High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Asymptotic Freedom and Vacuum Polarization Determine the Astrophysical End State of Relativistic Gravitational Collapse: Quark–Gluon Plasma Star Instead of Black Hole
Herman J. Mosquera Cuesta, Fabián H. Zuluaga Giraldo, Wilmer D. Alfonso Pardo et al. (+3 more)
A general relativistic model of an astrophysical hypermassive extremely magnetized ultra-compact self-bound
quark–
gluon plasma object that is supported against its ultimate gravitational implosion by the simultaneous action of the
vacuum polarization driven by nonlinear electrodynamics (NLED: light-by-light scattering) and the
quantum chromodynamics (QCD) asymptotic freedom, is presented. These QCD
stars can be the final figures of the
equilibrium of collapsing
stellar cores. Post-
supernova fallback material pushes the nascent remnant beyond its stability to collapse into a hybrid hypermassive
neutron star (HHMNS). Hypercritical
accretion can unbind the whole HHMNS's
baryons to spontaneously break away color confinement, powering a first-order
hadron-to-
quark phase transition to a sea of ever-freer
quarks and
gluons. This core is hydro-stabilized by the steady, endlessly compression-admitting asymptotic freedom state, possibly via
gluon-mediated enduring exchange of color charge among bound states. The nonlinear TOV equation indicates the occurrence of hypermassive QGP/QCD
stars with a wide mass spectrum ($0\lesssim$ M$^{\rm{QGP}}_{\rm{Star}}\lesssim$\,7\,M$_\odot$ and beyond), for
star radii ($0\lesssim R^{\rm{QGP}}_{\rm{Star}}\lesssim 24$\,km and beyond) with B-fields ($10^{14} \leq$ B$^{\rm{QGP}}_{\rm{Star}} \leq 10^{16}$\,G and beyond). Such QCD
stars can emulate what the true black holes are supposed to gravitationally do in most astrophysical settings. This color
quark star could be found through a search for its eternal “yo-yo” state gravitational-wave emission, or via
lensing phenomena like gravitational rainbows, as in this scenario it is expected that the light deflection angle, directly influenced by the larger effective mass/radius and
magnetic field of the deflecting object, increases as the incidence angle decreases for impact parameter lower values.
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All authors Herman J. Mosquera Cuesta, Fabián H. Zuluaga Giraldo, Wilmer D. Alfonso Pardo, Edgardo Marbello Santrich, Guillermo U. Avendaño Franco, Rafael Fragozo Larrazabal
Instrumentation and Methods for Astrophysics
aurel: A Python package for automatic relativistic calculations
Robyn L. Munoz, Christian T. Byrnes and Will J. Roper
aurel is an open-source Python package designed to automatically calculate relativistic quantities. It uses an efficient, flexible and user-friendly caching and dependency-tracking system, ideal for managing the highly nonlinear nature of general relativity. The package supports both symbolic and numerical calculations. The symbolic part extends SymPy with additional tensorial calculations. The numerical part computes a wide range of tensorial quantities, such as
curvature, matter kinematics and much more, directly from any spacetime and matter data arrays using finite-difference methods. Inputs can be either generated from analytical expressions or imported from Numerical Relativity (NR) simulations, with helper functions provided to read in data from standard NR codes. Given the increasing use of NR, aurel offers a timely post-processing tool to support the popularisation of this field.
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High Energy Astrophysical Phenomena
Unveiling BLR Structure in AGN with High Resolution X-Ray Spectra: An Analytic Approach to Wind Emission Line Profiles
Scott Hagen, Chris Done, Gabriele A. Matzeu et al. (+1 more)
XRISM has provided an unprecedented view of the emission and absorption lines in the X-ray. Notably, early results showed significant complexity to the Fe-K$\alpha$ line profile in AGN, with clear contributions from at least three emitting structures: an inner disc, intermediary broad line region (BLR) scale material, and an outer
torus. This poses a new challenge for the modelling of the emission lines, as while fast sophisticated models exist for disc line-profiles, large scale-height material is typically much more complex. In this paper we aim to address this gap, by building a fully analytic model for the emission line profiles from a wind, aimed towards BLR scale material, motivated on previous reverberation studies suggesting a wind on the inner edge of the BLR. Our approach gives a physically motivated, yet computationally fast, model for the intermediary component to the Fe-K$\alpha$ complex seen in the XRISM data. We demonstrate our model on the XRISM observations of NGC 4151 from the performance verification phase, showing that it gives a good description of the data, with physically reasonable parameters for BLR scale material. We also show that our model naturally gives the smooth line profile seen in the data, due to the large spatial extent of a wind. Finally, we make our model code public to the community, and name it xwind.
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All authors Scott Hagen, Chris Done, Gabriele A. Matzeu, Hirofumi Noda
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Monica Rincon-Ramirez, Nathan K. Johnson-McDaniel, Eugenio Bianchi et al. (+3 more)
The final state of a binary black hole merger is predicted with high precision by numerical relativity, but could there be a simple thermodynamic principle within general relativity that governs the selection of the remnant? Using post-Newtonian relations between the mass M (including the binding energy) and angular momentum J of quasi-circular, nonspinning binaries, we uncover a puzzling result: When the binary's instantaneous M and J are mapped to those of a hypothetical Kerr black hole, the corresponding
entropy exhibits a maximum during the
evolution. This maximum occurs at values of M and J strikingly close to those of the final remnant predicted by numerical relativity. Consistent behavior is observed when using the relation between M and J obtained from numerical relativity
evolution. Although this procedure is somewhat ad hoc, the agreement between the masses and
spins of the final state obtained from numerical relativity and the results of this maximum
entropy procedure is remarkable, with agreement to within a few percent when using either post-Newtonian or numerical relativity results for M and J. These findings allow us to propose an
entropy maximization
conjecture for binary black hole mergers, hinting that thermodynamic principles may govern the selection of the final black hole state.
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All authors Monica Rincon-Ramirez, Nathan K. Johnson-McDaniel, Eugenio Bianchi, Ish Gupta, Vaishak Prasad, B. S. Sathyaprakash
Cosmology and Nongalactic Astrophysics
How isotropic is dark energy?
