Susan E. Clark
VerifiedStanford University · Physics
Active 1947–2026
About
Susan E. Clark is an Assistant Professor of Physics at Stanford University, with a focus on experimental and observational astrophysics and cosmology, as well as theoretical astrophysics and cosmology. She earned her Ph.D. in Astrophysics from Columbia University in 2017 and her B.S. in Physics from The University of North Carolina at Chapel Hill in 2012. Her research interests include cosmic magnetism and interstellar physics, contributing to the understanding of astrophysical phenomena through both experimental and theoretical approaches.
Research topics
- Astronomy
- Astrophysics
- Physics
- Optics
- Remote sensing
- Computer Science
- Geography
- Geology
- Statistics
- Quantum mechanics
Selected publications
arXiv (Cornell University) · 2026-03-10
preprintOpen accessWe present a comprehensive polarimetric study of 26 nearby molecular clouds in four far-infrared bands (53 $μ$m to 214 $μ$m) using 52 archival SOFIA/HAWC+ datasets. Far-infrared dust polarization observations probe the plane-of-sky magnetic field. To investigate scale-dependent trends, we group the molecular clouds by distance and analyze the data at common angular ($25''$) and common physical (0.052 pc and 0.32 pc) resolutions. The two shorter wavelengths are more impacted by smoothing, exhibiting a larger decrease in percent polarization. We analyze the polarization spectrum -- the polarization fraction as a function of wavelength -- and find that it depends more strongly on column density than dust temperature. We find a "falling" spectrum at the 0.052 pc resolution, but find a "flat" spectrum at the 0.32 pc resolution, suggesting that resolution plays an important role in the observed polarization spectra. We propose that warm dust grain emission in small-scale structures ($\lesssim$ 0.1 pc) traces different magnetic field geometries only resolved in our close regime data. There is no preferred magnetic field orientation across our data, which suggests that the magnetic field in our $\sim$ parsec scale regions is decoupled from the large-scale field that is primarily parallel to the Galactic plane. The relationship between percent polarization and column density varies between clouds, but the correlation between percent polarization and angular dispersion is consistent across regions. This compendium of dust polarization maps highlights the value of observing at multiple far-infrared wavelengths and will enable additional population-level studies of magnetic fields and dust across star-forming environments.
A Path to an All-Sky Survey with Roman
arXiv (Cornell University) · 2026-02-24
articleOpen accessA deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.
The radial component of the local Galactic magnetic field in 3D
Monthly Notices of the Royal Astronomical Society · 2026-04-03
articleOpen accessABSTRACT We present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $B_{||}$, by combining a 3D electron density ($n_{\mathrm{ e}}$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $n_{\mathrm{ e}}$ map and compares to the Galactic Faraday rotation sky. We infer $B_{||}$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $|b| \gt 5^{\circ }$) map of $B_{||}$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $B_{||}$ of $1.63\pm 0.16\,\rm \mu G$. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $B_{||}$ field is seen to exhibit a 3D power spectrum with an average slope of $-2.73 \pm 0.19$. We validate our $B_{||}$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $n_{e}B_{||}$ to each pulsar’s distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $n_{e}$ map also correlate with measured DMs, albeit with significant scatter.
ArXiv.org · 2026-03-10
articleOpen accessWe present a comprehensive polarimetric study of 26 nearby molecular clouds in four far-infrared bands (53 $μ$m to 214 $μ$m) using 52 archival SOFIA/HAWC+ datasets. Far-infrared dust polarization observations probe the plane-of-sky magnetic field. To investigate scale-dependent trends, we group the molecular clouds by distance and analyze the data at common angular ($25''$) and common physical (0.052 pc and 0.32 pc) resolutions. The two shorter wavelengths are more impacted by smoothing, exhibiting a larger decrease in percent polarization. We analyze the polarization spectrum -- the polarization fraction as a function of wavelength -- and find that it depends more strongly on column density than dust temperature. We find a "falling" spectrum at the 0.052 pc resolution, but find a "flat" spectrum at the 0.32 pc resolution, suggesting that resolution plays an important role in the observed polarization spectra. We propose that warm dust grain emission in small-scale structures ($\lesssim$ 0.1 pc) traces different magnetic field geometries only resolved in our close regime data. There is no preferred magnetic field orientation across our data, which suggests that the magnetic field in our $\sim$ parsec scale regions is decoupled from the large-scale field that is primarily parallel to the Galactic plane. The relationship between percent polarization and column density varies between clouds, but the correlation between percent polarization and angular dispersion is consistent across regions. This compendium of dust polarization maps highlights the value of observing at multiple far-infrared wavelengths and will enable additional population-level studies of magnetic fields and dust across star-forming environments.
The radial component of the local Galactic magnetic field in 3D
ArXiv.org · 2026-04-01
articleOpen accessWe present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $B_{||}$, by combining a 3D electron density ($n_{e}$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $n_{e}$ map and compares to the Galactic Faraday rotation sky. We infer $B_{||}$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $|b|>5^{\circ}$) map of $B_{||}$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $B_{||}$ of $1.63\pm 0.16$ $μ$G. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $B_{||}$ field is seen to exhibit a 3D power spectrum with an average slope of $-2.73 \pm 0.19$. We validate our $B_{||}$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $n_{e}B_{||}$ to each pulsar's distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $n_{e}$ map also correlate with measured DMs, albeit with significant scatter.
