Narrow-Line Seyfert 1 Galaxies Beyond the Local X-ray Universe: An X-ray spectral sample

Kavli Affiliate: R. G. McMahon

| First 5 Authors: Jiachen Jiang, Dominic J. Walton, Luigi C. Gallo, Andrew C. Fabian, Dirk Grupe

| Summary:

Narrow-line Seyfert 1 AGNs (NLS1s) represent a unique stage in the black hole
growth history, characterised by low black hole masses of approximately
$10^{6}$-$10^{8}$ solar masses and around-Eddington accretion rates. X-ray
studies of NLS1s have largely been confined to the local Universe ($z < 0.2$),
while their broad-line counterparts and radio-loud quasars have been more
extensively investigated at higher redshifts. In this work, we conducted an
X-ray spectral analysis for 14 SDSS-observed NLS1s at $zapprox1$ in the eRASS1
catalogue. We found that all of their eROSITA observations agree with the
expected rest-frame 2 keV monochromatic luminosity given their rest-frame 2500
angstrom monochromatic luminosity, further supporting evidence of AGN emission.
Second, when fitted with a power-law model, most continuum spectra between
0.7-7 keV in their rest frames necessitate photon indices $Gammagtrsim2.5$.
Notably, the highest photon index of around 4.7 in one of our NLS1 AGNs hints
at a significant contribution from soft excess emission. Finally, our analysis
demonstrates that we can align the Eddington ratios with optical measurements
by applying a correction factor between 10-120 to their X-ray luminosity.
Although measurement uncertainty remains considerable, our findings suggest
that assumptions for the standard geometrically thin accretion disc model made
in previous estimations of this correction factor may not apply to near or
super-Eddington NLS1 AGNs. Finally, we also compare this sample with extremely
variable nearby NLS1s and other X-ray-weak AGNs, such as JWST-observed,
broad-line AGNs at $z=5-6$, and underscores the importance of deeper X-ray
surveys for more X-ray-weak NLS1s.

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