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

The Astrophysical Journal (Impact Factor: 5.99). 03/1995; 440(2). DOI: 10.1086/187758
Source: NTRS


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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Available from: Marianne Takamiya, Jun 01, 2015
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    ABSTRACT: We present a complete morphologically classified sample of 144 faint field galaxies from the HST Medium Deep Survey with 20.0 < I <22.0 mag. We compare the global properties of the ellipticals, early and late-type spirals, and find a non-negligible fraction (13/144) of compact blue [(V-I) < 1.0 mag] systems with $r^{1/4}$-profiles. We give the differential galaxy number counts for ellipticals and early-type spirals independently, and find that the data are consistent with no-evolution predictions based on conventional flat Schechter luminosity functions (LF's) and a standard cosmology. Conversely, late-type/Irregulars show a steeply rising differential number count with slope $(\frac{\delta log N}{\delta m}) = 0.64\pm 0.1$. No-evolution models based on the Loveday et al. (1992) and Marzke et al. (1994b) {\it local} luminosity functions under-predict the late-type/Irregular counts by 1.0 and 0.5 dex, respectively, at I = 21.75 mag. Examination of the Irregulars alone shows that $\sim 50$% appear inert and the remainder have multiple cores. If the inert galaxies represent a non-evolving late-type population, then a Loveday-like LF ($\alpha\simeq -1.0$) is ruled out for these types, and a LF with a steep faint-end ($\alpha\simeq -1.5$) is suggested. If multiple core structure indicates recent star-formation, then the observed excess of faint blue field galaxies is likely due to {\it evolutionary} processes acting on a {\it steep} field LF for late-type/Irregulars. The evolutionary mechanism is unclear, but 60% of the multiple-core Irregulars show close companions. To reconcile a Marzke-like LF with the faint redshift surveys, this evolution must be preferentially occurring in the brightest late-type galaxies with z > 0.5 at I = 21.75 mag. Comment: 29 pages, 1 catalog and 10 figures. The figures and catalog can be found at
    Full-text · Article · Nov 1995 · The Astrophysical Journal
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    ABSTRACT: Keck spectra and HST images have been used to derive characteristic velocity and length scales for an enigmatic component of the faint, blue, field galaxy population: the compact, narrow emission-line galaxies (CNELGs). These galaxies are very luminous, but have been found to be quite low mass systems (with typical masses similar to 10(9) M.) Their blue colors and strong emission lines indicate that they are undergoing a major burst of star formation. Following the completion of their current burst they will fade, becoming, in the absence of further major bursts, objects very similar to contemporary spheroidal galaxies. With mean sizes R(e) similar to 1.4 kpc and Gaussian velocity profiles with mean sigma = 45 km s(-1), the length scales and velocity widths of CNELGs are also quite consistent with the measured length scales and velocity widths of current spheroidals.
    Preview · Article · Jan 1996 · Proceedings of the International Astronomical Union
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    ABSTRACT: We present 18 spectra, obtained with the Keck 10 m telescope, of faint field galaxies (19 <I < 22, 0.2 < z < 0.84) previously imaged by the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2). Though small, our sample appears to be representative of field spirals with a magnitude limit of I <= 22. Combining the results from the spectral and imaging data, we have derived various quantitative parameters for the galaxies, including colors, inclinations, emission- line equivalent widths, redshifts, luminosities, internal velocity information, and physical scale lengths. In particular, disk scale lengths (with sizes ranging from ~1 to 5 kpc) have been measured from fits to the surface brightness profiles. We have also measured internal velocities with a rest frame resolution of σ = 55-80 km s^-1^ by fitting to the emission lines. The luminosity-disk size and luminosity- internal velocity (Tully-Fisher) relations for our moderate redshift galaxies are similar to the scaling relations seen for local galaxies, albeit with a modest brightening of ~1 mag. The one bulge-dominated galaxy in our sample (at z = 0.324) has a relatively blue color, reveals weak emission lines, and is ~0.5 mag brighter in the rest frame than expected for a passive local elliptical. Our data suggest that galaxies at about half the age of the universe have undergone mild luminosity evolution to the present epoch but are otherwise quantitatively similar to galaxies seen locally.
    Preview · Article · Apr 1996 · The Astrophysical Journal
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