Galaxy formation and evolution

Abstract:

We predict the evolution of the radio continuum sky at 1.4 GHz from the Horizon-AGN Adaptive Mesh Refinement (AMR) cosmological hydrodynamical simulation of a cubic volume of the Universe 100h−1 Mpc on a side. With empirically motivated models for the radio continuum emission due to both star formation and Active Galactic Nuclei (AGN), we estimate the contribution of each of these processes to the local radio continuum luminosity function (LF) and describe its evolution up to redshift 4. Despite the simplicity of these models, we find that our predictions for the local luminosity function are fairly consistent with Mauch & Sadler (2007) observations, with the faint end of the luminosity function dominated by star forming galaxies and the bright end by radio loud AGNs. At redshift one, a decent match to Smolcic et al. (2009) VLA data in the COSMOS field can only be achieved when we account for radio continuum emission from AGNs. We predict that the strongest evolution across the peak epoch of cosmic activity happens for low luminosity star forming galaxies L1.4GHz < 1022 W Hz−1 , whose contribution rises until z ∼ 2 and declines at higher redshifts. The contribution of low luminosity AGNs L1.4GHz < 1022 W Hz−1 steadily declines from z = 0 throughout the redshift range, whilst that of radio loud objects with luminosities in the range 1022 W Hz−1 < L1.4GHz < 1024 W Hz−1 rises dramatically until z = 4. Finally, high-luminosity radio loud AGNs, with L1.4GHz > 1024 W Hz−1 show surprisingly little evolution from z = 0 to z = 4.

Abstract:

We present a series of results from a clustering analysis of the first data release of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey. VIDEO is the only survey currently capable of probing the bulk of stellar mass in galaxies at redshifts corresponding to the peak of star formation on degree scales. Galaxy clustering is measured with the two-point correlation function, which is calculated using a non-parametric kernel-based density estimator. We use our measurements to investigate the connection between the galaxies and the host dark matter halo using a halo occupation distribution methodology, deriving bias, satellite fractions, and typical host halo masses for stellar masses between 10 9.35 and 10 10.85 M ⊙ , at redshifts 0.5 < z < 1.7. Our results show typical halo mass increasing with stellar mass (with moderate scatter) and bias increasing with stellar mass and redshift consistent with previous studies. We find that the satellite fraction increased towards low redshifts, from ~5 per cent at z ~ 1.5 to ~20 per cent at z ~ 0.6. We combine our results to derive the stellar mass-to-halo mass ratio for both satellites and centrals over a range of halo masses and find the peak corresponding to the halo mass with maximum star formation efficiency to be ~2 × 10 12 M ⊙ , finding no evidence for evolution.

Abstract:

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. We report a tight linear relation between the H i circular velocity measured at 6 R e and the stellar velocity dispersion measured within 1 R e for a sample of 16 early-type galaxies with stellar mass between 1010 and 1011 M ⊙ . The key difference from previous studies is that we only use spatially resolved v circ (H i) measurements obtained at large radius for a sizeable sample of objects. We can therefore link a kinematical tracer of the gravitational potential in the dark-matter dominated outer regions of galaxies with one in the inner regions, where baryons control the distribution of mass. We find that v circ (H i)= 1.33 σ e with an observed scatter of just 12 per cent. This indicates a strong coupling between luminous and dark matter from the inner- to the outer regions of early-type galaxies, analogous to the situation in spirals and dwarf irregulars. The v circ (H i)-σ e relation is shallower than those based on v circ measurements obtained from stellar kinematics and modelling at smaller radius, implying that v circ declines with radius - as in bulge-dominated spirals. Indeed, the value of v circ (H i) is typically 25 per cent lower than the maximum v circ derived at ~0.2 R e from dynamical models. Under the assumption of power-law total density profiles ρ ∝ r -γ , our data imply an average logarithmic slope 〈γ〉 = 2.18 ± 0.03 across the sample, with a scatter of 0.11 around this value. The average slope and scatter agree with recent results obtained from stellar kinematics alone for a different sample of early-type galaxies.