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The impact of the dynamical state of gas-rich satellite galaxies at the early moments of their infall into their host systems and the relation to their quenching process are not completely understood at the low-mass regime. Two such nearby systems are the infalling Milky Way (MW) dwarfs Leo~T and Phoenix located near the MW virial radius at \\(414 {\\rm kpc}\\,(1.4 R_{\\rm vir})\\), both of which present intriguing offsets between their gaseous and stellar distributions. Here we present hydrodynamic simulations with {\\sc ramses} to reproduce the observed dynamics of Leo~T: its \\(80{\\rm pc}\\) stellar-HI offset and the 35{\\rm pc} offset between its older (\\(\\gtrsim 5{\\rm Gyr}\\)) and younger (\\(\\sim\\!200\\!-\\!1000{\\rm Myr}\\)) stellar population. We considered internal and environmental properties such as stellar winds, two HI components, cored and cuspy dark matter profiles, and different satellite orbits considering the MW circumgalactic medium. We find that the models that best match the observed morphology of the gas and stars include mild stellar winds that interact with the HI generating the observed offset, and dark matter profiles with extended cores. The latter allow long oscillations of the off-centred younger stellar component, due to long mixing timescales (\\(\\gtrsim200 {\\rm Myr}\\)), and the slow precession of near-closed orbits in the cored potentials; instead, cuspy and compact cored dark matter models result in the rapid mixing of the material (\\(\\lesssim 200{\\rm Myr}\\)). These models predict that non-equilibrium substructures, such as spatial and kinematic offsets, are likely to persist in cored low-mass dwarfs and to remain detectable on long timescales in systems with recent star formation.

Leo T is a gas-rich dwarf located at 414kpc \\((1.4R_{\\rm vir})\\) distance from the Milky Way (MW) and it is currently assumed to be on its first approach. Here, we present an analysis of orbits calculated backward in time for the dwarf with our new code {\\sc delorean}, exploring a range of systematic uncertainties, e.g. MW virial mass and accretion, M31 potential, and cosmic expansion. We discover that orbits with tangential velocities in the Galactic Standard-of-Rest frame lower than \\(|\\vec{u}_{\\rm t}^{\\rm GSR}|\\!\\leq\\! 63^{+47}_{-39}{\\rm\\, km\\, s^{-1}}\\) result in backsplash solutions, i.e. orbits that entered and left the MW dark matter halo in the past, and that velocities above \\(|\\vec{u}_{\\rm t}^{\\rm GSR}|\\!\\geq\\!21^{+33}_{-21}{\\rm\\, km\\, s^{-1}}\\) result in wide orbit backsplash solutions with a minimum pericenter range of \\(D_{\\rm min}\\!\\geq\\!38^{+26}_{-16}{\\rm \\,kpc}\\), which would allow this satellite to survive gas stripping and tidal disruption. Moreover, new proper motion estimates match with our region of backsplash solutions. We applied our method to other distant MW satellites, finding a range of gas stripped backsplash solutions for the gas-less Cetus and Eridanus II, providing a possible explanation for their lack of cold gas, while only first in-fall solutions are found for the HI rich Phoenix I. We also find that the cosmic expansion can delay their first pericenter passage when compared to the non-expanding scenario. This study explores the provenance of these distant dwarfs and provides constraints on the environmental and internal processes that shaped their evolution and current properties.

The structures and dynamics of molecular, atomic, and ionized gases are studied around a low-luminosity active galactic nucleus (AGN) with a small (\\(2\\times 10^6 M_\\odot\\)) black hole using 3D radiation hydrodynamic simulations. We studied, for the first time, the non-equilibrium chemistry for the X-ray dominated region in the \"radiation-driven fountain\" (Wada 2012) with supernova feedback. A double hollow cone structure is naturally formed without postulating a thick \"torus\" around a central source. The cone is occupied with an inhomogeneous, diffuse ionized gas and surrounded by a geometrically thick (\\(h/r \\gtrsim 1\\)) atomic gas. Dense molecular gases are distributed near the equatorial plane, and energy feedback from supernovae enhances their scale height. Molecular hydrogen exists in a hot phase ( > 1000 K) as well as in a cold ( < 100 K), dense ( >\\(10^3\\) cm\\(^{-3}\\)) phase. The velocity dispersion of H\\(_2\\) in the vertical direction is comparable to the rotational velocity, which is consistent with near infrared observations of nearby Seyfert galaxies. Using 3D radiation transfer calculations for the dust emission, we find polar emission in the mid-infrared band (12\\(\\mu m\\)), which is associated with bipolar outflows, as suggested in recent interferometric observations of nearby AGNs. If the viewing angle for the nucleus is larger than 75 deg, the spectral energy distribution (~ 2 -- 60 \\(\\mu m\\)) of this model is consistent with that of the Circinus galaxy. The multi-phase interstellar medium observed in optical/infrared and X-ray observations is also discussed.

