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Since the beginning of mankind, the view of the sky was present through observations with the naked eye, then it developed with time, and the sciences and tools of astronomical observations developed, including photometric measurements, which reached a high degree of accuracy in describing various cosmic phenomena, including the study of galaxies, their composition, and the differences between them, and from here the importance of this study emerged, to determine the differences between two distinct types of classification of galaxies, which are normal and barred spiral galaxies, where two galaxies NGC 4662 and NGC 2649 were chosen that represented certain types of galaxies to study the morphological structure of the two galaxies, as well as the photometric study of the composition of the two galaxies, where a contour map was drawn, as well as finding the values of the photometric variables of the two galaxies, including the position angle, the ellipticity and B4. A fitting was made for the two galaxies to show the fundamental difference in composition, through which the basic differences between two known types of galaxies could be identified. [ABSTRACT FROM AUTHOR]

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.

Using N -body simulations, we explore the effects of growing a supermassive black hole (SMBH) prior to or during the formation of a stellar bar. Keeping the final mass and growth rate of the SMBH fixed, we show that if it is introduced before or while the bar is still growing, the SMBH does not cause a decrease in bar amplitude. Rather, in most cases, it is strengthened. In addition, an early-growing SMBH always either decreases the buckling amplitude, delays buckling, or both. This weakening of buckling is caused by an increase in the disk vertical velocity dispersion at radii well beyond the nominal black hole sphere of influence. While we find considerable stochasticity and sensitivity to initial conditions, the only case where the SMBH causes a decrease in bar amplitude is when it is introduced after the bar has attained a steady state. In this case, we confirm previous findings that the decrease in bar strength is a result of scattering of bar-supporting orbits with small pericenter radii. By heating the inner disk both radially and vertically, an early-growing SMBH increases the fraction of stars that can be captured by the inner Lindblad resonance (ILR) and the vertical ILR, thereby strengthening both the bar and the boxy-peanut-shaped bulge. Using orbital frequency analysis of star particles, we show that when an SMBH is introduced early and the bar forms around it, the bar is populated by different families of regular bar-supporting orbits than when the bar forms without an SMBH. [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 analysis of Hubble Space Telescope data from Wide Field Camera 3 (WFC3)/Ultraviolet Imaging Spectrometer, WFC3/IR, and the Advanced Camera for Surveys, investigating the young stellar cluster (YSC) population in the face-on spiral galaxy M83. Within the field of view of the IR pointings, we identify 454 sources with compact F814W continuum and Pa β line emission with a S/N ≥ 3 as possible YSC candidates embedded in dust. We refine this selection to 97 candidates based on their spectral energy distributions, multiwavelength morphology, and photometric uncertainties. For sources that are detected in all bands and have mass >10 ^2.8 M _⊙ (53 sources), we find that by 2 Myr 75% of IR-selected star clusters have an A _V ≤ 1 and that by 3 Myr the fraction rises to ∼82%. This evidence of early clearing implies that presupernova (pre-SN) feedback from massive stars is responsible for clearing the majority of the natal gas and dust that surround IR-selected star clusters in M83. Further, this result is consistent with previous estimates based on WFC3 observations and adds to the growing body of literature suggesting pre-SN feedback to be crucial for YSC emergence in normal star-forming galaxies. Finally, we find a weak correlation between the YSC concentration index and age over the first 10 Myr, which matches previous studies and indicates little or no change in the size of YSCs in M83 during their early evolution.

The secular evolution of disk galaxies is largely driven by resonances between the orbits of "particles" (stars or dark matter) and the rotation of non-axisymmetric features (spiral arms or a bar). Such resonances may also explain kinematic and photometric features observed in the Milky Way and external galaxies. In simplified cases, these resonant interactions are well understood: for instance, the dynamics of a test particle trapped near a resonance of a steadily rotating bar is easily analyzed using the angle-action tools pioneered by Binney, Monari, and others. However, such treatments do not address the stochasticity and messiness inherent to real galaxies—effects that have, with few exceptions, been previously explored only with complex N -body simulations. In this paper, we propose a simple kinetic equation describing the distribution function of particles near an orbital resonance with a rigidly rotating bar, allowing for diffusion of the particles' slow actions. We solve this equation for various values of the dimensionless diffusion strength Δ, and then apply our theory to the calculation of bar–halo dynamical friction. For Δ = 0, we recover the classic result of Tremaine and Weinberg that friction ultimately vanishes, owing to the phase mixing of resonant orbits. However, for Δ > 0, we find that diffusion suppresses phase mixing, leading to a finite torque. Our results suggest that stochasticity—be it physical or numerical—tends to increase bar–halo friction, and that bars in cosmological simulations might experience significant artificial slowdown, even if the numerical two-body relaxation time is much longer than a Hubble time. [ABSTRACT FROM AUTHOR]

