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We use the TNG100 simulation of the IllustrisTNG project to investigate the stellar specific angular momenta ($j_{\ast}$) of $\sim$12,000 central galaxies at $z=0$ in a full cosmological context, with stellar masses ($M_{\ast}$) ranging from $10^{9}$ to $10^{12} \, {\rm M}_{\odot}$. We find that the $j_{\ast}$-$M_{\ast}$ relations for early-type and late-type galaxies in IllustrisTNG are in good overall agreement with observations, and that these galaxy types typically `retain' $\sim$10-20 and $\sim$50-60 per cent of their host haloes' specific angular momenta, respectively, with some dependence on the methodology used to measure galaxy morphology. We present results for kinematic as well as visual-like morphological measurements of the simulated galaxies. Next, we explore the scatter in the $j_{\ast}$-$M_{\ast}$ relation with respect to the spin of the dark matter halo and the mass of the supermassive black hole (BH) at the galactic centre. We find that galaxies residing in faster spinning haloes, as well as those hosting less massive BHs, tend to have a higher specific angular momentum. We also find that, at fixed galaxy or halo mass, halo spin and BH mass are anticorrelated with each other, probably as a consequence of more efficient gas flow toward the galactic centre in slowly rotating systems. Finally, we show that halo spin plays an important role in determining galaxy sizes - larger discs form at the centres of faster-rotating haloes - although the trend breaks down for massive galaxies with $M_{\ast} \gtrsim 10^{11} \, {\rm M}_{\odot}$, roughly the mass scale at which a galaxy's stellar mass becomes dominated by accreted stars., Comment: 17 pages, 11 figures. Published in MNRAS

We introduce a multi-component chemo-dynamical method for splitting the Galactic population of Globular Clusters (GCs) into three distinct constituents: bulge, disc, and stellar halo. The latter is further decomposed into the individual large accretion events that built up the Galactic stellar halo: the Gaia-Enceladus-Sausage, Kraken and Sequoia structures, and the Sagittarius and Helmi streams. Our modelling is extensively tested using mock GC samples constructed from the AURIGA suite of hydrodynamical simulations of Milky Way (MW)-like galaxies. We find that, on average, a proportion of the accreted GCs cannot be associated with their true infall group and are left ungrouped, biasing our recovered population numbers to approximately 80 percent of their true value. Furthermore, the identified groups have a completeness and a purity of only 65 percent. This reflects the difficulty of the problem, a result of the large degree of overlap in energy-action space of the debris from past accretion events. We apply the method to the Galactic data to infer, in a statistically robust and easily quantifiable way, the GCs associated with each MW accretion event. The resulting groups' population numbers of GCs, corrected for biases, are then used to infer the halo and stellar masses of the now defunct satellites that built up the halo of the MW., 18 pages, 11 figures, + Appendices

We present a comparison of the physical properties of the ionized gas in the circumgalactic medium and intergalactic medium (IGM) at z ∼ 0 between observations and four cosmological hydrodynamical simulations: Illustris, TNG300 of the IllustrisTNG project, EAGLE, and one of the Magneticum simulations. For the observational data, we use the gas properties that are inferred from cross-correlating the Sunyaev–Zel’dovich effect (SZE) from the Planck CMB maps with haloes and large-scale structure. Both the observational and simulation results indicate that the integrated gas pressure in haloes deviates from the self-similar case, showing that feedback impacts haloes with $M_{500}\sim 10^{12\!-\!13}\, {\rm M_\odot }$. The simulations predict that more than half the baryons are displaced from haloes, while the gas fraction inferred from our observational data roughly equals the cosmic baryon fraction throughout the $M_{500}\sim 10^{12\!-\!14.5}\, {\rm M_\odot }$ halo mass range. All simulations tested here predict that the mean gas temperature in haloes is about the virial temperature, while that inferred from the SZE is up to one order of magnitude lower than that from the simulations (and also from X-ray observations). While a remarkable agreement is found for the average properties of the IGM between the observation and some simulations, we show that their dependence on the large-scale tidal field can break the degeneracy between models that show similar predictions otherwise. Finally, we show that the gas pressure and the electron density profiles from simulations are not well described by a generalized NFW profile. Instead, we present a new model with a mass-dependent shape that fits the profiles accurately.

We examine how the post-processed content of molecular hydrogen (H$_2$) in galaxies from the TNG100 cosmological, hydrodynamic simulation changes with environment at $z\!=\!0$, assessing central/satellite status and host halo mass. We make close comparisons with the carbon monoxide (CO) emission survey xCOLD GASS where possible, having mock-observed TNG100 galaxies to match the survey's specifications. For a representative sample of host haloes across $10^{11}\!\lesssim\!M_{\rm 200c}/{\rm M}_{\odot}\!, Comment: Accepted in MNRAS. Minor proofing and reference edits from v1. Main body: 19 pages, 11 figures

We use cosmological hydrodynamical simulations to examine the physical properties of the gas in the circumgalactic media (CGM) of star-forming galaxies as a function of angular orientation. We utilise TNG50 of the IllustrisTNG project, as well as the EAGLE simulation to show that observable properties of CGM gas correlate with azimuthal angle, defined as the galiocentric angle with respect to the central galaxy. Both simulations are in remarkable agreement in predicting a strong modulation of flow rate direction with azimuthal angle: inflow is more substantial along the galaxy major axis, while outflow is strongest along the minor axis. The absolute rates are noticeably larger for higher (log(M_* / M_sun) ~ 10.5) stellar mass galaxies, up to an order of magnitude compared to M^dot < 1 M_sun/yr/sr for log(M_* / M_sun) ~ 9.5 objects. Notwithstanding the different numerical and physical models, both TNG50 and EAGLE predict that the average metallicity of the CGM is higher along the minor versus major axes of galaxies. The angular signal is robust across a wide range of galaxy stellar mass 8.5 < log(M_* / M_sun) < 10.5 at z 100 kpc. Our results present a global picture whereby, despite the numerous mixing processes, there is a clear angular dependence of the CGM metallicity. We make forecasts for future large survey programs that will be able to compare against these expectations. Indeed, characterising the kinematics, spatial distribution and metal content of CGM gas is key to a full understanding of the exchange of mass, metals, and energy between galaxies and their surrounding environments., Accepted for publication in MNRAS; 13 pages, 6 figures

