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Contents §0 Introduction: Importance of Galactic Bars §1 General Observed Properties of Barred Galaxies §2 Dynamical Effects of Bars


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Barred Galaxies

Contents
§0 Introduction: Importance of Galactic Bars

§1 General Observed Properties of Barred Galaxies

§2 Dynamical Effects of Bars

§3 Dynamics of Bars

§4 Origins (Formation) of Bars

§5 Evolution of Bars

§6 High-z Bars: Cosmological Perspectives

 
§0 Introduction: Importance of Galactic Bars ( deserves one semester!)
0.1 Fundamentality and Ubiquity of bars

Disk galaxy = disk + bulge + bar

Hubble classification of galaxies

Bar incidence along Hubble Sequence

RC3 (B band visual morphology) (Elmegreen et al.,2004,ApJ,612,191)

Near-infrared





NGC 253

2MASS image (JHK)





Near-infrared (Eskridge et al., 2000,AJ,119,536)

Ohio State University (OSU) Bright Spiral Galaxy Survey (Eskridge et al. 2002, ApJS, 143, 73)

[・ BVRJHK imaging of 205 spirals (from RC3)

with 0 ≦ T ≦ 9, MB ≦ 12, D ≦ 6.5', -80° < δ < +50°

・ 6 telescopes (aperture 0.9-2.4m)]
186 galaxies with no companion, no peculiarities

Visual inspection of H band images  morphological types, bar types

Comparison with optical classification

RC3 (Third Reference Catalogue of Bright Glalaxies, de Vaucouleurs et al.,1991)

D25>1’, B<15.5, Vhel<15000km/s + other interesting objects

CAG (Carnegie Atlas of Galaxies, Sandage & Bedke, 1994)




 optically weak bars (SAB) tend to be classified as strongly barred (SB) in H band

 H-band bar fraction not dependent on Hubble types

 Early types: H-band bar frequency = optical bar frequency

 Late types : H-band bar frequency > optical bar frequency

( probably because of dust and young stars in late types)
0.2 Effect of bars on galaxy evolution

Non-axisymmetric gravitational field  redistribution of mass/angular momentum

- Trigger nuclear starbursts and AGN

- Secular formation of bulges

- Formation of rings





§1 General Observed Properties of Barred Galaxies 
1.1 Stellar Components (optical observations)

 

1.1.1 Components of barred galaxies

Disk + Bulge + Bar + Rings (nuclear ring, inner ring, outer ring) + Lens
1.1.2 Structural parameters of bars

length, ellipticity, shape of isophotes (deviation from perfect ellipses)

tangential force (Q)

Analysis:

- eye estimate on images

- quantitative analysis (Ellipse fit)

- Not ellipse fit (Chapelon et al., 1999, AA, 345, 81)

◆ Elmegreen & Elmegreen (1985,ApJ,288,438)

I band surface photometry of 15 barred galaxies

 luminosity profile, bar length (visual estimate)






◆ Martin (1995,AJ,109,2428)

Sample: 136 SAB and SB galaxies in CAG( Sandage & Bedke, 1988) Atlas (B-band)

Visual determination of bar semi-major (a) and semi-minor (b) axes
Lb(i)≡2a/D0

D0: deprojected diameter at 25 mag/arcsec2


◆ Regan & Elmegreen (1997,AJ,114,965)

K band photometry of 10 barred galaxies & Ellipse fit
7 = flat bar (half have isophotal twist in center)

3 = exponential bar (none has twist)

All bars have a maximum ellipticity at the bar end
◆ Whyte et al. (2002,MN,336,1281)

OSU sample (Ohio State University Bright Spiral Galaxy Survey)







1.1.3 Bar Colors
◆ Burkhead & Burgess (1973,AJ,78,606)

UBV photometry of NGC 1300(SBbc)

82inch reflector (McDonald Observatory)

major and minor (displaced from the nucleus) color profiles

bar major axis: bar redder than outside bar, bar color becoming redder to the center.

  : Q(reddening-free parameter) slightly increases toward the center.


