Solar and Stellar Astrophysics · Cross-listed from gr-qc
Structure of Anisotropic Magnetized Neutron Stars in f(R,T) Gravity with Realistic Equation of State
M. Savari, G. H. Bordbar, J. Sedaghat et al. (+1 more)
In this study, within the framework of f(R,T) modified
gravity, we investigate the influence of coupling parameter,
magnetic field and anisotropy parameter on the
neutron star structure. This work employs an accurate equation of state (EoS), derived from realistic microscopic calculations based on the AV18 nucleon-nucleon potential, to compute the structure of this compact object. Here, determination of Schwarzschild radius, compactness, gravitational surface
redshift and Kretschmann scalar within the f(R, T)
gravity, confirms that our theoretical results are consistent with the observational constraints. While established physical EoSs within the framework of Einstein
gravity have successfully characterized a broad range of compact objects, they remain inadequate in explaining certain massive objects residing within the mass gap (2.5 to 5 Msun). We show that some compact objects residing in the mass gap interpreted as candidates of
neutron stars within the framework of f(R, T)
gravity. Finally, we compare our results with the observational data from LIGO/Virgo/KAGRA and NICER, setting the parameters of the f(R, T) theory and anisotropy to successfully reproduce the masses and radii of the GW170817, PSR J0952-0607 and PSR J0740+6620 and the masses of the secondary components of GW190814 and GW200210-092254.
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All authors M. Savari, G. H. Bordbar, J. Sedaghat, A. Sheykhi
Cosmology and Nongalactic Astrophysics
Modeling Uncertainties in Modified Gravity Predictions for the Stochastic Gravitational-Wave Background
Rodrigo Fraga and Rafael C. Nunes
We investigate the impact of modified
gravity on the
stochastic gravitational-wave background (SGWB) generated by a cosmological population of unresolved binary black hole mergers. We consider two complementary classes of beyond-General Relativity (GR) effects: waveform-generation modifications described within the parametrized post-Einsteinian (ppE) framework and cosmological propagation effects associated with a modified gravitational-wave luminosity distance. Astrophysical uncertainties in the binary black hole population are consistently incorporated using a Power-Law plus Peak mass model combined with a Madau–Dickinson merger-rate
evolution. Using SGWB forecasts for Advanced LIGO, the Einstein
Telescope (ET), and
Cosmic Explorer (CE), we perform injection-recovery analyses jointly varying modified-
gravity and astrophysical population parameters. We show that frequency-dependent ppE corrections produce characteristic distortions in the SGWB spectral shape and can be meaningfully constrained by third-generation detectors, particularly CE. In contrast, modified propagation effects mainly induce smooth amplitude rescalings and exhibit stronger degeneracies with astrophysical uncertainties. Our results demonstrate that future SGWB observations will provide a complementary probe of gravitational physics across
cosmic history and may open new avenues for testing deviations from GR beyond individually resolved compact-binary events.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Cosmological Correlators in KLF and the Double-Exchange
Nathan Belrhali, Arthur Poisson and Sébastien Renaux-Petel
In this work, we present the procedure to find series representations of tree-level cosmological correlators using the Kontorovich-Lebedev-
Fourier (KLF) space formalism. This framework allows us to trade the in-in nested time integrals for frequency integrals over rational propagators and vertex functions, which encode interactions among
quantum fields on a de Sitter background. Because these functions are the key objects to understand in order to perform a diagrammatic computation, we derive their relevant analytic properties by using both their integral representation and series representation in terms of Lauricella functions. For a vertex involving any number of fields, we obtain the location of singularities, the corresponding residues and the large-frequency asymptotic behaviour. Gathering these properties at each frequency integration allows us to compute a tree-level correlator directly, without relying on the differential equations it satisfies. To illustrate this procedure, we provide a complete treatment of the double-exchange diagram. The computation naturally distinguishes the different physical contributions, whether to the background or to the cosmological
collider signal. The newly derived result is expressed at most in terms of a double series over hypergeometric functions, which simplifies the analytical expression of the correlator.
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Astrophysics of Galaxies
Weak Evolution of Cosmic Atomic Hydrogen over the Past 4.5 Billion Years
Chuan-Peng Zhang, Hong Guo, Yizhou Gu et al. (+49 more)
The
cosmic star formation rate density (CSFRD) has declined sharply toward the present day, but the roles of the atomic and molecular gas reservoirs remain uncertain. We measure the
cosmic HI density, $\Omega_{\mathrm{HI}}$, over $0<z<0.41$ by combining HI spectra from the Five-hundred-meter Aperture Spherical
Telescope with optical spectroscopy from the Dark Energy Spectroscopic Instrument for $\sim2.5$ million
galaxies across $\sim12,000\,{\rm deg}^2$. We measure a raw decrease in $\Omega_{\mathrm{HI}}$ by a factor of $1.35\pm0.10$ over the past 4.5 Gyr. Even after applying the conservative systematic corrections from our forward model, the inferred decline is only $1.12\pm0.10$ – still far weaker than the CSFRD decline (a factor of 2.46). The molecular gas density, in contrast, is known to evolve more closely with
star formation. At fixed
stellar mass, the average HI gas fraction evolves by less than 0.2 dex, showing that the weak
evolution is present across the
galaxy population. These quantitative differences rule out rapid depletion of
galaxy HI as the primary driver of the late-time CSFRD decline, and provide a stringent
benchmark for models of gas
accretion, phase conversion and
star-formation regulation.
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All authors Chuan-Peng Zhang, Hong Guo, Yizhou Gu, Amélie Saintonge, Xiaohu Yang, Dirk Scholte, Ming Zhu, Peng Jiang, Hu Zou, Manasvee Saraf, Wenlin Ma, Yirong Wang, Y. P. Jing, Zheng Zheng, Zhejie Ding, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. de la Macorra, P. Doel, E. Gaztañaga, G. Gutierrez, M. Ishak, R. Joyce, S. Juneau, R. Kehoe, D. Kirkby, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, FASHI Collaboration
Solar and Stellar Astrophysics
The steady incompressible ideal free-boundary flows of a hydromagnetic star
B. C. Low and S. W. McIntosh
This self-contained theoretical study treats incompressible, free-boundary flows in a gravitating, ideal hydromagnetic
star abutting
vacuum, centered on the steady field-aligned flows of Chandrasekhar, Prendergast and Tsinganos, together with a novel family of steady cross-field flows, all as solutions of the axisymmetric Tsinganos equation. In the absence of compressive waves and shocks, an incompressible fluid evolves by its frozen-in
magnetic field propagating as transverse Alfvèn waves along the field lines, with pressure reacting instantly in place. The origin of the steady flows rests on the Parker theory that everywhere-continuous flows are the exception rather than the rule because of a basic propensity for tangential field/flow discontinuities. Astrophysical viscosity and electrical resistivity are not zero but are significant only over scales much smaller than macroscopic scales. Such near-ideal fluids have the same propensity for tangential discontinuities but the near-discontinuities readily dissipate by small-scale, viscous-resistive
magnetic reconnections. The study treats the strictly ideal fluid separately in its own right, to construct a conceptual understanding of the turbulent creation of a steady flow in a self-organizing near-ideal fluid via irrepressible energy loss and field-
topology changes as episodic reconnections run out of free energy. The study suggests that metastable storage of steady
vortices and twisted fields is a natural product of the
solar internal dynamo, to explain a recent, multi-instrument observation of
solar-coronal eruptions persisting coherently in preferred longitudinal locations over
solar-rotational timescales.
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Astrophysics of Galaxies
Toward Unbiased Abundance Measurements in Inhomogeneous $\mathrm{H\,II}$ Regions
Eric Habjan, Christopher Faesi, Kathryn Kreckel et al. (+10 more)
Probing the chemical content of the interstellar medium (ISM) in nearby
galaxies provides key insight into their chemical
evolution and informs our interpretation of
galaxies at higher
redshift. However, nonlinear structure in the ISM, including density and temperature inhomogeneities, can bias chemical abundance measurements and systematically affect empirical calibrations derived from them. In this work, we investigate biases in $T_e$-derived oxygen abundance determinations and explore the physical properties that correlate with them. We combine $\mathrm{[O\,II]}\lambda\lambda3726, 3729$ measurements from SITELLE with a full suite of optical emission lines obtained with MUSE. From auroral emission lines ($\mathrm{[N\,II]}\lambda5755$, $\mathrm{[S\,III]}\lambda6312$, and $\mathrm{[O\,II]}\lambda\lambda7320, 7330$) and nebular emission lines (including $\mathrm{[N\,II]}\lambda6584$ and $\mathrm{[S\,III]}\lambda9069$), we derive electron densities, temperatures, and chemical abundances for a sample of $\mathrm{H\, II}$ regions in five
galaxies. We find that densities derived from the $\mathrm{[O\,II]}$ auroral-to-nebular ratio are $\sim10^3$ cm$^{-3}$, which is higher than the standard $\mathrm{[S\,II]}$ densities derived from nebular doublet ratios. We demonstrate that combining the $\mathrm{[N,II]}$ electron temperature with the density inferred from the $\mathrm{[O\,II]}$ auroral-to-nebular line ratio yields singly ionized oxygen abundances consistent with literature expectations for a prescription insensitive to density inhomogeneities. We also find that the $\mathrm{[S\,III]}$ temperature provides a reliable estimate of $T_{e,\mathrm{[O\,III]}}$, enabling robust measurements of doubly ionized oxygen abundances. Overall, these results indicate that the abundance discrepancy factor could be higher in more chemically evolved $\mathrm{H\, II}$ regions.
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All authors Eric Habjan, Christopher Faesi, Kathryn Kreckel, J. Eduardo Méndez-Delgado, Francesco Belfiore, Ryan J. Vaught, Brent Groves, Fabian Scheuermann, Thomas G. Williams, Ralf S. Klessen, Amirnezam Amiri, Kathryn Grasha, Simon Glover
High Energy Astrophysical Phenomena
AU or pc? Inferring the distance of magnetized plasma near FRBs from propagation diagnostics
Wanjin Lu, Dongzi Li, Zhenyin Zhao et al. (+1 more)
Fast
Radio Bursts (FRBs) are highly energetic, millisecond-duration
radio transients. A significant fraction of repeating FRBs are found in magneto-active environments significantly different from typical interstellar medium, offering important insights into their origins and evolutionary pathways. Possible explanations range from companion winds to young magneto-active supernvae remnants. The spatial scales of the magneto-active environment is a major distinction of different models. In this work, we present a new method to estimate the physical scale of the magneto-active region surrounding FRBs by jointly analyzing measurements of temporal scattering ($\tau_\mathrm{scat}$), depolarization ($\sigma_\mathrm{RM}$), and Faraday rotation measure (RM) variations ($\left|\Delta \mathrm{RM}/\Delta t\right|$) in repeating sources. We systematically apply this method to all active repeaters with multiple RM measurements. Despite the coarse sampling and large uncertainties, the inferred distances tentatively favor SNR-scale magneto-environments for FRB 20190303A, FRB 20190417A, and FRB 20190520B, while still allowing binary-scale structures for FRB 20180916B and FRB 20201124A under plausible assumptions. Better sampling of propagation effects, together with future advances in simultaneous wideband measurements of multiple effects with CHORD and the DSA, has the potential to systematic discrimination among the origins of FRB magneto-environments and constrain progenitor
evolution.
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All authors Wanjin Lu, Dongzi Li, Zhenyin Zhao, Fayin Wang
Instrumentation and Methods for Astrophysics
Trigger system for the Payload for Ultrahigh Energy Observations (PUEO) balloon-borne neutrino detector
Q. Abarr, J. Alfaro, P. Allison et al. (+67 more)
The Payload for Ultrahigh Energy Observations (PUEO) is a NASA balloon-borne instrument for the detection of ultra-high energy (UHE)
neutrinos with energies above $10^{17.5}~\textrm{eV}$ via either the Askaryan effect or geomagnetic emissions from an upward-going air shower. The main instrument trigger system for PUEO is a fully digital supersample rate beamformer based on 24 Xilinx
Radio Frequency System-on-a-Chip (RFSoC) digitizers sampling 192 channels operating at $3~\textrm{GSa/s}$ and a system clock frequency of $375~\textrm{MHz}$. The trigger implements frequency band conditioning, dynamic
radio-frequency interference (RFI) rejection, and matched filtering, with significant emphasis on optimization to reduce both the power and resource usage while maintaining sensitivity. The system implements 48 total synthetic
antenna beams with up to 8
antennas each, covering a $\sim25^\circ$ range in zenith and $\sim60^\circ$ range in azimuth. Preflight testing demonstrated a trigger performance of a minimum signal-to-noise ratio (SNR) of $\sim1.5$ using simulated signals while consuming between $5-7~\textrm{W}$ in the trigger logic.
