Massive Optically Dark Galaxies Unveiled by JWST Challenge Galaxy Formation Models

Over the past decade, the existence of a substantial population of optically invisible, massive galaxies at $z\gtrsim3$ has been implied from mid-infrared to millimeter observations. With the unprecedented sensitivity of the JWST, such extremely massive galaxy candidates have immediately been identified even at $z>7$, in much larger numbers than expected. These discoveries raised a hot debate. If confirmed, early, high-mass galaxies challenge the current models of galaxy formation. However, the lack of spectroscopic confirmations leads to uncertain stellar mass ($M_{\star}$) estimates, and the possible presence of active galactic nuclei (AGN) adds further uncertainty. Here, we present the first sample of 36 dust-obscured galaxies with robust spectroscopic redshifts at $z_{\rm spec}=5-9$ from the JWST FRESCO survey. The three most extreme sources at $z\sim5-6$ ($\sim$1 billion years after the Big Bang) are so massive (log$M_{\star}/M_{\odot}$ $\gtrsim11.0$) that they would require, on average, about 50% of the baryons in their halos to be converted into stars -- two to three times higher than even the most efficient galaxies at later times. The extended emission of these galaxies suggests limited contribution by AGN. This population of ultra-massive galaxies accounts for 20% of the total cosmic star formation rate density at $z\sim5-6$, suggesting a substantial proportion of extremely efficient star formation in the early Universe.Comment: Submitted to Nature. 22 pages, 4 main figures, 7 supplementary figures, 3 supplementary tables. Comments are welcom

Dusty Star-Forming Galaxies at High Redshift

Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10$^{13}$ L$_{\odot}$ with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars. When summed up, all of the dusty, star-forming galaxies in the Universe produce an infrared radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at ultraviolet and optical wavelengths. The bulk of this infrared extragalactic background light emanates from galaxies as diverse as gas-rich disks to mergers of intense starbursting galaxies. Major advances in far-infrared instrumentation in recent years, both space-based and ground-based, has led to the detection of nearly a million DSFGs, yet our understanding of the underlying astrophysics that govern the start and end of the dusty starburst phase is still in nascent stage. This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the best-understood subset (submillimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain et al., 2002), but also the selection and characterization of more recently discovered DSFG populations. We review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.Comment: 154 pages, 49 figures; Invited review article accepted for publication in Physics Report

Star formation across cosmic time with radio surveys. The promise of the SKA

This lecture briefly reviews the major recent advances in radio astronomy made possible by ultra-deep surveys, reaching microJansky flux density levels. A giant step forward in many fields, including the study of the evolution of the cosmic star formation history is expected with the advent of the Square Kilometer Array (SKA).Comment: 28 pages, 3 figures, to be published in the Proceedings of the 3rd Cosmology School in Cracow, July 201

Unveiling the inner morphology and gas kinematics of NGC 5135 with ALMA

Active galactic nuclei are thought to play a major role in the formation and evolution of galaxies, providing mechanisms for feedback from the supermassive black hole (SMBH) to its hosting galaxy and the intergalactic medium. In co-evolutionary scenarios, the SMBH properties are strictly connected to those of the host galaxy, in either high redshift quasars and in local Seyfert nuclei. Local Seyfert galaxies hosting both SMBHs and star forming regions, can be considered as the nearest counterparts of high redshift sub-mm heavily dust obscured star forming galaxies, where a significant fraction of the optical and UV photons are absorbed by dust are re-emitted in the IR and sub-mm bands. In the absence of major merging events and companions, the mechanisms that link the star formation (SF) and the accretion onto the black hole (BH) lie in the inner galactic regions (within ~1 kpc from the BH) and are responsible for the feeding of the BH and the quenching of the SF through feedback mechanisms from the BH itself. On the one hand, high resolution observations in the sub-mm band suggest that feeding might happen through the formation of bars at the inner end of the spiral galactic arms. On the other hand, outflows from the SMBHs have been observed and seem to be responsible for halting the gas infall and the SF in the inner galactic regions. Fuelling and outflows seem to constitute a self-regulating combination of processes on the small scales that determine the galaxy morphology and dynamics. How the small scales dynamics influences the overall galaxy morphology, what is the timescale on which different processes happen, and if the different evolutionary stages justify the different observed morphologies, are still open questions. This thesis project develops within the above astrophysical context, with the main goal of studying the morphology, the kinematics and the physical processes at play in the inner regions of the nearby Seyfert 2 galaxy NGC 5135 with ALMA

