arXiv subjects

Eric R. Switzer

Publications and source records attributed to Eric R. Switzer.

At least 37 records · Page 2Linked to original sources

arXiv2021

μ-Spec Spectrometers for the EXCLAIM Instrument

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a cryogenic balloon-borne instrument that will map carbon monoxide and singly-ionized carbon emission lines across redshifts from 0 to 3.5, using an intensity mapping approach. EXCLAIM will broaden our understanding of these elemental and molecular gases and the role they play in star formation processes across cosmic time scales. The focal plane of EXCLAIM's cryogenic telescope features six μ-Spec spectrometers. μ-Spec is a compact, integrated grating-analog spectrometer, which uses meandered superconducting niobium microstrip transmission lines on a single-crystal silicon dielectric to synthesize the grating. It features superconducting aluminum microwave kinetic inductance detectors (MKIDs), also in a microstrip architecture. The spectrometers for EXCLAIM couple to the telescope optics via a hybrid planar antenna coupled to a silicon lenslet. The spectrometers operate from 420 to 540 GHz with a resolving power R=λ/Δλ=512 and employ an array of 355 MKIDs on each spectrometer. The spectrometer design targets a noise equivalent power (NEP) of 2x10-18W/\sqrt{Hz} (defined at the input to the main lobe of the spectrometer lenslet beam, within a 9-degree half width), enabled by the cryogenic telescope environment, the sensitive MKID detectors, and the low dielectric loss of single-crystal silicon. We report on these spectrometers under development for EXCLAIM, providing an overview of the spectrometer and component designs, the spectrometer fabrication process, fabrication developments since previous prototype demonstrations, and the current status of their development for the EXCLAIM mission.

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arXiv2019

Microwave Spectro-Polarimetry of Matter and Radiation across Space and Time

This paper discusses the science case for a sensitive spectro-polarimetric survey of the microwave sky. Such a survey would provide a tomographic and dynamic census of the three-dimensional distribution of hot gas, velocity flows, early metals, dust, and mass distribution in the entire Hubble volume, exploit CMB temperature and polarisation anisotropies down to fundamental limits, and track energy injection and absorption into the radiation background across cosmic times by measuring spectral distortions of the CMB blackbody emission. In addition to its exceptional capability for cosmology and fundamental physics, such a survey would provide an unprecedented view of microwave emissions at sub-arcminute to few-arcminute angular resolution in hundreds of frequency channels, a data set that would be of immense legacy value for many branches of astrophysics. We propose that this survey be carried-out with a large space mission featuring a broad-band polarised imager and a moderate resolution spectro-imager at the focus of a 3.5m aperture telescope actively cooled to about 8K, complemented with absolutely-calibrated Fourier Transform Spectrometer modules observing at degree-scale angular resolution in the 10-2000 GHz frequency range. We propose two observing modes: a survey mode to map the entire sky as well as a few selected wide fields, and an observatory mode for deeper observations of regions of specific interest.

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arXiv2019

Advanced Astrophysics Discovery Technology in the Era of Data Driven Astronomy

Experience suggests that structural issues in how institutional Astrophysics approaches data-driven science and the development of discovery technology may be hampering the community's ability to respond effectively to a rapidly changing environment in which increasingly complex, heterogeneous datasets are challenging our existing information infrastructure and traditional approaches to analysis. We stand at the confluence of a new epoch of multimessenger science, remote co-location of data and processing power and new observing strategies based on miniaturized spacecraft. Significant effort will be required by the community to adapt to this rapidly evolving range of possible discovery moduses. In the suggested creation of a new Astrophysics element, Advanced Astrophysics Discovery Technology, we offer an affirmative solution that places the visibility of discovery technologies at a level that we suggest is fully commensurate with their importance to the future of the field.