The central super-massive black hole of the Milky Way, Sgr A*, accretes at a very low rate making it a very underluminous galactic nucleus. Despite the tens of Wolf-Rayet stars present within the inner parsec supplying \\({\\sim}10^{-3}\\rm\\ M_{\\odot}\\ yr^{-1}\\) in stellar winds, only a negligible fraction of this material (\\(<10^{-4}\\)) ends up being accreted onto Sgr A*. The recent discovery of cold gas (\\({\\sim}10^4\\rm\\ K\\)) in its vicinity raised questions about how such material could settle in the hostile (\\({\\sim}10^7\\rm\\ K\\)) environment near Sgr A*. In this work we show that the system of mass-losing stars blowing winds can naturally account for both the hot, inefficient accretion flow, as well as the formation of a cold disk-like structure. We run hydrodynamical simulations using the grid-based code Ramses starting as early in the past as possible to observe the state of the system at the present time. Our results show that the system reaches a quasi-steady state in about \\({\\sim}500\\rm\\ yr\\) with material being captured at a rate of \\({\\sim}10^{-6}\\rm\\ M_{\\odot}\\ yr^{-1}\\) at scales of \\({\\sim}10^{-4}\\rm\\ pc\\), consistent with the observations and previous models. However, on longer timescales (\\(\\gtrsim3000\\rm\\ yr\\)) the material accumulates close to the black hole in the form of a disk. Considering the duration of the Wolf-Rayet phase (\\({\\sim}10^5\\rm\\ yr\\)), we conclude that this scenario likely has already happened, and could be responsible for the more active past of Sgr A*, and/or its current outflow. We argue that the hypothesis of the mass-losing stars being the main regulator of the activity of the black hole deserves further consideration.

Giant clumps are a characteristic feature of observed high-redshift disk galaxies. We propose that these kpc-sized clumps have a complex substructure and are the result of many smaller clumps self-organizing themselves into clump clusters (CC). This bottom-up scenario is in contrast to the common top-down view that these giant clumps form first and then sub fragment. Using a high resolution hydrodynamical simulation of an isolated, fragmented massive gas disk and mimicking the observations from Genzel et al. (2011) at \\(z \\sim 2\\), we find remarkable agreement in many details. The CCs appear as single entities of sizes \\(R_{\\mathrm{HWHM}} \\simeq 0.9-1.4\\) kpc and masses \\(\\sim 1.5-3 \\times 10^9 \\ \\mathrm{M_{\\odot}}\\) representative of high-z observations. They are organized in a ring around the center of the galaxy. The origin of the observed clumps' high intrinsic velocity dispersion \\(\\sigma_{\\mathrm{intrinsic}} \\simeq 50 - 100 \\ \\mathrm{km \\ s^{-1}}\\) is fully explained by the internal irregular motions of their substructure in our simulation. No additional energy input, e.g. via stellar feedback, is necessary. Furthermore, in agreement with observations, we find a small velocity gradient \\(V_{\\mathrm{grad}} \\simeq 8 - 27 \\ \\mathrm{km \\ s^{-1} \\ kpc^{-1}}\\) along the CCs in the beam smeared velocity residual maps which corresponds to net prograde and retrograde rotation with respect to the rotation of the galactic disk. The CC scenario could have strong implications for the internal evolution, lifetimes and the migration timescales of the observed giant clumps, bulge growth and AGN activity, stellar feedback and the chemical enrichment history of galactic disks.

The inner parsec of our Galaxy contains tens of Wolf-Rayet stars whose powerful outflows are constantly interacting while filling the region with hot, diffuse plasma. Theoretical models have shown that, in some cases, the collision of stellar winds can generate cold, dense material in the form of clumps. However, their formation process and properties are not well understood yet. In this work we present, for the first time, a statistical study of the clump formation process in unstable wind collisions. We study systems with dense outflows (\\({\\sim}10^{-5}\\rm\\ M_{\\odot}\\ yr^{-1}\\)), wind speeds of \\(500\\)-\\(1500\\rm\\ km\\ s^{-1}\\), and stellar separations of \\({\\sim}20\\)-\\(200\\rm\\ au\\). We develop 3D high resolution hydrodynamical simulations of stellar wind collisions with the adaptive-mesh refinement grid-based code Ramses. We aim to characterise the initial properties of clumps that form through hydrodynamic instabilities, mostly via the non-linear thin shell instability (NTSI). Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes. Increasing either the wind speed or the degree of asymmetry increases the dispersion of the clump mass and ejection speed distributions. Nevertheless, the most massive clumps are very light (\\({\\sim}10^{-3}\\)-\\(10^{-2}\\rm\\ M_{\\oplus}\\)), about three orders of magnitude less massive than theoretical upper limits. Applying these results to the Galactic Centre we find that clumps formed through the NTSI should not be heavy enough either to affect the thermodynamic state of the region or to survive for long enough to fall onto the central super-massive black hole.

