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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 14 October

Astrophysics of Galaxies

The AURORA Survey: Ionizing Photon Production Efficiency with Minimal Nebular Dust Attenuation Systematics

Anthony J. Pahl, Alice Shapley, Naveen A. Reddy et al. (+11 more)

We present ionizing photon production efficiencies (${\xi}_{\rm ion}$) for 63 z=1.5-6.9 star-forming galaxies using precise nebular dust attenuation corrections from the JWST/AURORA survey. A subset of objects within AURORA have individually-determined nebular dust attenuation curves, which vary significantly in shape and normalization, resulting in reduced systematic uncertainty when constraining the total attenuation of H${\alpha}$ luminosity, and thus the intrinsic ionizing output within our sample. We find evidence for positive correlations between ${\xi}_{\rm ion}$ and redshift, equivalent width of [OIII]${\lambda}$5007, and O32=[OIII]${\lambda}$5007/[OII]${\lambda}$3726,3729, and negative correlations between ${\xi}_{\rm ion}$ and stellar attenuation, UV luminosity (L$_{\rm UV}$), stellar mass, and direct-method metallicity. We test alternate dust prescriptions within this sample, and find that the total attenuation is lower when using the commonly-assumed Galactic extinction curve or when assuming that stellar attenuation is equal to nebular attenuation. We also find that assuming either of these alternate dust prescriptions can change the slope of relationships between ${\xi}_{\rm ion}$ and galaxy property, notably inducing a flat trend between ${\xi}_{\rm ion}$ and L$_{\rm UV}$ within AURORA. While the novel nebular dust curves derived from AURORA spectroscopy reveal obscured ionizing photon production within star-forming galaxies at these redshifts, a more complete understanding of stellar attenuation is required to fully reduce dust systematics on ${\xi}_{\rm ion}$ for inclusion in reionization models.
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All authors Anthony J. Pahl, Alice Shapley, Naveen A. Reddy, Ryan Sanders, Michael W. Topping, Danielle A. Berg, Callum T. Donnan, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, K. Glazebrook, Derek J. McLeod, Max Pettini, Daniel Schaerer

Astrophysics of Galaxies

Beyond the Brightest: A Deep Learning Approach to Identifying Major and Minor Galaxy Mergers in CANDELS at $z \sim 1$

Aimee L. Schechter, Aleksandra Ćiprijanović, Xuejian Shen et al. (+5 more)

Galaxy mergers play an important role in galaxy evolution. Therefore, accurate merger identifications are paramount for achieving a complete understanding of how galaxies evolve. As we enter the era of large, deep, high-resolution imaging surveys, we can observe mergers extending to even lower masses and higher redshifts. Despite low-mass galaxies being more common, many previous merger identification methods were calibrated for high-mass galaxies, which are easier to identify. To prepare for upcoming surveys, we train a convolutional neural network (CNN) using mock $\textit{HST}$ CANDELS images at $z\sim1$ created from the IllustrisTNG50 cosmological simulation. We successfully identify galaxy mergers between a wide range of galaxies ($10^8M_\odot < M_\star < 10^{12.5}M_\odot$, and $q\geq1:10$), achieving overall accuracy, purity, and completeness of $\sim65\%$. We show, for the first time, that a CNN trained on this diverse set of galaxies is capable of identifying major mergers, especially at early stages (74% accuracy), similar to that of networks trained at lower redshifts and/or higher masses (with accuracies between $66-80$%). We discuss the inherent limits of galaxy merger identification due to orientation angle, finding 98% of mergers are correctly identified from at least one angle, and 61% from the majority of angles. We additionally explore the confounding variables, such as star formation, to consider when applying to real data.This network enables the exploration of the impact of previously overlooked mergers of high mass ratio and low stellar masses on galaxy evolution in CANDELS, and can be expanded to surveys from $\textit{JWST}$, Rubin, $\textit{Roman}$, and $\textit{Euclid}$.
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All authors Aimee L. Schechter, Aleksandra Ćiprijanović, Xuejian Shen, Rebecca Nevin, Julia M. Comerford, Aaron Stemo, Laura Blecha, Austin Fraley

Instrumentation and Methods for Astrophysics

CCAT: Optical Responsivity, Noise, and Readout Optimization of KIDs for Prime-Cam

Eliza Gazda, Quintin Meyers, Steve K. Choi et al. (+17 more)

The Prime-Cam instrument on the Fred Young Submillimeter Telescope (FYST) at the CCAT Observatory will conduct sensitive millimeter to submillimeter surveys for a range of astrophysical and cosmological sciences. Prime-Cam will use kinetic inductance detectors (KIDs) sensitive to multiple frequency bands spanning 280-850 GHz. With over 100,000 sensors under development, these KID arrays will soon form the largest submillimeter focal plane ever built. With fixed microwave tones probing amplitude and phase modulations in the KIDs due to incoming radiation, challenges arise in determining the optimal readout settings, especially under varying atmospheric loading. Realizing the science goals of FYST requires operating the detectors at optimal performance and determining accurate responsivities, which depend on readout tone placement and power. To address these challenges, we present laboratory measurements of sample pixels from the 280 GHz TiN and Al arrays using a blackbody cold load to simulate observing conditions. These measurements probe detector responsivity and noise across varying optical loading, tone power, and tone placement, providing the foundation to guide in situ calibration and operation of the >100,000 KIDs. We characterize detector sensitivity via the Noise Equivalent Power (NEP) as a function of readout tone power and placement, and measure the impact of detuning due to varying optical power on the NEP. Our test setup and methodology will inform the commissioning of Prime-Cam, in situ detector calibration procedures, the cadence of probe tone resetting, and potential design refinements for future arrays, supporting FYST's planned first light in 2026.
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All authors Eliza Gazda, Quintin Meyers, Steve K. Choi, James R. Burgoyne, Scott Chapman, Cody J. Duell, Anthony I. Huber, Inchara Jagadeesh, David Faulkner Katz, Ben Keller, Lawrence T. Lin, Paul Malachuk, Michael D. Niemack, Darshan A. Patel, Gordon J. Stacey, Benjamin J. Vaughan, Eve M. Vavagiakis, Samantha Walker, Yuhan Wang, Ruixuan Xie

