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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

While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic reionization is poorly understood due to a lack of knowledge of their physical properties. We isolate a sample of 35 z ≈ 4–5 continuum-faint Lyman-α emitters from deep VLT/MUSE spectroscopy and directly measure their H α emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than −16 (≈ 0.01 L⋆), implying a median Lyman-α equivalent width of 259 Å. By combining the H α measurement with the UV magnitude, we determine the ionizing photon production efficiency, ξion, a first for such faint galaxies. The measurement of log10 (ξion [Hz erg−1]) = 26.28 (+0.28−0.40) is in excess of literature measurements of both continuum- and emission line-selected samples, implying a more efficient production of ionizing photons in these lower luminosity, Lyman-α-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4 × 10−4 and 0.008, with light-weighted ages less than 3 Myr., Monthly Notices of the Royal Astronomical Society, 493 (4), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Fast Radio Burst (FRB) dispersion measures (DMs) record the presence of ionized baryons that are otherwise invisible to other techniques enabling resolution of the matter distribution in the cosmic web. In this work, we aim to estimate the contribution to FRB 180924 DM from foreground galactic halos. Localized by ASKAP to a massive galaxy, this sightline is notable for an estimated cosmic web contribution to the DM ($\rm DM_{cosmic} = 220~pc~cm^{-3}$), which is less than the average value at the host redshift ($\rm z = 0.3216$) estimated from the Macquart relation ($280~\rm pc~cm^{-3}$). In the favored models of the cosmic web, this suggests few intersections with foreground halos at small impact parameters ($\lesssim 100$ kpc). To test this hypothesis, we carried out spectroscopic observations of the field galaxies within $\sim$1' of the sightline with VLT/MUSE and Keck/LRIS. Furthermore, we developed a probabilistic methodology that leverages photometric redshifts derived from wide-field DES and WISE imaging. We conclude that there is no galactic halo that closely intersects the sightline and also that the net DM contribution from halos, $\rm DM_{halos}< 45~pc~cm^{-3}$ (95 % c.l.). This value is lower than the $\rm DM_{halos}$ estimated from an "average" sightline ($121~\rm pc~cm^{-3}$) using the Planck $\Lambda CDM$ model and the Aemulus halo mass function and reasonably explains its low $\rm DM_{cosmic}$ value. We conclude that FRB 180924 represents the predicted majority of sightlines in the universe with no proximate foreground galactic halos. Our framework lays the foundation for a comprehensive analysis of FRB fields in the near future., Comment: 10 pages, 6 figures, 1 extended, machine-readable table. See latex files for the full version of Table 1 (photom_tab_full.tex)

(Abridged) We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at $z=0.36-0.6$ discovered within the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS LLSs exhibit multi-component kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states that span several hundred km/s in line-of-sight velocity. Specifically, higher column density components (log N(HI)>16) in all four absorbers comprise dynamically cool gas with $\langle T \rangle =(2\pm1) \times10^4\,$K and modest non-thermal broadening of $5\pm3\,$ km/s. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modeling that takes into account the resolved component structures of HI and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $160^{+140}_{-50}$ pc. While obtaining robust metallicity constraints for the low-density, highly ionized phase remains challenging due to the uncertain N(HI), we demonstrate that the cool-phase gas in LLSs has a median metallicity of $\mathrm{[\alpha/H]_{1/2}}=-0.7^{+0.1}_{-0.2}$, with a 16-84 percentile range of $\mathrm{[\alpha/H]}=(-1.3,-0.1)$. Furthermore, the wide range of inferred elemental abundance ratios ($\mathrm{[C/\alpha]}$, $\mathrm{[N/\alpha]}$, and $\mathrm{[Fe/\alpha]}$) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the $z, Comment: Accepted for publication in MNRAS after a minor revision. 18 pages, 11 figures, and a nine-page Appendix with four additional figures

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 present the results from a MUSE survey of twelve $z\simeq3.15$ quasars, which were selected to be much fainter (20, Comment: Accepted to MNRAS. 17 pages, 7 figures

