Barred Galaxies

Chang, Seo-Won

Contents

1. Overview

2. Vertical structure of bars

3. Rings in SB galaxies

4. Dust lanes in SB galaxies

5. Lop-sidedness in SB galaxies

Overview

• What is the true fraction of Barred Spiral Galaxies? - F(bar) ~ as a function of redshift : understanding galaxy evolution

- Difficult to find at intermediate and high redshift

(not entirely a selection effect, need a high angular resolution and adequate wavelength band)

2004ApJ_612_191

Overview

• General properties (Bump and peak)

Overview

• Problems

1. Inclination ㅡㅡ ;

2. Bulge component ㅡㅡ ;;

-> Athanassoula et al. (1990), “Bulge masking method”

-> Fourier coefficient method

-> Least Square method

Overview

ε c

N-body simulation

Overview

•Surface brightness profile

-> Elmegreen et al. (1985, 1996)= Early–type system

= Late–type system

Vertical structure of bars

• We must obtain photometry of edge-on barred galaxies. -> Almost impossible.. ㅜㅡ

• Numerical simulations,

1. Thin bars seem to be unstable structures which buckle about their midpoints out of the plane of the bar -> thickened double-lobed structure

2. Round-bulge <-> peanut-shaped bulge

~25% edge-on Bulges seem to have boxy or peanut-shaped isophotes.

=> barred galaxies

~75%=> unbarred or barred galaxies

Vertical structure of bars

• However, this evidence is not conclusive.• Non-axisymmetric cases, Kuijken & Merrifield(1995)..

1. Orbits followed by material in a barred potential

2. Optical spectra to study the motions of the gas (Doppler shifts)

3. Non-circular orbits

Rings in SB galaxies

• Often contain rings and/or lenses.

• Buta (1986)

- Ringed galaxies based on the UK Schmidt and

ESO B Sky Survey films.

- Diameters, q, and PA

(1200 objects up to the time of this writingup to the time of this writing)

- Connection between rings and galactic orbital

resonances

* SA (nonbarred), SAB( weakly barred), SB (barred)

Rings in SB galaxies

Observation Gas density distribution model

Rings in SB galaxies• Results,1. Inner ring : ~75 % of samples 2. q ≥ 0.9 (SA), q = 0.8 (SB)3. True major axis of the ring = that of the bar (reprod

uced by a Model)

4. Outer rings : ~ 50 % of those (almost all in SBs)5. Slightly less elliptical than inner rings 6. Two alignment modes : perpendicular and parallel7. Some galaxies have more than one ring -> dynamical pattern? Diameter ratio, width

Rings in galaxies• Rings are visible in NIR and B-band frame,1. B-band : young stars (Resonance Hypothesis) 2. NIR : old stars

Rings in Early-type galaxy?

Rings in Early-type galaxy?

Rings in Early-type galaxy?

• Many SB gals display characteristic dust lanes.1. Not quite radially from the ends of the bar 2. Keep toward the side of the bar which leads in the rotation of whole galaxy

NGC 1300(SBb)

Dust lane in SB galaxies

Dust lane in SB galaxies

• In case of late-type rather than the SBb,1. Further removed from the principal axis of the bar, and through the less-well-illuminated disk

2. In VERY late-type ones, these may be seen to curve in toward the nucleus, thus partially obscuring the center of the galaxy. -> double peaked core

Lop-sidedness in SB galaxies

• Commonly lopsided.

• Most clearly seen in the Magellanic-type galaxies

(usually have rather egg-shaped bars) and in giant

SB systems (NGC4548)

Lop-sidedness in SB galaxies

NGC4548 in the Hubble atlas (right)

Lop-sidedness in SB galaxies

• Asymmetries in disk galaxies (Richter & Sancisi 1994)

• Lopsided HI distributions and kinematics usually result in an asymmetry of the global HI profile.

1

2

a b

c d