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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 26 September

Solar and Stellar Astrophysics

Successfully Reproducing Solar Orbiter Polar Field Observations with a Surface Flux Transport Model

Ruihui Wang, Jie Jiang, Yukun Luo et al. (+2 more)

The solar polar field plays a fundamental role in predicting solar-cycle strength and determines the large-scale structure of the heliospheric magnetic field. The High Resolution Telescope of the Polarimetric and Helioseismic Imager aboard Solar Orbiter (SO/PHI-HRT) provides unprecedented observations of the solar polar regions, as Solar Orbiter currently reaches heliographic latitudes of up to $\pm17^\circ$, about $10^\circ$ higher than those accessible from near-ecliptic observations. Using these observations to further test surface flux transport models, we present a successful simulation of the SO/PHI-HRT observations, reproducing the latitudinal profiles of the longitudinally averaged radial magnetic field in both polar regions. This result is achieved using the meridional-flow profile proposed by \citet{WangRH2026}, which also reproduces the evolution of the axial dipole strength, magnetic butterfly diagram, and high-latitude magnetic fields observed by SDO/HMI during Solar Cycle 25. We further compare simulations using this profile with simulations employing two representative meridional-flow profiles characterized by different peak latitudes. The latter fail to reproduce the observed high-latitude and polar fields. The comparison demonstrates that the meridional-flow profile strongly regulates poleward flux transport and the resulting polar-field evolution. Profiles peaking at higher latitudes produce stronger flux surges, and stronger and more concentrated polar fields. These results provide new constraints on the large-scale solar meridional flow.
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All authors Ruihui Wang, Jie Jiang, Yukun Luo, D. Calchetti, S. K. Solanki

Cosmology and Nongalactic Astrophysics

Cross-correlation between CMB B-modes and Faraday Rotation as a Novel Probe of Primordial Magnetic Fields

Toshiya Namikawa and Guanming Liang

We investigate the cross-bispectrum between the cosmic microwave background (CMB) $B$-mode polarization and two Faraday rotation (FR) angles as a new probe of primordial magnetic fields (PMFs). Assuming Gaussian PMFs with both non-helical and helical components, we derive the $B\alpha\alpha$ bispectrum and decompose it into parity-even and parity-odd contributions. The mixed non-helical–helical contribution appears in the parity-even sector, whereas the purely non-helical and purely helical contributions contribute to the parity-odd sector. This parity dependence provides sensitivity to PMF helicity that is absent in the FR power spectrum alone. We then forecast the detectability of the cross-bispectrum for SO-like and LiteBIRD-like CMB experiments, and find that future observations can probe PMFs with amplitudes at the sub-nG level. The $B\alpha\alpha$ bispectrum is dominated by the helicity-sensitive parity-even sector and provides a promising avenue for constraining both the amplitude and helicity of PMFs.
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High Energy Astrophysical Phenomena

Spin wandering of an accreting neutron star near torque balance: implications for gravitational wave searches

Andrew Melatos

Torque balance between gravitational radiation reaction and magnetocentrifugal accretion is one reason why accreting neutron stars rotate slower than centrifugal break-up. Random processes in the accretion disk, such as Rayleigh-Taylor instabilities and flicker noise, drive the spin frequency $f_\ast$ and gravitational wave frequency $f_{\rm gw}\propto f_\ast$ to wander stochastically around their torque balance values. Here it is shown theoretically, in terms of an idealized Ornstein-Uhlenbeck model, that the standard deviation of $f_{\rm gw}$ is given by $\sigma_{f_{\rm gw}}(h_0) \propto f_{\rm gw} h_0 D \beta T^{1/2}$, or equivalently $\sigma_{f_{\rm gw}}(F_{\rm X}) \propto f_{\rm gw}^{1/2} F_{\rm X}^{1/2} D \beta T^{1/2}$, where $h_0$ is the characteristic wave strain, $F_{\rm X}$ is the X-ray flux, $D$ is the source distance, and $\beta$ and $T$ are the fractional amplitude and autocorrelation time-scale of the stochastic torque. One can use $\sigma_{f_{\rm gw}}(h_0)$ and $\sigma_{f_{\rm gw}}(F_{\rm X})$ to check the physical consistency of a detection candidate in a gravitational wave search by comparing with $\sigma_{f_{\rm gw}}$ observed. Spin wandering impacts search design, because it sets the maximum time interval $\max(T_{\rm coh})$, during which the signal may be treated as coherent. The Ornstein-Uhlenbeck calculation predicts $10^{-1} \lesssim \max(T_{\rm coh}) / (1\, {\rm day}) \lesssim 10^3$, with $3\times 10^{-2} \lesssim \beta T^{1/2} / (1 \, {\rm s^{1/2}} ) \lesssim 4$, for Rayleigh-Taylor instabilities and flicker noise. The predicted $\max(T_{\rm coh})$ is shorter typically than the year-long observation runs of audio-band interferometers operating today, emphasizing the utility of semi-coherent search algorithms, which divide the data into multiple coherent segments of duration $\max(T_{\rm coh})$.
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Astrophysics of Galaxies

H-alpha Star Formation Rates of the SHIELD Dwarf Galaxies

Madeline Shepley, David G. Gormanous, John J. Salzer et al. (+9 more)

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) galaxy sample is an HI-selected catalog of galaxies that occupy the extreme low-mass end of the HI mass function. Our team is carrying out a comprehensive multi-wavelength observational program targeting these gas-rich, star-forming dwarf galaxies. The current paper presents H-alpha narrowband observations of the full SHIELD sample. We detect 55 of the 82 galaxies (67%) with nebular H-alpha emission, and infer sensitive upper limits to the H-alpha fluxes for the 27 non-detections. We derive H-alpha luminosities and star formation rates (SFRs), or upper limits, for all 82 SHIELD galaxies. We also present, for the first time, deep broadband and continuum-subtracted H-alpha images plus a summary of the properties for the entire sample. Our analysis of the H-alpha data re-affirms previous results which show that at low levels of star formation (log(SFR_{H-alpha}) < -2.5), H-alpha becomes an increasingly poor tracer of the recent average SFR as measured by far-UV (FUV) luminosities. However, we show that this effect is not strictly correlated with the mass of the galaxy. Some very low-mass SHIELD galaxies with higher H-alpha-based SFRs show good agreement with SFR_{FUV}. The SHIELD galaxies show no correlation between H-alpha SFR and gas mass fraction, but reveal a modest correlation between H-alpha specific SFR and gas mass fraction. Overall, the star formation efficiency exhibited by the SHIELD dwarfs is rather low, despite the gas-rich nature of the sample (68% have M_{gas} > M_{stellar}).
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All authors Madeline Shepley, David G. Gormanous, John J. Salzer, Nathalie Haurberg, Steven Janowiecki, John M. Cannon, Elizabeth A. K. Adams, Martha P. Haynes, Alec S. Hirschauer, Kristen B. W. McQuinn, Katherine L. Rhode, Evan D. Skillman

