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Intermediate-mass black hole (IMBH) mergers with masses 104–106 M ⊙ are expected to produce gravitational waves detectable by the Laser Interferometer Space Antenna (LISA) with high signal-to-noise ratios from the present day to cosmic dawn. IMBH mergers are expected to take place within dwarf galaxies; however, the dynamics, timescales, and effect on their hosts are largely unexplored. In a previous study, we examined how IMBHs would pair and merge within nucleated dwarf galaxies. IMBHs in nucleated hosts evolve very efficiently, forming a binary system and coalescing within a few hundred million years. Although the fraction of dwarf galaxies (107 M ⊙ ≤ M ⋆ ≤ 1010 M ⊙) hosting nuclear star clusters is between 60% and 100%, this fraction drops to 20%–70% for lower-mass dwarfs (M ⋆ ≈ 107 M ⊙), with the largest drop in low-density environments. Here, we extend our previous study by performing direct N -body simulations to explore the dynamics and evolution of IMBHs within nonnucleated dwarf galaxies, under the assumption that IMBHs exist within these dwarfs. To our surprise, none of the IMBHs in our simulation suite merge within a Hubble time, despite many attaining high eccentricities e ∼ 0.7–0.95. We conclude that extremely low stellar density environments in the centers of nonnucleated dwarfs do not provide an ample supply of stars to interact with an IMBH binary, resulting in its stalling, in spite of triaxiality and high eccentricity, common means to drive a binary to coalescence. Our findings underline the importance of considering all detailed host properties to predict IMBH merger rates for LISA. [ABSTRACT FROM AUTHOR]

We present the High- z Evolution of Large and Luminous Objects (HELLO) project, a set of |$\sim \!30$| high-resolution cosmological simulations aimed to study Milky Way analogues (⁠|$M_\star \sim 10^{10-11}$|   |${\mathrm{M}}_{\odot }$|⁠) at high redshift (⁠|$z\sim [2-4]$|⁠). Based on the numerical investigation of a hundred astrophysical objects, HELLO features an updated scheme for chemical enrichment and the addition of local photoionization feedback. Independently of redshift and mass, our galaxies exhibit a smooth progression along the star formation main sequence until |$M_\star \sim \!10^{10.5}$|⁠ , around which our sample at |$z \sim 4$| remains mostly unperturbed while the most massive galaxies at |$z \sim 2$| reach their peak star formation rate (SFR) and its subsequent decline, due to a mix of gas consumption and stellar feedback. While active galactic nucleus feedback remains subdominant with respect to stellar feedback for energy deposition, its localized nature likely adds to the physical processes leading to declining SFRs. The phase in which a galaxy in our mass range can be found at a given redshift is set by its gas reservoir and assembly history. Finally, our galaxies are in excellent agreement with various scaling relations observed with the Hubble Space Telescope and the JWST , and hence can be used to provide the theoretical framework to interpret current and future observations from these facilities and shed light on the transition from star-forming to quiescent galaxies. [ABSTRACT FROM AUTHOR]

Fuzzy dark matter (FDM) has recently emerged as an interesting alternative model to the standard cold dark matter (CDM). In this model, dark matter consists of very light bosonic particles with wave-like behaviour on galactic scales. Using the N -body code ax-gadget , we perform cosmological simulations of FDM that fully model the dynamical effects of the quantum potential throughout cosmic evolution. Through the combined analysis of FDM volume and high-resolution zoom-in simulations of different FDM particle masses (⁠|$m_{\chi }$| |$\sim$| |$10^{-23}\!-\!10^{-21}$| eV c−2), we study how FDM impacts the abundance of substructure and the inner density profiles of dark matter haloes. For the first time, using our FDM volume simulations, we provide a fitting formula for the FDM-to-CDM subhalo abundance ratio as a function of the FDM mass. More importantly, our simulations clearly demonstrate that there exists an extended FDM particle mass interval able to reproduce the observed substructure counts and, at the same time, create substantial cores (⁠|$r_{c} \sim 1$| kpc) in the density profile of dwarf galaxies (⁠|$\approx 10^{9}\!-\!10^{10}$| M |$_{\odot }$|⁠), which stands in stark contrast with CDM predictions even with baryonic effects taken into account. The dark matter distribution in the faintest galaxies offers then a clear way to discriminate between FDM and CDM. [ABSTRACT FROM AUTHOR]

It is well known that stars are subject to radial migration, i.e. over time, they move away from their birth location. This dynamical process tends to mix different stellar populations and hence hinders the determination of the true chemical evolution of a galaxy (e.g. metallicity gradients). One way to account for radial migration is to infer stellar birth radii for individual stars. Many attempts to do so have been performed over the last few years, but are limited to the Milky Way, as computing the birth position of stars requires precise measurements of stellar metallicity and age for individual stars that cover large Galactic radii. Fortunately, recent and future surveys will provide numerous opportunities for inferring birth radii for external galaxies such as the LMC. In this paper, we investigate the possibility of doing so using the NIHAO cosmological zoom-in simulations. We find that it is theoretically possible to infer birth radii with a ∼25 per cent median uncertainty for individual stars in galaxies with i) orderliness of the orbits, |$\langle v_\phi \rangle /\sigma _{v} > 2 $|⁠ , ii) a dark matter halo mass greater or equal to approximately the LMC mass (∼2 × 1011  |${\rm M}_\odot$|⁠), and iii) after the average azimuthal velocity of the stellar disc reaches ∼70 per cent of its maximum. From our analysis, we conclude that it is possible and useful to infer birth radii for the LMC and other external galaxies that satisfy the above criteria. [ABSTRACT FROM AUTHOR]

Cosmological galaxy formation simulations are powerful tools to understand the complex processes that govern the formation and evolution of galaxies. However, evaluating the realism of these simulations remains a challenge. The two common approaches for evaluating galaxy simulations is either through scaling relations based on a few key physical galaxy properties, or through a set of pre-defined morphological parameters based on galaxy images. This paper proposes a novel image-based method for evaluating the quality of galaxy simulations using unsupervised deep learning anomaly detection techniques. By comparing full galaxy images, our approach can identify and quantify discrepancies between simulated and observed galaxies. As a demonstration, we apply this method to SDSS imaging and NIHAO simulations with different physics models, parameters, and resolution. We further compare the metric of our method to scaling relations as well as morphological parameters. We show that anomaly detection is able to capture similarities and differences between real and simulated objects that scaling relations and morphological parameters are unable to cover, thus indeed providing a new point of view to validate and calibrate cosmological simulations against observed data. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) in cosmological simulations generate explosive feedback that regulates star formation in massive galaxies, modifying the gas phase structure out to large distances. Here, we explore the direct effects that AGN radiation has on gas heating and cooling within one high-resolution z  = 3 dark matter halo as massive as a quasar host (M h = 1012.5M⊙), run without AGN feedback. We assume AGN radiation to impact the circumgalactic medium (CGM) anisotropically, within a bi-cone of angle α. We find that even a relatively weak AGN (black hole mass M • = 108M⊙ with an Eddington ratio λ = 0.1) can significantly lower the fraction of halo gas that is catastrophically cooling compared to the case of gas photoionized only by the ultraviolet background (UVB). Varying M •, λ, and α, we study their effects on observables. A 109M⊙ AGN with λ = 0.1 and |$\alpha \approxeq 60^{^{\rm o}}$| reproduces the average surface brightness (SB) profiles of Ly α, He  ii , and C  iv , and results in a covering fraction of optically thick absorbers within observational estimates. The simulated SB |$_{\rm C\, \rm{\small IV}}$| profile is steeper than observed, indicating that not enough metals are pushed beyond the very inner CGM. For this combination of parameters, the CGM mass catastrophically cooling is reduced by half with respect to the UVB-only case, with roughly same mass out of hydrostatic equilibrium heating up and cooling down, hinting to the importance of self-regulation around AGNs. This study showcases how CGM observations can constrain not only the properties of the CGM itself, but also those of the AGN engine. [ABSTRACT FROM AUTHOR]

