arXiv subjects

Joop Schaye

Publications and source records attributed to Joop Schaye.

At least 307 records · Page 17Linked to original sources

arXiv2018

The impact of feedback and the hot halo on the rates of gas accretion onto galaxies

We investigate the physics that drives the gas accretion rates onto galaxies at the centers of dark matter haloes using the EAGLE suite of hydrodynamical cosmological simulations. We find that at redshifts $z{\le}2$ the accretion rate onto the galaxy increases with halo mass in the halo mass range $10^{10}-10^{11.7}M_{\odot}$, flattens between the halo masses $10^{11.7}-10^{12.7}M_{\odot}$, and increases again for higher-mass haloes. However, the galaxy gas accretion does not flatten at intermediate halo masses when AGN feedback is switched off. To better understand these trends, we develop a physically motivated semi-analytic model of galaxy gas accretion. We show that the flattening is produced by the rate of gas cooling from the hot halo. The ratio of the cooling radius and the virial radius does not decrease continuously with increasing halo mass as generally thought. While it decreases up to ${\sim}10^{13}M_{\odot}$ haloes, it increases for higher halo masses, causing an upturn in the galaxy gas accretion rate. This may indicate that in high-mass haloes AGN feedback is not sufficiently efficient. When there is no AGN feedback, the density of the hot halo is higher, the ratio of the cooling and virial radii does not decrease as much and the cooling rate is higher. Changes in the efficiency of stellar feedback can also increase or decrease the accretion rates onto galaxies. The trends can plausibly be explained by the re-accretion of gas ejected by progenitor galaxies and by the suppression of black hole growth, and hence AGN feedback, by stellar feedback.

astro-ph.GA↗

arXiv2018

The BAHAMAS project: the CMB--large-scale structure tension and the roles of massive neutrinos and galaxy formation

Recent studies have presented evidence for tension between the constraints on Omega_m and sigma_8 from the cosmic microwave background (CMB) and measurements of large-scale structure (LSS). This tension can potentially be resolved by appealing to extensions of the standard model of cosmology and/or untreated systematic errors in the modelling of LSS, of which baryonic physics has been frequently suggested. We revisit this tension using, for the first time, carefully-calibrated cosmological hydrodynamical simulations, which thus capture the back reaction of the baryons on the total matter distribution. We have extended the BAHAMAS simulations to include a treatment of massive neutrinos, which currently represents the best motivated extension to the standard model. We make synthetic thermal Sunyaev-Zel'dovich effect, weak galaxy lensing, and CMB lensing maps and compare to observed auto- and cross-power spectra from a wide range of recent observational surveys. We conclude that: i) in general there is tension between the primary CMB and LSS when adopting the standard model with minimal neutrino mass; ii) after calibrating feedback processes to match the gas fractions of clusters, the remaining uncertainties in the baryonic physics modelling are insufficient to reconcile this tension; and iii) if one accounts for internal tensions in the Planck CMB dataset (by allowing the lensing amplitude, A_Lens, to vary), invoking a non-minimal neutrino mass, typically of 0.2-0.4 eV, can resolve the tension. This solution is fully consistent with separate constraints from the primary CMB and baryon acoustic oscillations.

astro-ph.CO↗

arXiv2018

The diverse density profiles of galaxy clusters with self-interacting dark matter plus baryons

We present the first simulated galaxy clusters (M_200 > 10^14 Msun) with both self-interacting dark matter (SIDM) and baryonic physics. They exhibit a greater diversity in both dark matter and stellar density profiles than their counterparts in simulations with collisionless dark matter (CDM), which is generated by the complex interplay between dark matter self-interactions and baryonic physics. Despite variations in formation history, we demonstrate that analytical Jeans modelling predicts the SIDM density profiles remarkably well, and the diverse properties of the haloes can be understood in terms of their different final baryon distributions.

