A high black-hole-to-host mass ratio in a lensed AGN in the early Universe.

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth1-3. One of the most intriguing examples is an extremely red, point-like object that was found to be triply imaged by the strong lensing cluster Abell 2744 (ref. 4). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened (AV ≃ 3) broad emission line active galactic nucleus at a redshift of zspec = 7.0451 ± 0.0005. From the width of Hß (full width at half-maximum = 2,800 ± 250 km s-1), we derive a black hole mass of M BH = 4 - 1 + 2 × 1 0 7 M ⊙ . We infer a very high ratio of black-hole-to-galaxy mass of at least 3%, an order of magnitude more than that seen in local galaxies5 and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity (Lbol = (1.1 ± 0.3) × 1045 erg s-1) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black-hole-to-galaxy mass ratio of Abell2744-QSO1 suggest that it may represent the missing link between black hole seeds6 and one of the first luminous quasars7.

A massive compact quiescent galaxy at z = 2 with a complete Einstein ring in JWST imaging.

One of the surprising results from the Hubble Space Telescope was the discovery that many of the most massive galaxies at redshift z ≈ 2 are very compact, having a half-light radius of only 1-2 kpc. The interpretation is that massive galaxies formed inside out, with their cores largely in place by z ≈ 2 and approximately half of their present-day mass added later through minor mergers. Here we present a compact, massive, quiescent galaxy at a photometric redshift of zphot=1.94-0.17+0.13 with a complete Einstein ring. The ring was found in the James Webb Space Telescope COSMOS-Web survey and is produced by a background galaxy at zphot=2.98-0.47+0.42. Its 1.54″ diameter provides a direct measurement of the mass of the 'pristine' core of a massive galaxy, observed before the mixing and dilution of its stellar population during the 10 Gyr of galaxy evolution between z = 2 and z = 0. We find a mass for the lens Mlens=6.5-1.5+3.7×1011 M⊙ within a radius of 6.6 kpc. The stellar mass within the same radius is Mstars=1.1-0.3+0.2×1011 M⊙ for a Chabrier initial mass function and the fiducial dark matter mass is Mdm=2.6-0.7+1.6×1011 M⊙. Additional mass appears to be needed to explain the lensing results, either in the form of a higher-than-expected dark matter density or a bottom-heavy initial mass function.

A population of red candidate massive galaxies ~600 Myr after the Big Bang.

Galaxies with stellar masses as high as roughly 1011 solar masses have been identified1-3 out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 µm. Here we make use of the 1-5 µm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 1010 solar masses) at 7.4 ≤ z ≤ 9.1, 500-700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 1011 solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.

A trail of dark-matter-free galaxies from a bullet-dwarf collision.

The ultra-diffuse galaxies DF2 and DF4 in the NGC 1052 group share several unusual properties: they both have large sizes1, rich populations of overluminous and large globular clusters2-6, and very low velocity dispersions that indicate little or no dark matter7-10. It has been suggested that these galaxies were formed in the aftermath of high-velocity collisions of gas-rich galaxies11-13, events that resemble the collision that created the bullet cluster14 but on much smaller scales. The gas separates from the dark matter in the collision and subsequent star formation leads to the formation of one or more dark-matter-free galaxies12. Here we show that the present-day line-of-sight distances and radial velocities of DF2 and DF4 are consistent with their joint formation in the aftermath of a single bullet-dwarf collision, around eight billion years ago. Moreover, we find that DF2 and DF4 are part of an apparent linear substructure of seven to eleven large, low-luminosity objects. We propose that these all originated in the same event, forming a trail of dark-matter-free galaxies that is roughly more than two megaparsecs long and angled 7° ± 2° from the line of sight. We also tentatively identify the highly dark-matter-dominated remnants of the two progenitor galaxies that are expected11 at the leading edges of the trail.

Quenching of star formation from a lack of inflowing gas to galaxies.

Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old1. Very low amounts of molecular gas seem to be responsible for this, at least in some cases2-7, although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases8-11. Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly2-7, or stacked emission with its problems of averaging8,9. Here we report 1.3 mm observations of dust emission from 6 strongly lensed galaxies where star formation has been quenched, with magnifications of up to a factor of 30. Four of the six galaxies are undetected in dust emission, with an estimated upper limit on the dust mass of 0.0001 times the stellar mass, and by proxy (assuming a Milky Way molecular gas-to-dust ratio) 0.01 times the stellar mass in molecular gas. This is two orders of magnitude less molecular gas per unit stellar mass than seen in star forming galaxies at similar redshifts12-14. It remains difficult to extrapolate from these small samples, but these observations establish that gas depletion is responsible for a cessation of star formation in some fraction of high-redshift galaxies.

A galaxy lacking dark matter.

Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratio Mhalo/Mstars has a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 1010 solar masses) and increases both towards lower masses and towards higher masses. The scatter in this relation is not well known; it is generally thought to be less than a factor of two for massive galaxies but much larger for dwarf galaxies. Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy NGC1052-DF2, which has a stellar mass of approximately 2 × 108 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 108 solar masses. This implies that the ratio Mhalo/Mstars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. NGC1052-DF2 demonstrates that dark matter is not always coupled with baryonic matter on galactic scales.

