GALEX ultraviolet photometry of globular clusters in M31

Three-year results and a catalog

Soo Chang Rey, R. Michael Rich, Sangmo T. Sohn, Seok-Jin Yoon, Chul Chung, Sukyoung Yi, Young-Wook Lee, Jaehyon Rhee, Luciana Bianchi, Barry F. Madore, Kyungsook Lee, Tom A. Barlow, Karl Forster, Peter G. Friedman, D. Christopher Martin, Patrick Morrissey, Susan G. Neff, David Schiminovich, Mark Seibert, Todd Small & 6 others Ted K. Wyder, José Donas, Timothy M. Heckman, Bruno Milliard, Alex S. Szalay, Barry Y. Welsh

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Abstract

We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV) and far-ultraviolet (FUV), respectively. The UV properties of GCs have been analyzed using various combinations of UV-optical and optical-optical colors. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H] > -1) GCs in M31 produce significant FUV flux making their FUV- V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs, NGC 6388 and NGC 6441, with extended blue HB stars. Based on the models incorporating helium enriched subpopulations in addition to the majority of the population that have a normal helium abundance, we suggest that even small fraction of super-helium-rich subpopulations in GCs can reproduce the observed UV bright metal-rich GCs. Young clusters in M31 show distinct UVand optical properties from GCs in Milky Way. Population models indicate that their typical age is less than ∼2 Gyr and is consistent with the age derived from the most recent high-quality spectroscopic observations. A large fraction of young GCs have the kinematics of the thin, rapidly rotating disk component. Most GCs with bulge kinematics show old ages. The existence of young GCs on the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the thin-disk of M31. We detect 12(10) intermediate-age GC candidates in NUV (FUV) identified by previous spectroscopic observations. On the basis of comparing our UV photometry to population models, we suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB stars which contribute to enhanced UV flux as well as Balmer lines.

Original languageEnglish
Pages (from-to)643-658
Number of pages16
JournalAstrophysical Journal, Supplement Series
Volume173
Issue number2
DOIs
Publication statusPublished - 2007 Dec 1

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ultraviolet photometry
globular clusters
catalogs
galaxies
helium
subpopulation
kinematics
metal
optical property

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science

Cite this

Rey, Soo Chang ; Rich, R. Michael ; Sohn, Sangmo T. ; Yoon, Seok-Jin ; Chung, Chul ; Yi, Sukyoung ; Lee, Young-Wook ; Rhee, Jaehyon ; Bianchi, Luciana ; Madore, Barry F. ; Lee, Kyungsook ; Barlow, Tom A. ; Forster, Karl ; Friedman, Peter G. ; Martin, D. Christopher ; Morrissey, Patrick ; Neff, Susan G. ; Schiminovich, David ; Seibert, Mark ; Small, Todd ; Wyder, Ted K. ; Donas, José ; Heckman, Timothy M. ; Milliard, Bruno ; Szalay, Alex S. ; Welsh, Barry Y. / GALEX ultraviolet photometry of globular clusters in M31 : Three-year results and a catalog. In: Astrophysical Journal, Supplement Series. 2007 ; Vol. 173, No. 2. pp. 643-658.
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abstract = "We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV) and far-ultraviolet (FUV), respectively. The UV properties of GCs have been analyzed using various combinations of UV-optical and optical-optical colors. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H] > -1) GCs in M31 produce significant FUV flux making their FUV- V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs, NGC 6388 and NGC 6441, with extended blue HB stars. Based on the models incorporating helium enriched subpopulations in addition to the majority of the population that have a normal helium abundance, we suggest that even small fraction of super-helium-rich subpopulations in GCs can reproduce the observed UV bright metal-rich GCs. Young clusters in M31 show distinct UVand optical properties from GCs in Milky Way. Population models indicate that their typical age is less than ∼2 Gyr and is consistent with the age derived from the most recent high-quality spectroscopic observations. A large fraction of young GCs have the kinematics of the thin, rapidly rotating disk component. Most GCs with bulge kinematics show old ages. The existence of young GCs on the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the thin-disk of M31. We detect 12(10) intermediate-age GC candidates in NUV (FUV) identified by previous spectroscopic observations. On the basis of comparing our UV photometry to population models, we suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB stars which contribute to enhanced UV flux as well as Balmer lines.",
author = "Rey, {Soo Chang} and Rich, {R. Michael} and Sohn, {Sangmo T.} and Seok-Jin Yoon and Chul Chung and Sukyoung Yi and Young-Wook Lee and Jaehyon Rhee and Luciana Bianchi and Madore, {Barry F.} and Kyungsook Lee and Barlow, {Tom A.} and Karl Forster and Friedman, {Peter G.} and Martin, {D. Christopher} and Patrick Morrissey and Neff, {Susan G.} and David Schiminovich and Mark Seibert and Todd Small and Wyder, {Ted K.} and Jos{\'e} Donas and Heckman, {Timothy M.} and Bruno Milliard and Szalay, {Alex S.} and Welsh, {Barry Y.}",
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Rey, SC, Rich, RM, Sohn, ST, Yoon, S-J, Chung, C, Yi, S, Lee, Y-W, Rhee, J, Bianchi, L, Madore, BF, Lee, K, Barlow, TA, Forster, K, Friedman, PG, Martin, DC, Morrissey, P, Neff, SG, Schiminovich, D, Seibert, M, Small, T, Wyder, TK, Donas, J, Heckman, TM, Milliard, B, Szalay, AS & Welsh, BY 2007, 'GALEX ultraviolet photometry of globular clusters in M31: Three-year results and a catalog', Astrophysical Journal, Supplement Series, vol. 173, no. 2, pp. 643-658. https://doi.org/10.1086/516649

