We present the first measurements of the Lyman-continuum photon production efficiency xi(ion.0) at z similar to 4-5 for galaxies fainter than 0.2 L* (-19 mag). xi(ion.0) quantifies the production... Show moreWe present the first measurements of the Lyman-continuum photon production efficiency xi(ion.0) at z similar to 4-5 for galaxies fainter than 0.2 L* (-19 mag). xi(ion.0) quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of xi(ion.0) to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe xi(ion.0) to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and approximate to 300 3 < z < 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6] [4.5] colors are derived and used to infer the H alpha rest-frame equivalent widths, which range from 403 angstrom to 2818 angstrom. The derived xi(ion.0) is log(10)(xi(ion.0)/Hz erg(-1)) = 25.36 0.08 over-20.5 < Muv <-17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that 6011 shows no strong dependence on M-UV. The xi(ion.0) values found in our sample imply that the Lyman-continuum escape fraction for M-UV approximate to-19 star-forming galaxies cannot exceed approximate to 8-20% in the reionization era. Show less
The assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time. Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible... Show moreThe assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time. Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible to measure this beyond the local Universe. Here we present the spatial distribution of H{$α$} emission for a sample of 54 strongly star-forming galaxies at z \~{} 1 in the 3D-HST Treasury survey. By stacking the H{$α$} emission, we find that star formation occurred in approximately exponential distributions at z \~{} 1, with a median Sérsic index of n = 1.0 {\plusmn} 0.2. The stacks are elongated with median axis ratios of b/a = 0.58 {\plusmn} 0.09 in H{$α$} consistent with (possibly thick) disks at random orientation angles. Keck spectra obtained for a subset of eight of the galaxies show clear evidence for rotation, with inclination corrected velocities of 90-330 km s$^{-1}$. The most straightforward interpretation of our results is that star formation in strongly star-forming galaxies at z \~{} 1 generally occurred in disks. The disks appear to be ''scaled-up'' versions of nearby spiral galaxies: they have EW(H{$α$}) \~{} 100 Å out to the solar orbit and they have star formation surface densities above the threshold for driving galactic scale winds. Show less
