Compact Galaxies at Z = 0.2-1.3: Implications for Galaxy Evolution and the Star Formation History of the Universe

• Published in: Highlights of astronomy 1998, Vol.11 (1), p.147-148
• Main Authors: Guzman, R., Phillips, A.C., Gallego, J., Koo, D.C.
• Format: Article
• Language: English
• ISSN: 1539-2996
• DOI: 10.1017/S1539299600020293

We study the global properties of 51 compact field galaxies with redshifts z ~ 0.2 - 1.3 and apparent magnitudes I 814 < 23.74 in the flanking fields of the Hubble Deep Field. All these galaxies have angular half-light radii r e < 0.5 arcsec. Keck spectra covering ~4000-9000 Å, combined with HST І814 images and Keck V-band images, were used to derive redshifts, V 606 - I 814 colors, absolute blue magnitudes ( MB ), linear half-light radii ( R e ), blue average surface brightnesses within R e ( SB e ), velocity widths ( σ ), virial masses ( M ), mass-to-light ratios ( M/L ), excitations ( O[III]/Hβ ), and star formation rates (SFR). The results of this study can be summarized as follows: (i): Only 12% of the 51 compact galaxies have absorption-line dominated spectra, while 88% show strong, narrow emission lines, similar to the so-called CNELGs (e.g., Koo, this volume). (ii): Despite being very luminous (i.e., LB ~ L *; see figure la), compact emission-line galaxies are low-mass stellar sytems (i.e., M ≤ 10 10 M ʘ , typically; see figure lb). (iii): Roughly 60% of the compact emission-line galaxies have colors, sizes, surface brightnesses, luminosities, velocity widths, excitations, star formation rates, and mass-to-light ratios characteristic of young, star-forming HII galaxies (see figures 1 and 2). The remaining 40% form a more heterogeneous class of evolved starbursts, similar to local disk starburst galaxies. (iv): Without additional star formation, galaxy evolution models predict that HII-like distant compacts will fade to resemble today’s spheroidal galaxies such as NGC 205 (Koo, this volume).