Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Friday 25 September

Astrophysics of Galaxies

A VLA Study of the Disturbed Massive Cluster PLCK G165.7 + 67.0 and Its Two Narrow Angle Tail Galaxies

Aurora Wilde, Eric F. Jimenez-Andrade, Brenda L. Frye et al. (+11 more)

Since spectroscopic measurements provide only the line-of-sight velocity, transverse motions are difficult to constrain. As a result, transverse velocities have so far been measured only for local galaxies. Radio galaxies whose jets are bent back by ram pressure into nearly parallel Narrow-Angle Tails (NATs) offer a way to extend such measurements to higher redshifts. Here, we present proprietary 15 GHz (Ku-band) and archival 6 GHz (C-band) continuum observations from the Very Large Array (VLA) of seven radio galaxies in the galaxy cluster field PLCK G165.7+67.0 (G165). VLA imaging resolves two of the cluster galaxies into NATs whose tails both extend toward the Southwest, away from the cluster center of mass. Spectral index maps made at matched angular resolution resolve a steepening gradient consistent with radiative aging along the length of the tails. Physical properties of the NATs are measured and used to constrain two independent models: a Mach cone model and a nonrelativistic hydrodynamic flow model based on Euler's equation. The models returned space velocities of $\sim 2000 ~\rm km~ \rm s^{-1}$ for both galaxies. One NAT is the brightest cluster galaxy (BCG) and has a measured radial velocity of $-3300 ~\rm km ~\rm s^{-1}$, resulting in an even higher space velocity. The high inferred 3D velocity of the BCG may be explained if it is intercepted close to core passage.
Read the full abstract

All authors Aurora Wilde, Eric F. Jimenez-Andrade, Brenda L. Frye, Patrick S. Kamieneski, Kevin C. Harrington, Megan Donahue, Min S. Yun, Anton M. Koekemoer, Marcel Neeleman, Massimo Pascale, Nicholas Foo, Reagen Leimbach, Seth Cohen, Rogier A. Windhorst

Thursday 24 September

Astrophysics of Galaxies

Evidence for the Typhon Stellar Stream as the Remnant of a Recently-disrupted Dwarf Galaxy

João V. Nogueira-Santos, Guilherme Limberg, Silvia Rossi et al. (+4 more)

In the hierarchical model of galaxy formation, the Milky Way's stellar halo assembles through the successive accretion of dwarf galaxies. While many resulting substructures have been identified, the origin of the recently discovered Typhon stellar stream remains ambiguous, as dynamical data alone are insufficient to distinguish between a globular cluster and a dwarf galaxy progenitor. To resolve this, we combine astrometry from Gaia with spectroscopic data from available surveys to comprehensively analyze the stream's chemical and dynamical properties. We identify 107 candidate members, significantly expanding the known sample. Three of these candidates lie beyond $55\,\mathrm{kpc}$, with the farthest at $67\,\mathrm{kpc}$, lending further support to Typhon's inferred large apocentric distance. Our analysis yields a mean metallicity of $\rm[Fe/H]=-1.42\pm0.07$ and a metallicity dispersion of $\sigma_{\text{[Fe/H]}} = 0.26^{+0.06}_{-0.05}$ dex. This metallicity dispersion supports a dwarf-galaxy origin for the Typhon stream. Typhon's high orbital energy is consistent with a relatively recent accretion of a fully disrupted dwarf galaxy with a stellar mass in the range of $10^6 M_{\odot} < M_\star \lesssim 10^7 M_{\odot}$. Furthermore, Typhon is the only major dwarf-galaxy stellar stream in the Milky Way's halo to exhibit such an extreme orbital eccentricity of $e \gtrsim 0.85$. We conjecture that dwarf-galaxy streams from high-eccentricity mergers are fully dissolved much more rapidly than those on circular orbits, in line with Typhon's proposed recent accretion. Additional dwarf-galaxy stellar streams on high-eccentricity orbits should be discoverable with next-generation photometric surveys as well as future releases from the Gaia space mission.
Read the full abstract

All authors João V. Nogueira-Santos, Guilherme Limberg, Silvia Rossi, Hélio D. Perottoni, Lais Borbolato, Fabrícia O. Barbosa, André R. da Silva

Astrophysics of Galaxies

The JWST Proto-PAH project: Aromatic backbones with extensive aliphatic substitution account for both the aromatic and aliphatic emission

N. Clark, E. Peeters, J. Cami et al. (+18 more)

We find that the aromatic and aliphatic emission bands in four carbon-rich post-asymptotic giant branch stars with class D emission arise from a single carrier population: extensive aliphatic decoration of an aromatic skeleton, i.e. molecules with a coherent aromatic backbone and an unusually high aliphatic content. This conclusion is based on JWST NIRSpec and MIRI/MRS spectroscopy, covering 2.88-28.7um. The aliphatic 3.4um feature is stronger than the aromatic 3.3um feature, reversing the ratio seen in sources with typical polycyclic aromatic hydrocarbon (PAH) emission. If the aromatic emission arose from nominal PAHs, the 3.3um feature - unavailable in previous observations - together with the mid-infrared aromatic features, would constrain them to be large (greater than about carbon atoms), compact, and at least partially ionized. These properties predict a strong 8.6um feature. However, the 8.6um feature is weak or absent in all four sources, ruling out PAHs as the source of the aromatic emission. Instead, the emission must arise from the same carriers as the aliphatic emission. The position of the 6.9um feature and the broadened 11-14um out-of-plane emission independently support this. The CH2 and CH3 feature strengths vary across the sample, with the class D2 sources showing higher CH3 content. These carriers are far more aliphatic than the PAHs of planetary nebulae and the interstellar medium. However, they retain the aromatic skeleton that produces their aromatic features.
Read the full abstract

All authors N. Clark, E. Peeters, J. Cami, G. C. Sloan, K. Volk, K. E. Kraemer, H. L. Dinerstein, M. A. Gomez-Munoz, G. M. Wahlgren, N. C. Sterling, A. Ricca, A. A. Zijlstra, J. Li, M. Matsuura, D. A. Garcia-Hernandez, R. Sahai, B. Aringer, C. Bhatt, J. Bernard-Salas, D. Das, A. Manchado

Astrophysics of Galaxies

The JWST Proto-PAH project. Computational modeling of the emission carriers

A. Ricca, G. C. Sloan, E. Peeters et al. (+8 more)

The infrared spectra of many carbon-rich post-asymptotic giant branch stars are dominated by emission features from aromatic and aliphatic hydrocarbons, but the chemical structure of the carriers remains unidentified. Class D sources show unusual emission profiles with strong aliphatic emission, providing a stringent test of carrier candidates. Here we investigate whether hydrogenated carbonaceous molecular particles can be the carriers of these features. Rather than assuming candidate geometries we generate the initial structures using ab initio molecular dynamics simulations and optimize them using density functional theory. We then compare the computed emission spectra to JWST NIRSpec and MIRI/MRS observations of Class D sources. The structures providing the best agreements contain sizeable domains with defect-bearing aromatics and hydrogenated-aromatics connected by aliphatic bridges, in contrast to the "arophatic" cluster model of isolated two- to three-ring aromatics connected by aliphatic and olefinic bridges. As a representative example, we discuss in detail the molecular particle C130H96 (radius of 5.5 A) and compare its computed spectrum to the JWST spectra of IRAS 05110-6616, a Class D2 source with apparent shifts of the aromatic C-H out-of-plane bands. The calculated spectra are in qualitative agreement with the observed 3 micron profile, the aliphatic C-H bending bands, the broad 8 micron feature, the 11-14 micron C-H out-of-plane region, and the bands at 16 and 21 microns. We hypothesize that UV photo-driven fragmentation of such molecular particles releases aromatics linked by aliphatics, followed by the formation of polycyclic aromatic hydrocarbons and fullerenes as these objects evolve into planetary nebulae.
Read the full abstract

