AUTHOR=Shi Dong Dong , Zheng Xian Zhong , Pan Zhizheng , Luo Yu , Deng Hongxia , Hua Qunzhi , Luo Xinyu , Wu Qiming 

TITLE=Searching for nearby diffuse dwarf galaxies in the COSMOS field

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 12 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2025.1560380

DOI=10.3389/fspas.2025.1560380

ISSN=2296-987X

ABSTRACT=It remains challenging to systematically survey nearby diffuse dwarf galaxies and address the formation mechanism of this population distinguishing from regular ones. We carry out a pilot search for these galaxies in the COSMOS field using the deep HST/F814W imaging data. We report three diffuse dwarf galaxies satisfying the criteria: (1) redshift z<0.2, (2) effective radius re>1.′′0, and (3) central surface brightness μ0>24 mag arcsec−2. Two of the three galaxies, COSMOS-UDG1 and COSMOS-UDG2, are recognized as ultra-diffuse galaxies (UDGs) with redshift z=0.130 and 0.049, respectively. The third galaxy, COSMOS-dw1, is spectroscopically confirmed as a dwarf galaxy at z=0.004. We derive the physical properties through fitting their spectral energy distributions (SEDs) extracted from deep multiwavelength observations. COSMOS-dw1 has a stellar mass of 5.6−2.7+2.5×106M⊙, harboring neutral hydrogen gas of mass 4.90±0.90×106M⊙, hinting that this galaxy may be in the nascent stages of quenching. The estimated dynamical mass of 3.4×107 M⊙ further suggests that COSMOS-dw1 is predominantly of dark matter. COSMOS-UDG1 and COSMOS-UDG2 exhibit comparable stellar masses of ∼2×108M⊙. Notably, COSMOS-UDG1 is younger and more metal-rich than COSMOS-UDG2 and COSMOS-dw1. Conversely, COSMOS-UDG2 and COSMOS-dw1 have similar stellar metallicities, yet COSMOS-UDG2 is older than COSMOS-dw1. All three galaxies adhere to the stellar mass-metallicity relation (MZR) for dwarf galaxies in the local Universe, implying they belong to the dwarf galaxy population.