Lyman$-\alpha$ (Ly$\alpha$) emission lines are typically found to be redshifted with respect to the systemic redshifts of galaxies, likely due to resonant scattering of Ly$\alpha$ photons. Here we measure the average velocity offset for a sample of 96 $z\approx3.3$ Ly$\alpha$ emitters (LAEs) with a median Ly$\alpha$ flux (luminosity) of $\approx 10^{-17}~\rm erg~cm^{-2}~s^{-1}$ ($\approx10^{42}~\rm erg~s^{-1}$) and a median star formation rate (SFR) of $\approx1.3 \rm M_{\odot} yr^{-1}$ (not corrected for possible dust extinction), detected by the Multi-Unit Spectroscopic Explorer as part of our MUSEQuBES circumgalactic medium (CGM) survey. By postulating that the stacked CGM absorption profiles of these LAEs, probed by 8 background quasars, must be centered on the systemic redshift, we measure an average velocity offset, V$_{\rm offset} = 171 \pm 8$ $\rm km s^{-1}$, between the Ly$\alpha$ emission peak and the systemic redshift. The observed V$_{\rm offset}$ is lower by factors of $\approx1.4$ and $\approx2.6$ compared to the velocity offsets measured for narrow-band selected LAEs and Lyman break galaxies, respectively, which probe galaxies with higher masses and SFRs. Consistent with earlier studies based on direct measurements for individual objects, we find that the V$_{\rm offset}$ is correlated with the full width at half-maximum of the red peak of the Ly$\alpha$ line, and anti-correlated with the rest-frame equivalent width. Moreover, we find that $V_{\rm offset}$ is correlated with SFR with a sub-linear scaling relation, V$_{\rm offset}\propto \rm SFR^{0.16\pm0.03}$. Adopting the mass scaling for main sequence galaxies, such a relation suggests that V$_{\rm offset}$ scales with the circular velocity of the dark matter halos hosting the LAEs., Comment: Published on 15 May, 2020 along with an erratum (Ref: MNRAS 498, 4424, 2020, doi:10.1093/mnras/staa2668), since Fig. 2 has not been updated in the published version. There are other typos in the published version, introduced by the typesetter, which cannot be revised in the erratum. We feel that the astrp-ph version is more accurate than the published one

Redshift-space clustering distortions provide one of the most powerful probes to test the gravity theory on the largest cosmological scales. We perform a systematic validation study of the state-of-the-art statistical methods currently used to constrain the linear growth rate from redshift-space distortions in the galaxy two-point correlation function. The numerical pipelines are tested on mock halo catalogues extracted from large N-body simulations of the standard cosmological framework. We consider both the monopole and quadrupole multipole moments of the redshift-space two-point correlation function, as well as the radial and transverse clustering wedges, in the comoving scale range $1030$ \Mpch, the discrepancy is reduced below $5\%$. At higher redshifts, we find instead an overall good agreement between measurements and model predictions. Though this accuracy is good enough for clustering analyses in current redshift surveys, the models have to be further improved not to introduce significant systematics in RSD constraints from next generation galaxy surveys. The effect of redshift errors is degenerate with the one of small-scale random motions, and can be marginalised over in the statistical analysis, not introducing any statistically significant bias in the linear growth constraints, especially at $z\geq1$., Comment: 17 pages, 14 figures, 1 table

We report the discovery of three new "near-pristine" Lyman Limit Systems (LLSs), with metallicities ~1/1000 solar, at redshifts 2.6, 3.8 and 4.0, with a targeted survey at the Keck Observatory. High resolution echelle spectra of eight candidates yielded precise column densities of hydrogen and weak, but clearly detected, metal lines in seven LLSs; we previously reported the one remaining, apparently metal-free LLS, to have metallicity ~ -2.5 for the remaining four. Previous simulations suggest that near-pristine LLSs could be the remnants of PopIII supernovae, so comparing their detailed metal abundances with nucleosynthetic yields from supernovae models is an important goal. Unfortunately, at most two different metals were detected in each new system, despite their neutral hydrogen column densities (10^{19.2-19.4} cm^{-2}) being two orders of magnitude larger than the two previous, serendipitously discovered near-pristine LLSs. Nevertheless, the success of this first targeted survey for near-pristine systems demonstrates the prospect that a much larger, future survey could identify clear observational signatures of PopIII stars. With a well-understood selection function, such a survey would also yield the number density of near-pristine absorbers which, via comparison to future simulations, could reveal the origin(s) of these rare systems., Accepted by MNRAS. 21 pages, 27 figures

This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift $z\lesssim1$. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from $\log (n_{\rm H}/{\rm cm^{-3}}) \approx -4$ to $-1$, while the temperature of the gas is confined in a narrow range of $\log (T/{\rm K})\approx 4.3\pm 0.3$. In addition, a weak anti-correlation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30% of the components at $z\lesssim 1$ exhibit line widths driven by non-thermal motions, in comparison to $, Comment: 16 pages, 4 figures, 1 table, accepted for publication in MNRAS

