About

Gilbert Holder is a Professor of Physics and holds the Fortner Chair in Theoretical Astrophysics at the Department of Astronomy, Illinois College of Liberal Arts & Sciences. His research areas include Cosmology and Theory, focusing on understanding the universe through theoretical astrophysics. He is associated with the department located at 237C Loomis Laboratory, Urbana, IL, and can be contacted via email at gholder@illinois.edu or by phone at (217) 300-4612. His work involves exploring fundamental questions about the cosmos, contributing to the academic and research community in astrophysics.

Research topics

• Astrophysics
• Astronomy
• Physics
• Optics
• Quantum mechanics
• Statistics
• Particle physics

Selected publications

• SPT-3G D1: CMB temperature and polarization power spectra and cosmology from 2019 and 2020 observations of the SPT-3G main field

  Physical review. D/Physical review. D. · 2026-01-05 · 10 citations

  preprintOpen access

  Plenary talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/)

  PublisherOA PDFDOI

• Measurement of the Full Shape of the Thermal Sunyaev–Zel’dovich Power Spectrum from the South Pole Telescope and Herschel–SPIRE Observations

  The Astrophysical Journal Letters · 2026-04-24

  articleOpen access

  Abstract We present a measurement of the full shape of the power spectrum of the thermal Sunyaev–Zel’dovich (tSZ) effect down to arcminute scales using cosmic microwave background (CMB) data from the South Pole Telescope (SPT) over a roughly 100 deg 2 field. The analysis incorporates data from the 2019–2020 seasons of the SPT-3G survey in bands centered at 95, 150, and 220 GHz; from the full SPTpol dataset at 150 GHz; and from the Herschel–SPIRE survey in bands centered at 600 and 857 GHz. We combine data from all the above bands using linear combination (LC) techniques to produce a tSZ or Compton- y map. We modify the LC weights to produce multiple versions of the Compton- y map, including minimum-variance (MV) and foreground-minimized (-min) maps. We measure the auto- and cross-power spectra of a subset of these maps in the range ℓ ∈ [500, 5000]. While this power spectrum includes contributions from signals other than tSZ, we present numerous checks to show that the most challenging foreground signal, the cosmic infrared background (CIB), is much lower than the desired tSZ signal in the scales of interest in this work. The final tSZ power spectrum is measured at 9.3 σ with both the MV and CIB-min maps. Our results are consistent with those reported in other CMB surveys across the literature. Using the difference in the tSZ power spectrum from the MV and CIB-min maps, we reconstruct the scale-dependent tSZ–CIB cross correlation <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ℓ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">tSZ</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:mi mathvariant="normal">CIB</mml:mi> </mml:math> , finding 3.1 σ evidence for a nonzero correlation coefficient that is positive on large scales and approaches zero for ℓ &gt; 2500. This result represents the deepest tSZ maps ever produced and provides new constraints that can help refine astrophysical feedback mechanisms and models of the intracluster medium.

  PublisherDOI

• Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope

  Astronomy and Astrophysics · 2026-01-29 · 2 citations

  preprintOpen access

  Context . The South Pole Telescope third-generation camera (SPT-3G) has observed over 10 000 square degrees of sky at 95, 150, and 220 GHz (3.3, 2.0, 1.4 mm, respectively) and will significantly overlap the ongoing 14 000 square-degree Euclid Wide Survey. The Euclid collaboration recently released Euclid Deep Field South (EDF-S) observations of 23 square degrees at wide field depths in the first quick data release (Q1). Aims . With the goal of releasing complementary millimeter-wave data and encouraging legacy science, we performed dedicated observations of a 57-square-degree field overlapping the EDF-S. Methods . The observing time totaled 20 days, and we reached noise depths of 4.3, 3.8, and 13.2 μK-arcmin at 95, 150, and 220 GHz, respectively. Results . In this work we present the temperature maps and two catalogs constructed from these data. The emissive source catalog contains 601 objects (334 inside EDF-S) with 54% synchrotron-dominated sources and 46% thermal dust emission-dominated sources. The 5σ detection thresholds are 1.7, 2.0, and 6.5 mJy in the three bands. The cluster catalog contains 217 cluster candidates (121 inside EDF-S) with median mass M 500c = 2.12 × 10 14 M ⊙ /h 70 and median redshift z = 0.70, corresponding to an order-of-magnitude improvement in cluster density over previous tSZ-selected catalogs in this region (3.81 clusters per square degree). Conclusions . The overlap between SPT and Euclid data will enable a range of multiwavelength studies of the aforementioned source populations. This work serves as the first step toward joint projects between SPT and Euclid and provides a rich dataset containing information on galaxies, clusters, and their environments.

