Motions Of Galaxies Research Articles

Testing General Relativity through the E_{G} Statistic Using the Weyl Potential and Galaxy Velocities.

We combine measurements of galaxy velocities from galaxy surveys with measurements of the Weyl potential from the Dark Energy Survey to test the consistency of general relativity at cosmological scales. Taking the ratio of two model-independent observables-the growth rate of structure and the Weyl potential-we obtain new measurements of the E_{G} statistic with precision of 6.0-11.3% at four different redshifts. These measurements provide a considerable improvement to past measurements of E_{G}. They confirm the validity of general relativity at four redshifts, with a deviation of at most 1.6σ from the predicted values. Contrary to conventional methods that rely on a common galaxy sample with spectroscopic resolution to measure two types of correlations, we directly combine two observables that are independent of the galaxy bias. This provides a novel approach to testing the relation between the geometry of our Universe and the motion of galaxies with improved precision.

Dynamical friction in rotating ultralight dark matter galactic cores

Abstract Dynamical friction and stellar orbital motion in spiral galaxies with dark matter composed of ultralight bosons in the state of rotating Bose–Einstein condensate (BEC) are studied. It is found that the dynamical friction force is significantly affected by the topological charge of the vortex structure of the BEC core with the strongest effect at distances near the galactic center. It is also shown that the ultralight dark matter self-interaction plays an important role in studying the dynamical friction.

Carl Wirtz' Article From 1924 in Astronomische Nachrichten on the Radial Motions of Spiral Nebulae

ABSTRACTIn the year 1924, a paper by Carl Wirtz appeared in ‘Astronomische Nachrichten’, entitled ‘De Sitter's cosmology and the radial motion of spiral galaxies’. This paper and its author remained largely unnoticed by the community, but it seems to be the first cosmological interpretation of the redshift of galaxies as a time dilation effect and the expansion of the Universe. Edwin Hubble knew Wirtz' publications quite well. The modern reader would find Wirtz' own understanding diffuse and contradictory in some aspects, but that reflected the early literature on nebulae, to which he himself made important contributions. The 100th anniversary provides a good opportunity to present an English transcription to the community, which can be found in the appendix. This anniversary also provokes to ask for the present status of cosmology which many authors see in a crisis. From an observational viewpoint, it shall be illustrated that until today there is no consistent/convincing understanding of how the Universe evolved.

The Strength of Bisymmetric Modes in SDSS-IV/MaNGA Barred Galaxy Kinematics

The Sloan Digital Sky Survey-IV/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey data provide an unprecedented opportunity to study the internal motions of galaxies and, in particular, represent the largest sample of barred galaxy kinematic maps obtained to date. We present results from Nirvana, our nonaxisymmetric kinematic modeling code built with a physically motivated Bayesian forward modeling approach, which decomposes MaNGA velocity fields into first- and second-order radial and tangential rotational modes in a generalized and minimally supervised fashion. We use Nirvana to produce models and rotation curves for 1263 unique barred MaNGA galaxies and a matched unbarred control sample. We present our modeling approach, tests of its efficacy, and validation against existing visual bar classifications. Nirvana finds elevated noncircular motions in galaxies identified as bars in imaging, and bar position angles that agree well with visual measurements. The Nirvana-MaNGA barred and control samples provide a new opportunity for studying the influence of nonaxisymmetric internal disk kinematics in a large statistical sample.

Testing gravity through the distortion of time

The accelerated expansion of the Universe might be due to modifications in the laws of gravity on very large scales. We showed that standard tests of gravity based on the observed motions of galaxies are insufficient and must be extended by including measurements of another effect: the distortion of time.

On the Origin of Star Formation Quenching of Galaxies in Group Environments Using the NewHorizon Simulation

We study star formation (SF) quenching of satellite galaxies with M * > 107 M ⊙ within two low-mass groups (M vir = 1012.9 and 1012.7 M ⊙) using the NewHorizon simulation. We confirm that satellite galaxies (M * ≲ 1010 M ⊙) are more prone to quenching than their field counterparts. This quenched fraction decreases with increasing stellar mass, consistent with recent studies. Similar to the findings in cluster environments, we note a correlation between the orbital motions of galaxies within these groups and the phenomenon of SF quenching. Specifically, SF is suppressed at the group center, and for galaxies with M * > 109.1 M ⊙, there is often a notable rejuvenation phase following a temporary quenching period. The SF quenching at the group center is primarily driven by changes in SF efficiency and the amount of gas available, both of which are influenced by hydrodynamic interactions between the interstellar medium and surrounding hot gas within the group. Conversely, satellite galaxies with M * < 108.2 M ⊙ experience significant gas removal within the group, leading to SF quenching. Our analysis highlights the complexity of SF quenching in satellite galaxies in group environments, which involves an intricate competition between the efficiency of SF (which depends on the dynamical state of the gas) on the one hand, and the availability of cold dense gas on the other hand. This challenges the typical understanding of environmental effects based on gas stripping through ram pressure, suggesting a need for a new description of galaxy evolution under mild environmental effects.

