Molecular gas in the z~6 Molecular gas in the z~6 quasar host galaxiesquasar host galaxies

Molecular gas in the z~6 Molecular gas in the z~6 quasar host galaxiesquasar host galaxies

Ran WangNational Radio Astronomy Observatory

Steward Observatory, University of Atrizona

Collaborators: Bertoldi, F. (University of Bonn); Chris Carilli (NRAO); Cox, P. (IRAM); Fan, X. (University of Arizona); Menten, K. (MPIfR); Neri, R. (IRAM); Omont, A. (IAP); Riechers, D. (Caltech); Strauss, M. (Princeton); Wagg, J. (NRAO); Walter, F. (MPIfA)

• Study the formation and early evolution of the quasar-host systems in the most distant universe via mm and cm observations. – Mm dust/cm radio

continuum/fine structure interstellar cooling lines: star forming activities in the quasar host galaxies growth of the stellar bulge.

– Molecular CO emission: fuel of the star formation, dynamical mass of the spheroidal bulge.

SMBH-host evolution in the most distant universe

The formation of the SMBHs and their spheroidal bulges are suggested to be tightly coupled.

Fan et al. 2006

• A sample of 33 z~6 quasars has been observed with MAMBO at 250 GHz, with a median rms of ~0.6 mJy.

• Ten of them have been detected: ~30%.

The mm bright quasars at z~6

IRAM-30m

• Luminosity correlations (eg. FIR vs.

AGN, FIR vs. radio) consistent with the extreme star forming systems.

The mm bright quasars at z~6

• Strong FIR emission from ~40 to 60 K dust, exceeding that of the local optical quasar template.

Wang et al. 2008

Data: Fan et al. 2004; Jiang et al. 2006; Leipski et al. 2010; Beelen et al. 2006; Robson et al. 2004; Bertoldi et al. 2003; Carilli et al. 2004

The mm bright quasars at z~6

• A sample of 8 z~6 quasars with 250 GHz flux densities >= 1.8 mJy, based on the MAMBO dust continuum observations.

• The brightest mm detections: J1148+5251 and J0927+2001 have been detected in strong molecular CO line emission (Walter et al. 2003; Bertoldi et al. 2003; Carilli et al. 2007; Riechers et al. 2009).

• We observe the other six objects with the PdBI to search for high order CO transitions (6-5 and/or 5-4).

Walter et al. 2009 Riechers et al. 2009

D configuration: FWHM~5”, ~29 kpc at z~6;

• Two tracks on each of the targets, covering a band width of 1.8 GHz;

• FOV: FWHM~50”; • Unresolved.

IRAM-PdBI

• All the six z~6 quasars has been detected in molecular CO emission. – A sample of eight mm continuum and CO detected quasars at z~6.

• Host galaxy redshift: accurate to ≤0.002; • CO line width: 160 ~860 km/s.

– Line width distribution : similar to that of the SMGs and CO detected quasars at lower redshifts.

– The source with the largest line width show a possible double-peak line profile.

Molecular CO from the z~6 quasar hosts

Wang et al. 2010

• Molecular gas mass distributions : – similar to that of the SMGs and 1.4≤z≤5.0 CO-detected

quasars.– An order of magnitude smaller than that of the star

forming galaxies found at z~1 to 2 (eg. Daddi et al. 2010; Tacconi et al. 2010).

Molecular gas mass distribution

CO excitation in the z~6 quasar hosts

• Warm, highly excited molecular gas with Tkin~50 K and n(H2) ~104.2 cm-3

(Riechers et al. 2009).

• Similar to that in the FIR and CO detected quasars at lower redshifts (eg. BR1202-0725 at z=4.69, Riechers et al. 2006) and some nearby starburst galaxies (eg. M82, Weiss et al. 2005).

• FIR-CO luminosity relationship.

• Star formation rate: 530 to 2380 Msun yr-1

.

• Gas depletion time scale: 107 yr, similar to that of the extreme starburst systems, such as the SMGs, ULIRGs, and much smaller that of the star forming galaxies found at z~1 and 2 (Daddi et al. 2010; Tacconi et al. 2010).

Wang et al. 2010

• CO estimated stellar mass with assumption of disk radius, inclination angles. i.e. Mdyn: ~f·R·VFWHMCO

2/G/sin2i; Mbulge~Mdyn (R, sini)-Mgas.

Wang et al. 2010

• Small inclination angles of i <5 to 15 degree are required for most of the sources

• However, the obscured fraction is probably ≤50% for the very luminous quasars: large torus opening angle at high luminosity (Simpson 2005; Treister et al. 2008) inclination angle range of about 0 to 60 degree.

• An average inclination angle of 40 degree: MBH/Mbul~0.022, fifteen times higher than the present-day value.

Difficulties : How the observed CO line widths trace the bulge dynamical properties, unknown molecular disk size, inclination angle high-resolution observations

• Molecular CO has been detected in a sample of eight mm bright quasars at z~6.

• The CO detections suggest the presence of highly excited molecular gas in the quasar host galaxies, with molecular gas masses on order of 1010 Msun. The gas mass and line width distributions are similar to that of the CO detected SMGs and quasars at z from 1 to 5.

• FIR-CO luminosity relation: Active bulge building via massive star formation at a rate of a few 100 to 1000 Msun yr-1.

• Estimations of the dynamical mass of the quasar stellar bulge based on the CO observations suggest a black hole-bulge mass ratio about 15 times higher than that of the present-day value. However, high-resolution observations are still required to fully understand the molecular gas distribution and dynamical properties

Summary

Companion source close to J1048

• CO (6-5) line emission from a companion source northeast to the quasar: ~28”away, redshift z=6.2259, close to the quasar redshift of z=6.2284. Wang et al. 2010