Chemical Abundances, Dwarf Spheroidals and Tidal Streams

Steven Majewski Steven Majewski (University of Virginia)(University of Virginia)

Principal Collaborators:Principal Collaborators:

Mei-Yin Chou (UVa - Ph.D. thesis),Mei-Yin Chou (UVa - Ph.D. thesis), Katia Cunha, Verne Smith (NOAO), Katia Cunha, Verne Smith (NOAO), David MartDavid Martíínez-Delgado (IAC), David Law (UCLA), nez-Delgado (IAC), David Law (UCLA), Jeffrey Carlin (UVa - Ph.D. thesis), Ricardo Munoz (Yale)Jeffrey Carlin (UVa - Ph.D. thesis), Ricardo Munoz (Yale)

Image credit: David Law & SRM

Topics Discussed:1. Some Motivations to Study Chemistry of Tidal Streams

• Connection between dSphs and stars in the MW halo.• Reconstruct chemical distribution of original satellite galaxies.• Learn about SFHs, chemical enrichment histories, accretion histories.• Chemical fingerprinting stars to their parent source.

2. Case Study: MDF Variation along the Sgr Stream• Find a strong metallicity gradient along the Sgr tidal tail.• Shows that Sgr originally had significant radial metallicity gradient.

3. Case Study: Chemical Patterns in the Sgr System• Find relative chemical evolution/SFH between Sgr, MW & other satellites.• Use distinctive patterns to fingerprint other Sgr stars in Galactic halo.

4. Case Study: Fingerprinting the Tri-And Star Cloud• Testing the connection to the Monoceros stream.

5. The Future with New Surveys: Comments about APOGEE

Font et al. (2006)

Hierarchical Formation

of Halos

Today ~1 stream with < 30 mag/arcsec2

attached to still-bound satellite should be visible per MW-like galaxy.

(Johnston et al., in prep.)

Prominent Tidal Streams around Disk Galaxies

NGC 5907

Sgr Model (Law et al. 2005)

Martinez-Delgado, Gabany et al. (2008, 2009)

Milky WayNGC 4013

Chemical Histories

Distinctive abundance patterns-- [Distinctive abundance patterns-- [αα/Fe], s-process (Y, La, etc.)/Fe], s-process (Y, La, etc.)-- reflect the unique chemical history of the parent system, -- reflect the unique chemical history of the parent system,

e.g., [ e.g., [αα/Fe] (Ti, Mg, O, etc.) indicates the Type II/Type Ia SNe ratio of /Fe] (Ti, Mg, O, etc.) indicates the Type II/Type Ia SNe ratio of the parent systemthe parent system

From McWilliam (1997)

1) dSphs appear to differ from MW halo (and even from each other)

2) Chemical fingerprinting(e.g., Freeman & Bland-Hawthorn 2002 - “tagging”) may possibly connect field stars to dSphprogenitors

Chemical Histories:The MW Halo / dSph (Dis?)Connection

dSph stars

Halo Thick disk Thin disk

Compilation from Venn et al. (2004)

Explaining the Halo/dSph Chemical DichotomyExplaining the Halo/dSph Chemical DichotomyFont et al. (2006), Robertson et al. (2005):Font et al. (2006), Robertson et al. (2005):

Bulk of halo from massive, Magellanic Cloud-sized accreted Bulk of halo from massive, Magellanic Cloud-sized accreted early on, when chemistry dominated by SNII.early on, when chemistry dominated by SNII.

Explaining the Halo/dSph Chemical DichotomyExplaining the Halo/dSph Chemical DichotomyMajewski et al. (2002), Munoz et al. (2006, 2008):Majewski et al. (2002), Munoz et al. (2006, 2008):

Satellites with prolonged chemical evolution and tidal Satellites with prolonged chemical evolution and tidal disruption naturally leads to evolution in types of stars disruption naturally leads to evolution in types of stars

contributed to MW halo.contributed to MW halo.

Results in Chou et al. 2007Results in Chou et al. 2007, ApJ, 670, 346, Chou et al. 2009 (~submitted),

High resolution, high S/N (50-200) spectroscopy of 2MASS-selected M giants in Sgr and its stream.

•31 stars from KPNO 4-m (R~ 35000)•12 stars from TNG 3.5-m (R~ 45000) •16 stars from Magellan 6.5-m (R~ 19000)

Use of predominantly northern telescopes leadsto focus on the leading arm.

