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With the wavelength coverage, sensitivity, and high spatial resolution of JWST, it is now possible to peer through the dust attenuation to probe the rest-frame near-infrared (NIR) and stellar structures of extremely dusty galaxies at cosmic noon (z ∼ 1−3). In this paper we leverage the combined Atacama Large Millimeter/submillimeter Array (ALMA) and JWST/Hubble Space Telescope coverage in A2744 to study the multiwavelength (0.5−4.4 μ m) structures of 11 submillimeter detected galaxies at z ∼ 0.9−3.5 that are fainter than bright "classical" submillimeter galaxies, seven of which are detected in deep X-ray data. While these objects reveal a diversity of structures and sizes, all are smaller and more concentrated toward longer wavelengths. Of the X-ray-detected objects, only two show evidence for appreciable active galactic nucleus (AGN) flux contributions (at ≳2 μ m). Excluding the two AGN-dominated objects, the smaller long-wavelength sizes indicate that their rest-frame NIR light profiles, inferred to trace their stellar mass profiles, are more compact than their optical profiles. The submillimeter detections and visible dust lanes suggest that centrally concentrated dust is a key driver of the observed color gradients. Further, we find that more concentrated galaxies tend to have lower size ratios (rest-frame NIR to optical); this suggests that the galaxies with the most compact light distributions also have the most concentrated dust. The 1.2 mm flux densities and size ratios of these nine objects suggest that both total dust quantity and geometry impact these galaxies' multiwavelength structures. Upcoming higher-resolution 1.2 mm ALMA imaging will facilitate joint spatially resolved analysis and will directly test the dust distributions within this representative submillimeter population. [ABSTRACT FROM AUTHOR]

At the peak of cosmic star formation (1 ≲ z ≲ 2), the majority of star-forming galaxies hosted compact, star-forming clumps, which were responsible for a large fraction of cosmic star formation. By comparison, ≲5% of local star-forming galaxies host comparable clumps. In this work, we investigate the link between the environmental conditions surrounding local (z < 0.04) galaxies and the prevalence of clumps in these galaxies. To obtain our clump sample, we use a Faster R-CNN object detection network trained on the catalog of clump labels provided by the Galaxy Zoo: Clump Scout project, then apply this network to detect clumps in approximately 240,000 Sloan Digital Sky Survey galaxies (originally selected for Galaxy Zoo 2). The resulting sample of 41,445 u -band bright clumps in 34,246 galaxies is the largest sample of clumps yet assembled. We then select a volume-limited sample of 9964 galaxies and estimate the density of their local environment using the distance to their projected fifth nearest neighbor. We find a robust correlation between environment and the clumpy fraction (f clumpy) for star-forming galaxies (specific star formation rate, sSFR > 10−2 Gyr−1) but find little to no relationship when controlling for galaxies' sSFR or color. Further, f clumpy increases significantly with sSFR in local galaxies, particularly above sSFR > 10−1 Gyr−1. We posit that a galaxy's gas fraction primarily controls the formation and lifetime of its clumps, and that environmental interactions play a smaller role. [ABSTRACT FROM AUTHOR]

Using nearly 230,000 red clump stars selected from LAMOST and Gaia, we conduct a comprehensive analysis of the stellar age–velocity dispersion relations (AVRs) for various disk populations, within 5.0 ≤ R ≤ 15.0 kpc and ∣ Z ∣ ≤ 3.0 kpc. The AVRs of the whole red clump sample stars are accurately described as σ v = σ v,0 (τ + 0.1) β v , with β R , β ϕ , and β Z displaying a global exponential decreasing trend with R, which may point to the difference in spatial distributions of various disk heating mechanisms. The measurements of β – R for various disks suggest that the thin disk exhibits a radial dependence, with a global exponential decreasing trend in β R – R and β Z – R, while β ϕ remains a nearly constant value (around 0.20 ∼ 0.25) within 8.5 ≤ R ≤ 11.5 kpc. The thick disk displays a global increasing trend in β R – R, β ϕ – R, and β Z – R. These results indicate that the thin disk stars are likely heated by long-term heating from giant molecular clouds and spiral arms, while thick disk stars are likely heated by some violent heating process from merger and accretion, and/or formed by the inside-out and upside-down star formation scenarios, and/or born in the chaotic mergers of gas-rich systems and/or turbulent interstellar medium. Our results also suggest that the disk perturbation by a recent minor merger from Sagittarius may have occurred within 3.0 Gyr. [ABSTRACT FROM AUTHOR]

Thin stellar streams originating from globular clusters (GCs) are among the most sensitive tracers of low-mass dark matter subhalos. Joint analysis of the entire population of stellar streams will place the most robust constraints on the dark matter subhalo mass function, and therefore the nature of dark matter. Here we use a hierarchical model of GC formation to forecast the total number, masses, and radial distribution of dissolved GC in Milky Way–like galaxies. Furthermore, we generate mock stellar streams from these progenitors' orbital histories taking into account the clusters' formation and accretion times, mass, and metallicity. Out of ∼10,000 clusters more massive than 104 M ⊙, ∼9000 dissolved in the central bulge and are fully phase mixed at the present, while the remaining ∼1000 survive as coherent stellar streams. This suggests that the current census of ∼80 GC streams in the Milky Way is severely incomplete. Beyond 15 kpc from the Galactic center we are missing ∼100 streams, of which the vast majority are from accreted GCs. Deep Rubin photometry (g ≲ 27.5) would be able to detect these streams, even the most distant ones beyond >75 kpc. We also find that M31 will have an abundance of streams at galactocentric radii of 30–100 kpc. We conclude that future surveys will find a multitude of stellar streams from GCs, which can be used for dark matter subhalo searches. [ABSTRACT FROM AUTHOR]

We analyze the dark matter (DM) halos of a sample of dwarf ellipticals (dEs) and discuss cosmological and evolutionary implications. Using orbit modeling, we recover their density slopes and, for the first time, halo flattening. We find that the "cusp-core" tension is mild; on average, dEs have central slopes slightly below the Navarro–Frenk–White predictions. However, the measured flattenings are still more spherical than cosmological simulations predict. Unlike brighter early-type galaxies, the total density slopes of dEs are shallower, and their average DM density does not follow their scaling relation with luminosity. Conversely, dE halos are denser and the densities steeper than in late-type galaxies. We find average DM density and slope are strongly correlated with the environment and moderately with the angular momentum. Central, nonrotating dEs have dense and cuspy halos, whereas rotating dEs in Virgo's outskirts are more cored and less dense. This can be explained by a delayed formation of the dEs in the cluster outskirts, or alternatively by the accumulated baryonic feedback that the dEs in the outskirts have experienced during their very different star formation history. Our results suggest halo profiles are not universal (they depend on assembly conditions) and they evolve only mildly due to internal feedback. We conclude dEs in the local Universe have assembled at a higher redshift than local spirals. In these extreme conditions, star formation and halo assembly, for example, were very different, suggesting no new dEs are formed at present. [ABSTRACT FROM AUTHOR]

