Research Highlight

Dusty dark dwarf galaxy spotted by ALMA (press release)

 Our research team (PI: Kaiki Taro Inoue, Kindai University, Satoshi Matsushita, Academia Sinica, Takeo Minezaki, University of Tokyo, Masashi Chiba, Tohoku University)  have detected a misterious faint radio spot (we call it "Y") in the vicinity of the quadruply lensed quasar MG0414+0534 using Atacama Large Millimeter/submillimeter Array (ALMA).  The spot "Y" is most probably a radio emission from cold dust in a dark dwarf galaxy at a cosmological distance, which can simultaneously explain the anomalous flux ratio in the mid-infrared/radio band and the dust reddening in the optical/near-infrared band. The mass of the cold dust is 10^7 solar masses and the total (baryon and dark matter) mass of the dark dwarf galaxy is 10^9 solar masses assuming that the dust traces the total mass.  The dusty dark dwarf galaxy is considered to be gas-rich, possibly has neutral hydrogen of ~10^9 solar masses. The distance to the object is approximately 6 to 8 Giga light years from us.  The object may be a kind of an ultra diffuse galaxy (UDG) at a cosmologocal distance. However, it seems that the dominant component is gas rather than dark matter.  It may be associated with either a subhalo in the lensing elliptical galaxy G or a halo in the intergalactic space. In the universe, a large number of such dusty dark objects may remain to be discovered. The result was published in the Astrophysical Journal Letters , 30 Jan.  2017.

 

 

 MG0414+0534 is a quasar lensed by a foreground galaxy. The source is seen as quadruple images, A1, A2, B and C.

Radio image of MG0414+0534 observed by ALMA (340GHz). A mysterious faint spot Y is shown inside a red circle.