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All authors Q. Abarr, J. Alfaro, P. Allison, J. Alvarez-Muñiz, T. Anderson, H. Barnett, A. Basharina-Freshville, J. J. Beatty, L. Beaufore, D. Z. Besson, M. Betts, R. Bose, D. Braun, B. Chamanbahar, P. Chen, Y. Chen, J. M. Clem, T. Coakley, A. Connolly, K. Couberly, L. Cremonesi, A. Cummings, P. Dasgupta, C. Deaconu, J. Flaherty, C. Godden, P. W. Gorham, C. Hornhuber, J. Hoffman, K. Hughes, A. Hynous, A. Jung, A. M. Kofman, Y. Ku, D. Kullgren, C.-Y. Kuo, P. Linton, L. Lisalda, T. C. Liu, W. Luszczak, S. C. Mackey, Z. Martin, K. McBride, C. Miki, J. Nam, R. J. Nichol, A. Novikov, A. Nozdrina, E. Oberla, S. Prohira, H. Pumphrey, D. Radomski, B. F. Rauch, R. Scrandis, D. Seckel, M. F. H. Seikh, J. Shiao, G. Simburger, J. Tutt, A. G. Vieregg, S.-H. Wang, D. Washington, C. Welling, P. Windischhofer, S. A. Wissel, C. Xie, J. Yao, R. Young, E. Zas, A. Zeolla
Solar and Stellar Astrophysics
Circumbinary disk formation through AGB star winds
Shunquan Huang and Rebecca G. Martin
Circumbinary disks are commonly observed around post-asymptotic
giant branch (post-AGB)
star binaries, yet their formation and especially their long-term
evolution remain unclear. We investigate this process using smoothed-particle hydrodynamics simulations of AGB
star wind-binary interactions across different wind velocities, binary eccentricities, and mass ratios. When the wind is fast, or the companion is relatively low-mass, corresponding to the Bondi-Hoyle regime, the
outflow remains largely unbound and forms a spiral density pattern. In contrast, slower winds and more massive companions lead to wind Roche-lobe overflow (WRLOF), where a circumsingle disk forms around the companion and efficiently transfers angular momentum to the
outflow, producing a circumbinary disk. We perform simulations for over 600 binary orbital periods and find that the resulting disk properties depend sensitively on binary parameters, with higher eccentricities producing more extended and eccentric circumbinary disks, while lower mass companions reduce the disk density and growth rate. We further find that angular momentum transport within the circumbinary disk is dominated by spiral structures and shocks generated by the binary-wind interaction, corresponding to effective stresses comparable to or larger than the imposed viscosity. These results show that wind-binary interactions can naturally generate diverse circumbinary disk morphologies observed in AGB and post-AGB
star systems.
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Solar and Stellar Astrophysics
The birth of Be star disks III. SPH models of localised mass ejections
A. C. Rubio, A. C. Carciofi, D. Baade et al. (+4 more)
Classical Be
stars exhibit mass ejection events that feed their viscous decretion disks. Recent TESS space photometry and simultaneous spectroscopy revealed that these flickers are localised, short-lived, and associated with near-Keplerian rotating material close to the
stellar surface. We aim to constrain the geometrical and dynamical conditions required for a localised surface ejection to generate a Keplerian decretion disk and to predict the corresponding photometric, spectroscopic, and polarimetric observables. Material, and the injection radius. The SPH outputs were post-processed with the radiative transfer code HDUST to obtain synthetic observables. We scaled the density of the models to match the reference flicker for the Be
star f\,Car. A mildly super-Keplerian rotation of the injection volume, a high viscosity, and a mass-loss rate of the order $10^{-6}\,\rm M_\odot \, yr^{-1} \, str^{-1}$ are required for the ejected material to remain in orbit and form a small disk. The synthetic observables reproduce the behaviour of the reference flicker. The simulations confirm that during mass ejection the disk is asymmetric and dynamically evolving, and circularises within a few days after the end of the flicker. Models with too wide mass ejection angle or too high angular velocity fail to reproduce the observed light curve and line profile behaviour. The models are consistent with mass ejection happening very close to the
stellar equator. Localised, short-duration, mildly super-Keplerian ejections combined with high viscosity and high mass-loss rates can account for the short-timescale variability of the circumstellar environment of Be
stars. Be disks can be formed from such outbursts and realistic 3D injection geometries are essential to connect surface dynamics to disk build-up within the framework of the viscous decretion disk model.
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All authors A. C. Rubio, A. C. Carciofi, D. Baade, J. Labadie-Bartz, T. H. de Amorim, I. A. Gabitova, M. W. Suffak
High Energy Astrophysical Phenomena
The disk luminosity deficit as a tracer of receding disk during Soft-to-Hard transitions in Black Hole X-ray Binaries
Sai-En Xu, Bei You, Yi Long et al. (+4 more)
Tracing the
evolution of the thin
accretion disk during the soft-to-hard state transition in black hole X-ray binaries (BHXRBs) remains difficult because conventional spectral estimates of the disk inner radius become highly model-dependent once the thermal component weakens. We present evidence that the thin disk recedes during this transition, obtained from a systematic study of RXTE/PCA observations of 26 BHXRBs. In 24 outbursts, the disk luminosity decays exponentially in the soft state, then drops significantly below the extrapolated baseline. This thermal luminosity deficit is considered a signature of reduced
accretion efficiency, caused by the outward receding of the optically thick disk. Under this framework, we found that the estimated characteristic truncation radius increases rapidly as the systems evolve through the soft-to-hard transition. This interpretation is supported by timing analysis: in observations with well-constrained power density spectra, the characteristic frequencies of broadband noise and low-frequency QPOs generally decrease as the inferred truncation radius increases, consistent with the expansion of a hot inner flow. The onset and rapidity of recession vary substantially across different sources and outbursts. Our results demonstrate that luminosity deficits provide a practical empirical tracer of thin disk receding during soft-to-hard transitions, when direct spectral radius measurements become unreliable.
