[论文解读] Inside the bubble: exploring the environments of reionisation-era Lyman-$α$ emitting galaxies with JADES and FRESCO

Joris Witstok, Renske Smit+36 more|arXiv (Cornell University)|Jun 7, 2023

Galaxies: Formation, Evolution, Phenomena被引用 9

一句话总结

该论文利用 JWST/JADES 与 FRESCO 数据研究约在 z ~ 5.8–8 的 17 颗 Lyman-α 发射星系的环境，以推断电离气泡大小及周围超密度对重离子化时期 Lyα 透射的作用。

ABSTRACT

We present a study of the environments of 17 Lyman-$α$ (Ly$α$) emitting galaxies (LAEs) in the reionisation era ($5.8 < z < 8$) identified by JWST/NIRSpec as part of the JWST Advanced Deep Extragalactic Survey (JADES). Unless situated in sufficiently (re)ionised regions, Ly$α$ emission from these galaxies would be strongly absorbed by neutral gas in the intergalactic medium (IGM). We conservatively estimate sizes of the ionised regions required to reconcile the relatively low Ly$α$ velocity offsets ($Δv_ ext{Ly$α$}<300\,\mathrm{km\,s^{-1}}$) with moderately high Ly$α$ escape fractions ($f_\mathrm{esc,\,Lyα}>5\%$) observed in our sample of LAEs, suggesting the presence of ionised hydrogen along the line of sight towards at least eight out of 17 LAEs. We find minimum physical `bubble' sizes of the order of $R_ ext{ion}\sim0.1$-$1\,\mathrm{pMpc}$ are required in a patchy reionisation scenario where ionised bubbles containing the LAEs are embedded in a fully neutral IGM. Around half of the LAEs in our sample are found to coincide with large-scale galaxy overdensities seen in FRESCO at $z \sim 5.8$-$5.9$ and $z\sim7.3$, suggesting Ly$α$ transmission is strongly enhanced in such overdense regions, and underlining the importance of LAEs as tracers of the first large-scale ionised bubbles. Considering only spectroscopically confirmed galaxies, we find our sample of UV-faint LAEs ($M_ ext{UV}\gtrsim-20\,\mathrm{mag}$) and their direct neighbours are generally not able to produce the required ionised regions based on the Ly$α$ transmission properties, suggesting lower-luminosity sources likely play an important role in carving out these bubbles. These observations demonstrate the combined power of JWST multi-object and slitless spectroscopy in acquiring a unique view of the early Universe during cosmic reionisation via the most distant LAEs.

研究动机与目标

• Motivate how Lyα emission from reionisation-era galaxies traces ionised regions in an inhomogeneous IGM.
• Quantify the minimum ionised bubble sizes required to reconcile observed Lyα properties with IGM neutrality.
• Assess whether LAEs trace large-scale overdensities that facilitate Lyα visibility during reionisation.
• Evaluate the role of UV-faint galaxies and neighbours in carving out ionised regions.
• Demonstrate the utility of JWST multi-object and slitless spectroscopy for studying the early universe.

提出的方法

• Compile a sample of 17 LAEs at 5.8 < z < 8 identified by JWST/NIRSpec and FRESCO.
• Estimate Lyα velocity offsets (Δv_Lyα) and escape fractions (f_esc,Lyα) from R1000 spectra and literature.
• Infer minimum ionised bubble sizes (R_ion) required to allow Lyα transmission in a patchy reionisation scenario.
• Cross-correlate LAEs with spectroscopically confirmed neighbours and overdensities in FRESCO data at z ~ 5.8–5.9 and z ~ 7.3.
• Adopt a flat ΛCDM cosmology and a fixed hydrogen fraction to translate Lyα properties into bubble sizes.
• Present projected ionised-bubble visualizations around LAEs for context.

Figure 1: Redshift histogram of spectroscopically confirmed galaxies over GOODS-S. Sources confirmed in JADES NIRSpec observations ( Sect. 2.1 ) are shown by the black histogram , while the red distribution is of those identified in FRESCO data ( Oesch et al. 2023 ) , discussed in Sect. 2.3 . EoR (

实验结果

研究问题

• RQ1 What ionised bubble sizes are required around reionisation-era LAEs to enable observed Lyα transmission given their Δv_Lyα and f_esc,Lyα?
• RQ2 Are the LAEs predominantly located in or near large-scale overdensities that facilitate early bubble growth and Lyα visibility?
• RQ3 Do UV-faint LAEs and their neighbors collectively contribute to carving out the ionised regions around these galaxies?
• RQ4 How do JWST/NIRSpec and FRESCO data complement ground-based surveys in mapping the reionisation environment of distant LAEs?

主要发现

• Minimum ionised-region sizes required are of order R_ion ~ 0.1–1 pMpc in a patchy reionisation framework.
• Around half of the LAEs coincide with large-scale galaxy overdensities seen in FRESCO, suggesting enhanced Lyα transmission in overdense regions.
• UV-faint LAEs (M_UV ≳ -20 mag) and their direct neighbours generally cannot, by themselves, produce the required ionised regions, implying other, perhaps lower-luminosity sources contribute to bubble carving.
• Lyman-α transmission appears strongly enhanced in overdense regions, highlighting LAEs as tracers of early large-scale ionised bubbles.
• The study demonstrates the power of JWST multi-object and slitless spectroscopy in probing the reionisation-era environment via the most distant LAEs.

Figure 2: On-sky distribution of spectroscopically confirmed galaxies in the vicinity of $z\gtrsim 5.8$ LAEs identified in JADES NIRSpec observations over GOODS-S. Sources found in the JADES, FRESCO, and MUSE HUDF surveys are respectively shown by hexagons, squares, and circles; larger grey squares