A5048581349- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Advanced Statistical Methods and Models
- Cosmology and Gravitation Theories
- Astrophysical Phenomena and Observations
- Superconducting and THz Device Technology
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Remote Sensing in Agriculture
- Particle Detector Development and Performance
- Impact of Light on Environment and Health
- Calibration and Measurement Techniques
- Scientific Measurement and Uncertainty Evaluation
- Advanced Vision and Imaging
- Data-Driven Disease Surveillance
- Particle accelerators and beam dynamics
- Stellar, planetary, and galactic studies
- Solar and Space Plasma Dynamics
- Microwave Engineering and Waveguides
- Adaptive optics and wavefront sensing
- History and Developments in Astronomy
University of Richmond
2015-2024
Kavli Institute for Particle Astrophysics and Cosmology
2008-2022
Stanford University
2008-2022
SLAC National Accelerator Laboratory
2008-2013
University of California, Santa Barbara
2005-2007
Goddard Space Flight Center
2006
The ARCADE 2 instrument has measured the absolute temperature of sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic observing balloon altitudes with no emissive windows between beam-forming optics sky. An external blackbody calibrator provides in situ reference. Systematic errors were greatly reduced by differential radiometers cooling all critical components to physical temperatures approximating cosmic microwave background (CMB) temperature. A linear model is...
Here we introduce PHAT, the PHoto-z Accuracy Testing programme, an international initiative to test and compare different methods of photo-z estimation. Two environments are set up, one (PHAT0) based on simulations basic functionality codes, another (PHAT1) data from GOODS survey. The accuracy is expressed ranked by global bias, scatter, outlier rates. Most agree well PHAT0 but produce scatters that can differ up a factor two even in this idealised case. A larger spread found for PHAT1. Few...
We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of ARCADE 2 instrument, along with previous measurements at other frequencies, to constrain models extragalactic emission. Such emission is a combination cosmic microwave background (CMB) monopole, Galactic foreground emission, integrated contribution radio external galaxies, any spectral distortions present in CMB, source. After removal estimates our own Galaxy, an estimated we fits flat-spectrum CMB...
Gamma-ray bursts (GRBs), which have been observed up to redshifts z approx 9.5 can be good probes of the early universe and potential testing cosmological models. The analysis by Dainotti GRB Swift afterglow lightcurves with known definite X-ray plateau shows an anti-correlation between rest frame time when ends (the end time) calculated luminosity at that (or approximately duration luminosity). We present here update this correlation a larger data sample 101 GRBs lightcurves. Since some...
We use absolutely calibrated data from the ARCADE 2 flight in 2006 July to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure is consistent with a superposition of free–free synchrotron emission. Emission morphology traced by Haslam 408 MHz survey has spectral index βsynch = −2.5 ± 0.1, contributing 0.10 0.01 total plane lowest band 3.15 estimate toward polar caps using either simple plane-parallel csc |b| dependence or high-latitude radio COBE/FIRAS map C ii Both...
Abstract We summarize the second radio synchrotron background workshop, which took place on 2022 June 15–17 in Barolo, Italy. This meeting was convened because available measurements of diffuse zero level continue to suggest that it is several times higher than can be attributed known Galactic and extragalactic sources processes, rendering least well-understood electromagnetic at present a major outstanding question astrophysics. The workshop agreed next priorities for investigations this...
We calculate simultaneously the radio and optical luminosity evolutions of quasars, distribution in loudness R defined as ratio luminosities, using a flux limited data set containing 636 quasars with fluxes from White et al. first note that when dealing multivariate it is imperative to determine true correlations among variables, not those introduced by observational selection effects, before obtaining individual distributions variables. use methods developed Efron Petrosian which are...
Abstract We present results exploring the role that probabilistic deep learning models can play in cosmology from large-scale astronomical surveys through photometric redshift (photo- z ) estimation. Photo- uncertainty estimates are critical for science goals of upcoming such as Legacy Survey Space and Time (LSST); however, common machine methods typically provide only point lack uncertainties on predictions. turn to Bayesian neural networks (BNNs) a promising way accurate predictions values...
The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of cosmic microwave background Galactic extra-Galactic emission at six frequencies from 3 90 GHz. ARCADE 2 utilizes double-nulled design where sky compared that an external cryogenic full-aperture blackbody calibrator by switching radiometers containing internal reference loads. In order further minimize sources...
We present a determination of the distributions photon spectral index and gamma-ray flux - so called LogN-LogS relation for 352 blazars detected with greater than approximately seven sigma detection threshold located above +/- 20 degrees Galactic latitude by Large Area Telescope Fermi Gamma-ray Space in its first year catalog. Because depends on index, observed raw do not provide true counts or distribution index. use non-parametric methods developed Efron Petrosian to reconstruct intrinsic...
