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Post Info TOPIC: The Local Volume
Blobrana


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Local Group Galaxies
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Title: A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
Authors: Philip Massey, Reagin T. McNill, K. A. G. Olsen, Paul W. Hodge, Cynthia Blaha, George H. Jacoby, R. C. Smith, Shay B. Strong

We describe a search for H-alpha emission-lined stars in M31, M33, and seven dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at identifying new Luminous Blue Variables (LBVs) from their spectroscopic similarity to known LBVs, avoiding the bias towards photometric variability, which may require centuries to manifest itself if LBVs go through long quiescent periods. Follow-up spectroscopy with WIYN confirms that our survey detected a wealth of stars whose spectra are similar to the known LBVs. We "classify" the spectra of known LBVs, and compare these to the spectra of the new LBV candidates. We demonstrate spectacular spectral variability for several of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet star, which now shows FeI, FeII and Balmer emission lines but neither the NIII 4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes are also noted for other suspected and known LBVs. Several of the LBV candidates also show >0.5 mag changes in V over the past 10-20 years. The number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822, and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be several hundred, in contrast to the 8 known historically through large-scale photometric variability. This has significant implications for the time scale of the LBV phase. We also identify a few new WRs and peculiar emission-lined objects.

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Blobrana


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Posts: 131433
Date:
RE: The Local Volume
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Galaxies - The Local Group - The Milky Way
Carl Sagan brings us the Cosmos, everything that ever was and ever will be, in an approach that is easily accessible even for those of us that are not science wizards. This series covers everything from the history of astronomy, the challenges it faced at its creation, how the universe was created and how it all might end, to the evolution of life on Earth, and the nature of the human brain.
First aired in 1980 as a 13 part series, it has been broadcast in 60 countries and has been seen by an estimated 500 million to 1 billion viewers worldwide.
The series was awarded an Emmy and a Peabody Award.



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Blobrana


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Posts: 131433
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Title: Mapping Mass in the Local Universe
Authors: Karen L. Masters (Harvard-SAO Center for Asrophysics)

We only see a small fraction of the matter in the universe, but the rest gives itself away by the impact of its gravity. Peculiar velocities have the potential to be a powerful tool to trace this matter however previous peculiar velocity surveys have struggled to meet their potential because of the large errors on individual measurements, poor statistics and uneven sky coverage. The 2MASS Tully-Fisher (2MTF) survey will make use of existing high quality rotations widths, new HI widths and 2MASS (2 Micron All-Sky Survey) photometry to measure Tully-Fisher distances/peculiar velocities for all bright inclined spirals in the 2MASS redshift survey (2MRS). This survey based on the 2MASS galaxy catalogue will provide a qualitatively better sample. It will provide significant improvements in sky coverage especially near the plane of our Galaxy which crosses the poorly understood "great attractor" region. I will give a progress report on the 2MTF survey including a look at over 300 hours of HI observations from the Green Bank Telescope (GBT) and a report on ongoing southern hemisphere observations with the Parke s Radio Telescope. The new spiral I-band field (SFI++) sample is currently the best available peculiar velocity survey for use in the local universe. I will also report on some preliminary results from this sample.

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Blobrana


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Title: The Local Velocity Anomaly
Authors: R. Brent Tully

There is a velocity discontinuity at about 7 Mpc between the galaxies of the Local Sheet that are moving together with low internal velocity dispersion and the adjacent structures. The Local Sheet bounds the Local Void. The Local Sheet is determined to have a peculiar velocity of 260 km/s away from the centre of the void. In order for this large velocity to be generated by an absence of gravity, the Local Void must be at least 45 Mpc in diameter and be very empty.

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Blobrana


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Posts: 131433
Date:
The Local Void
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Title: The Local Void is Really Empty
Authors: R. Brent Tully

Are voids in the distribution of galaxies only places with reduced matter density and low star formation efficiency or are they empty of matter? There is now compelling evidence of expansion away from the Local Void at very high velocities. The motion is most reasonably interpreted as an evacuation of the void, which requires that the void be very large and very empty.

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Blobrana


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Posts: 131433
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RE: The Local Volume
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Title: The Distribution of ALFALFA Galaxies
Authors: Ann M. Martin

The ALFALFA blind HI survey will enable a census of the distribution of gas-rich galaxies in the local Universe. Sensitive to an HI mass of 10**7 solar masses at the distance of the Virgo cluster, ALFALFA will probe the smallest objects locally and provide a new consideration of near-field cosmology. Additionally, with a larger, cosmologically significant sample volume and wider bandwidth than previous blind surveys, a much larger number of detections in each mass bin is possible, with adequate angular resolution to eliminate the need for extensive follow-up observations. This increased sensitivity will greatly enhance the utility of cosmological probes in HI. ALFALFA will eventually measure the correlation function of HI selected galaxies in a large local volume. The larger sample and volume size of the ALFALFA dataset will also robustly measure the HI mass function (HIMF). Here, we present the preliminary results on the distribution of local gas-rich galaxies from a first ALFALFA catalogue covering 540 deg**2.

