1,542 research outputs found
Pressure-induced hole doping of the Hg-based cuprate superconductors
We investigate the electronic structure and the hole content in the
copper-oxygen planes of Hg based high Tc cuprates for one to four CuO2 layers
and hydrostatic pressures up to 15 GPa. We find that with the pressure-induced
additional number of holes of the order of 0.05e the density of states at the
Fermi level changes approximately by a factor of 2. At the same time the saddle
point is moved to the Fermi level accompanied by an enhanced k_z dispersion.
This finding explains the pressure behavior of Tc and leads to the conclusion
that the applicability of the van Hove scenario is restricted. By comparison
with experiment, we estimate the coupling constant to be of the order of 1,
ruling out the weak coupling limit.Comment: 4 pages, 4 figure
Right to Serve, Right to Lead: Lives and Legacies of the USCT
This is a catalog for an exhibit that follows the evolution of African-American participation in the Civil War, from slaves, to contrabands, to soldiers of the United States Colored Troops (USCT), as well as the lives of black veterans beyond the war, and their ultimate military and social legacy. Using a variety of period items, it creates a narrative that stretches from the Antebellum Period to the current day. In doing so, the exhibit shows how black sacrifice on the battlefield redefined the war\u27s purpose throughout the divided nation, how Jim Crowe suppressed the memory of black participation after Reconstruction, and how the illustrious African-American military tradition left by the USCT endures to this day in their modern heirs
The mass, colour, and structural evolution of today's massive galaxies since z~5
In this paper, we use stacking analysis to trace the mass-growth, colour
evolution, and structural evolution of present-day massive galaxies
() out to . We utilize the exceptional depth
and area of the latest UltraVISTA data release, combined with the depth and
unparalleled seeing of CANDELS to gather a large, mass-selected sample of
galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day
massive galaxies are identified via an evolving cumulative number density
selection, which accounts for the effects of merging to correct for the
systematic biases introduced using a fixed cumulative number density selection,
and find progenitors grow in stellar mass by since
. Using stacking, we analyze the structural parameters of the progenitors
and find that most of the stellar mass content in the central regions was in
place by , and while galaxies continue to assemble mass at all radii,
the outskirts experience the largest fractional increase in stellar mass.
However, we find evidence of significant stellar mass build up at
probing an era of significant mass assembly in
the interiors of present day massive galaxies. We also compare mass assembly
from progenitors in this study to the EAGLE simulation and find qualitatively
similar assembly with at . We identify as a
distinct epoch in the evolution of massive galaxies where progenitors
transitioned from growing in mass and size primarily through in-situ star
formation in disks to a period of efficient growth in consistent with
the minor merger scenario.Comment: 19 pages, 14 figures, accepted for publicatio
Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5<z<2.5
In this paper, we investigate the relationship between star formation and
structure, using a mass-complete sample of 27,893 galaxies at
selected from 3D-HST. We confirm that star-forming galaxies are larger than
quiescent galaxies at fixed stellar mass (M). However, in contrast
with some simulations, there is only a weak relation between star formation
rate (SFR) and size within the star-forming population: when dividing into
quartiles based on residual offsets in SFR, we find that the sizes of
star-forming galaxies in the lowest quartile are 0.270.06 dex smaller than
the highest quartile. We show that 50% of star formation in galaxies at fixed
M takes place within a narrow range of sizes (0.26 dex). Taken
together, these results suggest that there is an abrupt cessation of star
formation after galaxies attain particular structural properties. Confirming
earlier results, we find that central stellar density within a 1 kpc fixed
physical radius is the key parameter connecting galaxy morphology and star
formation histories: galaxies with high central densities are red and have
increasingly lower SFR/M, whereas galaxies with low central densities
are blue and have a roughly constant (higher) SFR/M at a given
redshift. We find remarkably little scatter in the average trends and a strong
evolution of 0.5 dex in the central density threshold correlated with
quiescence from . Neither a compact size nor high- are
sufficient to assess the likelihood of quiescence for the average galaxy;
rather, the combination of these two parameters together with M
results in a unique quenching threshold in central density/velocity.Comment: 20 pages, 15 figures, and 2 tables; Accepted for publication in the
Astrophysical Journa
X-Ray Properties of K-Selected Galaxies at 0.5 Less than z Less than 2.0: Investigating Trends with Stellar Mass, Redshift and Spectral Type
We examine how the total X-ray luminosity correlates with stellar mass, stellar population, and redshift for a K-band limited sample of approximately 3500 galaxies at 0.5 < z < 2.0 from the NEWFIRM Medium Band Survey in the COSMOS field. The galaxy sample is divided into 32 different galaxy types, based on similarities between the spectral energy distributions. For each galaxy type, we further divide the sample into bins of redshift and stellar mass, and perform an X-ray stacking analysis using the Chandra COSMOS data. We find that full band X-ray luminosity is primarily increasing with stellar mass, and at similar mass and spectral type is higher at larger redshifts. When comparing at the same stellar mass, we find that the X-ray luminosity is slightly higher for younger galaxies (i.e., weaker 4000 angstrom breaks), but the scatter in this relation is large. We compare the observed X-ray luminosities to those expected from low- and high-mass X-ray binaries (XRBs). For blue galaxies, XRBs can almost fully account for the observed emission, while for older galaxies with larger 4000 angstrom breaks, active galactic nuclei (AGN) or hot gas dominate the measured X-ray flux. After correcting for XRBs, the X-ray luminosity is still slightly higher in younger galaxies, although this correlation is not significant. AGN appear to be a larger component of galaxy X-ray luminosity at earlier times, as the hardness ratio increases with redshift. Together with the slight increase in X-ray luminosity this may indicate more obscured AGNs or higher accretion rates at earlier times
