Extended Ly a nebulae: cold accretion or Population III stars?

1. Extended Lya nebulae: cold accretion or Population III stars? C. Scarlata Spitzer Science Center James Colbert, Harry Teplitz Paul Francis, Povilas Palunas, Brian Siana, Gerard Williger, Bruce E. Woodgate

2. Lyablobs Identified first by Steidel et al. 2001 in an overdense region at z~3.1 Extended Lya emission 50-150 kpc Lyα luminosity of ~1044 erg/s (20/40 more powerful than normal Lya emitters) No association with powerful radio continuum sources Lya blobs are rare objects: few nebulae known so far (~20) at z~2-3 (but see Saito’s poster) What are these objects?

3. Possible Lyα Blob Energy Sources Photoionization (either stars or AGNs) UV light from an embedded AGN/starburst escaping along different lines of sight. Collisional excitation (Inflow – Cooling Radiation) Cooling radiation emitted by gas loosing potential energy while falling on a dark matter potential well. (Outflow - winds) Galactic superwinds driven by supernova explosions

4. z=2.4 Large Scale filament of Lya emitters 80Mpc • Identified within a narrow band survey • The Lya emitters trace a filamentary structure • Comparable to the largest structures seen in the local Universe • Three Lya blobs Palunas et al. (2004)

5. z=2.4 Large Scale filament 80Mpc • The Lya emitters trace a filamentary structure • Comparable to the largest structures seen in the local Universe (i.e. the Great Wall, Geller & Huchra 1989) • Four Lya blobs ~250Kpc Llya~1044 erg/s Palunas et al. (2004)

6. Followup data Spitzer+IRAC+MIPS Gemini south+GMOS 3.6 to 24 mm imaging Mid-IR spectroscopy Apex+ LaBoca Deep optical spectroscopy Imaging at 850 mm

7. Rest frame~0.1μm What is the origin of the continuum sources associated with the Lya nebula? ~1012 L○ in rest frame 7μm νFν Rest frame ~7μm

8. Rest frame~0.1μm c The broad band optical colors, are incompatible with those of a source at z=2.4

9. Rest frame~0.1μm c

10. Ly2: Rest frame UV spectroscopy f1500~3x10-18 erg/cm2/s/A Ly2 UV rest frame spectrum of Ly2 shows typical features of z~3 star-forming LBGs low and high ionization metal lines associated with the neutral and ionized ISM; velocity shift between Lya emission and the interstellar absorption lines (400 km/s)

11. Ly2: Spectral Energy Distribution 24 mm 850 mm LIR implies SFR~160 Mo/yr, consistent with the inferred SFR derived from the dust corrected f1500 Lline=fe-tfescfline SFR SFR of 103 Mo/yr to reproduce the extended Lya luminosity

12. Rest frame~0.1μm c

13. sHeII=170 km/s sLya< 160 km/s Ly1: Rest frame UV spectroscopy HeII 1640A

14. Templates: Polletta+06 Ly1: spectral energy distribution SED is a power law between rest frame 0.3 and 7 m --> AGN dominates the emission The SED of a QSO with strong absorption in the UV well reproduces the data points (LIR>1013 Lsol), no X-ray emission down to LX~1043erg/s

15. Ly1: Rest frame UV spectroscopy sHeII=170 km/s sLya< 160 km/s

16. AGN origin of the emission? Nagao+05 Nagao+05 HeII CIV/HeII >1

17. AGN origin of the emission? Two possibilities: 2. HeII is outside Ly1 and may or may not have an extended morphology Lya In this case the Lya nebula could be similar to the Lya nebulae associated with high-z radio galaxies and be the result of the interaction between the radio jet and the surrounding gas HeII Radio < 140 Jy @1.4 GHz

18. Metallicities Z=0, 10-7, 10-5, …,0.02=Zsun PopIII Zsun Zsun PopIII Schaerer 2003 Population III stars? 1) 2) Lline=fe-tfescfline SFR 1) Z=0 Salpeter IMF 50-500Msol 50Msol/yr, L1500=1.5 1042 erg/s/A 2) Z=10-5 Salpeter IMF 50-500Msol 1000Msol/yr,L1500=5 1043 erg/s/A Ly1 is more than an order of magnitude fainter than the most optimistic case; Ly2 is at least a factor of three

19. Population III stars? Considering the typical uncertainties in the modeling of PopIII stars Ly2 could be a starburst of metal free stars. However: Numerical results show that the expected contribution from PopIII stars to the SFR is almost insignificant at z~2.5; The UV spectrum of Ly2 shows strong metal features both of stellar and ISM origin; Another confirmation of the presence of dust is given by the detection of PAH emission lines in the mid-IR spectrum of Ly2; Ly2 is ~70kpc from the blob.

