Globular clusters role in formation of the halo Raffaele Gratton INAF – Osservatorio Astronomico di Padova Chemical evolution in the Universe

Collaborators Angela Bragaglia Angela Bragaglia Eugenio Carretta Eugenio Carretta Sara Lucatello Sara Lucatello Valentina D’Orazi Valentina D’Orazi Yazan Momany Yazan Momany Chris Sneden Chris Sneden Franca D’Antona Paolo Ventura Santi Cassisi Giampaolo Piotto Anna Fabiola Marino Antonino Milone Alessandro Villanova Chemical evolution in the Universe

GCs and Open Clusters GCs are more massive and older than OCs GCs host multiple stellar populations; OC do not

GC formation scenario (Carretta et al. 2010) Interaction between a still gaseous proto-dSph and the MW (or between proto-dSph’s) (Bekki) Interaction between a still gaseous proto-dSph and the MW (or between proto-dSph’s) (Bekki) Formation of a precursor population, with a raise in [Fe/H], sometimes fast Formation of a precursor population, with a raise in [Fe/H], sometimes fast Triggering formation of a large primordial population (first generation) Triggering formation of a large primordial population (first generation) Winds from massive stars and core collapse SNe stop further star formation and clean the region from primordial ISM Winds from massive stars and core collapse SNe stop further star formation and clean the region from primordial ISM Low velocity wind from massive AGB stars generates a cooling flow (Ventura et al., D’Ercole et al.) Low velocity wind from massive AGB stars generates a cooling flow (Ventura et al., D’Ercole et al.) Second generation stars form in this cooling flow Second generation stars form in this cooling flow Core collapse SNe for this second generation stops further star formation Core collapse SNe for this second generation stops further star formation In the meantime, decoupling between DM and gas In the meantime, decoupling between DM and gas Chemical evolution in the Universe

Possible variations Other polluters have been proposed: Other polluters have been proposed: Fast Rotating Massive Stars (Decressin et al.) Fast Rotating Massive Stars (Decressin et al.) Novae (Smith & Kraft; Maccarone et al.) Novae (Smith & Kraft; Maccarone et al.) Massive interacting binaries (De Mink et al.) Massive interacting binaries (De Mink et al.) Super Massive Stars (Denissenkov & Hartwick) Super Massive Stars (Denissenkov & Hartwick) However, most features of the scenario remain valid However, most features of the scenario remain valid Globular clusters should have been much more massive at their origin than now (from a few to ~15) Globular clusters should have been much more massive at their origin than now (from a few to ~15) Chemical evolution in the Universe

GC and dSph luminosity functions overlap We constructed a luminosity function for GCs (Harris catalogue) and DSph (likely incomplete at faint end) We constructed a luminosity function for GCs (Harris catalogue) and DSph (likely incomplete at faint end) Total integrated Mv for MW: Total integrated Mv for MW: GCs: (initially: from -15 up to -16) GCs: (initially: from -15 up to -16) dSph: dSph: Chemical evolution in the Universe

Globular clusters and dwarf galaxies: mass-to-light ratio From Dabringhausen et al MNRAS There is scarce evidence of dark matter in both GCs and UCD galaxies, in agreement with expectations for small dark matter halo. GCs have lower mass- to-light ratio likely because of dynamical evolution (since they are relaxed objects) Chemical evolution in the Universe

The luminosity-metallicity relation Kirby et al. 2008, arXiv: Chemical evolution in the Universe

The luminosity-metallicity relation dSph (mean) metallicity depends on luminosity (present baryonic mass?). This agrees with the concept that dSph make their own metals GCs metallicity is fairly independent of luminosity (mass?). This agrees with the concept that they inherited the metallicity of the medium where they formed GCs have a bimodal metallicity distribution (Disk/Halo) with a minimum at [Fe/H]~-0.9 At a given metallicity, the dSph luminosity is a lower envelope of GCs metallicities  Halo GCs formed in objects that were more massive than they currently are!

