Does cool halo gas prolong galaxy growth? The W. M. Keck observatory findings

An image to illustrate cool halo gas
This is an artist conception of gas streams (blue) feeding a galactic disk. The inflow fuels new star formation, and because the infalling gas is spinning, the size of the disk grows. © James Josephides, Swinburne Astronomy Productions

A group of astronomers have found that cool halo gas spins in the same direction as the galactic disks of typical star-forming galaxies.

The finding suggests that cool halo gas prolongs galaxy growth. The team was led by Crystal Martin and Stephanie Ho of the University of California, Santa Barbara.

Spiralling cool halo gas

The study used the W.M. Keck observatory and found that corotation of cool halo gas is both possible, and common in star-forming galaxies. The researchers’ findings suggest that the gas halos eventually spiral in towards the galactic disk.

Martin explained: “Just as ice skaters build up momentum and spin when they bring their arms inward, the halo gas is likely spinning today because it was once at much larger distances where it was deposited by galactic winds, stripped from satellite galaxies, or directed toward the galaxy by a cosmic filament.”

According to the University of California, Santa Barba, “Nearly a decade ago, theoretical models predicted that the angular momentum of the spinning cool halo gas partially offsets the gravitational force pulling it towards the galaxy, thereby slowing down the gas accretion rate and lengthening the period of disk growth.”

The team’s results confirm this theory because they show that the angular momentum of the gas is high enough to slow the infall rate but not high enough to shut down feeding the galactic disk.

Using quasars for the research

The co-author Ho, a physics graduate student at UC Santa Barbara, commented: “What sets this work apart from previous studies is that our team also used the quasar as a reference ‘star’ for Keck’s laser guide star AO system. This method removed the blurring caused by the atmosphere and produced the detailed images we needed to resolve the galactic disks and geometrically determine the orientation of the galactic disks in three-dimensional space.”

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