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We compare the results of thirteen cosmological gasdynamical codes used to simulate the formation of a galaxy in the LCDM structure formation paradigm. The various runs differ in their hydrodynamical treatment (SPH, moving-mesh and AMR) but share the same initial conditions and adopt their latest published model of cooling, star formation and feedback. Despite the common halo assembly history, we find large code-to-code variations in the stellar mass, size, morphology and gas content of the galaxy at z=0, due mainly to the different implementations of feedback. Compared with observation, most codes tend to produce an overly massive galaxy, smaller and less gas-rich than typical spirals, with a massive bulge and a declining rotation curve. A stellar disk is discernible in most simulations, though its prominence varies widely from code to code. There is a well-defined trend between the effects of feedback and the severity of the disagreement with observation. Models that are more effective at limiting the baryonic mass of the galaxy come closer to matching observed galaxy scaling laws, but often to the detriment of the disk component. Our conclusions hold at two different numerical resolutions. Some differences can also be traced to the numerical techniques: more gas seems able to cool and become available for star formation in grid-based codes than in SPH. However, this effect is small compared to the variations induced by different feedback prescriptions. We conclude that state-of-the-art simulations cannot yet uniquely predict the properties of the baryonic component of a galaxy, even when the assembly history of its host halo is fully specified. Developing feedback algorithms that can effectively regulate the mass of a galaxy without hindering the formation of high-angular momentum stellar disks remains a challenge., 28 pages, 16 figures, MNRAS accepted. High resolution figures and additional images can be found at http://www.aip.de/People/cscannapieco/aquila/

We calculate the colours and luminosities of redshift z = 0.1 galaxies from the EAGLE simulation suite using the GALAXEV population synthesis models. We take into account obscuration by dust in birth clouds and diffuse ISM using a two-component screen model, following the prescription of Charlot and Fall. We compare models in which the dust optical depth is constant to models where it depends on gas metallicity, gas fraction and orientation. The colours of EAGLE galaxies for the more sophisticated models are in broad agreement with those of observed galaxies. In particular, EAGLE produces a red sequence of passive galaxies and a blue cloud of star forming galaxies, with approximately the correct fraction of galaxies in each population and with g-r colours within 0.1 magnitudes of those observed. Luminosity functions from UV to NIR wavelengths differ from observations at a level comparable to systematic shifts resulting from a choice between Petrosian and Kron photometric apertures. Despite the generally good agreement there are clear discrepancies with observations. The blue cloud of EAGLE galaxies extends to somewhat higher luminosities than in the data, consistent with the modest underestimate of the passive fraction in massive EAGLE galaxies. There is also a moderate excess of bright blue galaxies compared to observations. The overall level of agreement with the observed colour distribution suggests that EAGLE galaxies at z = 0.1 have ages, metallicities and levels of obscuration that are comparable to those of observed galaxies., Comment: 20 pages, 7 figures, submitted to MNRAS

We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) suite of cosmological hydrodynamical simulations to study the global structure and kinematics of stellar spheroids of Milky Way mass disc galaxies. Font et al. have recently demonstrated that these simulations are able to successfully reproduce the satellite luminosity functions and the metallicity and surface brightness profiles of the spheroids of the Milky Way and M31. A key to the success of the simulations is a significant contribution to the spheroid from stars that formed in situ. While the outer halo is dominated by accreted stars, stars formed in the main progenitor of the galaxy dominate at r < ~30 kpc. In the present study we show that this component was primarily formed in a proto-disc at high redshift and was subsequently liberated from the disc by dynamical heating associated with mass accretion. As a consequence of its origin, the in situ component of the spheroid has different kinematics (namely net prograde rotation with respect to the disc) than that of the spheroid component built from the disruption of satellites. In addition, the in situ component has a flattened distribution, that is due in part to its rotation. We make comparisons with measurements of the shape and kinematics of local galaxies, including the Milky Way and M31, and stacked observations of more distant galaxies. We find that the simulated disc galaxies have spheroids of the correct shape (oblate with a median axis ratio of ~0.6 at radii of < ~30 kpc, but note there is significant system-to-system scatter in this quantity) and that the kinematics show evidence for two components (due to in situ vs. accreted), as observed. Our findings therefore add considerable weight to the importance of dissipative processes in the formation of stellar haloes and to the notion of a 'dual stellar halo'., 20 pages, 14 figures, MNRAS, in press

