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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Monday 17 August

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

SN 2023gfo: A Peculiar Type IIP Supernova with High Luminosity and Normal Plateau Duration

Riko Namba, Masayuki Yamanaka, Keiichi Maeda et al. (+9 more)

We present near-infrared (NIR) and optical observations of the highly reddened Type IIP supernova (SN) 2023gfo in the nearby galaxy NGC 4995 ($d = 26.4 \pm 3.2$ Mpc), which reached a high peak luminosity of $M_V = -18.6$ mag. The SN was initially detected as a faint red event, with $B-V = 0.8$ mag at the beginning of the plateau phase. By comparison with template, we estimate a total extinction of $A_V = 2.1$ mag. After correcting for this extinction, we derive a peak quasi-bolometric luminosity of $(5.9 \pm 1.5)\times10^{42}$ erg s$^{-1}$, placing this event among the most luminous SNe IIP, while its plateau duration remains within the normal range. The early-phase optical spectrum exhibits a P-Cygni profile of H$\alpha$, with a broad absorption of $V$ = $13{,}800$ km s$^{-1}$, which is among the highest observed for SNe IIP at comparable epochs. The high luminosity and the normal plateau duration suggest that this event represents an outlier. Applying an analytical model, we infer an unusually large progenitor radius. This may indicate that the progenitor experienced an extreme energy injection from the core to the envelope shortly before explosion, resulting in a substantially inflated radius. While ejecta-circumstellar matter (CSM) interaction could in principle account for the high luminosity, we find no observational evidence supporting strong interaction.
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All authors Riko Namba, Masayuki Yamanaka, Keiichi Maeda, Avinash Singh, Kenta Taguchi, Takahiro Nagayama, Miho Kawabata, Koji S. Kawabata, Tatsuya Nakaoka, Devendra Sahu, Anjasha Gangopadhyay, G. C. Anupama

Astrophysics of Galaxies

The Koi Pond: A Strongly Lensed Protocluster Core hosting a Diverse Population of DSFGs

Nicholas Foo, Kevin C. Harrington, Brenda L. Frye et al. (+29 more)

We present James Webb Space Telescope (JWST) and Atacama Large Millimeter Array (ALMA) observations of PJ0846+15, The Koi Pond, a strongly lensed protocluster core at Cosmic Noon. This field offers a magnified view of 11 dusty star-forming galaxies (DSFGs) all at $z=2.67$ (within $\Delta V=800$ km s$^{-1}$) spanning a projected extent of $>300$ kpc lensed by a $z=0.77$ foreground cluster. NIRCam and ALMA Band 6 continuum measurements map the stellar distribution and thermal dust emission respectively at a spatial resolution of $\sim$0.15$^{\prime\prime}$. This analysis reveals a diverse population of DSFGs, with evidence of both interacting and non-interacting systems exhibiting a wide range of morphological features including spiral arms, bars, bulges, clumps/stellar clusters, tidal tails/debris and displaced molecular gas reservoirs. Comparing the rest-frame J- band continuum (F444W) vs (i-J) color (F277W$-$F444W), we find a wide range of values, suggesting a $>$1-dex spread in stellar mass and a dust attenuation reddening of $\Delta A_{\mathrm{V}} > 1$ mag. The DSFG members exhibit varying dust sizes relative to the stellar emission, ranging from compact dusty cores to galaxy-wide emission. Resolved color maps of individual sources showing a spread as high as F277W$-$F444W$=2$ mag suggesting complex stellar-to-dust geometry. Although gas-rich mergers are identified in the core, the most red and dust emitting members are disks exhibiting clumpy structure indicating secular growth can drive these starburst events. Such a remarkable range in properties within this sample suggest DSFGs in protocluster core environments follow diverse evolutionary pathways towards their transition into quiescent, elliptical cluster galaxies.
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All authors Nicholas Foo, Kevin C. Harrington, Brenda L. Frye, Patrick S. Kamieneski, Melanie Kaasinen, Rafael Ortiz III, Alex Pigarelli, Gibson B. Bowling, Belén Alcalde Pampliega, Joe Bhangal, Timothy Carleton, Jianhang Chen, Seth H. Cohen, Camila de Sá-Freitas, Jose Diego, Román Fernández Aranda, Carlos Garcia Diaz, Nikhil Garuda, Eric F. Jiménez-Andrade, Daizhong Liu, James D. Lowenthal, Allison Man, Allison Noble, Massimo Pascale, Francesca Rizzo, Hannah R. Stacey, Amit Vishwas, Q. Daniel Wang, Rogier A. Windhorst, Ilsang Yoon, Min S. Yun, Dazhi Zhou

Sunday 16 August

Astrophysics of Galaxies

The Low-Mass Baryon Cycle in QUEST Dwarf Galaxies I: Sample definition and first results

Ava Polzin, Hsiao-Wen Chen, Zhijie Qu et al. (+3 more)

We introduce the QUEST Dwarfs program, which connects low-mass galaxies' stellar populations, interstellar medium, and circumgalactic medium in a large and coherently analyzed sample using a combination of optical spectroscopy, broadband imaging, and FUV absorption spectra of bright background sources .We present initial results from the first-release sample, comprising 14 galaxies with stellar mass $M_\mathrm{star} \leq 10^9 M_\odot$ at $z\approx0.001-0.017$, each with at least one CGM absorption probe at projected distances $d_\mathrm{proj}\lesssim 100$ kpc. This representative sample triples the number of available probes within 1/3 of the halo radius of dwarf galaxies outside of the Local Group. We find that the total silicon column density declines much more rapidly with projected distance than Hi, implying that chemically enriched cool gas is preferentially concentrated in the inner CGM, while the increasing ionization fraction of hydrogen with radius likely enhances this contrast. Accounting for unobserved silicon in higher ionization stages, we infer total metal masses of $\log M_Z/M_\odot\approx4.8$ and $6.5$ in the cool CGM within $0.3 R_\mathrm{vir}$ for dwarfs with median $\log M_\mathrm{star}/M_\odot=7.6$ and 8.6, respectively. These reservoirs correspond to $\approx3$% and $\approx16$% of the total metals produced over the galaxies' lifetimes. More massive galaxies also exhibit systematically stronger metal absorption, suggesting that projected distance governs the radial decline of metal absorption while stellar mass sets the normalization of the CGM metal profile. Individual ions reveal a multiphase structure, with low-ionization species concentrated in the inner halo and higher-ionization species extending farther. The full QUEST Dwarfs survey will provide the statistical power needed to isolate the dominant drivers of CGM enrichment in low-mass halos.
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All authors Ava Polzin, Hsiao-Wen Chen, Zhijie Qu, Erin Boettcher, Allison Strom, Tsang Keung Chan

Astrophysics of Galaxies

The reddening of NGC 7469 and evidence for variable extinction

C. Martin Gaskell, Ananya R. Kamath, Emily I. Kwan et al. (+1 more)

We estimate the reddening of the broad-line region and continuum of the active galactic nucleus NGC 7469 during the 1996 International AGN Watch multi-wavelength monitoring campaign using seven different reddening indicators. As was found for NGC 5548, these indicators support velocity-integrated broad hydrogen line ratios being close to Case B values. All the indicators point to substantial reddening of E(B-V) = 0.44 +/-0.03 for NGC 7469 during mid-1996. We find evidence for a gradual increase of about 10% in the reddening during the seven weeks of the 1996 campaign. Decades-long optical monitoring before and after the campaign is also consistent with modest changes in the extinction from year to year.
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All authors C. Martin Gaskell, Ananya R. Kamath, Emily I. Kwan, Divya G. Subramonian

Astrophysics of Galaxies

Multiphase turbulence as the origin of OH+, H2O+ and H3+ column density scatter in the local ISM

Uri Malamud, Shmuel Bialy, Benjamin Godard et al. (+2 more)

Observations of the reactive ions OH+, H2O+ and H3+ in the Galactic interstellar medium reveal large sight-line-to-sight-line scatter in their column densities, commonly interpreted as evidence for substantial variations in the cosmic-ray ionization rate (CRIR). We revisit this interpretation using high-resolution three-dimensional magneto-hydrodynamic simulations of the multiphase ISM with time-dependent chemistry for H, H2, H+ and electrons, building on the fiducial model of Godard et al. (2023). We find that a single CRIR of ~2 10^{-16} s^{-1}, together with standard Galactic-scale parameters, naturally produces broad column-density distributions for all three tracers in good agreement with the observed medians and percentile widths, with no fine tuning. Reaching this match requires that the post-processing of OH+, H2O+ and H3+ retain the time-dependent H2 field generated by the turbulent flow rather than assume chemical equilibrium: turbulence drives long-lived H2 enhancements in the unstable neutral medium where OH+ and H2O+ predominantly reside, and an equilibrium treatment under-predicts their columns substantially. H3+, which receives most of its column from denser CNM gas closer to equilibrium, is much less affected. Our results caution against interpreting sight-line-to-sight-line scatter as direct evidence for large CRIR fluctuations, and motivate a shift from independent 1D equilibrium analyses toward 3D dynamical frameworks when inferring ionization conditions in the ISM.
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All authors Uri Malamud, Shmuel Bialy, Benjamin Godard, David Neufeld, Blakesley Burkhart

Astrophysics of Galaxies · Cross-listed from gr-qc

Nonlinear Density Waves and a Galactic-Scale Estimate of the Graviton Mass

Miroslava Vukcevic

In February 2016 the LIGO and Virgo collaborations reported the discovery of gravitational waves in merging black holes, with the conclusion that their observational data did not show any violation of general relativity. The joint LIGO and Virgo team presented an upper limit on the graviton mass, using tests of modified gravitational dynamics. Yukawa-type gravitational potential corrections are often used as generic finite-range parametrisation in modified gravity contexts, including massive-gravity inspired models. Yukawa corrections are derived by semi-empirical approach, in the framework of f(R) gravity, a type of modified gravity which generalises Einsteins general relativity. Contrary to this approach, we use a classical Newtonian gravitational potential corrected by nonlinear effects in order to obtain a characteristic wavelength of the nonlinear density wave. This wavelength is then phenomenologically identified with an effective graviton Compton wavelength, leading to a model-dependent estimate of an effective graviton mass within the galaxy scale. The presented approach is independent from other methods published until now.
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Astrophysics of Galaxies

Theoretical emission lines and metallicity calibrations of H II regions in ASTRID simulation

Yao Yao, Kathryn Grasha, Stuart Wyithe et al. (+5 more)

We present a theoretical framework to derive redshift-dependent metallicity calibrations for galaxies at $z$=2-7. The ionization parameter ($U$) and gas pressure ($P$) in our approach are not assumed, but are predicted self-consistently. By combining the ASTRID cosmological simulation with stellar population synthesis (SPS) and MAPPINGS V photoionization modeling, we evolve young star clusters under an analytic wind-driven bubble model. This directly couples stellar feedback to the local ISM density, allowing \hii{} region properties to emerge from the underlying physics rather than being treated as free parameters. The emission-line predictions are validated against observed star-formation rate indicators (deviation <0.05 dex) and the \oiii{} luminosity function. We derive calibrations for common optical (e.g. R23, O3N2, N2, O32) and UV (e.g. C3O3, N3O3) diagnostics. We find significant redshift evolution in these relations, driven primarily by changing ionization conditions. A Bayesian analysis quantifies calibration performance under varying signal-to-noise, enabling diagnostic recommendations as a function of redshift and data quality. The R23 calibration performs well at all redshifts with minimal error in our model, while nitrogen- and carbon-based calibrations are highly sensitive to the abundance enrichment process and should be used with caution. These results provide a practical framework for interpreting JWST spectroscopy and tracing chemical evolution from cosmic noon to the epoch of reionization.
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All authors Yao Yao, Kathryn Grasha, Stuart Wyithe, Enci Wang, Nianyi Chen, Patrick Lachance, Tiziana Di Matteo, Yihao Zhou

Saturday 15 August

Astrophysics of Galaxies

Improved constraints on the Milky Way potential using the M68 stream and DESI spectroscopic data

Carles G. Palau, Wenting Wang, Jiaxin Han et al. (+41 more)

