342 research outputs found
Maximising the power of deep extragalactic imaging surveys with the James Webb Space Telescope
We present a new analysis of the potential power of deep, near-infrared,
imaging surveys with the James Webb Space Telescope (JWST) to improve our
knowledge of galaxy evolution. In this work we properly simulate what can be
achieved with realistic survey strategies, and utilise rigorous signal:noise
calculations to calculate the resulting posterior constraints on the physical
properties of galaxies. We explore a broad range of assumed input galaxy types
(>20,000 models, including extremely dusty objects) across a wide redshift
range (out to z~12), while at the same time considering a realistic mix of
galaxy properties based on our current knowledge of the evolving population (as
quantified through the Empirical Galaxy Generator: EGG). While our main focus
is on imaging surveys with NIRCam, spanning lambda(obs) = 0.6-5.0 microns, an
important goal of this work is to quantify the impact/added-value of: i)
parallel imaging observations with MIRI at longer wavelengths, and ii) deeper
supporting optical/UV imaging with HST (potentially prior to JWST launch) in
maximising the power and robustness of a major extragalactic NIRCam survey. We
show that MIRI parallel 7.7-micron imaging is of most value for better
constraining the redshifts and stellar masses of the dustiest (A_V > 3)
galaxies, while deep B-band imaging (reaching~28.5 AB mag) with ACS on HST is
vital for determining the redshifts of the large numbers of faint/low-mass, z <
5 galaxies that will be detected in a deep JWST NIRCam survey.Comment: 19 Pages, 11 Figures, Submitted to MNRA
A first look at JWST CEERS: massive quiescent galaxies from 3 < z < 5
We report a robust sample of 9 massive quiescent galaxies at redshift, , selected using the first data from the JWST CEERS programme. Three of these
galaxies are at , constituting the best evidence to date for
quiescent galaxies significantly before . These extreme galaxies have
stellar masses in the range logM, and formed
the bulk of their mass at , with two objects having star-formation
histories that suggest they had already reached logM
by . We report number densities for our sample, demonstrating that
previous work underestimated the number of quiescent galaxies at by
at least a factor of , due to a lack of ultra-deep imaging data at
m. This result deepens the existing tension between
observations and theoretical models, which already struggle to reproduce
previous estimates of quiescent galaxy number densities. Upcoming
wider-area JWST imaging surveys will provide larger samples of such galaxies,
as well as providing opportunities to search for quiescent galaxies at .
The galaxies we report are excellent potential targets for JWST NIRSpec
spectroscopy, which will be required to understand in detail their physical
properties, providing deeper insights into the processes responsible for
quenching star formation during the first billion years.Comment: 11 pages, 6 figures, submitted to MNRA
A surprising abundance of massive quiescent galaxies at 3 < z < 5 in the first data from JWST CEERS
Jockey perception of shoe and surface effects on hoof-ground interactions and implications for safety in the galloping thoroughbred racehorse
Optically modulated magnetic resonance of erbium implanted silicon
Er implanted Si is an important candidate for quantum and photonic applications, but the Er centres involved are poorly understood, which has hindered development of these applications. Here we present the first measurement of the crystal field splitting of the 4I13/2 manifold of Er implanted Si, using a technique we call optically modulated magnetic resonance (OMMR). Crystal field analysis allows us to determine that this splitting originates from a photoluminescence (PL) active O coordinated Er centre with orthorhombic symmetry, which is highly localised with, and magically coupled to, an electron paramagnetic resonance (ERP) active O coordinated Er centre with monoclinic symmetry. The orthorhombic centre has a g-factor in agreement with previous Zeeman measurements, and is associated with a previously unreported acceptor state at ~ Ev+425 cm-1, showing that Er in Si is amphoteric, and not a pure donor, as previously thought. The OMMR mechanism involves transitions from this acceptor state to the 4I13/2 manifold, followed by relaxation to the Zeeman ground state
First discoveries of z similar to 6 quasars with the Kilo-Degree Survey and VISTA Kilo-Degree Infrared Galaxy survey
This work is financially supported by the Netherlands Research School for Astronomy (NOVA) and Target. Target is supported by Samenwerkingsverband Noord Nederland, European fund for regional development, Dutch Ministry of economic affairs, Pieken in de Delta, Provinces of Groningen and Drenthe
Construction of microscopic model for f-electron systems on the basis of j-j coupling scheme
We construct a microscopic model for f-electron systems, composed of
f-electron hopping, Coulomb interaction, and crystalline electric field (CEF)
terms. In order to clarify the meaning of one f-electron state, here the j-j
coupling scheme is considered, since the spin-orbit interaction is generally
large in f-electron systems. Thus, the f-electron state at each site is
labelled by , namely, the z-component of total angular momentum j. By
paying due attention to f-orbital symmetry, the hopping amplitudes between
f-electron states are expressed using Slater's integrals. The Coulomb
interaction terms among the -states are written by Slater-Condon or Racah
parameters. Finally, the CEF terms are obtained from the table of Hutchings.
The constructed Hamiltonian is regarded as an orbital degenerate Hubbard model,
since it includes two pseudo-spin and three pseudo-orbital degrees of freedom.
For practical purposes, it is further simplified into a couple of two-orbital
models by discarding one of the three orbitals. One of those simplified models
is here analyzed using the exact diagonalization method to clarify ground-state
properties by evaluating several kinds of correlation functions. Especially,
the superconducting pair correlation function in orbital degenerate systems is
carefully calculated based on the concept of off-diagonal long-range order. We
attempt to discuss a possible relation of the present results with experimental
observations for recently discovered heavy fermion superconductors CeMIn
(M=Ir, Co, and Rh), and a comprehensive scenario to understand superconducting
and antiferromagnetic tendencies in the so-called ``115'' materials such as
CeMIn, UMGa, and PuCoGa from the microscopic viewpoint.Comment: 16 pages, Revtex, with 6 figures embedded in the text. Submitted to
Phys. Rev.
Connecting Terminal Carboxylate Groups in Nine-Coordinate Lanthanide Podates: Consequences on the Thermodynamic, Structural, Electronic, and Photophysical Properties
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