Mv of the GC progenitors Using the mass-metallicity relation for DSph we may assign an Mv to the progenitor of each GC For the halo the median ratio progenitor/GCs is 27 (depends on the exact form of the relation) Equal Mv See also Leaman et al. 2013, arXiv Median progenitor Mv~-11.5

GCs are tidally limited, dSph’s are not According to this scenario, GCs and dSph’s originated from similar systems but:  GCs progenitors interacted with the MW while still mainly gaseous  dSph’s evolved in isolation (  luminosity-metallicity relation) NFW halo Green: dSph’s Red: Bulge/thick disk GCs Blue: Inner Halo GCs Black: Outer Halo GCs Chemical evolution in the Universe Tidally limited region Evolved in isolation

GC and dwarf galaxies as survivors (tidal tails) Odenkirchen et al. 2001, ApJ 548, L165 GC: Pal 5dSph: Sagittarius Belokurov et al. 2006, ApJ 642, L137 Chemical evolution in the Universe

Halo and GCs  Current cosmological models (White & Rees 1978; Moore et al. 1999): the Milky Way’s stellar halo was assembled from many smaller systems  The metal-poor ([Fe/H]<-2) part of the halo may be made of objects like the smallest DSph’s  The bulk of the halo (-2<[Fe/H]<-1) is clearly different from DSph’s stars of similar metallicity (largest DSPh’s) (e.g. the run of [α/Fe] is different)  The primordial (FG) population of GCs is a plausible candidate (see also Vesperini et al., Martell & Grebel, Conroy) Chemical evolution in the Universe

Stars lost from the GCs  Violent relaxation following gas expulsion and mass loss from the most massive stars (see e.g. Baumgardt, Kroupa & Parmentier 2008)  On a longer timescale: evaporation due to two-body encounters and other mechanims (e.g. disk shocking: see e.g. Aguilar, Hut & Ostriker 1988)  Due to this second effect, some per cent of the stars should be removed within a relaxation time (~ yr at half mass, longer for more massive GCs, with a median value of about 5x10 8 yr: Harris 1996)  A substantial fraction of the original GC mass should have been lost, this loss being more efficient among smaller GCs Chemical evolution in the Universe

Evidences  Tidal tails around some GCs (see e.g. Odenkirchen et al. 2003)  Deficiency of small mass stars preferentially lost if energy equipartition holds (Henon 1969; Richer et al. 1991; De Marchi et al. 2007; De Marchi & Pulone 2007)  Current GCs are the survivors of a potentially larger initial population Chemical evolution in the Universe

 A major issue is whether a part (even large) of the Galactic field stars were formed in GCs and later ended up as a main component of the halo  Infant cluster mortality might be the major source of halo stars (see e.g. Baumgardt et al. 2008) Chemical evolution in the Universe

 The SG population is typical of GCs (Gratton et al. 2001)  The fraction (~2.5%) of Na-rich and/or CN- rich stars in the field halo (Carretta et al. 2010a; Martell & Grebel 2010)  stars evaporated from GCs Multiple stellar generations Chemical evolution in the Universe

GC stellar populations  FG with the typical composition of the ejecta of core-collapse SNe (e.g. Truran & Arnett 1971) are only 1/3 of the current total population  To reproduce n(FG)/n(SG), a large fraction of stars of the FG must have been lost from GCs  The same from theoretical studies and numerical simulations of dynamical evolution (Decressin et al. 2008, D’Ercole et al and references in Carretta et al. 2010a) Chemical evolution in the Universe

The present mass of the GCs compared to the mass of the halo  Mass of the inner halo GCs vs field population from in situ star counts (Juric et al. 2008)  To avoid contamination by the galactic thick disk, polar caps defined (Z>5 kpc, and r galactocentric 5 kpc, and r galactocentric <18 kpc).  We summed up the luminosity of all GCs in the Harris (1996) catalogue that are within this volume + M/L V = 2 (Mandushev et al. 1991; Pryor & Meylan 1993)  mass(GCs)=4.1x10 6 M o Chemical evolution in the Universe

Mass of the halo  Mass of halo stars:  Density law for the halo by Juric et al. (2008)  Their normalisation of halo/thin disk density in the solar neighbourhood  Local stellar density of M o /pc 3 (Jahreiss & Wielen 1997)  mass(Halo)=3.3x10 8 M o  mass(GCs)~1.2% of mass(Halo)  Similar value for the whole halo outside 4 kpc  Total stellar mass within halo GCs ~1.4x10 7 M o, in the field ~1.2x10 9 M o Chemical evolution in the Universe