We present simulated galaxy spectral energy distributions (SEDs) from the far-ultraviolet (FUV) through the far-infrared (FIR), created using hydrodynamic simulations and radiative transfer calculations, suitable for the validation of SED modeling techniques. SED modeling is an essential tool for inferring star formation histories from nearby galaxy observations, but it is fraught with difficulty due to our incomplete understanding of stellar populations, chemical enrichment processes, and the nonlinear, geometry-dependent effects of dust on our observations. Our simulated SEDs will allow us to assess the accuracy of these inferences against galaxies with known ground truth. To create the SEDs, we use simulated galaxies from the Numerical Investigation of Hundred Astrophysical Objects suite and the radiative transfer code Stellar Kinematics Including Radiative Transfer. We explore different subgrid post-processing recipes, using color distributions and their dependence on axis ratios of galaxies in the nearby Universe to tune and validate them. We find that subgrid post-processing recipes that mitigate limitations in the temporal and spatial resolution of the simulations are required for producing FUV to FIR photometry that statistically reproduce the colors of galaxies in the nearby Universe. With this paper, we release resolved photometry and spatially integrated spectra for our sample galaxies, each from a range of different viewing angles. Our simulations predict that there is a large variation in attenuation laws among galaxies, and that from any particular viewing angle that energy balance between dust attenuation and re-emission can be violated by up to a factor of 3. These features are likely to affect SED modeling accuracy. [ABSTRACT FROM AUTHOR]

We append two additional black hole (BH) accretion models, namely viscous disc and gravitational torque-driven accretion, into the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project of galaxy simulations. We show that these accretion models, characterized by a weaker dependence on the BH mass compared to the commonly used Bondi-Hoyle accretion, naturally create a common evolutionary track (co-existence) between the mass of the BH and the stellar mass of the galaxy, even without any direct coupling via feedback (FB). While FB is indeed required to control the final BH and stellar mass of the galaxies, our results suggest that FB might not be the leading driver of the cosmic co-evolution between these two quantities; in these models, co-evolution is simply determined by the shared central gas supply. Conversely, simulations using Bondi-Hoyle accretion show a two-step evolution, with an early growth of stellar mass followed by exponential growth of the central supermassive black hole (SMBH). Our results show that the modelling of BH accretion (sometimes overlooked) is an extremely important part of BH evolution and can improve our understanding of how scaling relations emerge and evolve, and whether SMBH and stellar mass co-exist or co-evolve through cosmic time. [ABSTRACT FROM AUTHOR]

Recent observations of the Milky Way (MW) found an unexpected steepening of the star-forming gas metallicity gradient around the time of the Gaia–Sausage–Enceladus (GSE) merger event. Here, we investigate the influence of early (t merger ≲ 5 Gyr) massive (⁠|$M_{\rm {gas}}^{\rm {merger}}/M_{\rm {gas}}^{\rm {main}}(t_{\rm {merger}})\gtrsim 10~{{\ \rm per\ cent}}$|⁠) merger events such as the Gaia–Sausage–Enceladus merger in the MW on the evolution of the cold gas metallicity gradient. We use the NIHAO-UHD suite of cosmological hydrodynamical simulations of MW-mass galaxies to study the frequency of massive early mergers and their detailed impact on the morphology and chemistry of the gaseous discs. We find a strong steepening of the metallicity gradient at early times for all four galaxies in our sample which is caused by a sudden increase in the cold gas disc size (up to a factor of 2) in combination with the supply of unenriched gas (∼0.75 dex lower compared to the main galaxy) by the merging dwarf galaxies. The mergers mostly affect the galaxy outskirts and lead to an increase in cold gas surface density of up to 200 per cent outside of ∼8 kpc. The addition of unenriched gas breaks the self-similar enrichment of the inter-stellar-medium and causes a dilution of the cold gas in the outskirts of the galaxies. The accreted stars and the ones formed later out of the accreted gas inhabit distinct tracks offset to lower [α/Fe] and [Fe/H] values compared to the main galaxy's stars. We find that such mergers can contribute significantly to the formation of a second, low-α sequence as is observed in the MW. [ABSTRACT FROM AUTHOR]

We present the first high-resolution zoom-in simulation of a Milky-way-like halo extracted from the Aquarius Project in the Fuzzy Dark Matter (FDM) framework. We use the N -body code AX-GADGET, based on a particle-oriented solution of the Schrödinger–Poisson equations, able to detail the complexity of structure formation while keeping track of the quantum effects in FDM. The halo shows a cored density profile, with a core size of several kpc for an FDM mass of m χ = 2.5 h  × 10−22 eV/ c 2. A flattening is observed also in the velocity profile, representing a distinct feature of FDM dynamics. We provide a quantitative analysis of the impact of fuzziness on subhaloes in terms of abundance, mass, distance, and velocity distribution functions, and their evolution with redshift. Very interestingly, we show that all collapsed structures, despite showing a flat density profile at z  = 0, do not reach the solitonic ground state at the time of formation: on the contrary, they asymptotically converge to it on a time-scale that depends on their mass and formation history. This implies that current limits on FDM mass – obtained by applying simple scaling relations to observed galaxies – should be taken with extreme care, since single objects can significantly deviate from the expected asymptotic behaviour during their evolution. [ABSTRACT FROM AUTHOR]

We present a catalogue of dynamical properties for 2368 late-type galaxies from the MaNGA survey. The latter complements the catalogue of photometric properties for the same sample based on deep optical dark energy sky instrument legacy imaging survey (DESI) photometry processed with autoprof. Rotation curves (RCs), extracted by model-fitting H α velocity maps from the MaNGA Data Analysis Pipeline, extend out to 1.4 (1.9)  R e for the primary (secondary) MaNGA samples, respectively. The RCs and ancillary MaNGA Pipe3D data products were used to construct various fundamental galaxy scaling relations that are also compared uniformly with similar relations from numerical investigation of a hundred astrophysical object (NIHAO) zoom-in simulations. Simulated NIHAO galaxies were found to broadly reproduce the observed MaNGA galaxy population for |$\log (M_*/{\rm {\rm M}_{\odot })\, \gt\, 8.5}$|⁠. Some discrepancies remain, such as those pertaining to central stellar densities and the diversity of RCs due to strong feedback schemes. Also presented are spatially resolved scatters for the velocity-size-stellar mass (VRM*) structural relations using MaNGA and NIHAO samples. The scatter for these relations in the galaxian interiors is a consequence of the diversity of inner RC shapes, while scatter in the outskirts is dictated by the large range of stellar surface densities, which is itself driven by sporadic star formation. The detailed, spatially resolved scatter analysis highlights the complex interplay between local and global astrophysical processes and provides a strong constraint to numerical simulations. [ABSTRACT FROM AUTHOR]

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Although active galactic nuclei (AGN) feedback is required in simulations of galaxies to regulate star formation, further downstream effects on the dark matter (DM) distribution of the halo and stellar kinematics of the central galaxy can be expected. We combine simulations of galaxies with and without AGN physics from the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) to investigate the effect of AGN on the DM profile and central stellar rotation of the host galaxies. Specifically, we study how the concentration-halo mass (c – M) relation and the stellar spin parameter (λ R ) are affected by AGN feedback. We find that AGN physics is crucial to reduce the central density of simulated massive (⁠|$\gtrsim 10^{12}\, {\rm M}_{\odot }$|⁠) galaxies and bring their concentration to agreement with results from the Spitzer Photometry & Accurate Rotation Curves (SPARC) sample. Similarly, AGN feedback has a key role in reproducing the dichotomy between slow and fast rotators as observed by the ATLAS3D survey. Without star formation suppression due to AGN feedback, the number of fast rotators strongly exceeds the observational constraints. Our study shows that there are several collateral effects that support the importance of AGN feedback in galaxy formation, and these effects can be used to constrain its implementation in numerical simulations. [ABSTRACT FROM AUTHOR]

