High-resolution spectra of distant compact narrow emission line galaxies: Progrenitors of spheroidal galaxies
ABSTRACT Emission-line velocity widths have been determined for 17 faint (B approximately 20-23) very blue, compact galaxies whose redshifts range from z = 0.095 to 0.66. The spectra have a resolution of 8 Km/s and were taken with the HIRES echelle spectrograph of the Keck 10 m telescope. The galaxies are luminous with all but two within 1 mag of M(sub B) approximately -21. Yet they exhibit narrow velocity widths between sigma = 28-157 km/s, more consistent with typical values of extreme star-forming galaxies than with those of nearby spiral galaxies of similar luminosity. In particular, objects with sigma is less than or equal to 65 km/s follow the same correlations between sigma and both blue and H beta luminosities as those of nearby H II galaxies. These results strengthen the identification of H II glaxies as thier local counterparts. The blue colors and strong emission lines suggest these compact galaxies are undergoing a recent, strong burst of star formation. Like those which characterize some H II galaxies, this burst could be a nuclear star-forming event within a much larger, older stellar population. If the burst is instead a major episode in the total star-forming history, these distant galaxies could fade enough to match the low luminosities and surface brightnesses typical of nearby spheroidals like NGC 185 or NGC 205. Together with evidence for recent star formation, exponential light profiles, and subsolar metallicities, the postfading correlations between luminosity and velocity width and bewtween luminosity and surface brightness suggest that among the low-sigma galaxies, we may be witnessing, in situ, the progenitors of today's spheroidal galaxies.
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ABSTRACT: We present stellar mass measurements for a sample of 36 luminous compact blue galaxies (LCBGs) at redshifts z = 0.4-1.2 in the flanking fields around the Hubble Deep Field-North. The technique is based on fitting a two-component galaxy population model to multi-broadband photometry. Best-fit models are found to be largely independent of the assumed values for the initial mass function (IMF) and the metallicity of the stellar populations, but they are sensitive to the amount of extinction and the extinction law adopted. On average, the best-fit model corresponds to a LMC extinction law with E(B-V) = 0.5. Stellar mass estimates, however, are remarkably independent of the final model choice. Using a Salpeter IMF, the derived median stellar mass for this sample is 5 × 109M☉, i.e., ~2 times smaller than previous virial mass estimates. Despite uncertainties of a factor of 2-3, our results strengthen prior claims that L* CBGs at intermediate redshifts are, on average, about 10 times less massive than a typical L* galaxy today.The Astrophysical Journal 02/2003; 586(1):L45. · 6.73 Impact Factor
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ABSTRACT: We present a dynamical study of the Cl 0023+0423 system at a redshift of z = 0.84. This system consists of two components separated in velocity space by ~2900 km s-1 and on the plane of the sky by ~0.23 h-1 Mpc. A kinematic analysis indicates that the two components are a poor cluster with a velocity dispersion of 415 km s-1 and a mass of ~3–6 × 1014h-1M☉, and a less massive group with a velocity dispersion of 158 km s-1 and a mass of ~1013h-1M☉. The dynamics of galaxy groups at high redshift can provide important insights into the creation of present-day galaxy clusters. Therefore, we have performed a dynamical study on this system in order to determine whether the two groups are infalling. This analysis includes an analytic two-body calculation and N-body simulations. The results of both studies indicate that the system is most likely not bound, but simply a chance projection on the sky; however, within the observational uncertainties, there exist bound solutions where the two galaxy groups are currently moving toward each other and will eventually merge into a larger system of galaxies. We have run 1000 N-body simulations with random initial conditions based on the observed parameters of the Cl 0023+0423 groups. A statistical analysis of these simulations indicates that there is a 20% chance that the two groups will merge. If the Cl 0023+0423 system does merge, it will appear as a cluster on the sky, as well as in velocity space, within 1–2 Gyr. The cluster will evolve dynamically for more than 3 Gyr, appearing during this time more similar to an open, irregular cluster. The final merged system has a velocity dispersion that is consistent with a local Abell richness class 1 cluster.The Astronomical Journal 08/1998; 116(2):643. · 4.97 Impact Factor
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ABSTRACT: We analyze 26 luminous compact blue galaxies (LCBGs) in the Hubble Space Telescope ACS Ultra Deep Field (UDF) at z ~ 0.2-1.3, to determine whether these truly are small galaxies or, rather, bright central starbursts within existing or forming large disk galaxies. Surface brightness profiles from UDF images reach fainter than rest-frame 26.5 B mag arcsec-2 even for compact objects at z ~ 1. Most LCBGs show a smaller, brighter component that is likely star-forming, and an extended, roughly exponential component with colors suggesting stellar ages from 100 Myr to a few gigayears. Scale lengths of the extended components are mostly 2 kpc, more than 1.5-2 times smaller than those of nearby large disk galaxies like the Milky Way. Larger, very low surface brightness disks can be excluded down to faint rest-frame surface brightnesses (26 B mag arcsec-2). However, one or two of the LCBGs are large, disklike galaxies that meet LCBG selection criteria because of a bright central nucleus, possibly a forming bulge. These results indicate that 90% of high-z LCBGs are small galaxies that will evolve into small disk galaxies, or low-mass spheroidal or irregular galaxies in the local universe, assuming passive evolution and no significant disk growth. The data do not reveal signs of disk formation around small, H II galaxy-like LCBGs, nor do they suggest a simple inside-out growth scenario for larger LCBGs with a disklike morphology. Irregular blue emission in distant LCBGs is relatively extended, suggesting that nebular emission lines from star-forming regions sample a major fraction of an LCBG's velocity field.The Astrophysical Journal 03/2006; 640(2):L143. · 6.73 Impact Factor