In recent years, multiple studies have reported substantial populations oflarge, low-surface-brightness galaxies in local galaxy clusters. Varioustheories that aim to explain the presence of such ultra-diffuse galaxies (UDGs)have since been proposed. A key question that will help to differentiatebetween models is whether UDGs have counterparts in lower-mass host haloes, andwhat their abundance as a function of halo mass is. In this study we extend ourprevious study of UDGs in galaxy clusters to galaxy groups. We measure theabundance of UDGs in 325 spectroscopically-selected groups from the Galaxy AndMass Assembly (GAMA) survey. We make use of the overlapping imaging from theESO Kilo-Degree Survey (KiDS), from which we can identify galaxies with meansurface brightnesses within their effective radii down to ~25.5 magarcsec$^{-2}$ in the r-band. We are able to measure a significant overdensityof UDGs (with sizes r_eff > 1.5 kpc) in galaxy groups down to M200=10^12 Msun,a regime where approximately only 1 in 10 groups contains a UDG that we candetect. We combine measurements of the abundance of UDGs in haloes that coverthree orders of magnitude in halo mass, finding that their numbers scale quitesteeply with halo mass; N_UDG (R<R200) $\propto$ M200^(1.11+/-0.07). To betterinterpret this, we also measure the mass-richness relation for brightergalaxies down to $M^*_r$+2.5 in the same GAMA groups, and find a much shallowerrelation of N_Bright (R<R200) $\propto$ M200^(0.78+/-0.05). This shows thatUDGs are relatively more abundant, compared to bright galaxies, in massiveclusters than in groups. We discuss implications, but whether this differenceis related to a higher destruction rate of UDGs in groups, or whether massivehaloes have a positive effect on their formation, is not yet clear.

Markov Chain Monte Carlo based Bayesian data analysis has now become themethod of choice for analyzing and interpreting data in almost all disciplinesof science. In astronomy, over the last decade, we have also seen a steadyincrease in the number of papers that employ Monte Carlo based Bayesiananalysis. New, efficient Monte Carlo based methods are continuously beingdeveloped and explored. In this review, we first explain the basics of Bayesiantheory and discuss how to set up data analysis problems within this framework.Next, we provide an overview of various Monte Carlo based methods forperforming Bayesian data analysis. Finally, we discuss advanced ideas thatenable us to tackle complex problems and thus hold great promise for thefuture. We also distribute downloadable computer software (available athttps://github.com/sanjibs/bmcmc/ ) that implements some of the algorithms andexamples discussed here.

We present a new analysis of the stellar mass function and morphology ofrecently-quenched galaxies (RQGs), whose star formation has been recentlyquenched for some reason. The COSMOS2015 catalog was exploited to select thosegalaxies at 0.2 < z < 4.8, over 1.5 deg2 of the Cosmic Evolution Survey(COSMOS) UltraVISTA field. This is the first time that RQGs are consistentlyselected and studied in such a wide range of redshift. We find increasingnumber density of RQGs with time in a broad mass range at z>1, while low-massRQGs start to grow very rapidly at z < 1. We also demonstrate that themigration of RQGs may largely drive the evolution of the stellar mass functionof passive galaxies. Moreover, we find that the morphological type distributionof RQGs are intermediate between those of star-forming and passive galaxies.These results indicate that RQGs represent a major transitional phase of galaxyevolution, in which star-forming galaxies turn into passive galaxies,accompanied by the build up of spheroidal component.

A new deep HI survey of the galaxy Messier 33 is presented, based onobservations obtained at the Dominion Radio Astrophysical Observatory. Weobserve a perturbed outer gas distribution and kinematics in M33, and confirmthe disk warping as a significant kinematical twist of the major axis of thevelocity field, though no strong tilt is measured, in agreement with previouswork. Evidence for a new low brightness HI component with anomalous velocity isreported. It harbours a large velocity scatter, as its kinematics both exceedsand lags the rotation of the disk, and leaks in the forbidden velocity zone ofapparent counter-rotation. The observations also reveal wide and multiple peakHI profiles which can be partly explained by crowded orbits in the framework ofthe warp model. Asymmetric motions are identified in the velocity field, aspossible signatures of a lopsided potential and the warp. The mass distributionmodeling of the hybrid Halpha-HI rotation curve favours a cuspy dark matterhalo with a concentration in disagreement with the LambdaCDM dark halomass-concentration relationship. The total mass enclosed in 23 kpc is 8 10^10Msol, of which 11% are stars and gas. At the virial radius of the cuspy halo,the resulting total mass is 5 10^11 Msol, but with a baryonic mass fraction of2% only. This strongly suggests a more realistic radius encompassing the totalmass of M33 well smaller than the virial radius of the halo, maybe comparableto the size of the HI disk.

We investigate the energy sources of random turbulent motions of ionised gasfrom H$\alpha$ emission in eight local star-forming galaxies from theSydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. Thesegalaxies satisfy strict pure star-forming selection criteria to avoidcontamination from active galactic nuclei (AGN) or strong shocks/outflows.Using the relatively high spatial and spectral resolution of SAMI, we find that-- on sub-kpc scales our galaxies display a flat distribution of ionised gasvelocity dispersion as a function of star formation rate (SFR) surface density.A major fraction of our SAMI galaxies shows higher velocity dispersion thanpredictions by feedback-driven models, especially at the low SFR surfacedensity end. Our results suggest that additional sources beyond star formationfeedback contribute to driving random motions of the interstellar medium (ISM)in star-forming galaxies. We speculate that gravity, galactic shear, and/ormagnetorotational instability (MRI) may be additional driving sources ofturbulence in these galaxies.