High-redshift Dusty Star-Forming Galaxies: a panchromatic approach to constrain massive galaxy evolution

The goal of this thesis is to investigate the early stages of massive galaxy evolution by defining an overall view of their physical properties combining the information extracted by all the details of their spectral behaviour. To this aim, I focused on the population of Dusty Star-Forming Galaxies at the Cosmic Noon ($zsim 2$). In my thesis project, I first deal with the modelling of the spatially-averaged time evolution of galaxy baryonic components, namely gas, stars, metals and dust, on the basis of a simple but effective approach that allows to solve analytically the equations that describe their evolution. Contrariwise to most of the analytic models on the market, the one developed during this PhD thesis self-consistently compute the metal and dust enrichment histories of the cold gas and stellar mass using as input the solutions for the evolution of the mass components. The solutions are coupled to specific prescriptions for parameter setting (inspired by extit{in-situ} galaxy-black hole co-evolution) and merger rates (based on numerical simulations) and, as such, reproduce the main statistical relationships followed by high-z massive star-forming galaxies and local ellipticals, that are thought to be their quiescent counterparts at $zsim0$. The analytic solutions are then exploited to interpret the spatially-averaged astrophysical properties of a pilot sample of (sub-)millimeter selected Dusty Star-Forming Galaxies in the multi-wavelength GOODS-S field and spectroscopically confirmed to be at the peak of Cosmic Star Formation History. Ultimately, they are used to disentangle the main physical processes regulating the evolution of these galaxies. The study highlights the importance of multi-wavelength broad-band and spectroscopic data to constrain dusty galaxy evolution at high-z and their role in the formation of spheroids, along with the need of a complete theoretical scenario that allows to self-consistently interpret the outcomes obtained from observational analyses. One possible framework is the one provided by the extit{in-situ} scenario for galaxy-black hole co-evolution, that has been used in this work to interpret the reconstructed panchromatic view combining spatially integrated (i.e. galaxy age, Star Formation Rate, stellar mass, dust mass, dust attenuation), spatially resolved (multi-wavelength sizes) and spectral (i.e. molecular gas content, kinematics and AGN/stellar driven outflows) properties of the aforementioned pilot sample of DSFG. The analysis is performed under specific requirements (e.g. spectroscopic measurement of galaxy redshift, complete sampling of galaxy multi-band emission) in order to unbiasedly constrain galaxy integral properties by performing an energy-balanced fit of the SED from the UV/optical to the radio band, including also galaxy X-ray emission, with the Code Investigating GALaxy Emission. Galaxy optical, far-infrared and radio sizes are measured from continuum maps at the highest spatial resolution currently available ($Delta hetalesssim1$ arcsec). CO spectral emission lines are extracted from publicly available data cubes in the Atacama Large Millimeter/sub-millimeter Array Archive and allow to measure the molecular gas content and to disentangle between a disk dominated configuration of the gaseous component and molecular outflows possibly driven by the central active nucleus. The multiple pieces of information coming from such a panchromatic study offer a clear description of the properties of individual galaxies and, once each of them is inscribed in the evolutionary context, offer a general view of the evolutionary mechanisms

Dusty Star-Forming Galaxies and Supermassive Black Holes at High Redshifts: In- Situ Coevolution

