Previous studies based on the analysis of Gaia DR2 data have revealed that accreted stars, possibly originating from a single progenitor satellite, are a significant component of the halo of our Galaxy, potentially constituting most of the halo stars at [Fe/H] <  −1 within a few kpc from the Sun and beyond. In this paper, we couple astrometric data from Gaia DR2 with elemental abundances from APOGEE DR14 to characterise the kinematics and chemistry of in-situ and accreted populations up to [Fe/H] ∼ −2. Accreted stars appear to significantly impact the galactic chemo–kinematic relations, not only at [Fe/H] <  −1, but also at metallicities typical of the thick and metal-poor thin discs. They constitute about 60% of all stars at [Fe/H] <  −1, the remaining 40% being made of (metal-weak) thick-disc stars. We find that the stellar kinematic fossil record shows the imprint left by this accretion event, which heated the old galactic disc. We are able to age-date this kinematic imprint, showing that the accretion occurred between nine and 11 Gyr ago, and that it led to the last significant heating of the galactic disc. An important fraction of stars with abundances typical of the (metal-rich) thick disc, and heated by this interaction, is now found in the galactic halo. Indeed, about half of the kinematically defined halo at few kpc from the Sun is composed of metal-rich thick-disc stars. Moreover, we suggest that this metal-rich thick-disc component dominates the stellar halo of the inner Galaxy. The new picture that emerges from this study is one where the standard, non-rotating in-situ halo population, the collapsed halo, seems to be more elusive than ever.

We report on the first in a series of studies of the Carina dwarf spheroidal galaxy, a nearby satellite of our Galaxy. Our two major results are: 1) precise BI photometry (σ B−I < ∼ 0.05 for V < ∼ 22) for 11,489 stars in the Carina field, and 2) the detection of two, morphologically distinct, horizontal branches in Carina, which confirms that star formation occurred in two well-separated episodes. The old horizontal branch and RR Lyrae instability strip belong to a > ∼ 10 Gyr stellar population, while the populous red-clump horizontal branch belongs, presumably, to a ∼ 6 Gyr stellar population. We derive a distance modulus (m − M ) 0 = 20.09 ± 0.06 for Carina from the apparent magnitudes of the old horizontal branch and the tip of the red giant branch (RGB), and discuss modifications to the previously estimated distance, total magnitude, and stellar ages of Carina. Using the color of the RGB, we estimate the metallicities of the younger and older populations to be [Fe/H] ≃ −2.0 and -2.2, respectively.

Multi-phase filamentary structures around Brightest Cluster Galaxies (BCG) are likely a key step of AGN-feedback. We observed molecular gas in 3 cool cluster cores: Centaurus, Abell S1101, and RXJ1539.5 and gathered ALMA (Atacama Large Millimeter/submillimeter Array) and MUSE (Multi Unit Spectroscopic Explorer) data for 12 other clusters. Those observations show clumpy, massive and long, 3-25 kpc, molecular filaments, preferentially located around the radio bubbles inflated by the AGN (Active Galactic Nucleus). Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the Hα/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 to 7 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100-400 km s −1 , with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin (as yet) unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the filament's radial extent, r fil , with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short cooling time region, where t cool /t ff <20 (9 of 13 sources). The range t cool /t ff , 8-23 at r fil , is likely due to (i) a more complex gravitational potential affecting the free-fall time t ff (sloshing, mergers. . . ); (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time t cool . For some of the sources, r fil lies where the ratio of the cooling time to the eddy-turnover time, t cool /t eddy , is approximately unity.