The transition of high-mass galaxies from being blue and star-forming to being red and dead is a crucial step in galaxy evolution, yet not fully understood. In this work, we use the NIHAO (Numerical Investigation of a Hundred Astrophysical Objects) suite of galaxy simulations to investigate the relation between the transition time through the green valley and other galaxy properties. The typical green valley crossing time of our galaxies is approximately 400 Myr, somewhat shorter than observational estimates. The crossing of the green valley is triggered by the onset of active galactic nucleus (AGN) feedback and the subsequent shutdown of star formation. Interestingly, the time spent in the green valley is not related to any other galaxy properties, such as stellar age or metallicity, or the time at which the star formation quenching takes place. The crossing time is set by two main contributions: the ageing of the current stellar population and the residual star formation in the green valley. These effects are of comparable magnitude, while major and minor mergers have a negligible contribution. Most interestingly, we find the time that a galaxy spends to travel through the green valley is twice the e -folding time of the star formation quenching. This result is stable against galaxy properties and the exact numerical implementation of AGN feedback in the simulation. Assuming a typical crossing time of about 1 Gyr inferred from observations, our results imply that any mechanism or process aiming to quench star formation must do it on a typical time-scale of 500 Myr. [ABSTRACT FROM AUTHOR]

An extensive catalogue of spatially resolved galaxy rotation curves (RCs) and multiband optical light profiles for 1752 observed spiral galaxies is assembled to explore the drivers of diversity in galaxy structural parameters, RC shapes, and stellar mass profiles. Similar data were extracted from the 'Numerical Investigation of a Hundred Astrophysical Objects' galaxy simulations to identify any differences between observations and simulations. Several parameters, including the inner slope |$\mathcal {S}$| of a RC, were tested for diversity. Two distinct populations are found in observed and simulated galaxies: (i) blue, low-mass spirals with stellar mass M ⋆ ≲ 109.3 M⊙ and roughly constant |$\mathcal {S}$|⁠ ; and (ii) redder, more massive and more diverse spirals with rapidly increasing |$\mathcal {S}$|⁠. In all cases, the value of |$\mathcal {S}$| seems equally contributed by the baryonic and non-baryonic (dark) matter. Diversity is shown to increase mildly with mass. Numerical simulations reproduce well most baryon-dominated galaxy parameter distributions, such as the inner stellar mass profile slope and baryonic scaling relations, but they struggle to match the full diversity of observed galaxy RCs (through |$\mathcal {S}$|⁠) and most dark matter-dominated parameters. To reproduce observations, the error broadening of the simulation's intrinsic spread of RC metrics would have to be tripled. The differences in various projections of observed and simulated scaling relations may reflect limitations of current subgrid physics models to fully capture the complex nature of galaxies. For instance, active galactic nuclei (AGNs) are shown to have a significant effect on the shapes of simulated RCs. The inclusion of AGN feedback brings simulated and observed inner RC shapes into closer agreement. [ABSTRACT FROM AUTHOR]

Recent observational and theoretical studies of the Local Group (LG) dwarf galaxies have highlighted their unique star-formation history, stellar metallicity, gas content, and kinematics. We investigate the commonality of these features by comparing constrained LG and field central dwarf halo simulations in the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project. Our simulations, performed with NIHAO-like hydrodynamics which track the evolution of the Milky Way (MW) and M31 along with ∼100 dwarfs in the LG, reveal the total gas mass and stellar properties (velocity dispersion, evolution history, etc.) of present-day LG dwarfs to be similar to field systems. However, relative to field galaxies, LG dwarfs have more cold gas in their central parts and more metal-rich gas in the halo stemming from interactions with other dwarfs living in a high-density environment like the LG. Interestingly, the direct impact of massive MW/M31 analogues on the metallicity evolution of LG dwarfs is minimal; LG dwarfs accrete high-metallicity gas mostly from other dwarfs at late times. We have also tested for the impact of metal diffusion on the chemical evolution of LG dwarfs, and found that it does not affect the stellar or gaseous content of LG dwarfs. Our simulations suggest that the stellar components of LG dwarfs offer a unique and unbiased local laboratory for galaxy-formation tests and comparisons, especially against the overall dwarf population in the Universe. [ABSTRACT FROM AUTHOR]

Cosmological galaxy formation simulations are still limited by their spatial/mass resolution and cannot model from first principles some of the processes, like star formation, that are key in driving galaxy evolution. As a consequence they still rely on a set of 'effective parameters' that try to capture the scales and the physical processes that cannot be directly resolved in the simulation. In this study, we show that it is possible to use Machine Learning techniques applied to real and simulated images of galaxies to discriminate between different values of these parameters by making use of the full information content of an astronomical image instead of collapsing it into a limited set of values like size, or stellar/ gas masses. In this work, we apply our method to the NIHAO simulations and the THINGS and VLA-ANGST observations of H  i maps in nearby galaxies to test the ability of different values of the star formation density threshold n to reproduce observed H  i maps. We show that observations indicate the need for a high value of n ≳ 80 cm−3 (although the numerical value is model-dependent), which has important consequences for the dark matter distribution in galaxies. Our study shows that with innovative methods it is possible to take full advantage of the information content of galaxy images and compare simulations and observations in an interpretable, non-parametric, and quantitative manner. [ABSTRACT FROM AUTHOR]

The contribution focuses on the vast Fortleben of the Voie d'Enfer et de Paradis by Pierre de l'Hôpital (1315-1336) and sheds light on the dynamics of transmission and re-adaptation in which the text was involved during the fourteenth century. On the basis of new elements derived from a contrastive analysis, the study aims firstly at confirming the hypothesis, supported by S. Menegaldo, of the filiation of Jean de Le Mote's allegorical voyage (1340) from Pierre de l'Hôpital's homonymous poem. Secondly, the paper traces as exhaustively as possible the processes of spectacularization and staging implemented in the text by its anonymous rewritings, namely the Songe de la voie d'enfer et de la voie de paradis (of which an approximate dating is also proposed) and the Speculum mondialle morality play. [ABSTRACT FROM AUTHOR]

With the advent of large spectroscopic surveys the amount of high quality chemodynamical data in the Milky Way (MW) increased tremendously. Accurately and correctly capturing and explaining the detailed features in the high-quality observational data is notoriously difficult for state-of-the-art numerical models. In order to keep up with the quantity and quality of observational data sets, improved prescriptions for galactic chemical evolution need to be incorporated into the simulations. Here we present a new, flexible, time-resolved chemical enrichment model for cosmological simulations. Our model allows us to easily change a number of stellar physics parameters such as the shape of the initial mass function (IMF), stellar lifetimes, chemical yields, or SN Ia delay times. We implement our model into the Gasoline2 code and perform a series of cosmological simulations varying a number of key parameters, foremost evaluating different stellar yield sets for massive stars from the literature. We find that total metallicity, total iron abundance, and gas phase oxygen abundance are robust predictions from different yield sets and in agreement with observational relations. On the other hand, individual element abundances, especially alpha-elements show significant differences across different yield sets and none of our models can simultaneously match constraints on the dwarf and MW mass scale. This offers a unique way of observationally constraining model parameters. For MW mass galaxies we find for most yield tables tested in this work a bimodality in the [α/Fe] versus [Fe/H] plane of rather low intrinsic scatter potentially in tension with the observed abundance scatter. [ABSTRACT FROM AUTHOR]

