[PPT] - Bar-driven Spirals? S 4 G perspective Heikki Salo, Univ. Oulu, PowerPoint Presentation

SLIDE 1

Bar-driven Spirals?

S4G perspective

Heikki Salo, Univ. Oulu, Finland

Dynamics of Disk Galaxies workshop, Seoul 21.10.2013 Thanks to: Eija Laurikainen, Simon Diaz, Martin Herrera, Jarkko Laine, Sebastien Comeron + S4G team

1

SLIDE 2

TOPIC: What is the observational evidence for a connection between bar and spiral structure? Ongoing study using the 3.6 micron data from S4G

(Spitzer Survey of Stellar Structure in Galaxies, PI K. Sheth)

2

SLIDE 3

BARS & SPIRALS

Different scenarios (see Jerry Sellwood’s review on Tuesday) 1) Spiral = direct extension of bar mode

Either in the sense of classical density wave picture or in manifold-theory (Lia Athanassoula on Tuesday)

2) Spiral mode is coupled to bar via resonance coupling 3) Spiral is an independent mode or transient pattern, not connected to the bar Not easy to distinguish these scenarious based on morphology: 1) ⇒ Expect correlation between amplitude of bars and spirals Same pattern speed ⇒ phases also related 2) ⇒ Correlation between amplitudes 3) ⇒ No correlation

3

SLIDE 4

OSUBGS Buta et al. 2005

0.0 0.2 0.4 0.6 0.8 maximum FT/FR (BAR) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 maximum FT/FR (SPIRAL)

Observational support for bar/spiral connection?

Pictorial examples easy to find

GD-spirals more frequent in barred (Kormendy 1979, D & B Elmegreen 1982)

Statistical near-IR studies: yes, perhaps, no?
Block et al. (2004): sample of 17 galaxies K

bar-related torque strength Qb strongly correlated with spiral-related Qs

Buta et. al 2005: 147 galaxies from OSUBGS (H-band, Eskridge 2002)

possible weak correlation between Qb and Qs

Buta et al. 2009: deep Ks sample with AAT, 23 galaxies: no correlation
Similar negative results: Durbala et al. 2009 (Sloan i, 46 galaxies ), Seiger et al. 2003 (K band, 41 galaxies)

4

SLIDE 5

100
50

50 100

100
50

50 100

NGC 1452 2.2µm

20 40 60 80 100 r (arcsec) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2

bar

max A2

20 40 60 80 100 r (arcsec) 0.0 0.2 0.4 0.6 0.8 FT/FR

Qb

/home/heikki/NGC1566_OULU2011.dir/NGC1452_schema_beijing2012 heikki@pc091079 Sun Oct 20 08:42:57 2013

Characterization of bar strength:

Azimuthal Fourier amplitudes of density

(e.g. Elmegreen & Elmegreen 1985)

I(r, φ) = I0(r) " 1 +

m=∞

X

m=1

Am(r) cos [m (φ − φm(r))] #

Tangential force amplitudes (normalized to axisymmetric force) (Combes and Sanders 1981)

F T/F R = max(|FT (r, φ)|) < |FR(r, φ)| > (≡ F T/F R in this talk)

⇒ maximum at bar region = Qb

5

SLIDE 6

200
100

100 200

200
100

100

ngc1566

50 100 150 200 0.0 0.5 1.0 A2 Rbar R2s

bar spirals

50 100 150 200 r (arcsec) 0.0 0.1 0.2 0.3 FT/FR

bar spirals bar+spiral

Bar and spiral forcing:

Separate non-axisymmetric bar and spiral contributions to density ⇒ A2(bar), A2(spiral) Qb, Qs

6

SLIDE 7

NGC936 NIRSOS 2MASS 2MASS: uncleaned

20 40 60 80 100 rad (") 0.0 0.1 0.2 0.3 FT/FR

CART POLAR: mMAX =8 mMAX =6 mMAX =4 mMAX =2

20 40 60 80 100 rad (") 0.0 0.1 0.2 0.3 20 40 60 80 100 rad (") 0.0 0.1 0.2 0.3

Calculation of forces with NIRQB-code:

(Salo et al. 1999, AJ 117, 792; Laurikainen and Salo 2002 MNRAS 337, 1118) (Applied to to 2MASS, OSUBSGS, NIRSOS, AAT samples in Buta et al. and Laurikainen et al. studies)

Assumed: near-IR light traces Σ

(M/L= constant, or a function of radius)

vertical scale height hz

(e.g. from hr or RK20; several choices for vertical profile exp, sech2, gaussian ...) 2-fold uncertainty in hz ⇒ <25% uncertainty in Qb

Azimuthal Fourier decomposition at radial zones (typically m=0, 2, 4, 6, 8...),

+ polar FFT force integration directly from m-components) azimuthal filtering

⇒ no spurious force peaks in the noisy outer disk

= Important advantage

ver Cartesian integration

7

SLIDE 8

0.0 0.5 1.0 1.5 max A2 (spiral) 0.0 0.2 0.4 0.6 0.8 1.0 max Qbar a) 0.0 0.5 1.0 1.5 max A2 (spiral) 0.0 0.1 0.2 0.3 0.4 0.5 Qbar (R=R2s) b)

