Bedin I

Bedin I is a dwarf spheroidal galaxy located in the constellation Pavo. It is situated around 28.38 million light-years from Earth, behind the globular cluster NGC 6752. Bedin I is possibly one of the oldest galaxies known, having formed around 10–13 billion years ago, and is one of the most isolated dwarf galaxies known, situated around 2.12 million light-years away from NGC 6744, its nearest neighbor with which it may be physically associated. As such, it has been deemed by astronomers as a "fossil" from the early universe. It was accidentally discovered by Italian astronomer Luigi Bedin, whose team was studying white dwarfs in NGC 6752 using the Hubble Space Telescope in September 2018; the discovery was announced in a paper published in January 2019.

Bedin I
Long-exposure photograph of Bedin I (left)[lower-alpha 1]
Observation data (J2000 epoch)
ConstellationPavo
Right ascension 19h 10m 45.41s
Declination−59° 55′ 04.32″
Distance8.7+0.5
−0.7 Mpc
Apparent magnitude (V)19.94
Absolute magnitude (V)−9.76
Characteristics
Size840 × 340 pc
Apparent size (V)20" × 8"

Nomenclature

Bedin I, pronounced /bɛˈdiːn/,[4] was named by its discovery team after their leader, Luigi Bedin,[5][6] who is a researcher at the National Institute for Astrophysics's observatory in Padua, Italy.[6][7] He was credited as the galaxy's sole discoverer.[8] Bedin and the team opted to avoid the galaxy being given "an anonymous identification based on its coordinates."[9]

Characteristics

Bedin I is an isolated dwarf spheroidal galaxy located around 8.7 megaparsecs, or around 28.38 million light-years, from Earth,[10][11][12] with similar characteristics to KKR 25 and the Tucana Dwarf Galaxy.[11] It is estimated to be around 840 by 340 parsecs, or 2,700 by 1,100 light-years, in size, which is a fifth the size of the Large Magellanic Cloud.[10] At a metallicity of −1.3, the galaxy's population is made up of metal-poor red giant stars,[13][14] and its luminosity is roughly a thousand times dimmer than the Milky Way Galaxy,[8][15] at an absolute magnitude of −9.76.[16] Bedin I is believed to have formed around 10–13 billion years ago with no star formation having occurred since then,[13][17][18] making it one of the oldest galaxies known.[18][19] Bedin I is also possibly the most isolated dwarf galaxy known,[18] located at least 650 kiloparsecs, or 2.12 million light-years, from its nearest neighbor, the intermediate spiral galaxy NGC 6744;[lower-alpha 2] the Milky Way and Andromeda galaxies are separated by a similar distance.[21] A physical association with NGC 6744 has been speculated however, due to the close angular distance between the galaxies, and their similar physical distances from Earth.[20] Its age, isolation, and lack of interaction with other galaxies has led to the galaxy being deemed a "fossil" from the early universe.[19][12]

Observation
External video
Zooming in on NGC 6752 and Bedin 1 (0:55) by European Space Agency

Bedin I is located in the constellation Pavo,[9] at a right ascension of  19h 10m 45.41s and declination of −59° 55′ 04.32″.[1] The galaxy is situated behind a group of unnamed foreground stars within the globular cluster NGC 6752.[2][22] Bedin I measures around 20 by 8 arcseconds across and has an apparent magnitude of 19.94,[16][23] although its visibility is significantly decreased by NGC 6752, one of the brightest globular clusters in the sky with an apparent magnitude of 5.4.[24][25] Bedin I was accidentally discovered by a team researching white dwarfs in the cluster in an effort to better determine the cluster's age.[6][15][22] The galaxy partially appeared in the field of view during program GO-15096 of the Hubble Space Telescope, led by principal investigator Luigi R. Bedin, which occurred between 7 and 18 September 2018.[3][26] The program, which saw the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) pointed at NGC 6752 for 75 exposures lasting 1,270 seconds each, was conducted over 40 orbits;[26] these exposures were able to capture objects with an apparent magnitude above 30.[27] Five of the orbits failed however, due to poor guide star acquisition.[26] The journal Monthly Notices of the Royal Astronomical Society: Letters published the team's three-part scientific paper on findings from the program on 31 January 2019, with the first part dedicated to the discovery of Bedin I.[19][28] A second program of 40 orbits, GO-15491, is currently scheduled for late 2019.[29]

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See also

References

Notes

  1. This photograph was taken in a three-day exposure of the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) aboard Hubble between 9–13 September 2018.[1] Bedin I is visible behind a group of stars at the far left of the image as a cluster of distant points of light; it is partly cut-off by the image's 1×1 arcminute field of view.[1][2][3]
  2. Bedin I is ∼650 kiloparsecs from NGC 6744 along the plane of the sky. More accurate measurements to judge its horizontal distance, and thus its true distance from NGC 6744, are needed.[20]

