arXiv subjects

Emanuele P. Farina

Publications and source records attributed to Emanuele P. Farina.

At least 19 recordsLinked to original sources

arXiv2026

Nearly pristine gas in a galaxy 1 billion years after the Big Bang

Excitation of carbon and oxygen ions is the primary mechanism by which collapsing gas clouds dissipate heat to form new stars. At early cosmic times, in galaxies with chemically pristine gas, many stars are expected to have masses far larger than the mass of our sun due to the deficit in these elements. We searched for ultra-metal-poor galaxies using their spectroscopic absorption signatures in front of bright background quasars, employing the new GHOST high-resolution spectrograph. Here we report the discovery of the first galaxy containing a reservoir of neutral hydrogen gas with metallicity below the ultra-metal-poor threshold: with a measured carbon-to-hydrogen ratio 11,000 times lower than the Sun, it is the most pristine ever found by a factor of four. UMP-DLA-1 is the only known galaxy with measured carbon and oxygen abundances too low to enable efficient formation of stars with solar mass or below. The low metallicity alone therefore guarantees a top-heavy stellar population, providing a direct view of the chemical composition imprinted by massive low-metallicity stars that perished long before the present day: an elevated oxygen-to-carbon ratio. The abundance pattern of UMP-DLA-1 is likely a close representation of the atomic yields of first- or early second-generation stars.

astro-ph.GA↗

arXiv2026

To be lensed or not to be lensed: on the nature of the alleged high-z lensed quasars J0109-5424 and P170+20

We present a detailed multi-wavelength analysis of two gravitationally lensed z>6 quasar candidates: J0109-5424 and P170+20. Using JWST/NIRSpec near-infrared data from the Aether survey, we demonstrate that J0109-5424 is in fact a FeLoBAL quasar at z=2.07, exhibiting strong iron broad absorption lines that mimic the Lyman break. From the Pabeta emission line, we estimate a black hole mass of 3.9 x 10^8 Msun and a bolometric luminosity of Lbol = 7.7 x 10^45 erg/s for this quasar. Follow-up HST/ACS WFC imaging of P170+20 with the F555W filter, probing emission below the Lyman limit of the quasar, reveals a compact source located 0.09+/-0.04 arcsec from the quasar position. PSF modelling and subtraction yield no evidence for extended emission. This is inconsistent with a foreground galaxy acting as a lens. Furthermore, we obtain Gemini-South/Flamingos 2 near-infrared observations to complement the existing optical Gemini-North/GMOS spectrum of P170+20. Our spectral analysis shows that the observed spectral shape of P170+20 is consistent with a composite quasar and M-dwarf spectrum. However, this interpretation remains uncertain, as a chance alignment between an ultracool dwarf and a quasar within 0.1 arcsec would be unlikely. Overall, our findings establish J0109-5424 as an intermediate redshift source and do not favor the lensed nature of P170+20, although this possibility cannot be conclusively ruled out, highlighting the challenges of selecting lensed quasars at high redshift.

astro-ph.GA↗

arXiv2025

Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys

Luminous quasars at $z>4$ provide key insights into the early Universe. Their rarity necessitates wide-field multi-band surveys to efficiently separate them from the main astrophysical contaminants (i.e., ultracool dwarfs). To expand the sample of high-$z$ quasars, we conducted targeted selections using optical, infrared, and radio surveys, complemented by literature-based quasar candidate catalogs. In this paper, we report the discovery of \nqsos\ new quasars at $4.6 6.5$ quasars we selected, but whose independent discovery has already been published in the literature. Three of the newly discovered quasars are strong radio emitters (L$_{1.4~\rm GHz}$$=0.09-1.0\times$10$^{34}$erg s$^{-1}$ Hz$^{-1}$). Among them, one source at $z=4.71$ exhibits typical blazar-like properties, including a flat radio spectrum, radio-loudness $\sim$1000, and multi-frequency variability. It is also detected by SRG/eROSITA X-ray telescope (f$_{\rm 0.2-2.3keV} \sim 1.3\times10^{-13}$erg s$^{-1}$ cm$^{-2}$). In addition, for seven $6.3 6$ quasars reported in the literature. A $z = 6.3$ quasar exhibits a velocity difference of approximately $9000$ km s$^{-1}$ between the C$\rm IV$ and Mg$\rm II$ emission lines, making it one of the most extreme C$\rm IV$ outflows currently known. Additionally, the sample includes three high-ionization broad absorption line quasars. One of these quasars shows potential evidence of an extremely fast outflow feature, reaching $48000$ km s$^{-1}$.

