Kevork N. Abazajian
A5032155044- Dark Matter and Cosmic Phenomena
- Cosmology and Gravitation Theories
- Astrophysics and Cosmic Phenomena
- Neutrino Physics Research
- Particle physics theoretical and experimental studies
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Stellar, planetary, and galactic studies
- Radio Astronomy Observations and Technology
- Computational Physics and Python Applications
- Radioactive Decay and Measurement Techniques
- Atomic and Subatomic Physics Research
- Scientific Research and Discoveries
- Particle Detector Development and Performance
- Pulsars and Gravitational Waves Research
- Relativity and Gravitational Theory
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Quantum, superfluid, helium dynamics
- Astronomical Observations and Instrumentation
- Black Holes and Theoretical Physics
- Astro and Planetary Science
- Space Science and Extraterrestrial Life
- Remote Sensing in Agriculture
University of California System
2025
University of California, Irvine
2015-2024
Irvine University
2016-2022
University of Chicago
2014
University of Maryland, College Park
2006-2012
Joint Space Science Institute
2011-2012
Los Alamos National Laboratory
2004-2007
Fermi National Accelerator Laboratory
2002-2005
University of California, Santa Barbara
2005
University of California, San Diego
1999-2003
This paper describes the Seventh Data Release of Sloan Digital Sky Survey (SDSS), marking completion original goals SDSS and end phase known as SDSS-II. It includes 11,663 deg2 imaging data, with most ∼2000 increment over previous data release lying in regions low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. survey also repeat on a 120° long, 25 wide stripe along celestial equator Southern Cap, some covered by many 90 individual runs. We...
We measure cosmological parameters using the three-dimensional power spectrum $P(k)$ from over 200 000 galaxies in Sloan Digital Sky Survey (SDSS) combination with Wilkinson Microwave Anisotropy Probe (WMAP) and other data. Our results are consistent a ``vanilla'' flat adiabatic cold dark matter model constant without tilt ${(n}_{s}=1),$ running tilt, tensor modes, or massive neutrinos. Adding SDSS information more than halves WMAP-only error bars on some parameters, tightening...
We measure the large-scale real-space power spectrum $P(k)$ using luminous red galaxies (LRGs) in Sloan Digital Sky Survey (SDSS) and use this measurement to sharpen constraints on cosmological parameters from Wilkinson Microwave Anisotropy Probe (WMAP). employ a matrix-based estimation method Pseudo-Karhunen-Lo\`eve eigenmodes, producing uncorrelated minimum-variance measurements 20 $k$-bands of both clustering its anisotropy due redshift-space distortions, with narrow well-behaved window...
We measure the mass function of dark matter halos in a large set collisionless cosmological simulations flat ΛCDM cosmology and investigate its evolution at z≲ 2. Halos are identified as isolated density peaks, their masses measured within series radii enclosing specific overdensities. argue that these spherical overdensity more directly linked to cluster observables than using friends-of-friends algorithm (FOF), therefore preferable for accurate forecasts halo abundances. Our simulation...
The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg2 five-band (ugriz) imaging with photometry for over 88 million unique objects, 367,360 spectra galaxies, quasars, stars, calibrating blank sky patches selected 2627 this area, tables measured parameters from these data. reach a depth r ≈ 22.2 (95% completeness limit point sources) are photometrically astrometrically calibrated to 2% rms 100 mas per...
The Sloan Digital Sky Survey has validated and made publicly available its First Data Release. This consists of 2099 square degrees five-band (u, g, r, i, z) imaging data, 186,240 spectra galaxies, quasars, stars calibrating blank sky patches selected over 1360 this area, tables measured parameters from these data. data go to a depth r ~ 22.6 are photometrically astrometrically calibrated 2% rms 100 milli-arcsec per coordinate, respectively. cover the range 3800--9200 A, with resolution...
This paper describes the Third Data Release of Sloan Digital Sky Survey (SDSS). release, containing data taken up through 2003 June, includes imaging in five bands over 5282 deg2, photometric and astrometric catalogs 141 million objects detected these data, spectra 528,640 selected 4188 deg2. The pipelines analyzing both images spectroscopy are unchanged from those used our Second Release.
This white paper addresses the hypothesis of light sterile neutrinos based on recent anomalies observed in neutrino experiments and latest astrophysical data.