We analyze the stellar structure of a sample of dwarf ellipticals (dEs) inhabiting various environments within the Virgo cluster. Integral-field observations with a high spectral resolution allow us to robustly determine their low-velocity dispersions (∼25 km s−1) and higher-order kinematic moments out to the half-light radius. We find the dEs exhibit a diversity in ages, with the younger dEs being less enhanced than the older, suggesting a complex star formation history for those dEs that recently entered Virgo, while others have been quenched shortly after reionization. Orbit-superposition modeling allowed us to recover viewing angles, stellar mass-to-light ratios (with gradients), as well as the intrinsic orbit structure. We find that the angular momentum of the dEs is strongly suppressed compared to ordinary early-type galaxies and correlates with the environment. Flattened dEs are so because of a suppressed kinetic energy perpendicular to their equatorial plane. Combining population and dynamical modeling results, we find an age-dependent stellar initial mass function or, alternatively, evidence for a more extended star formation history for those galaxies that have had higher initial mass and/or inhabited lower-density environments. dEs appear to have a spatially homogeneous stellar structure, but the state they were "frozen" in as they stopped forming stars varies dramatically according to their initial conditions. [ABSTRACT FROM AUTHOR]

Galactic disk warp has been widely characterized by stellar distributions and stellar kinematics but has not been traced by stellar chemistry. Here, we use a sample with over 170,000 red clump (RC) stars selected from LAMOST and APOGEE first to establish a correlation between the north–south asymmetry in metallicity ([Fe/H]) and the disk warp. Our results indicate that the height of the [Fe/H] midplane for the whole RC sample stars is accurately described as Z _w = 0.017 ( R − 7.112) ^2 sin( ϕ − 9.218). This morphology aligns closely with the warp traced by Cepheids, suggesting that the disk north–south asymmetry in [Fe/H] may serve as a new tracer for the Galactic warp. Our detailed analysis of the young/thin disk stars of this RC sample suggests that its warp is well modeled as Z _w = 0.016 ( R − 6.507) ^2 sin( ϕ − 4.240), indicating that the line of node of the Galactic warp is oriented at 4.240 ${}_{-1.747}^{+1.641}$ degrees.

We present the galaxy stellar mass–size relation in the rest-frame near-IR (1.5 μ m) and its evolution with redshift up to z = 2.5. Sérsic profiles are measured for ∼26,000 galaxies with stellar masses M ⋆ > 109 M ⊙ from JWST/NIRCam F277W and F444W imaging provided by the COSMOS-WEB and PRIMER surveys using coordinates, redshifts, colors, and stellar mass estimates from the COSMOS2020 catalog. The new rest-frame near-IR effective radii are generally smaller than previously measured rest-frame optical sizes, on average by 0.14 dex, with no significant dependence on redshift. For quiescent galaxies, this size offset does not depend on stellar mass, but for star-forming galaxies, the offset increases from −0.1 dex at M ⋆ = 109.5 M ⊙ to −0.25 dex at M ⋆ > 1011 M ⊙. That is, we find that the near-IR stellar mass–size relation for star-forming galaxies is flatter in the rest-frame near-IR than in the rest-frame optical at all redshifts 0.5 < z < 2.5. The general pace of size evolution is the same in the near-IR as previously demonstrated in the optical, with slower evolution (R e ∝ (1 + z)−0.7) for L * star-forming galaxies and faster evolution (R e ∝ (1 + z)−1.3) for L * quiescent galaxies. Massive (M ⋆ > 1011 M ⊙) star-forming galaxies evolve in size almost as fast as quiescent galaxies. Low-mass (M ⋆ < 1010 M ⊙) quiescent galaxies evolve as slow as star-forming galaxies. Our main conclusion is that the size evolution narrative as it has emerged over the past two decades does not radically change when accessing the rest-frame near-IR with JWST, a better proxy of the underlying stellar mass distribution. [ABSTRACT FROM AUTHOR]

We analyze four epochs of Hubble Space Telescope imaging over 18 yr for the Draco dwarf spheroidal galaxy. We measure precise proper motions for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass–anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally averaged value β B ¯ = − 0.20 − 0.53 + 0.28 , (where 1 – β B ≡ 〈 v tan 2 〉 / 〈 v rad 2 〉 in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, Γdark, is − 0.83 − 0.37 + 0.32 , consistent with the inner cusp predicted in ΛCDM cosmology. As expected given Draco's low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, and 942 pc at 1 σ, 2 σ, and 3 σ confidence, respectively, thus imposing important constraints on the self-interacting DM cross section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is 24.19 − 2.97 + 6.31 km s − 1 . We infer a dynamical distance of 75.37 − 4.00 + 4.73 kpc and show that Draco has a modest LOS rotation, with v / σ = 0.22 ± 0.09 . Our results provide a new stringent test of the so-called "cusp–core" problem that can be readily extended to other dwarfs. [ABSTRACT FROM AUTHOR]

The measurements of morphological indicators of galaxies are often influenced by a series of observational effects. In this study, we utilize a sample of 832 TNG50 simulated galaxies with log(M */ M ⊙)> 9 at 0.5 < z < 3 to investigate the differences in nonparametric morphological indicators (C, A, Gini, M 20, A O, and D O) derived from noise-free and high-resolution TNG50 images and mock images simulated to have the same observational conditions as JWST/NIRCam. We quantify the relationship between intrinsic and observed values of the morphological indicators and accordingly apply this calibration to 4733 galaxies in the same stellar mass and redshift ranges observed in JWST CEERS and JADES surveys. We find a significant evolution of morphological indicators with rest-frame wavelength (λ rf) at λ rf < 1 μ m, while essentially no obvious variations occur at λ rf > 1 μ m. The morphological indicators of star-forming galaxies (SFGs) and quiescent galaxies (QGs) are significantly different. The morphologies of QGs exhibit a higher sensitivity to rest-frame wavelength than SFGs. After analyzing the evolution of morphological indicators in the rest-frame V band (0.5–0.7 μ m) and rest-frame J band (1.1–1.4 μ m), we find that the morphologies of QGs evolve substantially with both redshift and stellar mass. For SFGs, the C, Gini, and M 20 show a rapid evolution with stellar mass at log(M */ M ⊙) ≥ 10.5, while the A O, D O, and A evolve with both redshift and stellar mass. Our comparison shows that TNG50 simulations effectively reproduce the morphological indicators we measured from JWST observations when the impact of dust attenuation is considered. [ABSTRACT FROM AUTHOR]

Classifying galaxies is an essential step for studying their structures and dynamics. Using GalaxyZoo2 (GZ2) fractions thresholds, we collect 545 and 11,735 samples in nongalaxy and galaxy classes, respectively. We compute the Zernike moments (ZMs) for GZ2 images, extracting unique and independent characteristics of galaxies. The uniqueness due to the orthogonality and completeness of Zernike polynomials, reconstruction of the original images with minimum errors, invariances (rotation, translation, and scaling), different block structures, and discriminant decision boundaries of ZMs’ probability density functions for different order numbers indicate the capability of ZMs in describing galaxy features. We classify the GZ2 samples, first into the galaxies and nongalaxies and second, galaxies into spiral, elliptical, and odd objects (e.g., ring, lens, disturbed, irregular, merger, and dust lane). The two models include the support vector machine (SVM) and 1D convolutional neural network (1D-CNN), which use ZMs, compared with the other three classification models of 2D-CNN, ResNet50, and VGG16 that apply the features from original images. We find the true skill statistic (TSS) greater than 0.86 for the SVM and 1D-CNN with ZMs for the oversampled galaxy–nongalaxy classifier. The SVM with ZMs model has a high-performance classification for galaxy and nongalaxy data sets. We show that the SVM with ZMs, 1D-CNN with ZMs, and VGG16 with vision transformer are high-performance (accuracy larger than 0.90 and TSS greater than 0.86) models for classifying the galaxies into spiral, elliptical, and odd objects. We conclude that these machine learning algorithms are helpful tools for classifying galaxy images. The Python notebooks are available on GitHub at https://github.com/hmddev1/machine_learning_for_morphological_galaxy_classification .

