Details

Autor(en) / Beteiligte

• Matthee, Jorryt
• Sobral, David
• Oteo, Iván
• Best, Philip
• Smail, Ian
• Röttgering, Huub
• Paulino-Afonso, Ana

Titel

The CALYMHA survey: Lyα escape fraction and its dependence on galaxy properties at z = 2.23

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2016-05, Vol.458 (1), p.449-467

Ort / Verlag

Oxford University Press

Erscheinungsjahr

2016

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We present the first results from our CAlibrating LYMan α with Hα (CALYMHA) pilot survey at the Isaac Newton Telescope. We measure Lyα emission for 488 Hα selected galaxies at z = 2.23 from High-z Emission Line Survey in the COSMOS and UDS fields with a specially designed narrow-band filter (λ c = 3918 Å, Δλ = 52 Å). We find 17 dual Hα-Lyα emitters [f Lyα > 5 × 10−17 erg s−1 cm−2, of which five are X-ray active galactic nuclei (AGN)]. For star-forming galaxies, we find a range of Lyα escape fractions (f esc, measured with 3 arcsec apertures) from 2 to 30 per cent. These galaxies have masses from 3 × 108 M⊙ to 1011 M⊙ and dust attenuations E(B − V) = 0–0.5. Using stacking, we measure a median escape fraction of 1.6 ± 0.5 per cent (4.0 ± 1.0 per cent without correcting Hα for dust), but show that this depends on galaxy properties. The stacked f esc tends to decrease with increasing star formation rate and dust attenuation. However, at the highest masses and dust attenuations, we detect individual galaxies with f esc much higher than the typical values from stacking, indicating significant scatter in the values of f esc. Relations between f esc and UV slope are bimodal, with high f esc for either the bluest or reddest galaxies. We speculate that this bimodality and large scatter in the values of f esc is due to additional physical mechanisms such as outflows facilitating f esc for dusty/massive systems. Lyα is significantly more extended than Hα and the UV. f esc continues to increase up to at least 20 kpc (3σ, 40 kpc [2σ]) for typical star-forming galaxies and thus the aperture is the most important predictor of f esc.