We present a selection of stars belonging to the stellar stream of the M68 (NGC 4590) globular cluster, also known as Fjörm. This star selection is an improvement on previous ones that used only Gaia data, as it incorporates spectroscopic measurements from the DESI survey and photometric data from the DESI Legacy Surveys. The selection contains 96 stars, each with five phase-space parameters from Gaia-DR3 and radial velocity from DESI, covering the entire observed section of the stream. This constitutes the largest selection of M68 stream stars with measured radial velocities to date. The observed stream is wider than expected from N-body simulations, and the stars farthest from the centre of the stream appear to be correlated in radial velocity space. This suggests that these stars cannot have been stripped from the cluster in a static axisymmetric potential. By modelling a mock sample of stream stars created using an N-body simulation, we found that we could reliably constrain the disc mass $M_{\rm d}$ and the dark matter halo axis ratio $q_{\rm h}$ of the Milky Way. This is because the stream flows close to and almost parallel to the disc. Using the 44 stars that are consistent with having been stripped from the cluster, combined with measurements of the Milky Way's rotation curve, we constrain the Galactic potential, obtaining $M_{\rm d} = 5.34 \pm 0.57 \times 10^{10}$ M$_{\rm sun}$ and an oblate halo of $q_{\rm h} = 0.83^{+0.06}_{-0.05}$. Additionally, by fitting the stream track, we estimate the Heliocentric distance of M68 to be $r=10.55\pm0.09$ kpc.
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All authors Carles G. Palau, Wenting Wang, Jiaxin Han, J. Aguilar, S. Ahlen, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, F. J. Castander, T. Claybaugh, A. Cuceu, A. de la Macorra, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, J. Guy, D. Kirkby, A. Kremin, M. Landriau, L. Le Guillou, A. Leauthaud, G. E. Medina, A. Meisner, R. Miquel, S. Nadathur, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, R. Ruggeri, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, M. Siudek, G. Tarlé, B. A. Weaver, H. Zou

Astrophysics of Galaxies

Aromatics and Aliphatics in Local Star-Forming Galaxies as Probed by AKARI

Junhao Peng, Xuejuan Yang and Aigen Li

Polycyclic aromatic hydrocarbon (PAH) molecules are abundant and widespread in galaxies and their infrared (IR) emission traces star formation. PAH molecules in astronomical environments often have aliphatic contents as revealed by the detection of the 3.4 micron aliphatic C–H stretch, a weak satellite feature accompanying the 3.3 micron aromatic C–H stretch. Here, we selected 102 local star-forming galaxies from the AKARI archive, including 66 galaxies each of which hosts an active galactic nucleus (AGN). We analyzed their AKARI near-IR spectra, which exhibit pronounced 3.3 micron aromatic and 3.4 micron aliphatic C–H emission. We also compiled their multi-wavelength photometric data and performed a decompositional analysis of their spectral energy distributions (SEDs) from the ultraviolet (UV) to the far-IR to derive the star formation rates (SFRs), stellar masses, metallicities, and luminosity of the galaxies. We explored the 3.3 micron PAH emission luminosity ($L_{3.3}$) as a calibrator of the SFR and found a close agreement with previous studies. We also found that $L_{3.3}/L_{\rm IR}$ and $L_{3.4}/L_{\rm IR}$ exhibit a strong dependence on metallicity, but remain nearly constant above 12+log(O/H)$\sim\,$8.5, where $L_{\rm IR}$ is the total luminosity emitted by dust, and $L_{3.4}$ is the luminosity of the 3.4 micron aliphatic emission. We derived from $L_{3.4}/L_{3.3}$ the PAH aliphatic fractions, defined as the fractions of carbon atoms in aliphatic units, to be in the range of $\sim\,$0.38%–6.8%, with a median fraction of $\sim\,$3.1%. The PAH aliphatic fractions are lower in AGN hosts and show a weak negative correlation with the SFR and $L_{\rm IR}$, suggesting that UV photons in regions with AGN or strong star formation activities may photodissociate the aliphatic structures associated with PAH molecules.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

An ALMA view of the Jet-Arc CO clouds toward the TeV $\gamma$-ray source HESS J1023-575 and Westerlund 2; Evidence for the footprints of microquasar jets, the very powerful cosmic-ray accelerator in the Galactic disk

Yasuo Fukui, Kisetsu Tsuge, Hidetoshi Sano et al. (+7 more)

The TeV $\gamma$-ray source HESS J1023-575 (HESSJ 1023 hereafter) is one of the brightest H.E.S.S. sources near the young massive cluster Westerlund 2. HESS J1023 shows a remarkable positional alignment with the Jet and Arc CO clouds on its eastern and western sides over 170 pc length. We have carried out sub-pc scale observations of the CO clouds with ALMA and have discovered that the clouds consist of numerous thin filamentary features of $\sim$0.5 pc width and 10–20 pc length at distance of 7.5 kpc, which are well aligned with the Jet-Arc axis. Based on the magneto-hydrodynamical model of microquasar jets launched from {the center of the $\gamma$-ray source} HESS J1023-575, we present an interpretation that the thin filamentary clouds are the footprints of the microquasar jets on the HI gas. The model also explains the dissimilar Jet vs. Arc clouds in terms of HI density difference on each side. By using the density of the CO and HI gas and the $\gamma$-ray luminosity, we have calculated the cosmic ray proton energy $W_{\rm p}$ to be 7$\times$10$^{48}$ erg under the hadronic scheme, which is ten times larger than those derived in the TeV $\gamma$-ray SNRs RX J1713.7-3946 and RX J0852.0-4622. It is likely that HESS~J1023 has been active over 1-10 Myr, which is significantly longer than the duration of cosmic ray acceleration of the SNRs. HESS~J1023 is therefore an outstanding source of cosmic rays equivalent to at least 1000 SNRs, and is possibly the most powerful CR accelerator in the Galactic disk. A high energy compact source in HESS~J1023, which is likely a Myr-old black hole or neutron star, remains veiled due to heavy extinction.
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All authors Yasuo Fukui, Kisetsu Tsuge, Hidetoshi Sano, G. R. Bhuvana, Rin I. Yamada, Ryoji Matsumoto, Yuta Asahina, Tsuyoshi Inoue, Tim Lukas Holch, Emma de Oña Wilhelmi

Astrophysics of Galaxies

Detection of Aliphatically Deuterated Aromatic Hydrocarbons in the Large Magellanic Cloud 30 Doradus Star-Forming Complex

Junhao Peng, Xuejuan Yang and Aigen Li

The unidentified infrared (IR) emission (UIE) bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 micron are ubiquitously seen in a wide variety of astrophysical environments. While the exact assignment of these UIE bands remains controversial, they are generally ascribed to C–H and C–C stretching and bending vibrations of aromatic hydrocarbon molecules. Here, based on observations made with the Near Infrared Spectrograph (NIRSpec) and the Mid Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST), we report that the UIE emitters in the 30 Doradus star-forming complex in the Large Magellanic Cloud (LMC) are deuterated and have an appreciable amount of aliphatic content. The spatially resolved NIRSpec and MIRI spectra of 30 Doradus reveal a widespread detection of the 3.4 and 6.85 micron emission features attributed to aliphatic C–H stretch and deformation, respectively, as well as the 4.65 micron feature attributed to aliphatic C–D stretch. Notably, the 6.85 micron feature exhibits three complex substructures at ~6.83, 6.86 and 6.88 micron that have never been reported before.
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Astrophysics of Galaxies

