I Zwicky 18

Last updated
I Zwicky 18
I Zwicky 18a.jpg
Hubble Space Telescope (HST) image of I Zwicky 18
Credit: HST/NASA/ESA
Observation data (J2000 epoch)
Constellation Ursa Major
Right ascension 09h 34m 02.0s [1]
Declination +55° 14′ 28″ [1]
Redshift 751 ± 2 km/s [1]
Distance 0.059 Gly
Apparent magnitude  (V)16.0 [1]
Characteristics
Type I, [1] Starburst Galaxy
Apparent size  (V)0.3′ × 0.2′ [1]
Other designations
UGCA 166, Mrk 116, PGC 27182 [1]

I Zwicky 18 is a blue compact dwarf galaxy located about 59 million light years away [2] in the constellation Ursa Major. The galaxy was first identified by Swiss astronomer Fritz Zwicky in a 1930s photographic survey of galaxies. [3]

Contents

Age

Studies at the Palomar Observatory some 40 years ago led astronomers to believe that the galaxy erupted with star formation billions of years after its galactic neighbours. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. Early observations with the Hubble Space Telescope suggested an age of 500 million years old for I Zwicky 18. [4]

Astronomers have hypothesised the existence of young dwarf galaxies in a cold dark matter-dominated Universe. Dwarfs as young as 500 million years would be, however, much fainter than I Zwicky 18. I Zwicky 18 is thus unlikely to have formed all its stars recently in a cold dark matter Universe. [5] [6]

Later observations with the Hubble Space Telescope found faint and old stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies. [7]

Contents

I Zwicky 18 and its component or companion I Zwicky 18 C Hubble - infant galaxy.jpg
I Zwicky 18 and its component or companion I Zwicky 18 C

Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is almost exclusively composed of hydrogen and helium, the main ingredients created in the Big Bang. The galaxy's primordial makeup suggests that its rate of star formation has been much lower than that of other galaxies of similar age. The galaxy has been studied with most of NASA's telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, the Far Ultraviolet Spectroscopic Explorer (FUSE), [2] and the James Webb Space Telescope. [8] However, it remains a mystery why I Zwicky 18 formed so few stars in the past, and why it is forming so many new stars right now. [2]

In 2015 a study found a very large region of ionised helium in this small galaxy, which tends to be more frequent in very distant galaxies with low presence of metals. The ionization of helium implies the presence of objects emitting a radiation intense enough to knock electrons off the helium atoms. [9] Scientists therefore hypothesise that I Zwicky 18 must contain Population III stars, which are almost absent in all other galaxies in the local universe. [10]

Distance

Astronomers at the Space Telescope Science Institute in Baltimore, Maryland and the European Space Agency discerned the distance by observing Cepheid variable stars within I Zwicky 18. These massive flashing stars pulse in a regular rhythm. The timing of their pulsations is directly related to their brightness. The team determined the observed brightness of three Cepheids and compared it with the actual brightness predicted by theoretical models. These models were calculated specifically for I Zwicky 18's deficiency in heavy elements, indicating the galaxy's stars formed before these elements were abundant in the universe. The Cepheid distance also was validated through the observed brightness of the brightest red stars older than one billion years. [7]

The Hubble data suggest that I Zwicky 18 is 59 million light-years from Earth. The galaxy's larger-than-expected distance may explain why astronomers have had difficulty detecting older, fainter stars within the galaxy. The faint, old stars in I Zwicky 18 are almost at the limit of Hubble's resolution and sensitivity. [11]

Classification

I Zwicky 18 is classified as a dwarf irregular galaxy and also a blue compact galaxy [12] and a starburst galaxy. [13] I Zwicky 18 is much smaller than our Milky Way and a mere 3,000 light-years across. [14] I Zwicky 18 may still be creating Population III stars—spectroscopy shows that its stars are composed almost entirely of hydrogen and helium, with heavier elements almost completely absent. [15] The concentrated bluish-white knots embedded in the heart of the galaxy are two major starburst regions where stars are forming at a furious rate. The wispy blue filaments surrounding the central starburst regions are bubbles of gas that have been blown away by stellar winds and supernovae explosions from a previous generation of hot, young stars. This gas is now heated by intense ultraviolet radiation unleashed by a new generation of hot, young stars. [16]

See also

Related Research Articles

<span class="mw-page-title-main">Fornax</span> Constellation in the southern celestial hemisphere

Fornax is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Fornax is one of the 88 modern constellations.

<span class="mw-page-title-main">Galaxy</span> Large gravitationally bound system of stars and interstellar matter

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.

<span class="mw-page-title-main">M81 Group</span> Galaxy group in Ursa Major and Camelopardalis

The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is located at a distance of 3.6 Mpc, making it one of the nearest groups to the Local Group. The group is estimated to have a total mass of ×1012M☉. The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster.

<span class="mw-page-title-main">Cepheid variable</span> Type of variable star that pulsates radially

A Cepheid variable is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period and amplitude.