We study the distribution and dynamics of the circumgalactic and intergalactic medium using a dense galaxy survey covering the field around the Q0107 system, a unique z ≈ 1 projected quasar triplet. With full Ly α coverage along all three lines-of-sight from z = 0.18 to z = 0.73, more than 1200 galaxy spectra, and two MUSE fields, we examine the structure of the gas around galaxies on 100-1000 kpc scales. We search for H i absorption systems occurring at the same redshift (within 500 km s-1) in multiple sightlines, finding with >99.9 per cent significance that these systems are more frequent in the observed quasar spectra than in a randomly distributed population of absorbers. This is driven primarily by absorption with column densities N(H i) > 1014 cm-2, whilst multi-sightline absorbers with lower column densities are consistent with a random distribution. Star-forming galaxies are more likely to be associated with multi-sightline absorption than quiescent galaxies. HST imaging provides inclinations and position angles for a subset of these galaxies. We observe a bimodality in the position angle of detected galaxy-absorber pairs, again driven mostly by high-column-density absorbers, with absorption preferentially along the major and minor axes of galaxies out to impact parameters of several hundred kpc. We find some evidence supporting a disc/outflow dichotomy, as H i absorbers near the projected major axis of a galaxy show line-of-sight velocities that tend to align with the rotation of that galaxy, whilst minor-axis absorbers are twice as likely to exhibit O vi at the same redshift., Monthly Notices of the Royal Astronomical Society, 506 (2), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Enormous Lyα nebulae, extending over 300−500 kpc around quasars, represent the pinnacle of galaxy and cluster formation. Here we present IRAM Plateau de Bure Interferometer observations of the enormous Lyα nebulae “Slug” (z = 2.282) and “Jackpot” (z = 2.041). Our data reveal bright, synchrotron emission associated with the two radio-loud active galactic nuclei embedded in the targeted nebulae as well as molecular gas, as traced via the CO(3−2) line, in three galaxies (two sources in Slug, and one in Jackpot). All of the CO emission is associated with galaxies detected in their rest-frame UV stellar emission. The total mass in molecular gas of these three galaxies [∼(3 − 5) × 1010 M⊙] is comparable with the total ionized gas mass responsible for the diffuse nebular emission. Our observations place limits on the molecular gas emission in the nebulae: the molecular gas surface density is ΣH2 < 12 − 25 M⊙ pc−2 for the Slug nebula and ΣH2 < 34 − 68 M⊙ pc−2 for the Jackpot nebula. These are consistent with the expected molecular gas surface densities, as predicted via photoionization models of the rest-frame UV line emission in the nebulae, and via Lyα absorption in the Jackpot nebula. Compared to other radio-loud quasars at z > 1 and high-redshift radio-loud galaxies, we do not find any strong trends relating the molecular gas reservoirs, the radio power, and the Lyα luminosities of these systems. The significant step in sensitivity required to achieve a detection of the molecular gas from the nebulae, if present, will require a substantial time investment with JVLA, NOEMA, or ALMA.

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

A prediction of the classic active galactic nuclei (AGN) unification model is the presence of ionisation cones with different orientations depending on the AGN type. Confirmations of this model exist for present times, but it is less clear in the early Universe. Here, we use the morphology of giant Ly$\alpha$ nebulae around AGNs at redshift z$\sim$3 to probe AGN emission and therefore the validity of the AGN unification model at this redshift. We compare the spatial morphology of 19 nebulae previously found around type I AGNs with a new sample of 4 Ly$\alpha$ nebulae detected around type II AGNs. Using two independent techniques, we find that nebulae around type II AGNs are more asymmetric than around type I, at least at radial distances $r>30$~physical kpc (pkpc) from the ionizing source. We conclude that the type I and type II AGNs in our sample show evidence of different surrounding ionising geometries. This suggests that the classical AGN unification model is also valid for high-redshift sources. Finally, we discuss how the lack of asymmetry in the inner parts (r$\lesssim$30 pkpc) and the associated high values of the HeII to Ly$\alpha$ ratios in these regions could indicate additional sources of (hard) ionizing radiation originating within or in proximity of the AGN host galaxies. This work demonstrates that the morphologies of giant Ly$\alpha$ nebulae can be used to understand and study the geometry of high redshift AGNs on circum-nuclear scales and it lays the foundation for future studies using much larger statistical samples., Comment: 15 pages, 13 figures, accepted for publication in MNRAS

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

During the last years, Ly$\alpha$ nebulae have been routinely detected around high-z, radio-quiet quasars (RQQs) thanks to the advent of sensitive integral field spectrographs. Constraining the physical properties of the Ly$\alpha$ nebulae is crucial for a full understanding of the circum-galactic medium (CGM), which is a venue of feeding and feedback processes. The most luminous quasars are privileged test-beds to study these processes, given their large ionizing fluxes and dense CGM environments in which they are expected to be embedded. We aim at characterizing the rest-frame UV emission lines in the CGM around a hyper-luminous, broad emission line, RQQ at z~3.6, that exhibits powerful outflows at both nuclear and host galaxy scales. We analyze VLT/MUSE observations of the quasar J1538+08 and perform a search for extended UV emission lines to characterize its morphology, emissivity, kinematics and metal content. We report the discovery of a very luminous ($\sim2 \times10^{44}~erg~s^{-1}$), giant Ly$\alpha$ nebula and a likely associated extended CIV nebula. The Ly$\alpha$ nebula emission exhibits moderate blueshift compared with the quasar systemic redshift and large average velocity dispersion ($\sigma_{v}$ ~700 $km~s^{-1}$) across the nebula, while the CIV nebula shows $\sigma_{v}$~$350~km~s^{-1}$. The Ly$\alpha$ line profile exhibits a significant asymmetry towards negative velocity values at 20-30 kpc south of the quasar and is well parameterized by two Gaussian components: a narrow ($\sigma$~$470~km~s^{-1}$) systemic one plus a broad ($\sigma$~1200 $km~s^{-1}$), blueshifted (~1500 $km~s^{-1}$) one. Our analysis of the MUSE observation of J1538+08 reveals metal-enriched CGM around this hyper-luminous quasar and our detection of blueshifted emission in the line profile of the Ly$\alpha$ nebula suggests that powerful nuclear outflows can propagate through the CGM over tens of kpc., Comment: 14 pages, 16 figures, 2 tables. Accepted for publication in A&A Journal

