28 research outputs found
A disc wind model for blueshifts in quasar broad emission lines
Blueshifts - or, more accurately, blue asymmetries - in broad emission lines
such as CIV 1550 are common in luminous quasars and correlate with
fundamental properties such as Eddington ratio and broad absorption line (BAL)
characteristics. However, the formation of these blueshifts is still not
understood, and neither is their physical connection to the BAL phenomenon or
accretion disc. In this work, we present Monte Carlo radiative transfer and
photoionization simulations using parametrized biconical disc-wind models. We
take advantage of the azimuthal symmetry of a quasar and show that we can
reproduce CIV blueshifts provided that (i) the disc-midplane is optically thick
out to radii beyond the line formation region, so that the receding wind bicone
is obscured; and (ii) the system is viewed from relatively low (that is, more
face-on) inclinations (). We show that CIV emission line
blueshifts and BALs can form in the same wind structure. The velocity profile
of the wind has a significant impact on the location of the line formation
region and the resulting line profile, suggesting that the shape of the
emission lines can be used as a probe of wind-driving physics. While we are
successful at producing blueshifts/blue asymmetries in outflows, we struggle to
match the detailed shape or skew of the observed emission line profiles. In
addition, our models produce redshifted emission-line asymmetries for certain
viewing angles. We discuss our work in the context of the CIV 1550
emission blueshift versus equivalent-width space and explore the implications
for quasar disc wind physics.Comment: 20 pages, 12 figures + 1 appendix. Supplementary material, simulation
data and plotting scripts available at:
https://github.com/jhmatthews/blueshift
Ranking Rankine: W. J. M. Rankine (1820–72) and the Making of ‘Engineering Science’ Revisited
No redshift evolution in the rest-frame UV emission line properties of quasars from z=1.5 to z=4.0
We analyse the rest-frame UV spectra of 2,531 high-redshift (3.5<z<4.0)
quasars from the Sloan Digital Sky Survey DR16Q catalogue. In combination with
previous work, we study the redshift evolution of the rest-frame UV line
properties across the entire redshift range, 1.5<z<4.0. We improve the systemic
redshift estimates at z>3.5 using a cross-correlation algorithm that employs
high signal-to-noise template spectra spanning the full range in UV emission
line properties. We then quantify the evolution of C IV and He II emission line
properties with redshift. The increase in C IV blueshifts with cosmological
redshift can be fully explained by the higher luminosities of quasars observed
at high redshifts. We recover broadly similar trends between the He II EW and C
IV blueshift at both 1.5<z<2.65 and 3.5<z<4.0 suggesting that the blueshift
depends systematically on the spectral energy density (SED) of the quasar and
there is no evolution in the SED over the redshift range 1.5<z<4.0. C IV
blueshifts are highest when L/LEdd > 0.2 and Mbh > 10^9 Mo for the entire
1.5<z<4.0 sample. We find that luminosity matching samples as a means to
explore the evolution of their rest-frame UV emission line properties is only
viable if the samples are also matched in the Mbh - L/LEdd plane. Quasars at
z>6 are on average less massive and have higher Eddington-scaled accretion
rates than their luminosity-matched counterparts at 1.5<z<4.0, which could
explain the observed evolution in their UV line properties.Comment: Accepted for publication in MNRAS, July 5th 2023. Supplementary
material will be available online through the journa
No redshift evolution in the rest-frame UV emission line properties of quasars from z=1.5 to z=4.0
We analyse the rest-frame UV spectra of 2,531 high-redshift (3.53.5 using a cross-correlation algorithm that employs high signal-to-noise template spectra spanning the full range in UV emission line properties. We then quantify the evolution of C IV and He II emission line properties with redshift. The increase in C IV blueshifts with cosmological redshift can be fully explained by the higher luminosities of quasars observed at high redshifts. We recover broadly similar trends between the He II EW and C IV blueshift at both 1.5 0.2 and Mbh > 10^9 Mo for the entire 1.56 are on average less massive and have higher Eddington-scaled accretion rates than their luminosity-matched counterparts at 1.
Testing AGN outflow and accretion models with CIV and HeII emission line demographics in z=2 quasars
Using 190,000 spectra from the seventeenth data release of the Sloan Digital Sky Survey, we investigate the ultraviolet emission line properties in z=2 quasars. Specifically, we quantify how the shape of CIV 1549A and the equivalent width (EW) of HeII 1640A depend on the black hole mass and Eddington ratio inferred from MgII 2800A. Above L/L_Edd>0.2, there is a strong mass dependence in both CIV blueshift and HeII EW. Large CIV blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5,300 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in HeII and 2 keV strength are broadly consistent with theoretical QSOSED models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z=2 may in general have low spins. We find a dramatic switch in behaviour at L/L_Ed
A disc wind model for blueshifts in quasar broad emission lines
Blueshifts - or, more accurately, blue asymmetries - in broad emission lines such as CIV 1550 are common in luminous quasars and correlate with fundamental properties such as Eddington ratio and broad absorption line (BAL) characteristics. However, the formation of these blueshifts is still not understood, and neither is their physical connection to the BAL phenomenon or accretion disc. In this work, we present Monte Carlo radiative transfer and photoionization simulations using parametrized biconical disc-wind models. We take advantage of the azimuthal symmetry of a quasar and show that we can reproduce CIV blueshifts provided that (i) the disc-midplane is optically thick out to radii beyond the line formation region, so that the receding wind bicone is obscured; and (ii) the system is viewed from relatively low (that is, more face-on) inclinations (). We show that CIV emission line blueshifts and BALs can form in the same wind structure. The velocity profile of the wind has a significant impact on the location of the line formation region and the resulting line profile, suggesting that the shape of the emission lines can be used as a probe of wind-driving physics. While we are successful at producing blueshifts/blue asymmetries in outflows, we struggle to match the detailed shape or skew of the observed emission line profiles. In addition, our models produce redshifted emission-line asymmetries for certain viewing angles. We discuss our work in the context of the CIV 1550 emission blueshift versus equivalent-width space and explore the implications for quasar disc wind physics