Solar and Stellar Astrophysics

Polar Filaments Capture High Latitude Solar Poloidal Field Interactions and can Foretell the Future Sunspot Cycle Amplitude before Polar Field Precursors

Srinjana Routh, Shaonwita Pal, Dibyendu Nandy et al. (+3 more)

Polar fields at the minimum of a sunspot cycle – which are a manifestation of the radial component of the Sun's poloidal field – are deemed to be the best indicator of the strength of the toroidal component, and hence the amplitude of the future sunspot cycle. However, the Sun's polar magnetic fields are difficult to constrain with ground-based or space-based observations from near the plane-of-ecliptic. In this context, polar filaments – dark, elongated structures that overlie polarity inversion lines – are known to offer critical insights into solar polar field dynamics. Through investigations of the long-term evolution of polar filament areas and length acquired from the Meudon Observatory and complimentary solar surface flux transport simulations, here we establish the common physical foundation connecting the Babcock-Leighton solar dynamo mechanism of solar polar field reversal and build-up with the origin and evolution of polar filaments. We discover a new relationship connecting the residual filament area of adjacent solar cycles with the amplitude of the next sunspot cycle – which can serve as a new tool for solar cycle forecasts – advancing the forecast window to earlier than polar field based precursors. We conclude that polar filament properties encapsulate the physics of interaction of the poloidal magnetic field of the previous and current sunspot cycles, the resultant of which is the net poloidal magnetic field at the end of the current cycle, thus encoding as a precursor the strength of the upcoming solar cycle.
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All authors Srinjana Routh, Shaonwita Pal, Dibyendu Nandy, Subhamoy Chatterjee, Dipankar Banerjee, Mohd. Saleem Khan

Cosmology and Nongalactic Astrophysics

Eternal inflation bubble collision signature on CMB remote dipole and quadrupole fields

Hongbo Cai, Pengjie Zhang and Yilun Guan

The remote dipole and quadrupole fields (RDF/RQF) encode information about the observable universe as seen from remote places within our past light cone. Sensitive to the superhorizon inhomogeneites, they provide a unique way to probe physics at the largest scales, bypassing the limitations of cosmic variance inherent in the primary cosmic microwave background (CMB). In this work, we focus on the bubble collision predicted by the eternal inflation theory, which can leave distinct azimuthally symmetric patterns on the superhorizon scales, potentially detectable through the RDF and RQF. We present the first analytic expression of the RQF signal induced by bubble collision and validate it against numerical calculations performed with $\texttt{RemoteField}$, a new public software tool we developed, finding excellent agreement between the two. Combining our new RQF calculation with the corresponding RDF signal calculated by prior work, we forecast the constraining power on bubble collision parameters using RDF/RQF reconstruction. We find that, for an CMB-S4-like and an LSST-like experiment, the RDF reconstruction can provide comparable constraining power as that from the primary CMB alone; and the RQF reconstruction can improve the constraining power by about an order of magnitude. We argue that these constraints can be improved further by including more RDF/RQF multipoles included and by using tomographic techniques to mitigate the standard $\Lambda$CDM signal. We anticipate the framework we developed in this work to be broadly applicable to probe other superhorizon-scale physics, such as cosmic topology and domain walls.
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Astrophysics of Galaxies

A Possible Shutting-Down Event of Mass Accretion in An Active Galactic Nucleus at z~1.8

Tomoki Morokuma, Malte Schramm, Toshihiro Kawaguchi et al. (+11 more)

We present the discovery of a large gradual apparent fading event in optical and near-infrared wavelengths in a quasar at z=1.767 by a factor of 20-30 (in optical) over a period of ~20 years in the observed frame. This pronounced fading trend in brightness was first identified by comparing the magnitudes measured in the Subaru/Hyper Suprime-Cam (HSC) images with those in the Sloan Digital Sky Survey (SDSS) images for ~3x10^4 quasars spectroscopically identified by SDSS. We performed follow-up observations, including optical imaging and spectroscopy as well as near-infrared imaging, with >4m-class telescopes such as Subaru, GTC, Keck, and SOAR telescopes. We combine these new data with the archival data to examine the variability behavior over ~20 years in detail and even the longer-term trend of the variability over ~70 years in the observed frame. We find that (i) the AGN component likely faded by a factor of ~50 from the early 2000s to 2023 and (ii) the observed brightness decline is best explained by a substantial decrease in accretion rate rather than time-varying line-of-sight dust obscuration. These findings are derived from multi-component (time-varying AGN + constant galaxy) spectral energy distribution fitting over multi-epochs, which is well consistent with the optical spectra. The Eddington ratio decreases by a factor of ~50, from ~0.4 to ~0.008 if we use the black hole mass measured with the SDSS spectrum, which could be highly uncertain because of the very large variability. The total brightness is dominated by the host galaxy in the rest-frame optical wavelength rather than the AGN as of 2023.
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All authors Tomoki Morokuma, Malte Schramm, Toshihiro Kawaguchi, Josefa Becerra González, Jose Antonio Acosta-Pulido, Nieves Castro-Rodríguez, Kana Morokuma-Matsui, Shintaro Koshida, Junko Furusawa, Hisanori Furusawa, Tsuyoshi Terai, Fumi Yoshida, Kotaro Niinuma, Yoshiki Toba

