Determining the spatial distribution and intrinsic physical properties of neutral hydrogen on cosmological scales is one of the key goals of next-generation radio surveys. We use the EAGLE galaxy formation simulations to assess the properties of damped Lyman-alpha absorbers (DLAs) that are associated with galaxies and their underlying dark matter haloes between 0 $\leq$ z $\leq$ 2. We find that the covering fraction of DLAs increases at higher redshift; a significant fraction of neutral atomic hydrogen (HI) resides in the outskirts of galaxies with stellar mass greater than or equal to 10$^{10}$ M$_\odot$; and the covering fraction of DLAs in the circumgalactic medium (CGM) is enhanced relative to that of the interstellar medium (ISM) with increasing halo mass. Moreover, we find that the mean density of the HI in galaxies increases with increasing stellar mass, while the DLAs in high- and low-halo-mass systems have higher column densities than those in galaxies with intermediate halo masses (~ 10$^{12}$ M$_\odot$ at z = 0). These high-impact CGM DLAs in high-stellar-mass systems tend to be metal-poor, likely tracing smooth accretion. Overall, our results point to the CGM playing an important role in DLA studies at high redshift (z $\geq$ 1). However, their properties are impacted both by numerical resolution and the detailed feedback prescriptions employed in cosmological simulations, particularly that of AGN.
The metallicity of strong HI systems, spanning from damped Lyman-alpha absorbers (DLAs) to Lyman-limit systems (LLSs) is explored between z = 5->0 using the EAGLE high-resolution cosmological hydrodynamic simulation of galaxy formation. The metallicities of LLSs and DLAs steadily increase with time in agreement with observations. DLAs are more metal rich than LLSs, although the metallicities in the LLS column density range (NHI = 10^17 -10^20 cm^-2) are relatively flat, evolving from a median HI-weighted metallicity of Z<10^-2 Zsol at z = 3 to ~10^-0.5 Zsol by z = 0. The metal content of HI sy…
Observed and simulated galaxies exhibit correlations between stellar mass, metallicity and morphology. We use the EAGLE cosmological simulation to examine the origin of these correlations for galaxies in the stellar mass range $10^9~\rm{M_\odot} \leqslant\ M_\star \leqslant 10^{10}~\rm{M_\odot}$, and the extent to which they contribute to the scatter in the mass-metallicity relation. We find that rotationally supported disc galaxies have lower metallicity than dispersion supported spheroidal galaxies at a given mass, in agreement with previous findings. In EAGLE, this correlation arises becaus…
We present results from a survey of galaxies in the fields of six z>3 Damped Lyman alpha systems (DLAs) using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We report a high detection rate of up to ~80% of galaxies within 1000 km/s from DLAs and with impact parameters between 25 and 280 kpc. In particular, we discovered 5 high-confidence Lyman alpha emitters associated with three DLAs, plus up to 9 additional detections across five of the six fields. The majority of the detections are at relatively large impact parameters (>50 kpc) with two detections being pla…
The gamma-ray burst (GRB) afterglows provide an unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-$α$ absorbers) contain a large neutral hydrogen column density, N(H I), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H$_2$) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H$_2$ lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36 re…
Modern hydrodynamical simulations reproduce many properties of the real universe. These simulations model various physical processes, but many of these are included using `subgrid models' due to resolution limits. Although different subgrid models have been successful in modelling the effects of supernovae (SNe) feedback on galactic properties, it remains unclear if, and by how much, these differing implementations affect observable halo gas properties. In this work, we use `zoom-in' cosmological initial conditions of two volumes selected to resemble the Local Group (LG) evolved with both the …
Evolution of the cosmic star formation rate (SFR) and molecular gas mass density is expected to be matched by a similarly strong evolution of the fraction of atomic hydrogen (HI) in the cold neutral medium (CNM). We use results from a recent commissioning survey for intervening 21-cm absorbers with the Australian Square Kilometre Array Pathfinder (ASKAP) to construct a Bayesian statistical model of the $N_{\rm HI}$-weighted harmonic mean spin temperature ($T_{\rm s}$) at redshifts between $z = 0.37$ and $1.0$. We find that $T_{\rm s} \leq 274$K with 95 per cent probability, suggesting that at …
We investigate the contentious issue of the presence, or lack thereof, of satellites mass segregation in galaxy groups using the Galaxy And Mass Assembly (GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological hydrodynamical simulation catalogues of galaxy groups. We select groups with halo mass $12 \leqslant \log(M_{\text{halo}}/h^{-1}M_\odot) <14.5$ and redshift $z \leqslant 0.32$ and probe the radial distribution of stellar mass out to twice the group virial radius. All the samples are carefully constructed to be complete in stellar mass at each redshift range and efforts are ma…
