The Nature of Luminous Quasars with Very Large C IV Equivalent Widths. (arXiv:2206.11631v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fu_S/0/1/0/all/0/1">Shuqi Fu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_W/0/1/0/all/0/1">W. N. Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zou_F/0/1/0/all/0/1">Fan Zou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laor_A/0/1/0/all/0/1">Ari Laor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garmire_G/0/1/0/all/0/1">Gordon P. Garmire</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ni_Q/0/1/0/all/0/1">Qingling Ni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Timlin_J/0/1/0/all/0/1">John D. Timlin III</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xue_Y/0/1/0/all/0/1">Yongquan Xue</a>
We report results for a complete sample of ten luminous radio-quiet quasars
with large C IV equivalent widths (EW > 150 A). For 8/10 we performed Chandra
snapshot observations. We find that, in addition to the enhanced C IV line EW,
their He II and Mg II lines are enhanced, but the C III] line is not. Their
X-ray emission is substantially stronger than expected from their ultraviolet
luminosity. Additionally, these large C IV EW quasars show small C IV
blueshifts and possibly low Eddington ratios, suggesting they are “extreme low
Eigenvector 1 (EV1)” quasars. The mean excess He II EW is well-matched by
Radiation Pressure Compression (RPC) photoionization models, with the harder
aox ionizing spectrum. However, these results do not reproduce well the
enhancement pattern of the C IV, Mg II, and C III] EWs, or the observed high C
IV/Mg II ratio. RPC calculations indicate that the C IV/Mg II line ratio is an
effective metallicity indicator, and models with sub-Solar metallicity gas and
a hard ionizing continuum reproduce well the enhancement pattern of all four
ultraviolet lines. We find that the C IV/Mg II line ratio in quasars is
generally correlated with the excess X-ray emission. Extremely high EV1 quasars
are characterized by high metallicity and suppressed X-ray emission. The
underlying mechanism relating gas metallicity and X-ray emission is not clear,
but may be related to radiation-pressure driven disk winds, which are enhanced
at high metallicity, and consequent mass loading reducing coronal X-ray
emission.
We report results for a complete sample of ten luminous radio-quiet quasars
with large C IV equivalent widths (EW > 150 A). For 8/10 we performed Chandra
snapshot observations. We find that, in addition to the enhanced C IV line EW,
their He II and Mg II lines are enhanced, but the C III] line is not. Their
X-ray emission is substantially stronger than expected from their ultraviolet
luminosity. Additionally, these large C IV EW quasars show small C IV
blueshifts and possibly low Eddington ratios, suggesting they are “extreme low
Eigenvector 1 (EV1)” quasars. The mean excess He II EW is well-matched by
Radiation Pressure Compression (RPC) photoionization models, with the harder
aox ionizing spectrum. However, these results do not reproduce well the
enhancement pattern of the C IV, Mg II, and C III] EWs, or the observed high C
IV/Mg II ratio. RPC calculations indicate that the C IV/Mg II line ratio is an
effective metallicity indicator, and models with sub-Solar metallicity gas and
a hard ionizing continuum reproduce well the enhancement pattern of all four
ultraviolet lines. We find that the C IV/Mg II line ratio in quasars is
generally correlated with the excess X-ray emission. Extremely high EV1 quasars
are characterized by high metallicity and suppressed X-ray emission. The
underlying mechanism relating gas metallicity and X-ray emission is not clear,
but may be related to radiation-pressure driven disk winds, which are enhanced
at high metallicity, and consequent mass loading reducing coronal X-ray
emission.
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