Observations have shown that massive star-forming clumps are present in theinternal structure of high-redshift galaxies. One way to study these clumps indetail with a higher spatial resolution is by exploiting the power of stronggravitational lensing which stretches images on the sky. In this work, wepresent an analysis of the clumpy galaxy A68-HLS115 at $z=1.5858$, locatedbehind the cluster Abell 68, but strongly lensed by a cluster galaxy member.Resolved observations with SINFONI/VLT in the near-infrared show Ha, Hb, [NII],and [OIII] emission lines. Combined with images covering the B band to thefar-infrared and CO(2-1) observations, this makes this galaxy one of the onlysources for which such multi-band observations are available and for which itis possible to study the properties of resolved star-forming clumps and toperform a detailed analysis of the integrated properties, kinematics, andmetallicity. We obtain a stability of $\upsilon_{rot}/\sigma_0 = 2.73$ bymodeling the kinematics, which means that the galaxy is dominated by rotation,but this ratio also indicates that the disk is marginally stable. We find ahigh intrinsic velocity dispersion of $80\pm10$ km s$^{-1}$ that could beexplained by the high gas fraction of $f_{gas}=0.75\pm0.15$ observed in thisgalaxy. This high $f_{gas}$ and the observed sSFR of $\rm 3.12 \, Gyr^{-1}$suggest that the disk turbulence and instabilities are mostly regulated byincoming gas. The direct measure of the Toomre stability criterion of$Q_{crit}=0.70$ could also indicate the presence of a quasi-stable thick disk.Finally, we identify three clumps in the Ha map which have similar velocitydispersions, metallicities, and seem to be embedded in the rotating disk. Thesethree clumps contribute together to $40\%$ on the SFR(Ha) of the galaxy andshow a SFR density about $100$ times higher than HII regions in the localUniverse.

We present a new method to study the characteristic scales of collapse andfragmentation in galactic disks. Clump formation is seeded in simulations viacontrolled perturbations with a specified wavelength and velocity. These areapplied to otherwise quiet gas disks ranging from analogues of present dayspirals to gas-rich, high-redshift galaxies. The results are compared to lineartheory, turbulently perturbed disks and observations. The results reflect theexpectations of linear, non-axisymmetric theory with a finite window for growthinto a bound clump. We identify two new modes of clump formation:rotation-driven fission and fragmentation of tidal tails, though both areexpected to rarely contribute to clump formation in observed disks. We findthat bound clumps are generally much smaller than the so-called Toomre mass.The preferred scale for fragmentation increases with the disk gas mass butcannot produce bound objects larger than $\sim10^9$ M$_{\odot}$. The mostlikely bound clump mass increases from $3\times10^6$ in low mass disks up to$5\times10^8$ M$_{\odot}$. We conclude that observed massive stellar andgaseous clumps on 1 kpc scales at high redshift are most likely aggregates ofmany initially distinct bound clumps.

Fossil groups (FGs) are galaxy aggregates with an extended and luminous X-rayhalo, which are dominated by a very massive early-type galaxy and lack of L*objects. FGs are indeed characterized by a large magnitude gap between theircentral and surrounding galaxies. This is explained by either speculating thatFGs are failed groups that formed without bright satellite galaxies and did notsuffer any major merger, or by suggesting that FGs are very old systems thathad enough time to exhaust their bright satellite galaxies through multiplemajor mergers. Since major mergers leave signatures in the stellar populationsof the resulting galaxy, we study the stellar population parameters of thebrightest central galaxies (BCGs) of FGs as a benchmark against which theformation and evolution scenarios of FGs can be compared. We present long-slitspectroscopic observations along different axes of NGC 6482 and NGC 7556, whichare the BCGs of two nearby FGs. The measurements include spatially resolvedstellar kinematics and radial profiles of line-strength indices, which weconverted into stellar population parameters using single stellar-populationmodels. NGC 6482 and NGC 7556 are very massive and large galaxies and host acentrally concentrated stellar population, which is significantly younger andmore metal rich than the rest of the galaxy. The age gradients of both galaxiesare somewhat larger than those of the other FG BCGs studied so far, whereastheir metallicity gradients are similarly negative and shallow. They havenegligible gradients of alpha-element abundance ratio. The measured metallicitygradients are less steep than those predicted for massive galaxies that formedmonolithically and evolved without experiencing any major merger. We concludethat the observed FGs formed through major mergers rather than being failedgroups that lacked bright satellite galaxies from the beginning.

Gas stripping of spiral galaxies or mergers are thought to be the formationmechanisms of lenticular galaxies. In order to determine the conditions inwhich each scenario dominates, we derive stellar populations of both the bulgeand disk regions of 279 lenticular galaxies in the MaNGA survey. We find aclear bimodality in stellar age and metallicity within the population of S0sand this is strongly correlated with stellar mass. Old and metal-rich bulgesand disks belong to massive galaxies, and young and metal-poor bulges and disksare hosted by low-mass galaxies. From this we conclude that the bulges anddisks are co-evolving. When the bulge and disk stellar ages are compared, wefind that the bulge is almost always older than the disk for massive galaxies($\textrm{M}_{\star} > 10^{10}~\textrm{M}_{\odot}$). The opposite is true forlower mass galaxies. We conclude that we see two separate populations oflenticular galaxies. The old, massive, and metal-rich population possess bulgesthat are predominantly older than their disks, which we speculate may have beencaused by morphological or inside-out quenching. In contrast, the less massiveand more metal-poor population have bulges with more recent star formation thantheir disks. We postulate they may be undergoing bulge rejuvenation (or diskfading), or compaction. Environment doesn't play a distinct role in theproperties of either population. Our findings give weight to the notion thatwhile the faded spiral scenario likely formed low-mass S0s, other processes,such as mergers, may be responsible for high-mass S0s.

The galaxies found in optical surveys fall in two distinct regions of adiagram of optical colour versus absolute magnitude: the red sequence and theblue cloud with the green valley in between. We show that the galaxies found ina submillimetre survey have almost the opposite distribution in this diagram,forming a `green mountain'. We show that these distinctive distributions follownaturally from a single, continuous, curved Galaxy Sequence in a diagram ofspecific star-formation rate versus stellar mass without there being the needfor a separate star-forming galaxy Main Sequence and region of passivegalaxies. The cause of the red sequence and the blue cloud is the geometricmapping between stellar mass/specific star-formation rate and absolutemagnitude/colour, which distorts a continuous Galaxy Sequence in the diagram ofintrinsic properties into a bimodal distribution in the diagram of observedproperties. The cause of the green mountain is Malmquist bias in thesubmillimetre waveband, with submillimetre surveys tending to select galaxieson the curve of the Galaxy Sequence, which have the highest ratios ofsubmillimetre-to-optical luminosity. This effect, working in reverse, causesgalaxies on the curve of the Galaxy Sequence to be underrepresented in opticalsamples, deepening the green valley. The green valley is therefore not evidence(1) for there being two distinct populations of galaxies, (2) for galaxies inthis region evolving more quickly than galaxies in the blue cloud and the redsequence, (c) for rapid quenching processes in the galaxy population.