I am not related to any Ertzgaards, but I do have a very beautiful charcoal drawing of a portrait of Christian Ertzgaard. The back of the portrait says he came to the US in 1888 from Trondhiem, Norway. I believe he settled in Minneapolis and married named Mary, also from Norway, according to the 1920 US Census.
My wife bought the portrait at an antique store in Duluth, GA. We still have it today. We have no idea how it got to GA. We often wondered why a family would part with such a family heirloom.