NGC 4622 - SA(r)a

NGC 4622

De Vaucouleurs Atlas Type: SA(r)a

Filter: V

Telescope: HST 2.4-m
North upper right, East upper left
Field Dimensions: 1.6 x 1.6 arcminutes

RC3 Type: (R')SA(r)a pec
RSA Type: ----
Surface Brightness Range Displayed: 18.5-26.0 mag per square arcsec
Absolute Blue Magnitude: -21.0

De Vaucouleurs Atlas Description:

This galaxy is best known for its counterwinding spiral structure (book Section 2.1.3). A strong, nearly circular but off-centered inner ring divides the galaxy into zones of leading and trailing spiral structure. Inside the ring a single, weak arm opens counterclockwise, while outside the ring two much stronger arms open clockwise. Buta, Byrd, and Freeman (2003) used the velocity field/near-side absorption technique (de Vaucouleurs 1958a) to show that the inner arm trails while the outer arms lead. This unusual configuration defies logic but could be due to an interaction. In the V-I color index map, the outer arms and half of the inner ring are affected by recent star formation. In contrast, much of the inner arm is stellar in nature. The solid white lines show the kinematic line of nodes in position angle 22o. The thin dust lanes to the left of these lines indicate that the east side is the nearside. From an H-alpha Fabry-Perot velocity field (Buta, Byrd, and freeman 2003), the north side is receding from us. Together, these pieces of information tell us that the galaxy is rotating clockwise.