%0 Generic %1 shull2017ultraviolet %A Shull, J. Michael %A Danforth, Charles W. %A Tilton, Evan M. %A Moloney, Joshua %A Stevans, Matthew L. %D 2017 %K LLS UV low-z survey %T An Ultraviolet Survey of Low-Redshift Partial Lyman-Limit Systems with the HST Cosmic Origins Spectrograph %U http://arxiv.org/abs/1710.03232 %X We present an ultraviolet spectroscopic survey of strong H I absorbers in the intergalactic medium, probing their evolution over the last 6-7 Gyr at redshifts $0.24 z 0.84$. We measure column densities $N_HI \,( cm^-2)$ from the pattern of Lyman-series absorption lines and flux decrement at the Lyman limit (LL) when available. We analyzed 220 H I absorbers in ultraviolet spectra of 102 active galactic nuclei (AGN) taken by the Cosmic Origins Spectrograph aboard the Hubble Space Telescope with G130M/G160M gratings (1134-1795 \AA). For 158 absorbers with $N_HI 15$, the mean frequency is $d N/dz = 4.95 0.39$ over pathlength $\Delta z = 31.94$ ($0.24 z 0.84)$. We identify 8 Lyman Limit Systems (LLS, $łog N_HI 17.2$) and 54 partial systems (pLLS) with $16.0 łog N_HI < 17.2$. Toward 159 AGN between $0.01 < z_abs < 0.84$ with $\Delta z 48$, we find four damped Ly$\alpha$ absorbers (DLA) with $(d N/dz)_DLA = 0.083^+0.066_-0.040$ at $z = 0.18$. The mean LLS frequency between $z = 0.24-0.48$ is $(d N/dz)_\rm LLS = 0.36^+0.20_-0.13$ fitted to $N(z) = (0.25^+0.13_-0.09)(1+z)^1.14$. For 54 pLLS we find $(d N/dz)_\rm pLLS = 1.69\pm0.23$ at $z = 0.39$, a frequency consistent with gaseous halo sizes $R 100 h^-1~kpc$ for ($0.3-3L^*$) galaxies. A maximum-likelihood analysis yields a distribution $f(N,z) = C_0 N^-\beta (1+z)^\gamma$ with $= 1.48 0.05$ and $= 1.14^+0.88_-0.89$ for $15 N_HI 17.5$. The far-UV opacity gradient is $d \tau_eff / dz (0.444)(1+z)^1.14$ over the range $15 N_HI 17$, implying mean LyC optical depth $\tau_eff 0.3-0.5$ toward sources at $z = 1-2$.

@misc{shull2017ultraviolet, abstract = {We present an ultraviolet spectroscopic survey of strong H I absorbers in the intergalactic medium, probing their evolution over the last 6-7 Gyr at redshifts $0.24 \leq z \leq 0.84$. We measure column densities $N_{\rm HI} \,( {\rm cm}^{-2})$ from the pattern of Lyman-series absorption lines and flux decrement at the Lyman limit (LL) when available. We analyzed 220 H I absorbers in ultraviolet spectra of 102 active galactic nuclei (AGN) taken by the Cosmic Origins Spectrograph aboard the Hubble Space Telescope with G130M/G160M gratings (1134-1795 \AA). For 158 absorbers with $\log N_{\rm HI} \geq 15$, the mean frequency is $d {\cal N}/dz = 4.95 \pm 0.39$ over pathlength $\Delta z = 31.94$ ($0.24 \leq z \leq 0.84)$. We identify 8 Lyman Limit Systems (LLS, $\log N_{\rm HI} \geq 17.2$) and 54 partial systems (pLLS) with $16.0 \leq \log N_{\rm HI} < 17.2$. Toward 159 AGN between $0.01 < z_{\rm abs} < 0.84$ with $\Delta z \approx 48$, we find four damped Ly$\alpha$ absorbers (DLA) with $(d {\cal N}/dz)_{\rm DLA} = 0.083^{+0.066}_{-0.040}$ at $\langle z \rangle = 0.18$. The mean LLS frequency between $z = 0.24-0.48$ is $(d {\cal N}/dz)_{\rm LLS} = 0.36^{+0.20}_{-0.13}$ fitted to $N(z) = (0.25^{+0.13}_{-0.09})(1+z)^{1.14}$. For 54 pLLS we find $(d {\cal N}/dz)_{\rm pLLS} = 1.69\pm0.23$ at $\langle z \rangle = 0.39$, a frequency consistent with gaseous halo sizes $R \approx 100 h^{-1}~{\rm kpc}$ for ($0.3-3L^*$) galaxies. A maximum-likelihood analysis yields a distribution $f(N,z) = C_0 N^{-\beta} (1+z)^{\gamma}$ with $\beta = 1.48 \pm 0.05$ and $\gamma = 1.14^{+0.88}_{-0.89}$ for $15 \leq \log N_{\rm HI} \leq 17.5$. The far-UV opacity gradient is $d \tau_{\rm eff} / dz \approx (0.444)(1+z)^{1.14}$ over the range $15 \leq \log N_{\rm HI} \leq 17$, implying mean LyC optical depth $\tau_{\rm eff} \approx 0.3-0.5$ toward sources at $z = 1-2$.}, added-at = {2017-10-11T10:00:58.000+0200}, author = {Shull, J. Michael and Danforth, Charles W. and Tilton, Evan M. and Moloney, Joshua and Stevans, Matthew L.}, biburl = {https://www.bibsonomy.org/bibtex/2356fe0e5813a6e8d388647781bd1be6a/miki}, description = {[1710.03232] An Ultraviolet Survey of Low-Redshift Partial Lyman-Limit Systems with the HST Cosmic Origins Spectrograph}, interhash = {db78a3cb279ce2378135e3f424f87b59}, intrahash = {356fe0e5813a6e8d388647781bd1be6a}, keywords = {LLS UV low-z survey}, note = {cite arxiv:1710.03232Comment: Accepted for publication (Astrophys J), 34 pages, 13 figures, 2 appendices}, timestamp = {2017-10-11T10:00:58.000+0200}, title = {An Ultraviolet Survey of Low-Redshift Partial Lyman-Limit Systems with the HST Cosmic Origins Spectrograph}, url = {http://arxiv.org/abs/1710.03232}, year = 2017 }