Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

We review the properties of the established Scaling Relations (SRs) of galaxies and active galactic nuclei (AGN), focusing on their origin and expected evolution back in time, providing a short history of the most important progresses obtained up to now and discussing the possible future studies. We also try to connect the observed SRs with the physical mechanisms behind them, examining to what extent current models reproduce the observational data. The emerging picture clarifies the complexity intrinsic to the galaxy formation and evolution process as well as the basic uncertainties still affecting our knowledge of the AGN phenomenon. At the same time, however, it suggests that the detailed analysis of the SRs can profitably contribute to our understanding of galaxies and AGN.

The post-Herschel view of intrinsic AGN emission: constructing templates for galaxy and AGN emission at IR wavelengths

ABSTRACT Measuring the star-forming properties of active galactic nucleus (AGN) hosts is key to our understanding of galaxy formation and evolution. However, this topic remains debated, partly due to the difficulties in separating the infrared (i.e. 1–1000 ${\rm \mu m}$) emission into AGN and star-forming components. Taking advantage of archival far-infrared data from Herschel, we present a new set of AGN and galaxy infrared templates and introduce the spectral energy distribution fitting code iragnsep. Both can be used to measure infrared host galaxy properties, free of AGN contamination. To build these, we used a sample of 100 local (z < 0.3), low-to-high luminosity AGNs (i.e. Lbol$\ \sim \ 10^{42-46}$ erg s−1), selected from the 105-month Swift–BAT X-ray survey, which have archival Spitzer–IRS spectra and Herschel photometry. We first built a set of seven galaxy templates using a sample of 55 star-forming galaxies selected via infrared diagnostics. Using these templates, combined with a flexible model for the AGN contribution, we extracted the intrinsic infrared emission of our AGN sample. We further demonstrate that we can reduce the diversity in the intrinsic shapes of AGN spectral energy distributions down to a set of three AGN templates, of which two represent AGN continuum, and one represents silicate emission. Our results indicate that, on average, the contribution of AGNs to the far-infrared (λ ≳ 50 ${\rm \mu m}$) is not as high as suggested by some recent work. We further show that the need for two infrared AGN continuum templates could be related to nuclear obscuration, where one of our templates appears dominated by the emission of the extended polar dust.

3-3-1 Self interacting dark matter and the galaxy core-cusp problem

The core–cusp problem remains a challenging discrepancy between observations and simulations in the standard [Formula: see text]CDM model for the formation of galaxies. The problem is that [Formula: see text]CDM simulations predict a steep power-law mass density profile at the center of galactic dark matter halos. However, observations of dwarf galaxies in the Local Group reveal a density profile consistent with a nearly flat distribution of dark matter near the center. A number of solutions to this dilemma have been proposed. Here, we summarize investigations into the possibility that the dark matter particles themselves self interact and scatter. Such self-interacting dark matter (SIDM) particles can smooth out the dark-matter profile in high-density regions. We also review the theoretical proposal that self-interacting dark matter may arise as an additional Higgs scalar in the 3–3–1 extension of the Standard Model (SM). We present new simulations of galaxy formation and evolution for this formulation of self-interacting dark matter. Current constraints on this self-interacting dark matter are then summarized.

Are Ly α emitters segregated in protoclusters regions?

ABSTRACT The presence of neutral hydrogen in the interstellar medium (ISM) and intergalactic medium (IGM) induces radiative transfer (RT) effects on $\rm {Ly}\,\alpha$ photons that affect the observability of Lyman alpha emitters (LAEs). We use the galform semi-analytic model of galaxy formation and evolution to analyse how these effects shape the spatial distribution of LAEs with respect to $\rm {H}\,\alpha$ emitters (HAEs) around high-density regions at high redshift. We find that when a large sample of protoclusters is considered, HAEs showing also $\rm {Ly}\,\alpha$ emission (HAEs + LAEs) populate the same regions as those that do not display the $\rm {Ly}\,\alpha$ line at $z$ = 2.2. We compare against the protocluster USS1558-003, one of the most massive protoclusters located at $z$ = 2.53. Our results indicate that the strong depletion of HAEs + LAEs present in the high-density regions of USS1558-003 may be due to cosmic variance. We find that at $z$ = 2.2 and $z$ = 3.0, RT of the ISM produces a strong decline (30–50 per cent) of the clustering amplitude of HAEs + LAEs with respect to HAEs towards the protoclusters centre. At $z$ = 5.7, given the early evolutionary state of protoclusters and galaxies, the clustering of HAEs + LAEs has a smaller variation (10–20 per cent) towards the protoclusters centre. Depending on the equivalent width and luminosity criteria of the emission-line galaxy sample, the IGM can have a mild or a null effect on galaxy properties and clustering in high-density regions.