Solar and Stellar Astrophysics

Self-constrained Magnetic Reconnection of a Solar Flare Co-spatial with a Non-ejected Filament

Ye Qiu, Changxue Chen, Anqin Chen et al. (+11 more)

For flares associated with eruptive filaments, the filament normally rises above the post-flare loops. Here, we report an unusual event in which the post-flare loops instead overlie a filament that remains non-ejected throughout the flare. This event was simultaneously captured by the Chinese H$\alpha$ Solar Explorer (CHASE), the Solar Extreme-UltraViolet Imager (SUVI) onboard Fengyun-4C, the Hard X-ray Imager (HXI) onboard the Advanced Space-based Solar Observatory (ASO-S) and the Solar Dynamics Observatory (SDO). Extreme Ultraviolet (EUV) observations provided by FY4C/SUVI and SDO show that two hot loop systems form at the flare onset. The western end of the northern loop system undergoes a southwestward drifting motion with gradually increasing shear, whereas the southern loop system progressively converges toward and eventually overlies the northern one. Meanwhile, three-dimensional magnetic field extrapolations reveal an increase in both the twist of the filament-supporting magnetic structure and its poloidal magnetic field after the flare. Taken together, these observations suggest that the flare is driven by a self-constraining zipper-type magnetic reconnection, in which highly sheared arcades reconnect to form a series of overlying flare arcades and an underlying flux rope. This reconnection continuously strengthens the magnetic confinement of the filament, preventing its outward eruption, while facilitating substantial plasma drainage along the reconnected magnetic field revealed by the CHASE H$\alpha$ spectroscopic observations.
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All authors Ye Qiu, Changxue Chen, Anqin Chen, Chuan Li, Yang Guo, Linggao Kong, Feng Lu, Xiaohu Zhang, Weiguo Zong, Jinsong Wang, Xinkai Li, Peng Wang, Kefei Song, Bo Chen

Astrophysics of Galaxies

Tracing Winds through the Fog: A Comprehensive Survey of LMC's Galactic Outflows with ULLYSES

Suraj Poudel, April Horton, Kathleen A. Barger et al. (+21 more)

We investigate nearside stellar-driven outflows from the Large Magellanic Cloud (LMC) using UV absorption-line spectroscopy of 170 OB stars, complemented by HI 21-cm emission and H$_{\alpha}$ emission. Using Voigt-profile fitting and AOD analysis of SiII, OI, and SII transitions, we map the velocity-dependent structure of foreground gas. The SiII column densities for the Voigt-fitted components decline smoothly from the LMC disk and reach a minimum at $v_{\rm LMCSR} \approx -100$ to $-200~{km~s^{-1}}$, marking the transition from a denser, slower wind to more diffuse high-velocity material. Comparisons with local star-formation rate surface densities reveal a modest positive correlation for the slower wind component, linking it to recent massive-stellar feedback. Photoionization modeling of 13 absorbers in the $+100\lesssim v_{\rm LSR} \lesssim +150~{km~s^{-1}}$ range reveals wide diversity in metallicity, dust depletion, and ionization conditions, consistent with multiple possible origins. While a substantial fraction of this predominately ionized gas is consistent with the high-velocity extension of the LMC wind, part of it may arise from contamination by Milky Way (MW) high-velocity clouds (HVCs) and Magellanic circumgalactic medium (CGM). We estimate a nearside cool-gas outflow mass of ${\sim}1.8\times10^{7}\,M_{\odot}$, implying $\dot{M}_{\rm out}\approx0.15$-$0.33\,M_{\odot}\,\mathrm{yr^{-1}}$ and a mass-loading factor of $\eta\approx0.6$-1.3. On regional scales, 30 Doradus contributes $\sim10\%$ and N11 contributes $\sim3\%$ of the total outflow mass, while the trailing side contains more wind material than the leading side, consistent with ram-pressure stripping. These results provide the comprehensive kinematic and physical characterization of how stellar feedback, galactic environment, and foreground contamination shape the multiphase wind emerging from the LMC.
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All authors Suraj Poudel, April Horton, Kathleen A. Barger, Frances H. Cashman, Jo Vazquez, Andrew J. Fox, Nicolas Lehner, J. Christopher Howk, Scott Lucchini, Dhanesh Krishnarao, Sabra Catalano, Anders Ripley, Wanyan Yuan, Natalie Van Tol, Citlali Alcala, Jordan Elliott, N. M. McClure Griffiths, Elena D'Onghia, Jason Tumlinson, Ananya Goon Tuli, Jacco Th. van Loon, Julia Roman-Duval, Yik Ki Ma, Callum Lynn

High Energy Astrophysical Phenomena

Polarization Signatures of Sgr A* with Tilted Hybrid Magnetic Fields

Yushu Feng, Hao Yin, Songbai Chen et al. (+1 more)

The magnetic field geometry in the near-horizon region is very important in shaping polarimetric signatures of black hole images. With a hybrid magnetic field consisting of an axisymmetric split-monopole field and a tilted uniform external field, we investigate the effects of external magnetic field inclination on the polarimetric signatures of Sgr A* by employing a stationary semi-analytical radiatively inefficient accretion flow (RIAF) model and general relativistic polarized radiative transfer simulations. Our results show that the external magnetic field tilt significantly modifies the electric vector position angle (EVPA) pattern and brightness distribution. The induced non-axisymmetry from the tilted magnetic filed component renders polarization morphology dependent on the observer's azimuthal angle, which is a novel behavior absent in purely axisymmetric magnetic field configurations. In combination with Event Horizon Telescope (EHT) data, we analyse the possibility of such hybrid magnetic fields around Sgr A*.
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All authors Yushu Feng, Hao Yin, Songbai Chen, Jiliang Jing

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Enhancing Conversion Gain in HEB Mixers using Negative Differential Resistance

Boris S. Karasik and Changyun Yoo

This work investigates how negative differential resistance (NDR) can be utilized to enhance conversion gain in superconducting niobium nitride (NbN) hot-electron bolometer (HEB) mixers. Conventional HEB operation avoids NDR regions due to parasitic oscillations caused by interactions between thermal inertia and bias-line reactance. Recent experimental results show that reducing the bias-T inductance suppresses these oscillations and enables stable biasing within the NDR regime, thereby increasing the mixer conversion gain beyond levels achievable under positive differential resistance (PDR) bias. Using a lumped thermal-electrical model, we interpret these experimental findings, derive stability conditions for NDR-biased operation, and predict the future performance limits achievable through optimized bias circuit designs. Our results indicate that further reductions in bias inductance, combined with appropriate load-line conditions, could yield several decibels of additional gain while maintaining practical IF bandwidths.
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Earth and Planetary Astrophysics