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arXiv2024

A blazar in the epoch of reionization

Relativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z=6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05-013919.88 at z=7 (Universe's age ~750 Myr), powered by a ~7x10^8 Msun black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios: in one, the jet in J0410-0139 is intrinsically low-power but appears highly luminous due to relativistic beaming, suggesting that most UV-bright quasars at this redshift host jets. Alternatively, if J0410-0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z~7 with properties similar to J0410-0139, a prediction in tension with observed quasar densities based on their UV luminosity function. These results support the hypothesis that rapid black hole growth in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.

astro-ph.GA↗

arXiv2024

Signatures of warm dark matter in the cosmological density fields extracted using Machine Learning

We aim to construct a machine-learning approach that allows for a pixel-by-pixel reconstruction of the intergalactic medium (IGM) density field for various warm dark matter (WDM) models using the Lyman-alpha forest. With this regression machinery, we constrain the mass of a potential WDM particle from observed Lyman-alpha sightlines directly from the density field. We design and train a Bayesian neural network on the supervised regression task of recovering the optical depth-weighted density field $Δ_τ$ as well as its reconstruction uncertainty from the Lyman-alpha forest flux field. We utilise the Sherwood-Relics simulation suite at $4.1\leq z \leq 5.0$ as the main training and validation dataset. Leveraging the density field recovered by our neural network, we construct an inference pipeline to constrain the WDM particle masses based on the probability distribution function of the density fields. We find that our trained Bayesian neural network can accurately recover within a $1σ$ error $\geq 85\%$ of the density field pixels from a validation simulated dataset that encompasses multiple WDM and thermal models of the IGM. When predicting on Lyman-alpha skewers generated using the alternative hydrodynamical code Nyx not included in the training data, we find a $1σ$ accuracy rate $\geq 75\%$. We consider 2 samples of observed Lyman-alpha spectra from the UVES and GHOST instruments, at $z=4.4$ and $z=4.9$ respectively and fit the density fields recovered by our Bayesian neural network to constrain WDM masses. We find lower bounds on the WDM particle mass of $m_{\mathrm{WDM}} \geq 3.8$ KeV and $m_{\mathrm{WDM}} \geq 2.2$ KeV at $2σ$ confidence, respectively. We are able to match current state-of-the-art WDM particle mass constraints using up to 40 times less observational data than Markov Chain Monte Carlo techniques based on the Lyman-alpha forest power spectrum.

astro-ph.CO↗

arXiv2024

QSO MUSEUM II: Search for extended Ly$α$ emission around eight $z \sim 3$ quasar pairs

Extended Ly$α$ emission is routinely found around single quasars (QSO) across cosmic time. However, few studies have investigated how such emission changes in fields with physically associated QSO pairs, which should reside in dense environments and are predicted to be linked through intergalactic filaments. We present VLT/MUSE snapshot observations (45 min./source) to unveil extended Ly$α$ emission on scales of the circumgalactic medium (CGM) around the largest sample of physically associated QSO pairs to date, encompassing 8 pairs (14 observed QSOs) at $z$~3 with $i$-band magnitude between 18 and 22.75. The pairs are either at close (~50-100 kpc, 5 pairs) or wide (~450-500 kpc, 3 pairs) separation with velocity differences of $Δ$v < 2000 km s$^{-1}$. We detect extended emission around 12 of the 14 targeted QSOs and investigate the luminosity, size, kinematics and morphology of these Ly$α$ nebulae. On average, they span 90 kpc and are 2.8 $\times 10^{43}$ erg s$^{-1}$ bright. Irrespective of the QSOs' projected distance, the nebulae often (~45 %) extend toward the other QSO in the pair, leading to asymmetric emission whose flux-weighted centroid is at an offset position from any QSO location. We show that large nebulae are preferentially aligned with the large-scale structure as traced by the two QSOs, and conclude that the cool gas (10$^4$ K) in the CGM traces well the direction of cosmic web filaments. Additionally, the radial profile of the Ly$α$ surface brightness around QSO pairs can be described by a power law with a shallower slope (~$-1.6$) with respect to single QSOs (~$-2$), indicative of increased CGM densities out to large radii and/or enhanced contribution from the intergalactic medium (IGM). The sample presented in this study contains excellent targets for ultra-deep observations to directly study filamentary IGM structures in emission.