(Abridged) We study the phase-space distribution of satellite galaxies associated with late-type galaxies in the GIMIC suite of simulations. GIMIC consists of re-simulations of 5 cosmologically representative regions from the Millennium simulation, which have higher resolution and incorporate baryonic physics. Whilst the disc of the galaxy is well aligned with the inner regions (r ~ 0.1r_200) of the dark matter halo, both in shape and angular momentum, there can be substantial misalignments at larger radii (r ~ r_200). Misalignments of > 45 deg are seen in ~ 30% of our sample. We find that the satellite population aligns with the shape (and angular momentum) of the outer dark matter halo. However, the alignment with the galaxy is weak owing to the mismatch between the disc and dark matter halo. Roughly 20% of the satellite systems with ten bright galaxies within r_200 exhibit a polar spatial alignment with respect to the galaxy --- an orientation reminiscent of the classical satellites of the Milky Way. We find that a small fraction (~10%) of satellite systems show evidence for rotational support which we attribute to group infall. There is a bias towards satellites on prograde orbits relative to the spin of the dark matter halo (and to a lesser extent with the angular momentum of the disc). This preference towards co-rotation is stronger in the inner regions of the halo where the most massive satellites accreted at relatively early times are located. We attribute the anisotropic spatial distribution and angular momentum bias of the satellites at z=0 to their directional accretion along the major axes of the dark matter halo. The satellite galaxies have been accreted relatively recently compared to the dark matter mass and have experienced less phase-mixing and relaxation --- the memory of their accretion history can remain intact to z=0., 19 pages, 17 Figures. Accepted by MNRAS

The existence of X-ray luminous gaseous coronae around massive disc galaxies is a long-standing prediction of galaxy formation theory in the cold dark matter cosmogony. This prediction has garnered little observational support, with non-detections commonplace and detections for only a relatively small number of galaxies which are much less luminous than expected. We investigate the coronal properties of a large sample of bright, disc-dominated galaxies extracted from the GIMIC suite of cosmological hydrodynamic simulations recently presented by Crain et al. Remarkably, the simulations reproduce the observed scalings of X-ray luminosity with K-band luminosity and star formation rate and, when account is taken of the density structure of the halo, with disc rotation velocity as well. Most of the star formation in the simulated galaxies (which have realistic stellar mass fractions) is fuelled by gas cooling from a quasi-hydrostatic hot corona. However, these coronae are more diffuse, and of a lower luminosity, than predicted by the analytic models of White & Frenk because of a substantial increase in entropy at z ~ 1-3. Both the removal of low entropy gas by star formation and energy injection from supernovae contribute to this increase in entropy, but the latter is dominant for halo masses M_200, Comment: 21 pages, 16 figures. Accepted for publication in MNRAS. Accompanying visualisations at http://pulsar.swin.edu.au/~rcrain/webpages/X-ray_coronae.html

Observational measures of the primordial helium mass fraction, $Y_{\rm P}$, are of interest for cosmology and fundamental particle physics. Current measures obtained from H II regions agree with the Standard Model prediction to approximately 1% precision, although these determinations may be affected by systematic uncertainties. This possibility can only be tested by independently measuring the helium abundance in new ways. Here, we propose a novel method to obtain a measurement of $Y_{\rm P}$ using hydrogen and helium recombination line emission from RELHICs: pristine, gas-rich but star-free low-mass dark matter haloes whose existence is predicted by hydrodynamical simulations. Although expected to be uncommon and intrinsically faint in emission, the primordial composition and simple physical properties of these objects make them an ideal laboratory to determine $Y_{\rm P}$. We present radiative transfer simulations to demonstrate the effectiveness of this approach, finding that comparing the emission in H and He lines, either via their volumetric emissivities, or integrated properties such as the surface brightness and total flux, may be used to infer $Y_{\rm P}$. Furthermore, we show that RELHICs can be used to provide an entirely novel constraint on the spectral slope of the ultraviolet background, and discuss the possibility of measuring this slope and the primordial helium abundance simultaneously., 10 pages, 9 figures. Accepted for publication in MNRAS

