Using spectra taken with the AAOmega spectrograph, we measure the radialvelocities of over 100 stars, many of which are intermediate age carbon stars,in the direction of the dwarf irregular galaxy NGC 6822. Kinematic analysissuggests that the carbon stars in the sample are associated with NGC 6822, andestimates of its radial velocity and galactic rotation are made from astar-by-star analysis of its carbon star population. We calculate aheliocentric radial velocity for NGC 6822 of $-51\pm3$ \kms\ and show that thepopulation rotates with a mean rotation speed of $11.2\pm2.1$ \kms\ at a meandistance of 1.1 kpc from the galactic centre, about a rotation axis with aposition angle of $26^\circ\pm13^\circ$, as projected on the sky. This is closeto the rotation axis of the HI gas disk and suggests that NGC 6822 is not apolar ring galaxy, but is dynamically closer to a late type galaxy. However,the rotation axis is not aligned with the minor axis of the AGB isodensityprofiles and this remains a mystery.

We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-FieldSpectrograph and extracted line-of-sight velocity distributions out to 3half-light radii. We constructed collisionless orbit models in order toconstrain NGC 3998's dark and visible structure, using kinematics from both theMitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric,seen nearly face on with a flattened intrinsic shape - i.e., a face-onfast-rotator. We find an I-band mass-to-light ratio of $4.7_{-0.45}^{+0.32}$ ingood agreement with previous spectral fitting results for this galaxy. Ourbest-fit orbit model shows a both a bulge and a disc component, with anon-negligible counter-rotating component also evident. We find that relativelylittle dark matter is needed to model this galaxy, with an inferred dark massfraction of just $(7.1^{+8.1}_{-7.1})\%$ within one half-light radius.

We present Hubble Space Telescope far-UV spectra of 4 QSOs whose sightlinespass through the halo of NGC 1097 at impact parameters of 48 -165 kpc. NGC 1097is a nearby spiral galaxy that has undergone at least two minor merger events,but no apparent major mergers, and is relatively isolated with respect to othernearby bright galaxies. This makes NGC 1097 a good case study for exploringbaryons in a paradigmatic bright-galaxy halo. Lyman-alpha absorption isdetected along all sightlines and Si III 1206 is found along the 3 smallestimpact parameter sightlines; metal lines of C II, Si II and Si IV are onlyfound with certainty towards the inner-most sightline. The kinematics of theabsorption lines are best replicated by a model with a disk-like distributionof gas approximately planar to the observed 21 cm H I disk, that is rotatingmore slowly than the inner disk, and into which gas is infalling from theintergalactic medium. Some part of the absorption towards the inner-mostsightline may arise either from a small-scale outflow, or from tidal debrisassociated with the minor merger that gives rise to the well known `dog-leg'stellar stream that projects from NGC 1097. When compared to other studies, NGC1097 appears to be a `typical' absorber, although the large dispersion inabsorption line column density and equivalent width in a single halo goesperhaps some way in explaining the wide range of these values seen inhigher-redshift studies.

We present results from deep, wide-field surface photometry of three nearby(D=4--7 Mpc) spiral galaxies: M94 (NGC 4736), M64 (NGC 4826), and M106 (NGC4258). Our imaging reaches limiting surface brightnesses of $\mu_{B} \sim$ 28-- 30 mag arcsec$^{-2}$ and probes colors down to $\mu_{B} \sim$ 27.5 magarcsec$^{-2}$. We compare our broadband optical data to available ultravioletand high column-density HI data to better constrain the star forming historyand stellar populations of the outermost parts of each galaxy's disk. Eachgalaxy has a well-defined radius beyond which little star formation occurs andthe disk light appears both azimuthally smooth and red in color, suggestive ofold, well-mixed stellar populations. Given the lack of ongoing star formationor blue stellar populations in these galaxies' outer disks, the most likelymechanisms for their formation are dynamical processes such as disk heating orradial migration, rather than inside-out growth of the disks. This is alsoimplied by the similarity in outer disk properties despite each galaxy showingdistinct levels of environmental influence, from a purely isolated galaxy (M94)to one experiencing weak tidal perturbations from its satellite galaxies (M106)to a galaxy recovering from a recent merger (M64), suggesting that a variety ofevolutionary histories can yield similar outer disk structure. While thissuggests a common secular mechanism for outer disk formation, the large extentof these smooth, red stellar populations---which reach several diskscalelengths beyond the galaxies' spiral structure---may challenge models ofradial migration given the lack of any non-axisymmetric forcing at such largeradii.

Cosmological $N$-body simulations predict dark matter (DM) haloes with steepcentral cusps (e.g. NFW, Navarro et al. 1996). This contradicts observations ofgas kinematics in low-mass galaxies that imply the existence of shallow DMcores. Baryonic processes such as adiabatic contraction and gas outflows can,in principle, alter the initial DM density profile, yet their relativecontributions to the halo transformation remain uncertain. Recent highresolution, cosmological hydrodynamic simulations (Di Cintio et al. 2014, DC14)predict that inner density profiles depend systematically on the ratio ofstellar to DM mass (M$_*$/M$_{\text{halo}}$). Using a Markov Chain Monte Carloapproach, we test the NFW and the M$_*$/M$_{\text{halo}}$-dependent DC14 halomodels against a sample of 147 galaxy rotation curves from the new {\itSpitzer} Photometry and Accurate Rotation Curves (SPARC) data set. Thesegalaxies all have extended H{\small I} rotation curves from radiointerferometry as well as accurate stellar mass density profiles fromnear-infrared photometry. The DC14 halo profile provides markedly better fitsto the data compared to the NFW profile. Unlike NFW, the DC14 halo parametersfound in our rotation curve fits naturally fall within two standard deviationsof the mass-concentration relation predicted by $\Lambda$CDM and the stellarmass-halo mass relation inferred from abundance matching with few outliers.Halo profiles modified by baryonic processes are therefore more consistent withexpectations from $\Lambda$ cold dark matter ($\Lambda$CDM) cosmology andprovide better fits to galaxy rotation curves across a wide range of galaxyproperties than do halo models that neglect baryonic physics. Our results offera solution to the decade long cusp-core discrepancy.