Article

High-resolution spectra of distant compact narrow emission line galaxies: Progrenitors of spheroidal galaxies

The Astrophysical Journal (Impact Factor: 6.28). 03/1995; DOI: 10.1086/187758
Source: NTRS

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.

0 Followers
 · 
66 Views
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1086/503556 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1086/374611 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The validity of the emission-line luminosity versus ionized gas velocity dispersion (L–σ) correlation for H II galaxies (HIIGx) and its potential as an accurate distance estimator are assessed. For a sample of 128 local (0.02 ≲ z ≲ 0.2) compact HIIGx with high equivalent widths of their Balmer emission lines, we obtained the ionized gas velocity dispersion from high signal-to-noise ratio (S/N) high-dispersion spectroscopy (Subaru High Dispersion Spectrograph (HDS) and European Southern Observatory (ESO) Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT–UVES)) and integrated Hβ fluxes from low-dispersion wide aperture spectrophotometry. We find that the L(Hβ)–σ relation is strong and stable against restrictions in the sample (mostly based on the emission-line profiles). The ‘Gaussianity’ of the profile is important for reducing the root-mean-square (rms) uncertainty of the distance indicator, but at the expense of substantially reducing the sample. By fitting other physical parameters into the correlation, we are able to decrease the scatter significantly without reducing the sample. The size of the star-forming region is an important second parameter, while adding the emission-line equivalent width or the continuum colour and metallicity produces the solution with the smallest rms scatter=δlog L(Hβ) = 0.233. The derived coefficients in the best L(Hβ)–σ relation are very close to what is expected from virialized ionizing clusters, while the derived sum of the stellar and ionized gas masses is similar to the dynamical mass estimated using the Hubble Space Telescope (HST) corrected Petrosian radius. These results are compatible with gravity being the main mechanism causing the broadening of the emission lines in these very young and massive clusters. The derived masses range from about 2 × 106 M⊙ to 109 M⊙ and their ‘corrected’ Petrosian radius ranges from a few tens to a few hundred pc.
    Monthly Notices of the Royal Astronomical Society 08/2014; 442(4):3565. DOI:10.1093/mnras/stu987 · 4.90 Impact Factor