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Register a new userThe Link between the Baryonic Mass Distribution and the Rotation Curve Shape
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The observed rotation curves of disc galaxies, ranging from late-type dwarf galaxies to early-type spirals, can be fit remarkably well simply by scaling up the contributions of the stellar and HI discs. This `baryonic scaling model can explain the full breadth of observed rotation curves with only two free parameters. For a small fraction of galaxies, in particular early-type spiral galaxies, HI scaling appears to fail in the outer parts, possibly due to observational effects or ionization of the HI. The overall success of the baryonic scaling model suggests that the well-known global coupling between the baryonic mass of a galaxy and its rotation velocity (known as the baryonic Tully-Fisher relation), applies at a more local level as well, and it seems to imply a link between the baryonic mass distribution and the distribution of total mass (including dark matter).
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Over the last decade it has become clear that there is a decoupling between the old stellar disk and young stellar disk in spiral galaxies. This has led to a scheme for classifying galaxies on the basis of their near-infrared morphology. The near-infrared provides a more physical framework for classifying galaxies as it is both relatively free from extinction and it traces the old stellar population, i.e. the dominant stellar mass distribution. The `dust penetrated class is dependent upon the spiral pitch angle of arms. We have observed 8 galaxies with UFTI on UKIRT in the K-band in order to investigate the theoretical link between disk dynamics and arm morphology, which is suggested both from numerical models and the dust penetrated class. We find that the pitch angle of spiral arms, i, correlates well with the shear rate of rotation curves, $A/omega$ (where A is the first Oort constant and $omega$ is the rotational velocity), over the same radial range.
With the increasing numbers of large stellar survey projects, the quality and quantity of excellent tracers to study the Milky Way is rapidly growing, one of which is the classical Cepheids. Classical Cepheids are high precision standard candles with very low typical uncertainties ($<$ 3%) available via the mid-infrared period-luminosity relation. About 3500 classical Cepheids identified from OGLE, ASAS-SN, Gaia, WISE and ZTF survey data have been analyzed in this work, and their spatial distributions show a clear signature of Galactic warp. Two kinematical methods are adopted to measure the Galactic rotation curve in the Galactocentric distance range of $4lesssim R_{rm GC} lesssim 19$ kpc. Gently declining rotation curves are derived by both the proper motion (PM) method and 3-dimensional velocity vector (3DV) method. The largest sample of classical Cepheids with most accurate 6D phase-space coordinates available to date are modeled in the 3DV method, and the resulting rotation curve is found to decline at the relatively smaller gradient of ($-1.33pm0.1$) ${rm km,s^{-1},kpc^{-1}}$. Comparing to results from the PM method, a higher rotation velocity (($232.5pm0.83$) ${rm km,s^{-1}}$) is derived at the position of Sun in the 3DV method. The virial mass and local dark matter density are estimated from the 3DV method which is the more reliable method, $M_{rm vir} = (0.822pm0.052)times 10^{12},M_odot$ and $rho_{rm DM,odot} = 0.33pm0.03$ GeV ${rm cm^{-3}}$, respectively.
We study the dynamical state and the integrated total mass profiles of 75 massive (M500 > 5 e+14 M_sun) SZ-selected clusters at 0.08<z< 1.1. The sample is built from the Planck catalogue, with the addition of 4 SPT clusters at z>0.9. Using XMM imaging observations, we characterise the dynamical state with the centroid shift, the concentration, and their combination, M, which simultaneously probes the core and the large scale gas morphology. Using spatially-resolved spectroscopy and assuming hydrostatic equilibrium, we derive the total integrated mass profiles. The mass profile shape is quantified by the sparsity, the ratio of M500 to M2500, the masses at density contrast 500 and 2500, respectively. We study the correlations between the various parameters and their dependence on redshift. We confirm that SZ-selected samples, thought to reflect most closely the underlying cluster population, are dominated by disturbed and non-cool core objects at all z. There is no significant evolution or mass dependence of either the cool core fraction or the centroid shift parameter. The M parameter evolves slightly with z, having a correlation coefficient of rho= -0.2 $pm$ 0.1 and a null hypothesis p-value of 0.01. In the high mass regime considered here, the sparsity evolves minimally with redshift, increasing by 10% between z<0.2 and z>0.55, an effect significant at less than 2 sigma. In contrast, the dependence of the sparsity on dynamical state is much stronger, increasing by a factor of $sim$60% from the 1/3 most relaxed to the 1/3 most disturbed objects, an effect significant at more than 3 sigma. This is the first observational evidence that the shape of the integrated total mass profile in massive clusters is principally governed by the dynamical state, and is only mildly dependent on redshift. We discuss the consequences for the comparison between observations and theoretical predictions.
The cosmic baryonic fluid at low redshifts is similar to a fully developed turbulence. In this work, we use simulation samples produced by the hybrid cosmological hydrodynamical/N-body code, to investigate on what scale the deviation of spatial distributions between baryons and dark matter is caused by turbulence. For this purpose, we do not include the physical processes such as star formation, supernovae (SNe) and active galactic nucleus (AGN) feedback into our code, so that the effect of turbulence heating for IGM can be exhibited to the most extent. By computing cross-correlation functions $r_m(k)$ for the density field and $r_v(k)$ for the velocity field of both baryons and dark matter, we find that deviations between the two matter components for both density field and velocity field, as expected, are scale-dependent. That is, the deviations are the most significant at small scales and gradually diminish on larger and larger scales. Also, the deviations are time-dependent, i.e. they become larger and larger with increasing cosmic time. The most emphasized result is that the spatial deviations between baryons and dark matter revealed by velocity field are more significant than that by density field. At z = 0, at the 1% level of deviation, the deviation scale is about 3.7 $h^{-1}$Mpc for density field, while as large as 23 $h^{-1}$Mpc for velocity field, a scale that falls within the weakly non-linear regime for the structure formation paradigm. Our results indicate that the effect of turbulence heating is indeed comparable to that of these processes such as SN and AGN feedback.
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 accurate intrinsic shape distributions. A further implication is that so-called prolate rotation, where the bulk of stars in prolate galaxies are thought to rotate around the projected major axis, is a misnomer.
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