We report the detection of extended Hα emission from the tip of the HI disc of the nearby edge-on galaxy UGC 7321, observed with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope. The Hα surface brightness fades rapidly where the HI column density drops below NHI∼10(19) cm(−2), consistent with fluorescence arising at the ionization front from gas that is photoionized by the extragalactic ultraviolet background (UVB). The surface brightness measured at this location is (1.2 ± 0.5) × 10(−19) erg s(−1) cm(−2) arcsec(−2), where the error is mostly systematic and results from the proximity of the signal to the edge of the MUSE field of view, and from the presence of a sky line next to the redshifted Hα wavelength. By combining the Hα and the HI 21 cm maps with a radiative transfer calculation of an exponential disc illuminated by the UVB, we derive a value for the HI photoionization rate of ΓHI∼(6--8)×10(−14) s(−1). This value is consistent with transmission statistics of the Lyα forest and with recent models of a UVB that is dominated by quasars., Monthly Notices of the Royal Astronomical Society, 467 (4), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We present results from a survey of galaxies in the fields of six z ≥ 3 damped Lyman α (Lyα) systems (DLAs) using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We report a high detection rate of up to ${\approx } 80{{\ \rm per\ cent}}$ of galaxies within 1000 km s−1 from DLAs and with impact parameters between 25 and 280 kpc. In particular, we discovered five high-confidence Lyα emitters associated with three DLAs, plus up to nine 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 plausible host galaxies. Among our detections, we report four galaxies associated with the most metal-poor DLA in our sample (Z/Z⊙ = −2.33 ± 0.22), which trace an overdense structure resembling a filament. By comparing our detections with predictions from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological simulations and a semi-analytic model designed to reproduce the observed bias of DLAs at z > 2, we conclude that our observations are consistent with a scenario in which a significant fraction of DLAs trace the neutral regions within haloes with a characteristic mass of $M_{\rm h} \approx 10^{11}-10^{12}~\rm M_\odot$, in agreement with the inference made from the large-scale clustering of DLAs. We finally show how larger surveys targeting ≈25 absorbers have the potential of constraining the characteristic masses of haloes hosting high-redshift DLAs with sufficient accuracy to discriminate between different models.

We present first results from Multi Unit Spectroscopic Explorer (MUSE) observations at the Very Large Telescope in the MUSE Ultra Deep Field (MUDF), a $\approx 1.2\times 1.4$ arcmin$^2$ region for which we are collecting $\approx$200 hours of integral field spectroscopy. The $\approx 40$-hour observation completed to date reveals the presence of a group of three Ly$\alpha$ nebulae associated with a bright quasar pair at $z\simeq3.23$ with projected separation of $\approx 500\rm~kpc$. Two of the nebulae are physically associated with the quasars which are likely powering the Ly$\alpha$ emission, and extend for $\gtrsim 100~\rm kpc$ at a surface brightness level of $\approx 6\times 10^{-19}~\rm erg~s^{-1}~cm^{-2}~arcsec^{-2}$. A third smaller ($\approx$35 kpc) nebula lies at a velocity offset of $\approx 1550$ km s$^{-1}$. Despite their clustered nature, the two large nebulae have properties similar to those observed in isolated quasars and exhibit no sharp decline in flux at the current depth, suggesting an even more extended distribution of gas around the quasars. We interpret the shape and the alignment of the two brighter nebulae as suggestive of the presence of an extended structure connecting the two quasar host galaxies, as seen for massive galaxies forming within gas-rich filaments in cosmological simulations., Comment: MNRAS Letters in press, 3 figures, revised version: minor changes following proofs

Photoheating of the gas in low-mass dark matter (DM) haloes prevents baryons from cooling, leaving the haloes free of stars. Gas in these 'dark' haloes remains exposed to the ultraviolet background (UVB), and so is expected to emit via fluorescent recombination lines. We present a set of radiative transfer simulations, which model dark haloes as spherical gas clouds in hydrostatic equilibrium with a DM halo potential, and in thermal equilibrium with the UVB at redshift z = 0. We use these simulations to predict surface brightnesses in H-alpha, which we show to have a characteristic ring-shaped morphology for haloes in a narrow mass range between 10^9.5 and 10^9.6 M_sun. We explore how this emission depends on physical parameters such as the DM density profile and the UVB spectrum. We predict the abundance of fluorescent haloes on the sky, and discuss possible strategies for their detection. We demonstrate how detailed observations of fluorescent rings can be used to infer the properties of the haloes which host them, such as their density profiles and the mass-concentration relation, as well as to directly measure the UVB amplitude., 14 pages, 13 figures. MNRAS, in press

