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; 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 !