Structural analysis of disc super star clusters of M82: size and profile shape at intermediate ages

Abstract

ABSTRACT We present the structural parameters of 99 super star clusters (SSCs) in the disc of M82. Moffat-EFF, King, and Wilson models were fitted using a χ2-minimization method to background-subtracted surface brightness profiles in the F435W (B), F555W (V), and F814W (I) bands of the Advanced Camera for Surveys (ACS) of the Hubble Space Telescope. The majority of the SSC profiles are best fitted by the Moffat-EFF profile. The scale parameter rd and the shape parameter γ in the three filters are identical within the measurement errors. The analysed sample is big enough to allow the characterization of the distributions of core radii Rc and γ. The obtained distribution of Rc follows a lognormal form, with centre and $\sigma \mathrm{ log}\big {(}\frac{R_{\rm c}}{pc}\big {)}$ being 1.73 pc and 0.25, respectively. The γ distribution is also lognormal with centre and σlog(γ) being 2.88 and 0.08, respectively. M82 is well known for the absence of current star formation in its disc, with all disc SSCs older than 50 Myr and hardly any cluster older than ∼300 Myr. The derived distributions compare very well with the distributions for intermediate-age clusters in the Large Magellanic Cloud (LMC), which is also a low-mass late-type galaxy similar to M82. On the other hand, the distributions of Rc in both these galaxies are shifted towards larger values as compared to SSCs of similar age in the giant spiral galaxy M83. M82 and LMC also span a narrower range of γ values as compared to that in M83.