A research team reports the discovery of COSMOS-74706, an unlensed barred spiral galaxy at a spectroscopic redshift z=3.1591 (about 2 billion years after the Big Bang). Using deep multi-band imaging from the Hubble Space Telescope and the James Webb Space Telescope, the study finds disk-like morphology and a clear spiral structure. An elongated central feature is observed aligned between the spiral arms, most noticeably in JWST/NIRCam filters F200W, F277W, and F356W. The authors support the presence of a stellar bar with three independent analysis methods: residuals from galaxy light-profile fitting, isophotal ellipse-fitting that shows bar-like changes in ellipticity and position angle, and Fourier decomposition that detects a strong central bisymmetric mode. The team also uses archival Keck/MOSDEF spectroscopy overlapping a blue clump to infer a robust redshift and confirm that the barred structure is at the same redshift as the main spiral. In a companion analysis, they perform stellar population modeling to estimate the star-formation history and physical properties. The galaxy has a constrained total stellar mass of log(M*/M☉)=10.63±0.13. The bar region contains roughly 30% of the stellar mass but contributes about 8% of recent star formation, and the older stellar ages in the bar region provide tentative evidence consistent with bar-related quenching.
Researchers identify a barred spiral galaxy at redshift 3.16 using HST and JWST data
A research team reports the discovery of COSMOS-74706, an unlensed barred spiral galaxy at a spectroscopic redshift z=3.1591 (about 2 billion years after the Big Bang). Using deep multi-band imaging f...
- A barred spiral galaxy, COSMOS-74706, is identified at spectroscopic redshift z=3.1591 using HST and JWST imaging.
- JWST/NIRCam observations show spiral morphology and an elongated central feature aligned between spiral arms.
- Three independent methods (residuals after profile fitting, ellipse-fitting, and Fourier decomposition) provide consistent evidence for a stellar bar.
- Keck/MOSDEF spectroscopy covering a blue clump supports the redshift and indicates the bar and main spiral are at the same distance.
- Stellar-population modeling finds log(M*/M☉)=10.63±0.13; the bar region holds ~30% of stellar mass but ~8% of recent star formation, with older stellar ages suggesting inside-out formation and possible early bar quenching.
arXiv:2606.23793v1 Announce Type: new Abstract: We present a detailed analysis of a massive barred galaxy at $z_{spec}=3.1591$ using deep multi-band imaging from HST and JWST. For the first time, we resolve its morphology and stellar structures thanks to the JWST/NIRCam NIR and MIR photometry. The galaxy possesses two distinct components with significantly different colors. Through careful image decomposition and masking, we isolate and characterize the flux contribution from each component. The galaxy exhibits a clear spiral morphology, and in a separate companion paper, we present evidence suggesting the presence of a stellar bar. Based on spatially resolved spectral energy distribution modeling with Prospector, we derive the star formation history and other physical properties of the bar and the surrounding regions. The total stellar mass of the galaxy is constrained as $\log(M_*/M_{\odot}) = 10.63\pm0.13$. We find that the bar region contains around 30% of the total stellar mass, but only accounts for around 8% of the recent star formation rate. The region containing the potential bar shows a significantly older mass-weighted stellar age, supporting the inside-out scenario for galaxy formation, and providing tentative evidence for bar quenching in the early stage. The quick onset of a stellar bar at this redshift requires a low dark matter fraction, suggesting the baryon-dominated nature of high-$z$ massive galaxies, and offering rare insight into galaxy evolution at around two billion years after the Big Bang.
17 hours agoarXiv:2606.23792v1 Announce Type: new Abstract: The formation of stellar bars is an important milestone in the secular evolution of spiral galaxies, which typically indicates the presence of a massive rotationally supported disk. Determining when these structures first appeared in the early universe is crucial to constraining the timeline of galactic disk assembly. Here, we report the discovery of COSMOS-74706, a barred spiral galaxy at $z_{spec} = 3.159$. Imaging of COSMOS-74706 with JWST/NIRCam indicates a disk-like morphology and spiral structure with an elongated central feature aligned between the spiral arms, most conspicuously visible in the F200W, F277W, and F356W filters. Three independent methods all support the presence of a bar: visual inspection of residuals from S\'ersic-profile fitting shows a linear structure, isophotal ellipse-fitting displays characteristic profiles of ellipticity and position angle consistent with a bar signature, and Fourier decomposition of the galaxy produces a central bisymmetric mode above a threshold strength calibrated to $z=1-3$ barred spirals. Leveraging archival Keck/MOSDEF spectroscopy overlapping with a blue clump on the edge of the galaxy, a robust redshift is inferred, with photometric constraints indicating that this structure lies at the same redshift as the main spiral. This spectroscopic evidence, placing an unlensed barred spiral at $z>3$ supports the idea that galaxies with rotationally supported disks and disk-halo properties that are conducive to bar formation were already in place within 2 Gyr after the Big Bang.
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