The cosmic web of the Local Universe: cosmic variance, matter content and its relation to galaxy morphology

摘要

We present, for the first time, a Local Universe (LU) characterization usinghigh precision constrained $N$-body simulations based on self-consistentphase-space reconstructions of the large-scale structure in the Two-MicronAll-Sky Galaxy Redshift Survey. We analyse whether we live in a special cosmicweb environment by estimating cosmic variance from a set of unconstrained$\Lambda$CDM simulations as a function of distance to random observers. Bycomputing volume and mass filling fractions for voids, sheets, filaments andknots, we find that the LU displays a typical scatter of about $1\sigma$ atscales $r>15\,h^{-1}\,{\rm Mpc}$, in agreement with $\Lambda$CDM, converging toa fair unbiased sample when considering spheres of about $60\,h^{-1}\,{\rmMpc}$ radius. Additionally, we compute the matter density profile of the LU andfound a reasonable agreement with the estimates of Karachentsev (2012) onlywhen considering the contribution of dark haloes. This indicates thatobservational estimates may be biased towards low density values. As a firstapplication of our reconstruction, we investigate the likelihood of differentgalaxy morphological types to inhabit certain cosmic web environments. Inparticular, we find that, irrespective of the method used to define the web,either based on the density or the peculiar velocity field, elliptical galaxiesshow a clear tendency to preferentially reside in clusters as opposed to voids(up to a level of $5.3\sigma$ and $9.8\sigma$ respectively) and conversely forspiral galaxies (up to a level of $5.6\sigma$ and $5.4\sigma$ respectively).These findings are compatible with previous works, albeit at higher confidencelevels.