The decomposition of the rotation curve of galaxies into contribution fromthe disc and dark halo remains uncertain and depends on the adopted mass tolight ratio (M/L) of the disc. Given the vertical velocity dispersion of starsand disc scale height, the disc surface mass density and hence the M/L can beestimated. We address a conceptual problem with previous measurements of thescale height and dispersion. When using this method, the dispersion and scaleheight must refer to the same population of stars. The scale height is obtainedfrom near-IR studies of edge-on galaxies and is weighted towards olderkinematically hotter stars, whereas the dispersion obtained from integratedlight in the optical bands includes stars of all ages. We aim to extract thedispersion for the hotter stars, so that it can then be used with the correctscale height to obtain the disc surface mass density. We use a sample ofplanetary nebulae (PNe) as dynamical tracers in the face-on galaxy NGC 628. Weextract two different dispersions from its velocity histogram -- representingthe older and younger PNe. We also present complementary stellar absorptionspectra in the inner regions of this galaxy and use a direct pixel fittingtechnique to extract the two components. Our analysis concludes that previousstudies, which do not take account of the young disc, underestimate the discsurface mass density by a factor of ~ 2. This is sufficient to make a maximaldisc for NGC 628 appear like a submaximal disc.

We present the stellar velocity maps of 25 massive galaxies located in denseenvironments observed with MUSE. Galaxies are selected to be brighter thanM_K=-25.7 magnitude, reside in the core of the Shapley Super Cluster or be thebrightest galaxy in clusters richer than the Virgo Cluster. We thus targetedgalaxies more massive than 10^12 Msun and larger than 10 kpc (half-lightradius). The velocity maps show a large variety of kinematic features:oblate-like regular rotation, kinematically distinct cores and various types ofnon-regular rotation. The kinematic misalignment angles show that massivegalaxies can be divided into two categories: those with small or negligiblemisalignment, and those with misalignment consistent with being 90 degrees.Galaxies in this latter group, comprising just under half of our galaxies, haveprolate-like rotation (rotation around the major axis). Among the brightestcluster galaxies the incidence of prolate-like rotation is 57 per cent, whilefor a magnitude limited sub-sample of objects within the Shapley Super Cluster(mostly satellites), 35 per cent of galaxies show prolate-like rotation.Placing our galaxies on the mass - size diagram, we show that they all fall ona branch extending almost an order of magnitude in mass and a factor of 5 insize from the massive end early-type galaxies, previously recognised asassociated with major dissipation-less mergers. The presence of galaxies withcomplex kinematics and, particularly, prolate-like rotators suggests, accordingto current numerical simulations, that the most massive galaxies growpredominantly through dissipation-less equal-mass mergers.

M82 is one of the best studied starburst galaxies in the local universe, andis consequently a benchmark for studying star formation feedback at both lowand high redshift. We present new VLA HI observations that reveal the cold gaskinematics along the minor axis in unprecedented detail. This includes thedetection of HI up to 10 kpc along the minor axis toward the South and beyond 5kpc to the North. A surprising aspect of these observations is that theline-of-sight HI velocity decreases substantially from about 120 km/s to 50km/s from 1.5 to 10 kpc off the midplane. The velocity profile is notconsistent with the HI gas cooling from the hot wind. We demonstrate that thevelocity decrease is substantially greater than the deceleration expected fromgravitational forces alone. If the HI consists of a continuous population ofcold clouds, some additional drag force must be present, and the magnitude ofthe drag force places a joint constraint on the ratio of the ambient medium tothe typical cloud size and density. We also show that the HI kinematics areinconsistent with a simple conical outflow centered on the nucleus, but insteadrequire the more widespread launch of the HI over the ~1 kpc extent of thestarburst region. Regardless of the launch mechanism for the HI gas, theobserved velocity decrease along the minor axis is sufficiently great that theHI may not escape the halo of M82. We estimate the HI outflow rate is much lessthan 1 M$_{\odot}$ per year at 10 kpc off the midplane.

Neutral gas is commonly believed to dominate over stars in the outskirts ofgalaxies, and investigations of the disk-halo interface are generallyconsidered to be in the domain of radio astronomy. This may simply be aconsequence of the fact that deep HI observations typically probe to a lowermass surface density than visible wavelength data. This paper presents lowsurface brightness optimized visible wavelength observations of the extremeoutskirts of the nearby spiral galaxy NGC 2841. We report the discovery of anenormous low-surface brightness stellar disk in this object. When azimuthallyaveraged, the stellar disk can be traced out to a radius of $\sim$70 kpc (5$R_{25}$ or 23 inner disk scale lengths). The structure in the stellar disktraces the morphology of HI emission and extended UV emission. Contrary toexpectations, the stellar mass surface density does not fall below that of thegas mass surface density at any radius. In fact, at all radii greater than$\sim$20 kpc, the ratio of the stellar to gas mass surface density is aconstant 3:1. Beyond $\sim$30 kpc, the low surface brightness stellar diskbegins to warp, which may be an indication of a physical connection between theoutskirts of the galaxy and infall from the circumgalactic medium. Acombination of stellar migration, accretion and in-situ star formation might beresponsible for building up the outer stellar disk, but whatever mechanismsformed the outer disk must also explain the constant ratio between stellar andgas mass in the outskirts of this galaxy.