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: exploring the halo occupation distribution model for emission line galaxies

ABSTRACT We study the modelling of the halo occupation distribution (HOD) for the eBOSS DR16 emission line galaxies (ELGs). Motivated by previous theoretical and observational studies, we consider different physical effects that can change how ELGs populate haloes. We explore the shape of the average HOD, the fraction of satellite galaxies, their probability distribution function (PDF), and their density and velocity profiles. Our baseline HOD shape was fitted to a semi-analytical model of galaxy formation and evolution, with a decaying occupation of central ELGs at high halo masses. We consider Poisson and sub/super-Poissonian PDFs for satellite assignment. We model both Navarro–Frenk–White and particle profiles for satellite positions, also allowing for decreased concentrations. We model velocities with the virial theorem and particle velocity distributions. Additionally, we introduce a velocity bias and a net infall velocity. We study how these choices impact the clustering statistics while keeping the number density and bias fixed to that from eBOSS ELGs. The projected correlation function, wp, captures most of the effects from the PDF and satellites profile. The quadrupole, ξ2, captures most of the effects coming from the velocity profile. We find that the impact of the mean HOD shape is subdominant relative to the rest of choices. We fit the clustering of the eBOSS DR16 ELG data under different combinations of the above assumptions. The catalogues presented here have been analysed in companion papers, showing that eBOSS RSD+BAO measurements are insensitive to the details of galaxy physics considered here. These catalogues are made publicly available.

SMASHing the low surface brightness SMC

ABSTRACT The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended stellar structure of the SMC using deep colour–magnitude diagrams, obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from Milky Way (MW) foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ‘conservative’ approach from which we calculated the general parameters of the SMC, finding a staggered surface brightness profile. We also traced the fainter outskirts by constructing a stellar density profile. This approach, based on stellar counts of the oldest main-sequence turn-off stars, uncovered a tidally disrupted stellar feature that reaches as far out as 12 deg from the SMC centre. We also serendipitously found a faint feature of unknown origin located at ∼14 deg from the centre of the SMC and that we tentatively associated with a more distant structure. We compared our results to in-house simulations of a 1 × 109 M⊙ SMC, finding that its elliptical shape can be explained by its tidal disruption under the combined presence of the MW and the Large Magellanic Cloud. Finally, we found that the older stellar populations show a smooth profile while the younger component presents a jump in the density followed by a flat profile, confirming the heavily disturbed nature of the SMC.

[O ii] emitters in MultiDark-Galaxies and DEEP2

ABSTRACT We use three semi-analytical models (SAMs) of galaxy formation and evolution run on the same 1 h−1 Gpc MultiDark Planck2 cosmological simulation to investigate the properties of [O ii] emission line galaxies at redshift z ∼ 1. We compare model predictions with different observational data sets, including DEEP2–firefly galaxies with absolute magnitudes. We estimate the [O ii] luminosity ($L{\left[\rm{O\,{\small II}}\right]}$) of our model galaxies using the public code get_ emlines , which ideally assumes as input the instantaneous star formation rates (SFRs). This property is only available in one of the SAMs under consideration, while the others provide average SFRs, as most models do. We study the feasibility of inferring galaxies’ $L{\left[\rm{O\,{\small II}}\right]}$ from average SFRs in post-processing. We find that the result is accurate for model galaxies with dust attenuated $L{\left[\rm{O\,{\small II}}\right]}$ ≲ 1042.2 erg s−1 ($\lt 5{{\ \rm per\ cent}}$ discrepancy). The galaxy properties that correlate the most with the model $L{\left[\rm{O\,{\small II}}\right]}$ are the SFR and the observed-frame u and g broad-band magnitudes. Such correlations have r-values above 0.64 and a dispersion that varies with $L{\left[\rm{O\,{\small II}}\right]}$ . We fit these correlations with simple linear relations and use them as proxies for $L{\left[\rm{O\,{\small II}}\right]}$ , together with an observational conversion that depends on SFR and metallicity. These proxies result in [O ii] luminosity functions and halo occupation distributions with shapes that vary depending on both the model and the method used to derive $L{\left[\rm{O\,{\small II}}\right]}$ . The amplitude of the clustering of model galaxies with $L{\left[\rm{O\,{\small II}}\right]}$ >1040.4 erg s−1 remains overall unchanged on scales above 1 $\, h^{-1}$ Mpc, independently of the $L{\left[\rm{O\,{\small II}}\right]}$ computation.

Light Speed Expansion and Rotation of a Very Dark Machian Universe Having Internal Acceleration

We present a Machian model of Quantum Cosmology with full dark matter and light speed expansion and rotation. During galaxy formation and evolution, fraction of dark matter transforms to visual matter with a relation of the form, m_vis = constant * (m_dark)^2/3. Using this relation and replacing MOND’s ‘critical acceleration’ with “current cosmic maximum angular acceleration”, galactic flat rotation speed range of (50 to 500) km/sec can be fitted well. Estimated flat rotation speeds of DD168, Milky Way and UGC12591 are 49.96 km/sec, 199.66 km/sec and 521.75 km/sec respectively. Based on these striking coincidences, it is possible to say that, MOND’s approach is implicitly connected with cosmological estimation of 95% invisible matter. Considering galactic total matter and current cosmic maximum angular acceleration, galactic working radii, angular velocity and visual matter density can be estimated. Even though, this model is free from ‘big bang’, ‘inflation’, ‘dark energy’, ‘flatness’ and ‘red shift’ issues, at 2.722 K, estimated present Hubble parameter is 66.24 km/sec/Mpc, cosmic radius is 146.3 times the Hubble radius, angular velocity is 146.3 times lower than the Hubble parameter and cosmic age is 146.3 times the Hubble age. With future observations and advanced telescopes, it may be possible to see far distant galaxies and very old stars far beyond the current observable cosmic radius.