Bulges of Spiral Galaxies Stellar Populations Structure and
Bulges of Spiral Galaxies: Stellar Populations, Structure, and Kinematics Bhasker Moorthy Jon Holtzman Anatoly Klypin New Mexico State University
Motivation – Why Bulges? n n n 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 q q q Merging and accretion Star formation Feedback from SN II and SN 1 a Galactic winds Secular processes - bar formation, vertical and radial transport, disk heating, new star formation, bar destruction?
Early-typed bulges: Late-types: Similar to ellipticals to disks n n n 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-s 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) n n n n Correlation in scale lengths (eg: Mac. Arthur et al. 2003) Small Sersic indices (eg: Balcells et al. 2003) Smaller SSP ages than ellipticals (Proctor & Sansom 2002) Similar colors (eg: Mac. Arthur et al. 2004) Emission lines (Prugniel et al. 2001) B/P bulges bars (eg: Chung & Bureau 2004; Athanassoula 2005) Rotational support (eg: Kormendy & Illingworth 1982)
Stellar Populations and Formation Mechanisms n n n 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: q n 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) q Not necessarily secular q
Our Project n Study stellar populations, structure, and kinematics of bulges as a means of constraining their formation mechanisms q n Long-slit spectroscopy with ARC 3. 5 m/DIS at APO q q q n Particularly interested in seeing whether or not stellar populations show evidence for secular evolution Wavelength coverage: 4000 -8000 Å at 6 -8 Å resolution Absorption (Lick indices) and emission lines Rotation curves and velocity dispersion profiles Imaging with ARC 3. 5 m/SPIcam q Bulge-to-disk decomposition to determine disk contamination and obtain structural properties
The Galaxy Sample n n n 38 nearby (vres<7000 km/s) mostly isolated galaxies spanning a wide range in Hubble type (S 0 -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)
(Vmax/s)bulge Rotational Vs. Pressure Support Bulge Ellipticity Based on Binney (1978) and Kormendy & Kennicutt (2004) Bulge Ellipticity
Hb Hb Central Line Strengths [Mg. Fe]’ SSP Models from Thomas, Maraston, & Bender (2003); Crosses from Trager et al. (1998) [Mg. Fe]’
[Mg. Fe]’ Mgb/<Fe> Central Line Strengths Vs. Kinematics and Dynamics s Vmax
Sa S 0 [Mg. Fe]’ Metallicity Gradients S 0 Sb Sc Sa Sb Radius (kpc)
S 0 Sb S 0 Mgb<Fe> Gradients in a/Fe Mgb/<Fe> Sa Sa Sc Sb Radius (kpc)
Main Results n Red bulges are similar to luminous ellipticals in their central stellar populations q q n Blue bulges exhibit larger scatter and appear similar to lowluminosity ellipticals in their central stellar populations q q q n Uniformly solar a/Fe Metal-poor class: Sb-Sc, emission lines Young metal-rich class: all Hubble types Central metallicity and a/Fe are sensitive to s and Vmax q n Hubble types S 0 -Sb Intermediate-large SSP age Super-solar Z/H Super-solar a/Fe Barred galaxies add scatter to Metallicity-Vmax relation but not a/Fe–Vmax relation Gradients support disk-driven evolution picture for many galaxies q 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 n Galaxies with largest central metallicities are barred or have b/p bulges q n 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 q Secular evolution with bar destruction?
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