Lyα Halo Research Articles

Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

We present the median-stacked Lyman-α (Lyα) surface brightness profiles of 968 spectroscopically selected Lyα emitting galaxies (LAEs) at redshifts 1.9 < z < 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Lyα detections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM <1.″4), excluding active galactic nuclei. The Lyα luminosities of the LAEs are 1042.4–1043 erg s−1. We detect faint emission in the median-stacked radial profiles at the level of from the surrounding Lyα halos out to r ≃ 160 kpc (physical). The shape of the median-stacked radial profile is consistent at r < 80 kpc with that of much fainter LAEs at 3 < z < 4 observed with the Multi Unit Spectroscopic Explorer (MUSE), indicating that the median-stacked Lyα profiles have similar shapes at redshifts 2 < z < 4 and across a factor of 10 in Lyα luminosity. While we agree with the results from the MUSE sample at r < 80 kpc, we extend the profile over a factor of two in radius. At r > 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation at z = 3. This suggests that the surface brightness of a Lyα halo at r ≲ 100 kpc is dominated by resonant scattering of Lyα photons from star-forming regions in the central galaxy, whereas at r > 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos.

Evidence for Cold-stream to Hot-accretion Transition as Traced by Lyα Emission from Groups and Clusters at 2 &lt; z &lt; 3.3

Abstract We present Keck Cosmic Web Imager observations of giant Lyα halos surrounding nine galaxy groups and clusters at 2 &lt; z &lt; 3.3, including five new detections and one upper limit. We find observational evidence for the cold-stream to hot-accretion transition predicted by theory by measuring a decrease in the ratio between the spatially extended Lyα luminosity and the expected baryonic accretion rate (BAR), with increasing elongation above the transition mass (M stream). This implies a modulation of the share of BAR that remains cold, diminishing quasi-linearly (logarithmic slope of 0.97 ± 0.19, 5σ significance) with the halo to M stream mass ratio. The integrated star formation rates (SFRs) and active galactic nucleus (AGN) bolometric luminosities display a potentially consistent decrease, albeit significant only at 2.6σ and 1.3σ, respectively. The higher scatter in these tracers suggests the Lyα emission might be mostly a direct product of cold accretion in these structures rather than indirect, mediated by outflows and photoionization from SFR and AGNs; this is also supported by energetics considerations. Below M stream (cold-stream regime), we measure L Lyα /BAR = 1040.51±0.16 erg s−1 M ⊙ − 1 yr, consistent with predictions, and SFR/BAR = 10−0.54±0.23: on average, 30 − 10 + 20 % of the cold streams go into stars. Above M stream (hot-accretion regime), L Lyα is set by M stream (within 0.2 dex scatter in our sample), independent of the halo mass but rising 10-fold from z = 2 to 3.

The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lyα Photons: A Case Study of a Protocluster Field at z = 3.1

Abstract We present a detailed characterization of the Lyα properties for 93 Lyα emitters (LAEs) at z ∼ 3.1 selected from the D1 field of the Canada–France–Hawaii Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lyα image shows an extended Lyα halo (LAH) surrounding the galaxy with the exponential scale length 4.9 ± 0.7 kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lyα escape fraction, f esc, is 40% ± 26%. Combining the data set with existing measurements, we find a dependence of f esc on the galaxy’s UV slope (β) and UV luminosity (L UV). The simultaneous use of both parameters allows prediction of f esc within 0.18 dex, a substantial improvement over 0.23 dex when only β is used. The correlation between f esc and E(B − V) suggests that Lyα photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lyα transmission is typically higher than that expected for continuum photons at a similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lyα transmission or production. Alternatively, the dust law may change with luminosity leading to an over- or underestimation of f esc. Finally, we report that protocluster LAEs tend to be bluer and more UV luminous than their field cousins, resulting in systematically higher f esc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

Mapping the “invisible” circumgalactic medium around a z ∼ 4.5 radio galaxy with MUSE

