2,746 research outputs found
All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8
In this paper we present photometric redshift (photo-) estimates for the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, currently
the most sensitive optical survey covering the majority of the extra-galactic
sky. Our photo- methodology is based on a machine-learning approach, using
sparse Gaussian processes augmented with Gaussian mixture models (GMMs) that
allow regions of parameter space to be identified and trained separately in a
purely data-driven way. The same GMMs are also used to calculate cost-sensitive
learning weights that mitigate biases in the spectroscopic training sample. By
design, this approach aims to produce reliable and unbiased predictions for all
parts of the parameter space present in wide area surveys. Compared to previous
literature estimates using the same underlying photometry, our photo-s are
significantly less biased and more accurate at , with negligible loss in
precision or reliability for resolved galaxies at . Our photo-
estimates offer accurate predictions for rare high-value populations within the
parent sample, including optically selected quasars at the highest redshifts
(), as well as X-ray or radio continuum selected populations across a
broad range of flux (densities) and redshift. Deriving photo- estimates for
the full Legacy Imaging Surveys Data Release 8, the catalogues provided in this
work offer photo- estimates predicted to be high quality for
galaxies over and
spanning , offering one of the most extensive samples of
redshift estimates ever produced.Comment: 22 pages, 19 figures - Accepted for publication in MNRAS. Catalogues
produced will be made available through queryable public databases - users
interested in the full catalogues or early access to subsets are also
encouraged to contact the author directl
Powering reionization:assessing the galaxy ionizing photon budget at z <10
We present a new analysis of the ionizing emissivity (,
s Mpc) for galaxies during the epoch of reionization and their
potential for completing and maintaining reionization. We use extensive SED
modelling -- incorporating two plausible mechanisms for the escape of Lyman
continuum photon -- to explore the range and evolution of ionizing efficiencies
consistent with new results on galaxy colours () during this epoch. We
estimate for the latest observations of the luminosity and
star-formation rate density at , outlining the range of emissivity
histories consistent with our new model. Given the growing observational
evidence for a UV colour-magnitude relation in high-redshift galaxies, we find
that for any plausible evolution in galaxy properties, red (brighter) galaxies
are less efficient at producing ionizing photons than their blue (fainter)
counterparts. The assumption of a redshift and luminosity evolution in
leads to two important conclusions. Firstly, the ionizing efficiency of
galaxies naturally increases with redshift. Secondly, for a luminosity
dependent ionizing efficiency, we find that galaxies down to a rest-frame
magnitude of alone can potentially produce sufficient
numbers of ionizing photons to maintain reionization as early as for a
clumping factor of .Comment: Accepted for publication in MNRA
Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004
Rupture of the Sunda megathrust on 26 December 2004 produced broad regions of uplift and subsidence. We define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great M_w ≈ 9.2 earthquake. In the region of the Andaman and Nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model. At the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls. Uplift extends from the middle of Simeulue Island, Sumatra, at ~2.5°N, to Preparis Island, Myanmar (Burma), at ~14.9°N. Thus the rupture is ~1600 km long. The distance from the pivot line to the trench varies appreciably. The northern and western Andaman Islands rose, whereas the southern and eastern portion of the islands subsided. The Nicobar Islands and the west coast of Aceh province, Sumatra, subsided. Tilt at the southern end of the rupture is steep; the distance from 1.5 m of uplift to the pivot line is just 60 km. Our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions
Photometric redshifts for the next generation of deep radio continuum surveys - II. Gaussian processes and hybrid estimates
Building on the first paper in this series (Duncan et al. 2018), we present a study investigating the performance of Gaussian process photometric redshift (photo-z) estimates for galaxies and active galactic nuclei detected in deep radio continuum surveys. A Gaussian process redshift code is used to produce photo-z estimates targeting specific subsets of both the AGN population - infrared, X-ray and optically selected AGN - and the general galaxy population. The new estimates for the AGN population are found to perform significantly better at z > 1 than the template-based photo-z estimates presented in our previous study. Our new photo-z estimates are then combined with template estimates through hierarchical Bayesian combination to produce a hybrid consensus estimate that outperforms both of the individual methods across all source types. Photo-z estimates for radio sources that are X-ray sources or optical/IR AGN are significantly improved in comparison to previous template-only estimates - with outlier fractions and robust scatter reduced by up to a factor of ∼4. The ability of our method to combine the strengths of the two input photo-z techniques and the large improvements we observe illustrate its potential for enabling future exploitation of deep radio continuum surveys for both the study of galaxy and black hole co-evolution and for cosmological studies