We present the goals, design, and first results of the MUSE Ultra Deep Field (MUDF) survey, a large programme using the Multi Unit Spectroscopic Explorer (MUSE) instrument at the ESO Very Large Telescope. The MUDF survey is collecting ~ 150 hours on-source of integral field optical spectroscopy in a 1.5 x 1.2 square arcmin region which hosts several astrophysical structures along the line of sight, including two bright z ~ 3.2 quasars with close separation (~ 500 kpc). Following the description of the data reduction procedures, we present the analysis of the galaxy environment and gaseous properties of seven groups detected at redshifts 0.5 < z < 1.5, spanning a large dynamic range in halo mass, log(Mh/Msun) ~ 11 - 13.5. For four of the groups, we find associated MgII absorbers tracing cool gas in high-resolution spectroscopy of the two quasars, including one case of correlated absorption in both sightlines at distance ~ 480 kpc. The absorption strength associated with the groups is higher than what has been reported for more isolated galaxies of comparable mass and impact parameters. We do not find evidence for widespread cool gas giving rise to strong absorption within these groups. Combining these results with the distribution of neutral and ionised gas seen in emission in lower-redshift groups, we conclude that gravitational interactions in the group environment strip gas from the galaxy haloes into the intragroup medium, boosting the cross section of cool gas and leading to the high fraction of strong MgII absorbers that we detect., 20 pages, 12 figures, 4 tables, Accepted for publication in MNRAS

We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$\sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations $R_\perp$$\leq$150 kpc and line of sight velocity separations $\lesssim$11,000 km/s. We construct a stacked ultraviolet (rest-frame wavelengths 700-2000\AA) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a $\sim$30% decrease in flux at $\lambda$=800-900\AA\ compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the HI ionizing radiation for pairs ($\lambda_{\rm mfp}^{912}=140.7\pm20.2~h_{70}^{-1}$Mpc) compared to single quasars ($\lambda_{\rm mfp}^{912}=213.8\pm28~h_{70}^{-1}$Mpc) at the average redshift $z\simeq2.44$. From the modelling of LLS absorption in these pairs, we find a higher ($\sim$20%) incidence of proximate LLSs with $\log N_{\rm HI}\geq17.2$ at $\delta v$$, Comment: Revised version with minor changes to the text following proof. Some of the references have been amended

We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrody- namical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital reso- nances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration timescales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes., Resubmitted to MNRAS

The existence of two kinematically and chemically distinct stellar subpopulations in the Sculptor and Fornax dwarf galaxies offers the opportunity to constrain the density profile of their matter haloes by measuring the mass contained within the well-separated half-light radii of the two metallicity subpopulations. Walker and Penarrubia have used this approach to argue that data for these galaxies are consistent with constant-density `cores' in their inner regions and rule out `cuspy' Navarro-Frenk-White (NFW) profiles with high statistical significance, particularly in the case of Sculptor. We test the validity of these claims using dwarf galaxies in the APOSTLE (A Project Of Simulating The Local Environment) Lambda cold dark matter cosmological hydrodynamics simulations of analogues of the Local Group. These galaxies all have NFW dark matter density profiles and a subset of them develop two distinct metallicity subpopulations reminiscent of Sculptor and Fornax. We apply a method analogous to that of Walker and Penarrubia to a sample of 53 simulated dwarfs and find that this procedure often leads to a statistically significant detection of a core in the profile when in reality there is a cusp. Although multiple factors contribute to these failures, the main cause is a violation of the assumption of spherical symmetry upon which the mass estimators are based. The stellar populations of the simulated dwarfs tend to be significantly elongated and, in several cases, the two metallicity populations have different asphericity and are misaligned. As a result, a wide range of slopes of the density profile are inferred depending on the angle from which the galaxy is viewed., 15 pages, 13 figures, accepted for publication in MNRAS

We present a MUSE and KMOS dynamical study 405 star-forming galaxies at redshift z=0.28-1.65 (median redshift z=0.84). Our sample are representative of star-forming, main-sequence galaxies, with star-formation rates of SFR=0.1-30Mo/yr and stellar masses M=10^8-10^11Mo. For 49+/-4% of our sample, the dynamics suggest rotational support, 24+/-3% are unresolved systems and 5+/-2% appear to be early-stage major mergers with components on 8-30kpc scales. The remaining 22+/-5% appear to be dynamically complex, irregular (or face-on systems). For galaxies whose dynamics suggest rotational support, we derive inclination corrected rotational velocities and show these systems lie on a similar scaling between stellar mass and specific angular momentum as local spirals with j*=J/M*\propto M^(2/3) but with a redshift evolution that scales as j*\propto M^{2/3}(1+z)^(-1). We identify a correlation between specific angular momentum and disk stability such that galaxies with the highest specific angular momentum, log(j*/M^(2/3))>2.5, are the most stable, with Toomre Q=1.10+/-0.18, compared to Q=0.53+/-0.22 for galaxies with log(j*/M^(2/3)), MNRAS in press. 21 pages; 12 figures. The full pdf, which includes an additional 32 pages of supplementary figures and data tables are available from http://astro.dur.ac.uk/~ams/MUSEcubes/

