Galaxy formation and evolution

Abstract:

Context. Feedback processes play a fundamental role in the regulation of the star formation (SF) activity in galaxies and, in particular, in the quenching of early-type galaxies (ETGs) as has been inferred by observational and numerical studies of Λ-CDM models. At z = 0, ETGs exhibit well-known fundamental scaling relations, but the connection between scaling relations and the physical processes shaping ETG evolution remains unknown.

Aims. This work aims to study the impact of the energetic feedback due to active galactic nuclei (AGN) on the formation and evolution of ETGs. We focus on assessing the impact of AGN feedback on the evolution of the mass–plane and the fundamental plane (FP; defined using mass surface density) as well as on morphology, kinematics, and stellar age across the FP.

Methods. The Horizon-AGN and Horizon-noAGN cosmological hydrodynamical simulations were performed with identical initial conditions, including the same physical processes except for the activation of the AGN feedback in the former. We selected a sample of central ETGs from both simulations using the same criteria and exhaustively studied their SF activity, kinematics, and scaling relations for z ≤ 3.

Results. We find that Horizon-AGN ETGs identified at z = 0 follow the observed fundamental scaling relations (mass–plane, FP, and mass–size relation) and qualitatively reproduce kinematic features albeit conserving a rotational inner component with a mass fraction regulated by the AGN feedback. We discover that AGN feedback seems to be required to reproduce the bimodality in the spin parameter distribution reported by observational works and the mass–size relation; more massive galaxies have older stellar populations, larger sizes, and are slower rotators. We study the evolution of the fundamental relations with redshift, finding a mild evolution of the mass–plane of Horizon-AGN ETGs for z <  1, whereas a stronger change is detected for z >  1. The ETGs in Horizon-noAGN show a strong systematic redshift evolution of the mass–plane. The FP of Horizon-AGN ETGs agrees with observations at z = 0. When AGN feedback is switched off, a fraction of galaxies depart from the expected FP at all analysed redshifts owing to the presence of a few extended galaxies with an excess of stellar surface density. We find that AGN feedback regulates the SF activity as a function of stellar mass and redshift being able to reproduce the observed relations. Our results show the impact of AGN feedback on the mass-to-light ratio (M/L) and its relation with the tilt of the luminosity FP (L-FP; defined using the averaged surface brightness). Overall, AGN feedback has an impact on the regulation of the SF activity, size, stellar surface density, stellar ages, rotation, and masses of ETGs that is reflected on the fundamental relations, particularly on the FP. We detect a dependence of the FP on stellar age and galaxy morphology that evolves with redshfit. The characteristics of the galaxy distribution on the FP according to these properties change drastically by z ∼ 1 in Horizon-AGN and hence this feature could provide further insight into the action of AGN feedback.

Abstract:

[Context] The INvestigating Stellar Population In RElics (INSPIRE) is an ongoing project targeting 52 ultra-compact massive galaxies at 0.1 2) through a short and intense star formation burst, and then have evolved passively and undisturbed until the present day. Relics provide a unique opportunity to study the mechanisms of star formation at high-z. [Aims] INSPIRE is designed to spectroscopically confirm and fully characterise a large sample of relics, computing their number density in the redshift window 0.1 < z < 0.5 for the first time, thus providing a benchmark for cosmological galaxy formation simulations. In this paper, we present the INSPIRE Data Release (DR1), comprising 19 systems with observations completed in 2020. [Methods] We use the methods already presented in the INSPIRE Pilot, but revisiting the 1D spectral extraction. For the 19 systems studied here, we obtain an estimate of the stellar velocity dispersion, fitting the two XSH arms (UVB and VIS) separately at their original spectral resolution to two spectra extracted in different ways. We estimate [Mg/Fe] abundances via line-index strength and mass-weighted integrated stellar ages and metallicities with full spectral fitting on the combined (UVB+VIS) spectrum. [Results] For each system, different estimates of the velocity dispersion always agree within the errors. Spectroscopic ages are very old for 13/19 galaxies, in agreement with the photometric ones, and metallicities are almost always (18/19) super-solar, confirming the mass-metallicity relation. The [Mg/Fe] ratio is also larger than solar for the great majority of the galaxies, as expected. We find that ten objects formed more than 75% of their stellar mass (M∗) within 3 Gyr from the big bang and classify them as relics. Among these, we identify four galaxies that had already fully assembled their M∗ by that time and are therefore 'extreme relics' of the ancient Universe. Interestingly, relics, overall, have a larger [Mg/Fe] and a more metal-rich stellar population. They also have larger integrated velocity dispersion values compared to non-relics (both ultra-compact and normal-size) of similar stellar mass. [Conclusions ]The INSPIRE DR1 catalogue of ten known relics is the largest publicly available collection, augmenting the total number of confirmed relics by a factor of 3.3, and also enlarging the redshift window. The resulting lower limit for the number density of relics at 0.17 < z < 0.39 is ρ ∼ 9.1 × 10-8 Mpc-3.CS is supported by an ‘Hintze Fellow’ at the Oxford Centre for Astrophysical Surveys, which is funded through generous support from the Hintze Family Charitable Foundation. CS, CT, FLB, AG, and SZ acknowledge funding from the INAF PRIN-INAF 2020 program 1.05.01.85.11. AFM has received financial support through the Postdoctoral Junior Leader Fellowship Programme from ‘La Caixa’ Banking Foundation (LCF/BQ/LI18/11630007). GD acknowledges support from CONICYT project Basal AFB-170002. DS is a member of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne

