arXiv subjects

Fiona McCarthy

Publications and source records attributed to Fiona McCarthy.

33 records · Page 2Linked to original sources

arXiv2024

Constraints on Dark Matter-Dark Energy Scattering from ACT DR6 CMB Lensing

The predicted present-day amplitude of matter fluctuations based on cosmic microwave background (CMB) anisotropy data has sometimes been found discrepant with more direct measurements of late-time structure. This has motivated many extensions to the standard cosmological model, including kinetic interactions between dark matter and dark energy that introduce a drag force slowing the growth of structure at late times. Exploring this scenario, we develop a model for quasi-linear scales in the matter power spectrum by calculating the critical overdensity in the presence of this interaction and a varying dark energy equation of state. We explicitly avoid modeling or interpretation of data on non-linear scales in this model (such as use of $Λ$CDM-calibrated priors), which would require numerical simulations. We find that the presence of the drag force hinders halo formation, thus increasing the deviation from $Λ$CDM in the mildly non-linear regime. We use CMB lensing observations from the sixth data release of the Atacama Cosmology Telescope up to $L=1250$ (in combination with Planck, Sloan Digital Sky Survey, and 6dFGS data) to derive the strongest constraints to date on the amplitude of the drag term, finding the dimensionless interaction strength $Γ_\mathrm{DMDE}/(H_0ρ_\mathrm{c})<0.831\; (2.81)$ at the 68\% (95\%) confidence level. The inclusion of non-linear corrections improves our constraints by about 35\% compared to linear theory. Our results do not exclude the best-fit values of $Γ_\mathrm{DMDE}$ found in previous studies using information from galaxy weak lensing, though we find no statistical preference for the dark matter-dark energy kinetic interactions over $Λ$CDM. We implement our model in a publicly available fork of the Boltzmann code CLASS at https://github.com/fmccarthy/Class_DMDE.

astro-ph.CO↗

arXiv2023

Converting dark matter to dark radiation does not solve cosmological tensions

Tensions between cosmological parameters (in particular the local expansion rate $H_0$ and the amplitude of matter clustering $S_8$) inferred from low-redshift data and data from the cosmic microwave background (CMB) and large-scale structure (LSS) experiments have inspired many extensions to the standard cosmological model, $Λ$CDM. Models which simultaneously lessen both tensions are of particular interest. We consider one scenario with the potential for such a resolution, in which some fraction of the dark matter has converted into dark radiation since the release of the CMB. Such a scenario encompasses and generalizes the more standard "decaying dark matter" model, allowing additional flexibility in the rate and time at which the dark matter converts into dark radiation. In this paper, we constrain this scenario with a focus on exploring whether it can solve (or reduce) these tensions. We find that such a model is effectively ruled out by low-$\ell$ CMB data, in particular by the reduced peak-smearing due to CMB lensing and the excess Integrated Sachs--Wolfe (ISW) signal caused by the additional dark energy density required to preserve flatness after dark matter conversion into dark radiation. Thus, such a model does not have the power to reduce these tensions without further modifications. This conclusion extends and generalizes related conclusions derived for the standard decaying dark matter model.

astro-ph.CO↗

arXiv2023

Cross-correlation of the thermal Sunyaev--Zel'dovich and CMB lensing signals in Planck PR4 data with robust CIB decontamination

We use the full-mission Planck PR4 data to measure the CMB lensing convergence ($κ$)--thermal Sunyaev-Zel'dovich (tSZ, $y$) cross-correlation, $C_\ell^{yκ}$. This is only the second measurement to date of this signal, following Hill \& Spergel (2014). We perform the measurement using foreground-cleaned tSZ maps built from the PR4 frequency maps via a tailored needlet internal linear combination (NILC) code in our companion paper, in combination with the Planck PR4 $κ$ maps and various systematic-mitigated PR3 $κ$ maps. A serious systematic is the residual cosmic infrared background (CIB) in the tSZ map, as the high CIB--$κ$ correlation can significantly bias the inferred tSZ--$κ$ cross-correlation. We mitigate this by deprojecting the CIB in our NILC, using a moment-deprojection approach to avoid leakage due to incorrect modelling of the CIB frequency dependence. We validate our method on mm-sky simulations. We fit a theoretical halo model to our measurement, finding a best-fit amplitude of $A=0.82\pm0.21$ (for the highest signal-to-noise PR4 $κ$ map) or $A=0.56\pm0.24$ (for a PR3 $κ$ map built from a tSZ-deprojected CMB map), indicating that the data are consistent with our model within $\sim 1$-$2σ$. Although our error bars are similar to those of the 2014 measurement, our method is significantly more robust to CIB contamination. Our moment-deprojection approach lays the foundation for future measurements of this signal with higher signal-to-noise maps from ground-based telescopes, which will precisely probe the astrophysics of the intracluster medium of galaxy groups and clusters in the intermediate-mass ($M\sim 10^{13} -10^{14} h^{-1} M_\odot$), high-$z$ ($z<\sim1.5$, c.f. $z<\sim0.8$ for the tSZ auto-power signal) regime, as well as CIB-decontaminated measurements of tSZ cross-correlations with other large-scale structure probes.