Infrared Spectroscopy of Cyanonaphthalenes under Interstellar Relevant Conditions and Their Potential Connection with Astronomical Aromatic Infrared Bands

Jiaqi Xin, Jianzhi Xu, Piero Ferrari et al. (+1 more)

Context. Aromatic infrared bands (AIBs) are widely observed in diverse astrophysical environments and are generally attributed to vibrational emission from polycyclic aromatic hydrocarbons (PAHs). The recent interstellar detection of 1-cyanonaphthalene (1-CNN) and 2-cyanonaphthalene (2-CNN) has motivated detailed infrared spectroscopic studies of cyano-substituted PAHs. Aims. We aim to characterize the infrared spectra and vibrational modes of neutral 1-CNN and 2-CNN under cold and gas-phase conditions and to assess their possible spectroscopic relevance to the astronomical AIBs. Methods. The gas-phase infrared spectra of neutral 1-CNN and 2-CNN were measured in a cold molecular beam using ion-dip spectroscopy. The observed bands were assigned with the aid of harmonic and anharmonic calculations at the B3LYP/N07D level. Infrared emission spectra were subsequently simulated from the experimental spectra within a single-photon approximation framework. Results. We report the infrared spectra of neutral 1-CNN and 2-CNN measured under cold and gas-phase conditions relevant to the interstellar medium. Their vibrational features were assigned in detail, including fundamental vibrations as well as overtone and combination bands. The simulated emission spectra exhibit features in several wavelength regions associated with prominent AIBs, including the aromatic CH stretching region near 3.3 micron, the CC stretching region near 6.2 micron, the mixed CH in-plane bending and CC stretching region at 8.6-8.9 microns, and the CH out-of-plane bending region between 10 and 15 microns. Conclusions. The present spectra provide laboratory reference data for small cyano-substituted PAHs and offer useful clues for interpreting selected AIB regions. These results suggest that cyanonaphthalene molecules are promising contributors to the aromatic infrared bands.
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All authors Jiaqi Xin, Jianzhi Xu, Piero Ferrari, Gao-Lei Hou

Friday 14 August

Astrophysics of Galaxies

Local Interstellar Flow Parameters from the First Intersection of IMAP-Lo's Parameter Tubes

Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard et al. (+24 more)

The Sun's motion through the interstellar medium creates a flow of interstellar neutral (ISN) atoms through the heliosphere. ISN He, due to its high universal abundance and relatively low ionization rate, is the most abundant of the interstellar species near 1 au and ideal for flow parameter determination. The Interstellar Boundary Explorer (IBEX) measurements of ISN He flow parameters (speed, temperature, and direction) yielded a tube in 4D parameter space – narrow in cross-section but highly extended along one parameter axis (e.g., ecliptic longitude direction). This “4D parameter tube” results in large systematic uncertainties, a direct consequence of IBEX-Lo's fixed viewing orientation on the spacecraft. On the Interstellar Mapping and Acceleration Probe (IMAP), the articulation of the IMAP-Lo boresight using its pivot platform enables multiple viewing orientations of the ISN flow for significant systematic uncertainty reduction. We provide first results that definitively intersect ISN parameter tubes for elongation angles $79^\circ$, 94$^\circ$, and 109$^\circ$, resulting in precise interstellar parameters: speed $26.37 \pm 0.82$ km s$^{-1}$, ecliptic longitude direction $74.85^\circ \pm 0.96^\circ$, ecliptic latitude direction $-5.212^\circ \pm 0.035^\circ$, and temperature $7740^{+770}_{-730}$ K. The inferred flow of the Very Local Interstellar Medium is not consistent with either the Local Interstellar Cloud or the G-Cloud, but rather an intermediate state. IMAP is now positioned to study the detailed physics of this complex, nearby interstellar region. By resolving and understanding its physics, we determine how the heliosphere responds to the local interstellar flow, and how it may evolve in time
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All authors Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard, Eberhard Moebius, Hafijul Islam, Jonathan S. Bower, Maciej Bzowski, Eric R. Christian, Ken Fairchild, Herbert O. Funsten, Stephen A. Fuselier, Andre Galli, Jonathan Gasser, Matina Gkioulidou, David Heirtzler, Izabela Kowalska-Leszczyska, Marzena A. Kubiak, David J. McComas, Jonathan T. Niehof, Jamie S. Rankin, Justyna Sokol, Pawel Swaczyna, Jamey R. Szalay, Carol Weaver, Peter Wurz, Gary P. Zank, Eric J. Zirnstein

Astrophysics of Galaxies

VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023

Douglas Carlos, Ciriaco Goddi, Alejandro Mus et al. (+5 more)

We present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterize the compact cores in total intensity and polarization, focusing on the behavior or the linear polarization fraction (LP), electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigate both individual objects–such as M87, Sgr A*, 3C273, and 3C279–and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multi-band measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow–particularly in the case of Sgr A*–cannot be ruled out.
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All authors Douglas Carlos, Ciriaco Goddi, Alejandro Mus, Nicola Marchili, Kazi L.J. Rygl, Ezequiel Albentosa-Ruíz, Iván Martí-Vidal, The Event Horizon Telescope Collaboration

Astrophysics of Galaxies

High-spectral-resolution Observations of the [S II] Emission-line Doublet in the Filamentary Nebula Surrounding NGC 1275

Benjamin Vigneron, Julie Hlavacek-Larrondo, Carter Lee Rhea et al. (+10 more)

We analyze new high-spectral resolution SITELLE observations (R = $\lambda/\Delta\lambda$ = 7000) of the filamentary nebula surrounding NGC 1275, central galaxy of the Perseus cluster. We present here analysis of the \sii$\lambda6716$ and \sii$\lambda6731$ emission line doublet, using its ratio to determine the electron density of the optically emitting filaments. We compare these measurements with electron densities derived from deep Chandra X-ray observations of the intra-cluster medium (ICM) to determine if any correlations in density can be found. We report the detection of a clear dichotomy between the outer filaments, displaying on average lower \sii\text{ }emission line ratio of $\sim 1.1$ and the inner filaments displaying higher ratios of $\sim 1.3$. These results indicate that most of the gaseous filaments lie close to the low-density threshold for the density measurement of $\sim 10^2\text{ cm}^{-3}$. Using radial profiles, we find that the inner filaments have a roughly constant density, whereas the ICM density decreases with radius. In the outer filaments, we observe hints of local connections between the densities of the ICM and optical filaments, but no clear correlation seems to be observed overall. We also combined these density measurements with cold molecular CO gas observations to derive a relationship between temperature, density and pressure for the multiphase environment surrounding NGC 1275. Finally, we investigated potential models to explain the observed density measurements and explored similar studies of filamentary nebula around other central galaxies of cool-core galaxy clusters.
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All authors Benjamin Vigneron, Julie Hlavacek-Larrondo, Carter Lee Rhea, Christoph Pfrommer, Greg L. Bryan, Megan Donahue, Alastair Edge, Andrew Fabian, Michael McDonald, Annabelle Richard-Lafferrière, Laurie Rousseau-Nepton, G. Mark Voit, Norbert Werner

