of element specific ultrafast magnetization dynamics in ferromagnetic thin films with a sub 15 fs time resolution. Our experiment relies on a split and delay approach which allows us to fully exploit the shortest X rays pulses delivered by X ray Free Electrons Lasers close to the attosecond range , in an X ray pump X ray probe geometry. The setup performance is demonstrated by measuring the ultrafast elemental response of Ni and Fe during demagnetization of ferromagnetic Ni and Ni80Fe20 Permalloy samples upon resonant excitation at the corresponding absorption edges. The transient demagnetization process is measured in both reflection and transmission geometry using, respectively, the transverse magneto optical Kerr effect T MOKE and the Faraday effect as probing mechanism
Toward ultrafast magnetic depth profiling using time resolved x ray resonant magnetic reflectivity
During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time resolved x ray resonant magnetic reflectivity, can distinguish local and non local effects. Here, we demonstrate the feasibility of this technique in a pump probe geometry using a custom built reflectometer at the FLASH2 free electron laser FEL . Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 amp; 8201;nm amp; 8771;310 amp; 8201;eV , we were able to probe close to the Fe L3 edge 706.8 amp; 8201;eV of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non homogeneous loss of magnetization and a significant dilation of 2 amp; 8201; of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetizatio
Measurement of the Lifetime Difference Between B_s Mass Eigenstates
We present measurements of the lifetimes and polarization amplitudes for B_s
--> J/psi phi and B_d --> J/psi K*0 decays. Lifetimes of the heavy (H) and
light (L) mass eigenstates in the B_s system are separately measured for the
first time by determining the relative contributions of amplitudes with
definite CP as a function of the decay time. Using 203 +/- 15 B_s decays, we
obtain tau_L = (1.05 +{0.16}/-{0.13} +/- 0.02) ps and tau_H = (2.07
+{0.58}/-{0.46} +/- 0.03) ps. Expressed in terms of the difference DeltaGamma_s
and average Gamma_s, of the decay rates of the two eigenstates, the results are
DeltaGamma_s/Gamma_s = (65 +{25}/-{33} +/- 1)%, and DeltaGamma_s = (0.47
+{0.19}/-{0.24} +/- 0.01) inverse ps.Comment: 8 pages, 3 figures, 2 tables; as published in Physical Review Letters
on 16 March 2005; revisions are for length and typesetting only, no changes
in results or conclusion
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a measurement of the top quark pair production cross section in
ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with
the Collider Detector at Fermilab. We select ttbar decays into the final states
e nu + jets and mu nu + jets, in which at least one b quark from the t-quark
decays is identified using a secondary vertex-finding algorithm. Assuming a top
quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat)
+1.1-0.9 (syst) pb. We also report the first observation of ttbar with
significance greater than 5 sigma in the subsample in which both b quarks are
identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3
(syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page
Evidence for the exclusive decay Bc+- to J/psi pi+- and measurement of the mass of the Bc meson
We report first evidence for a fully reconstructed decay mode of the
B_c^{\pm} meson in the channel B_c^{\pm} \to J/psi \pi^{\pm}, with J/psi \to
mu^+mu^-. The analysis is based on an integrated luminosity of 360 pb$^{-1} in
p\bar{p} collisions at 1.96 TeV center of mass energy collected by the Collider
Detector at Fermilab. We observe 14.6 \pm 4.6 signal events with a background
of 7.1 \pm 0.9 events, and a fit to the J/psi pi^{\pm} mass spectrum yields a
B_c^{\pm} mass of 6285.7 \pm 5.3(stat) \pm 1.2(syst) MeV/c^2. The probability
of a peak of this magnitude occurring by random fluctuation in the search
region is estimated as 0.012%.Comment: 7 pages, 3 figures. Version 3, accepted by PR
- …