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M EET THE N EIGHBORS : SEGUE R ESULTS F OR T HE D ISK Jennifer - - PowerPoint PPT Presentation
M EET THE N EIGHBORS : SEGUE R ESULTS F OR T HE D ISK Jennifer - - PowerPoint PPT Presentation
M EET THE N EIGHBORS : SEGUE R ESULTS F OR T HE D ISK Jennifer Johnson Ohio State University B EAUTIFUL S PIRAL G ALAXIES T HE P RIME OF T HE M ILKY W AY The Milky Way has a record of this, if we can disentangle it! Hopkins & Beacom 2006;
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THE PRIME OF THE MILKY WAY
The Milky Way has a record of this, if we can disentangle it!
Hopkins & Beacom 2006; Fakhouri et al. 2010
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THE PRIME OF THE MILKY WAY
The Milky Way has a record of this, if we can disentangle it!
Hopkins & Beacom 2006; Fakhouri et al. 2010
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FOCUS ON THE THICK DISK
Thick disks common in spiral galaxies (Morrison
et al. 1993, Yoachim & Dalcanton 2005)
Stars are not left to circle the Galaxy
undisturbed!
What has the history of the Galaxy done to the
disk?
Radial mixing (e.g ., Roskar et al. 2008, Schoenrich &
Binney 2009)
Other secular evolution (e.g. effects of bar) Satellite pass bys (e.g. Quinn et al. 1993) Satellite merging (e.g Abadi et al. 2003) Gas infall
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PRESENTATION OF DISK WORK IN PROGRESS
Kinematics for Chemically Distinct Stars
- Y. S. Lee, T. Beers +
Radial Metallicity Gradient in the Milky Way
Disk
- J. Cheung, C. Rockosi, H. Morrison, R. Schoenrich, +
The Milky Way Metallicity Distribution as a
Function of Position and Kinematics
- K. Schlesinger, JAJ, H. Morrison, Kelly Holley-
Bockelmann, L. Palladino, R. Schoenrich
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A SINGLE PLOT TO REPRESENT YEARS OF RESEARCH
Bensby et al. 2004
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ADVANTAGES OF SEGUE
Kinematically unbiased Photometrically biased Defined color cut criteria ugriz photometry Target information in the CAS 400,000 spectra = lots! Spectra: radial velocities, [Fe/H], [α/Fe], large
number of spectra indices (Lee et al. 2008, Yanny et al. 2009, Smolinski et al. 2010)
Proper motions for nearby stars
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LEE ET AL
KINEMATICS FOR CHEMICALLY DISTINCT STARS
- SEGUE F/G type stars in the color range of 0.2 < g-r < 0.55
- Among 70,000, about 48,000 selected with well determined
stellar parameters, including [α/Fe], from the SSPP, radial velocities, distances, and proper motions
- Computed U, V, W, Vφ, Rapo, Rperi, Zmax, and eccentricity
- Selected ~ 20,000 stars with log g > 4.2, S/N > 30, |Z| < 2 kpc,
7 < R/kpc < 11, [Fe/H] > -1.4, and Vφ > 50 km/s
- Define thin disk stars = [α/Fe] < 0.2, thick disk stars =
[α/Fe] > 0.3
- [α/Fe] derived from SEGUE spectra (Lee et al. 2010, AJ, in
press)
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DISTRIBUTION OF [FE/H] AND VΦ
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TREND OF ROTATIONAL VELOCITY
See also, e.g. Navarro et al. 2010
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DISTRIBUTION OF ECCENTRICITY
Sales et al. (2009) SEGUE sample
See also Dierickx, et al. 2010, Wilson et al. 2010
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CHEUNG, ET AL RADIAL METALLICITY GRADIENTS IN THE DISK
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SAMPLE
Low-latitude target scheme – focused on turnoff
stars
7712 stars with 5000 < T < 7000 K Distance for turnoff stars are tricky Observed Distribution weighted Area Sampling Color-Magnitude Sampling Luminosity Sampling Ongoing tests include comparing “observed”
Schoenrich model with underlying parameters
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PRELIMINARY RADIAL GRADIENTS
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COMPARISON OF SLOPES WITH LITERATURE
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SCHLESINGER, ET AL METALLICITY DISTRIBUTION FUNCTIONS
Based on “G” and “K” sample, broad color cuts
- nly – not true for all categories – DR7
S/N > 10, log g > 4.1, SSPP-measured [Fe/H] For most metallicities, color cuts redder than
turnoff – distance estimation easier
Isochrone-based distances and masses “Volume”-limited samples G+K sample : 0.75 kpc – 1.8 kpc G sample 0.75 kpc – 5 kpc ~35,700 G and 20,900 K dwarfs with parameters Volume-limited: 19,482 G+K dwarfs; 26,269 G
dwarfs
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MDF CORRECTIONS
Weighting to account for
uneven sampling of spectra in the g-r,r plane
Correction for targeting in
multiple categories (i.e. G dwarf and metal-poor)
LF function correction Effect on distances of
including subgiants and binaries (Schlesinger et al. 2010, ApJ, in press)
[Fe/H] measurements from
SSPP (above solar) = DR8
Effect of isochrone choice
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METALLICITY DISTRIBUTION FUNCTION
Preliminary result Volume-limited sample of G and K dwarfs Compare with other results, e.g., Geneva- Copenhagen Compare with models: Besancon and TRILEGAL, for example
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MDF AS A FUNCTION OF Z FOR GD
See e.g, Gilmore & Wyse 1995, Allende Prieto et al. 2006
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MDFS AND KINEMATICS
Preliminary result Volume-limited sample
- f G and K dwarfs
MDF of all Galactic components (within 1.8 kpc) Interesting connection to work within SEGUE to characterize the metal-rich halo component.
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