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Red: CO from Mini survey. Philamentary Structure and Velocity Gradients in the Orion A Cloud. Spitzer Orion Cloud Survey: 10 sq. degrees in Orion A and Orion B mapped between 2004-2009 IR-ex: 3352 IR-ex + coup: 3845 IR-ex + coup + corr: 4300 Megeath et al. (y+1) y = current year. Orion B.

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philamentary structure and velocity gradients in the orion a cloud
Red: CO from Mini surveyPhilamentary Structure and Velocity Gradients in the Orion A Cloud

Spitzer Orion Cloud Survey:

10 sq. degrees in Orion A and Orion B mapped between 2004-2009

IR-ex: 3352

IR-ex + coup: 3845

IR-ex + coup + corr: 4300

Megeath et al. (y+1)

y = current year

Orion B

Orion A

Green dots: YSOs

Blue stars: OB stars

slide2
Orion A: A 50 parsec Long Star Forming Filament

stars with disks

Ph-actoid:

Two of Phil’s postdocs did their

Ph.D. theses on L1641:

-Lori Allen

-Hua Chen

protostars

ONC

ONC

L1641

L1641

Red: AV map

IR-ex: 2791

IR-ex+COUP: 3214

IR-ex+COUP+corr: 3400

350 protostars

slide3
Clustering in the Orion Clouds

Nearest neighbor density

10/p r102

Orion

Orion Nebula

ONC cluster

Orion Nebula Cluster

Color: stars in clusters

Black: isolated stars

Taurus

Identify contiguous groups of stars with local surface densities 10 pc -2

velocity structure of orion a
Velocity Structure of Orion A

ONC

ONC

L1641

L1641

Velocity Integrated

Position-Velocity

Filamentary structure in the Orion Molecular Cloud

Bally et al. 1987

the orion nebula cluster
The Orion Nebula Cluster

12 pc long cluster

2232: IR-ex (corrected)

Highly elongated: 15 pc long

mean radius of 4.2 pc

The density peaks sharply in the center of the cluster in the Orion nebula.

Rings show that massive stars are dispersing the gas.

Blue dots: protostars

Green dots: stars with disks

Image: Blue 3.6 mm, green 4.5 mm, red 8 mm

properties of the onc
Properties of the ONC

Degree of Asymmetry

Stellar Surface Density

Relaxation time = 500,000 years

circularly symmetric

circularly symmetric

Azimuthal Asymmery Parameter

(Gutermuth et al. 2005)

spectroscopic survey of onc with hectoshell and mike tobin et al 2009
Spectroscopic Survey of ONC with Hectoshell and Mike (Tobin et al. 2009)

Also Furesz et al. 2008

Proszkow et al. 2009

Stars moving with gas

Gradient due to infall?

Evidence for explosive motions?

Greyscale: gas

Blue: stars

cs 2 1 data of the onc region
CS (2-1) Data of the ONC Region

OMC 2/3

OMC 2/3

ONC

ONC

Acceleration consistent to material falling from 1.5 parsecs onto a 500 solar mass object

velocity structure of orion a9
Velocity Structure of Orion A

0.25 km s-1/pc

This is usually interpreted as a filament expanding along its long axis

Integrated

Position-Velocity

Filamentary structure in the Orion Molecular Cloud

Bally et al. 1987

motivation
Motivation

Consider an expanding filament with a linear velocity gradient

v

Does gravity or kinetic energy win?

What is the dominant form of kinetic energy: thermal, turbulent or large scale velocity gradient?

You can derive a length, at which velocity gradient wins.

Length prop 1/velocity gradient

slide11
Breaking up the Orion A Filament by Cluster

10 pc

Red: isolated IR-ex

Other colors: clusters

slide12
Breaking up the Orion A Filament by Cluster

0.5 km s-1/pc

5 pc

For the observed gradient (and making NUMEROUS assumptions)

at a length of 0.5 pc, the velocity gradient dominates.

where to go next
Where to go next
  • Filaments show complicated and significant velocity structure.
  • Some evidence for infall along filament
  • Expansion may help define clusters and separation between clusters
  • Need to understand motions more: what is driving velocity gradients?
  • Need to find more examples: are such gradients common?
  • Need to simulate star formation in filaments with velocity gradients
  • Need to ask Phil what he thinks!
quick census embedded ysos within 500 pc
Quick Census: Embedded YSOs within 500 pc

Ophiuchus

Ophiuchus & Perseus

Av cloud map: CompleteYSOs: IR-ex from Spitzer C2D

Taurus

Av cloud map: Lombardi & Alves YSOs: all known from K Luhman

Orion

Av cloud map: R. Gutermuth

YSOs: IR-ex from Spitzer Megeath in prep. + COUP

Orion GMC

3838 YSOs

298 YSOs

Perseus

Parsecs

387 YSOs

Taurus

296 YSOs

460 protostars larger than c2d sample
The Distribution of Stars Follows the Distribution of Gas460 protostars(larger than C2D sample)

2900 stars + disk

NGC 2068

Orion B

NGC 2024

Orion A

ONC

Red: AV map from 2MASS (Gutermuth)

slide16
We find that all GMCs associated with massive stars contain significant numbers of low mass stars in small groups and relative isolation.

Even in GMCs containing young massive stars, many low mass stars are found in relative isolation, parsecs away from the hot OB stars.

<10 10-100 > 100

slide17
Orion-Like vs Taurus-Like Regions

2MASS Images

L1551 in Taurus

Orion Nebula Cluster

In the star formation literature, there are two archetypes for star forming regions:

The Taurus Molecular Cloud – the prototypical distributed star forming region

The Orion Molecular Clouds – the prototypical clustered star forming region

slide18
Orion – prototypical clustered star formation

Nearest neighbor density

10/p r102

How do you identify clusters?

One approach is to use a surface density criteria.

For the following analysis, I adopt a threshold of 10 pc-2

10 pc-2

Taurus – prototypical isolated star formation

10 pc-2

processes controlling star formation
Processes Controlling Star Formation

Large Scale Motions in the ISM ( creates molecular clouds)

Global Gravitational Collapse (collapse of clouds or large regions within clouds)

Jeans Fragmentation (forms ~stellar mass sized unstable fragments)

Small Scale Collapse of Fragments into Stars

Turbulence within Molecular Clouds (turbulent fragmentation creates fine scale structure needed for small scale collapse, resists global collapse)

Magnetic Fields (resists collapse, particularly on small scales)

Feedback from Stars (outflows, winds and UV radiation)

Dynamical Motions of Stars in Clusters (eject stars from cloud)

slide20
Comparing Clustered and Distributed Modes

Relative importance of clustered and distributed stars appears to be linked to the organization of gas in the clouds.

Taurus – spaghetti like filaments, no major clumps with large column densities.

Ophiuchus – star formation found in one large clump, perhaps the result of compression by Upper Scorpius association.

Does compression from external stars play role? Do magnetic fields inhibit the formation of clumps?

Ophiuchus

Taurus

298 YSOs

296 YSOs

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