J/PASJ/74/283 NIR identified X-ray sources in Galactic bulge (Morihana+, 2022) ================================================================================ Deep near-infrared imaging observation of the faint X-ray point sources constituting the Galactic bulge X-ray emission. Morihana K., Tsujimoto M., Ebisawa K., Gandhi P. =2022PASJ...74..283M (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Milky Way ; X-ray sources ; Infrared sources Keywords: Galaxy: stellar content - novae, cataclysmic variables - stars: late-type - X-rays: diffuse background - X-rays: stars Abstract: The presence of the apparently extended hard (2-10keV) 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., 2009Natur.458.1142R). 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 near-infrared (NIR) imaging and spectroscopic studies (Morihana et al., 2013ApJ...766...14M, Cat. J/ApJ/766/14; Morihana et al., 2016PASJ...68...57M) 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 ~18mag in the J, H, and K_s_ 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 white dwarf (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. Description: A deep JHKs imaging observation of the Chandra bulge field (CBF) was carried out using MOIRCS on the Subaru telescope. MOIRCS is equipped with two 2048x2048 HgCdTe HAWAII-2 arrays and covers a 4x7-arcmin^2^ field of view with a pixel scale of 0.117"/pixel in the imaging mode. We look for candidate NIR counterparts to the Chandra X-ray sources. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table3.dat 117 264 NIR identified X-ray source catalog -------------------------------------------------------------------------------- See also: J/ApJ/766/14 : Deep Chandra bulge field X-ray point sources (Morihana+, 2013) Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 --- Seq X-ray catalog source number in Morihana et al. (2013ApJ...766...14M, Cat. J/ApJ/766/14) 6- 23 A18 --- CXOU CXOU J designation (HHMMSS.ss+DDMMSS.s) 25- 34 F10.6 deg RAdeg X-ray right ascension (J2000) 36- 44 F9.5 deg DEdeg X-ray declination (J2000) 46- 54 F9.5 deg RANdeg NIR right ascension (J2000) 56- 64 F9.5 deg DENdeg NIR declination (J2000) 66- 68 F3.1 arcsec ePos X-ray position error (1{sigma}) 70- 76 E7.2 mW/m2 F0.5-8keV Photometric flux in the total (0.5-8.0keV) band (1) 78- 84 E7.2 mW/m2 F2-8keV ?=- Photometric flux in the hard (2.0-8.0keV) band (1) 86- 90 F5.2 mag Jmag ?=0 Subaru J magnitude 92- 95 F4.2 mag e_Jmag ?=0 Subaru J magnitude error 97-101 F5.2 mag Hmag ?=0 Subaru H magnitude 103-106 F4.2 mag e_Hmag ?=0 Subaru H magnitude error 108-112 F5.2 mag Ksmag ?=0 Subaru Ks magnitude 114-117 F4.2 mag e_Ksmag ?=0 Subaru Ks magnitude error -------------------------------------------------------------------------------- Note (1): The photometric flux is defined as count rate multiplied by the median energy divided by the average effective area (Tsujimoto et al., 2005AJ....130.2212T, Cat. J/AJ/130/2212, Morihana et al., 2013ApJ...766...14M, Cat. J/ApJ/766/14) -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Patricia Vannier [CDS] 21-Sep-2022