We present the results of a study of the amount and distribution of coldatomic gas, as well its correlation with recent star formation in a sample ofextremely faint dwarf irregular galaxies. Our sample is drawn from the FaintIrregular Galaxy GMRT Survey (FIGGS) and its extension, FIGGS2. We use twodifferent methods to identify cold atomic gas. In the first method,line-of-sight HI spectra were decomposed into multiple Gaussian components andnarrow Gaussian components were identified as cold HI. In the second method,the brightness temperature (T_B) is used as a tracer of cold HI. We find thatthe amount of cold gas identified using the T_B method is significantly largerthan the amount of gas identified using Gaussian decomposition. We also findthat a large fraction of the cold gas identified using the T_B method isspatially coincident with regions of recent star formation, although theconverse is not true. That is only a small fraction of the regions with recentstar formation are also covered by cold gas. For regions where the starformation and the cold gas overlap, we study the relationship between the starformation rate density and the cold \HI column density. We find that the starformation rate density has a power law dependence on the HI column density, butthat the slope of this power law is significantly flatter than that of thecanonical Kennicutt-Schmidt relation.

We study the evolution of global shapes of galaxies using cosmologicalsimulations. The shapes refer to the components of dark matter (DM), stars andgas at the stellar half-mass radius. Most galaxies undergo a characteristiccompaction event into a blue nugget at $z\sim2-4$, which marks the transitionfrom a DM-dominated central body to a self-gravitating baryonic core. We findthat in the high-$z$, DM-dominated phase, the stellar and DM systems tend to betriaxial, preferentially prolate and mutually aligned. The elongation issupported by an anisotropic velocity dispersion that originates from theassembly of the galaxy along a dominant large-scale filament. We estimate thattorques by the dominant halo are capable of inducing the elongation of thestellar system and its alignment with the halo. Then, in association with thetransition to self-gravity, small-pericenter orbits puff up and the DM andstellar systems evolve into a more spherical and oblate configuration, alignedwith the gas disc and associated with rotation. This transition typicallyoccurs when the stellar mass is $\sim 10^9$ M$_\odot$ and the escape velocityin the core is $\sim 100$ km s$^{-1}$, indicating that supernova feedback maybe effective in keeping the core DM-dominated and the system prolate. The earlyelongated phase itself may be responsible for the compaction event, and thetransition to the oblate phase may be associated with the subsequent quenchingin the core.

New deep VLA D array HI observations of the highly inclined nearby spiralgalaxy NGC 2683 are presented. Archival C array data were processed and addedto the new observations. To investigate the 3D structure of the atomic gasdisk, we made different 3D models for which we produced model HI data cubes.The main ingredients of our best-fit model are (i) a thin disk inclined by 80degrees; (ii) a crude approximation of a spiral and/or bar structure by anelliptical surface density distribution of the gas disk; (iii) a slight warp ininclination; (iv) an exponential flare; and (v) a low surface-density gas ring.The slope of NGC 2683's flare is comparable, but somewhat steeper than those ofother spiral galaxies. NGC 2683's maximum height of the flare is alsocomparable to those of other galaxies. On the other hand, a saturation of theflare is only observed in NGC 2683. Based on the comparison between the highresolution model and observations, we exclude the existence of an extendedatomic gas halo around the optical and thin gas disk. Under the assumption ofvertical hydrostatic equilibrium we derive the vertical velocity dispersion ofthe gas. The high turbulent velocity dispersion in the flare can be explainedby energy injection by (i) supernovae, (ii) magneto-rotational instabilities,(iii) ISM stirring by dark matter substructure, or (iv) external gas accretion.The existence of the complex large-scale warping and asymmetries favorsexternal gas accretion as one of the major energy sources that drivesturbulence in the outer gas disk. We propose a scenario where this externalaccretion leads to turbulent adiabatic compression that enhances the turbulentvelocity dispersion and might quench star formation in the outer gas disk ofNGC 2683.

We present MUSE observations of AM1354-250, confirming its status as acollisional ring galaxy which has recently undergone an interaction, creatingits distinctive shape. We analyse the stellar and gaseous emission throughoutthe galaxy finding direct evidence that the gaseous ring is expanding with avelocity of $\sim$70km.s$^{-1}$ and that star formation is occurring primarilyin HII regions associated with the ring. This star formation activity is likelytriggered by the interaction. We find evidence for several excitationmechanisms in the gas, including emission consistent with shocked gas in theexpanding ring and a region of LINER-like emission in the central core of thegalaxy. Evidence of kinematic disturbance in both the stars and gas, possiblyalso triggered by the interaction, can be seen in all of the velocity maps. Thering galaxy retains weak spiral structure, strongly suggesting the progenitorgalaxy was a massive spiral prior to the collision with its companion anestimated $140 \pm 12$ Myr ago.