arXiv subjects

J. Colin Hill

Publications and source records attributed to J. Colin Hill.

At least 163 records · Page 9Linked to original sources

arXiv2016

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales.

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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

The Kinematic Sunyaev-Zel'dovich Effect with Projected Fields: A Novel Probe of the Baryon Distribution with Planck, WMAP, and WISE Data

The kinematic Sunyaev-Zel'dovich (kSZ) effect --- the Doppler boosting of cosmic microwave background (CMB) photons due to Compton-scattering off free electrons with non-zero bulk velocity --- probes the abundance and distribution of baryons in the Universe. All kSZ measurements to date have explicitly required spectroscopic redshifts. Here, we implement a novel estimator for the kSZ -- large-scale structure cross-correlation based on projected fields: it does not require redshift estimates for individual objects, allowing kSZ measurements from large-scale imaging surveys. We apply this estimator to cleaned CMB temperature maps constructed from Planck and Wilkinson Microwave Anisotropy Probe data and a galaxy sample from the Wide-field Infrared Survey Explorer (WISE). We measure the kSZ effect at 3.8-4.5$σ$ significance, depending on the use of additional WISE galaxy bias constraints. We verify that our measurements are robust to possible dust emission from the WISE galaxies. Assuming the standard $Λ$CDM cosmology, we directly constrain $( {f_{b}}/{0.158} ) ( {f_{\rm free}}/{1.0} ) = 1.48 \pm 0.19$ (statistical error only) at redshift $z \approx 0.4$, where $f_{b}$ is the fraction of matter in baryonic form and $f_{\rm free}$ is the free electron fraction. This is the tightest kSZ-derived constraint reported to date on these parameters. The consistency between the $f_{b}$ value found here and the values inferred from analyses of the primordial CMB and Big Bang nucleosynthesis verifies that baryons approximately trace the dark matter distribution down to $\sim$Mpc scales. While our projected-field estimator is already competitive with other kSZ approaches when applied to current datasets (because we are able to use the full-sky WISE photometric survey), it will yield enormous signal-to-noise when applied to upcoming high-resolution, multi-frequency CMB surveys.

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arXiv2016

The Kinematic Sunyaev-Zel'dovich Effect with Projected Fields II: prospects, challenges, and comparison with simulations

The kinematic Sunyaev-Zel'dovich (kSZ) signal is a powerful probe of the cosmic baryon distribution. The kSZ signal is proportional to the integrated free electron momentum rather than the electron pressure (which sources the thermal SZ signal). Since velocities should be unbiased on large scales, the kSZ signal is an unbiased tracer of the large-scale electron distribution, and thus can be used to detect the "missing baryon" that evade most observational techniques. While most current methods for kSZ extraction rely on the availability of very accurate redshifts, we revisit a method that allows measurements even in the absence of redshift information for individual objects. It involves cross-correlating the square of an appropriately filtered cosmic microwave background (CMB) temperature map with a projected density map constructed from a sample of large-scale structure tracers. We show that this method will achieve high signal-to-noise when applied to the next generation of high-resolution CMB experiments, provided that component separation is sufficiently effective at removing foreground contamination. Considering statistical errors only, we forecast that this estimator can yield $S/N \approx $ 3, 120 and over 150 for Planck, Advanced ACTPol, and hypothetical Stage-IV CMB experiments, respectively, in combination with a galaxy catalog from WISE, and about 20% larger $S/N$ for a galaxy catalog from the proposed SPHEREx experiment. This work serves as a companion paper to the first kSZ measurement with this method, where we used CMB temperature maps constructed from Planck and WMAP data, together with galaxies from the WISE survey, to obtain a 3.8 - 4.5$σ$ detection of the kSZ$^2$ amplitude.

