ALMA/NAOJ: Two Cosmic Peacocks Show Violent History of Magellanic Clouds

[bystander]

Two Cosmic Peacocks Show Violent History of Magellanic Clouds
ALMA | NAOJ | NRAO | ESO | 2019 Nov 14

ALMA images of two molecular clouds: N159E-Papillon Nebula (left) and N159W South (right). Red and green show the distributions of molecular gas with different velocities mapped by 13CO emissions. The blue region in N159E-Papillon Nebula shows the ionized hydrogen gas observed with the Hubble Space Telescope. The blue part in N159W South shows the emissions from dust particles obtained with ALMA. Credit: ALMA (ESO/NAOJ/NRAO)/Fukui et al./Tokuda et al./NASA-ESA Hubble

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Two peacock-shaped gas clouds were revealed in the Large Magellanic Cloud (LMC) by observations with the Atacama Large Millimeter / submillimeter Array (ALMA). A team of astronomers found several massive baby stars in the complex filamentary clouds, which agrees well with computer simulations of giant collisions of gas clouds. The researchers interpret this to mean that the filaments and young stars are telltale evidence of violent interactions between the LMC and the Small Magellanic Cloud (SMC) 200 million years ago.

Astronomers know that stars are formed in collapsing clouds in space. However, the formation processes of giant stars, 10 times or more massive than the Sun, are not well understood because it is difficult to pack such a large amount of material into a small region. Some researchers suggest that interactions between galaxies provide a perfect environment for massive star formation. Due to the colossal gravity, clouds in the galaxies are stirred, stretched, and often collide with each other. A huge amount of gas is compressed in an unusually small area, which could form the seeds of massive stars.

A research team used ALMA to study the structure of dense gas in N159, a bustling star formation region in the LMC. Thanks to ALMA’s high resolution, the team obtained a very detailed map of the clouds in two sub-regions, N159E-Papillon Nebula and N159W South.

Interestingly, the cloud structures in the two regions look very similar: fan-shaped filaments of gas extending to the north with the pivots in the southernmost points. The ALMA observations also found several massive baby stars in the filaments in the two regions. ...

An ALMA View of Molecular Filaments in the Large Magellanic Cloud. I. The Formation of
High-Mass Stars and Pillars in the N159E-Papillon Nebula Triggered by a Cloud–Cloud Collision ~ Yasuo Fukui et al

• Astrophysical Journal 886(1):14 (20 Nov 2019) DOI: 10.3847/1538-4357/ab4900
• arXiv.org > astro-ph > arXiv:1811.00812 > 02 Nov 2018 (v1), 13 Nov 2019 (v5)

An ALMA View of Molecular Filaments in the Large Magellanic Cloud. II. An Early Stage
of High-mass Star Formation Embedded at Colliding Clouds in N159W-South ~ Kazuki Tokuda et al

• Astrophysical Journal 886(1):15 (20 Nov 2019) DOI: 10.3847/1538-4357/ab48ff
• arXiv.org > astro-ph > arXiv:1811.04400 > 11 Nov 2018 (v1), 13 Nov 2019 (v4)

[neufer]

<<Astronomers have long assumed that the Magellanic Clouds have orbited the Milky Way at approximately their current distances, but evidence suggests that it is rare for them to come as close to the Milky Way as they are now. Observation and theoretical evidence suggest that the Magellanic Clouds have both been greatly distorted by tidal interaction with the Milky Way as they travel close to it. The LMC maintains a very clear spiral structure in radio-telescope images of neutral hydrogen. Streams of neutral hydrogen connect them to the Milky Way and to each other, and both resemble disrupted barred spiral galaxies. Their gravity has affected the Milky Way as well, distorting the outer parts of the galactic disk.

Aside from their different structure and lower mass, they differ from our galaxy in two major ways. First, they are gas-rich; a higher fraction of their mass is hydrogen and helium compared to the Milky Way. They are also more metal-poor than the Milky Way; the youngest stars in the LMC and SMC have a metallicity of 0.5 and 0.25 times solar, respectively. Both are noted for their nebulae and young stellar populations, but as in our own galaxy their stars range from the very young to the very old, indicating a long stellar formation history.

Measurements with the Hubble Space Telescope, announced in 2006, suggest the Magellanic Clouds may be moving too fast to be long term companions of the Milky Way. If they are in orbit, that orbit takes at least 4 billion years. They are possibly on a first approach and we are witnessing the start of a galactic merger that may overlap with the Milky Way's expected merger with the Andromeda Galaxy (and perhaps the Triangulum Galaxy) in the future.>>