This study presents a catalog of 8107 molecular clouds that covers the entireGalactic plane and includes 98% of the $^{12}$CO emission observed within$b\pm5^\circ$. The catalog was produced using a hierarchical clusteridentification method applied to the result of a Gaussian decomposition of theDame et al. data. The total H$_2$ mass in the catalog is $1.2\times10^9M_\odot$, in agreement with previous estimates. We find that 30% of the sightlines intersect only a single cloud, with another 25% intersecting only twoclouds. The most probable cloud size is $R\sim30$ pc. We find that $M\proptoR^{2.2\pm0.2}$, with no correlation between the cloud surface density,$\Sigma$, and $R$. In contrast with the general idea, we find a rather largerange of values of $\Sigma$, from 2 to $300 M_\odot$ pc$^{-2}$, and asystematic decrease with increasing Galactic radius, $R_{\rm gal}$. The cloudvelocity dispersion and the normalization $\sigma_0=\sigma_v/R^{1/2}$ bothdecrease systematically with $R_{\rm gal}$. When studied over the wholeGalactic disk, there is a large dispersion in the line width-size relation, anda significantly better correlation between $\sigma_v$ and $\Sigma\,R$. Thenormalization of this correlation is constant to better than a factor of twofor $R_{\rm gal}<20$ kpc. This relation is used to disentangle the ambiguitybetween near and far kinematic distances. We report a strong variation of theturbulent energy injection rate. In the outer Galaxy it may be maintained byaccretion through the disk and/or onto the clouds, but neither source can drivethe 100 times higher cloud-averaged injection rate in the inner Galaxy.

The gas accretion and star-formation histories of galaxies like the Milky Wayremain an outstanding problem in astrophysics. Observations show that 8 billionyears ago, the progenitors to Milky Way-mass galaxies were forming stars 30times faster than today and predicted to be rich in molecular gas, in contrastwith low present-day gas fractions ($<$10%). Here we show detections ofmolecular gas from the CO(J=3-2) emission (rest-frame 345.8 GHz) in galaxies atredshifts z=1.2-1.3, selected to have the stellar mass and star-formation rateof the progenitors of today's Milky Way-mass galaxies. The CO emission revealslarge molecular gas masses, comparable to or exceeding the galaxy stellarmasses, and implying most of the baryons are in cold gas, not stars. Thegalaxies' total luminosities from star formation and CO luminosities yield longgas-consumption timescales. Compared to local spiral galaxies, thestar-formation efficiency, estimated from the ratio of total IR luminosity toCO emission,} has remained nearly constant since redshift z=1.2, despite theorder of magnitude decrease in gas fraction, consistent with results for othergalaxies at this epoch. Therefore the physical processes that determine therate at which gas cools to form stars in distant galaxies appear to be similarto that in local galaxies.

Theoretical studies on the response of interstellar gas to a gravitationalpotential disc with a quasi-stationary spiral arm pattern suggest that the gasexperiences a sudden compression due to standing shock waves at spiral arms.This mechanism, called a galactic shock wave, predicts that gas spiral armsmove from downstream to upstream of stellar arms with increasing radius insidea corotation radius. In order to investigate if this mechanism is at work inthe grand-design spiral galaxy M51, we have measured azimuthal offsets betweenthe peaks of stellar mass and gas mass distributions in its two spiral arms.The stellar mass distribution is created by the spatially resolved spectralenergy distribution fitting to optical and near infrared images, while the gasmass distribution is obtained by high-resolution CO and HI data. For the innerregion (r < 150"), we find that one arm is consistent with the galactic shockwhile the other is not. For the outer region, results are less certain due tothe narrower range of offset values, the weakness of stellar arms, and thesmaller number of successful offset measurements. The results suggest that thenature of two inner spiral arms are different, which is likely due to aninteraction with the companion galaxy.

