%0 Generic %1 pezzulli2016faint %A Pezzulli, Edwige %A Valiante, Rosa %A Orofino, Maria C. %A Schneider, Raffaella %A Gallerani, Simona %A Sbarrato, Tullia %D 2016 %K high-z quasars visibility %R 10.1093/mnras/stw3243 %T Faint progenitors of luminous $z 6$ quasars: why don't we see them? %U http://arxiv.org/abs/1612.04188 %X Observational searches for faint active nuclei at $z > 6$ have been extremely elusive, with a few candidates whose high-$z$ nature is still to be confirmed. Interpreting this lack of detections is crucial to improve our understanding of high-$z$ supermassive black holes (SMBHs) formation and growth. In this work, we present a model for the emission of accreting BHs in the X-ray band, taking into account super-Eddington accretion, which can be very common in gas-rich systems at high-$z$. We compute the spectral energy distribution for a sample of active galaxies simulated in a cosmological context, which represent the progenitors of a $z 6$ SMBH with $M_BH 10^9 \, M_ødot$. We find an average Compton thick fraction of $45\%$ and large typical column densities ($N_H 10^23 \, cm^2$). However, faint progenitors are still luminous enough to be detected in the X-ray band of current surveys. Even accounting for a maximum obscuration effect, the number of detectable BHs is reduced at most by a factor 2. In our simulated sample, observations of faint quasars are mainly limited by their very low active fraction ($f_act \sim 1 \%$), which is the result of short, super-critical growth episodes. We suggest that to detect high-$z$ SMBHs progenitors, large area surveys with shallower sensitivities, such as Cosmos Legacy and XMM-LSS+XXL, are to be preferred with respect to deep surveys probing smaller fields, such as CDF-S.

@misc{pezzulli2016faint, abstract = {Observational searches for faint active nuclei at $z > 6$ have been extremely elusive, with a few candidates whose high-$z$ nature is still to be confirmed. Interpreting this lack of detections is crucial to improve our understanding of high-$z$ supermassive black holes (SMBHs) formation and growth. In this work, we present a model for the emission of accreting BHs in the X-ray band, taking into account super-Eddington accretion, which can be very common in gas-rich systems at high-$z$. We compute the spectral energy distribution for a sample of active galaxies simulated in a cosmological context, which represent the progenitors of a $z \sim 6$ SMBH with $M_{\rm BH} \sim 10^9 \, M_\odot$. We find an average Compton thick fraction of $\sim 45\%$ and large typical column densities ($N_H \gtrsim 10^{23} \rm \, cm^2$). However, faint progenitors are still luminous enough to be detected in the X-ray band of current surveys. Even accounting for a maximum obscuration effect, the number of detectable BHs is reduced at most by a factor 2. In our simulated sample, observations of faint quasars are mainly limited by their very low active fraction ($f_{\rm act} \sim 1 \%$), which is the result of short, super-critical growth episodes. We suggest that to detect high-$z$ SMBHs progenitors, large area surveys with shallower sensitivities, such as Cosmos Legacy and XMM-LSS+XXL, are to be preferred with respect to deep surveys probing smaller fields, such as CDF-S.}, added-at = {2016-12-14T11:26:35.000+0100}, author = {Pezzulli, Edwige and Valiante, Rosa and Orofino, Maria C. and Schneider, Raffaella and Gallerani, Simona and Sbarrato, Tullia}, biburl = {https://www.bibsonomy.org/bibtex/2f1cf24208fa437789b0dd609ce20dd3a/miki}, description = {[1612.04188] Faint progenitors of luminous $z \sim 6$ quasars: why don't we see them?}, doi = {10.1093/mnras/stw3243}, interhash = {d7934a95eb525b4801f5adffed8f6945}, intrahash = {f1cf24208fa437789b0dd609ce20dd3a}, keywords = {high-z quasars visibility}, note = {cite arxiv:1612.04188Comment: 12 pages, 9 figures, accepted for publication in MNRAS}, timestamp = {2016-12-14T11:26:35.000+0100}, title = {Faint progenitors of luminous $z \sim 6$ quasars: why don't we see them?}, url = {http://arxiv.org/abs/1612.04188}, year = 2016 }