In this paper we present Multi Unit Spectroscopic Explorer integral field unit spectroscopic observations of the ∼70 × 30 kpc2 Lyα halo around the radio galaxy 4C04.11 at z = 4.5077. High-redshift radio galaxies are hosted by some of the most massive galaxies known at any redshift and are unique markers of concomitant powerful active galactic nucleus (AGN) activity and star formation episodes. We map the emission and kinematics of the Lyα across the halo as well as the kinematics and column densities of eight H I absorbing systems at −3500 &lt; Δv &lt; 0 km s−1. We find that the strong absorber at Δv ∼ 0 km s−1 has a high areal coverage (30 × 30 kpc2), being detected across a large extent of the Lyα halo, a significant column density gradient along the southwest to northeast direction, and a velocity gradient along the radio jet axis. We propose that the absorbing structure, which is also seen in C IV and N V absorption, represents an outflowing metal-enriched shell driven by a previous AGN or star formation episode within the galaxy and is now caught up by the radio jet, leading to jet-gas interactions. These observations provide evidence that feedback from AGN in some of the most massive galaxies in the early Universe may play an important role in redistributing material and metals in their environments.

An Ancient Massive Quiescent Galaxy Found in a Gas-rich z ∼ 3 Group

Abstract Deep Atacama Large Millimeter/submillimeter Array and Hubble Space Telescope observations reveal the presence of a quenched massive galaxy within the z = 2.91 galaxy group RO-1001. With a mass-weighted stellar age of 1.6 ± 0.4 Gyr this galaxy is one of the oldest known at z ∼ 3, implying that most of its 1011 M ⊙ of stars were rapidly formed at z &gt; 6–8. This is a unique example of the predominantly passive evolution of a galaxy over at least 3 &lt; z &lt; 6 following its high-redshift quenching and a smoking-gun event pointing to the early imprint of an age–environment relation. At the same time, being in a dense group environment with extensive cold gas reservoirs as betrayed by a giant Lyα halo, the existence of this galaxy demonstrates that gas accretion shutdown is not necessary for quenching and its maintenance.

RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy at z ∼ 7

Abstract We report the discovery of a spectroscopically confirmed strong Lyα emitter at z = 7.0281 ± 0.0003, observed as part of the Reionization Lensing Cluster Survey (RELICS). This galaxy, dubbed “Dichromatic Primeval Galaxy” at z ∼ 7 (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity ( ∼ 0.3 L UV * , where L UV * is the characteristic luminosity), DP7 has one of the highest observed Lyα equivalent widths (EWs) among Lyα emitters at z &gt; 6 (&gt;200 Å in the rest frame). The strong Lyα emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope β of the galaxy as a whole is redder than typical star-forming galaxies at these redshifts, −1.13 ± 0.84, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measure β for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyα is spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyα halo. Rejuvenation or merging events could explain these results. Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured active galactic nucleus. DP7, with its low UV luminosity and high Lyα EW, represents the typical galaxies that are thought to be the major contribution to the reionization of the universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope.

The Ionized- and Cool-gas Content of the BR1202−0725 System as Seen by MUSE and ALMA

Abstract We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202−0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Lyα emitters (“LAE 1” and “LAE 2”), and an additional companion discovered in this work “LAE 3” just 5″ to the north of the QSO. We find that QSO BR1202−0725 exhibits a large Lyα halo, covering ≈55 pkpc on-sky at surface-brightness levels of SB ≥ 1 × 10−17 erg s−1 cm−2 arcsec−2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Lyα halo. The QSO’s halo exhibits high velocity widths (∼1000 km s−1) but the gas motion is to some extent kinematically coupled with the previously observed [C ii] bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Lyα emission, rather, its profile is more consistent with being part of the QSO’s extended Lyα halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure F Lyα (LAE 3) = 0.24 ± 0.03 × 10−16 erg s−1 cm−2, corresponding to SFRLyα ≈ 5.0 ± 0.5 M ⊙ yr−1. The velocity width is Δv(LAE 3) ≈ 400 km s−1, and the equivalent width is EW0( Å, consistent with star formation being the primary driver of Lyα emission. We also note a coherent absorption feature at ∼−400 km s−1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.

