Long GMC Lifetimes: Using the Method and Data of Meidt et al. 2015 with A Correction

TL;DR

This paper revisits the estimation of giant molecular cloud (GMC) lifetimes in M51 by correcting for spiral arm pattern speed, resulting in significantly longer lifetimes of 60-500 million years compared to previous estimates.

Contribution

It introduces a correction to previous GMC lifetime estimates by incorporating the spiral pattern speed, providing a more accurate measurement of GMC lifetimes in M51.

Findings

GMC lifetimes are longer when accounting for spiral pattern speed.

Revised GMC lifetimes range from 60 to 500 million years.

Previous estimates of 20-30 million years are underestimated.

Abstract

Meidt et al. 2015 derived short lifetimes of 20-30Myr for giant molecular clouds (GMCs) in M51. Their novel approach utilizes a decline of the GMC population during their inter-arm passage from one spiral arm to the next. Using the inter-arm travel time "t_travel" as a fiducial clock, they converted the decline rate to GMC lifetimes. They implicitly adopted zero as the pattern speed of the spiral arms, resulting in a very short t_travel. However, it is well established that the spiral arm pattern in M51 is rotating (Meidt et al. 2008, 2013), and that t_travel should be measured with respect to the rotating spiral pattern. Here we use the same method and data of Meidt et al. 2015 and re-evaluate GMC lifetimes by accounting for the pattern speed given by Meidt et al. 2013. This correction gives a longer t_travel and consequently longer GMC lifetimes of 60-500Myr.