We study the properties of 66 galaxies with kinematically misaligned gas andstars from MaNGA survey. The fraction of kinematically misaligned galaxiesvaries with galaxy physical parameters, i.e. M*, SFR and sSFR. According totheir sSFR, we further classify these 66 galaxies into three categories, 10star-forming, 26 "Green Valley" and 30 quiescent ones. The properties ofdifferent types of kinematically misaligned galaxies are different in that thestar-forming ones have positive gradient in D4000 and higher gas-phasemetallicity, while the green valley/quiescent ones have negative D4000gradients and lower gas-phase metallicity on average. There is evidence thatall types of the kinematically misaligned galaxies tend to live in moreisolated environment. Based on all these observational results, we propose ascenario for the formation of star forming galaxies with kinematicallymisaligned gas and stars - the progenitor accretes misaligned gas from agas-rich dwarf or cosmic web, the cancellation of angular momentum from gas-gascollisions between the pre-existing gas and the accreted gas largelyaccelerates gas inflow, leading to fast centrally-concentrated star-formation.The higher metallicity is due to enrichment from this star formation. For thekinematically misaligned green valley and quiescent galaxies, they might beformed through gas-poor progenitors accreting kinematically misaligned gas fromsatellites which are smaller in mass.

We present Magellan/IMACS spectroscopy of the recently discovered Milky Waysatellite Tucana III (Tuc III). We identify 26 member stars in Tuc III, fromwhich we measure a mean radial velocity of v_hel = -102.3 +/- 0.4 (stat.) +/-2.0 (sys.) km/s, a velocity dispersion of 0.1^+0.7_-0.1 km/s, and a meanmetallicity of [Fe/H] = -2.42^+0.07_-0.08. The upper limit on the velocitydispersion is sigma < 1.5 km/s at 95.5% confidence, and the corresponding upperlimit on the mass within the half-light radius of Tuc III is 9.0 x 10^4 Msun.We cannot rule out mass-to-light ratios as large as 240 Msun/Lsun for Tuc III,but much lower mass-to-light ratios that would leave the systembaryon-dominated are also allowed. We measure an upper limit on the metallicityspread of the stars in Tuc III of 0.19 dex at 95.5% confidence. Tuc III has asmaller metallicity dispersion and likely a smaller velocity dispersion thanany known dwarf galaxy, but a larger size and lower surface brightness than anyknown globular cluster. Its metallicity is also much lower than those of theclusters with similar luminosity. We therefore tentatively suggest that Tuc IIIis the tidally-stripped remnant of a dark matter-dominated dwarf galaxy, butadditional precise velocity and metallicity measurements will be necessary fora definitive classification. If Tuc III is indeed a dwarf galaxy, it is one ofthe closest external galaxies to the Sun. Because of its proximity, the mostluminous stars in Tuc III are quite bright, including one star at V=15.7 thatis the brightest known member star of an ultra-faint satellite.

Massive early-type galaxies have higher metallicities and higher ratios of$\alpha$ elements to iron than their less massive counterparts. Reproducingthese correlations has long been a problem for hierarchical galaxy formationtheory, both in semi-analytic models and cosmological hydrodynamic simulations.We show that a simulation in which gas cooling in massive dark haloes isquenched by radio-mode active galactic nuclei (AGNs) feedback naturallyreproduces the observed trend between $\alpha$/Fe and the velocity dispersionof galaxies, $\sigma$. The quenching occurs earlier for more massive galaxies.Consequently, these galaxies complete their star formation before $\alpha$/Feis diluted by the contribution from type Ia supernovae. For galaxies moremassive than $\sim 10^{11}~M_\odot$ whose $\alpha$/Fe correlates positivelywith stellar mass, we find an inversely correlated mass-metallicity relation.This is a common problem in simulations in which star formation in massivegalaxies is quenched either by quasar- or radio-mode AGN feedback. The earlysuppression of gas cooling in progenitors of massive galaxies prevents themfrom recapturing enriched gas ejected as winds. Simultaneously reproducing the[$\alpha$/Fe]-$\sigma$ relation and the mass-metallicity relation is, thus,difficult in the current framework of galaxy formation.