The Murmur of the Sleeping Black Hole: Detection of Nuclear Ultraviolet Variability in LINER Galaxies

By D. Maoz, N. Nagar, Heino Falcke, A. S. Wilson. 2005

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LINER nuclei, which are present in many nearby galactic bulges, may be the manifestation of low-rate or low-radiative-efficiency accretion onto supermassive central black holes. However, it has been unclear whether the compact UV nuclear sources present in many LINERs are clusters of massive stars, rather than being directly related to the accretion process. We have used the Hubble Space Telescope to monitor the UV variability of a sample of 17 galaxies with LINER nuclei and compact nuclear UV sources. Fifteen of the 17 galaxies were observed more than once, with two to five epochs per galaxy, spanning up to a year. We detect significant variability in most of the sample, with peak-to-peak amplitudes from a few percent to 50%. In most cases, correlated variations are seen in two independent bands (F250W and F330W). Comparison to previous UV measurements indicates, for many objects, long-term variations by factors of a few over decade timescales. Variability is detected in LINERs with and without detected compact radio cores, in LINERs that have broad Hα wings detected in their optical spectra ("LINER 1s"), and in those that do not ("LINER 2s"). This variability demonstrates the existence of a nonstellar component in the UV continuum of all types and sets a lower limit to the luminosity of this component. Interestingly, all the LINERs that have detected radio cores have variable UV nuclei, as one would expect from bona fide active galactic nuclei. We note a trend in the UV color (F250W/F330W) with spectral type—LINER 1s tend to be bluer than LINER 2s. This trend may indicate a link between the shape of the nonstellar continuum and the presence or the visibility of a broad-line region. In one target, the poststarburst galaxy NGC 4736, we detect variability in a previously noted UV source that is offset by 2.″5 (~60 pc in projection) from the nucleus. This may be the nearest example of a binary active nucleus and of the process leading to black hole merging.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/978f4719070c387d179d5260a4c74faa7695d985

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Citations in the corpus

Refining the fundamental plane of accreting black holes (2006, methodology): “For nearby AGN we use updated distances from Maoz et al. (2005); Tonry et al. (2001).”
Active galactic nuclei: what’s in a name? (2017, background): “A clear case among the observational evidence (e.g. Chiaberge et al. 1999; Maoz et al. 2005; Müller-Sánchez et al. 2013) is the nearby LEG M87, that has been shown to lack the thermal radiation of the torus (Whysong and Antonucci 2004; Perlman et al. 2007).”
The Coincidence of Nuclear Star Clusters and Active Galactic Nuclei (2008, background): “Several recent studies of LINER galaxies suggest that a majority of them do in fact indicate the presence of an MBH based on high resolution radio observations (Nagar et al. 2005), Xray emission (Dudik et al. 2005; González-Mart́ın et al. 2006), and UV variability (Maoz et al. 2005).”
Evolution of broad-line emission from active galactic nuclei (2013, unknown): “This is qualitatively consistent with the detection of variable nuclear ultraviolet emission in type 2 LINERs (Maoz et al. 2005) and X-ray cores with low levels of intrinsic absorption (Ho 2008, and references therein).”
The AGN-obscuring Torus: The End of the “Doughnut” Paradigm? (2006, unknown): “In fact, among the LINERs monitored and found to be variable by Maoz et al. (2005), there were both sources with broad H a wings (type 1) and those without (type 2).”
The host galaxies and classification of active galactic nuclei (2006, background): “…Fellow; kewley@ifa.hawaii.edu 1997; Bower et al. 1996), while others have compact radio cores (Falcke et al. 2000; Ulvestad & Ho 2001; Filho et al. 2002, 2004; Anderson et al. 2004), evidence for hard Xray spectra (Terashima et al. 2000; Ho et al. 2001), and/or UV variability (Maoz et al. 2005).”
Observational evidence for intermediate-mass black holes (2017, background): “…line region (LINERs) are associated with low-luminosity AGN (e.g., Nagar et al. 2005; Mezcua & Prieto 2014) (Binder et al. 2011), UV variability (Maoz et al. 2005), unresolved and variable hot dust emission (Seth et al. 2010), and mid-infrared (MIR) AGN-like emission lines (Satyapal et al.…”
THE NGC 404 NUCLEUS: STAR CLUSTER AND POSSIBLE INTERMEDIATE-MASS BLACK HOLE (2010, background): “…do in fact appear to be AGN, with a majority of them having detected X-ray cores (Dudik et al. 2005; González-Mart́ın et al. 2006; Zhang et al. 2009), radio cores (Nagar et al. 2005), and many of them possesing mid-IR coronal lines (Satyapal et al. 2004) and UV variable cores (Maoz et al. 2005).”
OPTICAL DISCOVERY OF PROBABLE STELLAR TIDAL DISRUPTION FLARES (2010, background): “…tidal flare found in UV and X-ray surveys is not an exceptionally variable AGN is hampered because, although the amplitude of AGN variability at these wavelengths is much greater than in the optical (Maoz et al. 2005; Saxtonet al. 2011), the range of variation has not yet been well-characterized.”
Nuclear Activity in Nearby Galaxies (2008, background): “There is certainly no indication that type 2 sources are preferentially brighter in the UV; in the case of LINERs, type 2 sources, if anything, tend to be redder than type 1 sources (Maoz et al. 2005).”
Dynamics of triple black hole systems in hierarchically merging massive galaxies (2006, background): “Maoz et al. (1995, 2005) observed a variable UV source, possibly a second active nucleus, at a projected separation of ∼ 60 pc from the primary nucleus in the spiral galaxy NGC 4736, which shows signs of a recent merger.”