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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Friday 9 October

Astrophysics of Galaxies

Insights from the stability of methanol maser flare properties I: G9.62+0.20E

S.P. van den Heever and D.J. van der Walt

The brightest 6.7 GHz methanol maser in the Galaxy is associated with the high-mass star-forming region (HMSFR) G009.62+0.20E. Additionally, this methanol maser shows periodic flaring observed at 6.7 and 12.2 GHz. Several models have been hypothesized to explain the periodicity, including periodic accretion, spiral shocks in the gaps of circumbinary disks, pulsating stars, dicke's superradiance, and a colliding wind binary (CWB) system. We analyzed the time series of the 1.22 km s-1 feature of the 6.7 GHz methanol maser spectrum and the 1.25 km s-1 feature of the 12.2 GHz methanol maser spectrum over the monitoring duration of roughly 20 years, to determine an updated period, analyze the stability and repeatability of the flares, the temporal behavior of the flare profile, and the duty cycle of the flare profile based on the updated period. From these results, it is argued for or against any of the mechanisms that have been proposed to explain the periodicity. Lomb-Scargle (LS) and phase dispersion minimization (PDM) methods were used to determine the methanol maser period at 6.7 and 12.2 GHz. Once the period has been determined, phase-folding or period-folding was used to analyze the flare shape, flare stability, and duty cycle of the flares. The periods of the 6.7 and 12.2 GHz methanol masers were determined to be ~ 243.0 +- 0.3 days. The flares are highly repeatable, stable, and show almost identical shapes, as well as their duty cycles. A replicated kernel density estimator (KDE) of the flare shape reproduces the time series very well over a time span of ~ 8000 days. After careful consideration of the proposed mechanisms for periodic methanol masers, we conclude that all but one, the CWB model, have been ruled out as a possible driver of this flare profile. It has also been established that the CWB model can qualitatively explain the flare profile of the periodic methanol masers.
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Astrophysics of Galaxies

A dust-reddened quasar in a [C II]-luminous host at z=6.55

Daming Yang, Joseph F. Hennawi, Rychard Bouwens et al. (+18 more)

Most known quasars at $z>6$ were selected through their rest-frame UV emission. Only a small number of reddened quasars have been identified at these redshifts, leaving their nuclear and host-galaxy properties poorly constrained. We present JWST/NIRSpec spectroscopy and ALMA band 6 observations of the quasar J1440+0019 at $z=6.5488$, revealing its dust-reddened nature and jointly characterizing its nucleus and host galaxy. The continuum is best described by an SMC-like extinction law with $E(B-V)=0.20\pm0.03$. Three absorption systems detected in N V, Si IV, and C IV are blueshifted by approximately $900$–$3600$ km s$^{-1}$ and likely trace an ionized nuclear outflow. The broad Mg II line and extinction-corrected continuum yield a black-hole mass of $\log(M_{\rm BH}/M_\odot)=9.04\pm0.42$, a bolometric luminosity of $L_{\rm bol}\simeq1.1\times10^{47}$ erg s$^{-1}$, and an Eddington ratio of $\lambda_{\rm Edd}\simeq0.8$. ALMA observations further reveal its host galaxy to be among the most [C II]-luminous known at $z>6$, with $L_{\mathrm{[C II]}}=(7.21\pm0.25)\times10^9 L_\odot$. For a fiducial dust temperature of 47 K and emissivity index $\beta=1.6$, the dust continuum implies $L_{\rm TIR}=8.9\times10^{12} L_\odot$ and $M_{\rm dust}=4.0\times10^8 M_\odot$. The inferred dynamical mass places J1440+0019 in the region of the $M_{\rm BH}$–$M_{\rm dyn}$ plane occupied by high-redshift blue quasars. These observations reveal a moderately reddened, rapidly accreting quasar in a luminous, dust-rich host during reionization. Its measured nuclear and host-galaxy properties provide an observational reference for identifying and characterizing similar systems in future systematic searches with wide-area infrared surveys.
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All authors Daming Yang, Joseph F. Hennawi, Rychard Bouwens, Timo Kist, Eduardo Bañados, Hiddo S. B. Algera, Aaron J. Barth, Sarah E. I. Bosman, Frederick B. Davies, Anna-Christina Eilers, Xiaohui Fan, Victoria A. Fawcett, Yuming Fu, Anniek J. Gloudemans, Francesco Guarneri, Bin Jia, Elia Pizzati, Huub Röttgering, Jan-Torge Schindler, Feige Wang, Jinyi Yang

Astrophysics of Galaxies

A strategy for astrometric quasar selection with Gaia DR3 and its application to discover new luminous $z>2$ quasars

J. Li and J. P. U. Fynbo

We aim to provide a cookbook for purely astrometric selection of quasars with Gaia DR3 and to provide an example of its use for the identification of very luminous $z>2$ quasars. We analyse the Gaia DR3 astrometry of confirmed quasars and stationary sources. We show that the proper motion signal to noise $\mu/\sigma_{\mu}$ follows a Rayleigh-like distribution. We also show the importance of properly taking into account the correlation between proper motions in right ascension and declination, as well as the non-linear error propagation. We adopt the Mahalanobis distance to the null proper-motion hypothesis. A scaled $\chi^2$ distribution with $k=2$ and scale $s=1.1485$ is fitted to Gaia-CRF3; the corresponding $\pm2\sigma$ Gaussian-equivalent threshold is $D^2_{M(\mu)}<7.097$. The final criteria combine this with the parallax condition and $\mathrm{ruwe}<1.4$. Applying the new criteria to the SDSS DR16Q confirmed quasars, the recovery rate is $90.25\%$. The suggested purely astrometric selection significantly improves both completeness and purity compared to other strategies used in the literature, reaching a quasar purity of approximately $95\%$ ($\sim2\sigma$ Gaussian-equivalent). It can be used to improve the selection purity and completeness for future quasar surveys. As an example, we use the suggested strategi to locate 24 very bright $z>2$ quasars without redshifts in the literature. Our proposed astrometric selection strategy recovers 95% of known quasars. Its potential use for new discoveries is demonstrated by the identification of 24 very luminous $z>2$ quasars. Ten of these are new discoveries and for an additional seven we correct the redshifts determined by other methods.}
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Astrophysics of Galaxies

Turbulence modes in molecular clouds in M33: a challenging test of the Brunt-Federrath framework

Raffaele Rani, Ayu Konishi, Kazuyuki Muraoka et al. (+5 more)