All authors A. Ricca, G. C. Sloan, E. Peeters, J. Cami, N. Clark, M. Matsuura, R. Sahai, J. Bernard-Salas, D. A. Garcìa-Hernàndez, J. Li, C. Bhatt

Astrophysics of Galaxies

Breaking the AGB Color Degeneracy with Variability and H$_2$O: A Consistent Picture of AGB Chemistry, Dust, and the J-Region Across Environments

Caroline D. Huang, Massimo Marengo, Antonio Capodagli et al. (+7 more)

Resolved asymptotic giant branch (AGB) populations present many observational puzzles. We consider three often treated separately: photometric C/O classification boundaries must be redrawn empirically in new environments; hydrostatic model grids are too blue in bands sampling H2O absorption; and J-region (JAGB) luminosities can differ between fields of a single galaxy. Pulsation connects them into a coherent picture. Using SPHEREx spectroscopy of AGB stars in the Large Magellanic Cloud (LMC) with JWST/NIRCam photometry and HST time-series of the SN Ia host M101, placed on a common scale by synthetic photometry, we investigate how AGB variability, surface chemistry, and circumstellar dust depend on environment. We develop an F182M index sensitive to 1.9$\mu$m H2O absorption that chemically classifies variable AGB stars and reveals oxygen-rich (O-rich) stars degenerate with carbon-rich (C-rich) stars in broadband colors. Because these features arise in extended atmospheric layers, hydrostatic grids struggle to reproduce them. Pulsation and circumstellar dust are asymmetrically linked: nearly all stars with substantial infrared excess are variable, while many variables show little dust. This supports mass loss initiated by pulsation and enhanced by dust formation. Variable O-rich AGB stars in M101 are up to ~0.7 mag redder than their LMC counterparts in dust-sensitive colors, consistent with more efficient silicate-dust production at higher metallicity, while C-rich populations depend less on environment. Color windows that select C-rich stars cleanly in the LMC are therefore 33-68% O-rich in the metal-rich M101. This challenges the J-region's universality as a standard candle while evading standard self-consistency checks. We recommend combining variability, or the infrared excess that implies it, with photometry of molecular features to improve AGB classification at 0.75-5.0$\mu$m.
Read the full abstract

All authors Caroline D. Huang, Massimo Marengo, Antonio Capodagli, Adam G. Riess, Louise Breuval, Stefano Casertano, Patricia A. Whitelock, Gagandeep S. Anand, Randall K. Smith, Wenlong Yuan

Astrophysics of Galaxies

Collisional excitation of E- and Z-ethanimine to model cold molecular clouds

Francesca Tonolo, Vivek Vijay, Ernesto Quintas-Sánchez et al. (+5 more)

Context. Ethanimine is a prebiotically relevant complex organic molecule that has been proposed as a key precursor of amino acids in the interstellar medium. To date, both its E and Z isomers have only been detected toward the Sgr B2(N) molecular cloud. The pronounced non-local thermodynamic equilibrium (non-LTE) effects predicted for this molecule require accurate collisional rate coefficients for reliable astrophysical modeling and future astronomical searches. Aims. We aim to provide the first collisional datasets for both ethanimine isomers with the main cold molecular clouds collision partners, He and para-H2, in order to support non-LTE radiative-transfer modeling. Methods. State-to-state rate coefficients for collisions with He were computed by integration over mixed close-coupling (CC) and coupled-states (CS) scattering cross sections at different energy ranges. In addition, comparisons with mixed quantum-classical theory (MQCT) calculations performed for both He and para-H2 collisions enabled the derivation of transition-specific scaling factors, which were applied to predict collisional rate coefficients for para-H2. Results. We present the first state-to-state collisional datasets for both E- and Z-ethanimine in collision with He and para-H2, including all rotational transitions involving levels below 50 cm-1 and over the 5-100 K temperature range. Conclusions. The datasets reported here provide the first collisional information suitable for non-LTE modeling of ethanimine in cold interstellar environments. They represent a key step toward more reliable abundance determinations and may facilitate future astronomical detections of both ethanimine isomers beyond Sgr B2(N).
Read the full abstract

All authors Francesca Tonolo, Vivek Vijay, Ernesto Quintas-Sánchez, Adrian Batista Planas, Carolin Joy, Richard Dawes, François Lique, Dmitri Babikov

Astrophysics of Galaxies

A tidal disruption event in a quasar at redshift 7.19

S. Fujimoto, Q. Fei, G. B. Brammer et al. (+41 more)

We report a long-lived nuclear transient in GNz7q, a red quasar at $z=7.19$ powered by a $\sim3\times10^{7}\,M_\odot$ black hole and hosted by a compact, dusty starburst galaxy. The transient was identified in more than two decades of imaging with HST, Spitzer, and JWST. After a rapid rise, the source faded smoothly by $\Delta m\simeq1.1$ mag in the rest-frame ultraviolet over $\sim2$ rest-frame yr, with coherent, wavelength-dependent evolution across 1–5 $\mu$m that places GNz7q above the 99.9th percentile of the SDSS quasar variability distribution and is absent at $z\gtrsim5$. The duration and energetics disfavor superluminous supernovae, and stochastic quasar variability reproduces the multi-band evolution with a probability of $\lesssim10^{-5}$. A panchromatic model combining a thermal continuum with a $t^{-5/3}$ decline reproduces the light curves, yielding a peak bolometric luminosity of $\simeq3\times10^{45}$ erg s$^{-1}$ and a radiated energy of $\simeq1.5\times10^{53}$ erg, which imply the tidal disruption of a star of a few solar masses and place the event among the most energetic tidal disruption events (TDEs) known. A redshifted, extremely broad Balmer-line component in independent JWST/NIRSpec spectroscopy is consistent with a transient, non-virialized broad-line region. JWST/MIRI photometry further reveals delayed mid-infrared emission from $\simeq1500$ K dust at a sub-parsec radius, consistent with a dust echo of the flare. The relatively low black-hole mass and dense star-forming nucleus of GNz7q are conditions under which TDEs are expected to be most efficient. These observations provide a time-domain view of episodic black-hole fueling and its dusty nuclear environment 700 million years after the Big Bang. Wide-field surveys with Roman and Euclid in the near-infrared, complemented by LSST at lower redshifts, may uncover such transients in large numbers.
Read the full abstract

All authors S. Fujimoto, Q. Fei, G. B. Brammer, K. Inayoshi, V. Kokorev, L. C. Ho, R. Li, F. Walter, V. Bromm, L. Colina, P. Dayal, S. L. Finkelstein, M. Ginolfi, Z. Liu, G. C. K. Leung, G. E. Magdis, J. Matthee, R. P. Naidu, P. Oesch, M. Onoue, P. G. Pérez-González, D. Watson, J. Álvarez-Márquez, J. Antwi-Danso, Y. Asada, G. Barro, C. M. Casey, J. Chisholm, S. Gillman, R. Marques-Chaves, J. P. U. Fynbo, T. R. Greve, I. Labbe, R. A. Meyer, F. Rizzo, A. Robbins, R. Schneider, C. L. Steinhardt, S. Toft, A. Trinca, F. Valentino, R. Valiante, M. Vestergaard, M. Xiao

