54,420 research outputs found
The infrared imaging spectrograph (IRIS) for TMT: sensitivities and simulations
We present sensitivity estimates for point and resolved astronomical sources
for the current design of the InfraRed Imaging Spectrograph (IRIS) on the
future Thirty Meter Telescope (TMT). IRIS, with TMT's adaptive optics system,
will achieve unprecedented point source sensitivities in the near-infrared
(0.84 - 2.45 {\mu}m) when compared to systems on current 8-10m ground based
telescopes. The IRIS imager, in 5 hours of total integration, will be able to
perform a few percent photometry on 26 - 29 magnitude (AB) point sources in the
near-infrared broadband filters (Z, Y, J, H, K). The integral field
spectrograph, with a range of scales and filters, will achieve good
signal-to-noise on 22 - 26 magnitude (AB) point sources with a spectral
resolution of R=4,000 in 5 hours of total integration time. We also present
simulated 3D IRIS data of resolved high-redshift star forming galaxies (1 < z <
5), illustrating the extraordinary potential of this instrument to probe the
dynamics, assembly, and chemical abundances of galaxies in the early universe.
With its finest spatial scales, IRIS will be able to study luminous, massive,
high-redshift star forming galaxies (star formation rates ~ 10 - 100 M yr-1) at
~100 pc resolution. Utilizing the coarsest spatial scales, IRIS will be able to
observe fainter, less massive high-redshift galaxies, with integrated star
formation rates less than 1 M yr-1, yielding a factor of 3 to 10 gain in
sensitivity compared to current integral field spectrographs. The combination
of both fine and coarse spatial scales with the diffraction-limit of the TMT
will significantly advance our understanding of early galaxy formation
processes and their subsequent evolution into presentday galaxies.Comment: SPIE Astronomical Instrumentation 201
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
Halo-Galaxy Lensing: A Full Sky Approach
The halo-galaxy lensing correlation function or the average tangential shear
profile over sampled halos is a very powerful means of measuring the halo
masses, the mass profile, and the halo-mass correlation function of very large
separations in the linear regime. We reformulate the halo-galaxy lensing
correlation in harmonic space. We find that, counter-intuitively, errors in the
conventionally used flat-sky approximation remain at a % level even at very
small angles. The errors increase at larger angles and for lensing halos at
lower redshifts: the effect is at a few % level at the baryonic acoustic
oscillation scales for lensing halos of , and comparable with the
effect of primordial non-Gaussianity with at large
separations. Our results allow to readily estimate/correct for the full-sky
effect on a high-precision measurement of the average shear profile available
from upcoming wide-area lensing surveys.Comment: 12 pages, 4 figure
Anatomy of the AGN in NGC 5548: I. A global model for the broadband spectral energy distribution
An extensive multi-satellite campaign on NGC 5548 has revealed this
archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy
absorption. Our observations taken in 2013-2014 with XMM-Newton, Swift, NuSTAR,
INTEGRAL, Chandra, HST and two ground-based observatories have together enabled
us to establish that this unexpected phenomenon is caused by an outflowing
stream of weakly ionised gas (called the obscurer), extending from the vicinity
of the accretion disk to the broad-line region. In this work we present the
details of our campaign and the data obtained by all the observatories. We
determine the spectral energy distribution of NGC 5548 from near-infrared to
hard X-rays by establishing the contribution of various emission and absorption
processes taking place along our line of sight towards the central engine. We
thus uncover the intrinsic emission and produce a broadband continuum model for
both obscured (average summer 2013 data) and unobscured ( 2011) epochs of
NGC 5548. Our results suggest that the intrinsic NIR/optical/UV continuum is a
single Comptonised component with its higher energy tail creating the 'soft
X-ray excess'. This component is compatible with emission from a warm,
optically-thick corona as part of the inner accretion disk. We then investigate
the effects of the continuum on the ionisation balance and thermal stability of
photoionised gas for unobscured and obscured epochs.Comment: Accepted for publication in A&A, 19 pages, 13 figure
Dark-field transmission electron microscopy and the Debye-Waller factor of graphene
Graphene's structure bears on both the material's electronic properties and
fundamental questions about long range order in two-dimensional crystals. We
present an analytic calculation of selected area electron diffraction from
multi-layer graphene and compare it with data from samples prepared by chemical
vapor deposition and mechanical exfoliation. A single layer scatters only 0.5%
of the incident electrons, so this kinematical calculation can be considered