Stellar bars have been found to substantially influence the properties of stellar populations in galaxies, affecting their ability to form stars. While this can be easily seen when studying galaxies in relatively isolated environments, such type of analysis requires a higher degree of complexity when cluster galaxies are considered, due to the variety of interactions that can potentially occur in these denser environments. We use IFU MUSE data from the GASP survey to study the combined effect of the presence of a stellar bar and ram pressure, on spatially resolved properties of stellar populations. We have analyzed spatially resolved indicators of both recent star formation rates (SFRs) and average stellar population ages to check for signatures of anomalous central star formation activity, also taking into account the possible presence of nuclear activity. We found an increase in central SFR in ram-pressure-affected galaxies when compared with unperturbed ones. The most extreme cases of increased SFR and central rejuvenation occur in barred galaxies that are at advanced stages of ram pressure stripping. For low-mass barred galaxies affected by ram pressure, the combined effect is the systematic enhancement of the star formation activity as opposed to the case of high-mass galaxies, which present both enhancement and suppression. Barred galaxies that present suppression of their star formation activity also present signatures of nuclear activity. Our results indicate that the combined effect of the presence of a bar and strong perturbation by ram pressure is able to trigger the central star formation activity and probably ignite nuclear activity. [ABSTRACT FROM AUTHOR]

Galactic bars induce characteristic motions deviating from pure circular rotation, known as noncircular motions. As bars are nonaxisymmetric structures, stronger bars are expected to show stronger noncircular motions. However, this has not yet been confirmed by observations. We use a bisymmetric model to account for the stellar kinematics of 14 barred galaxies obtained with the Multi-Unit Spectroscopic Explorer and characterize the degree of bar-driven noncircular motions. For the first time, we find tight relations between the bar strength (bar ellipticity and torque parameter) and the degree of stellar noncircular motions. We also find that the bar strength is strongly associated with the stellar radial velocity driven by bars. Our results imply that stronger bars exhibit stronger noncircular motions. Noncircular motions beyond the bar are found to be weak, comprising less than 10% of the strength of the circular motions. We find that galaxies with a boxy/peanut (B/P) bulge exhibit a higher degree of noncircular motions and higher stellar radial velocity compared to galaxies without a B/P bulge, by 30% ∼ 50%. However, this effect could be attributed to the presence of strong bars in galaxies with a B/P feature in our sample, which would naturally result in higher radial motions, rather than to the B/P bulges themselves inducing stronger radial motions. More observational studies, utilizing both stellar and gaseous kinematics on statistically complete samples, along with numerical studies are necessary to draw a comprehensive view of the impact that B/P bulges have on bar-driven noncircular motions.

Dark matter (DM) bars that shadow stellar bars have been previously shown to form in idealized simulations of isolated disk galaxies, but have yet to be studied in a fully cosmological context. In this work, we analyze a population of disk galaxies within the TNG50 simulation to determine the characteristics of their dark bars. We estimate bar strength and orientation using both the in-plane Fourier A _2 density moments and the quadrupolar coefficients of the spherical harmonic basis function expansions of the density. We additionally present two novel methods for measuring the bar pattern speed Ω _p and rotation axis orientation using these coefficients, and apply them to one sample galaxy located in a TNG50 subbox. Consistent with isolated simulations, DM bars are shorter than their stellar counterparts and are 75% weaker in A _2 . DM bars dominate the shape of the inner halo potential and are apparent in the time series of quadrupolar coefficients. In our selected subbox galaxy, the stellar and dark bars remain co-aligned throughout the last 8 Gyr and have identical Ω _p . Pattern speed Ω _p evolves considerably over the last 8 Gyr, consistent with torques on the bars due to dynamical friction and gas accretion, and is seen to increase following a merger at t _lb = 1.5 Gyr. Rather than remaining static in time, the bar rotation axis displays both precession and nutation possibly caused by torques outside the plane of rotation. We find that the shape of the stellar and DM mass distributions are tightly correlated with Ω _p .

