spitzer observations of lyman break galaxies
DESCRIPTION
Extreme Starbursts: Near and Far, 14-20 August, Lijiang, China. Spitzer observations of Lyman Break Galaxies. Dimitra Rigopoulou (Oxford,UK) J.-S. Huang, G. Fazio,(CfA, Harvard),& the IRAC team C. Papovich, E. Egami (Arizona, MIPS). The observations - PowerPoint PPT PresentationTRANSCRIPT
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Spitzer observations of Lyman Break Spitzer observations of Lyman Break GalaxiesGalaxies
Dimitra Rigopoulou (Oxford,UK)J.-S. Huang, G. Fazio,(CfA, Harvard),& the IRAC team
C. Papovich, E. Egami (Arizona, MIPS)
Extreme Starbursts: Near and Far, 14-20 August, Lijiang, China
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The observations
Deep IRAC & MIPS imaging (part of the IRAC GTOprogram)
IRAC: 3 hrs/pointingMIPS: slow scanning
2 deg x 10 arcmin Limiting flux densities (5 sigma)
(3.6 µm) : 0.5 µJy(4.5 µm) : 0.5 µJy(5.8 µm) : 2.7 µJy(8.0 µm) : 2.7 µJy(24 µm) : 60 µJy
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Extended Groth Strip (EGS)
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The EGS Lyman Break Galaxies sample
• Among 334 LBGs in the EGS area, 193 with spectroscopic redshfit (Steidel et al 2003)
• 244 are in the Spitzer EGS field
• ~200 are detected in the 3.6/4.5µm band
• ~50 are detected in the 5.8/8.0µm band
• 6 are detected in the 24µm band
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R [3.6] [4.5] [5.8] [8.0] [24]
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Rest-frame shifted and R-normalised SEDs
• Spitzer reveals the diversity of LBGs
• IRAC-bright LBGs have more dust? more massive?
• MIPS detections probes the rest—frame mid-infrared
U G R J K IRAC MIPS
Mag
(A
B)
Rest wavelength (microns)
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Estimating stellar masses• Use Bruzual and Charlot (2003) code with• Padova 1994 tracks
• Exponentially decaying SFR α exp (-t / τ) where τ=0.05, 0.1,0.5,2.0, 5.0 Gyr (e-folding times) t = age• Constant SFR
• Solar metallicity
• Calzetti (2000) extinction law
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Constant vs. exponentially decaying SF models
Huang et al. 2005
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Huang et al. 2005
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BC03 model fits
Rigopoulou et al. 2005
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Blue LBGRed LBG
Constant vs. Exponentially decaying Mass estimates
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Large scatter in [3.6] fluxes
4 magnitudes in [3.6]
1.5 magnitude in [K](Shapley et al. 2001)
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[5.8] rest frame H-band
[3.6] rest frame I-band
Mid-IR colours of LBGs
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Mid-IR colours of LBGs
[8.0] rest—frame K-band
Best tracer for mass
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Massive LBGs have R-[3.6] >=3
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A test – case: Westphal D49
In K-selected LBG sample of Shapley et al. (2001)
Constant SFR model U G R J K U G R J K IRAC Shapley et al. (1991) Our model: Age: 1139 Myr Age: 1350 MyrE(B - V) : 0.17 E(B - V): 0.35
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Does extinction matter?
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IRAC has “discovered” a new class of LBGs:
• luminous at [8.0] microns
• faint in the optical bands
• significant(?) dust extinction
• slightly older stellar pops
• …. massive, M > 1011 M
missing link to SCUBA galaxies?
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SCUBA galaxies
Cold SED: Arp220
80—90% of sampleStarburst-like
Warm SED: Mrk 231
Egami et al. (2004)
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Origin of the [24] emission
@ z=3 [3.6] — [8.0] [z’] – [K]blue for SBred for AGN
[8.0] – [24] [K] – [6.0]red for SBblue for AGN
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Ivison et al. 2004
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Saracco 04
Drory 04
Cole et al 00
This work
Number density as a function of redshift
= 0.7 , m = 0.3, H0 = 70)
Kauffmann99
Baugh03
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Summary
• LBGs are detected in the mid-IR. Optical does not reveal full complexity.
• Large scatter in IRAC fluxes variations in mass, age, extinction
• Average SED young populations
• We detect more massive LBGs at z=3
than predicted by hierarchical models
(downsizing…..)