The synchrony of production and escape: half the bright Ly alpha emitters at z approximate to 2 have Lyman continuum escape fractions approximate to 50 per cent
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The synchrony of production and escape : half the bright Ly alpha emitters at z approximate to 2 have Lyman continuum escape fractions approximate to 50 per cent. / Naidu, Rohan P.; Matthee, Jorryt; Oesch, Pascal A.; Conroy, Charlie; Sobral, David; Pezzulli, Gabriele; Hayes, Matthew; Erb, Dawn; Amorin, Ricardo; Gronke, Max; Schaerer, Daniel; Tacchella, Sandro; Kerutt, Josephine; Paulino-Afonso, Ana; Calhau, Joao; Llerena, Mario; Rottgering, Huub.
In: Monthly Notices of the Royal Astronomical Society, Vol. 510, No. 3, 01.03.2022, p. 4582-4607.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - The synchrony of production and escape
T2 - half the bright Ly alpha emitters at z approximate to 2 have Lyman continuum escape fractions approximate to 50 per cent
AU - Naidu, Rohan P.
AU - Matthee, Jorryt
AU - Oesch, Pascal A.
AU - Conroy, Charlie
AU - Sobral, David
AU - Pezzulli, Gabriele
AU - Hayes, Matthew
AU - Erb, Dawn
AU - Amorin, Ricardo
AU - Gronke, Max
AU - Schaerer, Daniel
AU - Tacchella, Sandro
AU - Kerutt, Josephine
AU - Paulino-Afonso, Ana
AU - Calhau, Joao
AU - Llerena, Mario
AU - Rottgering, Huub
PY - 2022/3/1
Y1 - 2022/3/1
N2 - The ionizing photon escape fraction [Lyman continuum (LyC) f(esc)] of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshifts. Here we circumvent this uncertainty by inferring f(esc) using resolved (R > 4000) Lyman alpha (Ly alpha) profiles from the X-SHOOTER Ly alpha survey at z = 2 (XLS-z2). With empirically motivated criteria, we use Ly alpha profiles to select leakers (f(esc) > 20 per cent) and non-leakers (f(esc) < 5 per cent) from a representative sample of >0.2L* Lyman alpha emitters (LAEs). We use median stacked spectra of these subsets over lambda(rest) approximate to 1000-8000 angstrom to investigate the conditions for LyC f(esc). Our stacks show similar mass, metallicity, M-UV, and beta(UV). We find the following differences between leakers versus non-leakers: (i) strong nebular C IV and He II emission versus non-detections; (ii) [O III]/[O II] approximate to 8.5 versus approximate to 3; (iii) H alpha/H beta indicating no dust versus E(B - V) approximate to 0.3; (iv) Mg II emission close to the systemic velocity versus redshifted, optically thick Mg II; and (v) Ly alpha f(esc) of approximate to 50 per cent versus approximate to 10 per cent. The extreme equivalent widths (EWs) in leakers ([O III]+H beta approximate to 1100 Arest frame) constrain the characteristic time-scale of LyC escape to approximate to 3-10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers - extremely ionizing stellar populations, low column densities, a dust-free, high-ionization state interstellar medium (ISM) - occur simultaneously in the f(esc) > 20 per cent stack, suggesting they are causally connected, and motivating why indicators like [O III]/[O II] may suffice to constrain f(esc) at z > 6 with the James Webb Space Telescope (JWST). The leakers comprise half of our sample, have a median LyC f(esc) approximate to 50 per cent (conservative range: 20-55 per cent), and an ionizing production efficiency log(xi(ion)/Hz erg(-1)) approximate to 25.9 (conservative range: 25.7-25.9). These results show LAEs - the type of galaxies rare at z approximate to 2, but that become the norm at higher redshift - are highly efficient ionizers, with extreme xi(ion) and prolific f(esc) occurring in sync.
AB - The ionizing photon escape fraction [Lyman continuum (LyC) f(esc)] of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshifts. Here we circumvent this uncertainty by inferring f(esc) using resolved (R > 4000) Lyman alpha (Ly alpha) profiles from the X-SHOOTER Ly alpha survey at z = 2 (XLS-z2). With empirically motivated criteria, we use Ly alpha profiles to select leakers (f(esc) > 20 per cent) and non-leakers (f(esc) < 5 per cent) from a representative sample of >0.2L* Lyman alpha emitters (LAEs). We use median stacked spectra of these subsets over lambda(rest) approximate to 1000-8000 angstrom to investigate the conditions for LyC f(esc). Our stacks show similar mass, metallicity, M-UV, and beta(UV). We find the following differences between leakers versus non-leakers: (i) strong nebular C IV and He II emission versus non-detections; (ii) [O III]/[O II] approximate to 8.5 versus approximate to 3; (iii) H alpha/H beta indicating no dust versus E(B - V) approximate to 0.3; (iv) Mg II emission close to the systemic velocity versus redshifted, optically thick Mg II; and (v) Ly alpha f(esc) of approximate to 50 per cent versus approximate to 10 per cent. The extreme equivalent widths (EWs) in leakers ([O III]+H beta approximate to 1100 Arest frame) constrain the characteristic time-scale of LyC escape to approximate to 3-10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers - extremely ionizing stellar populations, low column densities, a dust-free, high-ionization state interstellar medium (ISM) - occur simultaneously in the f(esc) > 20 per cent stack, suggesting they are causally connected, and motivating why indicators like [O III]/[O II] may suffice to constrain f(esc) at z > 6 with the James Webb Space Telescope (JWST). The leakers comprise half of our sample, have a median LyC f(esc) approximate to 50 per cent (conservative range: 20-55 per cent), and an ionizing production efficiency log(xi(ion)/Hz erg(-1)) approximate to 25.9 (conservative range: 25.7-25.9). These results show LAEs - the type of galaxies rare at z approximate to 2, but that become the norm at higher redshift - are highly efficient ionizers, with extreme xi(ion) and prolific f(esc) occurring in sync.
KW - galaxies: evolution
KW - galaxies: high-redshift
KW - intergalactic medium
KW - dark ages, reionization, first stars
KW - cosmology: observations
KW - ultraviolet: galaxies
KW - STAR-FORMING GALAXIES
KW - SPECTRAL ENERGY-DISTRIBUTION
KW - EMISSION-LINE DIAGNOSTICS
KW - HIGH-REDSHIFT GALAXIES
KW - O III EMITTERS
KW - IONIZING-RADIATION
KW - LUMINOSITY FUNCTION
KW - STELLAR MASS
KW - COSMIC REIONIZATION
KW - EMITTING GALAXIES
U2 - 10.1093/mnras/stab3601
DO - 10.1093/mnras/stab3601
M3 - Journal article
VL - 510
SP - 4582
EP - 4607
JO - Royal Astronomical Society. Monthly Notices
JF - Royal Astronomical Society. Monthly Notices
SN - 0035-8711
IS - 3
ER -
ID: 303443500