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We illustrate the extraordinary potential of the (far-IR) Origins Survey Spectrometer (OSS) on board the Origins Space Telescope (OST) to address a variety of open issues on the co-evolution of galaxies and AGNs. We present predictions for blind surveys, each of 1000 h, with different mapped areas (a shallow survey covering an area of 10 deg2 and a deep survey of 1 deg2) and two different concepts of the OST/OSS: with a 5.9m telescope (Concept 2, our reference configuration) and with a 9.1 m telescope (Concept 1, previous configuration). In 1000 h, surveys with the reference concept will detect from ~ 1.9 × 106 to ~ 8.7 × 106 lines from ~ 4.8 × 105-2.7 × 106 star-forming galaxies and from ~ 1.4 × 104 to ~ 3.8 × 104 lines from ~ 1.3 × 104-3.5 × 104 AGNs. The shallow survey will detect substantially more sources than the deep one; the advantage of the latter in pushing detections to lower luminosities/higher redshifts turns out to be quite limited. The OST/OSS will reach, in the same observing time, line fluxes more than one order of magnitude fainter than the SPICA/SMI and will cover a much broader redshift range. In particular it will detect tens of thousands of galaxies at z ≥ 5, beyond the reach of that instrument. The polycyclic aromatic hydrocarbons lines are potentially bright enough to allow the detection of hundreds of thousands of star-forming galaxies up to z ~ 8.5, i.e. all the way through the re-ionization epoch. The proposed surveys will allow us to explore the galaxy-AGN co-evolution up to z ~ 5.5 - 6 with very good statistics. OST Concept 1 does not offer significant advantages for the scientific goals presented here.

We investigate the constraints provided by the Euclid space observatory on the physical properties of dusty star-forming galaxies (DSFGs) at |$z\gtrsim 1.5$| detected in wide area submillimetre surveys with Herschel. We adopt a physical model for the high- z progenitors of spheroidal galaxies, which form the bulk of DSFGs at |$z\gtrsim 1.5$|⁠. We improve the model by combining the output of the equations of the model with a formalism for the spectral energy distribution (SED). After optimizing the SED parameters to reproduce the measured infrared luminosity function and number counts of DFSGs, we simulated a sample of DSFGs over 100  |$\hbox{deg}^2$| and then applied a |$5\, \sigma$| detection limit of |$37\,$|  mJy at 250  |$\mu$| m. We estimated the redshifts from the Euclid data and then fitted the Euclid + Herschel photometry with the code CIGALE to extract the physical parameters. We found that 100 per cent of the Herschel galaxies are detected in all 4 Euclid bands above |$3\, \sigma$|⁠. For 87 per cent of these sources the accuracy on |$1 + z$| is better than 15 per cent. The sample comprises mostly massive, i.e. |$\log (M_{\star }/{\rm M}_{\odot })\sim 10.5{\!-\!}12.9$|⁠ , highly star forming, i.e. |$\log (\hbox{SFR}/{\rm M}_{\odot }\hbox{yr}^{-1})\sim 1.5{\!-\!}4$|⁠ , dusty, i.e. |$\log (M_{\rm dust}/{\rm M}_{\odot })\sim 7.5{\!-\!}9.9$|⁠ , galaxies. The measured stellar masses have a dispersion of 0.19 dex around the true value, thus showing that Euclid will provide reliable stellar mass estimates for the majority of the bright DSFGs at |$z\gtrsim 1.5$| detected by Herschel. We also explored the effect of complementing the Euclid photometry with that from the Vera C. Rubin Observatory/LSST. [ABSTRACT FROM AUTHOR]