We use hydrodynamical cosmological simulations to show that it is possible to create, via tidal interactions, galaxies lacking dark matter (DM) in a DM-dominated universe. We select dwarf galaxies from the NIHAO project, obtained in the standard cold dark matter model and use them as initial conditions for simulations of satellite–central interactions. After just one pericentric passage on an orbit with a strong radial component, NIHAO dwarf galaxies can lose up to 80 per cent of their DM content, but, most interestingly, their central (≈8 kpc) DM-to-stellar mass ratio changes from a value of ∼25, as expected from numerical simulations and abundance matching techniques, to roughly unity as reported for NGC 1052-DF2 and NGC 1054-DF4. The stellar velocity dispersion drops from ∼30  |$\, \rm km\, s^{-1}$| before infall to values as low as 6 ± 2  |$\, \rm km\, s^{-1}$|⁠. These, and the half-light radius around 3 kpc, are in good agreement with observations from van Dokkum and collaborators. Our study shows that it is possible to create a galaxy without DM starting from typical dwarf galaxies formed in a DM-dominated universe, provided they live in a dense environment. [ABSTRACT FROM AUTHOR]

We investigate how the NIHAO galaxies match the observed star formation main sequence (SFMS) and what the origin of its scatter is. The NIHAO galaxies reproduce the SFMS and generally agree with observations, but the slope is about unity and thus significantly larger than observed values. This is because observed galaxies at large stellar masses, although still being part of the SFMS, are already influenced by quenching. This partial suppression of star formation by AGN feedback leads to lower star formation rates and therefore to lower observed slopes. We confirm that including the effects of AGN in our galaxies leads to slopes in agreement with observations. We find the deviation of a galaxy from the SFMS is correlated with its z  = 0 dark matter halo concentration and thus with its halo formation time. This means galaxies with a higher-than-average star formation rate (SFR) form later and vice versa. We explain this apparent correlation with the SFR by re-interpreting galaxies that lie above the SFMS (higher-than-average SFR) as lying to the left of the SFMS (lower-than-average stellar mass) and vice versa. Thus later forming haloes have a lower-than-average stellar mass, this is simply because they have had less-than-average time to form stars, and vice versa. It is thus the nature, i.e. how and when these galaxies form, that sets the path of a galaxy in the SFR versus stellar mass plane. [ABSTRACT FROM AUTHOR]

We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the response of cold dark matter (CDM) haloes to baryonic processes. Previous work has shown that the halo response is primarily a function of the ratio between galaxy stellar mass and total virial mass, and the density threshold above which gas is eligible to form stars, n [cm−3]. At low n all simulations in the literature agree that dwarf galaxy haloes are cuspy, but at high n ≳ 100 there is no consensus. We trace halo contraction in dwarf galaxies with n ≳ 100 reported in some previous simulations to insufficient spatial resolution. Provided the adopted star formation threshold is appropriate for the resolution of the simulation, we show that the halo response is remarkably stable for n ≳ 5, up to the highest star formation threshold that we test, n  = 500. This free parameter can be calibrated using the observed clustering of young stars. Simulations with low thresholds n ≤ 1 predict clustering that is too weak, while simulations with high star formation thresholds n ≳ 5, are consistent with the observed clustering. Finally, we test the CDM predictions against the circular velocities of nearby dwarf galaxies. Low thresholds predict velocities that are too high, while simulations with n ∼ 10 provide a good match to the observations. We thus conclude that the CDM model provides a good description of the structure of galaxies on kpc scales provided the effects of baryons are properly captured. [ABSTRACT FROM AUTHOR]

We explore a function with two shape parameters for the dark-matter halo density profile subject to baryonic effects, which is a special case of the general Zhao family of models applied to simulated dark-matter haloes by Dekel et al. This profile has variable inner slope and concentration parameter, and analytic expressions for the gravitational potential, velocity dispersion, and lensing properties. Using the Numerical Investigation of a Hundred Astrophysical Objects cosmological simulations, we find that it provides better fits than the Einasto profile and the generalized NFW profile with variable inner slope, in particular towards the halo centres. We show that the profile parameters are correlated with the stellar-to-halo mass ratio M star/ M vir. This defines a mass-dependent density profile describing the average dark-matter profiles in all galaxies, which can be directly applied to observed rotation curves of galaxies, gravitational lenses, and semi-analytic models of galaxy formation or satellite–galaxy evolution. The effect of baryons manifests itself by a significant flattening of the inner density slope and a 20 per cent decrease of the concentration parameter for M star/ M vir = 10−3.5–10−2, corresponding to |$M_{\rm star} \!\sim \! 10^{7-10}\, \mathrm{ M}_\odot$|⁠. The accuracy by which this profile fits simulated galaxies is similar to certain multiparameter mass-dependent profiles, but its fewer parameters and analytic nature make it most desirable for many purposes. [ABSTRACT FROM AUTHOR]

In recent years, a new window on galaxy evolution opened, thanks to the increasing discovery of galaxies with a low-surface brightness, such as Ultra Diffuse Galaxies (UDGs). The formation mechanism of these systems is still a much debated question and so are their kinematical properties. In this work, we address this topic by analysing the stellar kinematics of isolated UDGs formed in the hydrodynamical simulation suite Numerical Investigation of a Hundred Astrophysical Objects (NIHAO). We construct projected line-of-sight velocity and velocity dispersion maps to compute the projected specific angular momentum, λR, to characterize the kinematical support of the stars in these galaxies. We found that UDGs cover a broad distribution, ranging from dispersion to rotation-supported galaxies, with similar abundances in both regimes. The degree of rotation support of simulated UDGs correlates with several properties such as galaxy morphology, higher H  i fractions, and larger effective radii with respect to the dispersion-supported group, while the dark matter halo spin and mass accretion history are similar among the two populations. We demonstrate that the alignment of the infalling baryons into the protogalaxy at early z is the principal driver of the z  = 0 stellar kinematic state: pressure-supported isolated UDGs form via misaligned gas accretion while rotation-supported ones build up their baryons in an ordered manner. Accounting for random inclination effects, we predict that a comprehensive survey will find nearly half of field UDGs to have rotationally supported stellar discs, when selecting UDGs with effective radius larger than 1 kpc. [ABSTRACT FROM AUTHOR]

We present a comprehensive test of the relation between stellar and total masses in galaxies as predicted by popular models based on abundance matching (AM) techniques. We use the 'Spectroscopy and H -band Imaging of Virgo cluster galaxies' (SHIVir) survey with photometric and dynamical profiles for 190 Virgo cluster galaxies to establish a relation between the stellar and dynamical masses measured within the isophotal radius r 23.5. Various dark matter and galaxy scaling relations are combined with results from the NIHAO (Numerical Investigation of Hundred Astrophysical Objects) suite of hydrodynamical simulations to recast AM predictions in terms of these observed quantities. Our results are quite insensitive to the exact choice of dark matter profile and halo response to baryon collapse. We find that theoretical models reproduce the slope and normalization of the observed stellar-to-halo mass relation (SHMR) over more than three orders of magnitude in stellar mass (108 < M */M⊙ < 2 × 1011). However, the scatter of the observed SHMR exceeds that of AM predictions by a factor of ∼5. For systems with stellar masses exceeding 5 × 1010 M⊙, AM overpredicts the observed stellar masses for a given dynamical mass. The latter offset may support previous indications of a different stellar initial mass function in these massive galaxies. Overall, our results support the validity of AM predictions on a wide dynamical range. [ABSTRACT FROM AUTHOR]