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All authors Sai-En Xu, Bei You, Yi Long, Zhen Yan, Andrzej A. Zdziarski, Rui-Xiang Hu, Alex Markowitz
High Energy Astrophysical Phenomena
The emergence of X-ray emission lines during relativistic radio-jet formation in the changing-look active galactic nucleus 1ES 1927+654
Dev R. Sadaula, Sibasish Laha, Eileen T. Meyer et al. (+27 more)
We present results from a comprehensive multi-wavelength monitoring campaign of the changing-look active
galactic nucleus 1ES 1927+654 during the onset and
evolution of a relativistic
radio jet $\sim$(May 2022 - August 2025), using observations from XMM-Newton, Swift, TNG, ZTF, VLA, and VLBA. The soft X-ray emission lines at $\sim 0.56$ keV and $\sim 1$ keV have appeared with variable strength and width during the formation of the nascent jet. We note that the $\sim 1$ keV feature has been persisting since the post-2017
flare phase. We also report the detection of a broad ($\sim 800$ eV) FeK emission feature at $(6-7)$ keV in the $\sim 70$ ks stacked EPIC-pn spectra, marking the first such detection, which historically was lacking in this source. The joint spectral fitting of XMM-Newton EPIC-pn and RGS data reveals the presence of ionized absorbers in 2022 ($\log{\xi\mathrm{/erg\ cm\ s^{-1}}}\sim 1.5\pm 0.3$, $\mathrm{N_H} \sim 2.5\pm 0.9\times 10^{20} \mathrm{cm^{-2}}$), but weaker than that detected during the high
accretion state in 2018 (Eddington ratio, $\lambda_{\rm Edd}>1$). The absorption features further weakened in 2023-2025 and were marginally detectable ($\mathrm{N_H} \le 10^{20}\mathrm{cm^{-2}}$). The entire scenario is suggestive of a real-time transition of the
accretion flow (from $\lambda_{\rm Edd}>1$ to $\lambda_{\rm Edd}\sim 0.3$) during which the winds become weaker and the jet starts to form and evolve. Furthermore, both the soft X-ray $(0.3-2)$ keV and 5 GHz
radio fluxes, which increased by factors of $\sim 10$ and $\sim 60$, respectively, since 2022, have recently plateaued at elevated levels, indicating a stabilized
accretion disk, corona, and jet configuration.
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All authors Dev R. Sadaula, Sibasish Laha, Eileen T. Meyer, Onic I. Shuvo, Main Pal, Ritesh Ghosh, Matteo Guainazzi, Fabio Pacucci, Stefano Bianchi, Luigi Gallo, Rostom Mbarek, Amelia M. Hankla, Fabio La Franca, Tahir Yaqoob, Megan Masterson, Erin Kara, Missagh Mehdipour, Claudio Ricci, Javier A Garcia, Timothy R. Kallman, Ralf Ballhausen, Mitchell C. Begelman, Alexander Philippov, Suvendu Rakshit, Francesca Panessa, Ehud Behar, S. Bradley Cenko, Federica Ricci, Ilaria Villani, James N. Reeves
High Energy Astrophysical Phenomena
Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport
Youyou Li, Oscar Macias, Manuela Vecchi et al. (+1 more)
TeV
halos around Geminga and Monogem (B0656+14) reveal regions of strongly suppressed
diffusion near middle-aged
pulsars. Determining the sizes and
magnetic-field strengths of these slow-
diffusion zones is important for modelling
lepton transport and assessing their contribution to the local positron excess. The Cherenkov
Telescope Array Observatory (CTAO) will provide arcminute-scale imaging of extended gamma-ray emission. We construct two-zone
diffusion models for Geminga and Monogem with GALPROP v57, injecting electrons and positrons according to the
pulsar spin-down history and following their propagation through an evolving slow-
diffusion bubble and the ambient interstellar medium. Calibrating to HAWC and
Fermi-LAT measurements, we forward-fold the models through official CTAO instrument response functions, including realistic diffuse and instrumental backgrounds. For 50 h observations, both
halos are detected with high significance ($\sim 13$–$30,\sigma$) from either site. Under optimistic background assumptions, CTAO can distinguish changes of $\Delta\gamma_1 \simeq 0.2$ in the high-energy injection index and $\Delta B \simeq 2,\mu{\rm G}$ in
magnetic-field strength. For Monogem, compact bubbles with $R_{\rm SDZ}\approx30,{\rm pc}$ can be distinguished from extended ($\gtrsim50,{\rm pc}$) cases, although very large bubbles remain degenerate because of the finite field of view. Using an alternative
Galactic diffuse template in the fit changes detection significances and parameter sensitivities by $\lesssim10%$, indicating robustness against plausible diffuse-background mismodelling.
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All authors Youyou Li, Oscar Macias, Manuela Vecchi, Shinichiro Ando
Instrumentation and Methods for Astrophysics
Auxiliary-Channel-Assisted Cross-Talk Noise Removal in LISA Pathfinder
Hui Sun, Geyu Qin and Jibo He
LISA Pathfinder (LPF) is the technology demonstration mission for the future
Laser Interferometer Space
Antenna (LISA). Besides the science interferometric channel, LPF is equipped with numerous auxiliary channels that monitor the instrument and environment disturbances, some of which contain information correlated with noise in the science channel. In this work, we investigate cross-talk noise subtraction in LPF using a frequency-domain transfer-function approach, in which the coherence between the science channel and auxiliary channels is used to estimate and remove correlated noise. The effectiveness of this method is first validated using simulated science and auxiliary channel data with a common disturbance. The simulation shows that the subtraction performance strongly depends on the auxiliary-channel noise level, providing a practical framework for determining the auxiliary-channel noise requirement needed to achieve a desired subtraction performance. This method is then used to analyze 9 auxiliary channels in publicly available LPF telemetry data. In the cross-talk dominated frequency band from $1\times10^{-2}$ to $6\times10^{-2}\,\mathrm{Hz}$, this method achieves cross-talk noise suppression comparable to the standard fitting based subtraction. Above $6\times10^{-2}\,\mathrm{Hz}$, it further suppresses the residual noise by avoiding the introduction of auxiliary-channel readout noise associated with the fitting procedure, resulting in better performance than the standard pipeline.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Pathways and impediments towards a detection of the relic neutrino wind
Andrew J. Long, Michiru Uwabo-Niibo and Masahide Yamaguchi
A direct detection of the
cosmic neutrino background (CNB) in laboratories on Earth has been called the “holy grail” of experimental
neutrino physics, but a still more glorious prize awaits. Beyond simply detecting the presence of relic
neutrinos and measuring their flux, one may aspire to measure their energy distribution, polarization, anisotropies, temporal variation, and other properties. In this work we focus on the CNB wind, which is the approximately dipolar anisotropy in the CNB flux resulting from the relative velocity of the CNB rest frame and the lab frame. We consider a CNB detection strategy based on measuring the angular distribution of recoiling electrons at the tritium $\beta$-decay endpoint. In order to quantify the difficulty of detecting the CNB wind, we calculate the required exposure (detector mass times observation duration) for a $3\sigma$ discovery. We find that detecting the CNB wind would require an exposure that is at least $10^{5}$ times larger than what's required for detecting the CNB flux alone. Additionally if the experimental energy resolution were to exceed the
neutrino mass scale, then an exceptionally good control of systematic uncertainties would also be required. For nonrelativistic
neutrinos, the Majorana wind signal is suppressed relative to the Dirac case by the cancellation of the leading helicity-odd angular-correlation term, leading parametrically to an exposure penalty of order $(m_\nu/T_\nu)^2$.
