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Dust attenuation with GALEX and maybe more…

Dust attenuation with GALEX and maybe more…. Kazuyuki Tamura AST 491/591: Journal Club October 31, 2008. Papers. Extinction Radial Prifiles of M83 from GALEX UV Imaging Boissier, S., et al. 2005, ApJ, 619, L83

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Dust attenuation with GALEX and maybe more…

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  1. Dust attenuation with GALEXand maybe more… Kazuyuki Tamura AST 491/591: Journal Club October 31, 2008

  2. Papers • Extinction Radial Prifiles of M83 from GALEX UV Imaging • Boissier, S., et al. 2005, ApJ, 619, L83 • Radial Variation of Attenuation and Star Fromation in the Largest Late-Type Disks Observed with GALEX • Boissier, S., et al. 2007, ApJS, 173, 524 • Heckman et al. 1998, ApJ, 503, 646 • Dale et al. 2001, ApJ, 549, 215 • Kong et al. 2004, MNRAS, 349, 769 • Buat et al. 2005, ApJ, 619, L51 • Calzetti et al. 2005, ApJ, 633, 871 • Thilker et al. 2005, ApJS, 173, 572 • Relano et al. 2006, A&A, 452, 413

  3. Galaxy in different l

  4. Galaxy in different l

  5. What do you see? • http://www.jpl.nasa.gov/news/features.cfm?feature=1219

  6. AV: Balmer Decrement • Ha/Hb (or Ha/Paa) ratio • Theoretical ratio of 2.86 (Osterbrock 1989) • Star formation (HII) regions • Limitations • Need high resolution spectrograph • Affected by absorption • Limited spatial coverage

  7. AV: UV Spectral Slople, b • Spectral shape of lb • Heckman et al. 1995, Meurer et al. 1995, 1999 (IUE 1300—2600 Å) • Kong et al. 2004 (GALEX FUV—NUV) • Popular method in recent years • Limitations • Calibrated with starburst galaxy • Colors from similar l’s (small baseline) • Sensitive to dust

  8. AV: Total-IR/UV Ratio • Depending weekly on: • Geometry of stars and dust • Extinction law • Star formation history • Buat & Xu 1996; Will & Gordon 2000; Panuzzo et al. 2003 • Limitations • Low spatial resolution

  9. Observations: M83 • Ha and Hb • Narrow band (FWHM = 60Å) imaging • 40”, Las Campanas Obs. (LCO, Chile) • Long-slit spectrum • WFCCD spec. at LCO 100” (2.5 m) • GALEX FUV/NUV • 1352 sec on June 7, 2003 • IRAS 60 and 100 mm • By IRAS-HIRES request (Rice 1993) • 60 mm image is convolved to 100 mm (~90”) image

  10. AFUV from Ha/Hb • Balmer Decrement (Relano et al. 2006) where te is the electron temp in units of 104 K • AFUV= 1.4 AHa

  11. GALEX Images (M83)

  12. UV Spectral Slope (bGLX) • Kong et al. 2004, MNRAS, 349, 769 • Model (b0) based on Boissier & Prantzos (2000) • Updated SF law with angular velocity (Boissier et al. 2003)

  13. AFUV from bGLX (IRX-b) • IRX-b relation (Kong et al. 2004) • or where ‘b’ is “present-to-past average SF ratio”

  14. AFUV from TIR/UV • FIR-to-UV (Dale et al. 2001, Buat et al. 2005)

  15. Radial Extinction Profile: M83 • AFUV(b-model) = 0.86 + 0.91 (bGLX—bo)

  16. Various AFUV-b • Red Crosses – AFUV by TIR/UV • Red Dotted line – least square fit • Shaded area – Buat et al. 2005 • TIR/UV with total flux • Short-long dashed line – Kong et al. 2004 • IRX-b for starburst • Solid curve – Kong et al. 2004 • Model with present-to-past SF ratio, b • Log b = 0.2 • Short-dashed curve – Witt & Gordon 2000 • b with shell-homogeneous dust dist. Model • Long-dashed curve – Witt & Gordon 2000 • b with dusty-clumpy dust dist. model

  17. Recent Findings • GALEX observations cast “???” • Buat et al. 2005; Cortese et al. 2006; Seibert et al. 2005; Gil de Paz et al. 2007 • Other studies also disagree with IRX-b • Normal spirals: Bell 2002 • Individual regions in LMC: Bell et al. 2002 • No relationship (very noisy) • Different from starburst relationship • Based on selection sample method?

