The Imprint of Warm Dark Matter on the Cosmological 21-cm Signal

We investigate the effects of warm dark matter (WDM) on the cosmic 21-cm signal. If dark matter exists as WDM instead of cold dark matter (CDM), its non-negligible velocities can inhibit the formation of low-mass halos that normally form first in CDM models, therefore delaying star-formation. The absence of early sources delays the build-up of UV and X-ray backgrounds that affect the 21-cm radiation signal produced by neutral hydrogen. With use of the 21CMFAST, code, we demonstrate that the pre-reionization 21-cm signal can be changed significantly in WDM models with a free-streaming length equivalent to that of a thermal relic with mass mx of up to ~10-20 keV. In such a WDM cosmology, the 21-cm signal traces the growth of more massive halos, resulting in a delay of the 21-cm absorption signature and followed by accelerated X-ray heating. CDM models where astrophysical sources have a suppressed photon-production efficiency can delay the 21-cm signal as well, although its subsequent evolution is not as rapid as compared to WDM. This motivates using the gradient of the global 21-cm signal to differentiate between some CDM and WDM models. Finally, we show that the degeneracy between the astrophysics and mx can be broken with the 21-cm power spectrum, as WDM models should have a bias-induced excess of power on large scales. This boost in power should be detectable with current interferometers for models with mx < 3 keV, while next generation instruments will easily be able to measure this difference for all relevant WDM models.Comment: 9 pages, 7 figure

Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 -- 2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that will yield constraints on the BAO power spectrum and provide a test-bed for our calibration scheme. I will discuss the CHIME calibration requirements and describe instrumentation we are developing to meet these requirements

Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder

A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beamforming that characterized previous designs. The Pathfinder consists of two cylinders 37\,m long by 20\,m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of $\sim$100\,degrees by 1-2\,degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every $\sim$30\,cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800\,MHz, and directly sampled at 800\,MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation.Comment: 20 pages, 12 figures. submitted to Proc. SPIE, Astronomical Telescopes + Instrumentation (2014

4D-Var inversion of European NH3 emissions Using CrIS NH3 measurements and GEOS-Chem adjoint with bi-directional and uni-directional flux schemes

We conduct the first 4D-Var inversion of NH3 accounting for NH3 bi-directional flux, using CrIS satellite NH3 observations over Europe in 2016. We find posterior NH3 emissions peak more in springtime than prior emissions at continental to national scales, and annually they are generally smaller than the prior emissions over central Europe, but larger over most of the rest of Europe. Annual posterior anthropogenic NH3 emissions for 25 European Union members (EU25) are 25% higher than the prior emissions and very close (<2% difference) to other inventories. Our posterior annual anthropogenic emissions for EU25, the UK, the Netherlands, and Switzerland are generally 10%–20% smaller than when treating NH3 fluxes as uni-directional emissions, while the monthly regional difference can be up to 34% (Switzerland in July). Compared to monthly mean in-situ observations, our posterior NH3 emissions from both schemes generally improve the magnitude and seasonality of simulated surface NH3 and bulk NHx wet deposition throughout most of Europe, whereas evaluation against hourly measurements at a background site shows the bi-directional scheme better captures observed diurnal variability of surface NH3. This contrast highlights the need for accurately simulating diurnal variability of NH3 in assimilation of sun-synchronous observations and also the potential value of future geostationary satellite observations. Overall, our top-down ammonia emissions can help to examine the effectiveness of air pollution control policies to facilitate future air pollution management, as well as helping us understand the uncertainty in top-down NH3 emissions estimates associated with treatment of NH3 surface exchange

Models and probes of the early and dark Universe : inflation and 21-cm radiation in cosmology

The prevailing model of modern cosmology stipulates the existence of exotic substances such as dark matter and dark energy and events such as inflation. However, their underlying nature is not currently known. In this thesis, we explore new models and measurement techniques that may be used to characterize their cosmological effects and shed light on their inner workings. A model of inflation driven by a substance that may be described macroscopically as a cosmological elastic solid is studied. The proper techniques for the quantization of perturbations within the elastic solid are presented. We find that a sufficiently rigid elastic solid with slowly varying sound speeds can produce an inflationary period. Interestingly, we find models where the elastic solid has an equation of state significantly greater than -1 that nevertheless produces nearly scale-invariant scalar and tensor spectra. The remaining chapters of this thesis concern the use of 21-cm radiation as a probe of the physics of dark matter and dark energy. The effects of warm dark matter on the highly-redshifted 21-cm signal is examined. If dark matter is warm instead of cold, its non-negligible velocities may inhibit the formation of low-mass halos, thereby delaying star-formation, which may delay the emission and absorption signals expected in the mean 21-cm signal. The effects of warm dark matter on both the mean 21-cm signal, as well as on its power spectrum, are described and degeneracies between the effects of warm dark matter and other astrophysical parameters are quantified. One of the primary goals of 21-cm radiation intensity mapping is to measure baryon acoustic oscillations over a wide range of redshifts to constrain the properties of dark energy from the expansion history of the late-time Universe. We forecast the constraining power of the CHIME radio telescope on the matter power spectrum and dark energy parameters. Lastly, we devise new calibration algorithms for the gains of an interferometric radio telescope such as CHIME.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Speed and blood on the bypass: the new automobilities of inter-war London

The article considers the impact of new arterial roads on the mobilities of the wealthier inter-war Londoner, and argues that they occasioned an emergent form of automobility that was modern, sensational and exciting for the metropolitan driver, but was also highly dangerous, particularly for pedestrians and cyclists living in suburban homes near these roads