Gas morphology and kinematics in the Milky Way contain key information for understanding the formation and evolution of our Galaxy. We present a high resolution hydrodynamical simulation based on a realistic barred Milky Way potential constrained by recent observations. Our model can reproduce most features in the observed longitude-velocity diagram, including the Central Molecular Zone, the Near and Far 3-kpc arms, the Molecular Ring, and the spiral arm tangents. It can also explain the non-circular motions of masers obtained by the recent BeSSeL2 survey. The central gas kinematics are consistent with a mass of $6.9\times10^8\; {\rm M}_{\odot}$ in the Nuclear Stellar Disk. Our model predicts the formation of an elliptical gaseous ring surrounding the bar, which is composed of the 3-kpc arms, Norma arm, and the bar-spiral interfaces. This ring is similar to those "inner" rings in some Milky Way analogs with a boxy/peanut-shaped bulge. The kinematics of gas near the solar neighbourhood are governed by the Local arm, which is induced by the four major stellar spiral arms. The bar pattern speed constrained by our gas model is $37.5-40\; {\rm km}\;{\rm s}^{-1}\;{\rm kpc}^{-1}$, corresponding to a corotation radius of $R_{\rm CR}=6.0-6.4\;{\rm kpc}$. The rotation curve of our model rises gently within the central $\sim5\;{\rm kpc}$, which is significantly less steep than those predicted by modern zoom-in cosmological simulations such as Auriga.
We present the initial results of a census of 684 barred galaxies in the MaNGA galaxy survey. This large sample contains galaxies with a wide range of physical properties, and we attempt to link bar properties to key observables for the whole galaxy. We find the length of the bar, when normalised for galaxy size, is correlated with the distance of the galaxy from the star formation main sequence, with more passive galaxies hosting larger-scale bars. Ionised gas is observed along the bars of low-mass galaxies only, and these galaxies are generally star-forming and host short bars. Higher-mass g…
Based on a high quality $N$-body simulation of a double bar galaxy model, we investigate the evolution of the bar properties, including their size, strength and instantaneous pattern speed derived by using three distinct methods: the Fourier, Jacobi integral, and moment of inertia methods. The interaction of the two bars, which rotate at distinct speeds, primarily affects the size, strength and pattern speed of the inner bar. When the two bars are perpendicular to each other, the size and the pattern speed of the inner bar decrease and its strength increases. The emergence of a strong Fourier …
We measure the variation of the escape speed of the Galaxy across a range of $\sim$ 40 kpc in Galactocentric radius. The local escape speed is found to be $521^{+46}_{-30}\,\mathrm{km\,s^{-1}}$, in good agreement with other studies. We find that this has already fallen to $379^{+34}_{-28}\,\mathrm{km\,s^{-1}}$ at a radius of 50 kpc. Through measuring the escape speed and its variation, we obtain constraints on the Galactic potential as a whole. In particular, the gradient in the escape speed with radius suggests that the total mass contained within 50 kpc is $29^{+7}_{-5}\times10^{10}\mathrm{M…
We revisited barium abundance in a sample of giant stars in the dwarf spheroidal Fornax galaxy. Non-local thermodynamic equilibrium (NLTE) synthesis was used to derive the barium abundance from two Ba II lines. Our new NLTE result for barium shows that in the range of metallicities from -1 to -0.5 the abundance of this element is almost the same as in the stars of the Milky Way. We conclude that the evolution of barium abundance in the dSph Fornax galaxy resembles that of the Milky Way at the epoch of the corresponding metallicity level.
