arXiv subjects

Gilbert Holder

Publications and source records attributed to Gilbert Holder.

At least 19 recordsLinked to original sources

arXiv2026

The $\tau$ of Neutral Hydrogen: Increased CMB Optical Depth at Long Wavelengths

At wavelengths longer than 21 cm, photons from the long-wavelength tail of the cosmic microwave background (CMB) have a non-zero probability of being absorbed by distant neutral hydrogen. This provides an additional suppression of the observed CMB clustering in addition to the usual Thomson scattering. The optical depth as a function of frequency is sensitive to the 21 cm spin temperature $T_s$ of the gas as a function of cosmic time, with the excess optical depth peaking at a level of a few percent around 100 MHz. The details depend on the specifics of the heating of cosmic gas and the evolution of the neutral fraction $x_{HI}$. It is likely difficult to detect the CMB at these long radio wavelengths, but the cause is aided by the ability to cross-correlate with the already well-characterized fluctuations at cm/mm frequencies. We find that detecting CMB fluctuations at radio wavelengths corresponding to the 21 cm ``dark ages'' in cross-correlation with mm-wave maps may be easier than detecting the intrinsic 21 cm fluctuations. Measurement of the amplitude of CMB fluctuations as a function of radio wavelength provides a path for a new type of direct measurement of the combination $x_{HI}/T_s$ as a function of redshift.

astro-ph.CO↗

arXiv2025

The kSZ optical depth degeneracy and future constraints on local primordial non-Gaussianity

Recent reconstructions of the large-scale cosmological velocity field with kinetic Sunyaev Zeldovich (kSZ) tomography have returned an amplitude that is low with respect to the halo model prediction, captured by the kSZ velocity reconstruction bias $b_v <1$. This suggests that common choices for modeling the galaxy-electron cross correlation have systematically overestimated the true power, at least over scales and redshifts used in the velocity reconstruction measurements. In this paper, we study the implications of this overestimation for constraints on local-type primordial non-Gaussianity in current and near-future cosmological surveys. For concreteness, we focus on kSZ velocity reconstruction from a Vera Rubin Observatory-like survey in tandem with contemporary cosmic microwave background measurements. Assuming standard choices for the fiducial model of the small-scale galaxy-electron cross correlation, we find that upcoming kSZ tomography measurements can significantly improve constraints on local primordial non-Gaussianity via measurement of scale-dependent galaxy bias, in broad concordance with previous studies of the application of kSZ tomography to primordial non-Gaussianity. However, when we instead modify the assumed galaxy-electron cross-spectrum to be consistent with recent measurements of the velocity reconstruction bias, this picture can change appreciably. Specifically, we find that if the inferred suppression of galaxy-electron power persists at higher redshifts $z\gtrsim 1$, kSZ-driven improvement in local primordial non-Gaussianity constraints may be less significant than previously estimated. We explore how these conclusions depend on various modeling and experimental assumptions and discuss implications for the emerging program of kSZ velocity reconstruction.

astro-ph.CO↗

arXiv2025

An Image-Plane Approach to Gravitational Lens Modeling of Interferometric Data

Strong gravitational lensing acts as a cosmic telescope, enabling the study of the high-redshift universe. Astronomical interferometers, such as the Atacama Large Millimeter/submillimeter Array (ALMA), have provided high-resolution images of strongly lensed sources at millimeter and submillimeter wavelengths. To model the mass and light distributions of lensing and source galaxies from strongly lensed images, strong lens modeling for interferometric observations is conventionally performed in the visibility space, which is computationally expensive. In this paper, we implement an image-plane lens modeling methodology for interferometric dirty images by accounting for noise correlations. We show that the image-plane likelihood function produces accurate model values when tested on simulated ALMA observations with an ensemble of noise realizations. We also apply our technique to ALMA observations of two sources selected from the South Pole Telescope survey, comparing our results with previous visibility-based models. Our model results are consistent with previous models for both parametric and pixelated source-plane reconstructions. We implement this methodology for interferometric lens modeling in the open-source software package lenstronomy.

astro-ph.GA↗

arXiv2025

Cosmological information content of Betti curves and $k$-nearest neighbor distributions

We compare the cosmological constraints that can be obtained from halo clustering on non-linear scales ($2 h^{-1}$ Mpc < $r$ < $50 h^{-1}$ Mpc) using Betti curves, a topological summary statistic, and $k$-th nearest neighbor ($k$NN) distributions. We quantify the information content of each summary statistic through Fisher matrices computed from the Quijote simulations. Due to the use of simulation-based Fisher forecasts, we pay careful attention to the convergence of the Fisher matrices by looking at their eigendecompositions. We find that, in general, only two directions in the parameter space have constraints that are well converged given the number of Quijote simulations available. We then compare the information content of each summary statistic in the reduced parameter space $\{\Omega_m, \sigma_8\}$. We find that almost all of the information present in the Betti curves comes from the first two, $\beta_0$ and $\beta_1$, which track the number of connected components and one-dimensional loops respectively, and almost no constraining power comes from $\beta_2$ which tracks the number of topological voids. In comparison, we find that the $k$NNs provide very competitive constraints along with several potential advantages in regards to real data. Finally, we find that while the $k$NNs and Betti curves provide some complementary constraints, they are not fully independent, potentially indicating a connection between the two statistics.

