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Hubble Space Telescope FUV observations of M31's globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Hubble Space Telescope FUV observations of M31's globular clusters suggest a spatially homogeneous helium-enriched subpopulation
Hubble Space Telescope FUV observations of M31's globular clusters suggest a spatially homogeneous helium-enriched subpopulation

We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters inM31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal branch (HB) stars, which dominate the emission in the F140LP images. We confirm that some of these clusters have excess FUV emission, suggesting additional hot populations beyond those expected by canonical single stellar population models.We find no evidence that the hot populations are spatially distinct from the majority populations in these clusters, as would be expected if the excess FUV emission is a result of a dynamically enhanced population of extreme-HB stars. We conclude that a second population of stars with significantly enhanced helium abundance is a viable explanation for the observed FUV emission that is both bright and distributed similarly to the rest of the cluster light. Our results support the use of FUV observations as a path to characterizing helium-enhanced subpopulations in extragalactic clusters. These M31 clusters also show a correlation such that more massive and denser clusters are relatively FUV bright. Similar to extant Milky Way results, this may indicate the degree of helium enrichment, or second population fraction increases with cluster mass.

Galaxies: individual:M31, Galaxies: star clusters: general, Globular clusters: general, Stars: horizontal branch, Ultraviolet: galaxies
0035-8711
3313-3324
Peacock, Mark B.
e337b49e-aec5-45d4-9270-ae25c5a8b64b
Zepf, Stephen E.
108fcc75-6611-48a3-b405-99737b38af85
Maccarone, Thomas J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Kundu, Arunav
ece8dcd2-e6dc-4f02-a90b-016ba9b573ed
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Dieball, Andrea
5f595453-aa6b-4067-a3e1-026867fb9f7a
Strader, Jay
2b225e8e-ac84-429d-9f91-dc340d75e40e
Peacock, Mark B.
e337b49e-aec5-45d4-9270-ae25c5a8b64b
Zepf, Stephen E.
108fcc75-6611-48a3-b405-99737b38af85
Maccarone, Thomas J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Kundu, Arunav
ece8dcd2-e6dc-4f02-a90b-016ba9b573ed
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Dieball, Andrea
5f595453-aa6b-4067-a3e1-026867fb9f7a
Strader, Jay
2b225e8e-ac84-429d-9f91-dc340d75e40e

Peacock, Mark B., Zepf, Stephen E., Maccarone, Thomas J., Kundu, Arunav, Knigge, Christian, Dieball, Andrea and Strader, Jay (2018) Hubble Space Telescope FUV observations of M31's globular clusters suggest a spatially homogeneous helium-enriched subpopulation. Monthly Notices of the Royal Astronomical Society, 481 (3), 3313-3324. (doi:10.1093/mnras/sty2461).

Record type: Article

Abstract

We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters inM31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal branch (HB) stars, which dominate the emission in the F140LP images. We confirm that some of these clusters have excess FUV emission, suggesting additional hot populations beyond those expected by canonical single stellar population models.We find no evidence that the hot populations are spatially distinct from the majority populations in these clusters, as would be expected if the excess FUV emission is a result of a dynamically enhanced population of extreme-HB stars. We conclude that a second population of stars with significantly enhanced helium abundance is a viable explanation for the observed FUV emission that is both bright and distributed similarly to the rest of the cluster light. Our results support the use of FUV observations as a path to characterizing helium-enhanced subpopulations in extragalactic clusters. These M31 clusters also show a correlation such that more massive and denser clusters are relatively FUV bright. Similar to extant Milky Way results, this may indicate the degree of helium enrichment, or second population fraction increases with cluster mass.

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Accepted/In Press date: 5 September 2018
e-pub ahead of print date: 10 September 2018
Published date: 11 December 2018
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: [2018] [The Authors] Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Keywords: Galaxies: individual:M31, Galaxies: star clusters: general, Globular clusters: general, Stars: horizontal branch, Ultraviolet: galaxies

Identifiers

Local EPrints ID: 425960
URI: http://eprints.soton.ac.uk/id/eprint/425960
ISSN: 0035-8711
PURE UUID: 3e3b051c-87c2-4a57-8a9b-de78c662440a

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Date deposited: 07 Nov 2018 17:30
Last modified: 07 Oct 2020 00:58

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Contributors

Author: Mark B. Peacock
Author: Stephen E. Zepf
Author: Thomas J. Maccarone
Author: Arunav Kundu
Author: Andrea Dieball
Author: Jay Strader

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