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A massive barred spiral galaxy at z = 5.102 discovered by JWST

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Xiaohan Wang, Fengwu Sun, Yoshihisa Asada, Yunjing Wu, Xiaojing Lin, Shude Mao, Sijia Cai, Zheng Cai
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Chian-Chou Chen, Wenlei Chen, Cheng Cheng, Christopher J. Conselice, Miroslava Dessauges-Zavadsky, Daneil Espada, Brenda L. Frye, Jean-Baptiste Jolly, Anton M. Koekemoer, Kotaro Kohno, Mingyu Li, Nicholas Martis, Hideki Umehata, Weichen Wang, Rogier A. Windhorst, Adi Zitrin

Astrophysics of Galaxies · Submitted 23 Jun 2026 · 124 references

Pith's verdict: A z=5.1 barred spiral candidate whose morphology claim needs more checks against AGN and companion effects.

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arXiv ID2606.25022 (version 1)
Pith IDU7OVSVVM, Pith's permanent record of this paper and its review
CitationAdi Zitrin, Anton M. Koekemoer, Brenda L. Frye, Cheng cheng, Chian-Chou Chen, Christopher J. Conselice, Daneil Espada, Fengwu Sun, Hideki Umehata, Jean-Baptiste Jolly, Kotaro Kohno, Mingyu Li, Miroslava Dessauges-Zavadsky, Nicholas Martis, Rogier A. Windhorst, Shude Mao, Sijia Cai, Weichen Wang, Wenlei Chen, Xiaohan Wang, Xiaojing Lin, Yoshihisa Asada, Yunjing Wu, Zheng Cai. "A massive barred spiral galaxy at z = 5.102 discovered by JWST." arXiv:2606.25022 (2026). https://pith.science/paper/U7OVSVVM
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The paper

The paper claims

A barred spiral galaxy exists at redshift 5.102, the highest-redshift example identified so far.

The reading

The paper reports the identification of M1149-BSG-z5 as a barred spiral galaxy at z = 5.102 in JWST and HST imaging. Isophote fitting and structural modeling show a stellar bar roughly 4.5 kpc long together with extended spiral arms. The object is a massive main-sequence star-forming galaxy that also contains a broad-line AGN and sits in an overdense region with a companion. These features together indicate that a large, chemically evolved disk galaxy with a bar had already assembled within the first 1.2 billion years after the Big Bang.

What carries the argument

Isophote ellipse fitting and two-dimensional structural modeling that together extract the bar length, disk scale, and spiral-arm locations from the observed light distribution.

Extended reading notes

Core claim

M1149-BSG-z5 is a barred spiral galaxy at z = 5.102 with a stellar bar of length a_bar ≈ 4.5 kpc and spiral arms peaking at r ≈ 5.5 kpc, embedded in an extended disk with global Sérsic index n = 2.37 and effective radius R_e = 2.61 kpc; the galaxy has stellar mass 10^10.45 M_⊙, star-formation rate 144 M_⊙ yr^−1, and hosts a broad-line AGN with M_BH/M_* ∼ 10^−3.

Load-bearing premise

The observed light profile at the available resolution and wavelength traces a true stellar bar in a stable disk rather than projection effects, merger remnants, or other morphological features.

Editorial extensions

If this is right

  • Complex galactic structures such as bars and spiral arms can form and remain stable by z = 5.102.
  • Interaction with a nearby companion in an overdense environment can trigger bar formation at early times.
  • Baryon-dominated, gas-rich conditions enable gravitational instabilities that accelerate bar growth on short timescales.
  • The galaxy's size and Sérsic index are already comparable to barred systems observed at 2 < z < 4, implying rapid structural maturation.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If this single detection is representative, the epoch when bars first appear may need to be pushed earlier in galaxy-formation models.
  • Targeted JWST surveys of other overdense fields at z > 5 could test whether interaction-driven bars are common at these redshifts.
  • Future integral-field spectroscopy could measure the bar's pattern speed and confirm dynamical stability directly.
Original abstract