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arXiv2019

Evidence for CII diffuse line emission at redshift $z\sim2.6$

CII is one of the brightest emission lines from star-forming galaxies and is an excellent tracer for star formation. Recent work measured the CII emission line amplitude for redshifts $2<z<3.2$ by cross-correlating Planck High Frequency Instrument emission maps with tracers of overdensity from the Baryon Oscillation Spectroscopic Sky Survey, finding $I_{\mathrm{CII}}=6.6^{+5.0}_{-4.8}\times 10^4$ Jy/sr at $95\%$ confidence. In this paper, we present a refinement of this earlier work by improving the mask weighting in each of the Planck bands and the precision in the covariance matrix. We report a detection of excess emission in the 545 GHz Planck band separate from the cosmic infrared background (CIB) present in the 353-857 GHz Planck bands. This excess is consistent with redshifted CII emission, in which case we report $b_{\mathrm{CII}}I_{\mathrm{CII}} =2.0^{+1.2}_{-1.1}\times 10^5$ Jy/sr at $95\%$ confidence, which strongly favors many collisional excitation models of CII emission. Our detection shows strong evidence for a model with a non-zero CII parameter, though line intensity mapping observations at high spectral resolution will be needed to confirm this result.

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arXiv2019

Science from an Ultra-Deep, High-Resolution Millimeter-Wave Survey

Opening up a new window of millimeter-wave observations that span frequency bands in the range of 30 to 500 GHz, survey half the sky, and are both an order of magnitude deeper (about 0.5 uK-arcmin) and of higher-resolution (about 10 arcseconds) than currently funded surveys would yield an enormous gain in understanding of both fundamental physics and astrophysics. In particular, such a survey would allow for major advances in measuring the distribution of dark matter and gas on small-scales, and yield needed insight on 1.) dark matter particle properties, 2.) the evolution of gas and galaxies, 3.) new light particle species, 4.) the epoch of inflation, and 5.) the census of bodies orbiting in the outer Solar System.

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arXiv2018

The Atacama Cosmology Telescope: Two-season ACTPol Extragalactic Point Sources and their Polarization properties

We report on measurements of the polarization of extragalactic sources at 148 GHz made during the first two seasons of the Atacama Cosmology Telescope Polarization (ACTPol) survey. The survey covered 680 deg$^{2}$ of the sky on the celestial equator. Polarization measurements of 169 intensity-selected sources brighter than 30 mJy, that are predominantly Active Galactic Nuclei, are presented. Above a total flux of 215 mJy where the noise bias removal in the polarization measurement is reliable, we detect 26 sources, 14 of which have a detection of linear polarization at greater than 3$σ_{p}$ significance. The distribution of the fractional polarization as a function of total source intensity is analyzed. Our result is consistent with the scenario that the fractional polarization of our measured radio source population is independent of total intensity down to the limits of our measurements and well described by a Gaussian distribution with a mean fractional polarization $p=0.028\pm$0.005 and standard deviation $σ_{\mathrm{p}}=0.054$, truncated at $p=0$. Extrapolating this model for the distribution of source polarization below the ACTPol detection threshold, we predict that one could get a clean measure of the E-mode polarization power spectrum of the microwave background out to $\ell=6000$ with 1 $μ$K-arcminute maps over 10$\%$ of the sky from a future survey. We also study the spectral energy distribution of the total and polarized source flux densities by cross-matching with low radio frequency catalogs. We do not find any correlation between the spectral indices for total flux and polarized flux.

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arXiv2017

Global 21-cm signal extraction from foreground and instrumental effects I: Pattern recognition framework for separation using training sets

The sky-averaged (global) highly redshifted 21-cm spectrum from neutral hydrogen is expected to appear in the VHF range of $\sim20-200$ MHz and its spectral shape and strength are determined by the heating properties of the first stars and black holes, by the nature and duration of reionization, and by the presence or absence of exotic physics. Measurements of the global signal would therefore provide us with a wealth of astrophysical and cosmological knowledge. However, the signal has not yet been detected because it must be seen through strong foregrounds weighted by a large beam, instrumental calibration errors, and ionospheric, ground and radio-frequency-interference effects, which we collectively refer to as "systematics". Here, we present a signal extraction method for global signal experiments which uses Singular Value Decomposition (SVD) of "training sets" to produce systematics basis functions specifically suited to each observation. Instead of requiring precise absolute knowledge of the systematics, our method effectively requires precise knowledge of how the systematics can vary. After calculating eigenmodes for the signal and systematics, we perform a weighted least square fit of the corresponding coefficients and select the number of modes to include by minimizing an information criterion. We compare the performance of the signal extraction when minimizing various information criteria and find that minimizing the Deviance Information Criterion (DIC) most consistently yields unbiased fits. The methods used here are built into our widely applicable, publicly available Python package, $\texttt{pylinex}$, which analytically calculates constraints on signals and systematics from given data, errors, and training sets.