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Blobrana


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Title: ALFALFA in the Leo Region: Looking for Missing Satellites in HI
Authors: Sabrina Stierwalt

The location of two nearby galaxy groups within ~20 Mpc in the Leo region allows for a detailed study of low-mass galaxies. A catalogue of HI line detections in Leo (9h36m < RA <11h36m, +8deg < dec < +16deg) has been made from the blind HI survey ALFALFA. More sensitive single-pixel Arecibo observations targeted Leo dwarf candidates noted optically by Karachentsev et al 2004 (K04) to determine group members and allow for a comparison of HI and optically-selected samples. This presentation highlights the differences between the two samples and the significant contribution blind HI surveys can make to the missing satellites problem.

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Blobrana


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Posts: 131433
Date:
Andromeda XII
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A recently discovered dwarf galaxy known as Andromeda XII is crashing our local party. The diminutive new arrival may be a latecomer, but its making up for lost time by approaching our cluster of galaxies the Local Group at breakneck speed.

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Blobrana


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Posts: 131433
Date:
Local Group Galaxies
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Title: Dependence of the Local Reionisation History on Halo Mass and Environment: Did Virgo Reionise the Local Group?
Authors: Simone M. Weinmann (1), Andrea V. Maccio' (2), Ilian T. Iliev (3), Garrelt Mellema (4), Ben Moore (1) ((1) University of Zurich, (2) MPIA, (3) CITA, (4) Stockholm Observatory)
(Version v2)

The reionisation of the universe has profound effects on the way galaxies form and on their observed properties at later times. Of particular importance is the relative timing of the reionisation history of a region and its halo assembly history, which can affect the nature of the first stars formed in that region, the properties and radial distribution of its stellar halo, globular cluster population and its satellite galaxies. We distinguish two basic cases for the reionisation of a halo - internal reionisation, whereby the stars forming in situ reionise their host galaxy, and external reionisation, whereby the progenitor of a galaxy is reionised by external radiation before its own stars are able to form in sufficient numbers. We use a set of large-scale radiative transfer and structure formation simulations, based on cosmologies derived from both WMAP 1-year and WMAP 3-year data to evaluate the mean reionisation redshifts and the probability of internal/external reionisation for Local Group-like systems, galaxies in the field and central cD galaxies in clusters. We find that these probabilities are strongly dependent on the underlying cosmology and the efficiency of photon production, but also on the halo mass. There is a rapid transition between predominantly external and predominantly internal reionisation at a mass scale of 1.0e12 Msun (corresponding roughly to L*galaxies), with haloes less massive than this being reionised preferentially from distant sources. We provide a fit for the reionisation redshift as a function of halo mass, which could be helpful to parameterise reionisation in semi-analytical models of galaxy formation on cosmological scales. We find no statistical correlation between the reionisation history of field galaxies and their environment.

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Blobrana


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Posts: 131433
Date:
AndXII dwarf spheroidal galaxy
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Title: Strangers in the night: Discovery of a dwarf spheroidal galaxy on its first Local Group infall
Authors: S. C. Chapman, J. Penarrubia, R. Ibata, A. McConnachie, N. Martin, M. Irwin, A. Blain, G. F. Lewis, B. Letarte, K. Lo, A. Ludlow, K. O'neil

We present spectroscopic observations of the AndXII dwarf spheroidal galaxy using DEIMOS/Keck-II, showing it to be moving rapidly through the Local Group (-556 km/s heliocentric velocity, -281 km/s relative to Andromeda from the MW), falling into the Local Group from ~115 kpc beyond Andromeda's nucleus. AndXII therefore represents a dwarf galaxy plausibly falling into the Local Group for the first time, and never having experienced a dense galactic environment. From Green Bank Telescope observations, a limit on the H{I} gas mass of <3000 Msun suggests that AndXII's gas could have been removed prior to experiencing the tides of the Local Group galaxies. Orbit models suggest the dwarf is close to the escape velocity of M31 for published mass models. AndXII is our best direct evidence for the late infall of satellite galaxies, a prediction of cosmological simulations.

andx11
The escape velocity is shown for M31 assuming the Geehan et al. (2005) mass model (solid line), derived from the circular velocity (dashed line), as a function of three dimensional distance of M31 from its satellites (data from Cote et al. 2000, and McConnachie et al. 2005). AndXII is shown with a circle. Recently discovered satellites AndXIV (Majewski et al. 2007) and AndXI, AndXIII (Martin et al. 2006, Chapman et al. 2007) are highlighted.

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