A Spitzer View of Mon OB1 East/NGC 2264

TL;DR

This study uses Spitzer infrared data to analyze young stellar objects in Mon OB1 East/NGC 2264, revealing their distribution, relationship with gas density, and disk fractions, indicating ongoing and heterogeneous star formation.

Contribution

First detailed infrared survey of Mon OB1 East/NGC 2264 linking YSO distribution with gas density and star formation history.

Findings

YSO surface density correlates with gas column density.

NGC 2264 has a high YSO density for its gas content.

Disk fraction varies between 45% in NGC 2264 and 19% in surrounding regions.

Abstract

We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 micron images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and 2MASS photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power law index of ~2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding more distributed regions show a disk fraction of 19%. This may be explained by the presence an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.