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arXiv2017

CMB-S4 Technology Book, First Edition

CMB-S4 is a proposed experiment to map the polarization of the Cosmic Microwave Background (CMB) to nearly the cosmic variance limit for angular scales that are accessible from the ground. The science goals and capabilities of CMB-S4 in illuminating cosmic inflation, measuring the sum of neutrino masses, searching for relativistic relics in the early universe, characterizing dark energy and dark matter, and mapping the matter distribution in the universe have been described in the CMB-S4 Science Book. This Technology Book is a companion volume to the Science Book. The ambitious science goals of CMB-S4, a "Stage-4" experiment, require a step forward in experimental capability from the current Stage=II experiments. To guide this process, we summarize the current state of CMB instrumentation technology, and identify R&D efforts necessary to advance it for use in CMB-S4. The book focuses on technical challenges in four broad areas: Telescope Design; Receiver Optics; Focal-Plane Optical Coupling; and Focal-Plane Sensor and Readout.

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arXiv2017

Tracing the cosmological evolution of stars and cold gas with CMB spectral surveys

A full account of galaxy evolution in the context of LCDM cosmology requires measurements of the average star-formation rate (SFR) and cold gas abundance across cosmic time. Emission from the CO ladder traces cold gas, and [CII] fine structure emission at 158 um traces the SFR. Intensity mapping surveys the cumulative surface brightness of emitting lines as a function of redshift, rather than individual galaxies. CMB spectral distortion instruments are sensitive to both the mean and anisotropy of the intensity of redshifted CO and [CII] emission. Large-scale anisotropy is proportional to the product of the mean surface brightness and the line luminosity-weighted bias. The bias provides a connection between galaxy evolution and its cosmological context, and is a unique asset of intensity mapping. Cross-correlation with galaxy redshift surveys allows unambiguous measurements of redshifted line brightness despite residual continuum contamination and interlopers. Measurement of line brightness through cross-correlation also evades cosmic variance and suggests new observation strategies. Galactic foreground emission is $\sim 10^3$ times larger than the expected signals, and this places stringent requirements on instrument calibration and stability. Under a range of assumptions, a linear combination of bands cleans continuum contamination sufficiently that residuals produce a modest penalty over the instrumental noise. For PIXIE, the $2 σ$ sensitivity to CO and [CII] emission scales from $\sim 5 \times 10^{-2}$ kJy/sr at low redshift to ~2 kJy/sr by reionization.

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arXiv2016

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the LCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. Adding the new data to planck temperature data tightens the limits on damping tail parameters, for example reducing the joint uncertainty on the number of neutrino species and the primordial helium fraction by 20%.

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arXiv2016

Robust Likelihoods for Inflationary Gravitational Waves from Maps of Cosmic Microwave Background Polarization

The B-mode polarization of the cosmic microwave background (CMB) provides a unique window into tensor perturbations from inflationary gravitational waves. Survey effects complicate the estimation and description of the power spectrum on the largest angular scales. The pixel-space likelihood yields parameter distributions without the power spectrum as an intermediate step, but it does not have the large suite of tests available to power spectral methods. Searches for primordial B-modes must rigorously reject and rule out contamination. Many forms of contamination vary or are uncorrelated across epochs, frequencies, surveys, or other data treatment subsets. The cross power and the power spectrum of the difference of subset maps provide approaches to reject and isolate excess variance. We develop an analogous joint pixel-space likelihood. Contamination not modeled in the likelihood produces parameter-dependent bias and complicates the interpretation of the difference map. We describe a null test that consistently weights the difference map. Excess variance should either be explicitly modeled in the covariance or be removed through reprocessing the data.

