Discovery of a Peculiar Galaxy with a “Red Potato” Appearance

Using the James Webb Space Telescope (JWST), an international team of astronomers has discovered a new massive and quiescent red galaxy, which they dubbed «Red Potato.» The discovery was reported in a research paper published January 28 on the arXiv pre-print server.

A potato in the cosmic web

A team of astronomers led by Weichen Wang of the University of Milan, Italy, has recently observed a gas-rich cosmic web node at a redshift of approximately 3.25, designated MQN01. In general, such cosmic web nodes and protoclusters at high redshifts are known to host rich reservoirs of cool and molecular gas. Therefore, these structures are expected to be sites of exceptionally efficient formation of massive galaxies via gas accretion.

By investigating MQN01 with JWST’s Near Infrared Camera (NIRCam) and Near Infrared Spectrograph (NIRSpec), Wang’s team has serendipitously discovered a new massive red galaxy. Due to its morphology and color, they named it «Red Potato.»

«In this work, we present the discovery of a massive quiescent galaxy in a gas-rich environment of a cosmic web node or protocluster at z ∼ 3.2, identified and spectroscopically confirmed from a JWST program,» the researchers write in the paper.

Massive and quiescent

The Red Potato, or MQN01 J004131.9-493704, has a half-light radius of about 3,260 light years and stellar mass of 110 billion solar masses. The molecular gas mass of the galaxy was calculated to be less than 7 billion solar masses, which yields a molecular gas fraction smaller than 0.06.

The non-detection of carbon monoxide and sodium D-lines indicate that the Red Potato is poor in molecular and neutral gas. Moreover, no gas outflows have been detected from the galaxy. In general, the Red Potato galaxy appears to be a dispersion-dominated system according to the kinematics of ionized gas.

The study found that Red Potato has a star-formation rate (SFR) at a level of 4.0 solar masses per year, which is at least one dex below the star-forming main sequence (SFMS). This is a relatively low SFR given that the galaxy is located at the center of a large reservoir of cool circumgalactic medium (CGM).

X-ray jet causing gas turbulence

The stellar velocity dispersion of Red Potato was found to be 268 km/s, suggesting elevated levels of gas turbulence in the CGM. Furthermore, deep X-ray data point to the presence of an extended X-ray jet which most likely emanates from a neighboring luminous X-ray active galactic nucleus (AGN), indicating a certain form of jet-mode feedback acting on the Red Potato’s CGM.

«We argue that the jet feedback may have led to increased CGM turbulence around the Red Potato and thus have reduced the gas accretion onto the galaxy, which is indicated by the high gas velocity dispersion measured from the Lyα and Hα line profiles,» the authors of the paper conclude.

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