arXiv subjects

Thomas Dunn

Publications and source records attributed to Thomas Dunn.

4 recordsLinked to original sources

arXiv2026

Constraining the timescale of activity in Mrk 1018

We present analysis of an extended emission line region projected 3.77 kpc from the nucleus of the canonical changing-look AGN Mrk~1018, found in MUSE integral-field observations from the Close AGN Reference Survey. Emission-line ratios show that the region exhibits AGN ionisation but has a very low velocity dispersion, $77 \pm 1$ kms$^{-1}$, ruling out an ionised outflow. The lower limit on the light travel time is $12{,}300 \pm 2{,}300$ yr, implying that the nucleus has therefore been active for at least this long. This is much longer than the duration of either observed changing-look transition, which occurred over several years. This implies that Mrk 1018's multi-year variations are occurring within a longer term active phase.

astro-ph.GA↗

arXiv2026

A recurring changing state AGN discovered in the SAMI Galaxy Survey and SDSS

We present a detailed analysis of the AGN in galaxy J085337.26+014303.6 at z=0.0582. A combination of SDSS and SAMI Galaxy Survey data shows that this object has gone through at least one full changing-look AGN cycle, from type 1.9 in 2001 to type 1 in 2015 and 2021, and then type 1.9 again in 2022. While the broad lines in this object show evidence of dust obscuration, detailed spectral analysis plus WISE photometry demonstrate that the changes in this object are related to a physical state change, not changing obscuration. In fact, the WISE light curve suggests that this object may have briefly returned to a type 1.9 state in 2020. In the optical, the host galaxy dominates the light (e.g. only ~10 per cent contribution from the AGN at 4000 Angstoms within a central aperture), even in the high state. In contrast, the brightest WISE W2-band measurements place the AGN at a similar luminosity to the entire host galaxy. The broad Balmer lines show evidence of multiple components, with a weak very-broad component (FWHM=5000-6000 km/s) visible in the low type 1.9 state, and a stronger broad component of FWHM~2000 km/s dominating in the high type 1 state. We propose that this is caused by two spatially distinct regions within the broad line region.

astro-ph.GA↗

arXiv2025

A century of change: new changing-look event in Mrk 1018's past

We investigate the long-term variability of the known Changing Look Active Galactic Nuclei (CL AGN) Mrk 1018, whose second change we discovered as part of the Close AGN Reference Survey (CARS). Collating over a hundred years worth of photometry from scanned photographic plates and five modern surveys we find a historic outburst between ~1935-1960, with variation in Johnson B magnitude of ~0.8 that is consistent with Mrk 1018's brightness before and after its latest changing look event in the early 2010s. Using the combined modern and historic data, a Generalised Lomb-Scargle suggests broad feature with P = 29-47 years. Its width and stability across tests, as well as the turn-on speed and bright phase duration of the historic event suggests a timescale associated with long-term modulation, such as via rapid flickering in the accretion rate caused by the Chaotic Cold Accretion model rather than a strictly periodic CL mechanism driving changes in Mrk 1018. We also use the modern photometry to constrain Mrk 1018's latest turn-off duration to less than ~1.9 years, providing further support for a CL mechanism with rapid transition timescales, such as a changing mode of accretion.

astro-ph.GA↗

arXiv2012

A linear formula for the generalized multiplicity sequence

For an arbitrary ideal I in a local ring R and a finitely generated R-module M, we prove a formula expressing each generalized multiplicity sequence c_k(I,M) as a linear combination of certain local multiplicities. As a consequence, when M is formally equidimensional, we prove that if I is contained in J and c_k(I,M)=c_k(J,M) for all k, then I is a reduction of (J,M). The converse of this statement is also known to be true by a result of Ciuperca. This theorem gives a complete numerical characterization of the integral closure, generalizing a well known theorem of Rees.

math.AC↗