Pronounced Star Formation Activity, and its Effect on the Interstellar Medium and Evolution in the Magellanic Irregular Galaxy, NGC 4449

Details Pronounced Star Formation Activity, and its Effect on the Interstellar Medium and Evolution in the Magellanic Irregular Galaxy, NGC 4449 Pronounced Star Formation Activity, and its Effect on the Interstellar Medium and Evolution in the Magellanic Irregular Galaxy, NGC 4449

Sep 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........15h&link_type=abstract

Thesis (PHD). THE CATHOLIC UNIVERSITY OF AMERICA , Source DAI-B 58/03, p. 1330, Sep 1997, 215 pages.

Computer Science

2

Scientific paper

NGC 4449, a nearby Magellanic Irregular Galaxy (at 5.4 Mpc, v = 214 km s-1) provides a unique laboratory to explore the processes that cause star formation. This UV bright galaxy exhibits a high star formation rate (SER) despite having a modest size and a lack of a spiral structure. Of the 22 OB associations in NGC 4449, UV spectra are taken from the seven brightest OB associations (or 'knots') using the SWP camera (at low dispersion mode) aboard the IUE satellite. Analysis using our newly developed Population Synthesis Code and Stellar library yields accurate ages, stellar populations and luminosities for each knot after assuming a initial mass function with a power law slope (α = 1.0) and a appropriate dust extinction law. UV rocket imagery (1430 A) and ground imagery at Hα (6563 A) and Hβ(4861A) supplement our analysis of NGC 4449. The OB associations (Knot 6, 10, 14, 16, and 18) that reside on the 'major ridge' of the galaxy, have at least two successive bursts of star formation in the last 12 Myr. Each of these knots exhibit a older generation of stars residing near a smaller, younger association at age 5 Myr. Knots 19 and 21 (11 & 12 Myr) have only a single burst of star formation. Our analysis of these knots indicate a high SFR spanning 0.013Msolaryr-1 to 0.063 Msolar yr-1 with a galactic SFR = 0.055 Msolar yr-1 (no reddening) to 2.4 Msolar yr-1 (corrected for internal galactic reddening). The high SFR implies a high supernova rate (SNR), with one supernova every 3 × 104 yr (knot 16) to 2 × 105 yr (knot 10). Future star formation regions are predicted in NGC 4449 using a simple plane-parallel model of star formation. The short-range plane-parallel model predicts localized, sequential star formation in a photoionization shock layer propagating in dense H2 clouds near OB stars. Long-range star formation using a thin-shell plane-parallel approximation show that star formation will propagate outwards to a range of 500pc (knot 6). A composite spatial map from these models detailing future star formation regions and supershell expansion is presented for NGC 4449.

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