Understanding how super-massive black holes form and grow in the early Universe has become a major challenge1,2 since it was discovered that luminous quasars existed only 700 million years after the Big Bang3,4. Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust5. Although the last phase has been identified out to a redshift of 7.6 (ref. 6), a transitioning quasar has not been found at similar redshifts owing to their faintness at optical and near-infrared wavelengths. Here we report observations of an ultraviolet compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of 7.1899 ± 0.0005. The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 parsec. A red point source in the far-ultraviolet is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, which indicates the emergence of a uniquely ultraviolet compact star-forming region or a Compton-thick super-Eddington black-hole accretion disk at the dusty starburst core. In the latter case, the observed properties are consistent with predictions from cosmological simulations7 and suggest that GNz7q is an antecedent to unobscured luminous quasars at later epochs.
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This paper makes use of HST data from the programmes 9583, 9727, 9728, 10189, 10339, 11600, 12442, 12443, 12444, 12445, 13063, 13420 and 13779, available at https://archive.stsci.edu/. The reduced HST and Spitzer image mosaics are available at https://doi.org/10.5281/zenodo.4469734. Other products from the CHArGE project are avilable at https://gbrammer.github.io/projects/charge/. The NOEMA data that support our finding consists of ED19AD and W20EO, which are available at https://www.iram-institute.org/EN/content-page-386-7-386-0-0-0.html. The SED of the SDSS quasar at z = 3.11 used in Fig. 1 is available from the SDSS DR12 website at https://dr12.sdss.org/spectrumDetail?plateid=6839 mjd=56425 fiber=146. The SEDs of local quasar and starburst are available from the SWIRE template website at http://www.iasf-milano.inaf.it/~polletta/templates/swire_templates.html. The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.
The HST and Spitzer data were processed with grizli and golfir, available at https://github.com/gbrammer/grizli and https://github.com/gbrammer/golfir, respectively. The HST F125W image was analysed with galfit, which is available at https://users.obs.carnegiescience.edu/peng/work/galfit/galfit.html. The NOEMA data were reduced using the GILDAS software. The CASA pipeline version of 5.6 is also used for imaging the NOEMA interferometric data. These are available at https://casa.nrao.edu/casa_obtaining.shtml and https://www.oso.nordic-alma.se/software-tools.php. The online Portable Interactive Multi-Mission Simulator is available at https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/w3pimms/w3pimms.pl.
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We thank M. Onoue, K. Ichikawa, Y. Harikane and Y. Ono for discussions on the physical properties of GNz7q and the AGN fraction among the brightest Lyman-break galaxies at z ≈ 7; E. Murphy and F. Owen for sharing their JVLA data; D. Marrone for sharing the best-fit SED model of SPT0311-58W; K. Whitaker for a helpful advice on writing the manuscript. This work is based on the archival data of Hubble Space Telescope, Spitzer, Chandra, Subaru, Herschel, James Clerk Maxwell Telescope and the Karl G. Jansky Very Large Array, and the observations of IRAM/NOEMA interferometer (programme ID: E19AD and W20EO). We acknowledge support from: the Danish National Research Foundation under grant number 140; the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant number 648179); Independent Research Fund Denmark grants DFF-7014-00017 and DFF-8021-00130; the Villum Fonden research grant 37440, ‘The Hidden Cosmos’.
The authors declare no competing interests.
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Extended data figures and tables
The rest-frame 1,450 Å luminosity as a function of redshift (a) and the UV continuum slope (b). GNz7q falls between the typical luminosity ranges of quasars and galaxies in the literature2,6,47,48, where both faint quasars and luminous galaxies have been also identified49,50,51,52,53,54,56,148. GNz7q shows the reddest UV continuum slope among both galaxies and quasars at z > 6. The galaxies without spectroscopic redshifts and the quasars without a UV continuum slope measurement are displayed in the open symbols. The error bars denote the 1σ measurement uncertainty.
a, HST 4″ × 4″ cutout in the HST WFC3/IR filters of F105W, F125W, F140W, and F160W (left), instrumental point spread function (PSF) models168 (centre), and PSF fit residuals (right). b, Radial profile for the rest-frame UV continuum of GNz7q observed in F125W. The black circles show the observed values, while the dark and light red squares and lines present the PSF and the best-fit Sérsic models (Methods). The error bars denote the 68th percentile in each annulus, and the dotted line indicates the standard deviation of the pixel.
