arXiv subjects

Georg Herzog

Publications and source records attributed to Georg Herzog.

3 recordsLinked to original sources

arXiv2026

The environmental dependence of the circumgalactic medium in a high-resolution cosmological simulation

There is increasing evidence from observations that the circumgalactic medium (CGM) of galaxies depends on the large-scale structure in which they are embedded. When probing the CGM in absorption using quasar sightlines, studies find an enhanced sky coverage in the CGM of galaxies in overdensities compared to galaxies in isolation. However, the exact reason for this environmental dependence is still unclear. In this work we aim to model for the first time the influence of the large-scale structure on the cool and warm ($T\sim10^{4-5}$ K) gas phases of the CGM. We use a high-resolution ($m_{gas}\approx 4.5\times 10^4$ M$_{\odot}$, $m_{dm}\approx 2.4\times 10^5$ M$_{\odot}$) cosmological simulation based on the EAGLE model of galaxy formation. We select all galaxies at $z=0$ with stellar mass $M_*>10^8$ M$_\odot$ and split them into galaxies in overdensities (group galaxies) and galaxies in isolation using a Friends-of-Friends algorithm. For these two samples, we investigate how the large-scale structure influences the physical properties of the CGM and the measured covering fractions of the cool and warm gas phases. When the two samples of group and isolated galaxies are matched in stellar mass, halo mass, and we use only central galaxies, we do not find any significant difference in the physical properties of the CGM and the measured covering fractions. However, when satellite galaxies are included, we recover the observational trends in the difference of covering fractions with the environment. The difficulty of recovering the observational trends shows the complexity of capturing the multiphase CGM in simulations. However, since our results concerning the admixture of satellites are independent of the employed subgrid physics, this work shows that central galaxies and satellites need to be disentangled in observational studies to clearly discern the role of the environment on the CGM.

astro-ph.GA↗

arXiv2022

The present-day gas content of simulated field dwarf galaxies

We examine the gas content of field dwarf galaxies in a high-resolution cosmological simulation. In agreement with previous work, we find that galaxies inhabiting dark matter haloes with mass below a critical value, $M_{200} \lesssim M_{\rm crit} \approx 5\times 10^{9} \ M_{\odot}$, are quiescent at the present day. The gas content of these galaxies is thus insensitive to feedback from evolving stars. Almost half of these quiescent systems today have gas masses much smaller than that expected for their mass. We find that gas-deficient galaxies originate from 1) past interactions with massive hosts, in which a dwarf loses gas and dark matter via tidal and ram-pressure forces; and 2) from hydrodynamic interactions with the gaseous filaments and sheets of the cosmic web, in which a dwarf loses gas via ram-pressure. We refer to these systems as ``flybys'' and ``COSWEBs''. Flybys locate in high-density regions, tracing the location of the most massive galaxies in the simulation. In contrast, COSWEBs are dispersed throughout the volume and trace the cosmic web. For sub-critical systems, $M_{200} < M_{\rm crit}$, the fraction of COSWEB galaxies can be as high as $35 \%$, and much higher for flybys, which make up 100 per cent of the galaxies with $M_{200}<3\times 10^8 \ \rm M_{\odot}$. The deficit of gas caused by these mechanisms may preclude the detection of a large fraction of field dwarfs in future HI surveys. For galaxies inhabiting halos with mass $M_{200} > M_{\rm crit}$, we find that cosmic web stripping, on average, shuts down star formation in more than $70\%$ of the affected systems.

astro-ph.GA↗

arXiv2021

Neutron Stars in Palatini $R+αR^2$ and $R+αR^2+βQ$ Theories

We study solutions of the stellar structure equations for spherically symmetric objects in Palatini $f(R)=R+αR^2$ and $f(R,Q)=R+αR^2+βQ$ in the mass-radius region associated to neutron stars. We illustrate the potential impact of the $R^2$ and $Q$ terms by studying a range of viable values of $α$ and $β$. Similarly, we use different equations of state (SLy, FPS, HS(DD2) and HS(TMA)) as a simple way to account for the equation of state uncertainty. Our results show that for certain combinations of the $α$ and $β$ parameters and equation of state, the effect of modifications of general relativity on the properties of stars is sizeable. Therefore, with increasing accuracy in the determination of the equation of state for neutron stars, astrophysical observations may serve as discriminators of modifications of General Relativity.

gr-qc↗