We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded u, g and i-band image obtained with the DECam wide-field camera mounted on the 4meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the Next Generation Fornax Survey (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii 0.1 < r e < 2.8 kpc and average effective surface brightness values 22.0 < µ i < 28.0 mag arcsec −2 . We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters. We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of M i = −8.0 mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of > 75% at luminosities brighter than M i ≃ −15.0 mag to 0% at luminosities fainter than M i ≃ −10.0 mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below ∼100 kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.

We present a photometric study of the dwarf galaxy population in the core region (≲ r vir 4) of the Fornax galaxy cluster based on deep u ′ g ′ i ′ photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4-meter Blanco telescope at the Cerro-Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities −17 ≲ M g ′ ≲ −8 mag, corresponding to typical stellar masses of 9.5 ≳ log M ⋆ M ⊙ ≳ 5.5, reaching ∼ 3 mag deeper in point-source luminosity and ∼4 mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by singlecomponent Sérsic models with average Sérsic indices of ⟨n⟩ u ′ ,g ′ ,i ′ = (0.78 − 0.83) ± 0.02, and average effective radii of ⟨r e ⟩ u ′ ,g ′ ,i ′ = (0.67 − 0.70) ± 0.02 kpc. Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ∼5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: i) dwarf galaxies assemble mass inside the half-mass radius up to log M ⋆ ≈ 8.0, ii) isometric mass assembly in the range 8.0 ≲ log M ⋆ M ⊙ ≲ 10.5, and iii) massive galaxies assemble stellar mass predominantly in their halos at log M ⋆ ≈10.5 and above.

We present the results of a wide spectroscopic survey aimed at detecting extragalactic globular clusters (GCs) in the core of the Fornax cluster. About 4500 low resolution spectra (from 4800 to 10000Å) were observed in 25 VLT/VIMOS masks covering the central 1 deg 2 around the dominant galaxy NGC 1399 corresponding to ∼175 kpc galactocentric radius. We describe the methodology used for data reduction and data analysis. We found a total of 387 unique physical objects (372 GCs and 15 ultra compact dwarfs) in the field covered by our observations. Most of these objects are associated with NGC 1399, with only 10% likely belonging to other giant galaxies. The new VIMOS dataset is complementary to the many GC catalogues already present in the literature and it brings the total number of tracer particles around NGC 1399 to more than 1130 objects. With this comprehensive radial velocity sample we have found that the velocity dispersion of the GC population (equally for red and blue GC populations) shows a relatively sharp increase from low velocity dispersion (∼ 250 − 350 km s −1 ) to high velocity dispersion (∼ 300 − 400 km s −1 ) at projected radius of ≈ 10 arcmin (∼ 60 kpc) from the galaxy centre. This suggests that at a projected radius of ≈ 60 kpc both blue and red GC populations begin to be governed by the dominating Fornax cluster potential, rather than by the central NGC 1399 galaxy potential. This kinematic evidence corroborates similar results found using surface brightness analysis and planetary nebulae kinematics.

The NGVS-IR project (Next Generation Virgo Survey -Infrared) is a contiguous near-infrared imaging survey of the Virgo cluster of galaxies. It complements the optical wide-field survey of Virgo (NGVS). The current state of NGVS-IR consists of K s -band imaging of 4 deg 2 centered on M87, and J and K s -band imaging of ∼ 16 deg 2 covering the region between M49 and M87. In this paper, we present the observations of the central 4 deg 2 centered on Virgo's core region. The data were acquired with WIRCam on the Canada-France-Hawaii Telescope and the total integration time was 41 hours distributed in 34 contiguous tiles. A survey-specific strategy was designed to account for extended galaxies while still measuring accurate sky brightness within the survey area. The average 5σ limiting magnitude is K s = 24.4 AB mag and the 50% completeness limit is K s = 23.75 AB mag for point source detections, when using only images with better than 0.7 seeing (median seeing 0.54 ). Star clusters are marginally resolved in these image stacks, and Virgo galaxies with µ Ks 24.4 AB mag arcsec −2 are detected. Combining the K s data with optical and ultraviolet data, we build the uiK s color-color diagram which allows a very clean color-based selection of globular clusters in Virgo. This diagnostic plot will provide reliable globular cluster candidates for spectroscopic follow-up campaigns needed to continue the exploration of Virgo's photometric and kinematic sub-structures, and will help the design of future searches for globular clusters in extragalactic systems. We show that the new uiK s diagram displays significantly clearer substructure in the distribution of stars, globular clusters, and galaxies than the gzK s diagram -the NGVS+NGVS-IR-equivalent of the BzK diagram, which is widely used in cosmological surveys. Equipped with this powerful new tool, future NGVS-IR investigations based on the uiK s diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies.