We study the cross correlation of damped Ly$α$ systems (DLAs) and their background quasars, using the most updated DLA catalog and the Planck 2018 CMB lensing convergence field. Our measurement suggests that the DLA bias $b_{\rm DLA}$ is smaller than $3.1$, corresponding to $\log(M/M_\odot h^{-1})\leq 12.3$ at a confidence of $90\%$. These constraints are broadly consistent with Alonso et al. (2018) and previous measurements by cross-correlation between DLAs and the Ly$α$ forest (e.g. Font-Ribera et al. 2012; Perez-Rafols et al. 2018). Further, our results demonstrate the potential of obtainin…
The Hubble sequence provides a useful classification of galaxy morphology at low redshift. However, morphologies are not static, but rather evolve as the growth of structure proceeds through mergers, accretion and secular processes. We investigate how kinematically defined disc and spheroidal structures form and evolve in the EAGLE hydrodynamic simulation of galaxy formation. At high redshift most galaxies of all masses are asymmetric. By redshift $z\simeq 1.5$ the Hubble sequence is established and after this time most of the stellar mass is in spheroids whose contribution to the stellar mass…
We study the morphologies of 3,964 galaxies and their progenitors with $M_\star > 10^{10} M_\odot$ in the reference EAGLE hydrodynamical simulation from redshifts $z=1$ to $z=0$, concentrating on the redshift evolution of the bar fraction. We apply two convolutional neural networks (CNNs) to classify 35,082 synthetic g-band images across 10 snapshots in redshift. We identify galaxies as either barred or unbarred, while also classifying each sample into one of four morphological types: elliptical (E), lenticular (S0), spiral (Sp), and irregular/miscellaneous (IrrM). We find that the bar fractio…
We use the EAGLE galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales $k{\stackrel{>}{{}_\sim}} 4{h\,{\rm Mpc}^{-1}}$ the effect of baryons on the amplitude of the total matter power spectrum is greater than $1\%$. The back-reaction of baryons affects the density field of the dark matter at the level of $\sim3\%$ on scales of $1\leq k/({h\,{\rm Mpc}^{-1}})\leq 5$. The dark matter velocity divergence power spectrum at $k{\stackrel{<}{{}_\sim}}0.5{h\,{\…
We present the characteristics of the Damped Lyman-$α$ (DLA) systems found in the data release DR16 of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey (SDSS). DLAs were identified using the convolutional neural network (CNN) of~\cite{Parks2018}. A total of 117,458 absorber candidates were found with $2 \leq \zdla \leq 5.5$ and $19.7 \leq \lognhi \leq 22$, including 57,136 DLA candidates with $\lognhi \geq 20.3$. Mock quasar spectra were used to estimate DLA detection efficiency and the purity of the resulting catalog. Restricting the quasar sample t…
We compare global predictions from the EAGLE hydrodynamical simulation, and two semi-analytic (SA) models of galaxy formation, L-GALAXIES and GALFORM. All three models include the key physical processes for the formation and evolution of galaxies and their parameters are calibrated against a small number of observables at $z\approx 0$. The two SA models have been applied to merger trees constructed from the EAGLE dark matter only simulation. We find that at $z\leq 2$, both the galaxy stellar mass functions for stellar masses $M_*<10^{10.5} M_{\odot}$ and the median specific star formation rate…
Using the GAEA semi-analytic model, we analyse the connection between Damped Lyman-$α$ systems (DLAs) and HI in galaxies. Our state-of-the-art semi-analytic model is tuned to reproduce the local galaxy HI mass function, and that also reproduces other important galaxy properties, including the galaxy mass - gas metallicity relation. To produce catalogs of simulated DLAs we throw $10^5$ random lines of sight in a composite simulated volume: dark matter haloes with log$(\frac{M_{200}}{ M_{\odot}}) \geq 11.5$ are extracted from the Millennium Simulation, while for $9.2 \leq \log(\frac{M_{200}}{ M_…
We investigate the dark matter halos of 256 star-forming disc-like galaxies at $z\sim 1$ using the KMOS redshift one spectroscopic survey (KROSS). This sample covers the redshifts $0.6 \leq z \leq 1.04$, effective radii $0.69 \leq R_e [\mathrm{kpc}] \leq 7.76$, and total stellar masses $8.7 \leq log(M_{\mathrm{star}} \ [\mathrm{M_\odot}]) \leq 11.32$. We present a mass modelling approach to study the rotation curves of these galaxies, which allow us to dynamically calculate the physical properties associated with the baryons and the dark matter halo. For the former we assume a Freeman disc, wh…
We contrast the latest observations of the cosmic metal density in neutral gas ($ρ_{\rm met,neu}$) with three cosmological galaxy evolution simulations: L-GALAXIES 2020, TNG100, and EAGLE. We find that the fraction of total metals that are in neutral gas is $<40$ per cent at $3\lesssim{} z \lesssim{} 5$ in these simulations, whereas observations of damped Lyman-$α$ (DLA) systems suggest $\gtrsim{}85$ per cent. In all three simulations, hot, low-density gas is also a major contributor to the cosmic metal budget, even at high redshift. By considering the evolution in cosmic SFR density ($ρ_{\rm …
