ABSTRACT
We present measurements of the redshift-dependent clustering of a DESI-like luminous red galaxy (LRG) sample selected from the Legacy Survey imaging data set, and use the halo occupation ...distribution (HOD) framework to fit the clustering signal. The photometric LRG sample in this study contains 2.7 million objects over the redshift range of 0.4 < z < 0.9 over 5655 deg2. We have developed new photometric redshift (photo-z) estimates using the Legacy Survey DECam and WISE photometry, with σNMAD = 0.02 precision for LRGs. We compute the projected correlation function using new methods that maximize signal-to-noise ratio while incorporating redshift uncertainties. We present a novel algorithm for dividing irregular survey geometries into equal-area patches for jackknife resampling. For a five-parameter HOD model fit using the MultiDark halo catalogue, we find that there is little evolution in HOD parameters except at the highest redshifts. The inferred large-scale structure bias is largely consistent with constant clustering amplitude over time. In an appendix, we explore limitations of Markov chain Monte Carlo fitting using stochastic likelihood estimates resulting from applying HOD methods to N-body catalogues, and present a new technique for finding best-fitting parameters in this situation. Accompanying this paper, we have released the Photometric Redshifts for the Legacy Surveys catalogue of photo-z’s obtained by applying the methods used in this work to the full Legacy Survey Data Release 8 data set. This catalogue provides accurate photometric redshifts for objects with z < 21 over more than 16 000 deg2 of sky.
Abstract
We use luminous red galaxies selected from the imaging
surveys that are being used for targeting by the Dark Energy
Spectroscopic Instrument (DESI) in combination with CMB lensing maps
from ...the Planck collaboration to probe the amplitude of large-scale
structure over 0.4 ≤
z
≤ 1. Our galaxy sample, with an angular
number density of approximately 500 deg
-2
over 18,000
sq.deg., is divided into 4 tomographic bins by photometric redshift
and the redshift distributions are calibrated using spectroscopy
from DESI. We fit the galaxy autospectra and galaxy-convergence
cross-spectra using models based on cosmological perturbation
theory, restricting to large scales that are expected to be well
described by such models. Within the context of ΛCDM,
combining all 4 samples and using priors on the background cosmology
from supernova and baryon acoustic oscillation measurements, we find
S
8
= σ
8
(Ω
m
/0.3)
0.5
= 0.73 ± 0.03. This result is
lower than the prediction of the ΛCDM model conditioned on
the Planck data. Our data prefer a slower growth of structure at
low redshift than the model predictions, though at only modest
significance.
ABSTRACT
The canonical Lambda cold dark matter (ΛCDM) cosmological model makes precise predictions for the clustering and lensing properties of galaxies. It has been shown that the lensing amplitude ...of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) is lower than expected given their clustering properties. We present new measurements and modelling of galaxies in the BOSS LOWZ sample. We focus on the radial and stellar mass dependence of the lensing amplitude mismatch. We find an amplitude mismatch of around $35{{\ \rm per\ cent}}$ when assuming ΛCDM with Planck Cosmological Microwave Background (CMB) constraints. This offset is independent of halo mass and radial scale in the range Mhalo ∼ 1013.3−1013.9h−1 M⊙ and $r=0.1\!-\!60 \, h^{-1} \mathrm{Mpc}$ ($k \approx 0.05\!-\!20 \, h \, {\rm Mpc}^{-1}$). The observation that the offset is both mass and scale independent places important constraints on the degree to which astrophysical processes (baryonic effects, assembly bias) can fully explain the effect. This scale independence also suggests that the ‘lensing is low’ effect on small and large radial scales probably have the same physical origin. Resolutions based on new physics require a nearly uniform suppression, relative to ΛCDM predictions, of the amplitude of matter fluctuations on these scales. The possible causes of this are tightly constrained by measurements of the CMB and of the low-redshift expansion history.
We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array ...Pathfinder. We imaged a 30 deg2 field at ΔT = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date.
Abstract
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical
grz
imaging over ...≈20,000 deg
2
from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in four bands (spanning 3.4–22
μ
m) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger than
R
(26) ≈ 25″ and
r
< 18 measured at the 26 mag arcsec
−2
isophote in the
r
band. The atlas delivers precise coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and multimessenger astronomical events; and more.