Abstract We explore whether an independent determination of the distance‒redshift relation, and hence cosmological model parameters, can be obtained from apparent correlations between two different wave-band luminosities or fluxes, as has been claimed in recent works using X-ray ultraviolet fluxes quasars. show that such is possible only if correlation independently measured redshifts, for example, based on sound theoretical models unrelated observations. In particular, we determined...
We investigate different scenarios for the origin of extragalactic radio background. The surface brightness background, as reported by ARCADE 2 collaboration, is several times higher than that which would result from currently observed sources. consider contributions to background diffuse synchrotron emission clusters and intergalactic medium, previously unrecognized flux low regions sources, faint point sources below limit existing surveys. By examining source counts available in...
The Large Synoptic Survey Telescope (LSST) is a large aperture, wide-field facility designed to provide deep images of half the sky every few nights. There only single instrument on telescope, 9.6 square degree visible-band camera, which mounted close secondary mirror, and points down toward tertiary. requirements of the LSST camera present substantial technical design challenges. To cover entire 0.35 1 μm visible band, camera incorporates an array 189 over-depleted bulk silicon CCDs...
We determine the radio and optical luminosity evolutions true distribution of loudness parameter R, defined as ratio to luminosity, for a set more than 5000 quasars combining SDSS FIRST data. apply method Efron Petrosian access intrinsic parameters, taking into account truncations correlations inherent in find that population exhibits strong positive evolution with redshift both wavebands, somewhat greater optical. With accounted for, we density local functions. The R is found be quite...
Aims. We present a custom support vector machine classification package for photometric redshift estimation, including comparisons with other methods. also explore the efficacy of galaxy shape information in estimation. Support machines, type learning, utilize optimization theory and supervised learning algorithms to construct predictive models based on content data way that can treat different input features symmetrically, which be useful estimator contained additional beyond photometry,...
ABSTRACT The origin of the radio synchrotron background (RSB) is currently unknown. Its understanding might have profound implications in fundamental physics or reveal a new class emitters. In this work, we consider scenario which RSB due to extragalactic sources and measure angular cross-correlation Low-Frequency Array (LOFAR) images diffuse sky with matter tracers at different redshifts, provided by galaxy catalogues cosmic microwave lensing. We compare these measured cross-correlations...
We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of ARCADE 2 instrument, along with previous measurements at other frequencies, to constrain models extragalactic emission. Such emission is a combination Cosmic Microwave Background (CMB) monopole, Galactic foreground emission, integrated contribution radio external galaxies, any spectral distortions present in CMB, source. After removal estimates our own Galaxy, estimated we fits flat-spectrum CMB potential...
We summarize the radio synchrotron background workshop that took place 2017 July 19–21 at University of Richmond. This first scientific meeting dedicated to topic was convened because current measurements diffuse monopole reveal a surface brightness is several times higher than can be straightforwardly explained by known Galactic and extragalactic sources processes, rendering it far least well understood photon present. It conclusion majority participants level or near reported ARCADE 2...
The calibration methods for the ARCADE II instrument are described and accuracy estimated. Steelcast coated aluminum cones which comprise calibrator have a low reflection while maintaining 94% of absorber volume within 5mK base temperature (modeled). demonstrates an with active part less than one wavelength thick only marginally larger mouth largest horn yet black (less −40dB or 0.01% reflection) over five octaves in frequency.
We present a determination of the effects including galaxy morphological parameters in photometric redshift estimation with an artificial neural network method. Neural networks, which recognize patterns information content data unbiased way, can be useful estimator additional contained extra parameters, such as those describing morphology, if input are treated on equal footing. use imaging and five band magnitudes from All-wavelength Extended Groth Strip International Survey (AEGIS). It is...
We present the largest low frequency (120~MHz) arcminute resolution image of radio synchrotron background (RSB) to date, and its corresponding angular power spectrum anisotropies (APS) with scales ranging from $3^\circ$ $0.3^\prime$. show that RSB around North Celestial Pole has a significant excess anisotropy at all over model unclustered point sources based on source counts known classes. This excess, which does not seem attributable diffuse Galactic emission, could be linked surface...
We present a determination of the distributions gamma-ray photon flux – so-called LogN–LogS relation and spectral index for blazars, based on third extragalactic source catalogue FermiGamma-ray Space Telescope's Large Area Telescope, considering energy range from 100 MeV to GeV. The data set consists 774 blazars in Clean sample detected with greater than approximately 7σ detection threshold located above ±20° Galactic latitude. use non-parametric methods verified previous works reconstruct...
We describe the electromagnetic and thermal design, performance, fabrication for two types of radiometric- waveguide load calibrators. A simple theory is presented used to minimize total volume absorber structure. These devices have been from room temperature below 4 K in microwave millimeter wavebands. The estimated precision calibrator better than 1 mK absolute at temperatures near 2.7 K.