astro-ph.CO↗

arXiv2018

The connection between mass, environment and slow rotation in simulated galaxies

Recent observations from integral field spectroscopy (IFS) indicate that the fraction of galaxies that are slow rotators, $F_{\rm SR}$, depends primarily on stellar mass, with no significant dependence on environment. We investigate these trends and the formation paths of slow rotators (SRs) using the EAGLE and Hydrangea hydro-dynamical simulations. EAGLE consists of several cosmological boxes of volumes up to $(100\,\rm Mpc)^3$, while Hydrangea consists of $24$ cosmological simulations of galaxy clusters and their environment. Together they provide a statistically significant sample in the stellar mass range $10^{9.5}\,\rm M_{\odot}-10^{12.3}\,\rm M_{\odot}$, of $16,358$ galaxies. We construct IFS-like cubes and measure stellar spin parameters, $λ_{\rm R}$, and ellipticities, allowing us to classify galaxies into slow/fast rotators as in observations. The simulations display a primary dependence of $F_{\rm SR}$ on stellar mass, with a weak dependence on environment. At fixed stellar mass, satellite galaxies are more likely to be SRs than centrals. $F_{\rm SR}$ shows a dependence on halo mass at fixed stellar mass for central galaxies, while no such trend is seen for satellites. We find that $\approx 70$% of SRs at $z=0$ have experienced at least one merger with mass ratio $\ge 0.1$, with dry mergers being at least twice more common than wet mergers. Individual dry mergers tend to decrease $λ_{\rm R}$, while wet mergers mostly increase it. However, $30$% of SRs at $z=0$ have not experienced mergers, and those inhabit halos with median spins twice smaller than the halos hosting the rest of the SRs. Thus, although the formation paths of SRs can be varied, dry mergers and/or halos with small spins dominate.

astro-ph.GA↗

arXiv2018

The innate origin of radial and vertical gradients in a simulated galaxy disc

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.

astro-ph.GA↗

arXiv2018

The origin of diverse $α$-element abundances in galaxy discs

Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit a spread in $\mathrm{[α/Fe]}$ at fixed $\mathrm{[Fe/H]}$, manifest at some locations as a bimodality. The origin of these diverse, and possibly distinct, stellar populations in the Galactic disc is not well understood. We examine the Fe and $α$-element evolution of 133 Milky Way-like galaxies from the EAGLE simulation, to investigate the origin and diversity of their $\mathrm{[α/Fe]}$-$\mathrm{[Fe/H]}$ distributions. We find that bimodal $\mathrm{[α/Fe]}$ distributions arise in galaxies whose gas accretion histories exhibit episodes of significant infall at both early and late times, with the former fostering more intense star formation than the latter. The shorter characteristic consumption timescale of gas accreted in the earlier episode suppresses its enrichment with iron synthesised by Type Ia SNe, resulting in the formation of a high-$\mathrm{[α/Fe]}$ sequence. We find that bimodality in $\mathrm{[α/Fe]}$ similar to that seen in the Galaxy is rare, appearing in approximately 5 percent of galaxies in our sample. We posit that this is a consequence of an early gas accretion episode requiring the mass accretion history of a galaxy's dark matter halo to exhibit a phase of atypically-rapid growth at early epochs. The scarcity of EAGLE galaxies exhibiting distinct sequences in the $\mathrm{[α/Fe]}$-$\mathrm{[Fe/H]}$ plane may therefore indicate that the Milky Way's elemental abundance patterns, and its accretion history, are not representative of the broader population of $\sim L^\star$ disc galaxies.

astro-ph.GA↗

arXiv2017

Data release of UV to submm broadband fluxes for simulated galaxies from the EAGLE project

We present dust-attenuated and dust emission fluxes for sufficiently resolved galaxies in the EAGLE suite of cosmological hydrodynamical simulations, calculated with the SKIRT radiative transfer code. The post-processing procedure includes specific components for star formation regions, stellar sources, and diffuse dust, and takes into account stochastic heating of dust grains to obtain realistic broad-band fluxes in the wavelength range from ultraviolet to sub-millimeter. The mock survey includes nearly half a million simulated galaxies with stellar masses above 10^8.5 solar masses across six EAGLE models. About two thirds of these galaxies, residing in 23 redshift bins up to z=6, have a sufficiently resolved metallic gas distribution to derive meaningful dust attenuation and emission, with the important caveat that the same dust properties were used at all redshifts. These newly released data complement the already publicly available information about the EAGLE galaxies, which includes intrinsic properties derived by aggregating the properties of the smoothed particles representing matter in the simulation. We further provide an open source framework of Python procedures for post-processing simulated galaxies with the radiative transfer code SKIRT. The framework allows any third party to calculate synthetic images, SEDs, and broadband fluxes for EAGLE galaxies, taking into account the effects of dust attenuation and emission.