We present a systematic analysis of the reaction of dark matter distribution to galaxy formation across more than eight orders of magnitude in stellar mass. We extend the previous work presented in the NIHAO-IV paper by adding 46 new high-resolution simulations of massive galaxies performed with the inclusion of black hole feedback. We show that outflows generated by the active galactic nucleus (AGN) are able to partially counteract the dark matter contraction due to the large central stellar component in massive haloes. The net effect is to relax the central dark matter distribution that moves to a less cuspy density profiles at halo mass larger than ≈3 × 1012 M⊙. The scatter around the mean value of the density profile slope (α) is fairly constant (Δα ≈ 0.3), with the exception of galaxies with halo masses around 1012 M⊙, at the transition from stellar to AGN feedback dominated systems, where the scatter increases by almost a factor of 3. We provide useful fitting formulae for the slope of the dark matter density profiles at few per cent of the virial radius for the whole stellar mass range: 105–1012 M⊙ (2 × 109 to 5 × 1013 M⊙ in halo mass). [ABSTRACT FROM AUTHOR]

We present a simple model for the response of a dissipationless spherical system to an instantaneous mass change at its centre, describing the formation of flat cores in dark matter haloes and ultra-diffuse galaxies (UDGs) from feedback-driven outflow episodes in a specific mass range. This model generalizes an earlier simplified analysis of an isolated shell into a system with continuous density, velocity, and potential profiles. The response is divided into an instantaneous change of potential at constant velocities due to a given mass-loss or mass-gain, followed by energy-conserving relaxation to a new Jeans equilibrium. The halo profile is modelled by a two-parameter function with a variable inner slope and an analytic potential profile, which enables determining the associated kinetic energy at equilibrium. The model is tested against NIHAO cosmological zoom-in simulations, where it successfully predicts the evolution of the inner dark matter profile between successive snapshots in about 75 per cent of the cases, failing mainly in merger situations. This model provides a simple understanding of the formation of dark matter halo cores and UDGs by supernova-driven outflows, and a useful analytic tool for studying such processes. [ABSTRACT FROM AUTHOR]

Simulating thin and extended galactic discs has long been a challenge in computational astrophysics. We introduce the NIHAO-UHD suite of cosmological hydrodynamical simulations of Milky Way (MW) mass galaxies and study stellar disc properties such as stellar mass, size, and rotation velocity which agree well with observations of the MW and local galaxies. In particular, the simulations reproduce the age–velocity dispersion relation and a multicomponent stellar disc as observed for the MW. Half of our galaxies show a double exponential vertical profile, while the others are well described by a single exponential model which we link to the disc merger history. In all cases, mono-age populations follow a single exponential whose scale height varies monotonically with stellar age and radius. The scale length decreases with stellar age while the scale height increases. The general structure of the stellar discs is already set at time of birth as a result of the inside–out and upside–down formation. Subsequent evolution modifies this structure by increasing both the scale length and height of all mono-age populations. Thus, our results put tight constraints on how much dynamical memory stellar discs can retain over cosmological time-scales. Our simulations demonstrate that it is possible to form thin galactic discs in cosmological simulations provided there are no significant stellar mergers at low redshifts. Most of the stellar mass is formed in situ with only a few per cent (⁠|${\lesssim}5{{\ \rm per\ cent}}$|⁠) brought in by merging satellites at early times. Redshift zero snapshots and halo catalogues are publicly available. [ABSTRACT FROM AUTHOR]

We implement an optically thin approximation for the effects of the local radiation field from stars and hot gas on the gas heating and cooling in the N -body smoothed particle hydrodynamics code gasoline2. We resimulate three galaxies from the NIHAO project: one dwarf, one Milky Way-like, and one massive spiral, and study what are the local radiation field effects on various galaxy properties. We also study the effects of varying the ultraviolet background (UVB) model, by running the same galaxies with two different UVBs. Galaxy properties at |$z$|  = 0 like stellar mass, stellar effective mass radius, H  i mass, and radial extent of the H  i disc show significant changes between the models with and without the local radiation field, and smaller differences between the two UVB models. The intrinsic effect of the local radiation field through cosmic time is to increase the equilibrium temperature at the interface between the galaxies and their circumgalactic media (CGM), moving this boundary inwards, while leaving relatively unchanged the gas inflow rate. Consequently, the temperature of the inflow increases when considering the local radiation sources. This temperature increase is a function of total galaxy mass, with a median CGM temperature difference of one order of magnitude for the massive spiral. The local radiation field suppresses the stellar mass growth by 20 per cent by |$z$|  = 0 for all three galaxies, while the H  i mass is roughly halved. The differences in the gas phase diagrams, significantly impact the H  i column densities, shifting their peaks in the distributions towards lower N H  i . [ABSTRACT FROM AUTHOR]

We use 38 high-resolution simulations of galaxy formation between redshift 10 and 5 to study the impact of a 3 keV warm dark matter (WDM) candidate on the high-redshift Universe. We focus our attention on the stellar mass function and the global star formation rate and consider the consequences for reionization, namely the neutral hydrogen fraction evolution and the electron scattering optical depth. We find that three different effects contribute to differentiate warm and cold dark matter (CDM) predictions: WDM suppresses the number of haloes with mass less than few 109 M⊙; at a fixed halo mass, WDM produces fewer stars than CDM, and finally at halo masses below 109 M⊙, WDM has a larger fraction of dark haloes than CDM post-reionization. These three effects combine to produce a lower stellar mass function in WDM for galaxies with stellar masses at and below 107 M⊙. For z > 7, the global star formation density is lower by a factor of two in the WDM scenario, and for a fixed escape fraction, the fraction of neutral hydrogen is higher by 0.3 at z ∼ 6. This latter quantity can be partially reconciled with CDM and observations only by increasing the escape fraction from 23 per cent to 34 per cent. Overall, our study shows that galaxy formation simulations at high redshift are a key tool to differentiate between dark matter candidates given a model for baryonic physics. [ABSTRACT FROM AUTHOR]

The direction of the spin vectors of disc galaxies change over time. We present the tilting rate of a sample of galaxies in the NIHAO suite of cosmological hydrodynamical simulations. Galaxies in our sample have been selected to be isolated and to have well-determined spins. We compare the tilting rates to the predicted observing limit of Gaia , finding that our entire sample lies above the limit, in agreement with previous work. To test the role of dark matter and of gas, we compare the weighted Pearson's correlation coefficients between the tilting rates and various properties. We find no correlation between the dark halo's tilting rate, shape, or misalignment with respect to the disc, and the tilting rate of the stellar disc. Therefore, we argue that, in the presence of gas, the dark halo plays a negligible role in the tilting of the stellar disc. On the other hand, we find a strong correlation between the tilting rate of the stellar disc and the misalignment of the cold gas warp. Adding the stellar mass fraction improves the correlation, while none of the dark matter's properties together with the cold gas misalignment improves the correlation to any significant extent. This implies that the gas cooling on to the disc is the principal driver of disc tilting. [ABSTRACT FROM AUTHOR]

The similarity between the distributions of spins for galaxies (λgal) and for dark-matter haloes (λhalo), indicated both by simulations and observations, is naively interpreted as a one-to-one correlation between the spins of a galaxy and its host halo. This is used to predict galaxy sizes in semi-analytic models via R e ≃ fj λhalo R vir, where R e is the half-mass radius of the galaxy, fj is the angular momentum retention factor, and R vir is the halo radius. Using two suites of zoom-in cosmological simulations, we find that λgal and the λhalo of its host halo are in fact barely correlated, especially at z ≥ 1, in line with previous indications. Since the spins of baryons and dark matter are correlated at accretion into R vir, the null correlation in the end reflects an anticorrelation between fj and λhalo, which can arise from mergers and a 'wet compaction' phase that many high-redshift galaxies undergo. It may also reflect that unrepresentative small fractions of baryons are tapped to the galaxies. The galaxy spin is better correlated with the spin of the inner halo, but this largely reflects the effect of the baryons on the halo. While λhalo is not a useful predictor for R e, our simulations reproduce a general relation of the form of R e = AR vir, in agreement with observational estimates. We find that the relation becomes tighter with A  = 0.02(c /10)−0.7, where c is the halo concentration, which in turn introduces a dependence on mass and redshift. [ABSTRACT FROM AUTHOR]

