Quasar feedback in the early Universe: the case of SDSS J1148+5251

Galaxy-scale gas outflows triggered by active galactic nuclei have been proposed as a key physical process to regulate the co-evolution of nuclear black holes and their host galaxies. The recent detection of a massive gas outflow in one of the most distant quasar, SDSS J1148+5251 at z = 6.4, presented by Maiolino et al. (2012) strongly supports this idea and suggests that strong quasar feedback is already at work at very early times. In a previous work, Valiante et al. (2011), we have presented a hierarchical semi-analytical model, GAMETE/ QSOdust, for the formation and evolution of high-redshift quasars, and we have applied it to the quasar SDSS J1148+5251, with the aim of investigating the star formation history, the nature of the dominant stellar populations and the origin and properties of the large dust mass observed in the host galaxy. A robust prediction of the model is that the evolution of the nuclear black hole and of the host galaxy are tightly coupled by quasar feedback in the form of strong galaxy-scale winds. In the present letter, we show that the gas outflow rate predicted by GAMETE/QSOdust is in good agreement with the lower limit of 3500 Msun/yr inferred by the observations. According to the model, the observed outflow at z = 6.4 is dominated by quasar feedback, as the outflow rate has already considerably depleted the gas content of the host galaxy, leading to a down-turn in the star formation rate at z < 7 - 8. Hence, supernova explosions give a negligible contribution to the observed winds at z = 6.4.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter

Molecular Gas in Infrared Ultraluminous QSO Hosts

We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in these objects is in a range of 0.2--2.1$\times 10^{10}M_\odot$ (adopting a CO-to-${\rm H_2}$ conversion factor $\alpha_{\rm CO}=0.8 M_\odot {\rm (K km s^{-1} pc^2)^{-1}}$). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency ($L_{\rm FIR}/L^\prime_{\rm CO}$) and the CO (1-0) line widths, are indistinguishable from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of low- and high-redshift CO detected QSOs reveals a tight correlation between L$_{\rm FIR}$ and $L^\prime_{\rm CO(1-0)}$ for all QSOs. This suggests that, similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust heated by star formation rather than by active galactic nuclei (AGNs), confirming similar findings from mid-infrared spectroscopic observations by {\it Spitzer}. A correlation between the AGN-associated bolometric luminosities and the CO line luminosities suggests that star formation and AGNs draw from the same reservoir of gas and there is a link between star formation on $\sim$ kpc scale and the central black hole accretion process on much smaller scales.Comment: 30 pages, 9 figures, accepted for publication in The Astrophysical Journa

Properties of the molecular gas in a starbursting QSO at z=1.83 in the COSMOS field

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

Millimetre observations of a sample of high-redshift obscured quasars

We present observations at 1.2 mm with MAMBO-II of a sample of z>~2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. Five out of 21 sources (24%) are detected at a significance of >=3sigma. Stacking all sources leads to a statistical detection of = 0.96+-0.11 mJy and stacking only the non-detections also yields a statistical detection, with = 0.51+-0.13 mJy. This corresponds to a typical far-infrared luminosity L_FIR~4x10^12 Lsol. If the far-infrared luminosity is powered entirely by star-formation, and not by AGN-heated dust, then the characteristic inferred star-formation rate is ~700 Msol yr-1. This far-infrared luminosity implies a dust mass of M_dust~3x10^8 Msol. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. We present dust SEDs for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. There is a hint that the host galaxies of obscured quasars must have higher far-infrared luminosities and cool-dust masses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z=2.767, we detect the CO(3-2) transition, with S_CO Delta nu=630+-50 mJy km s-1, corresponding to L_CO(3-2)= 3.2x10^7 Lsol, or L'_CO(3-2)=2.4x10^10 K km s-1 pc2. For another source at z=4.17, the lack of detection of the CO(4-3) line yields a limit of L'_CO(4-3)<1x10^10 K km s-1 pc2. Molecular gas masses, gas depletion timescales and gas-to-dust ratios are estimated (Abridged).Comment: Accepted by ApJ, 25 pages, 11 figures, 4 table