  PublisherDOI

• Cosmology from CMB lensing and delensed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi><mml:mi>E</mml:mi></mml:math> power spectra using 2019–2020 SPT-3G polarization data

  Physical review. D/Physical review. D. · 2025-04-16 · 57 citations

  articleOpen access

  From CMB polarization data alone, we reconstruct the CMB lensing power spectrum, comparable in overall constraining power to previous temperature-based reconstructions, and an unlensed $E$-mode power spectrum, with clear detections of the third through the tenth acoustic peaks. The observations, taken in 2019 and 2020 with the South Pole Telescope (SPT) and the SPT-3G camera, cover $1500\text{ }\text{ }{\mathrm{deg}}^{2}$ at 95, 150, and 220 GHz with arcminute resolution and roughly $4.9\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{K}\text{\ensuremath{-}}\mathrm{arcmin}$ coadded noise in polarization. The power spectrum estimates, together with systematic parameter estimates and a joint covariance matrix, follow from a Bayesian analysis using the marginal unbiased score expansion (MUSE) method. The $E$-mode spectrum at $\ensuremath{\ell}&gt;2000$ and lensing spectrum at $L&gt;350$ are the most precise to date. Assuming the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, and using only these SPT data and priors on $\ensuremath{\tau}$ and absolute calibration from Planck, we find ${H}_{0}=66.81\ifmmode\pm\else\textpm\fi{}0.81\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, comparable in precision to the Planck determination and in $5.4\ensuremath{\sigma}$ tension with the most precise ${H}_{0}$ inference derived via the distance ladder. We also find ${S}_{8}\ensuremath{\equiv}{\ensuremath{\sigma}}_{8}({\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}/0.3{)}^{0.5}=0.850\ifmmode\pm\else\textpm\fi{}0.017$, providing further independent evidence of a slight tension with low-redshift structure probes. The $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model provides a good simultaneous fit to the combined Planck, ACT, and SPT data, and thus passes a powerful test. Combining these CMB datasets with BAO observations, we explore extensions to the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. We find that the effective number of neutrino species, spatial curvature, and primordial helium fraction are consistent with standard model values, and that the 95% confidence upper limit on the neutrino mass sum is 0.075 eV, close to the minimum sum expected from observations of solar and atmospheric neutrino oscillations. The SPT data are consistent with the somewhat weak ($&lt;3\ensuremath{\sigma}$) preference for excess lensing power seen in Planck and ACT data relative to predictions of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model given the combined Planck, ACT, and BAO datasets. We also detect at greater than $3\ensuremath{\sigma}$ the influence of nonlinear evolution in the CMB lensing power spectrum and discuss it in the context of the ${S}_{8}$ tension. Forthcoming SPT-3G analyses will feature deeper and wider observations in temperature and polarization, providing even tighter constraints and more powerful tests of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model.

  PublisherOA PDFDOI

• Measurement and Modeling of Polarized Atmosphere at the South Pole with SPT-3G

  The Astrophysical Journal · 2025-03-11 · 7 citations

  articleOpen access

  Abstract We present the detection and characterization of fluctuations in linearly polarized emission from the atmosphere above the South Pole. These measurements make use of data from the SPT-3G receiver on the South Pole Telescope in three frequency bands centered at 95, 150, and 220 GHz. We use the cross-correlation between detectors to produce an unbiased estimate of the power in Stokes I , Q , and U parameters on large angular scales. Our results are consistent with the polarized signal being produced by the combination of Rayleigh scattering of thermal radiation from the ground and thermal emission from a population of horizontally aligned ice crystals with an anisotropic distribution described by Kolmogorov turbulence. The measured spatial scaling, frequency scaling, and elevation dependence of the polarized emission are explained by this model. Polarized atmospheric emission has the potential to significantly impact observations on the large angular scales being targeted by searches for inflationary B-mode CMB polarization. We present the distribution of measured angular power spectrum amplitudes in Stokes Q and I for 4 yr of Austral winter observations, which can be used to simulate the impact of atmospheric polarization and intensity fluctuations at the South Pole on a specified experiment and observation strategy. We present a mitigation strategy that involves both downweighting significantly contaminated observations and subtracting a polarized atmospheric signal from the 150 GHz band maps. In observations with the SPT-3G instrument, the polarized atmospheric signal is a well-understood and subdominant contribution to the measured noise after implementing the mitigation strategies described here.