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Astrophysics of Galaxies
Comparing gravitational wave background predictions from cosmological simulations to pulsar timing observations
Stephanie Buttigieg, Debora Sijacki, Christopher J. Moore et al. (+2 more)
The recent detection of a gravitational wave background (GWB) by
pulsar timing arrays (PTAs) may represent the first evidence of gravitational waves from merging supermassive black hole binaries, opening a new window on the low-frequency end of the gravitational wave spectrum. These inspiralling binaries are expected to dominate the signal, although most theoretical models seem to predict somewhat lower amplitudes than what is observed. We present the first comprehensive statistical framework to quantify the tension between PTA measurements and theoretical predictions, maximising the constraining power of current data and allowing straightforward application to future PTA
datasets. We further investigate how different assumptions in the observational inference, particularly the use of a power-law model for the GWB spectrum, can bias tension estimates and potentially overstate discrepancies with theory. We apply our framework to compare predictions from the FABLE cosmological simulation with the NANOGrav 15-year
dataset. For our fiducial black hole population, we find tension values of $1\sigma$-$2.5\sigma$, indicating no statistically significant disagreement with the observations. We further explore physically motivated modifications to the merging black hole population, guided by electromagnetic observations and theoretical uncertainties. In particular, scenarios with boosted black hole masses at high
redshift and more equal-mass mergers substantially increase the predicted GWB amplitude, improving agreement with PTA data. Finally, we investigate the high-mass end of the black hole mass function and the impact of finite simulation volume. We find that the $(100 \, \mathrm{cMpc} \, h^{-1})^3$ FABLE box is sufficient to robustly predict the GWB signal at the most constraining frequency.
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All authors Stephanie Buttigieg, Debora Sijacki, Christopher J. Moore, Martin A. Bourne, Alberto Sesana
Solar and Stellar Astrophysics
The Recurrent Nova TCrB: A Method for Predicting the Next Eruptive Event in Nova Cycles
Stefano Sello
The symbiotic recurrent nova (SyRNe) TCrB (T-Coronae Borealis) is perhaps the most famous example of the group of known four symbiotic nova systems, for which at least two previous nova eruptions are known and accurately recorded: in 1866 and 1946. B.E. Schaefer (2023) has identified the dates of two other previous eruptive events: in 1787 and 1217. Its peak magnitude V was found to be 2.50+-0.10, making it the brightest of its class. In its quiescent phase, TCrB is the brightest of all known novae, with a mean magnitude of 9.8. Careful studies, especially photometric ones, have led to different predictions for the next nova eruption, taking into account the recurrence times extrapolated from previous eruptions, which an average value about 80 years. Schaefer, in particular, has produced various forecasts, including one made in 2023 based on B and V light curves for the period: 1842-2022, which predicts the next nova eruption should occur in 2025.5+-1.3 and is therefore still valid today. Using the Schaefer's remarkable work in accurately determining the key physical parameters that drive the dynamics of the TCrB symbiotic system, we propose here a new semi-empirical method to derive the variations in the nova recurrence time, Trec, and thus obtain a forecast estimate for the next eruption for the date: 26-Feb-2027, which is currently compatible and consistent with the observed behavior and would also justify the supposed "delay" for the next event of this nova as commented by various authors.
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Earth and Planetary Astrophysics
Planetary-Mass Exosatellite Detected Around the Substellar Companion of a Star
Kevin Hoy, Alice Zurlo, Pablo A. Peña R. et al. (+10 more)
Despite more than 6000
exoplanets being discovered to date, no satellite orbiting an
exoplanet, an exomoon, has ever been confidently detected. While there are some candidates, they lack clear and convincing confirmation and remain controversial. Beyond the innate value of discovering new types of objects in the Universe, satellites can help give key insights into
planet formation mechanisms and the dynamical
evolution histories of their systems. In this work, we show strong evidence for the existence of satellites orbiting the directly-imaged brown
dwarf companion CD-35 2722 B. We have applied radial velocity analysis, the same technique used to discover the first
exoplanet around a
Solar-type
star, on spectra of this brown
dwarf obtained with VLT/CRIRES+. We have found what appears to be the periodic signal induced by at least one orbiting satellite. This is the first time this technique has successfully produced evidence of satellites. We produce a strong detection of a satellite candidate with a minimum mass of 0.743 Jupiter masses and an orbital period of 169 days. The best-fitting model also includes a second, closer satellite with minimum mass of 0.277 Jupiter masses and a period of 87 days, although these parameters for this smaller satellite candidate are less certain. These periods would place them very near a 2:1 mean motion resonance, a phenomenon also seen in the Galilean moons of Jupiter. The discovery of these satellites will unlock many future avenues of study, including
planet formation, system dynamics, and even the search for life in the Universe.
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All authors Kevin Hoy, Alice Zurlo, Pablo A. Peña R., Jana Köhler, Silvano Desidera, Raffaele Gratton, Cecilia Lazzoni, Simon Petrus, Florian Rodler, Jonathan Smoker, Valentina D'Orazi, Ilaria Carleo, Ilaria Giovannini
High Energy Astrophysical Phenomena
Spectropolarimetric detection of baryonic mass loading in a transient relativistic jet: application to the black hole X-ray binary Swift J1727.8$-$1613
A. K. Hughes, R. P. Fender, G. R. Sivakoff et al. (+10 more)
Radio emission during X-ray binary outbursts is dominated by synchrotron radiation from relativistic jets, but is usually studied through total-intensity diagnostics such as flux density, spectra, variability, and proper motion.
