Abstract
We present the CAlibrating LYMan-$\alpha$ with H$\alpha$ (CALYMHA) pilot
survey and new results on Lyman-$\alpha$ (Lya) selected galaxies at z~2. We use
a custom-built Lya narrow-band filter at the Isaac Newton Telescope, designed
to provide a matched volume coverage to the z=2.23 Ha HiZELS survey. Here we
present the first results for the COSMOS and UDS fields. Our survey currently
reaches a 3$\sigma$ line flux limit of ~4x10$^-17$ erg/s/cm$^2$, and a Lya
luminosity limit of ~10$^42.3$ erg/s. We find 188 Lya emitters over
7.3x10$^5$ Mpc$^3$, but also find significant numbers of other line emitting
sources corresponding to HeII, CIII and CIV emission lines. These sources are
important contaminants, and we carefully remove them, unlike most previous
studies. We find that the Lya luminosity function at z=2.23 is very well
described by a Schechter function up to L~10$^43$ erg/s with
L$^*=10^42.59+-0.05$ erg/s, $\phi^*=10^-3.09+-0.08$ Mpc$^-3$ and
$\alpha$=-1.75+-0.15. Above L~10$^43$ erg/s the Lya luminosity function
becomes power-law like, driven by X-ray AGN. We find that Lya-selected emitters
have a high escape fraction of 37+-7%, anti-correlated with Lya luminosity and
correlated with Lya equivalent width. Lya emitters have ubiquitous large (~40
kpc) Lya haloes, 2x larger than their Ha extents. By directly comparing our Lya
and Ha luminosity functions we find that the global/overall escape fraction of
Lya photons (within a 13 kpc radius) from the full population of star-forming
galaxies is 5.1+-0.2% at the peak of the star formation history. An extra
3.3+-0.3% of Lya photons likely still escape, but at larger radii.
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