Galaxies follow a tight radial acceleration relation (RAR): the acceleration observed at every radius correlates with that expected from the distribution of baryons. We use the Markov chain Monte ...Carlo method to fit the mean RAR to 175 individual galaxies in the SPARC database, marginalizing over stellar mass-to-light ratio (ϒ⋆), galaxy distance, and disk inclination. Acceptable fits with astrophysically reasonable parameters are found for the vast majority of galaxies. The residuals around these fits have an rms scatter of only 0.057 dex (~13%). This is in agreement with the predictions of modified Newtonian dynamics (MOND). We further consider a generalized version of the RAR that, unlike MOND, permits galaxy-to-galaxy variation in the critical acceleration scale. The fits are not improved with this additional freedom: there is no credible indication of variation in the critical acceleration scale. The data are consistent with the action of a single effective force law. The apparent universality of the acceleration scale and the small residual scatter are key to understanding galaxies.
The Milky Way and Andromeda galaxies are each surrounded by a thin plane of satellite dwarf galaxies that may be corotating. Cosmological simulations predict that most satellite galaxy systems are ...close to isotropic with random motions, so those two well-studied systems are often interpreted as rare statistical outliers. We test this assumption using the kinematics of satellite galaxies around the Centaurus A galaxy. Our statistical analysis reveals evidence for corotation in a narrow plane: Of the 16 Centaurus A satellites with kinematic data, 14 follow a coherent velocity pattern aligned with the long axis of their spatial distribution. In standard cosmological simulations, <0.5% of Centaurus A-like systems show such behavior. Corotating satellite systems may be common in the universe, challenging small-scale structure formation in the prevailing cosmological paradigm.
ABSTRACT In a Λ cold dark matter (ΛCDM) cosmology, the baryonic Tully-Fisher relation (BTFR) is expected to show significant intrinsic scatter resulting from the mass-concentration relation of dark ...matter halos and the baryonic-to-halo mass ratio. We study the BTFR using a sample of 118 disk galaxies (spirals and irregulars) with data of the highest quality: extended rotation curves (tracing the outer velocity) and Spitzer photometry at 3.6 m (tracing the stellar mass). Assuming that the stellar mass-to-light ratio ( ) is nearly constant at 3.6 m, we find that the scatter, slope, and normalization of the BTFR systematically vary with the adopted . The observed scatter is minimized for , corresponding to nearly maximal disks in high-surface-brightness galaxies and BTFR slopes close to ∼4. For any reasonable value of , the intrinsic scatter is ∼0.1 dex, below general ΛCDM expectations. The residuals show no correlations with galaxy structural parameters (radius or surface brightness), contrary to the predictions from some semi-analytic models of galaxy formation. These are fundamental issues for ΛCDM cosmology.
Abstract We present Wide-field Infrared Survey Explorer (WISE) W1 photometry of the Spitzer Photometry and Accurate Rotation Curves sample. The baseline of near-IR fluxes is established for use by ...stellar mass models, a key component to the baryonic Tully–Fisher relation and other kinematic galaxies scaling relations. We focus this paper on determination of the characteristics of the W1 fluxes compared to IRAC 3.6 μ m fluxes, internal accuracy limitations from photometric techniques, external accuracy by comparison to other work in the literature and the range of W1 to IRAC 3.6 μ m colors. We outline the behavior of SDSS g , W1 and IRAC 3.6 colors with respect to underlying spectral energy distribution features. We also note a previously unknown correlation between WISE colors and the central surface brightness, probably related to the low metallicity of low-surface-brightness dwarfs.
Cosmological models predict that galaxies forming in the early Universe experience a chaotic phase of gas accretion and star formation, followed by gas ejection due to feedback processes. Galaxy ...bulges may assemble later via mergers or internal evolution. Here we present submillimeter observations (with spatial resolution of 700 parsecs) of ALESS 073.1, a starburst galaxy at redshift Formula: see text when the Universe was 1.2 billion years old. This galaxy's cold gas forms a regularly rotating disk with negligible noncircular motions. The galaxy rotation curve requires the presence of a central bulge in addition to a star-forming disk. We conclude that massive bulges and regularly rotating disks can form more rapidly in the early Universe than predicted by models of galaxy formation.
Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep ...FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.
Abstract We use a new deprojection formula to infer the gravitational potential around isolated galaxies from weak gravitational lensing. The results imply circular velocity curves that remain flat ...for hundreds of kiloparsecs, greatly extending the classic result from 21 cm observations. Indeed, there is no clear hint of a decline out to 1 Mpc, well beyond the expected virial radii of dark matter halos. Binning the data by mass reveals a correlation with the flat circular speed that closely agrees with the baryonic Tully–Fisher relation known from kinematic data. These results apply to both early- and late-type galaxies, indicating a common universal behavior.
We explore the use of the baryonic Tully-Fisher relation (bTFR) as a new distance indicator. Advances in near-IR imaging and stellar population models, plus precise rotation curves, have reduced the ...scatter in the bTFR such that distance is the dominant source of uncertainty. Using 50 galaxies with accurate distances from Cepheids or the tip magnitude of the red giant branch, we calibrate the bTFR on a scale independent of Ho. We then apply this calibrated bTFR to 95 independent galaxies from the SPARC sample, using CosmicFlows-3 velocities, to deduce the local value of Ho. We find Ho = 75.1 2.3 (stat) 1.5 (sys) km s−1 Mpc−1.
For disk galaxies (spirals and irregulars), the inner circular-velocity gradient dRV0 (inner steepness of the rotation curve) correlates with the central surface brightness ∑*,0 with a slope of ~0.5. ...This implies that the central dynamical mass density scales almost linearly with the central baryonic density. Here I show that this empirical relation is consistent with a simple model where the central baryonic fraction ƒbar,0 is fixed to 1 (no dark matter) and the observed scatter is due to differences in the baryonic mass-to-light ratio Mbar / LR (ranging from 1 to 3 in the R-band) and in the characteristic thickness of the central stellar component Δz (ranging from 100 to 500 pc). Models with lower baryonic fractions are possible, although they require some fine-tuning in the values of Mbar/LR and Δz. Regardless of the actual value of ƒbar,0, the fact that different types of galaxies do not show strong variations in ƒbar,0 is surprising, and may represent a challenge for models of galaxy formation in a Λ Cold Dark Matter (ΛCDM) cosmology.
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