We investigate the relations between the properties of bars and their host galaxies in a sample of 77 nearby barred galaxies, spanning a wide range of morphological types and luminosities, with 34 SB0-SBa and 43 SBab-SBc galaxies. The sample includes all the galaxies with reliable direct measurement of their bar pattern speed based on long-slit or integral-field stellar spectroscopy using the Tremaine-Weinberg method. We limited our analysis to the galaxies with a relatively small relative error on the bar pattern speed (smaller than 50 per cent) and not hosting an ultrafast bar. For each gala…
Cloud-cloud collision (CCC) has been suggested as a mechanism to induce massive star formation. Recent simulations suggest that a CCC speed is different among galactic-scale environments, which is responsible for observed differences in star formation activity. In particular, a high-speed CCC is proposed as a cause of star formation suppression in the bar regions in barred spiral galaxies. Focusing on the strongly barred galaxy NGC1300, we investigate the CCC speed. We find the CCC speed in the bar and bar-end tend to be higher than that in the arm. The estimated CCC speed is $\sim20~\rm km~s^…
Recently, both simulations and observations have revealed that flybys - fast, one-time interactions between two galaxy halos - are surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three co-planer flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flyby…
We analyze how the orbital support of the inner bar in a double-barred galaxy (nested bars) depends on the angular velocity (i.e. pattern speed) of this bar. We study orbits in seven models of double bars using the method of invariant loops. The range of pattern speed is covered exhaustively. We find that not all pattern speeds are allowed when the inner bar rotates in the same direction as the outer bar. Below a certain minimum pattern speed orbital support for the inner bar abruptly disappears, while at high values of this speed the orbits indicate an increasingly round bar that looks more l…
We present surface photometry and stellar kinematics of NGC 4264, a lenticular galaxy in the region of the Virgo Cluster undergoing a tidal interaction with its neighbour, NGC 4261. We measured the bar radius and strength from SDSS imaging and the bar pattern speed from MUSE integral-field spectroscopy. We find that NGC 4264 hosts a strong and large bar, which is rotating fast. The accurate measurement of the bar rotation rate allows us to exclude that the formation of the bar was triggered by the ongoing interaction.
Elongated, bar-like galaxies without a significant disk component, with little rotation support and no gas, often form as a result of tidal interactions with a galaxy cluster, as was recently demonstrated using the IllustrisTNG-100 simulation. Galaxies that exhibit similar properties are, however, also found to be infalling into the cluster for the first time. We use the same simulation to study in detail the history of such a galaxy over cosmic time in order to determine its origin. The bar appears to be triggered at t=6.8 Gyr by the combined effect of the last significant merger with a subha…
We track the angular momentum transfer in n-body simulations of barred galaxies by measuring torques to understand the dynamical mechanisms responsible for the evolution of the bar-disc-dark matter halo system. We find evidence for three distinct phases of barred galaxy evolution: assembly, secular growth, and steady-state equilibrium. Using a decomposition of the disc into orbital families, we track bar mass and angular momentum through time and correlate the quantities with the phases of evolution. We follow the angular momentum transfer between particles and identify the dominant torque cha…
We present surface photometry and stellar kinematics of IC 3167, a dwarf galaxy hosting a lopsided weak bar and infalling into the Virgo cluster. We measured the bar radius and strength from broad-band imaging and bar pattern speed by applying the Tremaine-Weinberg method to stellar-absorption integral-field spectroscopy. We derived the ratio of the corotation radius to bar radius (R = 1.7 + 0.5 - 0.3) from stellar kinematics and bar pattern speed. The probability that the bar is rotating slowly is more than twice as likely as that the bar is fast. This allows us to infer that the formation of…
A significant fraction of barred spiral galaxies exhibits peanut/X-shaped structures in their central regions. Bars are known to rotate with a single pattern speed, and they eventually slow down over time due to the dynamical friction with the surrounding dark matter halo. However, the nature of the decay in pattern speed values and whether all peanut bars rotate with a single pattern speed remain to be investigated. Using N-body simulation of a collisionless stellar disc, we study the case of a long bar with a three-dimensional peanut structure prominent in both edge-on and face-on projection…
