galaxy spiral arms, disk disturbances and statistics · the gas cloud disk + inert high dispersion...
TRANSCRIPT
![Page 1: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/1.jpg)
1
GALAXY SPIRAL ARMS,DISK DISTURBANCES AND
STATISTICS Part I: NGC3081 to build background for
NGC4622. Co-authors for Parts I and II: G. Byrd (Univ. of Alabama, Tuscaloosa),
T. Freeman (Bevill State Comm. Coll. Fayette,AL),
R. Buta (Univ. of Alabama, Tuscaloosa)
Support NASA STScI and NSF RUI
![Page 2: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/2.jpg)
2
NGC 3081
Galaxy type (R1R2’)SAB(r,nr)0/aaccording to Ron Buta
quintessential resonance ring galaxy
results of ground based and HST WFPC2studies
analysis of individual point sources in innerring
![Page 3: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/3.jpg)
3
NGC 3081 Observational Studies
HST study Buta, Byrd, & T. Freeman 2001
Surface photometry & kinematics Buta &Purcell 1998
Goals:
Star Formation Dynamics
Bar Strength
Disk Surface Density
![Page 4: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/4.jpg)
[1]. North is top. UL is B band. Bar=30”≈ 5.4 kpc. URis a deep B. LL is B-I. LR is B with disk subtracted.
![Page 5: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/5.jpg)
5
HST blue image.
![Page 6: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/6.jpg)
HST image processed to reveal individualassociations.
![Page 7: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/7.jpg)
Images with possilbe ILR, CR,and OLR marked.
CR most important here.
Note gap between ``r” ring andR1 with CR in middle.
![Page 8: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/8.jpg)
8
Nodes, Doppler shifts, CR. Disk must turn CCW.
Stars formed near CR age in CCW sense.
![Page 9: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/9.jpg)
9
B and I band colors around ``r” ring.
B higher than I implies blue, young stars have formed.
Blue stars 0 to 90o and 180 to 270o
Like previous diagram => CCW orbit.
![Page 10: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/10.jpg)
![Page 11: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/11.jpg)
![Page 12: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/12.jpg)
![Page 13: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/13.jpg)
13
Analytic Solutionfor the Inner
Ring. 37’’ outeredge is well inside
CR) at 52”. Vo=221 km/s, 18 kpc equal to 100”, and
a perturbation pot amp. -qVo2 where q=0.025.
Pointy ends match our images and our simulations.Inside of the ring is more circular as observed [1].
Points are at equal intervals of t. At smaller radii, theangular displacement is larger as observed.
![Page 14: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/14.jpg)
14
Fourier m=2componentposition anglesfrom majoraxes around``r” ring.
Note I, V, Bgoing CCWfrom major axis
IVB is a CCWcolor-agesequence
![Page 15: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/15.jpg)
15
Simulation (and analytic) ringshape like our HST image.
The gas cloud disk + inert highdispersion stellar disk and halo221 km/s=Vo. Cloud disk surfacemass density 1/15 to produce Vo.
Clumps of gas clouds(``associations”) form.
Simulation ring life is several 109
yrs < ~400.106 yr.
Too low a halo _ a chaotic non-ring disk;
too high _ ring but noassociations.
![Page 16: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/16.jpg)
16
Obtaining Disk Parameters
For flat rotation curve.
More general formulas are possible.
Ratio a/b inner ring, r, = (1-sqrt(2q))/(1-2 sqrt(q))
Ftan/Frad =2q
Sur. Density = (q/(I 2/I0))x(Vo2/(2" G ro)) =
(q/(I 2/I0))x(100% Mestel disk)
Halo/Disk = 100% disk/ 3081 disk surface density =f = (I 2/I0)/q
![Page 17: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/17.jpg)
17
Conclusions: ``r” and ``R” rings arestar formation laboratories.
IVB color age sequence.M/L disk is not constant with radius.
May actually rise.
Radius“, kpc I2/IO Msun/pc2Halo/disk40 or 7.20.6812.819.450 or 9.000.5911.816.970 or 12.60.2519.47.14
![Page 18: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/18.jpg)
18
GALAXY SPIRAL ARMS, DISKDISTURBANCES AND
STATISTICS:
PART II: THE STRANGE CASE OFNGC4622, AN EXCEPTION TO THERULE
![Page 19: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/19.jpg)
19
Do spiral arms lead or trailoutward relative to orbital motion?
Lindblad (1941) said they lead. Thesketch shows thin arms & arrow fordisk orbital motion.
Hubble (1943) said they trailed. =>
G. deVaucouleurs (1958) found all totrail in a small sample of highlyinclined spirals.
Trailing accepted as the rule today.
![Page 20: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/20.jpg)
20
Byrd et al 1989pointed outNGC4622’s two-way arms.
It must haveleading arm(s)!
HST photo showsarms in disk &young blueassociations
Outer pair windsout CW
Inner arm CCW
![Page 21: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/21.jpg)
21
SimulatingNGC4622’s Arms
Byrd, Freeman, and Howard (BFH 1993) found anew, plunging, disk plane passage by a smallperturber produced a two-way pattern.
