Extended Lyman alpha haloes around individual high-redshift galaxies revealed by MUSE (1509.05143v2)

Abstract: We report the detection of extended Ly alpha emission around individual star-forming galaxies at redshifts z = 3-6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness (1sigma) of ~1 x 10^-19 erg s^-1 cm^-2 arcsec^-2 in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Ly alpha-emitting, but mostly continuum-faint (m_AB >~ 27) galaxies. In most objects the Ly alpha emission is considerably more extended than the UV continuum light. While 5 of the faintest galaxies in the sample show no significantly detected Ly alpha haloes, the derived upper limits suggest that this is just due to insufficient S/N. Ly alpha haloes therefore appear to be (nearly) ubiquitous even for low-mass (~10^8-10^9 M_sun) star-forming galaxies at z>3. We decompose the Ly alpha emission of each object into a compact `continuum-like' and an extended halo component, and infer sizes and luminosities of the haloes. The extended Ly alpha emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5-15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor ~5, than Ly alpha haloes around low-redshift star-forming galaxies. Between ~40% and >90% of the observed Ly alpha flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Ly alpha halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z > 3.

• The paper demonstrates that extended Lyman α haloes are detected in 21 of 26 high-redshift galaxies, with halo sizes up to 15 times larger than the UV continuum.
• The analysis uses a two-component model to quantify halo scale lengths between 1 and 7 kpc, highlighting the distinct spatial distribution of Lyα emission.
• The study finds that nearly 70% of the total Lyman α emission originates from the extended component, underscoring its significance in the circumgalactic medium.

Analysis of Extended Lyman Alpha Haloes at High Redshift Using MUSE Observations

The paper "Extended Lyman α haloes around individual high-redshift galaxies revealed by MUSE," authored by L. Wisotzki and colleagues, provides a thorough exploration of extended Lyman-alpha (Lyα) emission in star-forming galaxies at redshifts ranging from 3 to 6. Utilizing the MUSE instrument on the ESO-VLT, this paper explores the spatial distribution of Lyα emission to understand the circumgalactic medium (CGM) of galaxies at these epochs. The authors analyze data from 26 galaxies, revealing that Lyα haloes are nearly ubiquitous in this redshift range, thereby offering new insights into the CGM's properties and its role in galactic evolution.

Key Findings

1. Detection of Extended Lyα Emission: The paper reveals that most of the galaxies exhibit significantly extended Lyα emission when compared to their UV continuum emission, pointing to the presence of substantial gaseous haloes. The authors statistically validate this extended nature for 21 out of 26 sampled galaxies, attributing to them Lyα haloes that are several times larger than their stellar counterparts.
2. Morphological Characteristics: By fitting the Lyα emission profiles with a two-component model—combining a compact component aligned with the UV continuum and an extended exponential halo—the authors quantify the surface brightness distribution of Lyα. The scale lengths of these haloes are found to be between 1 to 7 kpc, typically a factor of 5–15 greater than the associated UV continuum scale lengths.
3. Lyα Luminosity and Halo Fractions: The extensive data analysis elucidates a mean that approximately 70% of the total Lyα emission originates from the extended component. This fraction is consistent across the sample and corroborates prior stacking studies, suggesting that extended emission is a prevalent feature among high-redshift galaxies.
4. Size Comparison and Evolutionary Trends: A notable finding is the observed decrease in halo sizes with increasing redshift within the sample. Additionally, comparisons with local Lyα emitters indicate significant evolutionary changes in halo size, reinforcing the concept that the CGM evolves substantially from the early universe to the present day.
5. Implications for Star Formation and Galaxy Properties: The paper estimates star formation rates based on both Lyα and UV continuum emissions, suggesting that the galaxies reside in dark matter haloes with masses typically less than $10^{11} M_\odot$. This implies that even low-mass galaxies were surrounded by significant Lyα haloes during these epochs.

Implications and Future Directions

The findings offer profound implications for our understanding of the cosmic web and the role of the CGM in galaxy formation and evolution. The prevalence and characteristics of these Lyα haloes suggest that neutral hydrogen is distributed extensively around galaxies, influencing both inflow and outflow processes integral to galaxy growth.

Future research could benefit from more extensive datasets across multiple fields to mitigate sample size restrictions and provide a broader context. Additionally, multi-wavelength observations are necessary to better constrain galaxy properties like stellar mass and dust content. This paper sets a foundation for further theoretical work to model the interplay between ionizing radiation, star formation, and the CGM. As MUSE continues to explore the high-redshift universe, it will undoubtedly refine our understanding of these intricate processes.