Richard A. Battye and Adam Moss
Tensions in late-time expansion data have renewed interest in models beyond $\Lambda$CDM. We ask: how isotropic must dark energy be? Working in Bianchi~I, we allow time-dependent anisotropic stress and introduce a parameterisation that enforces a vanishing line-of-sight integral of the shear, thereby satisfying the CMB ISW quadrupole bound by construction. Using Pantheon+SH0ES SNe together with DESI BAO distances, single-bin (constant) and five-bin anisotropic models improve the fit over $w$CDM by $\Delta(-2\ln L_{\rm iso})=14.8$ and $26.6$ respectively, but both violate the quadrupole constraint. In contrast, a five-bin constrained model achieves $\Delta(-2\ln L_{\rm iso})=15.4$ while remaining compatible with the quadrupole limit. The fit improvement arises from two sources: capturing directional structure in the Pantheon+ SNe data, and partially alleviating the tension between the SH0ES $H_0$ value and DESI BAO distances.
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Solar and Stellar Astrophysics
Conversion Layer Controls the Evolution of Magnetic Deflections Near the Alfven Surface
Dominic Payne, Mojtaba Akhavan-Tafti, Joshua Goodwill et al. (+10 more)
We examine the statistics of Alfvenic deflections in both sub-Alfvenic and super-Alfvenic
solar wind with particular focus on a common parameter that underlies the definition of switchbacks: the
magnetic deflection angle. Our findings are in general agreement with earlier studies that suggest
magnetic deflection angles > 90 degrees are very unlikely to occur in sub-Alfvenic regimes. We find that their upper limit exhibits an identifiable trend with the Alfven Mach number Ma, suggesting that gradual steepening of Alfvenic deflections with increasing Ma is a plausible mechanism controlling deflection angles in the young
solar wind. Further analysis reveals that large velocity fluctuations tend to be important in the largest sub-Alfvenic
magnetic deflections with increasing contributions from the parallel component very close to Ma = 1, while virtually no
magnetic deflections in the super-Alfvenic regime exhibit such large velocity perturbations. We also determine the local ratio of radial Poynting flux SR to kinetic energy flux KR and find that large sub-Alfvenic deflection angles tend to be dominated by SR, while super-Alfvenic deflections are eventually dominated by the KR associated with the radial
solar wind flow. Our results show that within the vicinity of the Alfven surface (where Ma = 1), there is a critical region of parameter space within which velocity deflections approach the Alfven velocity and KR/SR is close to unity. We refer to this region (where | log10(Ma)| < 0.2) as the conversion layer. The conversion layer may play a significant role in the
evolution of
magnetic defections by providing the medium for converting
magnetic energy to particle energy and likely driving the formation of
magnetic switchbacks in super-Alfvenic
solar wind.
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All authors Dominic Payne, Mojtaba Akhavan-Tafti, Joshua Goodwill, Samuel Badman, Riddhi Bandyopadhyay, Subash Adhikari, William Matthaeus, Gary Zank, Chen Shi, Michael Stevens, Roberto Livi, Yeimy Rivera, Kristoff Paulson
High Energy Astrophysical Phenomena
Testing the Association of Supermassive Black Hole Infrared Flares and High-energy Neutrinos
Megan Wang, Christos Panagiotou, Kishalay De et al. (+3 more)
The physical origin of the observed
cosmic neutrinos remains an open question and the subject of active research. While matter
accretion onto supermassive black holes is long thought to accelerate particles to high energies, it has recently been suggested that
tidal disruption events, and
accretion flares in general, with prominent IR echoes can account for a fraction of the diffuse high-energy
neutrino signal. Motivated by this result, we compile a sample of nearby
accretion flares detected in the NEOWISE survey featuring strong IR echoes, and we cross-match it with the latest catalog of
neutrino alerts, IceCat-1. We recover only a single spatial coincidence between the two catalogs, consistent with a chance coincidence. We find no temporal and spatial coincidences between the two samples, which, given the properties of our sample, appears to challenge previous conclusions. We discuss the physical implications of our results and potential future explorations.
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All authors Megan Wang, Christos Panagiotou, Kishalay De, Erin Kara, Megan Masterson, Foteini Oikonomou
Solar and Stellar Astrophysics
Editorial: Mass and Angular Momentum Transport of Rapidly Rotating Hot Stars
P. A. Scowen, Carol E. Jones, René D. Oudmaijer et al. (+2 more)
This dedicated journal collection will present and discuss a variety of science cases that can be used to extend our knowledge of massive
stars and the influence of their rapid rotation on their subsequent
evolution. The aim is to build understanding of this pivotal class of
stellar objects that provides the energy and processed material driving
galactic evolution and setting the stage for subsequent
star and
planet formation. This collection of papers offers a unique discussion of physical factors that are driven by rapid rotation and whose influence directly impact the
evolution and end-of-life state of massive
stars. They are presented together to give the reader a perspective that only the ensemble can provide instead of a single paper. We hope that we are successful in our goal of shedding light on the scope and outcome of this important facet of massive
star physics.
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All authors P. A. Scowen, Carol E. Jones, René D. Oudmaijer, Jamie Lomax, Jeremy J. Drake
Cosmology and Nongalactic Astrophysics
Tensions in Cosmology: Interpreting Them Through Inhomogeneous Models
Valerio Marra
We review a subset of the current tensions affecting the standard $\Lambda$CDM cosmological model, emphasizing the role of chronic systematics and significance inflation in shaping their interpretation. As a unifying framework, we consider the spherically symmetric inhomogeneous $\Lambda$LTB model and use it as a set of "glasses" through which to reinterpret the Hubble, dipole, and dark-energy tensions. Large-scale spatial gradients in this model introduce anisotropic expansion and position-dependent observables, allowing local estimates of $H_{0}$ to shift, dipolar signatures to arise, and an apparently evolving dark-energy equation of state to be mimicked without invoking genuinely dynamical dark energy. We discuss how these effects are constrained once the full
supernova, CMB, and large-scale-structure data sets are included, and argue that it remains unclear whether any single $\Lambda$LTB configuration can simultaneously account for all major anomalies. More broadly, we highlight that cosmology currently lacks a widely accepted baseline model that is both theoretically well founded and capable of accommodating the Hubble and dark-energy tensions, leaving us without a true concordance framework for
forecasting future surveys.