  18. More Samples: Data • 43 Large nearby Late-type galaxies • GALEX Atlas of Nearby Galaxies (Gil de Paz et at. 2007) • RC3 T-type 0 to +10 (S0/a to Sm/Im) • R > 8’ (at DB_25) • GALEX FUV/NUV + IRAS 60/100 mm • Foreground Galactic Al = ClE(B – V) • Profiles are azimuthally averaged within annuli • Annuli = resolution steps (88”—114”) • Regions (stellar populations) at same radius are relatively homogeneous

  19. AFUV(TIR/UV) Radial Profile • Global decrease of extinction with r • 0-6 mag at center  AFUV≈ 0at edge • Minimal effect from AGN, UV-upturn, etc. • Similar results from • Boissier et al. 2004 – 6 galaxies with FOCA/IRAS • Popescu et al. 2005 – M 101 • Holwerda et al. 2005a – with a “synthetic field method” • Holwerda et al. 2005 b – with back ground galaxies

  20. IRX-b Relationships • Green line – Starbursts • Radial profile • Red – 0 ≤ b/a ≤ 1/3 • Black – 1/3 ≤ b/a ≤ 2/3 • Blue – 2/3 ≤ b/a ≤ 1 • Integrated light • Gray – Atlas of Nearby Galaxies • FUV-NUV ≥ 1, different SF history? • Gray with circle – This study

  21. Reasons for tightness • Azimuthally averaged annuli • Small-scale SF histories/radiative transfer peculiarities are smoothed out • Radial Profile • Separate the central activity effect • Fluxes are re-derived ab initio • All galaxies in exactly the same procedure • No published fluxes

  22. IRX-b for 43 Galaxy Samples • Non-linear square fits • with sy as weight (red dashed) • without weight (blue dotted)

  23. SINGS studies • Calzetti et al. 2005 • M51 • Thilker et al. 2007 • NGC 7331

  24. Possible Cause(s) of shift • Large variety of SF histroy (b) values? • Kong et al. 2004 • Simple offset from starbursts? • Gil de Paz et al. 2007, Cortese et al. 2006, Seibert et al. 2005 • Impact by UV bump (metallicity)? • Burgarella et al. 2006 • Geometrical effect (IUE aperture effect)? • Gil de Paz et al. 2007, Cortese et al. 2006, Seibert et al. 2005 • Relative calibration between IUE and GALEX?

  25. So, what affects AFUV? • AFUVdepends on radius…

  26. AFUV and Gas Density? • Common concept • Extinction (AV) is proportional to gas density (NH) • Study in Milky Way – i.e., Bohlin et al. 1978 • NH = 2 x 1021AV – Komugi et al. 2005 • Correlation between AFUV and Sinc (NH)…? • No CO observation • Published data • Cause of some error?

  27. Gas Density (and V(R)) Refs • Bajaja et al. 1984, 1985 • Begeman 1987, 1989 • Boissier et al. 2003, 2005 + Refs • Boselli et al. 2006 + Refs • Bosma 1978, 1981 • Braun et al. 1994, 1997 • Broeils & van Woerden 1994 • Carignan & Puche 1990ab • Casertano & van Gorkom 1991 • Cayatte et al. 1994 • Corbelli 2003 • Dame et al. 1993 • Heyer et al. 2004 • Heyer et al. 2004 • Hunter et al. 2001 • Jackson et al. 2004 • Kenney & Young 1988 • Kenney et al. 1991 • Lake & Skillman 1989 • Martimbeau et al. 1994 • Mulder & van Driel 1993 • Newton & Emerson 1977 • Nieten et al. 2006 • Ondrechen et al. 1989 • Paglione et al. 2001 • Pisano et al. 1998 • Puche et al. 1990, 1991ab • Rand 1994 • Regan et al. 2001 • Sakamoto et al. 1997 • Sancisi & Allen 1979 • Shostak & van derKruit 1984 • Sofue 1997 • Sorai et al. 2000 • van Driel et al. 1988, 1995 • Wevers et al. 1986 • Young & Scoville 1982 • Young et al. 1995 • Zhang et al. 1993

  28. AFUV vs. SHI and SH2 • .

  29. AFUV vs. S(HI+H2) • No trend for low S • Large uncertainty • Some trend in high S • Dominated by H2 gas • Still too large variation

  30. No SGAS Dependence • A/NH ≠ constant • AFUV is NOT a measure of the dust mass • Mass ~ cold dust (need longer l) • Out of the scope of this paper • AFUV ~ amount of dust heated by nearby young massive stars • Geometrical effect • Dust grain properties (type, distribution, etc.)