astro-ph.GA↗

arXiv2017

The extent of chemically enriched gas around star-forming dwarf galaxies

Supernova driven winds are often invoked to remove chemically enriched gas from dwarf galaxies to match their low observed metallicities. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circum-galactic medium or CGM) and pollute the intergalactic medium (IGM). Here, we present a survey of the CGM and IGM around 18 star-forming field dwarfs with stellar masses of $\log\,M_*/M_\odot\approx8-9$ at $z\approx0.2$. Eight of these have CGM probed by quasar absorption spectra at projected distances, $d$, less than the host virial radius, $R_{\rm h}$. Ten are probed in the surrounding IGM at $d/R_{\rm h}=1-3$. The absorption measurements include neutral hydrogen, the dominant silicon ions for diffuse cool gas ($T\sim10^4$ K; Si II, Si III, and Si IV), moderately ionized carbon (C IV), and highly ionized oxygen (O VI). Metal absorption from the CGM of the dwarfs is less common and $\approx4\times$ weaker compared to massive star-forming galaxies though O VI absorption is still common. None of the dwarfs probed at $d/R_{\rm h}=1-3$ have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM of the dwarfs accounts for only $2-6\%$ of the expected silicon budget from the yields of supernovae associated with past star-formation. The highly ionized O VI accounts for $\approx8\%$ of the oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of $\lesssim 0.2$, the highly ionized CGM may represent a significant metal reservoir even for dwarfs not expected to maintain gravitationally shock heated hot halos.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey X. Ly$α$ Equivalent Widths at $2.9 < z < 6.6$

We present rest-frame Ly$α$ equivalent widths (EW) of 417 Ly$α$ emitters (LAEs) detected with Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) at $2.9 < z < 6.6$ in the Hubble Ultra Deep Field. Based on the deep MUSE spectroscopy and ancillary Hubble Space Telescope (HST) photometry data, we carefully measured EW values taking into account extended Ly$α$ emission and UV continuum slopes ($β$). Our LAEs reach unprecedented depths, both in Ly$α$ luminosities and UV absolute magnitudes, from log($L_{\rm Lyα}$/erg s$^{-1}$) $\sim$41.0 to 43.0 and from Muv $\sim$ -16 to -21 (0.01-1.0 $L^{*}_{\rm z=3}$). The EW values span the range of $\sim$ 5 to 240 Å or larger, and their distribution can be well fitted by an exponential law $N = N_{\rm 0}$ exp($-$EW/$w_{\rm 0}$). Owing to the high dynamic range in Muv, we find that the scale factor, $w_{\rm 0}$, depends on Muv in the sense that including fainter Muv objects increases $w_{\rm 0}$, i.e., the Ando effect. The results indicate that selection functions affect the EW scale factor. Taking these effects into account, we find that our $w_{\rm 0}$ values are consistent with those in the literature within $1σ$ uncertainties at $2.9 < z < 6.6$ at a given threshold of Muv and $L_{\rm Lyα}$. Interestingly, we find 12 objects with EW $>200$ Å above $1σ$ uncertainties. Two of these 12 LAEs show signatures of merger or AGN activity: the weak CIV $λ1549$ emission line. For the remaining 10 very large EW LAEs, we find that the EW values can be reproduced by young stellar ages ($< 100$ Myr) and low metallicities ($\lesssim 0.02$ $Z_{\rm \odot}$). Otherwise, at least part of the Ly$α$ emission in these LAEs needs to arise from anisotropic radiative transfer effects, fluorescence by hidden AGN or quasi-stellar object activity, or gravitational cooling.

astro-ph.GA↗

arXiv2017

The MUSE-Wide survey: A measurement of the Ly$α$ emitting fraction among $z>3$ galaxies

