Disk galaxies at intermediate redshift ($z\sim0.7$) have been found inprevious work to display more optically thick behaviour than their localcounterparts in the rest-frame B-band surface brightness, suggesting anevolution in dust properties over the past $\sim$6 Gyr. We compare the measuredluminosities of face-on and edge-on star-forming galaxies at differentwavelengths (Ultraviolet (UV), mid-infrared (MIR), far-infrared (FIR), andradio) for two well-matched samples of disk-dominated galaxies: a local SloanDigital Sky Survey (SDSS)-selected sample at $z\sim0.07$ and a sample of disksat $z\sim0.7$ drawn from Cosmic Evolution Survey (COSMOS). We have derivedcorrection factors to account for the inclination dependence of the parametersused for sample selection. We find that typical galaxies are transparent at MIRwavelengths at both redshifts and that the FIR and radio emission is alsotransparent as expected. However, reduced sensitivity at these wavelengthslimits our analysis; we cannot rule out opacity in the FIR or radio.Ultra-violet attenuation has increased between $z\sim0$ and $z\sim0.7$, withthe $z\sim0.7$ sample being a factor of $\sim$3.4 more attenuated. The largerUV attenuation at $z\sim0.7$ can be explained by more clumpy dust aroundnascent star-forming regions. There is good agreement between the fittedevolution of the normalisation of the SFR$_{\text{UV}}$ versus 1-cos(i) trend(interpreted as the clumpiness fraction) and the molecular gas fraction/dustfraction evolution of galaxies found out to $z<1$.

Taking advantage of the Gaia DR1, we combined TGAS parallaxes with theTycho-2 and APASS photometry to calculate the star formation history (SFH) ofthe solar neighbourhood within 250 pc using the colour-magnitude diagramfitting technique. Our dynamically-evolved SFH is in excellent agreement withthat calculated from the Hipparcos catalogue within 80 pc of the Sun, showingan enhanced star formation rate (SFR) in the past ~4 Gyr. We then correct theSFR for the disc thickening with age to obtain a SFR that is representative ofthe whole solar cylinder, and show that even with an extreme correction ourresults are not consistent with an exponentially decreasing SFR as found byrecent studies. Finally, we discuss how this technique can be applied out to ~5kpc thanks to the next Gaia data releases, which will allow us to quantify theSFH of the thin disc, thick disc and halo in situ.

Spiral patterns in some disc galaxies have two arms in the centre, and threeor more arms on the periphery. The same result is also obtained in numericalsimulations of stellar and gaseous discs. We argue that such patterns may occurdue to fast cooling of the gas, resulting in formation of giant molecularclouds. The timescale of this process is 50 Myr, the factor of 10 shorter thanof ordinary secular instability. The giant molecular clouds give rise tomultiarm spirals through the mechanism of swing amplification.

We present new parallax measurements of 7 long-period (> 10 days) Milky WayCepheids (SS CMa, XY Car, VY Car, VX Per, WZ Sgr, X Pup and S Vul) usingastrometry from spatial scanning of WFC3 on HST. Observations were obtained at6 month intervals over 4 years. The distances are 1.7--3.6 kpc with a meanprecision of 45 microarcseconds and a best of 29 microarcseconds (SNR = 14).The accuracy of the parallaxes is demonstrated through independent analyses of>100 reference stars. This raises to 10 the number of long-period Cepheids withsignificant parallax measurements, 8 obtained from this program. We alsopresent high-precision F555W, F814W, and F160W magnitudes of these Cepheids,allowing a direct, zeropoint-independent comparison to >1800 extragalacticCepheids in the hosts of 19 SNeIa. This sample addresses two outstandingsystematic uncertainties affecting prior comparisons of Milky Way andextragalactic Cepheids used to calibrate H_0: their dissimilarity of periodsand photometric systems. Comparing the new parallaxes to their predicted valuesderived from reversing the distance ladder gives a ratio (or independent scalefor H_0) of 1.034+/-0.036, consistent with no change and inconsistent at the3.3 sigma level with a ratio of 0.91 needed to match the value predicted byPlanck+LCDM. Using these data instead to augment the Riess et al. (2016)measurement of H_0 improves the precision to 2.3%, yielding 73.45+/-1.66km/s/Mpc, and tension with Planck+LCDM increases to 3.7 sigma. The futurecombination of Gaia parallaxes and HST spatial scanning photometry of 50 MilkyWay Cepheids can support a < 1% calibration of H_0.

