arXiv subjects

Nicolas Peschken

Publications and source records attributed to Nicolas Peschken.

7 recordsLinked to original sources

arXiv2026

Simulating winds in the Galactic centre: I. Supernova-driven multiphase outflows and HI cloud acceleration

The centre of the Milky Way (MW) hosts powerful multiphase outflows, as evidenced by the Fermi and eROSITA bubbles, and by cold atomic hydrogen (HI) gas clouds detected up to a few kiloparsecs above the disc. In this paper, we investigate the process of launching gaseous outflows in the nuclear region of our Galaxy from supernova feedback. Using the PIERNIK code, we perform a simulation of the Galaxy with 3 pc resolution in both the Central Molecular Zone (CMZ) and the surrounding outflows. Our model follows the entire gas dynamics, from accretion onto the central star-forming ring through the dust lanes to star formation, feedback and the launching of outflows. Star formation occurs in cycles of starbursts followed by quiescent periods, mainly driven by intermittent gas inflows along the dust lanes. Stellar feedback generates hot ($\sim 10^7$ K) winds launched from the CMZ at velocities of order 1000 km/s, as well as colder ($\sim 10^4$ K) Hi gas clouds with velocities of $\sim 100$ km/s at heights of 1 - 2 kpc from the mid-plane. The spatial distribution, kinematics, and masses of our simulated clouds are broadly consistent with observations. Their properties indicate that they are accelerated out of the disc by entrainment from the hot phase. At least 20% of these clouds return to the disc in fountain flows, while the majority are disrupted by interaction with the hot phase. While periods of intense star formation and supernova activity lead to more numerous outflowing clouds with higher masses and densities, quiescent phases with star formation rates close to that observed in the CMZ still produce Hi clouds consistent with data. These results suggest that stellar feedback alone, operating in a time-variable nuclear environment, can account for the observed population of cold clouds in the Galactic centre outflow.

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arXiv2026

Blueberry and Green Pea galaxies live in low density environments

Little is currently known about the large-scale environments of Green Pea (GP) and Blueberry (BB) galaxies, which are low-mass, compact systems with extreme specific star-formation rates (sSFR). Their environments are inherently linked to their formation mechanism, and they may serve as crucial local analogues for high-redshift, reionizing galaxies. This paper aims to investigate the clustering properties of GPs and BBs, leveraging large-scale survey data to quantify their spatial distribution relative to the broader galaxy population. We here investigate a sample of these galaxies, consisting of 339 GPs $\rm (0.1 < z \le 0.33)$ and 56 BBs $\rm (0 < z \le 0.1)$, whose clustering properties we analyse relative to an extensive control sample derived from the SDSS MPA-JHU DR8 catalogue, binned by stellar mass and sSFR. We use the number of neighbours within a 5 Mpc radius as a proxy for environmental density, i.e. clustering, and employ a pair-matching and bootstrapping methodology to ensure statistical robustness. We observe that galaxy clustering depends strongly on star-formation activity, with passive galaxies being more clustered than their high star-formation rate counterparts, with GPs and BBs lying at the extreme end of this relation, exhibiting the lowest neighbour counts among all subsamples. The nearest neighbours of BBs also tend to have lower masses than other classes of dwarf galaxies. GPs and BBs predominantly reside in isolated, low-density environments, suggesting that their intense starbursts are unlikely to be triggered by common environmental processes such as mergers or starburst cycles. Their low metallicities and weak clustering instead support scenarios in which recent starbursts are driven by internal processes or pristine gas accretion, reinforcing their role as nearby analogues of young, low-mass galaxies in the early Universe.

astro-ph.GA↗

arXiv2026

A survey of molecular clouds in the Galactic center's outflow

The nucleus of the Milky Way is known to drive a large-scale, multiphase galactic outflow, with gas phases ranging from the hot highly-ionized to the cold molecular component. In this work, we present the first systematic search for molecules in the Milky Way wind. We use the Atacama Pathfinder EXperiment (APEX) to observe the 12CO(2-1) emission line in 19 fields centered on previously known high-velocity atomic hydrogen (HI) clouds associated with the outflow. Over 200 CO clumps are detected within 16 different HI clouds. These clumps have typical radii of 1 - 3 parsec, high velocity dispersions of 1 - 6 km/s and molecular gas masses ranging from a few to several hundred solar masses. Molecular clumps in the wind sit on the low-mass end of the mass - size relation of regular molecular clouds, but are far displaced from the mass (or size) - linewidth relation, being generally more turbulent and showing high internal pressures. Nearly 90% of the clumps are gravitationally unbound with virial parameters >> 10 - 100, indicating that these structures are either being disrupted or they must be confined by external pressure from the surrounding hot medium. While the observed properties of CO clumps do not seem to evolve clearly with latitude, we find that molecular gas is not detected in any of the 6 HI clouds with projected distances over 1 kpc from the Galactic Center, suggesting the existence of a maximum timescale of ~ 3 Myr for the dissociation of molecular gas within the wind. Overall, current observations in the Galactic center support a scenario in which a hot wind entrains cold gas clouds from the disk, driving their progressive transformation from molecular to atomic and ultimately ionized gas through stripping, turbulence, and dissociation.

