📝 Original Info
- Title: The Chandra COSMOS Survey, I: Overview and Point Source Catalog
- ArXiv ID: 0903.2062
- Date: 2009-09-29
- Authors: Researchers from original ArXiv paper
📝 Abstract
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra} program that has imaged the central 0.5 sq.deg of the COSMOS field (centered at 10h, +02deg) with an effective exposure of ~160ksec, and an outer 0.4sq.deg. area with an effective exposure of ~80ksec. The limiting source detection depths are 1.9e-16 erg cm(-2) s(-1) in the Soft (0.5-2 keV) band, 7.3e(-16) erg cm^-2 s^-1 in the Hard (2-10 keV) band, and 5.7e(-16) erg cm(-2) s(-1) in the Full (0.5-10 keV) band. Here we describe the strategy, design and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2e(-5) (1655 in the Full, 1340 in the Soft, and 1017 in the Hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (to 12%) exposure across the inner 0.5 sq.deg field was obtained, leading to a sharply defined lower flux limit. The widely different PSFs obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. (Puccetti et al. Paper II). This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with sub-arcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper (Civano et al. Paper III). The full catalog is described here in detail, and is available on-line.
💡 Deep Analysis
Deep Dive into The Chandra COSMOS Survey, I: Overview and Point Source Catalog.
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra} program that has imaged the central 0.5 sq.deg of the COSMOS field (centered at 10h, +02deg) with an effective exposure of ~160ksec, and an outer 0.4sq.deg. area with an effective exposure of ~80ksec. The limiting source detection depths are 1.9e-16 erg cm(-2) s(-1) in the Soft (0.5-2 keV) band, 7.3e(-16) erg cm^-2 s^-1 in the Hard (2-10 keV) band, and 5.7e(-16) erg cm(-2) s(-1) in the Full (0.5-10 keV) band. Here we describe the strategy, design and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2e(-5) (1655 in the Full, 1340 in the Soft, and 1017 in the Hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (to 12%) exposure across the inner 0.5 sq.deg field was obtained, leading to a sharply defined lower flux limit. The widely different PSFs obtained in each exposure
📄 Full Content
The co-evolution of galaxies and quasars or active galactic nuclei (AGNs) has been vigorously pursued both observationally and theoretically for a decade, ever since the discovery that the mass of the central black hole is tightly correlated both with the luminosity (Magorrian et al. 1998;Marconi & Hunt 2003) and the velocity dispersion of the spheroid (M BH -σ relation; Ferrarese & Merrit 2000;Gebhardt et al. 2000;Tremaine et al. 2002). Tackling this large subject requires the study of both galaxies and AGNs back to the epoch when both were growing rapidly, i.e. z∼1-3, requiring deep observations across many wavelengths, from radio through the infrared, optical and ultraviolet, to the X-rays. At the same time, the wide range of cosmic density and the rapid changes in this large scale structure (LSS) require wide field observations that sample the Universe at close to their true fractions.
The Cosmic Evolution Survey (COSMOS, Scoville et al. 2007a) is a deep and wide extragalactic survey designed to have sufficient area to overcome most cosmic variance, which requires sampling regions some 50 Mpc on a side (Fig. 1; Scoville et al. 2007a), and with sufficient depth to sample the z = 1 -3 galaxy and AGN population. The contiguous 2 sq.deg COSMOS field samples a volume of ∼6×10 6 Mpc 3 at z = 0.5 -1 (Wright 2006). This is ∼10% of the volume imaged by the Sloan Digital Sky Survey (SDSS) in the local (z<0.1) universe (5.7×10 7 Mpc 3 , 8000 sq.deg, DR51 ). COSMOS is a region of low, uniform, Galactic obscuration (E(B-V)≃0.02 mag, N H (2.7×10 20 cm -2 , Dickey & Lockman 1990). COSMOS is likely to be the largest survey of this type for the next decade.
The location of the COSMOS area near the equator (10 h , +02 • ) allows all major and future facilities 2 (notably EVLA, ALMA, and SKA) to target this region down to faint limits (Scoville et al. 2007a). Space-based imaging has been undertaken in the F840W (∼ i-band) with Hubble Space Telescope (HST, Scoville et al. 2007b), in the 3.5 µm-70µm infrared using Spitzer IRAC and MIPS (Sanders et al. 2007), in the UV using GALEX (Zamojski et al. 2007), and in 0.5-10 keV X-rays with XMM (Hasinger et al. 2007, Cappelluti et al. 2007). Ground-based imaging spans the radio (1400 MHz VLA, Schinnerer et al. 2007), the near-IR with CTIO and KPNO (Capak et al. 2007) and CFHT (McCracken et al. 2009, in preparation), the optical to AB∼26-27 with Subaru in 21 bands (Taniguchi et al. 2007). Finally, large dedicated ground-based spectroscopy programs in the optical with Magellan/IMACS (Trump et al. 2007), and VLT/VIMOS (Lilly et al. 2008) are well underway.
This wealth of data has resulted in an initial 15-band photometric catalog of ∼10 6 objects (Capak et al. 2007) from which photometric redshifts good to <3% for z<1.2 and r <24 have been derived (Mobasher et al. 2007). Recently, more photometric bands have been added, resulting in improved photo-z’s for the galaxy population accurate to ∆z/(1+z)<1% (Ilbert et al. 2009) and to ∆z/(1+z)∼2% for the AGN population (Salvato et al. 2009).
We have undertaken the Chandra-COSMOS survey (C-COSMOS) to cover the central Right: Large scale structure seen in galaxy distributions in the COSMOS field (Scoville et al. 2007c), ranging in size from 1 -20 Mpc, based on photo-z’s accurate to ∼1%. Blue is centered on z=0.35, Green on z=0.55, and Red on z=0.75, each with ∆z=0.05. The C-COSMOS field outline is shown as the white tilted square, with the dashed line delineating the high exposure area as in the left panel. A scale showing 10 Mpc at the three redshifts is shown at the top. In both panels North is up, East is to the left. 0.9 sq.deg region of the COSMOS field (Fig. 1, left), containing a wide range of cosmic overdensity (Fig. 1, right), with the ACIS-I CCD imager (Garmire et al. 2003) on board the Chandra X-ray Observatory (Weisskopf et al. 2002). The survey took 1.8 Msec of Chandra observing time (∼21 days) and was the largest guest observer program approved in a single AO at the time it was undertaken (2006November -2007 June). C-COSMOS employed a series of 36 heavily overlapped ACIS-I 50 ksec pointings to give an exposure of ∼160 ksec over the inner area to a depth of ∼1.9×10 -16 erg cm -2 s -1 (0.5-2 keV), providing an unprecedented combination of contiguous area and depth in the X-ray band. This overlapping tiling strategy gives highly uniform exposure, and so a well-defined flux limit.
Several of the deepest COSMOS surveys are now concentrating on this same central sub-field of COSMOS: the z-COSMOS Deep spectroscopic survey (to B∼25, Lilly et al. 2007), the deep VLA survey (6 µJy rms, Schinnerer et al. 2009, in preparation), and several millimeter and sub-millimeter surveys (MAMBO, Bertoldi et al. 2007 andAzTEC, Scott et al. 2008). GALEX has observed the central field deeply (Zamojksi et al. 2007) and is currently monitoring this area. The Ultra-VISTA survey will undertake a deep yJHK survey of the central 1.5 sq.deg, half of which w
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