Extreme Emission Line Galaxy
Extreme Emission-Line Galaxies ( EELG for short ) are dwarf galaxies at cosmological distances whose emission lines show an equivalent width of the forbidden doubly ionized oxygen and / or the hydrogen lines (mostly Hα ) of more than 100 Angstroms . They are interpreted as a short phase with an extreme starburst , during which the majority of the stars in these galaxies are formed.
properties
Extreme Emission-Line Galaxies have the following properties:
- The equivalent width of the [OIII] or Hα / Lyα is between 100 and 1000 Angstroms.
- The activity can not be explained by a central black hole in the form of an active galaxy core , due to e.g. B. the lack of X-rays or a jet in the radio range .
- The mass of the dwarf galaxies is in the range of 10 7 to 10 10 solar masses .
- The galaxies show a strong blue color index .
- The metallicity is low, with a median of 20 percent of solar incidence .
- The morphology of the galaxy is not axially symmetrical , often with a comet- like or lump-like shape.
- The EELGs are isolated systems with a low redshift (z < 1), which rarely occur in groups . At greater distances, the possibly existing companions are too faint to be able to detect them.
- The EELGs show little evidence of dust, and their star populations are therefore very young before large numbers of supernovae and AGB stars have formed.
- While the frequency of EELGs in the local universe is quite low, it increases by more than an order of magnitude for redshifts with z > 2.
interpretation
The Extreme Emission-Line Galaxies are interpreted as a short phase of up to 30 million years with a strong starburst. The star formation rate reaches values of up to 35 solar masses per year, whereby the majority of the stars observed today in dwarf galaxies in the local universe are likely to have formed. The properties of the Extreme Emission-Line Galaxies correspond to extreme examples of HII galaxies as well as the blue compact dwarf galaxies in the local universe.
From the observed frequencies of EELGs it is concluded that most dwarf galaxies have passed through a phase as the Extreme Emission-Line Galaxy .
Special objects in EELGs
Low-hydrogen, super-luminous supernovae and less pronounced gamma ray bursts occur disproportionately often in EELGs. These results support the assumption that these stellar explosions only occur in metal-poor regions with stars of more than 75 solar masses.
literature
- G. Leloudas et al .: Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1409.8331v1 .
- Hakim Atek et al .: Hubble Space Telescope Grism Spectroscopy of Extreme Starbursts Across Cosmic Time: The Role of Dwarf Galaxies in the Star Formation History of the Universe . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1406.4132v1 .
- Michael V. Maseda et al .: The Nature of Extreme Emission Line Galaxies at z = 1-2: Kinematics and Metallicities from Near-Infrared Spectroscopy . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1406.3351v1 .
- Ricardo Amorín et al .: Extreme emission-line galaxies out to z ∼1 in zCOSMOS-20k. I. Sample and characterization of global properties . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1403.3441v1 .
- A. van der Wel et al .: Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at z> 1 . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1107.5256v2 .
Individual evidence
- ↑ G. Leloudas et al .: Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies . In: Cornell University . 2014. arxiv : 1409.8331v1 .