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The CALYMHA survey: Ly$\alpha$ escape fraction and its dependence on galaxy properties at $z=2.23$
- Publication Year :
- 2016
-
Abstract
- We present the first results from our CAlibrating LYMan-$\alpha$ with H$\alpha$ (CALYMHA) pilot survey at the Isaac Newton Telescope. We measure Ly$\alpha$ emission for 488 H$\alpha$ selected galaxies at $z=2.23$ from HiZELS in the COSMOS and UDS fields with a specially designed narrow-band filter ($\lambda_c$ = 3918 {\AA}, $\Delta\lambda$= 52 {\AA}). We find 17 dual H$\alpha$-Ly$\alpha$ emitters ($f_{\rm Ly\alpha} >5\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, of which 5 are X-ray AGN). For star-forming galaxies, we find a range of Ly$\alpha$ escape fractions (f$_{\rm esc}$, measured with 3$"$ apertures) from $2$\%$-30$\%. These galaxies have masses from $3\times10^8$ M$_{\odot}$ to 10$^{11}$ M$_{\odot}$ and dust attenuations E$(B-V)=0-0.5$. Using stacking, we measure a median escape fraction of $1.6\pm0.5$\% ($4.0\pm1.0$\% without correcting H$\alpha$ for dust), but show that this depends on galaxy properties. The stacked f$_{\rm esc}$ tends to decrease with increasing SFR and dust attenuation. However, at the highest masses and dust attenuations, we detect individual galaxies with f$_{\rm esc}$ much higher than the typical values from stacking, indicating significant scatter in the values of f$_{\rm esc}$. Relations between f$_{\rm esc}$ and UV slope are bimodal, with high f$_{\rm esc}$ for either the bluest or reddest galaxies. We speculate that this bimodality and large scatter in the values of f$_{\rm esc}$ is due to additional physical mechanisms such as outflows facilitating f$_{\rm esc}$ for dusty/massive systems. Ly$\alpha$ is significantly more extended than H$\alpha$ and the UV. f$_{\rm esc}$ continues to increase up to at least 20 kpc (3$\sigma$, 40 kpc [2$\sigma$]) for typical SFGs and thus the aperture is the most important predictor of f$_{\rm esc}$.<br />Comment: Accepted for publication by MNRAS
- Subjects :
- Astrophysics - Astrophysics of Galaxies
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1602.02756
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1093/mnras/stw322