Kinematical Fluctuations Vary with Galaxy Surface Mass Density

The Galaxy inner parts are generally considered to be optically symmetric, as well as kinematically symmetric for most massive early-type galaxies. At the lower-mass end, many galaxies contain lots of small patches in their velocity maps, causing their kinematics to be nonsmooth in small scales and far from symmetry. These small patches can easily be mistaken for measurement uncertainties and have not been well discussed. We used the comparison of observations and numerical simulations to demonstrate the small patches existence beyond uncertainties. For the first time we have found that the fluctuation degrees have an approximate inverse loglinear relation with the galaxy stellar surface mass densities. This tight relation among galaxies that do not show obvious optical asymmetry that traces environmental perturbations indicates that stellar motion in galaxies has inherent asymmetry besides external environment influences. The degree of the kinetic asymmetry is closely related to and constrained by the intrinsic properties of the host galaxy.

Evaluating bulk flow estimators for CosmicFlows–4 measurements

ABSTRACT For over a decade there have been contradictory claims in the literature about whether the local bulk flow motion of galaxies is consistent or in tension with the ΛCDM model. While it has become evident that systematics affect bulk flow measurements, systematics in the estimators have not been widely investigated. In this work, we thoroughly evaluate the performance of four estimator variants, including the Kaiser maximum likelihood estimator (MLE) and the minimum variance estimator (MVE). We find that these estimators are unbiased, however their precision may be strongly correlated with the survey geometry. Small biases in the estimators can be present leading to underestimated bulk flows, which we suspect are due to the presence of non-linear peculiar velocities. The uncertainty assigned to the bulk flows from these estimators is typically underestimated, which leads to an overestimate of the tension with ΛCDM. We estimate the bulk flow for the CosmicFlows–4 data and use mocks to ensure the uncertainties are appropriately accounted for. Using the MLE we find a bulk flow amplitude of 408 ± 165 kms−1 at a depth of $49\, \mathrm{Mpc} h^{-1}$, in reasonable agreement with ΛCDM. However using the MVE which can probe greater effective depths, we find an amplitude of 428 ± 108 kms−1 at a depth of $173\, \mathrm{Mpc} h^{-1}$, in tension with the model, having only a 0.11 per cent probability of obtaining a larger χ2. These measurements appear directed towards the Great Attractor region where more data may be needed to resolve tensions.

Study of structural parameters and systemic proper motion of Sextans dwarf spheroidal galaxy with Subaru Hyper Suprime-Cam data

ABSTRACT We use the Subaru Hyper Suprime-Cam (HSC) data to study structural parameters and systemic proper motion of the Sextans dwarf spheroidal galaxy at the heliocentric distance of 86 kpc, which is one of the most important targets for studies of dark matter nature and galaxy formation physics. Thanks to the superb image quality and wide area coverage, the HSC data enable a secure selection of member star candidates based on the colour–magnitude cut, yielding about 10 000 member candidates at magnitudes down to i ∼ 24. We use a likelihood analysis of the two-dimensional distribution of stars to estimate the structural parameters of Sextans taking into account the contamination of foreground halo stars in the Milky Way, and find that the member star distribution is well fitted by an elliptical King profile with ellipticity ϵ ≃ 0.25 and the core and tidal radii of Rc = (368.4 ± 8.5) pc and Rt = (2.54 ± 0.046) kpc, respectively. Then using the two HSC data sets of 2.66 yr time baseline on average, we find the systemic proper motions of Sextans to be (μα, μδ) = (−0.448 ± 0.075, 0.058 ± 0.078) mas yr−1, which are consistent with some of the previous works using the Gaia data of relatively bright member stars in Sextans. Thus, our results give a demonstration that ground-based, large-aperture telescope data that cover a wide solid angle of the sky and have a long time baseline, such as the upcoming data from Legacy Survey of Space and Time (LSST), can be used to study systemic proper motions of dwarf galaxies.