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arXiv2016

Constraining Multiplicative Bias in CFHTLenS Weak Lensing Shear Data

Several recent cosmological analyses have found tension between constraints derived from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) data and those derived from other data sets, such as the Planck cosmic microwave background (CMB) temperature anisotropies. Similarly, a direct cross-correlation of the CFHTLenS data with Planck CMB lensing data yielded an anomalously low amplitude compared to expectations based on Planck or WMAP-derived cosmological parameters (Liu & Hill 2015). One potential explanation for these results is a multiplicative bias afflicting the CFHTLenS galaxy shape measurements, from which shears are inferred. Simulations are used in the CFHTLenS pipeline to calibrate such biases, but no data-driven constraints have been presented to date. In this paper, we cross-correlate CFHTLenS galaxy density maps with CFHTLenS shear maps and Planck CMB lensing maps to calibrate an additional multiplicative shear bias (m) in CFHTLenS (beyond the multiplicative correction that has already been applied to the CFHTLenS galaxy shears), following methods suggested by Vallinotto (2012) and Das et al. (2013). We analyze three magnitude-limited galaxy samples, finding 2-4sigma evidence for m<1 using the deepest sample (i<24), while the others are consistent with m=1 (no bias). This matches the expectation that the shapes of faint galaxies are the most prone to measurement biases. Our results for m are essentially independent of the assumed cosmology, and only weakly sensitive to assumptions about the galaxy bias. We consider three galaxy bias models, finding in all cases that the best-fit multiplicative shear bias is less than unity. A value of m~0.9 would suffice to reconcile the amplitude of density fluctuations inferred from the CFHTLenS shear two-point statistics with that inferred from Planck CMB temperature data. This scenario is consistent with our results.

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arXiv2016

Evidence for the Thermal Sunyaev-Zel'dovich Effect Associated with Quasar Feedback

Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar catalogue, spanning redshifts 0.5-3.5, we derive the mean millimetre and far-infrared quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We constrain the form of the far-infrared emission and find 3$σ$-4$σ$ evidence for the thermal Sunyaev-Zel'dovich (SZ) effect, characteristic of a hot ionized gas component with thermal energy $(6.2 \pm 1.7)\times 10^{60}$ erg. This amount of thermal energy is greater than expected assuming only hot gas in virial equilibrium with the dark matter haloes of $(1-5)\times 10^{12}h^{-1}$M$_\odot$ that these systems are expected to occupy, though the highest quasar mass estimates found in the literature could explain a large fraction of this energy. Our measurements are consistent with quasars depositing up to $(14.5 \pm 3.3)~τ_8^{-1}$ per cent of their radiative energy into their circumgalactic environment if their typical period of quasar activity is $τ_8\times~10^8$ yr. For high quasar host masses, $\sim10^{13}h^{-1}$M$_\odot$, this percentage will be reduced. Furthermore, the uncertainty on this percentage is only statistical and additional systematic uncertainties enter at the 40 per cent level. The SEDs are dust dominated in all bands and we consider various models for dust emission. While sufficiently complex dust models can obviate the SZ effect, the SZ interpretation remains favoured at the 3$σ$-4$σ$ level for most models.

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arXiv2015

Taking the Universe's Temperature with Spectral Distortions of the Cosmic Microwave Background

The cosmic microwave background (CMB) energy spectrum is a near-perfect blackbody. The standard model of cosmology predicts small spectral distortions to this form, but no such distortion of the sky-averaged CMB spectrum has yet been measured. We calculate the largest expected distortion, which arises from the inverse Compton scattering of CMB photons off hot, free electrons, known as the thermal Sunyaev-Zel'dovich (tSZ) effect. We show that the predicted signal is roughly one order of magnitude below the current bound from the COBE-FIRAS experiment, but can be detected at enormous significance ($\gtrsim 1000σ$) by the proposed Primordial Inflation Explorer (PIXIE). Although cosmic variance reduces the effective signal-to-noise to $230σ$, this measurement will still yield a sub-percent constraint on the total thermal energy of electrons in the observable universe. Furthermore, we show that PIXIE can detect subtle relativistic effects in the sky-averaged tSZ signal at $30σ$, which directly probe moments of the optical depth-weighted intracluster medium electron temperature distribution. These effects break the degeneracy between the electron density and temperature in the mean tSZ signal, allowing a direct inference of the mean baryon density at low redshift. Future spectral distortion probes will thus determine the global thermodynamic properties of ionized gas in the universe with unprecedented precision. These measurements will impose a fundamental "integral constraint" on models of galaxy formation and the injection of feedback energy over cosmic time.

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arXiv2015

Neutral hydrogen structures trace dust polarization angle: Implications for cosmic microwave background foregrounds

Using high-resolution data from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey, we show that linear structure in Galactic neutral hydrogen (HI) correlates with the magnetic field orientation implied by Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. At high Galactic latitudes, where the Planck data are noise-dominated, the HI data provide an independent constraint on the Galactic magnetic field orientation, and hence the local dust polarization angle. We detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either HI-derived angles, starlight polarization angles, or Planck 353 GHz angles. The HI data thus provide a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.

