The spatial and kinematic distribution of warm gas in and around the ComaCluster is presented through observations of Lyman-alpha absorbers usingbackground QSOs. Updates to the Lyman-alpha absorber distribution found in Yoonet al. (2012) for the Virgo Cluster are also presented. At 0.2-2.0 R_vir ofComa we identify 14 Lyman-alpha absorbers (N_HI = 10^{12.8-15.9} cm^-2) towards5 sightlines and no Lyman-alpha absorbers along 3 sightlines within3\sigmav_coma. For both Coma and Virgo, most Lyman-alpha absorbers are foundoutside the virial radius or beyond 1\sigmav consistent with them largelyrepresenting the infalling intergalactic medium. The few exceptions in thecentral regions can be associated with galaxies. The Lyman-alpha absorbersavoid the hot ICM, consistent with the infalling gas being shock-heated withinthe cluster. The massive dark matter halos of clusters do not show theincreasing column density with decreasing impact parameter relationship foundfor the smaller mass galaxy halos. In addition, while the covering fractionwithin R_vir is lower for clusters than galaxies, beyond R_vir the coveringfraction is somewhat higher for clusters. The velocity dispersion of theabsorbers compared to the galaxies is higher for Coma, consistent with theabsorbers tracing additional turbulent gas motions in the cluster outskirts.The results are overall consistent with cosmological simulations, with thecovering fraction being high in the observations standing out as the primarydiscrepancy.

We characterize the contribution from accreted material to the galactic discsof the Auriga Project, a set of high resolution magnetohydrodynamiccosmological simulations of late-type galaxies performed with the moving-meshcode AREPO. Our goal is to explore whether a significant accreted (or ex-situ)stellar component in the Milky Way disc could be hidden within thenear-circular orbit population, which is strongly dominated by stars bornin-situ. One third of our models shows a significant ex-situ disc but thisfraction would be larger if constraints on orbital circularity were relaxed.Most of the ex-situ material ($\gtrsim 50\%$) comes from single massivesatellites ($> 6 \times 10^{10}~M_{\odot}$). These satellites are accreted witha wide range of infall times and inclination angles (up to $85^{\circ}$).Ex-situ discs are thicker, older and more metal-poor than their in-situcounterparts. They show a flat median age profile, which differs from thenegative gradient observed in the in-situ component. As a result, thelikelihood of identifying an ex-situ disc in samples of old stars onnear-circular orbits increases towards the outskirts of the disc. We show threeexamples that, in addition to ex-situ discs, have a strongly rotating darkmatter component. Interestingly, two of these ex-situ stellar discs show anorbital circularity distribution that is consistent with that of the in-situdisc. Thus, they would not be detected in typical kinematic studies.

In this paper we investigate the statistical properties of the Tully-Fisherrelation for a sample of 32 galaxies with measured distances from the Cepheidperiod-luminosity relation and/or TRGB stars. We take advantage of panchromatic photometry in 12 bands (from FUV to 4.5$\mu$m) and of spatially resolved HI kinematics. We use these data togetherwith three kinematic measures ($W^{i}_{50}$, $V_{max}$ and $V_{flat}$)extracted from the global HI profiles or HI rotation curves, so as to construct36 correlations allowing us to select the one with the least scatter. Weintroduce a tightness parameter $\sigma_{\perp}$ of the TFr, in order to obtaina slope-independent measure of the goodness of fit. We find that the tightestcorrelation occurs when we select the 3.6 $\mu$m photometric band together withthe $V_{flat}$ parameter extracted from the HI rotation curve.