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SDSSBALQS2 - Sloan Digital Sky Survey Broad Absorption Line Quasars Catalog (5th Data Release)

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Overview

This table contains a catalog of 5035 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range greater than or equal to 2000 km s-1. The authors have fitted ultraviolet (UV) continua and line emission in each case, enabling them to report common diagnostics of BAL strengths and velocities in the range from -25,000 to 0 km s-1 for Si IV 1400 Angstroms, C IV 1549 A, Al III 1857 A, and Mg II 2799 A. The authors calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. They confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs, and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise ratio (S/N); for higher S/N sources, the authors find an observed BAL fraction of about 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their C IV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker C IV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from overionization and enable radiative acceleration. In a scenario in which BAL trough shapes are primarily determined by outflow geometry, observed differences in Si IV and C IV trough shapes would suggest that some outflows have ion-dependent structure.

The authors fit SDSS spectra using the algorithm of Gibson et al. (2008, ApJ, 675, 985), which we summarize here. For QSOs at z >= 1.7, their continuum model is a power law reddened using the Small Magellanic Cloud (SMC) reddening curve of Pei (1992, ApJ, 395, 130). For QSOs at lower redshifts, the authors use a fourth- or sixth-degree polynomial; in their experience this nonphysical model is able to reproduce well the complex continuum at longer wavelengths. They initially fit regions that are generally free from strong absorption or emission features: 1250-1350, 1700-1800, 1950-2200, 2650-2710, 2950-3700, 3950-4050, 4140-4270, 4400-4800, 5100-6400, and > 6900 Angstroms. They then iteratively fit the continuum, ignoring at each step wavelength bins that deviate by more than 3 sigma from the current fit in order to exclude strong absorption and emission features. They fit Voigt profiles to the strongest emission lines expected in the spectrum: Si IV 1400, C IV 1549, Al III 1857, C III 1909, and Mg II 2799. These wavelengths are taken from the SDSS vacuum wavelength list used by the SDSS pipeline to determine emission-line redshifts.

Much more information on the SDSS is available at the project's web site at http://www.sdss.org/.


Catalog Bibcode

2009ApJ...692..758G

References

A Catalog of Broad Absorption Line Quasars in Sloan Digital Sky Survey
Data Release 5
    Gibson R.R., Jiang L., Brandt W.N., Hall P.B., Shen Y., Wu J., Anderson
    S.F., Schneider D.P., Vanden Berk D., Gallagher S.C., Fan, X., York D.G.
    <Astrophys. J. 692, 758-777, (2009)
    =2009ApJ...692..758G

Provenance

This table was created by the HEASARC in April 2009 based on the machine-readable version of Table 1 from the reference paper obtained from the ApJ web site.

Parameters

Name
The SDSS DR5 source identification for the BAL QSO in the standard format, e.g., 'SDSS JHHMMSS.ss+DDMMSS.s'.

RA
The Right Ascension of the quasar in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees (0.0036 arcseconds) in the original table.

Dec
The Declination of the quasar in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees (0.0036 arcseconds) in the original table.

LII
The Galactic Longitude of the quasar.

BII
The Galactic Latitude of the quasar.

Redshift
The redshift of the quasar taken from the DR5 QSO Catalog, with the exception of two sources, SDSS J100424.88+122922.2 and SDSS J153029.05+553247.9, which the authors consider to be misclassified. They assign these sources redshifts of 4.66 and 1.73, respectively.

Si_IV_BI
The Si IV balnicity index BI(Si IV), in km s-1. The authors smoothed each spectrum using a boxcar three bins wide and then searched the smoothed spectra for BALs by calculating BI, the traditional "balnicity index" of Weymann et al. (1991, ApJ, 373, 23). The balnicity index is defined as the integral from 3,000 to 25,000 km s-1 of (1 - f(-v)/0/9) x C dV, where f(v) is the continuum-normalized spectral flux at a velocity v (in km s-1) from the line rest wavelength 1402.77 A (in the system frame). The dimensionless value C is 0 unless the observed spectrum has fallen at least 10% below the continuum for a velocity width of at least 2000 km s-1 on the red side of the absorption trough, at which point C is set to 1. Traditional BALs are defined to have BI > 0.

Si_IV_Mod_BI
The Si IV modified balnicity index BI_0(Si IV), in km s-1. Because the standard BI metric does not include a large number of broad absorption features at lower outflow velocities, the authors also define and calculate BI_0 in a similar fashion to BI, but integrate to 0 km s-1 instead of -3000 km s-1 as for BI.

