ZusammenfassungDie Milchstraße, wie auch die Andromeda‐ und Centaurus‐A‐Galaxien, ist von Satellitengalaxien umgeben. Die Verteilung und Bewegung dieser kleineren Galaxien ist überraschend abgeflacht ...und kohärent und erinnert an rotierende Satellitenebenen. Im kosmologischen Standardmodell, das auf der Existenz Dunkler Materie basiert, sollten Satellitengalaxiensysteme deutlich zufälliger arrangiert sein. Strukturen ähnlich den beobachteten Satellitenebenen sind in kosmologischen Simulationen sehr selten, weshalb sich aus diesen Beobachtungen das Satellitengalaxien‐Ebenen‐Problem des kosmologischen Modells ergibt.
Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. It has previously been suspected that ...dwarf galaxies may not be isotropically distributed around our Galaxy, because several are correlated with streams of H I emission, and may form coplanar groups. These suspicions are supported by recent analyses. It has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. However, other studies dispute this conclusion. Here we report the existence of a planar subgroup of satellites in the Andromeda galaxy (M 31), comprising about half of the population. The structure is at least 400 kiloparsecs in diameter, but also extremely thin, with a perpendicular scatter of less than 14.1 kiloparsecs. Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum. Intriguingly, the plane we identify is approximately aligned with the pole of the Milky Way's disk and with the vector between the Milky Way and Andromeda.
We report on the discovery of three new dwarf galaxies in the Local Group. These galaxies are found in new CFHT/MegaPrime image imaging of the southwestern quadrant of M31, extending our extant ...survey area to include the majority of the southern hemisphere of M31's halo out to 150 kpc. All these galaxies have stellar populations which appear typical of dwarf spheroidal (dSph) systems. The first of these galaxies, Andromeda XVIII, is the most distant Local Group dwarf discovered in recent years, at image1.4 Mpc from the Milky Way (image600 kpc from M31). The second galaxy, Andromeda XIX, a satellite of M31, is the most extended dwarf galaxy known in the Local Group, with a half-light radius of image kpc. This is approximately an order of magnitude larger than the typical half-light radius of many Milky Way dSphs, and reinforces the difference in scale sizes seen between the Milky Way and M31 dSphs (such that the M31 dwarfs are generally more extended than their Milky Way counterparts). The third galaxy, Andromeda XX, is one of the faintest galaxies so far discovered in the vicinity of M31, with an absolute magnitude of order image. Andromeda XVIII, XIX, and XX highlight different aspects of, and raise important questions regarding, the formation and evolution of galaxies at the extreme faint end of the luminosity function. These findings indicate that we have not yet sampled the full parameter space occupied by dwarf galaxies, although this is an essential prerequisite for successfully and consistently linking these systems to the predicted cosmological dark matter substructure.
We derive constraints on the parameters of the radiatively decaying dark matter (DM) particle, using the XMM–Newton EPIC spectra of the Andromeda galaxy (M31). Using the observations of the outer ...(5–13 arcmin) parts of M31, we improve the existing constraints. For the case of sterile neutrino DM, combining our constraints with the latest computation of abundances of sterile neutrinos in the Dodelson–Widrow (DW) scenario, we obtain the lower mass limit ms < 4 keV, which is stronger than the previous one ms < 6 keV, obtained recently by Asaka, Laine & Shaposhnikov. Comparing this limit with the most recent results on Lyman α forest analysis of Viel et al. (ms > 5.6 keV), we argue that the scenario in which all the DM is produced via the DW mechanism is ruled out. We discuss, however, other production mechanisms and note that the sterile neutrino remains a viable candidate for DM, either warm or cold.
Abstract
Photometric observations spanning the UV to the near-IR during the nine most recent eruptions (2014–2022) of the extragalactic nova M31N 2008-12a are presented and analyzed in order to ...explore whether the lightcurve properties for a given eruption, specifically the peak magnitudes and fade rates, are correlated with the time interval since the previous eruption. No significant correlation between the pre-eruption interval and the rate of decline was found, however it appears that the brightness at the peak of an outburst may be positively correlated with the time interval since the previous eruption.
PDF