◆ Benedict(1976,AJ,81,799)

B,V photometry of N4548(SBb),N4596(SB0+),N4608(SB0)

B, B-V profiles along bar major and minor axes

N4548: bulge B-V=1.02, bar B-V=0.90, arm/disk B-V=0.82

N4596: 0.90 0.85 0.79

N4608: 0.91 0.86 0.89

bar has no internal color variation

bar is a little bluer than bulge


◆ Elmegreen & Elmegreen (1985,ApJ,288,438)

B and I photometry of 15 barred galaxies

Bar has the same color as the inter-bar regions (while spiral arms are generally bluer than inter-arm regions) 
◆ Prieto et al. (2001,AA,367,405)

UBVRI photometry of 11 disk galaxies

1) Color map  qualitative idea of existing components in that galaxy.

2) Confirm each component by ellipticity and PA profiles

3) Fit the azimuthally averaged or individual profiles (i.e. profiles along major and minor axes of the bar, for strongly barred galaxies) by those components.
Minor axis profile  disk and bulge parameters

 these are subtracted from major axis profile  bar parameters

(Assume analytic functions for each component)
- Found bars in half of the sample.

- Half of these bars have the same color as the underlying structure,

while the other half have redder colors.
1.1.4 Rings and lenses
◆ Kormendy (1979,ApJ,227,714)

Properties and occurrence of inner rings, outer rings, lenses

Sample: 121 barred galaxies from RC2

1) SB classification, 2) BT<12.5, 3)δ >-30°, 4) not edge-on

Results:

- Lenses are more common in early-type galaxies, and inner rings in late-type galaxies (Table 3).

- A significant fraction of galaxies of all types have neither a ring nor a lens (Table3).

- Shapes of lenses and inner rings



 inner rings are round and planar.

 lenses cannot be fit with planar ellipses ( lenses are slightly triaxial, moderately to highly flattened ellipsoids, with a typical axial ratio in plane of about 0.9 ).
- Outer rings

13 out of 121 galaxies have an outer ring

Outer rings are elongated ( = 0.76) perpendicularly to bar, and have length

2.2 ☓ bar length


- Spiral structures


§2 Dynamical Effects of Bars  
2.1 Basic Dynamics: linear theory in non-axisymmetric gravitational field
Equation of motion in rotating coordinate system

R – Rθ2 = - + 2RθΩb + Ωb2R

Rθ + 2Rθ = - - 2RΩb

Gravitational potential: Φ(R,θ) = Φ0(R) + Φ1(R,θ), where |Φ1/Φ0|≪1.

Consider perturbations

R(t)=R0 + R1(t) ; θ(t)= θ0(t) + θ1(t)


1) 0-th order equation

R0θ02 ­= ()R0 - 2R0θ0Ωb b2R0  R00b)2 = ()R0

Introduce Ω(R)≡  and Ω0≡Ω(R0)

θ0 ­=Ω0 –Ωb

θ0­ = (Ω0 –Ωb)t

2) 1st order equation

R1 + (2)R0R1 - 2R0θ1Ω0 = - | R0

θ1 + 2Ω0R1/R0 = - | R0


Assume Φ1(R,θ) =Φb(R)cos(mθ)

R1 + (2)R0R1 - 2R0θ1Ω0 = - | R0 cos[m(Ω0 –Ωb)t]

θ1 + 2Ω0R1/R0 = mΦb(R0)sin[m(Ω0 –Ωb)t]

Integration

θ1 = - 2Ω0R1/R0 - Φb(R0)cos[m(Ω0 –Ωb)t] + constant.

R1 + κ02 R1 = - [ + ]R0 cos[m(Ω0 –Ωb)t] + constant.

where κ02 ( +3Ω2)R0= (R +4Ω2)R0
Solution

R1 (t)= C1cos(κ0t+ψ) - [ + ]R0 cos[m(Ω0 –Ωb)t]/Δ (2.1.1)

where Δ≡κ02 –m20 –Ωb)2
Using θ0 instead of t,

R1 0)= C1cos(+ψ) + C2cos(mθ0) (2.1.2)

C2 ≡ - [ + ]R0 (2.1.3)
2.2 Observations of Gas Dynamics
◆Peterson et al. 1978, ApJ,219,31

NGC 5383 (SBb)

Observations:

long-slit emission line spectroscopy at various positions (Hα, [NII], [SII])

Stellar absorption line spectroscopy along the bar (Ca II, H,K)

Results:


Emission line velocity field is complex, and not described by pure rotation.

