The Low-Mass IMF - Deep Star Counts in the DSph Galaxy Ursa Minor

Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceeding


We present a new study of deep star counts in the Local Group dwarf spheroidal (dSph) in Ursa Minor. Both the luminosity function (LF) and the color-magnitude diagram (CMD) of the unevolved stars are compared with the LF and CMD of the old, metal-poor globular cluster M92. The main sequence locations and turn-offs are identical within the errors. Since we. know from the brighter evolved stars that the metallicities for these two disparate systems are the same this implies that they also have equal ages. A direct comparison of faint LFs is then equivalent to a comparison of the low-mass stellar initial mass functions (IMF). We find that the LFs are identical within the mass range covered (similar to 0.35 - 0.8 M-circle dot). The Ursa Minor dSph has one of the highest apparent M/L ratios known in the Local Group, and is an extremely low surface brightness external galaxy. M92 is a typical high surface brightness globular cluster, with no apparent dark matter. Our findings lead to the conclusion that the low-mass stellar IMF in systems that formed at high redshift is independent of environment. Indeed, it is consistent with the low-mass IMF in star-forming regions today.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology
Original languageEnglish
Title of host publicationModes of Star Formation and the Origin of Field Populations, ASP Conference Proceedings
EditorsEva K. Grebel, Walfgang Brandner.
PublisherAstronomical Society of the Pacific (ASP)
ISBN (Print)1-58381-128-1
Publication statusPublished - 2002
Publication categoryResearch
EventWorkshop on Modes of Star Formation and the Origin of Field Populations - Heidelberg, Germany
Duration: 2000 Oct 92000 Oct 13

Publication series



ConferenceWorkshop on Modes of Star Formation and the Origin of Field Populations