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High Energy Astrophysical Phenomena
High energy neutrinos from pulsar-powered optical transients: LFBOTs as potential origin of the KM3NeT event KM3-230213A
Mainak Mukhopadhyay and Shigeo S. Kimura
Recently, the KM3NeT Collaboration reported the detection of an ultra-high energy ($\sim 220$ PeV)
neutrino event, KM3-230213A. In this work, we perform a detailed investigation into whether this event could originate from the diffuse
neutrino flux produced by a class of
pulsar-powered optical transients. In particular, we consider populations of ordinary
supernovae (SNe), super-luminous
supernovae (SLSNe), and luminous fast blue optical transients (LFBOTs) with a newly formed magnetar as the central engine. We discuss both the thermal electromagnetic and non-thermal
neutrino emission from such sources. We scan the parameter space of the dipolar
magnetic field strength and the initial
spin period to determine characteristic optical emission properties and lightcurve timescales of these transients. Additionally, our scan identifies which classes of these transients can reproduce the required diffuse flux level and
neutrino energies. Combining our results, we conclude that a diffuse
neutrino flux from a population of LFBOTs can explain the KM3NeT event. Therefore,
pulsar-powered optical transients may serve as promising sources for the current and upcoming high-energy and ultra-high energy
neutrino telescopes.
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Astrophysics of Galaxies
Fast, dust-poor outflows in the local candidate dual AGN MCG-03-34-64 observed with VLT/ERIS
I. Lamperti, F. Mannucci, E. Bertola et al. (+28 more)
We present VLT/ERIS IFU J-band observations of MCG-03-34-64, a nearby (z = 0.0167) Seyfert
galaxy hosting a candidate dual AGN system with a separation of ~100 pc between the
nuclei. The observations cover, among others, the HeI1.083um, [FeII]1.257um and Pa$\beta$ emission lines, over a FoV of 3"x3"(~1x1 kpc$^2$). We analyse the ionised gas kinematics and identify two regions with enhanced velocity dispersion (W80~1500 km/s), suggestive of fast outflowing gas, spatially coincident with the position of the two candidate active
nuclei. The spectra of the two
outflows show a prominent blueshifted wing with velocities vmax ~ -1700 km/s corresponding to the highest 2-5 percentiles of samples of local AGN with similar bolometric luminosities. For the ionised phase of the two
outflows, we derive comparable masses of $(4\pm1)\times 10^5$ $M_{\odot}$ and mass
outflow rates of $20\pm5$ $M_{\odot}$/yr. The two distinct
outflows could be associated with the two
nuclei, or be generated by the interaction of the
radio jet with the ISM. We also analyse the peculiar profile of the [Fe VII]6087A optical coronal line from an archival VLT/X-shooter spectrum. The comparison with the [NeV]3425A and [FeII]1.257um profiles indicates that [Fe VII] emission likely arises only from the
outflow. The absence of the systemic component in [Fe VII] - unlike in [NeV], which has similar ionisation potential and critical density - suggests suppression of [Fe VII] due to iron depletion onto
dust grains, while its detection in the
outflow implies a lower
dust content than in the host ISM. The additional information gained from the ERIS data are consistent with the scenario of a dual AGN, however further observations are required to confirm its nature.
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All authors I. Lamperti, F. Mannucci, E. Bertola, A. Marconi, G. Cresci, E. Nardini, Q. D'Amato, M. Perna, A. Rojas-Lilayú, C. Bracci, V. Braito, E. Cataldi, M. Ceci, A. Chakraborty, C. Cicone, A. De Rosa, A. Feltre, M. Ginolfi, E. Lusso, C. Marconcini, B. Moreschini, E. Portaluri, K. Rubinur, M. Scialpi, P. Severgnini, G. Tozzi, A. Trindade Falcão, L. Ulivi, G. Venturi, C. Vignali, M.V. Zanchettin
High Energy Astrophysical Phenomena
X-Ray Analysis of an Off-Axis Merger Stage Binary Galaxy Cluster: PSZ2 G279.79+39.09
Sibel Döner, Turgay Caglar, Krista L. Smith et al. (+4 more)
We present an X-ray analysis of the merging
galaxy cluster system PSZ2 G279.79+39.09 ($z=0.29$) using archival XMM-Newton and Chandra observations. The surface brightness image is bimodal, elongated east-west with a projected core separation of $\sim 1.35$ Mpc. We measure gas temperatures of 5.36 keV for the eastern subcluster (PSZ-E) and 5.44 keV for the western component (PSZ-W). Assuming isothermal intracluster gas, the hydrostatic masses are $\log(M_{500}/M_\odot)=14.76$ for PSZ-E and 14.54 for PSZ-W, implying a mass ratio of $\sim 1:1.7$. PSZ-E shows X-ray concentration indices of $c_{40}/c_{400}=0.124$ and $c_{100}/c_{500}=0.278$, together with a centroid shift of $w=0.016$, indicating a disturbed
halo that still hosts a compact cool core; PSZ-W is comparably disturbed even in its core. Both subclusters exhibit ICM asymmetries consistent with ram-pressure stripping, and PSZ-W displays an X-ray tail extending nearly to the outskirts of PSZ-E. The orientation and length of this tail support an off-axis merger geometry. Thermodynamic maps reveal a hot ($\sim 7.3$ keV), high-pressure, high-
entropy bridge between the cores. From the Rankine-Hugoniot temperature jump, we infer a Mach number $M=1.48^{+0.30}_{-0.28}$, consistent with a weak merger shock propagating at $1695^{+316}_{-300}$ km s$^{-1}$. These results indicate a merger with a non-zero impact parameter, likely observed near core passage ($\lesssim 0.5$ Gyr before or after), with the pre-pericenter scenario slightly preferred based on the projected separation and thermodynamic structure.