Abstract
We report the first results of a high-redshift (
z
≳ 5) quasar survey using the Dark Energy Spectroscopic Instrument (DESI). As a DESI secondary target program, this survey is designed to ...carry out a systematic search and investigation of quasars at 4.8 <
z
< 6.8. The target selection is based on the DESI Legacy Imaging Surveys (the Legacy Surveys) DR9 photometry, combined with the Pan-STARRS1 data and
J
-band photometry from public surveys. A first quasar sample has been constructed from the DESI Survey Validation 3 (SV3) and first-year observations until 2022 May. This sample includes more than 400 new quasars at redshift 4.7 ≤
z
< 6.6, down to 21.5 magnitude (AB) in the
z
band, discovered from 35% of the entire target sample. Remarkably, there are 220 new quasars identified at
z
≥ 5, more than one-third of existing quasars previously published at this redshift. The observations so far result in an average success rate of 23% at
z
> 4.7. The current spectral data set has already allowed analysis of interesting individual objects (e.g., quasars with damped Ly
α
absorbers and broad absorption line features), and statistical analysis will follow the survey’s completion. A set of science projects will be carried out leveraging this program, including quasar luminosity function, quasar clustering, intergalactic medium, quasar spectral properties, intervening absorbers, and properties of early supermassive black holes. Additionally, a sample of 38 new quasars at
z
∼ 3.8–5.7 discovered from a pilot survey in the DESI SV1 is also published in this paper.
We report a gate-tunable dimensional crossover in sub-micrometer-scale channels created at the LaAlO3/SrTiO3 interface. Conducting channels of widths 10 nm and 200 nm are created using conducting ...atomic force microscope lithography. Under sufficient negative back-gate tuning, the orbital magnetoconductance of the 200 nm channel is strongly quenched, and residual signatures of low-field weak-antilocalization become strikingly similar to that of the 10 nm channel. The dimensional crossover for the 200 nm channel takes place near the conductance quantum G = 2e
2/h. The ability to tune the dimensionality of narrow LaAlO3/SrTiO3 channels has implications for interpreting transport in a variety of gate-tunable oxide-heterostructure devices.
ABSTRACT
Studies of cosmology, galaxy evolution, and astronomical transients with current and next-generation wide-field imaging surveys like the Rubin Observatory Legacy Survey of Space and Time are ...all critically dependent on estimates of photometric redshifts. Capsule networks are a new type of neural network architecture that is better suited for identifying morphological features of the input images than traditional convolutional neural networks. We use a deep capsule network trained on ugriz images, spectroscopic redshifts, and Galaxy Zoo spiral/elliptical classifications of ∼400 000 Sloan Digital Sky Survey galaxies to do photometric redshift estimation. We achieve a photometric redshift prediction accuracy and a fraction of catastrophic outliers that are comparable to or better than current methods for SDSS main galaxy sample-like data sets (r ≤ 17.8 and zspec ≤ 0.4) while requiring less data and fewer trainable parameters. Furthermore, the decision-making of our capsule network is much more easily interpretable as capsules act as a low-dimensional encoding of the image. When the capsules are projected on a two-dimensional manifold, they form a single redshift sequence with the fraction of spirals in a region exhibiting a gradient roughly perpendicular to the redshift sequence. We perturb encodings of real galaxy images in this low-dimensional space to create synthetic galaxy images that demonstrate the image properties (e.g. size, orientation, and surface brightness) encoded by each dimension. We also measure correlations between galaxy properties (e.g. magnitudes, colours, and stellar mass) and each capsule dimension. We publicly release our code, estimated redshifts, and additional catalogues at https://biprateep.github.io/encapZulate-1.
Target Selection and Validation of DESI Quasars Chaussidon, Edmond; Yèche, Christophe; Palanque-Delabrouille, Nathalie ...
The Astrophysical journal,
02/2023, Letnik:
944, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 <
z
< 2.1 and using Ly
α
...forests in quasar spectra at
z
> 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands (
g
,
r
,
z
) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 <
r
< 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ∼1000 s. With a 310 deg
−2
target density, the main selection allows DESI to select more than 200 deg
−2
quasars (including 60 deg
−2
quasars with
z
> 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.
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