Stellar streams are sensitive probes of the Milky Way’s gravitational potential. The mean track of a stream constrains global properties of the potential, while its fine-grained surface density constrains galactic substructure. A precise characterization of streams from potentially noisy data marks a crucial step in inferring galactic structure, including the dark matter, across orders of magnitude in mass scales. Here we present a new method for constructing a smooth probability density model of stellar streams using all of the available astrometric and photometric data. To characterize a stream’s morphology and kinematics, we utilize mixture density networks to represent its on-sky track, width, stellar number density, and kinematic distribution. We model the photometry for each stream as a single-stellar population, with a distance track that is simultaneously estimated from the stream’s inferred distance modulus (using photometry) and parallax distribution (using astrometry). We use normalizing flows to characterize the distribution of background stars. We apply the method to the stream GD-1, and the tidal tails of Palomar 5. For both streams we obtain a catalog of stellar membership probabilities that are made publicly available. Importantly, our model is capable of handling data with incomplete phase-space observations, making our method applicable to the growing census of Milky Way stellar streams.

This study investigates the structural parameters of the thin-disk population by analyzing the spatial distribution of evolved stars in the solar neighborhood. From the Gaia Data Release 3 database, about 39.1 million stars within 1 kpc and with relative parallax errors σ _ϖ / ϖ ≤ 0.10 were selected. The photometric data was corrected for extinction using a Galactic dust map. The sample was refined by considering the color–magnitude region ${M}_{{\rm{G}}}\times {({G}_{{\rm{BP}}}-{G}_{{\rm{RP}}})}_{0}$ associated with evolved stars, applying a stricter parallax error limit of σ _ϖ / ϖ ≤ 0.02, and yielding 671,600 stars. The star sample was divided into 36 regions based on their Galactic coordinates, with evolved stars in the absolute magnitude range of −1 < M _G (mag) ≤ 4 further split into five one-unit magnitude intervals. This led to 180 subgroups whose space-density profiles were modeled using a single-component Galaxy model. The analysis shows that the space densities are in agreement with the literature and that the scale heights vary with 200 < H (pc) < 600 interval to their absolute magnitudes. Red clump stars in the solar neighborhood were also estimated to have a scale height of 295 ± 10 pc. These findings indicate that evolved stars with bright absolute magnitudes originate from the evolution of the early spectral-type stars with short scale height, while fainter ones come from the evolution of the intermediate spectral-type stars with large scale height, suggesting that variations in scale height reflect the contribution of Galactic evolution processes.

We present a joint analysis of high-resolution CO(2–1) and Paschen- α (Pa α ) emission lines to trace gas dynamics and spatially resolved star formation in ASPECS-LP.3 mm.06, a z = 1.1 main-sequence galaxy. Utilizing data from the Atacama Large Millimeter/submillimeter Array and JWST NIRCam wide field slitless spectroscopy, we explore both ionized gas and molecular gas within this galaxy. With a substantial molecular gas fraction ( f _mol = 0.44 ± 0.02), ASPECS-LP.3 mm.06 remains on the star-forming main sequence and adheres to the Kennicutt–Schmidt relation, indicating typical gas-to-star conversion efficiency. Our analysis reveals extended structures across multiple wavelengths, suggesting regulated star formation within a stable disk. The spatially resolved star formation efficiency and kinematic analysis indicate that ASPECS-LP.3mm.06 features a smooth mass assembly process across the bulge and disk. Additionally, the galaxy exhibits modest dust extinction ( A _V = 0.8), potentially linked to self-regulation during bulge formation. These findings position ASPECS-LP.3mm.06 as a prototypical galaxy, offering valuable insights into the mechanisms governing normal disk galaxy growth at z ∼ 1.

An avenue for understanding cosmological galaxy formation is to compare morphometric parameters in observations and simulations of galaxy assembly. In this second paper of the ASymba: Asymmetries of H i in SIMBA Galaxies series, we measure atomic gas (H i ) asymmetries in spatially resolved detections from the untargeted Widefield ASKAP L -band Legacy All-sky Blind surveY (WALLABY) survey, and compare them to realizations of WALLABY-like mock samples from the SIMBA cosmological simulations. We develop a Scanline Tracing method to create mock galaxy H i data cubes that minimizes shot noise along the spectral dimension, compared to particle-based methods, and thus minimizes spurious asymmetry contributions. We compute 1D and 3D asymmetries for spatially resolved WALLABY Pilot Survey detections, and we find that the highest 3D asymmetries ( A _3D ≳ 0.5) stem from interacting systems or detections with strong bridges or tails. We then construct a series of WALLABY-like mock realizations drawn from the SIMBA 50 Mpc simulation volume and compare their asymmetry distributions. We find that the incidence of high A _3D detections is higher in WALLABY than in the SIMBA mocks, but that difference is not statistically significant ( p -value = 0.05). The statistical power of quantitative comparisons of asymmetries such as the one presented here will improve as the WALLABY survey progresses and as simulation volumes and resolutions increase.

The majority of disk galaxies manifest spirals and/or bars that are believed to result from dynamical instabilities. However, some galaxies have featureless disks, which are therefore inferred to be dynamically stable. Yet despite many years of effort, theorists have been unable to construct realistic models of galaxy disks that possess no instabilities and therefore could remain featureless. This conclusion has been reached through simulations for the most part, some of which have been confirmed by linear stability analyses. A. Toomre (1981) claimed that the Mestel disk, embedded in an equal-mass halo, is a notable counterexample, but his prediction of stability could not be reproduced in simulations, due to complicated nonlinear effects that caused secular growth of Poisson noise–driven disturbances until strong features emerged. Here, we revisit this issue and show that simply eliminating the most nearly circular orbits from Toomre's disk model can inhibit troublesome secular growth. We also present both 2D and 3D simulations of particle disks that remain featureless for over 50 orbit periods. We report that spiral evolution naturally depletes circular orbits and that the radial velocity distribution in the featureless disks of S0 galaxies should have negative kurtosis.

We present H α -region integral-field spectroscopy for 137 low-inclination, intermediate to late-type galaxies. Spectroscopic data, obtained with SparsePak and the Bench Spectrograph on the WIYN 3.5 m telescope, span 6475–6880 Å with an instrumental resolution of 13 km s ^−1 ( σ ). The spectral range includes H α and [N ii ] λλ 6548, 6584 for every source, and in most cases includes [S ii ] λλ 6717, 6731. We present and publicly release 18,288 calibrated spectra and visually inspected Gaussian line fits to the H α emission. Most measurements yield a signal-to-noise ratio above 5 in integrated H α line flux, adequate to derive reliable line centroids and widths. Second kinematic components are required to adequately describe the emission-line profile in 15% of reliable data. The H α velocity dispersion distribution peaks at 18 km s ^−1 , modestly increasing with H α surface brightness, reaching 20 km s ^−1 at Σ _H _α = 10 ^40 erg s ^−1 kpc ^−2 . Lower-flux secondary components, when present, have widths of ~50 km s ^−1 . These results agree well with previous echelle measurements of nearby galaxies. Velocity-field analysis yields kinematic inclinations, with a sample mean of 26°. Large kinematic asymmetries systematically affect kinematic inclination estimates in a small fraction of our sample. When deviations from circular motion are below 10% of the projected velocity, kinematic inclinations are consistent, within errors, to estimates from inverting the Tully–Fisher relation. This confirms previous disk-submaximality estimates for galaxies with regular kinematics based on inclinations derived from inverting the Tully–Fisher relation.

