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Astron. Astrophys. 354, L21-L24 (2000)

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2. The sample and optical data

The sample consists of five UV-bright examples of nearby galaxies chosen from a study of northern hemisphere starbursts: Markarian 8, NGC 3310, NGC 3690, NGC 7673, NGC 7678. These galaxies were imaged in several bands with the WIYN 3.5m telescope 1, located at the Kitt Peak National Observatory, using a 20482-pixel thinned SB2K CCD with a [FORMULA] arcmin2 field of view and a scale of 0.2 arcsec per pixel. The seeing during the observations on average was [FORMULA] FWHM. The R-band images used here are bias subtracted, flat-fielded, and cleared of foreground stars and background galaxies. These contaminating objects typically can cause rather high asymmetries if not properly removed. The (B-V) colors for all galaxies are from the RC3 catalog, except NGC 3690, where we adopt Weedman's (1973) value.

Each of the starbursts in our sample are benchmarks; i.e. they are relatively well studied and understood.

Markarian 8 hosts an intense starburst, with very blue colors (Huchra 1977). This galaxy contains several distinct `pieces' with visible tidal tails, and has long been recognized as a merger, or a strongly interacting double galaxy (Casini & Heidmann 1976; Keel & van Soest 1992). The interaction/merger between the multiple components of this galaxy are responsible for triggering the star-formation in the disk.

NGC 3310 , classified as a barred spiral (RC3), has it's very young starburst in a 1 kpc diameter ring around the nucleus. The bar and the size of the ringed structure suggest this starburst was triggered by a bar instability (Athanassoula 1992; Piner et al. 1995). Faint outer ripples are evidence for a minor merger or interaction with another galaxy, probably a dwarf (e.g. Balick & Heckman 1981; Schweizer & Seitzer 1988); this plausibly produced the bar instability which led to the starburst.

NGC 3690 , along with Markarian 8 are the most extreme interactions/mergers in our sample. The second `half ' of NGC 3690 is IC 694 (e.g. Gehrz et al. 1983). There is no disk structure to this galaxy, which is populated by very luminous, high surface-brightness star forming regions (Soifer et al. 1989).

NGC 7673 morphologically consists of an inner disturbed spiral structure, faint outer ripples (Homeier & Gallagher 1999), and huge, blue star-forming clumps embedded in a disturbed H I disk (Nordgren et al. 1997). These features are clues that this galaxy recently interacted with another galaxy, triggering the starburst.

NGC 7678 , classified as a barred spiral, contains a starburst located in a roughly symmetrical spiral pattern, similar to NGC 3310. This starburst consists of several bright H II regions (Goncalves et al. 1998) and contains a Seyfert nucleus (Kazarian 1993). NGC 7678 contains a large, massive blue arm where much of the starburst is located (Vorontsov-Velyaminov 1977).

Most of these galaxies show evidence for an interaction, but in various degrees and intensities. NGC 3310, NGC 7678 are probably minor mergers, or interactions that occurred in the distant past, while NGC 3690, NGC 7673, and Markarian 8 are obvious collisions that contain very disturbed structures.

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000