Galaxy cluster rotation revealed in the MACSIS simulations with the kinetic Sunyaev–Zeldovich effect

ABSTRACT The kinetic Sunyaev–Zeldovich (kSZ) effect has now become a clear target for ongoing and future studies of the cosmic microwave background (CMB) and cosmology. Aside from the bulk cluster motion, internal motions also lead to a kSZ signal. In this work, we study the rotational kSZ effect caused by coherent large-scale motions of the cluster medium using cluster hydrodynamic cosmological simulations. To utilize the rotational kSZ as a cosmological probe, simulations offer some of the most comprehensive data sets that can inform the modelling of this signal. In this work, we use the MACSIS data set to investigate the rotational kSZ effect in massive clusters specifically. Based on these models, we test stacking approaches and estimate the amplitude of the combined signal with varying mass, dynamical state, redshift, and map-alignment geometry. We find that the dark matter, galaxy and gas spins are generally misaligned, an effect that can cause a suboptimal estimation of the rotational kSZ effect when based on galaxy motions. Furthermore, we provide halo-spin–mass scaling relations that can be used to build a statistical model of the rotational kSZ. The rotational kSZ contribution, which is largest in massive unrelaxed clusters (≳100 $\mu$K), could be relevant to studies of higher order CMB temperature signals, such as the moving lens effect. The limited mass range of the MACSIS sample strongly motivates an extended investigation of the rotational kSZ effect in large-volume simulations to refine the modelling, particularly towards lower mass and higher redshift, and provide forecasts for upcoming cosmological CMB experiments (e.g. Simons Observatory, SKA-2) and X-ray observations (e.g. Athena/X-IFU).

A new framework for understanding the evolution of early-type galaxies

Context. We have recently suggested that the combination of the scalar virial theorem (Ms ∝ Reσ2) and the L = L0′σβ law, with L0′ and β changing from galaxy to galaxy (and with time), can provide a new set of equations valid for investigating the evolution of early-type galaxies. These equations are able to account for the tilt of the fundamental plane and to explain the observed distributions of early-type galaxies in all its projections. Aims. In this paper we analyze the advantages offered by these equations, derive the β and L0′ parameters for real and simulated galaxies, and demonstrate that depending on the value of β galaxies can move only along some permitted directions in the fundamental plane projections. Then we show that simple galaxy models that grow in mass by infall of gas and form stars with a star formation rate depending on the stellar velocity dispersion nicely reproduce the observed distributions of early-type galaxies in the fundamental plane projections and yield βs that agree with the measured values. Methods. We derive the mutual relationships among the stellar mass, effective radius, velocity dispersion, and luminosity of early-type galaxies as a function of β and calculate the coefficients of the fundamental plane. Then, using the simple infall models, we show that the star formation history of early-type galaxies is compatible with the σ-dependent star formation rate, and that both positive and negative values of β are possible in a standard theory of galaxy evolution. Results. The parameter β(t) offers a new view of the evolution of early-type galaxies. In brief, it gives a coherent interpretation of the fundamental plane and of the motions of galaxies in its projections; it is the fingerprint of their evolution; it measures the degree of virialization of early-type galaxies; and finally it allows us to infer their evolution in the near past.

Measuring the ICM velocity structure in the Ophiuchus cluster

ABSTRACT We have found evidence of bulk velocities following active galactic nucleus (AGN) bubbles in the Virgo cluster and galaxy motions in the Centaurus cluster. In order to increase the sample and improve our understanding of the intracluster medium (ICM), we present the results of a detailed mapping of the Ophiuchus cluster with XMM–Newton to measure bulk flows through very accurate Fe-K measurements. To measure the gas velocities, we use a novel EPIC-pn energy-scale calibration, which uses the Cu Kα instrumental line as reference for the line emission. We created 2D spectral maps for the velocity, metallicity, temperature, density, entropy, and pressure with a spatial resolution of 0.25 arcmin (∼26 kpc). The ICM velocities in the central regions where AGN feedback is most important are similar to the velocity of the brightest cluster galaxy. We have found a large interface region where the velocity changes abruptly from blueshifted to redshifted gas that follows a sharp surface brightness discontinuity. We also found that the metallicities and temperatures do not change as we move outwards from the giant radio fossil previously identified in radio observations of the cluster. Finally, we have found a contribution from the kinetic component of $\lt 25{{\ \rm per\ cent}}$ to the total energy budget for large distances.