The early fourteenth-century Voie d'Enfer et de Paradis by Pierre de l'Hôpital (of which the first critical edition is currently being prepared) has drawn only passing interest from critics, in spite of its importance for the development of the genre of the allegorical voyage. This paper aims to locate the still unedited work attributed to Pierre de l'Hôpital within the oitanic literature, specifically highlighting the differences that distinguish it from other literary representatives of the journey through the Afterlife and suggesting a possible intertextual link between the text typology of the Voie d'Enfer et de Paradis and that of the Songe d'Enfer by Raoul de Houdenc. Besides, after confirming the date of composition and the vast Fortleben that concerned the Voie, as well as the dynamics of reception that have influenced its fruition and subsequent theatrical re-writings, we will offer first precise account of all the four manuscript witnesses conserving the text. Moreover, we will also try to shed more light on the possible social identity and the origin of the author, whose figure has been richly miniated in some illuminations decorating a witness of the first re-adaptation of the text. [ABSTRACT FROM AUTHOR]

We introduce algorithms for black hole physics, i.e. black hole formation, accretion, and feedback, into the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project of galaxy simulations. This enables us to study high mass, elliptical galaxies, where feedback from the central black hole is generally thought to have a significant effect on their evolution. We furthermore extend the NIHAO suite by 45 simulations that encompass z  = 0 halo masses from 1 × 1012 to |$4 \times 10^{13}\, \mathrm{M}_{\odot }$|⁠ , and resimulate five galaxies from the original NIHAO sample with black hole physics, which have z  = 0 halo masses from 8 × 1011 to |$3 \times 10^{12}\, \mathrm{M}_{\odot }$|⁠. Now NIHAO contains 144 different galaxies and thus has the largest sample of zoom-in simulations of galaxies, spanning z  = 0 halo masses from 9 × 108 to |$4 \times 10^{13}\, \mathrm{M}_{\odot }$|⁠. In this paper we focus on testing the algorithms and calibrating their free parameters against the stellar mass versus halo mass relation and the black hole mass versus stellar mass relation. We also investigate the scatter of these relations, which we find is a decreasing function with time and thus in agreement with observations. For our fiducial choice of parameters we successfully quench star formation in objects above a z  = 0 halo mass of |$10^{12}\, \mathrm{M}_{\odot }$|⁠ , thus transforming them into red and dead galaxies. [ABSTRACT FROM AUTHOR]

We study ultra-diffuse galaxies (UDGs) in zoom in cosmological simulations, seeking the origin of UDGs in the field versus galaxy groups. We find that while field UDGs arise from dwarfs in a characteristic mass range by multiple episodes of supernova feedback (Di Cintio et al.), group UDGs may also form by tidal puffing up and they become quiescent by ram-pressure stripping. The field and group UDGs share similar properties, independent of distance from the group centre. Their dark-matter haloes have ordinary spin parameters and centrally dominant dark-matter cores. Their stellar components tend to have a prolate shape with a Sérsic index n ∼ 1 but no significant rotation. Ram pressure removes the gas from the group UDGs when they are at pericentre, quenching star formation in them and making them redder. This generates a colour/star-formation-rate gradient with distance from the centre of the dense environment, as observed in clusters. We find that ∼20 per cent of the field UDGs that fall into a massive halo survive as satellite UDGs. In addition, normal field dwarfs on highly eccentric orbits can become UDGs near pericentre due to tidal puffing up, contributing about half of the group-UDG population. We interpret our findings using simple toy models, showing that gas stripping is mostly due to ram pressure rather than tides. We estimate that the energy deposited by tides in the bound component of a satellite over one orbit can cause significant puffing up provided that the orbit is sufficiently eccentric. We caution that while the simulations produce UDGs that match the observations, they under-produce the more compact dwarfs in the same mass range, possibly because of the high threshold for star formation or the strong feedback. [ABSTRACT FROM AUTHOR]

We use 25 simulated galaxies from the NIHAO project to define and characterize a variety of kinematic stellar structures: thin and thick discs, large-scale single discs, classical and pseudo-bulges, spheroids, inner discs, and stellar haloes. These structures have masses, spins, shapes, and rotational support in good agreement with theoretical expectations and observational data. Above a dark matter halo mass of |$2.5\times 10^{\rm ~11}\, \mathrm{M}_{\odot }$|⁠ , all galaxies have a classical bulge and 70 per cent have a thin and thick disc. The kinematic (thin) discs follow a power-law relation between angular momentum and stellar mass |$J_{\rm *}=3.4M_{\rm *}^{\rm 1.26\pm 0.06}$|⁠ , in very good agreement with the prediction based on the empirical stellar-to-halo-mass relation in the same mass range, and show a strong correlation between maximum 'observed' rotation velocity and dark matter halo circular velocity |$v_{\rm c}=6.4v_{\rm max}^{0.64\pm 0.04}$|⁠. Tracing back in time these structures' progenitors, we find all of them to lose a fraction 1 − fj of their maximum angular momentum. Thin discs are significantly better at retaining their high-redshift spins (fj ∼ 0.70) than thick ones (fj ∼ 0.40). Stellar haloes have their progenitor baryons assembled the latest (z 1/2 ∼ 1.1) and over the longest time-scales (τ ∼ 6.2 Gyr), and have the smallest fraction of stars born in situ (f in situ = 0.35 ± 0.14). All other structures have 1.5 ≲ z 1/2 ≲ 3, τ = 4 ± 2 Gyr, and f in situ ≳ 0.9. [ABSTRACT FROM AUTHOR]

The existence of galaxies with a surface brightness μ lower than the night sky has been known since three decades. Yet, their formation mechanism and emergence within a Lambda cold dark matter universe has remained largely undetermined. For the first time, we investigated the origin of low surface brightness (LSB) galaxies with M ⋆ ∼ 109.5−10 M⊙, which we are able to reproduce within hydrodynamical cosmological simulations from the NIHAO suite. The simulated and observed LSB galaxies share similar properties, having large H  i reservoir, extended star formation histories and effective radii, low Sérsic index, and slowly rising rotation curves. The formation mechanism of these objects is explored: simulated LSB galaxies form as a result of coplanar co-rotating mergers and aligned accretion of gas at early times, while perpendicular mergers and misaligned gas accretion result in higher μ galaxies by z  = 0. The larger the merger, the stronger the correlation between merger orbital configuration and final μ. While the halo spin parameter is consistently high in simulated LSB galaxies, the impact of halo concentration, feedback-driven gas outflows, and merger time only plays a minor-to-no role in determining μ. Interestingly, the formation scenario of such 'classical' LSB galaxies differs from the one of less massive, M ⋆ ∼ 107–9 M⊙, ultra-diffuse galaxies, the latter resulting from the effects of SNae-driven gas outflows: an M ⋆ of ∼109 M⊙ thus represents the transition regime between a feedback-dominated to an angular-momentum-dominated formation scenario in the LSB realm. Observational predictions are offered regarding spatially resolved star formation rates through LSB discs: these, together with upcoming surveys, can be used to verify the proposed emergence scenario of LSB galaxies. [ABSTRACT FROM AUTHOR]

