On the Moduli space of $\lambda$-connections

Let $X$ be a compact Riemann surface of genus $g \geq 3$. Let $\cat{M}_{Hod}$ denote the moduli space of stable $\lambda$-connections over $X$ and $\cat{M}'_{Hod} \subset \cat{M}_{Hod}$ denote the subvariety whose underlying vector bundle is stable. Fix a line bundle $L$ of degree zero. Let $\cat{M}_{Hod}(L)$ denote the moduli space of stable $\lambda$-connections with fixed determinant $L$ and $\cat{M}'_{Hod}(L) \subset \cat{M}_{Hod}(L)$ be the subvariety whose underlying vector bundle is stable. We show that there is a natural compactification of $\cat{M}'_{Hod}$ and $\cat{M}'_{Hod} (L)$, and study their Picard groups. Let $\M_{Hod}(L)$ denote the moduli space of polystable $\lambda$-connections. We investigate the nature of algebraic functions on $\cat{M}_{Hod}(L)$ and $\M_{Hod}(L)$. We also study the automorphism group of $\cat{M}'_{Hod}(L)$.