Abstract:

We construct a dynamical model of the Milky Way disk from a data set that combines Gaia EDR3 and APOGEE data throughout galactocentric radii in the range 5.0 kpc ≤ R ≤ 19.5 kpc. We make use of the spherically aligned Jeans anisotropic method to model the stellar velocities and their velocity dispersions. Building upon our previous work, our model is now fitted to kinematic maps that have been extended to larger galactocentric radii due to the expansion of our data set, probing the outer regions of the Galactic disk. Our best-fitting dynamical model suggests a logarithmic density slope of αDM = −1.602 ± 0.079syst for the dark matter halo and a dark matter density of ρDM(R⊙) = (8.92 ± 0.56syst) × 10−3 M⊙ pc−3 (0.339 ± 0.022syst GeV cm3). We estimate a circular velocity at the solar radius of vcirc = (234.7 ± 1.7syst) km s−1 with a decline toward larger radii. The total mass density is ρtot(R⊙) = (0.0672 ± 0.0015syst) M⊙ pc−3 with a slope of αtot = −2.367 ± 0.047syst for 5 kpc ≤ R ≤ 19.5 kpc, and the total surface density is Σ(R⊙, ∣z∣ ≤ 1.1 kpc) = (55.5 ± 1.7syst) M⊙ pc−2. While the statistical errors are small, the error budget of the derived quantities is dominated by the three to seven times larger systematic uncertainties. These values are consistent with our previous determination, but the systematic uncertainties are reduced due to the extended data set covering a larger spatial extent of the Milky Way disk. Furthermore, we test the influence of nonaxisymmetric features on our resulting model and analyze how a flaring disk model would change our findings.

Abstract:

The light we observe from distant astrophysical objects including supernovae and quasars allows us to determine large distances in terms of a cosmological model. Despite the success of the standard cosmological model in fitting the data, there remains no underlying explanation for the accelerated expansion and dark matter. Furthermore, there is a current tension between early- and late-universe determinations of the Hubble constant. New techniques may offer the possibility of measuring out to larger distances, provide complementary information, or be able to side-step current limitations. After reviewing in detail the fundamentals of standard cosmology and gravitational lensing, including a derivation of the cosmological lens equation, this thesis investigates a novel method of cosmography based on combining the techniques of strong gravitational lensing time delay measurements and quasar reverberation mapping. The motivation for this method was the possibility of avoiding lens modelling challenges, such as the mass-sheet degeneracy, typically associated with time delay cosmography. It suggested that differential time delays originating from spatially separated signals in the Broad Line Region of a quasar could be distinguished and measured from the spectroscopy of the images, and utilised to provide a ratio of cosmological distances independent of the lensing potential. An analytic description of the effect of the differential lensing on the emission line spectral flux for axisymmetric Broad Line Region geometries is given, with the inclined ring or disk, spherical shell, and double cone as examples. This critical examination shows that the proposed method is unable to recover cosmological information, as the observed time delay and inferred line-of-sight velocity do not uniquely map to the three-dimensional position within the quasar.Comment: PhD Thesis, 191 page