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Molecular Gas and Star Formation in Nearby Galaxies

Molecular Gas and Star Formation in Nearby Galaxies. Jean Turner UCLA. with: David S. Meier, Lucian Crosthwaite, Chao-Wei Tsai, Sara Beck, Robert Hurt, Alaina Henry. Molecular gas and star formation in galaxies present and future CO, a tracer of star-forming gas in galaxies

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Molecular Gas and Star Formation in Nearby Galaxies

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  1. Molecular Gas and Star Formation in Nearby Galaxies Jean Turner UCLA with: David S. Meier, Lucian Crosthwaite, Chao-Wei Tsai, Sara Beck, Robert Hurt, Alaina Henry Space Telescope Science Institute

  2. Molecular gas and star formation in galaxies • present and future • CO, a tracer of star-forming gas in galaxies • Gas & star formation in spiral and dwarf galaxies • Beyond CO: chemical diagnostics and feedback • ALMA Space Telescope Science Institute

  3. CO is the tracer of molecular gas • Why not H2? • Excitation: first excited level is 510K above ground, but first quadrupole transition is J=2 rotational level… • You will see very warm (hundreds of K) gas, or fluorescent emission from H2 • You will NOT see thermal emission from typical GMCs (4-30K), nor absorption (Av > 3-5) Space Telescope Science Institute

  4. CO is the tracer of molecular gas • Why CO? • Abundant, chemically stable, transitions accessible from the ground ( = 3mm, 1mm) • Easily excited: first excited rotational (J=1) level 5.5K • Easily thermalized: collisional excitation dominates at densities > a few hundred/cc (low dipole moment and high opacity) Space Telescope Science Institute

  5. CO is a tracer of molecular (H2) mass • Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s, empirical • rays (CR+H) show Xco is good to x2 in Galaxy Bloemen et al. 1986, Strong et al. 1988 • arises from observed size-linewidth relation for GMCs • Larson 1980, Solomon et al. 1987 • can be understood in the context of virialized clouds Space Telescope Science Institute

  6. Virialized clouds? • Column density at which H => H2 is the same as the column density of the critically-bound Bonner-Ebert sphere (i.e., “Jeans mass”) at inner disk pressures. Clouds in high P regions more likely to be H2. • Scoville & Sanders 1987, Elmegreen 1989, Elmegreen & Parravano 1996 • Yet while clouds are bound they are not collapsing… otherwise SFR = 109 Msun/tff >200 Msun/yr, observed is 3-4 Msun/yr Zuckerman & Palmer 1974, Z & Evans 1974, Goldreich & Kwan 1979 • GMCs appear to be turbulently supported • Norman & Silk 1980, McKee Space Telescope Science Institute

  7. CO is a tracer of molecular (H2) mass • Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s • Ico = Tb dv ~ Tkv • Xco gives a dynamical mass like Tully-Fisher • relatively insensitive to metallicity • (Maloney & Black 1988, Elmegreen 1989) Space Telescope Science Institute

  8. Molecular gas and star formation in spirals and dwarfs big galaxies and small galaxies appear to form stars differently molecular observations: so far, anecdotal (small number statistics) galaxy colors & age-dependent features => SF depends on galaxy form Kauffmann et al. 2006, SDSS Space Telescope Science Institute

  9. IC 342 Red: HI Green: CO Blue: stars 1’ beam 9 kpc VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2001 Space Telescope Science Institute

  10. IC 342 Red: HI Green: CO Blue: stars 1’ beam VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2001 Space Telescope Science Institute

  11. IC 342 Red: HI Green: CO Blue: stars 1’ beam Interarm CO CO arms become HI arms HI & CO correlated Tilanus & Allen 1989-93 VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2001 Space Telescope Science Institute

  12. M83 Red: HI Green: CO Blue: stars 1’ beam 6 kpc VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2002; HI: Tilanus & Allen 1993 Space Telescope Science Institute

  13. M83 Red: HI Green: CO Blue: stars 1’ beam M83 has a sharp “edge” where both HI and H2 surface densities fall off at R ~ 6 kpc VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2002; HI: Tilanus & Allen 1993 Space Telescope Science Institute