We report the serendipitous detection of an H$_{2}$-bearing damped Lyman-$��$ absorber at z = 0.576 in the spectrum of the QSO J0111-0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from HST-COS in the far-ultraviolet reveal a damped absorber with log[N(HI)/cm^-2] = 20.1 +/- 0.2 and log[N(H$_{2}$)/cm^-2] = 18.97 (-0.06, +0.05). The diffuse molecular gas is found in two velocity components separated by dv = 60 km/s, with >99.9% of the total H$_{2}$ column density concentrated in one component. At a metallicity of $\approx$ 50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio $��_{\text{O}} \approx$ 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d, 19 pages, 6 figures. Accepted for publication in ApJ

The observed properties of the Lyman-$\alpha$ (Ly$\alpha$) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Ly$\alpha$ spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at $z=6.532$ with moderate Ly$\alpha$ equivalent width (EW$_0\approx38$ {\AA}). These data are combined with deep resolved [CII]$_{\rm 158 \mu m}$ spectroscopy obtained with ALMA and UV imaging from {\it HST} and we also detect UV continuum with MUSE. Ly$\alpha$ emission is clearly detected with S/N $\approx40$ and FWHM of 374 km s$^{-1}$. Ly$\alpha$ and [CII] are similarly extended beyond the UV, with effective radius r$_{\rm eff} = 2.1\pm0.2$ kpc for a single exponential model or r$_{\rm eff, Ly\alpha, halo} = 3.45^{+1.08}_{-0.87}$ kpc when measured jointly with the UV continuum. The Ly$\alpha$ profile is broader and redshifted with respect to the [CII] line (by 213 km s$^{-1}$), but there are spatial variations that are qualitatively similar in both lines and coincide with resolved UV components. This suggests that the emission originates from two components with plausibly different HI column densities. We place VR7 in the context of other galaxies at similar and lower redshift. The Ly$\alpha$ halo scale length is similar at different redshifts and velocity shifts with respect to the systemic are typically smaller. Overall, we find little indications of a more neutral vicinity at higher redshift. This means that the local ($\sim 10$ kpc) neutral gas conditions that determine the observed Ly$\alpha$ properties in VR7 resemble the conditions in post-re-ionisation galaxies., Comment: 13 pages, 10 figures. Accepted for publication in MNRAS

We present a study of the galaxy environment of 9 strong HI+CIV absorption line systems ($16.2, Comment: 19 pages (+2 pages appendices), 19 figures (+4 in appendices). Submitted to MNRAS

Post starburst E+A galaxies show indications of a powerful starburst that was quenched abruptly. Their disturbed, bulge-dominated morphologies suggest that they are merger remnants. The more massive E+A galaxies are suggested to be quenched by AGN feedback, yet little is known about AGN-driven winds in this short-lived phase. We present spatially-resolved IFU spectroscopy by the Keck Cosmic Web Imager of SDSS J003443.68+251020.9, at z=0.118. The system consists of two galaxies, the larger of which is a post starburst E+A galaxy hosting an AGN. Our modelling suggests a 400 Myrs starburst, with a peak star formation rate of 120 Msun/yr. The observations reveal stationary and outflowing gas, photoionized by the central AGN. We detect gas outflows to a distance of 17 kpc from the central galaxy, far beyond the region of the stars (about 3 kpc), inside a conic structure with an opening angle of 70 degrees. We construct self-consistent photoionization and dynamical models for the different gas components and show that the gas outside the galaxy forms a continuous flow, with a mass outflow rate of about 24 Msun/yr. The gas mass in the flow, roughly $10^9$ Msun, is larger than the total gas mass within the galaxy, some of which is outflowing too. The continuity of the flow puts a lower limit of 60 Myrs on the duration of the AGN feedback. Such AGN are capable of removing, in a single episode, most of the gas from their host galaxies and expelling enriched material into the surrounding CGM., Comment: submitted to MNRAS; comments are welcome!

