179 research outputs found
EC1483 Emergency Brooding
Extension circular 1483 is instruction for inexpensive brooding for the begginer
A dark siren measurement of the Hubble constant with the LIGO/Virgo gravitational wave event GW190412 and DESI galaxies
We present a measurement of the Hubble Constant using the gravitational
wave event GW190412, an asymmetric binary black hole merger detected by
LIGO/Virgo, as a dark standard siren. This event does not have an
electromagnetic counterpart, so we use the statistical standard siren method
and marginalize over potential host galaxies from the Dark Energy Spectroscopic
Instrument (DESI) survey. GW190412 is well-localized to 12 deg (90%
credible interval), so it is promising for a dark siren analysis. The dark
siren value for km/s/Mpc, with a posterior shape
that is consistent with redshift overdensities. When combined with the bright
standard siren measurement from GW170817 we recover
km/s/Mpc, consistent with both early and late-time Universe measurements of
. This work represents the first standard siren analysis performed with
DESI data, and includes the most complete spectroscopic sample used in a dark
siren analysis to date.Comment: Submitted to RNAA
The DESI One-Percent Survey: Constructing Galaxy-Halo Connections for ELGs and LRGs Using Auto and Cross Correlations
In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at N M . We measure the auto and cross correlation functions of ELGs and LRGs at 108.0 M ⊙ from the DESI One-Percent survey. Following Gao et al., we construct the galaxy-halo connections for ELGs and LRGs simultaneously. With the stellar-halo mass relation for the whole galaxy population (i.e., normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability z ∼ 0.2 of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent z ∼ 0.2 model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at z ∼ 0.7 z ∼ 1. We can also reproduce the auto correlations of ELGs at deg2 z ∼ 1 (0.6 < z < 1.6 z ∼ 1) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of ∼1012 M ⊙, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions for ELGs, which can be used to produce ELG mocks in coarse simulations without resolving subhalos
DESI Complete Calibration of the Color-Redshift Relation (DC3R2): Results from early DESI data
We present initial results from the Dark Energy Spectroscopic Instrument
(DESI) Complete Calibration of the Color-Redshift Relation (DC3R2) secondary
target survey. Our analysis uses 230k galaxies that overlap with KiDS-VIKING
photometry to calibrate the color-redshift relation and to inform
photometric redshift (photo-z) inference methods of future weak lensing
surveys. Together with Emission Line Galaxies (ELGs), Luminous Red Galaxies
(LRGs), and the Bright Galaxy Survey (BGS) that provide samples of
complementary color, the DC3R2 targets help DESI to span 56% of the color space
visible to Euclid and LSST with high confidence spectroscopic redshifts. The
effects of spectroscopic completeness and quality are explored, as well as
systematic uncertainties introduced with the use of common Self Organizing Maps
trained on different photometry than the analysis sample. We further examine
the dependence of redshift on magnitude at fixed color, important for the use
of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy
sample. We find that noise in the KiDS-VIKING photometry introduces a dominant,
apparent magnitude dependence of redshift at fixed color, which indicates a
need for carefully chosen deep drilling fields, and survey simulation to model
this effect for future weak lensing surveys.Comment: 19 pages, 16 figures, submitted to MNRAS, interactive visualizations
at https://jmccull.github.io/DC3R2_Overvie
Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. I. Sample from the Early Data
\ua9 2024. The Author(s). Published by the American Astronomical Society.Changing-look active galactic nuclei (CL AGNs) can be generally confirmed by the emergence (turn-on) or disappearance (turn-off) of broad emission lines (BELs), associated with a transient timescale (about 100 ∼ 5000 days) that is much shorter than predicted by traditional accretion disk models. We carry out a systematic CL AGN search by crossmatching the spectra coming from the Dark Energy Spectroscopic Instrument and the Sloan Digital Sky Survey. Following previous studies, we identify CL AGNs based on Hα, Hβ, and Mg ii at z ≤ 0.75 and Mg ii, C iii], and C iv at z > 0.75. We present 56 CL AGNs based on visual inspection and three selection criteria, including 2 Hα, 34 Hβ, 9 Mg ii, 18 C iii], and 1 C iv CL AGN. Eight cases show simultaneous appearances/disappearances of two BELs. We also present 44 CL AGN candidates with significant flux variation of BELs, but remaining strong broad components. In the confirmed CL AGNs, 10 cases show additional CL candidate features for different lines. In this paper, we find: (1) a 24:32 ratio of turn-on to turn-off CL AGNs; (2) an upper-limit transition timescale ranging from 330 to 5762 days in the rest frame; and (3) the majority of CL AGNs follow the bluer-when-brighter trend. Our results greatly increase the current CL census (∼30%) and would be conducive to exploring the underlying physical mechanism
DESI complete calibration of the colour–redshift relation (DC3R2): results from early DESI data
We present initial results from the Dark Energy Spectroscopic Instrument (DESI) complete calibration of the colour–redshift relation (DC3R2) secondary target survey. Our analysis uses 230 k galaxies that overlap with KiDS-VIKING ugriZYJHKs photometry to calibrate the colour–redshift relation and to inform photometric redshift (photo-z) inference methods of future weak lensing surveys. Together with emission line galaxies (ELGs), luminous red galaxies (LRGs), and the Bright Galaxy Survey (BGS) that provide samples of complementary colour, the DC3R2 targets help DESI to span 56 per cent of the colour space visible to Euclid and LSST with high confidence spectroscopic redshifts. The effects of spectroscopic completeness and quality are explored, as well as systematic uncertainties introduced with the use of common Self-Organizing Maps trained on different photometry than the analysis sample. We further examine the dependence of redshift on magnitude at fixed colour, important for the use of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy sample. We find that noise in the KiDS-VIKING photometry introduces a dominant, apparent magnitude dependence of redshift at fixed colour, which indicates a need for carefully chosen deep drilling fields, and survey simulation to model this effect for future weak lensing surveys
