Stellar Mass Research Articles

It's written in the massive stars: The role of stellar physics in the formation of black holes

In the age of gravitational-wave (GW) sources and newly discovered local black holes (BHs) and neutron stars (NSs), understanding the fate of stars is a key question. Not every massive star is expected to successfully explode as a supernova (SN) and leave behind a NS; some stars form BHs. The remnant left after core collapse depends on explosion physics but also on the final core structure, often summarized by the compactness parameter or iron core mass, where high values have been linked to BH formation. Several independent groups have reported similar patterns in these parameters as a function of mass, characterized by a prominent ``compactness peak'' followed by another peak at higher masses, pointing to a common underlying physical mechanism. Here, we investigate the origin of this pattern by computing detailed single-star models of 17 to 50 solar masses with MESA. We show that the timing and energetics of the last nuclear burning phases determine whether or not stars will reach a high final compactness and iron-core mass and will likely form BHs. The first and second compactness increases originate from core carbon and neon burning, respectively, becoming neutrino dominated, which enhances the core contraction and ultimately increases the iron-core mass and compactness. An early core neon ignition during carbon burning, and an early silicon ignition during oxygen burning, both help counter the core contraction and decrease the final iron core mass and compactness. Shell mergers between C/Ne-burning and O-burning shells further decrease the compactness and we show that these mergers are due to an enhanced entropy production in those layers. We find that the final structure of massive stars is not random but already ``written'' in their cores at core helium exhaustion, when the core structure is characterized by the central carbon mass fraction $X_ C $ and the CO core mass. The same mechanisms determine the final structure of any star in this core mass range, including binary products; though binary interactions induce a systematical shift in the range of expected BH formation due to changes in $X_ C $. Finally, we discuss the role of uncertainties in stellar physics and how to apply the findings presented here to studies of GW sources.

Exploring the spatially resolved initial mass function in SAMI star-forming galaxies

Abstract The initial mass function (IMF) is a construct that describes the distribution of stellar masses for a newly formed population of stars. It is a fundamental element underlying all of star and galaxy formation, and has been the subject of extensive investigation for more than 60 years. In the past few decades there has been a growing, and now substantial, body of evidence supporting the need for a variable IMF. In this light, it is crucial to investigate the IMF’s characteristics across different spatial scales and to understand the factors driving its variability. We make use of spatially resolved spectroscopy to examine the high-mass IMF slope of star-forming galaxies within the SAMI survey. By applying the Kennicutt method and stellar population synthesis models, we estimated both the spaxel-resolved (α res ) and galaxy-integrated (α int ) high-mass IMF slopes of these galaxies. Our findings indicate that the resolved and integrated IMF slopes exhibit a near 1:1 relationship for α int ≳ –2.7. We observe a wide range of α res distributions within galaxies. To explore the sources of this variability, we analyse the relationships between the resolved and integrated IMF slopes and both the star formation rate (SFR) and SFR surface density (ΣSFR). Our results reveal a strong correlation where flatter/steeper slopes are associated with higher/lower SFR and ΣSFR. This trend is qualitatively similar for resolved and global scales. Additionally, we identify a mass dependency in the relationship with SFR, though none was found in the relation between the resolved slope and ΣSFR. These findings suggest an scenario where the formation of high-mass stars is favoured in regions with more concentrated star formation. This may be a consequence of the reduced fragmentation of molecular clouds, which nonetheless accrete more material.

Recovering the properties of the interstellar medium through integrated spectroscopy: Application to the z∼0 ECO volume-limited star-forming galaxy sample

