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; Fakhouri et al. 2010
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; Fakhouri et al. 2010
F OCUS 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
P RESENTATION OF D ISK W ORK IN P ROGRESS 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
A S INGLE P LOT T O R EPRESENT Y EARS OF R ESEARCH Bensby et al. 2004
A DVANTAGES 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
L EE ET AL K INEMATICS FOR C HEMICALLY D ISTINCT S TARS • 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, V φ , R apo , R peri , Z max , 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 V φ > 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)
D ISTRIBUTION OF [F E /H] AND V Φ
T REND OF R OTATIONAL V ELOCITY See also, e.g. Navarro et al. 2010
D ISTRIBUTION OF E CCENTRICITY SEGUE sample Sales et al. (2009) See also Dierickx, et al. 2010, Wilson et al. 2010
C HEUNG , ET AL R ADIAL M ETALLICITY G RADIENTS IN THE D ISK
S AMPLE 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
P RELIMINARY R ADIAL G RADIENTS
C OMPARISON OF S LOPES WITH L ITERATURE
S CHLESINGER , ET AL M ETALLICITY D ISTRIBUTION F UNCTIONS Based on “G” and “K” sample, broad color cuts only – 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
MDF C ORRECTIONS 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
M ETALLICITY D ISTRIBUTION F UNCTION 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
MDF AS A FUNCTION OF Z FOR GD See e.g, Gilmore & Wyse 1995, Allende Prieto et al. 2006
MDF S AND K INEMATICS Preliminary result Volume-limited sample of 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.
P ROGRESS !
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