COSINE (Cometary Object Study Investigating their Nature and Evolution) II: Colors and Sizes of Comet Nuclei

Yuna G. Kwon, Dar W. Dahlen, Joseph R. Masiero et al. (+6 more)

Comet nuclei preserve a record of planetesimal formation, but their sizes are difficult to measure because the nucleus is usually blended with its coma. We present a catalog of nucleus sizes for 523 comets (235 long-period and 288 short-period comets; LPCs and SPCs) from the 14.5-year WISE/NEOWISE archive, supplemented by Spitzer photometry. A coma-nucleus decomposition of the radial profiles yields conservative upper limits for all 523 comets and diameters with uncertainties for 301 (107 LPCs and 194 SPCs), with median diameters of 5.3 and 2.5 km, respectively. Nucleus colors across the four WISE bands follow the heliocentric trend expected from the transition between reflected and thermal emission, with no measurable difference between the two dynamical classes. The cumulative size-frequency distribution of the SPCs has a slope of $\gamma = 1.45_{-0.13}^{+0.15}$ (68% confidence interval) over $D = 2$–15 km, steepening to $2.05_{-0.38}^{+0.47}$ for the perihelion $q < 2$ au subset. The LPC distribution is smoothly concave down: a broken power law places a break near 35 km, with slopes of $0.92_{-0.12}^{+0.13}$ below and $3.68_{-1.24}^{+1.96}$ above, while the $q < 2$ au subset gives $1.39_{-0.28}^{+0.35}$ over $D = 4$–20 km. All distributions flatten below the fitted ranges and level off near 1 km. We discuss the implications of our results and their connection with models of the destabilized trans-Neptunian population.
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All authors Yuna G. Kwon, Dar W. Dahlen, Joseph R. Masiero, Yanga R. Fernández, Adeline Gicquel, James M. Bauer, Yoonyoung Kim, Frank Masci, Amy K. Mainzer

Earth and Planetary Astrophysics

The NEID Earth Twin Survey. VI. Discovery of a Low-Mass Planet Orbiting HD 126053 and RV Signals Near the Rotation Periods of HD 168009 and HD 10780

Arvind F. Gupta, Sarah E. Logsdon, Jacob K. Luhn et al. (+19 more)

Extreme precision radial velocity (EPRV) spectrographs are making strides in extending the limits of radial velocity exoplanet detection. Perhaps the best evidence for this is how readily EPRV instruments are facilitating the discovery and detailed characterization of small-amplitude planetary signals around stars that have already been intensively monitored for decades with less stable instruments. In this paper, we use data from the ongoing NEID Earth Twin Survey (NETS) to detect and confirm the planet HD 126053 b (P=10.91 d), which is among the least massive planets (m sin i = 3.60 m M_\oplus) around solar-type stars within 25 pc. We then jointly characterize the known planet HD 168009 b (P=15.14 d; m sin i = 8.64 M_\oplus) orbiting a solar analog along with a previously unreported signal at 27.8 d which we tentatively attribute to rotational modulation of stellar activity (P_rot = 30.1 d). We also analyze and discuss periodic RV variations in HD 10780 arising from a combination of rotationally-modulated activity and a long-term activity cycle. We discuss HD 126053 b and HD 168009 b in the context of the broader small planet population and our sensitivity to long-period planets in these systems, and we comment on our capacity to disambiguate planet-induced and activity-induced radial velocity signals. HD 126053 is exceptionally RV-quiet, making it a promising target for continued RV monitoring in search of low-mass exoplanets in the habitable zone.
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All authors Arvind F. Gupta, Sarah E. Logsdon, Jacob K. Luhn, Evan Fitzmaurice, Suvrath Mahadevan, Paul Robertson, Eric B. Ford, Chad F. Bender, Mark R. Giovinazzi, Samuel Halverson, Te Han, Daniel M. Krolikowski, Andrea S.J. Lin, Joe P. Ninan, Michael L. Palumbo III, Leonardo A. Paredes, Jayadev Rajagopal, Arpita Roy, Christian Schwab, Gudmundur Stefansson, Ryan C. Terrien, Jason T. Wright

Friday 25 September

Cosmology and Nongalactic Astrophysics

Galaxy and Halo Assembly Bias in Alternative Dark Matter Models

Yikun Wang, Idit Zehavi, Sergio Contreras et al. (+6 more)

The clustering of dark matter halos depends not only on halo mass but also on secondary halo properties, a phenomenon known as halo assembly bias. Coupled with variations in halo occupation, this dependence impacts galaxy clustering, an effect termed galaxy assembly bias. While previous studies have found only weak cosmological dependence of assembly bias within the $\Lambda$CDM framework, its sensitivity to the underlying dark matter physics remains largely unexplored. We use the matched dark-matter-only and hydrodynamical simulations from the AIDA-TNG suite to measure assembly bias across four dark matter models: cold dark matter, warm dark matter, and self-interacting dark matter with constant cross-sections and velocity-dependent cross-sections. We find that at z = 0, halo assembly bias is nearly identical across the four models for concentration-selected halos, as is the concentration dependence of the halo occupation distribution. The resulting galaxy assembly bias signals likewise show only weak model dependence. For stellar-mass-selected galaxy samples with $n = 0.0586 h^{3} Mpc^{-3}$ at z = 0, the velocity-dependent self-interacting dark matter scenario exhibits the largest deviation from the fiducial cold dark matter model: its assembly bias contribution to galaxy clustering is enhanced by up to $\sim 6\%$, corresponding to a $\sim 3\%$ difference in the assembly bias amplitude. Although statistically distinguishable, this difference is small and unlikely to be detected in current analyses. The weak model dependence persists across different galaxy number densities and redshifts. Overall, within the TNG galaxy-formation framework, these results indicate that assembly bias is largely insensitive to the dark matter models explored here, providing a robust baseline for future studies of the galaxy-halo connection in alternative dark matter scenarios.
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All authors Yikun Wang, Idit Zehavi, Sergio Contreras, Jonás Chaves-Montero, Giulia Despali, Carlo Giocoli, Lauro Moscardini, Massimiliano Romanello, Mark Vogelsberger

Astrophysics of Galaxies

The AURORA Survey: Determining the Production Mechanism for OI $\mathbf{\lambda 8449}$ Emission in Star-forming Galaxies at Cosmic Noon

Leonardo Clarke, Alice E. Shapley, Zhiwei Shao et al. (+11 more)

