2001/05/21 by M. Tosi, E. Sabbi, M. Bellazzini +5 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #History and Developments in Astronomy #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/322104
aastex, 37 pages, 13 (reduced resolution) .ps figures. Accepted by AJ. Full resolution figures are available upon request to the first author
arxiv created 2001/05/21 · openalex publication_date 2001/09/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present HST photometry of the resolved stellar population in the dwarf irregular galaxy NGC 1705. The galaxy has been observed with both WFPC2 and NICMOS, and successful images have been obtained in the F555W, F814W, F110W and F160W bands. The optical fields cover most of the galaxy, while the infrared field (NIC2) maps only its central regions. The optical photometry provides \~20000 objects down to mF555W ~ 29 in the PC field of view and ~ 20000 in the three WFCs. In the infrared we have been able to resolve ~ 2400 stars down to mF110W, mF160W ~ 26. A subsample of 1834 stars have been unambiguously measured in all the four bands. The corresponding color-magnitude diagrams (CMDs) confirm the existence of an age gradient, showing that NGC 1705 hosts both young (a few Myr old) and very old (up to 15 Gyr old) stars, with the former strongly concentrated toward the galactic center and the latter present everywhere, but much more easily visible in the external regions. The tip of the red giant branch (TRGB) is clearly visible both in the optical and in the infrared CMDs and allows us to derive the galaxy distance. Taking into account the uncertainties related to both the photometry and the TRGB magnitude -- distance relation, we find that the distance modulus of NGC 1705 is (m-M)0=28.54 +- 0.26, corresponding to a distance D=5.1 +- 0.6 Mpc.