TY - JOUR
T1 - Hubble Space Telescope FUV observations of M31's globular clusters suggest a spatially homogeneous helium-enriched subpopulation
AU - Peacock, Mark B.
AU - Zepf, Stephen E.
AU - Maccarone, Thomas J.
AU - Kundu, Arunav
AU - Knigge, Christian
AU - Dieball, Andrea
AU - Strader, Jay
N1 - Publisher Copyright:
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2018/12/11
Y1 - 2018/12/11
N2 - 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.
AB - 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.
KW - Galaxies: individual:M31
KW - Galaxies: star clusters: general
KW - Globular clusters: general
KW - Stars: horizontal branch
KW - Ultraviolet: galaxies
UR - http://www.scopus.com/inward/record.url?scp=85054256966&partnerID=8YFLogxK
U2 - 10.1093/mnras/sty2461
DO - 10.1093/mnras/sty2461
M3 - Article
AN - SCOPUS:85054256966
SN - 0035-8711
VL - 481
SP - 3313
EP - 3324
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -