The signatures of long-lived spirals in disk galaxies The signatures - - PowerPoint PPT Presentation

The signatures of long-lived spirals in disk galaxies The signatures of long-lived spirals in disk galaxies The signatures of long-lived spirals in disk galaxies The signatures of long-lived spirals in disk galaxies

Eric E. Martínez-García (INAOE, Mexico) Collaborators: Rosa Amelia González (CRyA, UNAM) Gustavo Bruzual (CRyA) Gilberto Gómez (CRyA) Ivanio Puerari (INAOE) South Korea 2013

What is the origin of the spiral arms?

Early studies (60's) of spiral patterns propose density waves.

• Attempt to explain spiral structure, avoiding

the winding dilemma : Linblad, Lin & Shu, Roberts, Toomre, Kalnajs, Bertin, Contopoulos, inter alia.

“Chaotic” spirals

Kaufmann & Contopoulos (1996) invoke for the first time the need of chaotic

• rbits as building blocks of

spirals near the end bar. Part of the spirals attached to the bar are due to chaotic

• rbits (Patsis, 2006).

“Invariant manifolds” theory

• Romero-Gómez et al. (2006,

2007) Athanassoula et al. (2009a,b, 2010) consider a continuous flow of orbits along the manifolds emanating from L1

• r L2. “Lyapunov tube model”.
• Voglis et al. (2006a,b); Tsoutsis

et al. (2008, 2009) consider the apsidal sections of the manifolds.

“Invariant manifolds” theory

• Romero-Gómez et al. (2006,

2007) Athanassoula et al. (2009a,b, 2010) consider a continuous flow of orbits along the manifolds emanating from L1

• r L2. “Lyapunov tube model”.
• > Corroborated for galaxies in

which the spiral arms maintain a logarithmic shape al least for 70° in azimuth (Martinez-Garcia 2012).

Roberts (1969)

Large scale shocks in spiral arm regions.

Gittins & Clarke (2004)

Suggests that star formation is triggered near spiral arms.

Shocks may extend to high z (the height above the galactic midplane) above the arm (Martos et al. 1999, Alfaro et al. 2001)

Density contours and the velocity field.

Expected SF sequence across spiral arms.

see e.g., Foyle et al. (2011) Martinez-Garcia & Puerari (in preparation)

• > Photodissociated

(Louie et al. 2013)

Expected SF sequence across spiral arms.

Azimuthal gradients (age, color).

Spiral pattern:

Ωp≅ constant

Stars and gas: Differential rotation

Meidt et al. (2009); M101:

Black and blue curves:

The Ωp may vary as a function of radii for some objects. Radial Tremaine– Weinberg (TWR) method. The kinematic tracer (CO and HI) is assumed to obey the continuity equation. Must orbit in a single plane.

MHD simulations of gas orbits.

2-arm potential of Pichardo et al. 2003. Gas response: 4 arms (Martos et al. 2004).

Pattern Speed Variation with Radii. An effect of non-circular motions? (Martinez-Garcia et al. 2009, 2013)

May be an artifact produced by the non-circular streaming motions of shocked material. Besides, shocks may extend to high z (Martos et al. 1999)

Pattern Speed Variation with Radii. An effect of non-circular motions? (Martinez-Garcia et al. 2009, 2013)

Have azimuthal gradients been observed?

• Gónzalez & Graham

(1996), M99, first extragalactic reliable gradient~ 50´´ (4 kpc).

Avoid HII regions. Photometric index “Q”, reddening-free and star formation tracer.

Photometric index “Q” (Mihalas & Binney, 1981 ):

) ( ) ( ) ( ) ( ) ( V B V B E B U E B U UBV Q − − − − − =

) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( V B V B E B U E B U V B V B E B U E B U − − − − − = − − − − −

Defined in r, J, g, i : Reddening free (for screen model):

) ( ) ( ) ( ) ( ) ( i g i g E J r E J r Jgi r Q

s s s

− − − − − =

Do not confuse with Toomre's Q!

GG96 method.

05 . 2 50 . 2 50 . 2 05 . 2 10

log ) (

i r J g s

I I I I Jgi r Q

s

=

“Index Q”, star formation tracer: GG96 method.

Q predicted by stellar population synthesis models (Bruzual & Charlot).

Q

Young stars fraction between 0.5 y 2%, in agreement with Schweizer (1976).

“Index Q”,

for a mixture of dust and stars. Two-component dust model

• f Charlot & Fall (2000):

τv < 2 for face-on galaxies

(e.g. Peletier 1995)

CB07 2007, IMF limit: 100 Msun:

Witt et al. (1992) models:

CB07 2007, IMF limit: 10 Msun:

Structural type of the spiral arms.

From the point of view of their spiral arms, there are three different types of galaxies (e.g., Efremov 2011 ).

(1) Symmetric grand- design spirals (e.g., M81) (2) Multi-armed or “knee-like” spirals (e.g.,M101)

(3) Flocculent spiral

galaxies (e.g., NGC 2841) Mass arms maybe explained by DWs.

Structural type of the spiral arms.

