Understanding the processes that drive the formation of black holes (BHs) isa key topic in observational cosmology. While the observed$M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ correlation in bulge-dominated galaxiesis thought to be produced by major mergers, the existence of a$M_{\mathrm{BH}}$--$M_{\star}$ relation, across all galaxy morphological types,suggests that BHs may be largely built by secular processes. Recent evidencethat bulge-less galaxies, which are unlikely to have had significant mergers,are offset from the $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but lieon the $M_{\mathrm{BH}}$--$M_{\star}$ relation, has strengthened thishypothesis. Nevertheless, the small size and heterogeneity of current datasets,coupled with the difficulty in measuring precise BH masses, makes itchallenging to address this issue using empirical studies alone. Here, we useHorizon-AGN, a cosmological hydrodynamical simulation to probe the role ofmergers in BH growth over cosmic time. We show that (1) as suggested byobservations, simulated bulge-less galaxies lie offset from the main$M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but on the$M_{\mathrm{BH}}$--$M_{\star}$ relation, (2) the positions of galaxies on the$M_{\mathrm{BH}}$--$M_{\star}$ relation are not affected by their mergerhistories and (3) only $\sim$35 per cent of the BH mass in today's massivegalaxies is directly attributable to merging -- the majority ($\sim$65 percent) of BH growth, therefore, takes place gradually, via secular processes,over cosmic time.

We use Keck/DEIMOS spectroscopy to confirm the cluster membership of 16ultra-diffuse galaxies (UDGs) in the Coma cluster, bringing the total number ofspectroscopically con- firmed UDGs to 24. We also identify a new clusterbackground UDG. In this pilot study of Coma UDGs in velocity phase-space, wefind evidence that most present-day Coma UDGs have a recent infall epoch whilea few may be ancient infalls. These recent infall UDGs have higher absoluterelative line-of-sight velocities, bluer optical colors, and are smaller insize, unlike the ancient infalls. The kinematics of the spectroscopicallyconfirmed Coma UDG sample is similar to that of the cluster late-type galaxypopulation. Our velocity phase-space analysis suggests that present-day clusterUDGs have a predominantly accretion origin from the field, acquire velocitiescorresponding to the mass of the cluster at accretion as they are acceleratedtowards the cluster center, and become redder and bigger as they experience thevarious physical processes at work within the cluster.

In this second paper of the series we study, with new Keck/DEIMOS spectra,the stellar populations of 7 spectroscopically confirmed ultra--diffusegalaxies (UDGs) in the Coma cluster. We find typically intermediate to old ages(~7Gyr), low metallicities ([Z/H]~ -0.7dex) and slightly super-solar abundancepatterns ([Mg/Fe] ~ +0.16dex). These properties are similar to those of dwarfgalaxies inhabiting the same area in the cluster and are mostly consistent withbeing the continuity of the stellar mass scaling relations of more massivegalaxies. These UDGs' star formation histories imply a relatively recent infallinto the Coma cluster, consistent with the theoretical predictions for adwarf-like origin. However, considering the scatter in the resulting propertiesand including other UDGs in Coma, together with the results from the velocityphase-space study of the Paper I in this series, a mixed-bag of origins isneeded to explain the nature of all UDGs. Our results thus reinforce a scenarioin which most of the UDGs are field dwarf galaxies that become quenched throughtheir later infall in cluster environments, whereas some other UDGs are genuineprimordial galaxies that failed to develop due to an early quenching phase. Theunknown proportion of dwarf-like to primordial-like UDGs leaves the enigma ofthe nature of UDGs still open.

NGC7252, which is one of the nearest major-merger galaxy remnants, is anideal laboratory to study the processes inherent to the transformation of discgalaxies to ellipticals as observed about ~1Gyr after the collision. Weobtained wide-field IFU spectroscopy with the VLT-VIMOS integral-fieldspectrograph covering the central 50"x50" of NGC7252 to map the stellar andionised gas kinematics, and the distribution and conditions of the ionised gas,revealing the extent of ongoing star formation and recent star formationhistory. We find that the inner gas disc is not counter-rotating with respectto the stars and that the stellar kinematics appear complex with a clearindication of a prolate-like rotation component suggesting a polar mergerconfiguration. The ongoing star formation rate is 2.2+-0.6 M_sun/yr and impliesa typical depletion time of 2Gyr given the molecular gas content. Furthermore,the spatially-resolved star formation history suggests a slight radialdependence, moving outwards at later times. We confirm a large AGN-ionised gascloud previously discovered 5kpc south of the nucleus, and find higherionisation also at the galaxy centre relative to the surrounding gas disc.Although the higher ionisation towards the centre is potentially degeneratewithin the central star forming ring, it may be associated with alow-luminosity AGN. Although NGC7252 has been classified as post-starburstgalaxy at the centre, the elliptical-like major-merger remnant still appearsvery active. A central kpc-scale gas disc has presumably re-formed quicklywithin the last 100Myr after final coalescence. The disc features ongoing starformation, implying Gyr long timescale to reach the red sequence through gasconsumption alone. While NGC7252 is useful to probe the transformation fromdiscs to ellipticals, it is not well-suited to study the transformation fromblue to red at this point.

We use spatially resolved two-dimensional stellar velocity maps over a$107''\times 107''$ field of view to investigate the kinematic features of 90early-type galaxies above stellar mass $10^{11.5}M_\odot$ in the MASSIVEsurvey. We measure the misalignment angle $\Psi$ between the kinematic andphotometric axes and identify local features such as velocity twists andkinematically distinct components. We find 46% of the sample to be well aligned($\Psi < 15^{\circ}$), 33% misaligned, and 21% without detectable rotation(non-rotators). Only 24% of the sample are fast rotators, the majority of which(91%) are aligned, whereas 57% of the slow rotators are misaligned with anearly flat distribution of $\Psi$ from $15^{\circ}$ to $90^{\circ}$. We findthat 11 galaxies have $\Psi \gtrsim 60^{\circ}$ and thus exhibit minor-axisrotation (or "prolate" rotation) in which the rotation is preferentially aroundthe photometric major axis. We find kinematic misalignment to occur morefrequently for higher stellar mass, lower galaxy spin, lower ellipticity, ordenser galaxy environments. In terms of local kinematic features, 51% of thesample exhibit kinematic twists of larger than $20^{\circ}$, and 2 galaxieshave kinematically distinct components. The frequency of misalignment and thebroad distribution of $\Psi$ reported here suggest that the most massiveearly-type galaxies are likely to be at least mildly triaxial, and theformation processes resulting in kinematically misaligned slow rotators such asgas-poor mergers occur frequently in this mass range.

The Milky Way and Andromeda galaxy are each surrounded by a thin plane ofsatellite galaxies that may be corotating. Cosmological simulations predictthat most satellite galaxy systems are close to isotropic with random motions,so those two well-studied systems are often interpreted as rare statisticaloutliers. We test this assumption using the kinematics of satellite galaxiesaround the Centaurus A galaxy. Our statistical analysis reveals evidence forcorotation in a narrow plane: of the 16 Centaurus A's satellites with kinematicdata, 14 follow a coherent velocity pattern aligned with the long axis of theirspatial distribution. In standard cosmology simulations, < 0.5% of CentaurusA-like systems show such behavior. Corotating satellite systems may be commonin the Universe, challenging small-scale structure formation in the prevailingcosmological paradigm.