NIR counterparts to ULXs (III): completing the photometric survey and selected spectroscopic results
Abstract
We present results from the remaining sources in our search for near-infrared (NIR) candidate counterparts to ultraluminous X-ray sources (ULXs) within ≃10 Mpc. We observed 23 ULXs in 15 galaxies and detected NIR candidate counterparts to 6 of them. Two of these have an absolute magnitude consistent with a single red supergiant (RSG). Three counterparts are too bright for an RSG and spatially extended, and thus we classify them as stellar clusters. The other candidate is too faint for an RSG. Additionally, we present the results of our NIR spectroscopic follow-up of five sources: four originally classified as RSG and one as a stellar cluster on the basis of previous photometry. The stellar cluster candidate is actually a nebula. Of the four RSG candidates, one source has a broad H α emission line redshifted by ∼z = 1, making it a background active galactic nucleus (AGN). Two other sources show stellar spectra consistent with them being RSGs. The final RSG candidate is too faint to classify, but does not show strong (nebular) emission lines in its spectrum. After our search for NIR counterparts to 113 ULXs, where we detected a candidate counterpart for 38 ULXs, we have spectroscopically confirmed the nature of 12: 5 sources are nebulae, 1 source is not classified, 1 source is an AGN, and 5 are RSGs. These possible five ULX–RSG binary systems would constitute ≃(4±2) per cent of the observed ULXs, a fraction almost four times larger than what was predicted by binary evolution simulations.
Additional Information
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2020 May 31. Received 2020 May 27; in original form 2019 October 29. Published: 07 July 2020. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme 0102.D-0529(A). We are infinitely grateful to the anonymous referee for her/his thorough comments that greatly improved this manuscript. This research is based on observations made with: (a) the WHT operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias; (b) ESO Telescopes at the La Silla Paranal Observatory; (c) the 5-m Hale Telescope at the Palomar Observatory; and (d) the Keck I Telescope at the W. M. Keck Observatory. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. KML would like to thank Mischa Schirmer for his invaluable help with the data reduction pipeline THELI and the setting/adding of new instruments to it. We have made use of the SIMBAD data base, operated at CDS, Strasbourg, France; of the NASA/IPAC Extragalactic Database (NED) that is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; and of data obtained from the Chandra Data Archive and the Chandra Source Catalog. PGJ and KML acknowledge funding from the European Research Council under ERC Consolidator Grant agreement no. 647208. MH acknowledges the ESO fellowship programme. MAPT acknowledges support via a Ramón y Cajal Fellowship (RYC-2015-17854) and support by the Spanish Ministry of Economy, Industry and Competitiveness under grant AYA2017-83216-P. TPR acknowledges funding from Science and Technology Facilities Council (STFC) as part of the consolidated grant ST/L00075X/1. DJW acknowledges support from an STFC Ernest Rutherford Fellowship. Data Availability: The data underlying this article are available in Zenodo, at https://zenodo.org/record/3903160.Attached Files
Published - staa1920.pdf
Accepted Version - 2006.02795.pdf
Supplemental Material - staa1920_supplemental_files.zip
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Additional details
- Eprint ID
- 104380
- Resolver ID
- CaltechAUTHORS:20200714-121112590
- NASA/JPL/Caltech
- 647208
- European Research Council (ERC)
- European Southern Observatory (ESO)
- RYC-2015-17854
- Ramón y Cajal Fellowship
- AYA2017-83216-P
- Ministerio de Economía, Industria y Competitividad (MINECO)
- ST/L00075X/1
- Science and Technology Facilities Council (STFC)
- Created
-
2020-07-14Created from EPrint's datestamp field
- Updated
-
2023-10-20Created from EPrint's last_modified field
- Caltech groups
- Astronomy Department, Space Radiation Laboratory