Chemical Abundances, Dwarf Spheroidals and Tidal Streams

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Chemical Abundances, Dwarf Spheroidals and Tidal
Streams

• Steven Majewski
• (University of Virginia)
• Principal Collaborators
• Mei-Yin Chou (UVa - Ph.D. thesis), Katia Cunha,
  Verne Smith (NOAO), David Martínez-Delgado (IAC),
  David Law (UCLA), Jeffrey Carlin (UVa - Ph.D.
  thesis), Ricardo Munoz (Yale)

Image credit David Law SRM
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• Topics Discussed
• 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

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Hierarchical Formation of Halos

• Today 1 stream with
• lt 30 mag/arcsec2 attached to still-bound
  satellite should be visible per MW-like
  galaxy.(Johnston et al., in prep.)

Font et al. (2006)
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Prominent Tidal Streams around Disk Galaxies
NGC 4013
Milky Way
NGC 5907
Sgr Model (Law et al. 2005)
Martinez-Delgado, Gabany et al. (2008, 2009)
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Chemical HistoriesDistinctive abundance
patterns-- a/Fe, s-process (Y, La, etc.)--
reflect the unique chemical history of the parent
system, e.g., a/Fe (Ti, Mg, O, etc.)
indicates the Type II/Type Ia SNe ratio of the
parent system
From McWilliam (1997)
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Halo Thick disk Thin disk
Chemical HistoriesThe MW Halo / dSph
(Dis?)Connection
dSph stars
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 dSph progenitors
Compilation from Venn et al. (2004)
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Explaining the Halo/dSph Chemical Dichotomy

• Font et al. (2006), Robertson et al. (2005)
• Bulk of halo from massive, Magellanic Cloud-sized
  accreted early on, when chemistry dominated by
  SNII.

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Explaining the Halo/dSph Chemical Dichotomy

• Majewski et al. (2002), Munoz et al. (2006,
  2008)
• Satellites with prolonged chemical evolution and
  tidal disruption naturally leads to evolution in
  types of stars contributed to MW halo.

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Chemical Study of the Sgr dSph Tidal Stream

• Results 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 leads
• to focus on the leading arm.

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R 35000
Derivation of Abundances MOOG (Sneden 1973) An
LTE Stellar Line Analysis Program
Ti
Ti
- Teff from J-K (Houdashelt et al. 2000) - log g
from isochrone (Girardi et al. 2000) - Initial
metallicity guess
EW measurements
Model Atmosphere Line List
log g
MOOG
log Teff
Fe/H and x/Fe
If the output Fe/H not consistent
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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 Gyr 3 orbits ago
2.2 Gyr 4 orbits ago 3.1 Gyr 1 radial
period 0.85 Gyr
Model (Law et al. 2005)
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Sgr Leading Arms and an NGP Moving
Group Brightest stars (Klt 10) in Sgr
core Leading 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
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• 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
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Strong Metallicity Gradient along the tidal
tail! Chemical differences between the core and
the tails!
(Chou et al. 2007, ApJ, 670, 346)
-0.4

• 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 gradientor suffered a
  catastrophic loss withstars lost over a more
  normal gradient.

-0.7
-1.2
-1.0
Median Fe/H of NGP group is similar to Sgr
leading arm south
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• 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 core
MDF of Sgr tails
MDF of Sgr tails
Sum
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Chemical Distributions in Sgr Stream Ti/Fe vs.
Fe/H
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)
Sgr resembles LMC more than other dSphs LMC
stars from Pompéia et al. (2008)
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Chemical Distributions in Sgr Stream Y/Fe vs.
Fe/H
YII
Sgr resembles LMC more than other dSphs
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La II line affected by hyperfine splitting
Chemical Distributions in Sgr Stream La/Fe vs.
Fe/H
Here Sgr differs a little from LMC
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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

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Similar Enrichment, Different Timescales
Clear SFR difference among dSphs, LMC and Sgr
Hypothetical differences in chemical history
1 dex dSphs
0.5 dex LMC
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SFR differs in Galactic satellites
A universal enrichment historyvarying only by
rate??
Hypothetical differences in chemical history
1 dex dSphs
SFR slow to fast dSphs ? LMC ? Sgr ?MW
0.5 dex LMC
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• 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
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• 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 (R40k) H-band spectra

Model (Law et al. 2005)
72 in these regions
10 stars in each region from Gemini South
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Note that dynamically oldest of the Sgrstream
stars are ?-enhanced -- but contributed within
past few Gyr
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Explaining the Halo/dSph Chemical Dichotomy

• Font et al. (2006)
• Satellites accreted gt9 Gyr ago all destroyed,
  surviving satellites only recently accreted --gt
  implies not major contributorsSgr exceptionary
  case? (e.g., only dSph presently in inner halo)

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But Carina dSph is also contributing stars today

undoubtedly some with ?-enhancement.
Munoz et al. (2007, in prep.)
Carina
Koch et al. (2008)
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Slide removed (Work In Progress)
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Slide removed (Work In Progress)
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Slide removed (Work In Progress)
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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 lt 0.5 km/s
• 0.1 dex precision abundances for 15 chemical
  elements
• 105, 2MASS-selected, giant stars probing all
  Galactic populations

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• Expected elements and S/N tests _at_ R21k and 0.1
  dex precision
• precision will degrade for lower S/N
• S/N100 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/H0 Na 2673.7 309.8 56.0 S
1067.2 167.2 104.8 V 1504.7 164.4 42.4 K
505.6 75.3 44.6 Mn 184.9 50.9 46.9 Ni
101.6 45.7 46.4 Ca 89.5 42.7 41.0 Al
47.2 41.8 42.1 Si 35.2 38.6 35.7 N
147.3 41.7 21.4 Ti 110.0 36.5 38.9 Mg
33.1 36.7 26.4 Fe 41.6 34.3 21.3 C
40.4 14.8 8.3 O 24.5 14.6 9.1
Must have element Important to have/very
desirable element Nice to have element (also
not shown Cr, Co)
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The Promise of Detailed Chemical Abundance Studies
The Initial Mass Function
(SiCa) / Fe
(MgTi) / Fe

• Relative abundances of different a elements
  reflects mass of SN progenitors
• Probes IMF
• (e.g., McWilliam Rich 1997 differences in a
  elements for bulge --- on right, above)

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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
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• 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.