arXiv subjects

Gil Holder

Publications and source records attributed to Gil Holder.

13 recordsLinked to original sources

arXiv2022

Snowmass2021 CMB-HD White Paper

CMB-HD is a proposed millimeter-wave survey over half the sky that would be ultra-deep (0.5 uK-arcmin) and have unprecedented resolution (15 arcseconds at 150 GHz). Such a survey would answer many outstanding questions about the fundamental physics of the Universe. Major advances would be 1.) the use of gravitational lensing of the primordial microwave background to map the distribution of matter on small scales (k~10 h Mpc^(-1)), which probes dark matter particle properties. It will also allow 2.) measurements of the thermal and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density and velocity, another probe of cosmic structure. In addition, CMB-HD would allow us to cross critical thresholds: 3.) ruling out or detecting any new, light (< 0.1 eV) particles that were in thermal equilibrium with known particles in the early Universe, 4.) testing a wide class of multi-field models that could explain an epoch of inflation in the early Universe, and 5.) ruling out or detecting inflationary magnetic fields. CMB-HD would also provide world-leading constraints on 6.) axion-like particles, 7.) cosmic birefringence, 8.) the sum of the neutrino masses, and 9.) the dark energy equation of state. The CMB-HD survey would be delivered in 7.5 years of observing 20,000 square degrees of sky, using two new 30-meter-class off-axis crossed Dragone telescopes to be located at Cerro Toco in the Atacama Desert. Each telescope would field 800,000 detectors (200,000 pixels), for a total of 1.6 million detectors.

astro-ph.CO↗

arXiv2020

CMB-HD: Astro2020 RFI Response

CMB-HD is a proposed ultra-deep (0.5 uk-arcmin), high-resolution (15 arcseconds) millimeter-wave survey over half the sky that would answer many outstanding questions in both fundamental physics of the Universe and astrophysics. This survey would be delivered in 7.5 years of observing 20,000 square degrees, using two new 30-meter-class off-axis cross-Dragone telescopes to be located at Cerro Toco in the Atacama Desert. Each telescope would field 800,000 detectors (200,000 pixels), for a total of 1.6 million detectors.

astro-ph.CO↗

arXiv2019

CMB-HD: An Ultra-Deep, High-Resolution Millimeter-Wave Survey Over Half the Sky

A millimeter-wave survey over half the sky, that spans frequencies in the range of 30 to 350 GHz, and that is both an order of magnitude deeper and of higher-resolution than currently funded surveys would yield an enormous gain in understanding of both fundamental physics and astrophysics. By providing such a deep, high-resolution millimeter-wave survey (about 0.5 uK-arcmin noise and 15 arcsecond resolution at 150 GHz), CMB-HD will enable major advances. It will allow 1) the use of gravitational lensing of the primordial microwave background to map the distribution of matter on small scales (k~10/hMpc), which probes dark matter particle properties. It will also allow 2) measurements of the thermal and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density and gas pressure profiles of halos over a wide field, which probes galaxy evolution and cluster astrophysics. In addition, CMB-HD would allow us to cross critical thresholds in fundamental physics: 3) ruling out or detecting any new, light (< 0.1eV), thermal particles, which could potentially be the dark matter, and 4) testing a wide class of multi-field models that could explain an epoch of inflation in the early Universe. Such a survey would also 5) monitor the transient sky by mapping the full observing region every few days, which opens a new window on gamma-ray bursts, novae, fast radio bursts, and variable active galactic nuclei. Moreover, CMB-HD would 6) provide a census of planets, dwarf planets, and asteroids in the outer Solar System, and 7) enable the detection of exo-Oort clouds around other solar systems, shedding light on planet formation. CMB-HD will deliver this survey in 5 years of observing half the sky, using two new 30-meter-class off-axis cross-Dragone telescopes to be located at Cerro Toco in the Atacama Desert. The telescopes will field about 2.4 million detectors (600,000 pixels) in total.

astro-ph.CO↗

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.

