The isolated elliptical (IE) NGC 7796 is accompanied by an interestingearly-type dwarf galaxy, named NGC7796-DW1. It exhibits a tidal tail, very boxyisophotes, and multiple nuclei or regions (A, B, and C) that are bluer than thebulk population of the galaxy, indicating a younger age. These properties aresuggestive of a dwarf-dwarf merger remnant. We use the Multi-Unit SpectroscopicExplorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extractcharacteristic spectra to which we apply the STARLIGHT population synthesissoftware to obtain ages and metallicities of the various population componentsof the galaxy. The galaxy's main body is old and metal-poor. A surprisingresult is the extended line emission in the galaxy, forming a ring-likestructure with a projected diameter of 2.2 kpc. The line ratios fall into theregime of HII-regions, although OB-stellar populations cannot be identified byspectral signatures. Nucleus A is a relatively old (7 Gyr or older) andmetal-poor super star cluster, most probably the nucleus of the dwarf, nowdisplaced. The star-forming regions B and C show younger and distinctly moremetal-rich components. The emission line ratios of regions B and C indicate analmost solar oxygen abundance, if compared with radiation models of HIIregions. NGC7796-DW1 occupies a particular role in the group of transition-typegalaxies with respect to its origin and current evolutionary state, being thecompanion of an IE. The dwarf-dwarf merger scenario is excluded because of themissing metal-rich merger component. A viable alternative is gas accretion froma reservoir of cold, metal-rich gas. NGC7796 has to provide this gas within itsX-ray bright halo. As illustrated by NGC7796-DW1, cold accretion may be ageneral solution to the problem of extended star formation histories intransition dwarf galaxies. (abridged)

The Milky Way (MW) offers a uniquely detailed view of galactic structure andis often regarded as a prototypical spiral galaxy. But recent observationsindicate that the MW is atypical: it has an undersized supermassive black holeat its centre; it is surrounded by a very low mass, excessively metal-poorstellar halo; and it has an unusually large nearby satellite galaxy, the LargeMagellanic Cloud (LMC). Here we show that the LMC is on a collision course withthe MW with which it will merge in $2.4^{+1.2}_{-0.8}$ Gyrs (68% confidencelevel). This catastrophic and long-overdue event will restore the MW tonormality. Using the EAGLE galaxy formation simulation, we show that, as aresult of the merger, the central supermassive black hole will increase in massby up to a factor of 8. The Galactic stellar halo will undergo an equallyimpressive transformation, becoming 5 times more massive. The additional starswill come predominantly from the disrupted LMC, but a sizeable number will beejected onto the halo from the stellar disc. The post-merger stellar halo willhave the median metallicity of the LMC, [Fe/H]=-0.5 dex, which is typical ofother galaxies of similar mass to the MW. At the end of this exceptional event,the MW will become a true benchmark for spiral galaxies, at least temporarily.

Luminous red galaxies (LRGs) are the most massive galaxies at $z\sim 0.5$and, by selection, have negligible star formation. These objects have halomasses between those of $L_{*}$ galaxies, whose circumgalactic media (CGM) areobserved to have large masses of cold gas, and clusters of galaxies, whichprimarily contain hot gas. Here we report detections of strong and extendedmetal (CIII 977) and HI lines in the CGM of two LRGs. The CIII lines haveequivalent widths of $\sim 1.8$ \r{A} and $\sim 1.2$ \r{A} , and velocityspreads of $\sim 796$ km s$^{-1}$ and $\sim 1245$ km s$^{-1}$, exceeding allsuch measurements from local $\sim L_{*}$ galaxies (maximal CIII equivalentwidths $\sim 1$ \r{A}). The data demonstrate that a subset of halos hostingvery massive, quenched galaxies contain significant complexes of cold gas.Possible scenarios to explain our observations include that the LRGs' CGMoriginate from past activity (e.g., star formation or active galactic nucleidriven outflows) or from the CGM of galaxies in overlapping subhalos. We favorthe latter scenario, in which the properties of the CGM are more tightly linkedto the underlying dark matter halo than properties of the targeted galaxies(e.g., star formation).

Asymmetries in HI in galaxies are often caused by the interaction with closecompanions, making isolated galaxies an ideal framework to study secularevolution. The AMIGA project has demonstrated that isolated galaxies show thelowest level of asymmetry in their HI integrated profiles, yet some presentsignificant asymmetries. CIG 96 (NGC 864) is a representative case reaching a16% level. Our aim is to investigate the HI asymmetries of this spiral galaxyand what processes have triggered the star-forming regions observed in the XUVpseudoring. We performed deep optical observations at CAHA 1.23m, 2.2m and VSTtelescopes. We reach surface brightness (SB) limits of mu_2.2m = 27.5 magarcsec-2 (Cous R) and mu_VST = 28.7mag arcsec-2 (r) that show the XUVpseudoring of the galaxy in detail. Additionally, a wavelet filtering of the HIdata cube from our deep observations with E/VLA telescope allowed us to reach acolumn density of N_HI = 8.9x10^18 cm -2 (5sigma) (28"x28" beam), lower than inany isolated galaxy. We confirm that the HI extends farther than 4xr_25 in alldirections. Furthermore, we detect for the first time two gaseous structures(10^6 Msol) in the outskirts. The g-r colour index image from 1.23m showsextremely blue colours in certain regions of the pseudoring whereN_HI>8.5x10^20 cm-2 , whereas the rest show red colours. Galactic cirruscontaminate the field, setting an unavoidable detection limit at 28.5magarcsec-2 (r). We detect no stellar link within 1degx1deg or gaseous link within40'x40' between CIG 96 and any companion. The isolation criteria rule outinteractions with other similar-sized galaxies for at least 2.7Gyr. Usingexisting stellar evolution models, the age of the pseudoring is estimated at1Gyr or older. Undetected previously accreted companions and cold gas accretionremain as the main hypothesis to explain the optical pseudoring and HI featuresof CIG 96.