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White, Martin

Publications and source records attributed to White, Martin.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Reconstructing large-scale structure with neutral hydrogen surveys

Upcoming 21-cm intensity surveys will use the hyperfine transition in emission to map out neutral hydrogen in large volumes of the universe. Unfortunately, large spatial scales are completely contaminated with spectrally smooth astrophysical foregrounds which are orders of magnitude brighter than the signal. This contamination also leaks into smaller radial and angular modes to form a foreground wedge, further limiting the usefulness of 21-cm observations for different science cases, especially cross-correlations with tracers that have wide kernels in the radial direction. Here in this paper, we investigate reconstructing these modes within a forward modeling framework. Starting with an initial density field, a suitable bias parameterization and non-linear dynamics to model the observed 21-cm field, our reconstruction proceeds by {combining} the likelihood of a forward simulation to match the observations (under given modeling error and a data noise model) {with the Gaussian prior on initial conditions and maximizing the obtained posterior}. For redshifts z=2 and 4, we are able to reconstruct 21cm field with cross correlation, r c > 0.8 on all scales for both our optimistic and pessimistic assumptions about foreground contamination and for different levels of thermal noise. The performance deteriorates slightly at z=6. The large-scale line-of-sight modes are reconstructed almost perfectly. We demonstrate how our method also provides a technique for density field reconstruction for baryon acoustic oscillations, outperforming standard methods on all scales. We also describe how our reconstructed field can provide superb clustering redshift estimation at high redshifts, where it is otherwise extremely difficult to obtain dense spectroscopic samples, as well as open up a wealth of cross-correlation opportunities with projected fields (e.g. lensing) which are restricted to modes transverse to the line of sight.

21 cm↗
DOE OSTI2019

Cosmology with dropout selection: straw-man surveys & CMB lensing

In this study, we seek to prove the means, motive and opportunity of 2 ≤ z ≤ 5 dropout galaxies for large-scale structure. Together with low-z tracers, these samples would map practically every linear mode and facilitate a tomographic decomposition of the CMB lensing kernel over an unprecedented volume, thereby yielding a proxy for (the time evolution of) matter density fluctuations that provides compelling tests of horizon-scale General Relativity, neutrino masses and Inflation-- viz., curvature, running of the spectral index and a scale-dependent halo bias induced by (local) primordial non-Gaussianity. Focusing on color-color selection, we estimate the completeness, contamination, and spectroscopic survey speed of tailored Lyman-break galaxy (LBG) samples. We forecast the potential of CMB lensing cross-correlation, clustering redshifts and Redshift-Space Distortions (RSD) analyses. In particular, we estimate: the depth dependence of interlopers based on CFHTLS data and propagate this to biases in cosmology; new inferences of (non-linear) halo bias at these redshifts and depths using legacy data; detailed forecasts of LBG spectra as would be observed by DESI, PFS, and their successors. We further assess the relative competitiveness of potential spectroscopic facilities based on an intuitive figure-of-merit and define a modernisation of traditional selections to the photometric system of LSST where necessary. We confirm these science cases to be compelling for achievable facilities in the next decade by defining a LBG sample of increasing Lyman-alpha equivalent width with redshift, which delivers both percent-level RSD constraints on the growth rate at high- z and measurements of CMB lensing cross-correlation at z = 3 and 4 with a significance measured in the hundreds. Finally, we discuss the limitations and avenues for improvement beyond this initial exploration (abridged).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Mapping Quasar Light Echoes in 3D with Ly α Forest Tomography

The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced Ly (Ly) forest transmission in absorption spectra of background sightlines. In this work, we present a novel method based on Ly forest tomography, which is capable of mapping these quasar "light echoes" in three dimensions. Using a dense grid (10-100) of faint (m r ≈ 24.7 mag) background galaxies as absorption probes, one can measure the ionization state of the IGM in the vicinity of a foreground quasar, yielding detailed information about the quasar's radiative history and emission geometry. An end-to-end analysis-combining cosmological hydrodynamical simulations post-processed with a quasar emission model, realistic estimates of galaxy number densities, and instrument + telescope throughput-is conducted to explore the feasibility of detecting quasar light echoes. We present a new, fully Bayesian statistical method that allows one to reconstruct quasar light echoes from thousands of individual low-S/N transmission measurements. Armed with this tool, we undertake an exhaustive parameter study and show that light echoes can be convincingly detected for luminous (M 1450 <-27.5 mag, corresponding to m 1450 < 18.4 mag at z≃3.6) quasars at redshifts 3 < z QSO < 5, and that a relative precision better than 20% on the quasar age can be achieved for individual objects in the expected range of ages between 1 and 100 Myr. The observational requirements are relatively modest: Moderate-resolution (R ≳ 750), multiobject spectroscopy at a low signal-to-noise ratio (S/N > 5) is sufficient, requiring three-hour integrations using existing instruments on 8 m class telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Intensity mapping with neutral hydrogen and the Hidden Valley simulations