astro-ph.CO↗

arXiv2019

Ensemble photometric redshifts

Upcoming imaging surveys, such as LSST, will provide an unprecedented view of the Universe, but with limited resolution along the line-of-sight. Common ways to increase resolution in the third dimension, and reduce misclassifications, include observing a wider wavelength range and/or combining the broad-band imaging with higher spectral resolution data. The challenge with these approaches is matching the depth of these ancillary data with the original imaging survey. However, while a full 3D map is required for some science, there are many situations where only the statistical distribution of objects (dN/dz) in the line-of-sight direction is needed. In such situations, there is no need to measure the fluxes of individual objects in all of the surveys. Rather a stacking procedure can be used to perform an `ensemble photo-z'. We show how a shallow, higher spectral resolution survey can be used to measure dN/dz for stacks of galaxies which coincide in a deeper, lower resolution survey. The galaxies in the deeper survey do not even need to appear individually in the shallow survey. We give a toy model example to illustrate tradeoffs and considerations for applying this method. This approach will allow deep imaging surveys to leverage the high resolution of spectroscopic and narrow/medium band surveys underway, even when the latter do not have the same reach to high redshift.

astro-ph.GA↗

arXiv2018

Planet X in CMB and Optical Galaxy Surveys

We consider the possibility of detecting and tracking the hypothesized Planet 9 or other unknown planetary-mass distant solar system members, generically called Planet X, with a combination of CMB and optical imaging surveys. Planets are detectable via thermal emission in CMB surveys and via reflected sunlight in optical surveys. Since the flux from reflected light falls off faster with distance, the signal-to-noise of planetary observations with optical surveys falls off faster than for CMB surveys. A promising approach to detecting new solar system planets with future surveys such as the Simons Observatory, CMB-S4 and LSST, is for a detection in CMB data followed by tracking in the synoptic imaging survey. Even if the parallax were not detected in CMB data, point sources consistent with thermal spectra could be followed up by LSST. In addition to expanding the Planet X discovery space, the joint datasets would improve constraints on key orbital and thermal properties of outer solar system bodies. This approach would work for a Neptune-like planet up to distances of a few thousand AU, and for an Earth-like planet up to several hundred AU. We discuss the prospects for the next decade as well as nearer-term surveys.

astro-ph.EP↗

arXiv2016

Cosmologists in Search of Planet Nine: the Case for CMB Experiments

Cosmology experiments at mm-wavelengths can detect Planet Nine if it is the size of Neptune, has an effective temperature of 40 K, and is 700 AU from the Sun. It would appear as a ~30 mJy source at 1 mm with an annual parallax of ~5 arcmin. The challenge is to distinguish it from the approximately 4000 foreground asteroids brighter than 30 mJy. Fortunately, these asteroids are known to the Minor Planet Center and can be identified because they move across a resolution element in a matter of hours, orders of magnitude faster than Planet Nine. If Planet Nine is smaller, colder, and/or more distant than expected, then it could be as faint as 1 mJy at 1 mm. There are roughly $10^6$ asteroids this bright and many are unknown, making current cosmology experiments confusion limited for moving sources. Nonetheless, it may still be possible to find the proverbial needle in the haystack using a matched filter. This would require mm telescopes with high angular resolution and high sensitivity in order to alleviate confusion and to enable the identification of moving sources with relatively short time baselines. Regardless of its mm flux density, searching for Planet Nine would require frequent radio measurements for large swaths of the sky, including the ecliptic and Galactic plane. Even if Planet Nine had already been detected by other means, measuring its mm-flux would constrain its internal energy budget, and therefore help resolve the mystery of Uranus and Neptune, which have vastly different internal heat.

astro-ph.EP↗

arXiv2016

Combining galaxy and 21cm surveys

Acoustic waves traveling through the early Universe imprint a characteristic scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale can be used as a standard ruler to map the expansion history of the Universe, a technique known as Baryon Acoustic Oscillations (BAO). BAO offer a high-precision, low-systematics means of constraining our cosmological model. The statistical power of BAO measurements can be improved if the `smearing' of the acoustic feature by non-linear structure formation is undone in a process known as reconstruction. In this paper we use low-order Lagrangian perturbation theory to study the ability of $21\,$cm experiments to perform reconstruction and how augmenting these surveys with galaxy redshift surveys at relatively low number densities can improve performance. We find that the critical number density which must be achieved in order to benefit $21\,$cm surveys is set by the linear theory power spectrum near its peak, and corresponds to densities achievable by upcoming surveys of emission line galaxies such as eBOSS and DESI. As part of this work we analyze reconstruction within the framework of Lagrangian perturbation theory with local Lagrangian bias, redshift-space distortions, ${\bf k}$-dependent noise and anisotropic filtering schemes.

