Researchers explore the extremely metal-poor galaxy DDO 68

DDO 68 g-band LBT image. Credit: Pascale et al., 2021.

By performing hydrodynamic simulations, astronomers studied an extremely metal-poor galaxy known as DDO 68. The results of the study, presented in an article published October 25 on the arXiv preprint server, allowed to better understand the origin and nature of this strange galaxy.

Of particular importance to astronomers are low metallicity galaxies as they could provide crucial information about the chemical evolution of stars and the astrophysical processes occurring in the early universe.

At a distance of approximately 41.2 million light years from Earth, DDO 68 (also known as UGC 5340) is an irregular dwarf galaxy. It has a low average oxygen abundance and is one of the most metal-poor dwarf galaxies known to date. Its extremely low metallicity is particular in light of its relatively large total stellar mass (117 million solar masses) and its luminosity.

Previous observations of DDO 68 have shown that it has an unusual shape. The galaxy features a large, bright and distorted stellar component, dubbed the “comet tail”, emerging from the southeast edge of its main body. In addition, it has a rounded structure to the north, the so-called “comet head”. Astronomers have discovered that DDO 68 is, in fact, made up of two distinct systems: the DDO 68 A main body (including the cometary head) and a disturbed DDO 68 B satellite currently accredited by DDO 68 A and producing the cometary tail.

A team of astronomers led by Raffaele Pascale from the Astronomical Observatory in Bologna, Italy, took a closer look at DDO 68 and its peculiarities. They performed N-body hydrodynamic simulations of DDO 68 aimed at reproducing most of the available structural and kinematic observations of this galaxy derived in recent years.

“We have presented state-of-the-art N-body hydrodynamic simulations capable of explaining most of the peculiarities observed in DDO 68,” the researchers say.

The N-body model reproduced several known features of DDO 68, mainly the highly asymmetric and disturbed shape of the stellar component, the overall distribution of neutral atomic hydrogen (HI) and its velocity field, the star structure in the arc at l west, as well as the low surface light stellar flux observed in the north.

Based on the simulations, astronomers discovered that the galaxy is most likely the result of the interaction between three systems, namely a dominant galaxy, DDO 68, with a dynamic mass of a level of 10 billion solar masses and two smaller satellite galaxies – with masses about 0.05 and 0.0067 times the mass of DDO 68.

The researchers therefore concluded that the irregularities observed throughout DDO 68 are not due to an interaction with a smaller companion like DDO 68 C, and are more likely the result of multiple accretion of smaller systems.

“Based on cosmological simulations, it’s not surprising that galaxies like DDO 68 can host smaller-mass satellite galaxies. Indeed, isolated dwarf galaxies or in low density environments would be less sensitive to potentially disruptive interactions such as the same mass but close to more massive hosts ”, explained the authors.

Astronomers discover three new weak dwarf galaxies

More information:
R. Pascale et al, Dancing in the void: N-body hydrodynamic simulations of the galaxy extremely poor in metals DDO 68. arXiv: 2110.13175v1 [astro-ph.GA],

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