157 research outputs found
Site-Dilution in quasi one-dimensional antiferromagnet Sr2(Cu1-xPdx)O3: reduction of Neel Temperature and spatial distribution of ordered moment sizes
We investigate the Neel temperature of Sr2CuO3 as a function of the site
dilution at the Cu (S=1/2) sites with Pd (S=0), utilizing the muon spin
relaxation (muSR) technique. The Neel temperature, which is Tn=5.4K for the
undoped system, becomes significantly reduced for less than one percent of
doping Pd, giving a support for the previous proposal for the good
one-dimensionality. The Pd concentration dependence of the Neel temperature is
compared with a recent theoretical study (S. Eggert, I. Affleck and M.D.P.
Horton, Phys. Rev. Lett. 89, 47202 (2002)) of weakly coupled one-dimensional
antiferromagnetic chains of S=1/2 spins, and a quantitative agreement is found.
The inhomogeneity of the ordered moment sizes is characterized by the muSR time
spectra. We propose a model that the ordered moment size recovers away from the
dopant S=0 sites with a recovery length of \xi = 150-200 sites. The origin of
the finite recovery length \xi for the gapless S=1/2 antiferromagnetic chain is
compared to the estimate based on the effective staggered magnetic field from
the neighboring chains.Comment: 10 pages, 9 figures, submitted to PR
New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field
The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured
below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of
a parallel field, a new peak appears at finite frequency in the optical
conductivity at the expense of suppression of c-axis condensate weight. We
conclude that the dramatic change originates from different Josephson coupling
strengths between bilayers with and without Josephson vortices. We find that
the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under
parallel magnetic field; this indicates that the condensate weight at \omega =0
is distributed to the intra-bilayer mode as well as to the new optical
Josephson mode.Comment: 4 pages, 3 figure
Muon Spin Relaxation and Susceptibility Studies of Pure and Doped Spin 1/2 Kagom\'{e}-like system (CuZn)VO(OH) 2HO
Muon spin relaxation (SR) and magnetic susceptibility measurements have
been performed on the pure and diluted spin 1/2 kagom\'{e} system
(CuZn)VO(OH) 2HO. In the pure
system we found a slowing down of Cu spin fluctuations with decreasing
temperature towards K, followed by slow and nearly
temperature-independent spin fluctuations persisting down to = 50 mK,
indicative of quantum fluctuations. No indication of static spin freezing was
detected in either of the pure (=1.0) or diluted samples. The observed
magnitude of fluctuating fields indicates that the slow spin fluctuations
represent an intrinsic property of kagom\'e network rather than impurity spins.Comment: 4 pges, 4 color figures, Phys. Rev. Lett. in pres
Automated mining of the ALMA archive in the COSMOS field (A3COSMOS): II. Cold molecular gas evolution out to Redshift 6
We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the ALMA public archive in the COSMOS deep field (A3COSMOS). Our A3COSMOS dataset contains ~700 galaxies (0.3 < z < 6) with high-confidence ALMA detections in the (sub-)millimeter continuum and multi-wavelength spectral energy distributions (SEDs). Multiple gas mass calibration methods are compared and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans(RJ)-tail continuum) have been tested. Combining our A3COSMOS sample with ~1,000 CO-observed galaxies at 0 < z < 4 (75% at z < 0.1), we parameterize galaxies' molecular gas depletion time and molecular gas to stellar mass ratio (gas fraction) each as a function of the stellar mass, offset from the star-forming main sequence (Delta MS) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature), and implies a "downsizing" effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and "mass-quenching" (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semi-analytic modeling. These together provide a coherent picture of cold molecular gas, SFR and stellar mass evolution in galaxies across cosmic time
Probing star formation and ISM properties using galaxy disk inclination I: Evolution in disk opacity since z~0.7