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All authors Sibel Döner, Turgay Caglar, Krista L. Smith, Serap Ak, Andrea Botteon, M. Kiyami Erdim, John A. ZuHone
Cosmology and Nongalactic Astrophysics
Mapping dark matter in the Bullet Cluster using JWST imaging and spectroscopy
Gregor Rihtaršič, Maruša Bradač, Guillaume Desprez et al. (+23 more)
We present an updated gravitational lens model of the Bullet cluster (1E 0657-56) by combining JWST NIRCam imaging and NIRSpec spectroscopy. Although previous lens models relied on many multiply imaged
galaxies, only six systems had spectroscopic
redshifts prior to this work. Our lens model is constrained by a catalogue of 135 secure multiple images from 27 background
galaxies with spectroscopic
redshifts, uniformly covering both subclusters and a wide
redshift range of 0.9 - 6.7. We also provide a catalogue of 199 multiple image candidates. We modelled the cluster with Lenstool and incorporated several large-scale
haloes, cluster members, the intracluster gas, and group-scale
haloes surrounding the cluster core, motivated by spectroscopic studies of cluster member kinematics. We describe the main cluster component with a complex, elongated double-peaked distribution, and the subcluster with a single large-scale
halo aligning closely with the brightest cluster
galaxy ($4_{-2}^{+3}$ kpc). The uncertainty of the displacement has been improved threefold thanks to the addition of JWST systems. The addition of group-scale substructures, roughly following the two axes of cluster assembly, improves the fit to the multiple image positions and provides a physically motivated alternative to constant shear. Our lens model shows the closest agreement with previous studies in aperture mass profiles at $\sim60$ kpc from the brightest cluster
galaxies (BCGs), but exhibits significant differences in the detailed mass distribution as a result of different lens-modelling strategies and adopted constraints. The differences are reflected in small but spatially coherent deviations between the new spectroscopic
redshifts and
redshifts predicted by earlier lens models.
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All authors Gregor Rihtaršič, Maruša Bradač, Guillaume Desprez, Anishya Harshan, Nicholas S. Martis, Chris J. Willott, Yoshihisa Asada, Ghassan T. E. Sarrouh, Carla Cornil-Baiotto, Andrea Biviano, Douglas Clowe, Anthony H. Gonzalez, Christine Jones, Jon Judež, Stacy Y. Kim, Brian C. Lemaux, Marco Lombardi, Danilo Marchesini, Maxim Markevitch, Vladan Markov, Gaël Noirot, Annika H. G. Peter, Scott W. Randall, Andrew Robertson, Marcin Sawicki, Roberta Tripodi
Cosmology and Nongalactic Astrophysics
The LBT $Y_{\rm p}$ Project V: Cosmological Implications of a New Determination of Primordial $^4$He
Tsung-Han Yeh, Keith A. Olive, Brian D. Fields et al. (+5 more)
The
primordial abundance of $^4$He plays a central role in big-bang nucleosynthesis (BBN) and in the
cosmic microwave background (CMB). The LBT $Y_{\rm p}$ Project's new measurement of the
primordial $^4$He mass fraction $Y_{\rm p} =0.2458 \pm 0.0013$ is the most precise determination to date. In this paper, we combine our new $Y_{\rm p}$ value with the latest
primordial deuterium measurement, and assess the consequences for cosmology. For Standard BBN, where the number of light
neutrino species is fixed at $N_\nu=3$, the single free parameter is the
cosmic baryon density; the CMB measures this independently, with results consistent with each other. Combining $Y_{\rm p}$ , D/H, BBN, and the CMB, gives the
cosmic baryon-to-
photon ratio $\eta = (6.120 \pm 0.038) \times 10^{-10}$, corresponding to a
baryon density parameter $\Omega_{\rm B} h^2 = 0.02236 \pm 0.00014$. We then allow $N_\nu$ to vary and thus measure relativistic species present during nucleosynthesis. We find $\eta = (6.101 \pm 0.044) \times 10^{-10}$ or $\Omega_{\rm B} h^2= 0.02229 \pm 0. 00016$, and $N_\nu = 2.925 \pm 0.082$, and for $N_\nu \ge 3$, $\Delta N_\nu= N_\nu-3 \le 0.125$ (95% CL) during BBN and the CMB. Our results demonstrate consistency with the Standard Model of particle physics, and with the standard cosmology that links BBN at $\sim 1 \ \rm sec$ and the CMB at $\sim 400,000$ yr.
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All authors Tsung-Han Yeh, Keith A. Olive, Brian D. Fields, Erik Aver, Richard W. Pogge, Noah S. J. Rogers, Evan D. Skillman, Miqaela K. Weller
Cosmology and Nongalactic Astrophysics
The LBT Y$_\mathrm{p}$ Project IV: A New Value of the Primordial Helium Abundance
Erik Aver, Evan D. Skillman, Richard W. Pogge et al. (+7 more)
We present a new determination of the
primordial helium abundance based on new, high-quality Large Binocular
Telescope (LBT) observations of 54 metal-poor H II regions. These regions have been observed and analyzed uniformly. We also describe a number of updates to our methodology, including updated helium emissivities. Enabled by the large, high-quality
dataset, we examine our sample targets for potential systematic errors, which could bias their results. We perform a standard 95% confidence level $\chi^2$ cut and find that a significantly larger fraction (47/54 = 87%) of our sample qualifies than for previous
datasets. We also screen for quality and reliability, flagging targets which may introduce significant systematic errors, producing a
dataset of 41 targets. In a significant breakthrough for the field, that
dataset includes 15 high SNR targets with low
metallicity (O/H < 4 $\times$ 10$^{-5}$). Due to this low-
metallicity dataset, for the first time, a weighted average for determining the
primordial helium abundance (Y$_\mathrm{p}$) is well-justified and produces a robust result. By weighted average of our 15 low-
metallicity targets, we determine Y$_\mathrm{p}$ = 0.2458 $\pm$ 0.0013. This result achieves an unprecedented precision of 0.5%, and it is in good agreement with the BBN result, Y$_\mathrm{p}$ = 0.2467 $\pm$ 0.0002, based on the Planck determination of the
baryon density.