  14. M83 Gas “Edge” Falls at gas = 15 Msun/pc2 Space Telescope Science Institute

  15. NGC 6946 Red: HI Green: CO Blue: stars 1’ beam In NGC 6946 gas falls off gradually SFR = gas Schmidt law, n=1 as opposed to Kennicutt law, n=1.4 Crosthwaite & Turner 2007 also seen by Crosthwaite et al. 2002, Wong & Blitz 2003 VLA HI / NRAO 12m CO / DSS Space Telescope Science Institute

  16. Interferometric observations of CO: ~6” (200-400 pc) BIMA SONG: Regan et al. 2001, Helfer et al. 2003 Space Telescope Science Institute

  17. Interferometric CO: Maffei 2 3” beam Space Telescope Science Institute

  18. Interferometric CO: Maffei 2 3” beam Space Telescope Science Institute

  19. Interferometric CO: Maffei 2 3” beam 13 kpc 800 pc 320 pc OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  20. Interferometric CO: Maffei 2 3” beam 320 pc CO: contours greyscale: 3mm continuum, symbols: VLA subarcsec OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  21. Interferometric CO: Maffei 2 3” beam 320 pc Large star clusters forming here CO: contours greyscale: 3mm continuum, symbols: VLA subarcsec OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  22. Interferometric CO: Maffei 2 3” beam 320 pc clouds tidally stretched along bar OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  23. Interferometric CO: Maffei 2 3” beam 320 pc clouds tidally stretched along bar Xco too high by x2-4 - overpredicts cloud masses OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  24. Interferometric CO: Maffei 2 3” beam 320 pc clouds tidally stretched along bar OVRO & BIMA: Meier & Turner 2007 Space Telescope Science Institute

  25. Interferometric CO: Maffei 2 3” beam Big bar Little bar OVRO & BIMA, CO, 3” beam: Meier & Turner 2007 Space Telescope Science Institute

  26. Interferometric CO: Maffei 2 3” beam “P-V” diagram: effective “slit” along major axis Star formation occurs at the x1-x2 orbit intersections OVRO & BIMA, CO, 3” beam: Meier & Turner 2007 Space Telescope Science Institute

  27. Star formation and molecular gas in spirals • CO-emitting gas is star-forming gas; CO disk same as optical disk, HI disk is much bigger • SF needs a trigger: spiral arms or, in galactic centers, x1-x2 orbit intersections • Schmidt law dependence unclear, we find n=1 (SFR ~ gas) rather than Kennicutt law (n= 1.4) • Xco overpredicts H2 mass in tidally supported clouds in galactic centers Space Telescope Science Institute

  28. dwarf galaxies: NGC 5253 Looks like dE that has accreted gas Nelson & Caldwell 1989 Numerous bright young clusters, ages 3 to 50 Myr More IR clusters than optical STIS: field stars lack O stars of the clusters, consistent with cluster dissolution on 10 Myr timescales or or bimodel SF Calzetti et al. 1997, Tremonti et al. 2001 Alonso-Herrero et al. 2004 Calzetti et al. 1997 Gorjian 1996 Space Telescope Science Institute

  29. dwarf galaxies: NGC 5253 SF efficiency =M/( M+ Mgas) =75%, on 200 pc scales In Galaxy, SFE~1-3% on GMC scales (SFE~30% on pc scales, ONC) Lada et al 1984 SFE 2 orders of magnitude higher than in Galaxy Calzetti et al. 1997 Gorjian 1996 Meier, Turner, & Beck 2002 Space Telescope Science Institute

  30. dwarf galaxies: NGC 5253 E/VLA 7mm + NICMOS: Turner & Beck 2004 10 pc, 0.6” Calzetti et al. 1997 Gorjian 1996 embedded IR cluster only really visible ~1.9-2 microns Meier et al. 2002 Space Telescope Science Institute