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arXiv2016

The Primordial Inflation Polarization Explorer (PIPER)

The Primordial Inflation Polarization ExploreR (PIPER) is a balloon-borne telescope designed to measure the polarization of the Cosmic Microwave Background on large angular scales. PIPER will map 85% of the sky at 200, 270, 350, and 600 GHz over a series of 8 conventional balloon flights from the northern and southern hemispheres. The first science flight will use two 32x40 arrays of backshort-under-grid transition edge sensors, multiplexed in the time domain, and maintained at 100 mK by a Continuous Adiabatic Demagnetization Refrigerator. Front-end cryogenic Variable-delay Polarization Modulators provide systematic control by rotating linear to circular polarization at 3 Hz. Twin telescopes allow PIPER to measure Stokes I, Q, U, and V simultaneously. The telescope is maintained at 1.5 K in an LHe bucket dewar. Cold optics and the lack of a warm window permit sensitivity at the sky-background limit. The ultimate science target is a limit on the tensor-to-scalar ratio of r ~ 0.007, from the reionization bump to l ~ 300. PIPER's first flight will be from the Northern hemisphere, and overlap with the CLASS survey at lower frequencies. We describe the current status of the PIPER instrument.

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arXiv2016

Interpreting the unresolved intensity of cosmologically redshifted line radiation

Intensity mapping experiments survey the spectrum of diffuse line radiation rather than detect individual objects at high signal-to-noise. Spectral maps of unresolved atomic and molecular line radiation contain three-dimensional information about the density and environments of emitting gas, and efficiently probe cosmological volumes out to high redshift. Intensity mapping survey volumes also contain all other sources of radiation at the frequencies of interest. Continuum foregrounds are typically ~10^2-10^3 times brighter than the cosmological signal. The instrumental response to bright foregrounds will produce new spectral degrees of freedom that are not known in advance, nor necessarily spectrally smooth. The intrinsic spectra of foregrounds may also not be well-known in advance. We describe a general class of quadratic estimators to analyze data from single-dish intensity mapping experiments, and determine contaminated spectral modes from the data itself. The key attribute of foregrounds is not that they are spectrally smooth, but instead that they have fewer bright spectral degrees of freedom than the cosmological signal. Spurious correlations between the signal and foregrounds produce additional bias. Compensation for signal attenuation must estimate and correct this bias. A successful intensity mapping experiment will control instrumental systematics that spread variance into new modes, and it must observe a large enough volume that contaminant modes can be determined independently from the signal on scales of interest.

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arXiv2014

First Measurement of the Cross-Correlation of CMB Lensing and Galaxy Lensing

We measure the cross-correlation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2σ, which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.

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arXiv2014

The Atacama Cosmology Telescope: Lensing of CMB Temperature and Polarization Derived from Cosmic Infrared Background Cross-Correlation

We present a measurement of the gravitational lensing of the Cosmic Microwave Background (CMB) temperature and polarization fields obtained by cross-correlating the reconstructed convergence signal from the first season of ACTPol data at 146 GHz with Cosmic Infrared Background (CIB) fluctuations measured using the Planck satellite. Using an overlap area of 206 square degrees, we detect gravitational lensing of the CMB polarization by large-scale structure at a statistical significance of 4.5 sigma. Combining both CMB temperature and polarization data gives a lensing detection at 9.1 sigma significance. A B-mode polarization lensing signal is present with a significance of 3.2 sigma. We also present the first measurement of CMB lensing--CIB correlation at small scales corresponding to l > 2000. Null tests and systematic checks show that our results are not significantly biased by astrophysical or instrumental systematic effects, including Galactic dust. Fitting our measurements to the best-fit lensing-CIB cross power spectrum measured in Planck data, scaled by an amplitude A, gives A=1.02 +0.12/-0.18 (stat.) +/-0.06(syst.), consistent with the Planck results.

