Broadband + Narrowband (IVB + Hα & O-III) composite image of NGC 3077 using images acquired by the Hubble Space Telescope's Advanced Camera for Surveys instrument in September 2006 and its Wide Field Planetary Camera 2 instrument in May 2001.

Object Info:

NGC 3077 is a small galaxy in the Northern constellation of Ursa Major and is part of the M81 group of galaxies. It is an active galaxy, gravitational interaction with its larger neighbors has scattered dust clouds around and triggered star formation. NGC 3077 was discovered by William Herschel on November 8th, 1801.

Processing Details:

Image is a composite of broadband Infrared, Visible and Blue filter images taken with HST's ACS instrument, along with narrowband Hydrogen Alpha (Hα) and Doubly-ionized oxygen (O-III) filter images taken with HST's WFPC2 instrument. Broadband data was combined as a typical IVB image. With infrared band data assigned to red, visible band data assigned to green, and blue band data assigned to blue. Colors were calibrated using Rogelio Bernal Andreo's WhiteCal plugin for Adobe Photoshop. WhiteCal makes the simplifying assumption that the combined starlight from a galaxy is white in color. It then sets the white-balance of the image accordingly.

Narrowband data was overlaid on top of the broadband data, and then scaled up 200% to account for the differing pixel sizes between WFPC2 and ACS. Hα and O-III data were combined in an HOO palette, with Hα assigned to the red channel and O-III assigned to the green and blue channels. For the red channel, Hα was blended with O-III at an 80-20% ratio. This gives the Hα a more natural, pinkish appearance. O-III data was given a noise reduction and stretched significantly to make up for the weakness of the signal. Narrowband image was overlaid on top of the broadband image and blended in using the "Screen: blending mode.

Filters Used:

Broadband:

I : ACS/WFC - F814W

V: ACS/WFC - F606W

B: ACS/WFC - 475W

HST Proposal 10915

"ACS Nearby Galaxy Survey"

Principal Investigator: Julianne Dalcanton

https://archive.stsci.edu/proposal_search.php…

Narrowband:

Hα: WFPC2/WFC - F656N

O-III: WFPC2/WFC - F505N

HST Proposal 9144

"Calibrating Star Formation: The Impact of Environment"

Principal Investigator - Daniela Calzetti

https://archive.stsci.edu/proposal_search.php…

Notes:

North is up.

Credit: NASA/ESA/STScI/Demeter Alexandria