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

This paper presents a study of the galactic environment of a chemically-pristine (, Comment: 13 pages, 4 figures, published in MNRAS

Deep optical spectroscopic surveys of galaxies provide a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at z ∼ 2 − 4.5. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble Deep Field South, Ultra Deep Field, COSMOS, and several quasar fields with other publicly available data from VLT/VIMOS and VLT/FORS2 to construct a catalogue of He II λ1640 emitters at z ≳ 2. The deepest areas of our MUSE pointings reach a 3σ line flux limit of 3.1 × 10−19 erg s−1 cm−2. After discarding broad-line active galactic nuclei, we find 13 He II λ1640 detections from MUSE with a median MUV = −20.1 and 21 tentative He II λ1640 detections from other public surveys. Excluding Lyα, all except two galaxies in our sample show at least one other rest-UV emission line, with C III] λ1907, λ1909 being the most prominent. We use multi-wavelength data available in the Hubble legacy fields to derive basic galaxy properties of our sample through spectral energy distribution fitting techniques. Taking advantage of the high-quality spectra obtained by MUSE (∼10 − 30 h of exposure time per pointing), we use photo-ionisation models to study the rest-UV emission line diagnostics of the He II λ1640 emitters. Line ratios of our sample can be reproduced by moderately sub-solar photo-ionisation models, however, we find that including effects of binary stars lead to degeneracies in most free parameters. Even after considering extra ionising photons produced by extreme sub-solar metallicity binary stellar models, photo-ionisation models are unable to reproduce rest-frame He II λ1640 equivalent widths (∼0.2 − 10 Å), thus additional mechanisms are necessary in models to match the observed He II λ1640 properties.

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

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

Theory suggests that there are two primary modes of accretion through which dark-matter halos acquire the gas to form and fuel galaxies: hot- and cold-flow accretion. In cold-flow accretion, gas streams along cosmic web filaments to the centre of the halo, allowing for the efficient delivery of star-forming fuel. Recently, two quasar-illuminated H i Lyman ɑ (Lyα)-emitting objects were reported to have properties of cold, rotating structures1,2. However, the spatial and spectral resolution available was insufficient to constrain the radial flows associated with connecting filaments. With the Keck Cosmic Web Imager (KCWI)3, we now have eight times the spatial resolution, permitting the detection of these inspiralling flows. To detect these inflows, we introduce a suite of models that incorporate zonal radial flows, demonstrate their performance on a numerical simulation that exhibits cold-flow accretion, and show that they are an excellent match to KCWI velocity maps of two Lyα emitters observed around high-redshift quasars. These multi-filament inflow models kinematically isolate zones of radial inflow that correspond to extended filamentary emission. The derived gas flux and inflow path is sufficient to fuel the inferred central galaxy star-formation rate and angular momentum. Thus, our kinematic emission maps provide strong evidence that the inflow of gas from the cosmic web is building galaxies at the peak of star formation.

The well-known quasar SDSS J095253.83+011421.9 (J0952+0114) at z=3.02 has one of the most peculiar spectra discovered so far, showing the presence of narrow Ly$\alpha$ and broad metal emission lines. Although recent studies have suggested that a Proximate Damped Ly$\alpha$ system (PDLA) causes this peculiar spectrum, the origin of the gas associated with the PDLA is unknown. Here we report the results of MUSE observations that reveal a new giant ($\approx$ 100 physical kpc) Lyman $\alpha$ nebula. The detailed analysis of the Ly$\alpha$ velocity, velocity dispersion, and surface brightness profiles suggests that the J0952+0114 Ly$\alpha$ nebula shares similar properties of other QSO nebulae previously detected with MUSE, implying that the PDLA in J0952+0144 is covering only a small fraction of the QSO emission solid angle. We also detected bright and spectrally narrow CIV$\lambda$1550 and HeII$\lambda$1640 extended emission around J0952+0114 with velocity centroids similar to the peak of the extended and central narrow Ly$\alpha$ emission. The presence of a peculiarly bright, unresolved, and relatively broad HeII$\lambda$1640 emission in the central region at exactly the same PDLA redshift hints at the possibility that the PDLA originates in a clumpy outflow with a bulk velocity of about 500 km/s. The smaller velocity dispersion of the large scale Ly$\alpha$ emission suggests that the high-speed outflow is confined to the central region. Lastly, the derived spatially resolved HeII/Ly$\alpha$ and CIV/Ly$\alpha$ maps show a positive gradient with the distance to the QSO hinting at a non-homogeneous ionization parameter distribution., Comment: 17 pages, 13 figures and 2 tables; Accepted for publication in ApJ

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 report the discovery of six spatially extended (10-100 kpc) line-emitting nebulae in the z=0.57 galaxy group hosting PKS0405-123, one of the most luminous quasars at z, 9 pages, 3 figures, 2 tables. Accepted to ApJ Letters

