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The demographics of galactic bulges in the SDSS database


Keunho Kim

Sree Oh

Hyunjin Jeong

Rory Smith

Sukyoung K. Yi


We present a new database of our two-dimensional bulge–disk decompositions for 14,233 galaxies drawn from Sloan Digital Sky Survey DR12 in order to examine the properties of bulges residing in the local universe (0.005 < z < 0.05). We performed decompositions in the g and r bands by utilizing the galfit software. The bulge colors and bulge-to-total ratios are found to be sensitive to the details in the decomposition technique, and hence we hereby provide full details of our method. The g − r colors of bulges derived are almost constantly red regardless of bulge size, except for the bulges in the low bulge-to-total ratio galaxies (B/T r lesssim 0.3). Bulges exhibit similar scaling relations to those followed by elliptical galaxies, but the bulges in galaxies with lower bulge-to-total ratios clearly show a gradually larger departure in slope from the elliptical galaxy sequence. The scatters around the scaling relations are also larger for the bulges in galaxies with lower bulge-to-total ratios. Both the departure in slopes and larger scatters likely originate from the presence of young stars. The bulges in galaxies with low bulge-to-total ratios show signs of a frosting of young stars so substantial that their luminosity-weighted Balmer-line ages are as small as 1 Gyr in some cases. While bulges seem largely similar in optical properties to elliptical galaxies, they do show clear and systematic departures as a function of bulge-to-total ratio. The stellar properties and perhaps associated formation processes of bulges seem much more diverse than those of elliptical galaxies.


Kim, K., Oh, S., Jeong, H., Aragón-Salamanca, A., Smith, R., & Yi, S. K. (2016). The demographics of galactic bulges in the SDSS database. Astrophysical Journal Supplement, 225(1), Article 6.

Journal Article Type Article
Acceptance Date Apr 21, 2016
Publication Date Jul 13, 2016
Deposit Date Jan 10, 2017
Publicly Available Date Jan 10, 2017
Journal Astrophysical Journal Supplement Series
Print ISSN 0067-0049
Electronic ISSN 1538-4365
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 225
Issue 1
Article Number 6
Keywords galaxies: bulges;
galaxies: elliptical and lenticular, cD; galaxies: formation; galaxies: spiral; galaxies: stellar content; galaxies: structure
Public URL
Publisher URL;


Kim_2016_ApJS_225_6(1).pdf (3.2 Mb)

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