Astrophysics of Galaxies

Mixing stochasticity relinquishes evidence for magnetorotational hypernovae

Anmol Aggarwal and Ralph Schoenrich

A recent work claimed by fitting the observed elemental abundance pattern of a halo star with the total yields from single super-/hypernova events that only a magnetorotational hypernova event (a very energetic supernova event that also produces r-process elements) could be the source of the observed abundances. Here, we show that the star's peculiar abundance pattern is better fitted within the framework of mixing stochasticity with yields from a normal core collapse supernova (ccSN; Energy$_{\rm exp}$ $\sim 10^{51}$ erg.) and a neutron star merger (NSM). The stochastic mixing model outperforms the hypernova fitting significantly, (r.m.s 0.24 vs 0.44) i.e., favours the composition from common events (ccSN + NSM) over the magnetorotational hypernova scenario. We also discuss the origin of the star and the possibility of enrichment of its birth cloud by both a ccSN and a NSM.
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Astrophysics of Galaxies

ATLAS. IV. A JWST+MUSE Demographic Study of Ly$\alpha$ Profiles in Little Red Dots

Yuta Kageura, Masami Ouchi, Hiroto Yanagisawa et al. (+6 more)

We present an initial demographic study of Ly$\alpha$ profiles in little red dots (LRDs) at $z=3$–9 using $R\sim1000$–4000 spectroscopy. Our sample consists of 8 LRDs observed in the VLT/MUSE Deep and Wide surveys and 23 LRDs observed with JWST/NIRSpec grating spectroscopy from JADES, CANUCS, and GO programs including SPURS. We identify Ly$\alpha$ emission in 5 MUSE LRDs and 9 JWST LRDs. Only two of them exhibit broad Ly$\alpha$ emission (FWHM $>1000\ \mathrm{km\ s^{-1}}$), both reported previously. The other Ly$\alpha$-emitting LRDs show narrow Ly$\alpha$ emission (FWHM $<1000\ \mathrm{km\ s^{-1}}$), with FWHMs mostly in the range 300–600 $\mathrm{km\ s^{-1}}$, comparable to or slightly larger than those of high-redshift star-forming galaxies (100–500 $\mathrm{km\ s^{-1}}$). We measure the fraction of broad Ly$\alpha$ emitters above a broad Ly$\alpha$ luminosity threshold of $L_{\mathrm{Ly}\alpha,\mathrm{broad}}=10^{42}\ \mathrm{erg\ s^{-1}}$, obtaining $0.10^{+0.12}_{-0.07}$ for LRDs, about five times higher than the $2\sigma$ upper limit of $<0.02$ for high-redshift star-forming galaxies. Although we reproduce the broad Ly$\alpha$ component reported in a previous stacking analysis of eight LRDs, albeit with a large uncertainty, we find no evidence for broad Ly$\alpha$ emission in either the larger JWST stack, after excluding the two individually detected broad Ly$\alpha$ emitters, or the higher-resolution MUSE stack. These results suggest that broad Ly$\alpha$ emission is not ubiquitous among LRDs. Instead, LRDs with broad Ly$\alpha$ emission appear to represent a rare population that may correspond to a particular evolutionary stage, potentially associated with unusually strong outflows or other distinctive physical conditions.
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All authors Yuta Kageura, Masami Ouchi, Hiroto Yanagisawa, Makoto Ando, Yuichi Harikane, Tomokazu Kiyota, Minami Nakane, Yoshiaki Ono, Yui Takeda

Astrophysics of Galaxies

The deepest color-magnitude diagrams for the benchmark open cluster NGC 2437 from Gaia and VVVX

Tali Palma, Matías Gómez, Dante Minniti et al. (+8 more)

Deep photometry of Galactic star clusters provides one of the most powerful tools for determining their physical properties. In particular, in low Galactic latitude regions that suffer from heavy extinction and crowding. NGC2437 is the most extended star cluster in the near-IR footprint of the VVV Extended Survey (VVVX), covering more than one degree on the sky. We aim to characterize its physical properties using Gaia DR3 in the optical and the VVVX in the near-IR. We use Gaia DR3 proper motions to select NGC2437 members in order to make optical and near-IR color-magnitude and color-color diagrams. We further exploited the newly constructed VVVX deep stack images to obtain the deepest near-IR color-magnitude diagram currently available for this cluster. We estimate the main physical parameters for NGC2437, including the mean parallax of 0.608 mas and PMs (-3.85, 0.41) mas/yr. The mean reddening E(J-Ks) = 0.059 mag and extinction of A_k = 0.034 mag for the cluster field, with no significant differential reddening spread. A distance modulus of 11.08 mag is estimated, equivalent to a distance of 1644 pc. This places NGC2437 at z=115 pc above the Galactic plane and at a galactocentric distance of 9.24 kpc. We measure the cluster structural parameters, obtaining a core radius of 10.79 arcmin. The estimated total absolute magnitudes are Mk = -4.91 mag and Mv = -3.70 mag. The cluster mean age is 350 Myr, using PARSEC-COLIBRI isochrones for solar metallicity. We measure a binary fraction of 28.6%. We also discuss the implications of the revised cluster parameters for the nearby open cluster NGC2425, the planetary nebula NGC2438, and the evolved OH/IR source OH231.8+04.2. The VVVX deep stacks increase the Ks photometric depth by 1.6 mag, nearly doubling the detected point sources and enabling significantly improved studies of stellar populations throughout the southern Galactic plane.
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All authors Tali Palma, Matías Gómez, Dante Minniti, Alan Montecinos, Nicholas J.G. Cross, Javier Alonso-García, Daniel Majaess, Bruno Dias, Maren Hempel, Roberto K. Saito, Joyce B. Pullen

Astrophysics of Galaxies

OH Line Detections in Southern Galaxies of the IRAS Revised Bright Galaxy Sample

Han Zhao, Zhongzu Wu, Bo Zhang et al. (+4 more)

