Super-massive black holes, with masses larger than a million times that ofthe Sun, appear to inhabit the centers of all massive galaxies.Cosmologically-motivated theories of galaxy formation need feedback from thesesuper-massive black holes to regulate star formation. In the absence of suchfeedback, state-of-the-art numerical simulations dramatically fail to reproducethe number density and properties of massive galaxies in the local Universe.However, there is no observational evidence of this strongly coupledco-evolution between super-massive black holes and star formation, impeding ourunderstanding of baryonic processes within galaxies. Here we show that the starformation histories (SFHs) of nearby massive galaxies, as measured from theirintegrated optical spectra, depend on the mass of the central super-massiveblack hole. Our results suggest that black hole mass growth scales with gascooling rate in the early Universe. The subsequent quenching of star formationtakes place earlier and more efficiently in galaxies hosting more massivecentral black holes. The observed relation between black hole mass and starformation efficiency applies to all generations of stars formed throughout agalaxy's life, revealing a continuous interplay between black hole activity andbaryon cooling.

Energy feedback, either from active galactic nuclei (AGN) or from supernovae,is required to understand galaxy formation within a $\Lambda$-Cold Dark Mattercosmology. We study a sample of 127 low-mass galaxies, comparing their stellarpopulations properties to the mass of the central supermassive black hole, inorder to investigate the effect of AGN feedback. We find a loose couplingbetween star formation history and black hole mass, which seems to suggest thatAGN activity does not dominate baryonic cooling in low-mass galaxies. We alsofind that a break in the $M_\bullet$-$\sigma$ relation marks a transitionalstellar mass, M$_\mathrm{trans}=3.4\pm2.1 \times 10^{10}$ M$_{\odot}$,remarkably similar to M$_\star$. Our results are in agreement with a bi-modalstar formation process where the AGN-dominated feedback of high-mass galaxiestransitions towards a supernovae-driven regime in low-mass systems, assuggested by numerical simulations.

The baryon content around local galaxies is observed to be much less than isneeded in Big Bang nucleosynthesis. Simulations indicate that a significantfraction of these "missing baryons" may be stored in a hot tenuouscircum-galactic medium (CGM) around massive galaxies extending to or evenbeyond the virial radius of their dark matter halos. Previous observations inX-ray and Sunyaev-Zel'dovich (SZ) signal claimed that $\sim(1-50)\%$ of theexpected baryons are stored in a hot CGM within the virial radius. The largescatter is mainly caused by the very uncertain extrapolation of the hot gasdensity profile based on the detection in a small radial range (typicallywithin 10\%-20\% of the virial radius). Here we report stacking X-rayobservations of six local isolated massive spiral galaxies from the CGM-MASSsample. We find that the mean density profile can be characterized by a singlepower law out to a galactocentric radius of $\approx 200\rm~kpc$ (or$\approx130\rm~kpc$ above the 1~$\sigma$ background uncertainty), about halfthe virial radius of the dark matter halo. We can now estimate that the hot CGMwithin the virial radius accounts for $(8\pm4)\%$ of the baryonic mass expectedfor the halos. Including the stars, the baryon fraction is $(27\pm16)\%$, or$(39\pm20)\%$ by assuming a flattened density profile at $r\gtrsim130\rm~kpc$.We conclude that the hot baryons within the virial radius of massive galaxyhalos are insufficient to explain the "missing baryons".

We present interferometric observations of HI in nine slow rotator early-typegalaxies of the Atlas3D sample. With these data, we now have sensitive HIsearches in 34 of the 36 slow rotators. The aggregate detection rate is 32\%$\pm$ 8\%, consistent with previous work; however, we find two detections withextremely high HI masses, whose gas kinematics are substantially different fromwhat was previously known about HI in slow rotators. These two cases (NGC 1222and NGC 4191) broaden the known diversity of HI properties in slow rotators.NGC 1222 is a merger remnant with prolate-like rotation and, if it is indeedprolate in shape, an equatorial gas disc; NGC 4191 has two counterrotatingstellar discs and an unusually large HI disc. We comment on the implications ofthis disc for the formation of $2\sigma$ galaxies. In general, the HI detectionrate, the incidence of relaxed HI discs, and the HI/stellar mass ratios of slowrotators are indistinguishable from those of fast rotators. These broadsimilarities suggest that the HI we are detecting now is unrelated to thegalaxies' formation processes and was often acquired after their stars weremostly in place. We also discuss the HI nondetections; some of these galaxiesthat are undetected in HI or CO are detected in other tracers (e.g. FIR finestructure lines and dust). The question of whether there is cold gas in massivegalaxies' scoured nuclear cores still needs work. Finally, we discuss anunusual isolated HI cloud with a surprisingly faint (undetected) opticalcounterpart.

In this second paper of T$h$e role of $E$nvironment in shaping $L$ow-mass$E$arly-type $N$earby g$a$laxies (hELENa) series we study [Mg/Fe] abundancedistribution trends of early-type galaxies observed with the SAURON integralfield unit, spanning a wide range in mass and local environment densities: 20low-mass early-types (dEs) of Sybilska et al. (2017) and 258 massive earlytypes (ETGs) of the $ATLAS^{3D}$ project, all homogeneously reduced andanalyzed. We show that the [Mg/Fe] ratios scale with velocity dispersion($\sigma$) at fixed [Fe/H] and that they evolve with [Fe/H] along similar pathsfor all early-types, grouped in bins of increasing local and global {$\sigma$},as well as the second velocity moment $V_{rms}$, indicating a common inside-outformation pattern. We then place our dEs on the [Mg/Fe] $vs.$ [Fe/H] diagram ofLocal Group galaxies and show that dEs occupy the same region and show asimilar trend line slope in the diagram as the high-metallicity stars of theMilky Way and the Large Magellanic Cloud. This finding extends the similartrend found for dwarf spheroidal $vs.$ dwarf irregular galaxies and supportsthe notion that dEs have evolved from late-type galaxies that have lost theirgas at a point of their evolution, which likely coincided with them enteringdenser environments.