We present 25 cosmological zoom-in simulations of Milky Way-mass galaxies in the `MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE' (E-MOSAICS) project. E-MOSAICS couples a detailed physical model for the formation, evolution, and disruption of star clusters to the EAGLE galaxy formation simulations. This enables following the co-formation and co-evolution of galaxies and their star cluster populations, thus realising the long-standing promise of using globular clusters (GCs) as tracers of galaxy formation and assembly. The simulations show that the age-metal…
The existence of hot, accreted gaseous coronae around massive galaxies is a long-standing central prediction of galaxy formation models in the $Λ$CDM cosmology. While observations now confirm that extraplanar hot gas is present around late-type galaxies, the origin of the gas is uncertain with suggestions that galactic feedback could be the dominant source of energy powering the emission. We investigate the origin and X-ray properties of the hot gas that surrounds galaxies of halo mass, $(10^{11}-10^{14}) \mathrm{M}_\odot$, in the cosmological hydrodynamical EAGLE simulations. We find that the…
We investigate the properties of the galaxies that reionized the Universe and the history of cosmic reionization using the "Evolution and Assembly of GaLaxies and their environments" (EAGLE) cosmological hydrodynamical simulations. We obtain the evolution of the escape fraction of ionizing photons in galaxies assuming that galactic winds create channels through which 20~percent of photons escape when the local surface density of star formation is greater than $0.1$ M$_\odot$ yr$^{-1}$ kpc$^{-2}$. Such threshold behaviour for the generation of winds is observed, and the rare local objects which…
We investigate the impact of baryonic physics on the subhalo population by analyzing the results of two recent hydrodynamical simulations (EAGLE and Illustris), which have very similar configuration, but a different model of baryonic physics. We concentrate on haloes with a mass between $10^{12.5}$ and $10^{14}M_{\odot}h^{-1}$ and redshift between 0.2 and 0.5, comparing with observational results and subhalo detections in early-type galaxy lenses. We compare the number and the spatial distribution of subhaloes in the fully hydro runs and in their dark matter only counterparts, focusing on the …
A Compact Proto-group at $z \sim 5$: A Massive Galaxy Caught in Formation
National Astronomical Observatory of Japan（日本国立天文台）；The Graduate University for Advanced Studies（高级研究院）；Astronomical Institute, Tohoku University（东北大学天文学研究所）；Center for Frontier Science, Chiba University（千叶大学前沿科学中心）；Graduate School of Arts and Sciences, The University of Tokyo（东京大学大学院综合文化研究科）；Department of Astronomy & Astrophysics, The Pennsylvania State University（宾夕法尼亚州立大学天文学与天体物理学系）；Department of Astronomy, Tsinghua University（清华大学天文系）
We use the "Evolution and Assembly of GaLaxies and their Environments" ( EAGLE ) suite of hydrodynamical cosmological simulations to measure offsets between the centres of stellar and dark matter components of galaxies. We find that the vast majority (>95%) of the simulated galaxies display an offset smaller than the gravitational softening length of the simulations (Plummer-equivalent $ε= 700$ pc), both for field galaxies and satellites in clusters and groups. We also find no systematic trailing or leading of the dark matter along a galaxy's direction of motion. The offsets are consistent wit…
We use the IllustrisTNG cosmological hydrodynamical simulations to investigate how the specific star formation rates (sSFRs) of massive galaxies $(M_* > 10^{10} M_\odot)$ depend on the distance to their closest companions. We estimate sSFR enhancements by comparing with control samples that are matched in redshift, stellar mass, local density and isolation, and we restrict our analysis to pairs with stellar mass ratios of 0.1 to 10. At small separations (~15 kpc), the mean sSFR is enhanced by a factor of 2.0 $\pm$ 0.1 in the flagship (110.7 Mpc)$^3$ simulation (TNG100-1). Statistically signifi…
We present the Technicolor Dawn simulations, a suite of cosmological radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark matter halos down to $10^8 M_\odot$ within 12 $h^{-1}$ Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically-tuned parameter, the fraction $f_{\mathrm{esc,gal}}(z)$ of ionizing photons that escape the interstellar medium, is adjusted to match observations of…
We investigate the properties of the host galaxies of compact binary mergers across cosmic time, by means of population-synthesis simulations combined with galaxy catalogues from the EAGLE suite. We analyze the merger rate per galaxy of binary neutron stars (BNSs), black hole--neutron star binaries (BHNSs) and binary black holes (BBHs) from redshift zero up to redshift six. The binary merger rate per galaxy strongly correlates with the stellar mass of the host galaxy at any redshift considered here. This correlation is significantly steeper for BNSs than for both BHNSs and BBHs. Moreover, we f…
[Abridged] We study the abundance and clustering properties of HI at redshifts $z\leqslant5$ using TNG100, a large state-of-the-art magneto-hydrodynamic simulation of a 75 Mpc/h box size. We show that most of the HI lies within dark matter halos and quantify the average HI mass hosted by halos of mass M at redshift z. We find that only halos with circular velocities larger than $\simeq$ 30 km/s contain HI. While the density profiles of HI exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The HI in low-mass halos is mostly located in the central gal…