We present a study of the effect of bulge mass on the evolution of bar pattern speed in isolated disk galaxies using N-body simulations. Earlier studies have shown that disk stars at the inner resonances can transfer a significant amount of angular momentum to the dark matter halo and this results in the slow down of the bar pattern speed. In this paper we investigate how the mass of the other spheroidal component, the bulge, affects bar pattern speeds. In our galaxy models the initial bars are all rotating fast as the R parameter, which is the ratio of the corotation radius to bar radius is l…
Among the many processes involved in galaxy evolution, those of bar formation, quenching, and feedback from an active galactic nucleus (AGN) seem to be connected, however, the nature of these relations remains unclear. In this work, we aim to elucidate them by studying the formation of a barred galaxy in a major merger of two disks in the IllustrisTNG simulations. This merger involves a coalescence of two supermassive black holes and a sudden switch to the kinetic mode of AGN feedback implemented in the simulations, which leads to the removal of the gas from the inner part of the galaxy, follo…
Double bars are thought to be important features for secular evolution in the central regions of galaxies. However, observational evidence about their origin and evolution is still scarce. We report on the discovery of the first Box-Peanut (B/P) structure in an inner bar detected in the face-on galaxy NGC 1291. We use the integral field data obtained from the MUSE spectrograph within the TIMER project. The B/P structure is detected as bi-symmetric minima of the $h_4$ moment of the line-of-sight velocity distribution along the major axis of the inner bar, as expected from numerical simulations.…
(Abridge) Bars are very common in the centre of the disc galaxies, and they drive the evolution of their structure. A volume-limited sample of 2106 disc galaxies extracted from the Sloan Digital Sky Survey Data Release 5 was studied to derive the bar fraction, length, and strength as a function of the morphology, size, local galaxy density, light concentration, and colour of the host galaxy. The bars were detected using the ellipse fitting method and Fourier analysis method. The ellipse fitting method was found to be more efficient in detecting bars in spiral galaxies. The fraction of barred g…
Aims. We aim to show how encounters with low-mass satellite galaxies may alter the bar formation in a Milky Way-like disc galaxy. Methods. We use high-resolution N-body simulations of a disc galaxy prone to mild bar instability. For realistic initial conditions of satellites, we take advantage of cosmological simulations of Milky Way-like dark matter haloes. Results. The satellites may have a significant impact on the time of bar formation. Some runs with satellites demonstrate a delay, while others show an advancement in bar formation compared to the isolated run, with such time differences r…
Aims: We characterised the properties of the bar hosted in lenticular galaxy NGC 4277, which is located behind the Virgo cluster. Methods: We measured the bar length and strength from the surface photometry obtained from the broad-band imaging of the Sloan Digital Sky Survey and we derived the bar pattern speed from the stellar kinematics obtained from the integral-field spectroscopy performed with the Multi Unit Spectroscopic Explorer at the Very Large Telescope. We also estimated the co-rotation radius from the circular velocity, which we constrained by correcting the stellar streaming motio…
We aim at investigating the formation process of weak bars by measuring their properties in a sample of 29 nearby SAB galaxies, spanning a wide range of morphological types and luminosities. The sample galaxies were selected to have an intermediate inclination, a bar at an intermediate angle between the disc minor and major axes, and an undisturbed morphology and kinematics to allow the direct measurement of the bar pattern speed. Combining our analysis with previous studies, we compared the properties of weak and strong bars. We measured the bar radius and strength from the r-band images avai…
We have used Galaxy Zoo DECaLS (GZD) to study strong and weak bars in disk galaxies. Out of the 314,000 galaxies in GZD, we created a volume-limited sample (0.01 < z < 0.05, Mr < -18.96) which contains 1,867 galaxies with reliable volunteer bar classifications in the ALFALFA footprint. In keeping with previous Galaxy Zoo surveys (such as GZ2), the morphological classifications from GZD agree well with previous morphological surveys. GZD considers galaxies to either have a strong bar (15.5%), a weak bar (28.1%) or no bar (56.4%), based on volunteer classifications on images obtained from the DE…
We examine the HI total intensity maps of the VLA LITTLE-THINGS galaxies and identify an HI bar in the dwarf irregular galaxy DDO 168 which has a dense and compact dark matter halo that dominates at all radii. This is only the third galaxy found to host an HI bar. Using the HI kinematic data, we apply the Tremaine-Weinberg method to estimate the pattern speed of the bar. The HI bar is found to have an average pattern speed of $23.3 \pm 5.9$ km/s/kpc. Interestingly, for the first time, we find that the observed pattern speeds of the bar in the two kinematic halves are different. We identify the…