We analyze deep JWST/NIRSpec observations of 58 star-forming galaxies at $1.3< z <4.8$ in the AURORA survey to investigate the origin of the permitted OI $\lambda 8449$ emission feature. Based on the detection of OI $\lambda 8449$ in a stack of objects with non-detections, we infer that this feature is ubiquitous among star-forming galaxies at $\sim$0.5% the strength of H$\alpha$. We additionally compare our results with measurements of this line in local HII regions from the CHAOS survey and star-forming galaxies at $z<0.1619$ in the DESI survey, finding a similar strength of OI $\lambda 8449$ relative to H$\alpha$ in these objects. We evaluate four production mechanisms: recombination, collisional excitation, Ly$\beta$ fluorescence, and stellar continuum fluorescence. Of these mechanisms, stellar continuum fluorescence (rather than Ly$\beta$ fluorescence) provides the most compelling explanation for the OI $\lambda 8449$ emission based on the additional detection of the near-infrared OI $\lambda 11290$ and OI $\lambda 13168$ emission lines. Adopting physical conditions derived from a stacked composite spectrum, we make predictions for the contribution of the other mechanisms to OI $\lambda 8449$, determining that recombination, collisional excitation, and Ly$\beta$ fluorescence contribute negligibly to this feature. While a simple HII region model using Cloudy reproduces the average observed OI $\lambda 8449$/H$\alpha$ ratios in the AURORA sample, future works focused on refining model density profiles will be a valuable step in better explaining the near-infrared OI emission-line strengths.
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All authors Leonardo Clarke, Alice E. Shapley, Zhiwei Shao, Massimo Pascale, Ryan L. Sanders, Naveen A. Reddy, Tucker Jones, Harley Katz, Natalie Lam, Shreya Karthikeyan, Callum T. Donnan, Natascha M. Förster Schreiber, Anthony J. Pahl, Danielle A. Berg

Earth and Planetary Astrophysics

Investigating potential causes for high inferred intrinsic temperatures of warm transiting Neptune and Sub-Neptune planets

Saugata Barat, Jean-Michel Désert, Allona Vazan et al. (+7 more)

Atmospheric characterization of a warm 10-30 Myr old sub-Neptune progenitor (V1298 Tau b) and a $\sim$3.4 Gyr old warm super-Neptune (WASP-107b) using JWST have revealed extremely low methane abundance. Atmospheric forward models find higher than expected inferred intrinsic temperatures (450~K and 500~K) — inconsistent with theoretical planet formation and core-envelope evolution predictions (70K and 150K respectively) assuming a convective interior. We explore three hypotheses to reconcile the high intrinsic temperatures with evolutionary models — tidal heating, silicate rainout and heat trapping due to deep cloud condensation. Tidal heating requires high planetary obliquity ($\gtrsim70^{\circ}$) and low reduced tidal quality factor ($\sim$100) for V1298 Tau b, implying an extremely short obliquity damping timescale ($<$10$^{4}$ years). Although high obliquity may be maintained by spin–orbit resonant locking, it requires fine-tuning and is therefore unlikely. Silicate rainout can increase the temperature in the deep atmosphere of the young V1298 Tau b (0.1-1 bar) by $\sim$700K, without requiring extremely high intrinsic temperature, but is unlikely to explain WASP-107b, as silicate rainout timescales are expected to be much shorter than its age. Including cloud condensation in self-consistent atmospheric models reduces the inferred intrinsic temperature for V1298 Tau b from 500K to 300K, still exceeding the core-envelope prediction (150K). Future measurements of thermal emission from young transiting planets such as V1298 Tau b, combined with methane abundances as a function of age, will be needed to distinguish between these scenarios.
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All authors Saugata Barat, Jean-Michel Désert, Allona Vazan, Ritika Sethi, Sagnick Mukherjee, Sarah Millholland, Jonathan J. Fortney, William Misener, Hilke E. Schlichting, Sara Seager

Cosmology and Nongalactic Astrophysics

CMB Data Analysis in the example of the POLARBEAR experiment and the LiteBIRD experiment

Kolen Cheung

In this dissertation, I briefly go through my subject areas — from Astrophysics, Cosmology, to Cosmic Microwave Background (CMB) radiation; and Data Science & High-Performance Computing. I go through the beginning of the Universe briefly in part I and introduce the Physics of the CMB in part II. Then I move on to how it can be observed experimentally, mathematically, and computationally in part III. In parts IV to VI, I write about 2 specific CMB experiments — POLARBEAR & LiteBIRD, together with my research involved in them. In part V, original research on a measurement of the CMB $B$-mode at sub-degree scales is presented using the 3rd-5th seasons of POLARBEAR observations. This demonstrates the capability of a single medium aperture telescope with a Continuously Rotating Half-Wave Plate (CRHWP) to target both the low-$\ell$ and high-$\ell$ $B$-mode science at $50 \leq \ell \leq 3000$. In part VI, the effect of detector crosstalk systematics on the CMB power-spectra is studied in detail in the example of the LiteBIRD experiment. An analytical, map-domain solution is developed, a computational simulation method is implemented, and the two predictions are compared using the LiteBIRD experiment design specification. The general agreement of the two shows that the analytical model well describes the LiteBIRD experiment, and can be used to calculate the systematic effects without performing time-consuming time-domain simulations with a high degree of accuracy. This can be used to forecast the amount of crosstalk systematics and to develop mitigation strategies. A mitigation strategy is presented, which is a hardware-based mitigation method that minimizes the crosstalk systematic effects in the 2pt power-spectra.
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2609.32037 · 25 Sep · PhD thesis, University of California, Berkeley, 2022. 241 pages, 66 figures, 6 tables. Filed version: https://escholarship.org/uc/item/0hh4w9v6. v2 corrects errors: fig. 4.1 overstated the FIRAS 1{\sigma} uncertainty tenfold; fig. 13.2 showed a simulated CMB map, not the Planck one; the fig. 36.8 discussion named the wrong ordering as the worst. All changes are listed in the ancillary changelog

Abstract PDF $CSMC ×1$TSCP ×1

Instrumentation and Methods for Astrophysics

An Analytic Error-Budget Model for the Habitable Worlds Observatory Coronagraph: From Optical Disturbances to Flux-Ratio Noise