This article is an erratum for:[https://doi.org/10.1051/0004-6361/201834565]​​​​​​​

We investigate the ultraviolet (UV) spectral properties of faint Lyman-$\alpha$ emitters (LAEs) in the redshift range 2.93. We compute various averaged spectra of LAEs sub-sampled on the basis of their observational (e.g., Ly$\alpha$ strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We search for UV spectral features other than Ly$\alpha$, such as higher-ionization nebular emission lines and absorption features. We successfully observe the OIII]1666 and CIII]909 collisionally excited emission lines and the HeII1640 recombination feature, as well as the resonant CIV1550 doublet either in emission or P-Cygni. We compare the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly$\alpha$ equivalent widths, fainter UV magnitudes, bluer UV spectral slopes and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z>2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, low-mass and faint LAEs. We publicly release the stacked spectra as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope., Comment: 26 pages, 18 figures. Accepted for publication in A&A

We present an IGM H I tomographic map in a survey volume of 16 x 19 x 131 h(-3) comoving Mpc(3) (cMpc(3)) centered at MAMMOTH-1 nebula and three neighboring quasars at z = 2.3. The MAMMOTH-1 nebula is an enormous Ly alpha nebula (ELAN), hosted by a type-II quasar dubbed MAMMOTH1-QSO, that extends over 1 h(-1) cMpc with no clear physical origin. Here we investigate the H I-gas distribution around MAMMOTH1-QSO with the ELAN and three neighboring type-I quasars, making the IGM H I tomographic map with a spatial resolution of 2.6 h(-1) cMpc. Our H I tomographic map is reconstructed with H I Lya forest absorption of bright background objects at z = 2.4-2.9: one eBOSS quasar and 16 Keck/LRIS galaxy spectra. We estimate the radial profile of H I overdensity for MAMMOTH1-QSO, and find that MAMMOTH1-QSO resides in a volume with fairly weak H I absorption. This suggests that MAMMOTH1-QSO may have a proximity zone where quasar illuminates and photoionizes the surrounding H I gas and suppresses H I absorption, and that the ELAN is probably a photoionized cloud embedded in the cosmic web. The H I radial profile of MAMMOTH1-QSO is very similar to those of three neighboring type-I quasars at z = 2.3, which is compatible with the AGN unification model. We compare the distributions of the H I absorption and star-forming galaxies in our survey volume, and identify a spatial offset between density peaks of star-forming galaxies and H I gas. This segregation may suggest anisotropic UV background radiation created by star-forming galaxy density fluctuations. (© 2020 The American Astronomical Society). ISSN:0004-637X ISSN:2041-8213

We present spatially resolved maps of six individually-detected Lyman alpha haloes (LAHs) as well as a first statistical analysis of the Lyman alpha (Lya) spectral signature in the circum-galactic medium of high-redshift star-forming galaxies using MUSE. Our resolved spectroscopic analysis of the LAHs reveals significant intrahalo variations of the Lya line profile. Using a three-dimensional two-component model for the Lya emission, we measure the full width at half maximum (FWHM), the peak velocity shift and the asymmetry of the Lya line in the core and in the halo of 19 galaxies. We find that the Lya line shape is statistically different in the halo compared to the core for ~40% of our galaxies. Similarly to object-by-object based studies and a recent resolved study using lensing, we find a correlation between the peak velocity shift and the width of the Lya line both at the interstellar and circum-galactic scales. While there is a lack of correlation between the spectral properties and the spatial scale lengths of our LAHs, we find a correlation between the width of the line in the LAH and the halo flux fraction. Interestingly, UV bright galaxies show broader, more redshifted and less asymmetric Lya lines in their haloes. The most significant correlation found is for the FWHM of the line and the UV continuum slope of the galaxy, suggesting that the redder galaxies have broader Lya lines. The generally broad and red line shapes found in the halo component suggests that the Lya haloes are powered either by scattering processes through an outflowing medium, fluorescent emission from outflowing cold clumps of gas, or a mix of both. Considering the large diversity of the Lya line profiles observed in our sample and the lack of strong correlation, the interpretation of our results is still broadly open and underlines the need for realistic spatially resolved models of the LAHs., Comment: 17+4 pages, 12+3 figures, 2+1 tables, accepted for publication in A&A

