Abstract

Contributed Talk - Splinter LargeScale

Thursday, 10 September 2026, 17:45   (MW-2235)

MITRO: an adaptive friends-of-friend algorithm for Identifying gravitationally bound large-scale structures in galaxy-redshift survey

Prateek Gupta
Thuringer Landessternwarte

The universe at the present epoch is found to be a network of overdense and underdense regions of matter. The appropriate information about these overdense regions, i.e., proper halo-mass function, can precisely constrain the standard cosmological model parameters, dark energy models, or may also lead to an alternative evolutionary model for the universe. Identifying such gravitationally bound structures in the observational surveys is crucial, as it is greatly affected by the Finger-of-God effect, missing dark matter content information and limitations of instruments in detecting faint galaxies. So far, these structures are identified using various group finding codes, mostly based on the friend of friends (FoF) or spherical overdensity (SO) algorithms. While SO-based algorithms, by enforcing a spherical symmetry, fail to capture the real shape of the halos, whereas FoF algorithm is successful in discerning the real geometry of the halos but using a free parameter called the “linking length” whose choice mostly has no physical relevance. Even, no absolute relation has so far been established between linking-length and the overdensity of the FoF identified halos. This work presents the newly developed MITRO halo-finder algorithm for simulated mock catalogue as well as for large galaxy redshift surveys to identify overdense regions in the universe, e.g., clusters of galaxies or superclusters, within the well defined matter overdensity as well as obtaining the real unstructured geometry. The MITRO algorithm's unique feature is that the linking length is no longer a free parameter; it is instead assigned based on the mass property of each element, realising that at large scales (~a few 10's of Mpc) gravitational force largely governs the evolution of Universe. In this algorithm, an arm-length assigned to each element depending on their individual mass and the linking length is the sum of the arm-lengths between each unique pair of elements. This results in a distinct linking length for each unique pair of elements. This proposed algorithm is thus fundamentally new so at to capture the real unstructured geometry roughly within a predefined physically motivated density threshold. Such a thing has not been simultaneously achieved before, by any of the usual FoF or SO-based methods. In this talk, I will demonstrate the unique ability of the algorithm in the appropriate identification of structures, both from large volume cosmological simulations as well as from galaxy redshift surveys. And also substantiate the accountability for missing matter information and the Finger-of-God effect in observational surveys using the MITRO algorithm.