Evidences of Multiple Populations in GCs

GMT2010: Opening a New Frontier with the GMT (Oct. 2010) Jae-Woo Lee : Ca uvby Survey of GCs

Evidences of Multiple Populations in GCs


Multiple Populations of GCs Seen from

Ca uvby Photometry

Jae-Woo LeeDept. Astronomy & Space Science, Sejong Univ.

Astrophysical Research Center for the Structure and Evolution of the Cosmos

Center for Galaxy Evolution Research


Ca by system

• Ca H & K lines have been frequently used to calibrate metallicity for GCs (e.g. Zinn’s work in the 80s)

• The Ca filter was introduced by Bruce W. Carney in searching for metal poor halo stars (pre-CCD era).

• Later, Twarog + Anthony-Twarog expanded the Ca system in conjunction with the Stromgren system (Extended Stromgren system).


Utility of the Extended Stromgren photometric System

• hk index has half the sensitivity of m1 to reddening and twice the sensitivity to metallicity changes.– E(hk)/E(b-y) = -0.15– E(b-y) = 0.73E(B-V)

hk = (Ca–b) – (b–y)

m1 = (v-b) – (b-y)


M22 (Lee et al. 2009; Lee 2010, in prep)M22 (Lee et al. 2009; Lee 2010, in prep)


Sejong/ARCSEC Ca uvby Survey(launched in 2006 after 2 years’ of preparation)

1. Homogeneous photometry of GCs.- Flux limited blind survey : No prerequisite info. to select target

GCs.

2. Galactic Bulge formation & metal-poor stars in the Bulge.

3. Nearby dwarf galaxies.

Since 2009, + Yonsei (Y.-W. Lee, S.-I. Han) + UNC (B. W. Carney, B. Pohl)


Current Status(End of Phase I)

• So far,– ~ 150 nights with CTIO 1m tel + 4K CCD (2006 - 2010)– 7 nights with SOAR 4.2m/SOI (2009 – 2010, +UNC)– 3 nights with CTIO 4m/MOSAIC (July 2009, +Yonsei)

– ~ 60 GCs in southern hemisphere.– BW fields (2.5 sqr deg) + Disk fields + CMa fields– Sculptor

– All data have been fully reduced & calibrated except for those from in Aug 2010.

– Very homogeneous photometry :• A single instrument setup for most GCs.• Same observer + reduction methods (all done by J.-W. Lee).

- Will move on to Phase II in 2011.


Estimated Error BudgetsEstimated Error Budgets(for RGBs in typical GCs)(for RGBs in typical GCs)


Influence of elemental abundances on the hk index(hk index is a measure of calcium abundances)

Δhk

[Ca/H] = +0.3 +0.127

ΔY = +0.1 -0.002

Δ[C/Fe] = +1.0 -0.007

Δ[N/Fe] = +1.0 +0.002

Δ[O/Fe] = +1.0 -0.004

Δ[Al/Fe] = +1.0 +0.013

Δ[α/Fe] = +0.3(w/o Ca)

-0.008

Δ[s-process/Fe] = +0.5 +0.008


Normal GCsNormal GCs(RGB widths are comparable to measurement errors)(RGB widths are comparable to measurement errors)


Normal GCsNormal GCs


8 Exemplary GCs (Lee et al. 2009)8 Exemplary GCs (Lee et al. 2009)

~ 85 nights with CTIO 1m tel. using Ca + uvby (as of publication).

More than half of 40 GCs showbimodal or broad RGB distributionsin the hk index variations in their calcium abundances

Lack of normal GCs


Differences in Heavy Elemental Abundances(M22 sepc data: Brown & Wallerstein, N1851 spec data : Courtesy of David

Yong)


M22 (Lee + Marino 2009)


M22 (Lee + Da Costa 2009)


More GCs with Bimodal RGB


Cont.. (+ many more GCs not shown in here)


NGC2808 (Lee + Carretta; Lee 2010, in prep.)


NGC3201 (Lee + Carretta; Lee 2010, in prep)


47 Tuc : A Simple Metal-Rich GC

Hesser et al. (1987)


47 Tuc : Quite a complex GC

Norris & Freeman 1979, ApJL, 230, L179

Smith 1979, AJ, 84, 176


SGB splits in 47 Tuc (Anderson et al. 2009)


uvby Phtometry by Calamida et al. (2007)


Wide-Field Photometry of 47Tuc (Lee 2010, in prep)

Calamida et al. 2007



m1 index clearly show a bimodal distribution, (perhaps hk as well).

hk and m1 indices are larger in the core.

Spectroscopic follow-up study will be done.

Aug 2010 (+ Aug 2009) : CTIO 4m/Hydra

CN Strong

Ca Strong


ConclusionsConclusions

• The hk index provides a powerful method to distinguish multiple populations in GCs.

• Our results show that many GCs have multiple populations with distinct calcium abundances.

• Calcium and other heavy elements can only be supplied through numerous SNe explosions of massive stars.

• The gravitational potential of the present-day GCs cannot preserve most of ejecta from SNe, and therefore our results suggest that these GCs are most likely the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.

• A significant fraction of GCs is originated as galaxy building blocks predicted by the hierarchical merging paradigm.


Multiple Populations in GCsMultiple Populations in GCs

• GCs are known to be chemically inhomogeneous in lighter (CNO+Na+Al+Mg) elemental abundances.– Bimodal CN distribution– Na-O & Mg-Al anticorrelations– Some of them also show spread in the s-process elemental abundances.– AGB pollutions (Ventura et al. 2001)

• However, alpha- and iron-peak elements are believed to be constant in a GC (with some scatter) except for omega Cen and M22.

• Recent HST/ACS survey of GCs show multiple SGBs (Piotto et al.)

• EHB indicates the presence of multiple populations in GCs (Lee et al. 2007)

• Four viable chemical enrichment mechanisms– Fast rotating massive stars (lighter elements)– Type II SNe (alpha-, iron-peak and r-process elements)– Intermediate mass AGB stars (lighter and s-process elements)– Type Ia SNe (iron-peak elements)


CN Bimodality (Kayser et al. 2008, A&A, 486, 437)CN Bimodality (Kayser et al. 2008, A&A, 486, 437)


1200 RGBs in 19 GCs (VLT + GIRAFFE, R ~ 20K, 1200 RGBs in 19 GCs (VLT + GIRAFFE, R ~ 20K, Carretta et al. 2009)Carretta et al. 2009)


Double SGB in NGC1851Double SGB in NGC1851

Milone et al. 2008, ApJ, 673, 241


Double Red Clumps in Ter 5 (Ferraro et al. 2009)Double Red Clumps in Ter 5 (Ferraro et al. 2009)

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Evidences of Multiple Populations in GCs