Virgo Stellar Stream

Virgo Stellar Stream

·        INTRODUCTION

The Virgo Stellar Stream, also known as Virgo Over density, is the proposed name for a stellar stream in the constellation of Virgo which was discovered in 2005. The stream is thought to be the remains of a dwarf ellipsoidal galaxy that's within the method of merging with the Milky Way. It is the biggest galaxy visible from the planet, in terms of the realm of the night sky coated.

The stream was discovered from photometrical information from the Sloan Digital Sky Survey, that was wont to produce a three-dimensional map of the Milky Way, using the colors and brightness of sure characteristic kinds of stars to estimate their distance (a methodology referred to as "photometric parallax").the primary suggestion of a replacement galaxy in Virgo was created in 2001 from data obtained as a part of the search survey, that used the one-meter reflector at the field del Hate National Astronomical Observatory in Venezuela to go looking for RR Lyre variable stars. Five were found in a clump with a right ascension near 12.4 hours, and the astronomers speculated that this clump was part of a small galaxy being "cannibalized" by the Milky Way.

The stream covers over one hundred square degrees and possibly as much as one thousand square degrees (approximately five percent of the hemisphere visible at any one time, or five thousand times the area of the full moon). Despite its proximity to the scheme and therefore the angle that it consequently covers, the stream contains solely many hundred thousand stars. The low surface brightness of the galaxy (possibly as low as 32.5 mag/arcmin²) may have militated against its detection in surveys before SDSS. The number of stars within the stream isn't greatly in more than a star cluster, and it's been represented by a member of the team that discovered it as "a rather pathetic galaxy" in comparison to the Milky Way. Many of the stars have been known for centuries and thought of as normal Milky Way stars, although they have a lower metallicity than traditional Population I stars within the Milky Way.

The stream lies inside the Milky Way, approximately 10 kiloparsecs (30,000 light-years) from the Sun, and extending over a region of space at least 10 kpc across in three dimensions. It is close on the plane of the sky to the Sagittarius Dwarf Elliptical Galaxy, which was found in 1994 through a similar photometric analysis of a star survey. The Sagittarius Dwarf is another tiny galaxy that is additionally within the method of merging with the milk like Way; but, it is approximately 4 times further away than the stream, so the 2 area unit unlikely to be physically connected, although it is possible that the Virgo Stellar Stream is a remnant left behind by the disruption of the Sagittarius Dwarf as it had orbited round the Milky Way. The Virgo Stellar Stream also resembles the Monoceros Ring, found in 2002, which has similarly been attributed to the Canes Major Dwarf Galaxy merging with the Milky Way.

·       Exploring the Virgo Stellar Stream with SEKBO Survey RR Lyre Stars

A set of the RR Lyre (RRL) candidates known from the Southern Edgeworth-Kuiper Belt Object (SEKBO) survey information has been followed up photometrically (n=106) and spectroscopically (n=51). Period and lightweight curve fitting reveals a twenty-four +/_ seven-membered contamination of SEKBO survey information by non-RRLs. This paper focuses on the region of the Virgo Stellar Stream (VSS), particularly on its extension to the South of the declination limits of the SDSS and of the QUEST RRL survey. The distribution of radial velocities within the Galactic normal of rest frame (V_GSR) for the eleven RRLs discovered within the VSS region has 2 apparent peaks. The larger peak coincides with the four RRLs having =127 +/_ 10 kms-1 and dispersion sigma=27 kms-1, marginally larger than that expected from the errors alone. The two-type ab RRLs in this group have =-1.95 +/_ 0.1. Both the radial velocities and metal abundances are consistent with membership in the VSS. The second velocity peak, which occurs at =-175 +/_ 10 kms-1 may indicate the presence of stars from the Sir leading tidal tail, which is expected to have large negative velocities in this region. We explore the extent of the VSS by constructing luminosity functions from the SEKBO data and comparing them to data synthesized with the Besancon Galactic model. Analysis of the excess over the model predictions reveals the VSS as a large (~760 deg^2) over density centered at roughly (RA, Dec) ~ (186deg, -4deg), spanning a length of ~15 kpc in projection, assuming a heliocentric distance of 19kpc. The data reveal for the first time the more southern regions of the stream and trace it to Dec ~ -15deg and Galactic latitudes as low as b ~ 45deg.

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