1,142 research outputs found
SSSPM J15493544 Is Not a White Dwarf
Spectroscopy and photometry demonstrate that SSSPM J15493544 is not a cool
white dwarf but a high velocity metal-poor halo star.Comment: 8 pages, 1 figure, 2 tables, accepted to ApJ Letter
The Evolution of the Intracluster Medium Metallicity in Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5
We present the results of an X-ray spectral analysis of 153 galaxy clusters
observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These
clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected
sample of galaxy clusters discovered in the 2500 square degree South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure
time of 9.1 Ms, these data yield the strongest constraints to date on the
evolution of the metal content of the intracluster medium (ICM). We find no
evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz =
-0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of = 0.23 +/- 0.01 Zsun
and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the
metals in the ICM were already in place at z=1 (at 95% confidence), consistent
with the picture of an early (z>1) enrichment. We find, in agreement with
previous works, a significantly higher mean value for the metallicity in the
centers of cool core clusters versus non-cool core clusters. We find weak
evidence for evolution in the central metallicity of cool core clusters (dZ/dz
= -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced
central metallicity over the past ~10 Gyr. We find no evidence for metallicity
evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant
difference in the core-excised metallicity between cool core and non-cool core
clusters. This suggests that strong radio-mode AGN feedback does not
significantly alter the distribution of metals at r>0.15R500. Given the
limitations of current-generation X-ray telescopes in constraining the ICM
metallicity at z>1, significant improvements on this work will likely require
next-generation X-ray missions.Comment: 11 pages, 8 figures, 2 tables. Submitted to ApJ. Comments welcome
Free-electron Model for Mesoscopic Force Fluctuations in Nanowires
When two metal electrodes are separated, a nanometer sized wire (nanowire) is
formed just before the contact breaks. The electrical conduction measured
during this retraction process shows signs of quantized conductance in units of
G_0=2e^2/h. Recent experiments show that the force acting on the wire during
separation fluctuates, which has been interpreted as being due to atomic
rearrangements. In this report we use a simple free electron model, for two
simple geometries, and show that the electronic contribution to the force
fluctuations is comparable to the experimentally found values, about 2 nN.Comment: 4 pages, 3 figures, reference correcte
Baryon Content of Massive Galaxy Clusters (0.57 < z < 1.33)
We study the stellar, Brightest Cluster Galaxy (BCG) and intracluster medium
(ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with
median redshift and median mass . We
estimate stellar masses for each cluster and BCG using six photometric bands
spanning the range from the ultraviolet to the near-infrared observed with the
VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton
X-ray observations, and the virial masses are derived from the SPT
Sunyaev-Zel'dovich Effect signature.
At the BCG mass constitutes %
of the halo mass for a cluster, and this fraction
falls as . The cluster stellar mass function has a
characteristic mass , and the number of
galaxies per unit mass in clusters is larger than in the field by a factor
. Both results are consistent with measurements on group scales and
at lower redshift. We combine our SPT sample with previously published samples
at low redshift that we correct to a common initial mass function and for
systematic differences in virial masses. We then explore mass and redshift
trends in the stellar fraction (fstar), the ICM fraction (fICM), the cold
baryon fraction (fc) and the baryon fraction (fb). At a pivot mass of
and redshift , the characteristic values are
fstar=%, fICM=%, fc=% and fb=%.
These fractions all vary with cluster mass at high significance, indicating
that higher mass clusters have lower fstar and fc and higher fICM and fb. When
accounting for a 15% systematic virial mass uncertainty, there is no
statistically significant redshift trend at fixed mass in these baryon
fractions.
(abridged)Comment: Accepted for publication in MNRA
Ballistic Electron Emission Microscopy on CoSi/Si(111) interfaces: band structure induced atomic-scale resolution and role of localized surface states
Applying a Keldysh Green`s function method it is shown that hot electrons
injected from a STM-tip into a CoSi/Si(111) system form a highly focused
beam due to the silicide band structure. This explains the atomic resolution
obtained in recent Ballistic Electron Emission Microscopy (BEEM) experiments.
Localized surface states in the -reconstruction are found to be
responsible for the also reported anticorrugation of the BEEM current. These
results clearly demonstrate the importance of bulk and surface band structure
effects for a detailed understanding of BEEM data.Comment: 5 pages, RevTex, 4 postscript figures,
http://www.icmm.csic.es/Pandres/pedro.ht
Persistent Currents in the Heisenberg chain with a weak link
The Heisenberg chain with a weak link is studied, as a simple example of a
quantum ring with a constriction or defect. The Heisenberg chain is equivalent
to a spinless electron gas under a Jordan-Wigner transformation. Using density
matrix renormalization group and quantum Monte Carlo methods we calculate the
spin/charge stiffness of the model, which determines the strength of the
`persistent currents'. The stiffness is found to scale to zero in the weak link
case, in agreement with renormalization group arguments of Eggert and Affleck,
and Kane and Fisher.Comment: 14 pages, 7 figures, 2 tables, no changes to paper, author list
changed on archiv
SPT 0538-50: Physical conditions in the ISM of a strongly lensed dusty star-forming galaxy at z=2.8
We present observations of SPT-S J053816-5030.8, a gravitationally-lensed
dusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter
wavelengths by the South Pole Telescope. SPT 0538-50 is typical of the
brightest sources found by wide-field millimeter-wavelength surveys, being
lensed by an intervening galaxy at moderate redshift (in this instance, at z =
0.441). We present a wide array of multi-wavelength spectroscopic and
photometric data on SPT 0538-50, including data from ALMA, Herschel PACS and
SPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution
imaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of
the foreground lens. Combined with a source model derived from ALMA imaging
(which suggests a magnification factor of 21 +/- 4), we derive the intrinsic
properties of SPT 0538-50, including the stellar mass, far-IR luminosity, star
formation rate, molecular gas mass, and - using molecular line fluxes - the
excitation conditions within the ISM. The derived physical properties argue
that we are witnessing compact, merger-driven star formation in SPT 0538-50,
similar to local starburst galaxies, and unlike that seen in some other DSFGs
at this epoch.Comment: 16 pages, 11 figures. Accepted for publication in Ap
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