State-of-the-art cosmological hydrodynamical simulations of galaxy formation have reached the point at which their outcomes result in galaxies with ever more realism. Still, the employed sub-grid models include several free parameters such as the density threshold, n, to localize the star-forming gas. In this work, we investigate the possibilities to utilize the observed clustered nature of star formation (SF) in order to refine SF prescriptions and constrain the density threshold parameter. To this end, we measure the clustering strength, correlation length, and power-law index of the two-point correlation function of young (τ < 50 Myr) stellar particles and compare our results to observations from the HST Legacy Extragalactic UV Survey (LEGUS). Our simulations reveal a clear trend of larger clustering signal and power-law index and lower correlation length as the SF threshold increases with only mild dependence on galaxy properties such as stellar mass or specific star formation rate. In conclusion, we find that the observed clustering of SF is inconsistent with a low threshold for SF (n < 1 cm−3) and strongly favours a high value for the density threshold of SF (n > 10 cm−3), as, for example employed in the NIHAO project. [ABSTRACT FROM AUTHOR]

We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the impact of the threshold for star formation on the response of the dark matter (DM) halo to baryonic processes. The fiducial NIHAO threshold, |$n=10\, [{\rm cm}^{-3}]$|⁠, results in strong expansion of the DM halo in galaxies with stellar masses in the range |$10^{7.5} \lesssim {{M_{\rm star}}}\lesssim 10^{9.5} {{ {\rm M}_{\odot }}}$|⁠. We find that lower thresholds such as n  = 0.1 (as employed by the EAGLE/APOSTLE and Illustris/AURIGA projects) do not result in significant halo expansion at any mass scale. Halo expansion driven by supernova feedback requires significant fluctuations in the local gas fraction on sub-dynamical times (i.e. |$\lesssim $| 50 Myr at galaxy half-light radii), which are themselves caused by variability in the star formation rate. At one per cent of the virial radius, simulations with n  = 10 have gas fractions of ≃0.2 and variations of ≃0.1, while n  = 0.1 simulations have order of magnitude lower gas fractions and hence do not expand the halo. The observed DM circular velocities of nearby dwarf galaxies are inconsistent with CDM simulations with n  = 0.1 and n  = 1, but in a reasonable agreement with n  = 10. Star formation rates are more variable for higher n, lower galaxy masses, and when star formation is measured on shorter time-scales. For example, simulations with n  = 10 have up to 0.4 dex higher scatter in specific star formation rates than simulations with n  = 0.1. Thus observationally constraining the sub-grid model for star formation, and hence the nature of DM, should be possible in the near future. [ABSTRACT FROM AUTHOR]

We have used the NIHAO (Numerical Investigation of a Hundred Astrophysical Objects) simulations to explore how supernovae (SNe) affect star formation in galaxies. We find that SN feedback operates on all scales from the interstellar medium (ISM) to several virial radii. SNe regulate star formation by preventing condensation of Hi into h 2 and by moving cold neutral gas to the hot Hii phase. The first effect explains why the cold neutral gas in dwarf galaxies forms stars inefficiently. The second maintains the hot ISM of massive galaxies (Hii vents out at lower masses). At |$v_{\rm vir}\lower.5ex{\,\, \buildrel\gt \over \sim \,\,}67{\rm \, km\, s}^{-1}$|⁠, the outflow rate follows the relation: |$\skew4\dot{M}_{\rm out}=23\, (v_{\rm vir}/67{\rm \, km\, s}^{-1})^{-4.6}\, {\rm SFR}$|⁠. |$20{{\ \rm per\ cent}}$| – |$70{{\ \rm per\ cent}}$| of the gas expelled from galaxies escapes from the halo (ejective feedback) but outflows are dominated by cold swept-up gas, most of which falls back on to the galaxy on a |${\sim } 1\,$| Gyr time-scale. This 'fountain feedback' reduces the masses of galaxies by a factor of 2–4, since gas spends half to three quarter of its time in the fountain. Less than |$10{{\ \rm per\ cent}}$| of the ejected gas mixes with the hot circumgalactic medium and this gas is usually not reaccreted. On scales as large as 6 r vir, galactic winds divert the incoming gas from cosmic filaments and prevent it from accreting on to galaxies (pre-emptive feedback). This process is the main reason for the low baryon content of ultradwarves. [ABSTRACT FROM AUTHOR]

The phenomenological basis for Modified Newtonian Dynamics (MOND) is the radial acceleration relation (RAR) between the observed acceleration, |$a=V^2_{\rm rot}(r)/ r$|⁠, and the acceleration accounted for by the observed baryons (stars and cold gas), |$a_{\rm bar}=V_{\rm bar}^2(r)/r$|⁠. We show that the RAR arises naturally in the NIHAO sample of 89 high-resolution ΛCDM cosmological galaxy formation simulations. The overall scatter from NIHAO is just 0.079 dex, consistent with observational constraints. However, we show that the scatter depends on stellar mass. At high masses (⁠|$10^9 \lesssim M_{\rm star} \lesssim 10^{11}\, \rm M_{\odot }$|⁠) the simulated scatter is just ≃0.04 dex, increasing to ≃0.11 dex at low masses (⁠|$10^7 \lesssim M_{\rm star} \lesssim 10^{9}\, \rm M_{\odot }$|⁠). Observations show a similar dependence for the intrinsic scatter. At high masses the intrinsic scatter is consistent with the zero scatter assumed by MOND, but at low masses the intrinsic scatter is non-zero, strongly disfavouring MOND. Applying MOND to our simulations yields remarkably good fits to most of the circular velocity profiles. In cases of mild disagreement the stellar mass-to-light ratio and/or 'distance' can be tuned to yield acceptable fits, as is often done in observational mass models. In dwarf galaxies with |$M_{\rm star} \sim 10^6\, \rm M_{\odot }$| MOND breaks down, predicting lower accelerations than observed and in our ΛCDM simulations. The assumptions that MOND is based on (e.g. asymptotically flat rotation curves, zero intrinsic scatter in the RAR) are only approximately true in ΛCDM. Thus if one wishes to go beyond Newtonian dynamics there is more freedom in the observed RAR than assumed by MOND. [ABSTRACT FROM AUTHOR]

In this third paper of the series, we investigate the effects of warm dark matter (WDM) with a particle mass of |$m_\mathrm{WDM}=3\, \mathrm{keV}$| on the smallest galaxies in our Universe. We present a sample of 21 hydrodynamical cosmological simulations of dwarf galaxies and 20 simulations of satellite-host galaxy interaction that we performed both in a cold dark matter (CDM) and WDM scenario. In the WDM simulations, we observe a higher critical mass for the onset of star formation. Structure growth is delayed in WDM, as a result WDM haloes have a stellar population on average 2 Gyr younger than their CDM counterparts. Nevertheless, despite this delayed star formation, CDM and WDM galaxies are both able to reproduce the observed scaling relations for velocity dispersion, stellar mass, size, and metallicity at |$z$|  = 0. WDM satellite haloes in a Milky Way mass host are more susceptible to tidal stripping due to their lower concentrations, but their galaxies can even survive longer than the CDM counterparts if they live in a dark matter halo with a stee per central slope. In agreement with our previous CDM satellite study we observe a steepening of the WDM satellites' central dark matter density slope due to stripping. The difference in the average stellar age for satellite galaxies, between CDM and WDM, could be used in the future for disentangling these two models. [ABSTRACT FROM AUTHOR]

We study the impact of the host on dwarf galaxy properties using four new Milky Way (MW)-like, ultra-high-resolution simulations (N part > 107) from the NIHAO project. We split our sample into satellite (R < R 200), nearby (1 < R / R 200 < 2.5), and field (R > 2.5 R 200) galaxies. Simulated galaxies from all three groups are in excellent agreement with Local Group dwarf galaxies in terms of the stellar mass–velocity dispersion and stellar mass–metallicity relations, star formation histories, and stellar mass functions. Satellites and nearby galaxies show lower velocity dispersions and gas fractions compared to field galaxies. While field galaxies follow global abundance matching relations, satellites and nearby galaxies deviate from them, showing lower dark matter masses for a given stellar mass. The reason for this deficit in dark matter mass is the substantial mass loss experienced by satellites and ∼80 per cent of the nearby galaxies while orbiting inside R 200 at earlier times. However, both satellites and nearby objects fall back on to the relation for field galaxies if we use the maximum of their virial mass instead of the present-day value. This allows us to provide estimates for the peak masses of observed Local Group galaxies. Finally, using radial velocities, distances, and the velocity dispersion–stellar mass relation from our simulations, we derive a metric to distinguish between galaxies harassed by the central object and unaffected ones. Applying this metric to observed objects, we find that even far-away dwarf galaxies like Eri II (D  ≈ 370 kpc) have a strong probability (≈83 per cent) of having been affected by the MW in the past. This naturally explains the lack of gas and recent star formation seen in Eri II. [ABSTRACT FROM AUTHOR]