astro-ph.CO↗

arXiv2023

The Atacama Cosmology Telescope: High-resolution component-separated maps across one-third of the sky

Observations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-$y$ distortion due to the thermal Sunyaev-Zel'dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multi-wavelength observations to spectrally isolate one component. In this work, we present a new arcminute-resolution Compton-$y$ map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000 sq.~deg.). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) Data Release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the \textit{Planck} satellite at frequencies between 30 GHz and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing \textit{Planck} component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB.

astro-ph.CO↗

arXiv2022

Constraints on primordial non-Gaussianity from halo bias measured through CMB lensing cross-correlations

Local non-Gaussianities in the initial conditions of the Universe, parameterized by $f_{\rm NL}$, induce a scale-dependence in the large-scale bias of halos in the late Universe. This effect is a promising path to constrain multi-field inflation theories that predict non-zero $f_{\rm NL}$. While most existing constraints from the halo bias involve auto-correlations of the galaxy distribution, cross-correlations with probes of the matter density provide an alternative channel with fewer systematics. We present the strongest large-scale structure constraint on local primordial non-Gaussianity that uses cross-correlations alone. We use the cosmic infrared background (CIB) consisting of dusty galaxies as a halo tracer and cosmic microwave background (CMB) lensing as a probe of the underlying matter distribution, both from \textit{Planck} data. Milky Way dust is a key challenge in using the large-scale modes of the CIB. Importantly, the cross-correlation of the CIB with CMB lensing is far less affected by Galactic dust compared to the CIB auto-spectrum, which picks up an additive bias from Galactic dust. We find no evidence for primordial non-Gaussianity and find $-87<f_{\rm NL}<19$ with a Gaussian $σ(f_{\rm NL})\approx 41$, assuming universality of the halo mass function. We find that future CMB lensing data from Simons Observatory and CMB-S4 could achieve $σ(f_{\rm NL})$ of 23 and 20 respectively. The constraining power of such an analysis is limited by current Galactic dust cleaning techniques, requiring us to use a minimum multipole of $\ell=70$. If this challenge is overcome with improved analysis techniques or external data, constraints as tight as $σ(f_{\rm NL})=4$ can be achieved through the cross-correlation technique. More optimistically, constraints better than $σ(f_{\rm NL})=2$ could be achieved if the CIB auto-spectrum is dust-free down to the largest scales.

astro-ph.CO↗

arXiv2022

Maximum likelihood kinetic Sunyaev Zel'dovich velocity reconstruction

The kinetic Sunyaev Zel'dovich (kSZ) effect, cosmic microwave background (CMB) temperature anisotropies induced by the scattering of CMB photons from free electrons, will be measured by near-term CMB experiments at high significance. By combining CMB temperature anisotropies with a tracer of structure, such as a galaxy redshift survey, previous literature introduced a number of techniques to reconstruct the radial velocity field. This reconstructed radial velocity field encapsulates the majority of the cosmological information contained in the kSZ temperature anisotropies, and can provide powerful new tests of the standard cosmological model and theories beyond it. In this paper, we introduce a new estimator for the radial velocity field based on a coarse-grained maximum likelihood fit for the kSZ component of the temperature anisotropies, given a tracer of the optical depth. We demonstrate that this maximum likelihood estimator yields a higher fidelity reconstruction than existing quadratic estimators in the low-noise and high-resolution regime targeted by upcoming CMB experiments. We describe implementations of the maximum likelihood estimator in both harmonic space and map space, using either direct measurements of the optical depth field or a galaxy survey as a tracer. We comment briefly on the impact of biases introduced by imperfect reconstruction of the optical depth field.

