The nature of blue cores in spheroids: A possible connection with active galactic nuclei and star formation

Felipe Menanteau, André R. Martel, Paolo Tozzi, Brenda Frye, Holland C. Ford, Leopoldo Infante, Narciso Benítez, Gaspar Galaz, Daniel Coe, Garth D. Illingworth, George F. Hartig, Marc Clampin

Research output: Contribution to journalArticlepeer-review


We investigate the physical nature of blue cores in early-type galaxies through the first multiwavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep Hubble Space Telescope ACS/WFC griz multicolor observations of the cluster A1689. The resolved g-r, r-i, and i-z color maps reveal a prominent blue core identifying this galaxy as a "typical" case study, exhibiting variations of 0.5-1.0 mag in color between the center and the outer regions, opposite to the expectations of reddened metallicity-induced gradients in passively evolved elliptical galaxies. From a Magellan-Clay telescope spectrum we secure the galaxy redshift at z = 0.624. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an active galactic nucleus (AGN) in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field-South displays L X to be comparable to type 1/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's nonthermal component dominates at high-energy wavelengths, while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue for a probable association between the presence of blue cores in spheroids and AGN activity.

Original languageEnglish (US)
Pages (from-to)697-702
Number of pages6
JournalAstrophysical Journal
Issue number2 I
StatePublished - Feb 20 2005
Externally publishedYes


  • Galaxies: active
  • Galaxies: elliptical and lenticular, cD
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'The nature of blue cores in spheroids: A possible connection with active galactic nuclei and star formation'. Together they form a unique fingerprint.

Cite this