The Lyman alpha (lya) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km/s compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics and correlations with quasar absorption lines when only lya is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the lya line profile. We use spectroscopic observations of Lyman-Alpha Emitters (LAEs) for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z~3 and z~6 as part of various Multi Unit Spectroscopic Explorer (MUSE) Guaranteed Time Observations (GTO). We also include a compilation of spectroscopic lya data from the literature spanning a wide redshift range (z~0-8). First, restricting our analysis to double-peaked lya spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, Vpeak, and the separation of the peaks. Secondly, we find a correlation between Vpeak and the full width at half maximum of the lya line. Fitting formulas, to estimate systemic redshifts of galaxies with an accuracy of +-100 km/s when only the lya emission line is available, are given for the two methods., Comment: letter, accepted for publication in MNRAS

The Slug Nebula is one of the largest and most luminous Lyman-alpha (LyA) nebulae discovered to date, extending over 450 kiloparsecs (kpc) around the bright quasar UM287 at z=2.283. Characterized by high surface brightnesses over intergalactic scales, its LyA emission may either trace high-density ionized gas ("clumps") or large column densities of neutral material. To distinguish between these two possibilities, information from a non-resonant line such as Halpha is crucial. Therefore, we analyzed a deep MOSFIRE observation of one of the brightest LyA emitting regions in the Slug Nebula with the goal of detecting associated Halpha emission. We also obtained a deep, moderate resolution LyA spectrum of the nearby brightest region of the Slug. We detected an Halpha flux of F_(Halpha)= 2.62 +/- 0.47 x 10^-17 erg/cm^2/s (SB_(Halpha)=2.70 +/- 0.48 x 10^-18 erg/cm^2/s/sq") at the expected spatial and spectral location. Combining the Halpha detection with its corresponding LyA flux (determined from the narrow-band imaging) we calculate a flux ratio of F_(LyA_/F_(Halpha)= 5.5 +/- 1.1. The presence of a skyline at the location of the Halpha emission decreases the signal to noise ratio of the detection and our ability to put stringent constraints on the Halpha kinematics. Our measurements argue for the origin of the LyA emission being recombination radiation, suggesting the presence of high-density ionized gas. Finally, our high-resolution spectroscopic study of the LyA emission does not show evidence of a rotating disk pattern and suggest a more complex origin for at least some parts of the Slug Nebula., 17 pages, 9 figures, final version including referee's comments after acceptance

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$\alpha$ 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$\alpha$ 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 $240\,\mathrm{\AA}$ 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., Comment: 28 pages, 13 figures, 5 tables, submitted to ApJ

International audience; Using an ultra-deep blind survey with the MUSE integral field spectrograph on the European Southern Observatory Very Large Telescope, we obtain spectroscopic redshifts to a depth never before explored: galaxies with observed magnitudes m AB 30-32. Specifically, we detect objects via Lyα emission at 2.9

In a recent paper we reported on the detection of a diffuse H α glow in the outskirts of the nearby, edge-on disc galaxy UGC 7321 observed with the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope. By interpreting the H α emission as fluorescence arising from hydrogen ionized by an external (i.e. extragalactic) radiation field, we estimated the UV background (UVB) intensity in terms of H I ionization rate (per ion) at z ≃ 0 to be in the range ΓH I ∼ 6 − 8 × 10−14 s−1. In the present work, by performing radiative transfer calculations over a large set of models of the gaseous disc of UGC 7321, we refine our estimate and through an MCMC analysis derive a value for the photoionization rate of ΓH i = 7.27+−229390 × 10−14 s−1. In particular, our analysis demonstrates that this value is robust against large variations in the galaxy model and that the uncertainties are mainly driven by the errors associated with the observed H α surface brightness. Our measurement is consistent with several recent determinations of the same quantity by a completely independent technique (i.e. flux decrement analysis of the Lyα forest), and support the notion that the low-redshift UVB is largely dominated by active galactic nuclei, possibly with no need of further contribution from star-forming galaxies

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

In this work we report deep MUSE observations of a broad absorption line (BAL) quasar at z ~ 5, revealing a Lyα nebula with a maximum projected linear size of ~60 kpc around the quasar (down to our 2σ SB limit per layer of ~ 9 × 10-19 erg s-1 cm-2 arcsec-2 for a 1 arcsec2 aperture). After correcting for the cosmological surface brightness dimming, we find that our nebula, at z~5, has an intrinsically less extended Lyα emission than nebulae at lower redshift. However, such a discrepancy is greatly reduced when referring to comoving distances, which take into account the cosmological growth of dark matter (DM) haloes, suggesting a positive correlation between the size of Lyα nebulae and the sizes of DM haloes/structures around quasars. Differently from the typical nebulae around radio-quiet non-BAL quasars, in the inner regions (~10 kpc) of the circumgalactic medium of our source, the velocity dispersion of the Lyα emission is very high (FWHM > 1000 km s-1), suggesting that in our case we may be probing outflowing material associated with the quasar.

