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تسجيل مستخدم جديدResolving the Source Populations that Contribute to the X-ray Background: The 2 Ms Chandra Deep Field-North Survey
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With ~2 Ms of Chandra exposure, the Chandra Deep Field-North (CDF-N) survey provides the deepest view of the Universe in the 0.5-8.0 keV band. Five hundred and three (503) X-ray sources are detected down to on-axis 0.5-2.0 keV and 2-8 keV flux limits of ~1.5x10^{-17} erg cm^{-2} s^{-1} and ~1.0x10^{-16} erg cm^{-2} s^{-1}, respectively. These flux limits correspond to L_{0.5-8.0 keV}~3x10^{41} erg s^{-1} at z=1 and L_{0.5-8.0 keV}~2x10^{43} erg s^{-1} at z=6; thus this survey is sensitive enough to detect starburst galaxies out to moderate redshift and Seyfert galaxies out to high redshift. We present the X-ray observations, describe the broad diversity of X-ray selected sources, and review the prospects for deeper Chandra exposures.
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We present catalogs for the ~2 Ms Chandra Deep Field-North, currently the deepest X-ray observation of the Universe in the 0.5-8.0 keV band. Five hundred and three (503) X-ray sources are detected over an ~448 sq.arcmin area in up to seven bands; 20
of these X-ray sources lie in the Hubble Deep Field-North. Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is ~0.3 arcsecs. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including some possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright R<~23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. We investigate the source-free background, determine the maximum photon-limited exposures, and investigate source confusion. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the ~1 Ms Chandra Deep Field-South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy (ABRIDGED).
An extremely deep X-ray survey (about 1 Ms) of the Hubble Deep Field North and its environs (about 450 arcmin^2) has been performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. This is one of the two deepest X-ra
y surveys ever performed; for point sources near the aim point it reaches 0.5-2.0 keV and 2-8 keV flux limits of 3 x 10^{-17} erg/cm^2/s and 2 x 10^{-16} erg/cm^2/s, respectively. Here we provide source catalogs along with details of the observations, data reduction, and technical analysis. Observing conditions, such as background, were excellent for almost all of the exposure. We have detected 370 distinct point sources: 360 in the 0.5-8.0 keV band, 325 in the 0.5-2.0 keV band, 265 in the 2-8 keV band, and 145 in the 4-8 keV band. Two new Chandra sources in the HDF-N itself are reported and discussed. Source positions are accurate to within 0.6-1.7 arcsec (at 90% confidence) depending mainly on the off-axis angle. We also detect two highly significant extended X-ray sources and several other likely extended X-ray sources. We present basic number count results for sources located near the center of the field. Source densities of 7100^{+1100}_{-940} deg^{-2} (at 4.2 x 10^{-17} erg/cm^2/s) and 4200^{+670}_{-580} deg^{-2} (at 3.8 x 10^{-16} erg/cm^2/s) are observed in the soft and hard bands, respectively.
We present improved point-source catalogs for the 2 Ms Chandra Deep Field-North (CDF-N) and the 250 ks Extended Chandra Deep Field-South (E-CDF-S), implementing a number of recent improvements in Chandra source-cataloging methodology. For the CDF-N/E
-CDF-S, we provide a main catalog that contains 683/1003 X-ray sources detected with wavdetect at a false-positive probability threshold of $10^{-5}$ that also satisfy a binomial-probability source-selection criterion of $P<0.004$/$P<0.002$. Such an approach maximizes the number of reliable sources detected: a total of 196/275 main-catalog sources are new compared to the Alexander et al. (2003) CDF-N/Lehmer et al. (2005) E-CDF-S main catalogs. We also provide CDF-N/E-CDF-S supplementary catalogs that consist of 72/56 sources detected at the same wavdetect threshold and having $P$ of $0.004-0.1$/$0.002-0.1$ and $K_sle22.9/K_sle22.3$ mag counterparts. For all $approx1800$ CDF-N and E-CDF-S sources, including the $approx500$ newly detected ones (these being generally fainter and more obscured), we determine X-ray source positions utilizing centroid and matched-filter techniques; we also provide multiwavelength identifications, apparent magnitudes of counterparts, spectroscopic and/or photometric redshifts, basic source classifications, and estimates of observed AGN and galaxy source densities around respective field centers. Simulations show that both the CDF-N and E-CDF-S main catalogs are highly reliable and reasonably complete. Background and sensitivity analyses indicate that the on-axis mean flux limits reached represent a factor of $approx1.5-2.0$ improvement over the previous CDF-N and E-CDF-S limits. We make our data products publicly available.
We present point-source catalogs for the ~2 Ms exposure of the Chandra Deep Field-South (CDF-S); this is one of the two most-sensitive X-ray surveys ever performed. The survey covers an area of ~436 arcmin^2 and reaches on-axis sensitivity limits of
~1.9x10^{-17} and ~1.3x10^{-16} ergs/cm^2/s for the 0.5-2.0 and 2-8 keV bands, respectively. Four hundred and sixty-two X-ray point sources are detected in at least one of three X-ray bands that were searched; 135 of these sources are new compared to the previous ~1 Ms CDF-S detections. Source positions are determined using centroid and matched-filter techniques; the median positional uncertainty is ~0.36. The X-ray-to-optical flux ratios of the newly detected sources indicate a variety of source types; ~55% of them appear to be active galactic nuclei while ~45% appear to be starburst and normal galaxies. In addition to the main Chandra catalog, we provide a supplementary catalog of 86 X-ray sources in the ~2 Ms CDF-S footprint that was created by merging the ~250 ks Extended Chandra Deep Field-South with the CDF-S; this approach provides additional sensitivity in the outer portions of the CDF-S. A second supplementary catalog that contains 30 X-ray sources was constructed by matching lower significance X-ray sources to bright optical counterparts (R<23.8); the majority of these sources appear to be starburst and normal galaxies. The total number of sources in the main and supplementary catalogs is 578. R-band optical counterparts and basic optical and infrared photometry are provided for the X-ray sources in the main and supplementary catalogs. We also include existing spectroscopic redshifts for 224 of the X-ray sources. (Abstract abridged)
We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 AGN detected in the 2 Ms Chandra Deep Field-North survey with > 200 background-subtracted 0.5-8.0 keV counts [F(0.5-8.0 keV)=(1.
4-200)e-15 erg cm^{-2} s^{-1}]. Our preliminary spectral analyses yield median spectral parameters of Gamma=1.61 and intrinsic N_H=6.2e21 cm^{-2} (z=1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived N_H distribution and, to a lesser extent, the X-ray luminosity distribution. Ten of the 136 AGN (~7%) show significant Fe Kalpha emission-line features with equivalent widths in the range 0.1-1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Gamma < 1.0 and large Fe Kalpha equivalent width). Finally, we find that 81 (~60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (~80-90%) when better photon statistics are available.
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