R2s/Rbar<1.5 R2s/Rbar>1.5 R2s/Rbar<1.5 R2s/Rbar>1.5

Re-analysis of bar-spiral correlation: OSUBSGS and AAT-samples

Salo, Laurikainen, Buta, Knapen 2010:

Small samples/selections effects

⇒ explain earlier inconclusive resuts

Stronger correlation when comparing

spiral amplitude A2(r) against the gravity forcing by bar at the same distance, Qbar(r) (instead of using the maximum values) Example: Buta et al. (2009) deep AAT-sample: No correlation: max of Qbar and max of A2(spiral) Clear correlation: between local forcing due to bar, if evaluated at the location of radial maximum of spiral A2

8

SLIDE 9

0.0 0.1 0.2 0.3 Qbar(r) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(r)

r/Rbar= 1.1

rsample = 0.64 p = 1.3e-11 0.00 0.05 0.10 0.15 Qbar(r) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(r)

r/Rbar= 1.3

rsample = 0.57 p = 1.2e-08 0.00 0.02 0.04 0.06 0.08 Qbar(r) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(r)

r/Rbar= 1.5

rsample = 0.30 p = 0.0040 0.00 0.01 0.02 0.03 0.04 Qbar(r) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(r)

r/Rbar= 1.7

rsample = 0.074 p = 0.26

For both OSUBSGS and AAT -samples:

Statistically significant correlation between local bar forcing and local spiral amplitude up to 1.5 bar lengths

(Salo et al. 2010)

m > 0 density amplitude set to zero for r > Rbar in calculation of forces correlation between local FT/FT and A2 looked at 4 different distances outside the bar

9

SLIDE 10

NGC1097 .SBS3.. uc=0

50 100 150 200 250 300 a (arcsec) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 ELLIP max: 95.1" 0.646 min: 120.6" 0.513 50 100 150 200 250 300 a (arcsec) 50 100 150 200 PA dPA -28.2

200
100

100 200 arcsec

200
100

100 200

BARLEN = 96.2" (sky-plane) uc=0

/home/heikki/S4G_BARS.dir/barlen_270611_inc65.dir/NGC1097_barlen

heikki@hiisi.oulu.fi Mon Jun 27 15:38:21 2011

Analysis of S4G sample

Need: Sky-subtracted, cleaned images Reliable (=visually checked) galaxy orientation parameters (P4) and bar lengths Calculation of Fourier amplitudes and forces

Original S4G with 2352 galaxies ⇒ bar force calculated for 532 galaxies

removed 374 ’bad’ cases (too small FOV, image defects, bright star, large sky-gradient, superposed companion, deformed, or with unreliable orientation) ⇒ 1978 galaxies limit to i < 65◦ ⇒ 1172 galaxies barred (bar length can be estimated) ⇒ 786 galaxies barred + trailing/leading sense of spirals visible ⇒ 729 galaxies force calculations so far for 532 galaxies

Example of bar length measurements: visual bar length, position angle, max ellipticity (Martin Herrera / Simon Diaz)

10

SLIDE 11

ALL SB, SAB

0.0 0.2 0.4 0.6 0.8 1.0 Qb (bar) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(spir) N_SB =261 0.269 p=0.0000 N_SAB=227 0.286 p=0.0000

For S4G-sample: (Salo et al. in preparation) Significant correlation between max Qb(bar) and max A2(spiral) Holds both for strongly (SB) and weakly-barred (SAB) galaxies

11

SLIDE 12

ALL SB, SAB

0.0 0.2 0.4 0.6 0.8 1.0 Qb (bar) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(spir) [1.5 < R/Rbar < 2.0] N_SB =282 0.314 p=0.0000 N_SAB=238 0.345 p=0.0000

ALL SB, SAB

0.0 0.2 0.4 0.6 0.8 1.0 Qb (bar) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(spir) [2.5 < R/Rbar < 3.0] N_SB =279 0.199 p=0.0008 N_SAB=233 0.246 p=0.0002

ALL SB, SAB

0.0 0.2 0.4 0.6 0.8 1.0 Qb (bar) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 A2(spir) [3.0 < R/Rbar < 3.5] N_SB =264 0.244 p=0.0001 N_SAB=223 0.252 p=0.0001

1.5 - 2.0 Rbar 2.5 - 3.0 Rbar 3.0 - 3.5 Rbar

max FT/FR(BAR) vs. A2(R)

1 2 3 4 R/Rbar 0.0 0.2 0.4 0.6 0.8 rank correlation

SB 236 SAB 203

The correlation of max Qbar and max spiral A2 is significant even at ≈ 3 bar radii.

rank correlation between Qbar and A2(r) as a function of R/Rbar Symbols: correlation significant (p < 0.02)

12

SLIDE 13

max FT/FR(BAR) vs. A2(R)

1 2 3 4 R/Rbar 0.0 0.2 0.4 0.6 0.8 rank correlation

SB 236 SAB 203

local FT/FR(BAR) vs. A2(R)

1 2 3 4 R/Rbar 0.0 0.2 0.4 0.6 0.8 rank correlation

SB SAB

GLOBAL LOCAL Correlation between local Qbar and local spiral A2 even stronger near the bar, but drops more rapidly with distance

(consistent with salo et al. 2010: local values showed correlation, global not)

13

SLIDE 14

T-interval = -3,-1