The far infra-red SEDs of main sequence and starburst galaxies

We compare observed far infra-red/sub-millimetre (FIR/sub-mm) galaxy spectral energy distributions (SEDs) of massive galaxies ($M_{\star}\gtrsim10^{10}$ $h^{-1}$M$_{\odot}$) derived through a stacking analysis with predictions from a new model of galaxy formation. The FIR SEDs of the model galaxies are calculated using a self-consistent model for the absorption and re-emission of radiation by interstellar dust based on radiative transfer calculations and global energy balance arguments. Galaxies are selected based on their position on the specific star formation rate (sSFR) - stellar mass ($M_{\star}$) plane. We identify a main sequence of star-forming galaxies in the model, i.e. a well defined relationship between sSFR and $M_\star$, up to redshift $z\sim6$. The scatter of this relationship evolves such that it is generally larger at higher stellar masses and higher redshifts. There is remarkable agreement between the predicted and observed average SEDs across a broad range of redshifts ($0.5\lesssim z\lesssim4$) for galaxies on the main sequence. However, the agreement is less good for starburst galaxies at $z\gtrsim2$, selected here to have elevated sSFRs$>10\times$ the main sequence value. We find that the predicted average SEDs are robust to changing the parameters of our dust model within physically plausible values. We also show that the dust temperature evolution of main sequence galaxies in the model is driven by star formation on the main sequence being more burst-dominated at higher redshifts.Comment: 20 pages, 13 figures. Accepted to MNRA

Clustering, host halos and environment of z∼\sim2 galaxies as a function of their physical properties

Using a sample of 25683 star-forming and 2821 passive galaxies at $z\sim2$, selected in the COSMOS field following the BzK color criterion, we study the hosting halo mass and environment of galaxies as a function of their physical properties. Spitzer and Herschel provide accurate SFR estimates for starburst galaxies. We measure the auto- and cross-correlation functions of various galaxy sub-samples and infer the properties of their hosting halos using both an HOD model and the linear bias at large scale. We find that passive and star-forming galaxies obey a similarly rising relation between the halo and stellar mass. The mean host halo mass of star forming galaxies increases with the star formation rate between 30 and 200 M$_\odot$.yr$^{-1}$, but flattens for higher values, except if we select only main-sequence galaxies. This reflects the expected transition from a regime of secular co-evolution of the halos and the galaxies to a regime of episodic starburst. We find similar large scale biases for main-sequence, passive, and starburst galaxies at equal stellar mass, suggesting that these populations live in halos of the same mass. We detect an excess of clustering on small scales for passive galaxies and showed, by measuring the large-scale bias of close pairs, that this excess is caused by a small fraction ($\sim16$) of passive galaxies being hosted by massive halos ($\sim 3 \times 10^{13}$ M$_\odot$) as satellites. Finally, extrapolating the growth of halos hosting the z$\sim$2 population, we show that M$_\star \sim 10^{10}$ M$_\odot$ galaxies at z$\sim$2 will evolve, on average, into massive (M$_\star \sim 10^{11}$ M$_\odot$), field galaxies in the local Universe and M$_\star \sim 10^{11}$ M$_\odot$ galaxies at z=2 into local, massive, group galaxies. The most massive main-sequence galaxies and close pairs of massive, passive galaxies end up in today's clusters.Comment: 18 pages, 16 figures, Accepted by A&

Towards a new modelling of gas flows in a semi-analytical model of galaxy formation and evolution

