Composite Bulges. III. A Study of Nuclear Star Clusters in Nearby Spiral Galaxies

Creators: Ashok, Aishwarya¹; Seth, Anil¹; Erwin, Peter^{2, 3}; Debattista, Victor P.⁴; de Lorenzo-Cáceres, Adriana⁵; Gadotti, Dmitri A.⁶; Méndez-Abreu, Jairo^{5, 7}; Beckman, John E.^{5, 7, 8}; Bender, Ralf^{2, 3}; Drory, Niv⁹; Fisher, Deanne¹⁰; Hopp, Ulrich^{2, 3}; Kluge, Matthias^{2, 3}; Kolcu, Tutku¹¹; Maciejewski, Witold¹¹; Mehrgan, Kianusch^{2, 3}; Parikh, Taniya^{2, 3}; Saglia, Roberto^{2, 3}; Seidel, Marja^{12, 13}; Thomas, Jens^{2, 3}

1. University of Utah
2. Max Planck Society
3. Ludwig-Maximilians-Universität München
4. University of Central Lancashire
5. Instituto de Astrofísica de Canarias
6. Durham University
7. University of La Laguna
8. Spanish National Research Council
9. The University of Texas at Austin
10. Swinburne University of Technology
11. Liverpool John Moores University
12. Infrared Processing and Analysis Center
13. California Institute of Technology

Abstract

We present photometric and morphological analyses of nuclear star clusters (NSCs)—very dense, massive star clusters present in the central regions of most galaxies—in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the NSC and bulge components. We derive NSC radii and magnitudes in all three bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify NSCs in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass–NSC radius and galaxy mass–NSC mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of ∼300.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We would like to thank David Ohlson for sharing his galaxy catalog with us prepublication (Ohlson et al. 2023). We would also like to thank Luis Ho for providing us with optical images from the Carnegie-Irvine Galaxy Survey and Preben Grosbøl for providing us with near-IR images from Grosbøl & Dottori (2012).

This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program HST-GO-15133. Support for this work was provided from that program. J.M.A. acknowledges the support of the Viera y Clavijo Senior program funded by ACIISI and ULL. This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. It has also made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We also made use of data from the Sloan Digital Sky Survey.

Software References

Software: Astropy (Astropy Collaboration et al. 2013, 2018), DrizzlePac (Hack et al. 2013), imfit (Erwin 2015, v1.8), and grizli (Brammer 2019).

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