Browsing by Author "Reines, Amy E"

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Intermediate-mass black holes and the Fundamental Plane of black hole accretion
(Oxford University Press, 2022-09) Gültekin, Kayhan; Nyland, Kristina; Gray, Nichole; Fehmer, Greg; Huang, Tianchi; Sparkman, Matthew; Reines, Amy E; Greene, Jenny E; Cackett, Edward M; Baldassare, Vivienne
We present new 5 GHz Very Large Array observations of a sample of eight active intermediate-mass black holes with masses 104.9 M⊙ < M < 106.1 M⊙ found in galaxies with stellar masses M* < 3 × 109 M⊙. We detected five of the eight sources at high significance. Of the detections, four were consistent with a point source, and one (SDSS J095418.15+471725.1, with black hole mass M < 105 M⊙) clearly shows extended emission that has a jet morphology. Combining our new radio data with the black hole masses and literature X-ray measurements, we put the sources on the Fundamental Plane of black hole accretion. We find that the extent to which the sources agree with the Fundamental Plane depends on their star-forming/composite/active galactic nucleus (AGN) classification based on optical narrow emission-line ratios. The single star-forming source is inconsistent with the Fundamental Plane. The three composite sources are consistent, and three of the four AGN sources are inconsistent with the Fundamental Plane. We argue that this inconsistency is genuine and not a result of misattributing star formation to black hole activity. Instead, we identify the sources in our sample that have AGN-like optical emission-line ratios as not following the Fundamental Plane and thus caution the use of the Fundamental Plane to estimate masses without additional constraints, such as radio spectral index, radiative efficiency, or the Eddington fraction.
Multiwavelength scrutiny of X-ray sources in dwarf galaxies: ULXs versus AGNs
(Oxford University Press, 2023-01) Thygesen, Erica; Plotkin, Richard M; Soria, Roberto; Reines, Amy E; Greene, Jenny E; Anderson, Gemma E; Baldassare, Vivienne F; Owens, Milo G; Urquhart, Ryan T; Gallo, Elena; Miller-Jones, James C A; Paul, Jeremiah D; Rollings, Alexandar P
Owing to their quiet evolutionary histories, nearby dwarf galaxies (stellar masses M⋆≲3×109M⊙⁠) have the potential to teach us about the mechanism(s) that ‘seeded’ the growth of supermassive black holes, and also how the first stellar mass black holes formed and interacted with their environments. Here, we present high spatial resolution observations of three dwarf galaxies in the X-ray (Chandra), the optical/near-infrared (Hubble Space Telescope), and the radio (Karl G. Jansky Very Large Array). These three galaxies were previously identified as hosting candidate active galactic nuclei on the basis of lower resolution X-ray imaging. With our new observations, we find that X-ray sources in two galaxies (SDSS J121326.01+543631.6 and SDSS J122111.29+173819.1) are off-nuclear and lack corresponding radio emission, implying they are likely luminous X-ray binaries. The third galaxy (Mrk 1434) contains two X-ray sources (each with LX ≈ 1040 erg s−1) separated by 2.8 arcsec, has a low metallicity [12 + log(O/H) = 7.8], and emits nebular He ii λ4686 line emission. The northern source has spatially coincident point-like radio emission at 9.0 GHz and extended radio emission at 5.5 GHz. We discuss X-ray binary interpretations (where an ultraluminous X-ray source blows a ‘radio bubble’) and active galactic nucleus interpretations (where an ≈4×105M⊙ black hole launches a jet). In either case, we find that the He ii emission cannot be photoionized by the X-ray source, unless the source was ≈30–90 times more luminous several hundred years ago.