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ECDFSOID - Extended Chandra Deep Field-South Survey Optical Identifications Catalog

HEASARC
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Overview

This table contains the first results of the authors' optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South (ECDFS). A total of 339 sources (listed herein) were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. The authors have measured redshifts for 186 X-ray sources, including archival data and a literature search. They find that the active galactic nucleus (AGN) host galaxies have on average redder rest-frame optical colors than nonactive galaxies, and that they live mostly in the "green valley." The dependence of the fraction of AGNs that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGNs show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGNs, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.

Catalog Bibcode

2009ApJ...693.1713T

References

Optical spectroscopy of X-ray sources in the Extended Chandra Deep Field South
    Treister E., Virani S., Gawiser E., Urry C.M., Lira P., Francke H.,
    Blanc G.A., Cardamone C.N., Damen M., Taylor E.N., Schawinski K.
   <Astrophys. J., 693, 1713-1727 (2009)>
   =2009ApJ...693.1713T
The extended Chandra Deep Field-South survey: X-ray point-source catalog.
    Virani S.N., Treister E., Urry C.M., Gawiser E.
   <Astron. J., 131, 2373-2382 (2006)>
   =2006AJ....131.2373V

Provenance

This table was created by the HEASARC in April 2009 based on the electronic version of Table 2 from the Treister et al. (2009) paper obtained from the ApJ web site, except for the source positions which were taken from Virani et al. (2006). The full table from the latter paper is also available in Browse (the ECDFSCXO table).

Parameters

Source_Number
A unique identification number for each X-ray source in this catalog, with source numbers from 1 to 587, inclusive, being the 'primary' ECDFS sources (Table 4 of the Virani et al. paper) and those from 588 to 651, inclusive, being the 'secondary' (lower significance) sources (Table 5 of the same paper). Note that only 339 of the 651 X-ray sources listed by Virani et al. have follow-up optical and IR data listed herein.

Name
The source number-based designation for the X-ray source, in the form '[VTU2006] NNN', where VTU2006 refers to the authors (Virani, Treister, Urry) and the publication date, and NNN is the source number.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original Virani et al. (2006) tables.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original Virani et la. (2006) tables.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

SB_Flux
The soft-band flux (in units of ergs cm-2 s-1) calculated from the corresponding count rate and assuming a photon slope of power-law index Gamma = 1.4 corrected for Galactic absorption. If a source was undetected in the soft band but was detected in the full or hard band, the full- or hard-band flux (in that order of priority) was used to extrapolate to the soft band assuming a photon slope of 1.4.

HB_Flux
The hard-band flux (in units of ergs cm-2 s-1) calculated from the corresponding count rate and assuming a photon slope of power-law index Gamma = 1.4 corrected for Galactic absorption. If a source was undetected in the hard band but was detected in the full or soft band, the full- or soft-band flux (in that order of priority) was used to extrapolate to the hard band assuming a photon slope of 1.4.

Hardness_Ratio
The hardness ratio. HR, defined as the ratio between the difference of the hard band (typically 2-8 keV for Chandra observations) and soft band (0.5-2 keV) count rates and their sum. This parameter may be used to characterize the X-ray spectral shape when the number of detected counts is not enough to perform X-ray spectral fitting.

Hardness_Ratio_Pos_Err
The positive error in the hardness ratio, HR.

Hardness_Ratio_Neg_Err
The negative error in the hardness ratio, HR.

Redshift
The spectroscopic redshift of the optical counterpart to the X-ray source. For 186 of the X-ray sources, the authors were able to identify the nature of the source and measure the redshift, giving an average efficiency of 55%. Of those, 180 were detected in the high-significance primary sample of the X-ray catalog. Null redshift values (listed as 9.99 in the original table) correspond to a targeted source for which the redshift could not be measured.