Astrophysics of Galaxies

SN Helios: A Multiply Imaged Type II Supernova Opening Time-Delay Cosmography beyond redshift of 3

Seiji Fujimoto, Conor Larison, Justin D. R. Pierel et al. (+64 more)

We report the discovery and spectroscopic confirmation of SN Helios, a strongly lensed, multiply imaged Type II supernova (SN) at $z=3.34$ behind the galaxy cluster RXC J0018.5+1626. The transient was identified as a red F150W-dropout source (F277W = 26.1 mag) in JWST/NIRCam imaging taken on 2026 July 3 for the VENUS survey, with no counterpart in 2024 December imaging. Director's Discretionary Time observations on 2026 August 17 added second-epoch NIRCam imaging and a deep NIRSpec prism spectrum. The spectrum shows a strong, spectrally resolved H$\alpha$ emission line (FWHM $\approx 7900$ km/s) with a P-Cygni absorption blueshifted by 8800 km/s, together with corresponding H$\beta$ and He I $\lambda$10830 features, establishing a hydrogen-rich photosphere at $z=3.34$. Template fits classify SN Helios as a Type II SN, and light-curve comparisons with well-studied local SNe II yield a phase of $27.5\pm2.8$ rest-frame days past B-band maximum. Independent cluster lens models magnify the observed image by $\mu\approx 10$-20 and predict another image within $\simeq 2$-6 yr, offering a rare opportunity for a time-delay measurement of $H_{0}$ with a source at $z>3$. The host galaxy is undetected in deep rest-frame ultraviolet and optical imaging, in emission lines, and in ALMA 2 mm dust continuum, leaving a heavily obscured counterpart unlikely. Its de-lensed $M_{\rm UV}\gtrsim -13$ places it far below blank-field limits and adds support to an elevated core-collapse rate per unit star formation in ultra-faint galaxies. Without the multi-epoch data, SN Helios would masquerade as a convincing $z\approx 16$ Lyman-break galaxy, with galaxy-template fits strongly disfavoring any low-redshift solution even with multiple medium bands. Its spectrum thus provides an empirical SED template with which high-redshift searches can vet similar dropout candidates.
Read the full abstract

All authors Seiji Fujimoto, Conor Larison, Justin D. R. Pierel, Lukas J. Furtak, Masamune Oguri, Adi Zitrin, Jose M. Diego, Keren Sharon, David A. Coulter, Gabriel Brammer, Vasily Kokorev, Chelsea Nash, Pedram Abedi, Christa DeCoursey, Armin Rest, Andreas L. Faisst, Brenda L. Frye, Tiger Yu-Yang Hsiao, Kohei Inayoshi, Kotaro Kohno, Jorryt Matthee, Matteo Messa, Yoshiaki Ono, Fengwu Sun, Eros Vanzella, Rogier A. Windhorst, Abdurro'uf, Aadya Agrawal, Joseph F. V. Allingham, Yoshihisa Asada, Hakim Atek, Maruša Bradač, Larry D. Bradley, Mateusz Bronikowski, Dan Coe, Christopher J. Conselice, Pratika Dayal, Eiichi Egami, Michael Engesser, Gavin Scott Farley, Qinyue Fei, Ori D. Fox, Yoshinobu Fudamoto, Miriam Golubchik, Yuichi Harikane, Gourav Khullar, Tomokazu Kiyota, Paulo A. A. Lopes, Ray A. Lucas, Guillaume Mahler, Ashish Kumar Meena, Rohan P. Naidu, Gautham Narayan, Gaël Noirot, Pascal A. Oesch, Masami Ouchi, José María Palencia, Massimo Pascale, Luke Robbins, M. R. Siebert, Roberta Tripodi, Francesco Valentino, Darach Watson, Hayley Williams, Hiroto Yanagisawa, Erik Zackrisson, Anita Zanella

Astrophysics of Galaxies

Saturation Mechanism of Cosmic Ray Streaming Instabilities with a Shell Distribution

Mohamad Shalaby, Rouven Lemmerz and Christoph Pfrommer

Cosmic rays (CRs) drive galactic winds and regulate galaxy growth while contributing to heating the central cooling plasma in dense galaxy clusters, making the nonlinear saturation of the instabilities that govern their transport a problem of central importance in astrophysics. Using fully kinetic particle-in-cell (PIC) simulations, we find that the streaming instability driven by CRs with a shell momentum distribution saturates through gyro-phase bunching around driven Alfvén waves. Fluid-PIC (FPIC) simulations with both ideal and Landau closures reproduce the PIC saturation amplitude, and the same gyro-phase bunching mechanism, indicating that nonlinear Landau damping (NLLD) does not determine the saturation level at our simulation parameters ($v_{\rm A} = 0.01c$, $n_{\rm CR}/n_i = 0.01$). Notably, the CR ions fully isotropize in the Alfvén-wave frame in all simulations, including the FPIC run with an ideal closure in which NLLD is entirely absent, showing that this isotropization does not require NLLD. We additionally confirm, using the FPIC ideal closure, that this saturation amplitude is unchanged across a tenfold increase in domain size, indicating that the mechanism is local rather than dependent on domain-scale processes. Together, these results indicate that, at least in this regime, NLLD is not the dominant saturation mechanism for the CR streaming instability, in tension with common assumptions built into CR transport models used in galaxy formation and interstellar medium simulations. Whether this conclusion extends to the lower CR densities and Alfvén speeds characteristic of the interstellar medium remains an open question that we address in an upcoming work.
Read the full abstract

Astrophysics of Galaxies

TRICEPS. I. Tracing cold gas, dust, and stars at sub-kpc scales in massive star-forming galaxies at z = 4-5

Federico Lelli, Lingrui Lin, Zhi-Yu Zhang et al. (+11 more)

We introduce the TRICEPS (Tracing Resolved Ionized Carbon Emission in Primeval Systems) survey. TRICEPS focuses on a sample of 16 massive galaxies at z = 4 - 5 with top-quality data: (i) ALMA band-7 observations of the [CII]-158 micron line, tracing the cold gas distribution and kinematics at spatial resolutions of about 0.1" (~0.8 kpc), (ii) ALMA maps of the rest-frame 160 micron continuum emission, tracing the dust distribution at similar spatial resolutions, (iii) multi-band JWST images from NIRCam and MIRI, tracing the stellar mass distribution and star formation activity at spatial resolutions of 0.1"-0.2", and (iv) multi-line CO observations from ALMA and the VLA, including the CO(1-0) line, tracing the molecular gas content. In this first paper, we describe the TRICEPS scientific goals, the basic properties of the galaxy sample, and the ALMA band-7 observations. TRICEPS galaxies were selected based only on bright [CII] fluxes (>2 Jy km/s). They lie on the top-end of the star-forming main sequence at z = 4-5, having stellar masses between about 10^10.5-10^12 Msun and star-formation rates between about 100 - 3000 Msun/yr. To date, TRICEPS is the largest sample of galaxies at z = 4-5 for which the gas distribution and kinematics are exceptionally well resolved: on average, 46 resolution elements per galaxy with signal-to-noise ratio higher than 3. By survey design, half of the TRICEPS targets are in galaxy pairs; clear signs of tidal interactions are present in three of the four pairs. In all galaxies, the [CII] velocity fields display regular rotation, albeit the interacting galaxies tend to be somewhat more disturbed. The TRICEPS observations suggest that regular rotation is ubiquitous among massive star-forming galaxies when the Universe was less than ~1.5 Gyr old.
Read the full abstract