Deriving physical parameters from integrated galaxy spectra is paramount to interpret the cosmic evolution of the star formation, chemical enrichment, and energetic processes at play. Previous studies have highlighted the power of interstellar medium tracers but also the associated complexities that can be captured only through sophisticated modeling approaches. We developed modeling techniques to characterize the ionized gas properties in the subset of $2052$ star-forming galaxies from the volume-limited, dwarf-dominated, z∼0 ECO catalog (stellar mass range M_*∼10^8-11,M_⊙). Our study sheds light on the internal distribution and average values of parameters such as the metallicity, ionization parameter, and electron density within galaxies. We used the MULTIGRIS statistical framework to evaluate the performance of various models using strong lines as constraints. The reference model involves physical parameters distributed as power laws with free parameter boundaries. Specifically, we used combinations of 1D photoionization models (i.e., considering the propagation of radiation toward a single cloud) to match optical H2 region lines, in order to provide probability density functions of the inferred parameters. The inference predicts nonuniform physical conditions within galaxies. The integrated spectra of most galaxies are dominated by relatively low-excitation gas with a metallicity around $0.3$,Z_⊙. Using the average metallicity in galaxies, we provide a new fit to the mass-metallicity relationship which is in line with direct abundance method determinations from the low-metallicity calibrated range up to high-metallicity stacks. The average metallicity shows a weakly bimodal distribution which may be due to external (e.g., refueling of non-cluster early-type galaxies) or internal processes (higher star-formation efficiency in metal-rich regions). The specific line set used for inference affects the results and we identify potential issues with the use of the S2 line doublet. Complex modeling approaches may capture diverse physical conditions within galaxies but require robust statistical frameworks. Such approaches are limited by the inherent 1D model database as well as caveats regarding the gas geometry. Our results highlight, however, the possibility to extract useful and significant information from integrated spectra.

Asymmetries and Circumstellar Interaction in the Type II SN 2024bch

Abstract We present a comprehensive multi-epoch photometric and spectroscopic study of SN 2024bch, a nearby (19.9 Mpc) Type II supernova (SN) with prominent early high-ionization emission lines. Optical spectra from 2.8 days after the estimated explosion reveal narrow lines of H i, He ii, C iv, and N iv that disappear by day 6. High-cadence photometry from the ground and Transiting Exoplanet Survey Satellite show that the SN brightened quickly and reached a peak M V ~ −17.8 mag within a week of explosion, and late-time photometry suggests a 56Ni mass of 0.050 M ⊙. High-resolution spectra from days 7.9 and 43 trace the unshocked circumstellar medium (CSM) and indicate a wind velocity of 30–40 km s−1, a value consistent with a red supergiant (RSG) progenitor. Comparisons between models and the early spectra suggest a pre-SN mass-loss rate of M ̇ ~ 1 0 − 3 – 1 0 − 2 M ⊙ yr − 1 , which is too high to be explained by quiescent mass loss from RSGs, but is consistent with some recent measurements of similar SNe. Persistent blueshifted H i and [O i] emission lines seen in the optical and near-IR spectra could be produced by asymmetries in the SN ejecta, while the multicomponent Hα may indicate continued interaction with an asymmetric CSM well into the nebular phase. SN 2024bch provides another clue to the complex environments and mass-loss histories around massive stars.

FEASTS: Radial Distribution of H i Surface Densities Down to 0.01 M⊙ pc−2 of 35 Nearby Galaxies

Abstract We present the H i surface density (ΣH i ) radial distributions based on total-power H i images obtained by FAST in the FEASTS program, for 35 galaxies with inclinations lower than 72°. We derive the H i radius R 001, which is the radius for the 0.01 M ⊙ pc−2 (~1018.1 cm−2) isodensity level, 100 times deeper than the 1 M ⊙ pc−2 level previously commonly used to measure R 1. The profile shapes show a large diversity at a given radius in units of kpc, group virial radius, and R 1, but they align more tightly with the radius normalized by R 001. The universal H i profile has a scatter of ~0.2 dex and a scale length of ~0.11R 001 in the outer region. We derive a new R 001–M H i relation, which has a scatter of 0.03 dex and a similar slope of ~​​​​​​0.5 to the previously known R 1–M H i relation. Excluding strongly tidal-interacting galaxies, the ratio R 001/R 1 (anti)correlates strongly and significantly with the H i-to-stellar mass ratio and specific star formation rate, but not with the stellar mass, M H i , dark matter mass, or star formation rate. The strongly tidal-interacting galaxies tend to show deviations from these trends and have the most flattened profiles. These results imply that, in the absence of major tidal interactions, physical processes must cooperate so that ΣH i distributes in a self-similar way in the outer region down to the 0.01 M ⊙ pc−2 level. Moreover, they may drive gas flows in such a way that H i-richer galaxies have H i disks that not only extend further but also transport H i inward more efficiently from R 001 to R 1.