Understanding the turbulent structure of molecular clouds is essential for linking galactic environment to the regulation of star formation. Although Galactic molecular clouds have been studied extensively, extending turbulence-mode analysis beyond the Milky Way remains challenging because of the limited spatial resolution and dynamic range of extragalactic observations. We assess the applicability of the Brunt & Federrath (2014; BF14) framework to molecular clouds in M33. We apply BF14 to 128 $^{13}$CO(2-1) clouds, selecting a primary quality-controlled sample of 54 clouds and a more restrictive 25-cloud subsample defined using a stricter extraction-padding criterion (PAD=2) for quantitative analysis.Tests of cloud and noise power spectra, Fourier-space cutoffs, extraction padding, and Monte Carlo uncertainties demonstrate that the retained spatial frequencies are dominated by astrophysical signal and that the inferred turbulence-mode fractions are robust against reasonable analysis choices. Both samples yield consistent distributions of the solenoidal fraction, with mean values of $R \simeq 0.22$ for both samples and median values of $R \simeq 0.18$ and $0.17$, respectively, indicating that compressive motions dominate the turbulent energy budget. No strong systematic variations of $R$ are found with galactocentric distance or tracers of recent star formation. These results demonstrate that, despite the challenging spatial resolution of current extragalactic molecular-line observations, the BF14 framework can be applied reliably to nearby galaxies using spectroscopic observations alone. To our knowledge, this constitutes the first application of the full BF14 formalism to extragalactic molecular-cloud observations.
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All authors Raffaele Rani, Ayu Konishi, Kazuyuki Muraoka, Toby J. T. Moore, David J. Eden, Karan Fernandes, Yueh-Ning Lee, Shih-Ping Lai

Astrophysics of Galaxies

High Resolution Spectro-Polarimetric Observations of the Optical Filaments surrounding NGC 1275 with ESPaDOnS

Benjamin Vigneron, Julie Hlavacek-Larrondo, Luca Fabiani et al. (+6 more)

We analyze archival high spectral resolution ESPaDOnS spectropolarimetric observations (R = $\lambda/\Delta\lambda$ = 68000) of three targeted locations within the filamentary nebula surrounding NGC 1275. We present here the analysis of the main filaments emission lines, namely: [NII]$\lambda6584$, H$\alpha$, and [NII]$\lambda6548$, across our three pointings displaying clear detectable emission, with one also showing additional [SII]$\lambda6716$ and [SII]$\lambda6731$ emission line doublet. Using a Markov Chain Monte-Carlo (MCMC) algorithm and thanks to the exceptionally high spectral resolution of the observations, we resolve for the first time each of the emission lines within one of the pointings into a set of three emission components with a remarkable velocity dispersion contrast ($\sigma_1 \sim 25$ km/s, $\sigma_2 \sim 90$ km/s and $\sigma_3 \sim 208$ km/s). We also perform flux ratios of the three detected emission components, which reveal differences in electron density and ionization sources. Consequently, the ESPaDOnS observations appear to reveal for the first time the overlap of an outer quiescent filament and a central turbulent filament likely affected by the AGN activity at a distance of $\sim 6.8''$ ($\sim 2.5$ kpc) from the central BCG. Finally, ESPaDOnS polarimetric data of one of the pointing allows us to confirm an average linear polarization degree of $\sim 0.15-0.14\%$ and an angle of polarization of $5.3\pm25.7^\circ$ for the optical emission of the filaments, as well as polarization dips associated with the H$\alpha$ emission line and its multiple emission components. We interpret these features and measurements as tentative polarization due to dust scattering.
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All authors Benjamin Vigneron, Julie Hlavacek-Larrondo, Luca Fabiani, Lison Malo, Carter Lee Rhea, Megan Donahue, Jorge Karolt Barrera Ballesteros, Hyunseop Choi, Nadine Manset

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

X-Shooter view of planetary nebulae microstructures I: The case of NGC 7009 knots

L. Konstantinou, S. Akras, K. Bouvis et al. (+4 more)

The properties of NGC 7009 knots are investigated by employing UV-to-near-infrared data from the X-Shooter spectrograph. These structures belong to the category of low-ionization structures (LISs), which are characterized by enhanced emission from low-ionization species and whose origin remains enigmatic. Our main goal is to conduct the first dedicated spectroscopic study of LISs using X-Shooter, that covers a wide spectral range from the UV to the near-IR, simultaneously. As a pilot study, we focus on NGC 7009 to investigate its ionized, atomic, and molecular gas, aiming to better characterize the physical properties of its LISs and explore their largely unexplored molecular content. The spectrum was processed through the ESO Reflex pipeline, and the physical properties of LISs were derived with the latest version of PyNeb. More than 250 emission lines were detected in the spectra of NGC 7009 LISs, including rare, forbidden transitions from low- ionization species such as Fe+ and Ni+, as well as two transitions from P+, identified here for the first time in LISs. The detection of multiple shock tracers, together with the shock excitation of [Fe II] and [O I], as revealed by emission-line diagnostics, supports the presence of shocks at LISs. The richness of the spectrum allowed us to derive electron temperatures and densities at the LISs using both collisionally excited and optical recombination lines. In the near-IR spectrum of the LISs, nine ro-vibrational H2 emission lines were detected, seven of which were reported here for the first time. These lines were used to construct the H2 excitation diagram, providing new insights into the physical conditions of the nebular gas. The excitation of molecular hydrogen is most likely dominated by collisional processes through shocks.
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All authors L. Konstantinou, S. Akras, K. Bouvis, P. Boumis, J. Garcia-Rojas, D.R. Gonçalves, K.N. Gourgouliatos

Astrophysics of Galaxies

The Silk Nebula: A Newly Discovered Giant [OIII] Emission Filament

Yi-Fei Wu, Songyu Jia, Chao-Jian Wu et al. (+14 more)

We report [O\,iii] narrow-band imaging of an extremely large-scale nebula, the Silk Nebula, discovered by the SWONS (Super Wide-Field [O\,iii] Narrow-band Survey), together with multi-fiber medium-resolution spectroscopic data covering the H$\alpha$, [N\,ii], [S\,ii], and [O\,iii] emission lines, acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) as part of the Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N). Based on 2,684 high-quality spectra, we measured its physical parameters, including relative line intensities, radial velocities (RVs), and full widths at half-maximum (FWHMs). The [S\,ii]/H$\alpha$ ratio of the nebula significantly exceeds the shock-excitation threshold of 0.4. Its location in BPT diagnostic diagrams and spatial morphology of [O\,iii] both support the optical emission is dominated by shock-heated gas. The oxygen abundance is near solar and spatially uniform, consistent with a shock propagating into the ambient interstellar medium. Because [O\,iii] is the only emission line that clearly traces the nebular morphology, we base our distance estimate exclusively on the [O\,iii] kinematics, obtaining a fiducial distance of $\sim$160 pc. At this distance, the nebula has a physical extent of $\sim$28 pc along the north-south direction. We suggest that the Silk Nebula is a large [O\,iii] filament possibly associated with a supernova remnant, although a diffuse-ionized-gas (DIG) or ionized-bubble origin cannot be ruled out with the present data, and one of the largest angular-scale [O\,iii] emission structures documented to date. Future deep X-ray observations and shock-modeling efforts are required to firmly establish its nature.
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All authors Yi-Fei Wu, Songyu Jia, Chao-Jian Wu, Chao Zhang, Li-Yue Zhang, Shu Wang, Juan-Juan Ren, Quzhen Dongyang, Hong-Yun Qiu, Zhi-Hong He, Jichen Zhang, Guo-You Sun, Wei-Guo Zhang, Jian-Jun Chen, Hong-Liang Yan, Xiang-Song Fang, Hong Wu