Radio spectropolarimetry provides a complementary probe of the magneto-ionic
plasma through Faraday rotation and depolarisation. When the Faraday rotating material is local to the source, these effects can constrain the jet
plasma composition and mass content, but this approach is rarely applied to transient jetted sources. We present MeerKAT L-band spectropolarimetry of the black hole X-ray binary \src\ during its 2023 outburst, focusing on the brightest
radio flaring interval, when relativistic jets were being launched intermittently. Using multiple spectropolarimetric techniques, we identify transient Faraday-complex structure coincident with the major
radio flares. The close temporal association with the flaring activity, together with the stability of the foreground Faraday screen, favours an origin local to the jet rather than in the ISM or in a separate local screen external to the emitting
plasma. Since internal Faraday rotation is suppressed in a pure electron–positron
plasma, the data favour a dominant electron–
proton component. Interpreting the characteristic Faraday thickness as internal rotation, and anchoring the
magnetic-field and size scales with synchrotron self-absorption arguments, we infer a characteristic Faraday-rotating mass of order $M_{\rm rot}\sim10^{21}{\rm\,g}$, corresponding to only a small fraction, $f_{\rm rot}\sim10^{-3}$, of the accreted mass available during the
flare. These results show that time-domain spectropolarimetry can turn transient Faraday complexity into a diagnostic of jet composition, mass loading, and
plasma evolution in X-ray binary outbursts, and potentially other transient jetted sources.
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All authors A. K. Hughes, R. P. Fender, G. R. Sivakoff, F. J. Cowie, I. Heywood, J. H. Matthews, K. Savard, F. Carotenuto, T. D. Russell, C. M. Wood, M. C. Baglio, S. Corbel, S. E. Motta
Astrophysics of Galaxies
Emergence of high-mass stars in complex fiber networks (EMERGE) VI. Turbulence dissipation and the formation of dense fibers
F. Bonanomi, A. Hacar, A. Socci et al. (+1 more)
(Abridged) The turbulent cascade naturally generates a hierarchy of filaments within molecular clouds, with fibers suggested to be the first (tran-)sonic components formed out of it. We aim to investigate the diffuse gas kinematics and its interaction with the dense gas composing fibers using HNC as molecular tracer. We use high-resolution (4.5" or 2000au) large-scale ALMA+IRAM-30m mosaics to survey five
star-forming regions in Orion, as part of the EMERGE Early ALMA Survey covering a wide range of
stellar activity, cloud morphology, and evolutionary stages. We observe our targets in HNC(1-0) as probe of diffuse gas in the regions and compare it to the N2H+(1-0) emission tracing the dense gas. Our high resolution observations reveal that HNC traces lukewarm, diffuse ($\sim5\times10^{21}$ cm$^{-2}$) material around dense fibers. The properties of the diffuse gas appear to be similar across our sample, despite the wide range of different environments. Compared to the quiescent and subsonic gas inside fibers, the diffuse gas is, however, more turbulent ($M_\text{s}=2.9$). Understanding the dissipation process is crucial to mark the transition between the dense subsonic gas and diffuse turbulent material occurs. We investigated the
turbulence dissipation through the statistical analysis of the HNC velocity gradients. We identified high-shear regions showing higher gradients with $\nabla V_{lsr}\ge10~\mathrm{km~s^{-1}~pc^{-1}}$ concentrated in small features of 0.1-0.3 pc in size located near the dense gas. These high-shear structures appear to be major contributors of the
turbulence dissipation in our targets. Our results suggest that in Orion the transition to coherence occurs at the fiber level, as suggested by the
turbulence being effectively dissipated before the formation of cores and during the formation of these first dense structures.
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All authors F. Bonanomi, A. Hacar, A. Socci, S. Heigl
Instrumentation and Methods for Astrophysics
Commensal image plane transient search methods with the SKAO
Alex Andersson, Dougal Dobbie, Natasha Hurley-Walker et al. (+7 more)
This chapter outlines the key, state of the art, techniques required to conduct commensal image plane transient searches. Using significant experience and expertise from conducting transient searches with the SKA pathfinders, we have developed efficient fast imaging strategies, automated transient detection pipelines, determined careful filtering techniques to avoid artifacts, and identified the most useful triggered reprocessing tools. Using these strategies, we will be ideally placed to optimally and reliably detect transient sources from commensal image plane transient surveys. The tools and methods presented in this chapter can be used for all SKA-Mid and SKA-Low array deployments from AA* inclusive.
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All authors Alex Andersson, Dougal Dobbie, Natasha Hurley-Walker, Hao Qiu, Kaustubh Rajwade, Antonia Rowlinson, Iris de Ruiter, Fabian Schüssler, Oleg M. Smirnov, Ben Stappers
Solar and Stellar Astrophysics
Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum
Hugh Hudson, Anne-Marie Broomhall, Lyndsay Fletcher et al. (+5 more)
Convectively driven motions in the
solar photosphere can generate broadband Doppler variability across the chromosphere, transition region and corona. Here we investigate this variability using "Sun-as-a-
Star" observations from the Extreme Ultraviolet Variability Experiment (EVE) aboard the
Solar Dynamics Observatory, constructing high signal-to-noise Doppler power spectra by incoherently averaging spectra from 3-hour sequences of the centroid wavelengths of emission lines that span wavelengths 35-104 nm. The spectra reveal a broad power-spectral continuum with two "Harvey" components, one of which extends to the Nyquist frequency at 50 mHz with a steep power-law tail. All emission lines have substantial power both above and below the nominal acoustic cutoff frequency at 5 mHz, but none of the power spectra show maxima corresponding to p-mode or chromospheric 3-minute oscillations. Lines formed in the corona, as compared with those of the chromosphere/transition region, have substantially less Doppler amplitude in the Harvey spectrum associated with granulation-scale convection. Based on the observed continuum, there is no evidence (in any of the 26 lines studied) for Kolmogorov
turbulence, which predicts a flat continuum component with Doppler variance <v^2>~f^(-5/3) as a function of frequency f. The total inferred RMS velocities (>0.1 mHz) are roughly consistent with coronal microturbulence estimates from excess line widths. These observations provide the first clear detection of Sun-as-a-
star EUV Doppler variability above ~10 mHz and demonstrate the potential of full-disk EUV spectroscopy to probe turbulent energy transport throughout a
stellar atmosphere.
