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28 March 2024
 
  » arxiv » 0712.4205

 Article overview


Andromeda IV: a new Local Volume very metal-poor galaxy
S.A.Pustilnik ; A.L.Tepliakova ; A.Y.Kniazev ; A.N.Burenkov ; Russia; ; SAAO ; South Africa ;
Date 27 Dec 2007
AbstractAnd IV is a low-surface brightness (LSB) dwarf galaxy projecting close to Messier 31. Ferguson et al. (2000, FGW), from the Hubble Space Telescope (HST) study placed it at the distance of 6.1 Mpc. On the results of its several HII regions spectroscopy they also estimated their oxygen abundance 12+log(O/H) of ~7.90 via the empirical calibration R_23 method. In this paper the results of the spectroscopy of And IV two brightest HII regions with the SAO 6-m telescope (BTA) are presented. In both of them the faint line [OIII]4363A was detected that allowed us to determine their O/H by the classical T_e method. Their mean 12+log(O/H)=7.42+-0.10. The line intensities of these HII regions from FGW paper, with addition of I([OIII]4363) roughly estimated from their plots for the respective spectra were used to recalculate O/H via the classical T_e method. The derived mean value of 12+log(O/H) for the same two HII-regions appeared of 7.67+-0.14. Thus, the two independent values O/H are consistent each with other within their uncertainties. Their weighted mean is of 12+log(O/H)=7.50+-0.10 (in the old scale). For And IV blue luminosity of M_B=-12.6, the latter value of O/H fits much better to the ’standard’ relation between O/H and L_B for dwarf irregular galaxies (DIGs). Also, the new value of O/H is better consistent with the known unusually large value of M(HI)/L_B 13 for galaxy And IV. And IV appears to be a new representative of the extremely metal-deficient gas-rich galaxies in the Local Volume. The very large range of M(HI) for LSB galaxies with close metallicities and luminosities indicates that the simple models of LSBG chemical evolution are too limited to predict such striking diversity.
Source arXiv, 0712.4205
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