Dust attenuation with GALEXand maybe more…

Kazuyuki TamuraAST 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

• 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

Galaxy in different

Galaxy in different

What do you see?

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

AV: Balmer Decrement

• H/H (or H/Pa) ratio– Theoretical ratio of 2.86 (Osterbrock 1989)– Star formation (HII) regions

• Limitations– Need high resolution spectrograph• Affected by absorption

– Limited spatial coverage

AV: UV Spectral Slople, • Spectral shape of

– 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 ’s (small baseline)– Sensitive to dust

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

Observations: M83• H and H– 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 m– By IRAS-HIRES request (Rice 1993)– 60 m image is convolved to 100 m (~90”) image

AFUV from H/H• Balmer Decrement (Relano et al. 2006)

where te is the electron

temp in units of 104 K

• AFUV= 1.4 AH

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AHα = 5.25 × logHα Hβ

2.859te−0.07

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⎝ ⎜

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GALEX Images (M83)

UV Spectral Slope (GLX)

– Kong et al. 2004, MNRAS, 349, 769

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GLX =log f FUV − log f NUV

logλ FUV − log λ NUV

– Model (0) based on Boissier & Prantzos (2000)Updated SF law with angular velocity (Boissier et al. 2003)

AFUV from GLX (IRX-)

• IRX- relation (Kong et al. 2004)

• or

where ‘b’ is “present-to-past average SF ratio”

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AFUV =A0 + A1( ) x − x0( )

2+

A1 − A0( )σ 0

2ln cosh

x − x0

σ 0

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⎝ ⎜

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⎡

⎣ ⎢

⎤

⎦ ⎥+ A2

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x0 = 0.26

σ 0 = 0.42

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AFUV = 3.78 +1.87 βGLX + 0.4 logb( )€

x ≡ log LTIR LFUV( )

LTIR LFUV =10 2.10+0.85β GLX( ) − 0.95

A0−2 = 0.39,1.86, 0.75[ ]

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

AFUV from TIR/UV

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FFIR =1.26 ×10−14 2.58 f60μm + f100μm( )

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log FTIR( ) = log FFIR( ) + a0 + a1x +a2x 2 + a3x 3 + a4 x 4

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x = log f60μm f100μm( )

a0−4 = 0.2738, − 0.0282, 0.7281, 0.6208, 0.9118[ ]

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AFUV = A0 + A1y + A2y 2 + A3y 3

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y = log FTIR υ FUV fFUV( )

A0−3 = 0.4967,1.1960, 0.3522, − 0.0333[ ]

Radial Extinction Profile: M83

• AFUV(-model) = 0.86 + 0.91 (GLX—o)

Various AFUV-• 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- 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– with shell-homogeneous dust dist. Model

• Long-dashed curve – Witt & Gordon 2000– with dusty-clumpy dust dist. model

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-• 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?

More Samples: Data

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

IRX- 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

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

IRX- for 43 Galaxy Samples

• Non-linear square fits

– with y as weight (red dashed)

–

– without weight (blue dotted)

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y = log 10ax +b − c( )

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x = FUV − NUV

y = log FTIR FFUV( )

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a, b, c[ ] = 0.570, 0.671, 3.220[ ]

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a, b, c[ ] = 0.561, 0.713, 3.136[ ]

SINGS studies

• Calzetti et al. 2005– M51

• Thilker et al. 2007– NGC 7331

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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AFUV = 3.78 +1.87 βGLX + 0.4 logb( )

So, what affects AFUV?

• AFUV depends on radius…

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 inc (NH)…?– No CO observation• Published data• Cause of some error?

Gas Density (and V(R)) Refs

AFUV vs. HI and H2

• .

AFUV vs. (HI+H2)

• No trend for low – Large uncertainty

• Some trend in high – Dominated by H2 gas

– Still too large variation

No GAS Dependence

• A/NH ≠ constant– AFUV is NOT a measure of the dust mass

– Mass ~ cold dust (need longer )• 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.)

• 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

Metallicity?

• Other studies also agrees– Boissier et al. 2004– Cortese et al. 2006

• Slightly stronger trend

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AFUV =1.02 × 12 + log O H( )[ ] − 7.84

• Least-square fit to b/a > 0.4

Starbursts (Heckman et al. 1998)

Conclusion

• IRX- 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?

AV with V and 3.6 m

• Tamura et al. 2008, in prep• AAS poster, Jan 2009

Want More?• Next topic:– Star formation at outer disk• Difference between H and UV observation

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:

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SFR = αΣGASn

Molecular Gas

• SFR and H2 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

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 H profiles of 16 nearby spirals

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SFR = αΣGASn V R( )

R

Neutral & Molecular Gas

Total Gas

Simple Schmidt Law

• Kenniccutt 1998– SFR from H– Shaded region – H threshold– Flux from r < R25

• This study– SFR from UV radial profile vs.

total gas– Connected line – M31

• Inner 50’ – Another paper…

H 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

Radial Profiles

• Black – H– 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

Why with UV?

• Variation in the IMF…?• SF levels are low– Less O stars– H and UV measure different timescales• H ~107 years• UV ~108 years

Further Test

• H profile from Martin & Kennicutt 2001• 1 kpc aperture– At 17 Mpc, 10” ~ 0.8 kpc

• 1 – SFR within aperture– Salpeter IMF– 0.1—100 MSun

– M > 10 MSun as <107 years

Result

• At Rthreshold

– 19% with > 1 O star

• Beyond Rthreshold

– Hard to catch O star within aperture

– Stochastic SF (HII regoins)

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

Conclusion 2

• The “Threshold Radius” – Is the last radius with enough H – 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

Cortese et al. 2006 Fig 4

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 (GLX—o)

– Average AFUV/(GLX—o) = 1.9

Boissier et al. 2004 (Fig. 9)