The Redshift Evolution of Rest-UV Spectroscopic Properties to z~5. (arXiv:1910.04179v1 [astro-ph.GA])

The Redshift Evolution of Rest-UV Spectroscopic Properties to z~5. (arXiv:1910.04179v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pahl_A/0/1/0/all/0/1">Anthony J. Pahl</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shapley_A/0/1/0/all/0/1">Alice Shapley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Faisst_A/0/1/0/all/0/1">Andreas L. Faisst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Capak_P/0/1/0/all/0/1">Peter L. Capak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Du_X/0/1/0/all/0/1">Xinnan Du</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reddy_N/0/1/0/all/0/1">Naveen A. Reddy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laursen_P/0/1/0/all/0/1">Peter Laursen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Topping_M/0/1/0/all/0/1">Michael W. Topping</a>

We perform a comprehensive analysis of the redshift evolution of the rest-UV
spectra of star-forming galaxies out to z~5. We combine new z~5 measurements of
HI Ly$alpha$ and low- and high-ionization interstellar metal absorption
features with comparable measurements at z~2-4. This redshift range covers the
peak epoch of star formation in the Universe and extends back towards the epoch
of reionization. We measure the equivalent widths of interstellar absorption
features using stacked spectra in bins of Ly$alpha$ equivalent width, and
perform corrections to the strength of Ly$alpha$ based on a model for the
transmission of the intergalactic medium. We find a strong trend of decreasing
low-ionization line strength with increasing Ly$alpha$ emission strength over
the redshift range z~2-5, suggesting that both of these quantities are
fundamentally linked to neutral gas covering fraction. At the highest
Ly$alpha$ equivalent widths, we see evolution with increasing redshift towards
greater Ly$alpha$ emission strength at fixed low-ionization absorption
strength. This evolution suggests a higher intrinsic production rate of
Ly$alpha$ photons at z~5 than at lower redshift. Our conclusion is supported
by the joint evolution of the relationships among Ly$alpha$ emission strength,
interstellar absorption strength, and dust reddening. We perform additional
analysis in bins of stellar mass, star-formation rate, UV luminosity, and age,
examining how the relationships between galaxy properties and Ly$alpha$
emission evolve towards higher redshift. We conclude that increasing intrinsic
Ly$alpha$ photon production and strong detection of nebular CIV emission
(signaling lower metallicity) at z~5 indicate an elevated ionized photon
production efficiency ($xi_{rm ion}$).

We perform a comprehensive analysis of the redshift evolution of the rest-UV
spectra of star-forming galaxies out to z~5. We combine new z~5 measurements of
HI Ly$alpha$ and low- and high-ionization interstellar metal absorption
features with comparable measurements at z~2-4. This redshift range covers the
peak epoch of star formation in the Universe and extends back towards the epoch
of reionization. We measure the equivalent widths of interstellar absorption
features using stacked spectra in bins of Ly$alpha$ equivalent width, and
perform corrections to the strength of Ly$alpha$ based on a model for the
transmission of the intergalactic medium. We find a strong trend of decreasing
low-ionization line strength with increasing Ly$alpha$ emission strength over
the redshift range z~2-5, suggesting that both of these quantities are
fundamentally linked to neutral gas covering fraction. At the highest
Ly$alpha$ equivalent widths, we see evolution with increasing redshift towards
greater Ly$alpha$ emission strength at fixed low-ionization absorption
strength. This evolution suggests a higher intrinsic production rate of
Ly$alpha$ photons at z~5 than at lower redshift. Our conclusion is supported
by the joint evolution of the relationships among Ly$alpha$ emission strength,
interstellar absorption strength, and dust reddening. We perform additional
analysis in bins of stellar mass, star-formation rate, UV luminosity, and age,
examining how the relationships between galaxy properties and Ly$alpha$
emission evolve towards higher redshift. We conclude that increasing intrinsic
Ly$alpha$ photon production and strong detection of nebular CIV emission
(signaling lower metallicity) at z~5 indicate an elevated ionized photon
production efficiency ($xi_{rm ion}$).

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