A giant galaxy in the young Universe with a massive ring

Abstract

In the local (z ≈ 0) Universe, collisional ring galaxies make up only ∼0.01% of galaxies 1 and are formed by head-on galactic collisions that trigger radially propagating density waves 2-4 . These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe 5-9 . However, not much is known about distant (z > 0.1) collisional rings [10][11][12][13][14] . Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5−2.2 times larger and is forming stars 50 times faster. The extended, diffuse stellar light outside of the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved 15,16 , the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals [17][18][19][20][21] . Contrary to previous predictions 10-12 , this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.The ring galaxy (ID 5519, hereafter R5519) was discovered in our systematic search for z 2 spiral galaxies in the Cosmic Evolution Survey (COSMOS) field of the FourStar Galaxy Evolution survey (ZFOURGE 22 ). We used ZFOURGE catalogue images to identify spiral structures in galaxies within the photometric redshift range of 1.8 z p 2.5. Owing to the surface brightness dimming and smaller sizes of galaxies at z > 1, our visual identification of spiral features was restricted to galaxies with illuminated pixels larger than a radius of 0. 5 (>4 kpc at z ≈ 2) in the Hubble Space Telescope (HST) images. Our visual inspection simultaneously identified ring galaxies and other morphologically distinct objects such as mergers and gravitationally lensed galaxies. R5519 was flagged as one of the largest galaxies among the ∼4000 galaxies inspected, with a clear ring structure as well as a large diffuse disk ( Fig.1 and Supplementary Figs.1-2).We confirm the spectroscopic redshift of R5519 to be z s = 2.192 ± 0.001 based on our Keck/MOSFIRE near-infrared (NIR) spectroscopy and Keck/OSIRIS adaptive-optics aided NIR integral field spectroscopy . A joint analysis of the MOS-FIRE and OSIRIS spectroscopic data, in combination with the groundbased Hα narrow-band image from the ZFOURGE catalogue, shows that the Hα kinematics are consistent with a tilted rotating and expanding/contracting circular ring model (Fig.2, Methods). Taking the inclination angle (i = 29 • ± 5) and the position angle (PA = 28 • ± 10) from an ellipse fit to the ring morphology (Supplementary Table 1, Supplementary Fig.1) as inputs to the kinematic model, the inferred rotational velocity at the fixed ring...

Possible formation of ring galaxies by torus-shaped magnetic wormholes

“…The most strong field is close to the entrance and particles captured by the field remain always near the entrance. In the primordial plasma before the recombination such a wormhole traps all baryons 5 propagating near it and thus forms a primeval structure of a galaxy (a protogalaxy). Such a scheme works only for wormholes which possess sufficiently strong magnetic fields, since high-energy baryons cannot be captured by the wormhole.…”

“…At the redshift z = z r it is extremely small and has the order (z r ) ∼ (7 ÷ 8) × 10 −15 pc. Consider a wormhole throat with the big radius R w (0) ∼ 15 kpc which corresponds to a galaxy size [5], while the radius of the baryon cloud has the order r cl ∼ 0.2R w . Then we find R w (z r ) ∼ 15 × 10 −9 pc (z r ) and from (4) we get δ b (z r ) ∼ (0.5 ÷ 0.6) × 10 −5 .…”

“…Some part of galaxies are shaped like a doughnut, the so-called ring galaxies [3,4], and may contain a hole in the a e-mail: ka98@mail.ru (corresponding author) b e-mail: sep_22.12.79@inbox.ru middle, e.g., see the recently found giant ring galaxy (ID 5519) [5]. In fact, more than a half of disk galaxies have ring structures of different scales [4] which may also have an irregular form [6].…”

“…In the rest, the final form of the ring galaxy formed by a wormhole does not differ from that predicted by standard mechanisms. Indeed, upon the recombination epoch in the case when the wormhole collapses the ring may contain a more dense and old collection of stars (a small galaxy) in the center of the ring (as in the case of the Hoag's object), or, when the wormhole expands further, the center part of the ring may remain empty, e.g., see examples in [5,16].…”

Collisions of young disc galaxies in the early universe

“…2 School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China galaxy, named as R5519, at z=2.19 (Yuan et al 2020), nearby which there is a companion galaxy. Yuan et al (2020) believed that this is a CRG in the very young universe. Confusingly, the morphology of this CRG is an symmetric empty ring galaxy without a central nucleus.…”