Background X-ray Radiation Fields Produced by Young Embedded Star Clusters

TL;DR

This paper quantifies the background X-ray radiation fields produced by young embedded star clusters, showing they can significantly influence ionization, chemistry, and heating in circumstellar disks and cluster environments.

Contribution

It provides a detailed analysis of X-ray luminosity and flux distributions in star clusters, highlighting their potential impact on star and planet formation processes.

Findings

X-ray flux levels exceed cosmic and galactic backgrounds by factors of 10-1000

Background X-ray flux dominates stellar X-ray emission beyond 9-14 AU in disks

Cluster X-ray background increases ionization rates by 4-8 times compared to cosmic rays

Abstract

Most star formation in our galaxy occurs within embedded clusters, and these background environments can affect the star and planet formation processes occurring within them. In turn, young stellar members can shape the background environment and thereby provide a feedback mechanism. This work explores one aspect of stellar feedback by quantifying the background X-ray radiation fields produced by young stellar objects. Specifically, the distributions of X-ray luminosities and X-ray fluxes produced by cluster environments are constructed as a function of cluster membership size $N$. Composite flux distributions, for given distributions of cluster sizes $N$, are also constructed. The resulting distributions are wide and the X-ray radiation fields are moderately intense, with the expected flux levels exceeding the cosmic and galactic X-ray backgrounds by factors of $\sim10-1000$ (for energies 0.2 -- 15 keV). For circumstellar disks that are geometrically thin and optically thick, the X-ray flux from the background cluster dominates that provided by a typical central star in the outer disk where $r \ga 9 - 14$ AU. In addition, the expectation value of the ionization rate provided by the cluster X-ray background is $\zeta_X\sim8\times10^{-17}$ s$^{-1}$, about 4 -- 8 times larger than the canonical value of the ionization rate from cosmic rays. These elevated flux levels in clusters indicate that X-rays can affect ionization, chemistry, and heating in circumstellar disks and in the material between young stellar objects.