A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Turbulence driven by active galactic nuclei activity, cluster mergers, and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. proposed a viable heating mechanism based on the anisotropy of the plasma pressure under ICM conditions. The present paper builds upon that work and shows that particles can be heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated, and demonstrate that the particle distribution function acquires a high-energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field B (t). When B (t) grows (dwindles), a pressure anisotropy P ⊥ > P ∥(P ⊥ < P ∥) builds up (P ⊥ and P ∥ are, respectively, the pressures perpendicular and parallel to B (t)). These pressure anisotropies excite mirror (P ⊥ > P ∥) and oblique firehose (P ∥ > P ⊥) instabilities, which trap and scatter the particles, limiting the anisotropy, and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.

Model-independent test for gravity using intensity mapping and galaxy clustering

We propose a novel method to measure the $E_G$ statistic from clustering alone. The $E_G$ statistic provides an elegant way of testing the consistency of General Relativity by comparing the geometry of the Universe, probed through gravitational lensing, with the motion of galaxies in that geometry. Current $E_G$ estimators combine galaxy clustering with gravitational lensing, measured either from cosmic shear or from CMB lensing. In this paper, we construct a novel estimator for $E_G$, using only clustering information obtained from two tracers of the large-scale structure: intensity mapping and galaxy clustering. In this estimator, both the velocity of galaxies and gravitational lensing are measured through their impact on clustering. We show that with this estimator, we can suppress the contaminations that affect other $E_G$ estimators and consequently test the validity of General Relativity robustly. We forecast that with the coming generation of surveys like HIRAX and Euclid, we will measure $E_G$ with a precision of up to 7% (3.9% for the more futuristic SKA2).

Relative velocity in pseudo-Riemannian spacetime

We give a coordinate independent definition of relative velocity of test particle in pseudo-Riemannian spacetime as measured along the observer’s line-of-sight in general and several instructive cases. In doing this, the test particle is considered as a luminous object, otherwise, if it is not, we assume that a light source is attached to it, which has neither mass nor volume. Then we utilize the general solution of independent definition of relative velocity of a luminous source in generic pseudo-Riemannian spacetime. As a corollary, we discuss the implications for the Minkowski metric, the test particle and observer at rest in an arbitrary stationary metric, the uniform gravitational field, the rotating reference frame, the Schwarzschild metric, the Kerr-type metrics, and the spatially homogeneous and isotropic Robertson-Walker (RW) spacetime of standard cosmological model. In the last case, it leads to cosmological consequence that the resulting, so-called, kinetic recession velocity of an astronomical object is always subluminal even for large redshifts of order one or more, so that it does not violate the fundamental physical principle of causality. We also calculate the measure of carrying away of a galaxy at redshift z by the expansion of space, which proves, in particular, that cosmological expansion of a flat 3D–space is fundamentally different from a kinematics of galaxies moving in a non-expanding flat 3D-space. So, it is impossible to mimic the true cosmological redshift by a Doppler effect caused by motion of galaxies in a non-expanding 3D-space, flat or curved. We also give a reappraisal of the `standard ́ kinematic interpretation of redshifts in RW spacetime as accumulated Doppler-shifts.

Testing modified gravity scenarios with direct peculiar velocities

ABSTRACT The theoretical basis of dark energy remains unknown and could signify a need to modify the laws of gravity on cosmological scales. In this study, we investigate how the clustering and motions of galaxies can be used as probes of modified gravity theories, using galaxy and direct peculiar velocity auto- and cross-correlation functions. We measure and fit these correlation functions in simulations of ΛCDM, DGP, and f(R) cosmologies and, by extracting the characteristic parameters of each model, we show that these theories can be distinguished from General Relativity (GR) using these measurements. We present forecasts showing that with sufficiently large data samples, this analysis technique is a competitive probe that can help place limits on allowed deviations from GR. For example, a peculiar velocity survey reaching to z = 0.5 with $20{{\ \rm per\ cent}}$ distance accuracy would constrain model parameters to 3-σ confidence limits log10|fR0| &amp;lt; −6.45 for f(R) gravity and $r_\mathrm{ c} \gt 2.88 \, \mathrm{ c}/H_0$ for nDGP, assuming a fiducial GR model.