  PublisherDOI

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

  ArXiv.org · 2025-02-13 · 1 citations

  preprintOpen accessSenior author

  We compare the cosmological constraints that can be obtained from halo clustering on non-linear scales ($2 h^{-1}$ Mpc &lt; $r$ &lt; $50 h^{-1}$ 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 $\{Ω_m, σ_8\}$. We find that almost all of the information present in the Betti curves comes from the first two, $β_0$ and $β_1$, which track the number of connected components and one-dimensional loops respectively, and almost no constraining power comes from $β_2$ 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.

  PublisherOA PDFDOI

• Constraints on Inflationary Gravitational Waves with Two Years of SPT-3G Data

  ArXiv.org · 2025-05-05

  preprintOpen access

  We present a measurement of the $B$-mode polarization power spectrum of the cosmic microwave background anisotropies at 32 $\le$ $\ell$ $&lt;$ 502 for three bands centered at 95, 150, and 220 GHz using data from the SPT-3G receiver on the South Pole Telescope. This work uses SPT-3G observations from the 2019 and 2020 winter observing seasons of a $\sim$1500 deg$^2$ patch of sky that directly overlaps with fields observed with the BICEP/Keck family of telescopes, and covers part of the proposed Simons Observatory and CMB-S4 deep fields. Employing new techniques for mitigating polarized atmospheric noise, the SPT-3G data demonstrates a white noise level of 9.3 (6.7) $μ$K-arcmin at $\ell \sim 500$ for the 95 GHz (150 GHz) data, with a $1/\ell$ noise knee at $\ell$=128 (182). We fit the observed six auto- and cross-frequency $B$-mode power spectra to a model including lensed $Λ$CDM $B$-modes and a combination of Galactic and extragalactic foregrounds. This work characterizes foregrounds in the vicinity of the BICEP/Keck survey area, finding foreground power consistent with that reported by the BICEP/Keck collaboration within the same region, and a factor of $\sim$ 3 higher power over the full SPT-3G survey area. Using SPT-3G data over the BICEP/Keck survey area, we place a 95% upper limit on the tensor-to-scalar ratio of $r &lt; 0.25$ and find the statistical uncertainty on $r$ to be $σ(r) = 0.067$.

  PublisherOA PDFDOI

• Gravitational Lensing of Galaxy Clustering

  The Open Journal of Astrophysics · 2025-03-27

  articleOpen access

  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 ~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.

  PublisherDOI

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

  ArXiv.org · 2025-08-11

  preprintOpen access

  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.

  PublisherOA PDFDOI

• Measurements of the temperature and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi></mml:math>-mode polarization of the cosmic microwave background from the full 500-square-degree SPTpol dataset

  Physical review. D/Physical review. D. · 2025-06-10 · 7 citations

  articleOpen access

  The authors build upon, and extend, previous work to now use the Full 500-square-degree South Pole Telescope Cosmic Microwave Background (CMB) polarization dataset. They confirm previous \ensuremath{\Lambda}CDM-consistent results and obtain the most sensitive measurements of the lensed-CMB damping tail to date.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Searching for Dark Matter Subhalos in Distant Strong Gravitational Lenses

  NSF · $341k · 2017–2021

Frequent coauthors

• J. E. Carlstrom

  349 shared

• K. K. Schaffer

  University of Chicago

  308 shared

• C. L. Chang

  Argonne National Laboratory

  295 shared

• B. A. Benson

  Netherlands Institute for Radio Astronomy

  290 shared

• J. J. Mohr

  265 shared

• L. E. Bleem

  University of Chicago

  250 shared

• S. S. Meyer

  239 shared

• M. Dobbs

  Canadian Institute for Advanced Research

  233 shared

Labs

• Compact ObjectsPI