The original GC mass  Carretta et al. (2009): SG=2/3 of GC stars  Carretta et al. (2010) and Martell and Grebel (2010): stars with a composition similar to SG in GCs (i.e. Na-rich and/or CN-rich): ~2.5% of current halo stars  If:  They are SG stars lost by GC  SG stars are lost after GC formation at the same rate as FG ones  stars lost by GCs after the formation of SG stars ~3.7% of the current halo stars Chemical evolution in the Universe

The original GC mass  Currently 1.2% of the halo mass is still in GCs  they should have lost some 75% of their original mass  They were originally ~4 times more massive than they are now  ~5% of the halo were in GCs (after the formation of SG stars) Chemical evolution in the Universe

The mass of the FG  However, mass involved in the process of formation of GCs >> GCs mass after formation of the SG  Bulk of the SG stars formed from the ejecta of only a fraction of the FG stars Chemical evolution in the Universe

The mass of the FG  With simple, realistic assumptions on:  IMFs of FG and SG stars  initial-final mass relation  on suitable mass ranges for the most favourite candidate polluters (Carretta et al. 2010)  m(FG)/m(after formation of SG stars) ~5-10  m(FG) ~25-50% of the halo mass Even more if part of the mass lost by the polluters was not used to form SG stars  The galactic halo might be made of the FG Chemical evolution in the Universe

Tests Metallicity distribution Chemistry Density Distribution BHB LFs Filled circles = field stars (Ivezic et al.) Red solid lines = generalised histograms for GCs Solid line = best fit through data Dotted line = slope of the inner halo density (Juric et al. 2008). GC (Piotto et al. 2003) :solid histogram Field (Brown et al. 2008: red dashed line). Black dots = field stars (Venn et al.) Red solid lines = range for GCs (Also binaries: Lucatello et al. 2013, in preparation) Chemical evolution in the Universe

An upper limit from Fornax GCs We may set an upper limit to the original mass of GC by counting stars in GCs and the field in a dSph with a high specific frequency of GCs (Carretta et al. 2010) We may set an upper limit to the original mass of GC by counting stars in GCs and the field in a dSph with a high specific frequency of GCs (Carretta et al. 2010) Fornax DSph has 5 GCs Fornax DSph has 5 GCs They show a Na-O anticorrelation (signature of multiple generations: Latarte et al. 2006) They show a Na-O anticorrelation (signature of multiple generations: Latarte et al. 2006) Our original estimate: an upper limit of ~15 Our original estimate: an upper limit of ~15 Chemical evolution in the Universe

Larsen et al. 2012, A&A, 544, L14 Cluster [Fe/H] Cluster [Fe/H] Larsen et al. (2012 A&A, 546, 53) Larsen et al. (2012 A&A, 546, 53) Letarte et al. (2006, A&A, 453, 547) Letarte et al. (2006, A&A, 453, 547) Two sets consistent within 0.1 dex Two sets consistent within 0.1 dex Field star [Fe/H] Field star [Fe/H] Battaglia et al. (2006), based on Rutledge et al. (1997) calibration of the Ca triplet on the Carretta & Gratton (1997) scale Battaglia et al. (2006), based on Rutledge et al. (1997) calibration of the Ca triplet on the Carretta & Gratton (1997) scale Corrections for distribution within the galaxy Corrections for distribution within the galaxy Conclusion: there are only ~4-5 metal-poor Fornax field stars for every GC star Conclusion: there are only ~4-5 metal-poor Fornax field stars for every GC star Chemical evolution in the Universe

Larsen et al Chemical evolution in the Universe

How many GCs should be considered? How many GCs should be considered? F4 is more metal-rich than the four other clusters F4 is more metal-rich than the four other clusters F1 (smaller cluster ) is consistent with pure FG (D’Antona et al. 2013, MNRAS, 434, 1138) F1 (smaller cluster ) is consistent with pure FG (D’Antona et al. 2013, MNRAS, 434, 1138) Are Fornax GCs identical to those of our galaxy? Possibly they keep more FG stars… Are Fornax GCs identical to those of our galaxy? Possibly they keep more FG stars… D’Antona et al. (2013): F2, F3 and F5 contain substantial fractions of SG stars (0.54 – 0.65) D’Antona et al. (2013): F2, F3 and F5 contain substantial fractions of SG stars (0.54 – 0.65) However, only 2 out of 9 stars observed by Latarte et al. are Na-rich stars  SG: probability that this happens by chance is only 2.5% if the fraction of SG stars is 0.6 However, only 2 out of 9 stars observed by Latarte et al. are Na-rich stars  SG: probability that this happens by chance is only 2.5% if the fraction of SG stars is 0.6

