With Thanks to the Former and Current Contributing Students and Postdocs:
q Daniel Harbeck
q Michael Odenkirchen
q Andrea Kayser The Globular Cluster – q Katrin Jordi Halo Connection q Sarah Martell q Şeyma Çalışkan
q Maria Cordero
q Andreas Koch
Odenkirchen & Grebel 2001
17.08.2018 Grebel: GC Contribution to the Halo Field Population 0 17.08.2018 Grebel: GC Contribution to the Halo Field Population 1
What We Know and What We Don’t Know - Yet q Known: Star formation usually happens in clusters and associations. q Associations dissolve quickly, open clusters typically within a few 100 q Myr (but: exceptions); GCs survive for a Hubble time (but: exceptions). q Observed: Ongoing star formation in the disk, associations, clusters. q Unknown: Modes of star formation in the halo. q Observed: Old field stars and old globular clusters. q Known: Satellite accretion onto the Milky Way is happening (e.g., Sgr). q Unknown: How much, when, what progenitors. q Known: Satellite accretion can include GCs (e.g., from Sgr). q Unknown: How many GCs were accreted, which ones, from which q progenitors. How many GCs formed in situ? q Known: GC disruption in the Milky Way is happening (e.g., Pal 5). q Unknown: How many dissolved GCs (regardless of origin). Odenkirchen & Grebel 2001 q How much mass (i.e., stars) was lost from surviving GCs?
17.08.2018 Grebel: GC Contribution to the Halo Field Population 2 17.08.2018 Grebel: GC Contribution to the Halo Field Population 3 “Vital Diagram” for Galactic Globular Clusters Detection of Globular Cluster Stars in the Field
How many GCs were q Ongoing globular cluster dissolution via detected tidal tails, e.g.: formed initially? q Palomar 5 (Odenkirchen, Grebel, et al. 2001) GCs can be destroyed q NGC 5466 (Odenkirchen & Grebel 2004) or “reduced” by various q NGC 5053 (Lauchner et al. 2006) dynamical processes. q Pal 1 (Niederste-Ostholt et al. 2010) q Eri, Pal 15 (Myeong et al. 2017)
Today we see the 1997 q NGC 7492 (Navarrete et al. 2017) survivors of these processes. q NGC 288, 1261, 1851, 1904 (Shipp et al. 2018) Ostriker
Survival depends on & intrinsic mass and
density as well as Gnedin on the gravitational
potential, galacto- et al. 2017 centric distance and orbits within tails tidal 15 , Pal the host galaxy. Myeong Eri Odenkirchen, Grebel et al. 2001 17.08.2018 Grebel: GC Contribution to the Halo Field Population 4 17.08.2018 Grebel: GC Contribution to the Halo Field Population 5
Detection of Globular Cluster Stars in the Field Detection of Globular Cluster Stars in the Field q Ongoing significant star loss via detected extratidal overdensities and q Photometrically detected streams with potential GC progenitors, e.g., q apparent/potential onset of tidal tails, e.g.: q GD1 (Grillmair & Dionatos 2006) q NGC 7492 (Lee et al. 2004) q EBS (Grillmair 2006) q NGC 4147, 5053, 7078, 5904, 7006; Pal 1,14...(Jordi & Grebel 2010) q Acheron, Cocytos, Lethe, Styx (Grillmair 2009) q M15, M30, M53, NGC 5053... (Chun et al. 2010) q Triangulum/Andromeda (Bonaca et al. 2012) q NGC 2298 (Balbinot et al. 2011) q Hermus, Hyllus (Grillmair 2014) q Pal 11 (Sollima et al. 2011) q Ophiuchus (Bernard et al. 2014) q NGC 6266, 6626, 6642, 6723 (bulge) (Chun et al. 2015) q NGC 1851, 1904, 2298, 2808 (Carballo-Bello et al. 2018)
Jordi & Grebel Chun et al. Carballo-Bello et al. 2018 2010: NGC 4147 2010: M15 Dionatos & Dec Grillmair 2006: GD1 stream
R.A. R.A. 17.08.2018 Grebel: GC Contribution to the Halo Field Population 6 17.08.2018 Grebel: GC Contribution to the Halo Field Population 7 Detection of Globular Cluster Stars in the Field Detection of Globular Cluster Stars in the Field q Spectroscopically detected extratidal stars via abundances & radial q Hence, evidence for: q velocitites, e.g.: q Completely disrupted GCs (only tidal streams are left) q M22, NGC 1851, NGC 3201 (Kunder, ..., Grebel, et al. 2015) q Ongoing dissolution of GCs (tidal streams/extratidal overdensities) q NGC 3201, 362, ω Cen (Anguiano, ..., Grebel, et al. 2015, 2016) q Minor (“secular”) star loss from GCs (individual stars) q NGC 1851 (Simpson et al. 2017) But how to quantify the GC contribution to the field? q NGC 6441 (RR Lyr RVs, bulge) (Kunder et al. 2018) Not all dissolution events will still be recognizable as tidal tails.