<span class="mw-page-title-main">Hubble Deep Field</span> Multiple exposure image of deep space in the constellation Ursa Major

The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area about 2.6 arcminutes on a side, about one 24-millionth of the whole sky, which is equivalent in angular size to a tennis ball at a distance of 100 metres. The image was assembled from 342 separate exposures taken with the Space Telescope's Wide Field and Planetary Camera 2 over ten consecutive days between December 18 and 28, 1995.

<span class="mw-page-title-main">Spitzer Space Telescope</span> Infrared space telescope (2003–2020)

The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), is an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, following IRAS (1983) and ISO (1995–1998). It was the first spacecraft to use an Earth-trailing orbit, later used by the Kepler planet-finder.

<span class="mw-page-title-main">Starburst galaxy</span> Galaxy undergoing an exceptionally high rate of star formation

A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy, or the star formation rate observed in most other galaxies.

<span class="mw-page-title-main">Centaurus A</span> Radio galaxy in the constellation Centaurus

Centaurus A is a galaxy in the constellation of Centaurus. It was discovered in 1826 by Scottish astronomer James Dunlop from his home in Parramatta, in New South Wales, Australia. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance. NGC 5128 is one of the closest radio galaxies to Earth, so its active galactic nucleus has been extensively studied by professional astronomers. The galaxy is also the fifth-brightest in the sky, making it an ideal amateur astronomy target. It is only visible from the southern hemisphere and low northern latitudes.

<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

<span class="mw-page-title-main">NGC 2403</span> Galaxy in the constellation Camelopardalis

NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. It is an outlying member of the M81 Group, and is approximately 8 million light-years distant. It bears a similarity to M33, being about 50,000 light years in diameter and containing numerous star-forming H II regions. The northern spiral arm connects it to the star forming region NGC 2404. NGC 2403 can be observed using 10×50 binoculars. NGC 2404 is 940 light-years in diameter, making it one of the largest known H II regions. This H II region represents striking similarity with NGC 604 in M33, both in size and location in galaxy.

<span class="mw-page-title-main">Sculptor Galaxy</span> Intermediate spiral galaxy in the constellation Sculptor

The Sculptor Galaxy is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently undergoing a period of intense star formation.

<span class="mw-page-title-main">Tip of the red-giant branch</span> Primary distance indicator used in astronomy

Tip of the red-giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy. It has been used in conjunction with observations from the Hubble Space Telescope to determine the relative motions of the Local Cluster of galaxies within the Local Supercluster. Ground-based, 8-meter-class telescopes like the VLT are also able to measure the TRGB distance within reasonable observation times in the local universe.

<span class="mw-page-title-main">NGC 6822</span> Galaxy in the constellation Sagittarius

NGC 6822 is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884, with a six-inch refractor telescope. It is the closest non-satellite galaxy to the Milky Way, but lies just outside its virial radius. It is similar in structure and composition to the Small Magellanic Cloud. It is about 7,000 light-years in diameter.

<span class="mw-page-title-main">NGC 1309</span> Spiral galaxy in the constellation Eridanus

NGC 1309 is a spiral galaxy located approximately 120 million light-years away, appearing in the constellation Eridanus. It is about 75,000 light-years across, and is about 3/4s the width of the Milky Way. Its shape is classified as SA(s)bc, meaning that it has moderately wound spiral arms and no ring. Bright blue areas of star formation can be seen in the spiral arms, while the yellowish central nucleus contains older-population stars. NGC 1309 is one of over 200 members of the Eridanus Group of galaxies.

<span class="mw-page-title-main">NGC 5253</span> Irregular galaxy in the M83 group of galaxies

NGC 5253 is an irregular galaxy in the constellation Centaurus. It was discovered by William Herschel on 15 March 1787.

<span class="mw-page-title-main">Pea galaxy</span> Possible type of luminous blue compact galaxy

A Pea galaxy, also referred to as a Pea or Green Pea, might be a type of luminous blue compact galaxy that is undergoing very high rates of star formation. Pea galaxies are so-named because of their small size and greenish appearance in the images taken by the Sloan Digital Sky Survey (SDSS).

<span class="mw-page-title-main">Haro 11</span> Galaxy in the constellation Sculptor

Haro 11 (H11) is a small galaxy at a distance of 300,000,000 light-years (redshift z=0.020598). It is situated in the southern constellation of Sculptor. Visually, it appears to be an irregular galaxy, as the ESO image to the right shows. H11 is named after Guillermo Haro, a Mexican astronomer who first included it in a study published in 1956 about blue galaxies. H11 is a starburst galaxy that has 'super star clusters' within it and is one of nine galaxies in the local universe known to emit Lyman continuum photons (LyC).

<span class="mw-page-title-main">NGC 1614</span> Galaxy in the constellation Eridanus

NGC 1614 is the New General Catalogue identifier for a spiral galaxy in the equatorial constellation of Eridanus. It was discovered on December 29, 1885 by American astronomer Lewis Swift, who described it in a shorthand notation as: pretty faint, small, round, a little brighter middle. The nebula was then catalogued by Danish-Irish astronomer J. L. E. Drayer in 1888. When direct photography became available, it was noted that this galaxy displayed some conspicuous peculiarities. American astronomer Halton Arp included it in his 1966 Atlas of Peculiar Galaxies. In 1971, Swiss astronomer Fritz Zwicky described it as a "blue post-eruptive galaxy, compact patchy core, spiral plumes, long blue jet SSW".

