Stellar “Infant Mortality” in Spiral Galaxy NGC 1313

[Left] - This is a view of the barred spiral galaxy NGC 1313 taken with the the European Southern Observatory's Very Large Telescope (VLT) in Chile on Dec. 16, 2003 through various broad-band (B, R, z) and narrow-band filters (H-alpha, [o I], [O III]). The color composited image was made by assigning B to the blue channel, [O I] and [O III] to the green channel, and R, z, and H-alpha to the red channel. This gives many of the nebulous shells along the outer spiral arms a yellow/red hue. The outline of the central region indicates the area observed with Hubble's Advanced Camera for Surveys.

[Right] - This is a NASA Hubble Space Telescope image of the central region of the barred spiral galaxy NGC 1313. Hubble was used to resolve stars within the galaxy to do a census of various classes of stars distributed across the galaxy. The observations show that hot blue stars (of class B) are widely scattered across the galaxy. This is evidence of "infant mortality" in which the young, so-called open clusters where stars are born, quickly became gravitationally "unglued" and scattered their resident stars into the galaxy. NGC 1313 is 50,000 light-years across and lies 14 million light-years away in the southern constellation of Reticulum.

The image is a combination of many separate Advanced Camera for Surveys (ACS) exposures using several different filters which sample broad wavelength ranges. The color results from assigning different hues to each monochromatic image. In this case, the assigned colors are: F435W (B) blue, F555W (V) green, and F814W (I) red. Although no direct oxygen filter was used in the ACS observations, the strong {O III} emission falls within the range of the visible filter. Shells of gas and nebulosity therefore appear green in the ACS images, while in the ground-based VLT image, they appear yellow/red. The H-alpha emission is not perceived in the ACS filters selected. The Hubble data were taken in November 2003 and February 2004.