Photometric Determination of Unresolved Main-sequence Binaries in the Pleiades: Binary Fraction and Mass-ratio Distribution

Abstract Accurate determination of binary fractions (f b) and mass ratio (q) distributions is crucial for understanding the dynamical evolution of open clusters. We present an improved multiband fitting technique to enhance the analysis of binary properties. This approach enables an accurate photometric determination of f b and q distribution in a cluster. The detectable mass ratio can be down to the q lim , limited by the minimum stellar mass in theoretical models. First, we derived an empirical model for magnitudes of Gaia DR3 and 2MASS bands that match the photometry of single stars in the Pleiades. We then performed a multiband fitting for each cluster member, deriving the probability density function (PDF) of its primary mass ( M 1 ) and q in the Bayesian framework. 1154 main-sequence (MS) single stars or unresolved MS+MS binaries are identified as members of the Pleiades. By stacking their PDFs, we conducted a detailed analysis of binary properties of the cluster. We found the f b of this sample is 0.34 ± 0.02. The q distribution exhibits a three-segment power-law profile: an initial increase, followed by a decrease, and then another increase. This distribution can be interpreted as a fiducial power-law profile with an exponent of −1.0 that is determined in the range of 0.3 < q < 0.8, but with a deficiency of binaries at lower q and an excess at higher q. The variations of f b and q with M 1 reveal a complex binary distribution within the Pleiades, which might be attributed to a combination of primordial binary formation mechanisms, dynamical interactions, and the observational limit of photometric binaries imposed by q lim ( M 1 ) .

Radiative properties and QPOs around charged black hole in Kalb–Ramond gravity

Studies of accretion disc luminosities and quasiperiodic oscillations around black holes may help us understand the gravitational properties of black hole spacetime. This work is devoted to studying the radiation properties of the accretion disk around the black holes in Kalb–Ramond gravity. We investigate the event horizon of the black hole spacetime and calculate the effective gravitational mass of the spacetime. Also, we analyze the circular motion of test particles in the black hole spacetime. The effects of the black hole charge and KR parameters on the particles’ effective mass, energy, and angular momentum at circular orbits and innermost stable circular orbits are studied. The frequency of Keplerian orbits and the radial and vertical oscillations of the particles along stable orbits are calculated and applied to analyze the existence of QPO in relativistic precession, warped disc, and epicyclic resonance models. QPO orbits’ locations with ratios of upper and lower frequencies of twin-peaked QPOs 3:2, 4:3, and 5:4 are analyzed compared to ISCO. We also obtain constrain values for the black hole mass, charge, KR field parameter, and QPO orbits found using Markovian chain Monte Carlo (MCMC) simulations for stellar mass (XTE J1550, GRS 1915+105), intermediate mass (M82-X1), and supermassive black holes (Sgr A*). Finally, we explore the radiative properties of the accretion disk around the charged black hole in KR gravity, such as the total radiation flux, accretion disc temperature, and differential luminosity.

