Telescope: Planewave 24" f6.7 on a Planewave HD Mount Camera: SBIG 16803

Location: Stellar Winds Observatory at DSNM, Animas, New Mexico

Exposure: LRGB 1000min total

NGC 4435-4438, Arp 120 or The Eyes Galaxies


NGC 4435 is a barred lenticular galaxy currently interacting with NGC 4438. Studies of the galaxy by the Spitzer Space Telescope revealed a relatively young (190 million years) stellar population within the galaxy's nucleus, whose origin may have arose through the interaction with NGC 4438 compressing gas and dust in that region, triggering a starburst. It also has a long tidal tail possibly caused by the interaction with the mentioned galaxy; however other studies suggest that tail is actually a galactic cirrus in the Milky Way totally unrelated to NGC 4435.

NGC 4438 is the most curious interacting galaxy in the Virgo Cluster, due to the uncertainty surrounding the energy mechanism that heats the nuclear source; this energy mechanism may be a starburst region, or a black hole-powered active galactic nucleus (AGN). Both hypotheses are currently under investigation by astronomers.

This galaxy shows a highly distorted disk, including long tidal tails due to the gravitational interactions with other galaxies in the cluster and its companion. The aforementioned features explain why sources differ to classify it as a lenticular or spiral galaxy. NGC 4438 also shows signs of a past, extended, -but modest- starburst, a considerable deficience of neutral hydrogen, as well as a displacement of the components of its interstellar medium -atomic hydrogen, molecular hydrogen, interstellar dust, and hot gas- in the direction of NGC 4435. This observation suggests both a tidal interaction with NGC 4435 and the effects of ram-pressure stripping as NGC 4438 moves at high speed through Virgo's intracluster medium, increased by the encounter between both galaxies.