Slava G. Turyshev

A coronagraph stability allocation must protect a planet measurement, not merely satisfy a contrast target. Residual starlight both generates photon noise and interferes with small field perturbations, coupling optical stability to detection reliability. We develop a modular analytic model for the Habitable Worlds Observatory (HWO), using a reduced two-roll angular-differential-imaging realization of its OS-1 scenario. Complex-field sensitivities, wavefront sensing/control, finite observing windows, polarization, detector calibration are propagated to flux-ratio noise (FRN) and detection probabilities. Joint-visit Gaussian quadratic moments retain differential bias, cross covariance; spatial overlap/field phase determine which disturbances resemble a planet. A 6-m, 500-nm benchmark shows why the science test must precede category allocation. For a 115.46-parts-per-trillion (ppt) quadrature planet, 30,000 independent Gaussian search statistics, and a $10^{-3}$ family-wise false-alarm objective, 20-ppt FRN gives 64.55% conditional detection power; 99% requires 14.94 ppt. Photon and calibration noise exhaust the optical remainder at 8.11 pc in 100 h under the fixed response, so tighter stability alone cannot restore feasibility. An unrecognized 1% high-variance component carrying twenty percent of the variance tightens the modal allowance by a factor of 2.88; an ideal, exactly known state label reduces that penalty to 1.29 under equal conditional false-alarm limits and the same average-power objective. Thus, requirements depend on both the optical response and the information retained by the observing protocol. The framework identifies when suppression, stability, calibration, or state monitoring addresses the limiting mechanism. Numerical tolerances are controlled model results; flight allocation requires architecture-specific responses and calibrated disturbance state-estimation laws.
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Instrumentation and Methods for Astrophysics

A Delayed Rejection Reversible Jump Markov Chain Monte Carlo Method for Multi-Resolution Maps of the Stochastic Gravitational Wave Background with Pulsar Timing Array Data

Taha T. Moursy and Nihan S. Pol

Pulsar timing array anisotropy analyses often use a naive counting argument to set resolutions of inferred maps of the stochastic gravitational wave background (GWB). We present a data-driven method in the form of a delayed rejection reversible jump sampler tailored to multi-resolution pixel decompositions of the angular power density of the GWB. We also consider a rapid, frequentist alternative based on information criteria statistics. We verify our methods with a series of injection-and-recovery simulations, finding that the standard counting argument would lead to drastic overfitting of the data and that our data-driven methods reduce the number of parameters in the models by one to three orders of magnitude yet can achieve higher resolution than the standard counting argument when justified by the data. We make our sampler and frequentist method implementation available on GitHub.
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Earth and Planetary Astrophysics

The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: the 5.4-hour planet TOI-2431 b

Sebastian Zieba, Billy Edwards, Samuel N. Quinn et al. (+18 more)

We present an HST/WFC3 G141 phase-curve observation of the ultra-short-period rocky planet TOI-2431 b and detect its secondary eclipse in the near infrared. Combined with the TESS optical eclipse, these measurements constrain the planet's dayside brightness temperature, reflected light contribution, albedo, and heat redistribution. We detect the eclipse in the optical and near infrared wavelengths of TESS and HST/WFC3 G141, with a planet-to-star flux ratio of 37+/-10 ppm and 69(+14/-13) ppm, respectively. Assuming negligible reflected light, the joint TESS+HST fit yields a brightness temperature T_b,joint=2524(+77/-84) K and a brightness temperature ratio of R_joint=T_b,joint/T_p,max=0.980(+0.032/-0.034) consistent with the zero-albedo, no-redistribution limit T_p,max=2574(+36/-35) K. The HST phase curve is consistent with zero nightside emission and no measurable hotspot offset, consistent with inefficient day-night heat distribution. Under this thermal-dominated interpretation, TOI-2431 b lies at the zero-albedo, no-redistribution limit and contrasts with previously observed lava worlds. At optical and near-infrared wavelengths, however, thermal emission is degenerate with reflected light. For a geometric albedo of A_g=0.1, reflected light would contribute approximately 11 ppm in each bandpass, reducing the temperature to T_b,joint(A_g=0.1)=2407(+91/-102) K. Longer-wavelength observations are required to isolate the thermal component. Planned JWST/MIRI LRS observations are expected to substantially reduce this degeneracy and provide more direct constraints on heat redistribution and possible silicate-atmosphere spectral features. This marks the first secondary eclipse detection of a rocky exoplanet using HST and establishes TOI-2431 b as a benchmark target for studying properties of lava worlds.
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All authors Sebastian Zieba, Billy Edwards, Samuel N. Quinn, Leoni J. Janssen, Nicolas B. Cowan, Laura Kreidberg, Mercedes Lopez-Morales, Lisa Dang, Luca Malavolta, Yamila Miguel, T. Giang Nguyen, Andrew Vanderburg, Thomas G. Wilson, Mantas Zilinskas, Nicholas J. Connors, Ian J. M. Crossfield, Oliver Herbort, Adam L. Kraus, Tim Lichtenberg, Mariana Sastre, Joost P. Wardenier

Cosmology and Nongalactic Astrophysics

SLICE: Unveiling the Multi-Component Merging Core of SPT-CLJ1150-2805 Through Strong-Lensing Mass Modelling

James R. Betts, Benjamin Beauchesne, Mathilde Jauzac et al. (+16 more)

We present a new strong-lensing and X-ray mass model of the merging galaxy cluster SPT-CLJ1150-2805 ($z=0.383$), combining JWST NIRCam, HST, Chandra, and VLT/MUSE data to robustly decompose its collisionless and collisional components. Exploiting JWST, we expand the multiple-image catalogue with 66 new images (30 comprising 6 new systems). Our baseline model uses 118 spectroscopically confirmed images from 20 systems, achieving an image-plane root-mean-square offset of $0.56''$. An expanded model incorporating 31 additional photometric images from 8 additional systems yields a near-identical mass distribution, confirming excellent model stability. We resolve a complex multi-axis post-merger system requiring five cluster-scale dark matter haloes, including a bimodal core with distinct haloes coincident with each brightest cluster galaxy. The remaining mass components are independently supported by kinematics of 291 cluster members ($\sigma_v=1960^{+84}_{-92}$ km s$^{-1}$), which reveal two new galaxy substructures - the northernmost of which we tentatively identify as the baryonic counterpart to our fifth dark matter halo. The cluster is an extraordinarily efficient lens, possessing an effective Einstein radius $\theta_E=42.41^{+0.05}_{-0.04}{''}$ and an enclosed mass $M(<\theta_E)=3.35^{+0.04}_{-0.03}\times10^{14}M_\odot$ for a source at $z_s=2$. For a high-redshift source at $z_s=9$, it produces a magnification cross-section of $A(>10)\simeq0.15$ arcmin$^2$ and $A(>30)\simeq0.020$ arcmin$^2$. This global lensing power surpasses all Hubble Frontier Fields clusters. In a regime where systematic uncertainties between mass models dominate high-redshift magnification errors, the stability of our reconstruction sets this lens apart. This combination of extreme lensing power and a robust mass model establishes SPT-CLJ1150-2805 as a premier cosmic telescope for high-redshift studies.
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All authors James R. Betts, Benjamin Beauchesne, Mathilde Jauzac, David Lagattuta, Guillaume Mahler, Jean-Paul Kneib, Gavin Leroy, Marceau Limousin, Priyamvada Natarajan, Sameeksha Saini, Keren Sharon, Stephane V. Werner, Catherine Cerny, Isaque Dutra, Dominique Eckert, Alaina Einsig, Michael D. Gladders, Gourav Khullarm, Manon Regamey

