Pure disk galaxies without any bulge component, i.e., neither classical norpseudo, seem to have escaped the affects of merger activity inherent tohierarchical galaxy formation models as well as strong internal secularevolution. We discover that a significant fraction (15 - 18 %) of disk galaxies in theHubble Deep Field (0.4 < z < 1.0) as well as in the local Universe (0.02 < z <0.05) are such pure disk systems (hereafter, PDS). The spatial distribution oflight in these PDS is well described by a single exponential function from theoutskirts to the centre and appears to have remained intact over the last 8billion years keeping the mean central surface brightness and scale-lengthnearly constant. These two disk parameters of PDS are brighter and shorter,respectively, than of those disks which are part of disk galaxies with bulges. Since the fraction of PDS as well as their profile defining parameters do notchange, it indicates that these galaxies have not witnessed either majormergers or multiple minor mergers since z~1. However, there is substantialincrease in their total stellar mass and total size over the same time range.This suggests that smooth accretion of cold gas via cosmic filaments is themost probable mode of their evolution. We speculate that PDS are dynamicallyhotter and cushioned in massive dark matter halos which may prevent them fromundergoing strong secular evolution.

We investigate the relative importance of two galactic outflow suppressionmechanisms : a) Cosmological infall of the intergalactic gas onto the galaxy,and b) the existence of a hot circumgalactic medium (CGM). Considering onlyradial motion, the infall reduces the speed of outflowing gas and even haltsthe outflow, depending on the mass and redshift of the galaxy. For star forminggalaxies there exists an upper mass limit beyond which outflows are suppressedby the gravitational field of the galaxy. We find that infall can reduce thisupper mass limit approximately by a factor of two (independent of theredshift). Massive galaxies ($\gtrsim 10^{12} M_{\odot}$) host large reservoirof hot, diffuse CGM around the central part of the galaxy. The CGM acts as abarrier between the infalling and outflowing gas and provides an additionalsource of outflow suppression. We find that at low redshifts ($z\lesssim3.5$),the CGM is more effective than the infall in suppressing the outflows.Together, these two processes give a mass range in which galaxies are unable tohave effective outflows. We also discuss the impact of outflow suppression onthe enrichment history of the galaxy and its environment.

Taking advantage of the Sloan Digital Sky Survey Stripe82 data, we haveexplored the spatial distribution of ultra-diffuse galaxies (UDGs) within anarea of 8$\times$8 Mpc$^2$ centred around the galaxy cluster Abell 168 ($z$ =0.045). This intermediate massive cluster ($\sigma$ = 550 km s$^{-1}$) issurrounded by a complex large-scale structure. Our work confirms the presenceof UDGs in the cluster and in the large-scale structure that surrounds it, andit is the first detection of UDGs outside clusters. Approximately 50 per centof the UDGs analysed in the selected area inhabit the cluster region ($\sim$11$\pm$ 5 per cent in the core and $\sim$39 $\pm$ 9 per cent in the outskirts),whereas the remaining UDGs are found outside the main cluster structure($\sim$50 $\pm$ 11 per cent). The colours and the spatial distribution of theUDGs within this large-scale structure are more similar to the dwarf galaxiesthan to L$_\star$ galaxies, suggesting that most of UDGs could be bona fidedwarf galaxies.