We report a faint nonaxisymmetric structure in NGC 1087 through the use of James Webb Space Telescope Near Infrared Camera, with an associated kinematic counterpart observed as an oval distortion in the stellar velocity map, H α , and CO J = 2 → 1 velocity fields. This structure is not evident in the MUSE optical continuum images but only revealed in the near-IR with the F200W and F300M band filters at 2 μ m and 3 μ m, respectively. Due to its elongation, this structure resembles a stellar bar although with remarkable differences with respect to conventional stellar bars. Most of the near-IR emission is concentrated within 6″∼500 pc with a maximum extension up to 1.2 kpc. The spatial extension of the large-scale noncircular motions is coincident with the bar, which undoubtedly confirms the presence of a nonaxisymmetric perturbation in the potential of NGC 1087. The oval distortion is enhanced in CO due to its dynamically cold nature rather than in H α . We found that the kinematics in all phases, including stellar, ionized, and molecular, can be described simultaneously by a model containing a bisymmetric perturbation; however, we find that an inflow model of gas along the bar major axis is also likely. Furthermore, the molecular mass inflow rate associated can explain the observed star-formation rate in the bar. This reinforces the idea that bars are mechanisms for transporting gas and triggering star formation. This work contributes to our understanding of nonaxisymmetry in galaxies using the most sophisticated data so far.

We report observations of the ground state transitions of ^12 CO, ^13 CO, C ^18 O, HCN, and HCO ^+ at 88–115 GHz in the inner region of the nearby galaxy IC 342. These data were obtained with the 16 pixel spectroscopic focal plane array Argus on the 100 m Robert C. Byrd Green Bank Telescope (GBT) at 6″–9″ resolution. In the nuclear bar region, the intensity distributions of ^12 CO(1–0) and ^13 CO(1–0) emission trace moderate densities, and differ from the dense gas distributions sampled in C ^18 O(1–0), HCN(1–0), and HCO ^+ (1–0). We observe a constant HCN(1–0)-to-HCO ^+ (1–0) ratio of 1.2 ± 0.1 across the whole ∼1 kpc bar. This indicates that the HCN(1–0) and HCO ^+ (1–0) lines have intermediate optical depth, and that the corresponding ${n}_{{{\rm{H}}}_{2}}$ of the gas producing the emission is of order 10 ^4.5−6 cm ^−3 . We show that HCO ^+ (1–0) is thermalized and HCN(1–0) is close to thermalization. The very tight correlation between the HCN(1–0) and HCO ^+ (1–0) intensities across the 1 kpc bar suggests that this ratio is more sensitive to the relative abundance of the two species than to the gas density. We confirm an angular offset (∼10″) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the L _IR – ${L}_{\mathrm{HCN}}$ correlation at high spatial resolution due to the effect of incomplete sampling of star-forming regions by HCN emission in IC 342. The scatter of the L _IR – ${L}_{\mathrm{HCN}}$ relation decreases as the spatial scale increases from 10″ to 30″ (170–510 pc), and is comparable to the scatter of the global relation at a scale of 340 pc.

We investigate the morphological and structural evolution of disk galaxies in simulations for a wide range of Toomre’s Q parameters. In addition to the inspection of conventional bar modes, we compute the concentration, asymmetry, and clumpiness (CAS) parameters to enlarge the understanding of the galaxy evolution. These parameters are widely employed to analyze the light distribution of the observed galaxies, but the adaptation to numerical simulations is not much considered. While the bar formation takes place in a considerable range of Q around 1, barred galaxies originating from Q > 1 and Q < 1 disks yield CAS values that differ significantly. Disks starting with Q < 1 develop clumps due to local gravitational instabilities along with the bar, and these clumps play a central role in enhancing the CAS values. This process is absent in the Q > 1 counterparts in which the evolution is dominated by linearly unstable two-armed modes that lead to lower CAS values. Likewise, unbarred galaxies that are obtainable from disks with Q far below and far above 1 exhibit greatly different CAS magnitudes. It turns out that the CAS parameters can serve as indicators of the initial kinematical state and the evolution history of a disk of any morphology. In addition, we find an alternative mechanism of the formation of the lopsided barred galaxy when Q ≲ 1. Bars that evolve in the midst of the clumps can spontaneously become lopsided at the end.

We use 0.1″ observations from the Atacama Large Millimeter Array (ALMA), Hubble Space Telescope (HST), and JWST to study young massive clusters (YMCs) in their embedded “infant” phase across the central starburst ring in NGC 3351. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (∼10 ^5 M _⊙ ), small radii (≲ 5 pc), large escape velocities (6–10 km s ^−1 ), and short freefall times (0.5–1 Myr). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed H ii region–cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline, ranging from ∼1–2 Myr before cluster formation as starless clumps, to ∼4–6 Myr after as exposed H ii region–cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit a nonuniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows.