Si_IV_EW
The Si IV rest-frame absorption equivalent width EW_0 measured in BAL regions, i.e., in spectral bins which are part of a continuous absorption region >= 10% below the continuum and > 2000 km s-1 wide, in Angstroms. Narrower absorption troughs are not included in this measurement.

Si_IV_Min_Vel
The Si IV minimum velocity v_min, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Si_IV_Max_Vel
The Si IV maximum velocity v_max, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Si_IV_F_Deep
The Si IV BAL bin fraction f_deep defined to be the fraction of BAL bins that fall at least 50% below the continuum. (The definition of "spectral bin" is given in Section 2 of the reference paper).

C_IV_BI
The C IV balnicity index BI(C IV), in km s-1. The authors smoothed each spectrum using a boxcar three bins wide and then searched the smoothed spectra for BALs by calculating BI, the traditional "balnicity index" of Weymann et al. (1991, ApJ, 373, 23). The balnicity index is defined as the integral from 3,000 to 25,000 km s-1 of (1 - f(-v)/0/9) x C dV, where f(v) is the continuum-normalized spectral flux at a velocity v (in km s-1) from the line rest wavelength 1550.77 A (in the system frame). The dimensionless value C is 0 unless the observed spectrum has fallen at least 10% below the continuum for a velocity width of at least 2000 km s-1 on the red side of the absorption trough, at which point C is set to 1. Traditional BALs are defined to have BI > 0.

C_IV_Mod_BI
The C IV modified balnicity index BI_0(C IV), in km s-1. Because the standard BI metric does not include a large number of broad absorption features at lower outflow velocities, the authors also define and calculate BI_0 in a similar fashion to BI, but integrate to 0 km s-1 instead of -3000 km s-1 as for BI.

C_IV_EW
The C IV rest-frame absorption equivalent width EW_0 measured in BAL regions, i.e., in spectral bins which are part of a continuous absorption region >= 10% below the continuum and > 2000 km s-1 wide, in Angstroms. Narrower absorption troughs are not included in this measurement.

C_IV_Min_Vel
The C IV minimum velocity v_min, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

C_IV_Max_Vel
The C IV maximum velocity v_max, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

C_IV_F_Deep
The C IV BAL bin fraction f_deep defined to be the fraction of BAL bins that fall at least 50% below the continuum. (The definition of "spectral bin" is given in Section 2 of the reference paper).

Al_III_BI
The Al III balnicity index BI(Al III), in km s-1. The authors smoothed each spectrum using a boxcar three bins wide and then searched the smoothed spectra for BALs by calculating BI, the traditional "balnicity index" of Weymann et al. (1991, ApJ, 373, 23). The balnicity index is defined as the integral from 3,000 to 25,000 km s-1 of (1 - f(-v)/0/9) x C dV, where f(v) is the continuum-normalized spectral flux at a velocity v (in km s-1) from the line rest wavelength 1862.79 A (in the system frame). The dimensionless value C is 0 unless the observed spectrum has fallen at least 10% below the continuum for a velocity width of at least 2000 km s-1 on the red side of the absorption trough, at which point C is set to 1. Traditional BALs are defined to have BI > 0.

Al_III_Mod_BI
The Al III modified balnicity index BI_0(Al III), in km s-1. Because the standard BI metric does not include a large number of broad absorption features at lower outflow velocities, the authors also define and calculate BI_0 in a similar fashion to BI, but integrate to 0 km s-1 instead of -3000 km s-1 as for BI.

Al_III_EW
The Al III rest-frame absorption equivalent width EW_0 measured in BAL regions, i.e., in spectral bins which are part of a continuous absorption region >= 10% below the continuum and > 2000 km s-1 wide, in Angstroms. Narrower absorption troughs are not included in this measurement.

Al_III_Min_Vel
The Al III minimum velocity v_min, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Al_III_Max_Vel
The Al III maximum velocity v_max, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Al_III_F_Deep
The Al III BAL bin fraction f_deep defined to be the fraction of BAL bins that fall at least 50% below the continuum. (The definition of "spectral bin" is given in Section 2 of the reference paper).

Mg_II_BI
The Mg II balnicity index BI(Mg II), in km s-1. The authors smoothed each spectrum using a boxcar three bins wide and then searched the smoothed spectra for BALs by calculating BI, the traditional "balnicity index" of Weymann et al. (1991, ApJ, 373, 23). The balnicity index is defined as the integral from 3,000 to 25,000 km s-1 of (1 - f(-v)/0/9) x C dV, where f(v) is the continuum-normalized spectral flux at a velocity v (in km s-1) from the line rest wavelength 2803.53 A (in the system frame). The dimensionless value C is 0 unless the observed spectrum has fallen at least 10% below the continuum for a velocity width of at least 2000 km s-1 on the red side of the absorption trough, at which point C is set to 1. Traditional BALs are defined to have BI > 0.

