The Prevalence of Galaxy Overdensities Around UV-Luminous Lyman $\mathbfα$ Emitters in the Epoch of Reionization

Leonova, E.; Oesch, P. A.; Qin, Y.; Naidu, R. P.; Wyithe, J. S. B.; de Barros, S.; Bouwens, R. J.; Ellis, R. S.; Endsley, R. M.; Hutter, A.; Illingworth, G. D.; Kerutt, J.; Labbe, I.; Laporte, N.; Magee, D.; Mutch, S. J.; Roberts-Borsani, G. W.; Smit, R.; Stark, D. P.; Stefanon, M.; Tacchella, S.; Zitrin, A.

doi:10.48550/arxiv.2112.07675

Cited by 8 publications

(9 citation statements)

References 83 publications

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“…As shown in Figure 12, our spectroscopic detection of two galaxies in a single field is a 2σ outlier, with only 1/40 extracted regions encompassing more galaxies, making this field overdense by a factor of four. We also note that this overdensity factor is consistent with the 3-9x factor measured by Leonova et al (2021) in this same field, using different methods. Even further evidence supporting the presence of an overdensity in the EGS field.…”

Section: Implications Of An Overdensitysupporting

confidence: 88%

Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

Larson

Finkelstein

Hutchison

et al. 2022

ApJ

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We present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10 m Keck telescope to search for Lyα emission from candidate galaxies at z ∼ 9–10 in four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Lyα from one object in ∼8.1 hr of integration, at z = 8.665 ± 0.001 with an integrated signal-to-noise ratio > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field and lies physically close (3.5 physical Mpc [pMpc]) to another confirmed galaxy in this field with Lyα detected at z = 8.683. The detection of Lyα suggests the existence of large (∼1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV luminosity function down to M UV = −13). The Lyα we detect would be able to escape the predominantly neutral intergalactic medium at this epoch if our detected galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. This implies that the CANDELS EGS field is hosting an overdensity at z = 8.7 that is powering one or more ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field.

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Section: Implications Of An Overdensitysupporting

confidence: 88%

Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

Larson

Finkelstein

Hutchison

et al. 2022

ApJ

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“…A promising way to shed light on the sources of reionization is to investigate regions where this process is more advanced, and observations point to the presence of 'reionized bubbles' (Castellano et al 2016a;Higuchi et al 2019;Tilvi et al 2020;Jung et al 2021;Leonova et al 2021;. The analysis of the Lyα fraction in independent lines-ofsight suggests that reionization was a spatially inhomogeneous process (Treu et al 2012;Pentericci et al 2014).…”

Section: Introductionmentioning

confidence: 99%

The ionizing properties of two bright Lyα emitters in the Bremer Deep Field reionized bubble at z = 7

Castellano

Pentericci

Cupani

et al. 2022

A&A

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Aims. We investigate the ionizing properties of the pair of bright Lyα emitting galaxies BDF521 and BDF2195 at z = 7.012 in order to constrain their contribution to the formation of the Bremer Deep Field (BDF) ‘reionized bubble’ in which they have been shown to reside. Methods. We obtain constraints on four UV emission lines (the CIVλ1548 doublet, HeIIλ1640, the OIII]λ1660 doublet, and the CIII]λ1909 doublet) from deep VLT X-shooter observations and compare them to those available for other high-redshift objects, and to models with mixed stellar and active galactic nucleus (AGN) emission. We use this spectroscopic information, together with the photometry available in the field, to constrain the physical properties of the two objects using the spectro-photometric fitting code BEAGLE. Results. We do not detect any significant emission at the expected position of the UV lines, with 3σ upper limits of equivalent width (EW) ≲2–7 Å rest-frame. We find that the two objects have a lower CIII] emission than expected on the basis of the correlation between the Lyα and CIII] EWs. The EW limits on CIV and HeII emission exclude pure AGN templates at ∼2 − 3σ significance, and only models with a ≲40% AGN contribution are compatible with the observations. The two objects are found to be relatively young (∼20–30 Myrs) and metal-poor (≲0.3 Z⊙), with stellar masses of a few 109 M⊙. Their production rate of hydrogen ionizing photons per intrinsic UV luminosity is log(ξion*/Hz erg−1) = 25.02–25.26, consistent with values typically found in high-redshift galaxies, but more than twice lower than values measured in z > 7 galaxies with strong CIII] and/or optical line emission (≃25.6–25.7). Conclusions. The two BDF emitters show no evidence of higher-than-average ionizing capabilities and are not capable of reionizing their surroundings by their own means, under realistic assumptions of the escape fraction of ionizing photons. Therefore, a dominant contribution to the formation of the reionized bubble must have been provided by fainter companion galaxies. The capabilities of the James Webb Space Telescope will be needed for spectroscopic confirmation of these objects.