The dark matter halo properties, for example, mass, spin, and concentration, play a significant role in the formation and evolution of bars in disk galaxies. This study highlights the importance of a new parameter: the dark matter halo angular momentum distribution in the disk’s central region. We experiment with N -body galaxy models having a disk and dark matter similar to Milky Way–type galaxies. In these models, we vary the discontinuity of the angular momentum distribution of the halo (the total spin is the same for all models). Our N -body experiments suggest that bar forms in all models after a few Gyr of disk evolution. However, in the secular evolution of the bar, as we evolve these models until 9.78 Gyr, the bar gains its strength in the model with the most continuous halo angular momentum distribution, and the bar loses strength for the most discontinuous halo angular momentum distribution. The secular evolution of the bar suggests that box/peanut/x-shaped bulges similar to those found in the Milky Way disk should be more pronounced in halos with continuous halo angular momentum distributions. This study demonstrates the importance of the initial condition setup of galaxy systems, namely the discontinuity in the dark matter halo angular momentum distribution for a given density distribution, on the bar secular evolution in the disk galaxy simulations. Further, this study helps reconcile the conflicting results of bar secular evolution in a high-spinning halo of the recent literature.

Bars drive gas inflow. As the gas flows inward, shocks and shear occur along the bar dust lanes. Such shocks and shear can affect the star formation (SF) and change the gas properties. For four barred galaxies, we present H α velocity gradient maps that highlight bar-driven shocks and shear using data from the PHANGS-MUSE and PHANGS-ALMA surveys, which allow us to study bar kinematics in unprecedented detail. Velocity gradients are enhanced along the bar dust lanes, where shocks and shear are shown to occur in numerical simulations. Velocity gradient maps also efficiently pick up H ii regions that are expanding or moving relative to the surroundings. We put pseudo-slits on the regions where velocity gradients are enhanced and find that H α and CO velocities jump up to ∼170 km s ^−1 , even after removing the effects of circular motions due to the galaxy rotation. Enhanced velocity gradients either coincide with the peak of CO intensity along the bar dust lanes or are slightly offset from CO intensity peaks, depending on the objects. Using the Baldwin–Philips–Terlevich BPT diagnostic, we identify the source of ionization on each spaxel and find that SF is inhibited in the high-velocity gradient regions of the bar, and the majority of those regions are classified as a low-ionization nuclear emission-line region (LINER) or composite. This implies that SF is inhibited where bar-driven shear and shocks are strong. Our results are consistent with the results from the numerical simulations that show SF is inhibited in the bar where the shear force is strong.

The spin of dark halos has been shown to significantly affect bar formation and evolution in disk galaxies. To understand the physical role of halo spin in bar formation, we run N -body simulations of isolated, Milky Way–sized galaxies by varying the halo spin parameter in the range −0.16 ≤ λ ≤ 0.16 and the bulge mass. We find that our adopted halo alone is subject to swing amplification of an m = 2 nonaxisymmetric mode rotating in the same sense as the halo, which assists or inhibits the bar formation in a disk depending on its sense of rotation. The m = 2 mode in the disk, growing via swing amplification, interacts constructively (destructively) with the m = 2 mode in the prograde (retrograde) halo, promoting (delaying) bar formation. A bar grows by losing its angular momentum primarily to a halo. Since the halo particles inside (outside) the corotation resonance with the bar can emit (absorb) angular momentum to (from) the bar, the bar pattern speed decays more slowly for larger λ > 0, while it decreases relatively fast almost independent of λ ≤ 0. Models with a strong bar develop a boxy peanut-shaped bulge. In models without a bulge, this occurs rapidly via buckling instability, while bars with a bulge thicken gradually without undergoing buckling instability. Among the models considered in the present work, the bar in the λ = 0.06 model with a bulge of 10% of the disk mass best describes the Milky Way in terms of its length and pattern speed.

