We study the morphological and structural properties of the host galaxies associated with 57 optically-selected luminous type 2 AGN at $zsim$0.3-0.4: 16 high-luminosity Seyfert 2 (HLSy2, 8.0$le$log($L_{rm [OIII]}/L_{odot})<$8.3) and 41 obscured quasa
rs (QSO2, log($L_{rm [OIII]}/L_{odot})ge$8.3). With this work, the total number of QSO2 at $z<1$ with parametrized galaxies increases from $sim$35 to 76. Our analysis is based on HST WFPC2 and ACS images that we fit with {sc GALFIT}. HLSy2 and QSO2 show a wide diversity of galaxy hosts. The main difference lies in the higher incidence of highly-disturbed systems among QSO2. This is consistent with a scenario in which galaxy interactions are the dominant mechanism triggering nuclear activity at the highest AGN power. There is a strong dependence of galaxy properties with AGN power (assuming $L_ {rm [OIII]}$ is an adequate proxy). The relative contribution of the spheroidal component to the total galaxy light (B/T) increases with $L_ {rm [OIII]}$. While systems dominated by the spheoridal component spread across the total range of $L_ {rm [OIII]}$, most disk-dominated galaxies concentrate at log($L_{rm [OIII]}/L_{odot})<$8.6. This is expected if more powerful AGN are powered by more massive black holes which are hosted by more massive bulges or spheroids. The average galaxy sizes ($langle r_{rm e} rangle$) are 5.0$pm$1.5 kpc for HLSy2 and 3.9$pm$0.6 kpc for HLSy2 and QSO2 respectively. These are significantly smaller than those found for QSO1 and narrow line radio galaxies at similar $z$. We put the results of our work in context of related studies of AGN with quasar-like luminosities.
Massive Ultracompact Galaxies (MUGs) are common at z=2-3, but very rare in the nearby Universe. Simulations predict that the few surviving MUGs should reside in galaxy clusters, whose large relative velocities prevent them from merging, thus maintain
ing their original properties (namely stellar populations, masses, sizes and dynamical state). We take advantage of the high-completeness, large-area spectroscopic GAMA survey, complementing it with deeper imaging from the KiDS and VIKING surveys. We find a set of 22 bona-fide MUGs, defined as having high stellar mass (>8x10^10 M_Sun) and compact size (R_e<2 Kpc) at 0.02 < z < 0.3. An additional set of 7 lower-mass objects (6x10^10 < M_star/M_Sun < 8x10^10) are also potential candidates according to typical mass uncertainties. The comoving number density of MUGs at low redshift (z < 0.3) is constrained at $(1.0pm 0.4)x 10^-6 Mpc^-3, consistent with galaxy evolution models. However, we find a mixed distribution of old and young galaxies, with a quarter of the sample representing (old) relics. MUGs have a predominantly early/swollen disk morphology (Sersic index 1<n<2.5) with high stellar surface densities (<Sigma_e> ~ 10^10 M_Sun Kpc^-2). Interestingly, a large fraction feature close companions -- at least in projection -- suggesting that many (but not all) reside in the central regions of groups. Halo masses show these galaxies inhabit average-mass groups. As MUGs are found to be almost equally distributed among environments of different masses, their relative fraction is higher in more massive overdensities, matching the expectations that some of these galaxies fell in these regions at early times. However, there must be another channel leading some of these galaxies to an abnormally low merger history because our sample shows a number of objects that do not inhabit particularly dense environments. (abridged)
Using the exquisite depth of the Hubble Ultra Deep Field (HUDF12 programme) dataset, we explore the ongoing assembly of the outermost regions of the most massive galaxies ($rm M_{rm stellar}geq$ 5$times$10$^{10}$ M$_{odot}$) at $z leq$ 1. The outskir
ts of massive objects, particularly Early-Types Galaxies (ETGs), are expected to suffer a dramatic transformation across cosmic time due to continuous accretion of small galaxies. HUDF imaging allows us to study this process at intermediate redshifts in 6 massive galaxies, exploring the individual surface brightness profiles out to $sim$25 effective radii. We find that 5-20% of the total stellar mass for the galaxies in our sample is contained within 10 $< R <$ 50 kpc. These values are in close agreement with numerical simulations, and higher than those reported for local late-type galaxies ($lesssim$5%). The fraction of stellar mass stored in the outer envelopes/haloes of Massive Early-Type Galaxies increases with decreasing redshift, being 28.7% at $< z > =$ 0.1, 15.1% at $< z > =$ 0.65 and 3.5% at $< z > =$ 2. The fraction of mass in diffuse features linked with ongoing minor merger events is $>$ 1-2%, very similar to predictions based on observed close pair counts. Therefore, the results for our small albeit meaningful sample suggest that the size and mass growth of the most massive galaxies have been solely driven by minor and major merging from $z =$ 1 to today.
