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Dust and molecular gas in the most distant quasars Ran Wang Department of Astronomy, Peking University, China Supervisor: Chris Carilli ( NRAO) Collaborators: Bertoldi, F. (University of Bonn); Cox, P. (IRAM); Fan, X. (University of Arizona); Jiang, L. (University of Arizona); Menten, K. (MPIfR); Neri, R. (IRAM); Omont, A. (IAP); Strauss, M. (Princeton); Wagg, J. (NRAO); Walter, F. (MPIfA)
Introduction – the first discovery of dust and CO at z~6 Bertoldi et al. (2003) Beelen et al. 2006
Introduction – the first discovery of dust and CO at z~6 Bertoldi et al. 2003 Bertoldi et al. 2003 Walter et al. 2004; Carilli et al. 2008
Introduction – Black hole/bulge relations Tremaine et al. (2002) Marconi & Hunt. (2002) MBH~10-3MBulge MBH~σ4
Introduction – Black hole/bulge relations Coppin et al. (2008)
Introduction • What is the evolutionary stage of these z~6 quasars? • How the most massive black hole – bulge systems evolve at their early stage. • Can we see active building via massive star formation co-eval with rapid black hole accretion? • Dynamical mass; • Black hole – bulge ratios;
Introduction • The host galaxies of these z~6 quasars are still the only sample of the earliest galaxies that are detectable with our current millimeter and radio instruments. • What are the physical properties of these quasar host galaxies? • Dust and gas masses; • Dust temperature; • Molecular excitation; • Star formation history.
Introduction • We are pursuing cm and mm studies of all the quasars discovered at z~6 • We first do a millimeter and radio continuum survey with all the z~6 quasars. • Further observations at submm wavelengths with strong millimeter detections to measure the FIR SED and determine the dust temperature. • Search for CO with the millimeter detections.
Sample • There are totally Thirty-three quasars discovered at z~6. • z=5.71 to 6.43 • M_1450A < -25.0 • Twenty-two from the SDSS survey of ~8000 deg^2 area, with m_1450A < 20; Fan et al. 200x • Five from the SDSS Deep Stripe of ~260 deg^2, with 20 < m_1450A < 21.5; Jiang et al. 2007 • Four from the Canada-France High-z Quasar Survey (CFHQS), from ~400 deg^2 area, with m_1450A > 21; Willott et al. 2007 • IR (Spitzer) + optical: one; Cool et al. (2006) • Radio (FIRST) + optical: one; McGreer et al. (2006)
Sample • Most of these objects were optically selected from the SDSS survey Represent the most luminous quasar population at z~6. • Observations from X-ray to near-IR show spectral energy distributions similar to that of the typical optical quasars at low z (Jiang et al. 2006). • AGN activities similar to that in the low-z quasars dominate the X-ray to near-IR emission of these z~6 objects.
Observations MAMBO IRAM-30m VLA PdBI IRAM SHARC-II CSO
A summary of the (sub)mm and radio Results • MAMBO observations of 33 sources • rms in the range of 0.4 to 1.1 mJy with a median value of 0.6 mJy • Ten are detected at >= 3 sigma level • The detection rate is (30 +/-10) %, consistent with the (sub)mm detection rate of optically bright quasars at z~2 (Omont et al. 2003) and z~4 (Omont et al. 2001; Carilli et al. 2001)
A summary of the (sub)mm and radio Results • VLA observation of 32 sources • rms <= 20 uJy for most of the sources • Ten were detected, with two of them having flux densities > 1mJy • Three of them have radio loudness R ≥10 • The radio loud fraction at z~6: one out of the primary SDSS sample of 22 sources.
Analysis – the average FIR and radio emission • The mean 250 GHz flux density • The whole sample: 1.26 +/- 0.10 mJy • The subsample of 10 MAMBO detections: 2.73 +/- 0.06 mJy • The subsample of 23 MAMBO non-detections: • <f250GH>= 0.52 +/- 0.13 mJy • No difference in <f250GHz> when radio loud sources are excluded.
Analysis – the average FIR and radio emission Wang et al. (2008, in press.) FIR-millimeter spectral index ~2 • The FIR-to-1450A luminosity ratios of the three groups have a range of ~0.6dex. • The mean value of the non-detections matches the extrapolation of the template if a FIR-millimeter spectral index of a ≥ 2 is assumed.
Analysis – SEDs of MAMBO detections Wang et al. (2008, in press.)
Analysis – optically thin dust emission Assumption: optically thin gray-body • Get a better measurement of the excess FIR dust emission. • Determine the dust temperature (Td): 100 K or 30 – 60 K? • Need measurements at shorter wavelengths. • Determine the emissivity index (β): dust compositions • Need measurements at longer wavelengths.