Lyα Radiative Transfer: Modeling Spectrum and Surface Brightness Profiles of Lyα-emitting Galaxies at Z = 3–6

Abstract We perform Lyα radiative transfer calculations to reproduce the Lyα properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyα sources and H i plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We successfully reproduce both the spectra and the surface brightness profiles of eight star-forming galaxies at z = 3–6 observed with the Multi-Unit Spectroscopic Explorer using this outflowing-halo model with Lyα scattering. The best-fit model parameters (i.e., the outflowing velocity and optical depth) for these galaxies are consistent with those in other studies. We examine the impacts of individual model parameters and input spectrum on the emerging spectrum and surface brightness profile. Further investigations of the correlations among observables (i.e., the spatial extent of Lyα halos and Lyα spectral features) and model parameters, and of spatially resolved spectra are presented as well. We demonstrate that the combination of spectrum and surface brightness profile provides strong constraints on model parameters and thus on the spatial/kinematic distributions of the medium.

Resonant-line radiative transfer within power-law density profiles

ABSTRACT Star-forming regions in galaxies are surrounded by vast reservoirs of gas capable of both emitting and absorbing Lyman α (Lyα) radiation. Observations of Lyα emitters and spatially extended Lyα haloes indeed provide insights into the formation and evolution of galaxies. However, due to the complexity of resonant scattering, only a few analytic solutions are known in the literature. We discuss several idealized but physically motivated scenarios to extend the existing formalism to new analytic solutions, enabling quantitative predictions about the transport and diffusion of Lyα photons. This includes a closed form solution for the radiation field and derived quantities including the emergent flux, peak locations, energy density, average internal spectrum, number of scatters, outward force multiplier, trapping time, and characteristic radius. To verify our predictions, we employ a robust gridless Monte Carlo radiative transfer (GMCRT) method, which is straightforward to incorporate into existing ray tracing codes but requires modifications to opacity-based calculations, including dynamical core-skipping acceleration schemes. We primarily focus on power-law density and emissivity profiles, however both the analytic and numerical methods can be generalized to other cases. Such studies provide additional intuition and understanding regarding the connection between the physical environments and observational signatures of galaxies throughout the Universe.

Metal Enrichment in the Circumgalactic Medium and Lyα Halos around Quasars at z ∼ 3

Abstract Deep observations have detected extended Lyα emission nebulae surrounding tens of quasars at redshift 2–6. However, the metallicity of such extended halos is still poorly understood. We perform a detailed analysis on a large sample of 80 quasars at z ∼ 3 based on MUSE-VLT data. We find clear evidence of extended emission of the UV nebular lines such as C iv λ1549 or He ii λ1640 for about 20% of the sample, while C iii] λ1909 is only marginally detected in a few objects. By stacking the cubes, we detect emission of C iv, He ii, and C iii] out to a radius of about 45 kpc. C iv and He ii show a radial decline much steeper than Lyα, while C iii] shows a shallower profile similar to Lyα in the inner 45 kpc. We infer that the average metallicity of the circumgalactic gas within the central 30–50 kpc is ∼0.5 solar, or even higher. However, we also find evidence of a component of the Lyα halos, which has much weaker metal emission lines relative to Lyα. We suggest that the high metallicity of the circumgalactic medium within the central 30–50 kpc is associated with chemical pre-enrichment by past quasar-driven outflows and that there is a more extended component of the circumgalactic medium that has much lower metallicity and is likely associated with near-pristine gas accreted from the intergalactic medium. We show that our observational results are in good agreement with the expectations of the FABLE zoom-in cosmological simulations.

CHORUS. III. Photometric and Spectroscopic Properties of Lyα Blobs at z = 4.9–7.0

Abstract We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Lyα blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Lyα emitters with a bright ( ) and spatially extended Lyα emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7–6.6. The z70-1 LAB shows extended Lyα emission with a scale length of 1.4 ± 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N v λ1240 emission, or Lyα line broadening, while z49-1 has a strong C iv λ1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Lyα emission of the LABs. The Lyα scale lengths of the core (star-forming region) and halo components are r c = 0.6–1.2 kpc and r h = 2.0–13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Lyα luminosity L Lyα , Lyα rest-frame equivalent width EW0, and UV continuum magnitude M UV) of our LABs are similar to those of Lyα halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs.