Mg_II_Mod_BI
The Mg II modified balnicity index BI_0(Mg II), in km s-1. Because the standard BI metric does not include a large number of broad absorption features at lower outflow velocities, the authors also define and calculate BI_0 in a similar fashion to BI, but integrate to 0 km s-1 instead of -3000 km s-1 as for BI.

Mg_II_EW
The Mg II rest-frame absorption equivalent width EW_0 measured in BAL regions, i.e., in spectral bins which are part of a continuous absorption region >= 10% below the continuum and > 2000 km s-1 wide, in Angstroms. Narrower absorption troughs are not included in this measurement.

Mg_II_Min_Vel
The Mg II minimum velocity v_min, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Mg_II_Max_Vel
The Mg II maximum velocity v_max, in km s-1. The authors define v_max and v_min to be the outflow velocities corresponding to the shortest and longest wavelengths, respectively, in the BAL trough(s) of a given spectrum, where a BAL trough is any region for which the flux drops >= 10% below the continuum for a velocity range of > 2000 km s-1. For example, if a given spectrum has two C IV BALs extending from -20,000 to -15,000 km s-1 and from -8,000 to -5,000 km s-1, then for this source the C IV v_max = -20, 000 and v_min = -5,000 km s-1.

Mg_II_F_Deep
The Mg II BAL bin fraction f_deep defined to be the fraction of BAL bins that fall at least 50% below the continuum. (The definition of "spectral bin" is given in Section 2 of the reference paper).

Si_IV_EmLost_Flag
The Si IV EmLost boolean flag. The profile of the emission line at (nearly) zero velocity has been strongly absorbed and may not have been accurately reconstructed. The EmLost flag is set to 1 if a BAL is found for this ion and either the center of the (best-guess) emission-line fit is in the BAL region, the FWHM of the authors' (best-guess) emission-line fit is < 10 A, or there is evidence that a broad range of spectral bins in the line center are absorbed. Quantitatively, for the last criterion, the authors require that at least 15 adjacent bins (20 for Mg II) fall >= 5% below their emission model fit, and these absorbed bins lie in the wavelength region where the emission is above the line half-maximum. The authors' fitting experience indicates that characterizing emission lines is particularly difficult in cases meeting these criteria. Low-velocity absorption is very common; nearly half of the sources with C IV BI_0 > 0 have this flag set for the C IV emission line. Setting this flag indicates that measurements of BAL troughs are less certain in cases where the BAL extends to low velocities.

C_IV_EmLost_Flag
The C IV EmLost boolean flag. The profile of the emission line at (nearly) zero velocity has been strongly absorbed and may not have been accurately reconstructed. The EmLost flag is set to 1 if a BAL is found for this ion and either the center of the (best-guess) emission-line fit is in the BAL region, the FWHM of the authors' (best-guess) emission-line fit is < 10 A, or there is evidence that a broad range of spectral bins in the line center are absorbed. Quantitatively, for the last criterion, the authors require that at least 15 adjacent bins (20 for Mg II) fall >= 5% below their emission model fit, and these absorbed bins lie in the wavelength region where the emission is above the line half-maximum. The authors' fitting experience indicates that characterizing emission lines is particularly difficult in cases meeting these criteria. Low-velocity absorption is very common; nearly half of the sources with C IV BI_0 > 0 have this flag set for the C IV emission line. Setting this flag indicates that measurements of BAL troughs are less certain in cases where the BAL extends to low velocities.

Al_III_EmLost_Flag
The Al III EmLost boolean flag. The profile of the emission line at (nearly) zero velocity has been strongly absorbed and may not have been accurately reconstructed. The EmLost flag is set to 1 if a BAL is found for this ion and either the center of the (best-guess) emission-line fit is in the BAL region, the FWHM of the authors' (best-guess) emission-line fit is < 10 A, or there is evidence that a broad range of spectral bins in the line center are absorbed. Quantitatively, for the last criterion, the authors require that at least 15 adjacent bins (20 for Mg II) fall >= 5% below their emission model fit, and these absorbed bins lie in the wavelength region where the emission is above the line half-maximum. The authors' fitting experience indicates that characterizing emission lines is particularly difficult in cases meeting these criteria. Low-velocity absorption is very common; nearly half of the sources with C IV BI_0 > 0 have this flag set for the C IV emission line. Setting this flag indicates that measurements of BAL troughs are less certain in cases where the BAL extends to low velocities.

