2021/09/28 by Suman Sarkar, Sarkar, Suman, Arunima Banerjee +3
Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2109.13526
openalex publication_date 2021/09/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The existence of flat or bulgeless galaxies poses a challenge to the hierarchical structure formation scenario advocated by modern cosmology. We determine the geometrical environment of a sample of 315 flat galaxies from the Revised Flat Galaxy Catalog (RFGC) using `local dimension' D, which, on a given length scale, quantifies the dimension of the cosmic structure in which a galaxy is embedded. For galaxies residing in filaments, nodes and sheets, D ∼ 1, D ∼ 1.5 and D ∼ 2 respectively; D ∼ 3 represents field galaxies. We also determine the local dimensions of a sample of 15,622 non-flat galaxies identified in the Galaxy Zoo project from the Sloan Digital Sky Survey (SDSS). We find that the median values of D for the flat and the non-flat galaxies are 2.2 and 1.8 respectively, implying that flat galaxies are located in a relatively sparser environment compared to non-flat galaxies; a Kolmogorov-Smirnov (KS) test indicates that their geometrical environments are different at >99% confidence level. Further, using a group finding algorithm, we study the local environment of a subset of 779 flat galaxies with major-to-minor axes ratio a/b >10 identified as superthin galaxies. We find that the median clusterization index k_\rmmin for superthin flat galaxies ∼ 2.3 while ∼ 1.7 for other flat galaxies, confirming that the superthins reside in an under-dense environment compared to other flat galaxies at > 98 % confidence level. Our results may therefore have important implications for the formation and evolution models of flat galaxies in the universe.