In an ideal world: Chemical tagging and space motions of all field stars. (Thanks to Gaia and massive spectroscopic surveys, feasible for subset!)
[ Our approach: Exploit light element abundance anomaly prior!
Anguiano et al. 2016 (debris tracked across 80º)
Kunder et al. 2018 (bulge) 17.08.2018 Grebel: GC Contribution to the Halo Field Population 8 17.08.2018 Grebel: GC Contribution to the Halo Field Population 9
GCs: Light Element Abundance Anomalies q Na excess anticorrelated with O depletion Only seen in GCs, q Mg excess anticorrelated with Al depletion not in field stars. q C – N anticorrelation Found also in un- q Li and F enhancement evolved GC stars. q He enrichment
CN dichotomy: mean loci of CN-rich and CN-poor RGB stars in GCs
NGC 5286 NGC 362 M15 Ter 7 M55 Pal 12 NGC 288 M22
Kayser, ... Grebel, et al. 2008 17.08.2018 Grebel: GC Contribution to the Halo Field Population 10 17.08.2018 Grebel: GC Contribution to the Halo Field Population 11 What We Know and What We Don’t Know - Yet Constraining the GC Contribution to the Halo q 1st generation GC stars now in the halo field essentially not traceable. q Known: Most GCs show light element abundance variations. q (Or: ex-GC population with “normal” light elements hard to trace in field.) q Seen also in GCs in external galaxies q These stars are believed to have been main contributors to halo field q (e.g., Mucciarelli et al. 2009, Mateluna et al. 2012, Larsen et al. 2014, 2018). q via disruption of GCs. [Gaia will help] q (And even in massive intermediate-age clusters in the Clouds!) q But: 2nd generation stars from disrupted GCs are detectable because q Unknown: Origin. All current theories have problems. q of their abundance anomalies! q But for our particular approach: Not a problem. ➙ Origin other than GC origin of such stars in the field seems unlikely. q We just use light element abundance variations as a tool. ➙ Search for such stars in massive spectroscopic surveys. [ If stars with light element abundance anomalies are found in the field: ➙ Detection sets crude constraints on GC halo contribution. [ Likely GC origin. ➙ Our approach: Use SDSS, which permits exploitation of CN, CH bands. [ Possible constraint on (massive) GC contribution to stellar halo. q Note: If indeed lower mass limit exists for “2nd generation” formation Nomenclature: We call such stars with light element abundance anomalies q and hence light element abundance variations, this will only tell us about nd 4 “2 generation” for convenience. q contribution of “massive” (≥ 10 M¤?) clusters to stellar halo. This is not meant to imply that we favor models with ≧ 2 episodes of SF. q Quantitative interpretation depends on GC multiple population models. Martell & Grebel 2010 Martell et al. 2011 Carollo et al. 2013 17.08.2018 Grebel: GC Contribution to the Halo Field Population 12 17.08.2018 Grebel: GC Contribution to the Halo Field Population 13
Some of the Caveats (1) Some of the Caveats (2) q If formation of halo field stars occurred in q Uncertainties in q progenitors of globular clusters, q Stellar mass function with which GCs were born q open clusters, q Amount of mass GCs lose during “normal” evolution (relaxation) q associations st nd q here we only get information about GCs massive enough to have formed q Initial ratio of “1 / 2 generation” stars. q a “2nd generation” of stars (i.e., stars with light element anomalies). q Ratio variation and dependence on other parameters (e.g., [Fe/H])
Lower mass limit on light element abundance anomaly formation? For example:
➙ Empirical Galactic GC lower limit currently at ~ 4700 M (present-day). q “A typical GC [...] has lost about 75% of its mass since formation” q (NGC 6535; Bragaglia et al. 2017; see also ESO452-SC11 (Simpson 2018). q (Baumgardt & Sollima 2017) q But also: GCs apparently without 2nd gen. (Rup 106) q Anticorrelation between present-day MF slope and half-mass relaxation Lower age limit on light element abundance anomaly formation? q time of GCs (Sollima & Baumgardt 2017) ➙ see massive intermediate-age Magellanic Cloud clusters. ❑ Average GC: lost ~ 2/3 (Kruijssen 2015) ➙ Absent in open clusters? Na-O anticorrelations in fast-rotating MS stars ➙ These uncertainties affect interpretation of results. (v sin i ≧ 50 km/s) for Pleiades, Coma Ber., Ursa Major, Hyades (Pancino 2018).