astro-ph.CO↗

arXiv2024

Cross-correlating IceCube neutrinos with a large set of galaxy samples around redshift z ~ 1

The IceCube neutrino telescope has detected a diffuse flux of high-energy astrophysical neutrinos, but the sources of this flux have largely remained elusive. Using the 10-year IceCube public dataset, we search for correlations between neutrino events and tracers of large-scale structure (LSS). We conduct a combined cross-correlation analysis using several wide-area galaxy catalogs spanning a redshift range of z = 0.1 to z ~ 2.5 as well as maps of the cosmic infrared background. We do not detect a definitive signal, but find tantalizing hints of a potential positive correlation between neutrinos and the tracers of LSS. We additionally construct a simple model to interpret galaxy-neutrino cross-correlations in terms of the redshift distribution of neutrino sources. We put upper limits on the clustering amplitude of neutrinos based on the measured cross-correlations with galaxies and forecast the improvements on these constraints that can be obtained using future detectors. We show that, in the future, neutrino-galaxy cross-correlations should be a powerful probe to constrain properties of neutrino source populations.

astro-ph.HE↗

arXiv2024

Gravitational Lensing of Galaxy Clustering

We investigate lensing reconstruction using the clustered galaxy distribution as a source field, using both the traditional cosmic microwave background quadratic estimator and a shear-only estimator. We calculate the expected signal-to-noise ratio of the cross power spectrum of such reconstructions with cosmic shear measurements for an LSST-like galaxy survey. Modeling the galaxy field as a Gaussian random field, we find that there is substantial clustering signal in the source field at angular scales substantially smaller than those typically used by CMB reconstructions. The expected signal-to-noise for cross-correlations in LSST from cosmic shear is $\sim$60 in the presence of shape noise, while cross correlating with a sample-variance limited mass map would have signal-to-noise in the hundreds. This type of cross-correlation could be used as a way to identify systematic errors in lensing studies and is just one example of many possible higher order correlations in galaxy surveys that may contain substantial cosmological information.

astro-ph.CO↗

arXiv2023

Topological data analysis reveals differences between simulated galaxies and dark matter haloes

We use topological summaries based on Betti curves to characterize the large-scale spatial distribution of simulated dark matter haloes and galaxies. Using the IllustrisTNG and CAMELS-SAM simulations, we show that the topology of the galaxy distribution is significantly different from the topology of the dark matter halo distribution. Further, there are significant differences between the distributions of star-forming and quiescent galaxies. These topological differences are broadly consistent across all simulations, while at the same time there are noticeable differences when comparing between different models. Finally, using the CAMELS-SAM simulations, we show that the topology of the quiescent galaxies in particular depends strongly on the amount of supernova feedback. These results suggest that topological summary statistics could be used to help better understand the processes of galaxy formation and evolution.

astro-ph.CO↗

arXiv2022

Breaking bad degeneracies with Love relations: Improving gravitational-wave measurements through universal relations

The distance-inclination degeneracy limits gravitational-wave parameter estimation of compact binary mergers. Although the degeneracy can be partially broken by including higher-order modes or precession, these effects are suppressed in binary neutron stars. In this work, we implement a new parametrization of the tidal effects in the binary neutron-star waveform, exploiting the binary Love relations, that breaks the distance-inclination degeneracy. The binary Love relations prescribe the tidal deformability of a neutron star as a function of its source-frame mass in an equation-of-state insensitive way and, thus, allows direct measurement of the redshift of the source. If the cosmological parameters are assumed to be known, the redshift can be converted to a luminosity distance, and the distance-inclination degeneracy can thus be broken. We implement this new approach, studying a range of binary neutron-star observing scenarios using Bayesian parameter estimation on synthetic data. In the era of the third-generation detectors, for observations with signal-to-noise ratios ranging from 6 to 167, we forecast up to an $\sim70\%$ decrease in the $90\%$ credible interval of the distance and inclination and up to an $\sim50\%$ decrease in that of the source-frame component masses. For edge-on systems, our approach can result in moderate ($\sim50\%$) improvement in the measurements of distance and inclination for binaries with a signal-to-noise ratio as low as 10. This prescription can be used to better infer the source-frame masses and, hence, refine population properties of neutron stars, such as their maximum mass, impacting nuclear astrophysics. When combined with the search for electromagnetic counterpart observations, the work presented here can be used to put improved bounds on the opening angle of jets from binary neutron-star mergers.

