Bulges of Spiral Galaxies: Stellar Populations, Structure, and Kinematics Bhasker Moorthy Jon Holtzman Anatoly Klypin New Mexico State University

Motivation – Why Bulges? Key to understanding origin of Hubble sequence Bridge together properties of disks and ellipticals Provide insight into a wide range of mechanisms involved in the formation and evolution of galaxies  Merging and accretion  Star formation  Feedback from SN II and SN 1a  Galactic winds  Secular processes - bar formation, vertical and radial transport, disk heating, new star formation, bar destruction?

Early-typed bulges: Similar to ellipticals Same or similar fundamental plane relation (Falcón-Barroso et al. 2002) Similar light profiles (eg: Baggett et al. 1998; Carollo et al. 1997) Similar luminosity-weighted (SSP) ages and Mg-  relations (eg: Idiart et al. 1996) Color and line strength gradients (Balcells & Peletier 1994; Fisher et al. 1996) Milky Way bulge stars are predominantly old with larger Mg/Fe ratios than disk stars (eg: Feltzing & Gilmore 2000; Fulbright et al. 2004) Correlation in scale lengths (eg: MacArthur et al. 2003) Small Sersic indices (eg: Balcells et al. 2003) Smaller SSP ages than ellipticals (Proctor & Sansom 2002) Similar colors (eg: MacArthur et al. 2004) Emission lines  Prugniel et al  B/P bulges bars (eg: Chung & Bureau 2004; Athanassoula 2005) Rotational support (eg: Kormendy & Illingworth 1982) Late-types: Similar to disks

Stellar Populations and Formation Mechanisms Luminosity-weighted ages and abundance ratios (eg. Mg/Fe) constrain epochs and duration of star formation Similarities between bulge and disk populations suggestive of secular evolution Dissipationless Secular Evolution:  Decrease in scale length might amplify metallicity gradients while increase in velocity dispersion might wash them out Disk-driven evolution with gas funneling:  Could trigger new star formation, producing a negative metallicity gradient (Friedli et al. 1994)  Not necessarily secular

Our Project Study stellar populations, structure, and kinematics of bulges as a means of constraining their formation mechanisms  Particularly interested in seeing whether or not stellar populations show evidence for secular evolution Long-slit spectroscopy with ARC 3.5m/DIS at APO  Wavelength coverage: Å at 6-8 Å resolution  Absorption (Lick indices) and emission lines  Rotation curves and velocity dispersion profiles Imaging with ARC 3.5m/SPIcam  Bulge-to-disk decomposition to determine disk contamination and obtain structural properties

The Galaxy Sample 38 nearby (v res <7000 km/s) mostly isolated galaxies spanning a wide range in Hubble type (S0-Sc) Selected galaxies whose bulges are very similar in color to their disks and a control sample with redder bulges (Balcells & Peletier 1994; de Jong & van der Kruit 1994) Included 3 other galaxies previously identified as having disk-like bulges based on their structure and kinematics (Erwin et al. 2003; de Zeeuw et al. 2002; Sil’chenko et al. 2003; Pinkney et al. 2003; Kormendy & Kennicutt 2004 )

Rotational Vs. Pressure Support Bulge Ellipticity (V max /  bulge Bulge Ellipticity Based on Binney (1978) and Kormendy & Kennicutt (2004)

Central Line Strengths SSP Models from Thomas, Maraston, & Bender (2003); Crosses from Trager et al. (1998) [MgFe]’ HH HH

Central Line Strengths Vs. Kinematics and Dynamics [MgFe]’ Mgb/  V max

Metallicity Gradients Radius (kpc) [MgFe]’ Radius (kpc) [MgFe]’ Sa S0 Sb Sa S0 Sb Sc

Gradients in  /Fe Radius (kpc) Mgb Radius (kpc) Mgb/ Sa S0 SbS0 Sb Sc

Main Results Red bulges are similar to luminous ellipticals in their central stellar populations  Hubble types S0-Sb  Intermediate-large SSP age  Super-solar Z/H  Super-solar  /Fe Blue bulges exhibit larger scatter and appear similar to low- luminosity ellipticals in their central stellar populations  Uniformly solar  /Fe  Metal-poor class: Sb-Sc, emission lines  Young metal-rich class: all Hubble types Central metallicity and  /Fe are sensitive to  and V max  Barred galaxies add scatter to Metallicity-V max relation but not  /Fe–V max relation Gradients support disk-driven evolution picture for many galaxies  Bulges of barred galaxies, boxy/peanut bulges, and bulges with disk-like kinematics are more often similar to their disks in their stellar populations

Additional Hints Galaxies with largest central metallicities are barred or have b/p bulges  Extra enrichment from bar-driven gas inflow? NGC 2599 and late-typed blue bulges – Unbarred but bulge stellar populations nearly identical to those of disk  Secular evolution with bar destruction?