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The Sagittarius debris in SDSS stripe 82. 朱玲 Martin. smith. 2010.05.27. OUTLINE. Backgroud Motivation Sample selection A new stream Constrains to the sgr progenitor. The Sagittarius debris : a drawf galaxy being accreted by Milky way. sun. M. Niederste-Ostholt. et al 2009.
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The Sagittarius debris in SDSS stripe 82 朱玲 Martin. smith. 2010.05.27
OUTLINE • Backgroud • Motivation • Sample selection • A new stream • Constrains to the sgr progenitor
The Sagittarius debris: a drawf galaxy being accreted by Milky way sun M. Niederste-Ostholt. et al 2009 Hierarchical evolution of galaxy. M giants selected from 2MASS. (bright red stars at the typical sgr distance.) gray: SDSS footprint.
The Sagittarius debris Center of Milky Way In the orbital plane of sgr. distance distribution of the dot-dashed slice of the stream, width~6 kpc. To constrain the mass of the progenitor, we need the velocity dispersion of the sgr debris. sun M. Niederste-Ostholt. et al 2009
The SDSS stripe Over density. most of the stars do not have spectra. lots of stars in stripe 82 have spectra. ~ radial velocity, surface gravity, temperature, metallicity.
The kinds of stars that may trace sgr debris • RR lyrae • A-color stars (BHBs and BSs) • M-giants, Red-giants • Giants, sgr is far away, bright enough to be detected. • Distinguish from the halo stars. density distribution. • Distances can be obtained. Absolute mag ~ 0.7 An CMD from a old globular cluster.
Motive: try to select a clear sample of sgr in a small region • A-color stars. (BHBs + BSs) • SDSS dr8 • Try to pick out the the stars peaked at ~ -130 km/s. Pick out the sgr debris from the halo stars. • As clean as possible, as large as possible Velocity distribution of halo stars
Sample Selection • a) Color-color. surface Gravity. (BHBs + BSs, Red Giants) • b) Region. RA (15, 50) no features
Sample Selection BSs BHBs 19.2. 20 kpc • c) Distance. ~ apparant magnitude. • A-color = BHBs + BSs • The only parameter that can separate BHBs and BSs is surface gravity. • M0_BHB=0.7mag • M0_BS=2.7 mag (large dispersion). • m-M0=5logd/pc-5 18.7. 40 kpc 17.2. 20 kpc The apparant mag of G band Distance distribution of all the BHBs surface gravity not all the stars have surface gravity measurement. especially for some very faint stars.
Sample selection Most of stars fainter then 18.7 are BSs, Very rare BHBs exist at G0 > 18.7. Most of the faint stars with no logga measurement are BSs. G0 gt 18.7, RA (15, 50) Do not have logga,fainter Have logga
Sample selection BHB: 76 • BHBs: 2 < logga < 3.8, 17.2 < G0 < 18.7, 15 < RA < 50 • BSs: 3.8 < logga < 5, 18.3 < G0 < 20.7, 15 < RA < 50 • faint: no logga (logga < 0), G0 > 18.7 (if no features exist in d > 40 kpc, almost all of them are BSs), 15 < RA < 50 BS: 91 faint: 123 BHB+BS: p2*exp(-(x-p0)^2/(2*(p1^2))) -130.7 23.8 12.9 -44.8 16.4 6.2
A new stream? Black plus: BSs Blue Asterisk: BHBs Yellow diamond: faint stars without logga Measurement. 1) A compact stream at RA (15, 30), D (25,32) kpc. mainly BHBs. some faint. No BSs, due to detect limit 2) For sgr stream. small gradient with RA and no gradient with distance BSs and faint stars have been shifted 2 mag left, so magnitude represents distance. No pluses at this G0: detection limit
A new stream? metallicity distribution centus BSs BHBs 1) 'centus' are metal poor BHBs 2) BSs in Sag is much metal richer than BHBs. BHBs in sag have the same metallicity as halo BHBs, BSs in sag are metal richer than halo BSs. (halo BHBs and halo BSs have the same metal rich) There is no significant gradient between logga and G0 for BSs, So it is unlikely to be caused by measurement.
