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Register a new userProbing the full CO spectral line energy distribution (SLED) in the nuclear region of a quasar-starburst system at $z=6.003$
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We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO $(8-7)$, $(9-8)$, $rm H_{2}O (2_{0,2}-1_{1,1})$ and $rm OH^{+} (1_{1}-0_{1})$ and NOrthern Extended Millimeter Array (NOEMA) observations of CO $(5-4)$, $(6-5)$, $(12-11)$ and $(13-12)$ towards the $z = 6.003$ quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at $z = 6.003$, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature $T_{rm kin} = 228 rm K$, molecular gas density $log (n(rm H_{2})/rm cm^{-3}$ )=4.75, and CO column density $log(N(rm CO)/rm cm^{-2}) =17.5$, although a two-component model better fits the data. In either case, the CO SLED is dominated by a warm and dense component. Compared to samples of local (Ultra) Luminous Infrared Galaxies ((U)LIRGs), starburst galaxies and high redshift Submillimeter Galaxies (SMGs), J2310+1855 exhibits higher CO excitation at ($J geq 8$), like other high redshift quasars. The high CO excitation, together with the enhanced $L_{rm H_{2}O}/ L_{IR} $, $L_{rm H_{2}O}/ L_{CO} $ and $L_{OH^{+}}/L_{rm H_{2}O} $ ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic rays and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.
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Observing the interstellar medium (ISM) in $z gtrsim 6$ quasars host galaxies is essential for understanding the co-evolution between the supermassive black holes and their hosts. To probe the gas physical conditions and search for imprints of Active Galactic Nuclei (AGN) on the ISM, we report ALMA observations of the $rm [N II]_{122 mu m}$ and $rm [O I]_{146 mu m}$ lines and the underlying continuum from the $z=6.003$ quasar SDSS J231038.88+185519.7. Together with previous $rm [C II]_{158 mu m}$ and $rm [O III]_{88 mu m}$ observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-$z$ systems, this object exhibits a $rm [C II]_{158 mu m}$/$rm [O I]_{146 mu m}$ ratio comparable to the lowest values found in local (Ultra) luminous infrared galaxies, suggesting a warmer and denser gas component compared to typical local systems. The $rm [O III]_{88 mu m}$/$rm [O I]_{146 mu m}$ ratio is lower than that of other local and high-$z$ systems, indicating a smaller ionized gas fraction in this quasar. The $rm [O III]_{88 mu m}$/$rm [N II]_{122 mu m}$ ratio is comparable to that of local systems, and suggests a metallicity of $Z/Z_{odot}$=1.5$-$2.1. Based on the $rm [N II]_{122 mu m}$ detection, we estimate that $17%$ of the $rm [C II]_{158 mu m}$ emission is associated with ionized gas. The $rm [N II]_{122 mu m}$ line shows a flux deficit comparable to local systems. The $rm [O I]_{146 mu m}$ line, with a $rm [O I]_{146 mu m}$/FIR ratio $ge 2times$ than expected from the local relation, indicates no $rm [O I]_{rm 146 mu m}$ deficit. The low $rm [C II]_{158 mu m}$/$rm [O I]_{146 mu m}$ ratio, together with the high $rm [O I]_{146 mu m}$/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating to the ISM.
Submillimeter rotational lines of H2O are a powerful probe in warm gas regions of the ISM, tracing scales and structures ranging from kpc disks to the most compact and dust-obscured regions of galactic nuclei. The ortho-H2O(423-330) line at 448 GHz, which was recently detected in a local luminous infrared galaxy (Pereira-Santaella et al. 2017), offers a unique constraint on the excitation conditions and ISM properties in deeply buried galaxy nuclei since the line requires high far-IR optical depths to be excited. In this letter, we report the first high-redshift detection of the 448 GHz H2O(423-330) line using ALMA, in a strongly lensed submillimeter galaxy (SMG) at z=3.63. After correcting for magnification, the luminosity of the 448 GHz H2O line is ~10^6 L_sun. In combination with three other previously detected H2O lines, we build a model that resolves the dusty ISM structure of the SMG, and find that it is composed of a ~1 kpc optically thin (optical depth at 100{mu}m {tau}_{100}~0.3) disk component with dust temperature T_{dust} approx 50 K emitting a total infrared power of 5e12 L_sun with surface density Sigma_{IR}=4e11 L_sun kpc^{-2}, and a very compact (0.1 kpc) heavily dust-obscured ({tau}_{100} gtrsim 1) nuclear core with very warm dust (100 K) and Sigma_{IR}=8e12 L_sun kpc^{-2}. The H2O abundance in the core component, X_{H2O}~(0.3-5)e{-5}, is at least one order of magnitude higher than in the disk component. The optically thick core has the characteristic properties of an Eddington-limited starburst, providing evidence that radiation pressure on dust is capable of supporting the ISM in buried nuclei at high redshifts. The multi-component ISM structure revealed by our models illustrates that dust and molecules such as H2O are present in regions characterized by highly differing conditions and scales, extending from the nucleus to more extended regions of SMGs.