a, 1.3-mm continuum (left) and the velocity-integrated [C ii] maps (middle) with the natural weighting. We identify a nearby continuum object with a ~3″ offset from GNz7q at the northern east part, dubbed “ND1”. The intensity of the 1.3-mm continuum and the velocity integrated [C ii] is shown in the right panel in green and red contours, respectively, overlaid on the HST/F160W 4″ × 4″ cutout. The solid contours are drawn at 3σ, 5σ, and 7σ levels, while the dashed white contours are drown at −3σ level. The NOEMA synthesized beam is presented at the left bottom. b, [C ii] line spectrum within a 1″0 radius aperture. The blue curve is the best-fit Gaussian for the [C ii] line. The yellow shaded indicates the velocity range of [−200: +200] km s−1 used for the velocity-integrated map in panel a. c, [C ii] line kinematics. The top and bottom panel present the velocity-weighted and the velocity-dispersion maps (4″ × 4″), respectively.
Left: 3.3-mm continuum (top) and the velocity-integrated CO(7–6) maps with the natural weighting. The black (white) contours are drown at 3σ, 4σ, and 5σ (−3σ). Right: NOEMA 3-mm band spectrum for LSB (top) and USB (bottom) with a 2″0 radius aperture. The dashed vertical line indicates the observed frequency of the expected far-IR lines based on the source redshift of z = 7.1899 determined by the [C ii] line. The blue curve is the best-fit Gaussian for the CO(7–6) line. The yellow shade indicates the velocity range used for the velocity-integrated map in the left panel.
Left: Observed map, which is the same as Extended Data Fig. 3a. Middle: Residual map by subtracting the best-fit model visibility obtained with uvmodelfit. For the dust continuum, we subtract the best-fit model visibility by fixing the major-axis effective radius as the upper limit value of re,FIR = 0.48 kpc. The visibility of ND1 is subtracted by assuming its profile as a point source before running uvmodelfit. Right: Amplitude as a function of uv distance. The black circles shows the observed visibility. The error bars show the standard error of the mean in each uv distance bin. The red curve denotes the best-fit uv model for the [C ii] line, while the red dashed curve for the dust continuum indicates the uv model with the upper limit size.
The black and blue squares denote SDSS quasars18,80,169 at z ~ 0–4 and blue quasars76,81,82 at z > 5 respectively, taken from the literature. The arrows present the upper limits. The black line represents the best-fit relation based on 1544 quasars taken from the literature76. The gray shaded region denotes the 68th percentile derivation, evaluated by propagating the 1σ uncertainties of the parameters that define the best-fit relation. The αox upper limit of GNz7q (99% confidence level) is estimated after the extinction correction and deviated from the best-fit relation by more than 5σ.
The black and blue circles show the rest-frame UV size measurements in the literature for galaxies49,90 at z > 5.5 and for compact galaxies reported at z ~ 2–3, respectively16,89, but no objects similarly compact and luminous to GNz7q have been identified. The error bar denotes the 1σ measurement uncertainty, and the sources whose errors exceed the measurements are not presented. The dashed line indicates the SFR surface density (ΣSFR) by converting the UV luminosity to SFR111. If the compact UV emission in GNz7q is attributed to the star-forming activity, ΣSFR reaches ≳ 5,000 M⊙ yr−1 kpc−2. Note that the UV luminosity is the observed value, and thus ΣSFR of GNz7q after dust correction will be more extreme in the star-forming scenario.