gr-qc↗

arXiv2021

The radio SZ effect as a probe of the cosmological radio background

If there is a substantial cosmological radio background, there should be a radio Sunyaev-Zeldovich (SZ) effect that goes along with it. The radio background Comptonization leads to a slight photon excess at all wavelengths, while Comptonization of the CMB at low frequencies leads to a decrement. For levels of the radio background consistent with observations, these effects cancel each other around $\nu\simeq 735~$MHz, with an excess at lower frequencies and a decrement at higher frequencies. Assuming a purely cosmological origin of the observed ARCADE radio excess, at $\nu \lesssim 20\,{\rm GHz}$ the signal scales as $\Delta T / T_{\rm CMB}\simeq 2\,y\left[ (\nu/735\,{\rm MHz})^{-2.59}-1\right]$ with frequency and the Compton-$y$ parameter of the cluster. For a typical cluster, the total radio SZ signal is at the level of $\Delta T\simeq 1\,{\rm mK}$ around the null, with a steep scaling towards radio frequencies. This is above current raw sensitivity limits for many radio facilities at these wavelengths, providing a unique way to confirm the cosmological origin of the ARCADE excess and probe its properties (e.g., redshift dependence and isotropy). We also give an expression to compute the radio-analogue of the kinematic SZ effect, highlighting that this might provide a new tool to probe large-scale velocity fields and the cosmic evolution of the radio background.

astro-ph.CO↗

arXiv2021

Cosmology with Love: Measuring the Hubble constant using neutron star universal relations

Gravitational-wave cosmology began in 2017 with the observation of the gravitational waves emitted in the merger of two neutron stars, and the coincident observation of the electromagnetic emission that followed. Although only a $30\%$ measurement of the Hubble constant was achieved, future observations may yield more precise measurements either through other coincident events or through cross correlation of gravitational-wave events with galaxy catalogs. Here, we implement a new way to measure the Hubble constant without an electromagnetic counterpart and through the use of the binary Love relations. These relations govern the tidal deformabilities of neutron stars in an equation-of-state insensitive way. Importantly, the Love relations depend on the component masses of the binary in the source frame. Since the gravitational-wave phase and amplitude depend on the chirp mass in the observer (and hence redshifted) frame, one can in principle combine the binary Love relations with the gravitational-wave data to directly measure the redshift, and thereby infer the value of the Hubble constant. We implement this approach in both real and synthetic data through a Bayesian parameter estimation study in a range of observing scenarios. We find that for the LIGO/Virgo/KAGRA design sensitivity era, this method results in a similar measurement accuracy of the Hubble constant to those of current-day, dark-siren measurements. For third generation detectors, this accuracy improves to $\lesssim 10\%$ when combining measurements from binary neutron star events in the LIGO Voyager era, and to $\lesssim 2\%$ in the Cosmic Explorer era.

gr-qc↗

arXiv2020

Hunting for Dark Matter Subhalos in Strong Gravitational Lensing with Neural Networks

Dark matter substructures are interesting since they can reveal the properties of dark matter. Collisionless N-body simulations of cold dark matter show more substructures compared with the population of dwarf galaxy satellites observed in our local group. Therefore, understanding the population and property of subhalos at cosmological scale would be an interesting test for cold dark matter. In recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. In this work, we discuss the possibility of using deep neural networks to detect dark matter subhalos, and showing some preliminary results with simulated data. We found that neural networks not only show promising results on detecting multiple dark matter subhalos, but also learn to reject the subhalos on the lensing arc of a smooth lens where there is no subhalo.

astro-ph.CO↗

arXiv2020

The Terahertz Intensity Mapper (TIM): a Next-Generation Experiment for Galaxy Evolution Studies

Understanding the formation and evolution of galaxies over cosmic time is one of the foremost goals of astrophysics and cosmology today. The cosmic star formation rate has undergone a dramatic evolution over the course of the last 14 billion years, and dust obscured star forming galaxies (DSFGs) are a crucial component of this evolution. A variety of important, bright, and unextincted diagnostic lines are present in the far-infrared (FIR) which can provide crucial insight into the physical conditions of galaxy evolution, including the instantaneous star formation rate, the effect of AGN feedback on star formation, the mass function of the stars, metallicities, and the spectrum of their ionizing radiation. FIR spectroscopy is technically difficult but scientifically crucial. Stratospheric balloons offer a platform which can outperform current instrument sensitivities and are the only way to provide large-area, wide bandwidth spatial/spectral mapping at FIR wavelengths. NASA recently selected TIM, the Terahertz Intensity Mapper, with the goal of demonstrating the key technical milestones necessary for FIR spectroscopy. The TIM instrument consists of an integral-field spectrometer from 240-420 microns with 3600 kinetic-inductance detectors (KIDs) coupled to a 2-meter low-emissivity carbon fiber telescope. In this paper, we will summarize plans for the TIM experiment's development, test and deployment for a planned flight from Antarctica.