17.08.2018 Grebel: GC Contribution to the Halo Field Population 14 17.08.2018 Grebel: GC Contribution to the Halo Field Population 15 Constraining the GC Contribution to the Halo q 1960 SEGUE-1 and 561 SEGUE-2 red giants with −1.8 < [Fe/H] < −1.0: q 49 & 16 CN-strong stars,resp. (~2.5%); Martell & Grebel 2010, Martell et al. 2011.
inner / outer halo Carollo et al. 2013
Martell et al. 2011 index] bandstrength [CN [CN 17.08.2018 Grebel: GC Contribution to the Halo Field Population 16 17.08.2018 Grebel: GC Contribution to the Halo Field Population 17
Martell & Grebel 2010 Martell et al. 2011 Carollo et al. 2013 Constraining the GC Contribution to the Halo Constraining the GC Contribution to the Halo
q Drop-off in frequency of CN-strong stars at RGC > 20 kpc: q In a sample of 144 field stars with [Fe/H] < −1, Carretta et al. (2010) ➙ possible sign of transition from inner to outer halo. q find ~ 1.4% to be Na-rich stars with likely GC origin. Galaxy formation models suggest: ➙ ~ 2.8% of metal-poor halo field stars may have GC origin (minimum), or up to ten times as many (depending on the assumptions). § Stars formed in situ are dominant population at small RGC. § At small RGC, accretion of “massive” satellites dominates, which in q Schaerer & Charbonnel (2011), based on Martell & Grebel (2010) and § principle can contribute GCs (with similar abundance anomalies). q Carretta et al. (2010) samples, suggest that low-mass stars ejected § Stars accreted in minor mergers are majority at larger R (outer halo), GC q from the present-day population of GCs make up ~ 5–8% or 10–20% § where little GC disruption should occur. q of the mass of halo stars (depending on the assumptions). Spectroscopic results from field red giants in dSphs: ➙ Mild variations, but no Na enhancement like in 2nd gen. GC stars. q In a sample of 67 field stars with −1.6 < [Fe/H] < −0.4, Ramírez et al. q (2012) find two stars with GC-2nd-gen.-like O$ and Na#. Conclusions: ➙ At least 3 2% of the local metal-poor field population came from GCs. ➙ Inner stellar halo (field): significant contributions from GCs (17%). (actually, 2.5% of halo stars: 2nd generation chemistry) q Lind et al. (2015) analyzed ~ 7300 Gaia-ESO Survey spectra, finding ➙ Outer halo: dominated by stars formed in smaller dwarf galaxies q one star with GC 2nd-gen.-like Mg$ and Al#. Possible origin: ω Cen? ➙ (stars that did not form in GCs). 17.08.2018 Grebel: GC Contribution to the Halo Field Population 18 17.08.2018 Grebel: GC Contribution to the Halo Field Population 19 Constraining the GC Contribution Constraining the GC Contribution to Bulge & Halo
q Fernández-Trincado et al. (2016) found a −1.3 dex field giant with a GC q Schiavon et al. (2017) analyzed 5140 APOGEE spectra of bulge stars q 2nd gen-like low Mg-Al ratio ([Mg/Fe] = −0.31; [Al/Fe] = 1.49). If so, best q with mean [Fe/H] ~ −1: ➙ 58 stars with GC 2nd gen-like N#, Al#, C$ q progenitor is ω Cen. Star is kinematically consistent with disk, but q (corresponding to 1.1% of total population in inner bulge). q chemically with halo, so might also be a halo contaminant. q