All authors Federico Lelli, Lingrui Lin, Zhi-Yu Zhang, Cecilia Bacchini, Davide Bevacqua, Joe Bhangal, Marco Castellano, Carlos De Breuck, Giovanni Gandolfi, Allison W. S. Man, Antonino Marasco, Diego Paris, Borja Pérez-Díaz, Paola Santini

Astrophysics of Galaxies

Hidden in the Halo: New Diffuse Star Clusters in the M82 Starburst with JWST

Deepthi S. Prabhu, David J. Sand, Burcin Mutlu-Pakdil et al. (+12 more)

Diffuse star clusters (DSCs) occupy a poorly explored region of the size-luminosity plane between classical globular clusters (GCs) and dwarf galaxies. Here we report the discovery of four faint DSCs in the halo of the nearby starburst galaxy M82 using archival JWST/NIRCam imaging. We resolve individual stars in all four systems, whose color-magnitude diagrams are consistent with predominantly old ($\sim10$ Gyr) stellar populations, based on comparison with isochrones. DSC 1 hosts a metal-poor population ($[\mathrm{M/H}]\sim-2$), while DSCs 2, 3 and 4 are better represented by $[\mathrm{M/H}]\sim-0.8$ isochrones. To establish their nature, we measure their sizes and integrated magnitudes using curve-of-growth and radial profile fits, which yield consistent results between these methods. The sizes of DSCs range from $\sim$ 5.4 to 10.5 pc, making them more extended than typical GCs (2-3 pc). Their luminosities span M$_{\rm V}\simeq-4.1$ to $-6.4$, reaching $\sim$ 1 mag fainter than the previously known M82 star cluster (SC) population. At these low luminosities, the systems occupy a sparsely sampled region of the size-luminosity plane where the distinction between SCs and dwarf galaxies becomes increasingly ambiguous. Most notably, DSC 3 is the faintest SC candidate identified in M82 to date and approaches the regime occupied by Milky Way ultra-faint compact satellites. These faint DSCs were identified through visual inspection alone, suggesting they are likely underrepresented in existing star cluster catalogs, and that a JWST-based archival search of nearby galaxies would be fruitful.
Read the full abstract

All authors Deepthi S. Prabhu, David J. Sand, Burcin Mutlu-Pakdil, Adam Smercina, Denija Crnojevic, Michael G. Jones, Paul Bennet, Amandine Doliva-Dolinsky, Kristine Spekkens, Debasish Hazarika, Laura Congreve Hunter, Jaclyn Jensen, Benjamin N. Velguth, Dennis Zaritsky, Sasha N. Campana

Astrophysics of Galaxies

A Self-Consistent Jeans Analysis of the Milky Way Rotation Curve

Yongjun Jiao, Francois Hammer, Istiak Akib et al. (+2 more)

Jeans-based measurements of the Milky Way (MW) rotation curve (RC) have revealed a declining outer RC. The interpretation, however, depends sensitively on the tracer selection, the tracer density profile, gradient terms in the Jeans equation, and non-axisymmetric perturbations in the outer disk. We present a more self-consistent Jeans analysis of the MW RC and reassess whether the outer decline remains after a revised treatment of the main Jeans terms and their associated systematic uncertainties, including those related to non-axisymmetric perturbations. We select a kinematically homogeneous disk tracer sample designed to retain stars on nearly circular disk orbits, removing only 12% of the original sample. We estimate the tracer density profile from the same stars used for the kinematic moments, rather than adopting an external scale length. We find that the tracer density profile is better described by a double exponential over the validated range 12.5 < R < 21 kpc. We also assess the main systematic uncertainties associated with the fiducial Jeans equation terms, including the often neglected cross term, and account for different rotational velocities in the outer disk substructures. The derived RC remains nearly flat in the inner disk and declines at large radii. Over the adopted outer interval, $R\gtrsim16\,\mathrm{kpc}$, the RC slope is consistent with a Keplerian decline even after accounting for the systematic uncertainties. The corresponding mass modeling gives an extrapolated dynamical mass of $2.01^{+0.10}_{-0.08}\times10^{11}\,M_\odot$.
Read the full abstract

All authors Yongjun Jiao, Francois Hammer, Istiak Akib, Yanbin Yang, Haifeng Wang

Astrophysics of Galaxies

Igniting Galaxy Formation in the Postreionization Universe, II: Nature versus Nurture

Jorge Moreno, Defne Aluç, Eisha López et al. (+7 more)

Although the ultraviolet background from reionization is thought to conspire against the smallest halos, some gas-rich halos in the post-reionization Universe still form stars. We ask which properties, environmental or intrinsic, determine ignition. Using the FIREbox cosmological volume, we compare recently-ignited halos to a mass- and gas-matched sample of gas-resolved starless halos at $z=2$–6. We test three families of "third axis" properties beyond $M_{\rm vir}$, $M_{\rm gas}$, and $z$: geometric environment (the Perturbation Index and local galaxy density $\rho_5$), hydrodynamic environment (the $1$–$2,R_{\rm vir}$ gas-supply shell), and intrinsic halo properties (concentration and the neutral-gas reservoir). A nested random-forest classification finds that geometric environment adds little, while the hydrodynamic shell is modestly informative. Three complementary properties each discriminate ignited from starless halos beyond the mass–gas–redshift baseline (AUC $=0.635$, where $0.5$ is chance): total HI mass ($M_{\rm HI}$, AUC $=0.739$), the extent of the neutral gas ($r_{\rm HI,50}/R_{\rm vir}$, AUC $=0.738$), and the central HI density ($\rho_{\rm HI,0}$, AUC $=0.700$); jointly they reach AUC $=0.823$, the highest of any combination we test. At fixed halo mass, gas mass and redshift, recently-ignited halos harbor more HI over a larger radius than their matched controls, and these two enhancements are uncorrelated. The same reservoir sets when ignition can happen: from $z=6$ to $z=0$ the median starless halo keeps its gas ($+0.05$ dex) while its neutral fraction falls by $3.9$ dex, so the reservoir is ionized rather than exhausted and the ignition window closes below $z\simeq2$. In sum, a halo's own neutral-gas reservoir discriminates ignited from starless halos more sharply than its location in the cosmic web – nature over nurture.
Read the full abstract

All authors Jorge Moreno, Defne Aluç, Eisha López, Vivienne Wood, Emmanuel Santiago, Francisco J. Mercado, Caleb R. Choban, Coral Wheeler, M. Katy Rodriguez Wimberly, Robert Feldmann

Astrophysics of Galaxies

The geometric origin of the thermal eccentricity law

Václav Pavlík

The distribution $f(e)=2e$ is commonly referred to as the `thermal eccentricity distribution' of Keplerian binaries. However, the result does not require thermal equilibrium, and its usual derivations obscure why the distribution is linear in eccentricity. We seek a simple geometrical interpretation of this result and its relation to more general eccentricity distributions. We consider bound Kepler orbits in a Euclidean space of dimension $D\geq2$, with a phase-space distribution depending only on energy, and derive the eccentricity distribution from the Liouville measure. We obtain $f_D(e)=(D-1) e (1-e^2)^{(D-3)/2}$, so that, within this family, $D=3$ is the only case for which the distribution function is linear in $e$. This follows from the $D-1$ transverse momentum dimensions and the Kepler period degeneracy. We further show that two known generalisations – namely a power-law weighting of the normalised angular momentum and a constant velocity anisotropy – are, in fact, two representations of the same one-parameter family of eccentricity distributions.
Read the full abstract