The Far-Infrared--Radio Correlation at High Redshifts: Physical Considerations and Prospects for the Square Kilometer Array

(Abridged) I present a predictive analysis for the behavior of the FIR--radio correlation as a function of redshift in light of the deep radio continuum surveys which may become possible using the SKA. To keep a fixed ratio between the FIR and predominantly non-thermal radio continuum emission of a normal star-forming galaxy requires a nearly constant ratio between galaxy magnetic field and radiation field energy densities. While the additional term of IC losses off of the cosmic microwave background (CMB) is negligible in the local Universe, the rapid increase in the strength of the CMB energy density (i.e. $\sim(1+z)^{4})$ suggests that evolution in the FIR-radio correlation should occur with infrared (IR; 8-1000 \micron)/radio ratios increasing with redshift. At present, observations do not show such a trend with redshift; $z\sim6$ radio-quiet QSOs appear to lie on the local FIR-radio correlation while a sample of $z\sim4.4$ and $z\sim2.2$ SMGs exhibit ratios that are a factor of $\sim$2.5 {\it below} the canonical value. I also derive a 5$\sigma$ point-source sensitivity goal of $\approx$20 nJy (i.e. $\sigma_{\rm RMS} \sim 4$ nJy) requiring that the SKA specified be $A_{\rm eff}/T_{\rm sys}\approx 15000$ m$^{2}$ K$^{-1}$; achieving this sensitivity should enable the detection of galaxies forming stars at a rate of \ga25 M_{\sun} {\rm yr}^{-1}, at all redshifts if present. By taking advantage of the fact that the non-thermal component of a galaxy's radio continuum emission will be quickly suppressed by IC losses off of the CMB, leaving only the thermal (free-free) component, I argue that deep radio continuum surveys at frequencies \ga10 GHz may prove to be the best probe for characterizing the high-$z$ star formation history of the Universe unbiased by dust.Comment: 16 pages, 8 figures, accepted for publication in Ap

Evidence of strong quasar feedback in the early Universe

Most theoretical models invoke quasar driven outflows to quench star formation in massive galaxies, this feedback mechanism is required to account for the population of old and passive galaxies observed in the local universe. The discovery of massive, old and passive galaxies at z=2, implies that such quasar feedback onto the host galaxy must have been at work very early on, close to the reionization epoch. We have observed the [CII]158um transition in SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars known. We detect broad wings of the line tracing a quasar-driven massive outflow. This is the most distant massive outflow ever detected and is likely tracing the long sought quasar feedback, already at work in the early Universe. The outflow is marginally resolved on scales of about 16 kpc, implying that the outflow can really affect the whole galaxy, as required by quasar feedback models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever found. At this rate the outflow can clean the gas in the host galaxy, and therefore quench star formation, in a few million years.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter

Gas and dust in a z=2.8 obscured quasar

We present new detections of the CO(5-4), CO(7-6), [CI](1-0) and [CI](2-1) molecular and atomic line transitions towards the unlensed, obscured quasar AMS12 (z=2.7672), observed with the IRAM PdBI. This is the first unlensed, high redshift source to have both [CI] transitions detected. Continuum measurements between 70 $\mu$m and 3 mm are used to constrain the FIR SED, and we find a best fit FIR luminosity of log[Lfir/Lsol] = 13.5+/-0.1, dust temperature T_d = 88+/-8 K and emissivity index {\beta} = 0.6+/-0.1. The highly-excited molecular gas probed by CO(3-2), (5-4) and (7-6), is modelled with large velocity gradient (LVG) models. The gas kinetic temperature T_g, density n(H2), and the characteristic size r0, are determined using the dust temperature from the FIR SED as a prior for the gas temperature. The best fitting parameters are T_g = 90+/-8 K, n(H2) = 10^(3.9+/-0.1) cm^(-3) and r0 = 0.8+/-0.04 kpc. The ratio of the [CI] lines gives a [CI] excitation temperature of 43+/-10 K, indicating the [CI] and the high-excitation CO are not in thermal equilibrium. The [CI] excitation temperature is below that of T_d and T_g of the high-excitation CO, perhaps because [CI] lies at a larger radius where there may also be a large reservoir of CO at a cooler temperature, perhaps detectable through the CO(1-0). Using the [CI](1-0) line we can estimate the strength of the CO(1-0) line and hence the gas mass. This suggests that a significant fraction (~30%) of the molecular gas is missed from the high-excitation line analysis. The Eddington limited black hole mass is found from the bolometric luminosity to be Mbh >~ 1.5x10^9 Msol. Along with the stellar mass of 3x10^11 Msol, these give a black hole - bulge mass ratio of Mbh/Mbulge >~ 0.005. This is in agreement with studies on the evolution of the Mbh/Mbulge relationship at high redshifts, which find a departure from the local value ~0.002.Comment: Accepted by MNRAS, 17 pages, 9 figure