Astrophysics of Galaxies

Using gravitational lensing to probe for bright quintessential galaxies in the Epoch of Reionization

Joshua Roberson, Matthew B. Bayliss, M.D. Gladders et al. (+6 more)

Understanding the properties of the first generation of galaxies is an ongoing challenge in observational astrophysics. While advances in deep field observation have led to the identification of large numbers of galaxies within the Epoch of Reionization, there are very few observed galaxies at this range that are sufficiently bright for high signal-to-noise spectroscopy. To this end, we analyse HST and ground-based photometry of five candidate strongly lensed galaxies, all projected behind the cores of massive clusters and with similarly red optical-NIR colors. All are characterized by a drop-off in their spectra between the near-infrared and optical wavelengths, corresponding to a Lyman-break that sets a lower bound on their redshifts. Using the open-source SED modeling software Prospector, we characterize two of these galaxies as high-z (z $\sim$ 6.5-7) while the other three are low-z (z $\sim$ 2) despite all five having similar apparent magnitudes at the observed wavelengths. We demonstrate that for the brightest dropout candidates we can distinguish high-z galaxies from red or dusty low-z galaxies using limited photometric data. The bright sources enable deep constraints on the dropout color which, in combination with flat continua measured in redder bands, require high-z solutions when searching the parameter space. At the time of writing this work significantly increases the number of m_AB < 24 galaxies at or above a redshift of 6, and provides a path forward for future analysis on the early era of galaxy formation
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All authors Joshua Roberson, Matthew B. Bayliss, M.D. Gladders, Gourav Khullar, Keren Sharon, Keunho Kim, Dan Coe, Lindsey Bleem, Taweewat Somboonpanyakul

Instrumentation and Methods for Astrophysics

Very-Long Baseline Interferometry Imaging with Closure Invariants using Conditional Image Diffusion

Samuel Lai, Nithyanandan Thyagarajan, O. Ivy Wong et al. (+1 more)

Image reconstruction in very-long baseline interferometry operates under severely sparse aperture coverage with calibration challenges from both the participating instruments and propagation medium, which introduce the risk of biases and artefacts. Interferometric closure invariants offers calibration-independent information on the true source morphology, but the inverse transformation from closure invariants to the source intensity distribution is an ill-posed problem. In this work, we present a generative deep learning approach to tackle the inverse problem of directly reconstructing images from their observed closure invariants. Trained in a supervised manner with simple shapes and the CIFAR-10 dataset, the resulting trained model achieves reduced chi-square data adherence scores of $\chi^2_{\rm CI} \lesssim 1$ and maximum normalised cross-correlation image fidelity scores of $\rho_{\rm NX} > 0.9$ on tests of both trained and untrained morphologies, where $\rho_{\rm NX}=1$ denotes a perfect reconstruction. We also adapt our model for the Next Generation Event Horizon Telescope total intensity analysis challenge. Our results on quantitative metrics are competitive to other state-of-the-art image reconstruction algorithms. As an algorithm that does not require finely hand-tuned hyperparameters, this method offers a relatively simple and reproducible calibration-independent imaging solution for very-long baseline interferometry, which ultimately enhances the reliability of sparse VLBI imaging results.
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All authors Samuel Lai, Nithyanandan Thyagarajan, O. Ivy Wong, Foivos Diakogiannis

Earth and Planetary Astrophysics

Short-Lived Radioisotopic enrichment from AGB interlopers in low-mass star-forming regions

Joseph W. Eatson and Richard J. Parker

The decay of Short-Lived Radioisotopes (SLRs) can be a significant source of heating early in protoplanetary systems, though how a protoplanetary disk becomes enriched with these SLRs far above the galactic background level remains an open question. Observational evidence suggests that this enrichment occurs during the period from when the disk forms to when it progresses into a protoplanetary system, and is homogenous throughout the resultant planetary system. Whilst SLRs such as 26Al and 60Fe can be injected into disks through interaction with Wolf-Rayet winds and supernovae, these outflows can disrupt disks, and in the case of low-mass star-forming regions high-mass stars may not form at all. Recent research has determined the existence of AGB “interlopers”, Asymptotic Giant Branch stars that pass close to or through star-forming regions that could be an alternative source of SLR enrichment to WR winds and supernovae. In this paper we study the effect of AGB interlopers on star-forming regions from a dynamical perspective, determining the enrichment amount of 26Al and 60Fe in disks within small clusters via numerous N-body simulations via a parameter space exploration. We find that enrichment is widespread from AGB stars, with efficient enrichment dependent on the time at which the interloper intersects the star-forming region. Velocity is a factor, though interlopers travelling at 30 km/s are capable of enriching many disks in a star-forming region assuming they encounter a disk when the interloper is more evolved.
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Earth and Planetary Astrophysics

The Two-Zone Temperature Distribution Model: Inferences on the Structure and Composition of Dusty Protoplanetary Disks

William Grimble, Joel Kastner, B. Sargent et al. (+1 more)

In order to understand the mineralogy and structure of protoplanetary disks, it is important to analyze them from both an empirical spectrum-based perspective and a radiative transfer image-based perspective. In a prior paper, we set forth an empirical mineralogy mid-IR spectral model that conveyed spatial information and worked in tandem with a radiative transfer model, which formed the EaRTH Disk Model. In this article, we take the empirical portion of that model, the TZTD model, and refine it with a newly derived protoplanetary disk thermal emission formulation which uses a temperature distribution without requiring discrete integration; this simplified model uses an empirical relation between spatial distribution variables, which permits radiative transfer models to directly fit these spatial distribution variables more freely within the provided empirical constraints. We test this model against several $Spitzer~Space~Telescope$ Infrared Spectrograph (IRS) spectra, primarily transition disks, and discuss the mineralogical and structural implications of the fits, including the implications for grain growth and processing within the atmospheric zones of the disks.
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All authors William Grimble, Joel Kastner, B. Sargent, Keivan Stassun