The radial component of the local Galactic magnetic field in 3D
arXiv (Cornell University) · 2026-04-01
preprintOpen accessWe present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $B_{||}$, by combining a 3D electron density ($n_{e}$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $n_{e}$ map and compares to the Galactic Faraday rotation sky. We infer $B_{||}$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $|b|>5^{\circ}$) map of $B_{||}$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $B_{||}$ of $1.63\pm 0.16$ $μ$G. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $B_{||}$ field is seen to exhibit a 3D power spectrum with an average slope of $-2.73 \pm 0.19$. We validate our $B_{||}$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $n_{e}B_{||}$ to each pulsar's distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $n_{e}$ map also correlate with measured DMs, albeit with significant scatter.
Journal of Cosmology and Astroparticle Physics · 2026-04-01
articleOpen accessAbstract We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned extension of the survey duration to 2035, this expansion will significantly enhance SO's search for a B -mode signal in the polarisation of the cosmic microwave background, a potential signature of gravitational waves produced in the very early Universe. Assuming a 1/ f noise model with knee multipole ℓ knee = 50 and a moderately complex model for Galactic foregrounds, we forecast a 1 σ (or 68% confidence level) constraint on the tensor-to-scalar ratio r of σ r = 1.2 × 10 -3 , assuming no primordial B-modes are present. This forecast assumes that 70% of the B -mode lensing signal can ultimately be removed using high resolution observations from the SO Large Aperture Telescope (LAT) and overlapping large-scale structure surveys. For more optimistic assumptions regarding foregrounds and noise, and assuming the same level of delensing, this forecast constraint improves to σ r = 7 × 10 -4 . These forecasts represent a major improvement in SO's constraining power, being a factor of around 2.5 times better than what could be achieved with the originally planned campaign, which assumed the existing three SATs would conduct a five-year survey.
The Astrophysical Journal · 2026-04-06
articleOpen accessAbstract Polycyclic aromatic hydrocarbon (PAH) emission is widely used to trace the distribution of molecular gas in the interstellar medium, exhibiting a tight correlation with CO(2–1) emission across nearby galaxies. Using PHANGS-JWST and PHANGS-Atacama Large Millimeter/submillimeter Array (ALMA) data, we identify localized regions where this correlation fails, with CO flux exceeding that predicted from 7.7 μ m PAH emission by more than an order of magnitude. These outlier regions are found in 20 out of 70 galaxies and are located in galaxy centers and bars, without signs of massive star formation. We explore two scenarios to explain the elevated CO-to-PAH ratios, which can either be due to suppressed PAH emission or enhanced CO emissivity. We examine PAH emission in other bands (3.3 and 11.3 μ m) and the dust-continuum-dominated bands (10 and 21 μ m), finding consistently high CO-to-PAH (or CO-to-dust continuum) emission ratios, suggesting that 7.7 μ m PAH emission is not particularly suppressed. In some outlier regions, PAH sizes and spectral energy distribution of the radiation differ slightly from nearby control regions with normal CO-to-PAH ratios, though without a consistent trend. We find that the outlier regions show higher CO velocity dispersions (Δ v CO ). This increase in Δ v CO lowers CO optical depth and raises its emissivity for a given gas mass. Our results favor a scenario where shear along the bar lanes and shocks at the bar ends elevate CO emissivity, leading to the breakdown of the CO–PAH correlation. Future JWST spectroscopy and deep ALMA observations of CO isotopologues will provide critical tests of this scenario.
A Path to an All-Sky Survey with Roman
Open MIND · 2026-02-24
preprintA deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.
The Astrophysical Journal · 2025-10-21 · 1 citations
articleOpen accessAbstract Unraveling the multiphase structure of the diffuse interstellar medium as traced by neutral hydrogen (H i ) is essential to understanding the lifecycle of the Milky Way. However, H i phase separation is a challenging and underconstrained problem. The neutral gas phase distribution is often inferred from the spectral line structure of H i emission. In this work, we develop a data-driven phase-separation method that extracts H i phase structure solely from the spatial morphology of H i emission intensity structures. We combine scattering spectra (SS) statistics with a Gaussian-mixture variational autoencoder model to (1) derive an interpretable statistical model of different H i phases from their multiscale morphological structures, and (2) we use this model to decompose the 2D channel maps of GALFA-H i emission in diffuse high-latitude (∣ b ∣ > 30°) regions over narrow velocity channels (Δ v = 3 km s −1 ) into cold neutral medium (CNM), warm neutral medium (WNM), and noise components. We integrate our CNM map over velocity channels to compare it to an existing map produced by a spectrum-based method. We find that the two maps are highly correlated, but ours recovers more spatially coherent structures at small scales. Our work illustrates and quantifies a clear physical connection between the H i morphology and H i phase structure, and it unlocks a new avenue for improving future phase-separation techniques by making use of both H i spectral and spatial information to decompose H i in 3D position–position–velocity space. These results are consistent with a physical picture where processes that drive H i phase transitions also shape the morphology of H i gas, imprinting a sparse, filamentary CNM that forms out of a diffuse, extended WNM.
Recent grants
Turbulent structures in the magnetic interstellar medium
NSF · $478k · 2021–2024
Frequent coauthors
- 366 shared
Mrs Wry
Canadian Political Science Association
- 366 shared
J. C. Weldon
- 328 shared
John Hodgetts
University of Łódź
- 305 shared
Anthony Scott
- 291 shared
M Morgan
The University of Texas Southwestern Medical Center
- 284 shared
E Forsey
- 222 shared
J. H. Dales
- 219 shared
W Stankiewicz
Queen's University
Education
- 2017
Ph.D. , Astrophysics
Columbia University
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