Early Star Formation Traced by the Highest Redshift Quasars

Maiolino, R.; Juárez, Yectivani; Mújica, R.; Nagar, N. M.; Oliva, E.

doi:10.1086/379600

Cited by 80 publications

(122 citation statements)

References 28 publications

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“…Many of these spectra were already partly presented in previous works (Maiolino et al 2003(Maiolino et al , 2004bJuarez 2009). The data reduction process is presented in these previous papers, and here we summarize only the instrumental setup.…”

Section: Spectroscopic Data and Samplementioning

confidence: 89%

The extinction law at high redshift and its implications

Gallerani

Maiolino

Juárez

et al. 2010

A&A

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152

171

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We analyze the optical-near infrared spectra of 33 quasars with redshifts 3.9 ≤ z ≤ 6.4 to investigate the properties of dust extinction at these cosmic epochs. The SMC extinction curve has been shown to reproduce the dust reddening of most quasars at z < 2.2; we investigate whether this curve also provides a good description of dust extinction at higher redshifts. We fit the observed spectra with synthetic absorbed quasar templates obtained by varying the intrinsic slope (α λ ), the absolute extinction (A 3000 ), and by using a grid of empirical and theoretical extinction curves. We find that seven quasars in our sample are affected by substantial extinction (A 3000 ≥ 0.8), and characterized by very steep intrinsic slopes (α λ ≤ −2.3). All of the individual quasars require extinction curve deviating from that of the SMC, with a tendency to flatten at λ ≤ 2000 Å (in the rest frame of the source). However, due to the uncertainties in the individual extinction curves the SMC is still (marginally) consistent with the data in most cases. We obtain a mean extinction curve at z > 4, both by performing a simultaneous fit of all quasars and by averaging the extinction curves inferred for individual quasars. In the case of broad absorption line quasars (which are generally more absorbed by dust and possibly in a younger evolutionary stage), the mean extinction curve deviates from the SMC at a confidence level ≥95%. The difference between extinction curves in quasars at z > 4 and in quasars at lower redshift is indicative of either a different dust production mechanism at high redshift, or a different mechanism for processing dust into the ISM. We suggest that the same transitions may also apply to normal, star-forming galaxies at z > 4. In particular, the observed change in the average spectral slope of galaxies at z > 4 may be partially ascribed to a variation in the extinction curve, rather than a lower dust content at high redshift. In this scenario, the extinction curve inferred at z > 4 would imply a cosmic star-formation corrected for dust attenuation a factor of ∼2 higher than estimated in the past.

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Section: Spectroscopic Data and Samplementioning

confidence: 89%

The extinction law at high redshift and its implications

Gallerani

Maiolino

Juárez

et al. 2010

A&A

Self Cite

152

171

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“…The proxy usually used to trace the Fe/ Mg abundance ratio at high z is the Fe ii/Mg ii line ratio. In the past, numerous NIR spectroscopy studies have been carried out to analyze the Fe ii/Mg ii line ratio in high-z QSOs (e.g., Maiolino et al 2001Maiolino et al , 2003Pentericci et al 2002;Iwamuro et al 2002Iwamuro et al , 2004Barth et al 2003;Dietrich et al 2003;Freudling et al 2003;Willott et al 2003;Jiang et al 2007;Kurk et al 2007). The combined results revealed an increase in the scatter of the measured Fe ii/Mg ii line ratios as a function of redshift (see Kurk et al 2007).…”