Sources

  1. Bedin, Luigi; Salaris, Maurizio; Rich, R. Michael; Richer, Harvey; Anderson, Jay; Bettoni, Daniela; Nardiello, Domenico; Milone, Antonio P.; Marino, A. F.; Libralato, Mattia; Bellini, Andrea; Dieball, Andrea; Bergeron, Pierre; Burgasser, Adam J.; Apai, Daniel (10 January 2019). "The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf Galaxy in background". Monthly Notices of the Royal Astronomical Society: Letters. Oxford University Press. 484 (1): L54–L58. doi:10.1093/mnrasl/slz004. Archived from the original on 31 January 2019. Retrieved 31 January 2019.
  2. Plait, Phil (1 February 2019). "Astronomers accidentally discover a nearby galaxy in a Hubble image!". Syfy Wire. Archived from the original on 2 February 2019. Retrieved 2 February 2019.CS1 maint: ref=harv (link)

Citations

  1. Space Telescope Science Institute (31 January 2019). "Bedin 1 in NGC 6752". Hubblesite. Archived from the original on 1 February 2019. Retrieved 1 February 2019. Object Position - R. A. 19:10:45.41 Dec. -59:55:04.32; Dimensions - Image is about 1 arcmin across (about 9,000 light-years); Instrument - ACS/WFC; Exposure Dates - September 9–13, 2018
  2. Plait 2019, "...it's sitting right near the core of NGC 6752, so there are lots of far brighter stars sitting near and even on top of it, contaminating the sample. [...] the galaxy is near the edge of the image’s field of view."
  3. Bedin et al. 2019, "Unfortunately, Bedin I is very close to the border of the field of view, where the large dithers gave us an overall incomplete and shallower view with respect to the centre of the fov."
  4. Hubble discovers nearby galaxy - Bedin 1. Launch Pad Astronomy, YouTube. 6 February 2019. Event occurs at 3:41. Retrieved 21 February 2019. ...designated Bedin I
  5. Plait 2019, "which the astronomers named Bedin I, after the lead investigator on the team, Luigi Bedin"
  6. Wall, Mike (31 January 2019). "Hubble Telescope Discovers 'Living Fossil' Galaxy in Our Milky Way's Backyard". Space.com. Archived from the original on 1 February 2019. Retrieved 1 February 2019. The find was fortuitous. An international team of astronomers was using Hubble's Advanced Camera for Surveys instrument to study white dwarfs [...] nicknamed Bedin 1, after discovery team leader L. R. Bedin of the INAF-Osservatorio Astronomico di Padova in Italy...
  7. Instituto de Astrofísica de Canarias (1 August 2018). "After the Kepler supernova explosion, no survivors were left behind". Phys.org. Archived from the original on 1 February 2019. Retrieved 1 February 2019. ...says Luigi Bedin, researcher at Osservatorio Astronomico di Padova (INAF)
  8. Freeman, David (31 January 2019). "Tiny 'oddball' galaxy discovered lurking in our cosmic backyard". NBC News MACH. Archived from the original on 1 February 2019. Retrieved 1 February 2019. The newfound galaxy, dubbed Bedin 1 in an acknowledgment of the scientist's singular role in its discovery [...] It's about 30 times smaller than the Milky Way and a thousand times dimmer.
  9. Dvorsky, George (1 February 2019). "Astronomers Accidentally Discover a Hidden Galaxy Right Next Door". Gizmodo. Archived from the original on 2 February 2019. Retrieved 2 February 2019. Bedin 1 is located in the Pavo constellation [...] Bedin said he pleased with the galaxy’s new name, saying it was "nice to adopt a nickname from one of its discoverers instead of an anonymous identification based on its coordinates."
  10. Bedin et al. 2019, "Assuming the same reddening as for NGC 6752, we estimate a distance modulus of (m − M)0 = 29.70±0.13 from the observed red giant branch, i.e. 8.7 ± 0.5−0.7 Mpc, and size of ∼840 × 340 pc, about one-fifth the size of the Large Magellanic Cloud."
  11. Bedin et al. 2019, "We conclude that this object is most likely an isolated dwarf spheroidal galaxy [...] The size and the estimated ellipticity of Bedin I offer the closest resemblance to the Tucana dwarf spheroidal galaxy. KKR 25 is an almost identical isolated dwarf system, with similar luminosity...
  12. Griffin, Andrew (1 February 2019). "Astronomers accidentally find a tiny galaxy that is nearly as old as the universe itself". The Independent. Archived from the original on 2 February 2019. Retrieved 2 February 2019. Together, those porperties led astronomers to classify it as what is called a dwarf spheroidal galaxy. [...] Because it is so distant from any other galaxies – and so has been left largely undisturbed – as well as its old age, the astronomers refer to Bedin 1 as a fossil from the beginning of the cosmos.
  13. Bedin et al. 2019, "A comparison of the observed colour–magnitude diagram with synthetic counterparts, which account for the galaxy distance modulus, reddening, and photometric errors, suggests the presence of an old (∼13 Gyr) and metal-poor ([Fe/H] ∼ −1.3) population."
