Dust attenuation with GALEX

1
Dust attenuation with GALEX

• 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, AA, 452, 413

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Galaxy in different l
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Galaxy in different l
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What do you see?

• http//www.jpl.nasa.gov/news/features.cfm?feature
  1219

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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

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AV UV Spectral Slople, b

• Spectral shape of lb
• Heckman et al. 1995, Meurer et al. 1995, 1999
  (IUE 13002600 Å)
• Kong et al. 2004 (GALEX FUVNUV)
• Popular method in recent years
• Limitations
• Calibrated with starburst galaxy
• Colors from similar ls (small baseline)
• Sensitive to dust

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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

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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

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AFUV from Ha/Hb

• Balmer Decrement (Relano et al. 2006)
• where te is the electronic
• temp in units of 104 K
• AFUV 1.4 AHa

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GALEX Images (M83)
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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)

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AFUV from bGLX (IRX-b)

• IRX-b relation (Kong et al. 2004)
• or
• where b is present-to-past average SF ratio

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AFUV from TIR/UV

• FIR-to-UV (Dale et al. 2001, Buat et al. 2005)

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Radial Extinction Profile M83

• AFUV(b-model) 0.86 0.91 (bGLXbo)

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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

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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?

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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 gt 8 (at DB_25)
• GALEX FUV/NUV IRAS 60/100 mm
• Foreground Galactic Al Cl E(B V)
• Profiles are azimuthally averaged within annuli
• Annulus resolution steps (88114)
• Regions (stellar populations) at same radius are
  relatively homogeneous

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AFUV(TIR/UV) Radial Profile

• Global decrease of extinction with r
• 0-6 mag at center ? AFUV 0 at 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

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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

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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

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IRX-b for 43 Galaxy Samples

• Non-linear square fits
• with sy as weight (red dashed)
• without weight (blue dotted)

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SINGS studies

• Calzetti et al. 2005
• M51

• Thilker et al. 2007
• NGC 7331

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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?

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So, what affects AFUV?

• AFUV depends on radius

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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 1021 AV Komugi et al. 2005
• Correlation between AFUV and Sinc (NH)?
• No CO observation
• Published data
• Cause of some error

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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

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AFUV vs. SHI and SH2

• .

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AFUV vs. S(HIH2)

• No trend for low S
• Large uncertainty
• Some trend in high S
• Dominated by H2 gas
• Still too large variation

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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.)

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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 gt 0.4

• Other studies also agrees
• Boissier et al. 2004
• Cortese et al. 2006
• Slightly stronger trend

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Starbursts (Heckman et al. 1998)
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Conclusion

• IRX-b relation is a still valid measurement
• AFUV, TIR/FUV, correlates with metallicity
• No dependence on gas column density
• A/NH ? constant

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Want More?

• Next topic
• Star formation at outer disk
• Difference between Ha and UV observation

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Star Formation Law

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

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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

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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 Ha profiles of 16 nearby spirals

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Neutral Molecular Gas
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Total Gas
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Simple Schmidt Law

• Kenniccutt 1998
• SFR from Ha
• Shaded region Ha threshold
• Flux from r lt R25
• This study
• SFR from UV radial profile vs. total gas
• Connected line M31
• Inner 50
• Another paper

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Ha SFR Radial Threshold

• Abrupt break
• Gas density critical density
• Toomre 1964
• Thermal instability
• Schaye 2004
• Atomic gas extends out to larger radius
• Martin Kennicutt 2001

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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

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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

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Further Test

• Ha profile from Martin Kennicutt 2001
• 1 kpc aperture
• At 17 Mpc, 10 0.8 kpc
• y1 SFR within aperture
• Salpeter IMF
• 0.1100 MSun
• M gt 10 MSun as lt107 years

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Result

• At Rthreshold
• 19 with gt 1 O star
• Beyond Rthreshold
• Hard to catch O star within aperture
• Stochastic SF (HII regoins)

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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

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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

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Cortese et al. 2006 Fig 4
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Boissier et al. 2005 Fig. 3b

• Red Crosses AFUV by TIR/UV
• Outside bulge (r 50)
• Red Dotted line From equation
• AFUV 0.86 0.91 (bGLXbo)
• Average AFUV/(bGLXbo) 1.9

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Boissier et al. 2004 (Fig. 9)