 1)warped disk model fits observation (warp presumably caused by a companion UGC 8877)

 2)planar model with noncircular velocity also fits observation.
◆ Peterson & Huntley (1980,ApJ,242,913)

NGC 1300 (prototypical barred galaxy, SBb)

Observations:

long-slit emission line spectroscopy at various positions (Hα, [NII], [SII])

Stellar absorption line spectroscopy along the bar (Ca II, H,K)
Limitation: Emission regions are restricted to the nuclear region and spiral arms (No emission in bar region)
Emission line spectra  Gas velocity field drawn by eye (Fig.5)

- Stellar rotation curve along the bar = steep rise to 1/6 of bar radius (1.9Kpc), after which rotation velocity is constant.

- Gas rotation curve along the bar

Inner part = steeper than the stellar one (due to lack of random motions existing in stellar motions)

Outer part = lower than the stellar one (evidence for non-circular motion)
Comparison with models:

Model = Huntley (1980) gas dynamical simulation in the potential of the stellar N-body model by Miller & Smith (1979)

 Fig.5

Fig.6


 Spiral arm regions: Model agrees with observations

 Nuclear region: Model has less steep velocity gradient


Model was improved (‘augmented model’ by adding ‘bulge’ with mass = 5% of the disk, radius = 1.5Kpc)

 nuclear velocity field is better reproduced (Fig.6, Fig.8), because of appearance of ILRs and resulting change of gas orbits

 Offset dust lanes are better reproduced.


◆ Sancisi, Allen & Sullivan (1979,AA,78,217)

HI 21cm observation of NGC 5383

Resolution 25”× 37”(and low S/N make the velocity field difficult to determine)
Results:

- HI poor in the bar region.

- Velocity field: outer part = differential rotation

inner part = noncircular motion present (iso-velocity contours tend to align with bar)

Conclusions:

- HI data are consistent with Peterson et al (1978) optical data.

- Elliptical streaming lines (i.e., noncircular motions) in the bar region and

Differential pure rotation in outer region established.

- Kinematical disturbance due to the companion galaxy is unlikely.
◆ Blackman & Pence (1982, MN, 198, 517)

Motivation: NGC 5383 (Peterson et al. 1978, ApJ,219,31) may be distorted by a companion.

 Emission line (Hα) spectroscopy of isolated barred galaxies: NGC 2525 (SBc) & NGC 7741 (SBcd)

Accuracy ~15km/s


Model prediction : gas moves on elongated orbits aligned with or at most 45 deg inclined to the bar  v// < v⊥
Velocities along the slit placed on the bar (v//) were found to coincide with velocities along the slit perpendicular to the bar(v⊥) (for both NGC 2525 and NGC 7741)  circular motion without any deviation
◆ Blackman (1981,MN,195,451)

Long-slit spectroscopy (Hα, NII) of

- NGC 613(SBbc): v// and v⊥ profiles are coincident  no non-circular motion.

- NGC 1097 (SBb): spectra are confined to nuclear regions  no reliable discussion on velocity field.

- NGC 1365 (SBb): spectra confined to nuclear region and outer spiral arms (no spectra for the bar region) no reliable detection of non circular motions, but it may be required to get a reasonable total mass of this galaxy. (reasonable = consistent with typical M/L)

- NGC 1313 (SBd):pure circular motion cannot explain observations for plausible inclination and line-of-nodes for this galaxy  this galaxy may be tidally disturbed.

HI 21cm line observations will provide a better picture of velocity field in these

galaxies in future.


