Explore the vast range of titles available.

Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old 1 . Very low amounts of molecular gas seem to be responsible for this, at least in some cases 2 – 7 , although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases 8 – 11 . Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly 2 – 7 , or stacked emission with its problems of averaging 8 , 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 redshifts 12 – 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. The authors report 1.3 mm observations of dust emission from strongly lensed galaxies where star formation is quenched, demonstrating that gas depletion is responsible for the cessation of star formation in some high-redshift galaxies.

We have entered an era where the gas mass estimates of distant galaxies do not rely on a single tracer but rather on an inventory of different and independent methods, much like the case for the determination of the star formation rate (SFR) of the galaxies. This is crucial as the traditional M gas tracers, i.e. low-J CO transition lines and dust continuum emission are becoming highly uncertain as we move to higher redshifts due to metallicity and CMB effects. Here, we present a homogeneous and statistically significant investigation of the use of atomic carbon as an alternative M gas tracer (Valentino et al. 2018) and provide evidence of optically thick far-IR emission in high− z starbursts that point towards higher dust temperatures and lower dust and gas mass estimates than previously inferred (Cortzen et al. 2019, submitted). Finally, we present direct observations of the effect of the CMB on the far-IR SEDs of high-z SBs, manifested by unphyscally large (β = 2.5–3.5) apparent spectral indexes in R-J tail (Jin et al. 2019, submitted).

Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018 that brought together scientists working on different aspects of emission line simulations, in order to share knowledge and discuss the methodology. Emission lines across the spectrum from the millimeter to the UV were discussed, with most of the focus on the interstellar medium, but also some topics on the circumgalactic medium. The most important quality of a useful model is a good synergy with observations and experiments. Challenges in simulating line emission are identified, some of which are already being worked upon, and others that must be addressed in the future for models to agree with observations. Recent advances in several areas aiming at achieving that synergy are summarized here, from micro-physical to galactic and circum-galactic scale.

When the Universe was just 3 billion years old, half of the most massive galaxies had already ceased star formation, and such a galaxy has now been observed using gravitational lensing, unexpectedly turning out to be a compact, fast-spinning disk galaxy rather than a proto-bulge galaxy. Dead disk galaxy formed by incoming gas When the Universe was only three billion years old, half of the most massive galaxies were already 'dead', meaning that few new stars would form in them. It is believed that these galaxies grew into the massive local elliptical galaxies seen today. Sune Toft et al . report an analysis of a galaxy that has been strongly gravitationally lensed. This means that they can observe spatial scales that are far smaller than those accessible by any other means. They find that, surprisingly, the galaxy is a fast-spinning disk and that its stars formed in situ rather than in a nuclear starburst. They conclude that the gas out of which the stars formed was accreted from outside the galaxy in cold streams of gas. At redshift z  = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation 1 , 2 , 3 , 4 . It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions 5 , 6 , but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies 7 . Here we report an analysis of the stellar populations and kinematics of a lensed z  = 2.1478 compact galaxy, which—surprisingly—turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst 8 . The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo 9 . This result confirms previous indirect indications 10 , 11 , 12 , 13 that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

Using a combination of deep MID-IR observations obtained by IRAC, MIPS and IRS on board Spitzer we investigate the MID-IR properties of Lyman Break Galaxies (LBGs) at z~3, establish a better understanding of their nature and attempt a complete characterisation of the population. With deep mid-infrared and optical observations of ~1000 LBGs covered by IRAC/MIPS and from the ground respectively, we extend the spectral energy distributions (SEDs) of the LBGs to mid-infrared. Spitzer data reveal for the first time that the mid-infrared properties of the population are inhomogeneous ranging from those with marginal IRAC detections to those with bright rest-frame near-infrared colors and those detected at 24μm MIPS band revealing the newly discovered population of the Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity, we examine the photometric properties of the population and we use stellar population synthesis models to probe the stellar content of these galaxies. We find that a fraction of LBGs have very red colors and large estimated stellar masses M∗>5×1010M⊙. We discuss the link between these LBGs and submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7 μm emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01.

Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. This finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars. Using JWST, more than 40 individual stars have been detected in a distant galaxy, dating back to when the Universe was only half of its current age. The stars appear to be red (super)giants that are magnified by factors of hundreds.

At z=2, when the Universe was just 3 Gyr old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation1–4. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions5,6, but validating this scenario requires higher resolution observations of their centers than currently possible, even from space. Magnification due to gravitational lensing offers a unique opportunity to resolve their inner regions, as demonstrated in a recent study of a z=2.6 compact spheroidal galaxy which revealed a bulge, rotating at velocities comparable to the fastest rotating local ellipticals7. Following the same approach, here we map the stellar populations and kinematics of a lensed z=2.1478 compact galaxy, which surprisingly turn out to be a fast spinning, rotationally supported disk galaxy. Rather than in a merger-driven nuclear starburst8, its stars must thus have formed in a disk, likely fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo9. This result unambiguously confirm indications from a growing body of indirect evidence10–13 that the first galaxies to cease star formation must go through major changes not just in their structure, but also in their kinematics to evolve into present day ellipticals.

When the Universe was just 3 billion years old, half of the most massive galaxies had already ceased star formation, and such a galaxy has now been observed using gravitational lensing, unexpectedly turning out to be a compact, fast-spinning disk galaxy rather than a proto-bulge galaxy.

We report the spectroscopic confirmation of the background source of the most distant Einstein ring known to date, the COSMOS-Web ring. This system consists of a complete Einstein ring at \\(z=5.1\\), lensed by a massive early-type galaxy at \\(z\\sim2\\). The redshift \\(z=5.1043\\pm0.0004\\) is unambiguously identified with our NOEMA and Keck/MOSFIRE spectroscopy, where the NOEMA observations reveal the CO(4-3) and CO(5-4) lines at \\(>8\\,\\sigma\\), and the MOSFIRE data detect [O\\textsc{ii}] at \\(\\sim 6\\,\\sigma\\). Using multi-wavelength photometry spanning near-infrared to radio bands, we find that the lensed galaxy is a dust-obscured starburst (\\(M_{\\star} \\sim 1.8\\times10^{10}\\,{\\rm M_{\\odot}}\\), \\({\\rm SFR_{IR}\\sim 60\\,{\\rm M_{\\odot}} ~yr^{-1}}\\)) with high star-formation efficiency (gas depletion time \\(\\tau_{\\rm dep}<100~\\)Myr) as indicated by the [C\\textsc{i}](1-0) non-detection. The redshift confirmation revalidates that the total lens mass budget within the Einstein radius is fully accounted for by the stellar and dark matter components, without the need of modifying the initial mass function or dark matter distribution profile. This work paves the way for detailed studies and future follow-ups of this unique lensing system, providing an ideal laboratory for studying mass distribution at \\(z\\sim2\\) and physical conditions of star formation at \\(z\\sim5\\).

Strong gravitational magnification by massive galaxy clusters enable us to detect faint background sources, resolve their detailed internal structures, and in the most extreme cases identify and study individual stars in distant galaxies. Highly magnified individual stars allow for a wide range of applications, including studies of stellar populations in distant galaxies and constraining small-scale dark matter structures. However, these applications have been hampered by the small number of events observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of 46 significant microlensed stars in a single strongly-lensed high-redshift galaxy behind the Abell 370 cluster at redshift of 0.725 when the Universe was half of its current age (dubbed the ``Dragon arc''), based on two observations separated by one year with the James Webb Space Telescope (ıt JWST). These events are mostly found near the expected lensing critical curves, suggesting that these are magnified individual stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry and colors, we constrain stellar types and find that many of them are consistent with red giants/supergiants magnified by factors of thousands. This finding reveals an unprecedented high occurrence of microlensing events in the Dragon arc, and proves that ıt JWST's time-domain observations open up the possibility of conducting statistical studies of high-redshift stars and subgalactic scale perturbations in the lensing dark matter field.