… and its relationship to the the real world?

… and its relationship to the the real world?

What is this thing called . the Schmidt Law? ..

Barry F.MadoreBarry F.Madore

“Shit Happens”

Which one of these is a law?

(1) “Mercy falls, like the gentle rain, from heaven”

(2) “The rain in Spain falls mainly in the plain”

(3) “Rain forms in clouds”

(4) “Stars form in clouds”

(5) “Schmidt happens”

(6) “Star formation is like rabbit pie”

Which one of these is a law?

(1) “Mercy falls, like the gentle rain, from heaven”

(2) “The rain in Spain falls mainly in the plain”

(3) “Rain forms in clouds”

(4) “Stars form in clouds”

(5) “Schmidt happens”

(6) “Star formation is like rabbit pie”

Heidelberg (2010)

THE SCHMIDT LAW

GAS DENSITY regulates the RATE of of STAR FORMATION ?

What gas?

What density? Over what scale? **

What tracers?

What rate(s)? **

(And, what about efficiency?) **

… and what about collisions, and bars, and flows, and density waves and …ack?

THE SCHMIDT LAW

GAS DENSITY regulates the RATE of of STAR FORMATION ?

What gas?

What density? Over what scale? **

What tracers?

What rate(s)? **

(And, what about efficiency?) **

… and what about collisions, and bars, and flows, and density waves and …ack?

George Santayana

“Those who ignore history are doomed to repeat it” -- George Santayana

Recall that Schmidt (1959) originally stated that a power-law

dependence was suggested because the exponential scale heights of the young stars were smaller than the scale height of the gas layer.

In which direction is causality operating?

“Those who ignore history are doomed to repeat it” -- George Santayana

Recall that Schmidt (1959) originally stated that a power-law

dependence was suggested because the exponential scale heights of the young stars were smaller than the scale height of the gas layer.

In which direction is causality operating?

SMC: Neutral Hydrogen Column Density SMC: Neutral Hydrogen Column Density

Sanduleak (1969)This is what started it all!

SMC: Neutral Hydrogen and

Individually Resolved OB Stars

Sanduleak (1969)

Sanduleak (1969)

SMC: Neutral Hydrogen and

Individually Resolved OB Stars

Sanduleak (1969) substituted neutral hydrogen

surface densities for gas volume densities,

and used the area-average star density for the time-averaged star formation rate.

Note: This is the first spatially resolved determination of the Schmidt Law in an extragalactic setting.

Sanduleak (1969) substituted neutral hydrogen

surface densities for gas volume densities,

and used the area-average star density for the time-averaged star formation rate.

Note: This is the first spatially resolved determination of the Schmidt Law in an extragalactic setting.

M31 20um + Swift M31 20um + Swift

Andromeda (2010)

Data

M31: Andromeda

WISE Early Release Data

(12 and 22 um)

SWIFT: High-Resolution UV

Bigiel(209

0)

Bigiel(209

0)

Bigiel et al. (2009)

Star Formation Rate

versus

Total Gas (HI + H2) Surface Density

Madore (2010)

Cloud-Collapse and Stellar Evolutionary

Timescales

Cloud-Collapse and Stellar Evolutionary

Timescales

Madore (2010) Madore (2010)Madore (2010)

Star Formation and Stellar Evolution

Timescales Combined

Boissier (2007)

Radially Averaged Schmidt Law

Kennicutt (1998)

Globally-averaged Schmidt Law

Clumping

Spongebob 1 Spongebob 2

10 10 1 37 gas density10 10 1 1

<10> <10> <gas density>

SFR = density**2

100 100 1 1369 sfr100 100 1 1

<100> <342> <sfr>

The Global Schmidt Law is dominated by “sub-grid physics”

Spongebob 1 Spongebob 2

10 10 1 37 gas density10 10 1 1

<10> <10> <gas density>

SFR = density**2

100 100 1 1369 sfr100 100 1 1

<100> <342> <sfr>

The Global Schmidt Law is dominated by “sub-grid physics”

SBSP-1

Kennicutt (1998)

Global Schmidt Law

Complications (2010)

Additional (but non-trivial) Complications:

Plane thickness variations within individual galaxies, and between galaxies.

What controls the efficiency with which gas gets converted into stars within any given cycle of the star formation process?

Additional (but non-trivial) Complications:

Plane thickness variations within individual galaxies, and between galaxies.

What controls the efficiency with which gas gets converted into stars within any given cycle of the star formation process?

We need to finally “Bell the cat” and actually control the experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

We need to finally “Bell the cat” and actually control the experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

What is this thing called What is this thing called

the Schmidt Law? the Schmidt Law? . ..

Barry F.MadoreBarry F.Madore

Bell the cat!

We need to finally “Bell the cat” and actually control the experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

We need to finally “Bell the cat” and actually control the experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

What is this thing called What is this thing called

the Schmidt Law? the Schmidt Law? . ..

Barry F.MadoreBarry F.Madore

Bill the cat!

M31 20um M31 20um

Sanduleak (1969)

SMC: Neutral Hydrogen and

Individually Resolved OB Stars

Schmidt-Sanduleak Law

Schmidt-Kennicutt Law

Schmidt-Calzetti Law

Schmidt-Boissier Law

What is this thing called the Schmidt Law? … many things by many people

M31 20um M31 20um

Sanduleak (1969)

SMC: Neutral Hydrogen and

Individually Resolved OB Stars

Schmidt-Sanduleak Law

Schmidt-Kennicutt Law Schmidt-Calzetti Law

Schmidt-Boissier Law

What is this thing called the Schmidt Law? … many things by many people

“Kill Bill” - Uma Thurmon

“And once again were are forced to think”

- Martin Schwarschild

* No animals were harmed in the making of this presentation

“Kill Bill” - Uma Thurmon

“And once again were are forced to think”

- Martin Schwarschild

* No animals were harmed in the making of this presentation

What is this thing called . the Schmidt Law? ..

Barry F.MadoreBarry F.Madore

We need to finally “Bell the cat” and control this experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

We need to finally “Bell the cat” and control this experiment.

We need to remember that we are not reading the recipe. Causality plays a role, but we are observing input and end products simultaneously weighted by their various lifetimes.

Galaxies are 3D objects but we observe them only in projection.

Scales matter: Azimuthally-averaged and globally-averaged Schmidt Laws are not substitutes for the spatially resolved Schmidt Law.

Finally, we need to understand the physics behind star formation efficiency.

Understand the Magellanic Clouds.

What is this thing called . the Schmidt Law? ..

Barry F.MadoreBarry F.Madore