Astrophysics of Galaxies

The Population of Type~1 Active Galactic Nuclei in Dark Energy Spectroscopic Instrument. I. Profile-dependent Measurements of the Low-redshift Sample

Zhu-Heng Yao, Wei-Jian Guo, Shuo Zhai et al. (+8 more)

We present a spectral analysis of a large sample of low-redshift type 1 active galactic nuclei (AGNs) selected from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1). For objects at $z\le0.9$, we perform spectral fitting and ML-assisted refinement, yielding 114,754 type 1 AGNs. We use two fitting schemes that differ only in the broad-line model: the broad Balmer components are fitted with either a Lorentzian function or a sum of Gaussians. The continuum and [O III] luminosity measurements agree closely between the two schemes, whereas the Gaussians scheme generally yields larger broad-H$\beta$ full width at half maximum (FWHM) values, larger virial black hole masses, and lower accretion rates. The adopted broad-Balmer profile also changes the decomposition of narrow Balmer emission. Specifically, the anti-correlation between [O III]$\lambda5007$/narrow H$\beta$ and accretion rate is stronger under the Gaussians scheme with a Spearman rank correlation coefficient $r_{\rm s}=-0.412$, than under the Lorentzian scheme with $r_{\rm s}=-0.206$; the same tendency is observed in the narrow-line Seyfert 1 galaxies (NLS1s) subset ($r_{\rm s}=-0.435$ and $-0.259$ for the Gaussians and Lorentzian schemes, respectively), suggesting that the Gaussians scheme may provide a more self-consistent separation of the broad and narrow H$\beta$ components. Moreover, the consistent correlations recovered under both profile prescriptions favor a continuous type 1 accretion-state sequence, with NLS1s occupying its high-accretion end rather than constituting a distinct population.
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All authors Zhu-Heng Yao, Wei-Jian Guo, Shuo Zhai, Yu-Chang Li, Cheng Cheng, Jun-Rong Liu, Shuang Jin, Antonios Katsianis, Jing Wang, Da-Wei Xu, Jian-Yan Wei

Astrophysics of Galaxies

A Relationship Between Fast Radio Burst Dispersion Measure and Host Galaxy Inclination

Lachlan Marnoch, Stuart D. Ryder, Sunil Simha et al. (+9 more)

It is commonly thought that fast radio bursts (FRBs) trace star formation, and that they are produced by magnetars. Both hypotheses imply that their sources are hosted primarily (but not exclusively) in galactic disks. Although there is evidence in that direction, it has yet to be shown conclusively. In addition, a tension exists with the fact that at least one FRB source is found in a globular cluster far from the disk of the host. If FRBs originate primarily in disks, the galaxy orientation could leave an impression in the sample of observed FRBs, either as a selection bias against FRBs in edge-on galaxies or as a correlation with DMHost. Statistical tests against the inclinations of FRB host galaxies, derived from parametric morphology applied to optical and near-infrared imaging, can search for these effects. Such a search requires an adequately large sample of known FRB hosts that have been imaged to a sufficient depth, while estimates of DMHost also require the redshift of each host to be known. These conditions are best met in the Commensal Real-time ASKAP Fast Transient (CRAFT) survey sample of FRB host galaxies, for which the majority have been imaged at optical wavelengths with FORS2 on the Very Large Telescope (VLT). Here these data are fitted with the morphology software GALFIT to derive the elliptical axis ratio q (a proxy for inclination) for 34 hosts from the CRAFT sample, detected with ASKAP and followed up with VLT imaging. We find no bias against FRB detections from edge-on galaxies; instead, we uncover a new relationship between the inclination of an FRB host galaxy and DMHost. This is consistent with a primarily disk-based origin for CRAFT FRBs. Using this relationship we are able to reduce the scatter of the host sample about the Macquart relation by 40%, demonstrating a new empirical method for estimating DMHost that requires only deep optical imaging.
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All authors Lachlan Marnoch, Stuart D. Ryder, Sunil Simha, Alexa C. Gordon, R. M. Shannon, Nicolas Tejos, Marcin Glowacki, Ziteng Wang, Elizabeth K. Mahony, J. Xavier Prochaska, Wen-fai Fong, Richard M. McDermid

Astrophysics of Galaxies

Redshifted Cool Gas in the Disturbed HI Disk of the Starburst Dwarf NGC 4214

Shulan Yan, Taotao Fang, Xiaochuan Jiang et al. (+4 more)

We report redshifted cool gas toward the central star-forming region of the nearby starburst dwarf galaxy NGC 4214. HST/COS spectra show low-ionization absorbers redshifted relative to the systemic velocity, most clearly in SII ($\Delta v=19.8\pm2.6\ {\rm km\,s^{-1}}$) and supported by MgII ($\Delta v=30.3\pm3.0\ {\rm km\,s^{-1}}$), while PII remains tentative ($\Delta v=7.5\pm3.4\ {\rm km\,s^{-1}}$). The Keck/HIRES spectra also reveal a redshifted CaII absorption component ($\Delta v=25.6\pm1.5\ {\rm km\,s^{-1}}$). Because the absorption is detected against the central UV or optical continuum, the gas must lie in the foreground of the star-forming region and is moving away from the observer and toward the background UV source in projection. A VLA–THINGS HI spectrum extracted at the COS position within one VLA beam also shows a redshifted neutral component at $v_{\rm hel}=329.2\pm0.9\ {\rm km\ s^{-1}}$, offset by $38.2\pm1.3\ {\rm km\ s^{-1}}$ from systemic and by $27.6\pm1.0\ {\rm km\ s^{-1}}$ from the dominant local HI component. The FAST HI mapping further reveals an extended, kinematically disturbed neutral disk, with residual structures relative to a warped-disk model. Together, the redshifted UV absorption, the redshifted HI component, and the disturbed large-scale HI velocity field show that the central anomalous cool gas is observed in a galaxy with a disturbed extended neutral disk. This geometry suggests that the redshifted cool gas may trace inflow or recycled fallback toward the central region, although warped-disk or non-circular disk motions cannot be fully excluded.
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All authors Shulan Yan, Taotao Fang, Xiaochuan Jiang, Junfeng Wang, Qingzheng Yu, Chuanpeng Zhang, Ming Zhu

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

An Ultraviolet Instrument on the Habitable Worlds Observatory: Considerations and Capability Trades on the Multi-Object, Integral-field, and High-resolution modes of a potential UVI

Brian Fleming, Kevin France, Dmitry Vorobiev et al. (+4 more)

The Habitable Worlds Observatory (HWO) is NASA's next-generation astrophysics platform, delivering transformative capability in the search for life and study of the origins of the universe. Amongst the instruments under consideration for HWO is a multi-purpose ultraviolet spectrograph and imager that provides a deep toolbox for some of the most pressing science investigations of the next several decades. In this paper, we present a basic draft model of a potential UVI, including a multi-object spectrograph, far ultraviolet imager, high resolution spectrograph, and integral-field spectrograph. The draft designs for these channels of the UV instrument serve as a basis for a general discussion of the instrument architecture and design challenges, while also identifying potential trades, enhancements, and other considerations that the HWO project will need to address as it moves into the formulation phase. We conclude with a presentation of several scientific simulations that have helped guide the capabilities of the draft design. This paper is intended to serve as a summary of UV instrument modes, technology, and potential design ahead of planned instrument studies in the late 2020's, and then Phase A in the early 2030's.
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All authors Brian Fleming, Kevin France, Dmitry Vorobiev, Jeanette Donber, Eric Frater, Thomas Delker, Vicki Herde