We use N-body simulations to revisit the globular cluster (GC) ``timing problem'' in the Fornax dwarf spheroidal (dSph). In agreement with earlier work, we find that, due to dynamical friction, GCs sink to the center of dark matter halos with a cuspy inner density profile but ``stall'' at roughly 1/3 of the core radius ($r_{\rm core}$) in halos with constant-density cores. The timescales to sink or stall depend strongly on the mass of the GC and on the initial orbital radius, but are essentially the same for either cuspy (NFW) or cored halos normalized to have the same total mass within $r_{\rm core}$. Arguing against a cusp on the basis that GCs have not sunk to the center is thus no different from arguing against a core, unless all clusters are today at $\sim (1/3)\, r_{\rm core}$. This would imply a core radius exceeding $\sim 3$ kpc, much larger than seems plausible in any core-formation scenario. (The average projected distance of Fornax GCs is $\langle R_{\rm GC,Fnx}\rangle\sim 1$ kpc and its effective radius is $\sim 700$ pc.) A simpler explanation is that Fornax GCs have only been modestly affected by dynamical friction, as expected if clusters started orbiting at initial radii of order $\sim 1$-$2$ kpc, just outside Fornax's present-day half-light radius but well within the tidal radius imprinted by Galactic tides. This is not entirely unexpected. Fornax GCs are significantly older and more metal-poor than most Fornax stars, and such populations in dSphs tend to be more spatially extended than their younger and more metal-rich counterparts. Contrary to some earlier claims, our simulations further suggest that GCs do not truly ``stall'' at $\sim 0.3\, r_{\rm core}$, but rather continue decaying toward the center, albeit at reduced rates. We conclude that dismissing the presence of a cusp in Fornax based on the spatial distribution of its GC population is unwarranted., 7 pages, 4 figures. Submitted to MNRAS

We analytically derive the observed size-mass relation of galaxies' atomic hydrogen (HI), including limits on its scatter, based on simple assumptions about the structure of HI discs. We trial three generic profiles for HI surface density as a function of radius. Firstly, we assert that HI surface densities saturate at a variable threshold, and otherwise fall off exponentially with radius or, secondly, radius squared. Our third model assumes the total gas surface density is exponential, with the HI fraction at each radius depending on local pressure. These are tested against a compilation of 110 galaxies from the THINGS, LITTLE THINGS, LVHIS, and Bluedisk surveys, whose HI surface density profiles are well resolved. All models fit the observations well and predict consistent size-mass relations. Using an analytical argument, we explain why processes that cause gas disc truncation - such as ram-pressure stripping - scarcely affect the HI size-mass relation. This is tested with the IllustrisTNG(100) cosmological, hydrodynamic simulation and the Dark Sage semi-analytic model of galaxy formation, both of which capture radially resolved disc structure. For galaxies with m_*>10^9 M_solar and m_HI>10^8 M_solar, both simulations predict HI size-mass relations that align with observations, show no difference between central and satellite galaxies, and show only a minor, second-order dependence on host halo mass for satellites. Ultimately, the universally tight HI size-mass relation is mathematically inevitable and robust. Only by completely disrupting the structure of HI discs, e.g. through overly powerful feedback, could a simulation predict the relation poorly., Accepted in MNRAS. Post-proofing. 15 pages and 11 figures in main body (references and appendices additional)

We have carried out a controlled comparison of the structural and kinematic properties of the circumgalactic medium (CGM) around Milky Way mass galaxies in the Illustris and IllustrisTNG simulations. Very striking differences are found. At z=0, gas column density and temperature profiles at large radii ($\sim 100$ kpc) correlate strongly with disk gas mass fraction in Illustris, but not in TNG. The neutral gas at large radii is preferentially aligned in the plane of the disk in TNG, whereas it is much more isotropic in Illustris. The vertical coherence scale of the rotationally supported gas in the CGM is linked to the gas mass fraction of the galaxy in Illustris, but not in TNG. A tracer particle analysis allows us to show how these differences can be understood as a consequence of the different sub-grid models of feedback in the two simulations. A study of spatially matched galaxies in the two simulations shows that in TNG, feedback by supernovae and AGN helps to create an extended smooth reservoir of hot gas at high redshifts, that then cools to form a thin, rotationally-supported disk at later times. In Illustris, AGN dump heat in the form of hot gas bubbles that push diffuse material at large radii out of the halo. The disk is formed by accretion of colder, recycled material, and this results in more vertically extended gas distributions above and below the Galactic plane. We conclude that variations in the structure of gas around Milky Way mass galaxies are a sensitive probe of feedback physics in simulations and are worthy of more observational consideration in future., Comment: 16 pages, 14 figures, accepted for publication in MNRAS

Measurements of the rotation curves of dwarf galaxies are often interpreted as requiring a constant density core at the centre, at odds with the "cuspy" inner profiles predicted by $N$-body simulations of cold dark matter (CDM) haloes. It has been suggested that this conflict could be resolved by fluctuations in the inner gravitational potential caused by the periodic removal of gas following bursts of star formation. Earlier work has suggested that core formation requires a bursty and extended star formation history (SFH). Here we investigate the structure of CDM haloes of dwarf galaxies ($M_{{\rm DM}} \sim 10^9-5\times10^{10}\,{\rm M}_\odot$) formed in the APOSTLE ('A Project of Simulating the Local Environment') and AURIGA cosmological hydrodynamic simulations. Our simulations have comparable or better resolution than others that make cores ($M_{{\rm gas}} \sim 10^4\,{\rm M}_\odot$, gravitational softening $\sim 150$ pc). Yet, we do not find evidence of core formation at {\it any} mass or any correlation between the inner slope of the DM density profile and temporal variations in the SFH. APOSTLE and AURIGA dwarfs display a similar diversity in their cumulative SFHs to available data for Local Group dwarfs. Dwarfs in both simulations are DM-dominated on all resolved scales at all times, likely limiting the ability of gas outflows to alter significantly the central density profiles of their haloes. We conclude that recurrent bursts of star formation are not sufficient to cause the formation of cores, and that other conditions must also be met for baryons to be able to modify the central DM cusp., Comment: 15 pages, 9 figures, 2 tables. Updated version accepted for publication in MNRAS

