93 research outputs found
A Thirty-Four Billion Solar Mass Black Hole in SMSS J2157-3602, the Most Luminous Known Quasar
From near-infrared spectroscopic measurements of the MgII emission line
doublet, we estimate the black hole (BH) mass of the quasar, SMSS
J215728.21-360215.1, as being (3.4 +/- 0.6) x 10^10 M_sun and refine the
redshift of the quasar to be z=4.692. SMSS J2157 is the most luminous known
quasar, with a 3000A luminosity of (4.7 +/- 0.5) x 10^47 erg/s and an estimated
bolometric luminosity of 1.6 x 10^48 erg/s, yet its Eddington ratio is only
~0.4. Thus, the high luminosity of this quasar is a consequence of its
extremely large BH -- one of the most massive BHs at z > 4.Comment: 7 pages, 3 figures. Accepted for publication in MNRA
Spatially Dependent Photometric Activity of M dwarfs in the Solar Cylinder
We study the relationship between Galactic location () and photometric
activity for 3.6 million M dwarf stars within 1 kpc of the Sun. For this
purpose, we identify 906 unique flare events as a proxy for magnetic activity
from the SkyMapper Southern Survey DR3. We adopt vertical distance from
the Galactic disc as a proxy for age and confirm a strong trend of flaring
fraction decreasing with growing stellar age. Among M dwarfs within 50 pc of
the Sun, we find a flaring fraction of 1-in-1,500, independent of spectral type
from M2 to M7, suggesting that these stars are all in a flare-saturated young
evolutionary stage. We find a hint of a kink in the slope of the overall flare
fraction near 100 pc from the plane, where a steep decline begins; this slope
change is visible for mid-type M dwarfs (M3--M5), suggesting it is not an
artefact of mixing spectral type. Together with SDSS H emission, this
trend is additional evidence that the activity fraction of M dwarfs depends on
Galactic height and activity lifetime. While there is a hint of flattening of
the overall activity fraction above 500 pc, our data do not
constrain this further. Within 500 pc distance from the Sun, we find no
sign of radial disk gradients in flare activity, which may only be revealed by
samples covering a larger radial range.Comment: 13 pages, 11 figures, Accepted for publication in MNRA
SkyMapper SEDs of nearby galaxies: quenching and bursting probed by a change index for star formation
The wish list of astronomers includes a tool that reveals quenching of star
formation in galaxies directly as it proceeds. Here, we present a
proof-of-concept for a new quenching-and-bursting diagnostic, a "change index"
for star formation, that requires only photometric data, provided they include
filters such as the violet bands used by SkyMapper. The index responds
mostly to changes in star-formation rate on a timescale of 20 to 500 Myr and is
nearly insensitive to dust extinction. It works effectively to distances of 100
to 150 Mpc. We explore its application to eight example galaxies in SkyMapper
DR2, including known E+A and Seyfert-1 galaxies. Owing to the degeneracies
inherent in broad-band photometry, the change index can only be a qualitative
indicator of changes in star-formation rate. But once the SkyMapper Southern
Survey is complete, the change index will be available for every spatial
resolution element of every galaxy in the Southern sky within its working
distance range.Comment: 20 pages, 14 figures, submitted to PAS
Ultraluminous Quasars At High Redshift Show Evolution In Their Radio-Loudness Fraction In Both Redshift And Ultraviolet Luminosity
We take a sample of 94 ultraluminous, optical quasars from the search of over
14,486 deg^2 by Onken et al. 2022 in the range 4.4<redshift<5.2 and match them
against the Rapid ASKAP Continuum Survey (RACS) observed on the Australian
Square Kilometre Array Pathfinder (ASKAP). From this most complete sample of
the bright end of the redshift ~5 quasar luminosity function, there are 10
radio continuum detections of which 8 are considered radio-loud quasars. The
radio-loud fraction for this sample is 8.5 \pm 2.9 per cent. Jiang et al. 2007
found that there is a decrease in the radio-loud fraction of quasars with
increasing redshift and an increase with increasing absolute magnitude at rest
frame 2500 Angstroms. We show that the radio-loud fraction of our quasar sample
is consistent with that predicted by Jiang et al. 2007, extending their result
to higher redshifts.Comment: Accepted by MNRA
Reverberation Mapping of IC4329A
We present the results of a new reverberation mapping campaign for the
broad-lined active galactic nucleus (AGN) in the edge-on spiral IC4329A.
Monitoring of the optical continuum with band photometry and broad
emission-line flux variability with moderate-resolution spectroscopy allowed
emission-line light curves to be measured for H, H, and HeII
. We find a time delay of days for H,
a similar time delay of days for H, and an
unresolved time delay of days for HeII. The time delay for
H is consistent with the predicted value from the relationship between
AGN luminosity and broad line region radius, after correction for the
mag of intrinsic extinction at 5100A. Combining the measured time
delay for H with the broad emission line width and an adopted value of
, we find a central supermassive black hole mass of
. Velocity-resolved time
delays were measured across the broad H emission-line profile and may be
consistent with an ''M''-like shape. Modeling of the full reverberation
response of H was able to provide only modest constraints on some
parameters, but does exhibit agreement with the black hole mass and average
time delay. The models also suggest that the AGN structure is misaligned by a
large amount from the edge-on galaxy disk. This is consistent with expectations
from the unified model of AGNs, in which broad emission lines are expected to
be visible only for AGNs that are viewed at relatively face-on inclinations.Comment: 12 pages, 6 figures, 3 tables; accepted for publication in Ap
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