Disk galaxies at intermediate redshift () have been found in previous work to display more optically thick behaviour than their local counterparts in the rest-frame B-band surface brightness, suggesting an evolution in dust properties over the past 6 Gyr. We compare the measured luminosities of face-on and edge-on star-forming galaxies at different wavelengths (Ultraviolet (UV), mid-infrared (MIR), far-infrared (FIR), and radio) for two well-matched samples of disk-dominated galaxies: a local Sloan Digital Sky Survey (SDSS)-selected sample at and a sample of disks at drawn from Cosmic Evolution Survey (COSMOS). We have derived correction factors to account for the inclination dependence of the parameters used for sample selection. We find that typical galaxies are transparent at MIR wavelengths at both redshifts and that the FIR and radio emission is also transparent as expected. However, reduced sensitivity at these wavelengths limits our analysis; we cannot rule out opacity in the FIR or radio. Ultra-violet attenuation has increased between and , with the sample being a factor of 3.4 more attenuated. The larger UV attenuation at can be explained by more clumpy dust around nascent star-forming regions. There is good agreement between the fitted evolution of the normalisation of the SFR versus 1-cos(i) trend (interpreted as the clumpiness fraction) and the molecular gas fraction/dust fraction evolution of galaxies found out to
The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7
We present the KMOS^3D survey, a new integral field survey of over 600
galaxies at 0.7<z<2.7 using KMOS at the Very Large Telescope (VLT). The KMOS^3D
survey utilizes synergies with multi-wavelength ground and space-based surveys
to trace the evolution of spatially-resolved kinematics and star formation from
a homogeneous sample over 5 Gyrs of cosmic history. Targets, drawn from a
mass-selected parent sample from the 3D-HST survey, cover the star
formation-stellar mass () and rest-frame planes uniformly. We
describe the selection of targets, the observations, and the data reduction. In
the first year of data we detect Halpha emission in 191
Msun galaxies at z=0.7-1.1 and z=1.9-2.7. In
the current sample 83% of the resolved galaxies are rotation-dominated,
determined from a continuous velocity gradient and , implying
that the star-forming 'main sequence' (MS) is primarily composed of rotating
galaxies at both redshift regimes. When considering additional stricter
criteria, the Halpha kinematic maps indicate at least ~70% of the resolved
galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated
velocity dispersions reported in previous IFS studies at z>0.7. For
rotation-dominated disks, the average intrinsic velocity dispersion decreases
by a factor of two from 50 km/s at z~2.3 to 25 km/s at z~0.9 while the
rotational velocities at the two redshifts are comparable. Combined with
existing results spanning z~0-3, disk velocity dispersions follow an
approximate (1+z) evolution that is consistent with the dependence of velocity
dispersion on gas fractions predicted by marginally-stable disk theory.Comment: 20 pages, 11 figures, 1 Appendix; Accepted to ApJ November 2
ALPINE: A Large Survey to Understand Teenage Galaxies
A multiwavelength study of galaxies is important to understand their formation and evolution. Only in the recent past, thanks to the Atacama Large (Sub) Millimeter Array (ALMA), were we able to study the far-infrared (IR) properties of galaxies at high redshifts. In this article, we summarize recent research highlights and their significance to our understanding of early galaxy evolution from the ALPINE survey, a large program with ALMA to observe the dust continuum and 158 µm C+ emission of normal star-forming galaxies at z = 4–6. Combined with ancillary data at UV through near-IR wavelengths, ALPINE provides the currently largest multiwavelength sample of post-reionization galaxies and has advanced our understanding of (i) the demographics of C+ emission; (ii) the relation of star formation and C+ emission; (iii) the gas content; (iv) outflows and enrichment of the intergalactic medium; and (v) the kinematics, emergence of disks, and merger rates in galaxies at z > 4. ALPINE builds the basis for more detailed measurements with the next generation of telescopes, and places itself as an important post-reionization baseline sample to allow a continuous study of galaxies over 13 billion years of cosmic time
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