After its discovery in 1972, Andromeda IV was deemed an irregular satellite of our neighboring Andromeda galaxy. However, a new study conducted at the Special Astrophysical Observatory in Russia has discovered that it is actually a solitary, irregular dwarf galaxy that is abundant in gas, according to a news release. The finding was made by analyzing data obtained from the Advanced Camera for Surveys (ACS) installed on the Hubble Space Telescope, which is designed to gather sharp, clear images of deep space and see wavelengths in the range of ultraviolet all the way to visible light.
The data suggests that Andromeda IV is approximately 22 to 24 million light years away from Earth, as opposed to previous predictions that put it in the range of 16 to 26 million light years away.
"To measure total galaxy magnitude in each band, the galaxy image was first fitted with concentric ellipses. Then integrated photometry was performed in these ellipses with parameters defined from the center to the faint outskirts. The total magnitude was then estimated as the asymptotic value of the radial growth curve," the researchers said.
In addition to data gained from the ACS, the team also used the Giant Metrewave Radio Telescope (GMRT) in India to determine Andromeda IV's rotation curve for the 21-centimeter hydrogen line and integrate it with various mass models.
"The galaxy was modelled as consisting of three components, a stellar disk, a gas disk and dark matter halo. The structural parameters of the stellar disk were fixed using the photometry in I-band," the astronomers wrote in the paper.
Not only did the astronomers determine that Andromeda IV resides in a region with a low spatial density by galaxy numbers, making it very isolated, they detected a large amount of neutral hydrogen and a moderate activity of start formation, features typical of isolated dwarf galaxies.
"The galaxies with high gas-to-stellar mass ratio are usually isolated objects, with a low optical surface brightness and low metallicity," the researchers wrote.
The findings were published online in the Dec. 18 pre-print server arXiv.