We reliably extend the stellar mass - size relation over 0.2 ≤ z ≤ 2 to low stellar mass galaxies by combining the depth of Hubble Frontier Fields (HFF) with the large volume covered by CANDELS. Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e. half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 107M⊙, star-forming galaxies are well represented by a single power law on the mass-size plane over our entire redshift range. Conversely, the stellar mass - size relation is steep for quiescent galaxies with stellar masses ≥1010.3 M⊙ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of ∼1kpc at z ≤ 1. As a result, a double power law is preferred for the stellar mass - size relation of quiescent galaxies, at least above 107 M⊙. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses ≥109.5 M⊙ and quiescent galaxies with stellar masses ≥1010.3 M⊙ have undergone significant size growth since z ∼ 2, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass-size relation is continuous below 107 M⊙, but a more complicated functional form is necessary to describe the relation.

Clues to the formation and evolution of nuclear star clusters (NSCs) lie in their stellar populations. However, these structures are often very faint compared to their host galaxy, and spectroscopic analysis of NSCs is hampered by contamination of light from the rest of the system. With the introduction of wide-field integral field unit (IFU) spectrographs, new techniques have been developed to model the light from different components within galaxies, making it possible to cleanly extract the spectra of the NSCs and study their properties with minimal contamination from the light of the rest of the galaxy. This work presents the analysis of the NSCs in a sample of 12 dwarf galaxies in the Fornax Cluster observed with the Multi-Unit Spectroscopic Explorer (MUSE). Analysis of the stellar populations and star formation histories reveal that all the NSCs show evidence of multiple episodes of star formation, indicating that they have built up their mass further since their initial formation. The NSCs were found to have systematically lower metallicities than their host galaxies, which is consistent with a scenario for mass assembly through mergers with infalling globular clusters, whilst the presence of younger stellar populations and gas emission in the core of two galaxies is indicative of in-situ star formation. We conclude that the NSCs in these dwarf galaxies likely originated as globular clusters that migrated to the core of the galaxy that have built up their mass mainly through mergers with other infalling clusters, with gas-inflow leading to in-situ star formation playing a secondary role.

Context. Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L * galaxies through successive mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo. Aims. Considering that fossils are the remnants of mergers in ordinary groups, the merger history of the progenitor group is expected to be imprinted in the fossil central galaxy (FCG). We present for the first time radial gradients of single-stellar population (SSP) ages and metallicites in a sample of FCGs to constrain their formation scenario. We also measure line-strength gradients for the strongest absorption features in these galaxies. Methods. We took deep spectra with the long-slit spectrograph ISIS at the William Herschel Telescope (WHT) for six FCGs. The obtained spectra are fit with Pegase HR SSP models within the full-spectrum fitting package ULySS yielding SSP ages and metallicities of the stellar populations. We measure radial gradients of SSP ages and metallicities along the major axes. Lick indices are measured for the strongest absorption features to determine line-strength gradients and compare with the full-spectrum fitting results. Results. Our sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersion of σ 0 = 271 ± 28 km s −1 . Metallicity gradients are throughout negative with comparatively flat slopes of ∇ [Fe/H] = −0.19 ± 0.08 while age gradients are found to be insignificant (∇ age = 0.00 ± 0.05). All FCGs lie on the fundamental plane, suggesting that they are virialised systems. We find that gradient strengths and central metallicities are similar to those found in cluster ellipticals of similar mass. Conclusions. The comparatively flat metallicity gradients with respect to those predicted by monolithic collapse (∇ Z = −0.5) suggest that fossils are indeed the result of multiple major mergers. Hence we conclude that fossils are not "failed groups" that formed with a top-heavy luminosity function. The low scatter of gradient slopes suggests a similar merging history for all galaxies in our sample.

New wide-field u g r i z Dark Energy Camera observations centred on the nearby giant elliptical galaxy NGC 5128 covering ∼ 21 deg 2 are used to compile a new catalogue of ∼ 3 200 globular clusters (GCs). We report 2 404 newly identified candidates, including the vast majority within ∼ 140 kpc of NGC 5128. We find evidence for a transition at a galactocentric radius of R gc ≈ 55 kpc from GCs "intrinsic" to NGC 5128 to those likely to have been accreted from dwarf galaxies or that may transition to the intragroup medium of the Centaurus A galaxy group. We fit power-law surface number density profiles of the form Σ N,Rgc ∝ R Γ gc and find that inside the transition radius, the red GCs are more centrally concentrated than the blue, with Γ inner,red ≈ −1.78 and Γ inner,blue ≈ −1.40, respectively. Outside this region both profiles flatten, more dramatically for the red GCs (Γ outer,red ≈ −0.33) compared to the blue (Γ outer,blue ≈ −0.61), although the former is more likely to suffer contamination by background sources. The median (g −z ) 0 = 1.27 mag colour of the inner red population is consistent with arising from the amalgamation of two giant galaxies each less luminous than present-day NGC 5128. Both in-and out-ward of the transition radius, we find the fraction of blue GCs to dominate over the red GCs, indicating a lively history of minormergers. Assuming the blue GCs to originate primarily in dwarf galaxies, we model the population required to explain them, while remaining consistent with NGC 5128's present-day spheroid luminosity. We find that that several dozen dwarfs of luminosities L dw,V 10 6−9.3 L V, , following a Schechter luminosity function with a faint-end slope of −1.50 α −1.25 is favoured, many of which may have already been disrupted in NGC 5128's tidal field.