TY - JOUR

T1 - The Keck Lyman Continuum Spectroscopic Survey (KLCS)

T2 - The Emergent Ionizing Spectrum of Galaxies at z ∼ 3

AU - Steidel, Charles C.

AU - Bogosavljević, Milan

AU - Shapley, Alice E.

AU - Reddy, Naveen A.

AU - Rudie, Gwen C.

AU - Pettini, Max

AU - Trainor, Ryan F.

AU - Strom, Allison L.

N1 - Funding Information:
This work has been supported in part by the US National Science Foundation through grants AST-0606912, AST-0908805, and AST-1313472 (M.B., C.C.S., G.C.R., R.F.T., A.L.S.). C.C.S. acknowledges additional support from the John D. and Catherine T. MacArthur Foundation, the David and Lucile Packard Foundation, and the JPL/Caltech President’s and Director’s program. We thank J. J. Eldridge and Elizabeth Stanway for their continued work developing the BPASS SPS models and for many illuminating conversations. We are grateful to the dedicated staff of the W.M. Keck Observatory who keep the instruments and telescopes running effectively. We wish to extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.
Publisher Copyright:
© 2018. The American Astronomical Society.

PY - 2018/12/20

Y1 - 2018/12/20

N2 - We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at z ∼ 3. We measure the ratio of ionizing to non-ionizing UV flux density , where f 900 is the mean flux density evaluated over the range [880, 910] A. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of , including a full-sample average = 0.057 ± 0.006. We show that increases monotonically with , inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction f c of the stellar continuum is covered by gas with column density . We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L 900/L 1500)int along with f c, and f esc,abs, the absolute escape fraction of ionizing photons. We find a sample-averaged f esc,abs = 0.09 - 0.01, with subsamples falling along a linear relation . Using the far-UV luminosity function, the distribution function n(W(Lyα)), and the relationship between and , we estimate the total ionizing emissivity of z ∼ 3 star-forming galaxies with M uv ≤ -19.5, which exceeds the contribution of quasi-stellar objects by a factor of ∼3, and accounts for ∼50% of the total LyC at z ∼ 3 estimated using indirect methods.

AB - We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at z ∼ 3. We measure the ratio of ionizing to non-ionizing UV flux density , where f 900 is the mean flux density evaluated over the range [880, 910] A. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of , including a full-sample average = 0.057 ± 0.006. We show that increases monotonically with , inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction f c of the stellar continuum is covered by gas with column density . We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L 900/L 1500)int along with f c, and f esc,abs, the absolute escape fraction of ionizing photons. We find a sample-averaged f esc,abs = 0.09 - 0.01, with subsamples falling along a linear relation . Using the far-UV luminosity function, the distribution function n(W(Lyα)), and the relationship between and , we estimate the total ionizing emissivity of z ∼ 3 star-forming galaxies with M uv ≤ -19.5, which exceeds the contribution of quasi-stellar objects by a factor of ∼3, and accounts for ∼50% of the total LyC at z ∼ 3 estimated using indirect methods.

KW - cosmology: observations

KW - galaxies: evolution

KW - galaxies: high-redshift

KW - intergalactic medium

KW - ultraviolet: galaxies

UR - http://www.scopus.com/inward/record.url?scp=85059837662&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85059837662&partnerID=8YFLogxK

U2 - 10.3847/1538-4357/aaed28

DO - 10.3847/1538-4357/aaed28

M3 - Article

AN - SCOPUS:85059837662

VL - 869

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 123

ER -