  31. dwarf galaxies: NGC 5253 E/VLA 7mm + NICMOS: Turner & Beck 2004 10 pc, 0.6” Calzetti et al. 1997 Gorjian 1996 H53 Rodriguez-Rico et al. 2007 Meier et al. 2002 Space Telescope Science Institute

  32. HI: Yun, Ho, Lo 1994 image courtesy of NRAO/AUI Space Telescope Science Institute

  33. Star formation and molecular gas in dwarf galaxies • Star formation in dwarf galaxies may be driven by accretion from outside — could explain “burstiness” N5253: Meier et al. 2002, NGC 3077, Meier et al. 2003, Walter et al. 2004, He 2-10? Kobulnicky et al. 2002 (rotation) • Is this mode of star formation fundamentally different wrt star formation efficiency (is it easier to form bound clusters in dwarfs?) • Role of magnetic fields? Space Telescope Science Institute

  34. III. Beyond CO: chemical diagnostics & feedback Space Telescope Science Institute

  35. (Martin et al.,2006) CS CCH • NGC 253 2mm survey IRAM 30 m NGC 253 SURVEY First unbiased line survey in a galaxy IRAM: 129.1 - 175.2 GHz @ dv ~ 9 km/s IRAM 2MASS - Jarrett Space Telescope Science Institute

  36. Imaging Chemistry in Galaxies: IC 342 Owens Valley mm Array HNC HC3N C2H C34S CH3OH N2H+ HNCO contours: 13CO, color = molecules Meier & Turner 2005 central 300 pc 3mm lines: molecules have similar excitation differences are chemical Space Telescope Science Institute

  37. Imaging Chemistry in Galaxies: IC 342 Owens Valley mm Array HNC HC3N C2H C34S CH3OH N2H+ HNCO Meier & Turner 2005 PC Axis 1: Density-weighted mean column density Space Telescope Science Institute

  38. Imaging Chemistry in Galaxies: IC 342 Owens Valley mm Array HNC HC3N C2H C34S CH3OH N2H+ HNCO Meier & Turner 2005 PC Axis 1: Density-weighted mean column density PC Axis 2: Shock tracers vs PDR molecules Space Telescope Science Institute

  39. Imaging Chemistry in Galaxies: IC 342 Owens Valley mm Array HNC HC3N C2H C34S CH3OH N2H+ HNCO Meier & Turner 2005 PC Axis 1: Density-weighted mean column density PC Axis 2: Shock tracers vs PDR molecules C2H, C34S: PDR Methanol, HCNO: shocks CO, N2H+, HNC, HCN; gas tracers Space Telescope Science Institute

  40. Beyond CO: chemical diagnostics & feedback • High resolution imaging (ALMA) reduces chemical complexity by isolating regions of common chemistry in galaxies • Studies of nearby galaxies suggest that there are classes of molecules, such as: Gas tracers: CO, N2H+, HCN, HNC Grain chemistry (shocks?) tracers: methanol, HNCO (spiral arms) PDR tracers: C2H (B stars rather than O?) Space Telescope Science Institute

  41. IV. ALMA “up to 64” (currently 50) x 12m antennas 12 x 7m antennas (ACA) EU (ESO), NA (NRAO, Canada), J (Japan, Taiwan) in the Atacama desert of Northern Chile, 16,400 ft heterodyne receivers from 0.3 to 9.6mm (v < .05km/s) spatial resolution to 5 mas sensitivity: 7 Jy in 1 hr, continuum brightness 0.8mK Space Telescope Science Institute

  42. ALMA Science Drivers Detect CO in an L galaxy at z = 3. Resolve gas kinematics in protoplanetary disks at 150 AU. Imaging comparable to HST. Space Telescope Science Institute

  43. ALMA Site Space Telescope Science Institute

  44. ALMA is near San Pedro de Atacama Space Telescope Science Institute

  45. San Pedro de Atacama Space Telescope Science Institute

  46. San Pedro de Atacama Space Telescope Science Institute

  47. San Pedro de Atacama Space Telescope Science Institute

  48. ALMA site Space Telescope Science Institute

  49. Space Telescope Science Institute

  50. ALMA buildings Space Telescope Science Institute

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