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All authors Hugh Hudson, Anne-Marie Broomhall, Lyndsay Fletcher, David Graham, Sargam M. Mulay, Chris Osborne, Kirsty Williamson, Graham Woan
High Energy Astrophysical Phenomena
An 18-year Fermi-LAT stacking limit on GeV $\gamma$-ray emission from particle-accelerating colliding-wind binaries
Youngwan Son
The wind-collision regions of massive colliding-wind binaries (CWBs) accelerate relativistic particles, as shown by their non-thermal
radio synchrotron and, in $\eta$ Car, hard X-ray emission. Whether CWBs emit GeV $\gamma$rays as a population is unknown: only $\eta$ Car is unambiguously detected by the
Fermi Large Area
Telescope (LAT). We analyze 17.8 yr of
Fermi-LAT data above 1 GeV (where the sharp point-spread function controls plane confusion) at the 61 confirmed (list A) particle-accelerating CWBs (PACWBs) of De Becker & Raucq, using a two-dimensional (
photon index $\times$ flux) likelihood scan against 200 control fields matched in latitude, local source density, and diffuse intensity. Removing systems whose lines of sight coincide with bright catalogue $\gamma$-ray sources leaves a clean, mutually isolated sample of 6, whose stack is consistent with the control-field null ($p=0.83$): no evidence for collective GeV emission. Retaining those systems instead yields a spurious $\gtrsim3.5\sigma$ excess from chance catalogue coincidences, a caveat for
Galactic-plane stacking. The resulting 95% limit on the mean per-source flux, $F(>1\,\mathrm{GeV})\lesssim1.1\times10^{-11}~\mathrm{ph\,cm^{-2}\,s^{-1}} (\Gamma=2)$, implies a $\gamma$-ray production efficiency $\eta=L_\gamma/L_{\rm wind}\lesssim4\times10^{-6}\,(d/\mathrm{kpc})^2$, about two orders of magnitude below $\eta$ Car at the sample's median distance. A representative single-zone model then bounds the electron acceleration efficiency in CWB wind-collision regions unless their
magnetic field is comparable to or above the
magnetic-
photon equipartition value. Among the high-latitude systems accessible to a clean stack, $\eta$ Car thus appears to be a singular object rather than the brightest member of an emerging population.
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Astrophysics of Galaxies
Lyman-alpha haloes in the aftermath of reionisation
Daniil Smirnov, Lutz Wisotzki, Tanya Urrutia et al. (+8 more)
We present a comparative study of Ly$\alpha$
haloes (LAHs) around low-luminosity (L$_{\mathrm{Ly}\alpha}\lesssim 10^{42}$ erg s$^{-1}$) Ly$\alpha$-emitting
galaxies (LAEs) at very high
redshifts $z\geq6$ and a reference sample at $z\sim 3$ covering a similar Ly$\alpha$ luminosity and host
galaxy stellar mass range. Using data from the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO VLT, we extracted the samples such that at the different
redshifts we obtain the same intrinsic surface brightness sensitivity, accounting for cosmological dimming. We detect extended Ly$\alpha$ emission around 6 out of 18 high-$z$ LAEs in the MUSE eXtremely Deep Field (MXDF), more than doubling the number of known such objects at $z\geq6$. We obtain an only slightly higher individual LAH detection fraction of 40% among the lower
redshift comparison sample. Yet the typical exponential scale lengths at $z\geq6$ are three times smaller than those at $z\sim3$. Stacking the LAEs with undetected
haloes gives again drastically different results for the two samples, with a highly significant
halo detection at $z\sim 3$ but no trace of extended Ly$\alpha$ emission at $z\geq6$. We also find the Ly$\alpha$ spectral line widths of the high-$z$ sample to be $\sim$2.5 smaller in comparison to the lower
redshift objects. We discuss the potential mechanisms driving such strong changes. In a reionisation-driven scenario the higher neutral fraction in the intergalactic and circumgalactic media might lead to substantial scattering losses of escaping Ly$\alpha$ radiation, leaving detectable only emission from the vicinity of the
star-forming regions. In an alternative scenario the LAH properties might be linked more closely to the
evolution of their host
galaxies than previously thought.
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All authors Daniil Smirnov, Lutz Wisotzki, Tanya Urrutia, John Pharo, Ramona Augustin, Yucheng Guo, Daria Kozlova, Haruka Kusakabe, Jorryt Matthee, Ismael Pessa, Joop Schaye
Earth and Planetary Astrophysics
A cornucopia of null results: A statistical analysis of fireballs reported to the American Meteor Society
Althea V. Moorhead
In March 2026, the American Meteor Society announced that a "surge" of large fireballs had been reported to their website in the first quarter of the year, and that these fireballs had certain characteristics (radiant clustering and reports of delayed sound). We find this data set to be an excellent use case for Poisson regression, which, in our opinion, is underutilized in meteor astronomy. This report serves as a brief primer on Poisson regression and related statistical techniques as well as an analysis of AMS fireball counts. We find that the number of events reported in early 2026 is in line with the overall pattern of activity. We also find little evidence of the "February fireballs" phenomenon.
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Solar and Stellar Astrophysics
DSLR times of minima of selected eclipsing binaries
M. Kamenec, P. Gajdoš and Š. Parimucha
We present a collection of eclipse timings of eclipsing binary
stars obtained over the extended time interval 2014-2024. In all observations, a DSLR camera was used as the detector. The presented
dataset contains 250 previously unpublished minima of 86 eclipsing binary systems obtained at three observing sites. The minima were determined from calibrated light curves using the phenomenological modelling approach, and their uncertainties were estimated by bootstrap resampling. The presented measurements extend the available timing coverage of the observed systems and may contribute to future studies of orbital period variations and other long-term phenomena in eclipsing binaries.
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Cosmology and Nongalactic Astrophysics
Alleviating the Hubble Tension with Smooth Sign-Switching Dark Energy: Full CMB Constraints with DESI and PantheonPlus
Mariam Bouhmadi-López, Hsu-Wen Chiang and Beñat Ibarra-Uriondo
Sign-switching dark energy has recently been proposed as a minimal modification of the late-time expansion history aimed at alleviating tensions within the standard cosmological model. In this work, we investigate ECDM, a smooth realisation of this scenario, with the dark energy density gradually transitioning from a negative to a positive value. We develop a consistent formulation of the perturbation equations that remains well behaved even when the dark energy equation-of-state parameter diverges during the transition. We confront the model with a comprehensive set of cosmological observations, including
cosmic microwave background measurements from Planck 2018, ACT DR6 and SPT-3G,
baryon acoustic oscillation measurements from DESI DR2, Type Ia
supernova distances from Pantheon+, and local Hubble constant measurement of SH0ES. The inclusion of perturbations allows us to assess the impact of the model on structure growth and CMB anisotropies, providing a more thorough test of sign-switching dark energy. Our results show that this class of models is fully compatible with current precision cosmological observations while alleviating the Hubble tension and providing a compelling modification of the late-time dynamics of the Universe.