Evolution of the Sérsic index up to z = 2.5 from JWST and HST

Context. The Hubble Space Telescope (HST) has long been the only instrument able to allow us to investigate the structure of galaxies up to redshift z = 3, limited to the rest-frame UV and optical. The James Webb Space Telescope (JWST) is now unveiling the rest-frame near-IR structure of galaxies, less affected by dust attenuation and more representative of their underlying stellar mass profiles. Aims. We measure the evolution with redshift of the rest-frame optical and near-IR Sérsic index (n), and examine the dependence on stellar mass and star-formation activity across the redshift range 0.5 ≤ z ≤ 2.5. Methods. For an HST-selected parent sample in the CANDELS fields we infer rest-frame near-IR Sérsic profiles for ≈15 000 galaxies in publicly available NIRCam imaging mosaics from the COSMOS-Web and PRIMER surveys. We augment these with rest-frame optical Sérsic indices, previously measured from HST imaging mosaics. Results. The median Sérsic index evolves slowly or not at all with redshift, except for very high-mass galaxies (M⋆ > 1011 M⊙), which show an increase from n ≈ 2.5 to n ≈ 4 at z < 1. High-mass galaxies have higher n than lower-mass galaxies (the sample reaches down to M⋆ = 109.5 M⊙) at all redshifts, with a stronger dependence in the rest-frame near-IR than in the rest-frame optical at z > 1. This wavelength dependence is caused by star-forming galaxies that have lower optical than near-IR n at z > 1 (but not at z < 1). Both at optical and near-IR wavelengths, star-forming galaxies have lower n than quiescent galaxies, confirming and fortifying the result that across cosmic time a connection exists between star-formation activity and the radial stellar mass distribution. Besides these general trends that confirm previous results, two new trends emerge: (1) at z > 1 the median near-IR n varies strongly with star formation activity, but not with stellar mass, and (2) the scatter in near-IR n is substantially higher in the green valley (0.25 dex) than on the star-forming sequence and among quiescent galaxies (0.18 dex) – this trend is not seen in the optical because dust and young stars contribute to the variety in optical light profiles. Our newly measured rest-frame near-IR radial light profiles motivate future comparisons with radial stellar mass profiles of simulated galaxies as a stringent constraint on processes that govern galaxy formation.

Emergence of high-mass stars in complex fiber networks (EMERGE)

Context. Identified as parsec-size, gas clumps at the junction of multiple filaments, hub-filament systems (HFS) play a crucial role during the formation of young clusters and high-mass stars. These HFS still appear to be detached from most galactic filaments when compared in the mass–length (M–L) phase space. Aims. We aim to characterize the early evolution of HFS as part of the filamentary description of the interstellar medium (ISM). Methods. Combining previous scaling relations with new analytic calculations, we created a toy model to explore the different physical regimes described by the M–L diagram. Despite its simplicity, our model accurately reproduces several observational properties reported for filaments and HFS, such as their expected typical aspect ratio (A), mean surface density (Σ), and gas accretion rate (ṁ). Moreover, this model naturally explains the different mass and length regimes populated by filaments and HFS, respectively. Results. Our model predicts a dichotomy between filamentary (A ≥ 3) and spheroidal (A < 3) structures connected to the relative importance of their fragmentation, accretion, and collapse timescales. Individual filaments with low accretion rates are dominated by an efficient internal fragmentation. In contrast, the formation of compact HFS at the intersection of filaments triggers a geometric phase-transition, leading to the gravitational collapse of these structures at parsec-scales in ~1–2 Myr. In addition, this process also induces higher accretion rates.

The ALPINE-ALMA [CII] Survey: Unveiling the baryon evolution in the interstellar medium of z ∼ 5 star-forming galaxies