Astrophysics of Galaxies

Decomposing the Kinematics of SNR G180.0-01.7 with Medium-Resolution Spectra

Juan-Juan Ren, Wei Zhang, Chao-Jian Wu et al. (+3 more)

The exceptionally large angular diameter and intrinsic optical faintness of the Galactic supernova remnant (SNR) G180.0-01.7 (S147) have historically hindered a comprehensive spectroscopic census of its filamentary structure. We present the first dedicated medium-resolution (R ~ 7500) spectroscopic study of S147 using the LAMOST Medium-Resolution Spectroscopic survey of Galactic Nebulae (MRS-N). By implementing multi-Gaussian decomposition on the H$\alpha$, [NII], and [SII] emission complexes and applying combined spectroscopic and spatial criteria, we disentangle the shock-ionized filaments of the SNR from the pervasive foreground and background Diffuse Ionized Gas (DIG). Our analysis reveals a distinct bimodal radial velocity distribution for the SNR: a low-velocity population tracing the decelerated forward shock at a dense cavity wall, and a high-velocity population (with absolute radial velocities of ~ 70 $\pm$ 30 km/s) corresponding to ejecta within a low-density cavity. The co-existence of these populations provides kinematic evidence for the "supernova-in-a-cavity" scenario. Furthermore, we detect enhanced [SII]/H$\alpha$ ratios in the DIG along the eastern and northern boundaries of the remnant, signaling shock compression of the ambient interstellar medium and highlighting remnant's multifaceted feedback.
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All authors Juan-Juan Ren, Wei Zhang, Chao-Jian Wu, Chao Liu, Jian-Jun Chen, Hong Wu

Thursday 8 October

Astrophysics of Galaxies

Predicted state-to-state collisional rate coefficients from neural networks

Lisán David Cabrera-González, Carlos Cárdenas and Otoniel Denis-Alpizar

Molecular spectra observed in the interstellar medium are commonly analyzed using non-local thermodynamic equilibrium models, which requires accurate state-to-state collisional rate coefficients. Close-coupling calculations become prohibitively expensive for transitions from highly excited rotational states, therefore available datasets are often truncated at low initial states and temperatures; and since each new system also requires an accurate ab initio potential energy surface, many detected molecules have no collisional data. We employ two machine learning strategies to predict rotational state-to-state rate coefficients of molecules included in the train set beyond the range of initial states and temperatures computed so far, and predicting those of a molecule absent from training and validation sets. Feed-forward neural networks are trained on state-to-state de-excitation rate coefficients of 24 linear molecules colliding with para-H2. Scheme 1 includes all systems in the train+validation set, with 70%, 80%, and 90% initial-state boundaries and a 90% temperature boundary. Scheme 2 is trained on 22 systems described only by transition and molecular properties, and predicts two excluded systems, CS and CF+, whose astrophysical impact is explored with non-LTE calculations. For the 90% boundary, Scheme 1 predicts 99.4% of the test transitions within a factor of 2, and no prediction deviates from the reference value by more than a factor of 4.7. This model was used to complete 18 datasets. Scheme 2 reproduces the rate coefficients of two excluded systems within a factor of 3 for more than 92% of their transitions. Both schemes provide near-instantaneous complements to close-coupling calculations: Scheme 1 extends the range of a molecule already included in the training set with high accuracy, while Scheme 2 gives a reasonable first estimate for a molecule that has not been studied.
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Astrophysics of Galaxies

Bridging Theory and Observation: Synthetic Far-infrared Insights into Star Formation Efficiency

Alexander Escamilla, Michael Y. Grudić and Anna L. Rosen

The star formation efficiency per free-fall time ($\epsilon_{\rm ff}$) quantifies how efficiently giant molecular clouds (GMCs) convert gas into stars and is often observed to be orders of magnitude lower than expected for free-fall collapse. Observers typically estimate $\epsilon_{\rm ff}$ by mapping far-infrared (FIR) dust emission to infer gas surface densities ($\Sigma_{\rm gas}$) and counting embedded protostars, assuming simplified lifetimes and masses. Using the fiducial STARFORGE radiation-magnetohydrodynamics simulation of an $M_{\rm cl} = 2\times10^4 M_\odot$ GMC that self-consistently models star cluster formation and stellar feedback, we generate synthetic FIR observations and apply the same methodologies used in GMC surveys to investigate this discrepancy. We present the first $\epsilon_{\rm ff}-\Sigma_{\rm gas}$ analysis in a fully feedback-regulated GMC simulation that resolves the formation of stellar systems. Our synthetic measurements reproduce the low observationally inferred efficiencies, showing that feedback-regulated star formation naturally produces $\epsilon_{\rm ff} \sim 1-3\%$ without requiring extreme initial conditions. We also find that $\epsilon_{\rm ff}$ varies strongly over a GMC's lifetime, suggesting that much of the observed scatter reflects evolutionary sampling rather than intrinsic cloud-to-cloud differences. Finally, by comparing observational and simulation definitions, we show that methodological assumptions introduce systematic biases, with a transition near $\log \Sigma_{\rm gas} \approx 2.3 M_\odot {\rm pc}^{-2}$ that depends on resolution. Above this threshold, the smoothing of dense structure increases both the inferred free-fall time and enclosed gas, with the latter dominating and suppressing $\epsilon_{\rm ff}$. Below the threshold, the discrepancies are primarily driven by star formation rate assumptions.
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Astrophysics of Galaxies

Exploring Case B I: The Footprints of Hidden Radiation Fields in H I Balmer Decrements

Maryam Dehghanian, Fransisco Guzman, Peter van Hoof et al. (+2 more)

Theory predicts that H I emission from photoionized clouds should lie close to the Case B limit established by Menzel and Baker, and observations of nearby nebulae have largely confirmed this expectation. However, recent observations of more distant high-redshift systems have revealed a small fraction with striking departures from Case B. What additional physics might be at work in these objects? This paper is part of a series exploring the physical processes that can produce such departures. In Paper I (D26), we show that Case B remains remarkably robust over a broad range of physical conditions, consistent with observations of nearby nebulae. Here, we explore one additional ingredient: a soft, non-ionizing radiation field. Such a continuum can strongly perturb the Balmer spectrum. The largest effects occur for radiation fields resembling log(Teff K)\sim 3.2-4.2 blackbodies, where photoexcitation from the metastable 2s level alters the hydrogen level populations and subsequent radiative cascade. The resulting Halpha/Hbeta and Hgamma/Hbeta ratios follow a different trajectory from dust reddening, allowing the two effects to be distinguished using multiple Balmer lines. In unresolved systems, a cool source located near the line-emitting gas may provide an additional radiation field distinct from the hot stars responsible for ionization. Balmer decrements may therefore carry information about otherwise hidden components of the radiation field surrounding the emitting gas.
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All authors Maryam Dehghanian, Fransisco Guzman, Peter van Hoof, Chamani Gunasekera, Gary Ferland

