The NASA/ESA Hubble Space Telescope has captured this view of the dwarf galaxy UGC 5497, which looks a bit like salt dashed on black velvet in this image.
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| Wide field image of the region around UGC 5497 (the galaxy is marked with a red circle). Credit: SDSS-III |
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| The blue compact dwarf galaxy UGC 5497, imaged with the Hubble Space Telescope. Credit: ESA/Hubble & NASA |
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| Zoom on the nucleus of UGC 5497. Credit: ESA/Hubble & NASA |
UGC 5497 is considered part of the M81 group of galaxies, which is located about 12 million light-years away in the constellation Ursa Major (The Great Bear). UGC 5497 turned up in a ground-based telescope survey back in 2008 looking for new dwarf galaxy candidates associated with Messier 81.
According to the leading cosmological theory of galaxy formation, called Lambda Cold Dark Matter, there should be far more satellite dwarf galaxies associated with big galaxies like the Milky Way and Messier 81 than are currently known. Finding previously overlooked objects such as this one has helped cut into the expected tally — but only by a small amount.
Astrophysicists therefore remain puzzled over the so-called "missing satellite" problem.
The field of view in this image, which is a combination of visible and infrared exposures from Hubble’s Advanced Camera for Surveys, is approximately 3.4 by 3.4 arcminutes.
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| This and the following three images are partial views from the full resolution image of UGC 5497 published on the ESA Hubble website. Starting from the top left, clockwise, they show the regions at the four corners of the full resolution image. |
The inclusion of UGC 5497 and other dwarf galaxies in the M81 Group was proposed by Kristin Chiboucas, Igor D. Karachentsev and R. Brent Tully in a research paper published on January 2009 in The Astronomical Journal. Here below are the paragraphs from the paper in which data about UGC 5497 are analyzed:
The galaxy UGC 5497 (d1012+64) was observed on 2007 October 20 with an exposure time of 900 s under 25 seeing. Spectrophotometric standard stars were also observed for calibration.
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If we assume that all candidates are group members at the distance of M81, we find Mr' magnitudes range from –6.7 for d0944+69 to –13.3 for d1012+64. Half-light radii range from 90 to 490 pc for objects well fitted with Sérsic functions. Because we do not yet have distances to these galaxies, we estimate that intrinsic magnitudes and radii can vary by as much as 0.14 mag and 6% in size (assuming a distance range of ± r2t). ... For the largest galaxies, we expect larger magnitude measurement errors, up to 1 mag, due to large errors in the local sky determination and subsequent negative features in the images.
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Three new M81 candidate member galaxies (d1028+70, d0958+66, d1012+64) are of the poorly understood BCD class. Spectra of these galaxies were obtained with Subaru/FOCAS and BTA/SCORPIO. Radial velocities of ~+60, –100, and +150 km s–1 support group membership for d0958+66, d1028+70, and d1012+64, respectively. All spectra exhibit strong Balmer absorption lines indicative of recent star formation. The BTA 6 m spectra also find Hα emission in all three cases indicating active star formation, in agreement with the blue (V – I) ~ 0.8 colors found for these galaxies. These three candidates bring the total number of M81 Group BCDs to at least four, including UGC 6456, long considered an isolated member of the M81 Group (...). ... BCDs tend to be found more frequently in field environments than clusters and are one of the least clustered galaxy types known (...). All the three BCDs discovered here lie in low-density regions at a minimum projected distance of 140 kpc from M81, with d1012+64 lying outside of the second turnaround radius at a projected distance of 315 kpc. The excess of this type of galaxy observed in this group may indicate that the termination of star formation is due to processes such as ram pressure stripping, which preferentially occur in more massive and more dynamically-evolved groups/clusters. However, given the projected distances of the M81 BCD population, it is possible that these galaxies are on first infall orbits, and processes such as strangulation that serve to shut down star formation even in poor groups (...) have yet to act on these galaxies.
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| Spectrum of d1012+64 [UGC 5497] from the 6 m BTA telescope. Hα emission is detected and used to measure a heliocentric radial velocity. Credit: Kristin Chiboucas, Igor D. Karachentsev and R. Brent Tully, The Astronomical Journal 137 (2009) 3009 |
Sources:
- Compact Blue Dwarf Can’t Hide, ESA Hubble image release, June 11, 2012
- Kristin Chiboucas, Igor D. Karachentsev and R. Brent Tully, Discovery Of New Dwarf Galaxies In The M81 Group, The Astronomical Journal 137 (2009) 3009, January 13, 2009
- James S. Bullock (UC Irvine), Notes on the Missing Satellites Problem, arXiv.org, September 23, 2010
- Polychronis Papaderos, Blue Compact Dwarf Galaxies, Centro de Astrofísica da Universidade do Porto, May 5, 2010