Context. Recent observations suggest a significant and rapid buildup of dust in galaxies at high redshift (z > 4); this presents new challenges to our understanding of galaxy formation in the early Universe. Although our understanding of the physics of dust production and destruction in a galaxy’s interstellar medium (ISM) is improving, investigating the baryonic processes in the early universe remains a complex task owing to the inherent degeneracies in cosmological simulations and chemical evolution models. Aims. In this work we characterized the evolution of 98 z ∼ 5 star-forming galaxies observed as part of the ALMA Large Program ALPINE by constraining the physical processes underpinning the gas and dust production, consumption, and destruction in their ISM. Methods. We made use of chemical evolution models to simultaneously reproduce the observed dust and gas content of our galaxies, obtained respectively from spectral energy distribution (SED) fitting and ionized carbon measurements. For each galaxy we constrained the initial gas mass, gas inflows and outflows, and efficiencies of dust growth and destruction. We tested these models with both the canonical Chabrier and a top-heavy initial mass function (IMF); the latter allowed rapid dust production on shorter timescales. Results. We successfully reproduced the gas and dust content in most of the older galaxies (≳600 Myr) regardless of the assumed IMF, predicting dust production primarily through Type II supernovae (SNe) and no dust growth in the ISM, as well as moderate inflow of primordial gas. In the case of intermediate-age galaxies (300−600 Myr), we reproduced the gas and dust content through Type II SNe and dust growth in ISM, though we observed an overprediction of dust mass in older galaxies, potentially indicating an unaccounted dust destruction mechanism and/or an overestimation of the observed dust masses. The number of young galaxies (≲300 Myr) reproduced, increases for models assuming top-heavy IMF but with maximal prescriptions of dust production. Galactic outflows are required (up to a mass-loading factor of 2) to reproduce the observed gas and dust mass, and to recover the decreasing trend of gas and dust over stellar mass with age. Assuming the Chabrier IMF, models are able to reproduce ∼65% of the total sample, while with top-heavy IMF the fraction increases to ∼93%, alleviating the tension between the observations and the models. Observations from the James Webb Space Telescope (JWST) will allow us to remove degeneracies in the diverse intrinsic properties of these galaxies (e.g., star formation histories and metallicity), thereby refining our models.

Radial X-ray profiles of simulated galaxies. Contributions from hot gas and X-ray binaries

Theoretical models of structure formation predict the presence of a hot gaseous atmosphere around galaxies. While this hot circumgalactic medium (CGM) has been observationally confirmed through UV absorption lines, the detection of its direct X-ray emission remains scarce. Recent results from the eROSITA collaboration have claimed the detection of the CGM out to the virial radius for a stacked sample of Milky Way-mass galaxies. We investigate theoretical predictions of the intrinsic CGM X-ray surface brightness (SB) using simulated galaxies and connect them to their global properties, such as the gas temperature, hot gas fraction, and stellar mass. We selected a sample of central galaxies from the ultra-high-resolution cosmological volume ($48 cMpc $) of the Magneticum Pathfinder set of hydrodynamical cosmological simulations. We classified them as star-forming (SF) or quiescent (QU) based on their specific star formation rate (SFR). For each galaxy, we generated X-ray mock data using the X-ray photon simulator from which we obtained SB profiles out to the virial radius for different X-ray emitting components; namely, gas, active galactic nuclei (AGNs), and X-ray binaries (XRBs). We fit a β-profile to the gas component of each galaxy and observed trends between its slope and global quantities of the simulated galaxy. We found marginal differences among the average total SB profile in SF and QU galaxies beyond r>0.05 The relative contribution from hot gas exceeds $70%$ and is non-zero (lesssim 10%) for XRBs in both galaxy types. At small radii (r<0.05 XRBs dominate the SB profile over the hot gas for QU galaxies. We found positive correlations between the galaxies' global properties and the normalization of their SB profiles. The fitted β-profile slope is correlated with the total gas luminosity, which, in turn, shows strong connections to the current accretion rate of the central supermassive black hole (SMBH). We found the halo scaling relations to be consistent with the literature.

Massive black holes or stars first: the key is the residual cosmic electron fraction

Massive black holes or stars first: the key is the residual cosmic electron fraction

SN 2023ixf: An average-energy explosion with circumstellar medium and a precursor