Astrophysics of Galaxies

When dust growth takes over: the origin of dust in post-reionization galaxies

Omima Osman, Gabriella De Lucia, Andreas. L. Faisst et al. (+3 more)

The post-reionization epoch ($z\sim4$-6) marks a critical phase in galaxy evolution, during which galaxies rapidly assemble their stellar mass, enrich their interstellar medium, and build up substantial dust reservoirs. The physical processes responsible for such rapid dust enrichment remain uncertain. We investigate the dust enrichment history of the ALPINE-CRISTAL-JWST (ACJ) sample using the semi-analytic galaxy formation model GAlaxy Evolution and Assembly (GAEA), which follows galaxy assembly, chemical enrichment, and dust evolution. We select model galaxies matching the observed stellar masses, star formation rates, and metallicities of the ACJ sample, compare their dust properties with observed scaling relations, and trace their enrichment histories and environments. The model reproduces the observed dust mass-stellar mass relation and the dust-to-stellar mass, dust-to-gas, and dust-to-metal ratios as functions of stellar mass and metallicity. Reproducing these constraints requires efficient dust growth in the interstellar medium; stellar dust production alone cannot account for the observed dust reservoirs, even under the most optimistic assumptions. The combination of stellar mass, star formation rate, and metallicity provides a good predictor of galaxy dust content. Our model suggests rapid dust build-up consistent with the previously noted rapid metal enrichment, with evidence for a transition around $z\sim8$-9 below which dust growth becomes the dominant dust formation channel. Finally, ACJ-like galaxies preferentially reside in locally overdense environments, suggesting that environment may have contributed to their accelerated evolution. Taken together, these results support rapid and coupled stellar, metal, and dust build-up in ACJ galaxies during the post-reionization era.
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All authors Omima Osman, Gabriella De Lucia, Andreas. L. Faisst, Lizhi Xie, Fabio Fontanot, Michaela Hirschmann

Astrophysics of Galaxies

A Single Line-Emitter Identified in an Unbiased Search with JWST/NIRSpec: Multi-Object Coronagraphy for Slitless Spectroscopy

Mason S. Huberty, Claudia Scarlata, Matthew J. Hayes et al. (+13 more)

We report the detection of a previously unknown object with a single emission line within the Hubble Ultra Deep Field, using a new JWST NIRSpec technique called Multi-Object Coronagraphy for Slitless Spectroscopy (MOCSS) with the G140M/F100LP observing mode. The MOCSS technique involves opening almost all the shutters on the NIRSpec microshutter array, while simultaneously closing the shutters that lie on top of known low redshift objects, facilitating a wide field slitless spectroscopic search without contamination from bright objects. This observational technique has enabled the detection of a strong emission line in four different dither positions and in two position angles, and thus cannot be artificial. This line is detected at 1.60 $\rm \mu m$ with a line flux of $[2.5\pm 0.3]\times10^{-18} \rm erg\ s^{-1} cm^{-2}$ and a FWHM of $13.2\pm2.0$Å, and does not correspond to any known source with some of the deepest HST and JWST imaging in existence. Based upon the absence of imaging detection, we place a lower limit on the observed frame equivalent width (EW) of 7620Å on this object, which strongly limits the number of possible lines that this line can be. Given the wavelength, an EW limit that is near the ceiling of expectation, and the lack of other lines in the bandpass, this line cannot be easily explained by [OII] at $z=3.29$, [OIII] at $z=2.20$, H$\alpha$ at $z=1.44$, and Ly$\alpha$ at $z=12.16$. We discuss possible AGN and transient phenomena that could explain the finding.
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All authors Mason S. Huberty, Claudia Scarlata, Matthew J. Hayes, Alaina Henry, Danielle A. Berg, Vieri Cammelli, Richard Ellis, Anne E. Jaskot, Yu-Heng Lin, Vihang Mehta, Matilde Mingozzi, Pierluigi Monaco, Alberto Saldana-Lopez, Aayush Saxena, Jonathan C. Tan, Alice Young

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

Disk Structure May Determine AGN Variability and Explain the Accretion Disk Size Problem: No Broad Line Region Required

Amy Secunda, Yan-Fei Jiang and Jenny E. Greene

Variability is a crucial probe of active galactic nuclei (AGN) disks, but the impact of the structure and internal physics of the disk on this variability is poorly understood. We perform 3D multi-frequency radiation magnetohydrodynamic simulations of the $1300-5940~\rm{\AA}$ emitting region of an AGN disk. This turbulent disk simulation happens to stochastically have different disk thickness above and below the midplane. Light curves emitted from the thin top of the disk are broadly consistent with traditional variability models, where the X-ray irradiation emitted from the corona is the main driver of variability in UV-optical light curves. Conversely, the UV-optical light curves emitted from the thicker bottom of the disk are not strongly correlated with the X-ray light curve and have disk continuum reverberation mapping lags that are $3-5\times$ longer than the light travel time. While these features are inconsistent with traditional variability models, they are in good agreement with numerous recent observations. Our simulations allow us to interpret these recent observations with a new model for AGN disks, where the thicker disk leads to greater X-ray absorption, less X-ray reprocessing at larger disk radii, and a stronger signal from intrinsic variability driven by fluctuations in the AGN disk. In our simulations, we can measure the inflow timescale of these fluctuations as a long lag between light curves emitted from different disk radii. Understanding how disk structure impacts AGN variability and reverberation mapping can allow us to predict the thickness of AGN disks using UV-optical AGN light curves.
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Astrophysics of Galaxies

ACORN I. Massive Black Hole Seeding and Tidal Disruption Events from Star Clusters in Cosmological Simulations

Yihao Zhou, Tiziana Di Matteo, Claire E. Williams et al. (+6 more)

JWST has revealed massive star clusters at $z\gtrsim 6$, which provide promising environments for massive black hole (MBH) seed formation. We introduce a new MBH seeding model for cosmological simulations, physically motivated by the runaway collisions in star clusters. Subgrid star clusters are generated according to the local ISM and evolved through stellar evolution and two-body relaxation. The masses of MBH seeds formed through runaway collisions are determined by the properties of their host clusters, including the effects of metallicity-dependent stellar winds. We further follow tidal disruption events (TDEs) with the evolving clusters, which can be enhanced in MBH binaries, and account for gravitational-wave (GW) recoil following MBH mergers. We implement this model in a constrained simulation of a 5$\sigma$ overdense region, where seeds of $10^{3}-10^{5.6}\,M_\odot$ form in clusters with $10^{4}\leq m_{\rm SC}\leq 10^{8}\,M_\odot$. Because both the seed abundance and mass are directly connected to the local environment, we have a more physical $M_{\rm BH}\!-\!M_{\rm galaxy}$ scaling for low-mass galaxies ($M_{\rm galaxy}\sim10^{6-9}\,M_\odot$), a regime poorly described by previous seeding models. Multiple MBHs are naturally allowed to form in-situ within individual halos, producing a spatially clustered population. This increases the MBH merger rate by $\sim100$ relative to other seeding models, significantly enhancing the expected LISA event rate. TDEs can dominate the growth of $10^{3-4}\,M_\odot$ MBHs and produce luminous flares of $L_{\rm peak}\sim 10^{42-43}\,{\rm erg\,s^{-1}}$, increasing the observability of low-mass seeds. This seeding prescription accelerates early MBH growth at $z\gtrsim 8$, while subsequent self-regulated gas accretion drives the central MBH toward similar masses $\sim10^{8.6}\, M_\odot$ by $z=6$ across different seeding models.
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All authors Yihao Zhou, Tiziana Di Matteo, Claire E. Williams, Aklant Kumar Bhowmick, Marta Reina-Campos, Carl L. Rodriguez, Elena González Prieto, Laura Blecha, Rupert Croft

