Ring galaxies in the EAGLE hydrodynamical simulations

Abstract

We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations. We use the largest reference model Ref-L100N1504, a cubic cosmological volume of 100 comoving megaparsecs on a side, to identify and characterise these systems through cosmic time. The number density of ring galaxies in EAGLE is in broad agreement with the observations. The vast majority of ring galaxies identified in EAGLE (83 per cent) have an interaction origin, i.e., form when one or more companion galaxies drop-through a disk galaxy. The remainder (17 per cent) have very long-lived ring morphologies (> 2 Gyr) and host strong bars. Ring galaxies are HI rich galaxies, yet display inefficient star formation activity and tend to reside in the green valley particularly at z 0.5. This inefficiency is mainly due to the low pressure and metallicity of their interstellar medium (ISM) compared with the ISM of similar star-forming galaxies. We find that the interaction(s) is responsible for decreasing the ISM pressure by causing the ISM gas to flow from the inner regions to the outer disk, where the ring feature forms. At a fixed radius, the star formation efficiency of ring galaxies is indistinguishable from their star-forming counterparts, and thus the main reason for their integrated lower efficiency is the different gas surface density profiles. Since galaxy morphologies are not used to tune the parameters in hydrodynamical simulations, the experiment performed here demonstrates the success of the current numerical models in EAGLE.

Discovery of a large H i ring around the quiescent galaxy AGC 203001

“…This leads to the fragmentation of the ring in about 100 Myr (Theys & Spiegel 1977) and it fades almost completely in about 0.5 Gyr (Mapelli et al 2008) thus making the ring fairly shortlived. Interestingly, such collisional rings are also produced in large scale cosmological simulations whose SF properties are found to be consistent with observations (Snyder et al 2015;Elagali et al 2018).…”

Angular momentum regulates H igas content and H icentral hole size in the discs of spirals

“…The origin of such a symmetric ring is unclear, however, NGC 1543 is at the very edges of the Dorado group and as such, it is possible that it is a "backsplash" galaxy, meaning it has passed through the group at least once and along the way collided with a dwarf galaxy, driving the formation of the ring. Simulations support this scenario and indicate that an interaction via collision or drop-through is the most common way such ring galaxies are formed (see for example Elagali et al 2018). NGC 1543 is classified as an S0 galaxy and does not seem to possess a normal disc.…”

A giant galaxy in the young Universe with a massive ring

“…Throughout we adopt a Λ cold dark matter cosmology, where Λ is the cosmological constant, with Ω M =0.307, Ω Λ =0.693, and H 0 =67.7 km s −1 Mpc −1 , consistent with the Planck measurements 31 and the cosmological parameters used in EAGLE simulations 13 . At the redshift of z = 2.19, the look-back time is 10.8 Gyr and one arcsecond corresponds to a physical scale of 8.49 kpc.…”

“…These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe [5][6][7][8][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).…”

“…We quantify the size of the diffuse light by measuring R 80 , the radius within which 80% of the total luminosity is included (Methods, Table 1, Supplementary Figs. [12][13]. Comparing with other z ∼ 2 galaxies in the 3D-HST catalogue 29 , R5519's R 80 is 2.4σ larger than the mean size (5.4 kpc) of all late-type galaxies (log(M * /M ) > 9.5) and 1.5σ larger than the mean value (7.1 kpc) of the most massive (log(M * /M ) ≥ 10.6) latetype galaxies at z ≈ 2 ( Fig.3).…”