The MUSE Hubble Ultra Deep Field Survey

We present spatially resolved maps of six individually-detected Lyman α haloes (LAHs) as well as a first statistical analysis of the Lyman α (Lyα) spectral signature in the circum-galactic medium of high-redshift star-forming galaxies (−17.5 &gt; MUV &gt; −21.5) using the Multi-Unit Spectroscopic Explorer. Our resolved spectroscopic analysis of the LAHs reveals significant intrahalo variations of the Lyα line profile. Using a three-dimensional two-component model for the Lyα emission, we measured the full width at half maximum (FWHM), the peak velocity shift, and the asymmetry of the Lyα line in the core and in the halo of 19 galaxies. We find that the Lyα line shape is statistically different in the halo compared to the core (in terms of width, peak wavelength, and asymmetry) 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 Lyα line both at the interstellar and circum-galactic scales. This trend has been predicted by radiative transfer simulations of galactic winds as a result of resonant scattering in outflows. 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 (MUV &lt; −20) show broader, more redshifted, and less asymmetric Lyα 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 Lyα lines. The generally broad and red line shapes found in the halo component suggest that the Lyα 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 Lyα 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.

The REQUIEM Survey. I. A Search for Extended Lyα Nebular Emission Around 31 z &gt; 5.7 Quasars

Abstract The discovery of quasars a few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes as well as galaxy formation and evolution. Quasars' luminosity is produced by extreme gas accretion onto black holes, which have already reached masses of M BH &gt; 109 M ⊙ by z ∼ 6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources, we started a Very Large Telescope/Multi-Unit Spectroscopic Explorer (MUSE) effort aimed at characterizing the surroundings of a sample of 5.7 &lt; z &lt; 6.6 quasars, which we have dubbed the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Lyα halos around the first 31 targets observed as part of this program. Reaching 5σ surface brightness limits of 0.1–1.1 × 10−17 erg s−1 cm−2 arcsec−2 over a 1 arcsec2 aperture, we were able to unveil the presence of 12 Lyα nebulae, eight of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8 × 1042 to 2 × 1044 erg s−1, FWHMs between 300 and 1700 km s−1, sizes &lt;30 pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circumgalactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3 Gyr of the universe. A comparison with the extended Lyα emission observed around bright ( M 1450 ≲ −25 mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z ∼ 6 to z ∼ 3, followed by a decline in the average surface brightness down to z ∼ 2.

First Identification of 10 kpc [C ii] 158 μm Halos around Star-forming Galaxies at z = 5–7

Abstract We report the discovery of 10 kpc [C ii] 158 μm halos surrounding star-forming galaxies in the early universe. We choose deep Atacama Large Millimeter/submillimeter Array data for 18 galaxies, each with a star formation rate of ≃10–70 M ⊙ with no signature of an active galactic nucleus whose [C ii] lines are individually detected at z = 5.153–7.142, and we conduct stacking of the [C ii] lines and dust continuum in the uv-visibility plane. The radial profiles of the surface brightnesses show a 10 kpc scale [C ii] halo at the 9.2σ level, significantly more extended than the Hubble Space Telescope stellar continuum data by a factor of ∼5 on the exponential-profile basis, as well as the dust continuum. We compare the radial profiles of [C ii] and Lyα halos universally found in star-forming galaxies at this epoch, and we find that the scale lengths agree within the 1σ level. While two independent hydrodynamic zoom-in simulations match the dust and stellar continuum properties, the simulations cannot reproduce the extended [C ii] line emission. The existence of the extended [C ii] halo is evidence of outflow remnants in the early galaxies and suggests that the outflows may be dominated by cold-mode outflows expelling the neutral gas.

The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

AbstractThe physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (Mh) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)H despite low M⋆ and Mh, and that L(Lyα)H remains almost unchanged with M⋆ and perhaps with Mh. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)H and both predict steeper L(Lyα)H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H i gas masses implied from lower Mh at fixed M⋆, or from another Lyα source in the central part.

Photoionization models for extreme Lyα λ1216 and Hell λ1640 line ratios in quasar halos, and PopIII vs. AGN diagnostics

