Deep Near-infrared Imaging Observation of the Faint X-ray Point Sources Constituting the Galactic Bulge X-ray Emission
arXiv:2112.10355 · doi:10.1093/pasj/psab124
Abstract
Presence of the apparently extended hard (2-10 keV) X-ray emission along the Galactic plane has been known since the early 1980s. With a deep X-ray exposure using the Chandra X-ray Observatory of a slightly off-plane region in the Galactic bulge, most of the extended emission was resolved into faint discrete X-ray sources in the Fe K band (Revnivtsev et al.,2009). The major constituents of these sources have long been considered to be X-ray active stars and magnetic cataclysmic variables (CVs). However, recent works including our NIR imaging and spectroscopic studies (Morihana et al.,2013, 2016) argue that other populations should be more dominant. To investigate this further, we conducted a much deeper NIR imaging observation at the center of the Chandra's exposure field. We have used the MOIRCS on the Subaru telescope, reaching the limiting magnitude of ~18 mag in the J, H, and Ks bands in this crowded region, and identified ~50 % of the X-ray sources with NIR candidate counterparts. We classified the X-ray sources into three groups (A, B, and C) based on their positions in the X-ray color-color diagram and characterized them based on the X-ray and NIR features. We argue that the major populations of the Group A and C sources are, respectively, CVs (binaries containing magnetic or non-magnetic white dwarfs with high accretion rates) and X-ray active stars. The major population of the Group B sources is presumably WD binaries with low mass accretion rates. The Fe K equivalent width in the composite X-ray spectrum of the Group B sources is the largest among the three and comparable to that of the Galactic bulge X-ray emission. This leads us to speculate that there are numerous WD binaries with low mass accretion rates, which are not recognized as CVs, but are the major contributor of the apparently extended X-ray emission.
arXiv comment14 pages, 10 figures, accepted for publication in PASJ
References in corpus (43)
- The Gaia mission
- On the Absorption of X-rays in the Interstellar Medium
- Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
- Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
- An Overview of the Performance and Scientific Results from the Chandra X-Ray Observatory (CXO)
- VVV DR1: The First Data Release of the Milky Way Bulge and Southern Plane from the Near-Infrared ESO Public Survey VISTA Variables in the Via Lactea
- X-ray Emissions from Accreting White Dwarfs: a Review
- An Exploration of the Paradigm for the 2-3 Hour Period Gap in Cataclysmic Variables
- Discrete sources as the origin of the Galactic X-ray ridge emission
- RXTE Measurement of the Diffuse X-ray Emission From the Galactic Ridge: Implications for the Energetics of the Interstellar Medium
- Cataclysmic Variables from SDSS II. The Second Year
- Cataclysmic Variables from SDSS I. The First Results
- The complete set of ASCA X-ray observations of non-magnetic cataclysmic variables
- Chandra Deep X-ray Observation of a Typical Galactic Plane Region and Near-Infrared Identification
- New spectral classification technique for X-ray sources: quantile analysis
- Cataclysmic Variables from SDSS. VIII. The Final Year (2007-2008)
- Origin of the Hard X-ray Emission from the Galactic Plane
- A study of X-ray flares - II. RS CVn type Binaries
- Deriving an X-ray luminosity function of dwarf novae based on parallax measurements
- Cataclysmic Variables from SDSS VII. The Seventh Year (2006)
- Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables: III. A New Kind of Dwarf Nova Oscillation, and Further Examples of the Similarities to X-Ray Binaries
- A study of X-ray flares - I. Active late-type dwarfs
- Broad-band spectral analysis of the Galactic Ridge X-ray Emission
- Fe Line Diagnostics of Cataclysmic Variables and Galactic Ridge X-ray Emission
- Large X-ray Flares on Stars Detected with MAXI/GSC: A Universal Correlation between the Duration of a Flare and its X-ray Luminosity
- Spectral Study of the Galactic Ridge X-ray Emission with Suzaku
- X-ray Luminosities of Optically-Selected Cataclysmic Variables and Application to the Galactic Ridge X-ray Emission
- Infrared spectroscopy of cataclysmic variables: III. Dwarf novae below the period gap and novalike variables
- A new near-IR window of low extinction in the Galactic plane
- Dominance of Magnetic Cataclysmic Variables in the Resolved Galactic Ridge X-ray Emission of the Limiting Window
- Diffuse X-Ray Sky in the Galactic Center
- Scale heights and equivalent widths of the iron K-shell lines in the Galactic diffuse X-ray emission
- The X-ray source content of the XMM-Newton Galactic Plane Survey
- Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics
- ChaMPlane Deep Galactic Bulge Survey. I. Faint accretion-driven binaries in the Limiting Window
- Luminosity function of faint Galactic sources in the Chandra bulge field
- A Systematic X-ray Study of the Dwarf Novae Observed with Suzaku
- Detection of accretion X-rays from QS Vir: cataclysmic or a lot of hot air?
- XMM-Newton observations of the Galactic Centre Region - II: The soft thermal emission
- X-ray Point Source Populations Constituting the Galactic Ridge X-ray Emission
- X-ray and Near-infrared Studies of a Star-forming Cloud; L1448
- XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi
- Near-Infrared Spectroscopy of Faint Discrete X-ray Point Sources Constituting the Galactic Ridge X-ray Emission