Metallicities of galaxies in the nearby Lynx-Cancer void

Does the void environment have a sizable effect on the evolution of dwarf galaxies? If yes, the best probes should be the most fragile least massive dwarfs. We compiled a sample of about one hundred dwarfs with M_B in the range -12 to -18 mag, falling within the nearby Lynx-Cancer void. The goal is to study their evolutionary parameters -- gas metallicity and gas mass-fraction, and to address the epoch of the first substantial episode of Star Formation. Here we present and discuss the results of O/H measurements in 38 void galaxies, among which several the most metal-poor galaxies are found with the oxygen abundances of 12+log(O/H)=7.12-7.3 dex.Comment: 2 pages, one figure. To appear in proceedings of 'Environment and the Formation of Galaxies: 30 years later,' (Lisbon, September 2010), published by Springer-Verla

Observational physics of mirror world

The existence of the whole world of shadow particles, interacting with each other and having no mutual interactions with ordinary particles except gravity is a specific feature of modern superstring models, being considered as models of the theory of everything. The presence of shadow particles is the necessary condition in the superstring models, providing compensation of the asymmetry of left and right chirality states of ordinary particles. If compactification of additional dimensions retains the symmetry of left and right states, shadow world turns to be the mirror one, with particles and fields having properties strictly symmetrical to the ones of corresponding ordinary particles and fields. Owing to the strict symmetry of physical laws for ordinary and mirror particles, the analysis of cosmological evolution of mirror matter provides rather definite conclusions on possible effects of mirror particles in the universe. A general qualitative discussion of possible astronomical impact of mirror matter is given, in order to make as wide as possible astronomical observational searches for the effects of mirror world, being the unique way to test the existence of mirror partners of ordinary particles in the Nature

Study of galaxies in the Lynx-Cancer void. -- III. New extreme LSB dwarf galaxies

(Abridged) We present the results of the complex study of the low surface brightness dwarf (LSBD) gas-rich galaxies J0723+3621, J0737+4724 and J0852+1350, which reside in the nearby Lynx-Cancer void. Their ratios M(HI)/L_B, according to HI data obtained with the NRT, are respectively ~3.9, ~2, ~2.6. For the two latter galaxies, we derived oxygen abundance corresponding to the value of 12+log(O/H) <~7.3, using spectra from the Russian 6m telescope and from the SDSS database. We found two additional blue LSB dwarfs, J0723+3622 and J0852+1351, which appear to be physical companions of J0723+3621 and J0852+1350 situated at the projected distances of ~12--13 kpc. The companion relative velocities, derived from the BTA spectra, are dV = +89 km/s and +30 km/s respectively. The geometry and the relative orientation of orbits and spins in these pairs indicate, respectively, prograde and polar encounters for J0723+3621 and J0852+1350. The NRT HI profiles of J0723+3621 and J0723+3622 indicate a sizable gas flow in this system. The SDSS u,g,r,i images of the five dwarfs are used to derive the photometric parameters and the exponential or Sersic disc model fits. For three of them, the (u-g),(g-r),(r-i) colours of the outer parts, being compared with the PEGASE evolutionary tracks, evidence for the dominance of the old stellar populations with ages of T ~(8-10)+-3 Gyr. For J0723+3622 and J0737+4724, the outer region colours appear rather blue, implying the ages of the oldest visible stars of T <~1-3 Gyr. The new LSB galaxies complement the list of the known most metal-poor and `unevolved' dwarfs in this void, including DDO 68, SDSS J0926+3343 and others. This unique concentration of 'unevolved' dwarf galaxies in a small cell of the nearby Universe implies a physical relationship between the slow galaxy evolution and the void-type global environment.Comment: 16 pages, 5 tables, 9 figures. MNRAS, in pres

Dynamic response of one-dimensional interacting fermions

We evaluate the dynamic structure factor $S(q,\omega)$ of interacting one-dimensional spinless fermions with a nonlinear dispersion relation. The combined effect of the nonlinear dispersion and of the interactions leads to new universal features of $S(q,\omega)$. The sharp peak $S\propto q\delta(\omega-uq)$, characteristic for the Tomonaga-Luttinger model, broadens up; $S(q,\omega)$ for a fixed $q$ becomes finite at arbitrarily large $\omega$. The main spectral weight, however, is confined to a narrow frequency interval of the width $\delta\omega\sim q^2/m$. At the boundaries of this interval the structure factor exhibits power-law singularities with exponents depending on the interaction strength and on the wave number $q$

Universal theory of nonlinear Luttinger liquids

One-dimensional quantum fluids are conventionally described by using an effective hydrodynamic approach known as Luttinger liquid theory. As the principal simplification, a generic spectrum of the constituent particles is replaced by a linear one, which leads to a linear hydrodynamic theory. We show that to describe the measurable dynamic response functions one needs to take into account the nonlinearity of the generic spectrum and thus of the resulting quantum hydrodynamic theory. This nonlinearity leads, for example, to a qualitative change in the behavior of the spectral function. The universal theory developed in this article is applicable to a wide class of one-dimensional fermionic, bosonic, and spin systems.Comment: final published version with supporting online materia

Discovery of a massive variable star with Z=Zo/36 in the galaxy DDO 68

The Local Volume dwarf galaxy DDO 68, from the spectroscopy of its two brightest HII regions (Knots 1 and 2) was designated as the second most metal-poor star-forming galaxy [12+log(O/H)=7.14]. In the repeated spectral observations in 2008 January with the 6-m telescope (BTA) of the HII region Knot 3 [having 12+log(O/H)=7.10+-0.06], we find a strong evidence of a transient event related to a massive star evolution. From the follow-up observation with the higher spectral resolution in 2008 February, we confirm this phenomenon, and give parameters of its emission-line spectrum comprising of Balmer HI and HeI lines. The luminosities of the strongest transient lines (Ha, Hb) are of a few 10^36 erg s^-1. We also detected an additional continuum component in the new spectrum of Knot 3, which displays the spectral energy distribution raising to ultraviolet. The estimate of the flux of this continuum leads us to its absolute V-band magnitude of ~-7.1. Based on the spectral properties of this transient component, we suggest that it is related to an evolved massive star of luminous blue variable type with Z=Zo/36. We briefly discuss observational constraints on parameters of this unique (in the aspect of the record low metallicity of the progenitor massive star) event and propose several lines of its study.Comment: 6 pages, 5 Postscript figures, to appear in MNRAS Letters in June 2008 issu

HS 2134+0400 - new very metal-poor galaxy, a representative of void population?

We present the SAO 6m telescope spectroscopy of a blue compact galaxy (BCG) HS 2134+0400 discovered in frame of the dedicated Hamburg/SAO survey for Low Metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12+log(O/H) = 7.44), as well as other heavy elements (S, N, Ne, Ar), assigns this dwarf galaxy to the group of BCGs with the lowest metal content. There are only eight that low metallicity among several thousand known BCGs in the nearby Universe. The abundance ratios for the heavy elements (S/O, Ne/O, N/O, and Ar/O) are well consistent with the typical values of other very metal-poor BCGs. The global environment of HS 2134+0400 is atypical of the majority of BCGs. The object falls within the Pegasus void, the large volume with the very low density of galaxies with the normal (M_B* = -19.6) or high luminosity. Since we found in voids a dozen more the very metal-poor galaxies, we discuss the hypothesis that such objects can be representative of a substantial fraction of the void dwarf galaxy population.Comment: 6 pages, including 2 tables and 2 postscript figures. Submitted to Astronomy Letter