Astrophysics of Galaxies

Inflow-driven galaxy evolution - II: A hierarchy in the scaling relations of star-forming galaxies

Kai Wang, Carlton Baugh, Sownak Bose et al. (+7 more)

The star-forming main sequence (SFMS; $M_\star$–sSFR), the gas-to-stellar mass relation ($M_\star$–$M_{\rm gas}/M_\star$), and the mass–metallicity relation (MZR; $M_\star$–$Z_{\rm gas}$) are three core scaling relations for star-forming galaxies, and together they encode the information about the baryon cycle that operates during galaxy evolution. We investigate how these relations emerge by modelling the gas flows that regulate the baryon cycle, using both an ideal and a cosmological gas flow model, and identify a hierarchy among the three relations, with one further parameter entering the scatter budget at each step. In our model, the SFMS and its scatter are set primarily by the formation time of the host halo, with a weak dependence on the star formation efficiency and the mass-loading factor. The gas-to-stellar mass relation follows from the ratio of the sSFR to the star formation efficiency, and inherits the scatter of both. The MZR in turn follows from the gas-to-stellar mass relation together with the mass-loading factor, their relative contributions depending on the galaxy evolutionary state between the inflow-driven regime and equilibrium. This hierarchy naturally introduces further correlations among the three relations, such as the fundamental plane of star formation ($M_\star$–$M_{\rm gas}$–SFR), the fundamental metallicity relation ($M_\star$–SFR–$Z_{\rm gas}$) and its gaseous counterpart ($M_\star$–$M_{\rm gas}$–$Z_{\rm gas}$), and the correlations of each relation with galaxy size, which traces the star formation efficiency through the star formation law. Together, the three core scaling relations and the higher-dimensional correlations among them follow from a single framework, providing a foundation for linking the observables of star-forming galaxies to the underlying baryon cycle.
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All authors Kai Wang, Carlton Baugh, Sownak Bose, Shaun Cole, Carlos S. Frenk, Cedric Lacey, Julio F. Navarro, Kyle A. Oman, Amélie Saintonge, Tom Theuns

Astrophysics of Galaxies

JWST CAPERS: Spectroscopic evaluation of very high redshift galaxy candidates

Callum T. Donnan, Mark Dickinson, Lorenzo Napolitano et al. (+21 more)

JWST/NIRCam imaging has enabled efficient selection of a large number of galaxy candidates at very high redshifts. Accurate and robust selection is crucial for statistical analyses, such as measurement of the ultraviolet luminosity function (UV LF). A variety of selection methods and criteria have been proposed in the literature. We evaluate the selection methodology of galaxy candidates at $z\geq8.5$ using 183 candidates with secure spectroscopic redshifts obtained from the CAPERS JWST/NIRSpec PRISM program. The success of high-$z$ confirmation is strongly correlated with the photometric signal-to-noise ratio (SNR) in the detection filter, the strength of the Lyman-$\alpha$ break, and the $\Delta \chi^2$ between the best-fitting low-redshift and high-redshift spectral energy distribution model. However, the most efficient selection method is the use of a UV LF prior on the inferred $p(z)$ of a source, raising the success rate from $\simeq 35\%$ to $\simeq 77\%$ while achieving greater completeness than conservative SNR and $\Delta \chi^2$ cuts. Out of the 183 candidates we spectroscopically confirm 48 sources at $z\geq8.5$ via detections of emission lines and/or the Lyman-$\alpha$ break (particularly important for those with no emission line detection). We report the highest-redshift source in CAPERS as UDS-111893 at $z_{\mathrm{spec}}=12.98$, with no sources confirmed at $z>13$. This work provides spectroscopic quantification of JWST/NIRCam photometric selection at $z\geq8.5$, and demonstrates the effectiveness of a UV LF prior for high-redshift photometric selection.
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All authors Callum T. Donnan, Mark Dickinson, Lorenzo Napolitano, Pablo Arrabal Haro, Anthony J. Taylor, Hollis B. Akins, Ryan Begley, Davide Bevacqua, Adam C. Carnall, Marco Castellano, Fergus Cullen, James S. Dunlop, Steven L. Finkelstein, Carter Flayhart, Mauro Giavalisco, Michaela Hirschmann, Ray A. Lucas, Derek J. McLeod, Ross J. McLure, Casey Papovich, Laura Pentericci, Borja Pérez-Díaz, Thomas M. Stanton, L. Y. Aaron Yung

Astrophysics of Galaxies

Modeling CO Line Luminosity Using FIRE Simulations: I. Methodology and Validation of Molecular Gas and CO Abundance

Doğa Tolgay, Norman W. Murray, Dongwoo Chung et al. (+5 more)

We present a post-processing pipeline that predicts CO line luminosities, molecular hydrogen masses, and CO abundances for galaxies in the Feedback in Realistic Environments (FIRE-2) simulations, as a first step toward CO response functions for line intensity mapping mocks. SKIRT gives the radiation field reaching each gas cell. CLOUDY, tabulated on a five-parameter grid (metallicity, density, turbulent velocity, radiation field, cloud scale) and interpolated, gives $L'_{\rm CO(1-0)}$ and the $\rm H_2$ and CO masses. In this first of three papers we validate the pipeline against observations. For Milky Way (MW) molecular clouds, the predicted $L'_{\rm CO(1-0)}$ rises sharply at $A_V\sim1$ and matches the observed values above that column. For a uniform $3\,Z_\odot$ the summed luminosity is within 35% of the observed total. A factor of three increase in metallicity changes the total $L'_{\rm CO(1-0)}$ by an order of magnitude. Along MW sight lines, the predicted $N_{\rm CO}/N_{\rm H_2}$ reproduces the observed upturn within 0.3 dex in $N_{\rm H_2}$ but falls below the data at higher columns. At $z=0$ our molecular gas masses agree with xCOLD GASS for ${\rm SFR}\gtrsim0.3\,M_\odot\,yr^{-1}$ and are converged across our simulation resolutions. At $z\gtrsim1$ observed gas masses exceed ours at fixed stellar mass, though selection effects and conversion-factor assumptions limit this comparison. CO luminosities are compared with extragalactic observations in Paper II. Capturing the metallicity-dependent dust shielding of CO from photodissociation is essential for modeling CO emission in low-mass and high-redshift galaxies.
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All authors Doğa Tolgay, Norman W. Murray, Dongwoo Chung, J. Richard Bond, Nathan J. Carlson, Robert Feldmann, Andrew Wetzel, Guochao Sun