Monday 13 October

Instrumentation and Methods for Astrophysics · Cross-listed from hep-ex

A Search for Ultra-Light Vector Dark Matter with a Rotating Torsion Balance

M.P. Ross, E.A. Shaw, C. Gettings et al. (+3 more)

We search for ultra-light vector dark matter interacting with a rotating torsion balance with a baryon minus lepton number composition dipole. Our search spans candidate masses in the ultra-low mass range from 1.3~$\times10^{-22}$ to 1.9~$\times10^{-18}$ eV. We set limits on the coupling strength to baryon minus lepton number for each dark matter candidate reaching a peak sensitivity of $g_{B-L} \leq 9 \times 10^{-26}$.
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All authors M.P. Ross, E.A. Shaw, C. Gettings, S.K. Apple, I.A. Paulson, J.H. Gundlach

High Energy Astrophysical Phenomena

Embedding Reliability for Unsupervised Classification of Gamma Ray Burst progenitors from Prompt Gamma-ray Emission

Nicoló Cibrario and Michela Negro

We present a statistical method based on scDEED to assess the reliability of a 2D embedding showing a low-dimensional representation of the distribution of Gamma-Ray Bursts (GRBs) detected by the Fermi Gamma-ray Burst Monitor (GBM). The original dataset consists of 12 waterfall plots for each event, which contain key information about the prompt emission of each GRB. The dataset's dimensionality is first reduced to a 30-dimensional latent space using an autoencoder, and subsequently to 2D using UMAP. While the methodology and results are discussed in a previous work (arXiv:2406.03643), here we introduce a statistical approach to evaluate the reliability of the final 2D distribution based on the scDEED algorithm. Our analysis shows that the 2D embedding demonstrates overall good reliability, with more than 90% of the events classified as trustworthy.
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Astrophysics of Galaxies

Detecting Ca II Absorption Lines with a Fe II assisted Dual Neural Network

Lucas Wang, Jian Ge and Kevin Willis

Ca II absorbers, characterized by dusty and metal-rich environments, provide unique insights into the interstellar medium of galaxies. However, their rarity and weak absorption features have hindered comprehensive studies. In this work, we present a novel dual CNN approach to detect Ca II absorption systems, analyzing over 100,000 quasar spectra from the Sloan Digital Sky Survey (SDSS) Data Release 16. Our primary CNN identifies Ca II features, while a secondary CNN cross-verifies these detections using five Fe II absorption lines. This approach yielded 1,646 Ca II absorption systems, including 525 previously known absorbers and 1,121 new discoveries, nearly tripling the size of any previously reported catalog. Among our Ca II absorbers, 95 are found to show the 2175Å dust feature (2DA), corresponding to 22% of strong absorbers, 7% of weak absorbers, and $\sim$12% of the overall Ca II population at $0.8 < z_{\text{abs}} < 1.4$. Across the full redshift range of $0.36 < z_{\text{abs}} < 1.4$, $\sim$1.5% of Mg II absorbers host Ca II.
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Astrophysics of Galaxies

Condensation sequence of circumstellar cluster seeds (CSCCS)

David Gobrecht

Traditionally, the condensation sequence of circumstellar dust is predicted based on the thermodynamic stabilities of specific condensates in the macroscopic bulk phase. However, at the (sub-)nanometer scale clusters with non-crystalline structures and significantly different properties are energetically favoured. For this reason, we study the thermodynamic stabilities of metal oxide clusters with generic stoichiometries of M$_2$O$_3$ and M$_3$O$_4$, where M represents a metal atom. With an upper size limit of 50 atoms, we consider clusters with sizes n=1$-$10 for (M$_2$O$_3$)$_n$, and n=1$-$7 for (M$_3$O$_4$)$_n$. The M$_2$O$_3$ clusters comprise alumina (Al$_2$O$_3$), Mg-rich pyroxene (MgSiO$_3$) and a size-limited sample of titanates (CaTiO$_3$), whereas the M$_3$O$_4$ clusters include spinel (MgAl$_2$O$_4$), Mg-rich olivine (Mg$_2$SiO$_4$) and calcium aluminates (CaAl$_2$O$_4$). We find that, apart from the alumina monomer, the aluminum-bearing clusters (Al$_2$O$_3$)$_n$, n=1$-$10, and (MgAl$_2$O$_4$)$_n$, n=1$-$7, are favoured over their silicate counterparts (MgSiO$_3$)$_n$, n=1$-$10 and (Mg$_2$SiO$_4$)$_n$, n=1$-$7. Also, we find that calcium aluminate clusters, CaAl$_2$O$_4$, are energetically more favourable than magnesium aluminate clusters, MgAl$_2$O$_4$. Furthermore, for a limited data set of (CaTiO$_3$)$_n$, n=1$-$2, clusters we find significantly larger stabilities than for the other considered (M$_2$O$_3$)$_n$ clusters, namely Al$_2$O$_3$ and MgSiO$_3$. Future investigations, in particular on titanates and on Ca-rich silicates, are required to draw a more thorough and complete picture of the condensation sequence at the (sub-)nanoscale.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Phase space analysis of an exponential model in $f(Q)$ gravity including linear dark-sector interactions

