Hostname: page-component-78c5997874-t5tsf Total loading time: 0 Render date: 2024-11-11T03:10:11.358Z Has data issue: false hasContentIssue false
  • English
  • Français

A New Deep HST/ACS CMD of I Zw 18: Evidence for Red Giant Branch Stars

Published online by Cambridge University Press:  01 December 2006

A. Aloisi ,
F. Annibali ,
J. Mack ,
M. Tosi ,
R. van der Marel ,
G. Clementini ,
R. A. Contreras ,
G. Fiorentino ,
M. Marconi  and
I. Musella
...Show all authors
A. Aloisi
Affiliation:
Space Telescope Science Institute, Baltimore, USA email: aloisi@stsci.edu On Assignment from the Space Telescope Division of the European Space Agency
F. Annibali
Affiliation:
Space Telescope Science Institute, Baltimore, USA email: aloisi@stsci.edu
J. Mack
Affiliation:
Space Telescope Science Institute, Baltimore, USA email: aloisi@stsci.edu
M. Tosi
Affiliation:
INAF – Osservatorio Astronomico di Bologna, Bologna, Italy
R. van der Marel
Affiliation:
Space Telescope Science Institute, Baltimore, USA email: aloisi@stsci.edu
G. Clementini
Affiliation:
INAF – Osservatorio Astronomico di Bologna, Bologna, Italy
R. A. Contreras
Affiliation:
INAF – Osservatorio Astronomico di Bologna, Bologna, Italy
G. Fiorentino
Affiliation:
INAF – Osservatorio Astronomico di Bologna, Bologna, Italy
M. Marconi
Affiliation:
INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy
I. Musella
Affiliation:
INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy
A. Saha
Affiliation:
National Optical Astronomy Observatories, Tucson, USA
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We present results from new deep HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf galaxy in the nearby universe. It has been previously argued that this is a very young system that started forming stars only ≲500 Gyr ago, but other work has hinted that older (≳1 Gyr) red giant branch (RGB) stars may exist in this galaxy. Our deeper data indeed reveal evidence for an RGB. Underlying old (≳1 Gyr) populations are therefore present in even the most metal-poor systems, implying that star formation started at z ≳ 0.1. The RGB tip (TRGB) magnitude and the properties of Cepheid variables identified from our program indicate that I Zw 18 is farther away (D = 19.0 ± 1.8 Mpc) than previously believed.

Keywords

galaxies: dwarfirregularstarburststellar contentdistances and redshiftsCepheids
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S241: Stellar Populations as Building Blocks of Galaxies , December 2006 , pp. 310 - 314
Copyright
Copyright © International Astronomical Union 2007

References

Aloisi, A., Tosi, M., & Greggio, L. 1999, AJ 118, 302CrossRefGoogle Scholar
Aloisi, A., van der Marel, Mack J., Leitherer, C., Sirianni, M., & Tosi, M. 2005, ApJ 631, L45CrossRefGoogle Scholar
Babul, A., & Rees, M. J. 1992, MNRAS 255, 346CrossRefGoogle Scholar
Bellazzini, M., Ferraro, F. R., & Pancino, E. 2001, ApJ, 556, 635CrossRefGoogle Scholar
Cioni, M.-R. L., vander Marel, R. P. der Marel, R. P., Loup, C., & Habing, H. J. 2000, A&A, 359, 601Google Scholar
Izotov, Y. I., & Thuan, T. X. 1999, ApJ 511, 639CrossRefGoogle Scholar
Izotov, Y. I., & Thuan, T. X. 2004, ApJ 616, 768CrossRefGoogle Scholar
Momany, Y. et al. , 2005, A&A 439, 111Google Scholar
Östlin, G. 2000, ApJ 535, L99CrossRefGoogle Scholar
Tosi, M., Aloisi, A., Mack, J., & Maio, M. 2006, Proc. IAU Symp. 235, eds. Combes, F. & Palous, J., in pressGoogle Scholar