A Radial Velocity and Calcium Triplet abundance survey of field Small Magellanic Cloud giants

TL;DR

This study conducts a wide-field survey of red giants in the Small Magellanic Cloud, analyzing their radial velocities and metallicities to understand its structure, kinematics, and star formation history.

Contribution

It provides new radial velocity and metallicity data for SMC giants across multiple fields, revealing complex velocity components and metallicity distributions indicative of star formation episodes.

Findings

Double velocity peaks at ~160 km/s and ~200 km/s in eastern fields.

Metallicity distribution centered at [Fe/H] ~ -1.25, with a secondary peak at -0.6.

Edge of the SMC estimated at approximately 6 kpc from the center.

Abstract

We present the results of a pilot wide-field radial velocity and metal abundance survey of red giants in ten fields in the Small Magellanic Cloud (SMC). The targets lie at projected distances of 0.9 and 1.9 kpc from the SMC centre ($m-M=18.79$) to the North, East, South and West. Two more fields are to the East at distances of 3.9 and 5.1 kpc. In this last field we find only a few to no SMC giants, suggesting that the edge of the SMC in this direction lies approximately at 6 kpc from its centre. In all eastern fields we observe a double peak in the radial velocities of stars, with a component at the classical SMC recession velocity of $\sim 160$ km s$^{-1}$ and a high velocity component at about 200 km s$^{-1}$, similar to observations in H{\small I}. In the most distant field (3.9 kpc) the low velocity component is at 106 km s$^{-1}$. The metal abundance distribution in all fields is broad and centred at about [Fe/H] $\sim -1.25$, reaching to solar and possibly slightly supersolar values and down to [Fe/H] of about -2.5. In the two innermost (0.9 kpc) Northern and Southern fields we observe a secondary peak at metallicities of about $\sim -0.6$. This may be evidence of a second episode of star formation in the centre, possibly triggered by the interactions that created the Stream and Bridge.