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arXiv2015

The Sunyaev-Zel'dovich Effect and Large-Scale Structure

The thermal Sunyaev-Zel'dovich (tSZ) effect is the inverse-Compton scattering of cosmic microwave background (CMB) photons off hot, ionized electrons, primarily located in galaxy groups and clusters. Recent years have seen immense improvement in our ability to probe cosmology and the astrophysics of the intracluster medium using the tSZ signal. Here, I describe cross-correlations of the tSZ effect measured in Planck data with gravitational lensing maps from Planck and the Canada-France-Hawaii Telescope Lensing Survey, as well as hydrodynamical simulations which show that such measurements do not probe "missing baryons," but rather the pressure of ionized gas in groups and clusters over a wide range of halo masses and redshifts. I also present recent measurements of higher-order tSZ statistics using data from the Atacama Cosmology Telescope, which yield strong constraints on the amplitude of density fluctuations. I describe stacking analyses of tSZ data from Planck, focusing on the behavior of the gas pressure in low-mass galaxy groups. I close with a prediction for the tSZ monopole, including relativistic corrections, which is the largest guaranteed spectral distortion signal for the proposed Primordial Inflation Explorer mission. The tSZ monopole will yield a direct measurement of the total thermal energy in ionized electrons in the observable universe.

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arXiv2015

Evidence for the kinematic Sunyaev-Zeľdovich effect with ACTPol and velocity reconstruction from BOSS

We use microwave temperature maps from two seasons of data from the Atacama Cosmology Telescope (ACTPol) at 146 GHz, together with the Constant Mass CMASS galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the kinematic Sunyaev-Zeľdovich (kSZ) effect over the redshift range z = 0.4 - 0.7. We use galaxy positions and the continuity equation to obtain a reconstruction of the line-of-sight velocity field. We stack the cosmic microwave background temperature at the location of each halo, weighted by the corresponding reconstructed velocity. The resulting best fit kSZ model is preferred over the no-kSZ hypothesis at 3.3sigma and 2.9sigma for two independent velocity reconstruction methods, using 25,537 galaxies over 660 square degrees. The effect of foregrounds that are uncorrelated with the galaxy velocities is expected to be well below our signal, and residual thermal Sunyaev-Zeľdovich contamination is controlled by masking the most massive clusters. Finally, we discuss the systematics involved in converting our measurement of the kSZ amplitude into the mean free electron fraction of the halos in our sample.

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arXiv2015

Cross-correlation of Planck CMB Lensing and CFHTLenS Galaxy Weak Lensing Maps

We cross-correlate cosmic microwave background (CMB) lensing and galaxy weak lensing maps using the Planck 2013 and 2015 data and the 154 deg^2 Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). This measurement probes large-scale structure at intermediate redshifts ~0.9, between the high- and low-redshift peaks of the CMB and CFHTLenS lensing kernels, respectively. Using the noise properties of these data sets and standard Planck 2015 LCDM cosmological parameters, we forecast a signal-to-noise ratio ~4.6 for the cross-correlation. We find that the noise level of our actual measurement agrees well with this estimate, but the amplitude of the signal lies well below the theoretical prediction. The best-fit amplitudes of our measured cross-correlations are $A_{2013}=0.48\pm0.26$ and $A_{2015}=0.44\pm0.22$ using the 2013 and 2015 Planck CMB lensing maps, respectively, where $A=1$ corresponds to the fiducial Planck 2015 LCDM prediction. Due to the low measured amplitude, the detection significance is moderate (~2$σ$) and the data are in tension with the theoretical prediction (~2-$2.5σ$). The tension is reduced somewhat when compared to predictions using WMAP9 parameters, for which we find $A_{2013}=0.56\pm0.30$ and $A_{2015}=0.52\pm0.26$. We consider various systematic effects, finding that photometric redshift uncertainties, contamination by intrinsic alignments, and effects due to the masking of galaxy clusters in the Planck 2015 CMB lensing reconstruction are able to help resolve the tension at a significant level (~10% each). An overall multiplicative bias in the CFHTLenS shear data could also play a role, which can be tested with existing data. We close with forecasts for measurements of this cross-correlation using ongoing and future weak lensing surveys, which will definitively test the significance of the tension in our results with respect to LCDM.