The Most Massive Galaxies at 3.0<z<4.0 in the NEWFIRM Medium-Band Survey: Properties and Improved Constraints on the Stellar Mass Function
[Abridged] We use the NEWFIRM Medium-Band Survey (NMBS) to characterize the
properties of a mass-complete sample of 14 galaxies at 3.0<z<4.0 with
M_star>2.5x10^11 Msun, and to derive more accurate measurements of the
high-mass end of the stellar mass function (SMF) of galaxies at z=3.5, with
significantly reduced contributions from photometric redshift errors and cosmic
variance to the total error budget of the SMF. The typical very massive galaxy
at z=3.5 is red and faint in the observer's optical, with median r=26.1, and
rest-frame U-V=1.6. About 60% of the sample have optical colors satisfying
either the U- or the B-dropout color criteria, although ~50% of these galaxies
have r>25.5. About 30% of the sample has SFRs from SED modeling consistent with
zero. However, >80% of the sample is detected at 24 micron, with total infrared
luminosities in the range (0.5-4.0)x10^13 Lsun. This implies the presence of
either dust-enshrouded starburst activity (with SFRs of 600-4300 Msun/yr)
and/or highly-obscured active galactic nuclei (AGN). The contribution of
galaxies with M_star>2.5x10^11 Msun to the total stellar mass budget at z=3.5
is ~8%. We find an evolution by a factor of 2-7 and 3-22 from z~5 and z~6,
respectively, to z=3.5. The previously found disagreement at the high-mass end
between observed and model-predicted SMFs is now significant at the 3sigma
level. However, systematic uncertainties dominate the total error budget, with
errors up to a factor of ~8 in the densities, bringing the observed SMF in
marginal agreement with the predicted SMF. Additional systematic uncertainties
on the high-mass end could be introduced by either 1) the intense
star-formation and/or the very common AGN activities as inferred from the MIPS
24 micron detections, and/or 2) contamination by a significant population of
massive, old, and dusty galaxies at z~2.6.Comment: 20 pages, 11 figures. Accepted in ApJ. Minor changes to colors of
figures to match accepted versio
Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at z~2
Quiescent galaxies at z~2 have been identified in large numbers based on
rest-frame colors, but only a small number of these galaxies have been
spectroscopically confirmed to show that their rest-frame optical spectra show
either strong Balmer or metal absorption lines. Here, we median stack the
rest-frame optical spectra for 171 photometrically-quiescent galaxies at 1.4 <
z < 2.2 from the 3D-HST grism survey. In addition to Hbeta (4861A), we
unambiguously identify metal absorption lines in the stacked spectrum,
including the G-band (4304A), Mg I (5175A), and Na I (5894A). This finding
demonstrates that galaxies with relatively old stellar populations already
existed when the universe was ~3 Gyr old, and that rest-frame color selection
techniques can efficiently select them. We find an average age of 1.3^0.1_0.3
Gyr when fitting a simple stellar population to the entire stack. We confirm
our previous result from medium-band photometry that the stellar age varies
with the colors of quiescent galaxies: the reddest 80% of galaxies are
dominated by metal lines and have a relatively old mean age of 1.6^0.5_0.4 Gyr,
whereas the bluest (and brightest) galaxies have strong Balmer lines and a
spectroscopic age of 0.9^0.2_0.1 Gyr. Although the spectrum is dominated by an
evolved stellar population, we also find [OIII] and Hbeta emission.
Interestingly, this emission is more centrally concentrated than the continuum
with L_[OIII] = 1.7 +/- 0.3 x 10^40 erg s^-1, indicating residual central star
formation or nuclear activity.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
The plasma membrane ferrireductase activity of Saccharomyces cerevisiae is partially controlled by cyclic AMP
S-CANDELS: The Spitzer-Cosmic Assembly Near-Infrared Deep Extragalactic Survey. Survey Design, Photometry, and Deep IRAC Source Counts
The Spitzer-Cosmic Assembly Deep Near-Infrared Extragalactic Legacy Survey
(S-CANDELS; PI G. Fazio) is a Cycle 8 Exploration Program designed to detect
galaxies at very high redshifts (z > 5). To mitigate the effects of cosmic
variance and also to take advantage of deep coextensive coverage in multiple
bands by the Hubble Space Telescope Multi-Cycle Treasury Program CANDELS,
S-CANDELS was carried out within five widely separated extragalactic fields:
the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS,
the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon
the existing coverage of these fields from the Spitzer Extended Deep Survey
(SEDS) by increasing the integration time from 12 hours to a total of 50 hours
but within a smaller area, 0.16 square degrees. The additional depth
significantly increases the survey completeness at faint magnitudes. This paper
describes the S-CANDELS survey design, processing, and publicly-available data
products. We present IRAC dual-band 3.6+4.5 micron catalogs reaching to a depth
of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by
S-CANDELS are consistent with models based on known galaxy populations. The
increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a
significant additional contribution from discrete sources to the diffuse Cosmic
Infrared Background (CIB). Thus it remains true that only roughly half of the
estimated CIB flux from COBE/DIRBE is resolved.Comment: 23 pages, 19 figures, accepted by ApJ
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