Presentation on theme: "Chemistry and Dynamics of Stars in Low Mass Galaxies Bridging Dwarfs, Halos & Disks Kim Venn U. Victoria 22 July 2010."— Presentation transcript:
Chemistry and Dynamics of Stars in Low Mass Galaxies Bridging Dwarfs, Halos & Disks Kim Venn U. Victoria 22 July 2010
Rapidly changing fields: - Number of stars with detailed chemistry - Origins & characteristics of metal poor stars - Number & characteristics of dwarf galaxies - Role(s) of dwarf galaxies in Galaxy formation
“Tea it is for drinking, hair absolute being agricultural surname, smell in the ru a king's. The as early as absolute being agriculture is period, tea and its medicines use the value already disheveled hair now, and be used by medicine to turn into gradually daily life bevera ge” And information can be difficult to interpret...
In this review 1. Chemical abundances in the MW metal poor halo, dwarf satellite galaxies, and the ultra faint dwarfs. 2. Comment on the chemistry of stars in the thick and thin disks. 3. Chemical and dynamical properties of stars in gas rich dwarf galaxies
Chemistry of stars comes from high resolution spectroscopy: R > 20,000 or < 0.25 A/pix Carina-7002:- [Fe/H] = R ~ 20,000 (Magellan MIKE) - SNR ~ 20 Carina-484:- [Fe/H] = R ~ 45,000 (VLT UVES) - SNR ~ 30 Venn et al. 2010
Size & Efficiency Counts – simply need to feed as many photons as possible into the spectrograph
Chemistry of stars in the metal poor halo are primarily of stars in the solar neighbourhood with halo kinematics “armchair cartography” (Morrison, Sommer-Larson) Reminder:
(V-I) Tolstoy et al But for stars in dwarf galaxies : need a large telescope, but cleaner sample...not armchair cartography members non-members
The detailed chemistry of the stars in these Galactic components are very different... “chemical tagging” (Bland-Hawthorn & Freeman 2002)
Even if you don't know WHY there are chemical differences, it is clear that there ARE chemical differences. Venn et al HALO RETRO/ECC THICK THIN DSPH
If you are interested in WHY there are chemical differences: - IMF (yields with stellar mass) - SFR (chemical yields with time/age/metallicity of star) i.e., SN II rates & yields relative to those from SN Ia (& AGB) Timescales for Mo core collapse SN all short, compared to SNIa SN II SN Ia
Now, what about those chemical abundances in the dwarf galaxies?... in HALO RETRO/ECC THICK THIN DSPH There has been an impressive amount of work done on detailed chemical abundances in different environments in the past 6 years... metal poor halo, dwarf galaxies, UFDs... with lots more in the works (e.g., Zucker's talk)
Venn et al Frebel et al LOTS more metal-poor halo stars ! UFD dSph+ But this is a MIXED BAG of objects !
Maximum scientific return from a variety of chemical abundances in a specific stellar population – not a mixed bag Tolstoy, Hill, Tosi 2009 ARAA
alpha - elements Neutron-capture element SNII+SNIa s-process & Ia knee r process [alpha/Fe] ~ SN II/ SN Ia (or high/low mass stellar) yields & [Ba/Fe] ~ SN II yields early on, later AGB & SN Ia yields noting that AGB yields depend on metallicity
LMC Pompeia, Hill et al Milky-Way Venn et al [Mg/Fe] like Galactic disk But not [Ca/Fe] ! Different nucleosynthetic site for these two alpha elements? [Ba/Fe] late r-process (SN II) and s-process (AGB) contributions
LMC Pompeia, Hill et al Sgr Sbordone et al Fornax Letarte PhD 2007 Milky-Way Venn et al Different end metallicities, consistent with the mass-metallicity relationship [Mg/Fe] vs [Ca/Fe] offsets, different per galaxy Again, different nucl sites? [Ba/Fe] late r-process (SN II) and s-process (AGB) contributions, consistent with recent SF in each.
LMC Pompeia, Hill et al Sgr Sbordone et al Fornax Letarte PhD 2007 Sculptor Hill et al in prep + Geisler et al Milky-Way Venn et al Lowest end metallicity, consistent with mass-metallicity rel Can see the [Fe/H] where SN Ia began to contribute Fe. knee at [Fe/H] = -1.8 same Fe as two separate pops (Battaglia et al. 2008) No late r-process (SN II) or s-process (AGB) contribs, thus NO late SF in Scl, consistent with its CMD SFH.
LMC Pompeia, Hill et al Sgr Sbordone et al Fornax Letarte PhD 2007 Sculptor Hill et al in prep + Geisler et al Milky-Way Venn et al Surprisingly similar results from MRS (R<5000) Kirby et al 2009
LMC Pompeia, Hill et al Sgr Sbordone et al Fornax Letarte PhD 2007 Sculptor Hill et al in prep + Geisler et al Carina Koch et al. 2008, Venn et al Shetrone et al Milky-Way Venn et al Position of the [alpha/Fe] knee forms a sequence following SFH and galaxy mass/luminosity. Another knee in the r/s process, at lower Fe Since the r-process is more rare, then this knee is a finer tracer of enrichment times & mixing. Abundance patterns in the metal poor stars ([Fe/H] < -2) seem similar everywhere...
Comment on MWG disk(s) Dwarf stars do not resemble the MWG disk(s): + offset between thick & thin favours dilution in thin by HI (Bensby et al. 2003, Brook et al. 2005) THICK THIN How do you make younger (THIN) disk stars more metal-poor or more alpha-poor?