Gravitational instabilities play an important role in structure formation of gas-rich high-redshift disc galaxies. In this paper, we revisit the axisymmetric perturbation theory and the resulting growth of structure by taking the realistic thickness of the disc into account. In the unstable regime, which corresponds for thick discs to a Toomre parameter below the critical value Q_0,crit = 0.696, we find a fastest growing perturbation wavelength that is always a factor 1.93 times larger than in the classical razor-thin disc approximation. This result is independent of the adopted disc scaleheight and by this independent of temperature and surface density. In order to test the analytical theory, we compare it with a high-resolution hydrodynamical simulation of an isothermal gravitationally unstable gas disc with the typical vertical sech^2 density profile and study its break up into rings that subsequently fragment into dense clumps. In the first phase, rings form, that organize themselves discretely, with distances corresponding to the local fastest growing perturbation wavelength. We find that the disc scaleheight has to be resolved initially with five or more grid cells in order to guarantee proper growth of the ring structures, which follow the analytical prediction. These rings later on contract to a thin and dense line, while at the same time accreting more gas from the inter-ring region. It is these dense, circular filaments, that subsequently fragment into a large number of clumps. Contrary to what is typically assumed, the clump sizes are therefore not directly determined by the fastest growing wavelength.

The source G2 has already completed its pericentre passage around Sgr A*, the super-massive black hole in the centre of our Galaxy. Although it has been monitored for 15 years, its astrophysical nature and origin still remain unknown. In this work, we aim to test the hypothesis of G2 being the result of a stellar wind collision. To do so, we study the motion and final fate of gas clumps formed as a result of collisions of stellar winds in massive binaries. Our approach is based on a test-particle model in order to describe the trajectories of such clumps. The model takes into account the gravitational field of Sgr A*, the interaction of the clumps with the interstellar medium as well as their finite lifetimes. Our analysis allows us to reject the hypothesis based on four arguments: i) if G2 has followed a purely Keplerian orbit since its formation, it cannot have been produced in any of the known massive binaries since their motions are not consistent; ii) in general, gas clumps are evaporated through thermal conduction on very short timescale (< 100yr) before getting close enough to Sgr A*; iii) IRS 16SW, the best candidate for the origin of G2, cannot generate clumps as massive as G2; and iv) clumps ejected from IRS 16SW describe trajectories significantly different to the observed motion of G2.

A panchromatic view of the star forming ring and feeding process in the central kpc of the galaxy NGC 1097 is presented. The assembled IR to UV images at \\(\\sim\\)10 pc resolution allow us to characterise the population of circa 250 clusters in the ring and disentangle the network of filaments of dust and gas that enshroud and feed them. The ring is a place of intermittent star bursts over the last 100 Myr. Four major episodes covering a proto-cluster phase of eleven mid-IR sources at the molecular clouds core, and two (three) previous bursts with a time separation of 20 - 30 Myr are identified. The extinction map of the inner few kpc resolves NGC1097's two major dust lanes in bundles of narrow, \\(<\\)25 pc width, filaments running along the galaxy's bar. As they approach the ring, some circularise along it, others curve to the centre to produce a nuclear spiral. We believe these are kpc-scale dust-gas streamers feeding the ring and the black-hole. The total mass in clusters formed in the ring in the last 100 Myr is \\(< 10^7\\, \\rm{M_\\odot}\\), i.e. \\(< 1\\% \\) of the \\(10^{9} M_\\odot\\) of molecular gas in the ring; yet, at its current star formation rate, \\(\\sim1.8\\, \\rm{M_\\odot \\, yr^{-1}}\\), an order of magnitude more in stellar mass should have been produced over that period. This means that the availability of gas in the ring is not the sole star formation driver, perhaps the rate at which dense gas accumulates in the ring is key.

IC 630 is a nearby early-type galaxy with a mass of \\(6 \\times 10^{10} M_{\\odot}\\) with an intense burst of recent (6 Myr) star formation. It shows strong nebular emission lines, with radio and X-ray emission, which classifies it as an AGN. With VLT-SINFONI and Gemini North-NIFS adaptive optics observations (plus supplementary ANU 2.3m WiFeS optical IFU observations), the excitation diagnostics of the nebular emission species show no sign of standard AGN engine excitation; the stellar velocity dispersion also indicate that a super-massive black hole (if one is present) is small (\\(M_{\\bullet} = 2.25 \\times 10^{5}~M_{\\odot}\\)). The luminosity at all wavelengths is consistent with star formation at a rate of about \\(1-2 M_{\\odot}\\)/yr. We measure gas outflows driven by star formation at a rate of \\(0.18 M_{\\odot}\\)/yr in a face-on truncated cone geometry. We also observe a nuclear cluster or disk and other clusters. Photo-ionization from young, hot stars is the main excitation mechanism for [Fe II] and hydrogen, whereas shocks are responsible for the H\\(_2\\) excitation. Our observations are broadly comparable with simulations where a Toomre-unstable, self-gravitating gas disk triggers a burst of star formation, peaking after about 30 Myr and possibly cycling with a period of about 200 Myr.