Due to the inhomogeneity of electron number density, radio waves emitted by pulsars undergo scattering as they pass through the interstellar medium (ISM). However, a connection between large-scale pulsar scattering data and the structure of the Galactic ISM has yet to be established. In this paper, we explore the capability of pulsar scattering time data in discovering structures in the ISM. Using a large data set of scattering time measurements for 473 pulsars, we fit the pulsar reduced scattering intensity as a function of Galactic latitude and distance, constructing a smooth model of the Galactic pulsar scattering distribution. By comparing this smooth distribution with observational data, we identify two ISM structures responsible for pulsar scattering, one is associated with the Vela supernova remnant region within the Gum Nebula, while the other is a newly discovered structure—a distant superbubble, G38, located at a distance of 2.3 kpc with a size of ~50 pc. Analysis of the correlation coefficient of the pulsar scattering distribution shows that the correlation is dominated by structures smaller than 0.15 kpc—the closest separation approachable by the current data set. As measurements of the pulsar scattering time continue to increase in the future, they can potentially become an independent tool for exploring structures in the ISM.

We offer a new way to look at the LMC through stellar mono-abundance and mono-age mono-abundance maps. These maps are based on ≳500,000 member stars with estimates of [M/H] ( σ _[M/H] ~ 0.17) and age $({\sigma }_{{\rm{log}}\tau }\unicode{x0007E}0.15$ ), derived from Gaia Data Release 3 XP spectra and photometry, which are tied to and validated against APOGEE. This results in the first area-complete, metallicity- and age-differentiated stellar maps of any disk galaxy. Azimuthally averaged, these maps reveal a surprisingly simple picture of the Milky Way's largest satellite galaxy. For any [M/H] below −0.1 dex, the LMC's radial profile is well described by a simple exponential, but with a scale length that steadily shrinks toward higher metallicities, from nearly 2.3 kpc at [M/H] = −1.8 to only 0.75 kpc at [M/H] = −0.25, as fit by forward modeling the spatial distribution of mono-[M/H] populations. The prominence of the bar decreases dramatically with [M/H], making it barely discernible at [M/H] ≲ −1.5. Yet, even for metal-rich populations, the bar has little impact on the azimuthally averaged profile of the mono-abundance components. Including ages, we find that the scale length is a greater function of age than of metallicity, with younger populations far more centrally concentrated. Only at old ages does the scale length change, specifically decrease, with increasing metallicity. These findings provide quantitative support for a scenario in which the LMC built its stellar structure effectively outside-in.

Nuclear star clusters (NSCs) are commonly found in the centers of galaxies, but their dominant formation mechanisms remain elusive. We perform a consistent analysis of stellar populations of 97 nearby NSCs, based on spectroscopic data from the Very Large Telescope. The sample covers a galaxy stellar mass range of 10 ^7 –10 ^11 M _⊙ and is more than 3 times larger than any previous study. We identify three galaxy stellar mass regimes with distinct NSC properties. In the low-mass regime of $\mathrm{log}{M}_{{\rm{host}}}$ ≲ 8.5 ( M _host is in units of M _⊙ ), nearly all NSCs have metallicities lower than their circum-NSC host but similar to those of typical red globular clusters (GCs), supporting the GC inspiral–merger scenario of NSC formation. In the high-mass regime of $\mathrm{log}{M}_{{\rm{host}}}$ ≳ 9.5, nearly all NSCs have higher metallicities than their circum-NSC host and red GCs, suggesting significant contributions from in situ star formation. In the intermediate-mass regime, a comparable fraction of NSCs have higher or lower metallicities than their circum-NSC host and red GCs, with no clear dependence on NSC mass, suggesting intermittent in situ star formation. The majority of NSCs with higher metallicities than their host exhibit a negative age–metallicity correlation, providing clear evidence of long-term chemical enrichment. The average metallicity difference between NSC and host peaks broadly around $\mathrm{log}{M}_{{\rm{host}}}\sim 9.8$ and declines toward both higher and lower galaxy masses. We find that the efficiency of dynamical-friction-driven inspiral of GCs observed in present-day galaxies can explain the NSC mass at $\mathrm{log}{M}_{{\rm{host}}}\lesssim 9.5$ but falls short of observed ones at higher galaxy mass, reinforcing our conclusions based on stellar population analysis.

Galactic bars can form via the internal bar instability or external tidal perturbations by other galaxies. We systematically compare the properties of the bars formed through the two mechanisms with a series of controlled N -body simulations that form bars through internal or external mechanisms. We create three disk galaxy models with different dynamical “hotness” and evolve them in isolation and under flyby interactions. In the cold- and warm-disk models, where bars can form spontaneously in isolation, tidally induced bars are promoted to a more “advanced” evolutionary stage. However, these bars have similar pattern speeds to those formed spontaneously within the same disk. Bars formed from both mechanisms have similar distributions in pattern-speed–bar-strength (Ω _p − A _2 ) space and exhibit comparable ratios of corotation radius to bar length ( ${ \mathcal R }={R}_{{\rm{CR}}}/{R}_{{\rm{bar}}}$ ). Dynamical analyses suggest that the inner stellar disk loses the same amount of angular momentum, irrespective of the presence or intensity of the perturbation, which possibly explains the resemblance between tidally and spontaneously formed bars. In the hot-disk model, which avoids the internal bar instability in isolation, a bar forms only under perturbations and rotates more slowly than those in the cold and warm disks. Thus, if “tidally induced bars” refer exclusively to those in galaxies that are otherwise stable against bar instability, they indeed rotate slower than internally induced ones. However, the pattern speed difference is due to the difference in the internal properties of the bar host galaxies, not the different formation mechanisms.

Understanding the structure of the Galactic disk is crucial for understanding the formation and evolutionary history of the Milky Way. This study examines the structure of the Galactic disk by analyzing a sample of 138,667 primary red clump (RC) stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Gaia data sets. We have categorized these RC stars into mono-age populations and investigated their spatial distributions within the R – Z plane, estimating scale heights and lengths through the fitting of their vertical and radial density profiles. Our analysis indicates that the vertical profiles of these mono-age populations fit a dual-component disk model, where both components exhibit significant flaring, particularly in the outer disk regions. Within a constant Galactocentric radius R , the scale heights of the first component, representing the morphologically thin disk, rise with age. In contrast, the scale heights of the second component, corresponding to the morphologically thick disk, remain comparatively stable across different age groups. Additionally, the radial density profiles of both disk components predominantly peak within a radial range of 7.5–8.5 kpc. These findings underscore the importance of age as a crucial factor in shaping the spatial distribution and structural evolution of the Galactic disk, offering valuable insights into its complex dynamics and history.

Stellar streams that emerge from globular clusters (GCs) are thin stellar structures spread along the orbits of progenitor clusters. Numerical modeling of these streams is essential for understanding their interaction with the host galaxy's mass distribution. Traditional methods are either computationally expensive or oversimplified, motivating us to develop a fast and accurate approach using a particle spray algorithm. By conducting a series of N -body simulations of GCs orbiting a host galaxy, we find that the position and velocity distributions of newly escaped stream particles are consistent across various GC masses and orbital parameters. Based on these distributions, we develop a new algorithm that avoids computing the detailed internal cluster dynamics by directly drawing tracer particles from these distributions. This algorithm correctly reproduces the action space distribution of stream particles and achieves a 10% accuracy in stream morphology and velocities compared to N -body simulations. To facilitate broader use, we have implemented this algorithm in galactic dynamics codes agama , gala , galax , and galpy .