We calculate the incoherent resonant and non-resonant scattering production of sterile neutrinos in early universe. find ranges neutrino masses, vacuum mixing angles, initial lepton numbers which allow these species to constitute viable hot, warm, cold dark matter (HDM, WDM, CDM) candidates meet observational constraints. The constraints considered here include energy loss core collapse supernovae, density limits at big bang nucleosynthesis, those stemming from decay: observed cosmic...
We show the existence of a statistically significant, robust detection gamma-ray source in Milky Way Galactic Center that is consistent with spatially extended signal using about 4 years Fermi-LAT data. The flux annihilation dark matter particles thermal cross section if spatial distribution similar to predictions only simulations. find significant detections an spectrum particle masses approximately 10 GeV 1 TeV annihilating $b\overline{b}$ quarks and 10--30...
We present the science case, reference design, and project plan for Stage-4 ground-based cosmic microwave background experiment CMB-S4.
This book lays out the scientific goals to be addressed by next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned consist of dedicated telescopes at South Pole, high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies crossing critical thresholds in search for B-mode polarization signature primordial gravitational waves, determination number...
The predicted mass function of dark matter halos is essential in connecting observed galaxy cluster counts and models clustering to the properties primordial density field. We determine concordance $Λ$CDM cosmology, as well its uncertainty, using sixteen $1024^3$-particle nested-volume dark-matter simulations, spanning a range over five orders magnitude. Using nested volumes single-halo tests, we find correct for systematic error friends-of-friends halo-finding algorithm. fitting form full...
We construct empirical models of the diffuse gamma-ray background toward Galactic Center. Including all known point sources and a template emission associated with interactions cosmic rays molecular gas, we show that extended observed previously in Fermi Large Area Telescope data Center is detected at high significance for permutations model components. However, find fluxes spectra our change significantly depending on model. In particular, spectrum central Sgr A$^\ast$ source less steep...
We show that the canonical oscillation-based (non-resonant) production of sterile neutrino dark matter is inconsistent at $>99$% confidence with observations galaxies in Local Group. set lower limits on non-resonant mass $2.5$ keV (equivalent to $0.7$ thermal mass) using phase-space densities derived for dwarf satellite Milky Way, as well $8.8$ $1.8$ based subhalo counts $N$-body simulations M 31 analogues. Combined improved upper from significantly deeper X-ray data full consideration...
Abstract CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding origin evolution universe. Among science cases pursued with CMB-S4, quest for detecting primordial gravitational waves is a central driver experimental design. This work details development forecasting framework that includes power-spectrum-based semianalytic projection tool, targeted explicitly toward...
We identify galaxy groups and clusters in volume-limited samples of the SDSS redshift survey, using a redshift-space friends-of-friends algorithm. optimize linking lengths to recover systems that occupy same dark matter halos, set mock catalogs created by populating halos N-body simulations with galaxies. Extensive tests these show no combination perpendicular line-of-sight is able yield simultaneously true halo multiplicity function, projected size distribution, velocity dispersion. adopt...
I show that the spectrum and morphology of a recent Fermi-LAT observation Galaxy center are consistent with millisecond pulsar population in nuclear Central stellar cluster Milky Way. The Center gamma-ray is four eight globular clusters have been detected gamma-ray. A dark matter annihilation interpretation cannot be ruled out, though no unique features exist would require this conclusion.
We point out a serendipitous link between warm dark matter (WDM) models for structure formation on the one hand and high-sensitivity energy range (1-10 keV) X-ray photon detection Chandra XMM-Newton observatories other. This fortuitous match may provide either direct of or exclusion many candidates. estimate expected fluxes from field galaxies clusters if halos these objects are composed WDM candidate particles with rest masses in formation-preferred (~1 to ~20 small radiative decay...
We assess a mechanism which can transform neutrino-antineutrino asymmetries between flavors in the early universe, and confirm that such transformation is unavoidable near bimaximal framework emerging for neutrino mixing matrix. show process standard Mikheyev-Smirnov-Wolfenstein flavor dictated by synchronization of momentum states. also ``equilibration'' special feature maximal mixing, carefully examine new constraints placed on asymmetries. In particular, big bang nucleosynthesis limit...