An Accounting of the Dust-Obscured Star Formation and Accretion Histories Over the Last ~11~Billion Years

(Abridged) We report on an accounting of the star formation and accretion driven energetics of 24um detected sources in GOODS North. For sources having infrared (IR; 8-1000um) luminosities >3x10^12 L_sun when derived by fitting local SEDs to 24um photometry alone, we find these IR luminosity estimates to be a factor of ~4 times larger than those estimated when the SED fitting includes additional 16 and 70um data (and in some cases mid-infrared spectroscopy and 850um data). This discrepancy arises from the fact that high luminosity sources at z>>0 appear to have far- to mid-infrared ratios, as well as aromatic feature equivalent widths, typical of lower luminosity galaxies in the local Universe. Using our improved estimates for IR luminosity and AGN contributions, we investigate the evolution of the IR luminosity density versus redshift arising from star formation and AGN processes alone. We find that, within the uncertainties, the total star formation driven IR luminosity density is constant between 1.15 < z < 2.35, although our results suggest a slightly larger value at z>2. AGN appear to account for <18% of the total IR luminosity density integrated between 0< z < 2.35, contributing <25% at each epoch. LIRG appear to dominate the star formation rate (SFR) density along with normal star-forming galaxies (L_IR < 10^11 L_sun) between 0.6 < z < 1.15. Once beyond z >2, the contribution from ultraluminous infrared galaxies ULIRGs becomes comparable with that of LIRGs. Using our improved IR luminosity estimates, we find existing calibrations for UV extinction corrections based on measurements of the UV spectral slope typically overcorrect UV luminosities by a factor of ~2, on average, for our sample of 24um-selected sources; accordingly we have derived a new UV extinction correction more appropriate for our sample.Comment: Accepted for publication in Ap

MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields

We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the SWIRE survey. The sources are selected on the basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z~2 starburst galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The analysis of the sources multi-wavelength spectral energy distributions indicates that they are starburst galaxies with far-infrared luminosities ~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24um/millimeter flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared emission, and is likely associated with an AGN component. This constribution is consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultra-luminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.Comment: Accepted for publication in ApJ (51 pages; 16 figures). The quality of some figures has been degraded for arXiv purposes. Full resolution version available at this http://www.iasf-milano.inaf.it/~polletta/mambo_swire/lonsdale08_ApJ_accepted.pd

Deep, ultra-high-resolution radio imaging of submillimetre galaxies using Very Long Baseline Interferometry

We present continent-scale VLBI - obtained with the European VLBI Network (EVN) at a wavelength of 18cm - of six distant, luminous submm-selected galaxies (SMGs). Our images have a synthesized beam width of ~30 milliarcsec FWHM - three orders of magnitude smaller in area than the highest resolution VLA imaging at this wavelength - and are capable of separating radio emission from ultra-compact radio cores (associated with active super-massive black holes - SMBHs) from that due to starburst activity. Despite targeting compact sources - as judged by earlier observations with the VLA and MERLIN - we identify ultra-compact cores in only two of our targets. This suggests that the radio emission from SMGs is produced primarily on larger scales than those probed by the EVN, and therefore is generated by star formation rather than an AGN - a result consistent with other methods used to identify the presence of SMBHs in these systems.Comment: MNRAS, in pres