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

Discovery of the Slowest Radio Pulsar in the Small Magellanic Cloud

Weiyu Wang and Rahul Sengar

We report the discovery of a new radio pulsar PSR J0103$-$72 in the Small Magellanic Cloud (SMC) through a reanalysis of Parkes/Murriyang archival observations targeting supernova remnants and pulsar-wind nebulae in the SMC. Previously two pulsars were discovered in these observations, and PSR J0103$-$72 is the third which we independently detected in two observations of its target field. It has a spin period of 1.327 sec and a dispersion measure (DM) of $272\pm13~\mathrm{pc\,cm^{-3}}$, making it the slowest known radio pulsar in the SMC with the second-highest DM. We did not identify any plausible supernova remnant or pulsar-wind nebula associated with the pulsar. Subtracting the predicted Galactic foreground leaves a DM contribution of $\sim 230$–$242~\mathrm{pc\,cm^{-3}}$, which may suggest a long path through the ionized medium of the SMC, enhanced ionized gas along the sightline, or both. Although these data had previously been searched using both FFT and fast folding algorithms, our FFT-based reprocessing found PSR J0103$-$72 through search techniques which have previously been highly effective in discovering a large number of pulsars in other surveys. This discovery shows that candidates with weak Fourier-domain significance can reveal faint, narrow-duty cycle pulsars missed in earlier extragalactic pulsar searches.
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Astrophysics of Galaxies

Too many or too bright? Status and perspectives in the study of the UV Luminosity Function at z>10

A. Fontana, H. Atek, V. Bromm et al. (+20 more)

The finding that galaxies in the first 500Myr were much more numerous and/or brighter than expected is often cited as one of the main discoveries of the James Webb Space Telescope in its first four years of operation. This result is now solidly based on an impressive number of surveys that have detected, spectroscopically confirmed, and characterized a relatively large sample of galaxies up to z=14.44, the redshift of the most distant galaxy currently known. This finding has motivated the introduction of additional physical mechanisms into theoretical models to reproduce the observed numbers and luminosities. These results contrast with the failure, despite ongoing efforts, to confirm any galaxy candidate beyond this redshift. This review summarizes the status of the search for and characterization of galaxies at z>9, focusing on the evolution of the UV Luminosity Function (UVLF), which is the main statistical description of the galaxy population that can be obtained at these redshifts. We first provide a comprehensive overview of the full set of JWST data obtained so far. We perform a 'meta–analysis' on the entire data set and provide a simple yet effective description of the global evolution of the UVLF, averaging over the various surveys. We also compare these results extensively with theoretical models that were developed to match the new JWST observations and that explore different physical mechanisms able to drive the observed evolution. We conclude with a summary of the contrasting results regarding the search for galaxy candidates at z>15, and outline the requirements for future surveys aimed at breaking this barrier.
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All authors A. Fontana, H. Atek, V. Bromm, A. J. Bunker, M. Castellano, P. Dayal, F. D'Eugenio, D. Elbaz, A. Ferrara, S. L. Finkelstein, S. Fujimoto, M. Giavalisco, Y. Harikane, C. Kobayashi, F. Pacucci, P. G. Pérez-González, P. Rosati, A. Trinca, R. Tripodi, P. Santini, E. Vanzella, A. Venditti, A. Weibel

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

EWOCS-XI: Anisotropic expansion and shear in the cluster Westerlund 1. A 2D kinematic analysis with Gaia DR3

L. Prisinzano, F. Damiani, C. Ordenes-Huanca et al. (+14 more)

Westerlund 1 (Wd1) is one of the Milky Way's most massive young clusters, in which heavy extinction and field contamination have historically hampered its kinematic characterization. We aim to assess Wd1's internal kinematics, dynamical state, and formation scenario. Using a robust 5D clustering approach, we identified 559 bona fide members. We modeled their proper motions via a 2D first-order Taylor expansion to derive the velocity gradient tensor, mapping expansion, rotation, and shear. Restricting the kinematic analysis to 524 stars with proper motion uncertainties $<0.5~\mathrm{mas\,yr^{-1}}$, we find at least 103 gravitationally unbound members, including 14 walkaway stars. The 2D analysis reveals a statistically significant divergence (>4$\sigma$) highlighting preferred expansion along the Galactic latitude (position angle $164^\circ\pm10.1^\circ$). A detected cross-gradient ($\partial v_b / \partial l = -0.41 \pm 0.08$ km s$^{-1}$ pc$^{-1}$) provides a clear signature of shear on the plane of the sky. Wd1 does not behave as a single cohesive population, but comprises two decoupled subsystems: a stable, bound core in dynamical equilibrium and an escaping, unbound envelope. This prominent anisotropic expansion perpendicular to the Galactic plane has a kinematic timescale ($\Delta t_{\mathrm{kin}} = 2.08 \pm 0.44$ Myr) matching the independent orbital mid-plane crossing time ($\Delta t_{\mathrm{orbit}} = 2.10 \pm 0.05$ Myr). This temporal alignment indicates the expansion onset coincided with Wd1's Galactic disk passage, triggered either by internal dynamics (e.g., early supernova feedback) or external tidal perturbations. Finally, the robust unbound population demonstrates that active cluster dissolution is underway, driven by discrete dynamical ejection events rather than long-term stellar evaporation.
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All authors L. Prisinzano, F. Damiani, C. Ordenes-Huanca, M. Tarantino, S. Sciortino, N.J. Wright, V. Almendros-Abad, M. Andersen, A. Bayo, R. Bonito, V. Cusimano, M. Haberle, K. Mužic, I. Negueruela, E. Sabbi, A. Winter, M.G. Guarcello

Astrophysics of Galaxies

Binding Energies of Astrophysically Relevant Molecules on CO$_2$ Clusters: Benchmarking and the Donor-Acceptor Origin of Surface-Dependent Binding

Aneesa Ahmad, Catherine Walsh and Stefan Vogt-Geisse

Carbon dioxide (CO$_2$) is among the most abundant interstellar ices and has been observed by JWST in water-rich mixtures and pure CO$_2$ environments. Astrochemical models adopt binding energies (BEs) measured on water ice because few BEs are available for CO$_2$ ice. We calculate BE distributions for twelve adsorbates (N$_2$, CH$_4$, HCl, C$_2$H$_2$, H$_2$S, HF, HCN, H$_2$CO, HCOOH, HNC, CH$_3$OH, H$_2$O) on CO$_2$ clusters containing two to five molecules using DFT calibrated against CCSD(T)/CBS, a coupled-cluster treatment extrapolated to the complete-basis-set limit. Binding strength depends on whether the adsorbate requires the surface to donate a hydrogen bond (H-bond). CO$_2$ can accept an H-bond but cannot donate one, and all six species compared with water ice from Ahmad et al. (2026) bind more weakly on CO$_2$. The ratio of the BE on CO$_2$ to water ice ranges from 0.66 for H$_2$CO and 0.75 for H$_2$O to 0.87 for CH$_3$OH, 0.89 for HCOOH and 0.92 for C$_2$H$_2$. Formaldehyde is predicted to desorb near 57 K from CO$_2$-rich ice, compared with 85 K from water-rich ice, and could contribute to cold gas-phase H$_2$CO. Although the mean binding energies are changing with cluster size for several species, the differences can be traced to local binding interactions likely to remain important in larger ice models. The BEs vary by more than 500 K between sites, while the desorption peaks range from 11 K for CH$_4$ to 132 K for HCOOH. The limited H-bonding capacity of CO$_2$ may favour separation of mixed H$_2$O:CO$_2$ ice into CO$_2$-rich domains.
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Astrophysics of Galaxies · Cross-listed from physics.chem-ph

