Strong Bar Research Articles

The Effects of Bar Strength and Kinematics on Galaxy Evolution: Slow Strong Bars Affect Their Hosts the Most

We study how bar strength and bar kinematics affect star formation in different regions of the bar by creating radial profiles of EW[Hα] and Dn4000 using data from Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). Bars in galaxies are classified as strong or weak using Galaxy Zoo DESI, and they are classified as fast and slow bars using the Tremaine–Weinberg method on stellar kinematic data from the MaNGA survey. In agreement with previous studies, we find that strong bars in star-forming (SF) galaxies have enhanced star formation in their center and beyond the bar-end region, while star formation is suppressed in the arms of the bar. This is not found for weakly barred galaxies, which have very similar radial profiles to unbarred galaxies. In addition, we find that slow bars in SF galaxies have significantly higher star formation along the bar than fast bars. However, the global star formation rate is not significantly different between galaxies with fast and slow bars. This suggests that the kinematics of the bar do not affect star formation globally, but changes where star formation occurs in the galaxy. Thus, we find that a bar will influence its host the most if it is both strong and slow.

The active role of co-evolving haloes in stellar bar formation

ABSTRACT We use idealized N-body simulations of equilibrium discs in live and static haloes to study how dark matter co-evolution impacts the assembly of stellar particles into a bar and the halo response. Initial conditions correspond to a marginally unstable disc according to commonly used disc stability criteria, and are evolved for the equivalent of about 150 disc dynamical times (10 Gyr). An extensive convergence study ensures accurate modelling of the bar formation process. Live haloes lead to the formation of a strong bar, but the same disc remains unbarred when evolved in a static halo. Neither seeded disc instabilities nor longer (60 Gyr) simulations result in the formation of a bar when the halo is static. When the live halo is replaced with a static analogue at later times, the previously robust bar slowly dissipates, suggesting that (1) the co-evolution of the disc and halo is critical for the assembly and long-term survival of bars in marginally unstable discs and (2) global disc stability criteria must be modified for discs in the presence of live haloes. In our live halo runs, a ‘dark bar’ grows synchronously with the stellar bar. Processes that inhibit the transfer of angular momentum between the halo and disc may stabilize a galaxy against bar formation, and can lead to the dissolution of the bar itself. This raises further questions about the puzzling stability of observed discs that are marginally unstable, but unbarred.

Why does the Milky Way have a bar?

ABSTRACT There is no doubt that the Milky Way is a barred galaxy; however, factors that establish its prominent morphology remain largely elusive. In this work, we attempt to constrain the history of the MW by tracing the present-day parameters and evolution of a set of MW and M31 analogues from the TNG50 simulations. We find that the strength of bars at $z=0$ correlates well not only with the stellar mass build-up but also, more crucially, with the time of onset of stellar discs. Discs of strongly barred galaxies form early ($z \gtrsim 2-3$), compared to weakly and non-barred galaxies ($z \approx 1-1.5$). Although we are cautious to draw ultimate conclusions about the governing factor of discs formation due to the complexity and correlations between different phenomena, the observed morphological diversity can be tentatively explained by a substantial variation in the gas angular momentum around proto-galaxies already at $z\approx 3-5$; in such a way, early discs formed from gas with larger angular momentum. By comparing the formation time-scales of discs of barred galaxies in the TNG50 sample, we infer that the MW has a strong bar ($0.35\lt A_2\lt 0.6$), and that its stellar disc started to dominate over the spheroidal component already at $z \approx 2$, with a mass of $\approx 1 \pm 0.5 \times 10^{10} M_\odot$. We conclude that the presence of a strong bar in the MW is a natural manifestation of the early formation of the stellar disc, which made possible bursty but highly efficient star formation at high redshift.

Effects of Halo Spin on the Formation and Evolution of Bars in Disk Galaxies

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.