astro-ph.GA↗

arXiv2022

The phase structure of cosmic ray driven outflows in stream fed disc galaxies

Feeding with gas in streams is predicted to be an important galaxy growth mechanism. Using an idealised setup, we study the impact of stream feeding (with 10$^7$ M$_{\odot}$ Myr$^{-1}$ rate) on the star formation and outflows of disc galaxies with $\sim$10$^{11}$ M$_{\odot}$ baryonic mass. The magneto-hydrodynamical simulations are carried out with the PIERNIK code and include star formation, feedback from supernova, and cosmic ray advection and diffusion. We find that stream accretion enhances galactic star formation. Lower angular momentum streams result in more compact discs, higher star formation rates and stronger outflows. In agreement with previous studies, models including cosmic rays launch stronger outflows travelling much further into the galactic halo. Cosmic ray supported outflows are also cooler than supernova only driven outflows. With cosmic rays, the star formation is suppressed and the thermal pressure is reduced. We find evidence for two distinct outflow phases. The warm outflows have high angular momentum and stay close to the galactic disc, while the hot outflow phase has low angular momentum and escapes from the centre deep into the halo. Cosmic rays can therefore have a strong impact on galaxy evolution by removing low angular momentum, possibly metal enriched gas from the disc and injecting it into the circumgalactic medium.

astro-ph.GA↗

arXiv2021

The angular momentum structure of cosmic ray driven galactic outflows triggered by stream accretion

We investigate the impact of gas accretion in streams on the evolution of disc galaxies, using magneto-hydrodynamic simulations including advection and anisotropic diffusion of cosmic rays generated by supernovae as the only source of feedback. Stream accretion has been suggested as an important galaxy growth mechanism in cosmological simulations and we vary their orientation and angular momentum in idealised setups. We find that accretion streams trigger the formation of galactic rings and enhanced star formation. The star formation rates and consequently the cosmic ray driven outflow rates are higher for low angular momentum accretion streams, which also result in more compact, lower angular momentum discs. The cosmic ray generated outflows show a characteristic structure. At low outflow velocities (< 50 km/s) the angular momentum distribution is similar to the disk and the gas is in a fountain flow. Gas at high outflow velocities (> 200 km/s), penetrating deep into the halo, has close to zero angular momentum, and originates from the centre of the galaxies. As the mass loading factors of the cosmic ray driven outflows are of order unity and higher, we conclude that this process is important for the removal of low angular momentum gas from evolving disk galaxies and the transport of, potentially metal enriched, material from galactic centres far into the galactic haloes.

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arXiv2020

Disc galaxies formed from major mergers in Illustris

We show how wet major mergers can create disc galaxies in a cosmological context, using the Illustris simulation. We select a sample of 38 disc galaxies having experienced a major merger in their history with no subsequent significant minor merger, and study how they transform into discs after the merger. In agreement with what was previously found in controlled simulations of such mergers, we find that their disc is built gradually from young stars formed after the merger in the disc region, while the old stars born before the merger form an ellipsoidal component. Focusing on one fiducial case from our sample, we show how the gas was initially dispersed in the halo region right after the merger, but is then accreted onto a disc to form stars, and builds the disc component. We then select a sample of major mergers creating elliptical galaxies, to show that those cases correspond mainly to dry mergers, where the lack of star formation prevents the formation of a disc in the remnant galaxy. The amount of gas in the remnant galaxy after the merger is therefore essential to determine the final outcome of a major merger.

astro-ph.GA↗

arXiv2018

Tidally induced bars in Illustris galaxies

We study barred galaxies selected from the Illustris cosmological simulation, focusing on tidally induced bars formed from flyby interactions. To guarantee high enough resolution we focus on high mass disc galaxies ($M_*>8.3 \times 10^{10} M_{\odot}$). We find that the fraction of barred galaxies among those (21% at redshift $z=0$) is lower in Illustris than observed in the local Universe, and the fraction grows slightly with redshift. The bar fraction also increases with the stellar mass and decreases with the amount of gas in the disc. Only very few bars at redshift $z=0$ are formed in secular evolution ($\sim$ 7%) and most of them are triggered by external perturbers in mergers or flybys. Many of these bars disappear over time, mostly during secular evolution, which leads to a lower fraction of bars at redshift $z=0$. We then focus on the effect of flyby interactions on the disc and look at tidally induced bars created by a flyby, or pre-existing bars influenced by the passage of a perturber. In the latter case, the interaction can enhance or weaken the bar. During the interaction, the change in the bar strength occurs right after the pericentre passage. The resulting tidally induced bars tend to be stronger than the overall bar sample in Illustris. The preferred scenario to create or enhance a bar seems to be with a strong interaction involving a perturber on a prograde orbit. Furthermore, the strength of the created bar grows with the strength of the interaction.

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