Orbital evolution of the Carina dwarf galaxy and self-consistent determination of star formation history

Abstract

We present a new study of the evolution of the Carina dwarf galaxy that includes a simultaneous derivation of its orbit and star formation history. The structure of the galaxy is constrained through orbital parameters derived from the observed distance, proper motions, radial velocity, and star formation history. The different orbits admitted by the large proper motion errors are investigated in relation to the tidal force exerted by an external potential representing the Milky Way. Our analysis is performed with the aid of fully consistent N-body simulations that are able to follow the dynamics and the stellar evolution of the dwarf system in order to determine the star formation history of Carina self-consistently. We also find a star formation history characterized by several bursts, partially matching the observational expectation. We find also compatible results between dynamical projected quantities and the observational constraints. The possibility of a past interaction between Carina and the Magellanic Clouds is also separately considered and deemed unlikely.

VLT/FLAMES spectroscopy of red giant branch stars in the Carina dwarf spheroidal galaxy

“…This discrepancy may be related to the fact that the model assumes that the dwarf galaxy was isolated with a fixed gas reservoir. In contrast the complicated star formation history of Carina is probably driven by external physical processes (e.g., Pasetto et al, 2011). Carina has currently a very small galactocentric velocity (v galacto = 7 km/s) which suggests that it is at apocentre, and has been orbiting the Milky Way environment for a considerable time (e.g., Piatek et al, 2003).…”

Isolated dwarf galaxies: from cuspy to flat dark matter density profiles and metalicity gradients

“…the Carina dwarf galaxy. Our target is not to realize a specific model of the Carina dwarf galaxy, but first to use observationally motivated input physics and then extend our analysis to the dwarf galaxies class of systems (but see Pasetto et al 2010). The wealth of literature data available on this galaxy starts already in 1983 with studies of the stellar populations of Carina (Mould & Aaronson 1983).…”

“…Proper motion determinations were obtained by Piatek et al (2003) (see also Piatek et al 2004). Dynamical considerations are available for the orbit from timing arguments in Muñoz et al (2008) and for Carina's tidal tails in Muñoz et al (2006), which make this system well-suited for further orbit investigations (Pasetto et al 2010).…”

“…We thus adopted a starting value of M gas = M dark 50 85 100 = 3.3 × 10 6 M and M star = M dark 50 15 100 = 5.9 × 10 5 M for our reference model. These numbers can be considered as starting values for an orbiting dwarf galaxy (Pasetto et al 2010), but here we will work only on an isolated system, thus for us the gas amount retained by the dwarf galaxy after its oldest stellar population is formed will be considered as a free parameter. This approach was assumed because the present-day dSphs contain little or no gas, possibly because a large fraction of gas was expelled by the initial SNII component, by tidal interaction with a host galaxy or in general photoevaporation, rampressure, by star formation processes.…”

“…The evolution of the reference model presented here will be used as normalization case for the realization of a Carina-like dwarf galaxy model that is discussed in more detail in Paper II (Pasetto et al 2010). Carina is one of the few dSph galaxies in the Local Group that shows long-lasting star formation and pronounced intermediate-age populations.…”