224 research outputs found
Properties of the most metal-poor gas-rich LSB dwarf galaxies SDSS J0015+0104 and J2354-0005 residing in the Eridanus void
SDSS J0015+0104 is the lowest metallicity low surface brightness dwarf (LSBD)
galaxy known. The oxygen abundance in its HII region SDSS J001520.70+010436.9
(at ~1.5 kpc from the galaxy centre) is 12+log(O/H)=7.07 (Guseva et al.). This
galaxy, at the distance of 28.4 Mpc, appears to reside deeply in the volume
devoid of luminous massive galaxies, known as the Eridanus void. SDSS
J235437.29-000501.6 is another Eridanus void LSBD galaxy, with parameter
12+log(O/H)=7.36 (also Guseva et al.). We present the results of their HI
observations with the Nancay Radio Telescope revealing their high ratios of
M(HI)/L_B ~2.3. Based on the Sloan Digital Sky Survey images, we derived for
both galaxies their radial surface brightness profiles and the main photometric
parameters. Their colours and total magnitudes are used to estimate the galaxy
stellar mass and ages. The related gas mass-fractions, f_g ~0.98 and ~0.97, and
the extremely low metallicities (much lower than for their more typical
counterparts with the same luminosity) indicate their unevolved status. We
compare these Eridanus void LSBDs with several extreme LSBD galaxies residing
in the nearby Lynx-Cancer void. Based on the combination of all their unusual
properties, the two discussed LSBD galaxies are similar to the unusual LSBDs
residing in the closer void. This finding presents additional evidence for the
existence in voids of a4 figures, sizable fraction of low-mass unevolved
galaxies. Their dedicated search might result in the substantial increase of
the number of such objects in the local Universe and in the advancement of
understanding their nature.Comment: 8 pages, 4 figures, 2 tables, accepted to MNRAS 02.04.2013. arXiv
admin note: text overlap with arXiv:0909.134
On the metallicities of UM 133, UM 283 and UM 382
The study of group properties of the extremely metal-deficient gas-rich local
dwarfs is very promising for the understanding the galaxy formation process at
high redshifts. About 20 such objects have been picked up from the literature
in the recent review by Kunth & Ostlin(2000). However part of these galaxies
got low metallicity as a result of earlier observations, and can have rather
large uncertainties in their cited element abundances. Before to perform the
detailed studies of such galaxies as of some extreme group, it is useful to
revise their metallicities. We present the results of the SAO 6m telescope
spectrophotometry of two Blue Compact Galaxies (BCG) reported from earlier
studies as very metal-poor objects. Well measured [O III] line 4363 A allows to
deduce the temperature in HII regions and get reliable abundances of chemical
elements. For UM 133 we derive 12+log(O/H) = 7.63+/-0.02, coincident with the
published value. UM 382, according to our data, is significantly more
metal-rich: its 12+log(O/H) = 7.82+/-0.03 in comparison to the published value
7.45. The third galaxy, UM 283 seems have got its very low 12+log(O/H) = 7.59
due to a misprint. We used its published emission line intensities and derived
instead the value of 7.95. Thus the latter two galaxies should NOT be
considered as the extremely metal-poor BCGs.Comment: 5 pages, 2 figures, A&A in pres
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