Tens of early type galaxies have been recently reported to possess prolate rotation, i.e. significant amount of rotation around the major axis, including two cases in the Local Group. Although expected theoretically, this phenomenon is rarely observed and remains elusive. In order to explore its origin we study the population of well-resolved galaxies in the Illustris cosmological simulation. We identify 59 convincing examples of prolate rotators at the present time, more frequently among more massive galaxies, with the number varying very little with redshift. We follow their evolution back in time using the main progenitor branch galaxies of the Illustris merger trees. We find that the emergence of prolate rotation is strongly correlated with the time of the last significant merger the galaxy experienced, although other evolutionary paths leading to prolate rotation are also possible. The transition to prolate rotation most often happens around the same time as the transition to prolate shape of the stellar component. The mergers leading to prolate rotation have slightly more radial orbits, higher mass ratios, and occur at more recent times than mergers in the reference sample of twin galaxies we construct for comparison. However, they cover a wide range of initial conditions in terms of the mass ratio, merger time, radiality of the progenitor orbits, and the relative orientations of spins of the progenitors with respect to the orbital angular momenta. About half of our sample of prolate rotators were created during gas-rich mergers and the newly formed stars usually support prolate rotation.
We explore orbit properties of 35 prolate-triaxial galaxies selected from the Illustris cosmological hydrodynamic simulation. We present a detailed study of their orbit families, and also analyse relations between the relative abundance of the orbit families and the spin parameter, triaxiality, the ratio of the angular momentum and the baryon fraction. We find that box orbits dominate the orbit structure for most prolate-triaxial galaxies, especially in the central region. The fraction of irregular orbits in the prolate-triaxial galaxies is small, and it increases with galaxy radius. Both the …
The distribution of three dimensional intrinsic galaxy shapes has been a longstanding open question. The difficulty stems from projection effects meaning one must rely on statistical methods applied to galaxy samples to infer intrinsic shape distributions. Theoretical work using analytical galaxy potentials suggests a relationship between galaxy intrinsic shape (as defined by its "triaxiality", in practice a proxy for how prolate a galaxy is) and the intrinsic misalignment angle between kinematic and morphological axes ($Ψ_{\rm int}$). This relationship reduces the number of unknowns, providin…
Many recent integral integral field spectroscopy (IFS) survey teams have used stellar kinematic maps combined with imaging to statistically infer the underlying distributions of galaxy intrinsic shapes. With now several IFS samples at our disposal, the method, which was originally proposed by M. Franx and collaborators in 1991, is gaining in popularity, having been so far applied to ATLAS3D, SAMI, MANGA and MASSIVE. We present results showing that a commonly assumed relationship between dynamical and intrinsic shape alignment does not hold in Illustris, affecting our ability to recover accurat…
Stellar prolate rotation in dwarf galaxies is rather uncommon, with only two known galaxies in the Local Group showing such feature (Phoenix and And II). Cosmological simulations show that in massive early-type galaxies prolate rotation likely arises from major mergers. However, the origin of such kinematics in the dwarf galaxies regime has only been explored using idealized simulations. Here we made use of hydrodynamical cosmological simulations of dwarfs galaxies with stellar mass between $3\times10^5$ and $5\times10^8$ M$_{\odot}$ to explore the formation of prolate rotators. Out of $27$ dw…
A small fraction of early-type galaxies (ETGs) show prolate rotation, i.e. they rotate around their long photometric axis. In simulations, certain configurations of galaxy mergers are known to produce this type of rotation. We investigate the association of prolate rotation and signs of galaxy interactions among the observed galaxies. We collected a sample of 19 nearby ETGs with distinct prolate rotation from the literature and inspected their ground-based deep optical images for interaction signs - 18 in archival images and one in a new image obtained with the Milanković telescope. Tidal tail…
We present the stellar velocity maps of 25 massive early type galaxies located in dense environments observed with MUSE. Galaxies are selected to be brighter than M_K=-25.7 magnitude, reside in the core of the Shapley Super Cluster or be the brightest galaxy in clusters richer than the Virgo Cluster. We thus targeted galaxies more massive than 10^12 Msun and larger than 10 kpc (half-light radius). The velocity maps show a large variety of kinematic features: oblate-like regular rotation, kinematically distinct cores and various types of non-regular rotation. The kinematic misalignment angles s…
