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Post Info TOPIC: The Local Volume


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Posts: 131433
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Canes Venatici I Cloud
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Title: 3D-structure of the Canes Venatici I Cloud
Authors: R.I Uklein

We present the improved distance moduli of 30 galaxies in the Canes Venatici I Cloud using advanced Tip of Red Giant Branch (TRGB) method (Makarov et.al. 2006). The method was determined for accurate estimation of the distances even if TRGB situated near photometric limit. The data were taken from the Archive of the Hubble Space Telescope (HST). Based on ACS and WFPC2 images of the HST we construct the colour-magnitude diagrams of the resolved stellar population of the galaxies using Dolphot and HSTPhot packages. New refined method of the distance determination allows us to clarify the 3D structure of the Canes Venatici I Cloud. It consists of the central group of galaxies around M94 and the outskirt which is situated in gravitational field of the "core". The mass and mass-to-light ratio of the CVn have been estimated.

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RE: The Local Volume
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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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ALFALFA Survey
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Title: ALFALFA: an Exploration of the z=0 HI Universe
Authors: Riccardo Giovanelli (Cornell University)

The Arecibo Legacy Fast ALFA (ALFALFA) Survey is a program aimed at obtaining a census of HI-bearing objects over a cosmologically significant volume of the local Universe. It will cover 7074 square degrees of the high latitude sky accessible with the Arecibo 305m telescope, using the 7-beam feed L-band feed array (ALFA). Started in February 2005, as of Summer of 2007 survey observations are 44\% complete. ALFALFA offers an improvement of about one order of magnitude in sensitivity, 4 times the angular resolution, 3 times the spectral resolution, and 1.6 times the total bandwidth of HIPASS. Although it will cover only one quarter the sky solid angle surveyed by HIPASS, ALFALFA will detect approximately six times as many sources, with a median depth of 110 Mpc. Preliminary results of ALFALFA are presented, with emphasis on those related with the Virgo cluster.

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Pegasus dwarf galaxy
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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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Posts: 131433
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RE: The Local Volume
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With its powerful detectors, Integral has performed the most-sensitive all-sky survey ever, finding expected clumpy areas at large scales in our local universe. Scientists working with ground-based telescopes have found the same local clumps, while looking for sources of cosmic showers.
Integral performed the survey in the hard X-ray band of the electromagnetic spectrum. Although it wasn't the first such survey, Integral's strength lies in the fact that it is unbiased towards sources that are shrouded by dust or gas, invisible at optical and soft X-ray wavelengths.
An interesting correlation has been found in data collected with the Auger telescopes in Argentina. Such a correlation with optical data is opening a new door in the exploration of the local universe.

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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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75 neighbouring galaxies
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The "lifestyles" of 75 neighbouring galaxies are illuminated in this poster from NASA's Spitzer Space Telescope. Scientists say this fresh perspective of our cosmic neighbourhood provides valuable insights into growth process of galaxies at a glance.
Over the past four years, Spitzer snapped infrared portraits of some of our most fascinating galactic neighbours as part of the Spitzer Infrared Nearby Galaxy Survey (SINGS) Legacy project. By understanding the mechanisms that fuel and hinder star production in these nearby galaxies, SINGS astronomers hope to solve the mystery of where galaxies come from, and how they've developed throughout the universe's history.

"Once the SINGS observations were done, I began to wonder how to look at all of the galaxies and make sense of the big picture. The SINGS sample of 75 galaxies was just too many to display at once on a computer screen and still be able to appreciate the spatial details present in the images" - Dr. Karl Gordon, of the Space Science Telescope Institute, in Baltimore, Md., who is a member of the SINGS team.

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Credit: NASA/JPL-Caltech/K. Gordon (Space Telescope Science Institute) and SINGS Team

Eventually, Gordon decided to create a poster with the 75 galaxies organized by shape -- using the classification system that astronomer Edwin Hubble created in 1925, soon after the physical nature of galaxies was discovered. The grouping system is called "Hubble's Tuning-Fork" because its overarching shape resembles a musical tuning-fork.

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RE: The Local Volume
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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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Date:
Local Group dwarf Leo T
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Title: The Local Group dwarf Leo T: HI on the brink of star formation
Authors: Emma V. Ryan-Weber (1), Ayesha Begum (1), Tom Oosterloo (2,3), Sabyasachi Pal (4) Michael J. Irwin (1), Vasily Belokurov (1), N. Wyn Evans (1), Daniel B. Zucker (1), ((1) IoA, Cambridge, (2) Astron, (3) Kapteyn Institute, (4) NCRA)

We present Giant Meterwave Radio Telescope (GMRT) and Westerbork Synthesis Radio Telescope (WSRT) observations of the recently discovered Local Group dwarf galaxy, Leo T. The peak HI column density is measured to be 7x10^20 cm^-2, and the total HI mass is 2.8x10^5 Msun, based on a distance of 420 kpc. Leo T has both cold (~ 500 K) and warm (~ 6000 K) HI at its core, with a global velocity dispersion of 6.9 km/s, from which we derive a dynamical mass within the HI radius of 3.3x10^6 Msun, and a mass-to-light ratio of greater than 50. We calculate the Jeans mass from the radial profiles of the HI column density and velocity dispersion, and predict that the gas should be globally stable against star formation, especially at radii beyond 50 pc. This finding is inconsistent with the half light radius of Leo T, which extends to 170 pc, and indicates that local conditions must determine where star formation takes place. Leo T is not only the lowest luminosity galaxy with on-going star formation discovered to date, it is also the most dark matter dominated, gas-rich dwarf in the Local Group.

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Posts: 131433
Date:
RE: The Local Volume
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Title: Are the nearby groups of galaxies gravitationally bound objects?
Authors: Sami-Matias Niemi, Pasi Nurmi, Pekka Heinämäki, Mauri Valtonen

We have compared numerical simulations to observations for the nearby (< 40 Mpc) groups of galaxies (Huchra & Geller 1982 and Ramella et al. 2002). The group identification is carried out using a group-finding algorithm developed by Huchra and Geller (1982). Using cosmological N-body simulation code with the LambdaCDM cosmology, we show that the dynamical properties of groups of galaxies identified from the simulation data are, in general, in a moderate, within 2sigma, agreement with the observational catalogues of groups of galaxies. As simulations offer more dynamical information than observations, we used the N-body simulation data to calculate whether the nearby groups of galaxies are gravitationally bound objects by using their virial ratio. We show that in a LambdaCDM cosmology about 20 per cent of nearby groups of galaxies, identified by the same algorithm as in the case of observations, are not bound, but merely groups in a visual sense. This is quite significant, specifically because estimations of group masses in observations are often based on an assumption that groups of galaxies found by the friends-of-friends algorithm are gravitationally bound objects. Simulations with different resolutions show the same results. We also show how the fraction of gravitationally unbound groups varies when the apparent magnitude limit of the sample and the value of the cosmological constant is changed. In general, a larger value of the Omega_Lambda generates slightly more unbound groups.

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