Using a sample of 215 supernovae (SNe), we analyse their positions relativeto the spiral arms of their host galaxies, distinguishing grand-design (GD)spirals from non-GD (NGD) galaxies. Our results suggest that shocks in spiralarms of GD galaxies trigger star formation in the leading edges of armsaffecting the distributions of core-collapse (CC) SNe (known to haveshort-lived progenitors). The closer locations of SNe Ibc vs. SNe II relativeto the leading edges of the arms supports the belief that SNe Ibc have moremassive progenitors. SNe Ia having less massive and older progenitors, showsymmetric distribution with respect to the peaks of spiral arms.

We present high resolution simulations of an isolated dwarf spheroidal (dSph)galaxy between redshifts $z\sim10$ and $z\sim 4$, the epoch when several MilkyWay dSph satellites experienced extended star formation, in order to understandin detail the physical processes which affect a low-mass halo's ability toretain gas. It is well-established that supernova feedback is very effective atexpelling gas from a $3\times 10^7$M$_\odot$ halo, the mass of a typicalredshift 10 progenitor of a redshift 0 halo with mass $\sim10^9$M$_\odot$. Weinvestigate the conditions under which such a halo is able to retain sufficienthigh-density gas to support extended star formation. In particular, we explorethe effects of: an increased relative concentration of the gas compared to thedark matter; a higher concentration dark matter halo; significantly lowersupernova rates; enhanced metal cooling due to enrichment from earliersupernovae. We show that disk-like gas distributions retain more gas thanspherical ones, primarily due to the shorter gas cooling times in the disk.However, a significant reduction in the number of supernovae compared to thatexpected for a standard initial mass function is still needed to allow theretention of high density gas. We conclude that the progenitors of the observeddSphs would only have retained the gas required to sustain star formation iftheir mass, concentration and gas morphology were already unusual for those ofa dSph-mass halo progenitor by a redshift of 10.

A minimum in stellar velocity dispersion is often observed in the centralregions of disc galaxies. To investigate the origin of this feature, known as a{\sigma}-drop, we analyse the stellar kinematics of a high-resolution N-body +smooth particle hydrodynamical simulation, which models the secular evolutionof an unbarred disc galaxy. We compared the intrinsic mass-weighted kinematicsto the recovered luminosity-weighted ones. The latter were obtained byanalysing synthetic spectra produced by a new code, SYNTRA, that generatessynthetic spectra by assigning a stellar population synthesis model to eachstar particle based on its age and metallicity. The kinematics were derivedfrom the synthetic spectra as in real spectra to mimic the kinematic analysisof real galaxies. We found that the recovered luminosity-weighted kinematics inthe centre of the simulated galaxy are biased to higher rotation velocities andlower velocity dispersions due to the presence of young stars in a thin andkinematically cool disc, and are ultimately responsible for the {\sigma}-drop.

We present an analysis of the radial profiles of a sample of 43 HI-fluxselected spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) withresolved James Clerk Maxwell Telescope (JCMT) CO $J=3-2$ and/or Very LargeArray (VLA) HI maps. Comparing the Virgo and non-Virgo populations, we confirmthat the HI disks are truncated in the Virgo sample, even for these relativelyHI-rich galaxies. On the other hand, the H$_{2}$ distribution is enhanced forVirgo galaxies near their centres, resulting in higher H$_{2}$ to HI ratios andsteeper H$_{2}$ and total gas radial profiles. This is likely due to theeffects of moderate ram pressure stripping in the cluster environment, whichwould preferentially remove low density gas in the outskirts while enhancinghigher density gas near the centre. Combined with H$\alpha$ star formation ratedata, we find that the star formation efficiency (SFR/H$_{2}$) is relativelyconstant with radius for both samples, but Virgo galaxies have a $\sim40\%$lower star formation efficiency than non-Virgo galaxies.

We study the history from $z\sim2$ to $z\sim0$ of the stellar mass assemblyof quiescent and star-forming galaxies in a spatially resolved fashion. Forthis purpose we use multi-wavelength imaging data from the Hubble SpaceTelescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS)for the local population. We present the radial stellar mass surface densityprofiles of galaxies with $M_{\ast}>10^{10} M_{\odot}$, corrected formass-to-light ratio ($M_{\ast}/L$) variations, and derive the half-mass radius($R_{m}$), central stellar mass surface density within 1 kpc ($\Sigma_{1}$) andsurface density at $R_{m}$ ($\Sigma_{m}$) for star-forming and quiescentgalaxies and study their evolution with redshift. At fixed stellar mass, thehalf-mass sizes of quiescent galaxies increase from $z\sim2$ to $z\sim0$ by afactor of $\sim3-5$, whereas the half-mass sizes of star-forming galaxiesincrease only slightly, by a factor of $\sim2$. The central densities$\Sigma_{1}$ of quiescent galaxies decline slightly (by a factor of$\lesssim1.7$) from $z\sim2$ to $z\sim0$, while for star-forming galaxies$\Sigma_{1}$ increases with time, at fixed mass. We show that the centraldensity $\Sigma_{1}$ has a tighter correlation with specific star-formationrate (sSFR) than $\Sigma_{m}$ and for all masses and redshifts galaxies withhigher central density are more prone to be quenched. Reaching a high centraldensity ($\Sigma_{1} \gtrsim 10^{10} M_{\odot} \mathrm{kpc}^2$) seems to be aprerequisite for the cessation of star formation, though a causal link betweenhigh $\Sigma_{1}$ and quenching is difficult to prove and their correlation canhave a different origin.

We analyze new far-ultraviolet spectra of 13 quasars from the z~0.2 COS-Halossurvey that cover the HI Lyman limit of 14 circumgalactic medium (CGM) systems.These data yield precise estimates or more constraining limits than previousCOS-Halos measurements on the HI column densities NHI. We then apply aMonte-Carlo Markov Chain approach on 32 systems from COS-Halos to estimate themetallicity of the cool (T~10^4K) CGM gas that gives rise to low-ionizationstate metal lines, under the assumption of photoionization equilibrium with theextragalactic UV background. The principle results are: (1) the CGM of field L*galaxies exhibits a declining HI surface density with impact parameter Rperp(at >99.5%$ confidence), (2) the transmission of ionizing radiation through CGMgas alone is 70+/-7%; (3) the metallicity distribution function of the cool CGMis unimodal with a median of 1/3 Z_Sun and a 95% interval from ~1/50 Z_Sun toover 3x solar. The incidence of metal poor (<1/100 Z_Sun) gas is low, implyingany such gas discovered along quasar sightlines is typically unrelated to L*galaxies; (4) we find an unexpected increase in gas metallicity with decliningNHI (at >99.9% confidence) and, therefore, also with increasing Rperp. The highmetallicity at large radii implies early enrichment; (5) A non-parametricestimate of the cool CGM gas mass is M_CGM_cool = 9.2 +/- 4.3 10^10 Msun, whichtogether with new mass estimates for the hot CGM may resolve the galacticmissing baryons problem. Future analyses of halo gas should focus on theunderlying astrophysics governing the CGM, rather than processes that simplyexpel the medium from the halo.