Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21330703f&link_type=abstract
American Astronomical Society, AAS Meeting #213, #307.03; Bulletin of the American Astronomical Society, Vol. 41, p.278
Astronomy and Astrophysics
Astrophysics
1
Scientific paper
Highly isolated systems provide a baseline for assessing the role of interactions within galaxy evolution. We use the Sloan Digital Sky Survey (SDSS) data release 1 - 5 to identify extremely isolated early-type galaxies (IEGs) in the nearby universe. Redshifts derived from the SDSS spectra permit a robust three-dimensional assessment of the local environment surrounding candidate IEGs. Isolated galaxies are chosen utilizing a projected physical separation of 2.5 Mpc from any neighboring non-dwarf galaxy brighter than M$_{V}$ = $-$16.5. A minimum redshift separation of 350 km s$^{-1}$ between a candidate galaxy and a neighboring was imposed to further insure the candidate's isolation. The IEG sample contains 33 galaxies that exhibit a number of unexpected features.
Through the use of a bulge/disk decomposition technique using standard surface photometry, brightness profiles and model-subtracted images were created. Radial profiles of eccentricity, position angle, and surface brightness were employed with the model images to constrain the merger and interaction histories of the IEGs. The presence of shell and fan structures, signatures of recent mergers, were detected in approximately 12% of the sample. Dominant features of the IEG sample are blue colors and active star formation, atypical of normal early-type galaxies. The IEGs would require a substantial reservoir of neutral gas to fuel the levels of on-going star formation observed. We speculate that some of the IEGs may be the remains of a coalesced group of gas-rich dwarf galaxies. Three sample galaxies have red colors and undisturbed morphologies expected of a pristine isolated early-type galaxy formed early in cosmic time. We acknowledge support from NASA's Astrophysical Data Program; grant #NNG05C53G, the GALEX Guest Investigator program, and a Texas Space Grant Consortium Fellowship.
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