Galaxy Zoo DESI: large-scale bars as a secular mechanism for triggering AGNs

ABSTRACT Despite the evidence that supermassive black holes (SMBHs) co-evolve with their host galaxy, and that most of the growth of these SMBHs occurs via merger-free processes, the underlying mechanisms which drive this secular co-evolution are poorly understood. We investigate the role that both strong and weak large-scale galactic bars play in mediating this relationship. Using 48 871 disc galaxies in a volume-limited sample from Galaxy Zoo DESI, we analyse the active galactic nucleus (AGN) fraction in strongly barred, weakly barred, and unbarred galaxies up to $z = 0.1$ over a range of stellar masses and colours. After controlling for stellar mass and colour, we find that the optically selected AGN fraction is $31.6 \pm 0.9$ per cent in strongly barred galaxies, $23.3 \pm 0.8$ per cent in weakly barred galaxies, and $14.2 \pm 0.6$ per cent in unbarred disc galaxies. These are highly statistically robust results, strengthening the tantalizing results in earlier works. Strongly barred galaxies have a higher fraction of AGNs than weakly barred galaxies, which in turn have a higher fraction than unbarred galaxies. Thus, while bars are not required in order to grow an SMBH in a disc galaxy, large-scale galactic bars appear to facilitate AGN fuelling, and the presence of a strong bar makes a disc galaxy more than twice as likely to host an AGN than an unbarred galaxy at all galaxy stellar masses and colours.

The Rotation of Classical Bulges in Barred Galaxies in the Presence of Gas

Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We carried out a comprehensive set of hydrodynamical N-body simulations with different combinations of bulge masses and gas fractions. In these models, both massive bulges and high gas content tend to inhibit the formation of strong bars. For low-mass bulges, the resulting bar is stronger in cases of low gas content. In the stronger bar models, bulges acquire more angular momentum and thus display considerable rotational velocity. Such bulges also develop anisotropic velocity dispersions and become triaxial in shape. We found that the rotation of the bulge becomes less pronounced as the gas fraction is increased from 0 to 30%. These results indicate that the gas content has a significant effect on the dynamics of the classical bulge, because it influences bar strength. Particularly in the case of the low-mass bulges (10% bulge mass fraction), all of the measured rotational and structural properties of the classical bulge depend strongly and systematically on the gas content of the galaxy.

Distinctive mechanism and model for whole-life ratcheting of cement-stabilized aggregates in tensile fatigue tests

In light of the limited research on the fatigue damage and plastic strain evolution of cement-stabilized aggregates (CSA) despite their widespread application, this study aims at modeling the ratcheting of CSA, which provides better characterization of fatigue by counting plastic strain accumulation. Uniaxial and indirect tensile fatigue tests were conducted to obtain the plastic strain accumulation and stress-strain curves. A bar system was constructed to describe the ratcheting mechanism of CSA, which considers the non-homogeneity of CSA's components and composes parallel bars with a distribution of plastic-damage properties. The ratcheting rate variation was attributed to the strength distribution of the bars. Then, to prevent complex and hard-to-implement parameter fitting, a predigested ratcheting model was proposed, which focuses only on the secant modulus and simplifies the generation of ratcheting to the difference between reloading and unloading secant modulus. The test results revealed a three-stages characteristic in the ratcheting evolution of CSA. The non-coincidence of reloading and unloading curves was deemed the intuitive cause of the ratcheting. The numerical implementation of the proposed mechanism indicated that the strength and modulus discrepancies between weak and strong bars can lead to ratcheting. By comparing with the experimental results, the effectiveness of the proposed model was verified in describing the ratcheting evolution of CSA and to characterizing the non-linearity of the accumulation curves. Moreover, the parameter fitting process requires the results of the current fatigue test instead of parallel tests or other loading tests, successfully eliminating calibration difficulties resulted from significant property discrepancies among CSA specimens.

Saturation of spiral instabilities in disc galaxies

ABSTRACT Spiral density waves can arise in galactic discs as linear instabilities of the underlying stellar distribution function. Such an instability grows exponentially in amplitude at some fixed growth rate β before saturating non-linearly. However, the mechanisms behind saturation, and the resulting saturated spiral amplitude, have received little attention. Here, we argue that one important saturation mechanism is the non-linear trapping of stars near the spiral’s corotation resonance. Under this mechanism, we show analytically that an m-armed spiral instability will saturate when the libration frequency of resonantly trapped orbits reaches $\omega _\mathrm{lib} \sim \mathrm{a\, \, few}\times m^{1/2} \beta$. For a galaxy with a flat rotation curve, this implies a maximum relative spiral surface density $\vert \delta \Sigma /\Sigma _0\vert \sim \mathrm{a\, \, few} \times (\beta /\Omega _\mathrm{p})^2 \cot \alpha$, where Ωp is the spiral pattern speed and α is its pitch angle. This result is in reasonable agreement with recent N-body simulations, and suggests that spirals driven by internally-generated instabilities reach relative amplitudes of at most a few tens of per cent; higher amplitude spirals, like in M51 and NGC 1300, are likely caused by very strong bars and/or tidal perturbations.