astro-ph.CO↗

arXiv2021

Velocity reconstruction with the cosmic microwave background and galaxy surveys

The kinetic Sunyaev Zel'dovich (kSZ) and moving lens effects, secondary contributions to the cosmic microwave background (CMB), carry significant cosmological information due to their dependence on the large-scale peculiar velocity field. Previous work identified a promising means of extracting this cosmological information using a set of quadratic estimators for the radial and transverse components of the velocity field. These estimators are based on the statistically anisotropic components of the cross-correlation between the CMB and a tracer of large scale structure, such as a galaxy redshift survey. In this work, we assess the challenges to the program of velocity reconstruction posed by various foregrounds and systematics in the CMB and galaxy surveys, as well as biases in the quadratic estimators. To do so, we further develop the quadratic estimator formalism and implement a numerical code for computing properly correlated spectra for all the components of the CMB (primary/secondary blackbody components and foregrounds) and a photometric redshift survey, with associated redshift errors, to allow for accurate forecasting. We create a simulation framework for generating realizations of properly correlated CMB maps and redshift binned galaxy number counts, assuming the underlying fields are Gaussian, and use this to validate a velocity reconstruction pipeline and assess map-based systematics such as masking. We highlight the most significant challenges for velocity reconstruction, which include biases associated with: modelling errors, characterization of redshift errors, and coarse graining of cosmological fields on our past light cone. Despite these challenges, the outlook for velocity reconstruction is quite optimistic, and we use our reconstruction pipeline to confirm that these techniques will be feasible with near-term CMB experiments and photometric galaxy redshift surveys.

astro-ph.CO↗

arXiv2021

Baryonic feedback biases on fundamental physics from lensed CMB power spectra

Upcoming measurements of the small-scale primary cosmic microwave background (CMB) temperature and polarization power spectra ($TT$/$TE$/$EE$) are anticipated to yield transformative constraints on new physics, including the effective number of relativistic species in the early universe ($N_{\rm eff}$). However, at multipoles $\ell \gtrsim 3000$, the primary CMB power spectra receive significant contributions from gravitational lensing. While these modes still carry primordial information, their theoretical modeling requires knowledge of the CMB lensing convergence power spectrum, $C_L^{κκ}$, including on small scales where it is affected by nonlinear gravitational evolution and baryonic feedback processes. Thus, the high-$\ell$ primary CMB is sensitive to these late-time, nonlinear effects. Here, we show that inaccuracies in the modeling of $C_L^{κκ}$ can yield surprisingly large biases on cosmological parameters inferred from the primary CMB power spectra measured by the upcoming Simons Observatory and CMB-S4 experiments. For CMB-S4, the biases can be as large as $1.6σ$ on the Hubble constant $H_0$ in a fit to $Λ$CDM and $1.2σ$ on $N_{\rm eff}$ in a fit to $Λ$CDM+$N_{\rm eff}$. We show that these biases can be mitigated by explicitly discarding all $TT$ data at $\ell>3000$ or by marginalizing over parameters describing baryonic feedback processes, both at the cost of slightly larger error bars. We also discuss an alternative, data-driven mitigation strategy based on delensing the CMB $T$ and $E$-mode maps. Finally, we show that analyses of upcoming data will require Einstein-Boltzmann codes to be run with much higher numerical precision settings than is currently standard, so as to avoid similar -- or larger -- parameter biases due to inaccurate theoretical predictions.

astro-ph.CO↗

arXiv2020

Remote Dipole Field Reconstruction with Dusty Galaxies

The kinetic Sunyaev Zel'dovich (kSZ) effect, cosmic microwave background (CMB) temperature anisotropies induced by scattering of CMB photons from free electrons, forms the dominant blackbody component of the CMB on small angular scales. Future CMB experiments on the resolution/sensitivity frontier will measure the kSZ effect with high significance. Through the cross-correlation with tracers of structure, it will be possible to reconstruct the remote CMB dipole field (e.g. the CMB dipole observed at different locations in the Universe) using the technique of kSZ tomography. In this paper, we derive a quadratic estimator for the remote dipole field using the Cosmic Infrared Background (CIB) as a tracer of structure. We forecast the ability of current and next-generation measurements of the CMB and CIB to perform kSZ tomography. The total signal-to-noise of the reconstruction is order unity for current datasets, and can improve by a factor of up to $10^3$ for future datasets, based on statistical error only. The CIB-based reconstruction is highly correlated with a galaxy survey-based reconstruction of the remote dipole field, which can be exploited to improve constraints on cosmological parameters and models for the CIB and distribution of baryons.

astro-ph.CO↗

arXiv2020

Avoiding baryonic feedback effects on neutrino mass measurements from CMB lensing

A measurement of the sum of neutrino masses is one of the main applications of upcoming measurements of gravitational lensing of the cosmic microwave background (CMB). This measurement can be confounded by modelling uncertainties related to so-called "baryonic effects" on the clustering of matter, arising from gas dynamics, star formation, and feedback from active galactic nuclei and supernovae. In particular, a wrong assumption about the form of baryonic effects on CMB lensing can bias a neutrino mass measurement by a significant fraction of the statistical uncertainty. In this paper, we investigate three methods for mitigating this bias: (1) restricting the use of small-scale CMB lensing information when constraining neutrino mass; (2) using an external tracer to remove the low-redshift contribution to a CMB lensing map; and (3) marginalizing over a parametric model for baryonic effects on large-scale structure. We test these methods using Fisher matrix forecasts for experiments resembling the Simons Observatory and CMB-S4, using a variety of recent hydrodynamical simulations to represent the range of possible baryonic effects, and using cosmic shear measured by the Rubin Observatory's LSST as the tracer in method (2). We find that a combination of (1) and (2), or (3) on its own, will be effective in reducing the bias induced by baryonic effects on a neutrino mass measurement to a negligible level, without a significant increase in the associated statistical uncertainty.