We present a measurement of the fraction of Lyman $α$ (Ly$α$) emitters ($X_{\rm{Ly} α}$) amongst HST continuum-selected galaxies at $3<z<6$ with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. Making use of the first 24 MUSE-Wide pointings in GOODS-South, each having an integration time of 1 hour, we detect 100 Ly$α$ emitters and find $X_{\rm{Ly} α}\gtrsim0.5$ for most of the redshift range covered, with 29 per cent of the Ly$α$ sample exhibiting rest equivalent widths (rest-EWs) $\leq$ 15Å. Adopting a range of rest-EW cuts (0 - 75Å), we find no evidence of a dependence of $X_{\rm{Ly} α}$ on either redshift or UV luminosity.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey VIII : Extended Lyman-alpha haloes around high-redshift star-forming galaxies

We report the detection of extended Lyman-alpha (Lya) haloes around 145 individual star-forming galaxies at redshifts 3 M_{UV}> -22) Lya emitters (LAEs). Using a 2D, two-component decomposition of Lya emission assuming circular exponential distributions, we measure scale lengths and luminosities of Lya haloes. We find that 80% of our objects having reliable Lya halo measurements show Lya emission that is significantly more extended than the UV continuum detected by HST (by a factor ~4 to >20). The median exponential scale length of the Lya haloes in our sample is ~4.5 kpc. By comparing the maximal detected extent of the Lya emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Lya emission of our selected sample of LAEs probes a significant portion of the cold circum-galactic medium (CGM) of these galaxies (>50% in average). This result shows that there must be significant HI reservoirs in the CGM and reinforces the idea that Lya haloes are ubiquitous around high-redshift Lya emitting galaxies. Our characterization of the Lya haloes indicates that the majority of the Lya flux comes from the halo (~65%) and that their scale lengths seem to be linked to the UV properties of the galaxies. We do not observe a significant Lya halo size evolution with redshift. We also find that the Lya lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km/s. While the FWHM does not seem to be correlated to the Lya scale length, most compact Lya haloes and those that are not detected with high significance tend to have narrower Lya profiles. Finally, we investigate the origin of the extended Lya emission but we conclude that our data do not allow us to disentangle the possible processes.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey: VII. FeII* Emission in Star-Forming Galaxies

Non-resonant FeII* 2365, 2396, 2612, 2626 emission can potentially trace galactic winds in emission and provide useful constraints to wind models. From the 3'x3' mosaic of the Hubble Ultra Deep Field (UDF) obtained with the VLT/MUSE integral field spectrograph, we identify a statistical sample of 40 FeII* emitters and 50 MgII 2796, 2803 emitters from a sample of 271 [OII] 3726, 3729 emitters with reliable redshifts from z = 0.85 - 1.5 down to 2E-18 (3 sigma) ergs/s/cm^2 (for [OII]), covering the stellar mass range 10^8 - 10^11 Msun. The FeII* and MgII emitters follow the galaxy main sequence, but with a clear dichotomy. Galaxies with masses below 10^9 Msun and star formation rates (SFRs) of <1 Msun/year have MgII emission without accompanying FeII* emission, whereas galaxies with masses above 10^10 Msun and SFRs >10 Msun/year have FeII* emission without accompanying MgII emission. Between these two regimes, galaxies have both MgII and FeII* emission, typically with MgII P-Cygni profiles. Indeed, the MgII profile shows a progression along the main sequence from pure emission to P-Cygni profiles to strong absorption, due to resonant trapping. Combining the deep MUSE data with HST ancillary information, we find that galaxies with pure MgII emission profiles have lower star formation rate surface densities than those with either MgII P-Cygni profiles or FeII* emission. These spectral signatures produced through continuum scattering and fluorescence, MgII P-Cygni profiles and FeII* emission, are better candidates for tracing galactic outflows than pure MgII emission, which may originate from HII regions. We compare the absorption and emission rest-frame equivalent widths for pairs of FeII transitions to predictions from outflow models and find that the observations consistently have less total re-emission than absorption, suggesting either dust extinction or non-isotropic outflow geometries.