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arXiv2015

The Stacked Thermal SZ Signal of Locally Brightest Galaxies in Planck Full Mission Data: Evidence for Galaxy Feedback?

We use the Planck full mission temperature maps to examine the stacked thermal Sunyaev-Zel'dovich (tSZ) signal of 188042 "locally brightest galaxies'" (LBGs) selected from the Sloan Digital Sky Survey Data Release 7. Our LBG sample closely matches that of Planck Collaboration XI (2013, PCXI) but our analysis differs in several ways. We work directly in terms of physically observable quantities, requiring minimal assumptions about the gas pressure profile. We explicitly model the dust emission from each LBG and simultaneously measure both the stacked tSZ and dust signals as a function of stellar mass $M_*$. There is a small residual bias in stacked tSZ measurements; we measure this bias and subtract it from our results, finding that the effects are non-negligible at the lowest masses in the LBG sample. Finally, we compare our measurements with two pressure profile models, finding that the profile from Battaglia et al. (2012b) provides a better fit to the results than the Arnaud et al. (2010) "universal pressure profile." However, within the uncertainties, we find that the data are consistent with a self-similar scaling with mass --- more precise measurements are needed to detect the relatively small deviations from self-similarity predicted by these models. Consistent with PCXI, we measure the stacked tSZ signal from LBGs with stellar masses down to $\log_{10}(M_*/M_{\odot}) \sim 11.1-11.3$. For lower stellar masses, however, we do not see evidence for a stacked tSZ signal. We note that the stacked dust emission is comparable to, or larger than, the stacked tSZ signal for $\log_{10}(M_*/M_{\odot}) \lesssim 11.3$. Future tSZ analyses with larger samples and lower noise levels should be able to probe deviations from self-similarity and thus provide constraints on models of feedback and the evolution of hot halo gas over cosmic time.

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arXiv2015

Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos

We present evidence of the gravitational lensing of the cosmic microwave background by $10^{13}$ solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12,000 optically-selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles, and is favored over a null signal at 3.2 sigma significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.

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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

The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich One-Point PDF

We present a measurement of the one-point probability distribution function (PDF) of the thermal Sunyaev-Zel'dovich (tSZ) decrement in the pixel temperature histogram of filtered 148 GHz sky maps from the Atacama Cosmology Telescope (ACT). The PDF includes the signal from all galaxy clusters in the map, including objects below the signal-to-noise threshold for individual detection, making it a particularly sensitive probe of the amplitude of matter density perturbations, $σ_8$. We use a combination of analytic halo model calculations and numerical simulations to compute the theoretical tSZ PDF and its covariance matrix, accounting for all noise sources and including relativistic corrections. From the measured ACT 148 GHz PDF alone, we find $σ_8 = 0.793 \pm 0.018$, with additional systematic errors of $\pm 0.017$ due to uncertainty in intracluster medium gas physics and $\pm 0.006$ due to uncertainty in infrared point source contamination. Using effectively the same data set, the statistical error here is a factor of two lower than that found in ACT's previous $σ_8$ determination based solely on the skewness of the tSZ signal. In future temperature maps with higher sensitivity, the tSZ PDF will break the degeneracy between intracluster medium gas physics and cosmological parameters.

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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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arXiv2014

Precision Epoch of Reionization studies with next-generation CMB experiments

Future arcminute resolution polarization data from ground-based Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near $\ell=1500$ in the small angular-scale temperature measurements. Our projections are based on combining expected small-scale E-mode polarization measurements from Advanced ACTPol in the range $300<\ell<3000$ with simulated temperature data from the full Planck mission in the low and intermediate $\ell$ region, $2<\ell<2000$. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than $1\%$ accuracy. Assuming an efficient cleaning from multi-frequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic Sunyaev-Zel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a $15 σ$ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at $\ell>1500$, leading to a measurement of the amplitude of matter density fluctuations, $σ_8$, at $1\%$ precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with $σ(z_{\rm re})=1.1$ and $σ(Δz_{\rm re})=0.2$. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminute-scale resolution for future CMB surveys.

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arXiv2014

Toward an Understanding of Foreground Emission in the BICEP2 Region

BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyze the BICEP2 results and show that the 100x150 GHz and 150x150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarization signal. We give independent estimates of the dust polarization signal in the BICEP2 region using four different approaches. While these approaches are consistent with each other, the expected amplitude of the dust polarization power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarization angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin. (abridged)

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