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Register a new userFormation and Evolution of sub-structures in tidal tails: Spherical dark matter haloes
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Recently a theory about the formation of over-densities of stars along tidal tails of globular clusters has been presented, this theory predicts the position and time of formation of such over-densities and was successfully tested with N-body simulations of globular clusters in a point mass galactic potential. In this work we present a comparison between this theory and our simulations using a dwarf galaxy orbiting two differently shaped dark matter halos to study the effects of a cored and a cuspy halo on the formation and evolution of tidal tails. We find no difference using a cuspy or a cored halo, however, we find an intriguing asymmetry between the leading and trailing arm of the tidal tails. The trailing arm grows faster than the leading arm. This asymmetry is seen in the distance to first over-density and its size as well. We establish a relation between the distance to the first over-density and the size of this over-density.
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A rotation curve inequality that holds for spherically symmetric mass distributions is derived, and tested against the SPARC galaxy rotation curves dataset. We identify several Galaxies, eg NGC7793 and UGC05253, which are candidates for hosting non-spherical dark matter structures that could be detected by more precise measurements.
We have used V- and I- band images from the Hubble Space Telescope (HST) to identify compact stellar clusters within the tidal tails of twelve different interacting galaxies. The seventeen tails within our sample span a physical parameter space of HI/stellar masses, tail pressure and density through their diversity of tail lengths, optical brightnesses, mass ratios, HI column densities, stage on the Toomre sequence, and tail kinematics. Our preliminary findings in this study indicate that star cluster demographics of the tidal tail environment are compatible with the current understanding of star cluster formation in quiescent systems, possibly only needing changes in certain parameters or normalization of the Schechter cluster initial mass function (CIMF) to replicate what we observe in color-magnitude diagrams and a brightest absolute magnitude -- log N plot.
We use the halo occupation distribution (HOD) framework to characterise the predictions from two independent galaxy formation models for the galactic content of dark matter haloes and its evolution with redshift. Our galaxy samples correspond to a range of fixed number densities defined by stellar mass and span $0 le z le 3$. We find remarkable similarities between the model predictions. Differences arise at low galaxy number densities which are sensitive to the treatment of heating of the hot halo by active galactic nuclei. The evolution of the form of the HOD can be described in a relatively simple way, and we model each HOD parameter using its value at $z=0$ and an additional evolutionary parameter. In particular, we find that the ratio between the characteristic halo masses for hosting central and satellite galaxies can serve as a sensitive diagnostic for galaxy evolution models. Our results can be used to test and develop empirical studies of galaxy evolution and can facilitate the construction of mock galaxy catalogues for future surveys.
We present some results of numerical simulations of a globular cluster orbiting in the central region of a triaxial galaxy on a set of loop orbits. Tails start forming after about a quarter of the globular cluster orbital period and develop, in most cases, along the cluster orbit, showing clumpy substructures as observed, for example, in Palomar 5. If completely detectable, clumps can contain about 7,000 solar masses each, i.e. about 10% of the cluster mass at that epoch. The morphology of tails and clumps and the kinematical properties of stars in the tails are studied and compared with available observational data. Our finding is that the stellar velocity dispersion tends to level off at large radii, in agreement to that found for M15 and Omega Centauri.
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses ($10^{8.75}$ to $10^{11.3} M_{odot}$) and redshifts ($0.2 < z < 0.8$) than previous weak lensing studies. At redshift $z sim 0.5$, the stellar-to-halo mass ratio (SHMR) reaches a maximum of $4.0pm0.2$ percent as a function of halo mass at $sim 10^{12.25} M_{odot}$. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from $4.5 pm 0.3$ percent at $z sim 0.7$ to $3.4 pm 0.2$ percent at $z sim 0.3$, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched downsizes with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well-fit by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic time.
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