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All authors Erik Aver, Evan D. Skillman, Richard W. Pogge, Noah S. J. Rogers, Miqaela K. Weller, Keith A. Olive, Danielle A. Berg, John J. Salzer, John H. Miller Jr., José Eduardo Méndez-Delgado
Astrophysics of Galaxies
The LBT $Y_{\rm p}$ Project III: LUCI Spectra of Metal-Poor Nebulae
Miqaela K. Weller, Richard W. Pogge, Evan D. Skillman et al. (+6 more)
Accurately determining the elemental abundances of a low
metallicity nebula strongly depends on measuring the density (n$_e$) and temperature (T$_e$) of the gas. Because these two parameters are inherently degenerate when derived solely from H and He recombination lines, we rely on the density-sensitive HeI $\lambda$10830 line to assist in resolving this issue, especially for accurate He abundances. To facilitate this, we present near-IR (NIR) LUCI spectra of 48 low-
metallicity targets from the Large Binocular
Telescope (LBT) and homogeneously reduce them using Pypeit as part of the LBT $Y_{\rm p}$ Project. IR spectra require special care, and we wavelength calibrate by-hand using the bright OH emission lines, carefully apply proper telluric corrections, and co-add the spectra of LUCI1 and LUCI2 on a resampled grid to ensure accurate results. We use a Gaussian profile to fit the emission lines and measure the fluxes relative to Paschen-gamma (P$\gamma$), resulting in HeI $\lambda$10830 to P$\gamma$ ratios consistent with previous studies. As a result, this work significantly expands the available
dataset of NIR HeI $\lambda$10830 fluxes in low
metallicity galaxies. These high-quality measurements, where we find a median flux ratio uncertainty of $\widetilde{\sigma} = 0.08$, reduce the overall uncertainties in helium abundance estimates for individual targets. The increased size of the high-quality sample enables searching for systematic uncertainties and improves the reliability of the helium abundance determinations used to infer the
primordial helium abundance ($Y_{\rm p}$).
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All authors Miqaela K. Weller, Richard W. Pogge, Evan D. Skillman, Erik Aver, Noah S. J. Rogers, Danielle A. Berg, John J. Salzer, John H. Miller Jr., Jayde Spiegel
Astrophysics of Galaxies
The LBT $Y_{\rm p}$ Project II: MODS Spectra, Physical Conditions, and Oxygen Abundances in Local Metal-Poor Nebulae
Noah S. J. Rogers, Evan D. Skillman, Richard W. Pogge et al. (+7 more)
Empirically measuring the
primordial He mass fraction, $Y_{\rm p}$, requires a significant number of low-
metallicity nebulae with direct constraints on He/H and O/H abundances. This technique requires high-fidelity measurements of the gas-phase physical conditions, namely the electron temperature ($T_e$) and density ($n_e$). To this end, we present deep rest-optical spectroscopy for a sample of 62 low-
metallicity ($\lesssim$ 20%
solar O/H)
galaxies acquired using the Multi-Object Double Spectrographs (MODS) on the Large Binocular
Telescope (LBT) as part of the LBT $Y_{\rm p}$ Project. We discuss new fitting methods that recover the intensity of up to 61 H and He recombination lines, of which, up to 26 will be used to determine gas-phase He abundances, and we examine the emission line properties of the LBT $Y_{\rm p}$ Project sample. We assess different scaling relations in the low-
metallicity interstellar medium (ISM), finding that $n_e$[Ar IV] measured in 31 targets is systematically larger than $n_e$[S II] or $n_e$[O II]. The larger densities are insufficient to significantly bias $T_e$[O III] or the O/H abundance. $T_e$[S III] and $T_e$[O III] are strongly correlated over a range of $\sim$10$^4$ K with very low scatter, and we calibrate new $T_e$[S III]-$T_e$[O III] scaling relations for use in other low-
metallicity environments. We examine different $T_e$ measured in the low-ionization gas, finding significant scatter compared to $T_e$[O III]. The precision direct O/H derived in this analysis (median uncertainty $\sim$4%) are consistent with prior literature measurements, albeit with relatively large scatter. These data provide a key component necessary to empirically measure $Y_{\rm p}$ and the abundance patterns of other elements in the ISM.
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All authors Noah S. J. Rogers, Evan D. Skillman, Richard W. Pogge, Erik Aver, Miqaela K. Weller, Danielle A. Berg, John J. Salzer, John H. Miller Jr, Jayde Speigel, Allison L. Strom
Cosmology and Nongalactic Astrophysics
The LBT $Y_{\rm p}$ Project I: An Improved Determination of the Primordial Helium Abundance – Project Description, Sample Selection, Observations, and Methodology
Evan D. Skillman, Richard W. Pogge, Erik Aver et al. (+9 more)
Extremely low
metallicity HII regions have been observed with the goal of determining the
primordial helium abundance ($Y_{\rm p}$). $Y_{\rm p}$, combined with standard big bang nucleosynthesis and the half-life of the
neutron, provides a direct measurement of the number of
neutrino families, but $Y_{\rm p}$ must be measured very precisely to provide meaningful constraints on physics beyond the Standard Model. Here we describe a program to combine new Large Binocular
Telescope (LBT) observations with a new analysis methodology to significantly improve the determination of $Y_{\rm p}$. The LBT, with its MODS and LUCI instruments, produces spectra, which, when combined with our new analysis methodology, are capable of delivering He abundances in individual HII regions with uncertainties of approximately 2% or less. Archival LBT/MODS spectra of standard
stars over a four-year period enable the determination of a wavelength-dependent uncertainty in the MODS spectral response, resulting in improved relative emission line uncertainties. An optimized sample of low-
metallicity galaxies has been selected with the goal of producing a determination of $Y_{\rm p}$ with a precision of $\sim$ 0.5%, sufficient to provide an independent constraint on the effective number of
neutrino families of $\sim$ 3%.
