arXiv subjects

J. Palouš

Publications and source records attributed to J. Palouš.

6 recordsLinked to original sources

arXiv2026

The Star Formation Factory revisited I. The impact of metallicity on collapsing star-forming clouds

Context. Stellar feedback regulates star formation and shapes the interstellar medium, yet its role during the collapse of molecular clouds remains uncertain over a wide range of initial conditions. Aims. We explore how stellar winds and supernovae influence star formation in collapsing gas clouds that span a broad parameter space in mass, size, and metallicity. Methods. Using a one-dimensional numerical model, we follow the evolution of feedback-driven bubbles produced by embedded clusters, incorporating time-dependent energy and mass injection, self-gravity, integrated cloud collapse, radiative cooling, shell instabilities, and triggered star formation. Our treatment of gas cooling in the hot bubble explicitly accounts for heat transfer across the bubble-shell interface. Results. We find that metallicity acts as a key regulator of feedback, comparable in importance to cloud mass and radius. In low-metallicity clouds, reduced radiative cooling is offset by weaker stellar winds, leading to prolonged star formation and higher efficiencies. Across a substantial portion of parameter space, the expanding shell undergoes a stalling phase that further enhances the star formation efficiency, an outcome that is not observed at higher metallicities. Conclusions. Our results suggest that the diverse properties of star clusters across cosmic time may arise from the metallicity-dependent interplay between stellar feedback and gas cooling.

astro-ph.GA↗

arXiv2023

A 3D model for the stellar populations in the nuclei of NGC 1433,NGC 1566, and NGC 1808

Aims. We aim to characterize the properties of the stellar populations in the central few hundred parsecs of nearby galactic nuclei; specifically their age, mass, and 3D geometry. Methods. We use spatially resolved spectroscopic observations of NGC 1433, NGC 1566, and NGC 1808 obtained with SINFONI to constrain a 3D model composed of a spherically symmetric nuclear star cluster (NSC) and an extended thick stellar disk. We computed UV to mid-infrared single stellar population (UMISSP) spectra to determine the age of the stellar populations and construct synthetic observations for our model. To overcome degeneracies between key parameters, we simultaneously fit the spatially resolved line-of-sight velocity, line-of-sight-velocity-dispersion, low-spectral-resolution NIR continuum, and high-spectral-resolution CO absorption features for each pixel. Results. For the three objects, we derive the age and mass of the young and old stellar populations in the NSC and surrounding disk, as well as their 3D geometry: radius for the NSC; thickness, inclination, and position angle for the disk. These results are consistent with published independent measurements when available. Conclusions. The proposed method allows us to derive a consistent 3D model of the stellar populations in nearby galactic centers solely based on a near-infrared IFU observation.

astro-ph.GA↗

arXiv2022

How to create Sgr A East: Where did the supernova explode?

Sgr A East is the supernova remnant closest to the centre of the Milky Way. Its age has been estimated to be either very young, around 1-2 kyr, or about 10 kyr, and its exact origin remains unclear. We aspire to create a simple model of a supernova explosion that reproduces the shape, size, and location of Sgr A East. Using a simplified hydrodynamical code, we simulated the evolution of a supernova remnant in the medium around the Galactic centre. The latter consists of a nearby massive molecular cloud with which Sgr A East is known to be interacting and a wind from the nuclear star cluster. Our preferred models of the Sgr A East remnant are compatible with an age of around 10 kyr. We also find suitable solutions for older ages, but not for ages younger than 5 kyr. Our simulations predict that the supernova exploded at a distance of about 3.5 pc from the Galactic centre, below the Galactic plane, slightly eastwards from the centre and 3 pc behind it.

astro-ph.GA↗

arXiv2021

Flash-light on the Ring: hydrodynamic simulations of expandingsupernova shells near supermassive black holes

The way supermassive black holes (SMBH) in galactic centers accumulate their mass is not completely determined. At large scales, it is governed by galactic encounters, mass inflows connected to spirals arms and bars, or due to expanding shells from supernova (SN) explosions in the central parts of galaxies. The investigation of the latter process requires an extensive set of gas dynamical simulations to explore the muti-dimensional parameter space needed to frame the phenomenon. The aims of this paper are to extend our investigation of the importance of supernovae for inducing accretion onto a SMBH and carry out a comparison between the fully hydrodynamic code Flash and the much less computationally intensive code Ring, which uses the thin shell approximation. We simulate 3D expanding shells in a gravitational potential similar to that of the Galactic Center with a variety of homogeneous and turbulent environments. In homogeneous media, we find convincing agreement between Flash and Ring in the shapes of shells and their equivalent radii throughout their whole evolution until they become subsonic. In highly inhomogeneous, turbulent media, there is also a good agreement of shapes and sizes of shells, and of the times of their first contact with the central 1 pc sphere, where we assume that they join the accretion flow. The comparison supports the proposition that a SN occurring at a galactocentric distance of 5 pc typically drives 1 - 3 $M_\odot$ into the central 1 pc around the galactic center.

astro-ph.GA↗

arXiv2017

Kinematic clues to the origins of starless HI clouds : dark galaxies or tidal debris ?

Isolated HI clouds with no optical counterparts are often taken as evidence for galaxy-galaxy interactions, though an alternative hypothesis is that these are primordial 'dark galaxies' which have not formed stars. Similarly, certain kinematic features in HI streams are also controversial, sometimes taken as evidence of dark galaxies but also perhaps explicable as the result of harassment. We numerically model the passage of a galaxy through the gravitational field of cluster. The galaxy consists of SPH particles for the gas and n-bodies for the stars and dark matter, while the cluster includes the gravitational effects of substructure using 400 subhalos (the effects of the intracluster medium are ignored). We find that harassment can indeed produce long HI streams and these streams can include kinematic features resembling dark galaxy candidates such as VIRGOHI21. We also show that apparent clouds with diameter < 20 kpc and velocity widths < 50 km/s are almost invariably produced in these simulations, making tidal debris a highly probable explanation. In contrast, we show that the frequency of isolated clouds of the same size but velocity width > 100 km/s is negligible - making this a very unlikely explanation for the observed clouds in the Virgo cluster with these properties.

astro-ph.GA↗

arXiv2010

On the Hydrodynamic Interplay Between a Young Nuclear Starburst and a Central Super Massive Black Hole

We present 1D numerical simulations, which consider the effects of radiative cooling and gravity on the hydrodynamics of the matter reinserted by stellar winds and supernovae within young nuclear starbursts with a central supermassive black hole (SMBH). The simulations confirm our previous semi-analytic results for low energetic starbursts, evolving in a quasi-adiabatic regime, and extend them to more powerful starbursts evolving in the catastrophic cooling regime. The simulations show a bimodal hydrodynamic solution in all cases. They present a quasi-stationary accretion flow onto the black hole, defined by the matter reinserted by massive stars within the stagnation volume and a stationary starburst wind, driven by the high thermal pressure acquired in the region between the stagnation and the starburst radii. In the catastrophic cooling regime, the stagnation radius rapidly approaches the surface of the starburst region, as one considers more massive starbursts. This leads to larger accretion rates onto the SMBH and concurrently to powerful winds able to inhibit interstellar matter from approaching the nuclear starburst. Our self-consistent model thus establishes a direct physical link between the SMBH accretion rate and the nuclear star formation activity of the host galaxy and provides a good upper limit to the accretion rate onto the central black hole.

astro-ph.CO↗