We present an extended version of the semi-analytical model, GalICS. Like its predecessor, eGalICS applies a post-treatment of the baryonic physics on pre-computed dark-matter merger trees extracted from an N-body simulation. We review all the mechanisms that affect, at any given time, the formation and evolution of a galaxy in its host dark-matter halo. We mainly focus on the gas cycle from the smooth cosmological accretion to feedback processes. To follow this cycle with high accuracy we introduce some novel prescriptions: i) a smooth baryonic accretion with two phases: a cold mode and a hot mode built on the continuous dark-matter accretion. In parallel to this smooth accretion, we implement the standard photoionisation modelling to reduce the input gas flow on the smallest structures. ii) a complete monitoring of the hot gas phase. We compute the evolution of the core density, the mean temperature and the instantaneous escape fraction of the hot atmosphere by considering that the hot gas is in hydrostatic equilibrium in the dark-matter potential well, and by applying a principle of conservation of energy on the treatment of gas accretion, supernovae and super massive black hole feedback iii) a new treatment for disc instabilities based on the formation, the migration and the disruption of giant clumps. The migration of such clumps in gas-rich galaxies allows to form pseudo-bulges. The different processes in the gas cycle act on different time scales, and we thus build an adaptive time-step scheme to solve the evolution equations. The model presented here is compared in detail to the observations of stellar-mass functions, star formation rates, and luminosity functions, in a companion paper

Galaxy stellar mass assembly: the difficulty matching observations and semi-analytical predictions

Semi-analytical models (SAMs) are currently the best way to understand the formation of galaxies within the cosmic dark-matter structures. While they fairly well reproduce the local stellar mass functions, correlation functions and luminosity functions, they fail to match observations at high redshift (z > 3) in most cases, particularly in the low-mass range. The inconsistency between models and observations indicates that the history of gas accretion in galaxies, within their host dark-matter halo, and the transformation of gas into stars, are not well followed. Hereafter, we briefly present a new version of the GalICS semi-analytical model. We explore the impacts of classical mechanisms, such as supernova feedback or photoionization, on the evolution of the stellar mass assembly. Even with a strong efficiency, these two processes cannot explain the observed stellar mass function and star formation rate distribution and some other relations. We thus introduce an ad-hoc modification of the standard paradigm, based on the presence of a \textit{no-star-forming} gas component, and a concentration of the star-forming gas in galaxy discs. The main idea behind the existence of the no-star-forming gas reservoir is that only a fraction of the total gas mass in a galaxy is available to form stars. The reservoir generates a delay between the accretion of the gas and the star formation process. This new model is in much better agreement with the observations of the stellar mass function in the low-mass range than the previous models, and agrees quite well with a large set of observations, including the redshift evolution of the specific star formation rate. However, it predicts a large fraction of no-star-forming baryonic gas, potentially larger than observed, even if its nature has still to be examined in the context of the missing baryon problem

Panchromatic Study of the First Galaxies with Large ALMA Programs

Thanks to deep optical to near-IR imaging and spectroscopy, significant progress is made in characterizing the rest-frame UV to optical properties of galaxies in the early universe (z > 4). Surveys with Hubble, Spitzer, and ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and photometric redshifts, measurements of the spatial structure, stellar masses, and optical emission lines for large samples of galaxies. Recently, the Atacama Large (Sub) Millimeter Array (ALMA) has become a major player in pushing studies of high redshift galaxies to far-infrared wavelengths, hence making panchromatic surveys over many orders of frequencies possible. While past studies focused mostly on bright sub-millimeter galaxies, the sensitivity of ALMA now enables surveys like ALPINE, which focuses on measuring the gas and dust properties of a large sample of normal main-sequence galaxies at z > 4. Combining observations across different wavelengths into a single, panchromatic picture of galaxy formation and evolution is currently and in the future an important focus of the astronomical community.Comment: 4 pages, 2 figures. Submitted to Proceedings IAU Symposium No. 341, 201

A GIANT LY alpha NEBULA IN THE CORE OF AN X-RAY CLUSTER AT Z=1.99 : IMPLICATIONS FOR EARLY ENERGY INJECTION

We present the discovery of a giant >= 100 kpc Ly alpha nebula detected in the core of the X-ray emitting cluster CL J1449 +0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Lya nebulae and overdense regions of the universe to the dense core of a 5-7 x 10(13) M-circle dot cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly alpha to X-ray luminosity ratio (L-Ly alpha/L-X approximate to 0.3, greater than or similar to 10-1000 times. higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly alpha-emitting gas and the possible interplay with the X-ray phase, we argue that the Ly alpha nebula would be short-lived (less than or similar to 10 Myr) if not continuously replenished with cold gas at a rate of greater than or similar to 1000 M-circle dot yr(-1). We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of approximate to 2 keV per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds. of the mass, while the rest is supplied by supernovae-driven winds.Peer reviewe

