Very Luminous Carbon Stars in the Outer Disk of the Triangulum Spiral Galaxy

Abstract

Stars with masses in the range from about 1.3 to 3.5 Mo pass through an evolutionary stage where they become carbon stars. In this stage, which lasts a few Myr, these stars are extremely luminous pulsating giants. They are so luminous in the near-infrared that just a few of them can double the integrated luminosity of intermediate-age (0.6 to 2 Gyr) Magellanic Cloud clusters at 2.2 microns. Astronomers routinely use such near-infrared observations to minimize the effects of dust extinction, but it is precisely in this band that carbon stars can contribute hugely. The actual contribution of carbon stars to the outer disk light of evolving spiral galaxies has not previously been morphologically investigated. Here we report new and very deep near-IR images of the Triangulum spiral galaxy M33=NGC 598, delineating spectacular arcs of carbon stars in its outer regions. It is these arcs which dominate the near-infrared m=2 Fourier spectra of M33. We present near-infrared photometry with the Hale 5-m reflector, and propose that the arcs are the signature of accretion of low metallicity gas in the outer disk of M33.

arXiv comment4 pages, 4 figures. Revised version submitted to A&A Letters

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• The building up of the disk galaxy M33 and the evolution of the metallicity gradient
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• AGB stars as tracers of metallicity and mean age across M33
• Dynamics of Disks and Warps
• HI clouds in the proximity of M33
• Bar imprints on the inner gas kinematics of M33
• The Evolution and Star Formation History of M33
• The dark matter halo density profile, spiral arm morphology and black hole mass of M33
• Keck spectroscopy and Spitzer Space Telescope analysis of the outer disk of the Triangulum Spiral Galaxy M33
• Luminous AGB stars in nearby galaxies. A study using Virtual Observatory tools
• Is There a Fundamental Line for Disk Galaxies?
• Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning
• The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) II. The Spatially Resolved Recent Star Formation History of M33