2.3 Theoretical Treatments of Gas Dynamics
Modeling of interstellar gas

1) continuous fluid (Huntley et al, 1978,ApJ,221,521;1980,ApJ,238,524)

option: isothermal / radiative cooling / heating due to SN

2) ensemble of clouds dissipating energy by inelastic collisions (Combes & Gerin 1985,AA,150,327)

option: heating due to SN
Theoretical interests:

- gravitational torque & angular momentum exchange

- formation of shock (dust lane)

- gas inflow to the center (fueling activity)

- effect of resonances (ILR, CR, OLR, higher resonances)
◆ Sorensen, Matsuda, Fujimoto(1976,APSS,43,491)

Isothermal fluid in a given bar potential  ‘dark lane = shock’



◆ Schwarz, M.P. (1981,ApJ,247,77)

Gas dynamical simulation in a given gravitational field

Interstellar gas modeled by inelastically colliding particles (‘sticky particle method’) (to see difference from stellar response)

Potential: axisymmetric part + bar potential [A(r)cos(2θ)]

Ωb chosen so that there is no ILR

Results:



1) collisionless case (stellar response)

Initial spiral arms quickly disappear  symmetric distribution (Fig.3)

2) collisional case (gas response) (Fig.4)

- Spiral arms (extending from CR to OLR) last longer than in the collisionless case

- Gas between CR and OLR moves to near OLR  ring forms near OLR


Why spiral arms appear in gas?

▪ Gas tries to follow periodic orbits

▪ But there are two periodic orbit families near a resonance, which are

elongated perpendicularly and therefore crossing.

▪ Gas orbits cannot cross (difference from stellar orbits)

▪ Gas orbits change their orientation continuously, leading to spiral shape

This spiral configuration allows the bar to exert a torque on the gas and change its angular momentum

[Compare angular momentum changes (Fig.8 , Fig.9)]



Two types of outer rings: (depending on initial gas distribution)

- parallel to the bar  uniform gas distribution extending well beyond OLR

- perpendicular to the bar  more concentrated distribution

(Most observed outer rings are perpendicular to the bar, e.g., Kormendy, 1979,ApJ,227,714)

◆Schwarz (1984, MN, 209, 93)

Effect of bar strength and pattern speed

Gas particles experiencing energy dissipation (inelastic collisions)

ほぼ定常状態に落ち着いたところで粒子分布を比較した。

As bar becomes stronger,

- arm-interarm density contrast and pitch angle of spiral arms increase.

- barの両側の空白域が広がる。

As the pattern speed decreases

Spiral arm  ring at CR (4/1 resonance)(<->inner ring?) ring at ILR (<-> nuclear ring?)

◆ Sander & Tubbs (1980, ApJ, 235,803)

Gas dynamical simulation in a given gravitational potentail

Motivation: understanding observed kinematics of NGC 1300
Models: three components

1) central disk ( ⇔ disk): Kuz’min-Toomre disk (mass Md, length scale rd, maximum rotation velocity Vmax)

2) triaxial homogeneous ellipsoid ( ⇔ bar): (x/y/z semiaxes = a/b/c, mass Mb)

3) extended disk ( ⇔ halo): Kuz’min-Toomre disk (mass Me =3.17 Vmax 2a/G, length scale re=4a) (this choice was made to get a flat rotation for a
Independent parameters: Mb /Md, b/a, c/a, rd /a, rc /a

[rc: corotation radius i.e. Ωb=Ω(rc)]

Simulations in five-parameter space

Standard model : Mb /Md=0.53, b/a=1/4, c/a=1/4, rd /a=0.3, rc /a=1.1

(Hereafter b=c, because z-scale height does not affect the result significantly)


Compare models with observation

Keys of observed gas morphology (NGC 1300)

1) offset linear dust lanes on leading edges of the bar extending the whole bar length

2) spiral arms originating perpendicularly from the bar ends

3) bright large HII regions near the bar ends

Keys of observed gas kinematics (NGC 5383)

1)circular motion with constant velocity beyond the bar

2)iso-velocity contours skewed parallel to the bar in within bar radius

1. Comparison of morphology (Fig.3.4.5.6)


1) Mb /Md sequence

As Mb /Md increases: open spiral arms  gas bar with offset lanes too small offset