We report M1149-BSG-z5, a barred spiral galaxy at $z = 5.102$, identified in the parallel field of MACS J1149+2223 with JWST and HST. M1149-BSG-z5 is the highest redshift barred galaxy candidate to date. Both isophote ellipse fitting and structural modeling support a stellar bar of length $a_\mathrm{bar} \approx 4.5$ kpc, and extended spiral arms peaking at $r \approx 5.5$ kpc. M1149-BSG-z5 is a massive main sequence star-forming galaxy, with a stellar mass of $10^{10.45}\rm M_\odot$ and a star-formation rate of $144\,\rm M_\odot/yr$. A concentrated bulge is embedded in an extended disk with a global S\'ersic index $n = 2.37$. With an effective radius of $R_{e} = 2.61\rm \ kpc$, M1149-BSG-z5 is larger than typical galaxies at $z \sim 5$ and comparable to barred galaxies at $2 < z < 4$. M1149-BSG-z5 also hosts a broad-line AGN, with a relatively low black-hole-to-stellar mass ratio of $\rm M_{\rm BH}/M_\ast\sim10^{-3}$. Its metal-enriched emission-line properties indicate that it is already chemically evolved. These properties imply M1149-BSG-z5 as an early-assembled and structurally evolved galaxy. We also find that M1149-BSG-z5 resides in an overdense region with a nearby companion galaxy, suggesting an interaction-driven bar formation mechanism. Its concentrated light, early assembly and main-sequence star formation also suggest baryon-dominated, gas-rich conditions, where gravitational instability can further accelerate the bar formation.

Figures
Figure 1. Top left: composite false-color image of M1149-BSG-z5, created with JWST imaging data taken in F090W+F115W+F150W (blue), F200W+F277W+F300M (green), and F356W+F410M+F444W (red). Image size is 4. ′′35×4. ′′35 (north up, east left). Top right: HST and JWST images of M1149-BSG-z5 across 12 bands at 0.4–5.0 µm. The NIRSpec MSA coverage is shown with dashed squares in the image of F444W. Middle panel: best-fit SED model from CIGALE, accompanied with HST and JWST Kron photometry and JWST NIRSpec G395M/F290LP spectrum. The spectrum is scaled to the photometry observations. Botton panel,…
Figure 2. Ellipse isophote fitting and radial profiles of ellipticity and position angle for ellipse isophotes for JWST stacked images of F115W+F150W+F200W, and F277W+F356W+F444W. The southern clump and nearby galaxies are masked in ellipse fitting (black hatches). For short wavelengths (rest-frame UV), the ellipticity reaches maximum emax ∼ 0.50 at r ∼ 0. ′′33 = 2.10 kpc. For longer wavelengths (rest-frame optical), the ellipticity reaches maximum emax ∼ 0.47 at r ∼ 0. ′′71 = 4.50 kpc. Bar length abar is marked as the bold red ellipse in the left panel images and the red dashed line in the…
Figure 3. Structural modeling of M1149-BSG-z5 stacked image, F277W+F356W+F444W. Top: best-fit model and residual for single Sersic ´ fit. Bottom: best-fit model, sub-component models and residual for bulge + exponential disk fit. The upper-right panel shows the observed and model surface-brightness profiles. The single-Sersic model (black dotted line) underestimates the central brightness, as seen in the residuals, ´ while the bulge+disk model (black solid line) better matches the observed data (orange dots), reducing central residuals and reproducing the concentrated light, suggesting a…
Figure 4. Left: Location of M1149-BSG-z5 on the size-mass plane. The size-mass distribution of galaxies at similar redshifts, measured with F356W for TNG50 (L. Costantin et al. 2023b) and observations (R. G. Varadaraj et al. 2024; N. Allen et al. 2025) are included for reference. The size-mass for barred galaxies at 2 < z < 4 (Y. Guo et al. 2025) is also shown. M1149-BSG-z5 shows relatively larger galaxy size than galaxies at similar redshifts and comparable to barred galaxies at 2 < z < 4. Right: Location of M1149-BSG-z5 on the star-forming main sequence. Parameterized SFMS from J. S.…
Figure 5. Left: Location of M1149-BSG-z5 on the N2-BPT diagram. The dashed gray curve shows the AGN classification from G. Kauffmann et al. (2003), and the black solid curve shows the theoretical maximum-starburst boundary of L. J. Kewley et al. (2001). The green dashed line shows the classification of high redshift galaxies from J. Scholtz et al. (2025). The line ratios measured from stacked spectra of JADES AGNs at 3.5 < z < 5 and z > 5 (I. Juodzbalis et al. ˇ 2026) are shown as gray stars for reference. Right: Location of M1149-BSG-z5 on the MBH − M∗ relation. The black solid line and gray…
Figure 6. Left: Number density distribution of redshifts for galaxies within 1 arcmin around M1149-BSG-z5, compared with galaxies in GOODS-South (K. N. Hainline et al. 2024). Sources are selected with mF444W < 29 and (z84 − z16)/(1 + z50) < 10%. Photometric-redshift distribution for galaxies in the M1149 field around M1149-BSG-z5 is shown in shaded pink, with spectroscopic redshift confirmed galaxies shown in red, and the distribution for GOODS-South is shown in shaded gray. The M1149 distribution peaks at zphot ≃ 5.30, and the spectro￾scopic sample peaks at zspec ≃ 5.10, indicating that…
Figure 7. Best-fit CIGALE SED models and JWST photometry for the bulge and the two sides of the bar. The photometry is measured from the apertures shown in the inset, with all images PSF-matched to F480M. The bulge, east bar, and west bar are shown in red, blue, and orange. Observed photometries are shown in filler circles, and best-fit model fluxes for different filters are shown in squares. The east bar is slightly bluer than the west bar, consistent with its younger best-fit age and lower dust attenuation
Figure 8. Complementary to the bottom panel of