Two assumptions for mass budget problem: q Simpson et al. 2017: Of four extratidal candidates near NGC 1851, two q “Minimal” (1st gen/2nd gen = 1/2): nd are CH- and three are CN-enhanced as expected from 2 -gen. ➙ 1.7% GC contribution to the bulge (or ≤ 3.7% if this is thick disk) −11 Cluster destruction rate estimated to be 4.6 · 10 /yr. q “Maximal” (1st gen/2nd gen = 9/1): q Schiavon et al. (2017), bulge stars: Many show N, C, Al as in GCs ➙ 16% GC contribution to the bulge (or ≤ 40% if this is thick disk). q (high [N/Fe] anticorr. with [C/Fe], corr. with [Al/Fe]. [Fe/H] ~ −1. q Martell et al. (2016) analyzed 253 APOGEE spectra of halo stars q N-rich stars possible former GC stars ➙ mass in destroyed GCs q with − 1.8 < [Fe/H] < −1: ➙ 5 stars with GC 2nd gen-like N#, Al#, C$ 8x > mass in surviving GCs. 1st-gen > 2nd gen by factor of ≤ 9. q (corresponding to ~ 2%). Or: N-rich stars could be oldest stars in MW as by-product q “Minimal” (1st gen/2nd gen = 1/2): ➙ 4% GC contribution to halo. of chemical enrichment by 1st stellar gen. formed in MW center. q “Maximal”: 13%.
17.08.2018 Grebel: GC Contribution to the Halo Field Population 20 17.08.2018 Grebel: GC Contribution to the Halo Field Population 21
Constraining the GC Contribution to Halo Constraining the GC Contribution to Halo
q Fernández-Trincado et al. (2017) found 11 field red giants (APOGEE) q Koch et al., cont.: Assume 50% q with N#, Al#, C$, Mg $ in metal-rich ([Fe/H] ≧ −1 (contrary to typical q 2nd gen. stars (present-day), q findings in GCs of similar metallicity). Origin?? (exotic binaries?) q neglecting trends with mass). q Depending on adopted loss rate q Koch, Grebel, & Martell (in prep.): SDSS-IV DR14: SEGUE 1+2, eBOSS: q of 1st-gen. stars: Fraction of q as in Martell & Grebel only stars with −1.8 ≤ [Fe/H] ≤ −1, small errors, q stellar halo that originated from q S/N > 15/pixel in q disrupted GCs: 21 2%. CN-strong q region of 400 – 410 “CN normal” q nm: ~ 7000 bona q fide halo giants. ➜ 252 of 6801 halo ➜ giants: CN-strong ➜ and CH-weak (“2nd ➜ gen.”), (3.7 0.2)%. ➜ (4x more than in our earlier studies) 17.08.2018 Grebel: GC Contribution to the Halo Field Population 22 17.08.2018 Grebel: GC Contribution to the Halo Field Population 23 Constraining the GC Contribution to Halo ConstrainingSummary theSmall GC sample Contribution sizes and to uncertainties the Halo in assumptions (e.g., initial 1st vs. 2nd q Koch, Grebel, & Martell, CN-strong q In gen. fractions in GCs). “CN normal” q cont.: Distance However, the different studies all now q dependence: Declining seem to suggest that GC contribution q fraction for RGC > 20 kpc. to field populations ranged from a few q Inner/outer halo dichotomy; % to a few tens of % (1/4 – 1/5). q inner halo mainly in-situ; q outer halo mainly ex-situ. q 20 2nd-gen. stars > 30 kpc; q farthest at 48 5 kpc. Gaia may help us to trace 2nd-gen. field stars to their progenitors. Gaia will uncover more field stars of GC origin.
17.08.2018 Grebel: GC Contribution to the Halo Field Population 24 17.08.2018 Grebel: GC Contribution to the Halo Field Population 25