We present structural parameters from a wide-field homogeneous imaging survey of Milky Way satellites carried out with the MegaCam imagers on the 3.6m Canada-France-Hawaii Telescope (CFHT) and 6.5m Magellan-Clay telescope. Our survey targets an unbiased sample of "outer halo" satellites (i.e., substructures having Galactocentric distances greater than 25 kpc) and includes classical dSph galaxies, ultra-faint dwarfs, and remote globular clusters. We combine deep, panoramic gr imaging for 44 satellites and archival gr imaging for 14 additional objects (primarily obtained with the DECam instrument as part of the Dark Energy Survey), to measure photometric and structural parameters for 58 outer halo satellites. This is the largest and most uniform analysis of Milky Way satellites undertaken to date and represents roughly three quarters (58/81 72%) of all known outer halo satellites. We use a maximum-likelihood method to fit four density laws to each object in our survey: exponential, Plummer, King and Sérsic models. We examine systematically the isodensity contour maps and color magnitude diagrams for each of our program objects, present a comparison with previous results, and tabulate our best-fit photometric and structural parameters, including ellipticities, position angles, effective radii, Sérsic indices, absolute magnitudes, and surface brightness measurements. We investigate the distribution of outer halo satellites in the size-magnitude diagram, and show that the current sample of outer halo substructures spans a wide range in effective radius, luminosity and surface brightness, with little evidence for a clean separation into star cluster and galaxy populations at the faintest luminosities and surface brightnesses.

We study radial profiles in Hα equivalent width and specific star formation rate (sSFR) derived from spatially-resolved SDSS-IV MaNGA spectroscopy to gain insight on the physical mechanisms that suppress star formation and determine a galaxy's location in the SFR-M diagram. Even within the star-forming 'main sequence', the measured sSFR decreases with stellar mass, both in an integrated and spatially-resolved sense. Flat sSFR radial profiles are observed for log(M /M ) < 10.5, while star-forming galaxies of higher mass show a significant decrease in sSFR in the central regions, a likely consequence of both larger bulges and an inside-out growth history. Our primary focus is the green valley, constituted by galaxies lying below the star formation main sequence, but not fully passive. In the green valley we find sSFR profiles that are suppressed with respect to star-forming galaxies of the same mass at all galactocentric distances out to 2 effective radii. The responsible quenching mechanism therefore appears to affect the entire galaxy, not simply an expanding central region. The majority of green valley galaxies of log(M /M ) > 10.0 are classified spectroscopically as central low-ionisation emission-line regions (cLIERs). Despite displaying a higher central stellar mass concentration, the sSFR suppression observed in cLIER galaxies is not simply due to the larger mass of the bulge. Drawing a comparison sample of star forming galaxies with the same M and Σ 1 kpc (the mass surface density within 1 kpc), we show that a high Σ 1 kpc is not a sufficient condition for determining central quiescence.

We present an exhaustive census of Lyman alpha (Lyα) emission in the general galaxy population at 3 < z < 4.6. We use the Michigan/Magellan Fiber System (M2FS) spectrograph to study a stellar mass (M * ) selected sample of 625 galaxies homogeneously distributed in the range 7.6 < log M * /M < 10.6. Our sample is selected from the 3D-HST/CANDELS survey, which provides the complementary data to estimate Lyα equivalent widths (W Lyα ) and escape fractions (f esc ) for our galaxies. We find both quantities to anti-correlate with M * , star-formation rate (SFR), UV luminosity, and UV slope (β). We then model the W Lyα distribution as a function of M U V and β using a Bayesian approach. Based on our model and matching the properties of typical Lyman break galaxy (LBG) selections, we conclude that the W Lyα distribution in such samples is heavily dependent on the limiting M U V of the survey. Regarding narrowband surveys, we find their W Lyα selections to bias samples toward low M * , while their line-flux limitations preferentially leave out low-SFR galaxies. We can also use our model to predict the fraction of Lyα-emitting LBGs at 4 z 7. We show that reported drops in the Lyα fraction at z 6, usually attributed to the rapidly increasing neutral gas fraction of the universe, can also be explained by survey M U V incompleteness. This result does not dismiss reionization occurring at z ∼ 7, but highlights that current data is not inconsistent with this process taking place at z > 7.

The late assembly of massive galaxies is thought to be dominated by stellar accretion in their outskirts (beyond 2 effective radii R e ) due to dry, minor galaxy mergers. We use observations of 1010 passive early-type galaxies (ETGs) within z < 0.15 from SDSS IV MaNGA to search for evidence of this accretion. The outputs from the stellar population fitting codes FIREFLY, pPXF, and Prospector are compared to control for systematic errors in stellar metallicity (Z) estimation. We find that the average radial logZ/Z profiles of ETGs in various stellar mass (M * ) bins are not linear. As a result, these profiles are poorly characterized by a single gradient value, explaining why weak trends reported in previous work can be difficult to interpret. Instead, we examine the full radial extent of stellar metallicity profiles and find them to flatten in the outskirts of M * 10 11 M ETGs. This is a signature of stellar accretion. Based on a toy model for stellar metallicity profiles, we infer the ex-situ stellar mass fraction in ETGs as a function of M * and galactocentric radius. We find that ex-situ stars at R∼2R e make up 20% of the projected stellar mass of M * 10 10.5 M ETGs, rising up to 80% for M * 10 11.5 M ETGs. 5 pPXF