The fortunate proximity of the Type II supernova (SN) 2023ixf has allowed astronomers to follow its evolution from almost the moment of the collapse of the progenitor's core. SN,2023ixf can be explained as an explosion of a massive star with an energy of 0.7 erg but with a greatly reduced envelope mass, probably because of binary interaction. In our radiative-transfer simulations, the SN ejecta of 6 interact with circumstellar matter (CSM) of (0.55--0.83) extending to 10^15 cm, which results in a light curve (LC) peak matching that of SN,2023ixf. The origin of this required CSM might be gravity waves originating from convective shell burning, which could enhance wind-like mass loss during the late stages of stellar evolution. The steeply rising low-luminosity flux during the first hours after observationally confirmed non-detection, however, cannot be explained by the collision of the energetic SN shock with the CSM. Instead, we consider it as a precursor that we can fit by the emission from (0.5--0.9) of matter that was ejected with an energy of ∼10^49 erg a fraction of a day before the main shock of the SN explosion reached the surface of the progenitor. The source of this energy injection into the outermost shell of the stellar envelope could also be dynamical processes related to the convective activity in the progenitor's interior or envelope. Alternatively, the early rise of the LC could point to the initial breakout of a highly non-spherical SN shock or of fast-moving asymmetrically ejected matter that was swept out well ahead of the SN shock, potentially in a low-energy, nearly relativistic jet. We also discuss that pre-SN outbursts and LC precursors can be used to study or to constrain energy deposition in the outermost stellar layers by the decay of exotic particles, such as axions, which could be produced simultaneously with neutrinos in the newly formed hot neutron star. A careful analysis of the earliest few hours of the LCs of SNe can reveal elusive precursors and provide a unique window onto the surface activity of massive stars during their core collapse. This can greatly improve our understanding of stellar physics and consequently also offer new tools for searching for exotic particles.

A theoretical framework for BL Her stars III. A case study: Robust light curve optimization in the Large Magellanic Cloud

In the era of precision stellar astrophysics, classical pulsating stars play a crucial role in determinations of the cosmological distance scale thanks to their period-luminosity (PL) relations. Therefore, it is important to constrain their stellar evolution and pulsation models not only through a comparison of empirical and theoretical PL relations and properties at mean light, but also using their light curve structure over the complete pulsation cycle. We carried out an extensive light curve comparison of BL Her stars using observations from Gaia DR3 and stellar pulsation models computed using mesa-rsp with the goal of obtaining the best-matched observed-model pairs for BL Her stars in the Large Magellanic Cloud (LMC). We used the Fourier decomposition technique to analyze the light curves in the G band obtained from Gaia DR3 and from mesa-rsp and used a robust light-curve-fitting approach to score the observed-model pairs with respect to their pulsation periods and over their Fourier parameter space. We obtain the best-fit models for 48 BL Her stars in the LMC and thereby provide the stellar parameter estimates of these stars, 30 of which we classify as our ``gold sample'' due to their superior light curve fits. We find a relatively flat distribution of stellar masses between 0.5 and 0.65,M_⊙ for the gold sample of observed-model pairs. An interesting result is that the majority of the best-matched models in the gold sample were computed using the convection parameter sets without radiative cooling. The period-Wesenheit (PW) relation for the best-matched gold sample of 30 BL Her models has a slope of -2.805 ± 0.164 and the corresponding period-radius relation a slope of $0.565 ± 0.035$, both in good agreement with the empirical PW and period-radius slopes from BL Her stars in the LMC, respectively. We also used the Wesenheit magnitudes of the 30 best-matched observed-model pairs to estimate a distance modulus of LMC = 18.582 ± 0.067 to the LMC, which lies within the bounds of previous literature values. We also discuss the degeneracy in the stellar parameters of the BL Her models that result in similar pulsation periods and light curve structure, and highlight that caution must be exercised while using the stellar parameter estimates.

Modeling contact binaries. III. Properties of a population of close, massive binaries

Among massive stars, binary interaction is the rule rather than the exception. The closest binaries -- those with periods of less than unsim10 days -- undergo mass transfer during core-hydrogen burning, with many of them experiencing a nuclear-timescale contact phase. Current binary population synthesis models predict the mass-ratio distribution of contact binaries to be heavily skewed toward a mass ratio of unity, which is inconsistent with observations. It has been shown that effects of tidal deformation due to the Roche potential and energy transfer in the common layers of a contact binary alter the internal structure of close binary components. However, previous population studies neglected these effects. We aim to model a population of massive binary stars that undergo mass transfer during core-hydrogen burning, while consistently considering the effects of tidal deformation and energy transfer in contact phases. We used the MESA binary-evolution code to compute large grids of models with primary star masses of SIrange Msun at solar metallicity. We then performed a population-synthesis study to predict distribution functions of the observational properties of close binary systems, focusing in particular on the mass and luminosity ratio distribution. We find that the effects of tidal deformation and energy transfer have a limited effect on the predicted mass-ratio distribution of massive contact binaries. Only a small fraction of the population have their mass ratio significantly shifted toward a more unequal configuration. However, we suggest that orbital hardening could affect the evolution of contact binaries and their progenitors, and we advocate for a homogeneous set of observed contact binary parameters.

