Into the Lyα jungle: exploring the circumgalactic medium of galaxies at z ∼ 4 − 5 with MUSE

We present a study of the galaxy environment of 9 strong H I+C IV absorption line systems (16.2 < log(N(HI)) < 21.2) spanning a wide range in metallicity at z ∼ 4 − 5, using MUSE integral field and X-Shooter spectroscopic data collected in a z ≈ 5.26 quasar field. We identify galaxies within a 250 kpc and ±1000 km s−1 window for 6 out of the 9 absorption systems, with 2 of the absorption line systems showing multiple associated galaxies within the MUSE field of view. The space density of Lyα emitting galaxies (LAEs) around the H I and C IV systems is ≈10 − 20 times the average sky density of LAEs given the flux limit of our survey, showing a clear correlation between the absorption and galaxy populations. Further, we find that the strongest C IV systems in our sample are those that are most closely aligned with galaxies in velocity space, i.e. within velocities of ±500 km s−1. The two most metal poor systems lie in the most dense galaxy environments, implying we are potentially tracing gas that is infalling for the first time into star-forming groups at high redshift. Finally, we detect an extended Lyα nebula around the z ≈ 5.26 quasar, which extends up to ≈50 kpc at the surface brightness limit of 3.8 × 10−18 erg s−1 cm−2 arcsec−2. After scaling for surface brightness dimming, we find that this nebula is centrally brighter, having a steeper radial profile than the average for nebulae studied at z ∼ 3 and is consistent with the mild redshift evolution seen from z ≈ 2

The Evolution of O i over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium

We present a survey for metal absorption systems traced by neutral oxygen over 3.2 0.05 Å, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7–4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ~ 6 than at lower redshifts. Absorption from highly ionized metals traced by C iv is also weaker in higher-redshift O i systems, supporting this picture. The evolution of O i absorbers implies that metal-enriched circumgalactic gas at z ~ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch

Measuring the photo-ionization rate, neutral fraction and mean free path of HI ionizing photons at 4.9≤z≤6.0 from a large sample of XShooter and ESI spectra

We measure the mean free path (⁠λmfp,HI⁠), photo-ionization rate (⁠⟨ΓHI⟩⁠) and neutral fraction (⁠⟨fHI⟩⁠) of hydrogen in 12 redshift bins at 4.85 < z < 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modeled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (EX-CITE). EX-CITE uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution ΓHI fluctuation models. Our simulation with EX-CITE shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modeling the Lyα forest and comparing the effective optical depth (⁠τeff,HI⁠) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modeling parameters, observational systematics and cosmic variance. Our best fit parameters show significant evolution with redshift such that λmfp,HI and ⟨fHI⟩ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our λmfp,HI⁠, ⟨ΓHI⟩ and ⟨fHI⟩ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best fit parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best fit model that matches the τeff,HI distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters

Evidence of First Stars-enriched Gas in High-redshift Absorbers

The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ∼ 3–4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars

The MUSE Ultra Deep Field (MUDF). III. Hubble Space Telescope WFC3 Grism Spectroscopy and Imaging

We present extremely deep Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) observations of the MUSE Ultra Deep Field. This unique region of the sky contains two quasars at z ≈ 3.22 that are separated by only ∼500 kpc, providing a stereoscopic view of gas and galaxies in emission and absorption across ∼10 billion years of cosmic time. We have obtained 90 orbits of HST WFC3 G141 near-infrared grism spectroscopy of this field in a single pointing, as well as 142 hr of optical spectroscopy with the Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE). The WFC3 (F140W, F125W, and F336W) and archival WFPC2 (F702W and F450W) imaging provides five-filter photometry that we use to detect 3375 sources between z ≈ 0-6, including 1536 objects in a deep central pointing with both spectroscopic and photometric coverage. The F140W and F336W mosaics reach exceptional depths of m AB ≈ 28 and 29, respectively, providing near-infrared and rest-frame ultraviolet information for 1580 sources, and we reach 5σ continuum detections for objects as faint as m AB ≈ 27 in the grism spectra. The extensive wavelength coverage of MUSE and WFC3 allows us to measure spectroscopic redshifts for 419 sources, down to galaxy stellar masses of log(M/M ⊙) ≈7 at z ≈ 1-2. In this publication, we provide the calibrated HST data and source catalogs as High Level Science Products for use by the community, which includes photometry, morphology, and redshift measurements that enable a variety of studies aimed at advancing our models of galaxy formation and evolution in different environments.</p

Sub-damped Lyman α systems in the XQ-100 survey – II. Chemical evolution at 2.4 ≤ z ≤ 4.3

We present the measured gas-phase metal column densities in 155 sub-damped Ly α systems (subDLAs) with the aim to investigate the contribution of subDLAs to the chemical evolution of the Universe. The sample was identified within the absorber-blind XQ-100 quasar spectroscopic survey over the redshift range 2.4 ≤ zabs ≤ 4.3. Using all available column densities of the ionic species investigated (mainly C IV, Si II, Mg II, Si IV, Al II, Fe II, C II, and O I; in order of decreasing detection frequency), we estimate the ionization-corrected gas-phase metallicity of each system using Markov chain Monte Carlo techniques to explore a large grid of CLOUDY ionization models. Without accounting for ionization and dust depletion effects, we find that the H I-weighted gas-phase metallicity evolution of subDLAs is consistent with damped Ly α systems (DLAs). When ionization corrections are included, subDLAs are systematically more metal poor than DLAs (between ≈0.5σ and ≈3σ significance) by up to ≈1.0 dex over the redshift range 3 ≤ zabs ≤ 4.3. The correlation of gas phase [Si/Fe] with metallicity in subDLAs appears to be consistent with that of DLAs, suggesting that the two classes of absorbers have a similar relative dust depletion pattern. As previously seen for Lyman limit systems, the gas phase [C/O] in subDLAs remains constantly solar for all metallicities indicating that both subDLAs and Lyman limit systems could trace carbon-rich ejecta, potentially in circumgalactic environments