Barred galaxies exhibit boxy/peanut or X-shapes (BP/X) protruding from their disks in edge-on views. Two types of BP/X morphologies exist depending on whether the X-wings meet at the center (CX) or are off-centered (OX). Orbital studies indicate that various orbital types can generate X-shaped structures. Here we provide a classification approach that identifies the specific orbit families responsible for generating OX- and CX-shaped structures. Applying this approach to three different N -body bar models, we show that both OX and CX structures are associated with the x 1 orbit family, but OX-supporting orbits possess higher angular momentum (closer to x 1 orbits) than orbits in CX structures. Consequently, as the bar slows down, the contribution of higher angular momentum OX-supporting orbits decreases and that of lower angular momentum orbits increases, resulting in an evolution of the morphology from OX to CX. If the bar does not slow down, the shape of the BP/X structure and the fractions of OX/CX-supporting orbits remain substantially unchanged. Bars that do not undergo buckling but that do slow down initially show the OX structure and are dominated by high angular momentum orbits, transitioning to a CX morphology. Bars that buckle exhibit a combination of both OX- and CX-supporting orbits immediately after the buckling but become more CX dominated as their pattern speed decreases. This study demonstrates that the evolution of BP/X morphology and orbit populations strongly depends on the evolution of the bar angular momentum.

Noncircular (NC) motions represent the imprints of nonaxisymmetric structures in galaxies, providing opportunities to study the physical properties of gas departing from circular rotation. In this work, we have conducted a systematic study of the NC motions in a sample of 1624 gas-rich disk galaxies from the Mapping Nearby Galaxies at Apache Point Observatory (or MaNGA) Product Launch-11. By using the H α velocity as a tracer of the disk rotation, we find indications that the amplitude of the NC motions is related to the stellar mass, with the low-mass and late-type galaxies the most affected. In our sample, we find ratios of NC to circular rotation ranging from 5% to 20%. By implementing harmonic models to include NC motions associated with spiral arms and stellar bars, we find that the rotational curves traced with H α are barely affected by the NC motions induced by these structures. Consequently, in our sample, we do not find evidence that NC motions contribute to the scatter of the stellar Tully–Fisher relation. Our results suggest that NC motions might have a more localized effect in galaxies rather than a global one.

The dependence of the star formation efficiency (SFE) on galactic structures—especially whether the SFE in the bar region is lower than those in other regions—has recently been debated. We report the SFEs of 18 nearby gas-rich massive star-forming barred galaxies with large apparent bar major axes (≧75″). We statistically measure the SFE by distinguishing the center, the bar end, and the bar regions for the first time. The molecular gas surface density is derived from archival CO(1–0) and/or CO(2–1) data by assuming a constant CO-to-H2 conversion factor (α CO), and the star formation rate surface density is derived from a linear combination of far-UV and mid-IR intensities. The angular resolution is 15″, which corresponds to 0.3–1.8 kpc. We find that the ratio of the SFE in the bar to that in the disk was systematically lower than unity (typically 0.6–0.8), which means that the star formation in the bar is systematically suppressed. Our results are inconsistent with similar recent statistical studies, which have reported that the SFE tends to be independent of galactic structures. This inconsistency can be attributed to the differences in the definitions of the bar region, the spatial resolutions, the α CO, and the sample galaxies. Furthermore, we find a negative correlation between the SFE and the velocity width of the CO spectrum, which is consistent with the idea that the large dynamical effects—such as strong shocks, large shears, and fast cloud–cloud collisions caused by the noncircular motion of the bar—result in a low SFE. [ABSTRACT FROM AUTHOR]

JWST/Mid-Infrared Instrument imaging of the nearby galaxies IC 5332, NGC 628, NGC 1365, and NGC 7496 from PHANGS reveals a richness of gas structures that in each case form a quasi-regular network of interconnected filaments, shells, and voids. We examine whether this multiscale network of structure is consistent with the fragmentation of the gas disk through gravitational instability. We use FilFinder to detect the web of filamentary features in each galaxy and determine their characteristic radial and azimuthal spacings. These spacings are then compared to estimates of the most Toomre-unstable length (a few kiloparsecs), the turbulent Jeans length (a few hundred parsecs), and the disk scale height (tens of parsecs) reconstructed using PHANGS–Atacama Large Millimeter/submillimeter Array observations of the molecular gas as a dynamical tracer. Our analysis of the four galaxies targeted in this work indicates that Jeans-scale structure is pervasive. Future work will be essential for determining how the structure observed in gas disks impacts not only the rate and location of star formation but also how stellar feedback interacts positively or negatively with the surrounding multiphase gas reservoir.

