%0 Generic %1 atek2023first %A Atek, Hakim %A Labbé, Ivo %A Furtak, Lukas J. %A Chemerynska, Iryna %A Fujimoto, Seiji %A Setton, David J. %A Miller, Tim B. %A Oesch, Pascal %A Bezanson, Rachel %A Price, Sedona H. %A Dayal, Pratika %A Zitrin, Adi %A Kokorev, Vasily %A Weaver, John R. %A Brammer, Gabriel %A van Dokkum, Pieter %A Williams, Christina C. %A Cutler, Sam E. %A Feldmann, Robert %A Fudamoto, Yoshinobu %A Greene, Jenny E. %A Leja, Joel %A Maseda, Michael V. %A Muzzin, Adam %A Pan, Richard %A Papovich, Casey %A Nelson, Erica J. %A Nanayakkara, Themiya %A Stark, Daniel P. %A Stefanon, Mauro %A Suess, Katherine A. %A Wang, Bingjie %A Whitaker, Katherine E. %D 2023 %K astrophysics %T First spectroscopic observations of the galaxies that reionized the Universe %U http://arxiv.org/abs/2308.08540 %X High-redshift low-mass galaxies are believed to be the building blocks of present-day galaxies. Their sheer prevalence, compared to their more massive counterparts, makes them the most representative examples of the first generation of galaxies. Furthermore, they likely played a pivotal role in cosmic reionization between redshifts of $z=9$ and $z=6$. However, this population has continued to elude comprehensive spectroscopic studies. As a consequence, their role in comic reionization has remained unclear, owing to the uncertainties surrounding their photometric redshifts and the lack of constraints on both their ionizing photon production and escape fraction. Here we report the first spectroscopic analysis of 8 ultra-faint galaxies during the epoch of reionization with absolute magnitudes between M$_UV -17$ to $-15$ mag (down to 0.005 $L^\star$). The combination of ultra-deep NIRSpec (Near-Infrared Spectrograph) observations and the strong gravitational lensing of Abell~2744 allows us to explore an uncharted territory of early galaxy formation. Remarkably, some of these galaxies have stellar masses as low as $7.6_-1.4^+1.7 10^5$ \msol, comparable to dwarf galaxies in the local group, and extremely low metallicities of only 1 to 6\% $Z_ødot$. This sample allows us to derive the first combined spectroscopic constraints on both the prevalence of faint galaxies and their ionizing properties during the Universe's first billion years. We find that faint galaxies have an ionizing efficiency of log($\xi_ion$/ Hz erg$^-1$)=$25.80.05$, about a factor of 4 larger than canonical values. This means that the total ionizing photon budget produced by galaxies exceeds the reionization threshold, even for modest values of $f_esc$ =5%. These findings provide robust evidence that faint galaxies were the main drivers of cosmic reionization at $z\sim7$.

@misc{atek2023first, abstract = {High-redshift low-mass galaxies are believed to be the building blocks of present-day galaxies. Their sheer prevalence, compared to their more massive counterparts, makes them the most representative examples of the first generation of galaxies. Furthermore, they likely played a pivotal role in cosmic reionization between redshifts of $z=9$ and $z=6$. However, this population has continued to elude comprehensive spectroscopic studies. As a consequence, their role in comic reionization has remained unclear, owing to the uncertainties surrounding their photometric redshifts and the lack of constraints on both their ionizing photon production and escape fraction. Here we report the first spectroscopic analysis of 8 ultra-faint galaxies during the epoch of reionization with absolute magnitudes between M$_{\rm UV} \sim -17$ to $-15$ mag (down to 0.005 $L^{\star}$). The combination of ultra-deep NIRSpec (Near-Infrared Spectrograph) observations and the strong gravitational lensing of Abell~2744 allows us to explore an uncharted territory of early galaxy formation. Remarkably, some of these galaxies have stellar masses as low as $7.6_{-1.4}^{+1.7} \times 10^{5}$ \msol, comparable to dwarf galaxies in the local group, and extremely low metallicities of only 1 to 6\% $Z_{\odot}$. This sample allows us to derive the first combined spectroscopic constraints on both the prevalence of faint galaxies and their ionizing properties during the Universe's first billion years. We find that faint galaxies have an ionizing efficiency of log($\xi_{\rm ion}$/ Hz erg$^{-1}$)=$25.8\pm 0.05$, about a factor of 4 larger than canonical values. This means that the total ionizing photon budget produced by galaxies exceeds the reionization threshold, even for modest values of $f_{\rm esc}$ =5%. These findings provide robust evidence that faint galaxies were the main drivers of cosmic reionization at $z\sim7$.}, added-at = {2023-08-17T11:45:28.000+0200}, author = {Atek, Hakim and Labbé, Ivo and Furtak, Lukas J. and Chemerynska, Iryna and Fujimoto, Seiji and Setton, David J. and Miller, Tim B. and Oesch, Pascal and Bezanson, Rachel and Price, Sedona H. and Dayal, Pratika and Zitrin, Adi and Kokorev, Vasily and Weaver, John R. and Brammer, Gabriel and van Dokkum, Pieter and Williams, Christina C. and Cutler, Sam E. and Feldmann, Robert and Fudamoto, Yoshinobu and Greene, Jenny E. and Leja, Joel and Maseda, Michael V. and Muzzin, Adam and Pan, Richard and Papovich, Casey and Nelson, Erica J. and Nanayakkara, Themiya and Stark, Daniel P. and Stefanon, Mauro and Suess, Katherine A. and Wang, Bingjie and Whitaker, Katherine E.}, biburl = {https://www.bibsonomy.org/bibtex/2dea25a07acdea0a8c7053709a661d613/fboulang}, description = {First spectroscopic observations of the galaxies that reionized the Universe}, interhash = {0a14978639d34dfda2ab6c316d513790}, intrahash = {dea25a07acdea0a8c7053709a661d613}, keywords = {astrophysics}, note = {cite arxiv:2308.08540Comment: 29 pages, 7 figures, 2 tables}, timestamp = {2023-08-17T11:45:28.000+0200}, title = {First spectroscopic observations of the galaxies that reionized the Universe}, url = {http://arxiv.org/abs/2308.08540}, year = 2023 }