Ivan R. Vasquez and A. Oliveros

We present a cosmological analysis of an exponential $f(Q)$ gravity model, within the dynamical systems formalism. Following the method introduced by Böhmer et al [Universe 9 no.4, 166 (2023)], the modified Friedmann modified equations are successfully reduced to an autonomous system. Given the exponential form of $f(Q)$, the equilibrium conditions result in transcendental equations, which we approximate to identify the critical points. We therefore perform a general stability analysis of these points in terms of the model parameters. Finally, we extend the model by including a linear dark energy-dark matter interaction, where the equilibrium points are found with their stability properties. The model exhibits the three main domination epochs in the Universe, as well as a non-trivial impact on the late-time de Sitter attractor.
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Astrophysics of Galaxies

Deep JWST spectroscopy of galaxies in a candidate ionized bubble at $z = 8.7$: probing reionization at pMpc scales with Ly$\alpha$ emission

Lily Whitler, Daniel P. Stark, Charlotte A. Mason et al. (+5 more)

Strong Ly$\alpha$ emission observed from galaxies when the Universe is expected to be highly neutral is thought to trace large ionized regions that facilitate the transmission of Ly$\alpha$ through the IGM. In this work, we use deep JWST Ly$\alpha$ spectroscopy to constrain the size of a candidate ionized bubble at $z\sim8.7$ in the EGS field, with a potential radius of $R_b=2$ physical Mpc (pMpc) or larger. We measure a photometric galaxy density and find that the volume is a factor of $\sim2.5-3.6$ overdense, suggesting that there may be a large population of galaxies capable of creating an $R_b\sim2$ pMpc bubble. Then, we infer the Ly$\alpha$ transmission through the IGM for galaxies in the EGS volume using our deep spectroscopy, finding $\mathcal{T}_\mathrm{IGM}=0.26_{-0.14}^{+0.25}$. This transmission is consistent with the average at $z\sim9$ and is mildly inconsistent with the transmission expected for an $R_b\sim2$ pMpc bubble ($\mathcal{T}_{\mathrm{IGM},2\mathrm{pMpc}}=0.53-0.63$), implying that such a large bubble is unlikely to be present. However, the photometric galaxy density in the EGS field is larger than in several other deep fields. This overdensity and the moderate Ly$\alpha$ transmission may be consistent with smaller, $R_b\sim0.5-1$ pMpc bubbles in EGS. This additionally motivates the need for future wider area Ly$\alpha$ spectroscopy in EGS and other fields to obtain a more representative understanding of the sizes of ionized bubbles in the early stages of reionization, and the properties of the galaxies that create them.
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All authors Lily Whitler, Daniel P. Stark, Charlotte A. Mason, Mengtao Tang, Zuyi Chen, Ting-Yi Lu, Gonzalo Prieto-Lyon, Anne Hutter

High Energy Astrophysical Phenomena

Impact of Cosmic Ray Acceleration on the Early Evolution of Bow Shocks around Massive Runaway Stars

Keito Watanabe, Stefanie Walch, Tim-Eric Rathjen et al. (+3 more)

Bow shocks generated from the interaction of winds from massive runaway stars with the interstellar medium have been shown to be prominent particle accelerators through recent $\gamma$-ray and radio synchrotron observations. Here, we study particle acceleration from bow shocks by conducting 3D ideal cosmic ray magnetohydrodynamic simulations in the advection-diffusion limit. We use the Eulerian grid-based code FLASH, where stellar winds are injected through tabulated wind velocities and mass loss rates. We implement a gradient-based shock detection algorithm to resolve the shocked regions where the CRs are injected dynamically. Simulations are performed for different values of the CR diffusion coefficient and star velocities within an ISM-like environment up to 500 kyr to showcase the impact of dynamical CR injection on the early evolution of the wind-driven bow shock. With a simplified spectral model in post-processing, we calculate the expected upper limits of $\gamma$-ray and synchrotron emission and compare with those from current observations. We observe that variations of CR diffusion rates can strongly dictate the morphology of the bow shock and the overall $\gamma$-ray and radio synchrotron luminosity due to the balance between the CR injection efficiency and diffusion. Our results are underestimated as compared to current observations even with an overestimated particle acceleration primarily due to weaker wind luminosities and lack of stellar magnetic fields in our model. We conclude that CR acceleration, with varying CR diffusion rates, may substantially affect the morphology of wind-driven bow shocks and their non-thermal emission, if there is efficient particle acceleration in the forward shock. [abridged]
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All authors Keito Watanabe, Stefanie Walch, Tim-Eric Rathjen, Jonathan Mackey, Pierre Nürnberger, Philipp Girichidis

High Energy Astrophysical Phenomena

Rotation of Polarization Angle in Gamma-Ray Burst Prompt Phase. III. The Influence of the Magnetic Field Orientation

Xing-Yao Wang, Jia-Sheng Li and Mi-Xiang Lan

Polarization is very sensitive to the configuration of the magnetic field in the radiation region. In addition to polarization curve and polarization spectrum, studies of polarization angle (PA) rotation spectrum is also crucial. In this paper, we use a simple parametric magnetic reconnection model with a large-scale aligned magnetic field in the radiation region to study the effects of field orientation on the PA rotations. Under different field orientations, variations of the PA rotation with parameters and the PA rotation spectra are studied. We find that the conclusions obtained in our previous works are almost independent of the field orientations. The area of the parameter space with $\Delta$PA $>10^\circ$ will shrink as the value of field orientation ($\delta$) increases for $0^\circ<\delta<90^\circ$. The $\Delta$PA values would be the same for two complementary field orientations. For two particular magnetic field orientations ($\delta=0^\circ$ and $90^\circ$), the $\Delta$PA would also only be $0^\circ$ or $90^\circ$ within the burst duration.
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Astrophysics of Galaxies

GALACTICNUCLEUS: A high angular resolution JHKs imaging survey of the Galactic centre. V. Toward the GNS Second Data Release: Methodology, Photometric and Astrometric Performance