Section: Fe Ii/mg IImentioning

confidence: 99%

EVIDENCE FOR NON-EVOLVING Fe II/Mg II RATIOS IN RAPIDLY ACCRETINGz∼ 6 QSOs

Rosa

Decarli

Walter

et al. 2011

ApJ

224

265

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Quasars (QSOs) at the highest known redshift (z ∼ 6) are unique probes of the early growth of supermassive black holes (BHs). Until now, only the most luminous QSOs have been studied, often one object at a time. Here we present the most extensive consistent analysis to date of 4 < z < 6.5 QSOs with observed near-infrared spectra, combining three new z ∼ 6 objects from our ongoing Very Large Telescope-Infrared Spectrometer And Array Camera program with nineteen sources from the literature. The new sources extend the existing Sloan Digital Sky Survey (SDSS) sample toward the faint end of the QSO luminosity function. Using a maximum likelihood fitting routine optimized for our spectral decomposition, we estimate the BH mass (M BH ), the Eddington ratio (defined as L bol /L Edd ), and the Fe ii/Mg ii line ratio, a proxy for the chemical abundance, to characterize both the central object and the broad-line region gas. The QSOs in our sample host BHs with masses of ∼10 9 M that are accreting close to the Eddington luminosity, consistent with earlier results. We find that the distribution of observed Eddington ratios is significantly different than that of a luminosity-matched comparison sample of SDSS QSOs at lower redshift (0.35 < z < 2.25): the average log(L bol /L Edd ) = −0.37 (L bol /L Edd ∼ 0.43) with a scatter of 0.20 dex for the z > 4 sample and the log(L bol /L Edd ) = −0.80 (L bol /L Edd ∼ 0.16) with a scatter of 0.24 dex for the 0.35 < z < 2.25 sample. This implies that, at a given luminosity, the M BH at high-z is typically lower than the average M BH of the lower-redshift population, i.e., the z > 4 sources are accreting significantly faster than the lower-redshift ones. We show that the derived Fe ii/Mg ii ratios depend sensitively on the analysis performed: our self-consistent, homogeneous analysis significantly reduces the Fe ii/Mg ii scatter found in previous studies. The measured Fe ii/Mg ii line ratios show no sign of evolution with cosmic time in the redshift range 4 < z < 6.5. If the Fe ii/Mg ii line ratio is used as a secondary proxy of the Fe/Mg abundance ratio, this implies that the QSOs in our sample have undergone a major episode of Fe enrichment in the few 100 Myr preceding the cosmic age at which they are observed.

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“…We set the lower limit for the metallicity at the solar value and the upper limit at 5 Z . This is based on the inferred solar or supersolar metallicities in high-z QSOs (e.g., Barth et al 2003;Dietrich et al 2003;Fan et al 2003;Freudling et al 2003;Maiolino et al 2003;Di Matteo et al 2004;Becker et al 2006;Juarez et al 2009). We note that there are no strong constraints on the upper limit and therefore the zone above 5 Z is marked as light grey shaded region to account for the uncertainty.…”

Section: Metallicity and Sfrmentioning

confidence: 99%

“…Wang et al (2010) derived SFRs between 530-2300 M yr −1 from observations of a sample of QSOs at redshift z > 5. Observations of strong metal emission of high-z QSOs (e.g., Barth et al 2003;Dietrich et al 2003;Maiolino et al 2003;Becker et al 2006) indicate strong star forming activity in the QSO hosts and solar or supersolar metallicity (e.g., Fan et al 2003;Freudling et al 2003;Juarez et al 2009). Theoretical studies of the gas metallicity of QSO hosts also predict supersolar metallicities for z = 5-6 QSOs (e.g., Di Matteo et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Genesis and evolution of dust in galaxies in the early Universe

Gall

Andersen

Hjorth

2011

A&A

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Aims. We intend to assess the most plausible scenarios for generating large amounts of dust in high-z quasars (QSOs) on the basis of observationally derived physical properties of QSOs at z 6. Methods. We use a chemical evolution model to compute the temporal progression of quantities such as the amount of dust and gas, stellar masses, star formation rates (SFRs) and the metallicity for various combinations of the initial mass function (IMF), the mass of the galaxy, dust production efficiencies, and the degree of dust destruction in the ISM. We investigate the influence of the SFR on the evolution of these quantities, and determine the earliest epochs at which agreement with observations can be achieved. We apply the obtained results to individual QSOs at z 6. Results. We find that large quantities of dust can be generated rapidly as early as 30 Myr after the onset of the starburst when the SFR of the starburst is 10 3 M yr −1 . The amount of dust and several other physical quantities of individual QSOs at z 6 are satisfactorily reproduced by models at epochs 30, 70, 100, and 170 Myr for galaxies with initial gas masses of 1-3 × 10 11 M . The best agreement with observations is obtained with top-heavy IMFs. A sizable dust contribution from supernovae (SNe) is however required, while at these epochs dust production by asymptotic giant branch (AGB) stars is negligible. Moderate dust destruction in the ISM can be accommodated.

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Early Star Formation Traced by the Highest Redshift Quasars

Cited by 80 publications

References 28 publications

The extinction law at high redshift and its implications

The extinction law at high redshift and its implications

EVIDENCE FOR NON-EVOLVING Fe II/Mg II RATIOS IN RAPIDLY ACCRETINGz∼ 6 QSOs

Genesis and evolution of dust in galaxies in the early Universe

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