astro-ph.CO↗

arXiv2015

Prospects for Delensing the Cosmic Microwave Background for Studying Inflation

A detection of excess cosmic microwave background (CMB) B-mode polarization on large scales allows the possibility of measuring not only the amplitude of these fluctuations but also their scale dependence, which can be parametrized as the tensor tilt $n_T$. Measurements of this scale dependence will be hindered by the secondary B-mode polarization anisotropy induced by gravitational lensing. Fortunately, these contaminating B modes can be estimated and removed with a sufficiently good estimate of the intervening gravitational potential and a good map of CMB E-mode polarization. We present forecasts for how well these gravitational lensing B modes can be removed, assuming that the lensing potential can be estimated either internally from CMB data or using maps of the cosmic infrared background (CIB) as a tracer. We find that CIB maps are as effective as CMB maps for delensing at the noise levels of the current generation of CMB experiments, while the CMB maps themselves will ultimately be best for delensing at polarization noise below $Δ_P$=1 $μ$K-arcmin. At this sensitivity level, CMB delensing will be able to measure $n_T$ to an accuracy of 0.02 or better, which corresponds to the tensor tilt predicted by the consistency relation for single-field slow-roll models of inflation with $r=0.2$. However, CIB-based delensing will not be sufficient for constraining $n_T$ in simple inflationary models.

astro-ph.CO↗

arXiv2011

Impacts of Dark Stars on Reionization and Signatures in the Cosmic Microwave Background

We perform a detailed and systematic investigation of the possible impacts of dark stars upon the reionization history of the Universe, and its signatures in the cosmic microwave background (CMB). We compute hydrogen reionization histories, CMB optical depths and anisotropy power spectra for a range of stellar populations including dark stars. If dark stars capture large amounts of dark matter via nuclear scattering, reionization can be substantially delayed, leading to decreases in the integrated optical depth to last scattering and large-scale power in the EE polarization power spectrum. Using the integrated optical depth observed by WMAP7, in our canonical reionization model we rule out the section of parameter space where dark stars with high scattering-induced capture rates tie up more than ~90% of all the first star-forming baryons, and live for over ~250 Myr. When nuclear scattering delivers only moderate amounts of dark matter, reionization can instead be sped up slightly, modestly increasing the CMB optical depth. If dark stars do not obtain any dark matter via nuclear scattering, effects upon reionization and the CMB are negligible. The effects of dark stars upon reionization and its CMB markers can be largely mimicked or compensated for by changes in the existing parameters of reionization models, making dark stars difficult to disentangle from astrophysical uncertainties, but also widening the range of standard parameters in reionization models that can be made consistent with observations.

astro-ph.CO↗

arXiv2010

A Signature of Cosmic Strings Wakes in the CMB Polarization

We calculate a signature of cosmic strings in the polarization of the cosmic microwave background (CMB). We find that ionization in the wakes behind moving strings gives rise to extra polarization in a set of rectangular patches in the sky whose length distribution is scale-invariant. The length of an individual patch is set by the co-moving Hubble radius at the time the string is perturbing the CMB. The polarization signal is largest for string wakes produced at the earliest post-recombination time, and for an alignment in which the photons cross the wake close to the time the wake is created. The maximal amplitude of the polarization relative to the temperature quadrupole is set by the overdensity of free electrons inside a wake which depends on the ionization fraction $f$ inside the wake. The signal can be as high as $0.06 {\rm μK}$ in degree scale polarization for a string at high redshift (near recombination) and a string tension $μ$ given by $G μ= 10^{-7}$.

astro-ph.CO↗

arXiv2007

The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB

The inhomogeneous ionization state of the universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order ~0.01 μK, and local peak values of ~0.1 μK, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensing effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.

astro-ph↗

arXiv2004

Effects of sub-mm and radio point sources on the recovery of Sunyaev-Zeldovich galaxy cluster parameters

Observations of clusters in the 30 to 350 GHz range can in principle be used to determine a galaxy cluster's Comptonization parameter, y, peculiar velocity, v and gas temperature, T_e via the dependence of the kinetic and thermal Sunyaev-Zeldovich (SZ) effects on these parameters. Despite the significant contamination expected from thermal emission by dust in high-redshift galaxies, we find that the simultaneous determination of optical depth (tau), v and T_e is possible from observations with sensitivity of a few uK in three or more bands with arc minute resolution. After allowing for realistic levels of contamination by dusty galaxies and primary CMB anisotropy, we find that simultaneous determinations of velocities to an accuracy of better than 200 km/s and temperatures to roughly keV accuracy should be possible in the near future. We study how errors change as a function of cluster properties (angular core radius and gas temperature) and experimental parameters (observing time, angular resolution and observing frequencies). Contaminating synchrotron emission from cluster galaxies will probably not be a major contaminant of peculiar velocity measurements.

astro-ph↗