The Stability of Some Galaxy Disks is Still Perplexing

The problem of how some disk galaxies avoid forming bars remains unsolved. Many galaxy models having reasonable properties continue to manifest vigorous instabilities that rapidly form strong bars and no widely accepted idea has yet been advanced to account for how some disk galaxies manage to avoid this instability. It is encouraging that not all galaxies formed in recent cosmological simulations possess bars, but the dynamical explanation for this result is unclear. The unstable mode that creates a bar is understood as a standing wave in a cavity that reflects off the disk center and the corotation radius, with amplification at corotation. Here we use simulations to address one further idea that may inhibit the feedback loop and therefore contribute to stability, which is to make the disk center dynamically hot and/or to taper away mass from the inner disk, which could be masked by a bulge. Unfortunately, we find that neither strategy makes much difference to the global stability of the disk in the models we have tried. While deep density cutouts do indeed prevent feedback through the center, they still reflect incoming waves and thereby provoke a slightly different instability that again leads to a strong bar.

Stellar bars in spinning haloes: delayed buckling and absence of slowdown

ABSTRACT We use numerical simulations to analyse the stellar bar evolution in spinning dark matter (DM) haloes. Previous works have shown the halo spin has a substantial effect on bar evolution and can lead to bar dissolution following the vertical buckling instability. We invoke the DM spin sequence, λ = 0–0.09, and study the effect of DM density along this λ sequence by varying compactness of DM halo. We find that (1) varying DM density has a profound effect on bar evolution along λ sequence. (2) For λ ≳ 0.045, the buckling has been delayed progressively. (3) Stellar bars remain near maximal strength, and their amplitude plateau stage extends over 0.7–5 Gyr, terminating with the buckling. (4) Although stellar bars remain strong during the plateau, their pattern speed and size stay nearly constant. This unusual behaviour of stellar bars follows from highly reduced gravitational torques due to DM bar being aligned with the stellar bar. The orbital analysis shows that delayed buckling results from slow evolution of stellar oscillations along bar major and vertical axes, thus postponing the action of the vertical 2:1 resonance which pumps the rotational energy into vertical motions. (5) Peanut/boxy-shaped bulges form at the beginning of the plateau and grow with time. (6) Finally, strong bars in spinning haloes can avoid fast braking, resolving the long-standing discrepancy between observations and N-body simulations. This behaviour of stellar bars along the λ and DM density sequences reveals a wealth of stellar bar properties which require additional study.

H i-rich but low star formation galaxies in MaNGA: physical properties and comparison to control samples

ABSTRACT Gas-rich galaxies are typically star forming. We make use of H i-MaNGA, a programme of H i follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey of the Sloan Digital Sky Surveys, to construct a sample of unusual neutral hydrogen (H i, 21 cm)-rich galaxies that have low star formation rates (SFRs), using infrared colour from the Wide-field Infrared Survey Explorer as a proxy for specific SFR. Out of a set of 1575 MaNGA galaxies with H i-MaNGA detections, we find that 83 (5 per cent) meet our selection criteria to be H i rich with low SFR. We construct two stellar mass-matched control samples: H i-rich galaxies with typical SFR (high SF control) and H i-poor galaxies with low SFR (low H i control). We investigate the properties of each of these samples, comparing physical parameters such as ionization state maps, stellar and ionized gas velocity and dispersion, environment measures, metallicity, and morphology to search for the reasons why these unusual H i-rich galaxies are not forming stars. We find evidence for recent external accretion of gas in some galaxies (via high counter-rotating fractions), along with some evidence for active galactic nucleus (AGN) feedback (from a high central low-ionization emission-line region and/or red geyser fraction), and bar quenching (via an enhanced strong bar fraction). Some galaxies in the sample are consistent with simply having their H i in a high angular momentum, large-radius, low-density disc. We conclude that no single physical process can explain all H i-rich, low-SFR galaxies.

Stellar Bars in Isolated Gas-rich Spiral Galaxies Do Not Slow Down

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.