Solar and Stellar Astrophysics

Transport of Magnetic Fields by Thermohaline Convection in Crystallizing White Dwarfs

Nicolas Frazao Fernandes, J. R. Fuentes and Jim Fuller

The origins of strong magnetic fields observed in many white dwarfs are uncertain. Recent observations show that such fields are more common for white dwarfs with crystallized cores. Crystallization creates a destabilizing composition gradient that drives thermohaline convection in the star's fluid envelope, which may play an important role in magnetic field emergence. We perform 3D magnetohydrodynamical simulations of thermohaline convection with magnetic fields of various strengths and orientations, using the Boussinesq approximation in periodic Cartesian boxes. Our simulations suggest that thermohaline convection can generate magnetic fields when the magnetic Prandtl number is large (i.e., low magnetic diffusivity), but they are likely too weak to account for those observed in magnetic white dwarfs. However, the simulations indicate that strong magnetic fields can be advected outwards by the thermohaline convection without being destroyed, depending on the net magnetic flux. Hence, crystallization-induced thermohaline mixing may transport magnetic fields initially trapped in white dwarf interiors to their outer layers, allowing them to be observed. However, additional simulations using more realistic geometry and magnetic field configurations will be needed to confirm this possibility.
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Astrophysics of Galaxies

Dynamical Evolution of The Open Clusters Collinder 110 and NGC 2477

Zahra Al, Yüksel Karataş and Forough Rajaei

Using Gaia DR3 photometric and astrometric data, we identified the likely members of the open clusters Collinder 110 and NGC 2477, and derived their astrophysical and dynamical parameters. We obtained reddening values of $E(B-V) = 0.43 \pm 0.05$ and $0.33 \pm 0.04$, and ages of $1.82 \pm 0.10$ Gyr and $1.05 \pm 0.10$ Gyr for Collinder 110 and NGC 2477, respectively. Within the uncertainties, the distances derived from the color-magnitude diagrams ($2.09 \pm 0.06$ and $1.38 \pm 0.04$ kpc) are consistent with those obtained from Gaia DR3 parallaxes ($2.08 \pm 0.31$ and $1.45 \pm 0.11$ kpc). Both clusters exhibit large core and limiting radii. The core radius ($R_c$) of Collinder 110 does not follow the expected decreasing trend with increasing evolutionary parameter ($\log\tau_2$). In addition to losing part of its low-mass stellar content, its relatively large $R_c$ may reflect primordial conditions and/or the presence of a possible stellar-mass black hole. The relatively large $R_c/R_h$ ratios, together with their advanced dynamical evolution ($\log\tau_2 = 1.24$ and $1.34$), indicate that significant two-body relaxation and mass segregation have occurred within their central regions. The small values of $R_h/R_j$ ($0.32$ and $0.16$) suggest that low-mass stars have dynamically redistributed within the comparatively large Jacobi radii under the combined influence of internal and external processes. However, their large $R_t/R_j$ ratios ($1.60$ and $1.23$) imply that both clusters are tidally affected and have likely lost part of their low-mass stellar populations to the Galactic field. Despite these effects, their locations in the third Galactic quadrant, where giant molecular clouds are relatively scarce, may explain their survival to their present ages of $1.82$ and $1.05$ Gyr, respectively.
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Earth and Planetary Astrophysics

JWST Reveals the Kuiper Belt-like Compositions of the Uranian Rings and Small Moons

Matthew Belyakov, M. Ryleigh Davis, Zachariah Milby et al. (+2 more)

We present the JWST NIRSpec 1–5 micron spectra of the Uranian rings and four ringmoons: Puck, Perdita, Portia, and Juliet. We find that the compositions of the rings and moons strongly resemble water-type Kuiper belt objects, showing deep 3.0 micron O–H and water ice features as well as the CO$_2$ band at 4.27 micron. The volatiles show a radial trend of decreasing volatile abundance at closer radial distance to the planet, consistent with recent estimates of the densities of the innermost moons. Given the observed compositional signatures, we suggest two ways to reconcile the history of the small inner moons with that of the regular ones. The first is that the Uranus-tilting collision produced a disk from an impactor formed out of material similar to that which comprises water-rich Kuiper belt objects, and the ringmoons are small undifferentiated remnants of that process. Alternatively, the rings and ringmoons postdate the formation of the regular moons, and formed from the later tidal disruption of a several hundred kilometer sized undifferentiated water-type Kuiper belt object.
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All authors Matthew Belyakov, M. Ryleigh Davis, Zachariah Milby, Ian Wong, Michael E. Brown

Solar and Stellar Astrophysics

Spectroscopic Signatures of Nonuniform Lateral Expansion of a Coronal Mass Ejection in the Low Corona with ADITYA-L1/VELC

Saurabh Tripathi, Tanmoy Samanta and Jayant Joshi

Coronal mass ejections (CMEs) undergo rapid evolution in the low corona ($<2R_\odot$), yet their three-dimensional kinematics remain poorly constrained. We present a spectroscopic and imaging analysis of a CME observed on 2024 August 5 using the Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 and Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observator (SDO). The VELC Fe XIV 5303 Å spectra captured the erupting CME as it crossed the western slit. Space-time maps from single-Gaussian fits reveal coronal dimming and enhanced Doppler velocities during the eruption. Detailed spectral analysis reveals strongly Doppler-shifted secondary components associated with the CME front. These components appear as two spatially separated emission branches on opposite sides of the rest wavelength, producing a distinct bifurcated spectral morphology superposed on the nearly stationary reduced-intensity coronal emission. Double-Gaussian fitting yields line-of-sight (LOS) plasma velocities of up to 218 km/s, likely a lower limit as the secondary component reaches the edge of spectral window. AIA 211 Å observations measure a projected radial speed of 1135 km/s, larger than the plane-of-sky (POS) lateral speed of 692 km/s along the slit. To interpret the observed CME evolution and spectral structure, we developed a simplified three-dimensional geometric-kinematic model of an expanding axially tilted CME shell. Synthetic spectra from the model show that an inclined CME undergoing asymmetric lateral expansion can produce a bifurcated spectral morphology similar to that observed, with velocity components projected in the radial, POS-lateral, and LOS-lateral directions. Our results demonstrate that combining spectroscopy and EUV imaging constrains different components of CME kinematics during early evolution.
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Solar and Stellar Astrophysics

Negative and Positive Cascade Rates of Slow Alfvénic Turbulence in Switchback and Non-switchback Intervals: Wind Observations