astro-ph.GA↗

arXiv2024

Exploring the Mpc Environment of the Quasar ULAS J1342+0928 at z = 7.54

Theoretical models predict that z~6 quasars are hosted in the most massive halos of the underlying dark matter distribution and thus would be immersed in protoclusters of galaxies. However, observations report inconclusive results. We investigate the 1.1 pMpc2 environment of the z = 7.54 luminous quasar ULAS J1342+0928. We search for Lyman-break galaxy candidates (LBG) using deep imaging from the Hubble Space Telescope (HST) in the ACS/F814W, WFC3/F105W/F125W bands, and Spitzer/IRAC at 3.6 $μ$m and 4.5 $μ$m. We report a zphot = $7.69^{+0.33}_{-0.23}$ LBG with magF125W = 26.41 at 223 projected-pkpc from the quasar. We find no HST counterpart to one [CII]-emitter previously found with ALMA at 27 projected-pkpc and $z[CII]=7.5341\pm0.0009$ (Venemans et al. 2020). We estimate the completeness of our LBG candidates using results from CANDELS/GOODS deep blank field searches sharing a similar filter setup. We find that >50% of the z~7.5 LBGs with magF125W >25.5 are missed due to the absence of a filter redward of the Lyman-break in F105W, hindering the UV color accuracy of the candidates. We conduct a QSO-LBG clustering analysis revealing a low LBG excess of $0.46^{+1.52}_{-0.08}$ in this quasar field, consistent with an average or low-density field. Consequently, this result does not present strong evidence of an LBG overdensity around ULAS J1342+0928. Furthermore, we identify two LBG candidates with a zphot matching a confirmed z=6.84 absorber along the line-of-sight to the quasar. All these galaxy candidates are excellent targets for follow-up observations with JWST and/or ALMA to confirm their redshift and physical properties.

astro-ph.GA↗

arXiv2024

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Impact of Galaxies on the CGM Metal Enrichment at z > 6 Using the JWST and VLT

We characterize the multiphase circumgalactic medium and galaxy properties at z = 6.0-6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305-3150 to identify one new metal absorber at z = 6.2713 with multiple transitions (OI, MgI, FeII and CII). They are combined with the published absorbing systems in Davies et al. (2023a) at the same redshift range to form of a sample of nine metal absorbers at z = 6.03 to 6.49. We identify eight galaxies within 1000 km s$^{-1}$ and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [OIII]($λλ$4959, 5007) doublets and H$β$ emission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar mass ranging from 10$^{7.2}$ to 10$^{8.8}M_{\odot}$ and metallicity between 0.02 and 0.4 solar. Notably, the z = 6.2713 system in the J0305-3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances of $α$ elements to iron ([$α$/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [$α$/Fe] ratio. Our modeling of the galaxy's chemical abundance favors a top-heavy stellar initial mass function, and hints that we may be witnessing the contribution of the first generation Population III stars to the CGM at the end of reionization epoch.

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arXiv2023

Circumgalactic Ly$α$ emission around submillimeter-bright galaxies with different quasar contributions