Astrophysics of Galaxies

Breaking the Blend: A multi-tracer kinematic decomposition method for IFS data applied to disentangling the AGN outflow and circumnuclear ring in NGC 5728 with JWST

Oscar Veenema, Niranjan Thatte, Dimitra Rigopoulou et al. (+26 more)

Integral field spectroscopy (IFS) of the central kiloparsecs of active galactic nuclei (AGN) reveals a mixture of spatially coincident emission from star-formation and AGN feedback exciting the interstellar medium. Disentangling these components remains a challenge, as most spectral tracers are affected by both processes, limiting robust interpretation of kinematics and energetics. We present a new framework for decomposing IFS data into distinct components on a spaxel-by-spaxel basis using a multi-tracer, stacked kinematics approach. This method combines kinematic modelling with imposed flux decomposition per spaxel, quantifying the contribution of each component across the field of view. We apply this method to JWST IFS observations of the Seyfert galaxy NGC 5728 from the Galaxy Activity, Torus, and Outflow Survey (GATOS), analysing twelve mid-infrared fine-structure lines (4.49 < $\lambda$ < 25.89 $\mu$m, 7.9 < IP < 126.2 eV). We find that the circumnuclear emission can be decomposed into two dominant components: a star-forming ring and an AGN-driven biconical outflow. Our method separates these structures and recovers their detailed spatial morphology. This framework provides a general and scalable method for physically motivated component separation in IFS data, applicable across many wavelength ranges and targets, enabling reliable interpretation of complex emission line structures (or morphologies) in active galaxies and beyond.
Read the full abstract

All authors Oscar Veenema, Niranjan Thatte, Dimitra Rigopoulou, Richard I. Davies, Miguel Pereira-Santaella, Ismael García-Bernete, Almudena Alonso-Herrero, Anelise Audibert, Enrica Bellocchi, Andrew J. Bunker, Françoise Combes, Tanio Díaz Santos, Fergus R. Donnan, Donaji Esparza-Arredondo, Federico Esposito, Santiago García-Burillo, Begoña García-Lorenzo, Omaira Gonzalez Martin, Laura Hermosa Muñoz, Erin K. S. Hicks, Sebastian F. Hönig, Masatoshi Imanishi, Alvaro Labiano, Nancy A. Levenson, Enrique Lopez-Rodriguez, Cristina Ramos Almeida, Claudio Ricci, Rogemar A. Riffel, Marko Stalevski

Astrophysics of Galaxies

CERIDWEN: Fast and Flexible GPU-Accelerated Stellar Population Inference

Amanda Stoffers, Sandro Tacchella and Benjamin D. Johnson

JWST has increased both the number of high-redshift galaxies with high-quality spectral energy distributions (SEDs) and their information content. In parallel, wide-area surveys from Euclid, Rubin's LSST, and Roman will increase galaxy samples by orders of magnitude. Analysing these datasets requires stellar-population models that are both flexible and computationally efficient. We present CERIDWEN, a GPU-native SED fitting framework written in JAX, with an end-to-end differentiable forward model spanning stellar populations, nebular emission, dust attenuation and emission, and projection into the observer frame. Its vectorised, compiled architecture lets nested sampling replace a batch of live points in parallel on the GPU, which makes flexible stellar-population models tractable under full Bayesian inference. Automatic differentiation also provides exact gradients for the gradient-based samplers in the package. We jointly infer time-dependent chemical-enrichment histories instead of a single stellar metallicity, and demonstrate non-parametric star-formation histories (SFHs) with $\sim$120 age bins. Using $\alpha$-enhanced stellar libraries from FSPS, CERIDWEN can sample stellar [$\alpha$/Fe] jointly with [Fe/H], mass, and SFH, so that the joint posterior represents the [Fe/H]-[$\alpha$/Fe] degeneracy explicitly. In controlled mocks, CERIDWEN recovers parameters with well-calibrated posterior uncertainties, while fits to real JWST observations reproduce posteriors from the established Prospector framework: on a single GPU, CERIDWEN completes a fit in a median sampling time of $\sim$4 min, $\sim$134$\times$ faster per fit than equivalent CPU-based Prospector runs. CERIDWEN therefore makes full Bayesian inference practical for larger galaxy samples and more flexible stellar-population models, reducing computational constraints on the physical complexity explored in SED fitting.
Read the full abstract

Astrophysics of Galaxies

The JWST and ALMA view of local dwarf Pox 186: Evidence of stripped binaries driving a hard radiation field and little cold molecular gas resulting in high star-formation efficiency

Nimisha Kumari, Renske Smit, Claus Leitherer et al. (+5 more)

We present a JWST mid-infrared (MIR) view of Pox 186, one of the best local analogs of reionization-era galaxies based on its extreme properties in the ultraviolet, optical, and far-infrared (FIR). We extracted a high signal-to-noise spectrum of Pox 186 from the spatially resolved MIR data taken with the Medium Resolution Spectrometer (MRS) on the MIR Instrument (MIRI), and compared its MIR properties with those of the other dwarf galaxies in the Herschel Dwarf Galaxy Survey. We probe the radiation hardness of Pox 186 using the so-called softness diagram, based on the MIR line ratios [NeIII]/[NeII] and [SIV]/[SIII], which suggest that Pox 186 hosts ionization sources with a hard radiation field. We probe the dominant ionization source in Pox 186 using diagnostic diagrams based on MIR line ratios. Our photoionization models provide evidence that stripped binary stars are the main cause of the extreme MIR line ratios. Similarly, a young starburst is needed to reproduce the MIR dust continuum. We probe the warm and cold molecular gas content using the MIR H$_2$ rotational lines (S(1)-S(7)) from JWST, and the archival sub-mm CO(2-1) line from ALMA, which indicate a high star-formation efficiency (SFE; $>$ 15 $\times$ 10$^{-9}$ yr$^{-1}$) and low gas depletion time comparable to that of the reionization-era galaxies. This analysis strongly suggests that star formation rather than active galactic nuclei drives the hard radiation field observed in Pox 186, and cautions against relying solely on the UV diagnostics to establish the nature of high-z galaxies.
Read the full abstract

All authors Nimisha Kumari, Renske Smit, Claus Leitherer, J. Álvarez-Márquez, Katherine Ormerod, Joris Witstok, Suzanne Madden, Matthew Hayes

Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Two-rung ladder: $H_0$ from Tip of the Red Giant Branch and geometric anchors alone

Richard Stiskalek, Harry Desmond and Guilhem Lavaux

We infer the Hubble constant $H_0$ from the ~400 Extragalactic Distance Database hosts with a tip of the red giant branch (TRGB) distance, calibrated on the geometric anchors of the Large Magellanic Cloud and NGC 4258. We forward-model the tip magnitudes and host redshifts including magnitude-limited selection, sky exposure, and density-dependent galaxy bias, conditioning on each of the 80 Manticore-Local realisations of the local density and peculiar-velocity fields in turn. As most hosts lie at $cz_{\rm CMB} \lesssim 1000$ km/s, where peculiar velocities are important, the inference is limited by the variance of these fields rather than by the TRGB calibration. For a fixed realisation, the redshift likelihood and density smoothing each move $H_0$ by less than 1 km/s/Mpc and a velocity monopole by $5.4 \pm 3.4$ km/s/Mpc, whereas the field-to-field scatter in $H_0$ is 5.2 km/s/Mpc. Weighting the posteriors from each realisation equally gives $H_0 = 68.4 \pm 5.9$ km/s/Mpc, while weighting each by its Bayesian evidence gives $72.3 \pm 2.6$ km/s/Mpc. The latter value is set by a single particularly high-evidence realisation, making it sensitive to the finite sampling of the reconstruction posterior. This ladder therefore cannot yet arbitrate the Hubble tension. Extending the TRGB data beyond the present ~1000 km/s, together with improved reconstructions of the local Universe, would reduce the field-to-field scatter well below the 5.2 km/s/Mpc we find here.
Read the full abstract