GALEX ultraviolet photometry of globular clusters in M31 : Three-year results and a catalog. / Rey, Soo Chang; Rich, R. Michael; Sohn, Sangmo T.; Yoon, Seok-Jin; Chung, Chul; Yi, Sukyoung; Lee, Young-Wook; Rhee, Jaehyon; Bianchi, Luciana; Madore, Barry F.; Lee, Kyungsook; Barlow, Tom A.; Forster, Karl; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Seibert, Mark; Small, Todd; Wyder, Ted K.; Donas, José; Heckman, Timothy M.; Milliard, Bruno; Szalay, Alex S.; Welsh, Barry Y.

In: Astrophysical Journal, Supplement Series, Vol. 173, No. 2, 01.12.2007, p. 643-658.

Research output: Contribution to journalArticle

TY - JOUR

T1 - GALEX ultraviolet photometry of globular clusters in M31

T2 - Three-year results and a catalog

AU - Rey, Soo Chang

AU - Rich, R. Michael

AU - Sohn, Sangmo T.

AU - Yoon, Seok-Jin

AU - Chung, Chul

AU - Yi, Sukyoung

AU - Lee, Young-Wook

AU - Rhee, Jaehyon

AU - Bianchi, Luciana

AU - Madore, Barry F.

AU - Lee, Kyungsook

AU - Barlow, Tom A.

AU - Forster, Karl

AU - Friedman, Peter G.

AU - Martin, D. Christopher

AU - Morrissey, Patrick

AU - Neff, Susan G.

AU - Schiminovich, David

AU - Seibert, Mark

AU - Small, Todd

AU - Wyder, Ted K.

AU - Donas, José

AU - Heckman, Timothy M.

AU - Milliard, Bruno

AU - Szalay, Alex S.

AU - Welsh, Barry Y.

PY - 2007/12/1

Y1 - 2007/12/1

N2 - We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV) and far-ultraviolet (FUV), respectively. The UV properties of GCs have been analyzed using various combinations of UV-optical and optical-optical colors. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H] > -1) GCs in M31 produce significant FUV flux making their FUV- V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs, NGC 6388 and NGC 6441, with extended blue HB stars. Based on the models incorporating helium enriched subpopulations in addition to the majority of the population that have a normal helium abundance, we suggest that even small fraction of super-helium-rich subpopulations in GCs can reproduce the observed UV bright metal-rich GCs. Young clusters in M31 show distinct UVand optical properties from GCs in Milky Way. Population models indicate that their typical age is less than ∼2 Gyr and is consistent with the age derived from the most recent high-quality spectroscopic observations. A large fraction of young GCs have the kinematics of the thin, rapidly rotating disk component. Most GCs with bulge kinematics show old ages. The existence of young GCs on the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the thin-disk of M31. We detect 12(10) intermediate-age GC candidates in NUV (FUV) identified by previous spectroscopic observations. On the basis of comparing our UV photometry to population models, we suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB stars which contribute to enhanced UV flux as well as Balmer lines.

AB - We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV) and far-ultraviolet (FUV), respectively. The UV properties of GCs have been analyzed using various combinations of UV-optical and optical-optical colors. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H] > -1) GCs in M31 produce significant FUV flux making their FUV- V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs, NGC 6388 and NGC 6441, with extended blue HB stars. Based on the models incorporating helium enriched subpopulations in addition to the majority of the population that have a normal helium abundance, we suggest that even small fraction of super-helium-rich subpopulations in GCs can reproduce the observed UV bright metal-rich GCs. Young clusters in M31 show distinct UVand optical properties from GCs in Milky Way. Population models indicate that their typical age is less than ∼2 Gyr and is consistent with the age derived from the most recent high-quality spectroscopic observations. A large fraction of young GCs have the kinematics of the thin, rapidly rotating disk component. Most GCs with bulge kinematics show old ages. The existence of young GCs on the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the thin-disk of M31. We detect 12(10) intermediate-age GC candidates in NUV (FUV) identified by previous spectroscopic observations. On the basis of comparing our UV photometry to population models, we suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB stars which contribute to enhanced UV flux as well as Balmer lines.

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