Virgo Stellar Stream

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Virgo Stellar Stream
Sig07-008.jpg
Stellar streams (artist's impression)
Observation data (J2000 epoch)
Constellation Virgo
Right ascension ?
Declination ?
Distance 30 kly
Apparent magnitude  (V)?
Absolute magnitude  (V)?
Characteristics
Type remains of a dSph
Apparent size  (V)30° × 10°
Other designations
none

The Virgo Stellar Stream, also known as Virgo Overdensity, is the proposed name for a stellar stream in the constellation of Virgo which was discovered in 2005. [1] [2] The stream is thought to be the remains of a dwarf spheroidal galaxy that is in the process of merging with the Milky Way. It is the largest galaxy visible from the Earth, in terms of the area of the night sky covered.

Contents

The stream was discovered from photometric data from the Sloan Digital Sky Survey, which was used to create a three-dimensional map of the Milky Way, using the colors and brightness of certain characteristic types of stars to estimate their distance (a method known as "photometric parallax"). [3] The first suggestion of a new galaxy in Virgo was made in 2001 from data obtained as part of the QUEST survey, which used the one-metre Schmidt telescope at the Llano del Hato National Astronomical Observatory in Venezuela to search for RR Lyrae 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 "cannibalised" by the Milky Way. [4]

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 Solar System and the solid angle that it consequently covers, the stream contains only a few hundred thousand stars. The low surface brightness of the galaxy (possibly as low as 32.5  mag/arcmin 2) may have militated against its detection in surveys before SDSS. The number of stars in the stream is not greatly in excess of a star cluster, and it has been described by a member of the team that discovered it as "a rather pathetic galaxy" in comparison to the Milky Way. [5] Many of the stars have been known for centuries and thought of as normal Milky Way stars, although they have a lower metallicity than normal Population I stars in the Milky Way.

The stream lies within 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. [6] The Sagittarius Dwarf is another small galaxy which is also in the process of merging with the Milky Way; however, it is approximately 4 times further away than the stream, so the two are unlikely to be physically related, 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 around the Milky Way. [7] The Virgo Stellar Stream also resembles the Monoceros Ring, found in 2002, [8] which has similarly been attributed to the Canis Major Dwarf Galaxy merging with the Milky Way.

See also

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Sloan Digital Sky Survey Multi-spectral imaging and spectroscopic redshift survey

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Dwarf galaxy Small galaxy composed of up to several billion stars

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The Canis Major Overdensity or Canis Major Dwarf Galaxy is a disputed dwarf irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major.

Leo A

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The Monoceros Ring(monoceros: Latin for 'unicorn') is a long, complex, ringlike filament of stars that wraps around the Milky Way three times. This is proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy by tidal forces as part of the process of merging with the Milky Way over a period of billions of years, although this view has long been disputed. The ring contains 100 million solar masses and is 200,000 light years long.

Milky Way Barred Spiral galaxy containing our Solar System

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The Field of Streams is a patch of sky where several stellar streams are visible and crisscross.

Leo IV (dwarf galaxy)

Leo IV is a dwarf spheroidal galaxy situated in the Leo constellation, discovered in 2006 in the data obtained by the Sloan Digital Sky Survey. The galaxy is located at the distance of about 160 kpc from the Sun and moves away from the Sun with the velocity of about 130 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 130 pc.

Segue 2 is a dwarf spheroidal galaxy situated in the constellation Aries and discovered in 2009 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 35 kiloparsecs from the Sun and moves towards the Sun at a speed of 40 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with a half-light radius of about 34 parsecs.

Boötes III is an overdensity in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy. It is situated in the constellation Boötes and was discovered in 2009 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 46 kpc from the Sun and moves away the Sun with the speed of about 200 km/s. It has an elongated shape with the radius of about 0.5 kpc. The large size and an irregular shape may indicate that Bootes III in a transitional phase between a gravitationally bound galaxy and completely unbound system.

Pisces I or Pisces Overdensity is a clump of stars in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy. It is situated in the Pisces constellation and was discovered in 2009 by analysis of distribution of RR Lyrae stars in the data obtained by the Sloan Digital Sky Survey's data. The galaxy is located at the distance of about 80 kpc from the Sun and moves towards it with a speed of about 75 km/s.

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In astronomy, the Sagittarius Stream is a long, complex, structure made of stars that wrap around the Milky Way Galaxy in an orbit that nearly crosses the galactic poles. It consists of tidally stripped stars from the Sagittarius Dwarf Elliptical Galaxy, resulting from the process of merging with the Milky Way over a period of billions of years.

NGC 4147 Globular cluster in the constellation Coma Berenices

NGC 4147 is the New General Catalogue identifier for a globular cluster of stars in the northern constellation of Coma Berenices. It was discovered by English astronomer William Herschel on March 14, 1784, who described it as "very bright, pretty large, gradually brighter in the middle". With an apparent visual magnitude of 10.7, it is located around 60,000 light years away from the Sun at a relatively high galactic latitude of 77.2°.

The stellar halo of a galaxy refers to the component of its galactic halo containing stars. The halo extends far outside a galaxy's brightest regions and typically contains its oldest and most metal poor stars.

NGC 5053 Globular cluster in the constellation Coma Berenices

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References

  1. ↑ The Sloan Digital Sky Survey Reveals A New Milky Way Neighbor, SDSS press release, January 9, 2006
  2. ↑ Sonia Duffau, et al., 2006, Spectroscopy of QUEST RR Lyrae Variables: the new Virgo Stellar Stream, The Astrophysical Journal, Volume 636, Issue 2, pp. L97-L100 (ADS; arXiv : astro-ph/0510589
  3. ↑ Mario Juric, et al., October 2005, The Milky Way Tomography with SDSS, The Astrophysical Journal, submitted (arXiv : astro-ph/0510520)
  4. ↑ Katherina Vivas et al., 2001, The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 Kiloparsecs and Other Overdensities in the Outer Halo, The Astrophysical Journal, Volume 554, Issue 1, pp. L33-L36.
  5. ↑ "Stellar chemistry: Sloan Survey identifies new dwarf galaxy inside Milky Way". Space Daily. 10 January 2006. Retrieved 12 June 2018.
  6. ↑ Ibata, R. A., et al., 1994, A Dwarf Satellite Galaxy in Sagittarius, Nature, Volume 370, Number 6486, p. 194.
  7. ↑ The origin of the Virgo tidal stream Archived 2012-02-08 at the Wayback Machine , David Martínez-Delgado, Workshop on Dwarf Galaxies as Astrophysical and Cosmological Probes, 17 March 2006. (PDF)
  8. ↑ Newberg, H. J., et al., 2002, The Ghost of Sagittarius and Lumps in the Halo of the Milky Way, The Astrophysical Journal, Volume 569, Issue 1, pp. 245-274
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