Sofiane Bourouaine

We estimate the turbulent cascade rate in imbalanced Alfvénic turbulence in the slow solar wind using a Politano–Pouquet-based approach that does not require an isotropic assumption. We analyze selected 8-hour intervals provided by Wind spacecraft. These intervals are characterized by near-homogeneity, weak velocity shear, and imbalanced Alfvénic fluctuations, and are classified as switchback or non-switchback depending on the angular spread of the magnetic field relative to the mean field. Switchback intervals are identified by large magnetic-field rotations, whereas non-switchback intervals exhibit only small angular deviations. Our results show that non-switchback intervals exhibit a positive total cascade rate and power spectra consistent with a $-3/2$ scaling, indicative of a forward energy cascade. In contrast, switchback intervals are characterized by a negative total cascade rate (inverse cascade), and by steeper power spectra with a spectral index of approximately $-1.6$. This indicates that large magnetic-field rotations can substantially modify the scale-to-scale energy transfer in Alfvénic slow solar wind. The results suggest that switchbacks may be associated with additional physical processes, such as local instabilities, or reconnection-related structures, that alter the direction and magnitude of the turbulent cascade. These findings may help explain previous reports of negative cascade rates in imbalanced Alfvénic solar-wind turbulence.
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High Energy Astrophysical Phenomena

Not all spins of black-hole binaries formed in clusters are isotropic and not all spins of black-hole binaries formed in isolation are aligned

Sofia Dossena, Davide Gerosa and Tristan Bruel

Spin directions are promising observables for distinguishing between the formation channels of merging stellar-mass binary black holes with gravitational-wave observations. In this work, we challenge the standard expectation that binaries formed via dynamical interactions in stellar clusters have isotropically distributed spins and that binaries formed in isolation have spins aligned with the orbital angular momentum. For dynamically formed binaries, we account for observational findings suggesting that the spins of stars in clusters may exhibit a preferred degree of alignment and construct a simple geometrical description of the resulting black-hole spin directions. This results in an analytical joint distribution for the polar angles of first-generation black-hole binaries, whose key feature is a correlation between the two spin-orbit tilts. We show that, under reasonable assumptions and independently of the initial spin configuration, spins are fully randomized after a single black-hole merger, implying that binaries formed through hierarchical mergers have isotropically distributed spin orientations. For isolated binaries, we introduce a simple model for spin evolution as a function of the natal kick imparted during the first supernova explosion, while accounting for tidal interactions and mass-ratio reversal. The resulting distribution is also fully analytic. We investigate the impact of relativistic spin precession, as well as that of the finite escape speed of clusters, on our geometrically derived distributions. Our results provide a simple analytical framework for modeling the spin directions of merging black holes in gravitational-wave population fits.
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Earth and Planetary Astrophysics

Variable X-ray flux may explain variable helium escape from the habitable-zone exoplanet LHS 1140b

Collin Cherubim, Tim Cunningham and Jason A. Dittmann

A central goal in exoplanet science is to understand the conditions under which potentially habitable worlds retain atmospheres. This question is of special interest for worlds orbiting M stars, whose habitable-zone planets are more readily observable, but which also emit prolonged high-energy radiation that can erode planetary atmospheres. For one such world, LHS 1140b, a rocky planet orbiting in the habitable zone of an inactive star, time-variable helium absorption has been observed as the planet transited in front of its host star, consistent with atmospheric escape. We present X-ray/ultraviolet flux observations with the XMM-Newton space telescope, which serve to test whether the observed helium absorption variability can be explained by stellar XUV flux variability. We detect X-ray flux variability with an amplitude of $F_\mathrm{max}/F_\mathrm{min} = 8.5^{+9.4}_{-4.4}$ within the 18-hour observing window. We do not detect variability in the UV or visible flux. The integrated X-ray flux is fully consistent with the X-ray flux measured in 2018, suggesting stable XUV flux over years-long timescales. We find that the 2018 observation was not sensitive to the level of variability observed in 2026. We explore several models that fit both datasets and conclude that short-term XUV variability and/or small flares are more likely to explain the helium variability than long-term XUV variability. Simultaneous observations of the planet-transit in the near-infrared and stellar activity indicators like XUV flux are critical to confirm the link between the observed helium signal variability and the observed X-ray variability.
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Cosmology and Nongalactic Astrophysics

Observational Evidence of Velocity Anisotropy Assembly Bias in Galaxy Clusters

Facundo Rodriguez, Andrea Biviano, Ravi K. Sheth et al. (+2 more)

Cosmological simulations show that halo clustering depends on secondary internal properties beyond mass, an effect known as assembly bias. In particular, numerical models have shown that internal velocity anisotropy ($\beta$) is the halo property most tightly linked to secondary halo bias: at fixed mass, haloes with isotropic velocity profiles are more strongly clustered, whereas haloes in which radial motions dominate are more weakly clustered. Despite this robust theoretical prediction, direct observational detection of velocity anisotropy assembly bias has remained elusive. Here we present observational evidence for this effect using a sample of massive galaxy clusters from the eROSITA and DESI surveys. We measure the internal orbital anisotropy $\beta$ for 91 clusters via Jeans dynamical modelling with MAMPOSSt, considering three anisotropy profile models to ensure robustness. We divided the sample into two subpopulations: isotropic and radially anisotropic, verifying that they show no significant differences in halo mass. To quantify their large-scale clustering, we measured the projected cross-correlation function with We report evidence of velocity anisotropy assembly bias: clusters with isotropic internal kinematics exhibit stronger clustering than radially dominated ones, a segregation that is unlikely to be attributable to residual differences in cluster mass. This trend shows varying significance across three anisotropy profiles, from a mild tendency to a highly pronounced signal. Furthermore, the assembly bias remains distinct when restricting the sample to clusters consistently classified across all three models.
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All authors Facundo Rodriguez, Andrea Biviano, Ravi K. Sheth, Antonio D. Montero-Dorta, Manuel Merchán

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Milky Way White Dwarfs as Inelastic Dark Matter Detectors

Javier F. Acevedo

We show that white dwarfs in the Galactic Center are a sensitive probe of inelastic dark matter (IDM) annihilation. IDM particles traversing a white dwarf may become gravitationally captured without fully settling in its interior if their energy drops below the kinematic threshold for inelastic scattering. In this regime, a fraction of the incoming particles remains bound on long-lived orbits that extend beyond the white dwarf's volume, enabling annihilation to partially proceed outside of the object. Some of the annihilation products subsequently escape, rather than being absorbed by the stellar material, producing a potentially detectable signal. We estimate the collective gamma-ray flux from the external annihilation sourced by these systems, as a function of the IDM parameters, and compare it to H.E.S.S. observations within the central degree of the galaxy. From this comparison, we derive tentative limits on the IDM scattering cross-section at the TeV mass scale, under largely conservative assumptions for the IDM density in this region. As a concrete application, we map these results into specific parameter constraints for dark photon-mediated and higgsino models with mass splittings at the MeV scale.
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Solar and Stellar Astrophysics