Astrophysics of Galaxies

PAHSPECS: JWST/MIRI Spectroscopy of PAHs at Cosmic Noon

Irene Shivaei, Tanio Díaz Santos, Leindert A. Boogaard et al. (+14 more)

The physical conditions of the interstellar medium (ISM) are thought to differ greatly at high redshifts compared to local galaxies. Polycyclic aromatic hydrocarbons (PAHs) are key ISM constituents, mediating the heating and cooling of gas in photo-dissociation regions. However, PAHs are unexplored in main-sequence (MS) galaxies at z~1-2 (cosmic noon), limiting our view of the ISM's thermal and chemical balance. We present the PAH Spectroscopic Survey (PAHSPECS) JWST program, the first MIRI/MRS survey of the 3.3, 6.2, 7.7, 8.6 and 11.3$\mu$m PAH features in MS galaxies at z~1. The five targets come from the deep ALMA CO and continuum flux-limited sample in the HUDF. We detect the 6.2, 7.7 and 11.3$\mu$m PAHs in all galaxies, and the 3.3$\mu$m feature in only two. Spectral energy distribution (SED) fitting to broad-band mid-IR photometry recovers the 6.2 and 7.7$\mu$m PAH luminosities derived from spectral decomposition of the MRS spectra to within ~25% accuracy. However, the 3.3 and 11.3$\mu$m features are overestimated by ~50% (up to 3-5x). Spatially resolved maps of ASPECS-6, the most extended source, show variations of the 7.7$\mu$m PAH contribution to the MIRI F1500W flux, suggesting that while photometry can infer PAH luminosity accurately, IFU spectroscopy is necessary to study variations in PAH ratios and characterize galaxy dust properties. The PAH fraction of the total dust mass from photometric SED modeling roughly agrees with the $L_{\rm PAH}/L_{\rm IR}$ ratio measured from spectroscopy, but the correlation is not as tight as models predict. On average, PAHSPECS galaxies show an excess in 6.2$\mu$m equivalent width relative to nearby dusty luminous systems, but lower 3.3$\mu$m equivalent widths than local systems, similar to higher-mass starbursts at z~1-3. This points to differential changes in the size distributions of neutral and ionized PAHs in cosmic noon galaxies.
Read the full abstract

All authors Irene Shivaei, Tanio Díaz Santos, Leindert A. Boogaard, Karin Sandstrom, Cristina Lofaro, Fergus R. Donnan, Pablo G. Pérez González, Roman Fernández Aránda, Javier Álvarez Márquez, Manuel Aravena, Roberto Decarli, Frédéric Galliano, Hanae Inami, Göran Östlin, Gergö Popping, Fabian Walter, Paul van der Wer

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Exceptional Gamma-Ray Flaring Activity of the Blazar S4 0954+65 in Early 2025

Zhihao Ouyang, Jingyu Wu, Hubing Xiao et al. (+11 more)

S4 0954+65 (4FGL J0958.7+6534) is a TeV-detected blazar at a redshift of $z = 0.3694 \pm 0.0011$, classified as an intermediate-synchrotron-peaked BL Lac object. In early 2025, it entered an exceptional $\gamma$-ray high state. We aim to investigate the origin and physical properties of the exceptional 2025 flare, and to constrain the emission processes responsible for this flaring activity. We performed a multi-wavelength analysis using $\gamma$-ray, X-ray, optical/UV, radio, and 43 GHz Very Long Baseline Array (VLBA) observations. We examined multi-band correlations with the z-transformed discrete correlation function (zDCF), analyzed the spectral evolution and parsec-scale jet kinematics, and modeled the broadband spectral energy distributions (SEDs). The $\gamma$-ray variations lead the optical and radio emission by 3.22 days and possibly 18.26 days, respectively, while no significant correlation is found between the $\gamma$-ray and X-ray emission. The $\gamma$-ray spectra show a harder-when-brighter behavior, consistent with enhanced particle acceleration during the active state. A similar spectral trend is also observed in the X-ray band, where the photon index is anti-correlated with flux. During the major $\gamma$-ray flare, VLBA images reveal the emergence of a new superluminal radio knot from the core, whose extrapolated ejection time is consistent with the peak of the $\gamma$-ray flare. The temporal and structural evolution during the 2025 flare is consistent with a shock-in-jet scenario, in which a newly emerging disturbance propagates downstream and drives the flare. Broadband SED modeling shows that a leptonic synchrotron self-Compton plus external Compton model with dusty torus seed photons reproduces the multi-wavelength observations with physically plausible parameters. A lepto-hadronic interpretation remains possible but requires substantially higher jet power.
Read the full abstract

All authors Zhihao Ouyang, Jingyu Wu, Hubing Xiao, Lili Yang, Shangchun Xie, Shaohua Zhang, Zhijian Luo, Jianzhen Chen, Jianguo Wang, Mingjun Liu, Qinyu Wu, Huaqing Cheng, Wenda Zhang, Junhui Fan

Astrophysics of Galaxies

Discovery of an isolated RELHIC Candidate: J1351+0039

Jin-Long Xu, Alejandro Benitez-Llambay, Ming Zhu et al. (+6 more)

We report the discovery of J1351+0039, a new isolated dark galaxy candidate identified through a blind HI survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), combined with deep optical imaging from the DESI Legacy Survey. The object displays a compact HI structure with a systemic velocity of V_{LSR} = 429.0 \kms and an inferred HI mass of 4.8*10^5 Msun. No optical counterpart is detected in the DESI images, with a g-band surface brightness limit of 28.1 mag arcsec^{-2}, corresponding to a stellar mass limit of M_{star} of 1.5*10^{5} Msun. The dynamical mass is estimated to be M_{dyn} of 1.3*10^{8} Msun, yielding a dark-to-baryonic mass ratio of 200, implying that J1351+0039 is overwhelmingly dominated by dark matter. While week rotation is detected in J1351+0039, the kinematics are dominated by internal velocity dispersion, confirming pressure support and reminiscent of Reionization-Limited HI Clouds (RELHICs). J1351+0039 stands out as one of the most promising isolated RELHIC candidates, offering a unique laboratory for studying baryonic physics and dark matter in the absence of star formation.
Read the full abstract

All authors Jin-Long Xu, Alejandro Benitez-Llambay, Ming Zhu, Chuan-Peng Zhang, Nai-Ping Yu, Xiao-Lan Liu, Mei Ai, Ruilei Zhou, Bin Liu

Astrophysics of Galaxies

How Magnetic Fields Regulate Cooling and Mixing in Turbulent Radiative Mixing Layers

Rajsekhar Mohapatra, Lachlan Lancaster, Drummond Fielding et al. (+2 more)

