1999AJ....118..302A


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.12CEST14:25:56

1999AJ....118..302A - Astron. J., 118, 302-322 (1999/July-0)

The star formation history of I Zw 18.

ALOISI A., TOSI M. and GREGGIO L.

Abstract (from CDS):

The star formation history in I Zw 18 has been inferred from Hubble Space Telescope Wide Field Planetary Camera 2 archival data. This is done by comparing the derived V, B-V and V, V-I color-magnitude diagrams and luminosity functions with synthetic ones, based on various sets of stellar evolutionary tracks. At a distance of 10 Mpc, the stars resolved in the field of I Zw 18 allow for a look-back time up to 1 Gyr. We find that the main body is not experiencing its first episode of star formation. Instead, it has been forming stars over the last 0.5-1 Gyr, at a rate of ~(1-2)x10–2 M.yr–1.kpc–2. A more intense activity of (6-16)x10–2 M.yr–1.kpc–2 has taken place between 15 and 20 Myr ago. For the secondary body, the look-back time is 0.2 Gyr at most and the uncertainty is much higher because of the shallower diagrams and the small number of resolved stars. The derived range of star formation rate is (3-10)x10–3 M.yr–1.kpc–2. The IMF providing the best fit to the observed stellar populations in the main body has a slope 1.5, much flatter than in any similar galaxy analyzed with the same method. In the secondary body, it is peaked at α≃2.2, closer to Salpeter's slope (α=2.35).

Abstract Copyright:

Journal keyword(s): Galaxies: Evolution - galaxies: individual (I Zw 18) - Galaxies: Irregular - galaxies: photometry - Galaxies: Stellar Content

Simbad objects: 18

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Number of rows : 18

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME WLM Galaxy G 00 01 57.9 -15 27 50   11.50 11.10 10.93   ~ 575 2
2 NGC 147 GiG 00 33 12.120 +48 30 31.46   12.0 9.5     ~ 622 1
3 NAME Sculptor Dwarf Galaxy G 01 00 09.4 -33 42 32   9.79 8.6 8.81   ~ 1116 4
4 IC 1613 GiC 01 04 54.2 +02 08 00   10.42 10.01 9.77   ~ 1107 2
5 NGC 604 HII 01 34 32.1 +30 47 01           ~ 544 0
6 NAME Fornax Dwarf Spheroidal G 02 39 59.3 -34 26 57   9.02 7.4     ~ 1473 1
7 NGC 1569 IG 04 30 49.186 +64 50 52.52 11.72 11.86 11.03     ~ 1149 3
8 NGC 1705 SBG 04 54 13.500 -53 21 39.82 12.32 12.96 12.56 12.58 12.9 ~ 596 1
9 RMC 136 Cl* 05 38 42.396 -69 06 03.36           ~ 1736 1
10 NAME Zwicky's Flare HII 09 34 00.0 +55 14 25           ~ 21 0
11 Mrk 116 PaG 09 34 02.1 +55 14 25           ~ 997 1
12 NAME Sextans B H2G 10 00 00.8201300945 +05 20 09.572530884 12.77 12.25 11.89 11.71   ~ 468 0
13 NGC 3109 G 10 03 06.877 -26 09 34.46 11.10 10.42 10.04 9.91   ~ 695 2
14 NAME Leo I dSph G 10 08 28.12 +12 18 23.4   11.3 10.0     ~ 1045 1
15 NAME Dwarf Elliptical Galaxy in Sex G 10 13 02.9 -01 36 53   12 10.4     ~ 706 0
16 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1430 0
17 NAME Aquarius Dwarf G 20 46 51.7 -12 50 54 15.75 15.18 14.83 14.46   ~ 394 1
18 NAME Local Group GrG ~ ~           ~ 6973 0

    Equat.    Gal    SGal    Ecl

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2020.07.12-14:25:56

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