Work

Dissecting ultra-diffuse galaxies in the field

Year: 2026

Type: article

Abstract: Context . Ultra-diffuse galaxies (UDGs) in the field, gravitationally isolated from galaxy clusters, are faint systems that remain poorly represented in the literature due to lack of spectroscopic confirmation and the difficulty of obtaining high signal-to-noise emission-line measurements. Aims . We present a spectroscopic study of 17 blue UDG candidates in the field using optical emission lines to confirm their ultra-diffuse nature and characterise their physical properties. Methods . Data were collected using the MODS instrument at the Large Binocular Telescope Observatory and the MISTRAL instrument at the Observatoire de Haute-Provence. Using the software pandora EZ , we derived spectroscopic redshifts ( z spec ) for our field UDG candidates. We then computed their effective radii ( r eff ) and central surface brightnesses (µ 0,g ). We measured the H α and H β emission line fluxes in the 17 spectra and derived star formation rates (SFRs) from the line-luminosity relation. We performed forced photometry on our sample to obtain photometric fluxes and applied an aperture correction on the H α integrated fluxes, propagating the correction to the derived SFRs. Using colour relations and estimated dust attenuation, we then computed stellar masses (M ∗ ) and corrected the SFRs accordingly. Finally, we placed our sample on the star-forming main sequence, comparing its distribution with that of local star-forming galaxies. Two sources were further examined as potential giant low surface brightness galaxies (GLSBGs). Results . In our samples, we identify nine confirmed UDGs, eight other low surface-brightness galaxies (LSBGs), including one GLSBG. The z spec of our field UDGs span a range of 0.015–0.037. Their r eff ranges from 1.69–4.99 kpc, and their µ 0 ,g range from 24.05–24.98 mag arcsec −2 . Consistent with previous studies, the galaxies exhibit low to moderate dust content, with an average V-band attenuation of 0.29 mag . The spectroscopically confirmed UDGs presented in this work, after aperture correction, exhibit −2.95 ≤ log (SFR) ≤−1.60 M ⊙ yr −1 as an upper limit and 7.20 ≤ log (M ∗ ) ≤ 8.08 M ⊙ . These values place them along the star-forming main sequence. Conclusions . Our results indicate that blue field UDGs are characterised by heterogeneous dust attenuation and occupy the same region of the star formation–stellar mass plane as dwarf LSBGs. This is consistent with the broader population of local star-forming galaxies and indicates no distinct global star-forming behaviour.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202660916