Observations of Extragalactic Star Formation in [CI] (370  m) and CO J=7-6

1. 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 the SMA, 2005, Cambridge, MA

2. Star Formation in Galaxies • Star formation occurs in various locations in galaxies: • Spiral arms • Circum-nuclear regions • Bars • Tidal bridges/tails • Rings • 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 the SMA, 2005, Cambridge, MA

3. Signatures of Star Formation • ........ • Dense regions • Over pressured regions • Enhanced temperatures • Enhanced densities • Photodissociation Regions • ……. Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

4. Probing Star Forming Regions using mid- and high-J CO Transitions Some CO rotational transitions: 12CO ncrit=5.6106cm-3 503 K J =13 A=2.410-4s-1 200.273 mm J = 12 155 K J = 7 ncrit=3.9105cm-3 371.651 mm A=3.610-5s-1 116 K J = 6 ncrit=2.6105cm-3 433.338 mm A=2.210-5s-1 J = 5 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

5. ncrit=2.3105cm-3 111 K J = 6 453.497 mm A=2.010-5s-1 J = 5 Probing Star Forming Regions using mid- and high-J CO Transitions More CO rotational transitions: 13CO Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

6. [CI] 63K 3P2 ncrit=1.2103cm-3 370.415 mm 3P1 ncrit=4.7102cm-3 24K 609.135 mm 3P0 Probing Star Forming Regions using [CI] Fine Structure Lines The [CI] fine structure lines: [CI] line ratio gives Tgas Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

7. Probing Star Forming Regions using mid- and high-J CO Transitions Run of CO line intensity with J constrains molecular gas conditions Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

8. CO(7-6)/[CI] 370 m line intensity ratio vs. density for various values for the strength of the ISRF (Kaufman et al. 1999) Probing Star Forming Regions using CO J=7→6 and [CI] 370 m The CO J=7→6 to [CI] line ratio of particular interest, as it is very density sensitive Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

9. 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 the SMA, 2005, Cambridge, MA

10. SPIFI at the JCMT • JCMT: 15 m • SPIFI: • 55 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" Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

11. CO(7-6) and [CI] from NGC 4038/4039 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 the SMA, 2005, Cambridge, MA [Spitzer Space Telescope, IRAC; NASA/JPL-Caltech/ Z. Wang (Harvard Smithsonian CfA)] (Isaak, in preparation)

12. NGC 253 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

13. NGC 253 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 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

14. TMB = 1 K CO(76) [CI] SPIFI-JCMT [CI] 371 um & CO(76) (372 um) spectrum of the NGC 253 nucleus NGC 253 In 2001 we mapped the [CI] and CO(76) lines simultaneously from NGC 253: • The CO(76)/[CI] line ratio is density sensitive: strong CO(76) 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 abundance Consistent with our CO model  the primary heating source is cosmic rays from SN in starburst Added heat at cloud cores will inhibit cloud collapse – halting starburst Nikola et al. 2005 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

15. 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 the SMA, 2005, Cambridge, MA

16. N 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 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 the SMA, 2005, Cambridge, MA

17. NGC 6946 Israel et al. in preparation Madden et al. 1993, ApJ, 407, 579 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

18. 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=76 expected to be small; Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

19. Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

20. [NII] 205 mm and CO J=1312 Observations Using SPIFI on AST/RO • [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=1312 Observations: • Shocked gas (molecular outflows, cloud-cloud collisions) • Very warm, dense PDRs (constraining run of CO excitation) • Objects: • Galactic Center • Magellanic Clouds • M83 Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA

21. Summary • Data analysis is still ongoing • [CI] and CO J=76 is more compact in NGC 253 than in M82 • [CI] and CO J=76 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 the SMA, 2005, Cambridge, MA

22. The End Thank you very much for your attention. Submillimeter Astronomy in the era of the SMA, 2005, Cambridge, MA