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All authors Evan D. Skillman, Richard W. Pogge, Erik Aver, Noah S. J. Rogers, Miqaela K. Weller, Keith A. Olive, Danielle A. Berg, John J. Salzer, John H. Miller Jr, Jayde Spiegel, Tsung-Han Yeh, Brian D. Fields
High Energy Astrophysical Phenomena
Observational Implications of Cosmic Ray-Inverse Compton 'Boosted' Cool Cores in Clusters
Philip F. Hopkins, Emily Silich, Jack Sayers et al. (+2 more)
X-ray luminous cool-core (CC)
galaxy clusters contain powerful
cosmic ray (CR) sources. High-energy CRs powering GHz synchrotron lose energy rapidly, but long-lived (~Gyr-old) populations of 0.1-1 GeV CRs persist, propagating to ~100 kpc distances and radiating via inverse-Compton (IC) scattering of CMB
photons. We explore observable consequences of such CR-IC emission. This produces remarkably thermal X-ray spectra, which could contribute significantly to emission in CC centers. These naturally connect to ultra-steep
radio sources and
radio mini-
halos at younger ages, but become undetectable in most
radio, hard-X-ray, and $\gamma$-ray searches (though future imaging may detect them), while reproducing apparent density, temperature,
entropy, and mass deposition rates of CCs. This would provide an alternative resolution of the cooling flow problem: clusters may appear as strong CCs because of strong CR-IC, while not actually cooling so rapidly. This predicts many observed correlations between AGN/jet properties,
radio galaxy and minihalo properties, cooling radii, cavity radii and apparent X-ray cooling luminosity $L_{\rm X,cool}$. Since $L_{\rm X,cool}$ is actually from CR-IC, the observed
radio-X-ray ($L_{\rm radio}-L_{\rm X,cool}$), apparent cavity power ($P_{\rm cav}-L_{\rm X,cool}-L_{\rm radio}$), and strong CC-AGN correlations are predicted without free parameters. Since CR-IC leads to X-ray overestimates of thermal pressure, the ratio of SZ to X-ray pressures should drop in CC centers. CR-IC also suppresses abundances inferred from X-ray relative to optical/UV measurements in CC centers. Both of these appear to be seen in sufficiently-resolved CCs. Effects on cluster cosmology, hydrostatic mass estimation, and non-thermal pressure/
turbulence estimators are small.
Redshift evolution of CC surface brightness profiles could provide strong constraints or imply CR-IC at high-$z$.
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All authors Philip F. Hopkins, Emily Silich, Jack Sayers, Sam B. Ponnada, Isabel Sands
Astrophysics of Galaxies
Obscured AGN at z < 1.5: X-ray to Far-Infrared SEDs and Host Galaxy Morphologies in the GOODS Fields
William W.H. Jarvis, Connor Auge, David Sanders et al. (+9 more)
We present an analysis of spectral energy distributions (SEDs),
galaxy light profiles, and visual morphological classifications for 194 X-ray luminous AGN (intrinsic absorption-corrected log10 LX(0.5 to 7 keV) less than 42.5, with a maximum of 45.2 ergs per second) at
redshift z less than 1.5 in the GOODS fields. We generate X-ray to far-infrared SEDs normalized at 1 micron for all AGN and sort them according to their emission slopes in the ultraviolet and infrared. We visually classify their host
galaxy morphologies and compute their bulge-to-total light ratios using the software
Galaxy Shapes of Light (galight). Most (94 percent) GOODS AGN exhibit obscured SEDs, defined by diminished ultraviolet and/or mid-infrared emission, while only 6 percent show unobscured,
quasar-like SEDs. Secular processes appear to play a large role in stimulating AGN emission, as only around one-third of
galaxies are undergoing interactions. We also describe the morphological identification of a population of suspected post-merger spheroid
galaxies with obscured ultraviolet and infrared SEDs, and distinguish them from the host
galaxies of AGN with less obscuration in the ultraviolet or infrared.
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All authors William W.H. Jarvis, Connor Auge, David Sanders, Xuheng Ding, Jeana Kim-Bolt, C. Megan Urry, Eric Hooper, Alessandro Peca, Aritra Ghosh, Chuan Tian, Tonima T. Ananna, Md Mahmudunnobe
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Modified Teleparallel $f(T)$ Gravity, DESI BAO and the $H_0$ Tension
Mariam Bouhmadi-López, Carlos G. Boiza, Maria Petronikolou et al. (+1 more)
We investigate whether late-time modifications of
gravity in the teleparallel framework can impact the current tension in the Hubble constant $H_0$, focusing on $f(T)$ cosmology as a minimal and well-controlled extension of General Relativity. We consider three representative $f(T)$ parametrisations that recover the teleparallel equivalent of General Relativity at early times and deviate from it only at late epochs. The models are confronted with unanchored Pantheon+ Type~Ia
supernovae, DESI DR2
baryon acoustic oscillations, compressed Planck
cosmic microwave background distance priors, and
redshift-space distortion data, allowing us to jointly probe the background expansion and the growth of
cosmic structures. Two of the three models partially shift the inferred value of $H_0$ towards local measurements, while the third worsens the discrepancy. This behaviour is directly linked to the effective torsional dynamics, with phantom-like regimes favouring higher $H_0$ and quintessence-like regimes producing the opposite effect. A global statistical comparison shows that the minimal $f(T)$ extensions considered here are not favoured over $\Lambda$CDM by the combined data. Nevertheless, our results demonstrate that late-time torsional modifications can non-trivially redistribute current cosmological tensions among the background and growth sectors.
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All authors Mariam Bouhmadi-López, Carlos G. Boiza, Maria Petronikolou, Emmanuel N. Saridakis
Earth and Planetary Astrophysics
Warps survive beyond fly-by encounters in protoplanetary disks. RW Aur A as a case study
C. N. Kimmig, P. Weber, G. P. Rosotti et al. (+2 more)
Stellar fly-bys can have multiple dynamical effects on protoplanetary disks, including warping and the excitation of spiral arms. Since observations indicate that warps are common, we aim to investigate these effects for different fly-by trajectories. We further link our models to observations by applying them to the RW Aur system, which is a fly-by candidate with a relatively well constrained trajectory. We investigate the disk dynamics in grid-based hydrodynamical simulations, which allow for a lower disk viscosity than commonly used SPH models. We post-process our simulations of the RW Aur system with radiative transfer models to create synthetic images of the
dust continuum and gas kinematics. Fly-bys inclined with respect to the original disk plane can excite warps of a few degrees: the exact outcome depends on the specific geometry of the encounter. Specifically, we find that the position of the periastron with respect to the initial disk plane plays a role for the resulting warp strength. Within our parameter set, the strongest warp is excited for a retrograde fly-by with a periastron that is not in the same plane as the disk. Our models show that the warp can persist even after the perturber can no longer be clearly linked to the system, implying that past fly-bys are a possible origin of observed warps. Excited spirals arms, on the other hand, are much more short-lived than the warp. The RW Aur system presents a perfect opportunity to apply these results: we find that a warp of about 5{\deg} can be excited, and that the strong spiral arms have already disappeared at the current time of observation 300 years after periastron). This compares well with existing continuum observations, and our synthetic kinematic evaluations hint at remnant structures in the gas density that may be detectable.
