@article{21342,
  abstract     = {JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, z > 10,
where few such sources were expected. Here we present the most distant example of this class yet – MoM-z14, a luminous (MUV = −20.2) source in the COSMOS legacy field at zspec = 14.44+0.02−0.02 that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/prism spectroscopy through a sharp Lyman-α break and ≈ 3σ detections of five rest-UV emission lines. The number density of bright zspec ≈ 14 − 15 sources implied by our “Mirage or Miracle” survey spanning ≈ 350 arcmin2 is > 100× larger (182+329 −105×) than pre-JWST consensus models. The high EWs of UV lines (≈15−35˚A) signal a rising star-formation history, with a ≈10× increase in the last 5 Myr (SFR5Myr/SFR50Myr = 9.9 +3.0 −5.8). The source is extremely compact (circularized re = 74+15
−12 pc), and yet elongated (b/a = 0.25+0.11−0.06), suggesting an AGN is not the dominant source of UV light. The steep UV slope (β = −2.5 +0.2 −0.2) implies negligible dust attenuation
and a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a ≈ 100% neutral fraction. The nitrogen emission and highly supersolar [N/C]> 1 hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time. },
  author       = {Naidu, Rohan P. and Oesch, Pascal A. and Brammer, Gabriel and Weibel, Andrea and Li, Yijia and Matthee, Jorryt J and Chisholm, John and Pollock, Clara L. and Heintz, Kasper E. and Johnson, Benjamin D. and Shen, Xuejian and Hviding, Raphael E. and Leja, Joel and Tacchella, Sandro and Ganguly, Arpita and Witten, Callum and Atek, Hakim and Belli, Sirio and Bose, Sownak and Bouwens, Rychard and Dayal, Pratika and Decarli, Roberto and De Graaff, Anna and Fudamoto, Yoshinobu and Giovinazzo, Emma and Greene, Jenny E. and Illingworth, Garth and Inoue, Akio K. and Kane, Sarah G. and Labbe, Ivo and Leonova, Ecaterina and Marques-Chaves, Rui and Meyer, Romain A. and Nelson, Erica J. and Roberts-Borsani, Guido and Schaerer, Daniel and Simcoe, Robert A. and Stefanon, Mauro and Sugahara, Yuma and Toft, Sune and Van Der Wel, Arjen and Van Dokkum, Pieter and Walter, Fabian and Watson, Darach and Weaver, John R. and Whitaker, Katherine E.},
  issn         = {2565-6120},
  journal      = {The Open Journal of Astrophysics},
  publisher    = {Maynooth Academic Publishing},
  title        = {{A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST}},
  doi          = {10.33232/001c.156033},
  volume       = {9},
  year         = {2026},
}

@article{20192,
  abstract     = {We study the physical origin and spectroscopic impact of extreme nebular emission in high-redshift galaxies. The nebular continuum, which can appear during an extreme starburst, is of particular importance as it tends to redden UV slopes and has a significant contribution to the UV luminosities of galaxies. Furthermore, its shape can be used to infer the gas density and temperature of the interstellar medium. First, we provide a theoretical background, showing how different stellar populations (SPS models, initial mass functions (IMFs), and stellar temperatures) and nebular conditions impact observed galaxy spectra. We demonstrate that, for systems with strong nebular continuum emission, 1) UV fluxes can increase by up to 0.7~mag (or more in the case of hot/massive stars) above the stellar continuum, which may help reconcile the surprising abundance of bright high-redshift galaxies and the elevated UV luminosity density at z>10, 2) at high gas densities, UV slopes can redden from \beta<-2.5 to \beta\sim-1, 3) observational measurements of \xi_{\rm ion} are gross underestimates, and 4) UV downturns from two-photon emission can masquerade as damped Ly\alpha systems. Second, we present a dataset of 58 galaxies observed with NIRSpec on JWST at 2.5<z<9.0 that are selected to have strong nebular continuum emission via the detection of the Balmer jump. Five of the 58 spectra are consistent with being dominated by nebular emission, exhibiting both a Balmer jump and a UV downturn consistent with two-photon emission. For some galaxies, this may imply the presence of hot massive stars and a top-heavy IMF. We conclude by exploring the properties of spectroscopically confirmed z>10 galaxies, finding that UV slopes and UV downturns are in some cases redder or steeper than expected from SPS models, which may hint at more exotic (e.g. hotter/more massive stars or AGN) ionizing sources.},
  author       = {Katz, Harley and Cameron, Alex J. and Saxena, Aayush and Barrufet, Laia and Choustikov, Nicholas and Cleri, Nikko J. and De Graaff, Anna and Ellis, Richard S. and Fosbury, Robert A.E. and Heintz, Kasper E. and Maseda, Michael and Matthee, Jorryt J and Mcconachie, Ian and Oesch, Pascal A.},
  issn         = {2565-6120},
  journal      = {The Open Journal of Astrophysics},
  publisher    = {Maynooth Academic Publishing},
  title        = {{21 Balmer Jump Street: The nebular continuum at high redshift and implications for the bright galaxy problem, UV continuum slopes, and early stellar populations}},
  doi          = {10.33232/001c.142570},
  volume       = {8},
  year         = {2025},
}