arXiv subjects

Skylar Grayson

Publications and source records attributed to Skylar Grayson.

7 recordsLinked to original sources

arXiv2026

Supersonic Motion in the Driving Region of M82

The prototypical starburst galaxy M82 is host to an expansive, multiphase outflow whose driving mechanism is not fully understood. Longstanding models suggest that energy and mass injection from supernova into the hottest phase of the galactic wind could drive the cooler phases, but validating these models has been difficult due to the lack of constraints on the hot wind energetics. The high-resolution spectral capabilities of XRISM have generated the tightest constraints to date on the temperatures of the hot wind, as well as the first direct measurement of its velocity dispersion. In this work, we use these new observational constraints to test a model of a supernova-driven free wind. We generate a suite of highly idealized hydrodynamic simulations varying the energy and mass loading of the starburst and construct mock spectra to compare against the XRISM results. We find that the observed velocity dispersion is impossible to replicate using our free-wind model alone, and extra broadening is required to fit the spectrum. We interpret this broadening to be due not to bulk outflow, but rather to smaller scale non-thermal motions in the driving region of the starburst. This implies supersonic motion (Mach 1.71-3.14) of the hot gas in the central region of the galaxy. As supersonic motions are unexpected, it is possible that a significant amount of the energy that should go into heating the gas is instead going towards other sources such as amplifying magnetic fields and driving cosmic rays.

astro-ph.GA↗

arXiv2026

The First Insights into an Ultraluminous X-ray Pulsar with XRISM: Phase-Resolved High-Resolution Spectroscopy of the Fe K-shell Band of M82 X-2

During the performance verification phase, XRISM observed the M82 galaxy for a net exposure of 207.7 ks, with the ultraluminous X-ray pulsar (ULXP) X-2 included in the field of view. A pulsation search identified a candidate signal with a period close to the previously known value, 1.38727 s, at a significance of $3.15\sigma$ based on Monte Carlo simulations. Using this candidate period, phase-resolved spectral analysis with the high spectral resolution of Resolve was performed. The spectra suggest that, if the candidate pulsation is real, the Fe K$\alpha$ emission line in the pulse peak phase has a larger width ($36^{+60}_{-13}$ eV) than that in the remaining phase at a significance exceeding $3\sigma$. This suggests that at least a fraction of the Fe K$\alpha$ emission is associated with the ULXP system. The observed width corresponds to a velocity dispersion of $(1.7^{+2.8}_{-0.6})\times10^3$ km s$^{-1}$, which is too large to be explained by motions in the companion star atmosphere. The rise time of the pulsation constrains the line-emitting region to be smaller than $6.3\times10^4$ km, suggesting an origin in the accretion flow. This work demonstrates the capability of XRISM Resolve for pulsation-resolved high-resolution spectroscopy of ULX pulsars.

astro-ph.HE↗

arXiv2025

Introducing RAFIKI: Refining AGN Feedback in Kinetic Implementations

Modern cosmological simulations have now matured to the point of reproducing the evolution of realistic galaxy populations across cosmic time. These simulations rely on feedback from active galactic nuclei (AGN) to quench massive galaxies, yet the details of this process remain poorly understood. To address this issue, we introduce RAFIKI (Refining AGN Feedback In Kinetic Implementations), a novel suite of simulations built upon SIMBA-C that vary the mass loading of AGN-driven winds. Unlike the fiducial SIMBA-C simulation, RAFIKI separates the efficiencies of the two kinetic feedback modes, enabling a detailed study of their impact on galaxies, black holes, and the circumgalactic medium. We explore a range of galaxy and baryon properties in the RAFIKI runs and find that even with enhanced mass loading, the lower-velocity, quasar-type mode cannot quench massive galaxies. However, it plays a significant role in regulating black hole growth and star formation in intermediate-mass galaxies. We also uncover degeneracies in the parameter space that highlight the limited current constraints on AGN feedback. RAFIKI provides a controlled framework to disentangle these degeneracies using current and upcoming observations.

