%0 Generic %1 shull2015metagalactic %A Shull, J. Michael %A Moloney, Joshua %A Danforth, Charles W. %A Tilton, Evan M. %D 2015 %K phon production uvb %T The Metagalactic Ionizing Background: A Crisis in UV Photon Production or Incorrect Galaxy Escape Fractions? %U http://arxiv.org/abs/1502.00637 %X Recent suggestions of a "photon underproduction crisis" (Kollmeier et al 2014) have generated concern over the intensity and spectrum of ionizing photons in the metagalactic ultraviolet background (UVB). The balance of hydrogen photoionization and recombination determines the opacity of the low-redshift intergalactic medium (IGM). We calibrate the hydrogen photoionization rate ($\Gamma_H$) by comparing Hubble Space Telescope spectroscopic surveys of the low-redshift column density distribution of H I absorbers to new cosmological simulations. The distribution, $f(N_HI, z) = d^2N/d(log N_HI) dz$, is consistent with an increased UVB that includes contributions from both quasars and galaxies. Our recommended fit, $\Gamma_H(z) = (4.6x10^-14~s^-1)(1+z)^4.4$ for $0 < z < 0.5$, corresponds to unidirectional LyC photon flux $\Phi_0 = 5700$ cm$^-2$ s$^-1$ at z = 0. This flux agrees with observed IGM metal ionization ratios (C III / C IV and Si III / Si IV) and suggests a 25-30\% contribution of the Lya absorbers to the cosmic baryon inventory. The primary uncertainties in the low-redshift UVB are the contribution from massive stars in galaxies and the LyC escape fraction ($f_esc$), a highly directional quantity that is difficult to constrain statistically. We suggest that low-mass starburst galaxies are important contributors to the ionizing UVB at z < 2. Their additional flux would resolve any crisis in photon underproduction.

@misc{shull2015metagalactic, abstract = {Recent suggestions of a "photon underproduction crisis" (Kollmeier et al 2014) have generated concern over the intensity and spectrum of ionizing photons in the metagalactic ultraviolet background (UVB). The balance of hydrogen photoionization and recombination determines the opacity of the low-redshift intergalactic medium (IGM). We calibrate the hydrogen photoionization rate ($\Gamma_H$) by comparing Hubble Space Telescope spectroscopic surveys of the low-redshift column density distribution of H I absorbers to new cosmological simulations. The distribution, $f(N_{HI}, z) = d^2N/d(log N_{HI}) dz$, is consistent with an increased UVB that includes contributions from both quasars and galaxies. Our recommended fit, $\Gamma_H(z) = (4.6x10^{-14}~s^{-1})(1+z)^{4.4}$ for $0 < z < 0.5$, corresponds to unidirectional LyC photon flux $\Phi_0 = 5700$ cm$^{-2}$ s$^{-1}$ at z = 0. This flux agrees with observed IGM metal ionization ratios (C III / C IV and Si III / Si IV) and suggests a 25-30\% contribution of the Lya absorbers to the cosmic baryon inventory. The primary uncertainties in the low-redshift UVB are the contribution from massive stars in galaxies and the LyC escape fraction ($f_{esc}$), a highly directional quantity that is difficult to constrain statistically. We suggest that low-mass starburst galaxies are important contributors to the ionizing UVB at z < 2. Their additional flux would resolve any crisis in photon underproduction.}, added-at = {2015-02-04T11:53:11.000+0100}, author = {Shull, J. Michael and Moloney, Joshua and Danforth, Charles W. and Tilton, Evan M.}, biburl = {https://www.bibsonomy.org/bibtex/2072886fe1301f4c87b262c873b023b40/miki}, description = {[1502.00637] The Metagalactic Ionizing Background: A Crisis in UV Photon Production or Incorrect Galaxy Escape Fractions?}, interhash = {1c6256005a72607c123ba22543e91d7a}, intrahash = {072886fe1301f4c87b262c873b023b40}, keywords = {phon production uvb}, note = {cite arxiv:1502.00637Comment: Submitted to Astrophysical Journal, 8 pages with 2 tables and 2 figures}, timestamp = {2015-02-04T11:53:11.000+0100}, title = {The Metagalactic Ionizing Background: A Crisis in UV Photon Production or Incorrect Galaxy Escape Fractions?}, url = {http://arxiv.org/abs/1502.00637}, year = 2015 }