We use WIYN High-resolution Infrared Camera (WHIRC) H (1.6 micron) band imaging, archival Spitzer, HST, and GALEX data, simulations and data from the literature to argue for the presence of a strong end-on bar in nearby spiral galaxy NGC 6503. The evidence consists of both photometric and kinematic signatures as well as resonant structures present in the galaxy which are most often associated with bars. These include a central peak followed by a plateau in the surface brightness profile, an extreme decrement in the central stellar velocity dispersion (a sigma-drop), and the presence of an inne…
Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle ($i$), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high $i$) or as a barlens structure (at low $i$). We visually identify bars, boxy/peanut-s…
We study the shape and kinematics of simulated dwarf galaxy discs in the APOSTLE suite of $Λ$CDM cosmological hydrodynamical simulations. We find that a large fraction of these gas-rich, star-forming discs show weak bars in their stellar component, despite being dark matter-dominated systems. The bar pattern shape and orientation reflect the ellipticity of the dark matter potential, and its rotation is locked to the slow figure rotation of the triaxial dark halo. The bar-like nature of the potential induces non-circular motions in the gas component, including strong bisymmetric flows that can …
Applying spectral dynamics methods to one typical $N$-body model with a barlens, we dissect the modelled bar into separate components supported by completely different types of orbits. We identify at least four components: a narrow elongated bar, a boxy bar, and two components contributing to the barlens. We analyse the vertical structure of all components that make up the thick part of the bar, which has a boxy/peanut shape (B/P bulge). We show that the `peanut' shape is mainly due to the orbits that assemble the boxy part of the face-on bar. We associate the X-shape with the narrow and elong…
We have obtained two-dimensional velocity fields in the ionized gas of a set of 8 double-barred galaxies, at high spatial and spectral resolution, using their H$α$ emission fields measured with a scanning Fabry-Perot spectrometer. Using the technique by which phase reversals in the non-circular motion indicate a radius of corotation, taking advantage of the high angular and velocity resolution we have obtained the corotation radii and the pattern speeds of both the major bar and the small central bar in each of the galaxies; there are few such measurements in the literature. Our results show t…
An important dynamic parameter of barred galaxies is the bar pattern speed. Among several methods that are used for the determination of the pattern speed the Tremaine-Weinberg method has the advantage of model independency and accuracy. In this work we apply the method to a simulated bar including gas dynamics and study the effect of 2D spectroscopy data quality on robustness of the method. We added a white noise and a Gaussian random field to the data and measured the corresponding errors in the pattern speed. We found that a signal to noise ratio in surface density ~5 introduces errors of ~…
Fountain pattern of baryon cycle revealed in galaxy ecosystems
University of Science and Technology of China（中国科学技术大学）；Nanjing University（南京大学）；University of Massachusetts, Amherst（马萨诸塞大学阿默斯特分校）；Nanjing Normal University（南京师范大学）；Xiamen University（厦门大学）；Durham University（杜伦大学）
We report idealized simulations that mimic the growth of galaxy disks embedded in responsive halos and bulges. The disks manifested an almost overwhelming tendency to form strong bars that we found very difficult to prevent. We found that fresh bars formed in growing disks after we had destroyed the original, indicating that bar formation also afflicts continued galaxy evolution, and not just the early stages of disk formation. This behavior raises still more insistently the previously unsolved question of how some galaxies avoid bars. Since our simulations included only collisionless star and…
The MaNGA project has obtained IFU data for several thousand nearby galaxies, including barred galaxies. With the two dimensional spectral and kinematic information provided by IFUs, we can measure the pattern speed of a barred galaxy, which determines the bar dynamics. We apply the non-parametric method proposed by Tremaine \& Weinberg to estimate the bar pattern speed for 53 barred galaxies, making this the largest sample studied so far in this way. Our sample is selected from the MaNGA first public data release as part of SDSS Data Release 13 according mainly to the axis ratio and position …
Star formation activity depends on galactic-scale environments. To understand the variations in star formation activity, comparing the properties of giant molecular clouds (GMCs) among environments with different star formation efficiency (SFE) is necessary. We thus focus on a strongly barred galaxy to investigate the impact of the galactic environment on the GMCs properties, because the SFE is clearly lower in bar regions than in arm regions. In this paper, we present the $^{12}$CO($1-0$) observations toward the western bar, arm and bar-end regions of the strongly barred galaxy NGC1300 with A…
