Volume 572, December 2014
|Number of page(s)||9|
|Published online||24 November 2014|
1 Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
2 INAF − Osservatorio Astronomico di Teramo, Via Mentore Maggini, 64100 Teramo, Italy
3 Instituto de Astrofísica de Canarias, Calle Via Lactea, 38205 La Laguna, Tenerife, Spain
4 Departamento de Astrofísica, Universidad de La Laguna, 38205 Tenerife, Spain
5 INAF − Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italy
Received: 18 November 2013
Accepted: 25 August 2014
We present a detailed photometric study of the dwarf irregular galaxy NGC 6822 aimed at investigating the properties of its stellar populations and, in particular, the presence of stellar radial gradients. Our goal is to analyse the stellar populations in six fields, which cover the whole bar of this dwarf galaxy. We derived the quantitative star formation history (SFH) of the six fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived show an enhanced star formation rate (SFR) in Fields 1 and 3 during the past 500 Myr. The SFRs of the other fields are almost extinguished at very recent epochs and. We study the radial gradients of the SFR and consider the total mass converted into stars in two time intervals (between 0 and 0.5 Gyr ago and between 0.5 and 13.5 Gyr ago). We find that the scale lengths of the young and intermediate-to-old populations are perfectly compatible, with the exception of the young populations in Fields 1 and 3. The recent SF in these two fields is greater than in the other ones. This might be an indication that in these two fields we are sampling incipient spiral arms. Further evidence and new observations are required to prove this hypothesis. In addition, we derived the age-metallicity relations. As expected, the metallicity increases with time for all of the fields. We do not observe any radial gradient in the metallicity.
Key words: galaxies: individual: NGC 6822 / Local Group / galaxies: dwarf / galaxies: star formation
The photometric catalogue is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A26
© ESO, 2014
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