Turbulent radiative mixing layers (TRMLs) are expected wherever hot and cold gas move past one another, including in the solar corona, galactic winds, and cold filaments in galaxy clusters. These environments are often magnetized, but magnetic effects on mixing and cooling remain less well understood than in the hydrodynamic (HD) case. We present magnetohydrodynamic (MHD) simulations of TRMLs at resolutions up to $1024 \times 2048^2$, spanning fields aligned with and transverse to the shear, and polarity-reversing configurations in which oppositely directed fields form current sheets at the interface. Even initially weak hot-phase fields, with $\mathcal{M}_{\rm A,shear}\equiv v_{\rm shear}/v_{\rm A}\sim14$, reduce the mass and enthalpy flux and radiative cooling rate by up to an order of magnitude relative to HD. Magnetic tension weakens turbulent motions, reducing both the diffusion of hot gas into the layer and the folding of the cooling surface. Transverse fields suppress cooling somewhat more strongly than shear-aligned ones, although a transverse field exerts no tension against the initial linear instability. Polarity reversal changes the morphology of the cooling gas without restoring HD-like mixing. The dependence on the Damköhler number is similar to the HD case, but the degree of suppression is dependent on the initial field orientation. The net cooling rate appears resolution-independent in HD but declines with resolution in MHD, and has not converged, so our suppression factors are lower limits. Magnetic fields therefore strongly regulate cooling and mixing in multiphase gas, and quantitative predictions require careful treatment of transport processes.
Read the full abstract

All authors Rajsekhar Mohapatra, Lachlan Lancaster, Drummond Fielding, Eliot Quataert, Greg L. Bryan

Astrophysics of Galaxies · Cross-listed from gr-qc

Environmental Imprints of Dark Matter and Accretion Disks on Eccentric EMRIs around Kerr Black Holes

Hai-Chao Yuan and Yong Tang

Extreme-mass-ratio inspirals (EMRIs), systems in which a stellar-mass compact object spirals into a supermassive black hole ($M_1$), are prime targets for the space-based gravitational-wave interferometers and are acutely sensitive to their astrophysical environment. We quantify the joint imprint of a dark matter (DM) spike and an accretion disk on the waveforms of eccentric, equatorial Kerr EMRIs, integrating four modular effects—DM dynamical friction, DM self-gravity, Newtonian accretion-disk torques, and disk self-gravity—into a fifth post-Newtonian (5PN) augmented analytic kludge (AAK) waveform model, and assess their measurability via a Fisher-matrix analysis. The DM dynamical-friction dephasing peaks at $M_1\sim 10^6\,M_\odot$, reaching $\sim 10^2$–$10^3\,\mathrm{rad}$; there the DM spike slope is measurable to sub-percent precision and both DM channels are unambiguously detectable, while omitting DM biases the intrinsic parameters significantly. At $M_1\gtrsim 10^8\,M_\odot$ the DM and disk self-gravity channels dominate their dissipative counterparts. The disk parameters remain degenerate across the explored parameter space, since the supersonic regime dominates the inspiral and the subsonic-to-supersonic transition only mildly weakens this degeneracy without lifting it; a combined DM$+$disk analysis further reveals a cross-sector degeneracy between the DM slope and the disk parameters. This physical degeneracy, reflected in the near-singular Fisher matrix, implies that independently measuring the disk parameters requires a relativistic torque model or an electromagnetic counterpart.
Read the full abstract

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

AGN winds and outflows: from accretion-disc scales to the host galaxy

Delphine Porquet

Ultra-fast outflows (UFOs), launched from the inner accretion disc in active galactic nuclei (AGN), are among the prime candidates for driving AGN feedback in their host galaxies. Determining their physical properties and energetics is therefore essential for assessing their impact on galaxy evolution. This review highlights recent observational progress, with particular emphasis on the groundbreaking insights enabled by high-resolution X-ray spectroscopy. The first X-Ray Imaging and Spectroscopy Mission (XRISM)/Resolve observations of AGN winds have revealed that the innermost UFOs are kinematically structured and inhomogeneous. In the archetypal quasar PDS 456, these observations have led to a substantial upward revision of the inferred mass outflow rate, momentum flux and kinetic power. Complementary UV, optical, IR and mm observations trace the ionised, atomic and molecular phases of AGN-driven outflows from parsec to galactic scales. However, the physical coupling between the accretion-disc wind and the galactic outflows remains one of the major unresolved questions in AGN feedback. Building on the pioneering XRISM results, NewAthena's X-ray Integral Field Unit (X-IFU) will characterise the physical properties and energetics of accretion-disc winds with unprecedented precision from the local Universe up to cosmic noon, while complementary multi-wavelength observations with facilities such as the Extremely Large Telescope (ELT), James Webb Space Telescope (JWST), Atacama Large Millimeter/submillimeter Array (ALMA), and Square Kilometre Array (SKA) will determine whether and how their energy and momentum are transferred to the host galaxy.
Read the full abstract

Astrophysics of Galaxies

Galaxy And Mass Assembly (GAMA): The Most Isolated GAMA Galaxies

Steven Phillipps, Roberto De Propris, Malcolm N. Bremer et al. (+2 more)

While galaxies generally live in clusters and groups, particularly small groups, or other structures such as walls or filaments, some galaxies appear relatively `isolated', i.e. lacking in close neighbours. Here we use the GAMA survey, and an objective measure of isolation, to explore the most isolated galaxies. We then determine whether these have particular physical characteristics. We find that, as expected, while grouped galaxies split between blue, disk-like and star forming and red, spheroidal and quiescent, isolated galaxies are preferentially the former. However, there is a broad overlap in properties, with some isolated galaxies sharing the latter characteristics. Considering only the star-forming galaxies, when controlled by mass we find no differences between the grouped and isolated galaxies in terms of their star formation and stellar populations. Given the lack of significant interactions for the isolated sample, this implies that the evolution of present-day star-forming galaxies in all environments (at least outside rich clusters) has been, and remains, dominated by internal processes.
Read the full abstract

All authors Steven Phillipps, Roberto De Propris, Malcolm N. Bremer, Phil A. James, Andrew M. Hopkins

Astrophysics of Galaxies

Spatial segregation as the origin of anisotropic satellite quenching in haloes and beyond

Zhuoming Zhang, Weiguang Cui, Yun Chen et al. (+1 more)

Satellite galaxies in massive halos are seen to be preferentially quenched along the major axes of their central galaxies. In contrast, the AGN jet tends to point along the minor axis, which imposes interesting constraints on the role of AGN feedback in satellite galaxy quenching. Here we use the SIMBA, TNG100, EAGLE, and feedback-free SIMBA cosmological simulations at $z=0$ to show that this satellite anisotropy primarily originates from spatial segregation between quenched and unquenched populations. Quenched satellites are more centrally concentrated and more strongly aligned with the central galaxy's major axis, whereas unquenched satellites occupy larger radii and are more nearly isotropic. The persistence of this behaviour without stellar or active galactic nucleus feedback suggests that feedback is not important for satellite quenching. Beyond the halo boundary, the signal varies strongly among simulations and correlates with the excess number of galaxies along the major axis. This links large-scale anisotropic quenching to the direction-dependent distribution of groups, clusters and filamentary environments. Our results provide a unified geometrical interpretation of anisotropic satellite quenching across halo and extra-halo scales.
Read the full abstract

All authors Zhuoming Zhang, Weiguang Cui, Yun Chen, Romeel Davé

Astrophysics of Galaxies

Potential binary supermassive black holes in Markarian 231 as a scientific case for the spectropolarimeter POLLUX