Our work presents the Hidden Valley simulations, a set of trillion-particle N-body simulations in gigaparsec volumes aimed at intensity mapping science. We offer details of the simulations and their convergence, then specialize to the study of 21-cm fluctuations between redshifts 2 and 6. Neutral hydrogen is assigned to halos using three prescriptions, and we investigate the clustering in real and redshift-space at the 2-point level. In common with earlier work we find the bias of HI increases from near 2 at z = 2 to 4 at z = 6, becoming more scale dependent at high z . The level of scale-dependence and decorrelation with the matter field are as predicted by perturbation theory. Due to the low mass of the hosting halos, the impact of fingers of god is small on the range relevant for proposed 21-cm instruments. We show that baryon acoustic oscillations and redshift-space distortions could be well measured by such instruments. Taking advantage of the large simulation volume, we assess the impact of fluctuations in the ultraviolet background, which change HI clustering primarily at large scales.

21 cm↗
DOE OSTI2019

The reconstructed power spectrum in the Zeldovich approximation

Density-reconstruction sharpens the baryon acoustic oscillations signal by undoing some of the smoothing incurred by nonlinear structure formation. Here, we present an analytical model for reconstruction based on the Zeldovich approximation, which for the first time includes a complete set of counterterms and bias terms up to quadratic order and can fit real and redshift-space data pre- and post-reconstruction data in both Fourier and configuration space over a wide range of scales. We compare our model to n-body data at $z = 0$ from the ${\tt DarkSky}$ simulation, finding sub-percent agreement in both real space and in the redshift-space power spectrum monopole out to $k = 0.4\ h$ Mpc$^{-1}$, and out to $k = 0.2\ h$ Mpc$^{-1}$ in the quadrupole, with comparable agreement in configuration space. We compare our model with several popular existing alternatives, updating existing theoretical findings for exponential damping in wiggle/no-wiggle splits of the BAO signal and discuss the usually-ignored effect of higher bias contributions on the reconstructed signal. In the appendices, we re-derive the former within our formalism, present exploratory results on higher-order corrections due to nonlinearities inherent to reconstruction, and present numerical techniques with which to calculate the redshift-space power spectrum of biased tracers within the Zeldovich approximation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Astro2020 APC White Paper: The MegaMapper: a z > 2 Spectroscopic Instrument for the Study of Inflation and Dark Energy

MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at 2¡z¡5. A 6.5-m Magellan telescope will be coupled with DESI spectrographs to achieve multiplexing of 20,000. MegaMapper would be located at Las Campanas Observatory to fully access LSST imaging for target selection.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Synergies between radio, optical and microwave observations at high redshift

In this work, we study synergies between three promising methods to measure 2 2 and suffer from interloper problems even for spectroscopic surveys. Intensity mapping of the 21-cm signal can cover large volumes with exquisite fidelity, but is limited both by loss of information to foreground cleaning and by lack of knowledge of the mean signal. Cosmic microwave background (CMB) lensing is theoretically very clean, but ultimately measures just the projected variations in density. We find that cross-correlation between optical and radio can significantly improve the measurement of growth rate. Combining these with the CMB provides a promising avenue to detecting modified gravity at high redshifts, in particular by independently probing the Weyl and Newtonian potentials and by strengthening control of systematics. We find that cross-correlating a Stage {\sc ii} 21-cm survey with DESI quasars with a reasonable brightness temperature prior could enable measurements of the growth rate fσ 8 at sub 3% and sub 8% levels at z = 3, 4, representing a factor of 4 and 8 improvement over constraints obtainable from DESI quasars alone. Similarly, cross-correlating 21-cm data with a futuristic LBG survey to m UV <24.5 over 1000 square degrees will make possible fσ 8 measurements at close to 1% at z = 3 and 3% at z = 4, and improve similar constraints at z = 5 by close to a factor of 3 to sub-10% precision. Finally, combining the above with CMB lensing from a Stage 4 CMB survey and LSST data can additionally constrain the gravitational slip γ parameter to similar precision at these redshifts, enabling us to test the predictions of general relativity at large scales.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Biased tracers of two fluids in the Lagrangian picture

