On the precision of full-spectrum fitting of simple stellar populations.
  II. The dependence on star cluster mass in the wavelength range 0.3-5.0
  $\mu$m
  In this second paper of a series on the accuracy and precision of the
determination of age and metallicity of simple stellar populations (SSPs) by
means of the full spectrum fitting technique, we study the influence of star
cluster mass through stochastic fluctuations of the number of stars near the
top of the stellar mass function, which dominate the flux in certain wavelength
regimes depending on the age. We consider SSP models based on the Padova
isochrones, spanning the age range 7.0 $\leq$ log (age/yr) $\leq$ 10.1.
Simulated spectra of star clusters in the mass range $10^4 \leq M/M_{\odot} <
10^6$ are compared with SSP model spectra to determine best-fit ages and
metallicities using a full-spectrum fitting routine in four wavelength regimes:
the blue optical (0.35-0.70 $\mu$m), the red optical (0.6-1.0 $\mu$m), the
near-IR (1.0-2.5 $\mu$m), and the mid-IR (2.5-5.0 $\mu$m). We compare the power
of each wavelength regime in terms of both the overall precision of age and
metallicity determination, and of its dependence on cluster mass. We also study
the relevance of spectral resolution in this context by utilizing two different
spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR
regime in terms of identifying young massive clusters in dusty star forming
regions in external galaxies. The spectra of the simulated star clusters and
SSPs are made available online to enable follow-up studies by the community.