In this work, we analyze a sample of $\sim$4000 massive ($M_*\geq 10^{11} M_\odot$ at $z=0$) galaxies in TNG300, the $(300 \mathrm{Mpc})^3$ box of the IllustrisTNG simulation suite. We characterize the shape and kinematics of these galaxies with a focus on the kinematic misalignment ($Ψ_\mathrm{int}$) between the angular momentum (AM) and morphological major axis. We find that the traditional purely shape- or kinematics-based classifications are insufficient to characterize the diversity of our sample and define a new set of classes based on the rates of change of the galaxies' morphological a…
We have carried out a controlled comparison of the structural and kinematic properties of the circumgalactic medium (CGM) around Milky Way mass galaxies in the Illustris and IllustrisTNG simulations. Very striking differences are found. At z=0, gas column density and temperature profiles at large radii ($\sim 100$ kpc) correlate strongly with disk gas mass fraction in Illustris, but not in TNG. The neutral gas at large radii is preferentially aligned in the plane of the disk in TNG, whereas it is much more isotropic in Illustris. The vertical coherence scale of the rotationally supported gas i…
Prolate rotation (i.e. rotation around the long axis) has been reported for two Local Group dwarf galaxies: Andromeda II, a dwarf spheroidal satellite of M31, and Phoenix, a transition type dwarf galaxy. The prolate rotation may be an exceptional indicator of a past major merger between dwarf galaxies. We showed that this type of rotation cannot be obtained in the tidal stirring scenario, in which the satellite is transformed from disky to spheroidal by tidal forces of the host galaxy. However, we successfully reproduced the observed Andromeda II kinematics in controlled, self-consistent simul…
We use the Illustris simulation to study the distributions of ellipticities and kinematic misalignments of galactic projections, as well as the intrinsic shapes and rotation of the simulated galaxies. Our results for the projections of galaxies display clear trends of an overall increase of kinematic misalignment and a slight decrease of ellipticity for fast rotators with increasing masses, while revealing no clear distinction between slow rotators of different mass. It is also found that the number of very slow rotators with large ellipticities is much larger than found in observations. The i…
We analyze the kinematics as a function of stellar age for Andromeda (M31) mass analogs from the IllustrisTNG cosmological simulation. We divide the star particles into four age groups: less than 1 Gyr, 1 to 5 Gyr, 5 to 10 Gyr, and greater 10 Gyr, and compare the kinematics of these groups to that of the neutral gas cells. We calculate rotation curves for the stellar and gaseous components of each analog from 2 kpc to 20 kpc from the center of mass. We find that the lag, or asymmetric drift (AD), between the gas rotation curve and the stellar rotation curve on average increases with stellar ag…
We investigated, through numerical models, the flaring variability that may arise from the rotation of maser clouds of approximately spheroidal geometry, ranging from strongly oblate to strongly prolate examples. Inversion solutions were obtained for each of these examples over a range of saturation levels from unsaturated to highly saturated. Formal solutions were computed for rotating clouds with many randomly chosen rotation axes, and corresponding averaged maser light curves plotted with statistical information. The dependence of results on the level of saturation and on the degree of defo…
In this paper we derive a novel circular velocity relation for a test particle in a 3D gravitational potential applicable to every system of curvilinear coordinates, suitable to be reduced to orthogonal form. As an illustration of the potentiality of the determined circular velocity expression we perform the rotation curves analysis of UGC 8490 and UGC 9753 and we estimate the total and dark matter mass of these two galaxies under the assumption that their respective dark matter halos have spherical, prolate and oblate spheroidal mass distributions. We employ stellar population synthesis model…
The connection between surface brightness and satellite systems for central galaxies through Illustris TNG
Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba（科尔多瓦天文台，科尔多瓦国立大学）；Instituto de Astronomía Teórica y Experimental, UNC-CONICET（理论与实验天体物理研究所，科尔多瓦国立大学-阿根廷国家科学研究委员会）；Department of Physics and Astronomy, University of California, Riverside（物理学与天文学系，加州大学河滨分校）；Instituto de Astronomía y Física del Espacio, CONICET-UBA（空间天体物理与物理学研究所，阿根廷国家科学研究委员会-布宜诺斯艾利斯大学）；Instituto de Astrofísica, Pontificia Universidad Católica de Chile（天体物理研究所，智利天主教 Pontificia 大学）
We investigate the disc-halo connection in massive (Mstar/Msun>5e10) disc galaxies from the cosmological hydrodynamical simulations EAGLE and IllustrisTNG, and compare it with that inferred from the study of HI rotation curves in nearby massive spirals from the Spitzer Photometry and Accurate Rotation Curves (SPARC) dataset. We find that discrepancies between the the simulated and observed discs arise both on global and on local scales. Globally, the simulated discs inhabit halos that are a factor ~4 (in EAGLE) and ~2 (in IllustrisTNG) more massive than those derived from the rotation curve an…
