Broad Emission-Line Shifts in Quasars: An Orientation Measure for Radio-Quiet Quasars?

By Gordon Richards, D. V. vanden Berk, T. Reichard, P. Hall, D. Schneider, Mark SubbaRao, A. Thakar, D. York. 2002

303 citations recorded by the source corpus.

Using a sample of 3814 quasars from the Early Data Release of the Sloan Digital Sky Survey, we confirm that high-ionization, broad emission lines, such as C IV, are significantly blueshifted with respect to low-ionization, broad emission lines, such as Mg II, which are thought to be close to the systemic redshift. We examine the velocity shifts of the Mg II and C IV emission lines with respect to [O III] and Mg II, respectively. C IV emission-line peaks have a range of shifts from a redshift of 500 km s-1 to blueshifts well in excess of 2000 km s-1 as compared with Mg II. We confirm previous results that suggest an anticorrelation between the shift of the C IV emission-line peak and the rest equivalent width of the C IV emission line. Furthermore, by creating composite quasar spectra as a function of C IV shift, we are able to study in detail the profiles of the line as a function of velocity shift. We find that the apparent shift of the C IV emission-line peak is not a shift so much as it is a lack of flux in the red wing for the composite with the largest apparent shift. This observation should strongly constrain models for the broad emission-line region in quasars. The emission-line blueshift and equivalent width of C IV are also discussed in light of the well-known anticorrelation between the equivalent width of C IV emission and continuum luminosity, otherwise known as the Baldwin effect. We further discuss the C IV emission-line shift as a function of other quasar properties, such as spectral index, radio and X-ray detection. We find a possible correlation between the C IV emission-line shifts and the radio properties of the quasars, which is suggestive of orientation as the cause of the C IV velocity shifts. Finally, we explore whether the C IV emission-line blueshifts correlate with the presence of broad absorption line absorption troughs or with narrow, "associated" absorption, and how these might be related to orientation.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/fe3e29d339fc0ab5c1bdaa32a1ed22c94c84c0d1

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Nuclear and High Energy Physics

Citations in the corpus

Gemini Near-Infrared Spectroscopy of Luminous z ∼ 6 Quasars: Chemical Abundances, Black Hole Masses, and Mg II Absorption (2007, background): “…broad emission lines such as C iv can be significantly blueshifted with respect to quasar systematic redshifts, the Mg ii emission line has a small blueshift and thus provides a reliable redshift measurement (e.g., McIntosh et al. 1999; Vanden Berk et al. 2001; Richards et al. 2002).”
An Exploratory Chandra Survey of a Well-defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars (2006, background): “Apparently unreddened quasars exhibit a range of contin- 4 Gallagher et al. uum shapes (e.g., Richards et al. 2002), and so it is not clear how to measure accurately or correct for reddening in an individual quasar.”
Iron Emission in the z = 6.4 Quasar SDSS J114816.64+525150.3 (2003, background): “Richards et al. (2002) find that the SiIV λ1400 emission line of quasars is typically not strongly blueshifted, unlike CIV; Figure 1 shows that SDSS J1148+5251 appears to follow this trend.”
MASS FUNCTIONS OF THE ACTIVE BLACK HOLES IN DISTANT QUASARS FROM THE LARGE BRIGHT QUASAR SURVEY, THE BRIGHT QUASAR SURVEY, AND THE COLOR-SELECTED SAMPLE OF THE SDSS FALL EQUATORIAL STRIPE (2009, methodology): “…on scaling relations are less robust than the reverberation mapping masses and are potentially prone to systematic uncertainties (e.g., Krolik 2001; Richards et al. 2002; Vestergaard 2004a, 2004b, 2009) they perform surprisingly well considering the circumstances (e.g., Vestergaard 2004b, 2009;…”
A Systematic Analysis of Fe II Emission in Quasars: Evidence for Inflow to the Central Black Hole (2008, background): “Richards et al. (2002b) conducted a similar investigation in their analysis of velocity shifts for the C iv line.”
Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales (2005, methodology): “…that either (1) have colors consistent with the UV-excess region of color space (u g < 0:6) but outside the region populated bywhite dwarfs (Richards et al. 2002b), (2) match amember of the faint photometric catalog of Richards et al. (2004) (extended to the DR3 region), or (3) are…”
MOLECULAR GAS IN z ∼ 6 QUASAR HOST GALAXIES (2010, background): “This is consistent with the fact that the C IV emission is typically blue-shifted from the quasar systematic redshift by up to a few thousand km s−1 (Richards et al. 2002; Goodrich et al. 2001; Ryan-Weber et al. 2009).”
The Giant Gemini GMOS survey of zem > 4.4 quasars – I. Measuring the mean free path across cosmic time (2014, background): “It is now well appreciated that the standard approach taken by the SDSS to automatically estimate quasar redshifts gives values that are systematically in error (Richards et al. 2002; Hewett & Wild 2010).”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, background): “24 Å emission line (Richards et al. 2002).”
Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤zabs < 2 (2006, background): “…in two ways: (a) via a set of rules relating to colour space for the purpose of reducing the number of false positives (e.g. white dwarfs, A stars) (Richards et al. 2002a) and (b) via the inclusion of all known X-ray and radio sources of SDSS objects (Anderson et al. 2003; Stoughton et al. 2002).”
Continuum and Emission-Line Properties of Broad Absorption Line Quasars (2003, methodology): “We then applied these color corrections to the simulated quasar colors (Fan 1999; Richards et al. 2001) that were used to test the SDSS quasar target selection algorithm (Richards et al. 2002a).”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, background): “…effect used quasar systemic redshifts based on broad emission lines, which are increasingly recognized as biased measures as a result of inflows and outflows of material (Gaskell 1982; Tytler & Fan 1992; Vanden Berk et al. 2001; Richards et al. 2002; Hennawi et al. 2006; Hennawi & Prochaska 2007).”
The clustering of intermediate-redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey (2012, background): “The next lowest ionization line typically found in quasar spectra Mg IIλ2798, which is a good redshift indicator (Richards et al. 2002b), is shifted entirely beyond the BOSSspectral coverage nearz ∼ 2.5.”
A Survey of z > 5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at z > 6 (2003, background): “Note, however, high-ionization lines such as C iv are systematically blueshifted from the system redshift, which is better traced by low-ionization lines such as Mg ii, by several hundred kilometers per second (e.g., Richards et al. 2002).”
Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars (2005, methodology): “Because such quasars are very red and faint, and can be confused with cosmic rays and brown dwarfs, we do not use the automated SDSS quasar selection algorithm (Richards et al. 2002a) to select and target them.”
UNIFICATION OF LUMINOUS TYPE 1 QUASARS THROUGH C iv EMISSION (2010, methodology): “That said, our real fear in Richards et al. (2002a) was that, since the disk-wind model of Murray et al. (1995) produces a single-peaked C IV emission line through radiative transfer effects, such effects might also alter the symmetry of the line profile.”
The Sloan Digital Sky Survey Quasar Catalog. IV. Fifth Data Release (2007, methodology): “A detailed description of the quasar selection process and possible biases can be found in Richards et al. (2002a).”
What controls the C iv line profile in active galactic nuclei (2004, background): “Richards et al. (2002) constructed composite spectra for 794 SDSS quasars based on the C iv versus Mg ii velocity shift, and also found a decreasing C iv EW with increasing shift.”
The evolution of the broad-line region among SDSS quasars (2005, methodology): “…National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc., under corporative agreement with the National Science Foundation. shifted blueward or redward compared to the quasar rest frame (e.g., Gaskell 1982; Richards et al. 2002b).”