Metal Poor Stars: Are the abundance patterns similar in all of the metal poor stars ([Fe/H] < -2) in the MWG halo? and all of the dwarfs? and all of the UFDs? (whatever they may be) If so, what does that mean? Simon & Geha 2007
Helmi et al. 2006Kirby et al MRS (8 UFDs) but such small # statistics. A little bit of history: Early on (Helmi etal 2006), we had suggested that the MW halo could not be made from dSph at early times due to MDFs in the MW halo and dSphs We were unaware of scaling factors for the HES (Schoerck et al. 2008), and our [Fe/H] came from CaT (new calibration: Starkenburg et al. 2010)
Today : [alpha/Fe] the similar MDFs for metal poor stars in the MW halo & dSphs, and similarities in chemical patterns, do favour halo formation at early times from accretion of dwarf galaxies. SCL FNX - cleaner & more similar. SCL Com Ber, UMa II Hercules (Draco/Draco) - again, mixed bag... Frebel et al Tafelmeyer et al. 2010
Most metal poor stars in the dSph and UFDs are similar in chemistry to those in the MW halo. SCL FNX - cleaner & more similar. SCL Com Ber, UMa II Hercules (Draco/Draco) - weak/main r -process, SN winds ?? - AGB binary mass transfer Frebel et al Tafelmeyer et al Today : [Ba/Fe]
Frebel et al 2010 UFDs promising for finding metal poor stars, But scientific impact is severely limited by lack of stars Trimming of Willman 1 by Siegel, Shetrone & Irwin 2008
Scientific Impact of UFDs also limited by our lack of understanding of what they are : not all the same Strigari et al tidal features: Seg I, U Ma II members?: Willman 1, Hercules binaries: Boo I satellites of Sgr: Seg I, Seg II, Boo II, Coma UF star clusters: Seg III Niederste-Ostholt +l 2009, Munoz Siegel etal 2008, Aden etal 2009 Koposov et al 2010 Belokurov et al Belokurov et al. 2010
Aquarius simulations (Gao et al 2010): first stars at z=0 in dwarfs & bulge
1% earliest1% lowest metallicity White & Springel “low metallicity stars may be quite young, and indeed may continue to form today in low mass, isolated dwarf galaxies”
z=10 z=5 z=3 Tornatore, Ferrara, Schneider 2007 Inhomogeneous mixing in a hierarchical merging model
H2 cooling mini halos from before reionization Salvadori & Ferrara 2010 (May) Note: Salvadori et al comment that the MDFs from their H2 cooling minihalo model is ~the same as the inhomogeneous mixing hierarchical merging model (2007) and that “full physical modelling of metal mixing and diffusion remains one of the largest uncertainties in galaxy formation”
If UFDs are fossils from reionization OR If UFDs are late collapsing halos OR If UFDs are satellites of satellites But Not if UFDs are disrupted bits of star clusters Then they can be metal poor, and show some chemical evolution... But it is not clear that they would have the same chemical abundance patterns to one another...
SFH, IMF SN feedback Models by Fenner et al SFH + SN feedbk SFH z > 6 A - SN feedback
Stochastic sampling of the IMF? So little mass turned into stars, then cannot expect the IMF to be fully & similarly populated in each UFD. Heger & Woosley (2009) Pop III SN yields for 1.2B explosion, standard mixing, and different lower mass cut offs. Therefore, might expect variations in chemical abundance ratios from Pop III SN And certainly from Pop II SN, though uncertainties in the r-process(es) make predictions difficult beyond scaled-solar.
Summary: 1. The metal poor MW halo certainly formed from the accretion of dwarfs early on – but whether those building blocks resemble the dSph or UFDs that we see today remains unclear (except in the outer halo). 2. UFDs are a great place to find metal-poor stars, but it is not clear they are related to first stars or fossils from reionization. 3. dSphs include more stars overall, and also seem to have metal poor stars that could be more clearly linked to first stars, based on chemical evolution & CMD SFHs.
Properties of Isolated Dwarfs ???
WLM a gas rich, isolated dwarf
Leaman et al RGB members: velocities, ages, & metallicities. Targets, spectra, and metallicities:
WLM's stars lag the HI gas – v_rot stars ~ 20 km/s - center of rotation offsets - all stellar pops (young/old, metal rich/poor) decoupled from gas Leaman et al. 2009, 2010
Metal rich more central Outer metal-poor stars have higher velocity dispersion - starting to look like a halo - no outer AGB analysis yet Separate populations by metallicity and kinematics:
Youngest stars (<100 Myr) & gas are coupled, but not the RGBs (1-12 Gyr) HII: Lee et al AI : Venn et al BI : Bresolin et al 2005
Leaman et al Old, metal poor population fits closed/leaky box model better - Suggests cold HI infall has contributed to recent and intermediate-aged star formation events. Closed/leaky box model by age:
WLM & NGC Older, metal-poor stars in a spheroid, like dSphs - Younger, metal-rich RGB stars kinematically colder, like thick disk - HI and youngest stars in a thin disk de Blok & Walter 2008 NGC 6822
Case of Pegasus: Is WLM another polar ring galaxy? Are WLM & NGC 6822 both dSphs with recent cold HI infall!? Are all dwarfs stripped when they enter the Local Group? like Pegasus? McConnachie, KV, et al. 2009