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New data from the NASA / ESA Hubble Space Telescope provides further evidence of tidal disturbance in the NGC 1052-DF4 galaxy. This result explains an earlier discovery that this galaxy lacks most of its dark matter. By studying the distribution of light and globular clusters in the galaxy, astronomers have concluded that gravitational forces from neighboring galaxy NGC 1035 have stripped dark matter of NGC 1052-DF4 and are now tearing the galaxy apart. This image, created from images from Digitized Sky Survey 2, shows the sky around NGC 1052-DF4. Credit: ESA / Hubble, NASA, Digitized Sky Survey 2; Acknowledgments: Davide de Martin
In 2018, an international team of researchers using the NASA/THIS The Hubble Space Telescope and several other observatories have discovered, for the first time, a galaxy in our cosmic neighborhood that lacks most of its dark matter. This discovery of the galaxy NGC 1052-DF2 came as a surprise to astronomers, as it was understood that dark matter is a key constituent in current models of galaxy formation and evolution. In fact, without the presence of dark matter, the primordial gas would not have enough gravitational pull to begin to collapse and form new galaxies. A year later, another galaxy lacking in dark matter was discovered, NGC 1052-DF4, which sparked intense debate among astronomers about the nature of these objects.
Now, new Hubble data has been used to explain the reason for the absence of dark matter in NGC 1052-DF4, which resides 45 million light years away. Mireia Montes from the University of New South Wales in Australia led an international team of astronomers to study the galaxy using deep optical imagery. They found that the missing dark matter could be explained by the effects of tidal disturbance. The forces of gravity from the neighboring massive galaxy NGC 1035 tear apart NGC 1052-DF4. During this process, dark matter is removed, while stars feel the effects of interacting with another galaxy at a later stage.
Until now, the removal of dark matter in this way has remained hidden from astronomers as it can only be observed using extremely deep images which can reveal extremely faint features. “We used Hubble in two ways to find that NGC 1052-DF4 is interacting,” Montes explained. “This includes studying the light of the galaxy and the distribution of globular clusters in the galaxy.”
This image shows the region around the galaxy NGC 1052-DF4, taken by the IAC80 telescope at the Teide Observatory in Tenerife, Spain. The figure highlights the main galaxies in the field of view, including NGC 1052-DF4 (center of image) and its neighbor NGC 1035 (center left). Credit: M. Montes et al.
Thanks to the high resolution of Hubble, astronomers were able to identify the population of globular clusters in the galaxy. The 10.4-meter Gran Telescopio Canarias (GTC) telescope and the IAC80 telescope in the Canary Islands in Spain were also used to supplement Hubble’s observations by further studying the data.
“It is not enough to spend a lot of time observing the object, but careful processing of the data is vital,” explained Raúl Infante-Sainz, team member at the Instituto de Astrofísica de Canarias in Spain. “So it was important that we not only use one telescope / instrument, but several (land and space) to conduct this research. With the high resolution of Hubble we can identify the globular clusters, then with GTC photometry we get the physical properties.
Globular clusters are thought to form in the episodes of intense star formation that shaped galaxies. Their compact size and luminosity make them easily observable, and they are therefore good tracers of the properties of their host galaxy. In this way, by studying and characterizing the spatial distribution of clusters in NGC 1052-DF4, astronomers can develop insight into the current state of the galaxy itself. The alignment of these clusters suggests that they are “stripped” of their host galaxy, supporting the conclusion that a tidal disturbance is occurring.
While studying the light of the galaxy, astronomers also found evidence of tide tails, which are formed from material moving away from NGC 1052-DF4. This further confirms the conclusion that this is a disruptive event. Further analysis concluded that the central parts of the galaxy remain intact and that only about 7% of the galaxy’s stellar mass is hosted in these tidal tails. This means that dark matter, which is less concentrated than stars, was previously and preferentially cleared from the galaxy, and now the outer stellar component is starting to be as well.
“This result is a good indicator that, as the galaxy’s dark matter has evaporated from the system, the stars are only beginning to suffer from the disturbance mechanism,” said Ignacio Trujillo, member of the team. ‘Instituto de Astrofísica de Canarias in Spain. “Over time, NGC 1052-DF4 will be cannibalized by the large system around NGC 1035, with at least some of their stars floating freely in deep space.”
Finding evidence to support the tidal disturbance mechanism as an explanation for the galaxy’s missing dark matter has not only solved an astronomical conundrum, but also brought a sigh of relief to astronomers. Without it, scientists would have to rethink our understanding of the laws of gravity.
“This discovery reconciles existing knowledge about how galaxies form and evolve with the most favorable cosmological model,” Montes added.
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