⇒ 0.4b /Md<1.0

2) b/a sequence

As b/a decreases: open spiral arms  gas bar with offset lanes too small offset

⇒ 1/5 < b/a < 1/3




3) rd /a sequence

For large rd /a, offset dust lanes become less conspicuous

⇒ rd /a < 0.5

4) rc /a sequence

Small rc /a  curved dust lanes, large rc /a  entire gas response rotated with respect to the bar

⇒ 1.0 < rc /a < 1.5


Standard model satisfies all the three morphological requirement.

2. Comparison of kinematics



Standard model velocity field ⇒ elongated streaming in the bar region

Best fit to the observation given by the standard model in which rc /a was modified to 1.2 ⇒ skewing of velocity contours successfully produced.


◆ Athanassoula (1992,MN,259,345)

Dust lane morphology



Hydrodynamical simulation for isothermal gas

- Depletion of gas by star formation

- Supply of gas by infall
Potential: bulge + disk + bar

Parameters:

bar mass

bar axial ratio

bar pattern speed

bar central concentration


Results:

1) offset dust lane requires existence of x2 orbit family

shape of dust lane  gradual shift of orientation of flow lines from x1 to x2 orbits

2) offset shock of observed shape  constraints on model parameters

- pattern speed: rL=(1.2±0.2)a (a=bar major axis, rL =Lagrangian radius)

smaller rL (larger Ωb) centered shock, larger rL  ‘convex’ shock

- central concentration: too low  centered shock, too high  ‘convex’ shock

- large axial ratio (b/a) or low bar mass  curved shock (NGC 1433 type), small axial ratio  straight shock (NGC 1300 type)




Rings

◆ Athanassoula et al. (1982,AA,107,101)

Ring sizes measured by de Vaucouleurs & Buta (1980, AJ, 85, 637)

 Outer-to-inner ring ratio



Assume 0.7<δ<1.0 (typical for Sa and Sb analysed in this paper)



 strongly barred galaxies : outer ring = OLR, inner ring = CR or UHR

 consistent with theoretical results (Schwarz, 1981, ApJ, 247,77)

- bar just extend to CR

- inner rings form just inside CR, and outer rings just outside OLR


◆ Byrd et al (1994, AJ, 108, 476)

Gas dynamical simulations in a given gravitational potential

Gas initially distributed to around OLR

Pattern speed (Ωb) varied

- fast  no UHR , no ILR

- medium  UHR, no ILR

- slow  UHR, ILR
1)Two types of outer rings

R1 ring form quickly  after that R2 ring appears (for all Ωb)

Different from Schwarz’s results

Reasons : More particles were used

Different treatment of energy dissipation

Longer evolution was traced


Obs. IC 1438 : two outer rings

R1 is prominent in I band, whereas R2 in B band!


2) as Ωb decreases

R2 becomes relatively less prominent

Inner rings (UHR), offset dust lanes, Nuclear rings appear (ILR)

 nuclear rings should accompany R1 more often than R2

Buta & Crocker (1991, AJ, 102, 1715)

11 R1 galaxies  9 show nuclear star formation and offset bar dust lane

11 R2 galaxies  3 show nuclear star formation or offset bar dust lane



2.4 Star Formation and Activity
◆Hawarden et al. (1986 MN, 221, 41p)

Sample: all RSA galaxies

with S0/a-Scd type designation in RC2

with detection in four bands (12μm, 25μm, 60μm, 100μm) in IRAS

(Seyfert1, Seyfert2, LINERS excluded)

 186 galaxies



1) Barred galaxies have excess of F25 relative to F12 and F100

 starbursts in barred galaxies

Check

Model SA galaxies + IRAS observed fluxes of Galactic HII regions



 agree with SB galaxy FIR colors

2) Starbursts are concentrated in nuclei, because

- Disks of SA and SB are similar

- unresolved HI sources (21cm continuum) are observed exclusively in barred galaxies (Hummel, 1981, AA, 93, 93)