We present a systematic study of OH main-line emission and absorption in 186 southern galaxies from the IRAS Revised Bright Galaxy Sample, using archival MeerKAT snapshot data. OH features are detected in 38 galaxies, including eight with OH maser emission (three new) and 30 showing OH absorption, mostly unreported previously. Four absorption systems exhibit weak OH emission superposed on strong absorption. OH-emitting regions are generally more compact than the associated radio continuum. Most absorption profiles are well fit by two Gaussian components (1667 and 1665 MHz), with an average integrated line ratio of $\sim$1.5. LIRGs show an OH emission detection rate of ~13%, versus significantly lower rates in non-LIRGs. For sources with radio continuum flux densities >20 mJy, OH absorption detection rates reach ~36% (LIRGs) and ~27% (non-LIRGs), while no OH absorption features were detected among sources with lower radio continuum flux densities. This suggests that sufficient background continuum is likely an important factor for the detection of OH absorption. Detected OH emitters follow the empirical $L_{\rm OH}$–$L_{\rm FIR}$ relation, consistent with far-infrared pumping, while non-detections show upper limits below the relation. No significant differences are found between OH absorbers and non-detections in infrared luminosity or radio continuum compactness. Stacked spectra of non-detections reveal no significant OH features, suggesting that sensitivity and orientation alone do not fully explain the absence of absorption. In contrast, mid-infrared colors (e.g., W2–W3) and q_TIR differ between the two populations. OH absorption galaxies occupy an intermediate regime in L_HCN/L_CO between OH megamasers and non-detections, implying that OH absorption detectability is linked to dense molecular gas conditions, with extreme star formation potentially suppressing its occurrence.
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All authors Han Zhao, Zhongzu Wu, Bo Zhang, Timur Mufakharov, Yongjun Chen, Zhiqiang Shen, Yulia Sotnikova

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

XRISM reveals sloshing-driven gas motions in the core of Abell 2029

Yuusuke Uchida, Yuna Saito, Naomi Ota et al. (+13 more)

We investigate the velocity structure of the intracluster medium (ICM) in the core of the relaxed cool-core cluster Abell 2029 using XRISM Resolve spectroscopy. We analyze combined XRISM Resolve observations and divide the central region into several subregions. To account for photon mixing caused by the XRISM point spread function, we perform a spatial-spectral mixing analysis. We detect an ordered line-of-sight bulk-velocity gradient across the cluster core: the northern regions are blueshifted relative to the brightest cluster galaxy (BCG), while the southern regions are close to zero velocity or slightly redshifted. The maximum velocity difference is about $280~{\rm km\,s^{-1}}$. In contrast, the turbulent velocity dispersion is smaller, with measured values and upper limits of $\lesssim150~{\rm km\,s^{-1}}$, implying a non-thermal pressure fraction below $\sim2.5\%$. The velocity pattern is consistent with gas sloshing associated with the spiral structure seen in Chandra X-ray images. Averaged over all regions, the inferred turbulent heating rate is below the radiative cooling rate, indicating that turbulent dissipation alone is insufficient to offset cooling in the entire core. These results reveal that A2029 is not kinematically featureless: sloshing-induced bulk motions are present, while the observed line-of-sight velocity dispersion indicates only a limited contribution to pressure support and core heating.
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All authors Yuusuke Uchida, Yuna Saito, Naomi Ota, Erwin T. Lau, Ming Sun, Eric D. Miller, Tommaso Bartalesi, Stefano Ettori, Kotaro Fukushima, Caroline Kilbourne, Lorenzo Lovisari, Kyoko Matsushita, Brian R. McNamara, Arnab Sarkar, Kazunori Suda, Irina Zhuravleva

Astrophysics of Galaxies

The Galactic Centre G+0.633-0.0604 Molecular Cloud: A New Gold Mine for Astrochemistry

D. San Andrés, V. M. Rivilla, L. Colzi et al. (+4 more)

Astrochemistry is living a golden age, with more than a quarter of the ~350 molecules in the current interstellar census having been detected over the last three years. One of the sources driving this progress is the G+0.693-0.027 cloud, located in the northern part of the Galactic Centre Sgr B2 complex. In this contribution, we present the astrochemical characterisation of G+0.633-0.0604, a newly discovered chemically rich molecular cloud at the southern edge of Sgr B2. With an inventory of >120 species, G+0.633 provides robust second detections of several prebiotic molecules only reported towards G+0.693, establishing it as the first confirmed astrochemical twin of G+0.693 while demonstrating that the extraordinary chemistry of this cloud is not unique. Furthermore, G+0.633 offers an observational advantage over G+0.693 since it displays half narrower linewidths. Together, G+0.633 and G+0.693 form a unique benchmark pair for unveiling molecular complexity and prebiotic chemistry in the interstellar medium.
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All authors D. San Andrés, V. M. Rivilla, L. Colzi, M. Sanz-Novo, S. Martín, I. Jiménez-Serra, S. Zeng

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

Magnetoacoustic Portals in Quiet-Sun Fluxtubes Revealed by Chromospheric Spectropolarimetry with SUNRISE III/SCIP

Takayoshi Oba, Yukio Katsukawa, Masahito Kubo et al. (+36 more)

Acoustic waves propagate into the chromosphere, contributing to energy transport and their dynamics. Their upward propagation is restricted to frequencies above the acoustic cutoff frequency. The magnetic field configuration plays a key role in determining whether acoustic waves can propagate upward because the cutoff frequency is reduced in regions where the field is inclined with respect to gravity, forming so-called magnetoacoustic portals. Previous studies linked magnetic fields and oscillations in quiet regions, but these analyses were based on photospheric magnetic field information, leaving chromospheric structure unconstrained. This study investigates the coupling between acoustic waves and magnetic topology using photospheric and, for the first time, chromospheric spectropolarimetry in a quiet region, obtained with the Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP) aboard the Sunrise iii balloon-borne solar observatory launched in 2024. The SCIP sit-and-stare observations sampled magnetic features in which the line-of-sight field strength exhibits multiple sharp spatial peaks in the photosphere while becoming broader and weaker at two heights in the chromosphere, indicating expanding fluxtubes. The chromospheric velocity field in these fluxtubes exhibits strong 5-minute oscillations, while the surrounding regions show weak 3-minute oscillations. In these fluxtubes, sawtooth temporal velocity variations are associated with intensity enhancements, suggesting steepened shocks. Fluxtubes with low-frequency oscillations are identified not only in network regions but also in weak internetwork regions. These results provide observational evidence that fluxtubes expanding into the chromosphere act as magnetoacoustic portals, in both network and internetwork regions, allowing low-frequency waves to propagate upward and driving chromospheric dynamics via shocks.
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All authors Takayoshi Oba, Yukio Katsukawa, Masahito Kubo, Yusuke Kawabata, Takuma Matsumoto, Ryohtaroh T. Ishikawa, Yoshihiro Naito, Toshifumi Shimizu, Hirohisa Hara, Fumihiro Uraguchi, Toshihiro Tsuzuki, Kazuya Shinoda, Tomonori Tamura, Yoshinori Suematsu, Jose Carlos del Toro Iniesta, David Orozco Suárez, Maria Balaguer Jiménez, Azaymi L. Siu-Tapia, Carlos Quintero Noda, Sami K. Solanki, Andreas Lagg, Achim Gandorfer, Pietro Bernasconi, Thomas Berkefeld, Tino L. Riethmüller, Alberto Álvarez-Herrero, H. N. Smitha, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Hanna Strecker, Dušan Vukadinović