We study the dependency of the concentration on mass and redshift using three large N-body cosmological hydrodynamic simulations carried out by the Magneticum project. We constrain the slope of the mass-concentration relation with an unprecedented mass range for hydrodynamic simulations and find a negative trend on the mass-concentration plane and a slightly negative redshift dependency, in agreement with observations and other numerical works. We also show how the concentration correlates with the fossil parameter, defined as the stellar mass ratio between the central galaxy and the most massive satellite, in agreement with observations. We find that haloes with high fossil parameter have systematically higher concentration and investigate the cause in two different ways. First we study the evolution of haloes that lives unperturbed for a long period of time, where we find that the internal region keeps accreting satellites as the fossil parameter increases and the scale radius decreases (which increases the concentration). We also study the dependency of the concentration on the virial ratio and the energy term from the surface pressure $E_s$. We conclude that fossil objects have higher concentration because they are dynamically relaxed, with no in-fall/out-fall material and had time to accrete their satellites., Comment: 13 pages, 10 figures

We study the intrinsic large-scale distribution and evolution of seven ionized metals in the IllustrisTNG magneto-hydrodynamical cosmological simulation. We focus on the fractions of C\,\textsc{ii}, C\,\textsc{iv}, Mg\,\textsc{ii}, N\,\textsc{v}, Ne\,\textsc{viii}, O\,\textsc{vi}, and Si\,\textsc{iv} in different cosmic web structures (filaments, haloes, and voids) and gas phases (warm-hot intergalactic medium WHIM, hot, diffuse, and condensed gas) from $z=6$ to $z=0$. Our analysis provides a new perspective to the study of the distribution and evolution of baryons across cosmic time while offering new hints in the context of the well-known missing baryons problem. The cosmic web components are here identified using the local comoving dark matter density, which provides a simple but effective way of mapping baryons on large scales. Our results show that C\,\textsc{ii} and Mg\,\textsc{ii} are mostly located in condensed gas inside haloes in high-density and low-temperature star-forming regions ($\rho_{\rm gas}/\bar{\rho}_{\rm bar}\gtrsim10^3$, and ${\rm T}\lesssim10^{5}$~K). C\,\textsc{iv} and Si\,\textsc{iv} present similar evolution of their mass fractions in haloes and filaments across cosmic time. In particular, their mass budgets in haloes in condensed phase ($\rho_{\rm gas}/\bar{\rho}_{\rm bar}\gtrsim10^3$, and ${\rm T}\lesssim10^{5}$~K) are driven by gas cooling and star formation with a peak at $z\sim2$. Finally, our results confirm that O\,\textsc{vi}, Ne\,\textsc{viii}, and N\,\textsc{v} are good tracers of warm/hot and low-density gas at low redshift ($\rho_{\rm gas}/\bar{\rho}_{\rm bar}\lesssim10^3$, and ${\rm T}\gtrsim10^{5}$~K), regions that are likely to contain most of the missing baryons in the local Universe., Comment: 15 pages, 9 figures. Submitted to MNRAS

We present the first characterization of the circumgalactic medium of Ly α emitters (LAEs), using a sample of 96 z ≈ 3.3 LAEs detected with the VLT/MUSE in fields centred on eight bright background quasars. The LAEs have low Ly α luminosities ($\sim 10^{42}\, \text{erg}\, \text{s}^{-1}$) and star formation rates (SFRs) $\sim 1~\text{M}_\odot \, \text{yr}^{-1}$, which for main-sequence galaxies correspond to stellar masses of only $\sim 10^{8.6}\, \text{M}_\odot$. The median transverse distance between the LAEs and the quasar sightlines is 165 proper kpc (pkpc). We stacked the high-resolution quasar spectra and measured significant excess H i and C iv absorption near the LAEs out to 500 $\text{km}\, \text{s}^{-1}$ and at least ≈250 pkpc (corresponding to ≈7 virial radii). At $\lesssim 30~\text{km}\, \text{s}^{-1}$ from the galaxies, the median H i and C iv optical depths are enhanced by an order of magnitude. The absorption is significantly stronger around the ≈1/3 of our LAEs that are part of ‘groups’, which we attribute to the large-scale structures in which they are embedded. We do not detect any strong dependence of either the H i or C iv absorption on transverse distance (over the range ≈50–250 pkpc), redshift, or the properties of the Ly α emission line (luminosity, full width at half-maximum, or equivalent width). However, for H i, but not C iv, the absorption at $\lesssim 100\, \text{km}\, \text{s}^{-1}$ from the LAE does increase with the SFR. This suggests that LAEs surrounded by more H i tend to have higher SFRs.

