Composition and Kinematics of the Bulge Composition and Kinematics - PowerPoint PPT Presentation

Composition and Kinematics of the Bulge Composition and Kinematics of the Bulge R. Michael Rich (UCLA) , Christian Johnson (UCLA) Andreas Koch (ZAH) Juntai Shen (Shanghai Observatory) Christian Johnson (UCLA), Andreas Koch (ZAH), Juntai Shen (Shanghai Observatory), HongSheng Zhao (St. Andrews), John Kormendy (UT Austin), Will Clarskon (UCLA) Roberto de Propris (ESO and FINCA), Livia Origlia (Bologna) Annie Robin (Besancon), Mario Soto (STScI), Christian Howard (Google Inc) Annie Robin (Besancon), Mario Soto (STScI), Christian Howard (Google Inc) HST Legacy Funding: NSF AST-0709479

Bulges appear be either spheroidal (classical) or barlike (pseudobulge) barlike (pseudobulge) Canonical formation picture is that spheroidal Canonical formation picture is that spheroidal forms via early mergers, while pseudobulges/bars evolve from a buckling instability over longer evolve from a buckling instability over longer timescales. Milky Way has dynamics characteristic of pseudobulges, yet age/chemistry consistent with d b l t / h i t i t t ith rapid formation. 7 Korean Workshop

Imelli et al. 2004; Elmegreen et al. (2008) - major merger origin Clumps dissipate rapidly into bulge or Classical early merger.. Multiple star forming clumps might produce kinematic subgroups with distinct chemical or dynamical fingerprints. Abadi 2003 Imelli et al. 2004 See also Inoue et al 2013 Elmegreen et al See also Inoue et al. 2013, Elmegreen et al. 7 Korean Workshop

N-body bar models attractive for representing the bulge However, extended formation models favored; bar survival? , ; Bar dissolves due to central mass (Norman et al. 1996) Combes 09- bar resurrection via gas inflow inflow Vertical thickening of the bar into a bulge would leave no g f g abundance gradient in the z-direction. 7 Korean Workshop

Bulge in Context Bulge in Context 2MASS 2MASS 이미지를 표시할 수 없습니다 . 컴퓨터 메모리가 부족하여 이미지를 열 수 없거나 이미지가 손상되었습니다 . 컴퓨터를 다시 시작한 후 파일을 다시 여십시오 . 여전히 빨간색 x 가 나타나면 이미지를 삭제한 다음 다시 삽입해야 합니다 . Oph SFR (foreground) Baade's Window Baade s Window Sgr dSph Sgr dSph (28 kpc) Wyse et al. (1997) 7 Korean Workshop Courtesy J. Fulbright

Age constraint from PM separation Clarkson et al. 08 ~99% of bulge older than 5Gyr; pure 10+ Gyr likely (Clarkson+ 08, 09 7 Korean Workshop

Bensby et al. 2012, 2013 Microlensed bulge dwarfs: self-consistent log g, Teff > possible young, metal rich population, possible complexity o ng metal rich pop lation possible comple it A major goal of composition studies is to place limits on j g p p complexity of the populations. 7 Korean Workshop

BRAVA Rich et al. 2007 ApJ 658, L29 First proposal 2003 Rich 2007 Howard et al. 2008 , 2009 ApJ First proposal 2003 Rich+ 2007 Howard et al. 2008 , 2009 ApJ Shen et al. 2010 ApJ; Kunder et al. 2011 AJ Special thanks to Roberto de Propris and Andrea Kunder St t Strategy: Use M giants brighter than clump that can be observed even in high extinction U M i t b i ht th l th t b b d i hi h ti ti fields. M giants also trace the 2um light of the bulge Select M giants from 2MASS survey (excellent, uniform, astrometry and photometry; ease S l t M i t f 2MASS ( ll t if t t d h t t of developing links to spectra for a public database Clear red giant branch easily seen in 2MASS data; bulge membership Cl d i t b h il i 2MASS d t b l b hi Cross correlation from 7000 - 9000A (include Ca IR triplet) Abundances from either future IR studies or from modeling of optical spectra 3x10 min exposures with Hydra fiber spectrograph at CTIO Blanco 4m; 100 stars/field 3x10 min exposures with Hydra fiber spectrograph at CTIO Blanco 4m; ~100 stars/field R~4000 9 000 stars to date; website and public data release aim for 2010 9,000 stars to date; website and public data release aim for 2010 7 Korean Workshop

Survey Fields 2005: blue 2006: red 2007: green Goal: Grid of fields at 1 deg intervals, covering 10x10 deg box, pushing as close to plane as possible 7 Korean Workshop

Target Selection Howard et al. 2008 b=-4 dereddened Kunder et al. 2011, new sample 7 Korean Workshop

