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RE: Virgo
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A trail of gas connecting two galaxies shows they once suffered a high-speed collision. The event could help explain why many galaxies cannot form new stars.
One victim of this intergalactic accident is the "disturbed" spiral galaxy NGC 4438, which sits roughly 50 million light years from us in the Virgo galaxy cluster.
The spiral arms of this galaxy look mangled, and it is unusually poor in gas compared with similar spirals. Astronomers thought both of these symptoms could be the result of NGC 4438 colliding with another galaxy.

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Title: Spitzer Observations of Environmental Effects on Virgo Cluster Galaxies
Authors: Jeffrey D.P. Kenney, O. Ivy Wong, Anne Abramson, Justin H. Howell, Eric J. Murphy, George X. Helou

We present the initial results from SPITSOV, the Spitzer Survey of Virgo, which includes MIPS and IRAC observations for a carefully selected sample of 44 Virgo cluster spiral and peculiar galaxies. SPITSOV is part of a multiwavelength campaign to understand the effects of the cluster environment on galaxy evolution. These Virgo galaxies are different from galaxies outside of clusters, since most of them have been significantly modified by their environment. The SPITSOV data can serve the community as the Spitzer sample of nearby cluster spiral galaxies, a complement to the SINGS data for nearby non-cluster galaxies. In this paper we describe the sample, the goals of the study, and present preliminary results in 3 areas: 1) Evidence for ram pressure-induced disturbances in radio morphologies based on changes in the FIR-radio (70um-20cm) correlation; 2) Evidence for ram-pressure stripped extraplanar gas tails from comparisons of dust/PAH (8um) emission and optical dust extinction; 3) Evidence for unobscured star-forming regions with large ratios of H-alpha to 24um emission in some galaxies due to ram pressure stripping of dust.

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Title: A Spitzer study of star-forming regions in Virgo Cluster galaxies
Authors: O. Ivy Wong, Jeffrey D.P. Kenney

We present a preliminary study of the star formation distribution within three Virgo Cluster galaxies using the 24 micron Spitzer observations from the Spitzer Survey of Virgo (SPITSOV) in combination with H-alpha observations. The purpose of our study is to explore the relationship between the star formation distribution within galaxies and the type (and phase) of interactions experienced within the cluster environment. Neither highly-obscured star formation nor strongly enhanced star-forming regions along the leading edges of galaxies experiencing ICM-ISM interactions were found. However, very unobscured star-forming regions were found in the outer parts of one galaxy (NGC 4402), while relatively obscured star-forming regions were found in the extraplanar regions of another galaxy (NGC 4522). We attribute the observed differences between NGC 4402 and NGC 4522 to the direction of motion of each galaxy through the ICM.

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Virgo Cluster spirals
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Title: The magnetic fields of large Virgo Cluster spirals
Authors: M. Wezgowiec, M. Urbanik, B. Vollmer, R. Beck, K. T. Chyzy, M. Soida, Ch. Balkowski

Because of its proximity the Virgo Cluster is an excellent target for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated. Optical and/or \ion{H}{i} observations do not always show effects of weak interactions between galaxies and their encounters with the cluster medium. For this reason we searched for possible anomalies in the magnetic field structure in Virgo Cluster spirals which could be attributed to perturbations in their gas distribution and kinematics. Five angularly large Virgo Cluster spiral galaxies (NGC 4501, NGC 4438, NGC 4535, NGC 4548 and NGC 4654) were the targets for a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz. For two objects polarization data at higher frequencies have been obtained allowing Faraday rotation analysis. Distorted magnetic field structures were identified in all galaxies. Interaction-induced magnetized outflows were found in NGC 4438 (due to nuclear activity) and NGC 4654 (a combination of tidal tails and ram pressure effects). Almost all objects (except the anaemic NGC 4548) exhibit distortions in polarized radio continuum attributable to influence of the ambient gas. For some galaxies they agree with observations of other species, but sometimes (NGC 4535) the magnetic field is the only tracer of the interaction with the cluster environment. The cluster environment clearly affects the evolution of the galaxies due to ram pressure and tidal effects. Magnetic fields provide a very long-lasting memory of past interactions. Therefore, they are a good tracer of weak interactions which are difficult to detect by other observations.

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RE: Virgo
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Among the constellations that are well-placed for viewing during the evening skies this time of year is that of Virgo, the virgin.

The constellation contains the first magnitude star Spica.
Three other stars, Vindemiatrix, Awwa (Delta), Porrima (Gamma) are quite prominent. To the right of Spica is Heze (Zeta).

At a distance of only 50 million light-years away, the Virgo Cluster is the nearest galaxy cluster to us. It's a giant structure consisting of hundreds of galaxies, both large and small, spiral and elliptical; 16 objects in this cluster are members of the famous Messier list of space objects.
Astronomers have located a large number of planetary nebula floating in the "intercluster" space between galaxies, and theorise that they must be a fraction of the free floating stars and other objects which swarm around the cluster.
By measuring the path of these objects, astronomers have been able to track how the Virgo Cluster is still in the process of formation.
The photogenic Sombrero Galaxy, one of the largest galaxies in the nearby Virgo Cluster of Galaxies.
The Sombrero Galaxy, also known as Messier 104, spans about 50,000 light years across and lies 28 million light years away. M104 can be seen with a small telescope.

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VIRGO
The Constellation Virgo
00:47 UT on Friday 19 May 2006
Exposure Time 20 ms


VIRGO-2006-5-19-0h12m

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