Á. Martínez Arranz, R. Schödel, H. Bouy et al. (+1 more)

The center of the Milky Way is a unique environment of great astrophysical interest, but its extreme crowding and extinction make it difficult to study. The GALACTICNUCLEUS survey, a high-angular-resolution near-infrared imaging program, was designed to overcome these challenges. We present the methodology and first results of its second data release, which includes major improvements in reduction, calibration, and analysis, providing deeper photometry, improved astrometry, and high-precision proper motions across the Nuclear Stellar Disk. Observations were obtained with VLT/HAWK-I in two epochs separated by seven years, using speckle holography and a ground-layer adaptive optics system. Proper motions were derived both relative, by aligning epochs within the survey, and absolute, by tying to the Gaia reference frame. The new release achieves photometry about one magnitude deeper and astrometry about ten times more precise than the first release. Proper motions reach an accuracy of about 0.5 mas/yr relative to Gaia. In the Arches field, our clustering analysis recovers the cluster with mean velocities consistent with HST-based results. The second data release of the GALACTICNUCLEUS survey provides the most precise ground-based proper motion catalogs of the Galactic Center to date, enabling studies of the Nuclear Stellar Disk, young star kinematics, and new stellar cluster detections.
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All authors Á. Martínez Arranz, R. Schödel, H. Bouy, F. Nogueras-Lara

Instrumentation and Methods for Astrophysics

PLATOSpec: a precise spectrograph in support of space missions

P. Kabáth, M. Skarka, A. Hatzes et al. (+42 more)

The upcoming space missions that will characterize exoplanets, such as PLATO and Ariel, will collect huge amounts of data that will need to be complemented with ground-based observations. The aim of the PLATOSpec project is to perform science with an echelle spectrograph capable of measuring precise radial velocities. The main focus of the spectrograph will be to perform the initial screening and validation of exoplanetary candidates, in addition to study stellar variability. It will be possible to determine the physical properties of large exoplanets. The PLATOSpec blue-sensitive spectrograph, with a spectral range of 380 to 700\,nm and a resolving power of R=70,000, is installed on the 1.5-m telescope at the ESO La Silla Observatory in Chile. Initial results show that the radial-velocity limit given by the wavelength calibration is about 2-3 m/s. Tests on bright F-K main-sequence standard stars reveal a scatter of about 5 m/s over a few hours. The scatter over a few months is slightly higher. We demonstrate the capabilities of PLATOSpec on the mass determination of WASP-79 b and the spin-orbit alignment of WASP-62\,b via the Rossiter-McLaughlin effect. We show its possible usage on variable star research as demonstrated on the false-positive exoplanetary candidate TIC 238060327, which is proven a binary star. Investigation of line-profile variations of the roAp star alpha Cir shows that PLATOSpec can also be used for the surface mapping. Finally, we present new results on the active star UY Pic in the PLATO southern field. Our results show that PLATOSpec is a versatile spectrograph with great precision.
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All authors P. Kabáth, M. Skarka, A. Hatzes, E. Guenther, L. Vanzi, R. Brahm, J. Janík, P. Pintr, P. Gajdoš, J. Lipták, J. Žák, H. M. J. Boffin, L. Antonucci, G. Avila, Z. Balkóová, M. E. Ball, M. Flores, A. Fuentes, J. Fuchs, R. Greimel, A. Gajardo, V. D. Ivanov, J. Köhler, M. Leitzinger, T. Moravčík, J. Nečásek, R. J. U. Neubert, P. Odert, G. Olguin, M. Tala Pinto, M. Roth, L. Řezba, V. Schaffenroth, M. Sigwarth, J. Srba, A. Suárez, P. Škoda, J. Šubjak, J. Václavík, M. Veselý, R. Veselý, M. Vítková, J. U. Winkler, M. Zummer, E. Ždárská

Earth and Planetary Astrophysics

Near the Runaway: The Climate and Habitability of Teegarden's Star b

Ryan Boukrouche, Rodrigo Caballero and Neil Lewis

Teegarden's Star b, a nearby terrestrial world receiving an Earth-like instellation, is a prime candidate for next-generation observatories targeting temperate exoplanets in their habitable zones. We employ a suite of three-dimensional global climate model (GCM) simulations to (1) map the inner boundary of the habitable zone of Teegarden's Star b and (2) characterize its surface climate under the assumption of an Earth-analog atmosphere. Our simulations show that, with its most recently estimated instellation of 1481 Wm^-2, Teegarden's Star b remains below the runaway greenhouse threshold for both low (as=0.07, ocean-dominated) and moderate (as=0.30, land-dominated) surface albedos. However, a different estimate of 1565 Wm^-2 places it beyond the runaway threshold. The result that Teegarden's Star b is habitable under the most recent instellation measurement reinforces its status as one of the most compelling targets for future habitability and biosignature searches. Given the planet's proximity to the runaway threshold, it would benefit from a comparative study done with other models using different parameterizations.
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Solar and Stellar Astrophysics

Abundances of Rarely Detected s-process Elements Derived from the Ultraviolet Spectrum of the s-process-enhanced Metal-poor Star HD 196944

Ian U. Roederer, Vinicius M. Placco, Amanda I. Karakas et al. (+2 more)