We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to − β h = −3 yield an inner power-law slope of − γ h = - (0.97 − 0.21 + 0.17 ) , a scale radius of r 0 , h = 14.7 − 1.0 + 4.7 kpc , a halo density flattening q m, h = 0.75 ± 0.03, and a local dark matter density of ρ h,⊙ = 0.0114 ± 0.0007 M ⊙ pc−3. Freeing β yields β = 2.53 − 0.16 + 0.42 , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of 4.20 − 0.53 + 0.44 × 10 10 M ⊙ , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are 2.17 − 0.08 + 0.18 and 1.62 − 0.13 + 0.72 kpc , respectively, while their scale heights are 0.347 − 0.010 + 0.007 and 0.86 − 0.02 + 0.03 kpc , respectively. The virial mass of the favored model is M 200 = 1.09 − 0.14 + 0.19 × 10 12 M ⊙ , while the mass inside of 50 kpc is M R <50 = 0.46 ± 0.03 × 1012 M ⊙. We introduce the Large Magellanic Cloud (LMC) into the derived potential models, and fit the Orphan stream therein, finding a mass for the LMC that is consistent with recent estimates. Some salient highlights include the nearby trailing arm of ω Cen, and a nearby very metal-poor stream that was once a satellite of the Sagittarius dwarf galaxy. Finally, we unambiguously detect a hot component around the GD-1 stream, consistent with it having been tidally preprocessed within its own dark matter subhalo. [ABSTRACT FROM AUTHOR]

Thanks to the precise astrometric measurements of proper motions by the Gaia mission, a new tidal stellar stream has been discovered in the northern hemisphere. The distribution of star count shows that the stream is approximately 80° long and 1.°70 wide. Observations of 21 member stars, including 14 RR Lyrae stars, indicate that the stream has an eccentric and retrograde orbit with e = 0.58. The low metallicity, high total energy, and large angular momentum suggest that it is associated with the merging event Sequoia. This discovery suggests the possibility of finding more substructures with high eccentricity orbits, even in the inner halo. [ABSTRACT FROM AUTHOR]

We present a comprehensive search and analysis of high-redshift galaxies in a suite of nine public JWST extragalactic fields taken in Cycle 1, covering a total effective search area of ∼ 358 arcmin 2 . Through conservative (8 σ) photometric selection, we identify 341 galaxies at 5 < z < 14, with 109 having spectroscopic redshift measurements from the literature, including recent JWST NIRSpec observations. Our regression analysis reveals that the rest-frame UV size–stellar mass relation follows R eff ∝ M * 0.19 ± 0.03 , similar to that of star-forming galaxies at z ∼ 3, but scaled down in size by ∼0.7 dex. We find a much slower rate for the average size evolution over the redshift range, R eff ∝ (1 + z)−0.4±0.2, than that derived in the literature. A fraction (∼13%) of our sample galaxies are marginally resolved even in the NIRCam imaging (≲100 pc), located at ≳1.5 σ below the derived size–mass slope. These compact sources exhibit a high star formation surface density ΣSFR > 10 M ⊙ yr−1 kpc−2, a range in which only <0.01% of the local star-forming galaxy sample is found. For those with available NIRSpec data, no evidence of ongoing supermassive black hole accretion is observed. A potential explanation for the observed high [O iii ]-to-H β ratios could be high shock velocities, likely originating within intense star-forming regions characterized by high ΣSFR. Lastly, we find that the rest-frame UV and optical sizes of our sample are comparable. Our results are consistent with these early galaxies building up their structures inside out and being yet to exhibit the strong color gradient seen at lower redshift. [ABSTRACT FROM AUTHOR]

A key question in galaxy evolution has been the importance of the apparent "clumpiness" of high-redshift galaxies. Until now, this property has been primarily investigated in rest-frame UV, limiting our understanding of their relevance. Are they short-lived or are they associated with more long-lived massive structures that are part of the underlying stellar disks? We use JWST/NIRCam imaging from the Cosmic Evolution and Epoch of Reionization Survey to explore the connection between the presence of these "clumps" in a galaxy and its overall stellar morphology, in a mass-complete ( log M * / M ⊙ > 10.0) sample of galaxies at 1.0 < z < 2.0. Exploiting the uninterrupted access to rest-frame optical and near-IR light, we simultaneously map the clumps in galactic disks across our wavelength coverage, along with measuring the distribution of stars among their bulges and disks. First, we find that the clumps are not limited to the rest-frame UV and optical, but are also apparent in near-IR with ∼60% spatial overlap. This rest-frame near-IR detection indicates that clumps would also feature in the stellar-mass distribution of the galaxy. A secondary consequence is that these will hence be expected to increase the dynamical friction within galactic disks leading to gas inflow. We find a strong negative correlation between how clumpy a galaxy is and strength of the bulge. This firmly suggests an evolutionary connection, either through clumps driving bulge growth or the bulge stabilizing the galaxy against clump formation, or a combination of the two. Finally, we find evidence of this correlation differing from rest-frame optical to near-IR, which could suggest a combination of varying formation modes for the clumps. [ABSTRACT FROM AUTHOR]

A kinematic misalignment of the stellar and gas components is a phenomenon observed in a significant fraction of galaxies. However, the underlying physical mechanisms are not well understood. A commonly proposed scenario for the formation of a misaligned component requires any preexisting gas disk to be removed, via flybys or ejective feedback from an active galactic nucleus. In this Letter, we study the evolution of a Milky Way mass galaxy in the FIREbox cosmological volume that displays a thin, counterrotating gas disk with respect to its stellar component at low redshift. In contrast to scenarios involving gas ejection, we find that preexisting gas is mainly removed via the conversion into stars in a central starburst, triggered by a merging satellite galaxy. The newly accreted, counterrotating gas eventually settles into a kinematically misaligned disk. About 4% (8 out of 182) of FIREbox galaxies with stellar masses larger than 5 × 10 ^9 M _⊙ at z = 0 exhibit gas–star kinematic misalignment. In all cases, we identify central starburst-driven depletion as the main reason for the removal of the preexisting corotating gas component, with no need for feedback from, e.g., a central active black hole. However, during the starburst, the gas is funneled toward the central regions, likely enhancing black hole activity. By comparing the fraction of misaligned discs between FIREbox and other simulations and observations, we conclude that this channel might have a non-negligible role in inducing kinematic misalignment in galaxies.

We explore the morphological features and star formation activities of [O ii ] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. We also report the discovery of large filamentary structures traced by [O ii ] emitters surrounding an extremely overdense core with a galaxy number density ∼11× higher than the field average. These structures span over 50 cMpc, underscoring their large scale in the cosmic web at this epoch. After matching the stellar-mass distributions, the core galaxies show a higher frequency of disturbances (50% ± 9%) than those in the outskirts (41% ± 9%) and the field (21% ± 5%), indicative of more frequent mergers and interactions in the innermost ≲1.′5 region. Additionally, we observe that specific star formation rates are elevated in denser environments. A Kolmogorov–Smirnov test comparing the distribution of specific star formation rates of core and field galaxies yields a p -value of 0.02, suggesting an enhancement of star formation activity driven by the dense environment. Our findings underscore the environmental impact on galaxy evolution during a pivotal cosmic epoch and set the stage for further investigation with the increasing larger data from upcoming surveys.