What drives bar rotation? The effect of internal properties and galaxy interactions on bar pattern speeds
Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；Department of Physics, Durham University（杜伦大学物理系）；Institute of Computational Cosmology, Department of Physics, Durham University（杜伦大学物理学院计算宇宙学研究所）
The effects of bar strength and kinematics on galaxy evolution II: The global and local impacts of slow-strong bars
Haverford College（哈弗福德学院）；University of California Santa Cruz（加州大学圣克鲁兹分校）；University of Oxford（牛津大学）；University of Toronto（多伦多大学）；Lancaster University（兰开斯特大学）
Observations and simulations of barred spiral galaxies have shown that, in general, the spiral arms rotate at a different pattern speed to that of the bar. The main conclusion from the bibliography is that the bar rotates faster than the spiral arms with a double or even a triple value of angular velocity. The theory that prevails in explaining the formation of the spiral arms in the case of a barred spiral galaxy with two pattern speeds is the manifold theory, where the orbits that support the spiral density wave are chaotic, and are related to the manifolds emanating from the Lagrangian poin…
Most secular effects produced by stellar bars strongly depend on the pattern speed. Unfortunately, it is also the most difficult observational parameter to estimate. In this work, we measured the bar pattern speed of 97 Milky-Way Analogue galaxies from the MaNGA survey using the Tremaine-Weinberg method. The sample was selected by constraining the stellar mass and morphological type. We improve our measurements by weighting three independent estimates of the disc position angle. To recover the disc rotation curve, we fit a kinematic model to the H$_α$ velocity maps correcting for the non-circu…
We report the discovery of a bar, a pseudobulge and unresolved point source in the archetype collisional ring galaxy Cartwheel using careful morphological analysis of a near-infrared (NIR) K$_s$ band image of excellent quality (seeing=0.42\arcsec) at the ESO archive. The bar is oval-shaped with a semi-major axis length of 3.23\arcsec\($\sim$2.09~kpc), with almost a flat light distribution along it. The bulge is almost round (ellipticity=0.21) with an effective radius of 1.62\arcsec\ ($\sim$1.05~kpc) and a Sersic index of 0.99, parameters typical of pseudobulges in late-type galaxies. The newly…
We present near--infrared (NIR) imaging of FBQS J164442.5+261913, one of the few $γ$--ray emitting Narrow Line Seyfert 1 ($γ-$NLSy1) galaxies detected at high significance level by $Fermi$--LAT. This study is the first morphological analysis performed of this source and the third performed of this class of objects. Conducting a detailed two--dimensional modeling of its surface brightness distribution and analysing its $J-K_s$ colour gradients, we find that FBQS J164442.5+261913 is statistically most likely hosted by a barred lenticular galaxy (SB0). We find evidence that the bulge in the host …
Discovery of a Barred-Spiral Galaxy at $z_{spec}$ = 3.16 II. The Star Formation History
University of Washington（华盛顿大学）；University of Massachusetts Amherst（马萨诸塞大学阿默斯特分校）；University of Pittsburgh（匹兹堡大学）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CAB），西班牙国家科学研究委员会-国家航空航天技术研究所）；University of Wisconsin, Madison（威斯康星大学麦迪逊分校）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡弗里天体物理学与空间研究学院）
Stellar bars are a common morphological feature of spiral galaxies. While it is known that they can form in isolation, or be induced tidally, few studies have explored the production of stellar bars in galaxy merging. We look to investigate bar formation in galaxy merging using methods from deep learning to analyse our N-body simulations. The primary aim is to determine the constraints on the mass ratio and orientations of merging galaxies that are most conducive to bar formation. We further aim to explore whether it is possible to classify simulated barred spiral galaxies based on the mechani…
It has been suggested that a resonance between a rotating bar and stars in the solar neighbourhood can produce the so called 'Hercules stream'. Recently, a second bar may have been identified in the Galactic centre, the so called 'long bar', which is longer and much flatter than the traditional Galactic bar, and has a similar mass. We looked at the dynamical effects of both bars, separately and together, on orbits of stars integrated backwards from local position and velocities, and a model of the Galactic potential which includes the bars directly. Both bars can produce Hercules like features…
We derive the circular velocity curves of the gaseous and stellar discs of UGC 4056, a giant barred galaxy with an active galactic nucleus (AGN). We analyse UGC 4056 using the 2D spectroscopy obtained within the framework of the Mapping Nearby Galaxies at APO (MaNGA) survey. Using images and the colour index g-r from the Sloan Digital Sky Survey (SDSS), we determined the tilt of the galaxy, which allows us to conclude that the galaxy rotates clockwise with trailing spiral arms. We found that the gas motion at the central part of the UGC 4056 shows peculiar features. The rotation velocity of th…