astro-ph.GA↗

arXiv2017

Tidal dwarf galaxies in cosmological simulations

The formation and evolution of gravitationally bound, star forming substructures in tidal tails of interacting galaxies, called tidal dwarf galaxies (TDG), has been studied, until now, only in idealised simulations of individual pairs of interacting galaxies for pre-determined orbits, mass ratios, and gas fractions. Here, we present the first identification of TDG candidates in fully cosmological simulations, specifically the high-resolution simulations of the EAGLE suite. The finite resolution of the simulation limits their ability to predict the exact formation rate and survival timescale of TDGs, but we show that gravitationally bound baryonic structures in tidal arms already form in current state-of-the-art cosmological simulations. In this case, the orbital parameter, disc orientations as well as stellar and gas masses and the specific angular momentum of the TDG forming galaxies are a direct consequence of cosmic structure formation. We identify TDG candidates in a wide range of environments, such as multiple galaxy mergers, clumpy high-redshift (up to z = 2) galaxies, high-speed encounters, and tidal interactions with gas-poor galaxies. We present selection methods, the properties of the identified TDG candidates and a roadmap for more quantitative analyses using future high-resolution simulations.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey: V. Spatially resolved stellar kinematics of galaxies at redshift $0.2\lesssim z \lesssim 0.8$

We present spatially resolved stellar kinematic maps, for the first time, for a sample of 17 intermediate redshift galaxies (0.2 < z < 0.8). We used deep MUSE/VLT integral field spectroscopic observations in the Hubble Deep Field South (HDFS) and Hubble Ultra Deep Field (HUDF), resulting from ~30h integration time per field, each covering 1'x1' field of view, with ~0.65" spatial resolution. We selected all galaxies brighter than 25mag in the I band and for which the stellar continuum is detected over an area that is at least two times larger than the spatial resolution. The resulting sample contains mostly late-type disk, main-sequence star-forming galaxies with 10^8.5 - 10^10.5 Msun. Using a full-spectrum fitting technique, we derive two-dimensional maps of the stellar and gas kinematics, including the radial velocity V and velocity dispersion sigma. We find that most galaxies in the sample are consistent with having rotating stellar disks with roughly constant velocity dispersions and that the Vrms=sqrt{V^2+sigma^2} of the gas and stars, a scaling proxy for the galaxy gravitational potential, compare well to each other. These spatially resolved observations of intermediate redshift galaxies suggest that the regular stellar kinematics of disk galaxies that is observed in the local Universe was already in place 4 - 7 Gyr ago and that their gas kinematics traces the gravitational potential of the galaxy, thus is not dominated by shocks and turbulent motions. Finally, we build dynamical axisymmetric Jeans models constrained by the derived stellar kinematics for two specific galaxies and derive their dynamical masses. These are in good agreement (within 25%) with those derived from simple exponential disk models based on the gas kinematics. The obtained mass-to-light ratios hint towards dark matter dominated systems within a few effective radii.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection

We present the MUSE Hubble Ultra Deep Survey, a mosaic of nine MUSE fields covering 90\% of the entire HUDF region with a 10-hour deep exposure time, plus a deeper 31-hour exposure in a single 1.15 arcmin2 field. The improved observing strategy and advanced data reduction results in datacubes with sub-arcsecond spatial resolution (0.65 arcsec at 7000 A) and accurate astrometry (0.07 arcsec rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to mAB=28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3 sigma emission line detection limit for a point source is 1.5 and 3.1 10-19 erg.s-1.cm-2 for the single ultra-deep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (mAB>31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 hours of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range.

astro-ph.GA↗

arXiv2017

The multiphase circumgalactic medium traced by low metal ions in EAGLE zoom simulations

