Type Ia supernova feedback effects on globular clusters of different masses

TL;DR

The paper investigates how Type Ia supernova feedback influences SG star formation and chemical patterns in young globular clusters with $M_{ m FG}=10^5-10^6\,M_\odot$ using high-resolution 3D hydrodynamic simulations that couple AGB ejecta with pristine gas inflow. Type Ia SNe are implemented with a delay-time distribution tied to the single-degenerate channel, producing modest iron enrichment but significantly limiting the dilution of AGB ejecta, especially in low-density environments. The results show episodic quenching of star formation and substantial He enhancements in SG stars, with iron spreads remaining small, and reveal mass-density dependent effects that differ from SN-free cases. The findings suggest that SN Ia feedback alone cannot fully explain observed SG properties and highlight the need to incorporate additional feedback mechanisms or more nuanced gas accretion and SN timing to reconcile models with observations.

Abstract

Through 3D hydrodynamical simulations, we explore the impact of Type Ia supernova (SN) explosions on the star formation history and chemical properties of second-generation (SG) stars in young globular clusters with masses of 10^5-10^6 Msun. We assume that the SG is formed out of the asymptotic giant branch (AGB) ejecta of first-generation stars plus pristine interstellar medium gas which is modelled as a uniform gas moving at a constant velocity towards the cluster. We tested two values for the infalling gas density of 10^(-24) and 10^(23) g/cm^3. Type Ia SNe start to explode together with the release of gas from the most massive AGB stars. Three simulated models are analyzed. In the low-mass and low-density scenario, we find that SNe Ia quench star formation which however restarts when the gas cools down again in between two explosions. SG stars are dominated by a He-rich population (Y>0.33), which is poorly diluted by pristine gas. In the high-mass models, star formation is mildly affected, while the He composition is significantly altered as exploding SNe prevent the accretion of pristine gas and therefore extremely helium-rich stars form. In the high-density model, such weak gas accretion leads to a maximum enhancement in helium mass fraction much larger than the observed one and not correlating with the initial cluster mass as found in models without Type Ia SNe. As for the iron content, small spreads have been found in all models, but the SG is less homogeneous than the FG, at variance with current observations.

Figures (14)

• Figure 1: Two-dimensional maps of the gas density (left-hand panels) and of the temperature (central panels) and the pressure (right-hand panels) on the x-y plane for the M5I24 simulation. The corresponding evolutionary time of each set of panels is reported in the density map, together with the velocity field denoted by the white arrows (all arrows have the same length, so no information on the intensity of the field is reported), and the contours describing the region enclosing the 75% and 95% of the SG mass in red and black, respectively. The cyan points on the temperature map represent newborn stars (age <0.05 Myr).
• Figure 2: Two-dimensional mass surface density maps of the stellar component at four evolutionary times for the M5I24 simulation on the x-y plane.
• Figure 3: The mass distribution of Y (left) and [Fe/H] ratio (right) of the SG stars at the same time of the profiles. The distributions have been derived by summing the stellar masses in each bin and then normalizing every distribution to its maximum value. The black dashed lines represent the pristine gas composition both for Y and [Fe/H] ratio while the solid black line represents the normalized cumulative mass.
• Figure 4: Stellar helium mass fraction (Y) as a function of the stellar birthtime for the M5I24 model. The color scale indicates the number of SG stars. The black and red dashed vertical lines represent the time at which the infall and the AGB ejecta start to pollute the system, respectively (see \ref{['tab:simu']}). The green solid line represents the star formation rate.
• Figure 5: The same as Figure \ref{['fig:gas_map_M5I24']}, but for model M6I24.