We present the detection of the kinetic Sunyaev-Zel'dovich effect (kSZE) signals from groups of galaxies as a function of halo mass down to $\log (M_{500}/{\rm M_\odot}) \sim 12.3$, using the {\it Planck} CMB maps and stacking about $40,000$ galaxy systems with known positions, halo masses, and peculiar velocities. The signals from groups of different mass are constrained simultaneously to take care of projection effects of nearby halos. The total kSZE flux within halos estimated implies that the gas fraction in halos is about the universal baryon fraction, even in low-mass halos, indicating t…
We present a disc-halo N-body model of the low surface brightness galaxy UGC 628, one of the few systems that harbours a "slow" bar with a ratio of corotation radius to bar length of $\mathcal{R} \equiv R_c/a_b \sim 2$. We select our initial conditions using SDSS DR10 photometry, a physically motivated radially variable mass-to-light ratio profile, and rotation curve data from the literature. A global bar instability grows in our submaximal disc model, and the disc morphology and dynamics agree broadly with the photometry and kinematics of UGC 628 at times between peak bar strength and the ons…
We study the bar pattern speeds and corotation radii of 225 barred galaxies, using IFU 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 n…
The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample w…
Recent galaxy observations show that star formation activity changes depending on galactic environments. In order to understand the diversity of galactic-scale star formation, it is crucial to understand the formation and evolution of giant molecular clouds in an extreme environment. We focus on observational evidence that bars in strongly barred galaxies lack massive stars even though quantities of molecular gas are sufficient to form stars. In this paper, we present a hydrodynamical simulation of a strongly barred galaxy, using a stellar potential which is taken from observational results of…
Previous work has related the Galactic bar to structure in the local stellar velocity distribution. Here we show that the bar also influences the spatial gradients of the velocity vector via the Oort constants. By numerical integration of test-particles we simulate measurements of the Oort C value in a gravitational potential including the Galactic bar. We account for the observed trend that C is increasingly negative for stars with higher velocity dispersion. By comparing measurements of C with our simulations we improve on previous models of the bar, estimating that the bar pattern speed is …
Starting from the 1970s, some relations connecting dark matter and baryons were discovered, such as the Tully-Fisher relation. However, many of the relations found in galaxies are quite different from that found in galaxy clusters. Here, we report two new mysterious universal relations connecting dark matter and baryons in both galaxies and galaxy clusters. The first relation indicates that the total dynamical mass of a galaxy or a galaxy cluster $M_{500}$ has a power-law relation with its total baryonic mass $M_b$ within the `virial region': $M_{500} \propto M_b^a$, with $a \approx 3/4$. The …
The method to study oscillating potentials of double bars, based on invariant loops, is introduced here in a new way, intended to be more intelligible. Using this method, I show how the orbital structure of a double-barred galaxy (nested bars) changes with the variation of nuclear bar's pattern speed. Not all pattern speeds are allowed when the inner bar rotates in the same direction as the outer bar. Below certain minimum pattern speed orbital support for the inner bar abruptly disappears, while high values of this speed lead to loops that are increasingly round. For values between these two …
Gravitational lensing is a powerful probe of the mass distribution of galaxy clusters and cosmology. However, accurate measurements of the cluster mass profiles are limited by uncertainties in cluster astrophysics. In this work, we present a physically motivated model of baryonic effects on the cluster mass profiles, which self-consistently takes into account the impact of baryons on the concentration as well as mass accretion histories of galaxy clusters. We calibrate this model using the Omega500 hydrodynamical cosmological simulations of galaxy clusters with varying baryonic physics. Our mo…
Accurate estimation of the merger timescale of galaxy clusters is important to understand the cluster merger process and further the formation and evolution of the large-scale structure of the universe. In this paper, we explore a baryonic effect on the merger timescale of galaxy clusters by using hydrodynamical simulations. We find that the baryons play an important role in accelerating the merger process. The merger timescale decreases with increasing the gas fraction of galaxy clusters. For example, the merger timescale is shortened by a factor of up to 3 for merging clusters with gas fract…
