The Low-mass Stellar Population in L1641: Evidence for Environmental Dependence of the Stellar Initial Mass Function

TL;DR

This study investigates the low-mass stellar population in L1641 to assess whether the environment influences the upper end of the stellar initial mass function, finding a deficiency of high-mass stars compared to standard models.

Contribution

It provides the first comprehensive spectroscopic survey of L1641's low-mass stars and offers evidence for environmental dependence of the stellar initial mass function.

Findings

L1641 has a comparable low-mass star count to the Orion Nebula Cluster.

L1641 is significantly deficient in high-mass stars compared to standard IMF models.

Results support environmental influence on the upper mass end of the IMF.

Abstract

We present results from an optical photometric and spectroscopic survey of the young stellar population in L1641, the low-density star-forming region of the Orion A cloud south of the Orion Nebula Cluster (ONC). Our goal is to determine whether L1641 has a large enough low-mass population to make the known lack of high-mass stars a statistically-significant demonstration of environmental dependence of the upper mass stellar initial mass function (IMF). Our spectroscopic sample consists of IR-excess objects selected from the Spitzer/IRAC survey and non-excess objects selected from optical photometry. We have spectral confirmation of 864 members, with another 98 probable members; of the confirmed members, 406 have infrared excesses and 458 do not. Assuming the same ratio of stars with and without IR excesses in the highly-extincted regions, L1641 may contain as many as ~1600 stars down to ~0.1 solar mass, comparable within a factor of two to the the ONC. Compared to the standard models of the IMF, L1641 is deficient in O and early B stars to a 3-4 sigma significance level, assuming that we know of all the massive stars in L1641. With a forthcoming survey of the intermediate-mass stars, we will be in a better position to make a direct comparison with the neighboring, dense ONC, which should yield a stronger test of the dependence of the high-mass end of the stellar initial mass function upon environment.