A VERY LARGE ARRAY SEARCH for INTERMEDIATE-MASS BLACK HOLES in GLOBULAR CLUSTERS in M81
Change log
Authors
Abstract
jats:titleABSTRACT</jats:title> jats:pNantais et al. used the jats:italicHubble Space Telescope</jats:italic> to localize probable globular clusters (GCs) in M81, a spiral galaxy at a distance of 3.63 Mpc. Theory predicts that GCs can host intermediate-mass black holes (IMBHs) with masses jats:inline-formula jats:tex-math
</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aj523663ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Finding IMBHs in GCs could validate a formation channel for seed BHs in the early universe, bolster gravitational-wave predictions for space missions, and test scaling relations between stellar systems and the central BHs they host. We used the NRAO Karl G. Jansky Very Large Array to search for the radiative signatures of IMBH accretion from 206 probable GCs in a mosaic of M81. The observing wavelength was 5.5 cm, and the spatial resolution was 1.″5 (26.4 pc). None of the individual GCs are detected, nor are weighted-mean image stacks of the 206 GCs and the 49 massive GCs with stellar masses jats:inline-formula jats:tex-math
</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aj523663ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. We apply a semiempirical model to predict the mass of an IMBH that, if undergoing accretion in the long-lived, hard X-ray state, is consistent with a given radio luminosity. The 3jats:italicσ</jats:italic> radio-luminosity upper limits correspond to IMBH masses of jats:inline-formula jats:tex-math
</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aj523663ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for the all-cluster stack and jats:inline-formula jats:tex-math
</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aj523663ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> for the massive-cluster stack. We also apply the empirical fundamental-plane relation to two X-ray-detected clusters, finding that their individual IMBH masses at 95% confidence are jats:italicM</jats:italic> jats:subBH</jats:sub> < 99,000 jats:italicM</jats:italic> jats:sub⊙</jats:sub> and jats:inline-formula jats:tex-math
</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aj523663ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>. Finally, no analog of HLX-1, a strong IMBH candidate in an extragalactic star cluster, occurs in any individual GC in M81. This underscores the uniqueness or rarity of the HLX-1 phenomenon.</jats:p>
Description
Keywords
Journal Title
Conference Name
Journal ISSN
1538-3881