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Baryonic feedback is expected to play a key role in regulating the star formation of low-mass galaxies by producing galaxy-scale winds associated with mass-factors (β) of 1−50. We test this prediction in galaxies from the "DWarf galaxies Archival Local survey for Interstellar medium investigatioN" (DWALIN) sample using archival MUSE@VLT data.

Ionised gas in DWALIN galaxies is characterised by irregular velocity fields, indicating the presence of non-circular motions of a few tens of km/s within galaxy discs, but with intrinsic velocity dispersion that is only marginally larger than that measured in main-sequence galaxies. 

Only a few per cent of the ionised gas flux is found at velocities larger than the escape speed. Mass outflow rates and loading factors are strongly dependent on galaxy properties (stellar mass, SFR density, specific SFR), but the typical value of β is 0.02, which is more than two orders of magnitude smaller than that predicted by theoretical models of galaxy evolution.

In DWALIN, baryonic feedback stimulates a gentle gas cycle rather than causing a large-scale blow-out.

The high Galactic latitude sky is populated by gaseous complexes whose line-of-sight velocity is incompatible with that expected from the Galaxy differential rotation. These systems are divided into High- and Intermediate- velocity clouds (HVCs and IVCs), depending on how deviant their kinematics is. The HVCs are faster, more distant and metal poor than the IVCs, suggesting distinct origin for these two cloud populations.

In this study, we model the kinematics of the HVCs and IVCs observed in absorption towards a sample of 55 Galactic halo stars with accurate distance measurements from Gaia DR3 parallaxes. We find that at least two separate components are required to reproduce the data. A scenario where the HVCs and the IVCs are treated as distinct populations provides only a partial description of the data, which indicates that a pure velocity-based separation may give a biased vision of the gas physics at the Milky Way's disc-halo interface.

Instead, the data are better described by a combination of an inflow component and an outflow component, both characterised by rotation with Vϕ comparable to that of the disc and Vz of 50−100 km/s. Our findings indicate that the lower (|z|≲10kpc) Galactic halo is populated by a mixture of diffuse inflowing gas and collimated outflowing material, which are likely manifestations of a galaxy-wide gas cycle triggered by stellar feedback, that is, the galactic fountain.

The build-up of a galaxy can be thought as resulting from the competition between the "positive" process of gas accretion onto halos and "negative" ones like gas heating end expulsion caused by stellar and AGN feedback. As these processes both determine and are regulated by the growth rate of stars, BHs and DM halos, the existence of a relation between the properties of these three components must be expected at all redshift.

In this study, we test this scenario in the local Universe by using a sample of 55 nearby galaxies with robust measurements for their BH, stellar and halo masses. We found that these galaxies build a well-defined sequence in this 3D "mass" space, with an hint of a break at halo (BH) masses of ~1e12 (5e7) solar masses. The observed trends can be reproduced by a simple equilibrium model in the ΛCDM framework where galaxies smoothly accrete dark and baryonic matter at a cosmological rate, having their stellar and black hole build-up regulated both by the cooling of the available gas reservoir and by the negative feedback from star formation and AGN.

DATA! -> Download the galaxy catalogue used in this work here

PRESS RELEASE on Media INAF (Italian only)

MR 2251-178 and PG 1126-041 are two nearby QSOs hosting Ultra Fast Outflows (UFOs), consisting of high-speed (~ a tenth of the speed of light) ionised winds detected in X-ray at sub-pc scales. We used MUSE AO-assisted data (narrow field mode) to study the large-scale properties of the ionised wind, with the purpose of relating the outflows on different physical scales in order to better constrain the wind propagation mechanism. Our results suggest momentum-driven wind propagation, whereas an energy-driven mechanism is excluded unless ~ 100x additional momentum is locked in a molecular or atomic gas phase (not visible with MUSE). We also collected data from the literature for nearby QSOs hosting both UFOs and large-scale outflows and showed that the wind seem to lie systematically in either a momentum or an energy-driven regime, indicating that these two models bracket the physics of AGN-driven winds very well.

Massive spiral galaxies in the nearby Universe appear to host a considerable fraction of baryons - or, equivalently, have low dark matter fraction - within their disc (check it out here). Is this evidence backed up by most recent theoretical models of galaxy formation and evolution? We tried to answer this question by studying a sample of simulated massive spirals extracted from the cosmological hydrodynamical models EAGLE and IllustrisTNG. We found that discrepancies between simulated and real galaxies of similar stellar masses arise on both global and local scales. On the scales of the halos, the simulated discs show a factor ~2-4 more dark matter than real galaxies. On the scales of their discs, the simulated galaxies encloses a factor ~2 more dark matter than real galaxies. Such a mismatch in the disc-halo connection at high-masses is probably caused by an overly-efficient negative feedback in the simulations, which does not seem to occur in the real Universe (the so called "failed feedback" problem).

DATA! -> Download images and rotation curves for massive discs in EAGLE and IllustrisTNG here

In the last two decades, deep HI observations of nearby late-type galaxies have revealed the presence of extra-planar HI layers extending up to a few kpc above the galaxy midplane and accounting for ~10% of the total HI content. In the few cases studied in detail, these HI layers were found to be characterised by a slow-rotating, globally inflowing kinematics, which is expected by gas in a galactic fountain cycle triggered by stellar feedback.

We now present a homogenous and detailed analysis for a sample of 13 late-type galaxies with deep HI observations from the HALOGAS project. For each system we have masked out the HI emission coming from the rotating thin disk and produced synthetic data-cubes to model the leftover extra-planar emission. Our model features 3 structural and 4 kinematical global parameters, which are fit to the data via a Bayesian MCMC method.

We found that extra-planar HI layers are ubiquitous in disc galaxies, with HI masses that are in excellent agreement with predictions from simple models of galactic fountain powered by stellar feedback. In most cases, the kinematics show a global inflow with speed of 20-30 km/s in the vertical and radial directions, along with a vertical rotational lag of 5-20 km/s/kpc, suggesting an interaction between the material outflowing from the disc and the circumgalactic medium.

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