A massive, quiescent, population II galaxy at a redshift of 2.1.

Unlike spiral galaxies such as the Milky Way, the majority of the stars in massive elliptical galaxies were formed in a short period early in the history of the Universe. The duration of this formation period can be measured using the ratio of magnesium to iron abundance ([Mg/Fe]) in spectra, which reflects the relative enrichment by core-collapse and type Ia supernovae. For local galaxies, [Mg/Fe] probes the combined formation history of all stars currently in the galaxy, including younger and metal-poor stars that were added during late-time mergers. Therefore, to directly constrain the initial star-formation period, we must study galaxies at earlier epochs. The most distant galaxy for which [Mg/Fe] had previously been measured is at a redshift of z ≈ 1.4, with [Mg/Fe] = . A slightly earlier epoch (z ≈ 1.6) was probed by combining the spectra of 24 massive quiescent galaxies, yielding an average [Mg/Fe] = 0.31 ± 0.12 (ref. 7). However, the relatively low signal-to-noise ratio of the data and the use of index analysis techniques for both of these studies resulted in measurement errors that are too large to allow us to form strong conclusions. Deeper spectra at even earlier epochs in combination with analysis techniques based on full spectral fitting are required to precisely measure the abundance pattern shortly after the major star-forming phase (z > 2). Here we report a measurement of [Mg/Fe] for a massive quiescent galaxy at a redshift of z = 2.1, when the Universe was three billion years old. With [Mg/Fe] = 0.59 ± 0.11, this galaxy is the most Mg-enhanced massive galaxy found so far, having twice the Mg enhancement of similar-mass galaxies today. The abundance pattern of the galaxy is consistent with enrichment exclusively by core-collapse supernovae and with a star-formation timescale of 0.1 to 0.5 billion years-characteristics that are similar to population II stars in the Milky Way. With an average past star-formation rate of 600 to 3,000 solar masses per year, this galaxy was among the most vigorous star-forming galaxies in the Universe.

Ubiquitous time variability of integrated stellar populations.

Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

Episodic molecular outflow in the very young protostellar cluster Serpens South.

The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such 'episodic' ejection events have been observed during the class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of the turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a young, class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The (12)C(16)O (J = 2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes--one of the first detectable signs of star formation--which originate from the peak of 1-mm continuum emission. Emission from the surrounding C(18)O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic, accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.

A massive galaxy in its core formation phase three billion years after the Big Bang.

Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes, but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of solar masses per year. The star-forming gas has a velocity dispersion of 317 ± 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z ≈ 2 (refs 8-11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

A substantial population of low-mass stars in luminous elliptical galaxies.

The stellar initial mass function (IMF) describes the mass distribution of stars at the time of their formation and is of fundamental importance for many areas of astrophysics. The IMF is reasonably well constrained in the disk of the Milky Way but we have very little direct information on the form of the IMF in other galaxies and at earlier cosmic epochs. Here we report observations of the Na (I) doublet and the Wing-Ford molecular FeH band in the spectra of elliptical galaxies. These lines are strong in stars with masses less than 0.3M(⊙) (where M(⊙) is the mass of the Sun) and are weak or absent in all other types of stars. We unambiguously detect both signatures, consistent with previous studies that were based on data of lower signal-to-noise ratio. The direct detection of the light of low-mass stars implies that they are very abundant in elliptical galaxies, making up over 80% of the total number of stars and contributing more than 60% of the total stellar mass. We infer that the IMF in massive star-forming galaxies in the early Universe produced many more low-mass stars than the IMF in the Milky Way disk, and was probably slightly steeper than the Salpeter form in the mass range 0.1M(⊙) to 1M(⊙).

A high stellar velocity dispersion for a compact massive galaxy at redshift z = 2.186.

Recent studies have found that the oldest and most luminous galaxies in the early Universe are surprisingly compact, having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This finding has attracted considerable attention, as it suggests that massive galaxies have grown in size by a factor of about five over the past ten billion years (10 Gyr). A key test of these results is a determination of the stellar kinematics of one of the compact galaxies: if the sizes of these objects are as extreme as has been claimed, their stars are expected to have much higher velocities than those in present-day galaxies of the same mass. Here we report a measurement of the stellar velocity dispersion of a massive compact galaxy at redshift z = 2.186, corresponding to a look-back time of 10.7 Gyr. The velocity dispersion is very high at km s(-1), consistent with the mass and compactness of the galaxy inferred from photometric data. This would indicate significant recent structural and dynamical evolution of massive galaxies over the past 10 Gyr. The uncertainty in the dispersion was determined from simulations that include the effects of noise and template mismatch. However, we cannot exclude the possibility that some subtle systematic effect may have influenced the analysis, given the low signal-to-noise ratio of our spectrum.