We used high resolution dark matter only cosmological simulations to investigate the structural properties of Lambda Cold Dark Matter (ΛCDM) haloes over cosmic time. The haloes in our study range in mass from ∼1010 to |${\sim } 10^{12} \, \rm M_{\odot}$|⁠, and are resolved with 105 to 107 particles. We fit the spherically averaged density profiles of DM haloes with the three parameter Einasto function. For our sample of haloes, the Einasto shape parameter, α, is uncorrelated with the concentration, c, at fixed halo mass, and at all redshifts. Previous reports of an anticorrelation are traced to fitting degeneracies, which our fits are less sensitive to due to our higher spatial resolution. However, for individual haloes the evolution in α and c is anticorrelated: at redshift |$z$|  = 7, α ≃ 0.4 and decreases with time, while c  ≃ 3 and increases with time. The evolution in structure is primarily due to accretion of mass at larger radii. We suggest that α traces the evolutionary state of the halo, with dynamically young haloes having high α (closer to a top-hat: α−1 = 0), and dynamically relaxed haloes having low α (closer to isothermal: α = 0). Such an evolutionary dependence reconciles the increase of α versus peak height, ν, with the dependence on the slope of the power spectrum of initial density fluctuations found by previous studies. [ABSTRACT FROM AUTHOR]

We use 85 pairs of high-resolution lambda cold dark matter (LCDM) cosmological simulations from the NIHAO project to investigate why in dwarf galaxies neutral hydrogen (H  i) linewidths measured at 50 per cent of the peak flux W 50/2 (from the hydrodynamical simulations) tend to underpredict the maximum circular velocity |${V_{\rm max}^{\rm DMO}}$| (from the corresponding dark matter only simulations). There are two main contributing processes. (1) Lower mass galaxies are less rotationally supported. This is confirmed observationally from the skewness of linewidths in bins of H  i mass in both ALFALFA and HIPASS observations. (2) The H  i distributions are less extended (relative to the dark matter halo) in dwarf galaxies. Coupled to the lower baryon-to-halo ratio results in rotation curves that are still rising at the last measured data point, in agreement with observations from SPARC. Combining these two effects, in both simulations and observations lower mass galaxies have, on average, lower W 50/ W 20. Additionally, mass-loss driven by supernovae and projection effects (dwarf galaxies are in general not thin discs) further reduce the linewidths. The implied H  i linewidth velocity function from NIHAO is in good agreement with observations in the nearby Universe of dwarf galaxies: |$10 \, {{ {\rm km\, s^{-1}} }} \lt W_{50}/2 \lt 80 \, {{ {\rm km\, s^{-1}} }}$|⁠. The dark matter only slope of ≈−2.9 is reduced to ≈−1.0 in the hydro simulations. Future radio observations of unbiased samples with higher spatial resolution will enable stricter tests of the simulations, and thus of the LCDM model. [ABSTRACT FROM AUTHOR]

We study the origin of bulge stars and their angular momentum (AM) evolution in 10 spiral galaxies with baryonic masses above |$10^{10}\rm\, M_{\odot }$| in the Numerical Investigation of a Hundred Astrophysical Objects galaxy formation simulations. The simulated galaxies are in good agreement with observations of the relation between the specific AM and mass of the baryonic component and the stellar bulge-to-total ratio (B / T). We divide the star particles at |$z$|  = 0 into disc and bulge components using a hybrid photometric/kinematic decomposition method that identifies all the central mass above an exponential disc profile as the 'bulge'. By tracking the bulge star particles back in time, we find that on average 95 per cent of the bulge stars formed in situ, 3 per cent formed ex situ in satellites of the same halo, and only 2 per cent formed ex situ in external galaxies. The evolution of the AM distribution of the bulge stars paints an interesting picture: The higher the final B / T, the more the specific AM remains preserved during the bulge formation. In all cases, bulge stars migrate significantly towards the central region, reducing their average galactocentric radius by roughly a factor 2, independently of the final B / T value. However, in the higher B / T (≳ 0.2) objects, the velocity of the bulge stars increases and the AM of the bulge is almost conserved, whereas at lower B / T values, the velocity of the bulge stars decreases and the AM of the bulge reduces. The correlation between the evolution of the AM and B / T suggests that bulge formation and disc formation are closely linked and cannot be treated as independent processes. [ABSTRACT FROM AUTHOR]

We present the first results of applying Gaussian Mixture Models in the stellar kinematic space of normalized angular momentum and binding energy on NIHAO high-resolution galaxies to separate the stars into multiple components. We exemplify this method, using a simulated Milky Way analogue, whose stellar component hosts thin and thick discs, classical and pseudo bulges, and a stellar halo. The properties of these stellar structures are in good agreement with observational expectations in terms of sizes, shapes, and rotational support. Interestingly, the two kinematic discs show surface mass density profiles more centrally concentrated than exponentials, while the bulges and the stellar halo are purely exponential. We trace back in time the Lagrangian mass of each component separately to study their formation history. Between z ~ 3 and the end of halo virialization, z ~ 1.3, all components lose a fraction of their angular momentum. The classical bulge loses the most (~95 per cent) and the thin disc the least (~60 per cent). Both bulges formed their stars in situ at high redshift, while the thin disc formed ~98 per cent in situ, but with a constant SFR ~1.5M... yr-1 over the last ~11 Gyr. Accreted stars (6 per cent of total stellar mass) are mainly incorporated to the thick disc or the stellar halo, which formed ex situ 8 per cent and 45 per cent of their respective masses. Our analysis pipeline is freely available at https://github.com/aobr/gsf. [ABSTRACT FROM AUTHOR]

In an effort to search for Ly α emission from circum- and intergalactic gas on scales of hundreds of kpc around z ~ 3 quasars, and thus characterize the physical properties of the gas in emission, we have initiated an extensive fast survey with the Multi-Unit Spectroscopic Explorer (MUSE): Quasar Snapshot Observations withMUse: Search for Extended Ultraviolet eMission (QSO MUSEUM). In this work, we report the discovery of an enormous Ly α nebula (ELAN) around the quasar SDSS J102009.99+104002.7 at z = 3.164, which we followedup with deeper MUSE observations. This ELAN spans ~297 projected kpc, has an average Ly α surface brightness SBLyα ~ 6.04 × 10-18 erg s-1 cm-2 arcsec-2(within the 2σ isophote) and is associated with an additional four previously unknown embedded sources: two Ly α emitters and two faint active galactic nuclei (one type-1 and one type-2 quasar). By mapping at high significance, the line-of-sight velocity in the entirety of the observed structure, we unveiled a large-scale coherent rotation-like pattern spanning ~300 km s-1 with a velocity dispersion of <270 km s-1, which we interpret as a signature of the inspiraling accretion of substructures within the quasar's host halo. Future multiwavelength data will complement our MUSE observations and are definitely needed to fully characterize such a complex system. None the less, our observations reveal the potential of newsensitive integral-field spectrographs to characterize the dynamical state of diffuse gas on large scales in the young Universe, and thereby witness the assembly of galaxies. [ABSTRACT FROM AUTHOR]