Large-scale bars can fuel galaxy centers with molecular gas, often leading to the development of dense ringlike structures where intense star formation occurs, forming a very different environment compared to galactic disks. We pair ∼0.″3 (30 pc) resolution new JWST/MIRI imaging with archival ALMA CO(2–1) mapping of the central ∼5 kpc of the nearby barred spiral galaxy NGC 1365 to investigate the physical mechanisms responsible for this extreme star formation. The molecular gas morphology is resolved into two well-known bright bar lanes that surround a smooth dynamically cold gas disk ( R _gal ∼ 475 pc) reminiscent of non-star-forming disks in early-type galaxies and likely fed by gas inflow triggered by stellar feedback in the lanes. The lanes host a large number of JWST-identified massive young star clusters. We find some evidence for temporal star formation evolution along the ring. The complex kinematics in the gas lanes reveal strong streaming motions and may be consistent with convergence of gas streamlines expected there. Indeed, the extreme line widths are found to be the result of inter-“cloud” motion between gas peaks; ScousePy decomposition reveals multiple components with line widths of 〈 σ _CO,scouse 〉 ≈ 19 km s ^−1 and surface densities of $\langle \,{{\rm{\Sigma }}}_{{{\rm{H}}}_{2},\mathrm{scouse}}\rangle \,\approx \,800\,{M}_{\odot }\,{\mathrm{pc}}^{-2}$ , similar to the properties observed throughout the rest of the central molecular gas structure. Tailored hydrodynamical simulations exhibit many of the observed properties and imply that the observed structures are transient and highly time-variable. From our study of NGC 1365, we conclude that it is predominantly the high gas inflow triggered by the bar that is setting the star formation in its CMZ.

A primary new capability of JWST is the ability to penetrate the dust in star-forming galaxies to identify and study the properties of young star clusters that remain embedded in dust and gas. In this Letter we combine new infrared images taken with JWST with our optical Hubble Space Telescope (HST) images of the starbursting barred (Seyfert2) spiral galaxy NGC 1365. We find that this galaxy has the richest population of massive young clusters of any known galaxy within 30 Mpc, with ∼30 star clusters that are more massive than 10 ^6 M _⊙ and younger than 10 Myr. Sixteen of these clusters are newly discovered from our JWST observations. An examination of the optical images reveals that 4 of 30 (∼13%) are so deeply embedded that they cannot be seen in the Hubble I band ( A _V ≳ 10 mag), and that 11 of 30 (∼37%) are missing in the HST B band, so age and mass estimates from optical measurements alone are challenging. These numbers suggest that massive clusters in NGC 1365 remain completely obscured in the visible for ∼1.3 ± 0.7 Myr and are either completely or partially obscured for ∼3.7 ± 1.1 Myr. We also use the JWST observations to gain new insights into the triggering of star cluster formation by the collision of gas and dust streamers with gas and dust in the bar. The JWST images reveal previously unknown structures (e.g., bridges and overshoot regions from stars that form in the bar) that help us better understand the orbital dynamics of barred galaxies and associated star-forming rings. Finally, we note that the excellent spatial resolution of the NIRCAM F200W filter provides a better way to separate barely resolved compact clusters from individual stars based on their sizes.

Dusty star-forming galaxies (DSFGs) are among the most massive and active star-forming galaxies during the cosmic noon. Theoretical studies have proposed various formation mechanisms of DSFGs, including major merger-driven starbursts and secular star-forming disks. Here, we report J0107a, a bright (∼8 mJy at observed-frame 888 μ m) DSFG at z = 2.467 that appears to be a gas-rich massive disk and might be an extreme case of the secular disk scenario. J0107a has a stellar mass M _⋆ ∼ 5 × 10 ^11 M _⊙ , molecular gas mass M _mol ≳ 10 ^11 M _⊙ , and a star formation rate of ∼500 M _⊙ yr ^−1 . J0107a does not have a gas-rich companion. The rest-frame 1.28 μ m JWST NIRCam image of J0107a shows a grand-design spiral with a prominent stellar bar extending ∼15 kpc. The Atacama Large Millimeter/submillimeter Array Band 7 continuum map reveals that the dust emission originates from both the central starburst and the stellar bar. 3D disk modeling of the CO(4–3) emission line indicates a dynamically cold disk with rotation-to-dispersion ratio ${V}_{\max }/\sigma \sim 8$ . The results suggest a bright DSFG may have a nonmerger origin, and its vigorous star formation may be triggered by the bar and/or rapid gas inflow.

