Evolution and structure of the amorphous galaxy NGC 1800

Details Evolution and structure of the amorphous galaxy NGC 1800 Evolution and structure of the amorphous galaxy NGC 1800

Mar 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981aj.....86..344g&link_type=abstract

Astronomical Journal, vol. 86, Mar. 1981, p. 344-356.

Astronomy and Astrophysics

Astronomy

23

Astronomical Photometry, Galactic Evolution, Galactic Structure, Interstellar Magnetic Fields, Spectrum Analysis, Stellar Evolution, Abundance, Astronomical Models, Cosmic Gases, H Lines, Intergalactic Media, Stellar Temperature

Scientific paper

New optical and H I observations of the blue, noninteracting amorphous galaxy NGC 1800 provide a basis for the determination of fundamental system properties which are used to study the connections between this galaxy's unusual structure and the evolution of its stellar population. An empirical estimate of the massive star-formation rate obtained from the Hβ-emission luminosity is combined with a simple galactic evolution model which explicitly includes the form of the IMF to explore evolutionary scenarios. Although the current star-formation rate exceeds that of the Milky Way or SMC, the substantial light fraction contributed by cool stars allows the galaxy to be fit with a near-constant stellar birthrate over ∼1010 yr. Galaxy-wide star-formation bursts do not comfortably account for NGC 1800, and we instead suggest that high star-formation efficiency has produced a high surface brightness system with the observed low H I/L ratio. NGC 1800 thus provides an example of efficient star formation without the aid of density-wave-induced gas compression which may be of general relevance to astration in gas-rich galaxies. After reviewing the trade-offs between the flatness of the IMF and time dependence of the star-formation rate, we are led to question the importance of star-formation bursts in blue irregulars more luminous than MB ∼ -16. Possible links between NGC 1800- type systems and E/S0 galaxies which contain young stellar components are briefly examined in terms of an evolutionary sequence.

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