Starbursts and Star Clusters in the Ultraviolet

Abstract

Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies reveal them to be highly irregular, even after excluding compact sources (clusters and resolved stars). Most (7/9) are found to have a similar intrinsic effective surface brightnesses, suggesting that a negative feedback mechanism is setting an upper limit to the star formation rate per unit area. All starbursts in our sample contain UV bright star clusters indicating that cluster formation is an important mode of star formation in starbursts. On average about 20% of the UV luminosity comes from these clusters. The brightest clusters, or super star clusters (SSC), are preferentially found at the very heart of starbursts. The size of the nearest SSCs are consistent with those of Galactic globular clusters. The luminosity function of SSCs is well represented by a power law with a slope alpha ~ -2. There is a strong correlation between the far infrared excess and the UV spectral slope. The correlation is well modeled by a geometry where much of their dust is in a foreground screen near to the starburst, but not by a geometry of well mixed stars and dust.Comment: 47 pages, text only, LaTeX with aaspp.sty (version 3.0), compressed postscript figures available at ftp://eta.pha.jhu.edu/RecentPublications/meurer

Star Forming Dwarf Galaxies

“…While the luminosity profiles of dIs follow a simple exponential law, the more enhanced SF activity in the centres of BCGs, possibly linked to dynamical instabilities, show a more complex behavior [14,77,111]. BCGs often have morphologies reminiscent of mergers and sometimes experience strong starbursts.…”

“…Over long time scales it is controlled by feedback processes [111] and environmental influences. Starburst galaxies are rare and, in the present epoch, do not significantly influence the evolution of star forming dwarfs as a type [12,35,90].…”

“…The major difference between the bursting state and the normal one seems rather to be the mode of star formation, the tendency for stars to form in super star clusters (SSCs) [e.g. 1,111] and possibly switch to a flatter IMF [45,139,164].…”

Stellar population in LLAGN

“…They can be super stellar clusters (SSCs) or a compact unresolved AGN. In fact, SSCs are a common phenomenon in spirals (Carollo et al 2002), and in galaxies with nuclear starbursts (Meurer et al 1995). UV observations of these knots can clarify their origin because these wavelengths are the most direct tracer of unobscured young stellar clusters.…”

The Embedded Super-Star Cluster of SBS 0335-052

“…In these systems, we know that most of the energy emerges in the infrared, and this would tend to invalidate any result derived from optical-UV surveys of the distant Universe. Yet studies on the local starburst galaxy population appear to indicate a correlation between the total infrared luminosity and the extinction as measured by the slope of the UV continuum (Meurer et al 1995). Such a correlation, along with the establishment of an effective attenuation curve (Calzetti et al 1994), offers the hope to address the question of galaxy formation with optical-UV instruments, thus circumventing an important problem of most current infrared and submillimeter instruments: their lower spatial resolution that makes the identification of counterparts and subsequent determination of redshifts problematic.…”