The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation

Abstract

We investigate the physical nature of blue cores in early-type galaxies through the first multi-wavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep ACS/WFC griz multicolor observations of the cluster Abell 1689. 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 ellipticals. From a Magellan-Clay 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 AGN in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field South displays Lx to be comparable to Type I/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's non-thermal component dominates at high-energy wavelengths while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue about a probable association between the presence of blue cores in spheroids and AGN activity.

arXiv commentAccepted for publication in the Astrophysical Journal. 6 pages, 3 figures. Full resolution images available at http://acs.pha.jhu.edu/~felipe/e-prints

References in corpus (22)

• Star Formation in Galaxies Along the Hubble Sequence
• High Mass X-ray Binaries as a Star Formation Rate Indicator in Distant Galaxies
• The Chandra Deep Field South: Optical Spectroscopy I
• The 2-10 keV luminosity as a Star Formation Rate indicator
• Black Hole Demographics from the M(BH)-sigma Relation
• The evolution of field early-type galaxies to z~0.7
• Lx-SFR relation in star forming galaxies
• Evidence for Evolving Spheroidals in the Hubble Deep Fields North and South
• The Star Formation History of the Hubble Sequence: Spatially Resolved Colour Distributions of Intermediate Redshift Galaxies in the Hubble Deep Field
• GEMS Imaging of Red Sequence Galaxies at z~0.7: Dusty or Old?
• Spectral Evidence for Widespread Galaxy Outflows at z>4
• 2-10 keV luminosity of high-mass binaries as a gauge of ongoing star-formation rate
• Prevalence of X-ray variability in the Chandra Deep Field South
• The Canada-France Redshift Survey XII: Nature of emission-line field galaxy population up to z = 0.3
• The Seyfert-Starburst Connection in X-rays. II. Results and Implications
• The Internal Ultraviolet-to-Optical Color Dispersion: Quantifying the Morphological K-Correction
• On the Assembly History of Early-Type Galaxies in the Hubble Deep Field North
• Internal Color Properties of Resolved Spheroids in the Deep HST/ACS field of UGC 10214
• Chandra observation of Abell 1689: New determination of mass distribution and comparison to lensing measurements
• The Origin of Blue Cores in Hubble Deep Fields E/S0 galaxies
• Star Formation and X-ray Emission in Distant Star Forming Galaxies
• The cosmological evolution of colour gradients in spheroids

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• The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation
• The Properties and Evolution of a K-band Selected Sample of Massive Galaxies at z~0.4 - 2 in the Palomar/DEEP2 Survey
• Galaxy luminosity function per morphological type up to z=1.2
• Environmental dependence of AGN activity. I.: the effects of host galaxy
• The Structure and Star Formation History of Early-Type Galaxies in the UDF/GRAPES Survey
• A morphology revaluation of galaxies in common from the Catalog of Isolated Galaxies and the Sloan Digital Sky Survey (DR6)
• Exploring the formation of spheroidal galaxies out to z~1.5 in GOODS
• Colour gradients within SDSS DR7 galaxies: hints of recent evolution
• The Grism lens-amplified survey from space (GLASS). VII. The diversity of the distribution of star formation in cluster and field galaxies at 0.3<z<0.7
• The Nature of Blue Early-Type Galaxies in the Goods Fields
• Colour gradients in normal and compact early-type galaxies at 1<z<2
• Bulge evolution in face-on spirals and low surface brightness galaxies
• Star--forming galaxies at intermediate redshifts: morphology, ages and sizes
• The Effects of Interactions on the Structure and Morphology of Elliptical/Lenticular galaxies in Pairs
• Comparing narrow and broad-line AGNs, in a new diagnostic diagram for emission-line galaxies based on WISE data
• AKARI Near-Infrared Spectroscopy of SDSS-Selected Blue Early-Type Galaxies