We have exploited the continuity equation approach and the star-formation timescales derived from the observed \u2018main sequence\u2019 relation ( Star Formation Rate vs Stellar Mass), to show that the observed high abundance of galaxies with stellar masses 73 a few 10^10 M 99 at redshift z 73 4 implies the existence of a galaxy population featuring large star formation rates (SFRs) \u3c8 > 73 10^2 M 99 yr^ 121 in heavily dust-obscured conditions. These galaxies constitute the high-redshift counterparts of the dusty star-forming population already surveyed for z 72 3 in the Far-InfraRed (FIR) band by the Herschel space observatory. We work out specific predictions for the evolution of the corresponding stellar mass and SFR functions out to z 3c 10, elucidating that the number density at z 72 8 for SFRs \u3c8 73 30 M 99 yr^ 121 cannot be estimated relying on the UltraViolet (UV) luminosity function alone, even when standard corrections for dust extinction based on the UV slope are applied. We compute the number counts and redshift distributions (including galaxy-scale gravitational lensing) of this galaxy population, and show that current data from AzTEC-LABOCA, SCUBA-2 and ALMA-SPT surveys are already digging into it. We substantiate how an observational strategy based on a color preselection in the far-IR or (sub-)mm band with Herschel and SCUBA-2, supplemented by photometric data via on-source observations with ALMA, can allow to reconstruct the bright end of the SFR functions out to z 72 8. In parallel, such a challenging task can be managed by exploiting current UV surveys in combination with (sub-)mm observations by ALMA and NIKA2. The same could be done with radio observations by SKA and its precursors. In particular we have worked out predictions for the radio counts of star-forming galaxies down to nJy levels, along with redshift distributions down to the detection limits of the phase 1 Square Kilometer Array MID telescope (SKA1-MID) and of its precursors. To do that we exploited our SFR functions with relations between SFR and radio (synchrotron and free-free) emission. Our results show that the deepest SKA1- MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower com- pared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys. We finally provide a novel, unifying physical interpretation on the origin, the aver- age shape, the scatter, and the cosmic evolution for the main sequences (MS) of star- forming galaxies and active galactic nuclei at high redshift z 73 1. We achieve this goal in a model-independent way by exploiting the redshift-dependent SFR functions, and the deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and active galactic nucleus (AGN) bolometric luminosity functions at different redshifts via, again, the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data strongly support a scenario of in situ coevolution for star formation and black hole accretion, envisaging these as local, time coordinated processes

A radio view on the structural evolution of massive star-forming galaxies across cosmic time

It is not well understood what processes regulate the global formation of stars in galaxies throughout cosmic history. My work aims to measure the structural evolution of star-forming galaxies (SFGs), from the present back to when the Universe was ten percent of its current age. I focus on the population of massive SFGs with a total stellar mass that is one to ten times that of the Milky Way. I investigate possible differences in physical processes that regulate star formation throughout cosmic history, to address why typical massive galaxies in the early Universe formed stars an order of magnitude more intensely than today. I analyze observations at sub-millimeter-to-radio wavelengths of a large sample of 3184 massive SFGs in the COSMOS field. I inspect the spatial distribution of star formation (traced by radio continuum emission) in galaxies of the sample, and investigate how their molecular gas content (traced by carbon monoxide line emission) affected the star formation activity. I find that over the past 10 Gyr (redshift I present detailed studies of two massive SFGs in the very early Universe (12.5 Gyr ago, redshift = 4.5) that show extended, gas-rich disks with very high star formation rates and elevated star formation efficiencies, similar to that observed in present-day, merger-driven starbursts. Apparently, at these early epochs, strong gas accretion from the intergalactic medium fed unstable, gas-rich disks that broke into giant clumps that formed stars at high rates. I also show that in the very early Universe, the high star formation rate of satellite galaxies around massive SFGs drove large-scale outflows, which prevented further gas accretion and thus might have suppressed star formation in such companion galaxies. I conclude that throughout most of cosmic history, star formation in typical massive SFGs was primarily regulated by the smooth accretion of cold gas from the intergalactic medium, which sustained steady star formation activity in extended, rotating disks. The more intense star formation in early galaxies resulted from their larger gas reservoirs, which were distributed across fragmenting, gravitationally unstable disks. In this respect, the stellar birthrate and star formation efficiency of typical massive SFGs in the early Universe were similar to those observed in local, merger-driven (maximal) starbursts