Dark matter in ALFALFA galaxies: Investigating galaxy-halo connection

TL;DR

This study compares the dark matter content of gas-rich galaxies from the ALFALFA survey with TNG100 simulation predictions, revealing that many observed galaxies have less dark matter than simulated counterparts, especially at higher stellar masses.

Contribution

It introduces a dynamical method to measure dark matter in individual galaxies and applies it uniformly to both observational data and simulations, highlighting discrepancies in galaxy-halo connections.

Findings

ALFALFA galaxies have lower median dark matter masses than TNG100 simulations across stellar masses.

A significant fraction of massive late-type galaxies have less dark matter than predicted by simulations.

Discrepancies increase with stellar mass, indicating potential gaps in galaxy formation models.

Abstract

This paper aims to investigate the galaxy-halo connection using a large sample of individual galaxies with $\mathrm{H\,I}$ integrated spectra. We determine their dark matter content by applying a dynamical method based on $\mathrm{H\,I}$ line widths measured with the curve-of-growth technique, together with inclination corrections inferred from optical images. We build a sample of 2453 gas-rich predominantly late-type galaxies spanning a stellar mass range of $10^{8.7}M_\odot$ to $10^{11.4}M_\odot$ by matching them one-to-one with their counterparts from the ALFALFA survey and the TNG100 simulation, ensuring a direct match of stellar mass and $\mathrm{H\,I}$ radius. We generate mock images and mock $\mathrm{H\,I}$ integrated spectra for TNG100 galaxies, and apply the same dynamical method to both ALFALFA and TNG100 mock galaxies to infer their dark matter masses. Across all stellar mass bins, ALFALFA galaxies exhibit lower median dark matter masses than the mock TNG100 simulation results. In each bin, this offset is driven by a tail of galaxies with comparatively low dark matter content, which becomes more prominent toward higher stellar masses. In the highest mass bin ($M_* > 10^{11} M_\odot$), late-type ALFALFA galaxies show a median dark matter mass that is 23% lower than that of their counterparts in the TNG100 dark-matter-only simulation, with 32% of ALFALFA galaxies having $M_\mathrm{DM}(<R_\mathrm{HI})<10^{11.5} M_\odot$, compared to 17% in the mock TNG100 sample. These results suggest that a larger fraction of massive late-type galaxies reside in relatively less massive dark matter haloes than predicted by the TNG100 simulation.