20. Cooling radiation in cold accretion? Lya HeII Yang+06

21. Cooling radiation in cold accretion? Lya HeII Velocity dispersion distribution of the gas particles associated with the dark matter haloes in the simulation consistent with the observed value

22. Cooling radiation in cold accretion? Lya Surface brightness in the HeII emission line consistent with the observed value HeII Caveat: unknown spatial extension

23. Cooling radiation in cold accretion? Lya HeII

24. Conclusions • Lya nebula at z=2.4 with a strong HeII emission line detection • The HeII: • - is not of stellar origin (WR stars) • - is most likely associated with the extended nebula rather than coming from within the continuum source • The nebula is most likely not ionized by an active nucleus • Cold accretion? It does explain all observables.

25. Survey tuned to identify z=2.4 Lya emitters Flim=1.5x10-16 erg/cm2/s Narrow band survey tuned to identify Lya emitters at z=2.4 around a candidate high-z overdensity EW=125A 36 spectroscopically confirmed galaxies NB BB Palunas et al. (2004)

26. WOLF RAYET stars? >1000 km/s Leitherer+95

27. Pope+08: fit to galaxy mid-IR spectrum to quantify AGN/SF contribution If more than 50% of the mid-IR flux comes from the continuum component below the PAH then galaxy is classified as an AGN (diamonds) Ly2 Ly1 : AGN Ly2 : SF Ly1 Dust Obscured Galaxies (DOGs, Dey+05)

28. Star Formation Rate in Ly2 Using the best fit template derived to fit the mid to far-IR of the dust obscured galaxies we derive a SFR of ~ 200Msun/yr Comparable to the value obtained by using the de-reddened f1500 luminosity The mid-IR shape of the SED is different

29. HeII l1640 emission Lya is a resonant line with a very large optical depth Geometry of the ISM, gas velocity field, dust content can alter the Lya output both in terms of global energetic and in term of the line profile Lya is NOT a good diagnostic for the gas physical conditions However we do see the HeII emission line associated with Ly1 So any source of energy needs to account for both the large Lya luminosity AND the observed HeII flux Stellar HeII?

30. Ly1 Ly2

31. Mori & Umemura (2006)

32. Dey+05

33. Modes of gas accretion • Hot Mode • Gas shock heats to Tvir (106 K), cools slowly onto central object (cooling radiation emerges as Xray emission) • Cold Mode • Gas is not shock heated and radiates its potential energy away at T<<Tvir • Cold mode is expected to be the dominant way of gas accretion at z>2 and in small halos (Mhalo<1011M) for z<2 • Extended line emission coming from the cooling gas

34. Spectral Energy Distribution UBR JH 3.6,4.5,5.8,8 24m 850 Ly1 UBR JH 3.6,4.5,5.8,8 24m 850 Dust enshrouded star formation induced by the merger between Ly1 and Ly2? Ly2 Colbert+06

35. AGN origin of the emission? Two possibilities: 2. HeII is outside Ly1 and may or may not have an extended morphology Lya In this case the Lya nebula could be similar to the Lya nebulae associated with high-z radio galaxies and be the result of the interaction between the radio jet and the surrounding gas HeII

36. AGN origin of the emission? Two possibilities: 2. HeII is outside Ly1 and may or may not have an extended morphology Lya In this case the Lya nebula could be similar to the Lya nebulae associated with high-z radio galaxies and be the result of the interaction between the radio jet and the surrounding gas HeII Ly1 is radio quiet ! (f14GHz< 0.14 mJy)

37. Survey limits