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Markarian 71
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Title: Mrk 71/NGC 2366: The nearest Green Pea analogue
Author: Genoveva Micheva, M. S. Oey, Anne E. Jaskot, Bethan L. James

We present the remarkable discovery that the Local Group dwarf irregular galaxy NGC 2366 is an excellent analogue of the Green Pea (GP) galaxies, which are characterized by extremely high ionization parameters. The similarities are driven predominantly by the giant H II region Markarian 71 (Mrk 71). We compare the system with GPs in terms of morphology, excitation properties, specific star-formation rate, kinematics, absorption of low-ionization species, reddening, and chemical abundance, and find consistencies throughout. Since extreme GPs are associated with both candidate and confirmed Lyman continuum (LyC) emitters, Mrk 71/NGC 2366 is thus also a good candidate for LyC escape. The spatially resolved data for this Local Group object show a superbubble blowout generated by mechanical feedback from one of its two super star clusters (SSCs), Knot B, while the extreme ionization properties are driven by the < 1 Myr-old, enshrouded SSC Knot A, which has ~10 times higher ionizing luminosity. Very massive stars (>100 Msun) may be present in this remarkable object. Ionization-parameter mapping indicates the blowout region is optically thin in the LyC, and the general properties also suggest LyC escape in the line of sight. Mrk 71/NGC 2366 does differ from GPs in that it is 1-2 orders of magnitude less luminous. The presence of this faint GP analog and candidate LyC emitter (LCE) so close to us suggests that LCEs may be numerous and commonplace, and therefore could significantly contribute to the cosmic ionizing budget. Mrk 71/NGC 2366 offers an unprecedentedly detailed look at the viscera of a candidate LCE, and could clarify the mechanisms of LyC escape.

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NGC 2366
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NGC 2366 (also Markarian 71, UGC 3851, PGC 21102) is a magnitude +11.4 irregular galaxy located 10 million light-years away in the constellation Camelopardalis.

The galaxy was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at Windsor Road in Slough, Berkshire, on the 3rd December 1788.

Right Ascension 07h 28m 54.6s, Declination +69° 12' 57"

NGC 2363 is a star forming region within NGC 2366.
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Hubble Observes a Dwarf Galaxy with a Bright Nebula



The NASA/ESA Hubble Space Telescope has made detailed observations of the dwarf galaxy NGC 2366. While it lacks the elegant spiral arms of many larger galaxies, NGC 2366 is home to a bright, star-forming nebula and is close enough for astronomers to discern its individual stars.
The starry mist streaking across this image obtained by the NASA/ESA Hubble Space Telescope is the central part of the dwarf galaxy known as NGC 2366. The most obvious feature in this galaxy is a large nebula visible in the upper-right part of the image, an object listed just a few entries prior in the New General Catalogue as NGC 2363.

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