The assessment of the relationship between radio continuum luminosity and star formation rate (SFR) is of crucial importance to make reliable predictions for the forthcoming ultradeep radio surveys and to allow a full exploitation of their results to measure the cosmic star formation history. We have addressed this issue by matching recent accurate determinations of the SFR function up to high redshifts with literature estimates of the 1.4 GHz luminosity functions of star-forming galaxies (SFGs). This was done considering two options, proposed in the literature, for the relationship between the synchrotron emission (Lsynch), that dominates at 1.4 GHz, and the SFR:a linear relation with a decline of the Lsynch/SFR ratio at lowluminosities or a mildly non-linear relation at all luminosities. In both cases, we get good agreement with the observed radio luminosity functions but, in the non-linear case, the deviation from linearity must be small. The luminosity function data are consistent with a moderate increase of the Lsynch/SFR ratio with increasing redshift, indicated by other data sets, although a constant ratio cannot be ruled out. A stronger indication of such increase is provided by recent deep 1.4-GHz counts, down to µJy levels. This is in contradiction with models predicting a decrease of that ratio due to inverse Compton cooling of relativistic electrons at high redshifts. Synchrotron losses appear to dominate up to z Σ 5. We have also updated the Massardi et al. evolutionary model for radio loud AGNs. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation of the cosmological evolution of the luminosity function of galaxies and active galactic nuclei (AGNs) in the infrared (IR). Based on the observed dichotomy in the ages of stellar populations of early-type galaxies on one side and late-type galaxies on the other, the model interprets the epoch-dependent luminosity functions at z ⩾ 1.5 using a physical approach for the evolution of proto-spheroidal galaxies and of the associated AGNs, while IR galaxies at z < 1.5 are interpreted as being mostly late-type "cold" (normal) and "warm" (starburst) galaxies. As for proto-spheroids, in addition to the epoch-dependent luminosity functions of stellar and AGN components separately, we have worked out, for the first time, the evolving luminosity functions of these objects as a whole (stellar plus AGN component), taking into account in a self-consistent way the variation with galactic age of the global spectral energy distribution. The model provides a physical explanation for the observed positive evolution of both galaxies and AGNs up to z ≃ 2.5 and for the negative evolution at higher redshifts, for the sharp transition from Euclidean to extremely steep counts at (sub-)millimeter wavelengths, as well as the (sub-)millimeter counts of strongly lensed galaxies that are hard to account for by alternative, physical or phenomenological, approaches. The evolution of late-type galaxies and z < 1.5 AGNs is described using a parametric phenomenological approach. The modeled AGN contributions to the counts and to the cosmic infrared background (CIB) are always sub-dominant. They are maximal at mid-IR wavelengths: the contribution to the 15 and 24μm counts reaches 20% above 10 and 2 mJy, respectively, while the contributions to the CIB are of 8.6% and of 8.1% at 15μm and 24μm, respectively. The model provides a good fit to the multi-wavelength (from the mid-IR to millimeter waves) data on luminosity functions at different redshifts and on number counts (both global and per redshift slices). A prediction of the present model, useful to test it, is a systematic variation with wavelength of the populations dominating the counts and the contributions to the CIB intensity. This implies a specific trend for cross-wavelength CIB power spectra, which is found to be in good agreement with the data. [ABSTRACT FROM AUTHOR]

We present a new evolutionary model that describes the population properties of radio sources at frequencies ≲5 GHz, thus complementing the De Zotti et al. model, holding at higher frequencies. We find that simple analytic luminosity evolution is still sufficient to fit the wealth of available data on local luminosity functions, multifrequency source counts and redshift distributions. However, the fit requires a luminosity-dependent decline of source luminosities at high redshifts, at least for steep-spectrum sources, thus confirming earlier indications of a ‘downsizing’ also for radio sources. The upturn of source counts at sub-mJy levels is accounted for by a straightforward extrapolation, using the empirical far-infrared (far-IR)/radio correlation, of evolutionary models matching the far-IR counts and redshift distributions of star-forming galaxies. We also discuss the implications of the new model for the interpretation of data on large-scale clustering of radio sources and on the integrated Sachs–Wolfe (ISW) effect, and for the investigation of the contribution of discrete sources to the extragalactic background. As for the ISW effect, a new analysis, exploiting a very clean cosmic microwave background map, yields at a substantially higher significance than reported before. [ABSTRACT FROM AUTHOR]

We present the first far-infrared luminosity function in the AKARI Deep Field South, a premier deep field of the AKARI Space Telescope, using spectroscopic redshifts obtained with AAOmega. To date, we have found spectroscopic redshifts for 389 galaxies in this field and have measured the local (z<0.25) 90 μm luminosity function using about one-third of these redshifts. The results are in reasonable agreement with recent theoretical predictions. [ABSTRACT FROM PUBLISHER]