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arXiv2014

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich (SZ) effect associated with the halos that host them. The Atacama Cosmology Telescope (ACT) has conducted a survey at 148 GHz, 218 GHz and 277 GHz along the celestial equator. Using samples of radio sources selected at 1.4 GHz from FIRST and NVSS, we measure the stacked 148, 218 and 277 GHz flux densities for sources with 1.4 GHz flux densities ranging from 5 to 200 mJy. At these flux densities, the radio source population is dominated by active galactic nuclei (AGN), with both steep and flat spectrum populations, which have combined radio-to-millimeter spectral indices ranging from 0.5 to 0.95, reflecting the prevalence of steep spectrum sources at high flux densities and the presence of flat spectrum sources at lower flux densities. The thermal SZ effect associated with the halos that host the AGN is detected at the 5$σ$ level through its spectral signature. When we compare the SZ effect with weak lensing measurements of radio galaxies, we find that the relation between the two is consistent with that measured by Planck for local bright galaxies. We present a detection of the SZ effect in some of the lowest mass halos (average $M_{200}\approx10^{13}$M$_{\odot}h_{70}^{-1}$) studied to date. This detection is particularly important in the context of galaxy evolution models, as it confirms that galaxies with radio AGN also typically support hot gaseous halos. With Herschel observations, we show that the SZ detection is not significantly contaminated by dust. We show that 5 mJy$<S_{1.4}<$200 mJy radio sources contribute $\ell(\ell+1)C_{\ell}/(2π)=0.37\pm0.03μ$K$^2$ to the angular power spectrum at $\ell=3000$ at 148 GHz, after accounting for the SZ effect associated with their host halos.

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arXiv2014

Erasing the variable: Empirical foreground discovery for global 21 cm spectrum experiments

Spectral measurements of the 21 cm monopole background have the promise of revealing the bulk energetic properties and ionization state of our universe from z ~ 6-30. Synchrotron foregrounds are orders of magnitude larger than the cosmological signal, and are the principal challenge faced by these experiments. While synchrotron radiation is thought to be spectrally smooth and described by relatively few degrees of freedom, the instrumental response to bright foregrounds may be much more complex. To deal with such complexities, we develop an approach that discovers contaminated spectral modes using spatial fluctuations of the measured data. This approach exploits the fact that foregrounds vary across the sky while the signal does not. The discovered modes are projected out of each line-of-sight of a data cube. An angular weighting then optimizes the cosmological signal amplitude estimate by giving preference to lower-noise regions. Using this method, we show that it is essential for the passband to be stable to at least ~10^{-4}. In contrast, the constraints on the spectral smoothness of the absolute calibration are mainly aesthetic if one is able to take advantage of spatial information. To the extent it is understood, controlling polarization to intensity leakage at the ~10^{-2} level will also be essential to rejecting Faraday rotation of the polarized synchrotron emission.

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arXiv2014

The Atacama Cosmology Telescope: CMB Polarization at $200<\ell<9000$

We report on measurements of the cosmic microwave background (CMB) and celestial polarization at 146 GHz made with the Atacama Cosmology Telescope Polarimeter (ACTPol) in its first three months of observing. Four regions of sky covering a total of 270 square degrees were mapped with an angular resolution of $1.3'$. The map noise levels in the four regions are between 11 and 17 $μ$K-arcmin. We present TT, TE, EE, TB, EB, and BB power spectra from three of these regions. The observed E-mode polarization power spectrum, displaying six acoustic peaks in the range $200<\ell<3000$, is an excellent fit to the prediction of the best-fit cosmological models from WMAP9+ACT and Planck data. The polarization power spectrum, which mainly reflects primordial plasma velocity perturbations, provides an independent determination of cosmological parameters consistent with those based on the temperature power spectrum, which results mostly from primordial density perturbations. We find that without masking any point sources in the EE data at $\ell<9000$, the Poisson tail of the EE power spectrum due to polarized point sources has an amplitude less than $2.4$ $μ$K$^2$ at $\ell = 3000$ at 95\% confidence. Finally, we report that the Crab Nebula, an important polarization calibration source at microwave frequencies, has 8.7\% polarization with an angle of $150.7^\circ \pm 0.6^\circ$ when smoothed with a $5'$ Gaussian beam.

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