◆ Aguerri (1999,AA,351,43)

sample: 29 Sb-Sd galaxies (4 Sb + 25 later types)

= Martin (1995) sample + Sb-Sd galaxies from RC3 – galaxies with companions

[Companion = a galaxy within projected distance of 500 kpc and systemic velocity difference of 500 km/s]

No AGN

Bar parameters:



- Projected ellipticity (10(1-b/a))  ellipse fit to V band NED images

- relative bar length (Lb/D25)

Star formation activity = IRAS fluxes I25/I100
Results:

- ellipticity correlates with I25/I100

- relative length affects little

Spatial distribution of FIR emissions

- IRAS have insufficient resolution to locate star forming regions

- Devereux (1987, ApJ, 323, 91) see no strong concentration of FIR emission for late type barred galaxies (Sbc-)


◆Devereux (1987, ApJ, 323, 91)

Spatial distribution of 10μm luminosity

Ground-based observation (IRTF 3m telescope) + IRAS

Sample:


- 133 galaxies taken from Nearby Galaxies Catalog (Tully 1987)

(Vhel < 3000 km/s for this catalogue)

- inclusion in IRAS catalogue

- RC2 morphological and bar classification

- No interacting galaxies

- L60μm > 2.2☓109 L (for completeness)  LFIR(40-120) > 2.9☓109 L

Divided into barred (SAB,SB) and unbarred (SA) galaxies

into early (-Sb) and late (Sbc-) types


Central (typically < 500 pc) 10 micron luminosity by 3m NASA IRTF
Luminosity:

Early types : barred galaxies have larger L10μm than unbarred ones.

Late types : no difference

Compactness of emission:

(= Ground-based small-beam 10μm flux/ IRAS larger-beam 12μm flux)

 early types: more compact in barred than in unbarred galaxies.

 late types : no difference
Infrared colors (IRAS S25/S12):

 early types: barred galaxies have larger S25/S12 than unbarred ones

( S25/S12 correlates with compactness)

 late types : no difference


Source of emission: Seyfert activity and/or star formation (cannot be segregated because Seyfert 1, Seyfert 2, and HII overlap in α(100,60) vs α (60,25) diagram)
◆ Simkin,Su,Schwarz (1980,ApJ,237,404)

Seyfert activity in barred galaxies

All spiral and lenticular galaxies from RC2 with Vhel<5000km/s and morphological classifination

1) Seyfert slightly prefer B and AB

2) Seyfert prefer (rs) and (r)

3) Seyfert much prefer (R) and (R’)


Schwarz’s simulation

Bar  inner (r) and outer (R) rings

Bar  gas infall to the center

Seyfert without bars may be triggered by tidal interactions

◆Hunt & Malkan (1999,ApJ,516,660)

Extended 12 micron Galaxy Sample (E12GS, Rush et al. )

891 galaxies (mostly disk galaxies)

Selection effect? (because 12 micron selection may favor star formation activity)

Yes, but not so strong as to affect conclusions.
Activity class, morphological types, bar/ring classes, major and minor diameters, from NED (NED Morphology is largely from RC3)
Morphology

Seyfert 1: median =Sa, Seyfert2: 2, LINER: 3.5, HII:3, normal: 4

Normal galaxies in E12GS have similar axial ratios, morphological types, bar and ring fractions to other n ormal spirals.
- HII/starburst have higher fractions of bars (SAB+SB:82-85%)and peculiar morphplogy

- Seyfert/LINERs have the same bar fraction(61-68%) as normal galaxies(68-69%), but

higher incidence of rings (Seyfert: outer ring 40% opposed to 10% in normal 12 micron galaxies, LINER: inner ring 57% vs 40%)
Morphological effects? (because rings and Seyferts are both more frequent in

early type galaxies)

Consider only T<=2

Outer ring: normal=24%, Seyfert1=60%, Seyfert2=50%

Inner ring: normal=43%

( evolution scenario: bar formation  gas inflow  nuclear starbursts 

LINER/Seyfert)
Bar fraction and morphological type (Fig.3)

