The gas surrounding galaxies outside their disks or interstellar medium andinside their virial radii is known as the circumgalactic medium (CGM). Inrecent years this component of galaxies has assumed an important role in ourunderstanding of galaxy evolution owing to rapid advances in observationalaccess to this diffuse, nearly invisible material. Observations and simulationsof this component of galaxies suggest that it is a multiphase mediumcharacterized by rich dynamics and complex ionization states. The CGM is asource for a galaxy's star-forming fuel, the venue for galactic feedback andrecycling, and perhaps the key regulator of the galactic gas supply. We reviewour evolving knowledge of the CGM with emphasis on its mass, dynamical state,and coevolution with galaxies. Observations from all redshifts and from acrossthe electromagnetic spectrum indicate that CGM gas has a key role in galaxyevolution. We summarize the state of this field and pose unanswered questionsfor future research.

Cold hydrogen gas is the raw fuel for star formation in galaxies, and itspartition into atomic and molecular phases is a key quantity for galaxyevolution. In this paper, we combine Atacama Large Millimeter Array and Arecibosingle-dish observations to estimate the molecular-to-atomic hydrogen massratio for massive star-forming galaxies at $z\sim$ 0.2 extracted from the HIGHzsurvey, i.e., some of the most massive gas-rich systems currently known. Weshow that the balance between atomic and molecular hydrogen in these galaxiesis similar to that of local main-sequence disks, implying that atomic hydrogenhas been dominating the cold gas mass budget of star-forming galaxies for atleast the last three billion years. In addition, despite harboring gasreservoirs that are more typical of objects at the cosmic noon, HIGHz galaxieshost regular rotating disks with low gas velocity dispersions suggesting thathigh total gas fractions do not necessarily drive high turbulence in theinterstellar medium.

Aims. We use accurate data on distances and radial velocities of galaxiesaround the Local Group, as well as around 14 other massive nearby groups, toestimate their radius of the zero-velocity surface, $R_0$, which separates anygroup against the global cosmic expansion. Methods. Our $R_0$ estimate was based on fitting the data to the velocityfield expected from the spherical infall model, including effects of thecosmological constant. The reported uncertainties were derived by a Monte Carlosimulation. Results. Testing various assumptions about a location of the groupbarycentre, we found the optimal estimates of the radius to be$0.91\pm0.05$~Mpc for the Local Group, and $0.93\pm0.02$~Mpc for a syntheticgroup stacked from 14 other groups in the Local Volume. Under the standardPlanck model parameters, these quantities correspond to the total mass of thegroup $\sim (1.6\pm0.2) 10^{12} M_{\odot}$. Thus, we are faced with theparadoxical result that the total mass estimate on the scale of $R_0 \approx(3- 4) R_{vir}$ is only $~60$% of the virial mass estimate. Anyway, we concludethat wide outskirts of the nearby groups do not contain a large amount ofhidden mass outside their virial radius.

We present ALMA Cycle 4 observations of CO(1-0), CO(3-2), and $^{13}$CO(3-2)line emission in the brightest cluster galaxy of RXJ0821+0752. This is one ofthe first detections of $^{13}$CO line emission in a galaxy cluster. Half ofthe CO(3-2) line emission originates from two clumps of molecular gas that arespatially offset from the galactic center. These clumps are surrounded bydiffuse emission that extends $8~{\rm kpc}$ in length. The detected $^{13}$COemission is confined entirely to the two bright clumps, with any emissionoutside of this region lying below our detection threshold. Two distinctvelocity components with similar integrated fluxes are detected in the$^{12}$CO spectra. The narrower component ($60~{\rm km}~{\rm s}^{-1}$ FWHM) isconsistent in both velocity centroid and linewidth with $^{13}$CO(3-2)emission, while the broader ($130-160~{\rm km}~{\rm s}^{-1}$), slightlyblueshifted wing has no associated $^{13}$CO(3-2) emission. A simple localthermodynamic model indicates that the $^{13}$CO emission traces $2.1\times10^{9}~{\rm M}_\odot$ of molecular gas. Isolating the $^{12}$CO velocitycomponent that accompanies the $^{13}$CO emission yields a CO-to-H$_2$conversion factor of $\alpha_{\rm CO}=2.3~{\rm M}_{\odot}~({\rmK~km~s^{-1}})^{-1}$, which is a factor of two lower than the Galactic value.Adopting the Galactic CO-to-H$_2$ conversion factor in brightest clustergalaxies may therefore overestimate their molecular gas masses by a factor oftwo. This is within the object-to-object scatter from extragalactic sources, socalibrations in a larger sample of clusters are necessary in order to confirm asub-Galactic conversion factor.