Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Observations of Extragalactic Star Formation

in [CI] (370 m) and CO J=7-6

T. Nikola1, G.J. Stacey1, C.M. Bradford2, J.M. Jackson3, A.D. Bolatto4, S.J. Higdon1, F. Israel5, K. Isaak6

1Cornell University, 2JPL, 3Boston University, 4UC Berkeley, 5Sterrewacht Leiden, 6Cardiff University

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Star Formation in Galaxies

• Star formation occurs in various locations in galaxies:Spiral armsCircum-nuclear regionsBarsTidal bridges/tailsRings

• What regulates the star formation activity?How much differ the physical conditions in those regions?What are the similarities?How does star formation modify its environment?What other effects can influence star formation regions?

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Signatures of Star Formation

• ........• Dense regions• Over pressured regions

Enhanced temperaturesEnhanced densities

• Photodissociation Regions• …….

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Some CO rotational transitions:

371.651 m

116 K

155 K ncrit=3.9105cm-3

ncrit=2.6105cm-3

433.338 m

12CO

503 K

200.273 m

J =13

J = 7

J = 5

J = 6

J = 12

ncrit=5.6106cm-3

A=2.410-4s-1

A=3.610-5s-1

A=2.210-5s-1

Probing Star Forming Regions usingmid- and high-J CO Transitions

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

More CO rotational transitions:

13CO

453.497 m111 K ncrit=2.3105cm-3

A=2.010-5s-1

J = 5

J = 6

Probing Star Forming Regions usingmid- and high-J CO Transitions

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Probing Star Forming Regions using[CI] Fine Structure Lines

The [CI] fine structure lines:

609.135 m

370.415 m

3P2

3P1

3P0

[CI]

24K

63K ncrit=1.2103cm-3

ncrit=4.7102cm-3

[CI] line ratio gives Tgas

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Run of CO line intensity with J constrains molecular gas conditions

Probing Star Forming Regions usingmid- and high-J CO Transitions

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Probing Star Forming Regions using CO J=7→6 and [CI] 370 m

CO(7-6)/[CI] 370 m line intensity ratio vs. density for various values for the strength of the ISRF (Kaufman et al. 1999)

0

1

2

3

4

5

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

DensityC

O(7

-6)/

[CI]

Lin

e R

atio G = 10

G = 100

G = 1E3

G = 1E4

G = 1E5

The CO J=7→6 to [CI] line ratio of particular interest, as it is very density sensitive

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Galaxies Observed

We observed selected regions in the following galaxies:

• NGC 4038/39

• NGC 253

• M82

• NGC 6946

• (M51) (in collaboration with C. Wilson)

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

JCMT: 15 mSPIFI:• 55 pixel bolometer array• Adjustable spectral resolution

using Fabry-Perot Interferometers (set to 200 km/s)

• Setup to cover the 350 m telluric window

• CO J=7-6 and [CI] 370 m in a single spectral scan

• Field of view: 35"35"

SPIFI at the JCMT

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

CO(7-6) and [CI] from NGC 4038/4039

[Spitzer Space Telescope, IRAC; NASA/JPL-Caltech/ Z. Wang (Harvard Smithsonian CfA)] (Isaak, in preparation)

0.5 K

0.5 K 0.5 K

• [CI] Line intensity essentially constant

• CO(7 6) greatly enhanced at the starburst interaction zone reflecting the high gas excitation there

• Strong mid-J CO emission reflects influence of OB stars

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

NGC 253

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Results from LVG model• Single warm component• Warm molecular gas mass: 4×107

Msun (=30 times the mass in PDRs as traced by [OI] and [CII]!, Carral et al. 1994)

• Heating can be explained by Cosmic Rays

Plausible, because due to the large supernova rate in the nucleus of NGC 253 the CR heating rate is ~800 times grater than in the Galaxy.

Bradford et al. 2003, ApJ, 586, 891

NGC 253

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

In 2001 we mapped the [CI] and CO(76) lines simultaneously from NGC 253:

• The CO(76)/[CI] line ratio is density sensitive: strong CO(76) in NGC 253 very dense ISM

• The [CI] (370 um)/(610 um) line ratio (~ 1.9) is sensitive to gas temperature, and yields Tgas>100 K – consistent with our CO model

• From distribution and physical conditions, Co and CO well mixed Cosmic ray enhancement of Co

abundanceConsistent with our CO model the primary heating source is cosmic rays

from SN in starburst

SPIFI-JCMT [CI] 371 um & CO(76) (372 um) spectrum of the NGC 253 nucleus

[CI] CO(76)

TMB = 1 K

Added heat at cloud cores will inhibit cloud collapse – halting starburst

Nikola et al. 2005

NGC 253

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

NGC 253

• Dynamical heating (shocks, cloud collisions, SN blasts) does not provide enough heating

• PDR models don’t produce enough atomic gas as measured by e.g. [CII]

• Single component consistent with H2 ISO observation

• There are enough SN to provide cosmic rays to heat the molecular clumps

• Single cosmic ray heated component is simplest model consistent with the observations

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

M82• Observed area: 55"45"• Both lines detected over

extended (~ 400 pc ) regions

• CO(7 6) line is typically as strong as [CI] high excitation (density) medium

• High ratio also found for NGC 253 reflects effects of starbursts

• Co/CO abundance enhanced for many starbursters – Cosmic Ray or PDR origin?

• Strong 370 m [CI] indicates warm gas PDR origin more likely

N

Single SPIFI footprint on the nucleus of M82. Total integration time was 15 minutes. These data are one of 4 footprints we obtained on M82

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Israel et al. in preparation

Madden et al. 1993, ApJ, 407, 579

NGC 6946

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

NGC 6946

Previous observations (Israel & Baas 2001, A&A, 371, 433) suggest: Two components:

Tkin = 30 – 60 K, n = 3000 – 10,000 cm-3

Tkin = 100 – 150 K, n 1000 cm-3

In both cases (low temperature, low density) CO J=76 expected to be small;

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

[NII] 205 m and CO J=1312 ObservationsUsing SPIFI on AST/RO

Objects:• Galactic Center• Magellanic Clouds• M83

[NII] Observations:• Important coolant of diffuse ionized medium• Proxy for Lyman continuum photons in ionization bound HII regions• Constraining the fraction of [CII] from ionized gas regions

CO J=1312 Observations:• Shocked gas (molecular outflows, cloud-cloud collisions)• Very warm, dense PDRs (constraining run of CO excitation)

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

Summary

• Data analysis is still ongoing• [CI] and CO J=76 is more compact in NGC 253 than in M82• [CI] and CO J=76 provide additional important constrains about

the physical conditions in star forming regions (“cosmic ray model”)

• More data is needed to build “templates” of submillimeter line emission for various physical conditions and for comparison with theoretical models.

Submillimeter Astronomy in the era of tSubmillimeter Astronomy in the era of the SMA, 2005, Cambridge, MAhe SMA, 2005, Cambridge, MA

The End

Thank you very much for your attention.