We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column density damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 10(41) erg s(−1), which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10(−19) erg s(−1) cm(−2) arcsec(−2) at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width > 50 Å and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift. We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size ≫50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations., Monthly Notices of the Royal Astronomical Society, 471 (3), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We present new results on the auto- and cross-correlation functions of galaxies and OVI absorbers in a $\sim 18~\textrm{Gpc}^3$ comoving volume at $z < 1$. We use a sample of 51,296 galaxies and 140 OVI absorbers in the column density range $13 \lesssim \log N \lesssim 15$ to measure two-point correlation functions in the two dimensions transverse and orthogonal to the line-of-sight $\xi(r_{\perp}, r_{\parallel})$. We furthermore infer the corresponding 'real-space' correlation functions, $\xi(r)$, by projecting $\xi(r_{\perp}, r_{\parallel})$ along $r_{\parallel}$, and assuming a power-law form, $\xi(r) = (r / r_0)^{-\gamma}$. Comparing the results from the absorber-galaxy cross-correlation function, $\xi_{\textrm{ag}}$, the galaxy auto-correlation function, $\xi_{\textrm{gg}}$, and the absorber auto-correlation function, $\xi_{\textrm{aa}}$, we constrain the statistical connection between galaxies and the metal-enriched intergalactic medium as a function of star-formation activity. We also compare these results to predictions from the EAGLE cosmological hydrodynamical simulation and find a reasonable agreement. We find that: (i) OVI absorbers show very little velocity dispersion with respect to galaxies on $\sim$ Mpc scales, likely $\lesssim$ 100 \kms; (ii) OVI absorbers and galaxies may not linearly trace the same underlying distribution of matter in general. In particular, our results demonstrate that OVI absorbers are less clustered, and potentially more extended around galaxies than galaxies are around themselves; (iii) On $\gtrsim 100$ kpc scales, the likelihood of finding OVI absorbers around star-forming galaxies is similar to the likelihood of finding OVI absorbers around non star-forming galaxies (abridged), Comment: Revised submission to MNRAS, having addressed the referee's comments. 27 pages, 19 figures, 5 tables

We present HST/COS observations of highly ionized absorption lines associated with a radio-loud QSO at $z=1.1319$. The absorption system has multiple velocity components, tracing gas that is largely outflowing from the QSO at velocities of a few 100 km s$^{-1}$. There is an unprecedented range in ionization, with detections of HI, NIII, NIV, NV, OIV, OIV*, OV, OVI, NeVIII, MgX, SV and ArVIII. We estimate the total hydrogen number density from the column density ratio N(OIV*)/N(OIV) to be $\log(n_{\textrm{H}}/\textrm{cm}^3)\sim 3$. Assuming photoionization equilibrium, we derive a distance to the absorbing complex of $2.3, Comment: 27 pages, 17 figures, 5 tables. Accepted for publication in MNRAS

We present a study of the environment of 27 z=3-4.5 bright quasars from the MUSE Analysis of Gas around Galaxies (MAGG) survey. With medium-depth MUSE observations (4 hours on target per field), we characterise the effects of quasars on their surroundings by studying simultaneously the properties of extended gas nebulae and Lyalpha emitters (LAEs) in the quasar host haloes. We detect extended (up to ~ 100 kpc) Lyalpha emission around all MAGG quasars, finding a very weak redshift evolution between z=3 and z=6. By stacking the MUSE datacubes, we confidently detect extended emission of CIV and only marginally detect extended HeII up to ~40 kpc, implying that the gas is metal enriched. Moreover, our observations show a significant overdensity of LAEs within 300 km/s from the quasar systemic redshifts estimated from the nebular emission. The luminosity functions and equivalent width distributions of these LAEs show similar shapes with respect to LAEs away from quasars suggesting that the Lyalpha emission of the majority of these sources is not significantly boosted by the quasar radiation or other processes related to the quasar environment. Within this framework, the observed LAE overdensities and our kinematic measurements imply that bright quasars at z=3-4.5 are hosted by haloes in the mass range ~ 10^{12.0}-10^{12.5} Msun., Comment: 23 pages, 20 figures, accepted for publication in MNRAS

We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback implementations -- which produce different galaxy populations -- mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration, $g_{\dagger}$, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard cold dark matter paradigm., Comment: 6 pages, 3 figures, PRL in press

We present a study of metal-enriched halo gas traced by MgII and CIV absorption at z1. It is clear from our results that environmental processes have a significant impact on the distribution of metals around galaxies and need to be fully accounted for when analyzing correlations between gaseous haloes and galaxy properties., 27 pages; accepted for publication in MNRAS