Assuming a flat rotation curve, two trailing outerarms and a single inner leading arm could beproduced.
Predicted that NGC4622’s disk turns counter-clockwise (CCW on the sky). Wanted to check this.
![Page 22: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/22.jpg)
22
Checking predicted disk rotation Need
NGC4622’svelocity field anddisk orientation.
Ground-based HAlpha emissionvelocity field forNGC4622. =>
Red = away
Blue = toward
Ref. Scott 1996MS thesis
![Page 23: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/23.jpg)
23
NGC4622 Disk orientation The line of nodes is
the intersection ofthe disk with the skyplane.
The line is obtainedfrom the elongationof NGC4622’s outerisophotes ~NNEtoward SSW.
Need to know whichedge of disk is near
![Page 24: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/24.jpg)
24
Obtaining Orientation: HST V-I image Use GdV method.
Darker bluer. Whiterredder.
Note blue spiral armassociations along outerarms.
Central regions, nuclearbulge.
Near side of NGC4622disk shows sharper dustsilhouettes with reddercolor than far side.
East side is nearer.
![Page 25: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/25.jpg)
25
Boy, were wesurprised!
Why is the result sosurprising?
East edge is nearer.=>
North line of nodesrecedes.
The disk thus orbitsCW on the sky,opposite prediction.
Inner single armtrails & the outer pairleads!
![Page 26: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/26.jpg)
26
How can the outer two leading arms andinner trailing arm be triggered?
As in BFH, we simulate asmall, planar plungingperturber .
However , we must use anew unusual rising,steepening rotation curvefrom the observations.
We fit the observed curve vwith a formula giving v~ 100 km/s 16 to 30arcsec
v~ 0.08r^2 km/s at 45 to 60arcsec.
![Page 27: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/27.jpg)
Simulationvs HSTimage
Highcontrastimage.m=0 disksubtracted=>
Simulationplotfollows.
![Page 28: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/28.jpg)
28
Simulationdisk390x10^6 yrafter a lowmass plungingperturberentered thenleft along diskplane.
Outer armslead out CWlike diskorbital motion.
Inner armtrailssurrounded byoval.
![Page 29: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/29.jpg)
29
Two CR Disk Resonances
A decliningorbital angularrate through firstCR.
A rising orbitalangular ratethrough secondCR.
![Page 30: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/30.jpg)
30
m=1 armresonance
colorsequences
Inner set of perturbed orbits insidefirst CR of turning m=1 (one sided)disturbance. Orbits have faster CWangular rate than smaller CR.
Another set outside first CR. Orbitshave slower CW angular rate than CR.
![Page 31: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/31.jpg)
31
Position angle vs r ofm=1 intensity peaks.
I---, V…, & B solid
180o jump at ~21” (first CR) as expectedfor one set of m=1perturbed orbits insideCR & one outside.
Expected reversal of I,V, B color peaksequence CW insideand CCW outside 21”.
==> CW orbitalmotion & trailingsingle inner arm.
![Page 32: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/32.jpg)
32
Simulationdemonstrating m=1
CR resonance Flat rotation curve
region.
Rotating m=1perturbation acts ondisk of particles. Littleself-gravity producesbest match.
Empty region is CRresonance radius.
Trailing arm and ringinside and outside CR.
![Page 33: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/33.jpg)
33
Position angle vs r of m=2IVB peaks
m=2 IVB orderswitches at CR= 21”& CR2= 36” whereorbital angular rateequals pattern speed.Similar to m=1.
Confirms CW orbit& leading outer pairof arms!
Will use CR,CR2 torevise rotation curve.
![Page 34: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/34.jpg)
34
Another 2 Way Galaxy Found
R. Buta and graduatestudent R. Grouchy inrecent observationshave identifiedanother two-waygalaxy, ESO297-27
It has a single innerarm and two and threefold oppositelywinding outer arms.
![Page 35: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/35.jpg)
35
Summary Our conclusion from HST images that the two
outer NGC4622 arms lead was simply notacceptable to some. One prominent astronomerstated, ``You’re the backward astronomers whofound a backward galaxy.”
Here we have substantiated our conclusion. Withthe observed flat then rising rotation curve a plunging passage of a small galaxy could have
triggered the inner trailing arm & outer leading pair.
NGC4622’s disk orientation & m=1, 2 IVB sequencesversus radius are consistent with an inner trailing + anouter leading pair of density waves.
![Page 36: GALAXY SPIRAL ARMS, DISK DISTURBANCES AND STATISTICS · The gas cloud disk + inert high dispersion stellar disk and halo 221 km/s=Vo. Cloud disk surface mass density 1/15 to produce](https://reader033.vdocuments.net/reader033/viewer/2022050518/5fa275fdb5b49a461435ab78/html5/thumbnails/36.jpg)
36 Now we know the origin of crop circle creators!