Article

# Molecular gas in QSO host galaxies at z>5

07/2007; DOI:10.1051/0004-6361:20078136
Source: arXiv

ABSTRACT We present observations with the IRAM Plateau de Bure Interferometer of three QSOs at z>5 aimed at detecting molecular gas in their host galaxies as traced by CO transitions. CO (5-4) is detected in SDSSJ033829.31+002156.3 at z=5.0267, placing it amongst the most distant sources detected in CO. The CO emission is unresolved with a beam size of ~1", implying that the molecular gas is contained within a compact region, less than ~3kpc in radius. We infer an upper limit on the dynamical mass of the CO emitting region of ~3x10^10 Msun/sin(i)^2. The comparison with the Black Hole mass inferred from near-IR data suggests that the BH-to-bulge mass ratio in this galaxy is significantly higher than in local galaxies. From the CO luminosity we infer a mass reservoir of molecular gas as high as M(H2)=2.4x10^10 Msun, implying that the molecular gas accounts for a significant fraction of the dynamical mass. When compared to the star formation rate derived from the far-IR luminosity, we infer a very short gas exhaustion timescale (~10^7 yrs), comparable to the dynamical timescale. CO is not detected in the other two QSOs (SDSSJ083643.85+005453.3 and SDSSJ163033.90+401209.6) and upper limits are given for their molecular gas content. When combined with CO observations of other type 1 AGNs, spanning a wide redshift range (0<z<6.4), we find that the host galaxy CO luminosity (hence molecular gas content) and the AGN optical luminosity (hence BH accretion rate) are correlated, but the relation is not linear: L(CO) ~ [lambda*L_lambda(4400A)]^0.72. Moreover, at high redshifts (and especially at z>5) the CO luminosity appears to saturate. We discuss the implications of these findings in terms of black hole-galaxy co-evolution. Comment: Accepted for publication in A&A Letters, 6 pages, 3 figures

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##### Article: Properties of the molecular gas in a starbursting QSO at z=1.83 in the COSMOS field
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ABSTRACT: Using the IRAM 30m telescope, we have detected the CO J=2-1, 4-3, 5-4, and 6-5 emission lines in the millimeter-bright, blank-field selected AGN COSMOS J100038+020822 at redshift z=1.8275. The sub-local thermodynamic equilibrium (LTE) excitation of the J=4 level implies that the gas is less excited than that in typical nearby starburst galaxies such as NGC253, and in the high-redshift quasars studied to date, such as J1148+5251 or BR1202-0725. Large velocity gradient (LVG) modeling of the CO line spectral energy distribution (CO SED; flux density vs. rotational quantum number) yields H2 densities in the range 10^{3.5}--10^{4.0} cm-3, and kinetic temperatures between 50 K and 200 K. The H2 mass of (3.6 - 5.4) x 10^{10} M_sun implied by the line intensities compares well with our estimate of the dynamical mass within the inner 1.5 kpc of the object. Fitting a two-component gray body spectrum, we find a dust mass of 1.2 x 10^{9} M_sun, and cold and hot dust temperatures of 42+/-5 K and 160+/-25 K, respectively. The broad MgII line allows us to estimate the mass of the central black hole as 1.7 x 10^{9} M_sun. Although the optical spectrum and multi-wavelength SED matches those of an average QSO, the molecular gas content and dust properties resemble those of known submillimeter galaxies (SMGs). The optical morphology of this source shows tidal tails that suggest a recent interaction or merger. Since it shares properties of both starburst and AGN, this object appears to be in a transition from a strongly starforming submillimeter galaxy to a QSO. Comment: Accepted for publication in Astronomy & Astrophysics (A&A)
Astronomy and Astrophysics 09/2008; · 5.08 Impact Factor
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##### Article: Probing high-redshift quasars with ALMA. I. Expected observables and potential number of sources
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ABSTRACT: (abridged) We explore how ALMA observations can probe high-redshift galaxies in unprecedented detail. We discuss the main observables that are excited by the large-scale starburst, and formulate expectations for the chemistry and the fluxes in the center of active galaxies, where chemistry may be driven by the absorption of X-ray photons. We show that such X-ray dominated regions (XDRs) should be large enough to be resolved with ALMA, and predict the expected amount of emission in CO and various fine-structure lines. We discuss how such XDRs can be distinguished from a strong starburst on the same spatial scales based on the CO line SED. Our models are compared to known sources like NGC 1068 and APM 08279. We also analyze the properties of the z=6.42 quasar SDSS J114816.64+525150.3, and find that the observed emission in CO, [CII] and [CI] requires a dense warm and a low-density cold gas component. We estimate the expected number of sources at redshifts higher than 6, finding that one could expect one black hole with $10^6$ solar masses per arcmin$^2$. Comment: 15 pages, 17 figures, accepted by A&A
Astronomy and Astrophysics 01/2010; · 5.08 Impact Factor
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##### Article: The transition from population III to population II-I star formation
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Monthly Notices of the Royal Astronomical Society 03/2010; · 5.52 Impact Factor