| Name: Rashi Jain |
| Affiliation: National Centre for Radio Astrophysics - Tata Institute of Fundamental Research |
| Conference ID: ASI2026_838 |
| Title: Alaknanda: A Massive Grand-design Spiral Galaxy from the Universe's Infancy at redshift z~4 with JWST |
| Abstract Type: Oral |
| Abstract Category: Galaxies and Cosmology |
| Author(s) and Co-Author(s) with Affiliation: Rashi Jain(National Centre for Radio Astrophysics-TIFR), Yogesh Wadadekar(National Centre for Radio Astrophysics-TIFR) |
| Abstract: We report the discovery of Alaknanda, a large (∼10 kpc diameter), massive (log(M⋆/M⊙)∼10.2), grand-design spiral galaxy with photometric redshift zphot ∼ 4.05 in the UNCOVER and Medium band, Mega Science surveys with JWST. This is among the highest redshift spiral galaxies discovered with JWST. Our morphological analysis using GALFIT reveals that this galaxy is a well-formed disk, with two symmetric spiral arms that are clearly visible in the GALFIT residual. In the rest-frame near-UV and far-UV, we clearly see the beads-on-a-string pattern of star formation; in the rest-frame visible bands, each string appears as an arm. We further confirm the disk dominated nature of this galaxy with non parametric morphological measurements using Statmorph. Spectral energy distribution modeling using the BAGPIPES and Prospector codes is strongly constrained by detections and flux measurements in 21 JWST and HST filters. From the BAGPIPES modeling, the stellar mass-weighted age is ∼199 Myr, implying 50% of the stars in the galaxy formed after z ∼ 4.6. This is a highly star-forming galaxy with a star formation rate (SFR) of ∼63 M⊙ yr−1. We detect flux excesses in the F250M and F335M filters due to the presence of H-α+[NII] and [OIII]+H-β emission line complexes respectively which is consistent with our photometric redshift. Detection of a spiral galaxy at z ∼ 4 indicates that massive and large spiral galaxies and disks were already in place merely 1.5 billion years after the Big Bang. This discovery challenges the existing models of disk/spiral galaxy formation in the early universe. Future observations with NIRSpec IFU and ALMA will be able to probe the kinematics of the galactic disk, throwing light on the possible origin of the spiral arms in this galaxy. |
