Stellar population and dust extinction in an ultraluminous infrared galaxy at z = 1.135

1. Stellar population and dust extinction in an ultraluminous infrared galaxy at z = 1.135 K. Kawara et al. 2009. MNRAS MengXianmin

2. abstract • SST J1604+4304; an ULIRG at z=1.135; • IRAC, MIPS, HST, Subaru, UKIRT, MAGNUM photometry; • Gemini spectroscopy; XMM & VLA from literature. • Use CaII H & K, Balmer H lines to derive the upper limits of the age of SP. • Fit 0.44 to 5.8 m SED, 40 – 200 Myr SP with Z=2.5 Z⊙; • E(B-V)=0.8, foreground dust screen, starburst inside a dust shell; • Lir = 1.78×1012L⊙, twice of starlight, obscured starburst or AGN; inferred dust mass is 2.0×108 M⊙; • Starburst gives 19 SNe yr-1; 2.5 Z⊙ in stars reached when gas mass reduced to 30% of galaxy mass. Gas metallicity is 4.8 Z⊙; gas-to-dust ratio=120; dust production rate is 0.24 M⊙ per SN; • Link with other galaxy populations (LAEs, LBGs, DOGs, SMGs).

3. introduction • Optically buried AGN may exist in LIRGs, strong evidence of enhanced star formation is ongoing; kinetic energy from SNe, winds from starburst drives large-scale outflow; • ISO: z ~ 1; Spitzer: z = 2 – 4; • SMGs, ULIRGs, DOGs at z~1-2 are dominated by star formation (Pope et al. 2008); while the nature of SP is unclear; • It’s crucial to observe stellar absorption lines, which indicate the age of SP.

4. Observations & data analysis • Target • SST J1604+4304; Z = 1.135; ra: 16 04 25.538; dec: +43 04 26.55; J2000; • 32” away from a massive galaxy cluster CL 1604+4304 at z=0.90; magnification m = 1.17±0.09. • Spectroscopy • Gemini, GMOS • 5000 – 10000Å; • 1” slit, along long axis of galaxy;

6. Stellar populations and dust extinction • Spectroscopic diagnosis • Fig. 3, BC03 model, 400 Myr, E(B-V)=0.6; • Stellar obsorption lines: H 3970Å, H 3889Å, …, CaII HK 3968 & 3934Å; • No AGN indicator, Mg II 2798, NeV 3346,3426; 3 MgII EW = 22Å, < 52Å (184 QSO composit); neither X-ray or radio; • Unknown of reddening, use D(CaII) instead of Dn(4000): • D(CaII) = 0.03 ±0.11

7. 3 constraint: • Z=0.2 Z⊙,< 1000 Myr; • Z=0.4 Z⊙, < 750 Myr; • Z=Z⊙, < 600 Myr; • Z=2.5Z⊙, < 400 Myr

8. Analysis of uv to NIR SED • SED fitting: • B to 5.8 m, BC03 SSP, Chabrier IMF; • Calzetti law, Draine (2003) curve for MW; • Two dust geometric: foreground dust screen, internal dust model; • Extend Calzetti’s law > 2.2 m adopting Draine’s law; their 0.6-1.6m are identical; • Best-fit: t=40 Myr, E(B-V)=0.8, Z= 2.5Z⊙, foreground dust screen, Calzetti law

9. MW extinction is ruled out, ; • Internal dust model ruled out: • (>3) for Z=<Z⊙; • Z=2.5 Z⊙, not allowed by D(CaII) index; • Rich metal gives better fit, 7000Å concave;

10. For exponentially declining SFR, , set e ranges 0.01 – 5.0 Gyr, t from 0.01 – 7 Gyr; Calzetti curve; uniform dust screen geometry; D(Ca II) allows 2.5 Z⊙ models to have t< 500 Myr; best-fit =90 Myr, t=200 Myr;

11. Dust emission and energetics • Infrared luminosity • 24, 70, 160 m, fit Arp 220 template; • Upper line, 24, 70, 160; • Lower line, 70, 160; • Average Lir = 1.78±0.63×1012L⊙; • Energetics • Stellar luminosity = 8.9×1011L⊙, 1/2 of Lir; indicate obscured starburst site or AGN; • XMM and VLA data don’t support AGN, but may be not deep enough • Mid-infrared diagnostic: ; Starburst doinated have This one, 1.22±0.12, starburst; • Yan et al. 2007, z~2 IRLG This one , AGN?

12. Pope et al. 2008

13. Stern et al. 2005

14. Compare with M82 (local SB, dot), Arp220 (local ULIRG, solid), MIPS J142824.0+352619 (z=1.3 HyLIRG, Lir=3.2×1013L⊙, lacks any AGN activity, large PAH features, rich molecular, starburst-dominated) • match MIPS J142824.0+352619 • Dust mass: for ARP220, 32.5 K for MIPS J142824.0+352619, 35 K; ∝2 Mdust = 2.0±1.0 ×108M⊙

15. discussion • Stellar mass • M* ~ Lir/(L/M*), M* = 6-13×1010 M⊙; • If built up during 40-200 Myr, SFR=600 – 1650 M⊙ yr-1; • Dereddened [OII] implies 13 – 500 M⊙ yr-1  26 – 1000 M⊙ yr-1; • Comparison with other infrared galaxy populations • LAEs & LBGs: < 200 Myr, 106 -108 M⊙, no dust extinction or E(B-V)~0.3; SST J1604+4304 has 6–13×1010M⊙, E(B-V)=0.8, more massive and more dusty; • , meets 24 m high-redshift DOGs. DOGs & SMGs have larger Lir/LB than local ULIRGs, more than half DOGs have Lir > 1013 L⊙, SMGs have Lir = 2×1011-1014 L⊙; SFR 1000 M⊙yr-1 (Lir = 5×1012 L⊙) builds up 1011M⊙ in 100 Myr; Consider DOGs & SMGs are progenitors of local massive galaxies; SP? • SNe for dust and metal production • In 40-200 Myr, most of the dust is formed by SNe II; stars are > 8 M⊙; • 6.4±2.3×1010 M⊙;19 SNe per year; • From instantaneous recycling approximation, Z*=2.4-2.7 Z⊙, Zg=4.5-5.1 Z⊙; 0.1 stelar mass is ejected to ISM, total gas mass = 2.3×1010 M⊙; gas-to-dust ratio is 120±73, similar to a HyLIRG at z=1.3; • Dust production rate = 0.24±0.12 M⊙ per SN, 20% - 100% is destroyed by reverse shockes from SN and ISM.

16. discussion • Foreground dust screen • , E(B-V)=0.83 with Rv=4.05 gives thickness =0.0074, Tdust=32.5-35 K  l = 4.5 – 5.5 kpc or 0.56” - 0.65”, I814 band image 1.2” ×0.5”; • Impact by an obscured AGN • Stellar mass reduced to half, number of SNe also to half; • Dust mass remains; dust production rate increased by 2, 0.48 M⊙ per SN; metallicity remains, for SN reduced; • If AGN shines at Eddington rate, mass of AGN = 2.5×107 M⊙

17. Thank YOU !