astro-ph.CO↗

arXiv2020

Improving models of the cosmic infrared background using CMB lensing mass maps

The cosmic infrared background (CIB) sourced by infrared emission from dusty star-forming galaxies is a valuable source of information on the star formation history of the Universe. In measurements of the millimeter sky at frequencies higher than $\sim 300$ GHz, the CIB and thermal emission from Galactic dust dominate. A limited understanding of the CIB contribution at lower frequencies on the other hand can hinder efforts to measure the kinetic Sunyaev-Zeldovich spectrum on small scales as well as new physics that affects the damping tail of the cosmic microwave background (CMB). The Planck satellite has measured with high fidelity the CIB at 217, 353, 545 and 857 GHz. On very large scales, this measurement is limited by our ability to separate the CIB from Galactic dust, but on intermediate scales, the measurements are limited by sample variance in the underlying matter field traced by the CIB. We show how significant improvements (20-100%) can be obtained on parameters of star formation models by cross-correlating the CIB (as measured from existing {\it Planck} maps or upcoming CCAT-prime maps) with upcoming mass maps inferred from gravitational lensing of the CMB. This improvement comes from improved knowledge of the redshift distribution of star-forming galaxies as well as through the use of the unbiased matter density inferred from CMB lensing mass maps to cancel the sample variance in the CIB field. We also find that further improvements can be obtained on CIB model parameters if the cross-correlation of the CIB with CMB lensing is measured over a wider area while restricting the more challenging CIB auto-spectrum measurement to the cleanest 5% of the sky.

astro-ph.CO↗

arXiv2018

Dilatonic Imprints on Exact Gravitational Wave Signatures

By employing the moduli space approximation, we analytically calculate the gravitational wave signatures emitted upon the merger of two extremally charged dilatonic black holes. We probe several values of the dilatonic coupling constant $a$, and find significant departures from the Einstein--Maxwell ($a=0$) counterpart studied in arXiv:1704.08520. For (low energy) string theory black holes $(a=1)$ there are no coalescence orbits and only a memory effect is observed, whereas for an intermediate value of the coupling $(a=1/\sqrt{3})$ the late-time merger signature becomes exponentially suppressed, compared to the polynomial decay in the $a=0$ case without a dilaton. Such an imprint is in principle observable and could reveal the presence of a scalar field (as for example predicted by string theory) in black hole mergers.

gr-qc↗

arXiv2017

Breakdown of the Equal Area Law for Holographic Entanglement Entropy

We investigate a holographic version of Maxwell's equal area law analogous to that for the phase transition in the black hole temperature/black hole entropy plane of a charged AdS black hole. We consider proposed area laws for both the black hole temperature/holographic entanglement entropy plane and the black hole temperature/2-point correlation function plane. Despite recent claims to the contrary, we demonstrate numerically that neither proposal is valid. We argue that there is no physical reason to expect such a construction in these planes.

hep-th↗

arXiv2017

Holographic heat engines: general considerations and rotating black holes

We perform the first study of holographic heat engines where the working material is a rotating black hole, obtaining exact results for the efficiency of a rectangular engine cycle. We also make general considerations in the context of benchmarking these engines on circular cycles. We find an exact expression that is valid for black holes with vanishing specific heat at constant volume and derive an upper bound, below the Carnot efficiency and independent of spacetime dimension, which holds for any black hole of this kind. We illustrate our results with applications to a variety of black holes, noting the effects of spacetime dimension, rotation, and higher curvature corrections on the efficiency of the cycle.

hep-th↗

arXiv2016

Information-theoretic Interestingness Measures for Cross-Ontology Data Mining

Community annotation of biological entities with concepts from multiple bio-ontologies has created large and growing repositories of ontology-based annotation data with embedded implicit relationships among orthogonal ontologies. Development of efficient data mining methods and metrics to mine and assess the quality of the mined relationships has not kept pace with the growth of annotation data. In this study, we present a data mining method that uses ontology-guided generalization to discover relationships across ontologies along with a new interestingness metric based on information theory. We apply our data mining algorithm and interestingness measures to datasets from the Gene Expression Database at the Mouse Genome Informatics as a preliminary proof of concept to mine relationships between developmental stages in the mouse anatomy ontology and Gene Ontology concepts (biological process, molecular function and cellular component). In addition, we present a comparison of our interestingness metric to four existing metrics. Ontology-based annotation datasets provide a valuable resource for discovery of relationships across ontologies. The use of efficient data mining methods and appropriate interestingness metrics enables the identification of high quality relationships.

cs.AI↗