We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final instalment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as disky galaxies with stellar masses of Mstar = 10^10.5-11.2 Msun in relative isolation at z = 0. By defining satellites as galaxies with Mstar > 5*10^6 Msun within 300 kpc (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median (16th - 84th percentiles) TNG50 MW/M31-like galaxy hosts a total of 5 (2-11) satellites with Mstar > 5*10^6 Msun, reaching up to Mstar ~ 10^8.5 Msun (10^7.4-9.4 Msun). The abundance of subhaloes with Mdyn > 5*10^7 Msun is larger by a factor of more than 10. The number of all satellites (subhaloes) ever accreted is larger by a factor of 4-5 (3-5) than those surviving to z = 0. Hosts with larger galaxy stellar mass, brighter K-band luminosity, larger total halo mass, and more recent halo assembly typically have a larger number of surviving satellites. The satellite abundances around TNG50 MW/M31-like galaxies are consistent with similar hosts from observational surveys (e.g. SAGA) and previous simulations (e.g. Latte). While the observed MW satellite system falls within the TNG50 scatter across all stellar masses considered, M31 is slightly more satellite-rich than our 1 sigma scatter, possibly due to volume and mass limitations. We find a handful of systems with both a Large and a Small Magellanic Cloud-like satellite. There is no missing satellites problem with TNG50., Accepted by MNRAS. TNG50 is publicly available at https://www.tng-project.org/

Using deep (11.2hr) VLT/MUSE data from the MEGAFLOW survey, we report the first detection of extended MgII emission from a galaxy's halo that is probed by a quasar sightline. The MgII $\lambda\lambda$ 2796,2803 emission around the $z = 0.702$ galaxy ($\log(M_*/\mathrm{M_\odot}) = 10.05^{+0.15}_{-0.11}$) is detected out to $\approx$25 kpc from the central galaxy and covers $1.0\times10^3$ kpc$^2$ above a surface brightness of $14\times10^{-19} \mathrm{erg} \mathrm{s}^{-1} \mathrm{cm}^{-2}\,\mathrm{arcsec}^{-2}$ ($2 \sigma$; integrated over 1200 km s$^{-1}$ =19A and averaged over $1.5 \;\mathrm{arcsec}^2$). The MgII emission around this highly inclined galaxy ($\simeq$75 deg) is strongest along the galaxy's projected minor axis, consistent with the MgII gas having been ejected from the galaxy into a bi-conical structure. The quasar sightline, which is aligned with the galaxy's minor axis, shows strong MgII $\lambda$2796 absorption (EW$_0$ = 1.8A) at an impact parameter of 39kpc from the galaxy. Comparing the kinematics of both the emission and the absorption - probed with VLT/UVES -, to the expectation from a simple toy model of a bi-conical outflow, we find good consistency when assuming a relatively slow outflow ($v_\mathrm{out}= 130\;\mathrm{km}\,\mathrm{s}^{-1}$). We investigate potential origins of the extended MgII emission using simple toy models. With continuum scattering models we encounter serious difficulties in explaining the luminosity of the MgII halo and in reconciling density estimates from emission and absorption. Instead, we find that shocks might be a more viable source to power the extended MgII (and non-resonant [OII]) emission., Comment: Version as resubmitted to MNRAS after addressing referee's comments (24 pages, 18 figures)

We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $N_\mathrm{H\,I}\approx(1-3)\times10^{16}\,\mathrm{cm}^{-2}$ discovered at $z=0.5$ in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multi-phase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred $\alpha$-element abundance varying from $[\alpha/\text{H}]\approx\!{-0.8}$ to near solar and densities spanning over two decades from $\log n_\mathrm{H}\mathrm{cm}^{-3}\approx\!-2.2$ to $, Comment: Accepted for publication in MNRAS, 27 pages, 21 figures

We present a study of the metal-enriched cool halo gas traced by MgII absorption around 228 galaxies at z~0.8-1.5 within 28 quasar fields from the MUSE Analysis of Gas around Galaxies (MAGG) survey. We observe no significant evolution in the MgII equivalent width versus impact parameter relation and in the MgII covering fraction compared to surveys at z, Comment: Published in MNRAS

We use the IllustrisTNG simulations to show how the fractions of quenched galaxies vary across different environments and cosmic time, and to quantify the role AGN feedback and preprocessing play in quenching group and cluster satellites. At $z=0$, we select galaxies with $M_* = 10^{9-12} M_{\odot}$ residing within ($\leq R_{200c}$) groups and clusters of total host mass $M_{200c}=10^{13-15.2} M_{\odot}$. TNG predicts a quenched fraction of $\sim70-90\%$ (on average) for centrals and satellites $\gtrsim 10^{10.5} M_{\odot}$, regardless of host mass, cosmic time ($0\leq z\leq0.5$), clustercentric distance and time since infall in the $z=0$ host. Low-mass centrals ($\lesssim 10^{10} M_{\odot}$), instead, are rarely quenched unless they become members of groups ($10^{13-14} M_{\odot}$) or clusters ($\geq10^{14} M_{\odot}$), where the quenched fraction rises to $\sim80\%$. The fraction of low-mass passive galaxies is higher closer to the host center and for more massive hosts. The population of low-mass satellites accreted $\gtrsim$4-6 Gyr ago in massive hosts is almost entirely passive, thus suggesting an upper limit for the time needed for environmental quenching to occur. In fact, $\sim30\%$ of group and cluster satellites that are quenched at $z=0$ were already quenched before falling into their current host, and the bulk of them quenched as early as 4 to 10 billion years ago. For low-mass galaxies ($\lesssim10^{10-10.5}M_{\odot}$), this is due to preprocessing, whereby current satellites may have been members of other hosts, and hence have undergone environmental processes, before falling into their final host, this mechanism being more common and more effective for the purposes of quenching for satellites found today in more massive hosts. On the other hand, massive galaxies quench on their own and because of AGN feedback, regardless of whether they are centrals or satellites., 21 Pages, 11 figures, 2 tables, 1 appendix, published in MNRAS

