The low-mass Initial Mass Function in the young cluster NGC 6611

TL;DR

This study presents a deep photometric analysis of NGC 6611, revealing its low-mass Initial Mass Function extends into the brown dwarf regime and resembles that of low-mass star forming regions, with no significant environmental effects observed.

Contribution

First detailed IMF measurement of NGC 6611 down to brown dwarfs using Hubble data, comparing it with other regions to assess environmental impact.

Findings

IMF extends down to ~0.02 Msun including brown dwarfs

NGC 6611's IMF resembles Taurus more than Orion

No severe environmental effect on IMF detected

Abstract

NGC 6611 is the massive young cluster (2-3 Myr) that ionises the Eagle Nebula. We present very deep photometric observations of the central region of NGC 6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down to I ~ 26 mag. We construct the Initial Mass Function (IMF) from ~ 1.5 Msun well into the brown dwarf regime (down to ~ 0.02 Msun). We have detected 30-35 brown dwarf candidates in this sample. The low-mass IMF is combined with a higher-mass IMF constructed from the groundbased catalogue from Oliveira et al. (2005). We compare the final IMF with those of well studied star forming regions: we find that the IMF of NGC 6611 more closely resembles that of the low-mass star forming region in Taurus than that of the more massive Orion Nebula Cluster (ONC). We conclude that there seems to be no severe environmental effect in the IMF due to the proximity of the massive stars in NGC 6611.