Chemical Study of the Sgr dSph + Tidal Stream

Derivation of Abundances:MOOG (Sneden 1973): An LTE Stellar Line Analysis Program

MOOG

[Fe/H] and [x/Fe]

Model Atmosphere Line List

- Teff from J-K (Houdashelt et al. 2000)- log g from isochrone (Girardi et al. 2000)- Initial metallicity guess EW measurements

If the output[Fe/H] notconsistent

R~ 35000

log Teff

log

g

Ti Ti

The expected dynamical age of debris along the tidal stream:

Stars lost from Sgr:1 orbit ago; ~0.5 Gyr 2 orbits ago; ~1.4 Gyr3 orbits ago; ~2.2 Gyr 4 orbits ago; ~3.1 Gyr

1 radial period ~ 0.85 Gyr

Model (Law et al. 2005)

Sgr Leading Arms and an NGP Moving Group

Brightest stars (K< 10) in: Sgr coreLeading arm north (lost ~ 2 Gyrs ago)Leading arm south (lost ~ 3 Gyrs ago)

Also, peculiar group of ‘NGP’ M giant stars having radial velocities different from the main leading arm trend

Iron Abundance Analysis:

• 11 Fe I lines in a narrow spectral window ~ 7440-7590 Å (Smith & Lambert 1985, 1986, 1990)

• LTE code MOOG combined with a Kurucz ATLAS9 (1994) solar model

• Solar gf-values of Fe I lines

R ~ 35000

R ~ 45000

R ~ 19000

Strong Metallicity Gradient along the tidal tail!Chemical differences between the core and the tails!

Median [Fe/H] of NGP groupis similar to Sgr leading armsouth

-0.4

-0.7

-1.2

(Chou et al. 2007, ApJ, 670, 346)

-1.0

• Time dependence in the chemistryof stars contributed to halo.

• No MW dSph shows a metallicitygradient this strong -- e.g., largestis 0.5 dex variation across Sculptor (Tolstoy et al. 2004)

• Either Sgr lost mass over a smallradial range with enormous gradient…

…or suffered a catastrophic loss withstars lost over a more normal gradient.

Reconstructed MDF of Sgr core several Gyrs ago

• Relatively flat, more metal-poor than presently in the Sgr core

• The observed chemical properties of the presently surviving satellites may depend on their tidal stripping history

MDF of Sgr core

MDF of Sgr tails

MDF of Sgr core

MDF of Sgr tails

Sum

Chemical Distributions in Sgr Stream

[Ti/Fe] vs. [Fe/H]

Crosses are MW stars from Gratton, R. G. & Sneden, C. (1994), Fulbright, J. P. (2002), Johnson, J. (2002), and Reddy, B. E. et al. (2003)

Triangles are dSph stars from Shetrone et al. (2001 & 2003), Geisler et al. (2005),Sadakane et al. (2004)

[Fe/H]

Sgr resembles LMC more than other dSphs

LMC stars from Pompéia et al. (2008)

Chemical Distributions in Sgr Stream

[Y/Fe] vs. [Fe/H]

Sgr resembles LMC more than other dSphs

YII

Chemical Distributions in Sgr Stream

[La/Fe] vs. [Fe/H]

Here Sgr differs a little from LMC

La II line affected byhyperfine splitting

Chemical Distributions in Sgr Stream

[La/Y] vs. [Fe/H] – metal-poor AGB produce high [hs / ls], means slower SFR than MW

•Sgr resembles LMC•Sgr evolved faster than dSph,

slower than MW

+1 dex

dSphs+0.5 dex

LMC

Clear SFR difference among dSphs, LMC and Sgr

Similar Enrichment, Different Timescales

Hypothetical differences in chemical history

SFR differs in Galactic satellites

SFR slow to fast:dSphs LMC Sgr MW

+1 dex

dSphs +0.5 dex

LMC

Hypothetical differences in chemical history A “universal” enrichment historyvarying only by rate??

Chemical Fingerprinting:

What is the peculiar NGP group?

