Transcript Molecular gas in z~6 quasar host galaxies

Molecular gas in the z~6 quasar
host galaxies
Ran Wang
National 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)
SMBH-host evolution in the most distant universe
The formation of the SMBHs and
their spheroidal bulges are
suggested to be tightly
coupled.
• 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.
Fan et al. 2006
–Molecular CO emission: fuel
of the star formation,
The mm bright quasars at z~6
IRAM-30m
• 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
• Strong FIR emission
from ~40 to 60 K
dust, exceeding that
of the local optical
quasar template.
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
• Luminosity
correlations
Wang et al. 2008
(eg. FIR
vs. AGN, FIR vs. radio)
consistent with the
extreme star forming
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
IRAM-PdBI
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.
Molecular CO from the z~6 quasar hosts
• 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
Wang et al. 2010
double-peak line profile.
Molecular gas mass distribution
• Molecular gas mass distributions :
–similar to that of the SMGs and 1.4≤z≤5.0 COdetected 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).
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
Wang et al. 2010
• CO estimated stellar mass with assumption of disk
radius, inclination angles. i.e. Mdyn:
~f·R·VFWHMCO2/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
Difficulties : How the observed CO line widths trace the
higher than the present-day value.
bulge dynamical properties, unknown molecular disk size,
inclination angle  high-resolution observations
Summary
• 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
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