Excitation of vertical breathing motion in disc galaxies by tidally-induced spirals in fly-by interactions

ABSTRACT It is now clear that the stars in the Solar neighbourhood display large-scale coherent vertical breathing motions. At the same time, Milky Way-like galaxies experience tidal interactions with satellites/companions during their evolution. While these tidal interactions can excite vertical oscillations, it is still not clear whether vertical breathing motions are excited directly by the tidal encounters or are driven by the tidally-induced spirals. We test whether excitation of breathing motions are directly linked to tidal interactions by constructing a set of N-body models (with mass ratio 5:1) of unbound single fly-by interactions with varying orbital configurations. We first reproduce the well-known result that such fly-by interactions can excite strong transient spirals (lasting for ${\sim}2.9{-}4.2\,{\rm Gyr}$) in the outer disc of the host galaxy. The generation and strength of the spirals are shown to vary with the orbital parameters (the angle of interaction, and the orbital spin vector). Furthermore, we demonstrate that our fly-by models exhibit coherent breathing motions whose amplitude increases with height. The amplitudes of breathing motions show characteristic modulation along the azimuthal direction with compressing breathing motions coinciding with the peaks of the spirals and expanding breathing motions falling in the inter-arm regions – a signature of a spiral-driven breathing motion. These breathing motions in our models end when the strong tidally-induced spiral arms fade away. Thus, it is the tidally-induced spirals which drive the large-scale breathing motions in our fly-by models, and the dynamical role of the tidal interaction in this context is indirect.

Unexpected Dancing Partners: Tracing the Coherence between the Spin and Motion of Dark Matter Halos

A recent study conducted using CALIFA survey data has found that the orbital motions of neighbor galaxies are coherent with the spin direction of a target galaxy on scales of many megaparsecs. We study this so-called “large-scale coherence” phenomenon using N-body cosmological simulations. We confirm a strong coherence signal within 1 Mpc h −1 of a target galaxy, reaching out to 6 Mpc h −1. We divide the simulation halos into subsamples based on mass, spin, merger history, and local halo number density for both target and neighbor halos. We find a clear dependency on the mass of the target halo only. Another key parameter is the local number density of both target and neighbor halos, with high-density regions such as clusters and groups providing the strongest coherence signals, rather than filaments or lower-density regions. However we do not find a clear dependency on halo spin or time since last major merger. The most striking result we find is that the signal can be detected up to 15 Mpc h −1 from massive halos. These results provide valuable lessons on how observational studies could more clearly detect coherence, and we discuss the implications of our results for the origins of large-scale coherence.

Star and Black Hole Formation at High Redshift

Evidence for dark matter (DM) was originally discovered in 1933 by Zwicky (Zwicky 1933, 1937), and has defied all explanations since then. The original discovery was based on the motions of galaxies in clusters of galaxies. The MicroWave Back Ground (MWBG) observations by the Planck mission and other satellites give definitive numbers. Galaxy correlations give results down to small galaxies, which match theoretical expectations. Here we focus on a few interesting aspects, that may allow to determine the nature of dark matter: (1) Ultra Faint Dwarf (UFD) galaxies, that represent the oldest galaxies known. UFDs are almost devoid of baryonic matter. (2) Calculations show that there can be super-sonic flow of baryonic matter. It follows that there are ubiquitous shockwaves; commonly oblique they generate vorticity. (3) Early virialized clumps, mini-halos, have a density that is consistent with the density implied by Super Massive Black Holes (SMBHs) today, if we assume that SMBHs grow by merging, akin to the Press &amp; Schechter (1974) picture for galaxies. This implies that the oldest SMBHs observed today give powerful constraints on the very early phases.

Large-scale gas flows and streaming motions in simulated spiral galaxies

ABSTRACT From a galactic perspective, star formation occurs on the smallest scales within molecular clouds, but it is likely initiated from the large-scale flows driven by galactic dynamics. To understand the conditions for star formation, it is important to first discern the mechanisms that drive gas from large scales into dense structures on the smallest scales of a galaxy. We present high-resolution smoothed particle hydrodynamics simulations of two model spiral galaxies: one with a live stellar disc (N-body) and one with a spiral potential. We investigate the large-scale flows and streaming motions driven by the simulated spiral structure. We find that the strength of the motions in the radial direction tends to be higher than in the azimuthal component. In the N-body model, the amplitude of these motions decreases with galactocentric radius whereas for the spiral potential, it decreases to a minimum at the corotation radius, and increases again after this point. The results show that in both simulations, the arms induce local shocks, an increase in kinetic energy that can drive turbulence and a means of compressing and expanding the gas. These are all crucial elements in forming molecular clouds and driving the necessary conditions for star formation.