The Galactic Center Excess (GCE) of GeV gamma rays can be explained as a signal of annihilating dark matter or of emission from unresolved astrophysical sources, such as millisecond pulsars. Evidence for the latter is provided by a statistical procedure---referred to as Non-Poissonian Template Fitting (NPTF)---that distinguishes the smooth distribution of photons expected for dark matter annihilation from a "clumpy" photon distribution expected for point sources. In this paper, we perform an extensive study of the NPTF on simulated data, exploring its ability to recover the flux and luminosity function of unresolved sources at the Galactic Center. When astrophysical background emission is perfectly modeled, we find that the NPTF successfully distinguishes between the dark matter and point source hypotheses when either component makes up the entirety of the GCE. When the GCE is a mixture of dark matter and point sources, the NPTF may fail to reconstruct the correct contribution of each component. We further study the impact of mismodeling the Galactic diffuse backgrounds, finding that while a dark matter signal could be attributed to point sources in some outlying cases for the scenarios we consider, the significance of a true point source signal remains robust. Our work enables us to comment on a recent study by Leane and Slatyer (2019) that questions prior NPTF conclusions because the method does not recover an artificial dark matter signal injected on actual Fermi data. We demonstrate that the failure of the NPTF to extract an artificial dark matter signal can be natural when point sources are present in the data---with the effect further exacerbated by the presence of diffuse mismodeling---and does not on its own invalidate the conclusions of the NPTF analysis in the Inner Galaxy.
Detection of point sources in images is a fundamental operation in astrophysics, and is crucial for constraining population models of the underlying point sources or characterizing the background emission. Standard techniques fall short in the crowded-field limit, losing sensitivity to faint sources and failing to track their covariance with close neighbors. We construct a Bayesian framework to perform inference of faint or overlapping point sources. The method involves probabilistic cataloging, where samples are taken from the posterior probability distribution of catalogs consistent with an …
The origin of the extragalactic gamma-ray background (EGRB) radiation has been a mystery in astrophysics for a long time. Recently the Fermi gamma-ray satellite (Fermi) has revealed that ~22% of the unresolved EGRB would be explained by blazars, which are one population of beamed active galactic nuclei (AGNs). The remaining ~78% of the unresolved EGRB is still unknown. We estimate the contribution of gamma-ray loud radio galaxies, which are misaligned radio loud AGNs recently detected by Fermi, to EGRB using the radio luminosity function of radio-loud AGNs with the correlation between the radi…
The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey of the inner Milky Way (THOR) at $\lesssim$18" resolution covers $\sim 132$ square degrees of the Galactic plane and detects 10387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) surveys covers $\sim 16$ square degrees of the Galactic plane from 4-8 GHz at 18" resolution and detects 1575 sources. However, a large fraction of the unresolved discrete sources detected in these radio continuum surveys of the Galactic plane remain unclassified. Here, we study the …
In this paper we investigate the power spectrum of the unresolved 0.5-2 keV CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal which, on scales >30", is significantly higher than the Shot-Noise and is increasing with the angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like AGN, Galaxies and Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall, our modeling predicts that \sim 20% of the unresolved CXB flux is made by low luminos…
We present a new method to characterize unresolved point sources (PSs), generalizing traditional template fits to account for non-Poissonian photon statistics. We apply this method to Fermi Large Area Telescope gamma-ray data to characterize PS populations at high latitudes and in the Inner Galaxy. We find that PSs (resolved and unresolved) account for ~50% of the total extragalactic gamma-ray background in the energy range ~1.9 to 11.9 GeV. Within 10$^\circ$ of the Galactic Center with $|b| \geq 2^\circ$, we find that ~5-10% of the flux can be accounted for by a population of unresolved PSs, …
Excess GeV gamma rays from the Galactic Center (GC) have been measured with the Fermi Large Area Telescope (LAT). The presence of the GC excess (GCE) appears to be robust with respect to changes in the diffuse galactic background modeling. The three main proposals for the GCE are an unresolved population of millisecond pulsars (MSPs), outbursts of cosmic rays from the GC region, and self-annihilating dark matter (DM). The injection of secondary electrons and positrons into the interstellar medium (ISM) by an unresolved population of MSPs or DM annihilations can lead to observable gamma-ray emi…
We perform a composite likelihood analysis of subdivided regions within the central $26^\circ\times20^\circ$ of the Milky Way, with the aim of characterizing the spectrum of the gamma-ray galactic center excess in regions of varying galactocentric distance. Outside of the innermost few degrees, we find that the radial profile of the excess is background-model dependent and poorly constrained. The spectrum of the excess emission is observed to extend upwards of 10 GeV outside $\sim5^\circ$ in radius, but cuts off steeply between 10--20 GeV only in the innermost few degrees. If interpreted as a …
The Fermi Large Area Telescope has observed an excess of ~GeV energy gamma rays from the center of the Milky Way, which may arise from near-thermal dark matter annihilation. Firmly establishing the dark matter origin for this excess is however complicated by challenges in modeling diffuse cosmic-ray foregrounds as well as unresolved astrophysical sources, such as millisecond pulsars. Non-Poissonian Template Fitting (NPTF) is one statistical technique that has previously been used to show that at least some fraction of the GeV excess is likely due to a population of dim point sources. These res…
The Galactic Center Gamma-Ray Excess has a spectrum, angular distribution, and overall intensity that agree remarkably well with that expected from annihilating dark matter particles in the form of a $m_X \sim 50 \, {\rm GeV}$ thermal relic. Previous claims that these photons are clustered on small angular scales or trace the distribution of known stellar populations once appeared to favor interpretations in which this signal originates from a large population of unresolved millisecond pulsars. More recent work, however, has overturned these conclusions, finding that the observed gamma-ray exc…