In order to determine whether the arms are indeed mass DWs it is important to disentangle the contribution of young stars and clusters at longer wavelengths. Such contribution can reach up to 20%–30% in the NIR (e.g., Rix & Rieke 1993; GG96; Rhoads 1998; James & Seigar 1999; Patsis et al. 2001; Grosbøl et al. 2006).

Resolved maps of stellar mass.

Method of Zibetti et al. (2009).

Monte Carlo library of 50,000 stellar population spectra.

Constructed from the SPS models of Bruzual & Charlot (2003 ), and Charlot & Bruzual (2007). Each spectrum is computed by randomly drawing the model parameters:

➢Star formation history ➢Metallicity ➢Dust attenuation (dust model of

Charlot & Fall (2000).

Resolved maps of stellar mass.

Method of Zibetti et al. (2009).

Less degeneracy in M/L: g & i optical bands + 1 NIR

***) 19 nearly face-on SA and SAB spirals. Angular diameters between 4' y 6'. Deep images (30-60 minutes of exposure time). Taken during 1992-1995 Observatories: Lick, Kitt Peak, CTIO Optical data: bands g, r, i (near) IR: bands J y Ks (or H)

Data sample.

Sample of

• bjects &

mass maps.

By visual inspection, the following

• bjects were

rejected prior to analysis:

NGC 3162 NGC 3938 NGC 5371 NGC 7083 NGC 7126 NGC 7753 Remaining 13 objects analyzed with Fourier techniques in search for azimuthal color/age gradients.

Patterns with amplitudes between 0.02-0.06 mag in Q(rJgi).

FOURIER detection of color gradients.

Objects analyzed in rings for all radii.

CB 2007 models

) ( ) ( ) ( ) ( ) ( i g i g E J r E J r Jgi r Q

s s s

− − − − − =

FOURIER detection of color gradients.

) ( ) ( ) ( ) ( ) ( i g i g E J r E J r Jgi r Q

s s s

− − − − − =

CB 2007 models

Expected result from MHD simulation, with a constant pattern speed for all radii. The data diverge towards corotation ~0.6

Azimuthal phases method of Puerari & Dottori (1997 )

Where IR is the intensity of radiation with phase:

Based on computing the radial Fourier transform:

For m=2: π radians symmetry assumption.

Azimuthal phases of the g, r, i, and J Bands

Cautions:

➢Effect of dust obscuration? ➢Emission of the old stellar

arm (DW)?

➢π radian symmetry?

Results NGC 3338 and NGC 4254

Suggests a constant pattern speed for all radii.

NGC 4603

Can't suggest a constant pattern speed for all radii.

7 of 13 (54%) objects may present a constant pattern speed for all radii. Fourier results for detection of color gradients

For the remaining objects color gradients may be difficult to detect because of: 1) Dust extinction (phases method) 2) “Infant mortality” of star clusters (Lada & Lada 2003) 3) Overlapping radiation of HII regions 4) Physical conditions (magnetic field or pitch angle; Efremov 2010) 5) Not a constant pattern speed?

Pitch angle test

➔Complementary test of

DW presence.

➔Examine the pitch

angles of the spiral arms in different wavebands (g, r, i, and J) and in “resolved mass maps”.

Differences in wavelength should exist if age/color gradients are present across spiral arms!

Pitch angles Fourier method

✔ It is assumed again that the arms can be

represented by logarithmic spirals.

✔ Determines the “average” pitch angle inside a range

• f radii.

(e.g., Considere & Athanassoula 1988; Puerari & Dottori 1992; Seigar et al. 2006)

Pitch angle test results

✔Negative differences

indicate that the pitch angles are larger in the NIR than in the optical.

✔Agreement with Grosbøl &

Patsis (1998), who find tighter arms in bluer colors in images of four spirals, suggesting the presence of DWs.

✔Mass arms are

statistically more open than the arms in NIR light.

Other evidence; age gradients

Hα to far-UV flux ratio method: Sánchez-Gil et al. (2011) found age gradients across the spiral arms of the grand-design spirals M74 and M100.

Other evidence

Scarano & Lepine (2011,2013) found "breaks" in the radial metallicity distribution near corotation (CR). Implies that spiral arms must be long-lived structures. A dominant pattern speed must exist with a unique CR. Or otherwise any discontinuities in the radial metallicity profiles would be smoothed out (Scarano & Lepine 2013).

Relationship between Spiral arm pitch angle-Supermassive black hole mass

Seigar et al. (2008) Berrier et al. (2013) Suggests the presence of density waves in disk galaxies

Summary

➢With a Fourier technique for detecting gradients, we show that

~50% of spirals galaxies may present a constant pattern speed for all radii, indicating long-lived spiral structures.

➢Our results are consistent with other observational studies of age

patterns (or offsets) across spiral arms (Efremov 1985; Tamburro et al. 2008; Egusa et al. 2009; Grosbøl & Dottori 2009; Sánchez-Gil et al. 2011).

Future work

✔ Better constrain the fraction of grand-design (m=2) spirals

with positive evidence of long-lived modes

• > statistically significant sample.

✔ Discern the differences with the grand-design (m=2) spirals

that show no evidence of long-lived modes.

✔ Perform similar studies at various redshifts and look for

possible trends.

➔Pipeline 5: Mass maps

(Meidt et al. 2012, Querejeta et al.)

Thank you!