No evidence for gamma-ray emission from the Sagittarius dwarf spheroidal galaxy

TL;DR

This study critically re-evaluates claims of gamma-ray emission from the Sagittarius dwarf galaxy and finds no supporting evidence, highlighting the importance of background modeling in gamma-ray astrophysics.

Contribution

The paper introduces a data-driven background modeling method that reduces mis-modeling effects and reassesses gamma-ray signals from Sgr, challenging prior claims.

Findings

No gamma-ray emission detected from Sgr at previous claimed levels

Background modeling significantly impacts gamma-ray source detection

Millisecond pulsar population unlikely to explain the putative signal

Abstract

More than a decade ago, the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope unveiled the existence of two gigantic gamma-ray lobes known as the Fermi bubbles. While their origin is still unknown, various studies identified intricate spectral and morphological structures within the bubbles. One peculiar region, the cocoon, has recently been associated with gamma-ray emissions from the Sagittarius dwarf spheroidal (Sgr) galaxy. We assess the validity of this claim through adaptive-template fitting and pixel-count statistical methods. Our approach introduces a substantial advancement in data interpretation by enabling a data-driven optimisation of astrophysical background models, thereby reducing the impact of background mis-modelling. We do not find evidence for gamma-ray emission from the Sgr region at the level obtained in previous work. We demonstrate that there is no pronounced difference between the source population located within the cocoon region and a reference region at similar latitudes. We examine the hypothesis that a millisecond pulsar population in Sgr causes the putative signal via dedicated simulations finding that it is unlikely that we may have detected their presence in Sgr.