Analysis – the bright millimeter detections • Confirm the FIR excesses in the quasar SEDs. • A measurement of the dust temperature (combined with MAMBO, SCUBA, and PdBI data): • 40 to 50 K • A measurement of the dust mass: a few 108 Msun • The size of the dust emission region: 1013 Lsun FIR luminosity, optically thin Rdust~5kpc
Analysis – Luminosity correlation LFIR - LBol • The relationships between FIR and AGN bolometric luminosity derived from local quasar samples (Hao et al. 2005). • More than half of the MAMBO detected quasars at z~6 follow the relation defined by the IR luminous quasars hosted in ULIRGs • The average value of the non-detections. Wang et al. (2008, in press)
LFIR & Lya emission Wang et al. (2008 in press) • Quasars at z~6: • Most of the millimeter detections tend to have log(EW)Lya < 1.5. • The origin of this effect is not clear yet. • More observations…
Molecular CO in the z~6 quasars • Molecular CO emission has been detected in the mm bright quasars. • Gas mass : M(H2) ~ a few 1010 Msun. • CO line width of the new detections: FWHM ≥ 500 km/s. • The median value is 300 km/s for previous CO detected quasars at high-z.
Discussion – star formation in the z~6 quasars • About 30% of the optically selected quasars at z~6 have been detected, and most of the detections show FIR excesses in their SEDs. • The MAMBO undetected quasars at z~6: • The average FIR-to-radio SED is consistent with the templates of local optical quasars. • The average FIR to AGN-bolometric luminosity ratio follows the trend defined by local PG quasars. • FIR emission from the outer region of the dust torus. • Any contribution from star formation?
Discussion – star formation in the z~6 quasars • The average FIR luminosity: 1.2x1012 Lsun • Even 50% of the FIR emission from star formation, the star formation rate => 200 Msun yr-1 • Is the major bulge building stage via starburst finished ? • The mass relationship between SMBHs and their bulges may already be established ? • The observation is difficult.
Discussion – star formation in the z~6 quasars • The bright MAMBO detections: What we see • The FIR emission significantly exceeds the quasar templates • Dust temperature: 40~60 K • Given the 1013 Lsun FIR luminosity, the size of the FIR dust emission region is estimated to be a few kpc => Consistent with the size of the CO and C+ emission region. • CO detections • Luminosity correlations • FIR-to-radio emission consistent with typical star forming galaxies. • LFIR – Lbol correlation: follow the trends defined by local IR quasars – likely to be the high mass counterparts. • LFIR – LCO correlation.
Discussion – star formation in the z~6 quasars star formation? • It is likely that active star formation is ongoing in the host galaxies of the strong millimeter detected quasars at z~6. • Star formation rate: ≥103 Msun yr-1. • Star formation efficiency: comparable to ULIRGs and SMGs. • Gas mass: ~1010 Msun, which will turn to stars via the massive starburst. • If the quasar systems at z~6 follow the local black hole-bulge relationship, the mass of a mature stellar bulge should be ≥5x1011 Msun.
Discussion – the evolutionary stage of the z~6 quasars • We are seeing the end of the active bulge building in these strong mm quasars ? • The stellar bulge with a mass of a few 1011 to 1012 Msun already exist. • Require measurements of the bulge dynamical mass. • Resolve the stellar bulge at near-IR wavelengths. • Not yet; • Require gas supply from outside; • Rapid supper-massive black hole accretion occurs prior to the formation of the stellar bulge.
Further observations • CO and [C II] searches in all the z~6 quasars which have strong FIR excesses in the SEDs (PdBI, SMA) • The [C II] observation requires lots of time with the current instrument (SMA). ALMA is a better place to go! • CO excitation studies with new detections. (low-order CO transition with GBT, EVLA) • Need the frequency range of about 30 to 40 GHz -- Ka band of the EVLA • High resolution (<= 0.3’’) CO and dust mapping (PdBI, EVLA). • Extended FIR emission (a few kpc) associated with the CO emission: star formation. • Compact FIR emission: AGN dust heating • High resolution CO mapping: the dynamical mass within a few kpc.
Summary • The current sample of quasars at z~6 is studied at millimeter and radio wavelengths. • About 30% of these sources have been detected in warm dust continuum at 1.2 mm. • Molecular CO has been detected in the brightest mm detections. • We investigate the possible dust heating process, and star forming activities from the host galaxies of these object. • We discuss the evolutionary stage of these z~6 quasars.