We explore Lagrangian perturbation theory (LPT) for biased tracers in the presence of two fluids, focusing on the case of cold dark matter (CDM) and baryons. The presence of two fluids induces corrections to the Lagrangian bias expansion and tracer advection, both of which we formulate as expansions in the three linear modes of the Lagrangian equations of motion. We compute the linear-order two-fluid corrections in the Zeldovich approximation, finding that modifications to the bias expansion and tracer advection both enter as percent-level corrections over a large range of wavenumbers at low redshift and draw parallels with the Eulerian formalism. We then discuss nonlinear corrections in the two-fluid picture, and calculate contributions from the relative velocity effect ($\propto$ v$_r^2$) at one loop order. Finally, we conduct an exploratory Fisher analysis to assess the impact of two-fluid corrections on baryon acoustic oscillations (BAO) measurements, finding that while modest values of the relative bias parameters can introduce systematic biases in the measured BAO scale of up to 0.5 $σ$, fitting for these effects as additional parameters increases the error bar by less than 30% across a wide range of bias values.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Measuring the growth of structure with intensity mapping surveys

Line intensity mapping offers a new avenue for constraining cosmological parameters in the high redshift Universe. However measurements of the growth of structure, a sensitive probe of gravity, are affected by a well known degeneracy with astrophysical parameters, encoded in the mean brightness temperature of the specific line. In this work we show how to break this degeneracy, to a level that could allow constraints of the amplitude of cosmological fluctuations at the percent level, using information in the mildly non-linear regime of structure formation as described by Lagrangian Perturbation Theory. We focus on the 21-cm line with forecasts for HIRAX and the proposed Stage II experiment as illustrations.

21 cm↗
DOE OSTI2019

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.

galaxies:distances and redshifts↗
DOE OSTI2019

Exploring redshift-space distortions in large-scale structure

We explore and compare different ways large-scale structure observables in redshift-space and real space can be connected. These include direct computation in Lagrangian space, moment expansions and two formulations of the streaming model. Here we derive for the first time a Fourier space version of the streaming model, which yields an algebraic relation between the real- and redshift-space power spectra which can be compared to earlier, phenomenological models. By considering the redshift-space 2-point function in both configuration and Fourier space, we show how to generalize the Gaussian streaming model to higher orders in a systematic and computationally tractable way. We present a closed-form solution to the Zeldovich power spectrum in redshift space and use this as a framework for exploring convergence properties of different expansion approaches. While we use the Zeldovich approximation to illustrate these results, much of the formalism and many of the relations we derive hold beyond perturbation theory, and could be used with ingredients measured from N-body simulations or in other areas requiring decomposition of Cartesian tensors times plane waves. Lastly, we finish with a discussion of the redshift-space bispectrum, bias and stochasticity and terms in Lagrangian perturbation theory up to 1-loop order.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

The impact of wrong assumptions in BAO reconstruction

The process of density field reconstruction enhances the statistical power of distance scale measurements using baryon acoustic oscillations (BAO). During this process a fiducial cosmology is indicated in order to convert sky coordinates and redshifts into distances; fiducial bias and redshift-space-distortion parameters are also assumed in this procedure. We analytically determine the effect of incorrect cosmology and bias assumptions on the post-reconstruction power spectra using low-order Lagrangian perturbation theory, deriving general expressions for the incorrectly reconstructed spectra. Here, we find that the BAO peak location appears to shift only by a negligible amount due to wrong assumptions made during reconstruction. However, the shape of the BAO peak and the quadrupole amplitude can be affected by such errors (at the percent- and five-percent-level respectively), which potentially could cause small biases in parameter inference for future surveys; we outline solutions to such complications.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Some assembly required: assembly bias in massive dark matter halos