Astrophysics of Galaxies

A Reproducible Two-Boundary Kinematic Correction for Baryonic Rotation-Curve Reconstruction in an 84-Galaxy SPARC Benchmark

David C. Flynn

We present a reproducible computational validation and failure analysis of the empirical omega kinematic correction introduced by Flynn and Cannaliato (2025). The algorithm is deliberately minimal: one coefficient per galaxy is calculated from the innermost and outermost measured rotation-curve points and applied to the full observed radial profile before comparison with a baryonic reconstruction assembled from SPARC gas, disk, and bulge components. We preserve the predecessor's frozen 84-galaxy benchmark and publish its exact membership so that the transformation, not sample re-selection, is the object of validation. Without fitting the transformation to the baryonic residual, the primary maximum-disk reconstruction reduces the mean observed-baryonic discrepancy from 51.82 to 30.15 km/s across the frozen 84-galaxy benchmark. Bounded mass-to-light-ratio optimization further reduces the descriptive sensitivity-fit value to 25.45 km/s, while the simple Keplerian reference has a mean RMSE of 74.20 km/s in our earlier analysis [15]. Recalculation from the 84 per-galaxy records shows a resolved mass-to-light optimization benefit (delta RMSE > 0.05 km/s) in 53 galaxies and no resolved change in 31. Six galaxies do not beat the Keplerian reference; all six occur at Upsilon_max <= 0.111, whereas their omega values are not concentrated at the high end of the sample. We specify the complete deterministic workflow, native units, endpoint invariants, uncertainty propagation, and formula-level regression checks required to prevent grouping and sign errors. The complete 84-galaxy panel set, population-level error distributions, and failure diagnostics are retained as inspectable outputs. The result is a reproducible astronomical data-transformation benchmark rather than a proposed force law or replacement for dark matter or modified gravity.
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Astrophysics of Galaxies

The galaxies' energy balance problem solved

C. J. Inman, C. C. Popescu and D. Murphy

We attempt to resolve the long-standing energy balance problem encountered by Radiative Transfer (RT) models, particularly in edge-on galaxies by incorporating a treatment for the clumpy structure of the Interstellar Medium (ISM). A subgrid approach is adopted, treating the quiescent dust clouds as pseudo-dust grains, with equivalent optical and thermal emission properties. Deriving key quantities such as the absorption, scattering and extinction cross-sections enables the virtualisation of the macroscopic clump into a microscopic pseudo-grain that can be included alongside the existing dust model constituents. The addition of the pseudo-grain results in a flatter extinction curve. A library of clump emission spectral energy distributions (SEDs) is constructed for radiation fields of various colours and intensities. The new clumpy model is applied to the edge-on galaxy NGC 891 and, for the first time, is able to achieve a good energy balance, simultaneously fitting both the submm and Near Infrared (NIR) data. The clumpy model is further applied to a small sample of seven galaxies of various inclinations, and the results are compared with those from the purely diffuse models. The clumpy models are characterised by a reduction in dust opacity, and therefore attenuation, compared to their purely diffuse counterparts. Thus, the maximum face-on optical depth in the $B$-band, ${\mathrm max}(\tau^{\mathrm f}_{\mathrm B})$, derived from the clumpy models is found to be lower by factors ranging from 1.3 to 2.8. Of the seven galaxies, two are found to be optically thick in their centres, two are found to be moderately optically thick, and three are found to be optically thin.
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Astrophysics of Galaxies

The SAMI Galaxy Survey: Linking Tidal Features and Orbit Populations Using Schwarzschild Modelling

T. H. Rutherford, J. van de Sande, S. M. Croom et al. (+11 more)

The evolution of angular momentum in galaxies is shaped by a combination of internal secular processes and external mechanisms such as mergers. Orbit-superposition based dynamical modelling provides a powerful means of linking the intrinsic orbital structures of galaxies to their global properties and merger histories. We construct Schwarzschild orbit-superposition models of massive ($\log(M/M_{\odot})>10$) SAMI galaxies using the DYNAMITE code, utilising deep KiDS photometry to accurately reproduce each galaxy's luminosity distribution. We find that the fractions of hot, cold, warm, and counter-rotating orbits all show significant correlations with the spin parameter proxy $\lambda_{R_e}$, with the strongest correlation arising from the combined hot plus counter-rotating fraction. When controlling for stellar mass and environment, we find that the fraction of hot and cold orbits show significant correlations with stellar age, whereas warm orbits do not. We further find that the lower values of $\lambda_{R_e}$ for young galaxies with shell merger features as compared to the full sample is driven by an excess of hot orbits and a deficit of cold orbits, with no dependence on warm orbits. We suggest that the kinematic transformation in this SAMI sample proceeds through stars transitioning directly from cold to hot orbits. As warm orbits are expected to arise from secular heating processes, these findings indicate that merger-driven heating is the dominant mechanism governing the redistribution of angular momentum and the reduction of rotational support in massive galaxies.
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All authors T. H. Rutherford, J. van de Sande, S. M. Croom, A. Fraser-McKelvie, G. Santucci, G. van de Ven, S. M. Sweet, S. Brough, Y. Mai, J. Bryant, J. Bland-Hawthorn, M. Goodwin, J. Lawrence, N. P. F. Lorente

