Abstract
We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also important dust factories, we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was expanded to cover a much larger part of M33 including spiral arms. Here we present our methodology and describe results for the central square kiloparsec of M33 [1–4] and disc of M33 [5–8].
Highlights
Luminous, cool evolved stars are powerful tracers of the underlying stellar populations, as they stand out above all other stars especially at infrared wavelengths and are the first stars that can be resolved in increasingly distant galaxies
Asymptotic Giant Branch (AGB) stars in particular represent stellar populations ranging in age from tens of millions of years (i.e. “the present”) to more than ten billion years
The cool molecular atmospheres of AGB stars lead to broad absorption troughs in their optical spectra; while normally these are oxygen-bearing molecules such as TiO and VO, stars in certain mass ranges dredge up carbon – that had been synthesized in their interiors – and replace the absorption bands by entirely different ones due to C2 and CN
Summary
Cool evolved stars are powerful tracers of the underlying stellar populations, as they stand out above all other stars especially at infrared wavelengths and are the first stars that can be resolved in increasingly distant galaxies. A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified.
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