We present a survey of the [CII] 158 $\mu$m line and underlying far-infrared(FIR) dust continuum emission in a sample of 27 z>6 quasars using the AtacamaLarge Millimeter Array (ALMA) at ~1" resolution. The [CII] line wassignificantly detected (at >5-sigma) in 23 sources (85%). We find typical lineluminosities of $L_{\rm [CII]}=10^{9-10}$ L$_\odot$, and an average line widthof ~385 km/s. The [CII]-to-far-infrared luminosity ratio ([CII]/FIR) in oursources span one order of magnitude, highlighting a variety of conditions inthe star-forming medium. Four quasar host galaxies are clearly resolved intheir [CII] emission on a few kpc scales. Basic estimates of the dynamicalmasses of the host galaxies give masses between $2\times10^{10}$ and$2\times10^{11}$ M$_\odot$, i.e., more than an order of magnitude below what isexpected from local scaling relations, given the available limits on the massesof the central black holes ($>3\times10^8$ M$_\odot$, assumingEddington-limited accretion). In stacked ALMA [CII] spectra of individualsources in our sample, we find no evidence of a deviation from a singleGaussian profile. The quasar luminosity does not strongly correlate with eitherthe [CII] luminosity or equivalent width. This survey (with typical on-sourceintegration times of 8 min) showcases the unparalleled sensitivity of ALMA atmillimeter wavelengths, and offers a unique reference sample for the study ofthe first massive galaxies in the universe.

A randomly chosen star in today's Universe is most likely to live in a galaxywith a stellar mass between that of the Milky Way and Andromeda. Yet it remainsuncertain how the structural evolution of these bulge-disk systems proceeded.Most of the unobscured star formation we observe building Andromdedaprogenitors at 0.7<z<1.5 occurs in disks, but >90% of their star formation isreprocessed by dust and remains unaccounted for. Here we map 500micron dustcontinuum emission in an Andromeda progenitor at z=1.25 to probe where it isgrowing through dust-obscured star formation. Combining resolved dustmeasurements from the NOEMA interferometer with Hubble Space Telescope Halphamaps and multicolor imaging (including new UV data from the HDUV survey), wefind a bulge growing by dust-obscured star formation: while the unobscured starformation is centrally suppressed, the dust continuum is centrallyconcentrated, filling in the ring-like structures evident in the Halpha and UVemission. Reflecting this, the dust emission is more compact than theoptical/UV tracers of star formation with r_e(dust)=3.4kpc,r_e(Halpha)/r_e(dust)=1.4, and r_e(UV)/r_e(dust)=1.8. Crucially, however, thebulge and disk of this galaxy are building simultaneously; although the dustemission is more compact than the rest-optical emission(r_e(optical)/r_e(dust)=1.4), it is somewhat less compact than the stellar mass(r_e(M_*)/r_e(dust)=0.9). Taking the 500micron emission as a tracer of starformation, the expected structural evolution of this galaxy can be accountedfor by star formation: it will grow in size by Delta(r_e)/Delta(M_*)~0.3 andcentral surface density by Delta(Sigma_cen)/Delta(M_*)~0.9. Finally, ourobservations are consistent with a picture in which merging and diskinstabilities drive gas to the center of galaxies, boosting global starformation rates above the main sequence and building bulges.

Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit aspread in $\mathrm{[\alpha/Fe]}$ at fixed $\mathrm{[Fe/H]}$, manifest at somelocations as a bimodality. The origin of these diverse, and possibly distinct,stellar populations in the Galactic disc is not well understood. We examine theFe and $\alpha$-element evolution of 133 Milky Way-like galaxies from the EAGLEsimulation, to investigate the origin and diversity of their$\mathrm{[\alpha/Fe]}$-$\mathrm{[Fe/H]}$ distributions. We find that bimodal$\mathrm{[\alpha/Fe]}$ distributions arise in galaxies whose gas accretionhistories exhibit episodes of significant infall at both early and late times,with the former fostering more intense star formation than the latter. Theshorter characteristic consumption timescale of gas accreted in the earlierepisode suppresses its enrichment with iron synthesised by Type Ia SNe,resulting in the formation of a high-$\mathrm{[\alpha/Fe]}$ sequence. We findthat bimodality in $\mathrm{[\alpha/Fe]}$ similar to that seen in the Galaxy israre, appearing in approximately 5 percent of galaxies in our sample. We positthat this is a consequence of an early gas accretion episode requiring the massaccretion history of a galaxy's dark matter halo to exhibit a phase ofatypically-rapid growth at early epochs. The scarcity of EAGLE galaxiesexhibiting distinct sequences in the $\mathrm{[\alpha/Fe]}$-$\mathrm{[Fe/H]}$plane may therefore indicate that the Milky Way's elemental abundance patterns,and its accretion history, are not representative of the broader population of$\sim L^\star$ disc galaxies.