We explore the circumgalactic metal content traced by commonly observed low ion absorbers, including C II, Si II, Si III, Si IV, and Mg II. We use a set of cosmological hydrodynamical zoom simulations run with the EAGLE model and including a non-equilibrium ionization and cooling module that follows 136 ions. The simulations of z~0.2 L* (M_200=10^11.7-10^12.3 Msol) haloes hosting star-forming galaxies and group-sized (M_200=10^12.7-10^13.3 Msol) haloes hosting mainly passive galaxies reproduce key trends observed by the COS-Halos survey-- low ion column densities show 1) little dependence on galaxy specific star formation rate, 2) a patchy covering fraction indicative of 10^4 K clouds with a small volume filling factor, and 3) a declining covering fraction as impact parameter increases from 20-160 kpc. Simulated Si II, Si III, Si IV, C II, and C III column densities show good agreement with observations, while Mg II is under-predicted. Low ions trace a significant metal reservoir, ~10^8 Msol, residing primarily at 10-100 kpc from star-forming and passive central galaxies. These clouds tend to flow inwards and most will accrete onto the central galaxy within the next several Gyr, while a small fraction are entrained in strong outflows. A two-phase structure describes the inner CGM (<0.5 R_200) with low-ion metal clouds surrounded by a hot, ambient medium. This cool phase is separate from the O VI observed by COS-Halos, which arises from the outer CGM (>0.5 R_200) tracing virial temperature gas around L* galaxies. Physical parameters derived from standard photo-ionization modelling of observed column densities (e.g. aligned Si II/Si III absorbers) are validated against our simulations. Our simulations therefore support previous ionization models indicating that cloud covering factors decline while densities and pressures show little variation with increasing impact parameter.

astro-ph.GA↗

arXiv2017

Dark Galaxy Candidates at Redshift ~3.5 Detected with MUSE

Recent theoretical models suggest that the early phase of galaxy formation could involve an epoch when galaxies are gas-rich but inefficient at forming stars: a "dark galaxy" phase. Here, we report the results of our MUSE (Multi Unit Spectroscopic Explorer) survey for dark galaxies fluorescently illuminated by quasars at $z>3$. Compared to previous studies which are based on deep narrow-band (NB) imaging, our integral field survey provides a nearly uniform sensitivity coverage over a large volume in redshift space around the quasars as well as full spectral information at each location. Thanks to these unique features, we are able to build control samples at large redshift distances from the quasars using the same data taken under the same conditions. By comparing the rest-frame equivalent width (EW$_{0}$) distributions of the Ly$α$ sources detected in proximity to the quasars and in control samples, we detect a clear correlation between the locations of high EW$_{0}$ objects and the quasars. This correlation is not seen in other properties such as Ly$α$ luminosities or volume overdensities, suggesting the possible fluorescent nature of at least some of these objects. Among these, we find 6 sources without continuum counterparts and EW$_{0}$ limits larger than $240\,\mathrmÅ$ that are the best candidates for dark galaxies in our survey at $z>3.5$. The volume densities and properties, including inferred gas masses and star formation efficiencies, of these dark galaxy candidates are similar to previously detected candidates at $z\approx2.4$ in NB surveys. Moreover, if the most distant of these are fluorescently illuminated by the quasar, our results also provide a lower limit of $t=60$ Myr on the quasar lifetime.

astro-ph.GA↗

arXiv2017

The formation of hot gaseous haloes around galaxies

We use a suite of hydrodynamical cosmological simulations from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) project to investigate the formation of hot hydrostatic haloes and their dependence on feedback mechanisms. We find that the appearance of a strong bimodality in the probability density function (PDF) of the ratio of the radiative cooling and dynamical times for halo gas provides a clear signature of the formation of a hot corona. Haloes of total mass $10^{11.5}-10^{12}{\rm{M}}_{\odot}$ develop a hot corona independent of redshift, at least in the interval $z=0-4$ where the simulation has sufficiently good statistics. We analyse the build up of the hot gas mass in the halo, $M_{\rm{hot}}$, as a function of halo mass and redshift and find that while more energetic galactic winds powered by SNe increases $M_{\rm{hot}}$, AGN feedback reduces it by ejecting gas from the halo. We also study the thermal properties of gas accreting onto haloes and measure the fraction of shock-heated gas as a function of redshift and halo mass. We develop analytic and semianalytic approaches to estimate a `critical halo mass', $M_{\rm{crit}}$, for hot halo formation. We find that the mass for which the heating rate produced by accretion shocks equals the radiative cooling rate, reproduces the mass above which haloes develop a significant hot atmosphere. This yields a mass estimate of $M_{\rm{crit}} \approx 10^{11.7}{\rm{M}}_{\odot}$ at $z=0$, which agrees with the simulation results. The value of $M_{\rm{crit}}$ depends more strongly on the cooling rate than on any of the feedback parameters.

astro-ph.GA↗