Synthetic light-cone catalogues of modern redshift and weak lensing surveys waith abacussummit
The joint analysis of different cosmological probes, such as galaxy clustering and weak lensing, can potentially yield invaluable insights into the nature of the primordial Universe, dark energy, and dark matter. However, the development of high-fidelity theoretical models is a necessary stepping stone. Here, we present public high-resolution weak lensing maps on the light-cone, generated using the N-body simulation suite abacussummit, and accompanying weak lensing mock catalogues, tuned to the Early Data Release small-scale clustering measurements of the Dark Energy Spectroscopic Instrument. Available in this release are maps of the cosmic shear, deflection angle, and convergence fields at source redshifts ranging from z = 0.15 to 2.45 as well as cosmic microwave background convergence maps for each of the 25 base-resolution simulations (and Npart = 69123) as well as for the two huge simulations (and Npart = 86403) at the fiducial abacussummit cosmology. The pixel resolution of each map is 0.21 arcmin, corresponding to a healpix Nside of 16 384. The sky coverage of the base simulations is an octant until z ≈ 0.8 (decreasing to about 1800 deg2 at z ≈ 2.4), whereas the huge simulations offer full-sky coverage until z ≈ 2.2. Mock lensing source catalogues are sampled matching the ensemble properties of the Kilo-Degree Survey, Dark Energy Survey, and Hyper Suprime-Cam data sets. The mock catalogues are validated against theoretical predictions for various clustering and lensing statistics, such as correlation multipoles, galaxy-shear, and shear-shear, showing excellent agreement. All products can be downloaded via a Globus endpoint (see Data Availability section)
The frequency of metal enrichment of cool helium-atmosphere white dwarfs using the DESI early data release
There is an overwhelming evidence that white dwarfs host planetary systems; revealed by the presence, disruption, and accretion of planetary bodies. A lower limit on the frequency of white dwarfs that host planetary material has been estimated to be ≃ 25–50 per cent; inferred from the ongoing or recent accretion of metals on to both hydrogen-atmosphere and warm helium-atmosphere white dwarfs. Now with the unbiased sample of white dwarfs observed by the Dark Energy Spectroscopic Instrument (DESI) survey in their Early Data Release (EDR), we have determined the frequency of metal enrichment around cool-helium atmosphere white dwarfs as 21 ± 3 per cent using a sample of 234 systems. This value is in good agreement with values determined from previous studies. With the current samples we cannot distinguish whether the frequency of planetary accretion varies with system age or host-star mass, but the DESI data release 1 will contain roughly an order of magnitude more white dwarfs than DESI EDR and will allow these parameters to be investigated
The DESI One-Percent Survey: Modelling the clustering and halo occupation of all four DESI tracers with Uchuu
We present results from a set of high-fidelity simulated lightcones for the
DESI One-Percent Survey, created from the Uchuu simulation. This 8 (Gpc/h)^3
N-body simulation comprises 2.1 trillion particles and provides high-resolution
dark matter (sub)haloes in the framework of the Planck base-LCDM cosmology.
Employing the subhalo abundance matching (SHAM) technique, we populate the
Uchuu (sub)haloes with all four DESI tracers (BGS, LRG, ELG and QSO) to z =
2.1. Our method accounts for redshift evolution as well as the clustering
dependence on luminosity and stellar mass. The two-point clustering statistics
of the DESI One-Percent Survey align reasonably well with our predictions from
Uchuu across scales ranging from 0.1 Mpc/h to 100 Mpc/h. Some discrepancies
arise due to cosmic variance, incompleteness in the massive end of the stellar
mass function, and a simplified galaxy-halo connection model. We find that the
Uchuu BGS and LRG samples are adequately described using the standard
5-parameter halo occupation distribution model, while the ELGs and QSOs show
agreement with an adopted Gaussian distribution for central halos with a power
law for satellites. We observe a fair agreement in the large-scale bias
measurements between data and mock samples, although the data exhibits smaller
bias values, likely due to cosmic variance. The bias dependence on absolute
magnitude, stellar mass and redshift aligns with that of previous surveys.
These results improve simulated lightcone construction from cosmological models
and enhance our understanding of the galaxy-halo connection, with pivotal
insights from the first DESI data for the success of the final survey.Comment: 23 pages, 15 figures, 5 tables, submitted to MNRAS. The Uchuu-DESI
lightcones will be available at https://data.desi.lbl.go
Astrometric Calibration and Performance of the Dark Energy Spectroscopic Instrument Focal Plane
The Dark Energy Spectroscopic Instrument (DESI), consisting of 5020 robotic
fiber positioners and associated systems on the Mayall telescope at Kitt Peak,
Arizona, is carrying out a survey to measure the spectra of 40 million galaxies
and quasars and produce the largest 3D map of the universe to date. The primary
science goal is to use baryon acoustic oscillations to measure the expansion
history of the universe and the time evolution of dark energy. A key function
of the online control system is to position each fiber on a particular target
in the focal plane with an accuracy of 11m rms 2-D. This paper describes
the set of software programs used to perform this function along with the
methods used to validate their performance.Comment: 27 pages, 16 figures submitted to A
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