We present VLT/MUSE observations targeting the extended Lyman-$α$ (Ly$α$) emission of five high-redshift ($z\sim$3-4) submillimeter galaxies (SMGs) with increasing quasar (QSO) radiation: two SMGs, two SMGs hosting a QSO, and one SMG hosting a QSO with a SMG companion (QSO+SMG). These sources should be located in dark matter halos of comparable masses (average mass of $M_{\rm DM}\sim10^{12.2}\,{\rm M}_\odot$). We quantify the luminosity and extent of the Ly$α$ emission, together with its kinematics, and examine four Ly$α$ powering mechanisms: photoionization from QSOs/star formation, shocks by galactic/QSO outflows, gravitational cooling radiation, and Ly$α$ photons resonant scattering. We find a variety of Ly$α$ luminosities and extents, with the QSO+SMG system displaying the most extended and bright nebula, followed by the SMGs hosting a QSO, and finally the undetected circumgalactic medium (CGM) of SMGs. This diversity implies that gravitational cooling is unlikely to be the main powering mechanism. We show that photoionization from the QSO and QSO outflows can contribute to power the emission for average densities $n_{\rm H}>0.5\,$cm$^{-3}$. Moreover, the observed Ly$α$ luminosities scale with the QSO's budget of Ly$α$ photons modulo the dust content in each galaxy, highlighting a possible contribution from resonant scattering of QSO's radiation in powering the nebulae. We find larger Ly$α$ linewidths (FWHM$\gtrsim 1200\,$km$\,$s$^{-1}$) than usually reported around radio-quiet systems, pointing to large-scale outflows. A statistical survey targeting similar high-redshift massive systems with known host properties is needed to confirm our findings.

astro-ph.GA↗

arXiv2023

The luminosity-area relation of $z>2$ quasars' Ly$α$ nebulae

Cool ($T\sim10^4$~K) gas is commonly observed around $z>2$ quasars as traced by extended Ly$α$ emission. These large-scale nebulae are usually studied using circularly averaged surface brightness profiles, which suppress information on morphological differences. Here, we revisit the Ly$α$ nebulae around 78 $z\sim2-3$ quasars to obtain a novel estimate of their area and asymmetry using a common redshift-corrected surface-brightness threshold. We find a luminosity-area relation of the form ${{\rm log}(L_{\rm Lyα}^{\rm Neb})=a_1 log({\rm Area^{Neb})+a_0}}$. Most nebulae are symmetric and bright, the most lopsided ones being the faintest and the less extended. The Enormous Lyman-Alpha Nebulae, asymmetric due to the presence of active companions, are the exceptions to this trend. By using simulations able to reproduce $z\sim6$ quasar's nebulae, we show that the observed relation should not vary with redshift. Finally, we discuss possible mechanisms that drive the relation and future work needed to constrain them.

astro-ph.GA↗

arXiv2022

Hydrogen reionisation ends by $z=5.3$: Lyman-$α$ optical depth measured by the XQR-30 sample

The presence of excess scatter in the Ly-$α$ forest at $z\sim 5.5$, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionisation. However, low data quality and systematic uncertainties complicate the use of Ly-$α$ transmission as a precision probe of reionisation's end stages. In this paper, we assemble a sample of 67 quasar sightlines at $z>5.5$ with high signal-to-noise ratios of $>10$ per $\leq 15$ km s$^{-1}$ spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR $>20$ per pixel) spectra of 30 quasars at $z>5.7$. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-$α$ systems. We present improved measurements of the mean Ly-$α$ transmission over $4.9 3.5 σ$). Our results indicate that reionisation-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least $z=5.3$ ($t=1.1$ Gyr after the Big Bang). This is further evidence for a late end to reionisation.

astro-ph.CO↗

arXiv2022

AGN-driven outflows and the formation of Ly$α$ nebulae around high-z quasars

The detection of Ly$α$ nebulae around $z\gtrsim 6$ quasars provides evidence for extended gas reservoirs around the first rapidly growing supermassive black holes. Observations of $z > 6$ quasars can be explained by cosmological models provided that the black holes by which they are powered evolve in rare, massive dark matter haloes. Whether these theoretical models also explain the observed extended Ly$α$ emission remains an open question. We post-process a suite of cosmological, radiation-hydrodynamic simulations targeting a quasar host halo at $z>6$ with the Ly$α$ radiative transfer code RASCAS. A combination of recombination radiation from photo-ionised hydrogen and emission from collisionally excited gas powers Ly$α$ nebulae with a surface brightness profile in close agreement with observations. We also find that, even on its own, resonant scattering of the Ly$α$ line associated to the quasar's broad line region can also generate Ly$α$ emission on $\sim 100 \, \rm kpc$ scales, resulting in comparable agreement with observed surface brightness profiles. Even if powered by a broad quasar Ly$α$ line, Ly$α$ nebulae can have narrow line-widths $\lesssim 1000 \, \rm km \, s^{-1}$, consistent with observational constraints. Even if there is no quasar, we find that halo gas cooling produces a faint, extended Ly$α$ glow. However, to light-up extended Ly$α$ nebulae with properties in line with observations, our simulations unambiguously require quasar-powered outflows to clear out the galactic nucleus and allow the Ly$α$ flux to escape and still remain resonant with halo gas. The close match between observations and simulations with quasar outflows suggests that AGN feedback already operates before $z \, = \, 6$ and confirms that high-$z$ quasars reside in massive haloes tracing overdensities.