Architectural Implementation of NASA Space Telecommunications Radio System Specification
This software demonstrates a working implementation of the NASA STRS (Space Telecommunications Radio System) architecture specification. This is a developing specification of software architecture and required interfaces to provide commonality among future NASA and commercial software-defined radios for space, and allow for easier mixing of software and hardware from different vendors. It provides required functions, and supports interaction with STRS-compliant simple test plug-ins ("waveforms"). All of it is programmed in "plain C," except where necessary to interact with C++ plug-ins. It offers a small footprint, suitable for use in JPL radio hardware. Future NASA work is expected to develop into fully capable software-defined radios for use on the space station, other space vehicles, and interplanetary probes
Puzzling It Out: The Current State of Scientific Knowledge on Pre-Kindergarten Effects - A Consensus Statement
Scientific research has established that if all children are to achieve their developmental potential, it is important to lay the foundation during the earliest years for lifelong health, learning, and positive behavior. A central question is how well our public pre-kindergarten (pre-K) programs are doing to build this foundation.Forty-two states and the District of Columbia, through 57 pre-K programs, have introduced substantial innovations in their early education systems by developing the infrastructure, program sites, and workforce required to accommodate pre-K education. These programs now serve nearly 30 percent of the nation's 4-year-olds and 5 percent of 3-year-olds
Galaxy Merger Rates up to z ~ 3 using a Bayesian Deep Learning Model: A Major-Merger classifier using IllustrisTNG Simulation data
Merging is potentially the dominate process in galaxy formation, yet there is
still debate about its history over cosmic time. To address this we classify
major mergers and measure galaxy merger rates up to z 3 in all five
CANDELS fields (UDS, EGS, GOODS-S, GOODS-N, COSMOS) using deep learning
convolutional neural networks (CNNs) trained with simulated galaxies from the
IllustrisTNG cosmological simulation. The deep learning architecture used is
objectively selected by a Bayesian Optmization process over the range of
possible hyperparameters. We show that our model can achieve 90% accuracy when
classifying mergers from the simulation, and has the additional feature of
separating mergers before the infall of stellar masses from post mergers. We
compare our machine learning classifications on CANDELS galaxies and compare
with visual merger classifications from Kartaltepe et al. (2015), and show that
they are broadly consistent. We finish by demonstrating that our model is
capable of measuring galaxy merger rates, , that are consistent
with results found for CANDELS galaxies using close pairs statistics, with
. This is the
first general agreement between major mergers measured using pairs and
structure at z < 3.Comment: 22 pages, 13 figures, 3 tables, accepted for publication in Ap
One - play, two - play, five - play, and ten-play runs of Prisoner's Dilemma 1
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66600/2/10.1177_002200276601000307.pd
A consistent measure of the merger histories of massive galaxies using close-pair statistics I:Major mergers at z <3.5
We use a large sample of galaxies constructed by combining the
UKIDSS UDS, VIDEO/CFHT-LS, UltraVISTA/COSMOS and GAMA survey regions to probe
the major merging histories of massive galaxies ()
at . We use a method adapted from that presented in
Lopez-Sanjuan et al. (2014) using the full photometric redshift probability
distributions, to measure pair of flux-limited, stellar
mass selected galaxy samples using close-pair statistics. The pair fraction is
found to weakly evolve as with no dependence on stellar
mass. We subsequently derive major merger for galaxies at and at a constant number density of
Mpc, and find rates a factor of 2-3 smaller than previous works,
although this depends strongly on the assumed merger timescale and likelihood
of a close-pair merging. Galaxies undergo approximately 0.5 major mergers at , accruing an additional 1-4 in the
process. Major merger accretion rate densities of
yr Mpc are found for number density selected
samples, indicating that direct progenitors of local massive
() galaxies have experienced a steady supply of
stellar mass via major mergers throughout their evolution. While pair fractions
are found to agree with those predicted by the Henriques et al. (2014)
semi-analytic model, the Illustris hydrodynamical simulation fails to
quantitatively reproduce derived merger rates. Furthermore, we find major
mergers become a comparable source of stellar mass growth compared to
star-formation at , but is 10-100 times smaller than the SFR density at
higher redshifts.Comment: 26 pages, 18 figures, accepted to MNRA
The evolution of galaxy number density at z < 8 and its implications
The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z _ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies (_T), more massive than M∗ = 106 M⊙ , decreases as _T _ t−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M∗ > 107 M⊙ . By using the M∗ = 106 M⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0+0.7 −0.6 × 1012 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox
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