COSMOS-Web: Stellar mass assembly in relation to dark matter halos across 0.2<z<12 of cosmic history

We study the stellar mass assembly of galaxies via the stellar mass function (SMF) and the coevolution with dark matter halos via abundance matching in the largest redshift range to date, $0.2<z<12$. We used the $0.53 deg ^2$ imaged by JWST from the COSMOS-Web survey, in combination with ancillary imaging in over 30 photometric bands, to select highly complete samples (down to log$ ⋆ /M_ ⊙ = 7.5-8.8$) in 15 redshift bins. Our results show that the normalization of the SMF monotonically decreases from z=0.2 to z=12 with strong mass-dependent evolution. At z>5, we find increased abundances of massive (log$ ⋆ /M_ ⊙ >10.5$) systems compared to predictions from semi-analytical models and hydrodynamical simulations. These findings challenge traditional galaxy formation models by implying integrated star formation efficiencies (SFEs) of ε_ ⋆ ≡ M_ ⋆ b M_ halo ≳ 0.5. We find a flattening of the SMF at the high-mass end that is better described by a double power law at z>5.5, after correcting for the Eddington bias. At z 5.5, it transitions to a Schechter law, which coincides with the emergence of the first massive quiescent galaxies in the Universe, indicating that physical mechanisms that suppress galaxy growth start to take place at z∼5.5 on a global scale. By integrating the SMF, we trace the cosmic stellar mass density and infer the star formation rate density, which at z>7.5 agrees remarkably with recent JWST UV luminosity function-derived estimates. This agreement solidifies the emerging picture of rapid galaxy formation leading to increased abundances of bright and massive galaxies in the first ∼ 0.7 Gyrs. However, at z 3.5, we find significant tension (∼ 0.3 dex) with the cosmic star formation (SF) history from instantaneous SF measures, the causes of which remain poorly understood. We infer the stellar-to-halo mass relation (SHMR) and the SFE from abundance matching out to z=12, finding a non-monotonic evolution. The SFE has the characteristic strong dependence with mass in the range of $0.02 - 0.2$, and mildly decreases at the low-mass end out to z∼3.5. At z∼3.5, there is an upturn and the SFE increases sharply from ∼ 0.1 to approach a high SFE of $0.8-1$ by z∼ 10 for h /M_ ⊙ )≈11.5$, albeit with large uncertainties. Finally, we use the SHMR to track the SFE and stellar mass growth throughout the halo history and find that they do not grow at the same rate -- from the earliest times up until z∼3.5 the halo growth rate outpaces galaxy assembly, but at z>3.5 halo growth stagnates and accumulated gas reservoirs keep the SF going and galaxies outpace halos.

On the Response of Massive Main Sequence Stars to Mass Accretion and Outflow at High Rates

Abstract With a one-dimensional stellar evolution model, we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion. We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones. These jets remove the outer high-entropy layers of the mass-accreting star. This process operates in a negative feedback cycle, as the jets remove more envelope mass when the star expands. With the one-dimensional model, we mimic the mass removal by jets by alternating mass addition and mass removal phases. For the simulated models of 30M ⊙ and 60M ⊙, the star does not expand much if we remove more than about half of the added mass in not-too-short episodes. This holds even if we deposit the energy the jets do not carry into the envelope. As the star does not expand much, its gravitational potential well stays deep, and the jets are energetic. These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets, e.g., intermediate luminosity optical transients, including some luminous red novae, the grazing envelope evolution, and the 1837–1856 Great Eruption of Eta Carinae.