We present an analysis of the heavy-element abundances of HD 196944, a carbon-enhanced metal-poor (CEMP) star enriched with elements produced by the slow neutron-capture process (s-process). We obtained a new high-resolution ultraviolet (UV) spectrum of this star, the UV-brightest known CEMP-s star, with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. This spectrum extends deeper into the UV (2029 < lambda < 2303 Angstroms) than previous studies of any CEMP-s star. When combined with previous UV and optical analysis, a total of 35 elements heavier than zinc (Z = 30) can be detected in HD 196944, and upper limits are available for nine other heavy elements. The abundances can be well fit by models of s-process nucleosynthesis operating in a low-mass companion star that evolved through the asymptotic giant branch phase and transferred heavy elements to HD 196944. This s-process event did not contribute substantially to the Ga, Ge, or As abundances (31 <= Z <= 33). Our results demonstrate that UV spectroscopy can greatly expand the inventory of heavy elements detectable in CEMP-s stars.
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All authors Ian U. Roederer, Vinicius M. Placco, Amanda I. Karakas, Elizabeth A. Den Hartog, Timothy C. Beers

High Energy Astrophysical Phenomena

Ultraviolet radiation and neutrinos: two messengers from CCSNe in the CSM scenario

Silvia Gagliardini, Simone Dall'Osso, Dafne Guetta et al. (+4 more)

Massive stars (>8 $M_{\odot}$) often undergo intense mass loss through winds or eruptive events in the final stages of their evolution, leading to the formation of a dense circumstellar medium (CSM). This material, expelled months to years before core collapse, shapes the pre-explosion environment and influences the early supernova (SN) emission. In particular, the interaction of the SN ejecta with the dense CSM can power an extended emission into the UV/optical bands, as seen in a growing fraction of type II SN. Recent events such as SN 2023ixf and SN 2024ggi confirm the relevance of dense environments and highlight the value of UV observations. Moreover, Fast Blue Optical Transients (FBOTs) may represent extreme cases of this interaction, possibly linked to more compact/massive CSM. In this work, we model the SN-CSM shock interaction in order to (i) estimate the maximum detection horizons and expected rates for future UV missions like ULTRASAT, and (ii) to estimate the intensity and expected rate of potential neutrino signals detectable by IceCube and KM3NeT. We then discuss the prospects for multi-messenger observations of such events in the near future.
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All authors Silvia Gagliardini, Simone Dall'Osso, Dafne Guetta, Angela Zegarelli, Silvia Celli, Antonio Capone, Irene Di Palma

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Gravitational Wave Signatures from Lepton Number Breaking Phase Transitions with Flat Potentials

Gabriela Barenboim, Yeji Park and Liliana Velasco-Sevilla

Extensions of the Standard Model typically contain “flaton fields" defined as fields with large vacuum expectation values and almost flat potentials where scalar self-coupling is small or vanishes at tree level. Such potentials have been used to drive a secondary inflationary epoch after a primary phase of inflation, in what are called thermal inflation models. Although the primordial, high-scale inflationary epoch can solve the horizon and flatness problems, it does not always resolve difficulties associated with late-time relics produced in extensions of the Standard Model. These relics typically decay too late, injecting entropy and energetic particles that spoil successful predictions like Big Bang Nucleosynthesis. It is here that thermal inflation plays a crucial role: diluting unwanted relics by many orders of magnitude without erasing the baryon asymmetry or the large-scale structure set up by the earlier phase of inflation. The preferred scale for this phenomenon is in the range $10^6-10^8$ GeV if one considers supergravity, but without it, any scale above the EW scale is valid. We investigate a typical form of these potentials and determine what are the conditions for the potentials to develop a barrier such that when the flatons settle to the true minimum, the associated Gravitational Waves can be observed, focusing on first-order phase transitions from spontaneous lepton number breaking.
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Earth and Planetary Astrophysics

A Systematic North-South asymmetry in the Steady-state Climate of rapidly-rotating Oblique Water Worlds

Y Wu, S. Portegies Zwart and H Dijkstra

Planetary obliquity (axial tilt) plays an important role in regulating the climate evolution and habitability of water-covered planets. Despite the suspicion of large obliquities in several exoplanetary systems, this phenomenon remains hard to observe directly. We aimed to study the effect of mass, obliquity, and rotation on the steady state climate of water-covered planets. We simulated the climate evolution of such planets with varying obliquities, rotational speed, and mass using a general circulation model (GCM) of intermediate complexity, assuming aqua-planet configurations. High obliquity supports an asymmetry between the equilibrium climatological conditions in the northern and southern hemispheres. The polar temperature ratio deviates further from unity with increasing obliquity and rotation rate. Cloud coverage patterns also shift with obliquity, displaying distinct latitudinal bands and increased cloudiness in the warmer hemisphere. The climate of habitable-zone aqua-planets turns out to be sensitive to changes in obliquity and rotation rate, but are independent of planet mass. Our results highlight the importance of considering these factors when assessing the surface conditions of exoplanets. As a consequence, surface condition asymmetries in water-world exo-planets can be used to infer the planet's obliquity and rotation rate.
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Solar and Stellar Astrophysics

Magnetic Decay Index Profile and Coronal Mass Ejection Speed

Bernhard Kliem, Georgios Chintzoglou, Tibor Török et al. (+1 more)

We study the relationship between the speed of coronal mass ejections (CMEs) and the height profile of the ambient magnetic field, quantified by its decay index, n(h). Our sample is composed of 15 very fast CMEs (Vcme > 1500 km/s; all halo CMEs) and 22 halo CMEs below this speed limit from Solar Cycle 23. The very fast CMEs yield a high correlation of 0.81 between Vcme and the slope of n(h) in a height range above the onset height of the torus instability if one extremely fast outlier, which closely followed another very fast CME, is excluded. This is consistent with the hypothesis that the torus instability plays a decisive role in CME acceleration. The whole sample yields a weaker correlation, which is still significant if events with a broad torus-stable dip in n(h) are excluded. A parametric simulation study of flux-rope eruptions from quadrupolar and two-scale bipolar source regions confirms the decelerating effect of such dips. Very fast, moderate-velocity, and confined eruptions are found.
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All authors Bernhard Kliem, Georgios Chintzoglou, Tibor Török, Jie Zhang

