Transcript Dust and molecular gas in the most distant quasars

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 discovery of z~6 quasars
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)
MBH~σ4
Marconi & Hunt. (2002)
MBH~10-3MBulge
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.
MAMBO IRAM-30m
VLA
Observations
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
R
f v , 5 GHz
f v , 4 4 0 0A
• 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 nondetections:
•<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
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:
Rdust ~ [ ( 4 )(
LFIR
 v
0.5
]
B (T ~ 50 K ) dv
v
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.
Luminosity correlation LFIR – L’CO
The star formation efficiency
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.