Denise A. Smith

The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?*

Only two of the 20 highly luminous starburst galaxies analyzed by Smith et al. exhibit circumnuclear rings of star formation. These galaxies provide a link between ~1011 L☉ luminosity class systems and classical, less-luminous ringed systems. In this paper, we report the discovery of a near-infrared counterpart to the 1.6 kpc diameter nuclear ring of radio emission in NGC 7771 (UGC 12815). The ring contains ≈10 radio-bright clumps and ≈10 near-infrared-bright clumps. A displacement between the peaks of the radio and the near-infrared emission indicates the presence of multiple generations of star formation. The estimated thermal emission from each radio source is equivalent to that of ~35,000 O6 stars. Each near-infrared-bright knot contains ~5000 red supergiants, on average. In the case that the radio-bright knots are 4 Myr old and the near-infrared-bright knots are ≈10 Myr old, each knot is characterized by a stellar mass of 107 M☉, and the implied time-averaged star formation rate is ~40 M☉ yr-1. Several similarities are found between the properties of this system and other ringed and nonringed starbursts. Morphological differences between NGC 7771 and the starburst + Seyfert 1 galaxy NGC 7469 (UGC 12332) suggest that NGC 7771 may not be old enough to fuel an active galactic nucleus (AGN), or may not be capable of fueling an AGN. Alternatively, the differences may be unrelated to the presence or absence of an AGN and may simply reflect the possibility that star formation in rings is episodic.

Ultraviolet imaging of nearby starbursts: NGC 3310

Optical surveys for high-redshift (z∼2–5) star forming galaxies will preferentially identify UV-bright systems since the observed optical emission corresponds to the rest-frame UV. Studies of nearby UV-bright starbursts thus provide a unique opportunity to obtain a detailed understanding of the phenomena observed at high redshifts. We discuss the far-ultraviolet (FUV; λ∼1500 A) properties of the nearby blue starburst galaxy NGC 3310. The FUV morphology is compared to that observed at longer wavelengths. The stellar content of selected star forming regions is also discussed.

Far-ultraviolet emission from NGC 4038/4039, “The Antennae”: Massive star formation in compact clusters

Far-Ultraviolet (FUV) emission from NGC4038/4039 traces recent massive star formation in the system. The FUV is used to determine the massive star content and to identify compact regions of recent star formation. FUV measurements are combined with ground-based observations and starburst models to determine ages, mass functions, and current star formation rates.