Galaxy Zoo: kinematics of strongly and weakly barred galaxies

ABSTRACTWe study the bar pattern speeds and corotation radii of 225 barred galaxies, using integral field unit data from MaNGA and the Tremaine–Weinberg method. Our sample, which is divided between strongly and weakly barred galaxies identified via Galaxy Zoo, is the largest that this method has been applied to. We find lower pattern speeds for strongly barred galaxies than for weakly barred galaxies. As simulations show that the pattern speed decreases as the bar exchanges angular momentum with its host, these results suggest that strong bars are more evolved than weak bars. Interestingly, the corotation radius is not different between weakly and strongly barred galaxies, despite being proportional to bar length. We also find that the corotation radius is significantly different between quenching and star-forming galaxies. Additionally, we find that strongly barred galaxies have significantly lower values for $\mathcal {R}$, the ratio between the corotation radius and the bar radius, than weakly barred galaxies, despite a big overlap in both distributions. This ratio classifies bars into ultrafast bars ($\mathcal {R} \lt $ 1.0; 11 per cent of our sample), fast bars (1.0 $\lt \mathcal {R} \lt $ 1.4; 27 per cent), and slow bars ($\mathcal {R} \gt $ 1.4; 62 per cent). Simulations show that $\mathcal {R}$ is correlated with the bar formation mechanism, so our results suggest that strong bars are more likely to be formed by different mechanisms than weak bars. Finally, we find a lower fraction of ultrafast bars than most other studies, which decreases the recently claimed tension with Lambda cold dark matter. However, the median value of $\mathcal {R}$ is still lower than what is predicted by simulations.

2022 Heat Treating Society Strong Bar Competition

2022 Heat Treating Society Strong Bar Competition

Development of a Heat Treating Process for 9254 Steel Used to Create the Winning Entry in the 2022 Heat Treating Society Strong Bar Competition

This paper summarizes the development of a heat-treating process developed by an undergraduate student team competing in the 2022 Heat Treating Society Strong Bar Competition. The objective of the competition was to heat treat a 10 mm diameter rod of 9254 steel to realize the highest strength possible (with a minimum hardness of 50 HRC) while maintaining sufficient ductility to achieve at least 4 mm of deflection during a 3-point bend test. The process selected was a modified martempering heat treatment to achieve the desired properties. The modified martemper consisted of austenitizing the sample at 870 °C for twenty-five minutes and then quenching in corn oil held at a temperature of 200 °C. The sample remained immersed in the oil for three minutes and then air cooled to 100 °C. When the sample hit 100 °C, it was immediately tempered at 200 °C followed by air cooling to room temperature. Properties of the steel were measured on samples in four conditions: as received, as quenched, martemper + 450 °C tempering for two hours, and martemper + 200 °C temper for one hour. The heat treatment that resulted in the best properties was the martemper with the 200 °C temper for one hour. The average hardness for this method was 54.0 HRC, which met all requirements for the competition. The sample properties during a 3-point bend test were a maximum bend strength of 41.3 kN and a deflection of 8 mm. Post bend testing analysis of the microstructure of the competition sample revealed an internal crack approximately 0.1 mm in length. This paper describes the competition and the methods used by the student team to develop the heat treating process.

Central Star Formation in Early-type Galaxy I Zw 81 in the Bootes Void

The origin of star formation in customarily passively evolving early-type massive galaxies is poorly understood. We present a case study of a massive galaxy, I Zw 81, inside the Bootes void. The void galaxy is known to host active galactic nuclei (AGN). Our detailed 2D decomposition of the surface brightness distribution in the Canada France Hawaii Telescope (CFHT) g and r bands revealed multiple structural components such as a nuclear point source, a bar, a ring, and an inner exponential disk followed by an outer low surface brightness disk. I Zw 81 turns out to be a disk-dominated galaxy with lenticular morphology. The modeling of the multiwavelength spectral energy distribution shows that the galaxy is star-forming (SF), and belongs to the blue cloud. We find that the optical (g−r) color of the bar is bluer than the disks, and the far- and near-ultraviolet emission inside the galaxy observed with Imaging Telescope onboard AstroSat is concentrated in the central few kpc region enclosing the bar. The strong bar might be playing a pivotal role in driving the gas inflow and causing SF activity in tandem with the minor merger-like interactions as evident from the deep CFHT data. The low-luminosity AGN is insufficient to quench the central SF. The results are peculiar from the standpoint of a massive barred lenticular galaxy.

How Bar Fraction Depends on Baryon Fraction

We use Galaxy Zoo 2 morphologies (based on SDSS Legacy Imaging) alongside the completed Arecibo Legacy Fast ALFA survey measuring H i to investigate the correlation between bar fraction and an estimate of baryonic mass fraction for a sample of nearby (z < 0.06) disk galaxies (M ⋆ > 109 M ⊙). As expected from theoretical considerations, and as seen in previous work using different samples/morphological classifications, we find clear evidence of an increase in bar fraction, particularly strong bar fraction in galaxies with larger baryonic mass fractions (i.e., heavier discs for their dark matter halo).

