* Astronomy

Title: The Local Velocity Field
Authors: Karen L. Masters (CfA)

We only see a small fraction of the matter in the universe, but the rest gives itself away by the impact of its gravity. The distortions from pure Hubble flow (or peculiar velocities) that this matter creates have the potential to be a powerful cosmological tool, but are also a nuisance for extragalactic astronomers who wish to use redshifts to estimate distances to local galaxies. We provide a quick overview of work on the local peculiar velocity field, discussing both simple spherical infall models, non-parametric modelling using redshifts surveys, and full velocity and density field reconstruction from peculiar velocities. We discuss results from a multiattractor model fit to data from the SFI++ sample of peculiar velocities - the best peculiar velocity data currently available. We also talk about the future of samples for the study of the local velocity field, especially the 2MASS Tully-Fisher (2MTF) survey.

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A dwarf galaxy in the direction of the constellation Pegasus is being stripped of its gas, according to astronomers.
A galaxy needs its gas to create new stars. So we might be seeing this galaxy near the end of its ability to form stars.
Alan McConnachie at the University of Victoria in Canada and his colleagues studied hydrogen gas in the Pegasus dwarf galaxy. The gas is bunched up in the southeastern part of the galaxy and extended in the opposite direction. This suggests the galaxy is moving southeastward through material that is striking the galaxys gas and stripping it away.

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Title: Andromeda IV: a new Local Volume very metal-poor galaxy
Authors: S.A.Pustilnik (1), A.L.Tepliakova (1), A.Y.Kniazev (2,1), A.N.Burenkov (1); (1)SAO, Russia; (2) SAAO, South Africa

And 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.

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Title: Photometric properties of Local Volume dwarf galaxies
Authors: M. E. Sharina, I. D. Karachentsev, A. E. Dolphin, V. E. Karachentseva, R. Brent Tully, G. M. Karataeva, D. I. Makarov, L. N. Makarova, S. Sakai, E. J. Shaya, E. Yu. Nikolaev, A. N. Kuznetsov
(Version v2)

We present surface photometry and metallicity measurements for 104 nearby dwarf galaxies imaged with the Advanced Camera for Surveys and Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope.
In addition, we carried out photometry for 26 galaxies of the sample and for Sextans~B on images of the Sloan Digital Sky Survey. Our sample comprises dwarf spheroidal, irregular and transition type galaxies located within ~10 Mpc in the field and in nearby groups: M81, Centaurus A, Sculptor, and Canes Venatici I cloud. It is found that the early-type galaxies have on average higher metallicity at a given luminosity in comparison to the late-type objects. Dwarf galaxies with M_B > -12 -- -13 mag deviate toward larger scale lengths from the scale length -- luminosity relation common for spiral galaxies, h \propto L^{0.5}_B. The following correlations between fundamental parameters of the galaxies are consistent with expectations if there is pronounced gas-loss through galactic winds: 1) between the luminosity of early-type dwarf galaxies and the mean metallicity of constituent red giant branch stars, Z ~ L^0.4, 2) between mean surface brightness within the 25 mag/sq.arcsec isophote and the corresponding absolute magnitude in the V and I bands, SB_25 ~ 0.3 M_25, and 3) between the central surface brightness (or effective surface brightness) and integrated absolute magnitude of galaxies in the V and I bands, SB_0 ~ 0.5 M_L, SB_e ~ 0.5 M_e. The knowledge of basic photometric parameters for a large sample of dwarf galaxies is essential for a better understanding of their evolution.

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