We propose a simple geometrical mechanism for the flattening of galactic rotation curves, the local compression of field lines around their planes induced either by the presence of thin string-like objects at the centers of galaxies or by elongated dark-matter halos, and elaborate on its possible role in Nature. We fit 83 rotation curves from the SPARC database with logarithmic potentials produced by a thin "wire" at the origin and then, after selecting 2 galaxies that yield the most interesting fits, analyze them with an alternative model, deformed versions of two popular models of dark-matte…
Evolution of Galaxy Shapes from Prolate to Oblate through Compaction Events
我们使用宇宙学模拟研究星系整体形状的演化。这些形状是指暗物质、恒星和气体在恒星半质量半径处的组成部分。大多数星系在$z\sim2-4$经历了一个特征性的压缩事件，成为一个蓝块，这标志着从DM主导的中心体到自引力重子核的转变。我们发现，在高- $z$，DM占主导地位的阶段，恒星和DM系统往往是三轴，优先长轴和相互对齐。伸长是由各向异性的速度分散，起源于沿占主导地位的大尺度灯丝星系的组装支持。我们估计，扭矩的主导晕是能够诱导伸长的恒星系统和它的晕对齐。然后，与过渡到自引力，小近心轨道膨胀和DM和恒星系统演变成一个更球形和扁圆形的配置，与气体盘对齐，并与旋转相关。这种转变通常发生在恒星质量为$\sim 10^9$ M $_\odot$，核心逃逸速度为$\sim 100$ km s $^{-1}$时，这表明超新星反馈可能有效地保持核心DM主导和系统长扁。早期的拉长相本身可能是压实事件的原因，而向扁圆相的转变可能与随后的核心淬火有关。
We use a combination of data from the MaNGA survey and MaNGA-like observations in IllustrisTNG100 to determine the prevalence of misalignment between the rotational axes of stars and gas. This census paper outlines the typical characteristics of misaligned galaxies in both observations and simulations to determine their fundamental relationship with morphology and angular momentum. We present a sample of ~4500 galaxies from MaNGA with kinematic classifications which we use to demonstrate that the prevalence of misalignment is strongly dependent on morphology. The misaligned fraction sharply in…
We evaluate the capabilities of Schwarzschild's orbit-superposition method by applying it to galaxies from the large scale, high resolution Illustris simulation. Nine early-type galaxies with a range of triaxiality are selected, and we create mock integral field unit data for five line-of-sight projections of each galaxy. Each of the 45 mock data sets is taken as an independent observed galaxy. Using van den Bosch's 2008 triaxial Schwarzschild implementation, we assess model estimates of various galaxy properties, covering mass profiles, intrinsic shapes, stellar orbit distributions and veloci…
How mergers shape galaxy morphology in the IllustrisTNG simulation
The Chinese University of Hong Kong（香港中文大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；School of Physics and Microelectronics, Zhengzhou University（郑州大学物理与电气工程学院）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
The flattening of spiral-galaxy rotation curves is unnatural in view of the expectations from Kepler's third law and a central mass. It is interesting, however, that the radius-independence velocity is what one expects in one less dimension. In our three-dimensional space, the rotation curve is natural if, outside the galaxy's center, the gravitational potential corresponds to that of a very prolate ellipsoid, filament, string, or otherwise cylindrical structure perpendicular to the galactic plane. While there is observational evidence (and numerical simulations) for filamentary structure at l…
By inverting the distributions of galaxies' apparent ellipticities and misalignment angles (measured around the projected half-light radius $R_{\rm e}$) between their photometric and kinematic axes, we study the intrinsic shape distribution of 189 slow rotator early-type galaxies with stellar masses $2\times 10^{11} M_{\odot}<M_\ast<2\times 10^{12} M_{\odot}$, extracted from a sample of about 2200 galaxies with integral-field stellar kinematics from the DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow rotators, Graham+18 showed that there is clear structure in the misal…
We study the relationship between supermassive black hole (BH) feedback, BH luminosity and the kinematics of stars and gas for galaxies in IllustrisTNG. We use a sample of galaxies with mock MaNGA observations to identify kinematic misalignment at $z=0$ (difference in rotation of stars and gas), for which we follow the evolutionary history of BH activity and gas properties over the last 8 Gyrs. Misaligned low mass galaxies typically have boosted BH luminosity, BH growth and have had more energy injected into the gas over the last 8 Gyr in comparison to aligned galaxies. These properties likely…
On the kinematic nature of apparent discs at high redshifts: Local counterparts are not dominated by ordered rotation but by tangentially anisotropic random motion
In this thesis, we investigate some aspects of dark matter phenomenology and its predictive power in explaining the flattening of galaxy rotation curves at large distances. After outlining the Standard Model of particle physics, its symmetries and possible extensions in Chapter 2, we review key facts about dark matter and various types of dark matter models in Chapter 3. In Chapter 4 we discuss some alternatives to cold dark matter, which include modified Newtonian dynamics (MOND), superfluid dark matter and emergent gravity, and highlight the difficulties that are encountered in attempts to e…
