Dark matter in ALFALFA galaxies: Investigating galaxy-halo connection

TL;DR

This study directly probes the galaxy-halo connection by measuring the dark matter content within the HI radius $R_ ext{HI}$ for 4844 ALFALFA galaxies and comparing to mock observations from the TNG100 simulation. Using HI line widths and inclination corrections, the authors derive dynamical masses and, after accounting for baryons, enclosed dark matter masses $M_{DM}(<R_ ext{HI})$, then extrapolate halo masses $M_{200}$ via an NFW model. A one-to-one $M_*{-}R_ ext{HI}$ matching yields 2453 ALFALFA–TNG100 pairs, enabling a fair, galaxy-by-galaxy SHMR comparison. They find ALFALFA galaxies have systematically lower $M_{DM}(<R_ ext{HI})$ than the TNG100-mock, driven by a tail of massive, late-type galaxies residing in smaller halos (e.g., in the highest mass bin $M_* > 10^{11} M_\odot$, $M_{DM}(<R_ ext{HI})$ is 23% lower than in TNG100-DM). This suggests a higher fraction of massive late-type galaxies in relatively less massive halos than predicted by the TNG100 simulation, with potential implications for baryonic feedback and halo structure 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.

Figures (12)

• Figure 1: Left: the ALFALFA matched sample galaxies (blue) and the TNG100 matched sample (red) on the $\log(M_*) -\log(R_\mathrm{HI})$ plane. We plot the ALFALFA parent sample (light blue) and TNG100 H i galaxies (orange) in the background. Right: $R_\mathrm{HI}$ distribution for the aforementioned samples plotted in the same colour scheme.
• Figure 2: Colour-magnitude diagram for the sample galaxies. The ALFALFA sample is displayed with varying colours representing density and consists primarily of star-forming galaxies. Additionally, the NASA-Sloan Atlas catalogue is shown in the background with the contour lines 2011AJ....142...31B.
• Figure 3: $r$-band images and H i integrated spectra for an ALFALFA galaxy AGC008220 (top) and a mock galaxy TNG100-445271 (bottom) from the TNG100 simulation. The H i spectra panels (right) display the corresponding stellar mass, H i mass, and $R_\mathrm{HI}\,$ values for each galaxy.
• Figure 4: Histograms of the enclosed dynamical mass within $R_\mathrm{HI}\,$ for the ALFALFA sample and the TNG100 sample in five mass bins. The measurements for the ALFALFA sample are shown in blue, the true values of the TNG100 sample (TNG100-true) are plotted in orange, and the results obtained from the mock observations of the TNG100 sample (TNG100-mock) are shown in red. Median values for each dataset are indicated by a vertical dashed line matching the colour of the sample.
• Figure 5: Histograms of the enclosed dark matter mass within $R_\mathrm{HI}\,$ for the ALFALFA sample and the TNG100 sample in five mass bins. The measurements for the ALFALFA sample are shown in blue, the true values of the TNG100 sample (TNG100-true) are plotted in orange, and the results obtained from the mock observations of TNG100 sample (TNG100-mock) are shown in red. Median values for each dataset are indicated by a vertical dashed line matching the colour of the sample.