1 / 43

Globular clusters role in formation of the halo

Globular clusters role in formation of the halo. Raffaele Gratton INAF – Osservatorio Astronomico di Padova. Angela Bragaglia Eugenio Carretta Sara Lucatello Valentina D’Orazi Yazan Momany Chris Sneden. Franca D’Antona Paolo Ventura Santi Cassisi Giampaolo Piotto Anna Fabiola Marino

shakti
Download Presentation

Globular clusters role in formation of the halo

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

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

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

  4. GC formation scenario (Carretta et al. 2010) • 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 • 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 • 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 • Core collapse SNe for this second generation stops further star formation • In the meantime, decoupling between DM and gas Chemical evolution in the Universe

  5. Possible variations Chemical evolution in the Universe • Other polluters have been proposed: • Fast Rotating Massive Stars (Decressin et al.) • Novae (Smith & Kraft; Maccarone et al.) • Massive interacting binaries (De Mink et al.) • Super Massive Stars (Denissenkov & Hartwick) • 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)

  6. GC and dSph luminosity functions overlap • We constructed a luminosity function for GCs (Harris catalogue) and DSph (likely incomplete at faint end) • Total integrated Mv for MW: • GCs: -13.3 (initially: from -15 up to -16) • dSph: -14.4 Chemical evolution in the Universe

  7. Globular clusters and dwarf galaxies: mass-to-light ratio 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) From Dabringhausen et al. 2008 MNRAS 386 864 Chemical evolution in the Universe

  8. The luminosity-metallicity relation Kirby et al. 2008, arXiv:0807.1925 Chemical evolution in the Universe

  9. 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!

  10. 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 Median progenitor Mv~-11.5 See also Leaman et al. 2013, arXiv1309.0822

  11. 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) Evolved in isolation NFW halo Green: dSph’s Red: Bulge/thick disk GCs Blue: Inner Halo GCs Black: Outer Halo GCs Tidally limited region Chemical evolution in the Universe

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

  13. 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

  14. 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 (~108-109 yr at half mass, longer for more massive GCs, with a median value of about 5x108 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

  15. 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

  16. 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

  17. Multiple stellar generations • 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 Chemical evolution in the Universe

  18. 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. 2008 and references in Carretta et al. 2010a) Chemical evolution in the Universe

  19. 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 rgalactocentric<18 kpc). • We summed up the luminosity of all GCs in the Harris (1996) catalogue that are within this volume + M/LV= 2 (Mandushev et al. 1991; Pryor & Meylan 1993) mass(GCs)=4.1x106Mo Chemical evolution in the Universe

  20. 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 0.038 Mo/pc3 (Jahreiss & Wielen 1997)  mass(Halo)=3.3x108Mo  mass(GCs)~1.2% of mass(Halo) • Similar value for the whole halo outside 4 kpc • Total stellar mass within halo GCs ~1.4x107Mo, in the field ~1.2x109Mo Chemical evolution in the Universe

  21. 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

  22. 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

  23. 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

  24. 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

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

  26. An upper limit from Fornax GCs Chemical evolution in the Universe 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) FornaxDSph has 5 GCs They show a Na-O anticorrelation (signature of multiple generations: Latarte et al. 2006) Our original estimate: an upper limit of ~15

  27. Larsen et al. 2012, A&A, 544, L14 Chemical evolution in the Universe • Cluster [Fe/H] • Larsen et al. (2012 A&A, 546, 53) • Letarte et al. (2006, A&A, 453, 547) • Two sets consistent within 0.1 dex • 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 • Corrections for distribution within the galaxy • Conclusion: there are only ~4-5 metal-poor Fornax field stars for every GC star

  28. Larsen et al. 2013 Chemical evolution in the Universe

  29. Chemical evolution in the Universe • How many GCs should be considered? • 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) • 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) • 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

  30. Are the metallicity scales used for field and GCs consistent? Chemical evolution in the Universe • M15: • Latarte et al.: [Fe/H]= -2.40+/-0.03 • 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) • However, offset of 0.3-0.4 dex  In Battaglia et al sample, there are ~35 stars with [Fe/H]<-2 and 47 more with -2<[Fe/H]<-1.7

  31. A new upper limit Chemical evolution in the Universe • 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 metallicity scales for GCs and field stars are inconsistent (~2.3) • The product of these factors is ~3 • A ratio of ~15 is consistent with GC formation scenario derived from multiple populations

  32. The importance of Larsen et al. paper • 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) • Is this appropriate for the case of the FornaxdSph?  Clear excess of massive clusters! Chemical evolution in the Universe

  33. Conclusions Chemical evolution in the Universe 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 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

  34. The case of Sagittarius 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.) Mottini & Wallerstein, 2008, AJ 136, 731

  35. Heavy s-elements 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.) Mottini & Wallerstein, 2008, AJ 136, 731

  36. 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

  37. 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

  38. 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

  39. 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. 2010 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

  40. 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

  41. GCs vs field: light and -elements Chemical Evolution of Dwarf Galaxies and Stellar Clusters - Garching, July 21-25, 2008

  42. GCs vs field: Fe-peak elements

  43. 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

More Related