Broad and Luminous [OIII] and [NII] in Globular Cluster ULXs

Abstract

We consider an accretion-disc origin for the broad and luminous forbidden-line emission observed in ultraluminous X-ray (ULX) sources CXOJ033831.8-352604 and XMMU 122939.7+075333 in globular clusters hosted by elliptical galaxies NGC 1399 and NGC 4472, respectively. We will refer to the latter by the globular cluster name RZ2109. The first has strong [OIII] and [NII], the second only [OIII]. Both H$\alpha$ and H$\beta$ are very weak or undetected in both objects. We assume that the large line widths are due to Keplerian rotation around a compact object and derive expressions for maximum line luminosities. These idealized models require central masses $\gtrsim 100$ and $\gtrsim30000\Msun$ for CXOJ033831.8-352604 and RZ2109, respectively. An independent, bootstrap argument for the total disc mass yields, for both systems, $M_{\mathrm{disc}}\gtrsim10^{-4}\Msun$ for a purely metallic disc (and two orders of magnitude larger for solar metallicities). If Roche-lobe overflow is implicated, viscous time-scales are $\gtrsim 300$ yr. Standard disc theory then offers another limit on the central masses. Lobe radii for a $\sim1\Msun$ donor are $\gtrsim 10^{13}$ cm. We therefore rule out Roche-lobe overflow of a white dwarf in both systems. Red giants could fill the necessary lobes. Whether they are too metal-poor to produce the strong forbidden lines without strong hydrogen emission is unclear.

Accepted to MNRAS Letters, 5 pages, 6 figures

References in corpus (5)

• Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
• Very Broad [O III]4959,5007 Emission from the NGC 4472 Globular Cluster RZ2109 and Implications for the Mass of Its Black Hole X-ray Source
• Accretion Rates and Beaming in Ultraluminous X-ray Sources
• [OIII] 5007 Emission from the Black-Hole X-ray Binary in a NGC 4472 Globular Cluster
• Detailed Atmosphere Model Fits to Disk-Dominated ULX Spectra

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• Fading of the X-ray flux from the black hole in the NGC 4472 globular cluster RZ 2109
• Broad Components in Optical Emission Lines from the Ultra-Luminous X-ray Source NGC 5408 X-1
• Towards a dynamical mass of the ultraluminous X-ray source NGC 5408 X-1
• Luminous [O III] and [N II] from Tidally Disrupted Horizontal Branch Stars
• Spatially resolved spectroscopy of the globular cluster RZ 2109 and the nature of its black hole
• Velocity Structure and Variability of [O III] Emission in Black Hole Host Globular Cluster RZ2109
• Broad [OIII] in the globular cluster RZ 2109: X-ray ionized nova ejecta?
• An Extreme Ultra-Compact X-ray Binary in a Globular Cluster: Multi-Wavelength Observations of RZ2109 Explored in a Triple System Framework