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Register a new userMassive disc galaxies in cosmological hydrodynamical simulations are too dark matter-dominated
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We investigate the disc-halo connection in massive (Mstar/Msun>5e10) disc galaxies from the cosmological hydrodynamical simulations EAGLE and IllustrisTNG, and compare it with that inferred from the study of HI rotation curves in nearby massive spirals from the Spitzer Photometry and Accurate Rotation Curves (SPARC) dataset. We find that discrepancies between the the simulated and observed discs arise both on global and on local scales. Globally, the simulated discs inhabit halos that are a factor ~4 (in EAGLE) and ~2 (in IllustrisTNG) more massive than those derived from the rotation curve analysis of the observed dataset. We also use synthetic rotation curves of the simulated discs to demonstrate that the recovery of the halo masses from rotation curves are not systematically biased. We find that the simulations predict dark-matter dominated systems with stellar-to-total enclosed mass ratios that are a factor of 1.5-2 smaller than real galaxies at all radii. This is an alternative manifestation of the `failed feedback problem, since it indicates that simulated halos hosting massive discs have been too inefficient at converting their baryons into stars, possibly due to an overly efficient stellar and/or AGN feedback implementation.
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Low mass galaxies are expected to be dark matter dominated even within their centrals. Recently two observations reported two dwarf galaxies in group environment with very little dark matter in their centrals. We explore the population and origins of dark-matter-deficient galaxies (DMDGs) in two state-of-the-art hydrodynamical simulations, the EAGLE and Illustris projects. For all satellite galaxies with $10^9<M_*<10^{10}$ M$_{odot}$ in groups with $M_{200}>10^{13}$ M$_{odot}$, we find that about $2.6%$ of them in the EAGLE, and $1.5%$ in the Illustris are DMDGs with dark matter fractions below $50%$ inside two times half-stellar-mass radii. We demonstrate that DMDGs are highly tidal disrupted galaxies; and because dark matter has higher binding energy than stars, mass loss of the dark matter is much more rapid than stars in DMDGs during tidal interactions. If DMDGs were confirmed in observations, they are expected in current galaxy formation models.
Mass models for a sample of 18 late-type dwarf and low surface brightness galaxies show that in almost all cases the contribution of the stellar disks to the rotation curves can be scaled to explain most of the observed rotation curves out to two or three disk scale lengths. The concept of a maximum disk, therefore, appears to work as well for these late-type dwarf galaxies as it does for spiral galaxies. Some of the mass-to-light ratios required in our maximum disk fits are high, however, up to about 15 in the R-band, with the highest values occurring in galaxies with the lowest surface brightnesses. Equally well-fitting mass models can be obtained with much lower mass-to-light ratios. Regardless of the actual contribution of the stellar disk, the fact that the maximum disk can explain the inner parts of the observed rotation curves highlights the similarity in shapes of the rotation curve of the stellar disk and the observed rotation curve. This similarity implies that the distribution of the total mass density is closely coupled to that of the luminous mass density in the inner parts of late-type dwarf galaxies.
We searched for isolated dark matter deprived galaxies within several state-of-the-art hydrodynamical simulations: Illustris, IllustrisTNG, EAGLE, and Horizon-AGN and found a handful of promising objects in all except Horizon-AGN. While our initial goal was to study their properties and evolution, we quickly noticed that all of them were located at the edge of their respective simulation boxes. After carefully investigating these objects using the full particle data, we concluded that they are not merely caused by a problem with the algorithm identifying bound structures. We provide strong evidence that these oddballs were created from regular galaxies that get torn apart due to unphysical processes when crossing the edge of the simulation box. We show that these objects are smoking guns indicating an issue with the implementation of the periodic boundary conditions of the particle data in Illustris, IllustrisTNG, and EAGLE, which was eventually traced down to be a minor bug occurring for a very rare set of conditions.
We study galaxy formation in sterile neutrino dark matter models that differ signifi- cantly from both cold and from `warm thermal relic models. We use the EAGLE code to carry out hydrodynamic simulations of the evolution of pairs of galaxies chosen to resemble the Local Group, as part of the APOSTLE simulations project. We compare cold dark matter (CDM) with two sterile neutrino models with 7 keV mass: one, the warmest among all models of this mass (LA120) and the other, a relatively cold case (LA10). We show that the lower concentration of sterile neutrino subhalos compared to their CDM counterparts makes the inferred inner dark matter content of galaxies like Fornax (or Magellanic Clouds) less of an outlier in the sterile neutrino cosmologies. In terms of the galaxy number counts the LA10 simulations are indistinguishable from CDM when one takes into account halo-to-halo (or `simulation-to-simulation) scatter. In order for the LA120 model to match the number of Local Group dwarf galaxies, a higher fraction of low mass haloes is required to form galaxies than is predicted by the EAGLE simulations. As the census of the Local Group galaxies nears completion, this population may provide a strong discriminant between cold and warm dark matter models.
We perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomed-in initial conditions leading to the formation of a halo of mass $M_{rm halo, , DM} simeq 2 cdot 10^{12}$ M$_{odot}$ at redshift $z=0$. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of $(i)$ the assumed IMF, $(ii)$ the adopted stellar yields, and $(iii)$ the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa et al. (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar $alpha$-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local universe. On the other hand, the comparison of stellar metallicity profiles and $alpha$-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar $alpha$-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of $0.03$, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge.
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