Tololo 1247-232 (Tol 1247 or T1247) is a small

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

at a distance of (

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...

z=0.0480). It is situated in the southern equatorial

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Hydra Hydra generally refers to: * Lernaean Hydra, a many-headed serpent in Greek mythology * ''Hydra'' (genus), a genus of simple freshwater animals belonging to the phylum Cnidaria Hydra or The Hydra may also refer to: Astronomy * Hydra (constel ...

. Visually, Tol 1247 appears to be an irregular or possibly a barred spiral galaxy. Tol 1247 is named after the surveys that were carried at the

Cerro Tololo Inter-American Observatory The Cerro Tololo Inter-American Observatory (CTIO) is an astronomical observatory located on Cerro Tololo in the Coquimbo Region of northern Chile, with additional facilities located on Cerro Pachón about to the southeast. It is approximately ...

(CTIO), the first of which was in 1976. It is one of nine galaxies in the local universe known to emit

Lyman continuum photons Lyman continuum photons (abbrev. LyC), shortened to Ly continuum photons or Lyc photons, are the photons emitted from stars at photon energies above the Lyman limit. Hydrogen is ionized by absorbing LyC. Working from Victor Schumann's discovery ...

Background

Tol 1247-232 (T1247) was first described in 1985. It was observed in the infrared using the

(CTIO) 4m telescope, as part of a study of regions of intense star formation. Six years later, T1247 was identified as an HII galaxy in the paper 'A spectrophotometric catalogue of HII galaxies', a study of 425 emission-line galaxies. T1247 has also been classified as a

starburst galaxy 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. For example, the star formatio ...

, a blue compact dwarf and a

Wolf–Rayet galaxy 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. For example, the star formatio ...

Lyman continuum leakage

T1247 is one of nine galaxies in the local universe that have been identified as leaking Lyman continuum (LyC) photons. The first published detection of Lyman continuum photons from T1247 was made in 2013 by Leitet et al. using data from the

Far Ultraviolet Spectroscopic Explorer Far Ultraviolet Spectroscopic Explorer (FUSE, Explorer 77, and MIDEX-0) represented the next generation, high-orbit, ultraviolet space observatory covering the wavelength range of 90.5–119.5 nanometre (nm) of the NASA operated by the Johns Ho ...

(FUSE). It was the second-known LyC-leaking source in the local universe. Tololo-1247-232 v2

LyC leakage is crucial to the process known as

reionization In the fields of Big Bang theory and cosmology, reionization is the process that caused matter in the universe to reionize after the lapse of the " dark ages". Reionization is the second of two major phase transitions of gas in the universe (t ...

which is believed to have occurred within the first 10% of the age of the universe. The cosmic reionization is, after recombination, the second major phase-change of hydrogen in the universe. The epoch of reionization began when the first sources appeared which produced photons capable of ionizing the surrounding medium, and ended when all of the intergalactic medium (IGM) was ionized. LyC photons are responsible for this process. However, to date it is unclear which physical mechanisms effectively produce large amounts of LyC photons, such that the reionization of the universe could be powered. Two processes are currently discussed and under evaluation:

active galactic nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...

(AGN) and starbursts in dwarf galaxies. AGNs are known to produce large amounts of LyC emission, but in the early universe the number of AGNs is unknown, and often believed to be too small to power the reionization. On the other side, dwarf starbursts are known to be numerous in the early universe, but their LyC emission is unknown. For that reason local galaxies such as TOL1247 are studied in detail, in order to understand physical processes that produce escaping LyC photons. In TOL1247 it was found that bulk of the LyC photons emerges from two massive stellar clusters located in the central region of the galaxy. The escape is supported by the structure of the interstellar medium of the galaxy, which appears to be clumpy and highly ionized. Although Puschnig et al. (2017) could verify that LyC indeed escapes from TOL1247, their new spectroscopic data obtained with the

Cosmic Origins Spectrograph The Cosmic Origins Spectrograph (COS) is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 (STS-125) in May 2009. It is designed for ultraviolet (90–320 nm) spectroscopy of faint point sources w ...

of the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

indicates a relatively low number of escaping LyC photons (only 1.5% escape fraction). Thus, if galaxies in the early universe were similar to TOL1247, they would indeed contribute to

, but not sufficiently to explain the second major phase-change in the universe.

References

External links

Simulation of the Reionization of the Universe
- A video showing the gradual reionization of a typical patch of the universe (links to YouTube). {{Hydra (constellation), state=collapsed Starburst galaxies Hydra (constellation) 83589

Background

Lyman continuum leakage

See also

References

External links