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

The Astrophysical Journal (Impact Factor: 5.99). 03/1995; 440. 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
    The Astrophysical Journal 11/1995; 453(1). DOI:10.1086/176369 · 5.99 Impact Factor
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    Proceedings of the International Astronomical Union 01/1996; 171:229.
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    ABSTRACT: At B magnitudes >~ 24 there is a well-known excess of galaxies (compared to standard models) which is probably due to an (evolving) population of sub-L* galaxies at moderate redshifts (<~ 0.4). One particular hypothesis which is hard to test directly via number counts or even redshift surveys is the possibility that the faint blue galaxies are in fact sub-galactic objects destined to merge by the present day to form current giant galaxies. If this were the case we might expect to find the faint blue galaxies in the vicinity of ~ L* galaxies (at redshifts =~ 0.2 to 0.4) with which they can merge (the blue galaxies are already known to be weakly clustered among themselves, limiting the possibility for multiple mergers of small fragments). In this paper we look for evidence of such clustering of faint blue galaxies around larger systems using candidates chosen photometrically from deep multicolour CCD images using the Hitchhiker parallel camera. A sample of candidate L$^\ast$ galaxies expected to lie at redshifts z =~ 0.2 to 0.4 has been selected on the basis of apparent magnitude (B = 20.5 to 22.0 mag.) and colours typical of early-type spirals. The distribution of 152 blue galaxies having 23.5 < B < 25.0, (B-R)c < 1.2, around 13 candidate L* galaxies has been determined. No evidence has been found for any preferential clustering of blue galaxies about the L* candidates; the observed overdensity within 60 arcsec of the L* candidates is -0.02 +/- 0.76 per candidate. We have also looked for clustering between other photometrically selected samples (such as faint blue and faint red objects). Null results have been found in all cases, placing significant limits on the scenarios wherein dwarfs at medium redshifts are removed via mergers with larger objects.
    Astronomy and Astrophysics 07/1996; 318(3). · 4.38 Impact Factor
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