Stellar bars are key drivers of secular evolution in galaxies and can be effectively studied using rest-frame near-infrared (NIR) images, which trace the underlying stellar mass and are less impacted by dust and star formation than rest-frame UV or optical images. We leverage the power of JWST CEERS NIRCam images to present the first quantitative identification and characterization of stellar bars at z > 1 based on rest-frame NIR F444W images of high resolution (∼1.3 kpc at z ∼ 1–3). We identify stellar bars in these images using quantitative criteria based on ellipse fits. For this pilot study, we present six examples of robustly identified bars at z > 1 with spectroscopic redshifts, including the two highest-redshift bars at z ∼ 2.136 and 2.312 quantitatively identified and characterized to date. The stellar bars at z ∼ 1.1–2.3 presented in our study have projected semimajor axes of ∼2.9–4.3 kpc and projected ellipticities of ∼0.41–0.53 in the rest-frame NIR. The barred host galaxies have stellar masses ∼1 × 10 ^10 to 2 × 10 ^11 M _⊙ and star formation rates of ∼21–295 M _⊙ yr ^−1 , and several have potential nearby companions. Our finding of bars at z ∼ 1.1–2.3 demonstrates the early onset of such instabilities and supports simulations where bars form early in massive dynamically cold disks. It also suggests that if these bars at lookback times of 8–11 Gyr survive out to present epochs, bar-driven secular processes may operate over a long time and have a significant impact on some galaxies by z ∼ 0.

While bars are common in disk galaxies, their formation conditions are not well understood. We use N -body simulations to study the formation and evolution of a bar in isolated galaxies consisting of a stellar disk, a classical bulge, and a dark halo. We consider 24 galaxy models that are similar to the Milky Way but differ in the mass and compactness of the classical bulge and halo concentration. We find that the bar formation requires ${({Q}_{T,\min }/1.2)}^{2}+{(\mathrm{CMC}/0.05)}^{2}\lesssim 1$ , where ${Q}_{T,\min }$ and CMC refer to the minimum value of the Toomre stability parameter and the central mass concentration, respectively. Bars tend to be stronger and longer, and to rotate more slowly, in galaxies with a less massive and less compact bulge and halo. All bars formed in our models correspond to slow bars. A model with the bulge mass of ∼10%–20% of the disk under a concentrated halo produces a bar similar to that of the Milky Way. We discuss our findings in relation to other bar formation criteria suggested by previous studies.

Elongated bar-like features are ubiquitous in galaxies, occurring at the centers of approximately two-thirds of spiral disks in the nearby Universe. Due to gravitational interactions between the bar and the other components of galaxies, it is expected that angular momentum and matter will redistribute over long (Gyr) timescales in barred galaxies. Previous work ignoring the gas phase of galaxies has conclusively demonstrated that bars should slow their rotation over time due to their interaction with dark matter halos. We have performed a simulation of a Milky Way–like galactic disk hosting a strong bar, including a state-of-the-art model of the interstellar medium and a live dark matter halo. In this simulation, the bar pattern does not slow down over time, and instead it remains at a stable, constant rate of rotation. This behavior has been observed in previous simulations using more simplified models for the interstellar gas, but the apparent lack of secular evolution has remained unexplained. We find that the presence of the gas phase arrests the process by which the dark matter halo slows down a bar, a phenomenon we term bar locking. This locking is responsible for stabilizing the bar pattern speed. We find that, in a Milky Way–like disk, a gas fraction of only about 5% is necessary for this mechanism to operate. Our result naturally explains why nearly all observed bars rotate rapidly and is especially relevant for our understanding of how the Milky Way arrived at its present state.

Nuclear rings at the centers of barred galaxies are known to be strongly magnetized. To explore the effects of magnetic fields on star formation in these rings and nuclear gas flows, we run magnetohydrodynamic simulations in which there is a temporally constant magnetized inflow to the ring, representing a bar-driven inflow. The mass inflow rate is 1 M _⊙ yr ^−1 , and we explore models with a range of field strength in the inflow. We adopt the TIGRESS framework developed by Kim & Ostriker to handle radiative heating and cooling, star formation, and resulting supernova (SN) feedback. We find that magnetic fields are efficiently amplified in the ring due to rotational shear and SN feedback. Within a few 100 Myr, the turbulent component B _trb in the ring saturates at ∼35 μ G (in rough equipartition with the turbulent kinetic energy density), while the regular component B _reg exceeds 50 μ G. Expanding superbubbles created by clustered SN explosions vertically drag predominantly toroidal fields from near the midplane to produce poloidal fields in high-altitude regions. The growth of magnetic fields greatly suppresses star formation at late times. Simultaneously, strong magnetic tension in the ring drives radially inward accretion flows from the ring to form a circumnuclear disk in the central region; this feature is absent in the unmagnetized model.

