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تسجيل مستخدم جديدSurface brightness profile of the 3.5 keV line in the Milky Way halo
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We report a detection of 3.5 keV line in the Milky Way in 5 regions offset from the Galactic Center by distances from 10 to 35 degrees. We build an angular profile of this line and compare it with profiles of several astrophysical lines detected in the same observations. We compare our results with other detections and bounds previously obtained using observations of the Milky Way.
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We present a comprehensive search for the 3.5 keV line, using $sim$51 Ms of archival Chandra observations peering through the Milky Ways Dark Matter Halo from across the entirety of the sky, gathered via the Chandra Source Catalog Release 2.0. We con
sider the datas radial distribution, organizing observations into four data subsets based on angular distance from the Galactic Center. All data is modeled using both background-subtracted and background-modeled approaches to account for the particle instrument background, demonstrating statistical limitations of the currently-available $sim$1 Ms of particle background data. A non-detection is reported in the total data set, allowing us to set an upper-limit on 3.5 keV line flux and constrain the sterile neutrino dark matter mixing angle. The upper-limit on sin$^2$(2$theta$) is $2.58 times 10^{-11}$ (though systematic uncertainty may increase this by a factor of $sim$2), corresponding to the upper-limit on 3.5 keV line flux of $2.34 times 10^{-7}$ ph s$^{-1}$ cm$^{-2}$. These limits show consistency with recent constraints and several prior detections. Non-detections are reported in all radial data subsets, allowing us to constrain the spatial profile of 3.5 keV line intensity, which does not conclusively differ from Navarro-Frenk-White predictions. Thus, while offering heavy constraints, we do not entirely rule out the sterile neutrino dark matter scenario or the more general decaying dark matter hypothesis for the 3.5 keV line. We have also used the non-detection of any unidentified emission lines across our continuum to further constrain the sterile neutrino parameter space.
Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a sea
rch for a 3.5 keV emission line from the Milky Ways galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report non-detections of a $sim$3.5 keV emission line in four HaloSat observations near the Galactic Center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux and 7.1 keV sterile neutrino mixing angle: $F leq 0.077$ ph cm$^{-2}$ s$^{-1}$ sr$^{-1}$ and $sin^2(2theta) leq 4.25 times 10^{-11}$. The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Ways dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Ways dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature.
We present a spectroscopic sample of 910 distant halo stars from the Hypervelocity Star survey from which we derive the velocity dispersion profile of the Milky Way halo. The sample is a mix of 74% evolved horizontal branch stars and 26% blue straggl
ers. We estimate distances to the stars using observed colors, metallicities, and stellar evolution tracks. Our sample contains twice as many objects with R>50 kpc as previous surveys. We compute the velocity dispersion profile in two ways: with a parametric method based on a Milky Way potential model, and with a non-parametric method based on the caustic technique originally developed to measure galaxy cluster mass profiles. The resulting velocity dispersion profiles are remarkably consistent with those found by two independent surveys based on other stellar populations: the Milky Way halo exhibits a mean decline in radial velocity dispersion of -0.38+-0.12 km/s/kpc over 15<R<75 kpc. This measurement is a useful basis for calculating the total mass and mass distribution of the Milky Way halo.
High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E=3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Pe
rseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark-matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of Sxvi (E=3.44 keV rest-frame) -- a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.
I show that model dependencies in the analysis by Dessert, Rodd & Safdi (2020) relax their claimed constraint by a factor of ~20. After including conservative model choices, the derived limits are comparable to or slightly better than limits from pre
vious searches. Further model tests and expansion of the data energy may enhance or relax sensitivity of the methodology.
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