The Fermi-LAT data appear to have an excess of gamma rays from the inner 150 pc of the Galactic Center. The main explanations proposed for this are: an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The first two options have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope $γ=1.2$. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template base…
An excess of gamma rays has been identified at the centre of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the apparent point-like nature of the emission rules out the dark matter interpretation of the exc…
The origin of the extragalactic gamma-ray background (EGRB) is still an open question, even after nearly forty years of its discovery. The emission could originate from either truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EGRET (Energetic Gamma Ray Experiment Telescope) are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EGRB, and many studies have been carried out to understand their distribution, evolution and contrib…
Based on new and archival Chandra observations of the Sombrero galaxy (M 104), we study the diffuse X-ray emission in and around its massive stellar bulge. The 2-6 keV unresolved emission from the bulge region closely follows the K-band star light and most likely arises from unresolved stellar sources. At lower energies, however, the unresolved emission reaches a galactocentric radius of at least 23 kpc, significantly beyond the extent of the starlight, clearly indicating the presence of diffuse hot gas. We isolate the emission of the gas by properly accounting for the emission from unresolved…
We present a new extended gamma ray excess detected with the Fermi Satellite Large Area Telescope toward the Galactic Center that traces the morphology of infrared starlight emission. Combined with its measured spectrum, this new extended source is approximately consistent with inverse Compton emission from a high-energy electron-positron population with energies up to about 10 GeV. Previously detected emissions tracing the 20 cm radio, interpreted as bremsstrahlung radiation, and the Galactic Center Extended emission tracing a spherical distribution and peaking at 2 GeV, are also detected. We…
We study the performance of a typical near-future full sky CMB space mission, aiming at the characterization of the large scale $B$-modes polarization anisotropies with precision on $r\sim 0.001$, after a map-based parametric cleaning of galactic dust and synchrotron, and in the case of spatially varying astrophysical spectral emission laws. Ignoring the spatial variability of the spectral emission laws may result in a bias on $r$ as high as $\mathcal{O}(0.01)$ for realistic models of the variability. However, we show that the component separation formalism can be extended to suppress this bia…
Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray undetected galaxies that dominates the unresolved ~ 20-25% of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South HST z-band imaging of the central 6'-radius area of the 4 Ms CDF-S. The stacked 6-8 keV detection is significant at the 3.9 sigma level, but the stacked emission was not detected in the 4-6 keV band which indicates the existence of an underlying population of highly obscured active …
We present a detailed study of the Faraday depth structure of four bright (> 1 Jy), strongly polarized, unresolved, radio-loud quasars. The Australia Telescope Compact Array (ATCA) was used to observe these sources with 2 GHz of instantaneous bandwidth from 1.1 to 3.1 GHz. This allowed us to spectrally resolve the polarization structure of spatially unresolved radio sources, and by fitting various Faraday rotation models to the data, we conclusively demonstrate that two of the sources cannot be described by a simple rotation measure (RM) component modified by depolarization from a foreground F…
The contribution of unresolved sources to the diffuse gamma-ray background could produce anisotropies in this emission on small angular scales. Recent studies have considered the angular power spectrum and other anisotropy metrics as tools for identifying contributions to diffuse emission from unresolved source classes, such as extragalactic and Galactic dark matter as well as various astrophysical gamma-ray source populations. We present preliminary results of an anisotropy analysis of the diffuse emission measured by the Fermi-LAT.
We present new CRIRES spectroscopic observations of BrGamma in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H2O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us and based on spectroastrometry. The classical method …
One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modeling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325 MHz data obtained from the GMRT, a $6^\circ \times 6^\circ$ mosaiced map is produced with an RMS reaching 50 $μ$Jy $\mathrm{beam}^{-1}$. A source catalog containing 6186 sources is created, and the Euclidean nor…
Fermi Large Area Telescope data reveal an excess of GeV gamma rays from the direction of the Galactic Center and bulge. Several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (MSPs) and self-annihilating dark matter. It has been claimed that a key discriminant for or against the MSP explanation can be extracted from the properties of the luminosity function describing this source population. Specifically, is the luminosity function of the putative MSPs in the Galactic Center consistent with that characterizing the resolved MSPs in the …
Locating the exact point of origin of the core radiation in active galactic nuclei (AGN) would represent important progress in our understanding of physical processes in the central engine of these objects. However, due to our inability to resolve the region containing both the central compact object and the jet base, this has so far been difficult. Here, using an analysis in which the lack of resolution does not play a significant role, we demonstrate that it may be impossible even in most radio loud sources for more than a small percentage of the core radiation at radio wavelengths to come f…
Foreground removal is a major challenge for detecting the redshifted 21-cm neutral hydrogen (HI) signal from the Epoch of Reionization (EoR). We have used 150 MHz GMRT observations to characterize the statistical properties of the foregrounds in four different fields of view. The measured multi-frequency angular power spectrum C_l(Delta nu) is found to have values in the range 10^4 mK^2 to 2 x 10^4 mK^2 across 700 <= l <= 2 x 10^4 and Delta nu <= 2.5 MHz, which is consistent with model predictions where point sources are the most dominant foreground component. The measured C_l(Delta nu) does n…
