# Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG0414+0534

## TL;DR

This study reports the detection of a faint, dusty dark dwarf galaxy near a quadruply lensed quasar, using ALMA, revealing a new type of dark, dust-rich galaxy that influences gravitational lensing observations.

## Contribution

First detection of a dusty dark dwarf galaxy via ALMA, providing insights into dark substructures affecting gravitational lensing and galaxy formation models.

## Key findings

- Detected a faint object with ~0.3 mJy flux near MG0414+0534
- Object likely a dusty dark dwarf galaxy at z~0.5-1
- Mass of the object is approximately 10^9 solar masses

## Abstract

We report the $4 \, \sigma$ detection of a faint object with a flux of ~ 0.3 mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the lensed images observed in Band 7 and the mid-infrared (MIR) band and the reddening of the QSO light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of $0.5 \lesssim z \lesssim 1$. Using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is $\sim 10^9\, M_{\odot}$, the dust mass is $\sim 10^7\,M_{\odot}$ and the linear size is $\gtrsim 5\,$kpc. Thus our findings suggest that the object is a dusty dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects.