# Redshift, metallicity and size of two extended dwarf Irregular galaxies. A link between dwarf Irregulars and Ultra Diffuse Galaxies?

## TL;DR

This study reveals that two distant dwarf irregular galaxies share structural properties with Ultra Diffuse Galaxies, suggesting a potential link and continuum among different low surface brightness galaxy types.

## Contribution

The paper identifies a structural and compositional connection between dwarf irregulars and UDGs, expanding understanding of galaxy diversity and evolution.

## Key findings

- The two galaxies are unrelated to local HI clouds but resemble UDGs in size and luminosity.
- One galaxy exhibits an extremely high gas-to-stellar mass ratio (~90).
- Extended dwarf irregulars and UDGs form a continuous distribution in the size-luminosity plane.

## Abstract

We present the results of the spectroscopic and photometric follow-up of two field galaxies that were selected as possible stellar counterparts of local high velocity clouds. Our analysis shows that the two systems are distant (D>20 Mpc) dwarf irregular galaxies unrelated to the local HI clouds. However, the newly derived distance and structural parameters reveal that the two galaxies have luminosities and effective radii very similar to the recently identified Ultra Diffuse Galaxies (UDGs). At odds with classical UDGs, they are remarkably isolated, having no known giant galaxy within ~2.0 Mpc. Moreover, one of them has a very high gas content compared to galaxies of similar stellar mass, with a HI to stellar mass ratio M_HI/M_* ~90, typical of almost-dark dwarfs. Expanding on this finding, we show that extended dwarf irregulars overlap the distribution of UDGs in the M_V vs. log(r_e) plane and that the sequence including dwarf spheroidals, dwarf irregulars and UDGs appears as continuously populated in this plane.