  31. Metallicity? • Belley & Roy 1992 • Kennicutt et al. 2003 • Lee et al. 2003ab • Masegosa et al. 1991 • Roy et al. 1996 • Storchi-Bergmann et al. 1996 • van Zee et al. 1998 • Zartisky et al. 1994 • Least-square fit to b/a > 0.4 • Other studies also agrees • Boissier et al. 2004 • Cortese et al. 2006 • Slightly stronger trend

  32. Starbursts (Heckman et al. 1998)

  33. Conclusion • IRX-b relation is a still valid measurement • AFUV, TIR/FUV, correlates with metallicity • No dependence on gas column density • A/NH ≠ constant • Much more simpler way to measure A? • With more easily accessible broadband data? • Less dependent on metallicity and age? • Two-dimensional analysis?

  34. AV with V and 3.6 mm • Tamura et al. 2008, in prep • AAS poster, Jan 2009

  35. Want More? • Next topic: • Star formation at outer disk • Difference between Ha and UV observation

  36. Star Formation Law • Fundamental element of any galaxy model • Only rough theory • A few empirical relationship • Kennicutt 1998, ARA&A, 36, 189 • Elmgreen 2002, ApJ, 577, 206 • “Star Formation Law” • SF rate & other physical quantities • Schmidt law:

  37. Molecular Gas • SFR and SH2 follow the same r dependence • Beckert 2002 • SFR and molecular mass • L- or Z-dependent CO-to-H2 conversion • Bosseli et al, 2002 • Self-gravitating disk model • Schmidt law with total gas density • Kenniccutt 1998

  38. Schmidt Law with Dynamical Factor • Prantzos & Aubert 1995 • Milky Way: V(R) = constant, n = 1 • Boissier & Prantzos, 1999, 2000 • MW + Spirals: n = 1.5 • Agree with Haprofiles of 16 nearby spirals

  39. Neutral & Molecular Gas

  40. Total Gas

  41. Simple Schmidt Law • Kenniccutt 1998 • SFR from Ha • Shaded region – Ha threshold • Flux from r < R25 • This study • SFR from UV radial profile vs. total gas • Connected line – M31 • Inner 50’ • Another paper…

  42. HaSFR Radial Threshold • Abrupt break • Gas density & critical density • Toomre 1964 • Thermal instability • Schaye 2004 • Atomic gas extends out to larger radius • Martin & Kennicutt 2001

  43. Radial Profiles • Black – Ha • Martin & Kennicutt 2001 • Red – UV • This study • M81: Too large… • Near the edge of the GALEX FOV • Contamination by background • Spiral arm (in FUV) at outer disk

  44. Why with UV? • Variation in the IMF…? • SF levels are low • Less O stars • Ha and UV measure different timescales • Ha ~107 years • UV ~108 years

  45. Further Test • Haprofile from Martin & Kennicutt 2001 • 1 kpc aperture • At 17 Mpc, 10” ~ 0.8 kpc • y1 – SFR within aperture • Salpeter IMF • 0.1—100 MSun • M > 10 MSun as <107 years

  46. Result • At Rthreshold • 19% with > 1 O star • Beyond Rthreshold • Hard to catch O star within aperture • Stochastic SF (HII regoins)

  47. Other evidence of SF at large r • HII regions in extreme outer disk • Ferguson et al. 2001 • Resolved young blue B stars in M31 outer disk • Cuillandre et al. 2001 • Intermediate-age stars at large radii in M33 and NGC 2403 • Davidge 2003

  48. Conclusion 2 • The “Threshold Radius” • Is the last radius with enough Ha • NOT the end of star formation • UV emission at outer radius • Extended UV (XUV) disk? • Gil de Paz et al. 2005 • Thilker et al. 2005 • Further study with NGC 4625 • Gil de Paz et al. 2008 in prep

  49. Cortese et al. 2006 Fig 4

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