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Observational evidence for bar formation via cluster–cluster interactions

This study presents the first observational evidence for bar formation in disk galaxies through cluster-cluster interactions. The bar fraction is enhanced in interacting clusters, indicating a new mechanism of bar formation.

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Observational evidence for bar formation via cluster–cluster interactions

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  1. Observational evidence for bar formation via cluster–cluster interactions Yongmin Yoon, MyungshinIm, Gwang-ho Lee, Gu Lim, and Seong-kook Lee CEOU, Seoul National University Steward observatory, University of Arizona Korea Astronomy and Space Science Institute

  2. Introduction • Bars are commonly found in disk galaxies in the local universe. NGC 2217 M95 NGC 1365

  3. Introduction • Broadly, there are two main bar formation mechanisms: (1) internal; (2) external. Kwak et al. (2017) Spontaneous disk instability Tidal force from interactions Lang et al. (2014)

  4. Introduction • Not very well recognized mechanism : Bar formation by cluster-cluster interaction Bekki (1999) The time-dependent tidal gravitational field in interacting clusters induces a stellar bar. No observational study has been conducted yet.

  5. Introduction • In this study... Selecting clusters in pairs or with substructures (Interacting clusters) Finding galaxy clusters Bar fraction enhancement in interacting clusters? Comparison between interacting clusters with non-interacting clusters Bar classifications for galaxies inclusters

  6. Sample • SDSS MPA-JHU catalog • 0.010 < z < 0.065, log(Mstar/Msun) > 10.0 logM Count logMstar Redshift

  7. Analysis Friends-of-Friends (FoF) algorithm • Finding overdense regions Galaxies in overdense region (2 σ) Overdense region Mpc Mpc

  8. Analysis • Measuring dynamical masses • 105 clusters with log(M200/Msun) > 13.85 are found in 0.015<z<0.060. Count Count ΔV (km/s) ΔV (km/s) Demarco et al. (2010) Kim et al. (2016)

  9. Analysis • Selecting clusters in pairs • 7 cluster pairs (14 clusters) are found. Criteria for Velocity & Projected distance Mpc Mpc Mpc Mpc

  10. Analysis • Selecting clusters having substructures • 5 cluster are found (3 clusters are in pairs). Probability having substructure >99.99% DS test (Dressler & Shectman 1988) 16 clusters in pairs or with substructures  Interacting clusters Mpc Count ΔV (km/s) Mpc

  11. Analysis • Classifying bars for cluster member galaxies using the Ellipse task & visual inspection Ellipticity By visual inspection Correcting false detection & Reclassifying obvious bars missed in the automatic process arcsec PA(degree) arcsec

  12. Analysis • Comparison with Lee+12 catalog (only visual inspection): 89% of classifications are consistent. Barred galaxies Comparing the bar fractions of 16 interacting clusters with those of 89 non-interacting clusters Non-barred galaxies

  13. Results • Bars are more abundant in galaxies with lower B/T. • Bar fraction is enhanced (~1.5 times) in interacting clusters. Bar Fraction Count B/T Bar Fraction B/T<0.5  Disk-dominated galaxies KS test: 99.999% (4.5σ)

  14. Results • Bars are more abundant in galaxies with higher stellar masses. • Bar fraction is enhanced in interacting clusters. Bar Fraction logMstar

  15. Results • Bars are more abundant in galaxies having higher stellar masses and lower B/T at the same time. Non-Interacting Clusters Interacting Clusters B/T B/T logMstar logMstar

  16. Results • Bar fraction is not clearly dependent on the cluster mass. • Bar fraction is enhanced in interacting clusters. Bar Fraction logM200

  17. Conclusion • Our results stand as the first observational evidence for a bar formation mechanism, cluster-cluster interaction. Bekki (1999)

  18. Summary • 105 clusters with log(M200/Msun) > 13.85 are found in 0.015<z<0.060. • Among the cluster, we find that 16 clusters are in pairs or with substructures and they are defined as interacting clusters. • We detected bars using the Ellipse task & visual inspection • Bars are more abundant in galaxies having higher stellar masses and lower B/T at the same time. • Bar fraction is enhanced (~1.5 times) in interacting clusters compared with non-interacting clusters.

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