Supermassive black holes (SMBHs) that reside at the centres of galaxies can inject vast amounts of energy into the surrounding gas and are thought to be a viable mechanism to quench star formation in massive galaxies. Here, we study the 10[superscript 9-12.5] M[subscript ⨀] stellar mass central galaxy population of the IllustrisTNG simulation, specifically the TNG100 and TNG300 volumes at z = 0, and show how the three components – SMBH, galaxy, and circumgalactic medium (CGM) – are interconnected in their evolution. We find that gas entropy is a sensitive diagnostic of feedback injection. In particular, we demonstrate how the onset of the low-accretion black hole (BH) feedback mode, realized in the IllustrisTNG model as a kinetic, BH-driven wind, leads not only to star formation quenching at stellar masses $\gtrsim 10[superscript 10.5]M[subscript ⨀] but also to a change in thermodynamic properties of the (non-star-forming) gas, both within the galaxy and beyond. The IllustrisTNG kinetic feedback from SMBHs increases the average gas entropy, within the galaxy and in the CGM, lengthening typical gas cooling times from 10-100 Myr to 1-10 Gyr, effectively ceasing ongoing star formation and inhibiting radiative cooling and future gas accretion. In practice, the same active galactic nucleus (AGN) feedback channel is simultaneously ‘ejective’ and ‘preventative’ and leaves an imprint on the temperature, density, entropy, and cooling times also in the outer reaches of the gas halo, up to distances of several hundred kiloparsecs. In the IllustrisTNG model, a long-lasting quenching state can occur for a heterogeneous CGM, whereby the hot and dilute CGM gas of quiescent galaxies contains regions of low-entropy gas with short cooling times., NASA (Grant NNX17AG29G), NSF (Grants AST-1814053, AST-1814259 and AST-1909831)

We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in the inner regions, r, Comment: 21 pages, 14 figures, main results: figs 3, 7, 10 and 11; MNRAS accepted version, code and resources available at https://github.com/MariusCautun/Milky_Way_mass_profile

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z~ 17.2 over a total redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18, +0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to n(z)=1.08 (-0.25, +0.31) at z, Comment: 26 pages, 14 figures, MNRAS in press

We study the orbital phase space of dark matter (DM) haloes in the auriga suite of cosmological hydrodynamics simulations of Milky Way (MW) analogues. We characterize haloes by their spherical action distribution, $F\left(J_{{r}},L\right)$, a function of the specific angular momentum, L, and the radial action, Jr, of the DM particles. By comparing DM-only and hydrodynamical simulations of the same haloes, we investigate the contraction of DM haloes caused by the accumulation of baryons at the centre. We find a small systematic suppression of the radial action in the DM haloes of the hydrodynamical simulations, suggesting that the commonly used adiabatic contraction approximation can result in an underestimate of the density by $\sim 8{{ \rm {per\ cent}}}$. We apply an iterative algorithm to contract the auriga DM haloes given a baryon density profile and halo mass, recovering the true contracted DM profiles with an accuracy of $\sim 15{{ \rm {per\ cent}}}$, that reflects halo-to-halo variation. Using this algorithm, we infer the total mass profile of the MW’s contracted DM halo. We derive updated values for the key astrophysical inputs to DM direct detection experiments: the DM density and velocity distribution in the Solar neighbourhood.

The generation of simulated convergence maps is of key importance in fully exploiting weak lensing by Large Scale Structure (LSS) from which cosmological parameters can be derived. In this paper we present an extension of the PINOCCHIO code which produces catalogues of dark matter haloes so that it is capable of simulating weak lensing by LSS. Like WL-MOKA, the method starts with a random realisation of cosmological initial conditions, creates a halo catalogue and projects it onto the past-light-cone, and paints in haloes assuming parametric models for the mass density distribution within them. Large scale modes that are not accounted for by the haloes are constructed using linear theory. We discuss the systematic errors affecting the convergence power spectra when Lagrangian Perturbation Theory at increasing order is used to displace the haloes within PINOCCHIO, and how they depend on the grid resolution. Our approximate method is shown to be very fast when compared to full ray-tracing simulations from an N-Body run and able to recover the weak lensing signal, at different redshifts, with a few percent accuracy. It also allows for quickly constructing weak lensing covariance matrices, complementing PINOCCHIO's ability of generating the cluster mass function and galaxy clustering covariances and thus paving the way for calculating cross covariances between the different probes. This work advances these approximate methods as tools for simulating and analysing surveys data for cosmological purposes., Comment: Replaced to match the accepted version for publication in MNRAS. Added: comparison of diagonal and off-diagonal terms of the covariance matrices; cosmological constraints. Acceptance date: 2020-06-02

Low surface brightness galactic stellar halos provide a challenging but promising path towards unraveling the past assembly histories of individual galaxies. Here, we present detailed comparisons between the stellar halos of Milky Way-mass disk galaxies observed as part of the Dragonfly Nearby Galaxies Survey (DNGS) and stellar mass-matched galaxies in the TNG100 run of the IllustrisTNG project. We produce stellar mass maps as well as mock $g$ and $r$-band images for randomly oriented simulated galaxies, convolving the latter with the Dragonfly PSF and taking care to match the background noise, surface brightness limits and spatial resolution of DNGS. We measure azimuthally averaged stellar mass density and surface brightness profiles, and find that the DNGS galaxies generally have less stellar mass (or light) at large radii (>20 kpc) compared to their mass-matched TNG100 counterparts, and that simulated galaxies with similar surface density profiles tend to have low accreted mass fractions for their stellar mass. We explore potential solutions to this apparent "missing outskirts problem" by implementing several ad-hoc adjustments within TNG100 at the stellar particle level. Although we are unable to identify any single adjustment that fully reconciles the differences between the observed and simulated galaxy outskirts, we find that artificially delaying the disruption of satellite galaxies and reducing the spatial extent of in-situ stellar populations result in improved matches between the outer profile shapes and stellar halo masses, respectively. Further insight can be achieved with higher resolution simulations that are able to better resolve satellite accretion, and with larger samples of observed galaxies., Accepted for publication in MNRAS. 33 pages, 18 figures (main text). Key results are shown in Figures 6 and 17