Rare Occasions: Tidal Disruption Events Rarely Power the AGNs Observed in Dwarf Galaxies

Tidal disruption events (TDEs) could be an important growth channel for massive black holes in dwarf galaxies. Theoretical work suggests that the observed active galactic nuclei (AGNs) in dwarf galaxies are predominantly TDE-powered. To assess this claim, we perform variability analyses on the dwarf-hosted AGNs detected in the 7 Ms Chandra Deep Field-South survey, with observations spanning ≈16 yr. Based on the spectral energy distribution modeling with x-cigale, we select AGNs hosted by dwarf galaxies (stellar mass below 1010 M ⊙). We focus on X-ray sources with full-band detections, leading to a sample of 78 AGNs (0.122 ≤ z ≤ 3.515). We fit the X-ray light curves with a canonical TDE model of t −5/3 and a constant model. If the former outperforms the latter in fitting quality for a source, we consider the source as a potential TDE. We identify five potential TDEs, constituting a small fraction of our sample. Using true- and false-positive rates obtained from fitting models to simulated light curves, we perform Bayesian analysis to obtain the posterior of the TDE fraction for our sample. The posterior peaks close to zero (2.56%), and we obtain a 2σ upper limit of 9.80%. Therefore, our result indicates that the observed AGNs in dwarf galaxies are not predominantly powered by TDEs.

Tidal tails of nearby open clusters. I. Mapping with Gaia DR3

Tidal tails of open clusters are the result of stellar evaporation from the cluster through the Galactic potential and internal dynamics. With the recent availability of high-precision data, tidal tails are being detected for most of the nearby open clusters. We identify the tidal tail members for all open clusters within a distance of 400 pc that are older than 100 Myr and have $>$100 members. To do this, we use model-independent methods. We used the convergent-point (CP) method to identify the co-moving stars near the open clusters using Gaia DR3 data. A new method called the self-compact convergent-point (SCCP) method was proposed and applied to some of the clusters. It performed better overall in tracing the tails. We also analysed the colour-magnitude diagrams and orbital energy to diagnose possible contamination. Nineteen out of 21 clusters have tidal tails. Five of them were discovered for the first time through this work. The typical span of the tidal tails is 20--200 pc, and 30--700 member stars lie in the region inside the tidal radius and the tidal tails. Four out of 19 tidal tails are tilted away from direction of the Galactic centre. This contradicts the known theory of the tidal-tail formation. The luminosity functions of the tails and clusters are consistent with each other and with the canonical stellar interstellar mass function, but systematically higher radial velocities for the trailing tail than for the leading tail were observed for the first time. The CP method is useful for detecting tidal tails on a scale of ≈100 pc for clusters closer than 400 pc. A further analysis of theoretical N-body models is required to understand the incompleteness and biases in the current sample of tidal tails.

A Dual Active Black Hole Candidate with Mass Ratio ~7:1 in a Disk Galaxy

Abstract Dual active galactic nuclei (AGNs) with comparable masses are commonly witnessed among the major merged galaxies with interaction remnants. Considering almost every massive galaxy is associated with multiple dwarf satellites around it, minor mergers involving galaxies with disproportional stellar masses should be much more common than major mergers, which would naturally lead to black hole (BH) pairs with significantly different masses. However, dual AGNs generated by minor mergers involving one or two dwarf galaxies are exceptionally rare and understudied. Moreover, good estimates of the masses of both BHs are not yet available to test this idea. Here we report the evidence of a dual AGN candidate with mass ratio ~7:1 located in an undisturbed disk galaxy. We identify the central BH with mass of 9.4 × 106 M ⊙ from its radio emission as well as AGN-driven galactic-scale biconical outflows. The off-centered BH generates obvious broad and narrow emission-line regions, which gives us a robust estimation of a 1.3 × 106 M ⊙ BH mass. We explore alternative scenarios for explaining the observational features of this system, including the complex gas kinematics triggered by central AGN activity and dust attenuation of the broad-line region of the central BH, finding that they failed to fully account for the kinematics of both the redshifted off-centered broad and narrow emission-line components.