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Instrumentation and Methods for Astrophysics
The Atacama Large Aperture Submillimeter Telescope (AtLAST): enabling large-scale sub-mm science beyond 2030
Claudia Cicone, Tony Mroczkowski, Evanthia Hatziminaoglou et al. (+38 more)
AtLAST is designed to be the largest (sub-)mm single-dish astronomical observatory and the first
climate-neutral modern research infrastructure. It offers a unique combination of large aperture (50 m), large field of view (>1 deg), fast scanning speed (up to 3 deg/s), and high surface accuracy (20micron nighttime half wavefront error) that allows >=50% Ruze efficiency up to 1 THz. The design features a rocking chair mount with an active main reflector surface, a high precision closed-loop metrology system, and the space to house six major instruments. Instruments will be periodically updated as spectroscopic focal plane array, detector, coherent amplifier, and
semiconductor technologies used in readout and backend electronics will advance over the next decades. AtLAST will be a multi-purpose facility that will produce transformational results in nearly all fields of Astrophysics, such as Astrochemistry,
Galactic and Extragalactic Astronomy, Cosmology, Planetary science,
Stellar and
Solar Physics, High energy astrophysics, and Time domain astronomy. Its unrivalled throughput of 6170 m^2 deg^2 will enable wide-field unbiased surveys. These will overcome extragalactic confusion noise and enable the detection of normal
galaxy populations out to z=7. AtLAST will reveal and characterise the missing
baryons in the Universe, by mapping the elusive, low surface brightness gas within and around
galaxies across
cosmic time. AtLAST will be the first green off-grid observatory, powered by a bespoke renewable energy system and reusing its braking energy thanks to a cutting-edge energy recovery system. By sharing surplus power and technological know-how with local communities, AtLAST will contribute to energy justice in Chile. AtLAST's new bold
vision of a sustainable pursuit of breakthrough astronomy is an exceptional opportunity to shape the future of scientific research infrastructures. [abridged]
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All authors Claudia Cicone, Tony Mroczkowski, Evanthia Hatziminaoglou, Matthias Reichert, Sabrina Sartori, Amelie Saintonge, Pamela Klaassen, Francisco Montenegro-Montes, Martin Timpe, Aleksej Kiselev, Danilo Koeltzsch, Carlos De Breuck, Pamela Pizarro, Eelco van Kampen, Tinus Stander, Dirk Muders, Yiqing Song, Kotaro Kohno, Sergio Poppi, Yoichi Tamura, Stefan Thoms, Hans Kaercher, Sven Wedemeyer, Alessandro Attoli, Stephen Molyneux, Bruno Silva, Guillermo Valenzuela Venegas, Paola Velasco-Herrejon, Marianne Zeyringer, Yogesh Kumar Yadav, Mark Booth, Carlos Alberto Duran, Lars-Ake Nyman, Serni Ribo, Francisca Kemper, Manuel Groh, Leandro Aggio, Mathias Hudoba de Badyn, Benjamin Magnelli, Mats Kirkaune, Akira Endo
Instrumentation and Methods for Astrophysics
In-Band Scattering and Absorption of Infrared Blocking Foam Filters for Millimeter-wave Cameras
Alex Thomas, Bugao Zou, Shreya Sutariya et al. (+11 more)
Expanded closed-
cell polymer foams are widely used as thermal infrared (IR) blocking filters in millimeter-wave cameras, particularly for
Cosmic Microwave Background observations. Precise knowledge of their millimeter-wave properties is essential for optimizing sensitivity. We present broadband (150 GHz - 2 THz) transmittance spectroscopy of Styroace-II and several Zotefoam filters, fitting their spectra with a radiative transfer model incorporating dielectric absorption and Rayleigh, Mie, and higher-order scattering. For a typical 5~cm thick filter stack at 280~GHz, Styroace-II exhibits ${\sim}10\%$ scattering with absorption estimated as ${\lesssim}5\%$ by effective-medium theory, while Zotefoam HD30 offers superior performance at ${\sim}3\%$ scattering and absorption likewise bounded to ${{\lesssim}0.3\%}$. Each model component is constrained at the ${\sim}0.1\%$ transmittance level for millimeter wavelengths. We observe batch-to-batch scattering variability of up to 2 percentage points in foams with multiple tested batches. Less commonly used Zotefoam formulations (LD15 and LD24) can further reduce in-band scattering to ${<}1\%$ while maintaining negligible in-band absorption and likely comparable IR blocking due to shared polyethylene absorption features and similar
cell sizes. Based on this work, a filter constructed from the best measured LD24 batch has replaced the Styroace-II filter in a Simons Observatory 220/280 GHz Small Aperture
Telescope.
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All authors Alex Thomas, Bugao Zou, Shreya Sutariya, Yuhan Wang, Gabriele Coppi, Samuel Day-Weiss, Nicholas Galitzki, Kathleen Harrington, Erin Healy, Claire Lessler, Aashrita Mangu, Jeffrey McMahon, Michael D. Niemack, Edward J. Wollack
Cosmology and Nongalactic Astrophysics
Spectroscopic redshifts of selected flat-spectrum radio sources I
Dmitry Blinov, Alberto Floris, Andreas Zezas et al. (+5 more)
We present the first results of a spectroscopic campaign carried out as part of the Search for Milli-Lenses (SMILE) program, which aims to constrain the prevalence of gravitational lens systems on milli-arcsecond angular scales (milli-lenses) using high-resolution Very Long Baseline Interferometry (VLBI) imaging. The SMILE parent sample contains ~ 5000
radio-loud active
galaxies, selected as a flux-limited, complete subsample of CLASS (The
Cosmic Lens All-Sky Survey) sources. We compiled
redshift information for the full sample from multiple literature and catalog sources and found that 491 sources have no available
redshift estimate, either spectroscopic or photometric. A further 948 sources have only photometric
redshifts, many of which show substantial discrepancies between catalogs. Reliable
redshifts are essential for VLBI
radio-source studies because they convert angular measurements into physical linear scales, enable estimates of intrinsic luminosities and jet kinematics, and allow robust cosmological and population studies. To address this key limitation for
lensing and population studies, we initiated a dedicated spectroscopic campaign to secure reliable
redshifts for as many targets as possible. This paper focuses on the brightest sources in the SMILE sample. We report newly determined spectroscopic
redshifts for 6 targets out of 15 observed with the Skinakas 1.3 m
telescope.
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All authors Dmitry Blinov, Alberto Floris, Andreas Zezas, Carolina Casadio, Elias Kyritsis, Valentina Missaglia, Vangelis Pantoulas, Avinash Kumar