• [Fe/H] ~ -1, similar to Sgr leading arm south(dynamical age ~ 3 Gyrs)

• [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] resemble Sgr leading arm south

Suggests NGP stars are Sgr stars of same dynamical age

as leading arm south, but dynamics wrong for leading

arm

Proposed solution:NGP group are Sgr trailing arm stars overlapping with

Sgr leading arm north

Future Work on Sagittarius

• Metallicity gradient and chemical trends along the Sgr trailing arm Longer, and stars stripped at specific epoch can be more cleanly isolated.

• Gemini Phoenix (R~40k)H-band spectra

Model (Law et al. 2005)

10 stars in each region from Gemini South

7+2 in these regions

Note that dynamically oldest of the Sgrstream stars are -enhanced -- but contributed within past few Gyr

Explaining the Halo/dSph Chemical DichotomyExplaining the Halo/dSph Chemical DichotomyFont et al. (2006): Font et al. (2006):

Satellites accreted >9 Gyr ago all destroyed, surviving satellites Satellites accreted >9 Gyr ago all destroyed, surviving satellites only recently accreted --> implies not major contributorsonly recently accreted --> implies not major contributors

Sgr exceptionary case? (e.g., only dSph presently in inner halo)Sgr exceptionary case? (e.g., only dSph presently in inner halo)

Carina

Munoz et al. (2007, in prep.)

Koch et al. (2008)

But Carina dSph is also contributing stars But Carina dSph is also contributing stars todaytoday… …

… … undoubtedly some withundoubtedly some with-enhancement.-enhancement.

Slide removed (Work In Progress)

Slide removed (Work In Progress)

Slide removed (Work In Progress)

30

The Apache Point Observatory Galactic Evolution Experiment

(APOGEE)

APOGEE at a Glance

• Bright time 2011-Q2 to 2014-Q2, co-observing with MARVELS• 300 fiber, R ~ 24,000 cryogenic spectrograph• H-band window (1.51-1.68)• Minimum S/N = 100• Typical RV uncertainty < 0.5 km/s• 0.1 dex precision abundances for ~15 chemical elements• ~105, 2MASS-selected, giant stars probing all Galactic populations

Expected elements and S/N tests @ R=21k and 0.1 dex precision• precision will degrade for lower S/N• S/N=100 for faintest star in plugboard, higher S/N for brighter stars

Element SNR/pix SNR/pix SNR/pix

[Fe/H]=-2 [Fe/H]=-1 [Fe/H]=0

Na 2673.7 309.8 56.0S 1067.2 167.2 104.8V 1504.7 164.4 42.4K 505.6 75.3 44.6Mn 184.9 50.9 46.9Ni 101.6 45.7 46.4Ca 89.5 42.7 41.0Al 47.2 41.8 42.1Si 35.2 38.6 35.7N 147.3 41.7 21.4Ti 110.0 36.5 38.9Mg 33.1 36.7 26.4Fe 41.6 34.3 21.3C 40.4 14.8 8.3O 24.5 14.6 9.1

”Must have” element“Important to have/very desirable” element“Nice to have” element (also not shown Cr, Co)

The Promise of Detailed Chemical Abundance Studies

• Relative abundances of different elements reflects mass of SN progenitors:

Probes IMF (e.g., McWilliam & Rich 1997 differences in elements for bulge --- on right, above)

The Initial Mass Function

[(Si+Ca) / Fe][(Mg+Ti) / Fe]

MARVELS Coordination - APOGEE use of 30 hr fields

Solar metallicity RGB tip star:

int (hr) Hlim AV d(kpc) 3 12.5 5 27 10 13.4 10 27 30 14.1 15 26

[Fe/H]= -1.5 RGB tip star:

int (hr) Hlim AV d(kpc) 3 12.5 0 40 10 13.4 0 60 30 14.1 0 83

Summary:

• Sgr Stream shows strong metallicity gradient• Sgr originally had strong to very strong radial metallicity gradient.• Recent tidal stripping released stars, producing observed gradient in tails.

• Sgr core of today differs from Sgr core of “yester-Gyrs”.

• Sgr recently contributed -enhanced, metal-poor stars to MW; possibly other dSphs as well (e.g., Carina).

• Overall, abundance patterns along the stream are distinct from the dSphs and MW, similar to LMC SFR differences: dSphs LMC Sgr MW (slower faster)

• Application of chemical fingerprinting demonstrated.

• Tri-And Star Cloud not chemically linked to Monoceros.

• APOGEE will access ~10-15 chemical elements in streams.