Probing the Nature of the Circumstellar Material Surrounding SN 2024ggi: A Search for Precursor Emission and Constraints from Radio Observations

Tobias Géron, James K. Leung, Maria R. Drout et al. (+8 more)

We present an analysis of the pre-explosion optical light curve and post-explosion radio observations of the nearby supernova (SN) 2024ggi, a Type II SN discovered in NGC 3621 at a distance of ~7.2 Mpc. Early spectra confirmed that SN 2024ggi showed “IIn-like” features, suggesting the presence of dense circumstellar material (CSM). We searched for precursor emission in the light curve up to 8 years pre-explosion from ATLAS using ATClean, which cleaned the light curve and effectively convolved it with rolling Gaussians of several timescales. No significant evidence for precursor variability was found. We find 80% detection thresholds on the absolute magnitude of -11.28 mag and -8.98 mag for outbursts with timescales of 2 and 300 days, respectively. Our radio observations taken with the Australia Telescope Compact Array (ATCA) are consistent with a wind-like CSM density profile, with an inferred mass-loss rate of ${\sim} 8 \times 10^{-5} M_\odot$ yr$^{-1}$, assuming $v_{\rm wind} = 50$ km s$^{-1}$. However, including CSM density estimates from the literature implies a two-component structure in the overall CSM density profile, with a denser inner structure at smaller radii ($\lesssim 6\times10^{14}$ cm) and an extended wind-like profile at larger radii. We conclude that the dense CSM around SN 2024ggi is likely not deposited there by eruptive outbursts. Instead, we favor a scenario with a lower but more stable mass-loss rate, such as pulsation-driven superwinds, a model with extended chromospheres, or a combination of both.
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All authors Tobias Géron, James K. Leung, Maria R. Drout, Rami Z. E. Alsaberi, W. V. Jacobson-Galán, Charles D. Kilpatrick, A. Rest, S. Rest, Stuart D. Ryder, Toshikazu Shigeyama, Yuki Takei

High Energy Astrophysical Phenomena

Correlated Signatures of Plasma Lensing in Fast Radio Bursts

Paz Beniamini and Pawan Kumar

Plasma lensing has been proposed to explain narrow spectra, multiple burst copies, frequency drifts, interference fringes, and polarization changes in fast radio bursts (FRBs). Because many of these features are not unique to lensing, a convincing identification requires several correlated observables to be reproduced by one lens model. We derive such relations for a one-dimensional Gaussian plasma lens near a fold caustic. We distinguish the phase separation of the merging images from their observable group-delay difference and identify three regimes: resolved burst copies, overlapping images with negligible mutual coherence, and coherent spectral interference. We connect the magnification, image delay, spectral-envelope width, fringe spacing, differential dispersion, time-frequency caustic curvature, and the brightness and ordering of the third image. We derive separate finite-source constraints from large fold magnification and from fringe visibility, and relate the wave-optics magnification scale to the plasma column of the lens. High-contrast fringes simultaneously constrain the source size and the mutual coherence of the two image fields, which limits the intrinsic coherence of the FRB radiation once the observed spectrum and instrumental bandpass are accounted for. We also derive the conditions for differential Faraday rotation in magnetized lenses. Finally, we show that clean lensing by a volume-filling turbulent screen requires fine tuning between rare strong fluctuations and caustic confusion, suggesting that sparse sheets, filaments, interfaces, or shocked clumps are more promising lensing structures.
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Astrophysics of Galaxies

Quantifying the decline in CO(2-1) intensity around PHANGS-HST star clusters: Constraints on molecular gas dispersal, stellar feedback, and cluster formation efficiency

Hao He, Adam K. Leroy, Erik Rosolowsky et al. (+36 more)

We combine the largest survey of star clusters in nearby galaxies to-date, PHANGS-HST, with maps of molecular gas maps from PHANGS-ALMA to constrain the efficiency of cluster formation and the typical timescales over which clusters become dis-associated from their natal molecular gas. We analyse 29,233 clusters in 36 galaxies using CO maps at 150 pc resolution. For each star cluster with stellar mass $\geq 10^{3.5}$ M$_\odot$, we measure the radial profiles of CO(2-1) integrated intensity and obtain local background-subtracted CO intensity, $I_{\rm CO}^{\rm bkgsub}$, at cluster centre. We group the clusters by age and mass to quantify the dependence of $I_{\rm CO}^{\rm bkgsub}$ and corresponding molecular gas mass, $M_{\rm mol}$, on these cluster properties. To account for the cluster mass ($M_{\rm SC}$) dependence, we also calculate the normalised mass ratio of $(M_{\rm mol}/M_{\rm SC})$. We find that CO intensity varies systematically with cluster age and mass. Clusters that are spatially associated with H$\alpha$ emission exhibit the highest $I_{\rm CO}^{\rm bkgsub}$ of 7.4 K km s$^{-1}$, corresponding to a $M_{\rm mol}/M_{\rm SC}$ ratio of 82 and implying a cluster formation efficiency ($\epsilon_{\rm obs}$) of $\sim 1.2\%$. Young clusters without associated H$\alpha$ emission show lower and age-dependent $I_{\rm CO}^{\rm bkgsub}$ and $M_{\rm mol}/M_{\rm SC}$, decreasing from 1.3 K km s$^{-1}$ and 15 for clusters with age 1-3 Myr, to a level $\approx$ 0 for clusters older than 9–10 Myr. Clusters older than 10 Myr show no statistical excess of CO intensity. We use the clusters with H$\alpha$ association as initial conditions to model the impact of cluster drift and demonstrate that this is unlikely to drive the observed cluster-gas spatial disassociation on short timescales of 4-6 Myr. Instead, early stellar feedback seems likely to be the main driver.
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All authors Hao He, Adam K. Leroy, Erik Rosolowsky, Janice Lee, Brad Whitmore, David Thilker, Daniel A. Dale, Frank Bigiel, Annie Hughes, Jiayi Sun, Gagandeep Anand, Ashley T. Barnes, Zein Bazzi, Médéric Boquien, Rupali Chandar, Dario Colombo, Sinan Deger, Simthembile Dlamini, Hamid Hassani, Stephan Hannon, Ralf S. Klessen, Simon C.O. Glover, Kathryn Grasha, Ivan Grasimov, Remy Indebetouw, Kirsten Larson, Lukas Neumann, Elias K. Oakes, Hsi-An Pan, Miguel Querejeta, Lise Ramambason, M. Jimena Rodríguez, Sumit K. Sarbadhicary, Eva Schinnerer, Qiushi Tian, Leonardo Úbeda, Antonio Usero, Thomas G. Williams, Jianwen Zhou