The CO-to-H _2 conversion factor ( α _CO ) is central to measuring the amount and properties of molecular gas. It is known to vary with environmental conditions, and previous studies have revealed lower α _CO in the centers of some barred galaxies on kiloparsec scales. To unveil the physical drivers of such variations, we obtained Atacama Large Millimeter/submillimeter Array bands (3), (6), and (7) observations toward the inner ∼2 kpc of NGC 3627 and NGC 4321 tracing ^12 CO, ^13 CO, and C ^18 O lines on ∼100 pc scales. Our multiline modeling and Bayesian likelihood analysis of these data sets reveal variations of molecular gas density, temperature, optical depth, and velocity dispersion, which are among the key drivers of α _CO . The central 300 pc nuclei in both galaxies show strong enhancement of temperature T _k ≳ 100 K and density ${n}_{{{\rm{H}}}_{2}}\gt {10}^{3}$ cm ^−3 . Assuming a CO-to-H _2 abundance of 3 × 10 ^−4 , we derive 4–15 times lower α _CO than the Galactic value across our maps, which agrees well with previous kiloparsec-scale measurements. Combining the results with our previous work on NGC 3351, we find a strong correlation of α _CO with low- J ^12 CO optical depths ( τ _CO ), as well as an anticorrelation with T _k . The τ _CO correlation explains most of the α _CO variation in the three galaxy centers, whereas changes in T _k influence α _CO to second order. Overall, the observed line width and ^12 CO/ ^13 CO 2–1 line ratio correlate with τ _CO variation in these centers, and thus they are useful observational indicators for α _CO variation. We also test current simulation-based α _CO prescriptions and find a systematic overprediction, which likely originates from the mismatch of gas conditions between our data and the simulations.

Gas flows in the presence of two independently rotating nested bars remain not fully understood but are likely to play an important role in fueling the central black hole. We use high-resolution hydrodynamical simulations with detailed models of subgrid physics to study this problem. Our results show that the inner bar in double-barred galaxies can help drive gas flow from the nuclear ring to the center. In contrast, gas inflow usually stalls at the nuclear ring in single-barred galaxies. The inner bar causes a quasiperiodic inflow with a frequency determined by the difference between the two bar pattern speeds. We find that the star formation rate is higher in the model with two bars than in that with one bar. The inner bar in our model gradually weakens and dissolves due to gas inflow over a few billion years. Star formation produces metal-rich/ α -poor stars, which slows the weakening of the inner bar but does not halt its eventual decay. We also present a qualitative comparison of the gas morphology and kinematics in our simulations with those of observed double-barred galaxies.

We analyze TYPHOON long-slit-absorption line spectra of the starburst barred spiral galaxy NGC 1365 obtained with the Progressive Integral Step Method covering an area of 15 kpc ^2 . Applying a population synthesis technique, we determine the spatial distribution of ages and metallicities of the young and old stellar populations together with star formation rates, reddening, extinction, and the ratio R _V of extinction to reddening. We detect a clear indication of inside-out growth of the stellar disk beyond 3 kpc characterized by an outward increasing luminosity fraction of the young stellar population, a decreasing average age, and a history of mass growth, which was finished 2 Gyr later in the outermost disk. The metallicity of the young stellar population is clearly super solar but decreases toward larger galactocentric radii with a gradient of −0.02 dex kpc ^−1 . On the other hand, the metal content of the old population does not show a gradient and stays constant at a level roughly 0.4 dex lower than that of the young population. In the center of NGC 1365, we find a confined region where the metallicity of the young population drops dramatically and becomes lower than that of the old population. We attribute this to the infall of metal-poor gas, and additionally, to interrupted chemical evolution where star formation is stopped by active galactic nuclei and supernova feedback and then after several gigayears resumes with gas ejected by stellar winds from earlier generations of stars. We provide a simple model calculation as support for the latter.

Stickiness is a temporary confinement of orbits in a particular region of the phase space before they diffuse to a larger region. In a system of 2-degrees of freedom there are two main types of stickiness (a) stickiness around an island of stability, which is surrounded by cantori with small holes, and (b) stickiness close to the unstable asymptotic curves of unstable periodic orbits, that extend to large distances in the chaotic sea. We consider various factors that affect the time scale of stickiness due to cantori. The overall stickiness (stickiness of the second type) is maximum near the unstable asymptotic curves. An important application of stickiness is in the outer spiral arms of strong-barred spiral galaxies. These spiral arms consist mainly of sticky chaotic orbits. Such orbits may escape to large distances, or to infinity, but because of stickiness they support the spiral arms for very long times. [ABSTRACT FROM AUTHOR]