Solar and Stellar Astrophysics

A (very) simple proof of the gravitational energy formula of polytropic spheres

Luca Ciotti

It is shown how the well-known formula for the gravitational energy of self-gravitating regular polytropes of finite mass can be obtained in an elementary way by using Gauss's divergence theorem and the Chandrasekhar virial tensor, without resorting to lengthy algebra, to specific properties of Lane-Emden functions, and to thermodynamics arguments, as is instead commonly found in standard treatises and in astrophysical literature. The present approach, due to its simplicity, can be particularly useful to students and researchers, and it can be easily applied to the study of more complicated polytropic structures.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

New Tests of Low-Scale Quantum Gravity with Cosmic-Ray Collisions

Manuel Ettengruber and Gonzalo Herrera

Cosmic ray collisions at high center of mass energy could enable graviton and black hole production as expected in theories of low-scale quantum gravity, such as extra-dimensions, many species, or some versions of string theory. Here we propose three novel phenomenological tests of these theories. We first consider the collision of cosmic rays with ambient protons, electrons and photons in Active Galactic Nuclei (AGN), finding that high-energy neutrino data from the blazar TXS 0506+056 places a constraint on the fundamental scale of gravity of $M_f \gtrsim 0.3$ TeV, and future high-energy neutrino data could raise this bound to $M_f \gtrsim 200$ TeV. We then point out that collisions of pairs of cosmic rays could occur at a sizable rate in AGN where the accelerated cosmic rays are not collimated, or on supermassive black hole binaries. This consideration could potentially let us test unprecedented large fundamental scales of $M_f \gtrsim 2$ PeV. We further compute the corresponding thermal neutrino emission arising from the Hawking evaporation of black holes produced in cosmic ray collisions, finding a spectrum that clearly differs from that expected in meson decays. Finally, we speculate with an scenario which would produce high-energy neutrino and gamma-ray emission from regions in the sky where no multi-wavelength counterparts would be expected, via graviton propagation from a different brane, which then decays in our Universe.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Impact of facility timing and coordination for next-generation gravitational-wave detectors

Ssohrab Borhanian, Arianna Renzini, Philippa S. Cole et al. (+3 more)

While the Einstein Telescope and Cosmic Explorer proposals for next-generation, ground-based detectors promise vastly improved sensitivities to gravitational-wave signals, only joint observations are expected to enable the full scientific potential of these facilities, making timing and coordination between the efforts crucial to avoid missed opportunities. This study investigates the impact of long-term delays on the scientific capabilities of next-generation detector networks. We use the Fisher information formalism to simulate the performance of a set of detector networks for large, fiducial populations of binary black holes, binary neutron stars, and primordial black-hole binaries. Bootstrapping the simulated populations, we map the expected observation times required to reach a number of observations fulfilling scientific targets for key sensitivity and localization metrics across various network configurations. We also investigate the sensitivity to stochastic backgrounds. We find that purely sensitivity-driven metrics such as the signal-to-noise ratio are not strongly affected by delays between facilities. This is contrasted by the localization metrics, which are very sensitive to the number of detectors in the network and, by extension, to delayed observation campaigns for a detector. Effectively, delays in one detector behave like network-wide interruptions for the localization metrics for networks consisting of two next-generation facilities. We examine the impact of a supporting, current-generation detector such as LIGO India operating concurrently with next-generation facilities and find such an addition will greatly mitigate the negative effects of delays for localization metrics, with important consequences on multi-messenger science and stochastic searches.
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All authors Ssohrab Borhanian, Arianna Renzini, Philippa S. Cole, Costantino Pacilio, Michele Mancarella, Davide Gerosa

Earth and Planetary Astrophysics

The resilience of the sailboat stable region

Rafael Sfair, Tiago F. L. L. Pinheiro, Giovana Ramon et al. (+1 more)

Binary systems host complex orbital dynamics where test particles can occupy stable regions despite strong gravitational perturbations. The sailboat region, discovered in the Pluto-Charon system, allows highly eccentric S-type orbits at intermediate distances between the two massive bodies. This region challenges traditional stability concepts by supporting eccentricities up to 0.9 in a zone typically dominated by chaotic motion. We investigate the sailboat region's existence and extent across different binary system configurations. We examine how variations in mass ratio, secondary body eccentricity, particle inclination, and argument of pericenter affect this stable region. We performed 1.2 million numerical simulations of the elliptic three-body problem to generate four datasets exploring different parameter spaces. We trained XGBoost machine learning models to classify stability across approximately $10^9$ initial conditions. We validated our results using Poincaré surface of section and Lyapunov exponent analysis to confirm the dynamical mechanisms underlying the stability. The sailboat region exists only for binary mass ratios $\mu = [0.05, 0.22]$. Secondary body eccentricity severely constrains the region, following an exponential decay: $e_{s,\mathrm{max}} \approx 0.016 + 0.614 \exp(-25.6\mu)$. The region tolerates particle inclinations up to $90^\circ$ and persists in retrograde configurations for $\mu \leq 0.16$. Stability requires specific argument of pericenter values within $\pm 10^\circ$ to $\pm 30^\circ$ of $\omega = 0^\circ$ and $180^\circ$. Our machine learning models achieved over 97% accuracy in predicting stability. The sailboat region shows strong sensitivity to system parameters, particularly secondary body eccentricity. Among Solar System dwarf planet binaries, Pluto-Charon, Orcus-Vanth and Varda-Ilmarë systems could harbor such regions.
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All authors Rafael Sfair, Tiago F. L. L. Pinheiro, Giovana Ramon, Ernesto Vieira