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Discovery of a young and extremely metal poor dwarf galaxy
A nearby dwarf galaxy with an extremely low heavy element abundance has
been discovered. The gas-rich galaxy HIPASS J1131-31 with a radial velocity
of 716 km/s was detected as an emission source in the neutral hydrogen line
in the southern sky survey at the Parkes radio telescope. It was resolved
into individual stars in our observations with the Hubble Space Telescope.
The galaxy is concealed in such close proximity of a bright star that we
call it “hidden” (Peekaboo). The Peekaboo dwarf galaxy is located on the
outskirts of a galaxy group at a distance of 6.8±0.7 Mpc from us. The red
giant branch of the system is tenuous compared with the prominence of the
features of young populations in the color-magnitude diagram, inviting
speculation that star formation in the galaxy only began in the last few Gyr.
Spectral observations with the 10-meter South African telescope reveal
HIPASS J1131-31 to be one of the most extremely metal-poor galaxies known
with an oxygen abundance smaller than 2% of the Sun's. The proximity of
the discovered galaxy makes it an important target for further study
of the cosmic abundance of chemical elements and the nature of young
galaxies.
Authors:
Karachentsev I.D., Makarova L.N. (SAO RAS), Koribalski B.S. (Australia
Telescope National Facility; School of Science, Western Sydney University),
Anand G.S. (Space Telescope Science Institute), Tully R.B. (Institute for
Astronomy, University of Hawaii), Kniazev A.Y. (Southern African Large
Telescope Foundation; Sternberg Astronomical Institute, Lomonosov Moscow
State University)
Published:
Karachentsev I.D., Makarova L.N., Koribalski B.S., Anand G.S., Tully R.B., Kniazev A.Y.,
Peekaboo: the extremely metal poor dwarf galaxy HIPASS J1131-31,
Monthly Notices of the Royal Astronomical Society, 2023, Volume 518, Issue 4, pp.5893-5903,
DOI:10.1093/mnras/stac3284
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Unveiling of an unusual nitrogen-rich massive star in a metal-poor dwarf galaxy
While studying the ionized gas kinematics of the dwarf galaxy NGC 4068 with the
6-m SAO RAS telescope, a compact nebula with high velocity dispersion was
discovered. Follow-up spectroscopy performed at the 6-m and 2.5-m Caucasian
Mountain Observatory of SAI MSU telescopes has shown that there is a star at
the center of the nebula enriching the surrounding nebula with nitrogen,
so that the observed [N/O] ratio is almost solar, although in the gas
surrounding the galaxy itself, the abundance of heavier elements is only
1/10 of solar. Modeling with CMFGEN, a code for calculating expanding atmospheres,
has shown that we are talking about a massive star at a short stage of evolution
(a blue supergiant or a Wolf-Rayet star), when a powerful stellar wind actively
affects the environment. The bolometric luminosity of the star is
(1.5-1.7)·106 of solar, the estimated mass is about
80 solar masses. The radius of the surrounding expanding nebula is
smaller than 15 pc, and its kinematic age is smaller than 500,000 years.
Authors:
Yarovova A.D., Egorov O.V., Moiseev A.V., Maryeva O.V. (SAO RAS)
Published:
Yarovova A.D., Egorov O.V., Moiseev A.V., Maryeva O.V., Unveiling the nitrogen-rich massive
star in the metal-poor galaxy NGC 4068, 2022, Monthly Notices of the Royal Astronomical Society,
2023, Volume 518, Issue 2, pp.2256-2272, DOI: 10.1093/mnras/stac2949
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