TY - JOUR
T1 - Simultaneous ultraviolet and optical emission-line profiles of quasars
T2 - Implications for black hole mass determination
AU - Ho, Luis C.
AU - Goldoni, Paolo
AU - Dong, Xiao Bo
AU - Greene, Jenny E.
AU - Ponti, Gabriele
PY - 2012/7/20
Y1 - 2012/7/20
N2 - The X-shooter instrument on the Very Large Telescope was used to obtain spectra of seven moderate-redshift quasars simultaneously covering the spectral range 3000 Å to 2.5 μm. At z 1.5, most of the prominent broad emission lines in the ultraviolet to optical region are captured in their rest frame. We use this unique data set, which mitigates complications from source variability, to intercompare the line profiles of C IV λ1549, C III] λ1909, Mg IIλ2800, and Hα and evaluate their implications for black hole (BH) mass estimation. We confirm that Mg II and the Balmer lines share similar kinematics and that they deliver mutually consistent BH mass estimates with minimal internal scatter (≲0.1dex) using the latest virial mass estimators. Although no virial mass formalism has yet been calibrated for C III], this line does not appear promising for such an application because of the large spread of its velocity width compared to lines of both higher and lower ionization; part of the discrepancy may be due to the difficulty of deblending C III] from its neighboring lines. The situation for C IV is complex and, because of the limited statistics of our small sample, inconclusive. On the one hand, slightly more than half of our sample (4/7) have C IV line widths that correlate reasonably well with Hα line widths, and their respective BH mass estimates agree to within 0.15dex. The rest, on the other hand, exhibit exceptionally broad C IV profiles that overestimate virial masses by factors of 2-5 compared to Hα. As C IV is widely used to study BH demographics at high redshifts, we urgently need to revisit our analysis with a larger sample.
AB - The X-shooter instrument on the Very Large Telescope was used to obtain spectra of seven moderate-redshift quasars simultaneously covering the spectral range 3000 Å to 2.5 μm. At z 1.5, most of the prominent broad emission lines in the ultraviolet to optical region are captured in their rest frame. We use this unique data set, which mitigates complications from source variability, to intercompare the line profiles of C IV λ1549, C III] λ1909, Mg IIλ2800, and Hα and evaluate their implications for black hole (BH) mass estimation. We confirm that Mg II and the Balmer lines share similar kinematics and that they deliver mutually consistent BH mass estimates with minimal internal scatter (≲0.1dex) using the latest virial mass estimators. Although no virial mass formalism has yet been calibrated for C III], this line does not appear promising for such an application because of the large spread of its velocity width compared to lines of both higher and lower ionization; part of the discrepancy may be due to the difficulty of deblending C III] from its neighboring lines. The situation for C IV is complex and, because of the limited statistics of our small sample, inconclusive. On the one hand, slightly more than half of our sample (4/7) have C IV line widths that correlate reasonably well with Hα line widths, and their respective BH mass estimates agree to within 0.15dex. The rest, on the other hand, exhibit exceptionally broad C IV profiles that overestimate virial masses by factors of 2-5 compared to Hα. As C IV is widely used to study BH demographics at high redshifts, we urgently need to revisit our analysis with a larger sample.
KW - galaxies: Seyfert
KW - galaxies: active
KW - galaxies: nuclei
KW - quasars: emission lines
KW - quasars: general
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U2 - 10.1088/0004-637X/754/1/11
DO - 10.1088/0004-637X/754/1/11
M3 - Article
AN - SCOPUS:84863514153
SN - 0004-637X
VL - 754
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 11
ER -