  14. Plait 2019, "Still, enough individual stars are visible for the astronomers to examine them carefully. They were able to find quite a few red giant stars..."
  15. Carter, Jamie (31 January 2019). "The Milky Way Has A New Neighbor. Accidental Discovery As Ancient Galaxy Photobombs Hubble Telescope". Forbes. Archived from the original on 1 February 2019. Retrieved 1 February 2019. The astronomers that fortuitously discovered Bedin 1 were on a hunt for white dwarf stars in an effort to measure the age of NGC 6752 [...] it is roughly a thousand times dimmer than our Milky Way.
  16. Bedin et al. 2019, "amax-axis ∼20 arcsec (∼840 pc); bmax-axis ∼8 arcsec (∼340 pc); mF606W 19.94; MF606W −9.76"
  17. Bedin et al. 2019, "We conclude that this system likely formed more than 10 Gyr ago in a 'single' burst, and likely experienced no additional star formation since its formation."
  18. Bedin, Luigi; Jäger, Mathias (31 January 2019). "Hubble fortuitously discovers a new galaxy in the cosmic neighbourhood". ESA/Hubble. Archived from the original on 1 February 2019. Retrieved 1 February 2019. It lies about 30 million light-years from the Milky Way and 2 million light-years from the nearest plausible large galaxy host, NGC 6744. This makes it possibly the most isolated small dwarf galaxy discovered to date. [...] astronomers were able to infer that the galaxy is around 13 billion years old — nearly as old as the Universe itself.
  19. Bedin, Luigi; Villard, Ray (31 January 2019). "Hubble Accidentally Discovers a New Galaxy in Cosmic Neighborhood". NASA Solar System Exploration. Archived from the original on 1 February 2019. Retrieved 1 February 2019. Because of its 13-billion-year-old age, and its isolation — which resulted in hardly any interaction with other galaxies — the dwarf is the astronomical equivalent of a living fossil from the early universe. [...] The science team's results will be published online January 31, 2019, in the Monthly Notices of the Royal Astronomical Society: Letters.
  20. Bedin et al. 2019, "...but could be associated with NGC 6744. Indeed, NGC 6744 has a distance of 9.15±0.40 Mpc (Tully et al. 2013 catalogue gives (m − M)0 = 29.81±0.09), i.e. consistent with the dwarf within uncertainties, and it is at an angular distance of about 4 ° from the dwarf spheroidal (so, at a minimum distance of ∼650 kpc on the plane of the sky). [...] Our photometry is too shallow to reach the horizontal branch..."
  21. Plait 2019, "It does appear to be in the same region of sky and at about the same distance as the big spiral NGC 6744, but even then they're separated by at least two million light years, a huge distance (Andromeda is about that far from the Milky Way)..."
  22. ESA/Hubble Information Centre (31 January 2019). "Hubble fortuitously discovers a new galaxy in the cosmic neighbourhood". Phys.org. Archived from the original on 1 February 2019. Retrieved 1 February 2019. The aim of their observations was to use these stars to measure the age of the globular cluster, [...] Bedin 1, which lies far behind the foreground globular cluster NGC 6752.
  23. Plait 2019, "Their combined light brings this galaxy to a magnitude of about 20..."
  24. Bonnell, Jerry; Nemiroff, Robert J. (5 July 2013). "Globular Star Cluster NGC 6752". Archived from the original on 12 August 2019. Retrieved 12 August 2019. Over 10 billion years old, NGC 6752 follows clusters Omega Centauri and 47 Tucanae as the third brightest globular in planet Earth's night sky.
  25. O'Meara, Stephen James (8 April 2013). "113 The Starfish, The Windmill NGC 6752". Deep-Sky Companions: Southern Gems. Cambridge University Press. p. 411. ISBN 978-1-107-01501-2. At magnitude 5.4, it can be seen with the naked eye, and it ranks 5th among the globular clusters in total brightness.
  26. Bedin et al. 2019, "All images for this study were collected with the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) at the focus of the HST under program GO-15096 (PI: Bedin). Unfortunately, 5 of the planned 40 orbits failed because of poor guide star acquisition and will be reobserved at a later time. Usable data were collected between 2018 September 7 and 18, and consist of deep exposures of 1270 s each"
  27. Bedin et al. 2019, "...an Advanced Camera for Surveys/Wide Field Channel field was the subject of deep optical observations reaching magnitudes as faint as V ∼ 30."
  28. Bedin et al. 2019, "For completeness, Paper III of this series is focused on the white dwarfs of NGC 6752 in this very same ACS/WFC field, while Paper II deals with multiple stellar populations detected within NGC 6752 in our parallel observations with the infrared channel of the Wide Field Camera 3 (WFC3)."
  29. Bedin et al. 2019, "Note that this is an astrometric multicycle programme, and a second epoch (also of 40 orbits) has already been approved (GO-15491) and scheduled for late 2019."
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