We present the discovery of PSO J083.8371+11.8482, a weak emission line quasar with extreme star formation rate at $z=6.3401$. This quasar was selected from Pan-STARRS1, UHS, and unWISE photometric data. Gemini/GNIRS spectroscopy follow-up indicates a MgII-based black hole mass of $M_mathrm{BH}=left(2.0^{+0.7}_{-0.4}right)times10^9~M_odot$ and an Eddington ratio of $L_mathrm{bol}/L_mathrm{Edd}=0.5^{+0.1}_{-0.2}$, in line with actively accreting supermassive black hole (SMBH) at $zgtrsim6$. HST imaging sets strong constraint on lens-boosting, showing no relevant effect on the apparent emission. The quasar is also observed as a pure point-source with no additional emission component. The broad line region (BLR) emission is intrinsically weak and not likely caused by an intervening absorber. We found rest-frame equivalent widths of EW(Ly$alpha$+NV) $=5.7pm0.7$ Angstrom, EW(CIV) $leq5.8$ Angstrom (3-sigma upper limit), and EW(MgII) $=8.7pm0.7$ Angstrom. A small proximity zone size ($R_mathrm{p}=1.2pm0.4$ pMpc) indicates a lifetime of only $t_mathrm{Q}=10^{3.4pm0.7}$ years from the last quasar phase ignition. ALMA shows extended [CII] emission with a mild velocity gradient. The inferred far-infrared luminosity ($L_mathrm{FIR}=(1.2pm0.1)times10^{13},L_odot$) is one of the highest among all known quasar hosts at $zgtrsim6$. Dust and [CII] emissions put a constraint on the star formation rate of SFR $=900-4900~M_odot,mathrm{yr^{-1}}$, similar to that of hyper-luminous infrared galaxy. Considering the observed quasar lifetime and BLR formation timescale, the weak-line profile in the quasar spectrum is most likely caused by a BLR which is not yet fully formed rather than continuum boosting by gravitational lensing or a soft continuum due to super-Eddington accretion.
We present new observations of the highest-redshift quasar known, ULAS J1120+0641, redshift $z=7.084$, obtained in the optical, at near-, mid-, and far-infrared wavelengths, and in the sub-mm. We combine these results with published X-ray and radio observations to create the multiwavelength spectral energy distribution (SED), with the goals of measuring the bolometric luminosity $L_{rm bol}$, and quantifying the respective contributions from the AGN and star formation. We find three components are needed to fit the data over the wavelength range $0.12-1000,mu$m: the unobscured quasar accretion disk and broad-line region, a dusty clumpy AGN torus, and a cool 47K modified black body to characterise star formation. Despite the low signal-to-noise ratio of the new long-wavelength data, the normalisation of any dusty torus model is constrained within $pm40%$. We measure a bolometric luminosity $L_{rm bol}=2.6pm0.6times10^{47},$erg$,$s$^{-1}=6.7 pm 1.6times10^{13}L_{odot}$, to which the three components contribute $31%,32%,3%$, respectively, with the remainder provided by the extreme UV $<0.12,mu$m. We tabulate the best-fit model SED. We use local scaling relations to estimate a star formation rate (SFR) in the range $60-270,{rm M}_odot$/yr from the [C$,{scriptsize rm II}$] line luminosity and the $158,mu$m continuum luminosity. An analysis of the equivalent widths of the [C$,{scriptsize rm II}$] line in a sample of $z>5.7$ quasars suggests that these indicators are promising tools for estimating the SFR in high-redshift quasars in general. At the time observed the black hole was growing in mass more than 100 times faster than the stellar bulge, relative to the mass ratio measured in the local universe, i.e. compared to ${M_{rm BH}}/{M_{rm bulge}} simeq 1.4times10^{-3}$, for ULAS J1120+0641 we measure ${dot{M}_{rm BH}}/{dot{M}_{rm bulge}} simeq 0.2$.
We have acquired radio continuum data between 70,MHz and 48,GHz for a sample of 19 southern starburst galaxies at moderate redshifts ($0.067 < z < 0.227$) with the aim of separating synchrotron and free-free emission components. Using a Bayesian framework we find the radio continuum is rarely characterised well by a single power law, instead often exhibiting low frequency turnovers below 500,MHz, steepening at mid-to-high frequencies, and a flattening at high frequencies where free-free emission begins to dominate over the synchrotron emission. These higher order curvature components may be attributed to free-free absorption across multiple regions of star formation with varying optical depths. The decomposed synchrotron and free-free emission components in our sample of galaxies form strong correlations with the total-infrared bolometric luminosities. Finally, we find that without accounting for free-free absorption with turnovers between 90 to 500,MHz the radio-continuum at low frequency ($ u < 200$,MHz) could be overestimated by upwards of a factor of twelve if a simple power law extrapolation is used from higher frequencies. The mean synchrotron spectral index of our sample is constrained to be $alpha=-1.06$, which is steeper then the canonical value of $-0.8$ for normal galaxies. We suggest this may be caused by an intrinsically steeper cosmic ray distribution.
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