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“…If these highly UV-luminous systems are instead often situated in the center of very large (𝑅 3 physical Mpc) ionized bubbles (possibly as a result of surrounding strong galaxy overdensities; e.g. Barkana & Loeb 2004;Endsley & Stark 2021;Leonova et al 2021), we then estimate that 75-80% of their Ly𝛼 photons are transmitted through the IGM. Nevertheless, we expect that the high peak Ly𝛼 velocity offsets and large line widths of UV-luminous 𝑧 > 6 galaxies lead to a relatively high net transmission ( 50%) of Ly𝛼 photons through the IGM.…”

Section: Discussionmentioning

confidence: 99%

“…Barone-Nugent et al 2014;Harikane et al 2018a) often reside in large ionized bubbles powered by the enhanced number of neighboring galaxies in their local overdensities (e.g. Wyithe & Loeb 2005;Dayal et al 2009;Zitrin et al 2015;Castellano et al 2016;Hutter et al 2017;Weinberger et al 2018;Endsley et al 2021b;Garaldi et al 2021;Kannan et al 2021;Leonova et al 2021;Qin et al 2021). The presence of these HII regions boosts Ly𝛼 transmission by enabling the photons to cosmologically redshift past the resonant core and into the damping wing before encountering intergalactic HI (Mesinger et al 2004;Mason & Gronke 2020;Smith et al 2021).…”

mentioning

confidence: 99%

The ALMA REBELS Survey: Efficient Ly$α$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths

Endsley¹,

Stark²,

Schouws³

et al. 2022

Preprint

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Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly𝛼 transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly𝛼 profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at 𝑧 ∼ 7 remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [CII]-based redshifts from ALMA. Here we report MMT/Binospec Ly𝛼 spectroscopy of eight UV-bright (M UV ∼ −22) galaxies at 𝑧 7 selected from the ALMA REBELS survey. We detect Ly𝛼 in 4 of 8 galaxies and use the [CII] systemic redshifts to investigate the Ly𝛼 velocity profiles. The Ly𝛼 lines are significantly redshifted from systemic (average velocity offset=223 km/s) and broad (FWHM≈300-650 km/s), with two sources showing emission extending to ≈750 km/s. We find that the broadest Ly𝛼 profiles are associated with the largest [CII] line widths, suggesting a potential link between the Ly𝛼 FWHM and the dynamical mass. Since Ly𝛼 photons at high velocities transmit efficiently through the 𝑧 = 7 IGM, our data suggest that velocity profiles play a significant role in boosting the Ly𝛼 visibility of the most UV-luminous reionization-era galaxies.

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The Prevalence of Galaxy Overdensities Around UV-Luminous Lyman $\mathbfα$ Emitters in the Epoch of Reionization

Cited by 8 publications

References 83 publications

Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

The ionizing properties of two bright Lyα emitters in the Bremer Deep Field reionized bubble at z = 7

The ALMA REBELS Survey: Efficient Ly$α$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths

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