We present a measurement of the low-mass quiescent size–mass relation at cosmic noon (1 < z < 3) from the JWST PRIMER and UNCOVER treasury surveys, which highlights two distinct classes of quiescent galaxies. While the massive population is well studied at these redshifts, the low-mass end has been previously underexplored due to a lack of observing facilities with sufficient sensitivity and spatial resolution. We select a conservative sample of low-mass quiescent galaxy candidates using rest-frame UVJ colors and specific star formation rate criteria and measure galaxy morphology in both rest-frame UV/optical wavelengths (F150W) and rest-frame near-infrared (F444W). We confirm an unambiguous flattening of the low-mass quiescent size–mass relation, which results from the separation of the quiescent galaxy sample into two distinct populations at $\mathrm{log}({M}_{\star }/{M}_{\odot })\sim 10.3$ : low-mass quiescent galaxies that are notably younger and have disky structures, and massive galaxies consistent with spheroidal morphologies and older median stellar ages. These separate populations imply mass quenching dominates at the massive end while other mechanisms, such as environmental or feedback-driven quenching, form the low-mass end. This stellar mass-dependent slope of the quiescent size–mass relation could also indicate a shift from size growth due to star formation (low masses) to growth via mergers (massive galaxies). The transition mass between these two populations also corresponds with other dramatic changes and characteristic masses in several galaxy evolution scaling relations (e.g., star formation efficiency, dust obscuration, and stellar-to-halo mass ratios), further highlighting the stark dichotomy between low-mass and massive galaxy formation.

Whereas well-studied galaxies at cosmic noon are found to be baryon dominated within the effective radius, recent JWST observations of z ∼ 6–7 galaxies with stellar masses of only M _* ∼ 10 ^8−9 M _⊙ surprisingly indicate that they are dark matter dominated within r _e ≈ 1 kpc. Here, we place these high-redshift measurements in the context of the TNG50 galaxy formation simulation by measuring the central (within 1 kpc) stellar, gas, and dark matter masses of galaxies in the simulation. The central baryon fraction varies strongly with galaxy stellar mass in TNG50, and this M _* dependence is remarkably constant across 0 < z < 6: galaxies of low stellar mass ( M _* ∼ 10 ^8−9 M _⊙ ) are dark matter dominated as f _baryon (

We present the discovery of NGC253-SNFC-dw1, a new satellite galaxy in the remote stellar halo of the Sculptor Group spiral, NGC 253. The system was revealed using deep, resolved star photometry obtained as part of the Subaru Near-Field Cosmology Survey that uses the Hyper Suprime-Cam on the Subaru Telescope. Although rather luminous ( M _V = −11.7 ± 0.2) and massive ( M _* ∼ 1.25 × 10 ^7 M _⊙ ), the system is one of the most diffuse satellites yet known, with a half-light radius of R _h = 3.37 ± 0.36 kpc and an average surface brightness of ∼30.1 mag arcmin ^−2 within the R _h . The color–magnitude diagram shows a dominant, old (∼10 Gyr), and metal-poor ([M/H] = −1.5 ± 0.1 dex) stellar population, as well as several candidate thermally pulsing asymptotic giant branch stars. The distribution of red giant branch stars is asymmetrical and displays two elongated tidal extensions pointing toward NGC 253, suggestive of a highly disrupted system being observed at apocenter. NGC253-SNFC-dw1 has a size comparable to that of the puzzling Local Group dwarfs Andromeda XIX and Antlia 2 but is 2 magnitudes brighter. While unambiguous evidence of tidal disruption in these systems has not yet been demonstrated, the morphology of NGC253-SNFC-dw1 clearly shows that this is a natural path to produce such diffuse and extended galaxies. The surprising discovery of this system in a previously well-searched region of the sky emphasizes the importance of surface-brightness limiting depth in satellite searches.

We study the gas inflows toward the Galactic Central Molecular Zone (CMZ) based on the gas morphological and kinematic features from the Milky Way Imaging Scroll Painting in the region of l = 1.°2–19.°0 and ∣ b ∣ ≲ 3.°0. We find that the near dust lane appears to extend to l ∼ 15°, in which the end of the large-scale gas structure intersects with the 3 kpc ring at a distance of ∼5 kpc. Intriguingly, many filamentary molecular clouds (MCs), together with the bow-like/ballistic-like clouds and continuous CO features with notable velocity gradient, are finely outlined along the long structure. These MCs also have relatively large velocity dispersions, indicating the shocked gas generated by local continuous accretion and thus the enhanced turbulence along the entire gas structure. We suggest that the ∼3.1–3.6 kpc-long CO structure originates from the accretion molecular gas driven by the Galactic bar. The gas near the bar end at the 3 kpc ring region becomes an important reservoir for the large-scale accreting flows inward to the CMZ through the bar channel. The inclination angle of the bar is estimated to be ϕ _bar = 23° ± 3°, while the pattern speed of the bar is Ω _bar ≲ 32.5 ± 2.5 km s ^−1 kpc ^−1 . The total mass of the whole near gas lane is about 1.3 ± 0.4 × 10 ^7 M _⊙ according to the calculated X _CO ∼ 1.0 ± 0.4 × 10 ^20 cm ^−2 (K km s ^−1 ) ^−1 from the large-scale ^12 CO and ^13 CO data and the complementary H i data. We revisit the gas inflow rate as a mean value of 1.1 ± 0.3 M _⊙ yr ^−1 , which seems to be comparable to the outflow's rate of the Galactic nuclear winds after applying the updated lower X-factor above.

We investigate the contribution of host galaxies to the overall dispersion measures (DMs) for fast radio bursts (FRBs) using the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite. We calculate DMs from every star particle in the simulated L * galaxies by ray-tracing through their multiphase interstellar medium, summing the line-of-sight free thermal electron column for all gas elements within ±20 kpc of the galactic midplane. At z = 0, we find average (median) host-galaxy DMs of 74 (43) and 210 (94) pc cm ^−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. Inclination raises the median DM measured for older populations (≳10 Myr) in the simulations by a factor of ∼2 but generally does not affect the younger stars deeply embedded in H ii regions except in extreme edge-on cases (inclination ≳85°). In kinematically disturbed snapshots ( z = 1 in FIRE), the average (median) host-galaxy DMs are higher: 80 (107) and 266 (795) pc cm ^−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. FIRE galaxies tend to have higher DM values than cosmological simulations such as IllustrisTNG, with larger tails in their distributions to high DMs. As a result, FRB host galaxies may be closer (lower redshift) than previously inferred. Furthermore, constraining host-galaxy DM distributions may help significantly constrain FRB progenitor models.