We report the discovery of a 10^4 kpc^2 gaseous structure detected in [OII] in an over-dense region of the COSMOS-Gr30 galaxy group at z~0.725 thanks to deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse ionised gas to be of the order of (~5+-3)x10^10 Msun and explore its physical properties to understand its origin and the source(s) of the ionisation. The MUSE data allow the identification of a dozen of group members embedded in this structure from emission and absorption lines. We extracted spectra from small apertures defined for both the diffuse ionised gas and the galaxies. We investigated the kinematics and ionisation properties of the various galaxies and extended gas regions thanks to line diagnostics (R23, O32 and [OIII]/H\beta) available within the MUSE wavelength range. We compared these diagnostics to photo-ionisation models and shock models. The structure is divided in two kinematically distinct sub-structures. The most extended sub-structure of ionised gas is likely rotating around a massive galaxy and displays filamentary patterns linking some galaxies. The second sub-structure links another massive galaxy hosting an Active Galactic Nucleus to a low mass galaxy but also extends orthogonally to the AGN host disk over ~35 kpc. This extent is likely ionised by the AGN itself. The location of small diffuse regions in the R23 vs. O32 diagram is compatible with photo-ionisation. However, the location of three of these regions in this diagram (low O32, high R23) can also be explained by shocks, which is supported by their large velocity dispersions. One edge-on galaxy shares the same properties and may be a source of shocks. Whatever the hypothesis, the extended gas seems to be non primordial. We favour a scenario where the gas has been extracted from galaxies by tidal forces and AGN triggered by interactions between at least the two sub-structures., Comment: 21 pages, 12 figures, 3 tables, accepted for publication in A&A (27 October 2017)

We report the detection of extended Lyα haloes around 145 individual star-forming galaxies at redshifts 3 ≤ z ≤ 6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer (MUSE) at ESO-VLT. Our sample consists of continuum-faint (− 15 ≥ MUV ≥ −22) Lyα emitters (LAEs). Using a 2D, two-component (continuum-like and halo) decomposition of Lyα emission assuming circular exponential distributions, we measure scale lengths and luminosities of Lyα haloes. We find that 80% of our objects having reliable Lyα halo measurements show Lyα 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 Lyα haloes in our sample is ≈4.5 kpc with a few haloes exceeding 10 kpc. By comparing the maximal detected extent of the Lyα emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Lyα emission of our selected sample of Lyα emitters probes a significant portion of the cold circum-galactic medium of these galaxies (>50% in average). This result therefore shows that there must be significant HI reservoirs in the circum-galactic medium and reinforces the idea that Lyα haloes are ubiquitous around high-redshift Lyα emitting galaxies. Our characterization of the Lyα haloes indicates that the majority of the Lyα flux comes from the halo (≈65%) and that their scale lengths seem to be linked to the UV properties of the galaxies (sizes and magnitudes). We do not observe a significant Lyα halo size evolution with redshift, although our sample for z> 5 is very small. We also explore the diversity of the Lyα line profiles in our sample and we find that the Lyα lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km s-1. While the FWHM does not seem to be correlated to the Lyα scale length, most compact Lyα haloes and those that are not detected with high significance tend to have narrower Lyα profiles (-1). Finally, we investigate the origin of the extended Lyα emission but we conclude that our data do not allow us to disentangle the possible processes, i.e. scattering from star-forming regions, fluorescence, cooling radiation from cold gas accretion, and emission from satellite galaxies.

All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-alpha emission at redshift z ~ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ~10^-7, implying a physical connection between Lyman-alpha nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (~ 10^11 solar masses) of cool dense (volume density ~1 cm^-3) gas, which is in conflict with current cosmological simulations., accepted for publication in Science. Main text: 11 pages, 4 figures; Supplementary Online Material: 52 pages, 10 figures, 6 tables

We present a measurement of the fraction of Lyman $\alpha$ (Ly$\alpha$) emitters ($X_{\rm{Ly} \alpha}$) amongst HST continuum-selected galaxies at $3, Comment: 10 pages, 5 figures (MNRAS, updated as per version in press)

The radio-quiet quasar Q2059-360 at redshift $z=3.08$ is known to be close to a small Lyman $\alpha$ blob (LAB) and to be absorbed by a proximate damped Ly$\alpha$ (PDLA) system. Here, we present the Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopy follow-up of this quasi-stellar object (QSO). Our primary goal is to characterize this LAB in detail by mapping it both spatially and spectrally using the Ly$\alpha$ line, and by looking for high-ionization lines to constrain the emission mechanism. Combining the high sensitivity of the MUSE integral field spectrograph mounted on the Yepun telescope at ESO-VLT with the natural coronagraph provided by the PDLA, we map the LAB down to the QSO position, after robust subtraction of QSO light in the spectral domain. In addition to confirming earlier results for the small bright component of the LAB, we unveil a faint filamentary emission protruding to the south over about 80 pkpc (physical kpc); this results in a total size of about 120 pkpc. We derive the velocity field of the LAB (assuming no transfer effects) and map the Ly$\alpha$ line width. Upper limits are set to the flux of the N V $\lambda 1238-1242$, C IV $\lambda 1548-1551$, He II $\lambda 1640$, and C III] $\lambda 1548-1551$ lines. We have discovered two probable Ly$\alpha$ emitters at the same redshift as the LAB and at projected distances of 265 kpc and 207 kpc from the QSO; their Ly$\alpha$ luminosities might well be enhanced by the QSO radiation. We also find an emission line galaxy at $z=0.33$ near the line of sight to the QSO. This LAB shares the same general characteristics as the 17 others surrounding radio-quiet QSOs presented previously. However, there are indications that it may be centered on the PDLA galaxy rather than on the QSO., Comment: Accepted for publication in Astronomy & Astrophysics; 16 pages, 19 figures