Here, we study halo assembly bias for cluster-sized halos. Previous work has found little evidence for correlations between large-scale bias and halo mass assembly history for simulated cluster-sized halos, in contrast to the significant correlation found between bias and concentration for halos of this mass. This difference in behavior is surprising, given that both concentration and assembly history are closely related to the same properties of the linear-density peaks that collapse to form halos. Using publicly available simulations, we show that significant assembly bias is indeed found in the most massive halos with M ~ 10 15 M ⊙ , using essentially any definition of halo age. For lower halo masses M ~ 10 14 M ⊙ , no correlation is found between bias and the commonly used age indicator a 0.5 , the half-mass time. We show that this is a mere accident, and that significant assembly bias exists for other definitions of halo age, including those based on the time when the halo progenitor acquires some fraction f of the ultimate mass at z =0 . For halos with M vir ~ 10 14 M ⊙ , the sense of assembly bias changes sign at f =0.5 . We explore the origin of this behavior, and argue that it arises because standard definitions of halo mass in halo finders do not correspond to the collapsed, virialized mass that appears in the spherical collapse model used to predict large-scale clustering. Because bias depends strongly on halo mass, these errors in mass definition can masquerade as or even obscure the assembly bias that is physically present. Lastly, more physically motivated halo definitions using splashback should be free of this particular defect of standard halo finders.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

First Data Release of the COSMOS Ly α Mapping and Tomography Observations: 3D Ly α Forest Tomography at 2.05 < z < 2.55

Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-α forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck-I telescope. Over an observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we used 240 galaxies and quasars at 2.17

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The clustering of theSDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: measuring the anisotropic baryon acoustic oscillations with redshift weights

We present an anisotropic analysis of baryon acoustic oscillation (BAO) signal from the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar sample. The sample consists of 147 000 quasars distributed over a redshift range of 0.8 < z < 2.2. We apply the redshift weights technique to the clustering of quasars in this sample and achieve a 4.6 per cent measurement of the angular distance measurement DM at z = 2.2 and Hubble parameter H at z = 0.8. We parametrize the distance-redshift relation, relative to a fiducial model, as a Taylor series. The coefficients of this expansion are used to reconstruct the distance-redshift relation and obtain distance and Hubble parameter measurements at all redshifts within the redshift range of the sample. Reporting the result at two characteristic redshifts, we determine DM(z = 1) = 3405 ± 305 (rd/rd, fid) Mpc, H(z=1) = 120.7± 7.3 (r_d,fid / r_d) km s^{-1} Mpc^{-1} and DM(z = 2) = 5325 ± 249 (rd/rd, fid) Mpc, H(z=2) = 189.9± 32.9 (r_d,fid / r_d) km s^{-1} Mpc^{-1}. These measurements are highly correlated. We assess the outlook of BAO analysis from the final quasar sample by testing the method on a set of mocks that mimic the noise level in the final sample. We demonstrate on these mocks that redshift weighting shrinks the measurement error by over 25 per cent on average. We conclude redshift weighting can bring us closer to the cosmological goal of the final quasar sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Detection of z ~ 2.3 Cosmic Voids from 3D Ly α Forest Tomography in the COSMOS Field

We present the most distant detection of cosmic voids ( z ~ 2.3) and the first detection of three-dimensional voids in the Lyα forest. We used a 3D tomographic map of the absorption with an effective comoving spatial resolution of 2.5 h -1 Mpc and a volume of 3.15 &times; 10 5 h 3 Mpc 3 , which was reconstructed from moderate-resolution Keck I/LRIS spectra of 240 background Lyman-break galaxies and quasars in a 0.16 deg 2 footprint in the COSMOS field. Voids were detected using a spherical overdensity finder calibrated from hydrodynamical simulations of the intergalactic medium (IGM). This allows us to identify voids in the IGM corresponding to voids in the underlying matter density field, yielding a consistent volume fraction of voids in both data (19.5%) and simulations (18.2%). We fit excursion set models to the void radius function and compare the radially averaged stacked profiles of large voids ( r > 5 h -1 Mpc) to stacked voids in mock observations and the simulated density field. Comparing with 432 coeval galaxies with spectroscopic redshifts in the same volume as the tomographic map, we find that the tomography-identified voids are underdense in galaxies by 5.95σ compared to random cells.

79 ASTRONOMY AND ASTROPHYSICS↗