• Sat. Dec 2nd, 2023

The dark energy camera captures the galaxies in the tug of war, a precursor to the merger

The dark energy camera captures the galaxies in the tug of war, a precursor to the merger

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Spiral galaxy NGC 1532, also known as Halley’s Coronet, is locked in a tug-of-war with its smaller neighbor, dwarf galaxy NGC 1531. The US Department of Energy’s (DOE’s) Dark Energy Camera (VSF 4), housed at the National Energy Camera. Telescope at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF’s NOIRLab, captures the mutual gravitational effects of a giant-dwarf-galaxy merger. Credit: Association of Universities for Research in Astronomy

Galaxies grow and evolve over billions of years by absorbing nearby companions and merging with other galaxies. The early stages of this galaxy growth process are shown in a new image taken with the US Department of Energy’s (DOE) Dark Energy Camera (DECam) attached to the National Science Foundation’s (NSF) Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIONS) program.

The massive barred spiral galaxy NGC 1532, also known as Halley’s Coronet, lies about 55 million light-years away in the direction of the southern constellation Eridanus (River). Its sweeping spiral arms are seen edge-on from Earth, with the proximal arm dipping downward and the receding arm thrusting upward, dragging it toward its small, dwarf companion galaxy, NGC 1531. These gravitationally bound galaxies will eventually merge completely into its smaller NGC 153 2companion.

Despite its small stature, the dwarf galaxy exerts a remarkable gravitational pull on its larger companion, distorting one of its spiral arms, which can be seen rising above the galactic plane. Also, plumes of gas and dust can be seen between the two galaxies, like a bridge of stellar matter held by competing tidal forces. This interaction caused star formation in both galaxies.

Action-energy (J, E) space of the Milky Way showing globular clusters (top panels), stellar streams (middle panels) and satellite galaxies (bottom panels). Each object can be viewed as a “cloud” of 1000 Monte Carlo representations of its orbit (see Section 2.2). In each row, the left panel corresponds to the projected action-space map, where the horizontal axis is J .ϕ /JTot Vertical axis (Jz – JR )/JTot With JTot = JR + Jz + ∣ Jϕ ∣. In these panels, the points are colored by the total energy of their orbitals (E). The right panels show the z component of the angular momentum (Jϕ ≡ Lz ) vs. E, the points are colored by the orthogonal component of their angular momenta. Credit: The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac4d2a

This lopsided cosmic tug of war is a snapshot of how large galaxies grow and evolve by swallowing smaller galaxies and absorbing their stars and star-forming material. A similar process may have occurred in the Milky Way Six times beforeLarge streams of stars and other signs remain in the Milky Way’s halo.

The process of absorbing a small companion galaxy is quite different from the catastrophic merger of two spiral galaxies of comparable size. In the latter case, two massive galaxies collide to form a completely different galaxy with its own shape and characteristics. This type of galactic merger will occur in the Milky Way when it merges with the Andromeda Galaxy four billion years later.

DECam, with its unparalleled wide-field imaging capabilities, provides astronomers with highly detailed views of these large-scale galactic interactions. It also has remarkable sensitivity, aided by the 4-meter Blanco telescope, needed to detect faint objects in our solar system and the influence of dark matter on galaxies across the visible universe. Currently, DECam is used for programs covering a wide variety of sciences.

Journal Information:
Astrophysical Journal

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