Hubble Space Telescope imaging shows that most star-forming galaxies at cosmic noon—the peak of cosmic star formation history—appear disk-dominated, leaving the origin of the dense cores in their quiescent descendants unclear. With the James Webb Space Telescope’s high-resolution imaging to 5 μ m, we can now map the rest-frame near-infrared emission, a much closer proxy for stellar mass distribution, in these massive galaxies. We selected 70 star-forming galaxies with 10 < log( M ) < 12 and 1.5 < z < 3 in the CEERS survey and compare their morphologies in the rest-frame optical to those in the rest-frame near-IR. While the bulk of these galaxies are disk-dominated in 1.5 μ m (rest-frame optical) imaging, they appear more bulge-dominated at 4.4 μ m (rest-frame near-infrared). Our analysis reveals that in massive star-forming galaxies at z ∼ 2, the radial surface brightness profiles steepen significantly, from a slope of ∼0.3 dex ^−1 at 1.5 μ m to ∼1.4 dex ^−1 at 4.4 μ m within radii

In 2011 Blanchet and Marsat suggested a fully relativistic version of Milgrom's modified Newtonian dynamics in which the dynamical degrees of freedom consist of the spacetime metric and a foliation of spacetime, the khronon field. This theory is simpler than the alternative relativistic formulations. We show that the theory has a consistent nonrelativistic or slow-motion limit. Blanchet and Marsat showed that in the slow motion limit, the theory reproduces stationary solutions of modified Newtonian dynamics. We show that these solutions are stable to khronon perturbations in the low acceleration regime, for the cases of spherical, cylindrical, and planar symmetry. For nonstationary systems in the low acceleration regime, we show that the khronon field generally gives an order unity correction to the modified Newtonian dynamics. In particular, there will be an order unity correction to the MOND version of Kepler's third law, potentially relevant to ongoing efforts to test MOND using GAIA observations of wide binaries. [ABSTRACT FROM AUTHOR]

We study the mass–size relation of quiescent galaxies across various environments, with a particular focus on its environmental dependence at the low-mass part of log (M star / M ⊙) ≲ 10.0. Our sample consists of 13,667 quiescent galaxies with log (M star / M ⊙) ≥ 9.4 and 0.01 < z < 0.04 from the Sloan Digital Sky Survey. We discover that the mass–size relation of low-mass quiescent galaxies (LQGs) with log (M star / M ⊙) ≲ 10.0 depends on their environment, with LQGs in the highest-density environments exhibiting an average size ∼70% larger than those in isolated environments. Moreover, the slope of the mass–size relation for LQGs in high-density environments is significantly shallower than that of their counterparts in isolated environments. This is in contrast with high-mass quiescent galaxies with log (M star / M ⊙) ≳ 10.5 that show a nearly identical mass–size relation across all environments. Combined with additional discoveries that the mass–size relation slopes of LQGs and star-forming galaxies are similar to each other in high-density environments, and that LQGs in higher-density environments exhibit more disk-like structures, our results support the idea that LQGs in high-density environments have evolved from star-forming galaxies through environmental effects, which are capable of causing their quenching and transformation into quiescent galaxies. With the aid of an analysis of merger rates for simulated galaxies from a cosmological galaxy formation simulation, we suggest that the steep slope and low normalization of the mass–size relation of LQGs in the lowest-density environments may originate from recent gas-rich mergers, which occur over 10–30 times more frequently in the progenitors of LQGs in the lowest-density environments than in their counterparts in high-density environments at low redshifts. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the structure of the Local Group flocculent spiral galaxy M33, as measured using the Panchromatic Hubble Andromeda Treasury Triangulum Extended Region (PHATTER) survey. Leveraging the multiwavelength coverage of PHATTER, we find that the oldest populations are dominated by a smooth exponential disk with two distinct spiral arms and a classical central bar—completely distinct from what is seen in broadband optical imaging, and the first-ever confirmation of a bar in M33. We estimate a bar extent of ∼1 kpc. The two spiral arms are asymmetric in orientation and strength, and likely represent the innermost impact of the recent tidal interaction responsible for M33's warp at larger scales. The flocculent multiarmed morphology for which M33 is known is only visible in the young upper main-sequence population, which closely tracks the morphology of the interstellar medium. We investigate the stability of M33's disk, finding Q ∼ 1 over the majority of the disk. We fit multiple components to the old stellar density distribution and find that, when considering recent stellar kinematics, M33's bulk structure favors the inclusion of an accreted halo component, modeled as a broken power law. The best-fit halo has an outer power-law index of −3 and accurately describes observational evidence of M33's stellar halo from both resolved stellar spectroscopy in the disk and its stellar populations at large radius. Integrating this profile yields a total halo stellar mass of ∼5 × 108 M ⊙, for a stellar halo mass fraction of 16%, most of which resides in the innermost 2.5 kpc. [ABSTRACT FROM AUTHOR]

We present an analytic model for the cool, T ∼ 104 K, circumgalactic medium (CGM), describing the gas distribution, and thermal and ionization states. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation, and allows for nonthermal pressure support, parameterized by the ratio of thermal pressures, η = P hot,th/ P cool,th. We apply the model to the COS-Halos measurements and find that a nominal model with η = 3, gas distribution out to r ≈ 0.6 R vir, and M cool = 3 × 109 M ⊙, corresponding to a volume filling fraction of f V,cool ≈ 1%, reproduces the H i and low/intermediate metal ions (C ii, C iii, Si ii, Si iii, and Mg ii) mean column densities. Variation of ±0.5 dex in η or M cool encompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured C iv and Si iv columns, and these can be reproduced with (i) a cool phase with M cool ∼ 1010 M ⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with M ∼ 1.5 × 1010 M ⊙ and occupying ∼1/2 of the total CGM volume. For cool gas with f V,cool ≈ 1%, we estimate an upper limit on the cloud sizes, R cl ≲ 0.5 kpc. Our results suggest that for the average galaxy CGM, the mass and nonthermal support in the cool phase are lower than previously estimated, and extreme scenarios are not necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be offset, allowing M ̇ cool ≈ 0 over long timescales. [ABSTRACT FROM AUTHOR]

Giant star-forming clumps are a prominent feature of star-forming galaxies (SFGs) and contain important clues on galaxy formation and evolution. However, the basic demographics of clumps and their host galaxies remain uncertain. Using the Hubble Space Telescope/Wide Field Camera 3 F275W images from the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we detect and analyze giant star-forming clumps in galaxies at 0.5 ≤ z ≤ 1, connecting two epochs when clumps are common (at cosmic high noon, z ∼ 2) and rare (in the local Universe). We construct a clump sample whose rest-frame 1600 Å luminosity is 3 times higher than the most luminous local H ii regions (M UV ≤ −16 AB). In our sample, 35% ± 3% of low-mass galaxies (log[ M ∗/ M ⊙] < 10) are clumpy (i.e., containing at least one off-center clump). This fraction changes to 22% ± 3% and 22% ± 4% for intermediate (10 ≤ log[ M ∗/ M ⊙] ≤ 10.5) and high-mass (log[ M ∗/ M ⊙] > 10.5) galaxies, in agreement with previous studies. When compared to similar-mass nonclumpy SFGs, low- and intermediate-mass clumpy SFGs tend to have higher star formation rates (SFRs) and bluer rest-frame U − V colors, while high-mass clumpy SFGs tend to be larger than nonclumpy SFGs. However, clumpy and nonclumpy SFGs have similar Sérsic index, indicating a similar underlying density profile. Furthermore, we investigate how the UV luminosity of star-forming regions correlates with the physical properties of host galaxies. On average, more luminous star-forming regions reside in more luminous, smaller, and/or higher specific SFR galaxies and are found closer to their hosts' galactic centers. [ABSTRACT FROM AUTHOR]

The phenomenon of the Dark matter baffles the researchers: the underlying dark particle has escaped so far the detection and its astrophysical role appears complex and entangled with that of the standard luminous particles. We propose that, in order to act efficiently, alongside with abandoning the current ΛCDM scenario, we need also to shift the Paradigm from which it emerged.