Accurate Dust Temperature and Star Formation Rate in the Most Luminous z &gt; 6 Quasar in the Hyperluminous Quasars at the Epoch of Reionization (HYPERION) Sample

Funder: Istituto Nazionale di Astrofisica (INAF); Grant(s): “Progetti di Ricerca di Rilevante Interesse Nazionale” (PRIN), Bando 2019 “Piercing through the clouds: a multiwavelength study of obscured accretion in nearby supermassive black holes”Abstract We present ALMA Band 9 continuum observation of the ultraluminous quasi-stellar object (QSO) SDSS J0100+2802 providing a ∼10σ detection at ∼670 GHz. SDSS J0100+2802 is the brightest QSO with the most massive supermassive black hole (SMBH) known at z &gt; 6, and we study its dust spectral energy distribution in order to determine the dust properties and the star formation rate (SFR) of its host galaxy. We obtain the most accurate estimate so far of the temperature, mass, and emissivity index of the dust, which are T dust = 48.4 ± 2.3 K, M dust = (2.29 ± 0.83) × 107 M ⊙, and β = 2.63 ± 0.23, respectively. This allows us to measure the SFR with the smallest statistical error for this QSO, SFR = 265 ± 32 M ⊙yr−1. Our results enable us to evaluate the relative growth of the SMBH and host galaxy of J0100+2802. We find that the SMBH is dominating the process of black-hole galaxy growth in this QSO at z = 6.327, when the universe was 865 Myr old. Such unprecedented constraints on the host-galaxy SFR and dust temperature can only be obtained through high-frequency observations and highlight the importance of ALMA Band 9 to obtain a robust overview of the buildup of the first quasars’ host galaxies at z &gt; 6.</jats:p

First Constraints on Dense Molecular Gas at z = 7.5149 from the Quasar Pōniuā‘ena

Abstract We report the detection of CO(6–5) and CO(7–6) and their underlying continua from the host galaxy of quasar J100758.264+211529.207 (Pōniuā‘ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Pōniuā‘ena belongs to the HYPerluminous quasars at the Epoch of ReionizatION sample of 18 z &gt; 6 quasars selected to be powered by supermassive black holes, which experienced the fastest mass growth in the first cosmic gigayear. The one reported here is the highest-redshift measurement of the cold and dense molecular gas to date. The host galaxy is unresolved, and the line luminosity implies a molecular reservoir of M(H2) = (2.2 ± 0.2) × 1010 M ⊙, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor α = 0.8 M ⊙ ( K km s − 1 pc 2 ) − 1 . We model the cold dust spectral energy distribution to derive a dust mass of M dust = (1.7 ± 0.6) × 108 M ⊙ and thus, a gas-to-dust ratio ∼130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z ∼ 6–7. We use the CO detection to derive an estimate of the cosmic mass density of H2, Ω H 2 ≃ 1.31 × 10 − 5 . This value is in line with the general trend suggested by literature estimates at z &lt; 7 and agrees fairly well with the latest theoretical expectations of nonequilibrium molecular-chemistry cosmological simulations of cold gas at early times.</jats:p

The MUSE Ultra Deep Field (MUDF). III. Hubble Space Telescope WFC3 Grism Spectroscopy and Imaging

We present extremely deep Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) observations of the MUSE Ultra Deep Field. This unique region of the sky contains two quasars at z ≈ 3.22 that are separated by only ∼500 kpc, providing a stereoscopic view of gas and galaxies in emission and absorption across ∼10 billion years of cosmic time. We have obtained 90 orbits of HST WFC3 G141 near-infrared grism spectroscopy of this field in a single pointing, as well as 142 hr of optical spectroscopy with the Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE). The WFC3 (F140W, F125W, and F336W) and archival WFPC2 (F702W and F450W) imaging provides five-filter photometry that we use to detect 3375 sources between z ≈ 0–6, including 1536 objects in a deep central pointing with both spectroscopic and photometric coverage. The F140W and F336W mosaics reach exceptional depths of mAB ≈ 28 and 29, respectively, providing near-infrared and rest-frame ultraviolet information for 1580 sources, and we reach 5σ continuum detections for objects as faint as mAB ≈ 27 in the grism spectra. The extensive wavelength coverage of MUSE and WFC3 allows us to measure spectroscopic redshifts for 419 sources, down to galaxy stellar masses of log(M/M⊙) ≈7 at z ≈ 1–2. In this publication, we provide the calibrated HST data and source catalogs as High Level Science Products for use by the community, which includes photometry, morphology, and redshift measurements that enable a variety of studies aimed at advancing our models of galaxy formation and evolution in different environments