Are the metallicity scales used for field and GCs consistent? M15: M15: Latarte et al.: [Fe/H]= /-0.03 Latarte et al.: [Fe/H]= /-0.03 Rutledge et al.: [Fe/H]=-2.02+/-0.04 Rutledge et al.: [Fe/H]=-2.02+/-0.04 According to our last scale (Carretta et al. 2009, A&A, 508, 695): [Fe/H]=-2.33+/-0.02, close to (Latarte et al. 2006) According to our last scale (Carretta et al. 2009, A&A, 508, 695): [Fe/H]=-2.33+/-0.02, close to (Latarte et al. 2006) However, offset of dex  In Battaglia et al sample, there are ~35 stars with [Fe/H]<-2 and 47 more with -2<[Fe/H]<-1.7 However, offset of dex  In Battaglia et al sample, there are ~35 stars with [Fe/H]<-2 and 47 more with -2<[Fe/H]<-1.7 Chemical evolution in the Universe

A new upper limit The value of 4-5 given by Larsen et al. should be corrected for: The value of 4-5 given by Larsen et al. should be corrected for: The fraction of SG stars might be lower in Fornax GCs than in typical halo GCs. Let us assume ½ rather than 2/3 (~1.3) The fraction of SG stars might be lower in Fornax GCs than in typical halo GCs. Let us assume ½ rather than 2/3 (~1.3) The metallicity scales for GCs and field stars are inconsistent (~2.3) The metallicity scales for GCs and field stars are inconsistent (~2.3) The product of these factors is ~3 The product of these factors is ~3 A ratio of ~15 is consistent with GC formation scenario derived from multiple populations A ratio of ~15 is consistent with GC formation scenario derived from multiple populations Chemical evolution in the Universe

The importance of Larsen et al. paper Usually cluster mass function assumed to be represented by a Press-Schechter relation Usually cluster mass function assumed to be represented by a Press-Schechter relation See e.g. M82 clusters from Bastian et al. (2013, MNRAS, 419, 2606) See e.g. M82 clusters from Bastian et al. (2013, MNRAS, 419, 2606) Is this appropriate for the case of the Fornax dSph?  Clear excess of massive clusters! Is this appropriate for the case of the Fornax dSph?  Clear excess of massive clusters! Chemical evolution in the Universe

Conclusions GCs are complex objects hosting multiple generation of stars GCs are complex objects hosting multiple generation of stars They are the end result of the evolution of originally much more massive objects, possibly the inner halo counterpart of dSph They are the end result of the evolution of originally much more massive objects, possibly the inner halo counterpart of dSph Currently, ~1.2% of halo stars are in GCs, but likely ~5% of halo stars formed within GCs Currently, ~1.2% of halo stars are in GCs, but likely ~5% of halo stars formed within GCs Much more might have formed in the episodes that ultimately formed GCs Much more might have formed in the episodes that ultimately formed GCs Chemical evolution in the Universe

Globular clusters and dwarf galaxies Mass vs central density From Dabringhausen et al MNRAS Globular Clusters (GC) and Ultra-Compact Dwarf (UCD) galaxies seem to define a unique sequence. This suggests a similar formation scenario Dwarf Spheroidal (dSph) are clearly separated Chemical evolution in the Universe

Globular clusters and dwarf galaxies: relaxation time From Dabringhausen et al MNRAS GCs are relaxed objects, while UCDs are not

Distribution of metal abundances: halo, dwarf spheroidals, GCs Kirby et al. 2008, arXiv: Metallicity distribution of most metal- poor stars agree reasonably well with the metallicity of stars in ultra-faint dSph’s

