2008/01/31 by Jounghun Lee, Bomee Lee · 1 citation
Engineering · Physics and Astronomy · #Astronomy and Astrophysical Research #Bulge #Dimensionless quantity #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Halo #Lenticular galaxy #Redshift #Redshift survey #Shear (geology) #Space Technology and Applications #astro-ph
paper · pdf · doi:10.1086/592181
published as Astrophys.J. 688 (2008) 78 · ApJ in press, accepted version, analysis improved, new discussion added
arxiv created 2008/07/28 · openalex publication_date 2008/11/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Recent N -body simulations indicate that the assembly history of galactic halos depends on the density of the large-scale environment. This implies that galaxy properties such as age and size of the bulge may also vary with the surrounding large-scale structures, which are characterized by tidal shear as well as density. Using a sample of 15,882 well-resolved nearby galaxies from the Tully catalog and the real-space tidal field reconstructed from the 2MASS Redshift Survey, we investigate the dependence of galaxy morphological type on the shear of the large-scale environment in which they are embedded. We first calculate the large-scale dimensionless overdensities (δ) and ellipticities ( e ) of the regions where the galaxies are located, classify them according to morphological type, and create subsamples selected at similar δ-values but spanning different ranges in e . We calculate the mean ellipticity, ⟨ e ⟩, averaged over each subsample and find a signal of variation of ⟨ e ⟩ with morphological type: for 0.5 ≤ δ ≤ 1.0, elliptical galaxies are preferentially located in regions with low ellipticity; for –0.3 ≤ δ ≤ 0.1, the latest-type spirals are preferentially located in regions with high ellipticity. The null hypothesis that the mean ellipticities of the regions where the ellipticals and the latest-type spirals are located are the same as the global mean ellipticity averaged over all types is rejected at the 3 σ level when –0.3 ≤ δ ≤ 0.1. Yet, no signal of a galaxy-shear correlation is found in highly overdense or underdense regions. The observed trend suggests that the formation epochs of galactic halos might be a function of not only halo mass and large-scale density but also large-scale shear. Since the statistical significance of the overall trend is low, a sample of at least 100,000 galaxies is required to verify this correlation.