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arXiv2022

Constraining galaxy overdensities around three z~6.5 quasars with ALMA and MUSE

We quantify galaxy overdensities around three high-redshift quasars with known [CII] 158um companions: PJ231-20 (z=6.59), PJ308-21 (z=6.24) and J0305-3150 (z=6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMG) with sky separations $0.7'< θ< 2.4'$ from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [CII] emitters in the ALMA pointings and make use of archival MUSE observations to search for Lyman-$α$ Emitters (LAE) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [CII] line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7-6 and [CI] emission lines, we find that four SMGs in the field of PJ231-20 are at z~2.4, which is coincident with the redshift of a Mg II absorber in the quasar rest-frame UV spectrum. We report the discovery of 2 LAEs within <0.6 cMpc of PJ231-20 at the same redshift, indicating a LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Lyman-$α$- and [CII]-emitting galaxies around z>6 quasars and suggest that only wide-field observations, such as MUSE, ALMA or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the Universe.

astro-ph.GA↗

arXiv2021

A Multiwavelength Study of ELAN Environments (AMUSE$^2$). Mass budget, satellites spin alignment and gas infall in a massive $z\sim3$ quasar host halo

The systematic targeting of extended Ly$α$ emission around high-redshift quasars resulted in the discovery of rare and bright Enormous Ly$α$ Nebulae (ELANe) associated with multiple active galactic nuclei (AGN). We here initiate "a multiwavelength study of ELAN environments" (AMUSE$^2$) focusing on the ELAN around the $z\sim3$ quasar SDSS J1040+1020, a.k.a. the Fabulous ELAN. We report on VLT/HAWK-I, APEX/LABOCA, JCMT/SCUBA-2, SMA/850$μ$m, ALMA/CO(5-4) and 2mm observations and compare them to previously published VLT/MUSE data. The continuum and line detections enable a first estimate of the star-formation rates, dust, stellar and molecular gas masses in four objects associated with the ELAN (three AGNs and one Ly$α$ emitter), confirming that the quasar host is the most star-forming (${\rm SFR}\sim500$ M$_\odot$ yr$^{-1}$) and massive galaxy ($M_{\rm star}\sim10^{11}$ M$_{\odot}$) in the system, and thus can be assumed as central. All four embedded objects have similar molecular gas reservoirs ($M_{\rm H_2}\sim10^{10}$ M$_{\odot}$), resulting in short depletion time scales. This fact together with the estimated total dark-matter halo mass, $M_{\rm DM}=(0.8-2)\times10^{13}$ M$_{\odot}$, implies that this ELAN will evolve into a giant elliptical galaxy. Consistently, the constraint on the baryonic mass budget for the whole system indicates that the majority of baryons should reside in a massive warm-hot reservoir (up to $10^{12}$ M$_{\odot}$), needed to complete the baryons count. Additionally, we discuss signatures of gas infall on the compact objects as traced by Ly$α$ radiative transfer effects and the evidence for the alignment between the satellites' spins and their directions to the central.

astro-ph.GA↗

arXiv2021

Probing Early Super-massive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z <= 7.64

We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range $6.3< z\le7.64$, including 32 quasars at $z>6.5$, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the MgII emission lines are in the range $(0.3-3.6)\times10^{9}\,M_{\odot}$, which requires massive seed black holes with masses $\gtrsim10^{3-4}\,M_{\odot}$, assuming Eddington accretion since $z=30$. The Eddington ratio distribution peaks at $λ_{\rm Edd}\sim0.8$ and has a mean of 1.08, suggesting high accretion rates for these quasars. The CIV - MgII emission line velocity differences in our sample show an increase of CIV blueshift towards higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The FeII/MgII flux ratios derived for these quasars up to $z=7.6$, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for $z>6.5$ quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the CIV line. Our sample yields a strong broad absorption line quasar fraction of $\sim$24%, higher than the fractions in lower redshift quasar samples, although this could be affected by small sample statistics and selection effects.