Izevic et al. 2008, arXiv v2 Distribution of metal abundances: halo and GCs The metallicity distribution function of stars out of the galactic plane can be described as the sum of two components: A moderately metal-poor disk A more metal-poor halo These two components may very well be traced in the GC metallicity distribution function The disk GCs correspond to the moderately metal- poor disk at |Z|= kpc The halo GCs correspond to the metal-poor halo at |Z|=5-7 kpc The specific frequency of GCs is however much larger in the halo component than in the disk one

dSph vs field: O and Na abundances Geisler et al PASP,

dSph vs field: heavy elements Geisler et al PASP, Mc William et al. ApJ, 592, L21 dSph’s composition is clearly different from the bulk of the galactic halo: dSph’s are deficient in  -elements and Na dSph’s have a different run of Mn abundance dSph’s are overabundant in n-capture elements produced by s-process There are however some halo field stars with composition similar to the LMC and massive dSph’s (Sagittarius)

Age-metallicity relation t(Gy) [Fe/H] Milky WaySagittarius Mottini & Wallerstein, 2008, AJ 136, 731 Rosenberg et al. De Angeli et al. Tolstoy et al Sculptor

Age-metallicity relation Age-metallicity relation for different groups of GCs: outer halo clusters (green pentagons) outer halo clusters (green pentagons) inner halo clusters (blue circles) disk/bulge clusters (red squares). Green circles are GCs associated to dSphs. Different symbol sizes are used for clusters of different luminosity. Gratton et al. (2010) Chemical evolution in the Universe

The case of Sagittarius Mottini & Wallerstein, 2008, AJ 136, 731 Filled circles: Sgr GC’s Open circles: Sgr field (McWilliam & S,ecker-Hane) Open squares: Sgr field (Sbordone et al.) Filled squares: Fornax GC’s (Letarte et al.)

Heavy s-elements Mottini & Wallerstein, 2008, AJ 136, 731 Filled circles: Sgr GC’s Open circles: Sgr field (McWilliam & S,ecker-Hane) Open squares: Sgr field (Sbordone et al.) Filled squares: Fornax GC’s (Letarte et al.)

Binaries  Wide binaries may be destroyed in very dense fields  Within the galactic disk, binaries are more common in low density environments (like Taurus) rather than in higher density ones (like Orion) (Lada & Lada 2003)  The binary frequency and the maximum separation may then be used to estimate the density of the birth environment (Goodwin, 2010) Chemical evolution in the Universe

Field Frequency of spectroscopic binaries with periods less than 6000 days (Carney et al. 2003):  Field metal poor red giants: 16±4%  Field metal-poor dwarfs: 17±2%  These values are similar to those obtained for population I stars, if we restrict ourselves to the same period range, since only a third of the binaries in the solar neighbourhood have a period shorter than 6000 d (Duquennoy and Mayor 1991) Chemical evolution in the Universe

Globular Clusters  Binary fraction in GCs is much lower (Romani & Weinberg 1991)  From c-m diagrams (Milone et al. 2008): only a few per cent of stars in GCs are binaries (here, the total fraction of binaries, irrespective of their periods)  The binary fraction is a strong function of the cluster mass, from 2% for the most massive GCs, up to 20% for the less massive ones  The mass weighted average value is at most 1/3 than for field halo stars  Not surprising considering higher density in GCs  The fraction of wide binaries among halo stars indicates that they did not originate in GCs which subsequently disintegrated (Ryan 1992) Chemical evolution in the Universe

Binaries in FG and SG stars The incidence of binaries seems to be very different among FG and SG stars (see D’Orazi et al and Lucatello et al. 2010):  SG: 1%  FG: ~15% ~ field metal-poor stars Consistent with that obtained by Milone et al. (2008), if:  No long period binaries in GCs (reasonable)  FG made up only 1/3 of the GC population. Chemical evolution in the Universe

Consequences The difference between the frequency of binaries in FG and SG is dramatic:  most of the destruction of binaries (or lack of formation) among SG stars occurred before relaxation of the system, because later we do not expect large differences in the destruction rates between FG and SG  only the most compact binaries have a significant probability to form or survive in the very dense regions where SG stars of GC formed Chemical evolution in the Universe

Chemical Evolution of Dwarf Galaxies and Stellar Clusters - Garching, July , 2008 GCs vs field: light and  -elements

GCs vs field: Fe-peak elements

GCs vs field: n-capture elements GCs have a composition similar to that of the galactic halo, save for the O-Na anticorrelation (see last part of the talk) The P-population in GCs have a composition virtually identical to that of field stars