The California Molecular Cloud

TL;DR

This paper identifies a massive, nearby giant molecular cloud in Perseus, compares it to the Orion Molecular Cloud, and suggests a correlation between high-density gas and star formation activity.

Contribution

It reveals a previously unrecognized GMC in Perseus, providing its distance, mass, and star formation activity, and proposes a link between dense gas and star formation rates.

Findings

The cloud is approximately 450 parsecs away with a mass of 10^5 solar masses.

It has significantly less star formation activity than the Orion Molecular Cloud.

Star formation appears proportional to the amount of high extinction, dense gas.

Abstract

We present an analysis of wide-field infrared extinction maps of a region in Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis we have identified a massive, nearby, but previously unrecognized, giant molecular cloud (GMC). From comparison of foreground star counts with Galactic models we derive a distance of 450 +/- 23 parsecs to the cloud. At this distance the cloud extends over roughly 80 pc and has a mass of approximately 10^5 solar masses, rivaling the Orion (A) Molecular Cloud as the largest and most massive GMC in the solar neighborhood. Although surprisingly similar in mass and size to the more famous Orion Molecular Cloud (OMC) the newly recognized cloud displays significantly less star formation activity with more than an order of magnitude fewer young stellar objects than found in the OMC, suggesting that both the level of star formation and perhaps the star formation rate in this cloud are an order of magnitude or more lower than in the OMC. Analysis of extinction maps of both clouds shows that the new cloud contains only 10% the amount of high extinction (A_K > 1.0 mag) material as is found in the OMC. This, in turn, suggests that the level of star formation activity and perhaps the star formation rate in these two clouds may be directly proportional to the total amount of high extinction material and presumably high density gas within them and that there might be a density threshold for star formation on the order of a few times 10^4 hydrogen molecules per cc.