We report the discovery and analysis of only the third Lyman-limit system in which a high-quality resolution, echelle spectrum reveals no metal absorption lines, implying a metallicity $\lesssim$1/10000 solar. Our HIRES spectrum of the background quasar, PSS1723$+$2243, provides a neutral hydrogen column density range for LLS1723 of $N_\textrm{HI}=10^{\text{17.9--18.3}}$ cm$^{-2}$ at redshift $z_\textrm{abs}\approx4.391$. The lower bound on this range, and the lack of detectable absorption from the strongest low-ionisation metal lines, are combined in photoionisation models to infer a robust, conservative upper limit on the metallicity: $\log(Z/Z_\odot), Comment: 12 pages, 6 figures, 1 table, accepted for publication in MNRAS

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

Motivated by the discovery of rare enormous Lyman α nebulae (ELAN) around z ̃ 2 quasars, we initiated a long-term campaign with the MUSE/VLT instrument to directly uncover the astrophysics of the gas around quasars. We present here the first 61 targets under the acronym QSO MUSEUM. These quasars are characterized by a median redshift z = 3.17, absolute i magnitude in the range -29.67 ≤ Mi(z = 2) ≤ -27.03, and different levels of radio-loudness. This sample unveils diverse specimens of Ly α nebulosities extending for tens of kpc around these quasars (average maximum projected distance of 80 kpc) above a surface brightness SB > 8.8 × 10-19 erg s-1 cm-2 arcsec-2(2σ). The bulk of the Ly α emission is within R < 50 kpc, and is characterized by relatively quiescent kinematics, with average velocity dispersions Ly α> < 400 km s-1. Therefore, the motions within all these Ly α nebulosities have amplitudes consistent with gravitational motions expected in dark matter haloes hosting quasars at these redshifts, possibly reflecting the complexity in propagating a fast wind on large scales. Our current data suggest a combination of photoionization and resonant scattering as powering mechanisms of the Ly α emission. We discover the first z ̃ 3 ELAN, confirming a very low probability ({̃ }1{{ per cent}}) of occurrence of such systems at these redshifts. Finally, we discuss the redshift evolution currently seen in extended Ly α emission around radio-quiet quasars from z ̃ 3 to z ̃ 2, concluding that it is possibly linked to a decrease of cool gas mass within the circumgalactic medium of quasars from z ̃ 3 to z ̃ 2, and thus to the balance of cool versus hot media. Overall, QSO MUSEUM opens the path to statistical surveys targeting the gas phases in quasars' haloes along cosmic times.

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 use mock interferometric HI measurements and a conventional tilted-ring modelling procedure to estimate circular velocity curves of dwarf galaxy discs from the APOSTLE suite of {\Lambda}CDM cosmological hydrodynamical simulations. The modelling yields a large diversity of rotation curves for an individual galaxy at fixed inclination, depending on the line-of-sight orientation. The diversity is driven by non-circular motions in the gas; in particular, by strong bisymmetric fluctuations in the azimuthal velocities that the tilted-ring model is ill-suited to account for and that are difficult to detect in model residuals. Large misestimates of the circular velocity arise when the kinematic major axis coincides with the extrema of the fluctuation pattern, in some cases mimicking the presence of kiloparsec-scale density 'cores', when none are actually present. The thickness of APOSTLE discs compounds this effect: more slowly-rotating extra-planar gas systematically reduces the average line-of-sight speeds. The recovered rotation curves thus tend to underestimate the true circular velocity of APOSTLE galaxies in the inner regions. Non-circular motions provide an appealing explanation for the large apparent cores observed in galaxies such as DDO 47 and DDO 87, where the model residuals suggest that such motions might have affected estimates of the inner circular velocities. Although residuals from tilted ring models in the simulations appear larger than in observed galaxies, our results suggest that non-circular motions should be carefully taken into account when considering the evidence for dark matter cores in individual galaxies., Comment: 29 pages, 19 figures, 4 tables, supplementary materials available in arXiv tarball. MNRAS accepted version

We use high-resolution hydrodynamical simulation to test the difference of halo properties in cold dark matter (CDM) and a self-interacting dark matter (SIDM) scenario with a constant cross-section of $\sigma^\text{T}/m_{\chi}=1\;\text{cm}^{2}\text{g}^{-1}$. We find that the interplay between dark matter self-interaction and baryonic physics induces a complex evolution of the halo properties, which depends on the halo mass and morphological type, as well as on the halo mass accretion history. While high mass haloes, selected as analogues of early-type galaxies, show cored profiles in the SIDM run, systems of intermediate mass and with a significant disk component can develop a profile that is similar or cuspier than in CDM. The final properties of SIDM haloes - measured at z=0.2 - correlate with the halo concentration and formation time, suggesting that the differences between different systems are due to the fact that we are observing the impact self-interaction. We also search for signatures of self-interacting dark matter in the lensing signal of the main haloes and hints of potential differences in the distribution of Einstein radii, which suggests that future wide-field survey might be able to distinguish between CDM and SIDM models on this basis. Finally, we find that the subhalo abundances are not altered in the adopted SIDM model with respect to CDM., Comment: 11 pages, 11 figures, accepted for publication in MNRAS