Stellar migration in the Auriga simulations

ABSTRACT We study the presence and importance of stellar migration in the evolution of 17 Milky-Way like disc galaxies with stellar mass 10 &amp;lt; log(M*/M⊙) &amp;lt; 11 from the Auriga suite of zoom-in cosmological hydrodynamical simulations. We compare the birth radii of the stars to their radii at z = 0 for each system and present mean values of the strength of stellar migration as a function of radius and stellar age which vary between 1–4 kpc. We also investigate the effect of migration on age and metallicity radial profiles in the discs. We find several cases of age gradient flattening due to migration, but significant changes to metallicity profiles only for older stellar populations and discs that develop a strong bar. Furthermore, we study stellar migration from the perspective of the change of the galactocentric radius (ΔR) and orbital guiding centre radius (ΔRg) of stellar particles between given time intervals. We find that stars migrate approximately as a diffusion process only in the outer parts of the discs and for particular galaxies that have a weak bar. Strongly barred galaxies in our sample show larger stellar migration but its timestep evolution is slower-than-diffusion. Finally, we give parametrizations that encapsulate the dependence of the strength of the radial migration as a function of time and radius, for incorporation into (semi-)analytic models of galaxy evolution.

Renewable sorbent dispersive solid phase extraction automated by Lab-In-Syringe using magnetite-functionalized hydrophilic-lipophilic balanced sorbent coupled online to HPLC for determination of surface water contaminants

An automated methodology for magnetic dispersive solid phase microextraction integrating bead injection approach for renewable sorbent introduction is presented for the first time and was successfully applied to the enrichment of water contaminants. For this purpose, a simple procedure was developed for the functionalization of commercial SupelTM-Select HLB (Hydrophilic modified styrene polymer) sorbent beads that allowed embedding magnetite nanoparticles (Fe3O4). The sorbent was then used in a dispersive solid phase extraction procedure that was carried out entirely inside the void of an automatic syringe pump following the flow-batch concept of Lab-In-Syringe including automated renewal of the sorbent for each analysis. Mixing processes, sorbent dispersion, and sorbent recovery were enabled by using a strong magnetic stirring bar, fabricated from a 3D printed polypropylene casing and neodymium magnets, inside the syringe. The final extract was submitted to online coupled liquid chromatography with spectrometric detection. System and methodology were applied to determine mebendazole, bisphenol A, benzyl 4-hydroxybenzoate, diclofenac, and triclosan selected as models from different groups of environmental contaminants of current concern. Experimental parameters including extraction and elution times, composition and volume of eluent, and bead recollection were optimized. Required system elements were produced by 3D printing. Enlarging the sample volume by repeated extraction to enhance the sensitivity of the method was studied. Using double extraction from 3.5 mL, limits of detection ranged from 1.2 μg L−1 to 6.5 μg L−1 with an RSD (n = 6) value less than 7% for all the analytes at 25 μg L−1 level. The method was linear in the range of 5–200 μg L−1 and was successfully implemented for the analysis of surface waters with analyte recoveries ranging from 78.4% to 105.6%.

High and low Sérsic index bulges in Milky Way- and M31-like galaxies: origin and connection to the bar with TNG50

ABSTRACT We study bulge formation in MW/M31-like galaxies in a Λ-cold dark matter scenario, focusing on the origin of high- and low-Sersic index bulges. For this purpose, we use TNG50, a simulation of the IllustrisTNG project that combines a resolution of ∼8 × 104 M⊙ in stellar particles with a cosmological volume 52 cMpc in extent. We parametrize bulge surface brightness profiles by the Sérsic index and the bulge-to-total (B/T) ratio obtained from two-component photometric decompositions. In our sample of 287 MW/M31-like simulated galaxies, $17.1{{\ \rm per\ cent}}$ of photometric bulges exhibit high-Sérsic indices and $82.9{{\ \rm per\ cent}}$ show low-Sérsic indices. We study the impact that the environment, mergers and bars have in shaping the surface brightness profiles. We find no correlation between bulge properties and the environment where they reside. Simulated galaxies with higher Sérsic indices show, on average, a higher fraction of ex situ stars in their kinematically selected bulges. For this bulge population, the last significant merger (total mass ratio msat/mhost &amp;gt; 0.1) occurs, on average, at later times. However, a substantial fraction of low-Sérsic index bulges also experience a late significant merger. We find that bars play an important role in the development of the different types of photometric bulges. The fraction of simulated galaxies with bars is smaller for the high- than for the low-Sérsic index population, reaching differences of $20{{\ \rm per\ cent}}$ at z &amp;gt; 1. Simulated galaxies with high fractions of ex situ stars in the bulge do not develop strong bars. Conversely, simulated galaxies with long-lived strong bars have bulges with ex situ fractions, fex situ &amp;lt; 0.2.