Paper: astro-ph/0508484
Date: Tue, 23 Aug 2005 18:42:47 GMT (279kb)

Title: Do young galaxies exist in the Local Universe? - Red Giant Branch
detection in the metal-poor dwarf SBS 1415+437

Authors: A. Aloisi (STScI/ESA), R.P. van der Marel, J. Mack, C. Leitherer
(STScI), M. Sirianni (STScI/ESA), M. Tosi (INAF-OAB)

Comments: ApJ Letters, in press. For a complete version of the paper with high
resolution figures go to http://www.stsci.edu/~marel/psdir/SBS1.ps (.ps) or
http://www.stsci.edu/~marel/pdfdir/SBS1.pdf (.pdf)
\\
We present results from an HST/ACS imaging study of the metal-poor blue
compact dwarf galaxy SBS 1415+437. It has been argued previously that this is a
very young galaxy that started to form stars only less than 100 Myr ago.
However, we find that the optical color-magnitude diagram prominently reveals
asymptotic giant branch and red giant branch (RGB) stars. The brightness of the
RGB tip yields a distance of 13.6 Mpc. The color of the RGB implies that its
stars must be older than approximately 1.3 Gyr, with the exact age depending on
the assumed metallicity and dust extinction. The number of RGB stars implies
that most of the stellar mass resides in this evolved population. In view of
these and other HST results for metal-poor galaxies it seems that the local
Universe simply may not contain any galaxies that are currently undergoing
their first burst of star formation.

\\ ( http://arXiv.org/abs/astro-ph/0508484 , 279kb)