We use the IllustrisTNG (TNG) simulations to explore the galaxy-halo connection as inferred from state-of-the-art cosmological, magnetohydrodynamical simulations. With the high mass resolution and large volume achieved by combining the 100 Mpc (TNG100) and 300 Mpc (TNG300) volumes, we establish the mean occupancy of central and satellite galaxies and their dependence on the properties of the dark matter haloes hosting them. We derive best-fitting HOD parameters from TNG100 and TNG300 for target galaxy number densities of $\bar{n}_g = 0.032\,h^3$Mpc$^{-3}$ and $\bar{n}_g = 0.016\,h^3$Mpc$^{-3}$, respectively, corresponding to a minimum galaxy stellar mass of $M_\star\sim1.9\times10^9\,{\rm M}_\odot$ and $M_\star\sim3.5\times10^9\,{\rm M}_\odot$, respectively, in hosts more massive than $10^{11}\,{\rm M}_\odot$. Consistent with previous work, we find that haloes located in dense environments, with low concentrations, later formation times, and high angular momenta are richest in their satellite population. At low mass, highly-concentrated haloes and those located in overdense regions are more likely to contain a central galaxy. The degree of environmental dependence is sensitive to the definition adopted for the physical boundary of the host halo. We examine the extent to which correlations between galaxy occupancy and halo properties are independent and demonstrate that HODs predicted by halo mass and present-day concentration capture the qualitative dependence on the remaining halo properties. At fixed halo mass, concentration is a strong predictor of the stellar mass of the central galaxy, which may play a defining role in the fate of the satellite population. The radial distribution of satellite galaxies, which exhibits a universal form across a wide range of host halo mass, is described accurately by the best-fit NFW density profile of their host haloes., Comment: 20 pages, 13 figures, 1 table, comments welcome

We investigate the baryon content of the circumgalactic medium (CGM) within the virial radius of $M_h \sim 10^{12} \; M_\odot$ haloes at z ~ 3, by modelling the surface brightness profile of the giant Ly$\alpha$ nebulae recently discovered by MUSE around bright QSOs at this redshift. We initially assume fluorescent emission from cold photo-ionized gas confined by the pressure of a hot halo. Acceptable CGM baryon fractions (equal or smaller than the cosmological value) require that the cold gas occupies $\lesssim$ 1% of the volume, but is about as massive as the hot gas. CGM baryon fractions as low as 30% of the cosmic value, as predicted by some strongly ejective feedback models at this redshift, are not easy to reconcile with observations, under our assumptions, unless both the QSO-hosting haloes at $z\sim3$ are more massive than recent BOSS estimates based on clustering and the photo-ionized gas is colder than expected in a standard QSO ionizing radiation field. We also consider the option that the emission is dominated by photons scattered from the QSO broad line region. In this scenario, a very stringent lower limit to the baryon fraction can be obtained under the extreme assumption of optically thin scattering. We infer in this case a baryon fraction of at least 70% of the cosmic value, for fiducial parameters. Lower values require halo masses or gas temperatures different than expected, or that some mechanism keeps the cold gas systematically over-pressured with respect to the ambient medium., Comment: Accepted for publication in MNRAS. 22 pages, 10 Figures

Cosmic filaments play a crucial role in galaxy evolution transporting gas from the intergalactic medium into galaxies. However, little is known about the efficiency of this process and whether the gas is accreted in a homogenous or clumpy way. Recent observations suggest the presence of broad gas density distributions in the circumgalactic medium which could be related to the accretion of filaments. By means of high-resolution hydrodynamical simulations, we explore here the evolution of cold accreting filaments flowing through the hot circumgalactic medium (CGM) of high-z galaxies. In particular, we examine the nonlinear effects of Kelvin-Helmholtz instability (KHI) on the development of broad gas density distributions and on the formation of cold, dense clumps. We explore a large parameter space in filament and perturbation properties, such as, filament Mach number, initial perturbation wavelength, and thickness of the interface between the filament and the halo. We find that the time averaged density distribution of the cold gas is qualitatively consistent with a skewed log-normal probability distribution function (PDF) plus an additional component in form of a high density tail for high Mach-numbers. Our results suggest a tight correlation between the accreting velocity and the maximum densities developing in the filament which is consistent with the variance-Mach number relation for turbulence. Therefore, cosmological accretion could be a viable mechanism to produce turbulence and broad gas density distributions within the CGM., 12 pages, 14 figures, submitted to MNRAS on April 3rd 2019

We investigate the influence of environment on the cold-gas properties of galaxies at z=0 within the TNG100 cosmological, magnetohydrodynamic simulation, part of the IllustrisTNG suite. We extend previous post-processing methods for breaking gas cells into their atomic and molecular phases, and build detailed mocks to comprehensively compare to the latest surveys of atomic hydrogen (HI) in nearby galaxies, namely ALFALFA and xGASS. We use TNG100 to explore the HI content, star formation activity, and angular momentum of satellite galaxies, each as a function of environment, and find that satellites are typically a factor of ~3 poorer in HI than centrals of the same stellar mass, with the exact offset depending sensitively on parent halo mass. Due to the large physical scales on which HI measurements are made (~45--245 kpc), contributions from gas not bound to the galaxy of interest but in the same line of sight crucially lead to larger HI mass measurements in the mocks in many cases, ultimately aligning with observations. This effect is mass-dependent and naturally greater for satellites than centrals, as satellites are never isolated by definition. We also show that HI stripping in TNG100 satellites is closely accompanied by quenching, in tension with observational data that instead favour that HI is preferentially stripped before star formation is reduced., Published in MNRAS. Main body (full paper): 18 (22) pages, 10 (11) figures. New-found bug introduced in v4 mock plots fixed. BaryMP issue fixed per footnote in Dave et al. (2020). All changes are minor and do not affect text or conclusions