TY - JOUR
T1 - Weak Galactic Halo-Dwarf Spheroidal Connection from RR Lyrae Stars
AU - Fiorentino, Giuliana
AU - Bono, Giuseppe
AU - Monelli, Matteo
AU - Stetson, Peter B.
AU - Tolstoy, Eline
AU - Gallart, Carme
AU - Salaris, Maurizio
AU - Martínez-Vásquez, Clara E.
AU - Bernard, Edouard J.
PY - 2015/1
Y1 - 2015/1
N2 - We discuss the role that dwarf galaxies may have played in the formation
of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of
their ancient stellar component. The comparison is performed using two
observables (periods, luminosity amplitudes) that are reddening and
distance independent. Fundamental mode RRL in 6 dwarf spheroidals
(dSphs) and 11 ultra faint dwarf galaxies (~1300) show a Gaussian period
distribution well peaked around a mean period of langPabrang = 0.610
± 0.001 days (σ = 0.03). The Halo RRL (~15,000) are
characterized by a broader period distribution. The fundamental mode RRL
in all the dSphs apart from Sagittarius are completely lacking in High
Amplitude Short Period (HASP) variables, defined as those having P lsim
0.48 days and AV >= 0.75 mag. Such variables are not
uncommon in the Halo and among the globular clusters and massive dwarf
irregulars. To further interpret this evidence, we considered 18
globulars covering a broad range in metallicity (-2.3 lsim [Fe/H]
lsim -1.1) and hosting more than 35 RRL each. The metallicity
turns out to be the main parameter, since only globulars more metal-rich
than [Fe/H] ~ -1.5 host RRL in the HASP region. This finding
suggests that dSphs similar to the surviving ones do not appear to be
the major building-blocks of the Halo. Leading physical arguments
suggest an extreme upper limit of ~50% to their contribution. On the
other hand, massive dwarfs hosting an old population with a broad
metallicity distribution (Large Magellanic Cloud, Sagittarius) may have
played a primary role in the formation of the Halo.
AB - We discuss the role that dwarf galaxies may have played in the formation
of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of
their ancient stellar component. The comparison is performed using two
observables (periods, luminosity amplitudes) that are reddening and
distance independent. Fundamental mode RRL in 6 dwarf spheroidals
(dSphs) and 11 ultra faint dwarf galaxies (~1300) show a Gaussian period
distribution well peaked around a mean period of langPabrang = 0.610
± 0.001 days (σ = 0.03). The Halo RRL (~15,000) are
characterized by a broader period distribution. The fundamental mode RRL
in all the dSphs apart from Sagittarius are completely lacking in High
Amplitude Short Period (HASP) variables, defined as those having P lsim
0.48 days and AV >= 0.75 mag. Such variables are not
uncommon in the Halo and among the globular clusters and massive dwarf
irregulars. To further interpret this evidence, we considered 18
globulars covering a broad range in metallicity (-2.3 lsim [Fe/H]
lsim -1.1) and hosting more than 35 RRL each. The metallicity
turns out to be the main parameter, since only globulars more metal-rich
than [Fe/H] ~ -1.5 host RRL in the HASP region. This finding
suggests that dSphs similar to the surviving ones do not appear to be
the major building-blocks of the Halo. Leading physical arguments
suggest an extreme upper limit of ~50% to their contribution. On the
other hand, massive dwarfs hosting an old population with a broad
metallicity distribution (Large Magellanic Cloud, Sagittarius) may have
played a primary role in the formation of the Halo.
KW - Local Group
KW - stars: variables: RR Lyrae
UR - http://adsabs.harvard.edu/abs/2015ApJ...798L..12F
U2 - 10.1088/2041-8205/798/1/L12
DO - 10.1088/2041-8205/798/1/L12
M3 - Article
VL - 798
SP - L12-L17
JO - The Astrophysical Journal
JF - The Astrophysical Journal
ER -