- normal galaxies: bar fraction is constant except very late types (T>6),

which show high bar fractions (86%)

- HII and Seyfert 2: bar fraction is constant

- Seyfert1- bar fraction has a peak (90%) at T=3


◆ Chapelon et al. (1999,AA,345,81)

Two sample of barred galaxies , R band photometry

1) barred Markarian galaxies with IRAS detection

2) barred Frei et al. (1996) galaxies

1)+2) are classified into active (log(S25/S100)>-1.2) and normal galaxies

(most of Markarian and some Frei galaxies have also designation as starburst or Seyfert)


Bar measurement:

- Bar length a (determined by eye from bar major axis profile)

- Bar width b (at a/2): distance from bar major axis to the same isophotal level as the bar end (to avoid influence of bulge)
Galaxy diameter Dc from LEDA

 Early type bars are long and strong regardless of active/normal

 Late-type bars in active galaxies are longer and stronger than those in normal galaxies





Central Oxygen abundance

Longer bars  smaller O/H

(Probably due to dilution by bar)



◆ Ho,Filippenko,Sargent (1997,ApJ,487,591)

Sample: 319 spiral galaxies with

T=0-9 (S0/a-Sm), BT <12.5 mag, δ>0°

Bar morphology : SA,SAB,SB from RC3
Observation: spectroscopy of nuclear region

Moderate-resolution (2.5-4Å) long-slit spectra

Aperture 2”☓4” (typically 180pc ☓ 360pc)

(so may miss starburst nuclear rings typically with several 100 pc size)


Ho et al. 1997,ApJS,112,315

- Sample classified into HII nuclei & AGNs based on line strength ratios

(in similar manner to Veilleux & Osterbrock,1987,ApJS,63,295)

- Activity strength : luminosity L(Hα), equivalent width EW(Hα)


Results:

1) Barred and unbarred galaxies have similar luminosities in each Hubble type.

2) star formation activity in barred galaxies stronger than unbarred galaxies

only for late-types (Sc-Sm). (seems to contradict Devereux 1987, but is not discussed)

3) AGN activity similar in barred and unbarred galaxies both for early (S0/a-Sbc) and late (Sc-Sm) types.
Implication: Bar does not affect AGN activity. AGN are fueled by local processes

like tidal disruption of star by BH or stellar mass loss


◆ Laurikainen,Salo,Buta (2004,ApJ,607,103)
Sample: 149 OSUBGS + 22 2MASS spirals

- Inclination < 60°

- BT<12.0

- RC3 type 0

- -80° < δ < +50°
Classification into active and nonactive subsamples based on NED (which mostly rely on emission line ratios: Veilleux & Osterbrock 1987, ApJS,63,295)

Hereafter AGN = Seyfert + LINERS


Bar fraction by

1) RC3 classification

 AGN have similar bar fraction ( SB+SAB ) to nonactive galaxies

 HII/starburst have marginally larger bar fraction than nonactive galaxies

2) EFP02 B-band classification

 Same as 1)

3) EFP02 H-band classification

 Same as 1) but

 SB fraction is larger (67-72%) in Seyfert,LINER,HII than in non-active(58).

4) Fourier method for H-band images (m=2,4 components with phases nearly constant)

 SB fraction is larger (69-72%) in Seyfert,LINER,HII than in non-active(55).

 bar fraction depends on the method of identifying a bar.

 Fourier method picks up relatively strong bars (like SB).
Past near-IR studies

- KSP00,LSKP02: Bar fraction in Seyferts is higher than in non-active.

- MR97: Bar fraction in Seyfert similar to that in non-active. (reason: visual

identification of bars lead to inclusion of SAB into bar fraction. SAB fraction

in Seyfert is smaller than in non-active according to present work, which

explains discrepancy)



Bar strength statistics (Fig.8)

- early-type bars are longer, more massive (i.e., larger A2), and have weaker strength (i.e., smaller Qg) than late-type bars.

- Qg increases as A2, but correlation is shallower for early-type bars.