Left: Observed-frame SED of GNz7q traced by the Spitzer IRAC and MIPS 24 μm bands. The dark blue curve is the best-fit galaxy template (stellar continuum plus nebular emission from ionized gas in Hii regions) constrained at λobs < 10 μm. The thin light blue curves are additional galaxy templates that largely span the galaxy color space at lower redshifts93, and the thicker light blue curves are templates of nearby dusty starbursts M82 and Arp22094. The thick green curves are templates of Type 1 and 2 quasars94, and the brown curve is a composite spectrum of nearby quasars95. The light green curves show the broad-band SEDs of high-redshift quasars at 5 < z < 6.496 interpolated to the redshift of GNz7q. Other than the galaxy fit, all SEDs and templates are normalized to the observed 8 μm flux density of GNz7q. Right: Observed-frame MIR flux ratio diagram for the flux densities at 5.8 μm, 8 μm, and 24 μm as observed for GNz7q and integrated from the SEDs displayed in the left panel. No templates from stars and star formation alone (blue curves and points) can reproduce the flux enhancement at 24 μm (rest-frame 3 μm) of GNz7q, which is fully consistent with the colors of luminous quasars at both low and high redshifts and likely arises from hot dust associated with an active nucleus. The error bars are obtained by propagating the 1σ measurement uncertainty of each photometry.
We show L[CII]/LIR as a function of LIR (a) and ΣLIR (b). For comparison, we also show observational results of local composite systems of AGN and starburst (black square), dusty starbursts at z ~ 0–7 (orange diamond), blue quasars at z ~ 6–7 (blue square), and red quasars at z ~ 3–5 (magenta square) taken from the literature6,42,48,117,122,128,133,134,170. GNz7q is at the extreme end of the relationship painted by known starbursts and quasars. The LIR values of the blue quasars are calculated by assuming the single modified blackbody (Td = 47 K; βd = 1.6), where the blue bar at the bottom left of the left panel shows a potential error scale with a change of Td by ± 10 K from the assumption. For GNz7q, the error bar is obtained by propagating the 1σ uncertainties of L[CII] and LIR.
a–d, We show (a) SFR, (b) Mdust, (c) Mgas, (d) and τdepl. as a function of redshift. For comparison, we also show other galaxy populations with spectroscopic redshifts: blue quasars (blue square), red quasars (magenta circle and shaded region), Lyman-break galaxies (green triangle), and a dusty starburst galaxy (orange circle) that are taken from the literature6,25,136,42,48,85,117,123,137,138,139,140,141,142,143. The magenta shade represents the 68th percentile of the host galaxy properties of the super-Eddington accretion red quasar, W2246−0526, at z = 4.642,141. The host galaxy of GNz7q show the most vigorously star-forming system at z > 7 with the large gas reservoir. The filled and open symbols in c denote Mgas estimates from CO and [C ii] lines, respectively. The error bars of SFR and Mdust are estimated by propagating the 1σ measurement uncertainty and a 0.2-dex uncertainty of the Td assumption, when they are derived from a single submm-mm band (Section 8). The error bars of Mgas and τdepl. are estimated with the 1σ measurement uncertainty and the propagation from both SFR and Mgas uncertainties, respectively. For all populations, the different assumptions of the initial mass function and the dust opacity coefficient among the literature are corrected.
The colour scale and the vertical range of red-shade regions correspond to those of Fig. 3. The red circle and the red-shade regions show the potential MBH range of GNz7q suggested by its faint Lbol and extremely faint X-ray property, respectively. The horizontal range of the red-shade regions indicates the 68th percentile of the Mdyn estimate from the [C ii] line. For comparison, we also present MBH and Mdyn (or Mstar) estimates for blue quasars at z ~ 6–7 (blue squares)47,127,128,146,147,148,150,151 and red quasars at z ~ 2 (magenta circles)132. The error bars denote the 1σ uncertainties taken from the literature. The Mdyn values from the kinematic analysis based on the 3D modeling are shown in the filled blue squares with the 1σ error bars146,147. The Mdyn measurements based on the rotation-disk assumption in the literature are shown by the open blue squares. The best-fit relation for the filled blue squares is shown by the blue line146. The black solid line represents the best-fit relation between the bulge mass and MBH among local quiescent galaxies152. The black dashed line denotes the best-fit relation between the stellar mass of the entire system and MBH among local AGNs153. The shaded regions present the 1σ confidence level for the best-fit relations.
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Fujimoto, S., Brammer, G.B., Watson, D. et al. A dusty compact object bridging galaxies and quasars at cosmic dawn. Nature 604, 261–265 (2022). https://doi.org/10.1038/s41586-022-04454-1