Effect of galaxy mergers on dust masses

Dust mass (M_Dust ) is one of the key physical properties of galaxies that track the cold interstellar medium over cosmic history. However, the M_Dust in merging galaxies is poorly understood. Here, we aim to derive how the cold dust mass of galaxies is affected by major mergers at low redshifts. M_Dust was estimated for approximately 500 major mergers in the North Ecliptic Pole extragalactic field using four spectral energy distribution fitting runs with CIGALE, with different dust attenuation and emission models. We also analysed over 12,000 mergers from the SIMBA simulation using its M_Dust. We matched merging and non-merging systems in stellar mass, redshift, and local density, to enable a controlled comparison of M_Dust. We then performed a second comparison using a control sample additionally matched in star formation rate (SFR). Galaxies hosting active galactic nuclei (AGNs) were then removed and this matching was repeated. Each CIGALE run, and SIMBA, were matched independently. Observed mergers have a higher M_Dust than the non-mergers by up to a factor of 1.82±0.35, or 1.60±0.44 without AGN hosts. When matched by SFR, observed mergers show no significant change in M_Dust, both when including and excluding AGN hosts. SIMBA galaxies show similar trends when AGN hosts are included but there is still a slight increase in M_Dust when matched by SFR. When AGN hosts are excluded, the SIMBA mergers show smaller M_Dust by a factor of 0.98±0.03, or 0.97±0.02 when matched in SFR. The higher the mass of a merger, the greater the M_Dust increase for observations for two of the CIGALE runs, or the smaller the decrease for SIMBA. Observed mergers are typically dustier than their non-merging counterparts but only because they typically have higher SFRs, regardless of whether they host AGNs or not. SIMBA mergers follow observations when AGN hosts are included, but show a reduction in M_Dust when AGN hosts are excluded. Therefore, M_Dust in SIMBA is linked, directly or indirectly, to AGNs in a way that we do not see in observations.