astro-ph.GA↗

arXiv2021

ALMA reveals large overdensity and strong clustering of galaxies in quasar environments at $z\sim4$

We present an Atacama Large Millimeter/submillimeter Array (ALMA) survey of CO(4--3) line emitting galaxies in 17 quasar fields at $z\sim4$ aimed to perform the first systematic search of dusty galaxies in high$-z$ quasar environments. Our blind search of galaxies around the quasars results in 5 CO emitters with S/N$\geq5.6$ within a projected radius of $R\lesssim1.5\,h^{-1}\,$cMpc and a velocity range of $\rmΔ\,v=\pm1000\,$km\,s$^{-1}$ around the quasar. In blank fields, we expect to detect only 0.28 CO emitters within the same volume, implying a total overdensity of $17.6^{+11.9}_{-7.6}$ in our fields, and indicating that quasars trace massive structures in the early universe. We quantify this overdensity by measuring the small-scale clustering of CO emitters around quasars, resulting in a cross-correlation length of $r_{\rm 0,QG}=8.37^{+2.42}_{-2.04}\,h^{-1}\,$cMpc, assuming a fixed slope $γ=1.8$. This contradicts the reported mild overdensities (x1.4) of Lyman alpha emitters (LAEs) in the same fields at scales of $R\lesssim7\,h^{-1}\,$cMpc which is well described by a cross-correlation length 3 times lower than that measured for CO emitters. We discuss some possibilities to explain this discrepancy, including low star formation efficiency, and excess of dust in galaxies around quasars. Finally, we constrain, for the first time, the clustering of CO emitters at $z\sim4$, finding an auto-correlation length of $r_{\rm 0,CO}=3.14\pm1.71\,h^{-1}\,$cMpc (with $γ=1.8$). Our work together with the previous study of LAEs around quasars traces simultaneously the clustering properties of both optical and dusty galaxy populations in quasars fields, stressing the importance of multi-wavelength studies, and highlighting important questions about galaxy properties in high$-z$ dense environments.

astro-ph.GA↗

arXiv2020

No evidence for [CII] halos or high-velocity outflows in z>6 quasar host galaxies

We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z>6, using the [CII] 158um emission line and the underlying dust continuum observed at ~1kpc resolution with ALMA. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas, and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [CII] and the dust continuum emission can be described by a steep component within a radius of 2kpc, and a shallower component with a scale length of 2kpc, detected up to ~10kpc. The surface brightness of the extended emission drops below ~1% of the peak at radius of ~5kpc, beyond which it constitutes 10-20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [CII] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [CII] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [CII] broad-line emission (velocities in excess of >500km/s), that would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10kpc, whereas we find no evidence for halos or outflows.

astro-ph.GA↗

arXiv2020

Measurements of the z ~ 6 Intergalactic Medium Optical Depth and Transmission Spikes Using a New z > 6.3 Quasar Sample

We report new measurements of the intergalactic medium (IGM) Ly$α$ and Ly$β$ effective optical depth at $5.3 5.3$, $τ\propto(1+z)^{8.6\pm1.0}$. We then estimate the observed Ly$β$ effective optical depth using Ly$β$ forests and convert them to Ly$α$ optical depth for comparison, which provides additional constraints on the evolution of the IGM optical depth. The Ly$β$-based measurements are generally in agreement with the best-fit evolution obtained from Ly$α$ forests. Using this new sample, we identify 389 Ly$α$ and 50 Ly$β$ transmission spikes at $5.5<z<6.3$. The upper limits of Ly$α$ optical depth estimated using transmission spikes are well consistent with our best-fit evolution. The evolution in number density of these high-redshift transmission spikes suggests a rapid transition phase at the end of the reionization. Comparison of our optical depth measurements with hydrodynamical simulations indicates a IGM neutral hydrogen fraction $\langle f_{\rm HI}\rangle\gtrsim10^{-4}$ at $z=6$.

astro-ph.GA↗