<span class="mw-page-title-main">Peekaboo Galaxy</span> Peekaboo Galaxy nearby metal-poor dwarf galaxy

The Peekaboo Galaxy is an irregular compact blue dwarf galaxy in the constellation Hydra. The galaxy is relatively small, at about 1,200 light-years (0.00037 Mpc) across. It is also relatively nearby, at a distance of around 22 million light-years (6.7 Mpc) from Earth. The Peekaboo Galaxy is considered one of the most metal-poor, least chemically enriched, and seemingly primordial, galaxies known.

<span class="mw-page-title-main">Kiso 5639</span> Dwarf galaxy in Ursa Major

Kiso 5639 is an irregular dwarf galaxy in the constellation Ursa Major, approximately 85 million light-years from Earth. It has an elongated and flattened shape, with a maximum diameter that extends for approximately 2,700 light years. The new stars are distributed in about ten groups and have a mass corresponding to about one million solar masses. This intense activity also corresponds to the presence of areas in which the matter is rarefied, which were probably formed following a combination of stellar winds and supernovae explosions. The starburst of the galaxy is believed to have occurred around one million years ago.

References

  1. 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for I Zw 18. Retrieved 2007-03-15.
  2. 1 2 3 "Hubble Finds 'Dorian Gray' Galaxy". HubbleSite NewsCenter. Retrieved 2007-10-16.
  3. ↑ Ken Croswell (2001). The Universe at Midnight: Observations Illuminating the Cosmos . Free Press. p.  111. ISBN   0684859319.
  4. ↑ "Hubble Uncovers a Baby Galaxy in a Grown-Up Universe". NASA. December 1, 2004.
  5. ↑ Babul, A.; Rees, M. J. (1992-03-15). "On dwarf elliptical galaxies and the faint blue counts". Monthly Notices of the Royal Astronomical Society. 255 (2): 346–350. doi: 10.1093/mnras/255.2.346 . ISSN   0035-8711.
  6. ↑ Benitez-Llambay, Alejandro; Fumagalli, Michele (2021-11-01). "The Tail of Late-forming Dwarf Galaxies in ΛCDM". The Astrophysical Journal Letters. 921 (1): L9. arXiv: 2110.08279 . Bibcode:2021ApJ...921L...9B. doi: 10.3847/2041-8213/ac3006 . ISSN   2041-8205. S2CID   239016084.
  7. 1 2 "Hubble shows 'baby' galaxy is not so young after all" (Press release). Hubblesite: NASA. October 16, 2007. Retrieved 2015-03-24.
  8. ↑ "A duo of starbursts in I Zwicky 18". ESA/Webb. 2024-03-26. Retrieved 2024-03-26.
  9. ↑ "IZw18: the galaxy that reveals the history of the universe". Instituto de Astrofísica de Andalucía. March 23, 2015. Archived from the original on March 27, 2015. Retrieved March 24, 2015.
  10. ↑ C. Kehrig; J.M. Vilchez; E. Perez-Montero; J. Iglesias-Paramo; J. Brinchmann; D. Kunth; F. Durret; F.M. Bayo (March 10, 2015). "The extended HeIIλ4686-emitting region in IZw18: clues for peculiar ionizing sources". The Astrophysical Journal Letters. 801 (2): L28. arXiv: 1502.00522 . Bibcode:2015ApJ...801L..28K. doi:10.1088/2041-8205/801/2/L28. S2CID   119257004.
  11. ↑ "Baby Galaxy Not So Young After All". European Space Agency. 16 October 2007.
  12. ↑ R. Contreras Ramos, F. Annibali, G. Fiorentino, M. Tosi, A. Aloisi, G. Clementini, M. Marconi, I. Musella, A. Saha, R. P. van der Marel (28 June 2011). "Spatial distribution and evolution of the stellar populations and candidate star clusters in the Blue Compact Dwarf I Zwicky 18 Galaxy". The Astrophysical Journal . 739 (2): 74. arXiv: 1106.5613 . Bibcode:2011ApJ...739...74C. doi:10.1088/0004-637X/739/2/74. S2CID   118459969.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ↑ Dorottya Szecsi; Norbert Langer (1 June 2013). "Massive Star Evolution in the Dwarf Galaxy I Zwicky 18". Massive Stars: From Alpha to Omega: 103. Bibcode:2013msao.confE.103S.
  14. ↑ Nemiroff, R.; Bonnell, J., eds. (3 December 2004). "I Zwicky 18: Young Galaxy". Astronomy Picture of the Day . NASA.
  15. ↑ Lequeux, J.; Viallefond, F. (1980). "H I observations and star formation in the blue compact galaxy IZw 18". Astronomy and Astrophysics. 91 (3): 269–275. Bibcode:1980A&A....91..269L.
  16. ↑ "Hubble Finds Mature Galaxy Masquerading as Toddler". NASA. 2006. Archived from the original on 2015-04-02. Retrieved 2015-03-26.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.