We present new and accurate radial velocity ( RV ) measurements of luminous stars of all ages ( old horizontal branch , intermediate–age red clump , and young blue plume , as well as red giants of a range of ages ; 20.6 \leq V \leq 22 ) in the Carina dwarf spheroidal galaxy , based on low-resolution spectra collected with the FORS2 multi-object slit spectrograph at the VLT .
This data set was complemented by RV measurements based on medium and high-resolution archive spectra of brighter ( V \lesssim 20.6 ) Carina targets collected with the GIRAFFE multi-object fiber spectrograph at the VLT .
The combined sample includes more than 21,340 individual spectra of \approx 2,000 stars covering the entire body of the galaxy .
The mean ( < RV > =220.4 \pm 0.1 km s ^ { -1 } ) and the dispersion ( \sigma =11.7 \pm 0.1 km s ^ { -1 } ) of the RV distribution of candidate Carina stars ( \sim 1,210 objects , 180 \leq RV \leq 260 km s ^ { -1 } , 4 \sigma ) agree quite well with similar measurements available in the literature .
To further improve the statistics , the accurate RV measurements recently provided by Walker et al .
( 2007 ) were also added to the current data set .
We ended up with a sample of \sim 1,370 RV measurements of candidate Carina stars that is \approx 75 % larger than any previous Carina RV sample .
We found that the hypothesis that the Carina RV distribution is Gaussian can be discarded at 99 % confidence level .
The mean RV across the body of the galaxy varies from \sim 220 km s ^ { -1 } at a distance of 7′ ( \sim 200 pc ) from the center to \sim 223 km s ^ { -1 } at 13′ ( \sim 400 pc , 6 \sigma level ) and flattens out to a constant value of \sim 221 km s ^ { -1 } at larger distances ( 600 pc , 4 \sigma level ) .
Moreover and even more importantly , we found that in the Carina regions where the mean RV is smaller the dispersion is also smaller , and the RV distribution is more centrally peaked ( i.e .
the kurtosis attains larger values ) .
The difference in mean RV is more than 4 km s ^ { -1 } ( 9 \sigma level ) , when moving from E to W , and more than 3 km s ^ { -1 } ( \sim 7 \sigma level ) , when moving from N to S. The RV gradient appears to be in the direction of the Carina proper motion .
However , this parameter is affected by large uncertainties to reach a firm conclusion .
There is evidence of a secondary maximum in RV across the Carina center ( |D| \leq 200 pc ) .
The occurrence of a secondary feature across the Carina center is also supported by the flat-topped radial distribution based on the photometric catalog .
These findings are reminiscent of a substructure with transition properties , already detected in dwarf ellipticals , and call for confirmation by independent investigations .