astro-ph.IM↗

arXiv2020

BBN constraints on dark radiation isocurvature

The existence of dark radiation that is completely decoupled from the standard model in the early Universe leaves open the possibility of an associated dark radiation isocurvature mode. We show that the presence of dark radiation isocurvature leads to spatial variation in the primordial abundances of helium and deuterium due to spatial variation in $N_{\rm eff}$ during Big Bang nucleosynthesis. We use the result to constrain the existence of such an isocurvature mode on scales down to $\sim 1$ Mpc scales. By measuring the excess variance in the primordial helium to hydrogen and deuterium to hydrogen ratio in different galaxies, we constrain the variance in average isocurvature in a galaxy to be less than $0.13/\Delta \bar{N}_{\rm eff}$ at 95\% confidence. Here $\Delta \bar{N}_{\rm eff}$ is the spatially averaged increase in $N_{\rm eff}$ due to the additional dark radiation component.

astro-ph.CO↗

arXiv2019

Gravitational Lensing of the Cosmic Neutrino Background

We study gravitational lensing of the cosmic neutrino background. This signal is undetectable for the foreseeable future, but there is a rich trove of information available. At least some of the neutrinos from the early universe will be non-relativistic today, with a closer surface of last scattering (compared to the cosmic microwave background) and with larger angles of deflection. Lensing of massive neutrinos is strongly chromatic: both the amplitude of lensing and the cosmic time at which the potential is traversed depend on neutrino momentum, in principle giving access to our entire causal volume, not restricted to the light cone. As a concrete example, we focus on the case where the cosmic neutrino background would be strongly lensed when passing through halos of galaxy clusters and galaxies. We calculate the Einstein radius for cosmic neutrinos and investigate the impact of neutrino mass.

astro-ph.CO↗

arXiv2019

Research and Development for HI Intensity Mapping

Development of the hardware, data analysis, and simulation techniques for large compact radio arrays dedicated to mapping the 21 cm line of neutral hydrogen gas has proven to be more difficult than imagined twenty years ago when such telescopes were first proposed. Despite tremendous technical and methodological advances, there are several outstanding questions on how to optimally calibrate and analyze such data. On the positive side, it has become clear that the outstanding issues are purely technical in nature and can be solved with sufficient development activity. Such activity will enable science across redshifts, from early galaxy evolution in the pre-reionization era to dark energy evolution at low redshift.

astro-ph.IM↗

arXiv2019

Polarization of the Cosmic Infrared Background Fluctuations

The cosmic infrared background (CIB) is slightly polarized. Polarization directions of individual galaxies could be aligned with tidal fields around galaxies, resulting in nonzero CIB polarization. We use a linear intrinsic alignment model to theoretically predict angular correlations of the CIB polarization fluctuations and find that electriclike and curl-like ($B$-mode) polarization modes are equally generated with power four orders of magnitude less than its intensity. The CIB $B$-mode signal is negligible and not a concerning foreground for the inflationary $B$-mode searches at nominal frequencies for cosmic microwave background measurements, but could be detected at submillimetre wavelengths by future space missions.

astro-ph.CO↗

arXiv2019

An excess of non-Gaussian fluctuations in the cosmic infrared background consistent with gravitational lensing

The cosmic infrared background (CIB) is gravitationally lensed. A quadratic-estimator technique that is inherited from lensing analyses of the cosmic microwave background (CMB) can be applied to detect the CIB lensing effects. However, the CIB fluctuations are intrinsically strongly non-Gaussian, making CIB lensing reconstruction highly biased. We perform numerical simulations to estimate the intrinsic non-Gaussianity and establish a cross-correlation approach to precisely extract the CIB lensing signal from raw data. We apply this technique to CIB data from the Planck satellite and cross-correlate the resulting lensing estimate with the CIB data, galaxy number counts and the CMB lensing potential. We detect an excess that is consistent with a lensing contribution at $>4σ$.

astro-ph.CO↗

arXiv2019

Primordial Non-Gaussianity

Our current understanding of the Universe is established through the pristine measurements of structure in the cosmic microwave background (CMB) and the distribution and shapes of galaxies tracing the large scale structure (LSS) of the Universe. One key ingredient that underlies cosmological observables is that the field that sources the observed structure is assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps the most robust theoretical prediction of models that explain the observed Universe; itis necessarily present even in the simplest scenarios. In addition, most inflationary models produce far higher levels of non-Gaussianity. Since non-Gaussianity directly probes the dynamics in the early Universe, a detection would present a monumental discovery in cosmology, providing clues about physics at energy scales as high as the GUT scale.

astro-ph.CO↗