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All authors C. N. Kimmig, P. Weber, G. P. Rosotti, S. Facchini, C. P. Dullemond
Astrophysics of Galaxies
Insights into the Physical Nature of Polar Ring Galaxies from H I Observations
Niankun Yu, Han Zheng, Chao-Wei Tsai et al. (+10 more)
Polar ring
galaxies (PRGs) host an outer ring of gas and
stars oriented nearly perpendicular to the main
stellar body. They represent extreme examples of misaligned systems and provide valuable insight into
galaxy interactions, gas
accretion, and peculiar gas dynamics. We compile a complete sample of kinematically confirmed PRGs and collect their H I measurements. Combining literature data with new observations from FAST, we detect H I emission in 22 sources, identify one potential H I absorption feature, and find four non-detections among 40 confirmed PRGs. Compared to
galaxies in the ALFALFA and xGASS surveys, PRGs predominantly occupy the green valley or quenched regimes but exhibit higher gas fractions than typical early-type
galaxies, suggesting gas
accretion. The H I profile asymmetry and shape for PRGs are not consistent with that of the ALFALFA sample with p<0.05. We examine their Tully-Fisher relation (TFR) and baryonic TFR (bTFR), linking the systems' rotation velocities to their masses. The extreme outliers in TFRs for the control sample tend to display single-peaked H I profiles. PRGs do not follow a tight TFR or bTFR if the H I resides primarily in the host
galaxy. But the scatter decreases significantly if we assume the gas is mainly distributed in the polar ring. Spatially resolved H I observations are essential to disentangle the gas distribution and kinematics in PRGs, which are key to understanding their formation mechanisms.
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All authors Niankun Yu, Han Zheng, Chao-Wei Tsai, Pei Zuo, Luis C. Ho, Amelie Saintonge, Zheng Zheng, Nathan Deg, Ningyu Tang, Xin Ai, Junzhi Wang, Xiang Jie, Di Li
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Axions on a Hyperbolic Ride: Geometric Suppression of CMB Isocurvature and a Blue-Tilted Spectrum
Sai Chaitanya Tadepalli
CMB limits on cold-dark-matter isocurvature are often interpreted as excluding the simultaneous realization of high-scale inflation and large QCD
axion decay constants in pre-inflationary Peccei–Quinn (PQ) scenarios. This conclusion can be evaded by exploiting field-space geometry. For a minimal complex PQ scalar with a $U(1)$-symmetric potential and a nonlinear sigma-model kinetic term $d\sigma^{2}=dR^{2}+f^{2}(R)\,d\theta^{2}$, the observable
axion fluctuation is $\delta\theta\sim H_{\rm inf}/f(R)$, so an enhanced effective decay constant $f(R)$ suppresses isocurvature without explicit PQ breaking, extreme radial displacements, or additional couplings. We specialize to a
hyperbolic metric $f(R)\propto \sinh(R/L)$ with
curvature scale $L$. The same geometry also induces a time-dependent $\mathcal{O}(H_{\rm inf})$ effective mass for the canonical axial mode during radial slow-roll, and fixing the tilt and running of isocurvature. Thus, CMB-scale isocurvature is suppressed while a characteristic blue-tilted spectrum is generated. As a result, inflationary Hubble scales as large as $H_{\rm inf}\sim 10^{13}\,\mathrm{GeV}$ can be compatible with $f_a\sim 10^{14}$–$10^{16}\,\mathrm{GeV}$, reopening parameter space usually regarded as excluded. We present `observable'
benchmarks and a semi-analytic template that relates the scale-dependence of isocurvature to the
geometric lever arm $R/L$, providing a direct phenomenological probe on PQ field-space geometry.
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High Energy Astrophysical Phenomena
Subsolar mass black holes from stellar collapse induced by primordial black holes
Thomas W. Baumgarte and Stuart L. Shapiro
While no gravitational-wave detection of subsolar mass black holes has been confirmed to date, a number of candidate detections invite us to speculate on the origin of such black holes should a detection be confirmed. It is generally assumed that the observation of a black hole with subsolar mass $M_{\rm obs}$ would provide strong evidence for
primordial black holes (PBHs). The mass $M_{\rm PBH}$ of the PBH, however, does not necessarily have to be equal to $M_{\rm obs}$, as it would in what we term a “direct PBH scenario". Instead, a black hole of mass $M_{\rm obs}$ may form in a capture of a much smaller
primordial black hole, $M_{\rm PBH} \ll M_{\rm obs}$, by a
dwarf star of mass $M_* \simeq M_{\rm obs}$, followed by the total consumption of the
star by the PBH. We provide some rough estimates and demonstrate that such an “indirect PBH scenario" may also lead to significant populations of black holes with mass $M_{\rm obs}$, especially in
dwarf galaxies, and may be able to explain rare subsolar mass events.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
When inflationary perturbations refuse to classicalise: the role of non-Gaussianity in Wigner negativity
Aurora Ireland and Vincent Vennin
Inflationary perturbations are
quantum in origin. Yet, when computing cosmological observables, they are often treated as classical
stochastic fields. Do they nevertheless retain
quantum birthmarks? A hallmark of genuinely
quantum behaviour is
quantum interferences, arising from phase coherence between distinct branches of the wavefunction. Such interference is diagnosed by the non-positivity of the Wigner function, and according to Hudson's
theorem, the only pure states with positive Wigner functions are Gaussian states. Consequently, any departure from Gaussianity necessarily implies a non-positive Wigner function, precluding a description in terms of a classical distribution. This motivates us to compute the Wigner function of
curvature perturbations, accounting for
primordial non-Gaussianities, using the EFT of inflation. We find that the Wigner function develops pronounced interference fringes on super-Hubble scales, and in particular, its negativity grows as $a^2$ in ultra-slow-roll backgrounds. These results demonstrate that
quantum effects can remain significant at late times, and that squeezing alone does not ensure classicality, contrary to standard lore. This suggests that the prospects for detecting genuinely
quantum signatures of the universe's origins in cosmological observables may be less bleak than previously thought.