reliable for five or fewer layers. Dark-field transmission electron micrographs
of multi-layer graphene illustrate how knowledge of the diffraction peak
intensities can be applied for rapid mapping of thickness, stacking, and grain
boundaries. The diffraction peak intensities also depend on the mean-square
displacement of atoms from their ideal lattice locations, which is
parameterized by a Debye-Waller factor. We measure the Debye-Waller factor of a
suspended monolayer of exfoliated graphene and find a result consistent with an
estimate based on the Debye model. For laboratory-scale graphene samples,
finite size effects are sufficient to stabilize the graphene lattice against
melting, indicating that ripples in the third dimension are not necessary.Comment: 10 pages, 4 figure
The ATLAS 5.5 GHz survey of the Extended Chandra Deep Field South: Catalogue, Source Counts and Spectral Indices
Star forming galaxies are thought to dominate the sub-mJy radio population,
but recent work has shown that low luminosity AGN can still make a significant
contribution to the faint radio source population. Spectral indices are an
important tool for understanding the emission mechanism of the faint radio
sources. We have observed the extended Chandra Deep Field South at 5.5 GHz
using a mosaic of 42 pointings with the Australia Telescope Compact Array
(ATCA). Our image reaches an almost uniform sensitivity of ~12 microJy rms over
0.25 deg^2 with a restoring beam of 4.9 x 2.0 arcsec, making it one of the
deepest 6cm surveys to date. We present the 5.5 GHz catalogue and source counts
from this field. We take advantage of the large amounts of ancillary data in
this field to study the 1.4 to 5.5 GHz spectral indices of the sub-mJy
population. For the full 5.5 GHz selected sample we find a flat median spectral
index, alpha_med = -0.40, which is consistent with previous results. However,
the spectral index appears to steepen at the faintest flux density levels
(S_{5.5 GHz} < 0.1 mJy), where alpha_med = -0.68. We performed stacking
analysis of the faint 1.4 GHz selected sample (40 < S_{1.4 GHz} < 200 microJy)
and also find a steep average spectral index, alpha = -0.8, consistent with
synchrotron emission. We find a weak trend of steepening spectral index with
redshift. Several young AGN candidates are identified using spectral indices,
suggesting Gigahertz Peaked Spectrum (GPS) sources are as common in the mJy
population as they are at Jy levels.Comment: 18 pages, 16 figures, accepted for publication in MNRA
Band Topology and Linking Structure of Nodal Line Semimetals with Z2 Monopole Charges
We study the band topology and the associated linking structure of
topological semimetals with nodal lines carrying monopole charges,
which can be realized in three-dimensional systems invariant under the
combination of inversion and time reversal when spin-orbit coupling is
negligible. In contrast to the well-known -symmetric nodal lines protected
only by Berry phase in which a single nodal line can exist, the nodal
lines with monopole charges should always exist in pairs. We show that
a pair of nodal lines with monopole charges is created by a {\it double
band inversion} (DBI) process, and that the resulting nodal lines are always
{\it linked by another nodal line} formed between the two topmost occupied
bands. It is shown that both the linking structure and the monopole
charge are the manifestation of the nontrivial band topology characterized by
the {\it second Stiefel-Whitney class}, which can be read off from the Wilson
loop spectrum. We show that the second Stiefel-Whitney class can serve as a
well-defined topological invariant of a -invariant two-dimensional (2D)
insulator in the absence of Berry phase. Based on this, we propose that pair
creation and annihilation of nodal lines with monopole charges can
mediate a topological phase transition between a normal insulator and a
three-dimensional weak Stiefel-Whitney insulator (3D weak SWI). Moreover, using
first-principles calculations, we predict ABC-stacked graphdiyne as a nodal
line semimetal (NLSM) with monopole charges having the linking
structure. Finally, we develop a formula for computing the second
Stiefel-Whitney class based on parity eigenvalues at inversion invariant
momenta, which is used to prove the quantized bulk magnetoelectric response of
NLSMs with monopole charges under a -breaking perturbation.Comment: 4+28 pages, 3+17 figure
E3D, The Euro3D Visualization Tool I: Description of the program and its capabilities
We present the first version of E3D, the Euro3D visualization tool for data
from integral field spectroscopy. We describe its major characteristics, based
on the proposed requirements, the current state of the project, and some
planned future upgrades. We show examples of its use and capabilities.Comment: 4 pages, 6 figures, accepted for publishing in AN (ref.proc. of
Euro3D Science workshop, IoA Cambridge, May 2003
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