1,151 research outputs found
MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources
that change type within a short timescale of years or decades. This change is
characterised by the appearance or disappearance of broad emission lines, often
associated with dramatic AGN continuum flux changes that are orders of
magnitude larger than those expected from typical AGN variability. In this work
we study for the first time the host galaxy of a changing-look AGN, Mrk 590,
using high spatial resolution optical and near-infrared observations. We
discover that after ~ 10 yr absence, the optical broad emission lines of Mrk
590 have reappeared. The AGN optical continuum flux however, is still ~ 10
times lower than that observed during the most luminous state in the 1990s. The
host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and
cold molecular gas emission. Extended ionised and warm molecular gas emission
are detected in the nucleus, indicating that there is a reservoir of gas as
close as 60 pc from the black hole. We observe a nuclear gas spiral between
radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able
to drive the necessary gas to fuel AGN. We also discover blue-shifted and high
velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a
nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance
between gas inflow and outflow in the nucleus of the galaxy.Comment: Accepted for publication in MNRA
Modulation of charge-density waves by superlattice structures
We discuss the interplay between electronic correlations and an underlying
superlattice structure in determining the period of charge density waves
(CDW's), by considering a one-dimensional Hubbard model with a repeated
(non-random) pattern of repulsive (U>0) and free (U=0) sites. Density matrix
renormalization group diagonalization of finite systems (up to 120 sites) is
used to calculate the charge-density correlation function and structure factor
in the ground state. The modulation period can still be predicted through
effective Fermi wavevectors, k_F*, and densities, and we have found that it is
much more sensitive to electron (or hole) doping, both because of the narrow
range of densities needed to go from q*=0 to \pi, but also due to sharp
2k_F*-4k_F* transitions; these features render CDW's more versatile for actual
applications in heterostructures than in homogeneous systems.Comment: 4 pages, 5 figures, to appear in Phys Rev
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