Disk instabilities and star formationMulti-wavelength analysis using ALMA+IFS data at

sub-kpc scales

Javier Piqueras López & Miguel Pereira-Santaella (University of Oxford)

2nd SELGIFS Advance School on IFS Data Analysis 2016

Overview of the talk

2

๏ Introduction ๏ Luminous Infrared Galaxies (LIRGs) ๏ Gas disk instabilities: Toomre’s Q parameter

๏ ALMA data: cold molecular gas kinematics ๏ SINFONI data: star-formation ๏ Disk instabilities and star-forming regions

3

(U)LIRGs: a general perspective

Kartaltepe et al. 2010

๏ Definition: ๏ LIRGs: 1011L⊙≤LIR<1012L⊙

๏ ULIRGs: 1012L⊙≤LIR<1013L⊙ ๏ IR luminosity explained as the

output from reprocessed radiation from dust.

๏ Power source: Extreme star-formation activity and AGN.

๏ Large fraction of LIRGs and almost all the ULIRGs show signatures of recent interactions: triggering mechanisms

4

(U)LIRGs: a general perspective

Magnelli et al. 2013

๏ (U)LIRGs play a key role in galaxy evolution ๏ Detected in large quantities at high-z

(z>1) with Herschel. ๏ ULIRG contribution may be the

dominant component to the SFR at z>2 ๏ However, they are not very common in

the local Universe… ๏ Local (U)LIRGs

๏ Study of extreme environments with great amount of detail.

๏ Compact star-formation and coeval AGN.

๏ Feedback processes: outflows, quenching of the SF.

๏ Link to high-z: forthcoming studies with ALMA, JWST, E-ELT…

Instabilities of a gas disk

5

Instabilities of a gas disk

6

A rotating, symmetric and thin gas disk is unstable to gravitational fragmentation if Toomre’s Q-parameter:

Qgas =σ0κ

πGΣgas≤1

ωshearρσ

Gravity

Thermal+Dynamical

rΩ(r)

L

Pressure ~L2

Gravity ~L3 vs

Toomre 1964

Instabilities of a gas disk

7

Qgas =σ0κ

πGΣgas≤1

Gravity

Thermal+Dynamical

Region can collapse, fragment, form cold gas clouds and star-forming cores therein, and this collapse should take a gravitational free-fall time.

Q > 1

Q < 1

Any scale is stabilized either by pressure or rotation - scales smaller than the Jeans length are stabilized by the gas pressure, and the Jeans length is already large enough to be stabilized by rotation.

A rotating, symmetric and thin gas disk is unstable to gravitational fragmentation if Toomre’s Q-parameter:

Toomre 1964

Instabilities of a gas disk

8

Region can collapse, fragment, form cold gas clouds and star-forming cores therein, and this collapse should take a gravitational free-fall time.

Q > 1

Q < 1

Any scale is stabilized either by pressure or rotation - scales smaller than the Jeans length are stabilized by the gas pressure, and the Jeans length is already large enough to be stabilized by rotation.

Qgas =σ0κ

πGΣgas= σ0

vc

⎛⎝⎜

⎞⎠⎟

afgas

⎛

⎝⎜⎞

⎠⎟a = 2 for constant vc

A rotating, symmetric and thin gas disk is unstable to gravitational fragmentation if Toomre’s Q-parameter:

Toomre 1964

200 pc20 pc

Instabilities of a gas disk

9

2 kpc

2 pc

Renaud et al. 2013

Proposed Project

10

Goal: - To characterize the spatially-resolved Toomre parameter (Q) in two Luminous Infrared Galaxies (LIRGs) to trace disk instabilities at ~100 pc scales, and compare with the location of on-going star-formation sites.

Method: - Use ALMA CO data to trace the distribution and kinematics of the molecular gas to estimate the 2D distribution of the Toomre Q parameter. - Use SINFONI data to identify star-forming regions traced by the Brγ emission. - Explore the correlation between 2D distribution of Q and star-forming regions.

Optional: - Estimate the Q parameter for a disk of stars using the CO stellar absorptions from the SINFONI data cubes.

ALMA CO data analysis

11

๏ Observations of two LIRGs during ALMA Cycle 2

๏ CO (2-1) transition: tracer of the cold molecular gas phase, which fuels star formation

๏ FoV ~ 15” x 15” (~4-5 kpc) ๏ Spatial resolution of

~0.3” (~60-100 pc) ๏ Channel width ~5 km s-1

ALMA CO data analysis

Pereira-Santaella et al. 201612

Qgas =σ0

vc

⎛⎝⎜

⎞⎠⎟

afgas

⎛

⎝⎜⎞

⎠⎟

Velocity dispersion Line Flux

ALMA CO data analysis

Pereira-Santaella et al. 201613

Qgas =σ0

vc

⎛⎝⎜

⎞⎠⎟

afgas

⎛

⎝⎜⎞

⎠⎟

Velocity field

0.0 0.5 1.0 1.5 2.0 2.5r [kpc]

0

50

100

150

200

250

v [km

s-1]

Rotation curve

SINFONI data analysis

14

๏ SINFONI observations: ๏ K-band (1.95-2.40 μm),

R~3500, ~ 80 kms-1 ๏ Seeing limited, FWHM

~0.6” (~100-200 pc) ๏ FoV ~8”x8”, ~3x3 kpc

๏ Brγ emission line, tracing ionized gas by young star-forming regions.

๏ CO stellar absorptions, tracing giant and supergiant evolved stars. Brγ

H2 1-0S(1)

Characterisation of star-forming regions

15

K-band spectrum

1.9 2.0 2.1 2.2 2.3 2.4

Wavelength [µm]

1

10

No

rma

lise

d f

lux

Brδ

H2 1

−0S(

3)[S

iVI]

H2 1

−0S(

2)

HeI

H2 2

−1S(

3)

H2 1

−0S(

1)

Brγ

H2 1

−0S(

0)

H2 2

−1S(

1)

CO

(2−0

)

[CaV

III]

CO

(3−1

)

CO

(4−2

)

CO

(5−3

)

NaI

CaI

MgI

H2 3

−2S(

5)

H2 2

−1S(

2)

H2 3

−2S(

3)

−0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ised

Flu

x

−600 −400 −200 0 200 400 600Velocity (kms−1)

−2−1012

Spaxel-by-spaxel Gaussian* fit

1"

2D ionized gas distribution

Piqueras López et al. 2016

Star-forming regions

Disk instabilities and star-formation

16

Unstable Stable Unstable Stable Unstable Stable

This is done at > kpc scales for z ~1.3

🤔And for local LIRGs at ~100 pc scales…?

Wisnioski et al. 2012

HαQ