A Cosmic Miracle: A Remarkably Luminous Galaxy at $z_{\rm{spec}}=14.44$ Confirmed with JWST

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 ($M_{\rm{UV}}=-20.2$) source in the COSMOS field at $z_{\rm{spec}}=14.44^{+0.02}_{-0.02}$ 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 $\sim3σ$ detections of five rest-UV emission lines. The number density of bright $z_{\rm{spec}}\sim14-15$ sources implied by our "Mirage or Miracle" survey spanning $\sim350$ arcmin$^{2}$ is $>100\times$ larger ($182^{+329}_{-105}\times$) than pre-JWST consensus models. The high EWs of UV lines ($\sim15{-}35$ Å) signal a rising star-formation history, with a $\sim10\times$ increase in the last 5 Myr ($\rm{SFR_{\rm{5Myr}}}/\rm{SFR_{\rm{50Myr}}}=9.9^{+3.0}_{-5.8}$). The source is extremely compact (circularized $r_{\rm{e}} = 74^{+15}_{-12}$ 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 $\sim100\%$ neutral fraction. The nitrogen emission and highly super-solar [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.

Figures (16)

• Figure 1: JWST imaging and spectroscopy of MoM-z14.Top:$1\times1"$ NIRCam images spanning 0.9-5$\mu$m show a compact source detected at $\gtrsim2\mu$m that is entirely absent in bluer bands. Inset: NIRCam RGB image with NIRSpec MSA slitlets overlaid from our "Mirage or Miracle" survey. The source is well-centered and slit losses are modest such that the recovered spectral flux is fully consistent with the NIRCam imaging (see Appendix). Bottom: The prism spectrum (2D SNR spectrum on top, 1D spectrum with 1$\sigma$ errors on the bottom) reveals that the disappearance of the source below $2\mu$m in the imaging is due to an abrupt break whose sharpness implies it is a Lyman-$\alpha$ break. Furthermore, an array of emission lines (dashed lines) supporting the Lyman-$\alpha$ break interpretation is evident. The most prominent among these lines (N iv]$\lambda1487$Å, C iv$\lambda1548,1551$Å, C iii]$\lambda1907,1909$Å) are typically the strongest lines observed in UV spectra of luminous $z>10$ galaxies Bunker23Castellano24Carniani24.
• Figure 2: Summary of spectroscopic redshift constraints.Top-left: We use the sharp Lyman-$\alpha$ break to derive the redshift ($z_{\rm{break}}$). Our best-fit model (hot pink) accounts for the IGM neutral fraction along the line of sight ($\rm{x}_{\rm{HI}}$) as well as the shape and normalization of the spectrum ($\beta_{\rm{UV}}$, $M_{\rm{UV}}$). See §\ref{['sec:lyaz']} for details. Top-right: We are also able to determine the redshift by fitting the rest-UV emission lines that are detected in this source. Each individual line or blend is detected at $\approx3\sigma$. Collectively, this array of lines is detected at $\approx6\sigma$ resulting in an extremely precise redshift. Bottom-left: The photometric redshift distribution derived from NIRCam (silver) shows multiple peaks at $z<5$ ("Schrodinger galaxy"-like solutions; Naidu22Schro) and a dominant $z>10$ solution that led us to target this source. Bottom-right: Comparison of the break redshift and UV line redshift posteriors. Only a handful of galaxies of comparable luminosity at $z>10$ have shown a UV spectrum with multiple lines allowing for a precise redshift determination (Bunker23Castellano24; both interestingly point-like sources interpreted as putative AGN). Typically, only break redshifts with relatively wide posteriors as shown in pink have been possible Curtis-Lake23Wang23UNCOVERz12Carniani24.
• Figure 3: Compilation of absolute UV magnitude vs. spectroscopic redshift for sources at the cosmic frontier.Bottom: The galaxies shown in silver arise from $\approx600$ arcmin$^{2}$ surveyed by JWST in the first $\approx2.5$ years of its operations. See text for a full list of references. We highlight three of the most well-studied bright sources at these epochs that we reference regularly as points of comparison for MoM-z14 with square markers -- GNz11 Oesch16Bunker23Tacchella23GNz11, GLASS-z12/GHz2 Naidu22Castellano22Castellano24, and JADES-GS-z14-0 Robertson24JOFCarniani24. Top:$1"\times1"$ RGB stamps (F090W, F115W, F277W) of the sources highlighted with square markers. Three of these sources are extremely compact, with GS-z14 being the exception. For the silver points above, we extend the compilation from Roberts-Borsani24 and include the following papers: Curtis-Lake23Wang23UNCOVERz12Fujimoto23ArrabalHaro23Harikane24specuvlfHsiao24Napolitano25Kokorev25Witstok25.
• Figure 4: Results of morphology analysis. The model built with forcepho (middle row) is fit to the three bands simultaneously and provides a satisfactory match to the data (top row) with no appreciable residuals (bottom row). An extremely compact (circularized $r_{\rm{50}} = 74^{+15}_{-12}$ pc) source is recovered in these fits. From these fits it is clear that the object is not dominated by a point-source, as may be expected if its UV luminosity was dominated by an AGN.
• Figure 5: A size-abundance bimodality among bright $z>10$ galaxies. Figure adapted from Harikane2025UVLF who reported this trend (see also Schaerer24). Two types of sources are evident in the size-redshift plane (left) and size-EW plane (right) -- compact N iv] emitters such as MoM-z14 (purple, navy) and extended sources with weak N iv] such as JADES-GS-z14-0 (orange). The extrapolated size evolution from Shibuya15 (silver band) is shown in the left panel for guidance. MoM-z14 joins GNz11 and GLASSz12/GHz2 as extremely compact outliers at $z>10$, with sizes $<5-10\times$ what would be expected from the scaling relation. The measurements shown here are compiled from the following sources: GNz11 Tacchella23GNz11Bunker23, GLASS-z12/GHz2 Castellano24, GNz9p4 Schaerer24, JADES-GS-z14-0 Carniani24, Maisie's Galaxy Finkelstein23ArrabalHaro23, RXCJ2248-ID Topping24, Gz9p3 Boyett24, and CEERS2-588 Harikane24specuvlf.