Larger samples have not confirmed 2 stream candidates; all candidates will be followed up Reitzel candidates; all candidates will be followed up. Reitzel et al. (2007) simulations suggest ~1 “real” stream Stream followup important Possible origins from disrupted globular Stream followup important. Possible origins from disrupted globular clusters or dwarf galaxies, groups of stars in unusual orbit families; all candidates presently assumed to be Poisson statistics caused. p y 7 Korean Workshop

-4 -8 Cylindrical rotation y Zhao 1996 7 Korean Workshop

7 Korean Workshop

Most recent results (Kunder et al. 2011) 7 Korean Workshop

Major Axis showing cylindrical rotation (Fit is Shen et al. 2010) 7 Korean Workshop

Minor axis with Shen et al. (2010) fit 7 Korean Workshop

BRAVA BRAVA vs ARGOS (Ness+ 13) ARGOS (N + 13) At |l|>10 are stars bulge or disk members? 7 Korean Workshop

ARGOS all Metal Poor 5% likely inner halo members 7 Korean Workshop

Modeling the Milky Way Bulge Sh Shen, Rich et al. 2010 Ri h t l 2010 A simple model of the • Galactic bulge matches the BRAVA data extremely well in almost all aspects: b = ‐ 4 o major axis – b = ‐ 8 o degree major axis – l = 0 o degree minor axis – Surface density Surface density – – Shen, J., RMR, Kormendy et al 2010, ApJL submitted, al 2010, ApJL submitted, arXiv:1005.0385

Modeling the Milky Way Bulge --- Surface Brightness Map Sun DIRBE Composite map The bar angle from kinematic constraint is about ~ 20 o – The bar angle from kinematic constraint is about 20 – The bar’s axial ratio is about 0.5 to 0.6, and its half-length is ~4kpc

Th The Shen et al. 2010 model has an X-shaped structure Sh t l 2010 d l h X h d t t Li & Shen 2012 astro ph Li & Shen 2012 astro-ph 7 Korean Workshop

Modeling the Milky Way Bulge --- Modeling the Milky Way Bulge Match stellar kinematics in all strips strikingly well Black line = model; it is not a fit of data points

A Significant Classical Bulge is Excluded The data excludes a pre ‐ existing classical bulge with mass >~ 10% M di k mass >~ 10% M disk

Summary from modeling of the BRAVA kinematics Shen, J., RMR, Kormendy et al 2010 kinematics Shen, J., RMR, Kormendy et al 2010 • Our simple, but realistic, model can match BRAVA kinematics of the Galactic bulge strikingly well h G l i b l iki l ll – No need for a contrived model with many free parameters • The bulge is simply the bar viewed edge on; it is part of the disk • The bulge is simply the bar viewed edge-on; it is part of the disk, not a separate component. • A significant classical bulge is excluded so our MW is an nearly A significant classical bulge is excluded, so our MW is an nearly pure-disk galaxy • Giant pure disk galaxies like our own MW present a major • Giant, pure-disk galaxies like our own MW present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers dominated by hierarchical clustering and galaxy mergers • Many pure disk galaxies in local U. (Kormendy & Barentine 2010; Kormendy et al 2010) Kormendy et al. 2010) • N-body models support the idea that the bar formed from a massive disk massive disk completely consistent with BRAVA kinematics. l t l i t t ith BRAVA ki ti

A Problem: Abundance gradient in the outer bulge Cylindrical rotation a characteristic of pseudobulges but Cylindrical rotation a characteristic of pseudobulges, but should not exhibit abundance gradient, since buckling models are not dissipative. Location on Binney plot similar to NGC 4565. Zoccali et al. 2008 with Johnson et al. 2011 for -8 deg 7 Korean Workshop

But no abundance gradient <4 o (Rich, Origlia, Valenti; 2011) 7 Korean Workshop

Abundance Gradient Problem solved? Martinez-Valpuesta & Gerhard (2013) show that an N-body disk with a preexisting radial gradient can buckle and produce bar with strong vertical gradient. Loosely bound metal poor stars migrate to greater vertical distance. g y p g g New finding actually overturns earlier work in the subjct. 7 Korean Workshop

The Milky Way shares much in common with NGC 4565 K Kormendy & d & ( (peanut bulge, abudance b l b d Kennicutt 2004 gradient) BRAVA places Milky Way on Binney plot. Way on Binney plot. MW 7 Korean Workshop

Kormendy Illingworth 82 NGC 4565 has a boxy Proctor et al. 00 pseudobulge cylindrical pseudobulge, cylindrical rotation like in the Milky Way bulge, and has a steep abundance gradient in the z direction. Winds may be important 7 Korean Workshop

The Age/Pseudobulge Paradox Clarkson et al. 08 ~99% of bulge older than 5Gyr; pure 10+ Gyr likely (Clarkson+ 08, 09 Cylindrical rotation morphology consistent with pseudobulge (young?) Cylindrical rotation, morphology, consistent with pseudobulge (young?) Abundance gradient of MW, NGC 4565 – but how? If N-body models? 7 Korean Workshop