astro-ph.GA↗

arXiv2025

The hot circumgalactic medium in stacked X-rays: observations vs simulations

Current cosmological simulations rely on active galactic nuclei (AGN) feedback to quench star formation and match observed stellar mass distributions, but models for AGN feedback are poorly constrained. The circumgalactic medium (CGM) provides a valuable laboratory to study this process, as its metallicity, temperature, and density distributions are directly shaped by AGN activity. Recent observations from the eROSITA instrument provide constraints on the CGM through measurements of extended soft X-ray emission. In this work, we generate synthetic eROSITA observations from the EAGLE and SIMBA cosmological simulations and compare them to observations of galaxies stacked by stellar mass, halo mass, and star-formation rate. SIMBA outperforms EAGLE in matching observed surface brightness profiles, but neither simulation achieves consistent agreement with observations across the full range of galaxy properties we studied. We find that variations in CGM X-ray emission between simulations are primarily driven by density differences at $R \lesssim 0.2 R_{200c} $, and temperature and metallicity changes at larger radii. These results highlight the need for further refinement of AGN feedback models in cosmological simulations and demonstrate the power of stacked X-ray observations as a tool for constraining feedback physics.

astro-ph.GA↗

arXiv2025

Cross-correlating the patchy screening and kinetic Sunyaev-Zel'dovich effects as a new probe of reionization

The kinetic Sunyaev-Zel'dovich effect (kSZ) and patchy screening effect are two complementary cosmic microwave background (CMB) probes of the reionization era. The kSZ effect is a relatively strong signal, but is difficult to disentangle from other sources of temperature anisotropy, whereas patchy screening is weaker but can be reconstructed using the cleaner polarization channel. Here, we explore the potential of using upcoming CMB surveys to correlate a reconstructed map of patchy screening with (the square of) the kSZ map, and what a detection of this cross-correlation would mean for reionization science. To do this, we use simulations and theory to quantify the contributions to this signal from different redshifts. We then use the expected survey properties for CMB-S4 and CMB-HD to make detection forecasts. We find that, for or our fiducial reionization scenario, CMB-S4 will obtain a hint of this signal at up to 1.8$\sigma$, and CMB-HD will detect it at up to 14$\sigma$. We explore the physical interpretation of the signal and find that it is uniquely sensitive to the first half of reionization and to the bispectrum of the ionized gas distribution.

astro-ph.CO↗

arXiv2023

Distinguishing AGN Feedback Models with the Thermal Sunyaev-Zel'dovich Effect

Current models of galaxy formation require strong feedback from active galactic nuclei (AGN) to explain the observed lack of star formation in massive galaxies since z~2 but direct evidence of this energy input is limited. We use the SIMBA cosmological galaxy formation simulations to assess the ability of thermal Sunyaev-Zel'dovich (tSZ) measurements to provide such evidence, by mapping the pressure structure of the circumgalactic medium around massive z~0.2-1.5 galaxies. We undertake a stacking approach to calculate the total tSZ signal and its radial profile in simulations with varying assumptions of AGN feedback, and we assess its observability with current and future telescopes. By convolving our predictions with the 2.1' beam of the Atacama Cosmology Telescope (ACT), we show that current observations at z~1 are consistent with SIMBA's fiducial treatment of AGN feedback, and inconsistent with SIMBA models without feedback. At z~0.5, observational signals lie between SIMBA run with and without AGN feedback, suggesting AGN in SIMBA may inject too much energy at late times. By convolving our data with a 9.5'' beam corresponding to the TolTEC camera on the Large Millimeter Telescope Alfonso Serrano (LMT), we predict a unique profile for AGN feedback that can be distinguished with future higher-resolution measurements. Finally, we explore a novel approach to quantify the non-spherically symmetric features surrounding our galaxies by plotting radial profiles representing the component of the stack with m-fold symmetry.

astro-ph.GA↗

arXiv2023

Improving Undergraduate Astronomy Students' Skills with Research Literature via Accessible Summaries: An Exploratory Case Study with Astrobites-based Reading Assignments

Undergraduate physics and astronomy students are expected to engage with scientific literature as they begin their research careers, but reading comprehension skills are rarely explicitly taught in major courses. We seek to determine the efficacy of a reading assignment designed to improve undergraduate astronomy (or related) majors' perceived ability to engage with research literature by using accessible summaries of current research written by experts in the field. During the 2022-2023 academic year, faculty members from six institutions incorporated reading assignments using accessible summaries from Astrobites into their undergraduate astronomy major courses, surveyed their students before and after the activities, and participated in follow-up interviews with our research team. Quantitative and qualitative survey data from 52 students show that students' perceptions of their abilities with jargon and identifying main takeaways of a paper significantly improved with use of the tested assignment template. Additionally, students report increased confidence of their abilities within astronomy after exposure to these assignments, and instructors valued a ready-to-use resource to incorporate reading comprehension in their pedagogy. This exploratory case study with Astrobites-based assignments suggests that incorporating current research in the undergraduate classroom through accessible literature summaries may increase students' confidence and ability to engage with research literature, assisting in their preparation for participation in research careers.

physics.ed-ph↗