NGC 5248

NGC 5248 is a very compact barred-spiral (SAB) galaxy in the southwestern corner of the constellation Bootes, ten degrees south of Arcturus. It has an apparent magnitude of 10.2 and an apparent diameter of 6.5'.

Although within the boundaries of the Herdsman, NGC 5248 is actually part of the Virgo Cluster. NGC 5248 is estimated to be 50 million light years away. Short exposures of this galaxy show the bright structures of the central regions. Many dust lanes, HII (red) regions, and blue stellar associations populate this busy area. Deeper exposures begin to show the two dim, tenous outer arms of the galaxy. NGC 5248 appears to be a combination of M 81, with two distinct arms, and M 100, with a detailed nucleus.

For decades, NGC 5248 has been thought to host a short bar 1.6 kpc in radius. Dynamical and morphological arguments, however, argue that its spiral structure is being driven by a large-scale bar 8.6 kpc in radius. The bar is embedded within a fainter outer disk, visible out to a radius of 17.2 kpc. The recently discovered large-scale bar in NGC 5248 generates spiral structure that extends out 10 kpc, fuels star formation, and drives disk evolution. Deep inside the bar, two massive molecular spirals feed a starburst ring of super-star clusters 375 pc from the core.

The classical grand-design spirals of NGC 5248 lie on the leading edge of the large-scale stellar bar, and are accompanied by concave dust lanes. The offset between the dust and young stars is consistent with our understanding of gas flows in barred galaxies, where shock waves along the leading edges of a moderately strong bar compress the gas to form massive young stars. NGC 5248 illustrates how intense star formation along a moderately strong bar can lead to conspicuous open spiral arms within the bar itself.