Keywords

Keyword=galaxies: individual (NGC 4565)

Open all abstracts 1–1 of 1 results
DETECTION OF A PSEUDOBULGE HIDDEN INSIDE THE "BOX-SHAPED BULGE" OF NGC 4565

John Kormendy and John C. Barentine 2010 ApJL 715 L176

Numerical simulations show that box-shaped bulges of edge-on galaxies are not bulges: they are bars seen side-on. Therefore, the two components that are seen in edge-on Sb galaxies such as NGC 4565 are a disk and a bar. But face-on SBb galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the (pseudo)bulge in NGC 4565? We use archival Hubble Space Telescope H-band images and Spitzer Space Telescope 3.6 μm wavelength images, both calibrated to Two Micron All Sky Survey Ks band, to penetrate the prominent dust lane in NGC 4565. We find a high surface brightness, central stellar component that is clearly distinct from the boxy bar and from the disk. Its brightness profile is a Sérsic function with index n = 1.55 ± 0.07 along the major axis and 1.33 ± 0.12 along the minor axis. Therefore, it is a pseudobulge. It is much less luminous than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the galaxy is PB/T = 0.06 ± 0.01, much less than the previously believed value of B/T = 0.4 for the "boxy bulge." We infer that published B/T luminosity ratios of edge-on galaxies with boxy bulges have been overestimated. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. From a formation point of view, NGC 4565 is a giant, pure-disk galaxy. This presents a challenge to our picture of galaxy formation by hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565 without also making big classical bulges.