chemistry and dynamics of stars in low mass galaxies bridging dwarfs, halos & disks kim venn u....

Chemistry and Dynamicsof Stars

in Low Mass Galaxies

Bridging Dwarfs, Halos & Disks

Kim VennU. 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 alreadydisheveled hair now,

and be used bymedicine to

turn into graduallydaily life beverage”

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 thickand thin disks.

3. Chemical and dynamical properties of stars ingas rich dwarf galaxies

Chemistry of stars comes from high resolution spectroscopy:

R > 20,000 or < 0.25 A/pix

Carina-7002: - [Fe/H] = - 2.9 - R ~ 20,000 (Magellan MIKE) - SNR ~ 20

Carina-484: - [Fe/H] = -1.7 - 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 starsin the solar neighbourhood with halo kinematics“armchair cartography” (Morrison, Sommer-Larson)

Reminder:

(V-I)

(V-I)

Tolstoy et al. 2004

But for stars in dwarf galaxies :need a large telescope, but cleaner sample ...not armchair cartography

membersnon-members

The detailed chemistry of the stars in these Galactic componentsare 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. 2004

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 11-35 Mo core collapse SN all short, compared to SNIa

SN II

SN Ia

Now, what about those chemical abundances in the dwarf galaxies?

... in 2004 ...

HALO RETRO/ECC THICK

THIN

DSPH

There has been an impressive amount of work done ondetailed chemical abundances in different environmentsin the past 6 years ...

metal poor halo, dwarf galaxies, UFDs

... with lots more in the works (e.g., Zucker's talk)

Venn et al. 2004

Frebel et al. 2010

LOTS moremetal-poorhalo stars !

UFDdSph+

But this is aMIXED BAGof 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. 2008

Milky-Way Venn et al. 2004

[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


Sgr Sbordone et al. 2007

Fornax Letarte PhD 2007


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.




Sculptor Hill et al. 2008 in prep

+ Geisler et al. 2005


Lowest end metallicity,consistent with mass-metallicity rel

Can see the [Fe/H] where SN Iabegan 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.





+ Geisler et al. 2005


Surprisingly similar results from MRS (R<5000)

Kirby et al 2009





+ Geisler et al. 2005Carina Koch et al. 2008, Venn et al. 2010

+ Shetrone et al. 2003Milky-Way Venn et al. 2004 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 tracerof enrichment times & mixing.

Abundance patterns in the metalpoor 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) diskstars more metal-poor or more alpha-poor?

Metal Poor Stars:

Are the abundance patterns similar in all of themetal 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. 2006 Kirby et al. 2009 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 formationat early times from accretion of dwarf galaxies.

SCLFNX- cleaner & more similar.

SCLCom Ber, UMa IIHercules (Draco/Draco) - again, mixed bag...

Frebel et al. 2010

Tafelmeyer et al. 2010

Most metal poor stars in the dSph and UFDs aresimilar in chemistry to those in the MW halo.

SCLFNX- cleaner & more similar.

SCLCom Ber, UMa IIHercules (Draco/Draco) - weak/main r -process, SN winds ?? - AGB binary mass transfer

Frebel et al. 2010

Tafelmeyer et al. 2010

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 bySiegel, Shetrone & Irwin 2008

Scientific Impact of UFDs also limited by our lack ofunderstanding of what they are : not all the same

Strigari et al. 2008

tidal features: Seg I, U Ma IImembers?: Willman 1, Herculesbinaries: Boo Isatellites of Sgr: Seg I, Seg II, Boo II, Coma UF star clusters: Seg III

Niederste-Ostholt +l 2009, Munoz + 2010

Siegel etal 2008, Aden etal 2009Koposov et al 2010Belokurov et al. 2009Belokurov et al. 2010

Aquarius simulations (Gao et al 2010): first stars at z=0 in dwarfs & bulge

1% earliest 1% lowest metallicity

White & Springel 2000

...“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 ahierarchical merging model

H2 cooling mini halos from before reionization

Salvadori & Ferrara 2010 (May)

Note: Salvadori et al. 2009 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 reionizationOR If UFDs are late collapsing halosORIf UFDs are satellites of satellitesBut 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 samechemical abundance patterns to one another ...

SFH, IMFSN feedback

Models byFenner et al. 2006

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 befully & 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 fromPop III SN

And certainly from Pop II SN,though uncertainties in the r-process(es) make predictionsdifficult beyond scaled-solar.

Summary:

1. The metal poor MW halo certainly formed from the accretion ofdwarfs 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. 2009

78 RGB members: velocities, ages, & metallicities.

Targets, spectra, and metallicities:

-0.6

-2.0

200

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 centralOuter metal-poor stars havehigher 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. 2005AI : Venn et al. 2003BI : Bresolin et al 2005

Leaman et al. 2009

Old, metal poor populationfits closed/leaky box modelbetter -

Suggests cold HI infallhas contributed to recentand intermediate-agedstar formation events.

Closed/leaky box model by age:

WLM & NGC6822

- 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

Alot to learn from dwarfs

chemistry and dynamics of stars in low mass galaxies bridging dwarfs, halos & disks kim venn u....

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