Figures reproduced from arXiv:2606.25022 by the authors.

References

How the literature uses it

1 arXiv paper cite this in 2 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

What it cites · 23 sentences without a confident label

Uses the method or tool of 8 papers
Compares with 5 papers
  • M1149-BSG-z5 is typically larger than observed or simulated galaxies at similar redshifts [ref] .

    2401.1597 · SED fitting: locations on size-mass and SFMS · 0.99

  • M1149-BSG-z5 lies above both the empirical star-forming region of [ref] and the theoretical maximum-starburst boundary of [ref] .

    Theoretical Modeling of Starburst Galaxies · Emission-line analysis: AGN and metallicity · 0.99

  • In contrast, the vast majority of JWST-discovered high-redshift AGNs show systematically offsets with higher ionization and lower metallicity, overlapping with the star-forming region in the N2-BPT diagram [ref] .

    Diagnostics for PopIII galaxies and Direct Collapse Black Holes in the early universe · Emission-line analysis: AGN and metallicity · 0.91

Cites as support 1 paper
Cites as background 3 papers
  • At high redshifts, the cosmic environment is drastically different from the local Universe, characterized by high molecular gas fraction [ref] , higher merger and interaction rate [ref] , more intense star-forming activity [ref] and stronger feedback [ref] .

    Cosmic Star Formation History · Introduction · 0.92

  • At high redshifts, the cosmic environment is drastically different from the local Universe, characterized by high molecular gas fraction [ref] , higher merger and interaction rate [ref] , more intense star-forming activity [ref] and stronger feedback [ref] .

    Cool Gas in High Redshift Galaxies · Introduction · 0.92

  • Beyond internal secular evolution, bar structures may also be induced by tidal interactions [ref] and wet mergers [ref] .

    Tidally induced bars in Illustris galaxies · Introduction · 0.83

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