Biedermann. J, Marin. F, Neiner. C et al. (+1 more)

It is now widely accepted that a supermassive black hole (SMBH) resides in the core of nearly every galaxy. Within the context of mergers of galaxies, the central SMBHs from each system should form a gravitationally bound binary system. Given the frequency of galaxy mergers throughout cosmic time, the existence of such binary SMBHs is likely to occur within active galactic nuclei. However, identifying them observationally remains highly challenging. The majority of reported candidates rely on indirect evidence rather than unambiguous detection. The quasar Markarian 231 (Mrk 231) stands out because of its distinctive ultraviolet to optical properties, which includes a strong wavelength dependent polarization and an unusual flux decrease at 2500A. In this work, we investigate the potential of spectropolarimetry as a powerful tool for identifying and characterizing SMBH binaries in AGNs. We have developed a simplified analytical model to reproduce the spectral energy distribution of the quasar Mrk 231 assuming a binary SMBH geometry, and we compute both its total and polarized emission. The main aim is to test whether two separate emitting sources could explain the unique UV to optical signatures of Mrk 231. Such investigations highlight the importance of a future high-sensitivity UV spectropolarimetric instrument. For instance, the proposed Pollux spectropolarimeter for the Habitable Worlds Observatory (HWO) has the potential to significantly contribute to our understanding of AGNs structure and the role of SMBH binaries in quasars.
Read the full abstract

All authors Biedermann. J, Marin. F, Neiner. C, Bouret. Jean-Claude

Astrophysics of Galaxies

Probing binary supermassive black hole in quasars tough spectropolarimetry

J. Biedermann and F. Marin

Nearly all galaxies are believed to host a supermassive black hole at their center. In the context of galaxy mergers, the SMBHs from the progenitor galaxies are expected to form a bound binary system. Given the high frequency of such mergers throughout cosmic time, binary SMBHs should be relatively common in active galactic nuclei (AGNs). Yet, their direct detection remains a major observational challenge, with most candidates inferred only through indirect signatures. The quasar Markarian 231 presents unique ultraviolet-optical properties, including an atypical drop in the total flux around 2500 A and a strong wavelength-dependent polarization. In this work, we explore the potential of spectropolarimetry as a tool to detect and characterize SMBH binaries in AGNs. We construct a simple analytical model in order to reproduce the spectral energy distribution (SED) of Mrk 231 taking into account a binary SMBHs scenario and we compute the resulting total and polarized flux. Our goal is to test if the presence of two distinct sources can reproduce the unique ultraviolet-optical properties observed in Markarian 231. Such investigations support the case for future high-sensitivity UV spectropolarimeters in order to probe the inner structure of quasars. In particular, the next-generation instrument POLLUX, proposed for the Habitable Worlds Observatory, would be particularly suited to provide new insights into AGNs physics and supermassive black hole binaries in quasars.
Read the full abstract

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure

Aaron M. Meisner, Adam J. Burgasser, Chih-Chun Hsu et al. (+15 more)

We present JWST NIRSpec and MIRI observations of the metal-poor T dwarf WISEA J155349.96+693355.2. The combined NIRSpec/prism plus MIRI/LRS spectrum (R ~ 100) provides 0.6-12 $\mu$m spectroscopic coverage that reveals the presence of H$_2$O, CH$_4$, and NH$_3$ absorption features, enhanced collision-induced H$_2$ absorption, and weak or absent CO and CO$_2$ absorption, all indicators of a metal-poor low-temperature atmosphere. Comparison of the spectral data to a suite of atmosphere models yields an effective temperature $T_{\rm eff}$ = 960$^{+28}_{-32}$ K and a solar-scaled metallicity of [M/H] = -1.16$^{+0.28}_{-0.25}$ dex. We find indications that the uncertain trigonometric parallax, likely subject to Lutz-Kelker bias, may be overestimated. Adopting the photometric distance yields a bolometric luminosity log$_{10}L_{bol}/L_{\odot}$ = -5.29 $\pm$ 0.10, from which we infer $T_{\rm eff}$ = 974 $\pm$ 56 K, consistent with the temperature derived via our atmospheric model fits. From the moderate-resolution (R ~ 3,000) NIRSpec/G395H spectrum, we measure a radial velocity of -163 $\pm$ 5 km/s, which combined with the source's measured proper motion and estimated distance indicates a highly eccentric (e $\geq$ 0.9) Galactic orbit consistent with an accreted halo object. The UVW kinematics of WISEA J155349.96+693355.2, its bulk metallicity, and its modest alpha enrichment ([$\alpha$/Fe] = +0.15$^{+0.04}_{-0.06}$ dex) are all equivalent to stars identified in the Gaia-Enceladus Milky Way substructure, making it the first brown dwarf with kinematic and chemical evidence of association.
Read the full abstract

All authors Aaron M. Meisner, Adam J. Burgasser, Chih-Chun Hsu, Sherelyn Alejandro Merchan, Jacqueline K. Faherty, Genaro Suárez, ZengHua Zhang, Roman Gerasimov, Christian Aganze, Nicolas Lodieu, Eileen C. Gonzales, Adam C. Schneider, Stanimir A. Metchev, Dan Caselden, Michael C. Cushing, Christopher A. Theissen, Jason J. Wang, Harshil Kothari

Astrophysics of Galaxies

A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes

Jian-Guo He, Yong Shao, Yu-Dong Nie et al. (+5 more)

Gravitational-wave observations have revealed hundreds of stellar-mass black holes, yet only about two dozen are known in the Milky Way, almost all in binaries. We present POPKIN, a Python framework that couples single- and binary-star evolution with Galactic orbital dynamics to trace black-hole progenitors from the zero-age main sequence to the present-day isolated black-hole (IBH) population. Across ten models varying the supernova (SN) prescription, mass-transfer efficiency, and common-envelope ejection efficiency, the total IBH abundance is controlled primarily by the SN prescription. Our fiducial model, with a recently proposed metallicity- and stripping-history-dependent SN prescription, predicts $\sim4\times10^7$ IBHs in the Galaxy, including $\sim8\times10^4$ within $1\,\rm{kpc}$ of the Sun; alternative SN prescriptions predict $\sim(1-2)\times10^8$ IBHs. The fiducial model yields a bimodal mass distribution, peaking near $9\,M_{\odot}$ and $20\,M_{\odot}$, with a deficit at $13-17\,M_{\odot}$. This distinguishes it from alternative prescriptions, some of which populate the $2-5\,M_{\odot}$ mass-gap region. Non-kicked IBHs follow nearly circular orbits near the Galactic plane, with typical peculiar velocities of $20-30\,\rm{km\,s^{-1}}$, whereas kicked systems undergo stronger radial migration and span a broader velocity range. We estimate $\sim5\times10^3$ accreting IBHs with $F_{\rm X}>10^{-14}\,\rm{erg\,s^{-1}\,cm^{-2}}$, nearly all non-kicked; this estimate is sensitive to the adopted radiative-efficiency and hot-flow treatments. For a Roman-like bulge survey, our fiducial model predicts $\sim360$ intrinsic IBH microlensing events over five years in a $1.70\,\rm{deg^2}$ effective area, before survey-selection effects. We propose that long-timescale microlensing events from IBHs can strongly constrain the SN physics governing stellar-mass black hole formation.
Read the full abstract

All authors Jian-Guo He, Yong Shao, Yu-Dong Nie, Gui-Yu Wang, Xiao-Tian Xu, Chen Wang, Xiao-Jie Xu, Xiang-Dong Li