We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph(COS) absorption-line survey to study halo gas around 16 luminous red galaxies(LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar massMstar>1e11 Msun and no prior knowledge of the presence/absence of anyabsorption features. Based on observations of the full Lyman series, we obtainaccurate measurements of neutral hydrogen column density N(HI) and find thathigh-N(HI) gas is common in these massive quiescent halos with a median of <logN(HI)> = 16.6 at projected distances d<~160 kpc. We measure a mean coveringfraction of optically-thick gas with log N(HI)>~17.2 of<kappa>LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and<kappa>LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocityseparations between the HI absorbing gas and LRGs are characterized by a meanand dispersion of <v_{gas-gal}>=29 km/s and \sigma_v_{gas-gal}=171 km/s.Combining COS FUV and ground-based echelle spectra provides an expandedspectral coverage for multiple ionic transitions, from low-ionization MgII andSiII, to intermediate ionization SiIII and CIII, and to high-ionization OVIabsorption lines. We find that intermediate ions probed by CIII and SiIII arethe most prominent UV metal lines in LRG halos with a mean covering fraction of<kappa(CIII)>_{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc,comparable to what is seen for CIII in L* and sub-L* star-forming and redgalaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey showsthat massive quiescent halos contain widespread chemically-enriched cool gasand that little distinction between LRG and star-forming halos is found intheir HI and CIII content.

We present spatially resolved stellar population age maps, average radialprofiles and gradients for the first 62 Active Galactic Nuclei (AGN) observedwith SDSS-IV MaNGA to study the effects of the active nuclei on the starformation history of the host galaxies. These results, derived using theSTARLIGHT code, are compared with a control sample of non-active galaxiesmatching the properties of the AGN hosts. We find that the fraction of youngstellar populations (SP) in high-luminosity AGN is higher in the inner ($R \leq0.5\,R_e$) regions when compared with the control sample; low-luminosity AGN,on the other hand, present very similar fractions of young stars to the controlsample hosts for the entire studied range ($1\,R_e$). The fraction ofintermediate age SP of the AGN hosts increases outwards, with a clearenhancement when compared with the control sample. The inner region of thegalaxies (AGN and control galaxies) presents a dominant old SP, whose fractiondecreases outwards. We also compare our results (differences between AGN andcontrol galaxies) for the early and late-type hosts and find no significantdifferences. In summary, our results suggest that the most luminous AGN seemsto have been triggered by a recent supply of gas that has also triggered recentstar formation ($t\,\leq\,40\,Myrs$) in the central region.

Information on the star-formation histories of cD galaxies and their extendedstellar haloes lie in their spectra. Therefore, to determine whether thesestructures evolved together or through a two-phase formation, we need tospectroscopically separate the light from each component. We present a pilotstudy to use BUDDI to fit and extract the spectra of the cD galaxy NGC 3311 andits halo in an Integral Field Spectroscopy datacube, and carry out a simplestellar populations analysis to study their star-formation histories. UsingMUSE data, we were able to isolate the light of the galaxy and its halothroughout the datacube, giving spectra representing purely the light from eachof these structures. The stellar populations analysis of the two componentsindicates that, in this case, the bulk of the stars in both the halo and thecentral galaxy are very old, but the halo is more metal poor and less$\alpha$-enriched than the galaxy. This result is consistent with the haloforming through the accretion of much smaller satellite galaxies with moreextended star formation. It is noteworthy that the apparent gradients in ageand metallicity indicators across the galaxy are entirely consistent with theradially-varying contributions of galaxy and halo components, whichindividually display no gradients. The success of this study is promising forits application to a larger sample of cD galaxies that are currently beingobserved by IFU surveys.

We investigate the spatially resolved stellar populations of a sample ofseven nearby massive Early-type galaxies (ETGs), using optical and nearinfrared data, including K-band spectroscopy. This data offers good prospectsfor mitigating the uncertainties inherent in stellar population modelling bymaking a wide variety of strong spectroscopic features available. We report newVLT-KMOS measurements of the average empirical radial gradients out to theeffective radius in the strengths of the Ca I 1.98$\mu$m and 2.26$\mu$mfeatures, the Na I 2.21$\mu$m line, and the CO 2.30$\mu$m bandhead. Followingprevious work, which has indicated an excess of dwarf stars in the cores ofmassive ETGs, we pay specific attention to radial variations in the stellarinitial mass function (IMF) as well as modelling the chemical abundancepatterns and stellar population ages in our sample. Using state-of-the-artstellar population models we infer an [Fe/H] gradient of -0.16$\pm$0.05 per dexin fractional radius and an average [Na/Fe] gradient of -0.35$\pm$0.09. We finda large but radially-constant enhancement to [Mg/Fe] of $\sim$ 0.4 and a muchlower [Ca/Fe] enhancement of $\sim$ 0.1. Finally, we find no significant IMFradial gradient in our sample on average and find that most galaxies in oursample are consistent with having a Milky Way-like IMF, or at most a modestlybottom heavy IMF (e.g. less dwarf enriched than a single power law IMF with theSalpeter slope).

A fundamental quest of modern astronomy is to locate the earliest galaxiesand study how they influenced the intergalactic medium a few hundred millionyears after the Big Bang. The abundance of star-forming galaxies is known todecline from redshifts of about 6 to 10, but a key question is the extent ofstar formation at even earlier times, corresponding to the period when thefirst galaxies might have emerged. Here we present spectroscopic observationsof MACS1149-JD1, a gravitationally lensed galaxy observed when the Universe wasless than four per cent of its present age. We detect an emission line ofdoubly ionized oxygen at a redshift of $9.1096\pm0.0006$, with an uncertaintyof one standard deviation. This precisely determined redshift indicates thatthe red rest-frame optical colour arises from a dominant stellar component thatformed about 250 million years after the Big Bang, corresponding to a redshiftof about 15. Our results indicate the it may be possible to detect such earlyepisodes of star formation in similar galaxies with future telescopes.

We present 1,201 galaxies at $0.05<z<0.45$ that host tidal features, detectedfrom the first $\sim\! 200$ deg$^2$ of imaging from the Hyper Suprime-CamSubaru Strategic Program (HSC-SSP). All galaxies in the present sample havespectroscopic observations from the Sloan Digital Sky Survey (SDSS)spectroscopic campaigns, generating a sample of 21208 galaxies. Of thesegalaxies, we identify 214 shell systems and 987 stream systems. For 575 ofthese systems, we are additionally able to measure the $(g-i)$ colors of thetidal features. We find evidence for star formation in a subset of the streams,with the exception of streams around massive ellipticals, and find that streamhost galaxies span the full range of stellar masses in our sample. Galaxieswhich host shells are predominantly red and massive: we find that observableshells form more frequently around ellipticals than around disc galaxies of thesame stellar mass. Although the majority of the shells in our sample areconsistent with being formed by minor mergers, $15\% \pm 4.4\%$ of shell hostgalaxies have $(g-i)$ colors as red as their host galaxy, consistent with beingformed by major mergers. These "red shells" are additionally preferentiallyaligned with the major axis of the host galaxy, as previously predicted fromsimulations. We suggest that although the bulk of the observable shellpopulation originates from fairly minor mergers, which preferentially formshells that are not aligned with the major axis of the galaxy, major mergersproduce a significant number of observable shells.