Aims. We explore potential mechanisms to produce extremely high Lyα/HeII flux ratios, or to enhance the observed number of Lyα photons per incident ionizing photon, in extended active galactic nucleus (AGN) photoionized nebulae at high-redshift. Methods. We computed models to simulate, in the low density regime, photoionization of interstellar gas by the radiation field of a luminous AGN. We have explored the impact of ionization parameter, gas metallicity, ionizing spectrum, electron energy distribution, and cloud viewing angle on the relative fluxes of Lyα, HeII and other lines, and on the observed number of Lyα photons per incident ionizing photon. We have compared our model results with recent observations of quasar Lyα halos at z ∼ 3.5. Results. Low ionization parameter, a relatively soft or filtered ionizing spectrum, low gas metallicity, κ-distributed electron energies, or reflection of Lyα photons by neutral hydrogen can all result in significantly enhanced Lyα relative to other lines (≥10%), with log Lyα/HeII reaching values of up to 4.6. In the cases of low gas metallicity, reflection by HI, or a hard or filtered ionizing spectrum, the observed number of Lyα photons per incident ionizing photon is itself significantly enhanced above the nominal Case B value of 0.66 due to collisional excitation, reaching values as high as 5.3 in an “extreme case” model which combines several of these effects. We find that at low gas metallicity (e.g. Z/Z⊙ = 0.1) the production of Lyα photons is predominantly via collisional excitation rather than by recombination. In addition, we find that the collisional excitation of Lyα becomes much more efficient if the ionizing continuum spectrum has been pre-filtered through an optically thin screen of gas closer to the AGN (e.g. by a wide-angle, feedback-driven outflow). We also show that the Lyα and HeII emission line ratios of a sample of previously studied quasars at z ∼ 3.5 are consistent with AGN-photoionization of gas with moderate to low metallicity and/or low ionization parameter, without requiring exotic ionization or excitation mechanisms such as strong line-transfer effects. In addition, we present a set of UV-optical diagnostic diagrams to distinguish between photoionization by Pop III stars and photoionization by an AGN.

SILVERRUSH. VI. A simulation of Lyα emitters in the reionization epoch and a comparison with Subaru Hyper Suprime-Cam survey early data

Abstract The survey of Lyman α emitters (LAEs) with the Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al. 2018, PASJ, 70, S13), is producing massive data of LAEs at z ≳ 6. Here we present LAE simulations to compare the SILVERRUSH data. In 1623 comoving Mpc3 boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined 23 models depending on the presence or absence of dispersion of halo Lyα emissivity, dispersion of the halo Lyα optical depth, τα, and halo mass dependence of τα. The unique free parameter in our model, a pivot value of τα, is calibrated so as to reproduce the z = 5.7 Lyα luminosity function (LF) of SILVERRUSH. We compare our model predictions with Lyα LFs at z = 6.6 and 7.3, LAE angular auto-correlation functions (ACFs) at z = 5.7 and 6.6, and LAE fractions in Lyman break galaxies at 5 &amp;lt; z &amp;lt; 7. The Lyα LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of τα and the halo mass dependence of τα are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Lyα luminosity with a constant Lyα escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, $x_{\rm H\, \small {I}}$, from the observed Lyα luminosity density at z ≳ 6. We finally obtain $x_{\rm H\, \small {I}}=0.5_{-0.3}^{+0.1}$ as a volume-average at z = 7.3.

The Lyα Reference Sample. VIII. Characterizing Lyα Scattering in Nearby Galaxies

Abstract We examine the dust geometry and Lyα scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby ( ) Lyα-emitting and starbursting systems with Hubble Space Telescope Lyα, Hα, and Hβ imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media, while others of them show significantly lower Lyα emission compared to their Balmer decrement. With the LARS imaging, we present Lyα/Hα and Hα/Hβ maps with spatial resolutions as low as ∼40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Lyα photons only scatter. We show that the dust that affects the escape of Lyα is more restricted to the galaxies’ central regions, while the larger Lyα halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Lyα scatters in the halo, and find that this “characteristic” scattering distance correlates with the measured size of the Lyα halo. We note that there exists a slight anti-correlation between the scattering distance of Lyα and global dust properties.

The MUSE Hubble Ultra Deep Field Survey

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 &gt;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 (&gt;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&gt; 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 (&lt;350 km s-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.

Small-scale Intensity Mapping: Extended Lyα, Hα, and Continuum Emission as a Probe of Halo Star Formation in High-redshift Galaxies

Abstract Lyα halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources, , clustered around the central galaxies may play a major role in generating spatially extended Lyα, continuum (UV + VIS), and Hα halos. We apply the analytic formalism developed in Mas-Ribas &amp; Dijkstra to model the halos around Lyman Alpha Emitters (LAEs) at z = 3.1, for several different satellite clustering prescriptions. In general, our UV and Lyα surface brightness profiles match the observations well at physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future Hα observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Lyα and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.