Mg_II_EmLost_Flag
The Mg II EmLost boolean flag. The profile of the emission line at (nearly) zero velocity has been strongly absorbed and may not have been accurately reconstructed. The EmLost flag is set to 1 if a BAL is found for this ion and either the center of the (best-guess) emission-line fit is in the BAL region, the FWHM of the authors' (best-guess) emission-line fit is < 10 A, or there is evidence that a broad range of spectral bins in the line center are absorbed. Quantitatively, for the last criterion, the authors require that at least 15 adjacent bins (20 for Mg II) fall >= 5% below their emission model fit, and these absorbed bins lie in the wavelength region where the emission is above the line half-maximum. The authors' fitting experience indicates that characterizing emission lines is particularly difficult in cases meeting these criteria. Low-velocity absorption is very common; nearly half of the sources with C IV BI_0 > 0 have this flag set for the C IV emission line. Setting this flag indicates that measurements of BAL troughs are less certain in cases where the BAL extends to low velocities.

Si_IV_MBB_Flag
The Si IV BALManyBadBins boolean flag. Some putative BALs consist of a large number of spectral bins that have been flagged as "bad" in the SDSS pipeline. Unfortunately, the pipeline occasionally flags bins that are acceptable, and the low flux density and signal-to-noise (S/N) in BAL troughs make them especially susceptible to flagging. The authors report the BALManyBadBins flag when > 25% of the bins in a BAL have been flagged by the SDSS. However, they ignore the flags BRIGHTSKY and EMLINE, because these warnings can be triggered by the low flux levels in strong BAL troughs.

C_IV_MBB_Flag
The C IV BALManyBadBins boolean flag. Some putative BALs consist of a large number of spectral bins that have been flagged as "bad" in the SDSS pipeline. Unfortunately, the pipeline occasionally flags bins that are acceptable, and the low flux density and signal-to-noise (S/N) in BAL troughs make them especially susceptible to flagging. The authors report the BALManyBadBins flag when > 25% of the bins in a BAL have been flagged by the SDSS. However, they ignore the flags BRIGHTSKY and EMLINE, because these warnings can be triggered by the low flux levels in strong BAL troughs.

Al_III_MBB_Flag
The Al III BALManyBadBins boolean flag. Some putative BALs consist of a large number of spectral bins that have been flagged as "bad" in the SDSS pipeline. Unfortunately, the pipeline occasionally flags bins that are acceptable, and the low flux density and signal-to-noise (S/N) in BAL troughs make them especially susceptible to flagging. The authors report the BALManyBadBins flag when > 25% of the bins in a BAL have been flagged by the SDSS. However, they ignore the flags BRIGHTSKY and EMLINE, because these warnings can be triggered by the low flux levels in strong BAL troughs.

Mg_II_MBB_Flag
The Mg II BALManyBadBins boolean flag. Some putative BALs consist of a large number of spectral bins that have been flagged as "bad" in the SDSS pipeline. Unfortunately, the pipeline occasionally flags bins that are acceptable, and the low flux density and signal-to-noise (S/N) in BAL troughs make them especially susceptible to flagging. The authors report the BALManyBadBins flag when > 25% of the bins in a BAL have been flagged by the SDSS. However, they ignore the flags BRIGHTSKY and EMLINE, because these warnings can be triggered by the low flux levels in strong BAL troughs.

C_IV_BWA_Flag
The C IV BlueWingAbs boolean flag. Additional "blue wing" emission occurs on the blue side of the C IV emission line, and absorption is apparent between the blue wing and the line core. Since the authors fit only the line core and cannot accurately reconstruct the "blue wing" emission, they could potentially miss BAL absorption in these cases. The BlueWingAbs flag is set to 1 when 15 consecutive bins redward of 1500 A lie above the model fit, and 15 more consecutive bins further redward lie below the model, and all these bins are shortward of the wavelength at which the blue side of the C IV emission line reaches its half-maximum.

SNR_1700_A
The signal-to-noise ratio S/N_1700 at 1700 A. S/N_1700 is defined as the median of the flux divided by the noise (reported by the SDSS pipeline) for all spectral bins in the 1650-1750 A region, using the intrinsic binning provided in the SDSS spectra. This wavelength region was selected to be (typically) free of strong absorption, but still near the C IV BAL region. S/N_1700 depends on many factors, including the integration time and the source redshift and luminosity; the authors use it simply to construct samples of QSOs that are less influenced by selection effects associated with low S/N.

Log_Flux_1400_A
The logarithm of the 1400-Angstrom flux density, in erg s-1 cm-2 Hz-1.

Log_Flux_2500_A
The logarithm of the 2500-Angstrom flux density, in erg s-1 cm-2 Hz-1.


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Last Modified: 27-Apr-2009