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Session 105 - Galaxies: Counts & Kinematics.
Display session, Saturday, January 10
Exhibit Hall,
We present results of the photometric analysis of two samples of compact blue emission-line galaxies at intermediate redshift (0.1 < z <0.7) selected from faint field galaxy surveys. These samples appear to be without local counterparts -- at least at comparable space density (Phillips et al. 1997, Guzman et al. 1997). Based on multi-aperture photometry of HST WFPC-2 images, we establish the characteristics of Compact Narrow Emission-Line Galaxies (CNELGs, Koo et al. 1994) and Blue Nucleated Galaxies (BNGs, Schade et al. 1995). Using a parameter space defined by fundamental photometric properties -- surface brightness, color, image concentration, and luminosity -- we then explore the relationship of BNGs and CNELGs to local samples. Both BNGs and CNELGs are classes of faint field galaxies with very blue colors and irregular morphologies; the preponderance of evidence indicates they are undergoing a major starburst. The CNELGS are distinguished by their small sizes (half-light radii of order 0.3 arcsec), and may constitute a subclass of extremely compact BNGs. Starbursts triggered by mergers temporarily produce blue, strongly concentrated galaxies (Mihos amp; Hernquist 1994). Given their morphology, both CNELGs and BNGs are plausibly examples of recent mergers or interactions -- perhaps tracers of a physical process driving the evolution of blue galaxies. We explore what will happen to the BNG and CNELG samples if their star formation ceases; using galaxy evolution models to predict the reddening and fading of aging stellar populations, we infer the photometric properties of BNGs and CNELGs as they fade until the current time.
