%0 Generic %1 becker2021ionizing %A Becker, George D. %A D'Aloisio, Anson %A Christenson, Holly M. %A Zhu, Yongda %A Worseck, Gábor %A Bolton, James S. %D 2021 %K library %T The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization %U http://arxiv.org/abs/2103.16610 %X The mean free path of ionizing photons, $łambda_mfp$, is a key factor in the photoionization of the intergalactic medium (IGM). At $z 5$, however, $łambda_mfp$ may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of $łambda_mfp$ that address this bias and extend up to $z 6$ for the first time. Our measurements at $z 5$ are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At $z 6$ we use QSO spectra from Keck ESI and VLT X-Shooter. We measure $łambda_mfp = 9.09^+1.28_-1.60$ proper Mpc and $0.75^+0.65_-0.45$ proper Mpc (68% confidence) at $z = 5.1$ and 6.0, respectively. The results at $z = 5.1$ are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At $z = 6.0$, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at $z = 6.0$ falls well below extrapolations from lower redshifts, indicating rapid evolution in $łambda_mfp$ over $5 < z < 6$. This evolution disfavors models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by $z = 6$, but is qualitatively consistent with models wherein reionization completed at $z = 6$ or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20% neutral at $z = 6$, although our measurement at $z = 6.0$ is even lower than these models prefer.

@misc{becker2021ionizing, abstract = {The mean free path of ionizing photons, $\lambda_{\rm mfp}$, is a key factor in the photoionization of the intergalactic medium (IGM). At $z \gtrsim 5$, however, $\lambda_{\rm mfp}$ may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of $\lambda_{\rm mfp}$ that address this bias and extend up to $z \sim 6$ for the first time. Our measurements at $z \sim 5$ are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At $z \sim 6$ we use QSO spectra from Keck ESI and VLT X-Shooter. We measure $\lambda_{\rm mfp} = 9.09^{+1.28}_{-1.60}$ proper Mpc and $0.75^{+0.65}_{-0.45}$ proper Mpc (68% confidence) at $z = 5.1$ and 6.0, respectively. The results at $z = 5.1$ are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At $z = 6.0$, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at $z = 6.0$ falls well below extrapolations from lower redshifts, indicating rapid evolution in $\lambda_{\rm mfp}$ over $5 < z < 6$. This evolution disfavors models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by $z = 6$, but is qualitatively consistent with models wherein reionization completed at $z = 6$ or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20% neutral at $z = 6$, although our measurement at $z = 6.0$ is even lower than these models prefer.}, added-at = {2021-04-01T09:51:28.000+0200}, author = {Becker, George D. and D'Aloisio, Anson and Christenson, Holly M. and Zhu, Yongda and Worseck, Gábor and Bolton, James S.}, biburl = {https://www.bibsonomy.org/bibtex/24a4bf85f1adaf6dba8118b5f6a5680c8/gpkulkarni}, description = {The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization}, interhash = {4d329d78314a2e468fe6a1e070924971}, intrahash = {4a4bf85f1adaf6dba8118b5f6a5680c8}, keywords = {library}, note = {cite arxiv:2103.16610Comment: Submitted to MNRAS. Comments welcome}, timestamp = {2021-04-01T09:51:28.000+0200}, title = {The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization}, url = {http://arxiv.org/abs/2103.16610}, year = 2021 }