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), α -element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low- α disk, high- α disk, and total population independently. The low- α disk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc−1, which flattens with distance from the midplane. The high- α disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy. [ABSTRACT FROM AUTHOR]

Galaxy morphology is one of the most fundamental ways to describe galaxy properties, but the morphology we observe may be affected by wavelength and spatial resolution, which may introduce systematic bias when comparing galaxies at different redshift. Taking advantage of the broad wavelength coverage from optical to near-IR and the high-resolution NIRCam instrument of the JWST, we measure the nonparametric morphological parameters of a total of 1376 galaxies at z ≃ 0.8–3.0 in the CEERS field through an optimized code called statmorph_csst. We divide our sample into three redshift intervals and investigate the wavelength and redshift dependence of the morphological parameters. We also explore how the widely used galaxy type classification methods based on the morphological parameters depend on wavelength and spatial resolution. We find that there are variations in all morphological parameters with rest-frame wavelength (λ rf), especially at the short-wavelength end, and that λ rf mainly affects the classification between late- and early-type galaxies. As λ rf increases, the galaxies on the G – M 20 diagram move to the upper left with a slope of −0.23 ± 0.03 on average. We find that spatial resolution mainly affects the merger identification. The merger fraction in F200W resolution can be ≳2 times larger than that in F444W resolution. Furthermore, we compare the morphological parameter evolution of galaxies with different stellar masses. We find that there are differences in the morphological evolution of high- and low-mass (log M * ≥ 10 and 9 < log M * < 10) galaxies in the studied redshift range, which may be caused by their different evolutionary paths. [ABSTRACT FROM AUTHOR]

The Milky Way (MW) stellar disk has both a thin and a thick component. The thin disk is composed mostly of younger stars (≲8 Gyr) with a lower abundance of α -elements, while the thick disk contains predominantly older stars (≳8–12 Gyr) with a higher α abundance, giving rise to an α -bimodality most prominent at intermediate metallicities. A proposed explanation for the bimodality is an episode of clumpy star formation, where high- α stars form in massive clumps that appear in the first few billion years of the MW's evolution, while low- α stars form throughout the disk and over a longer time span. To better understand the evolution of clumps, we track them and their constituent stars in two clumpy MW simulations that reproduce the α -abundance bimodality, one with 10% and the other with 20% supernova feedback efficiency. We investigate the paths that these clumps take in the chemical space ([O/Fe]–[Fe/H]) as well as their mass, star formation rate (SFR), formation location, lifetime, and merger history. The clumps in the simulation with lower feedback last longer on average, with several lasting hundreds of millions of years. Some of the clumps do not reach high- α, but the ones that do on average have a higher SFR, longer lifetime, greater mass, and form closer to the Galactic center than the ones that do not. Most clumps that reach high- α merge with others and eventually spiral into the Galactic center, but shed stars along the way to form most of the thick-disk component. [ABSTRACT FROM AUTHOR]

We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [ α /M]. With this, we determine the mean kinematics, metallicities, α abundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (∼4–7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = − 0.149 − 0.081 + 0.067 dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ∼ −0.2), and is enhanced in α abundance (mean [ α /M] = 0.281 − 0.038 + 0.035 ). The disk of M31 within ∼7 kpc is enhanced in both metallicity ([M/H] = − 0.023 − 0.052 + 0.050 ) and α abundance ([ α /M] = 0.274 − 0.025 + 0.020 ). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc−1). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy's chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies. [ABSTRACT FROM AUTHOR]

In a seminal paper, Parker showed the vertical stratification of the interstellar medium (ISM) is unstable if magnetic fields and cosmic rays provide too large a fraction of pressure support. Cosmic ray acceleration is linked to star formation, so Parker's instability and its nonlinear outcomes are a type of star formation feedback. Numerical simulations have shown the instability can significantly restructure the ISM, thinning the thermal gas layer and thickening the magnetic field and cosmic ray layer. However, the timescale on which this occurs is rather long (∼0.4 Gyr). Furthermore, the conditions for instability depend on the model adopted for cosmic ray transport. In this work, we connect the instability and feedback problems by examining the effect of a single, spatially and temporally localized cosmic ray injection on the ISM over ∼1 kpc3 scales. We perform cosmic ray magnetohydrodynamic simulations using the Athena++ code, varying the background properties, dominant cosmic ray transport mechanism, and injection characteristics between our simulation runs. We find robust effects of buoyancy for all transport models, with disruption of the ISM on timescales as short as 100 Myr when the background equilibrium is dominated by cosmic ray pressure. [ABSTRACT FROM AUTHOR]

We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098 Z ⊙) and low stellar masses (104.7–107.6 M ⊙). Taking deep medium/high-resolution (R ∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H α emission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed H α flux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (v rot) of 5–23 km s−1 smaller than the velocity dispersions (σ 0) of 17–31 km s−1, indicating dispersion-dominated (v rot/ σ 0 = 0.29–0.80 < 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of f gas ≃ 0.9–1.0. Comparing our results with other H α kinematics studies, we find that v rot/ σ 0 decreases and f gas increases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high- z (z ∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations at z ∼ 7. [ABSTRACT FROM AUTHOR]

With its cored surface brightness profile, the elliptical galaxy NGC 5419 appears as a typical high-mass early-type galaxy (ETG). However, the galaxy hosts two distinct nuclei in its center. We use high-signal MUSE (Multi-unit Spectroscopic Explorer (Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 099.B-0193(A).)) spectral observations and novel triaxial dynamical orbit models to reveal a surprisingly isotropic central orbit distribution in NGC 5419. Recent collisionless simulations of merging massive ETGs suggest a two-phase core formation model, in which the low-density stellar core forms rapidly by supermassive black holes (SMBHs) sinking into the center due to dynamical friction. Only afterwards do the SMBHs form a hard binary, and the black hole scouring process slowly changes the central orbit distribution from isotropic to tangential. The observed cored density profile, the double nucleus, and the isotropic center of NGC 5419 together thus point to an intermediate evolutionary state where the first phase of core formation has taken place, yet the scouring process is only beginning. This implies that the double nucleus is an SMBH binary. Our triaxial dynamical models indicate a total mass of the two SMBHs in the center of NGC 5419 of M BH = (1.0 ± 0.08) × 1010 M ⊙. Moreover, we find that NGC 5419's complex kinematically distinct core can be explained by a coherent flip of the direction of orbital rotation of stars on tube orbits at ∼3 kpc distance from the galaxy center together with projection effects. This is also in agreement with merger simulations hosting SMBHs in the same mass regime. [ABSTRACT FROM AUTHOR]

The understanding of dark matter distribution in galaxies plays a crucial role in unraveling the structure and evolution of galaxies. This research utilizes Monte Carlo probability analysis to investigate the density distribution of dark matter in galaxies. Multiple distribution models, including the Beta Model, Brownstein Model, Burkert Model, Einasto Model, Spherical Exponential Model, and Isothermal Model, are employed to estimate the density of galaxy matter at different distances from the galactic center. The analysis involves assessing the goodness of fit, sensitivity analysis of parameters, and chi-square analysis to evaluate the compatibility and accuracy of each model with the observed data. The results highlight the variations in dark matter density with increasing distance from the galactic center, indicating a higher concentration near the center and a lower concentration in the galaxy's outer regions. Understanding the distribution of dark matter density provides insights into the gravitational effects, dynamics, and observed structures of galaxies. The Monte Carlo probability analysis facilitates the estimation of probability distributions and the assessment of model uncertainty, enhancing our understanding of the dark matter distribution in galaxies. The research findings suggest the suitability of certain distribution models, such as the Beta and Brownstein models, for describing the observed dark matter distribution. However, further research is required to validate and refine these models, considering the complexities and variabilities of dark matter distribution in galactic systems. [ABSTRACT FROM AUTHOR]