Spectrum_Source
The source of the optical spectrum and/or redshift, coded as follows:

(i) BERG: Archived data from the program of Bergeron et al. using the European Southern Observatory (ESO) Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS), ID 072.A-0139, for which 23 hr were granted in order to obtain spectroscopy of the X-ray sources detected by XMM-Newton. The area covered by XMM-Newton is well matched to the ECDF-S Chandra observations, so it is reasonable that a significant number of the Chandra sources were identified as part of this program;

(ii) FORS2: Archived data from the ESO VLT FOcal Reducer and low dispersion Spectrograph, Version 2;

(iii) IMACS: New observations made by the authors using the Inamori Magellan Areal Camera and Spectrograph (IMACS) mounted on the Magellan I Baade telescope at Las Campanas Observatory, as discussed in Section 2.1 of the Treister et al. (2009) reference paper;

(iv) SZOK: Identification and redshift from the Szokoly et al. (2004, ApJS, 155, 271) optical follow-up of the CDF-S X-ray sources;

(v) VIMOS: New observations made by the authors using the European Southern Observatory (ESO) Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS), as discussed in Section 2.2 of the Treister et al. (2009) reference paper;

(vi) VVDS: Identification and redshift from the VIMOS VLT Deep Survey optical follow-up of Le Fevre et al. (2005, A&A, 439, 845).

Broad_Type
The optical classification of the optical counterpart to the X-ray source, as follows:

  ALG:   absorption-line galaxy
  ELG:   emission-line galaxy
  OAGN:  obscured AGN
  STAR:  star
  UAGN:  unobscured AGN
  UNK:   unknown
  

Log_HB_Lx
The logarithm of the hard-band (2-8 keV) X-ray luminosity of the source, calculated from the corresponding X-ray flux and the redshift. A Lambda cold dark matter (Lambda CDM) cosmology with h_0 = 0.7, Omega_M = 0.3, and Omega_Lambda = 0.7, in agreement with the most recent cosmological observations has been assumed by the authors.

Flux_24_um
The Spitzer 24-micron flux density of the infrared counterpart to the X-ray source, in mJy.

Flux_24_um_Error
The uncertainty in the Spitzer 24-micron flux density, in mJy.

Ref_Flux_24_um
The source of the 24-micron photometry, where F means it is the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL) and G is the Great Observatories Origins Deep Survey (GOODS).

Spectral_Index
The X-ray power-law spectral index, Gamma. For the brighter X-ray sources it is possible to perform more accurate spectral fitting than can be provided by the hardness ratio. In the case of the ECDF-S, a total of 184 sources have more than 80 counts detected in the 0.5-8 keV Chandra band, making spectral fitting possible. The authors used a modified version of the Yaxx software to extract the spectrum of each high-significance source. For sources with more than 200 background-subtracted counts and measured redshifts, 72 in the ECDF-S, they simultaneously fitted a power-law spectrum and photoelectric absorption, with three free parameters: slope of the power law (Gamma), normalization, and observed neutral hydrogen column density (N_H). In all cases, they included the Galactic absorption, assuming an average NH of 6.8 x 1019 cm-2 for the ECDF-S, as measured by the survey of Galactic HI of Kalberla et al. (2005, A&A, 440, 775). For sources with less than 200 but more than 80 counts, it was not possible to perform such detailed fitting, so they fixed the slope of the power law to a value of Gamma = 1.9, very similar to the average value for the sources with a fitted slope (Gamma = 1.95), which also corresponds to the typical X-ray spectrum for unobscured AGNs.

Spectral_Index_Pos_Err
The positive error in Gamma.

Spectral_Index_Neg_Err
The negative error in Gamma

Log_NH
The logarithm of the neutral hydrogen column density, in atoms cm-2. The HEASARC believes that this is the intrinsic, not the observed, column density, inferred from the X-ray spectrum and redshift as discussed in Section 3 of the Treister et al. (2009) reference paper.

Class
The HEASARC Browse object classification, based on the value of the broad_type parameter.


Contact Person

Questions regarding the ECDFSOID database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 20-Apr-2009