Using the newly commissioned KCWI instrument on the Keck-II telescope, weanalyse the stellar kinematics and stellar populations of the well-studiedmassive early-type galaxy (ETG) NGC 1407. We obtained high signal-to-noiseintegral-field-spectra for a central and an outer (around one effective radiustowards the south-east direction) pointing with integration times of just 600sand 2400s, respectively. We confirm the presence of a kinematically distinctcore also revealed by VLT/MUSE data of the central regions. While NGC 1407 waspreviously found to have stellar populations characteristic of massive ETGs(with radially constant old ages and high alpha-enhancements), it was claimedto show peculiar super-solar metallicity peaks at large radius that deviatedfrom an otherwise strong negative metallicity gradient, which is hard toreconcile within a `two-phase' formation scenario. Our outer pointing confirmsthe near-uniform old ages and the presence of a steep metallicity gradient, butwith no evidence for anomalously high metallicity values at largegalactocentric radii. We find a rising outer velocity dispersion profile andhigh values of the 4th-order kinematic moment -- an indicator of possibleanisotropy. This coincides with the reported transition from a bottom-heavy toa Salpeter initial mass function, which may indicate that we are probing thetransition region from the `in-situ' to the accreted phase. With shortexposures, we have been able to derive robust stellar kinematics and stellarpopulations in NGC 1407 to about 1 effective radius. This experiment shows thatfuture work with KCWI will enable 2D kinematics and stellar populations to beprobed within the low surface brightness regions of galaxy halos in aneffective way.

Shells are fine stellar structures identified by their arc-like shapespresent around a galaxy and currently thought to be vestiges of galaxyinteractions and/or mergers. The study of their number, geometry, stellarpopulations and gas content can help to derive the interaction/merger historyof a galaxy. Numerical simulations have proposed a mechanism of shell formationthrough phase wrapping during a radial minor merger. Alternatively, there couldbe barely a space wrapping, when particles have not made any radial oscillationyet, but are bound by their radial expansion, or produce an edge-brightenedfeature. These can be distinguished, because they are expected to keep a highradial velocity. While shells are first a stellar phenomenon, HI and COobservations have revealed neutral gas associated with shells. Some of the gas,the most diffuse and dissipative, is expected to be driven quickly to thecenter if it is travelling on nearly radial orbits. Molecular gas, distributedin dense clumps, is less dissipative, and may be associated to shells, anddetermine their velocity, too difficult to obtain from stars. We present here asearch for molecular gas in nine shell galaxies with the IRAM-30m telescope.Six of them are detected in their galaxy center, and in three galaxies, weclearly detect molecular gas in shells. The derived amount of molecular gasvaries from 1.5 10$^8$ to 3.4 10$^9$ M$_\odot$ in the shells. For two of them(Arp 10 and NGC 3656), the shells are characteristic of an oblate system. Theirvelocity is nearly systemic, and we conclude that these shells arephase-wrapped. For the third one (NGCB3934) the shells appear to participate tothe rotation, and follow up with higher spatial resolution is required toconclude.

Context. The precise determination of the present-day expansion rate of theUniverse, expressed through the Hubble constant $H_0$, is one of the mostpressing challenges in modern cosmology. Assuming flat $\Lambda$CDM, $H_0$inference at high redshift using cosmic-microwave-background data from Planckdisagrees at the 4.4$\sigma$ level with measurements based on the localdistance ladder made up of parallaxes, Cepheids and Type Ia supernovae (SNeIa), often referred to as "Hubble tension". Independent,cosmological-model-insensitive ways to infer $H_0$ are of critical importance.Aims. We apply an inverse-distance-ladder approach, combining strong-lensingtime-delay-distance measurements with SN Ia data. By themselves, SNe Ia aremerely good relative distance indicators, but by anchoring them to stronggravitational lenses one can obtain an $H_0$ measurement that is relativelyinsensitive to other cosmological parameters. Methods. A cosmological parameterestimate is performed for different cosmological background models, both forstrong-lensing data alone and for the combined lensing + SNe Ia data sets.Results. The cosmological-model dependence of strong-lensing $H_0$ measurementsis significantly mitigated through the inverse distance ladder. In combinationwith SN Ia data, the inferred $H_0$ consistently lies around 73-74 km s$^{-1}$Mpc$^{-1}$, regardless of the assumed cosmological background model. Ourresults agree nicely with those from the local distance ladder, but there is a>2$\sigma$ tension with Planck results, and a ~1.5$\sigma$ discrepancy withresults from an inverse distance ladder including Planck, Baryon AcousticOscillations and SNe Ia. Future strong-lensing distance measurements willreduce the uncertainties in $H_0$ from our inverse distance ladder.