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Astrophysics of Galaxies
The Perpendicularity of Dust Lanes and Radio Jets in Early-Type Galaxies: Implications for AGN Feedback
Emma Jane Weller and Pieter van Dokkum
The orientation of
radio jets relative to their host
galaxies offers an interesting avenue for probing the connection between active
galactic nuclei (AGN) and their surroundings. Several studies have also investigated the orientation of
nuclear dust features. We follow up on this previous work with newer Hubble Space
Telescope imaging of early-type
radio galaxies, and a largely automated process for measuring position angles. We classify the
dust features as lanes, disks, or rings. Lanes are irregular structures that likely form from gas-rich minor mergers, while disks and rings are more well-defined and may form from settling lanes or internal mechanisms. We find that
dust lanes do not have a preferred
alignment relative to their host
galaxies, but are preferentially perpendicular to the jets. In contrast,
dust disks and rings tend to be closely aligned with the major axes of their host
galaxies, but have varying orientations relative to the jets. Our results suggest that infalling dusty material from mergers can influence the angle of the
radio jet. This would allow the jet orientation to change over time, and may help explain the role of AGN feedback in maintaining quiescence in massive
galaxies.
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Solar and Stellar Astrophysics
Drifters on the edge of town: $\lambda$ Boötis stars in clusters
Richard J. Parker and Megan Allen
$\lambda$ Boötis
stars are a subset of chemically peculiar A-
stars that display
Solar abundances in lighter elements (C, N, O, S, etc.) but a deficiency in Iron-peak elements. This difference has been attributed to the A-
stars accreting pristine (metal deficient) gas from the Interstellar Medium. However, the recent discovery of $\lambda$ Boötis
stars in clusters challenges this theory, due to the presence of ionising radiation from intermediate/massive ($>$5 M$_\odot$)
stars, which could prevent
accretion of pristine ISM gas. We use $N$-body simulations to track the dynamical histories of A-
stars during the
evolution of a
star cluster. We find that some
stars leave the confines of the cluster and travel beyond the
tidal radius, where they may be able to accrete pristine ISM gas. These A-
stars then sometimes move back into the inner regions of the cluster, but the photoionising radiation flux they receive is not high enough to prevent $\lambda$ Boötis abundances from occurring in these A-
stars. We find that A-
stars can develop $\lambda$ Boötis abundances and subsequently form a wide ($>100$ au) binary system, meaning that observations of binary systems that have different abundances between the component
stars would not rule out the ISM
accretion scenario. Whilst we have shown that $\lambda$ Boötis
stars can reside in and around
star clusters, further research is required to assess the validity of the
accretion rates required to explain their abundance patterns.
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Cosmology and Nongalactic Astrophysics
Physically-motivated priors in the local distance ladder significantly reduce the Hubble tension
Marcus Högås and Edvard Mörtsell
Determinations of the Hubble constant based on the local distance ladder remain in significant tension with early-Universe inferences from the
cosmic microwave background. While this tension is often discussed in terms of new physics or unmodeled systematics, the role of the assumed priors on the model parameters has received comparatively little
attention. Recently, Desmond et al. (2025) pointed out that the commonly adopted flat prior on distance
moduli upweights smaller distances and systematically favors high inferred values of the Hubble constant. Motivated by this observation, we perform a comprehensive
Bayesian recalibration of the distance ladder, applying physically motivated priors uniformly to all distances, including the Milky Way Cepheids, which are incorporated directly into the joint fit. Together with a conservative treatment of the
Gaia EDR3 residual parallax offset, the Hubble constant shifts from $H_0 = 73.0 \pm 1.0 \, \mathrm{km/s/Mpc}$ to $H_0 = 70.6 \pm 1.0 \, \mathrm{km/s/Mpc}$, reducing the Hubble tension from $5 \, \sigma$ to $2 \, \sigma$. Our results show that the assumed priors – often treated as innocuous defaults – may play a central role in the Hubble tension. Because all local distance ladders rely on the calibration of distances, similar prior-driven effects are expected to arise across distance-ladder methods.
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Astrophysics of Galaxies
The Little Blue and Red Dots Rosetta Stones: Non-Gaussian broad lines, hot dust, and X-ray weakness
M. Brazzini, F. D'Eugenio, R. Maiolino et al. (+31 more)
The population of Active
Galactic Nuclei (AGN) newly discovered by the James Webb Space
Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGN and high-
redshift quasars. Most of these sources are compact, appearing as 'little dots': among them, the sub-class (10-30% of the total) characterized by significantly red optical colors has been named 'Little Red Dots' (LRDs), while here we analogously introduce the term 'Little Blue Dots' (LBDs) for the remaining, bluer sources (70-90%). We then present a comparative analysis of the prototypical representatives ('Rosetta Stones') of the two classes: GN-28074 at z=2.26, the Red Rosetta Stone, and GS-3073 at z=5.55, the Blue Rosetta Stone. In both Rosetta Stones the broad Balmer lines are better described by exponential profiles rather than single Gaussians, similarly to normal low-
redshift type I AGN, indicating that exponential profiles are not unique to LRDs. They are both extremely X-ray weak, show strong auroral [OIII] 4363 emission, weak hot
dust mid-IR emission, and no time variability. However, they differ in terms of excitation diagnostics: the HeII 4686 line is undetected in the Red Rosetta but strongly detected in the Blue Rosetta in both narrow and broad components, with the latter much broader than hydrogen Balmer lines. This supports BLR stratification and disfavors the cocoon electron-scattering scenario. An additional difference is the presence of prominent Balmer absorption in the Red Rosetta – indicative of extremely dense gas along the line of sight – but absent in the Blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGN, while differing in the amount and geometry of dense gas surrounding the
accretion disk, and/or in their
accretion properties.
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All authors M. Brazzini, F. D'Eugenio, R. Maiolino, J. Lyu, C. DeCoursey, H. Übler, X. Ji, I. Juodžbalis, J. Scholtz, G. C. Jones, K. Hainline, E. Dalla Bontà, P. G. P érez-González, S. Geris, A. Harshan, C. Feruglio, M. Bischetti, G. Mazzolari, G. Rieke, S. Alberts, B. Trefoloni, S. Carniani, E. Parlanti, A. Marconi, G. Risaliti, C. Ramos Almeida, P. Rinaldi, M. Perna, S. Zamora, I. Lamperti, G. Venturi, G. Cresci, Andrew J. Bunker, L. R. Ivey