Emission signatures from galactic winds provide an opportunity to directly map the outflowing gas, but this is traditionally challenging because of the low surface brightness. Using deep observations (27 hours) of the Hubble Deep Field South from the Multi Unit Spectroscopic Explorer (MUSE) instrument, we identify signatures of an outflow in both emission and absorption from a spatially resolved galaxy at z = 1.29 with a stellar mass M* = 8 x 10^9 Msun, star formation rate SFR = 77 Msun/yr, and star formation rate surface brightness 1.6 Msun/kpc^2 within the [OII] half-light radius R_1/2,[OII] = 2.76 +- 0.17 kpc. From a component of the strong resonant MgII and FeII absorptions at -350 km/s, we infer a mass outflow rate that is comparable to the star formation rate. We detect non-resonant FeII* emission, at lambda 2626, 2612, 2396, and 2365, at 1.2-2.4-1.5-2.7 x 10^-18 egs s-1 cm-2 respectively. These flux ratios are consistent with the expectations for optically thick gas. By combining the four non-resonant FeII* emission lines, we spatially map the FeII* emission from an individual galaxy for the first time. The FeII* emission has an elliptical morphology that is roughly aligned with the galaxy minor kinematic axis, and its integrated half-light radius R_1/2,FeII* = 4.1 +- 0.4 kpc is 50% larger than the stellar continuum (R_1/2,* = 2.34 +- 0.17 kpc) or the [OII] nebular line. Moreover, the FeII* emission shows a blue wing extending up to -400 km/s, which is more pronounced along the galaxy minor kinematic axis and reveals a C-shaped pattern in a p-v diagram along that axis. These features are consistent with a bi-conical outflow., 13 pages, 6 figures, 4 tables, submitted to A&A - comments welcome

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

Several decades of observations and discoveries have shown that high-redshift AGN and massive galaxies are often surrounded by giant Lyα nebulae extending in some cases up to 500 kpc in size. In this chapter, I review the properties of the such nebulae discovered at z > 2 and their connection with gas flows in and around galaxies and their halos. In particular, I show how current observations are used to constrain the physical properties and origin of the emitting gas in terms of the Lyα photon production processes and kinematical signatures. The emerging picture from these studies suggests that recombination radiation is the most viable scenario to explain the observed Lyα luminosities and Surface Brightness for the large majority of the nebulae and imply that a significant amount of dense (n > 1 cm−3), ionized and cold (T ∼ 104 K) “clumps” should be present within and around the halos of massive galaxies. Spectroscopic studies suggest that, among the giant Lyα nebulae, the one associated with radio-loud AGN should have kinematics dominated by strong, ionized outflows within at least the inner 30–50 kpc. Radio-quiet nebulae instead present more quiescent kinematics compatible with “stationary” situation and, in some cases, suggestive of rotating structures, while definitive evidences for gas accretion from the Lyα emission are not clearly detected in current data. Deep surveys currently ongoing using other bright, non-resonant line such as Hα and He II 1640 will be crucial to search for clearer signatures of cosmological gas accretion onto galaxies and AGN.

We use hydrodynamic simulations post-processed with the radiative-transfer code RADAMESH to assess recent claims that the low HeII opacity observed in z>3 quasar spectra may be incompatible with models of HeII reionization driven by the observed population of active galactic nuclei (AGNs). In particular, building upon our previous work, we consider an early population of sources and start the radiative-transfer calculation at redshifts z>=5. Our model faithfully reproduces the emissivity of optically selected AGNs as inferred from measurements of their luminosity function. We find that HeII reionization is very extended in redshift ({\Delta} z>=2) and highly spatially inhomogeneous. In fact, mock spectra extracted from the simulations show a large variability in the evolution of the HeII effective optical depth within chunks of size {\Delta} z=0.04. Regions with low opacity ({\tau}^{eff}_{HeII}, Comment: 12 pages, 8 figures. Matches version accepted for publication in MNRAS