arXiv subjects

James A. Rose

Publications and source records attributed to James A. Rose.

20 records · Page 2Linked to original sources

arXiv2000

Starbursts versus Truncated Star Formation in Nearby Clusters of Galaxies

We present long-slit spectroscopy, B and R bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters which are known to be either in a star-forming phase or to have had star formation which recently terminated. From the long-slit spectra, obtained with the Blanco 4-m telescope, we find that emission lines in the star-forming cluster galaxies are significantly more centrally concentrated than in a sample of field galaxies. The broadband imaging reveals that two currently star-forming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has been concentrated. In contrast, the two galaxies for which star formation has already ended show no central color gradient. The Pegasus I galaxy with the most evident signs of ongoing star formation (NGC7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radiotelescope reveal the presence of ~4 x 10^8 solar masses of HI. Arecibo observations of other current or recent star-forming early-type galaxies in Pegasus I indicate smaller amounts of gas in one of them, and only upper limits in others.

astro-ph↗

arXiv1995

The Ages of Starbursts in Post-Starburst Galaxies

We present a new technique for accurately determining the ages of starbursts in post-starburst galaxies. In particular, it uses the strength of the Ca II H + H$ε$ absorption feature relative to that of Ca II K to separate the effects of burst strength from burst age in a spectrum comprised of a post-starburst population and an underlying old galaxy population. To test the technique we have measured spectral indices in the observed spectra of three post-starburst early-type galaxies. The three galaxies are shown to have different post-starburst ages, ranging from 0 Gyr to 1.5 Gyr after completion of the burst. We also demonstrate that if the burst contributes greater than 50\% of the light at 4000 Å\ then the technique can distinguish between a post-starburst systems and models in which a constant star formation history is suddenly truncated, such as that which could occur in a spiral that is rapidly stripped of its interstellar medium. Finally, we demonstrate that while the technique is well-suited for determining the time elapsed since the termination of a starburst (up until 2 Gyr after the end of the burst), the derived termination times are relatively insensitive to the duration of the burst.

astro-ph↗