The Main Sequences of Star-Forming Galaxies and Active Galactic Nuclei at High Redshift

We provide a novel, unifying physical interpretation on the origin, the average shape, the scatter, and the cosmic evolution for the main sequences of starforming galaxies and active galactic nuclei at high redshift z $\gtrsim$ 1. We achieve this goal in a model-independent way by exploiting: (i) the redshift-dependent SFR functions based on the latest UV/far-IR data from HST/Herschel, and re- lated statistics of strong gravitationally lensed sources; (ii) 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 AGN bolometric luminosity functions at different redshifts via the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data are consistently interpreted in terms of an in situ coevolution scenario for star formation and black hole accretion, envisaging these as local, time coordinated processes

Illuminating the Dark Side of Cosmic Star Formation II. A second date with RS-NIRdark galaxies in COSMOS

About 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled the environment with stars, metals and dust. How efficient was this process? How fast did these primordial galaxies form stars and dust? We can answer these questions by tracing the Star Formation Rate Density (SFRD) back to its widely unknown high redshift tail, traditionally observed in the Near-InfraRed (NIR), Optical and UV bands. Thus, the objects with a high amount of dust were missing. We aim to fill this knowledge gap by studying Radio Selected NIR-dark (\textit{RS-NIRdark}) sources, i.e. sources not having a counterpart at UV-to-NIR wavelengths. We widen the sample by Talia et al. (2021) from 197 to 272 objects in the COSMic evolution Survey (COSMOS) field, including also photometrically contaminated sources, previously excluded. Another important step forward consists in the visual inspection of each source in the bands from u* to MIPS-24$\mu$m. According to their "environment" in the different bands, we are able to highlight different cases of study and calibrate an appropriate photometric procedure for the objects affected by confusion issues. We estimate that the contribution of RS-NIRdark to the Cosmic SFRD at 3$<$z$<$5 is $\sim$10--25$\%$ of that based on UV-selected galaxies

Overcoming Confusion Noise with Hyperspectral Imaging from PRIMAger

The PRobe far-Infrared Mission for Astrophysics (PRIMA) concept aims to perform mapping with spectral coverage and sensitivities inaccessible to previous FIR space telescopes. PRIMA's imaging instrument, PRIMAger, provides unique hyperspectral imaging simultaneously covering 25-235 $\mu$m. We synthesise images representing a deep, 1500 hr deg$^{-2}$ PRIMAger survey, with realistic instrumental and confusion noise. We demonstrate that we can construct catalogues of galaxies with a high purity ($>95$ per cent) at a source density of 42k deg$^{-2}$ using PRIMAger data alone. Using the XID+ deblending tool we show that we measure fluxes with an accuracy better than 20 per cent to flux levels of 0.16, 0.80, 9.7 and 15 mJy at 47.4, 79.7, 172, 235 $\mu$m respectively. These are a factor of $\sim$2 and $\sim$3 fainter than the classical confusion limits for 72-96 $\mu$m and 126-235 $\mu$m, respectively. At $1.5 \leq z \leq 2$, we detect and accurately measure fluxes in 8-10 of the 10 channels covering 47-235 $\mu$m for sources with $2 \leq$ log(SFR) $\leq 2.5$, a 0.5 dex improvement on what might be expected from the classical confusion limit. Recognising that PRIMager will operate in a context where high quality data will be available at other wavelengths, we investigate the benefits of introducing additional prior information. We show that by introducing even weak prior flux information when employing a higher source density catalogue (more than one source per beam) we can obtain accurate fluxes an order of magnitude below the classical confusion limit for 96-235 $\mu$m.Comment: 14 pages, 11 figure