Gas-phase chemistry of $\mathrm{C}_3\mathrm{H}_3^+$: a key building block for carbon mass growth in space

Corentin Rossi, Jean-Christophe Loison, Anne P. Rasmussen et al. (+4 more)

The gas-phase chemistry of $\mathrm{C}_3\mathrm{H}_3^+$ plays a central role in the growth of carbonaceous species across a wide range of environments, from combustion systems to interstellar media. However, the presence of multiple isomers, primarily the linear propargyl cation and the cyclic cyclopropenyl cation, has so far prevented the determination of reliable isomer-specific reaction kinetics. In this work, we combine tunable vacuum-ultraviolet (VUV) photoionization with controlled ion–molecule reaction measurements to selectively produce and probe the reactivity of $\mathrm{C}_3\mathrm{H}_3^+$ isomers. By employing a titration approach, we extract isomer-specific reaction rate coefficients and branching ratios for reactions of $\mathrm{C}_3\mathrm{H}_3^+$ with $\mathrm{C}_2\mathrm{H}_4$, $\mathrm{C}_3\mathrm{H}_4$, and $\mathrm{C}_3\mathrm{H}_6$. Our results demonstrate a strong contrast in reactivity: the most stable cyclic isomer is found to be essentially unreactive under the investigated conditions, whereas the linear isomer exhibits efficient and diverse chemistry leading to the formation of larger hydrocarbon ions. In particular, the formation of $\mathrm{C}_6\mathrm{H}_5^+$ is observed, providing an important intermediate in pathways toward aromatic species. These findings help resolve long-standing ambiguities in previously reported rate coefficients and provide new quantitative constraints for kinetic and astrochemical models. More broadly, this work highlights the importance of isomer-specific chemistry in carbon growth processes and demonstrates the effectiveness of VUV-based photoionization methods for disentangling complex reaction networks in the gas phase.
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All authors Corentin Rossi, Jean-Christophe Loison, Anne P. Rasmussen, Roland Thissen, Nandana Pattathadathil, Christian Alcaraz, Ugo Jacovella

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

Probing Massive Star Formation with Intrinsic Multiplicity Constraints from TESS Eclipsing Binaries

Jasmine Vrancken, Alex Kemp, Andrew Tkachenko et al. (+2 more)

Massive stars play a central role in stellar and galactic evolution as progenitors of supernovae, neutron stars, black holes, and gravitational wave sources. Despite their importance, the dominant formation mechanisms of massive binaries remain poorly constrained observationally. We aim to use a large, homogeneous sample of eclipsing binaries to observationally constrain binary formation across a wide range of primary masses and test predictions from various formation scenarios. We combine photometric time series data from TESS with distance measurements from Gaia DR3 and near infrared photometry from 2MASS to analyze an all-sky sample of eclipsing binaries. By accounting for observational and geometric selection effects, we derive bias corrected estimates of the binary fractions and orbital parameter distributions across different mass bins. We derive bias corrected binary fractions and bias corrected distributions of orbital period and radius-to-separation ratio for systems spanning primary masses from 1.1 Msun to 47 Msun. For primary masses up to 5 Msun, the observed distributions show close agreement with theoretical predictions for systems formed via disk fragmentation followed by migration. At higher masses, we observe an apparent deficit of very short period systems relative to theoretical expectations, although this regime is also expected to be affected by incompleteness. Overall, the observed properties exhibit a gradual transition across the full range of primary masses. Within the orbital period range accessible to our sample, the results do not require a sharp transition in binary properties between F- and O-type stars. The observed continuity is consistent with disk fragmentation followed by migration acting across a broad range of stellar masses, although the present data do not uniquely require this formation pathway and alternative channels may also contribute.
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All authors Jasmine Vrancken, Alex Kemp, Andrew Tkachenko, Conny Aerts, Hugues Sana

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

Gravitational Microlensing

Aikaterini Vandorou and Stela Ishitani Silva

Gravitational microlensing is a unique planet-detection method that does not rely on detecting light from the host star or planet. Instead, planets are discovered when their gravitational field perturbs the light coming from a distant source. The mechanics of this method offer several advantages. It has the ability to detect wide-orbit planets of various masses around host stars of different types, at and beyond the system's snow line. Thus, microlensing complements the other detecting techniques that are more sensitive to close-orbit or high-mass planets. In this Chapter, we review the microlensing method and discuss how the physical properties, such as mass and distance, can be extracted from the microlensing light curve or from additional high-angular resolution observations. Microlensing is essential for the broader context of exoplanet demographics, as it can place constraints on planets, in wide orbits, beyond the snow line. Studying this parameter space can help us unravel the details of planet formation and how our own Solar System formed. Lastly, we provide an example of how to model a light curve and obtain accurate physical parameters for the host and planet.
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Astrophysics of Galaxies

Measuring radial flows in disc galaxies

Yi He, Filippo Fraternali, Pavel E. Mancera Piña et al. (+1 more)

Numerous theoretical studies suggest that gas accretion from the intergalactic medium is essential to feed star formation in galaxies throughout cosmic time. However, the mechanism of gas accretion remains poorly understood, as direct evidence is lacking. In some models, gas accretion is expected to take place in the outer discs of galaxies, from where it should be transferred to the inner star-forming discs through radial flows. Finding such flows and quantifying them, therefore, opens the possibility of inferring the detailed properties of the accreting gas. Unfortunately, detecting radial flows is challenging due to the large disparity between radial and rotational velocities. Additionally, the distortions in velocity fields produced by these flows resemble the effects of warped structures, further complicating their quantification. To address this, we have developed a new methodology to measure axisymmetric radial velocities in disc galaxies. Relying on the 3D kinematic fitting software \texttt{$^{\rm 3D}$Barolo}, we have designed a dedicated workflow to measure axisymmetric radial motions in disc galaxies and to obtain robust uncertainty estimates through a bootstrapping approach. We validated this approach using realistic axisymmetric mock galaxies as well as a small sample of `observed' Milky Way-like galaxies drawn from the TNG50 hydrodynamic simulation. These tests demonstrate that our method works well and is capable of overcoming the degeneracy between radial motions and warps. The TNG50 galaxies we analysed have large regions in their discs with non-axisymmetric inflows and outflows, but they show, on average, no global trend of coherent radial flows.
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All authors Yi He, Filippo Fraternali, Pavel E. Mancera Piña, Enrico M. Di Teodoro