218 research outputs found
Maximum Entropy Estimation of the Galactic Bulge Morphology via the VVV Red Clump
The abundance and narrow magnitude dispersion of Red Clump (RC) stars make
them a popular candidate for mapping the morphology of the bulge region of the
Milky Way. Using an estimate of the RC's intrinsic luminosity function, we
extracted the three-dimensional density distribution of the RC from deep
photometric catalogues of the VISTA Variables in the Via Lactea (VVV) survey.
We used maximum entropy based deconvolution to extract the spatial distribution
of the bulge from Ks-band star counts. We obtained our extrapolated
non-parametric model of the bulge over the inner 40 by 40 degrees squared
region of the Galactic centre. Our reconstruction also naturally matches onto a
parametric fit to the bulge outside the VVV region and inpaints overcrowded and
high extinction regions. We found a range of bulge properties consistent with
other recent investigations based on the VVV data. In particular, we estimated
the bulge mass to be in the range 13 to 17 billion solar masses, the
X-component to be between 18% and 25% of the bulge mass, and the bulge angle
with respect to the Sun-Galactic centre line to be between 18 and 32 degrees.
Studies of the Fermi Large Area Telescope (LAT) gamma-ray Galactic centre
excess suggests that the excess may be traced by Galactic bulge distributed
sources. We applied our deconvolved density in a template fitting analysis of
this Fermi-LAT GeV excess and found an improvement in the fit compared to
previous parametric based templates.Comment: 25 pages, 27 figures, minor typo correcte
Inverse Compton emission from millisecond pulsars in the Galactic bulge
Analyses of Fermi Gamma-Ray Space Telescope data have revealed a source of
excess diffuse gamma rays towards the Galactic center that extends up to
roughly 20 degrees in latitude. The leading theory postulates that this
GeV excess is the aggregate emission from a large number of faint millisecond
pulsars (MSPs). The electrons and positrons () injected by this
population could produce detectable inverse-Compton (IC) emissions by
up-scattering ambient photons to gamma-ray energies. In this work, we calculate
such IC emissions using GALPROP. A triaxial three-dimensional model of the
bulge stars obtained from a fit to infrared data is used as a tracer of the
putative MSP population. This model is compared against one in which the MSPs
are spatially distributed as a Navarro-Frenk-White squared profile. We show
that the resulting spectra for both models are indistinguishable, but that
their spatial morphologies have salient recognizable features. The IC component
above TeV energies carries information on the spatial morphology of the
injected . Such differences could potentially be used by future
high-energy gamma-ray detectors such as the Cherenkov Telescope Array to
provide a viable multiwavelength handle for the MSP origin of the GeV excess.Comment: 13 pages, 8 figures, 3 tables. Match the version published in PR
Strong Evidence that the Galactic Bulge is Shining in Gamma Rays
There is growing evidence that the Galactic Center Excess identified in the
-LAT gamma-ray data arises from a population of faint
astrophysical sources. We provide compelling supporting evidence by showing
that the morphology of the excess traces the stellar over-density of the
Galactic bulge. By adopting a template of the bulge stars obtained from a
triaxial 3D fit to the diffuse near-infrared emission, we show that it is
detected at high significance. The significance deteriorates when either the
position or the orientation of the template is artificially shifted, supporting
the correlation of the gamma-ray data with the Galactic bulge. In deriving
these results, we have used more sophisticated templates at low-latitudes for
the bubbles compared to previous work and the
three-dimensional Inverse Compton (IC) maps recently released by the team. Our results provide strong constraints on Millisecond Pulsar
(MSP) formation scenarios proposed to explain the excess. We find that an
scenario, in which some of the relevant binaries
are and the rest are formed , is
preferred over a primordial-only formation scenario at confidence
level. Our detailed morphological analysis also disfavors models of the
disrupted globular clusters scenario that predict a spherically symmetric
distribution of MSPs in the Galactic bulge. For the first time, we report
evidence of a high energy tail in the nuclear bulge spectrum that could be the
result of IC emission from electrons and positrons injected by a population of
MSPs and star formation activity from the same site.Comment: 21 pages, 13 figures, V2: Minor changes to match submitted version,
V3: matches JCAP published versio
Measurement of redshift dependent cross correlation of HSC clusters and Fermi rays
The cross-correlation study of the unresolved -ray background (UGRB)
with galaxy clusters has a potential to reveal the nature of the UGRB. In this
paper, we perform a cross-correlation analysis between -ray data by the
Fermi Large Area Telescope (Fermi-LAT) and a galaxy cluster catalogue from the
Subaru Hyper Suprime-Cam (HSC) survey. The Subaru HSC cluster catalogue
provides a wide and homogeneous large-scale structure distribution out to the
high redshift at , which has not been accessible in previous
cross-correlation studies. We conduct the cross-correlation analysis not only
for clusters in the all redshift range () of the survey, but
also for subsamples of clusters divided into redshift bins, the low redshift
bin () and the high redshift bin (), to utilize
the wide redshift coverage of the cluster catalogue. We find the evidence of
the cross-correlation signals with the significance of 2.0-2.3 for all
redshift and low-redshift cluster samples. On the other hand, for high-redshift
clusters, we find the signal with weaker significance level (1.6-1.9).
We also compare the observed cross-correlation functions with predictions of a
theoretical model in which the UGRB originates from -ray emitters such
as blazars, star-forming galaxies and radio galaxies. We find that the detected
signal is consistent with the model prediction.Comment: 11 pages, 24 figures, accepted by MNRA
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