| | |
| | |
Stat |
Members: 3645 Articles: 2'504'928 Articles rated: 2609
25 April 2024 |
|
| | | |
|
Article overview
| |
|
I Zw 18 revisited with HST/ACS and Cepheids: New Distance and Age | A. Aloisi
; G. Clementini
; M. Tosi
; F. Annibali
; R. Contreras
; G. Fiorentino
; J. Mack
; M. Marconi
; I. Musella
; A. Saha
; M. Sirianni
; R. P. van der Marel
; | Date: |
16 Jul 2007 | Abstract: | We present new V and I-band HST/ACS photometry of I Zw 18, the most
metal-poor blue compact dwarf (BCD) galaxy in the nearby universe. It has been
argued in the past that I Zw 18 is a very young system that started forming
stars only < 500 Myr ago, but other work has hinted that older (> 1 Gyr) red
giant branch (RGB) stars may also exist. Our new data, once combined with
archival HST/ACS data, provide a deep and uncontaminated optical
color-magnitude diagram (CMD) that now strongly indicates an RGB. The RGB tip
(TRGB) magnitude yields a distance modulus (m-M)_0 = 31.30 +/- 0.17, i.e., D =
18.2 +/- 1.5 Mpc. The time-series nature of our observations allows us to also
detect and characterize for the first time three classical Cepheids in I~Zw~18.
The time-averaged Cepheid <V> and <I> magnitudes are compared to the VI
reddening-free Wesenheit relation predicted from new non-linear pulsation
models specifically calculated at the metallicity of I Zw 18. For the one
bona-fide classical Cepheid with a period of 8.63 days this implies a distance
modulus (m-M)_0 = 31.42 +/- 0.26. The other two Cepheids have unusually long
periods (125.0 and 129.8 d) but are consistent with this distance. The coherent
picture that emerges is that I Zw 18 is older and farther away than previously
believed. This rules out the possibility that I Zw 18 is a truly primordial
galaxy formed recently (z < 0.1) in the local universe. | Source: | arXiv, arxiv.0707.2371 | Services: | Forum | Review | PDF | Favorites |
|
|
No review found.
Did you like this article?
Note: answers to reviews or questions about the article must be posted in the forum section.
Authors are not allowed to review their own article. They can use the forum section.
browser Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
|
| |
|
|
|
| News, job offers and information for researchers and scientists:
| |