9 research outputs found
Dark Matter signals from Draco and Willman 1: Prospects for MAGIC II and CTA
The next generation of ground-based Imaging Air Cherenkov Telescopes (IACTs)
will play an important role in indirect dark matter searches. In this article,
we consider two particularly promising candidate sources for dark matter
annihilation signals, the nearby dwarf galaxies Draco and Willman 1, and study
the prospects of detecting such a signal for the soon-operating MAGIC II
telescope system as well as for the planned installation of CTA, taking special
care of describing the experimental features that affect the detectional
prospects. For the first time in such a study, we fully take into account the
effect of internal bremsstrahlung, which has recently been shown to
considerably enhance, in some cases, the gamma-ray flux at the high energies
where Atmospheric Cherenkov Telescopes operate, thus leading to significantly
harder annihilation spectra than traditionally considered. While the detection
of the spectral features introduced by internal bremsstrahlung would constitute
a smoking gun signature for dark matter annihilation, we find that for most
models the overall flux still remains at a level that will be challenging to
detect unless one adopts rather (though by no means overly) optimistic
astrophysical assumptions about the distribution of dark matter in the dwarfs.Comment: 10 pages, 4 figures, minor changes, matches the published version
(JCAP
The Least Luminous Galaxy: Spectroscopy of the Milky Way Satellite Segue 1
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low luminosity (M_V
= -1.5) Milky Way satellite companion. While the combined size and luminosity
of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we
present spectroscopic evidence that this object is a dark matter-dominated
dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean
heliocentric recession velocity of 206 +/- 1.3 kms. We measure an internal
velocity dispersion of 4.3+/-1.2 kms. Under the assumption that these stars are
in dynamical equilibrium, we infer a total mass of 4.5^{+4.7}_{-2.5} x 10^5
Msun in the case where mass-follow-light; using a two-component maximum
likelihood model, we determine a similar mass within the stellar radius of 50
pc. This implies a mass-to-light ratio of ln(M/L_V) = 7.2^{+1.1}_{-1.2} or
M/L_V = 1320^{+2680}_{-940}. The error distribution of the mass-to-light ratio
is nearly log-normal, thus Segue 1 is dark matter-dominated at a high
significance. Using spectral synthesis modeling, we derive a metallicity for
the single red giant branch star in our sample of [Fe/H]=-3.3 +/- 0.2 dex.
Finally, we discuss the prospects for detecting gamma-rays from annihilation of
dark matter particles and show that Segue 1 is the most promising satellite for
indirect dark matter detection. We conclude that Segue 1 is the least luminous
of the ultra-faint galaxies recently discovered around the Milky Way, and is
thus the least luminous known galaxy.Comment: 12 pages, 6 figures, ApJ accepte