- Bars in Seyfert and LINER have weaker strength (Qg) than bars in HII or

non-active galaxies (Seyfert and LINER preferentially occus in early-type galaxies, whereas HII galaxies are generally late-types)

- Bulges dilute Qg (Fig.11) but do not affect length (Fig.12) and mass (Fig.13) of bars much.

- Some late-type bars exist with large A2, large Qg, and small rQg/Rbar.

These bars are generally non-active. (Fig.16)












2.5 Chemical Compositions (Radial Mixing of Disk Matter)
Abundance gradient (Metallicity generally decreases outward in unbarred galaxies)
◆ Vila-Costas & Edmunds (1992, MN, 259, 121)

30 galaxies with published HII region emission line strength

 (O/H) was calculated

Morphological types (Hubble types and bar types) taken from RC2


Results:

- barred galaxies have smaller gradient than unbarred galaxies

- unbarred galaxies: later types have steeper gradient than early types in [dex/kpc] but difference vanishes if normalized by R25



◆ Martin & Roy (1994, ApJ, 424, 599)

Spectroscopy of HII regions in 3 galaxies to get their metallicity

(other measured galaxies from the literature also included in the analysis)



More quantitative evaluation of bar strength

Visual measurement (on Sandage-Bedke Atlas) of

Bar semi-major axis a and bar ellipticity EB≡10(1-b/a)

(both are inclination corrected)







 Gradient becomes flatter as bar length increases

 Gradient becomes flatter as bar ellipticity increases (stronger than bar length dependence)

 dilution by bar-induced gas inflow

(but star formation should be maintained at low level)

Stellar population gradient

◆ Gadotti & Dos Anjos (2001, AJ, 122, 1298)

- UBV color profiles of 257 Sbc barred (SB,SAB) and unbarred (SA) galaxies

from aperture photometry in published data (Longo & de Vaucouleurs, 1983, 1985, Univ. Texas Monogr. Astron. No.3, No.3A)

- Bar morphology from RC3


 U-B, B-V color gradient: (no external or internal correction)

 total and bulge colors:

1) color within the smallest aperture = bulge color

color within R25 aperture = total color

2) bulge color

(color within 1/5 effective radius of the galaxy)

total color



(color within 2 effective radius)

(G = color gradient)



= color index at B-band effective radius given by RC3

- Galactic reddening correction



with E(B-V) given by Schlegel et al. (1998, ApJ, 500, 525)

- internal extinction

I band (Giovanelli et al. 1994, AJ, 107, 2036)



where a and b are galaxy major and minor axes (log(a/b) given by R25 in RC3)

AU,AB,AV = (3.81,3.17,2.38)☓AI

(Elmegreen 1998, in ‘Galaxies and Galactic Structure’ ed. Englewood, Cliffs)


These values were checked by independent CCD observation of 14 galaxies

 barred galaxy G(U-B) (both for face-on and edge-on) are smaller and wider


AGN fraction (Veron-Cetty & Veron 1998, ‘Quasars and Active galactic Nuclei’)

8% for negative gradient (G<-0.1)

36% for positive gradient (G>0.1)

(both for U-B and B-V)


Colors reflect both age and metallicity

No correlation with metallicity gradient  Fig.7

(Martin 1995, AJ, 109, 2428; Zaritsky et al., 1994, ApJ, 420, 87)

 colors reflect ages (effects of dust also possible)


One interpretation

1) Galaxy forms through monolithic scenario (lower-left of Fig.7)

2) Bar forms ( lower right)

(because abundance gradient becomes shallower, but color gradient hardly changes, because timescale for gas inflow is shorter than the time required for star formation in the center)

3) Star formation starts in the center ( upper right)

4) Bar destruction by accumulated material

 Gas inflow stops ( upper left)

5) Star formation stops ( lower left)

6)  2)
Color gradients have no correlation with bar parameters (by Martin 1995)(Fig.8)
Bulge colors


 total color is the same for all gradient classes

 bulge is bluer as G increases





 Bulge and total colors are correlated in both negative and positive gradient cases

 But, bulge colors are systematically bluer for positive case



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