Astrophysics of Galaxies

How mergers shape galaxy morphology in the IllustrisTNG simulation

Guangquan Zeng, Lan Wang and Liang Gao

How galaxy mergers drive morphological evolution remains an open question. Traditional views hold that major mergers produce elliptical galaxies, while minor mergers form dispersion-dominated components such as galactic bulges. However, more recent work has challenged this simple picture, suggesting a more complex evolutionary scenario. In this study, we use the IllustrisTNG cosmological simulation to investigate how mergers shape galaxy morphology, across a broad range of galaxy masses and merger mass ratios. Our results show that the post-merger galaxy morphology is primarily determined by three factors: collision angle $\overline{\theta}$, cold gas fraction $f_\mathrm{cold\,gas}$, and pre-merger galaxy morphology $\mathrm{(B/T)_{*,pre}}$. Specifically, spiral-in mergers with large $\overline{\theta}$ increase the rotational support of the system, allowing the gas to settle into an extended disk. When the system is rich in cold gas, star formation within the newly formed gas disk can further strengthen the disk-dominated structure of the remnant. On the other hand, head-on mergers with small $\overline{\theta}$ typically disrupt ordered galactic motion, producing more dispersion-supported remnants. Overall, we interpret our results within a unified picture of merger-driven morphological transformation in galaxies.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

A chemo-dynamical search for planet-candidate hosts of possible extragalactic origin

Sun Tiancheng, Chen Xunzhou, Xiang Maosheng et al. (+2 more)

To date, all known exoplanetary systems have been identified around stars currently residing in the Milky Way, whereas planets formed in external galaxies remain largely unexplored. Such systems would offer a unique probe of planet formation in galactic environments distinct from the Milky Way. We combine a literature-compiled sample of Kepler, K2, and TESS planet-candidate host stars with Gaia DR3 astrometry and radial velocities, and incorporate metallicities and [Mg/Fe] abundances from the LAMOST DR9 DD-Payne catalogue, to search for candidate accreted-halo planet hosts. We identify 11 planet-candidate hosts with halo-like kinematics, five of which have reliable chemical abundance measurements. Among these, four systems exhibit low metallicities ([Fe/H]<-0.7) and low [Mg/Fe] ratios that are inconsistent with the canonical Milky Way thick-disc sequence, indicative of enrichment histories characteristic of accreted dwarf galaxies. We further carry out a uniform false-positive assessment using Gaia RUWE, Gaia DR3 neighbourhood checks, odd–even transit-depth comparisons, secondary-eclipse searches, independent BLS period recovery, and comparison with ExoFOP and available follow-up information. This vetting identifies EPIC~211407755 and TIC~239541449 as the most plausible, although still unvalidated, planet-candidate systems. TIC~293432942 is more likely associated with a blended or otherwise binary-related false positive, whereas TIC~184739529 remains a high-risk giant-companion candidate whose planetary nature is uncertain. If confirmed, EPIC~211407755 and TIC~239541449 would suggest that planetary systems can form in dwarf-galaxy environments and subsequently survive accretion into the Milky Way.
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All authors Sun Tiancheng, Chen Xunzhou, Xiang Maosheng, Zhou Jianzhao, Lu Zixuan

Astrophysics of Galaxies

Energy Partitioning in Dust-catalyzed $\mathrm{H_2}$ and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects

Xiaolong Yang, Lile Wang, Di Li et al. (+1 more)

Molecular hydrogen formation on interstellar dust grains is a key surface process in the interstellar medium, but the redistribution of the recombination energy between the substrate and the nascent molecule remains poorly understood. Here, we use ring-polymer molecular dynamics (RPMD) with a machine-learning force field to investigate energy partitioning during $\mathrm{H_2}$ and $\mathrm{HD}$ formation on graphene at $T=25, 50$ and $100 \mathrm{K}$. We focus on the chemisorbed-H recombination pathway previously identified as the dominant low-temperature channel on bare graphitic surfaces when nuclear quantum effects are included. The desorbing molecule retains the major fraction of the effective surface-mediated released energy, while graphene absorbs a smaller but non-negligible part. This molecular retention fraction is nearly temperature-independent over the investigated range. In contrast, the post-formation molecular kinetic-energy distribution changes more strongly with temperature: rovibrational motion dominates at low temperature, whereas center-of-mass translation becomes increasingly important at $100 \mathrm{K}$. $\mathrm{H_2}$ and $\mathrm{HD}$ exhibit broadly similar total energy retention, with only modest isotope-dependent differences in their internal kinetic-energy partitioning. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution in $\mathrm{H_2}$/$\mathrm{HD}$ formation, with implications for formation-pumping signatures in high-excitation $\mathrm{H_2}$ lines, vibrationally excited $\mathrm{H_2}$ chemistry, and collisional excitation of coexisting molecules by translationally hot nascent $\mathrm{H_2}$ in cold interstellar gas.
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All authors Xiaolong Yang, Lile Wang, Di Li, Shenzhen Xu

Thursday 13 August

Astrophysics of Galaxies

The CMZ Asymmetries: Feeding or Feedback?

John Bally

Three-fourths of the dense gas and dust in the CMZ is located at positive longitudes and positive radial velocities. The majority of compact 24 micrometer wavelength sources are at negative longitudes. These two asymmetries indicate either a recent asymmetric injection of gas along the bar dust lanes, or that most of the molecular gas is contained in a small number of massive, gravitationally bound clouds, or a major feedback episode which dissociated an entire sector of the CMZ's dense gas.
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Astrophysics of Galaxies

Old Disks Die Hard: How Does AGN Feedback Suppress Disk Formation in Milky Way Mass Galaxies?

Patricia Fofie, James S. Bullock, Sarah Wellons et al. (+3 more)

The connection between a galaxy's visual shape and its star formation rate is one of the oldest established trends in galaxy evolution, yet the origin of this trend remains unsettled. We analyze two Milky-Way mass halos simulated with FIRE-2 galaxy formation physics, each run without AGN and with up to three implementations of AGN feedback. We use them to study how and why AGN star formation suppression affects morphological evolution over cosmic time. Both runs without AGN feedback produce prominent, thin, star-forming spiral disks at $z=0$. Each of the AGN runs has less late-time star formation, and ends up with a higher spheroid fraction and a lower thin-disk mass fraction. In two instances, the AGN runs produce quenched lenticular galaxies with no cool gas at $z=0$. The main reason for these morphological differences is that AGN feedback becomes effective just after the onset of disk formation, at “spin up," in every run. This time-differentiated impact suppresses the formation of disk stars, especially thin-disk stars, preferentially because thin-disk formation occurs late. The spheroidal components are assembled early in all runs, before AGN feedback is effective, and are therefore similar in mass and size across runs.
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All authors Patricia Fofie, James S. Bullock, Sarah Wellons, Jorge Moreno, Francisco J. Mercado, Andrew Wetzel