We study the evolution of the scaling relations between the maximum circular velocity, stellar mass and optical half-light radius of star-forming disc-dominated galaxies in the context of Λ cold dark ...matter-based galaxy formation models. Using data from the literature combined with new data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) and All-wavelength Extended Groth Strip International Survey (AEGIS) surveys, we show that there is a consistent picture for the evolution of these scaling relations from z∼ 2 to z= 0, both observationally and theoretically. The evolution of the observed stellar scaling relations is weaker than that of the virial scaling relations of dark matter haloes, which can be reproduced, both qualitatively and quantitatively, with a simple, cosmologically motivated model for disc evolution inside growing Navarro-Frenk-White dark matter haloes. In this model optical half-light radii are smaller, both at fixed stellar mass and at maximum circular velocity, at higher redshifts. This model also predicts that the scaling relations between baryonic quantities (baryonic mass, baryonic half-mass radii and maximum circular velocity) evolve even more weakly than the corresponding stellar relations. We emphasize, though, that this weak evolution does not imply that individual galaxies evolve weakly. On the contrary, individual galaxies grow strongly in mass, size and velocity but in such a way that they move largely along the scaling relations. Finally, recent observations have claimed surprisingly large sizes for a number of star-forming disc galaxies at z≃ 2, which has caused some authors to suggest that high-redshift disc galaxies have abnormally high spin parameters. However, we argue that the disc scalelengths in question have been systematically overestimated by a factor of ∼2 and that there is an offset of a factor of ∼1.4 between Hα sizes and optical sizes. Taking these effects into account, there is no indication that star-forming galaxies at high redshifts (z≃ 2) have abnormally high spin parameters.
There is a large observational scatter toward low velocities in the stellar mass Tully-Fisher (TF) relation if disturbed and compact objects are included. However, this scatter can be eliminated if ...one replaces rotation velocity with S{sub 0.5}, a quantity that includes a velocity dispersion term added in quadrature with the rotation velocity. In this work, we use a large suite of hydrodynamic N-body galaxy merger simulations to explore a possible mechanism for creating the observed relations. Using mock observations of the simulations, we test for the presence of observational effects and explore the relationship between S{sub 0.5} and intrinsic properties of the galaxies. We find that galaxy mergers can explain the scatter in the TF as well as the tight S{sub 0.5}-stellar mass relation. Furthermore, S{sub 0.5} is correlated with the total central mass of a galaxy, including contributions due to dark matter.
In the standard picture of disc galaxy formation, baryons and dark matter receive the same tidal torques, and therefore approximately the same initial specific angular momentum. However, observations ...indicate that disc galaxies typically have only about half as much specific angular momentum as their dark matter haloes. We argue this does not necessarily imply that baryons lose this much specific angular momentum as they form galaxies. It may instead indicate that galaxies are most directly related to the inner regions of their host haloes, as may be expected in a scenario where baryons in the inner parts of haloes collapse first. A limiting case is examined under the idealized assumption of perfect angular momentum conservation. Namely, we determine the density contrast Δ, with respect to the critical density of the Universe, by which dark matter haloes need to be defined in order to have the same average specific angular momentum as the galaxies they host. Under the assumption that galaxies are related to haloes via their characteristic rotation velocities, the necessary Δ is ∼600. This Δ corresponds to an average halo radius and mass which are ∼60 per cent and ∼75 per cent, respectively, of the virial values (i.e. for Δ= 200). We refer to this radius as the radius of baryonic collapse R
BC, since if specific angular momentum is conserved perfectly, baryons would come from within it. It is not likely a simple step function due to the complex gastrophysics involved; therefore, we regard it as an effective radius. In summary, the difference between the predicted initial and the observed final specific angular momentum of galaxies, which is conventionally attributed solely to angular momentum loss, can more naturally be explained by a preference for collapse of baryons within R
BC, with possibly some later angular momentum transfer.
The shutdown of star formation in galaxies is generally termed "quenching." This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy ...structural parameters such as stellar mass (M sub(*)), M sub(*)/r sub(e), surface stellar mass density (~M sub(*)/r super(2) sub(e)), and Sersic index (n). We analyze the rest-frame U-B color correlations versus these structural parameters using a sample of galaxies in the redshift range 0.5 < or =, slant z < 0.8 from the DEEP2/AEGIS survey. We assess the tightness of the color relationships by measuring their "overlap regions," defined as the area in color-parameter space in which red and blue galaxies overlap; the parameter that minimizes these overlap regions is considered to be the most effective color discriminator. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass buildup.
We present photometrically calibrated images and surface photometry in the B, V, R, J, H, and K bands of 25, and in the g, r, and K bands of five nearby bright (BT super(0) < 12.5 mag) spiral ...galaxies with inclinations of 30-65 spanning the Hubble sequence from Sa to Scd. Data are from The Ohio State University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the Sloan Digital Sky Survey Second Data Release. Radial surface brightness profiles are extracted, and integrated magnitudes are measured from the profiles. Axis ratios, position angles, and scale lengths are measured from the near-infrared images. A one-dimensional bulge/disk decomposition is performed on the near-infrared images of galaxies with a nonnegligible bulge component, and an exponential disk is fit to the radial surface brightness profiles of the remaining galaxies.
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 ≤ z ≤ 2.5 with star formation rates of SFR ∼ 100 M {sub ☉} yr{sup –1} and ...masses of log(M/M {sub ☉}) ∼10.8. Their high integrated gas velocity dispersions of σ{sub int} =230{sub −30}{sup +40} km s{sup –1}, as measured from emission lines of Hα and O III, and the resultant M {sub *}-σ{sub int} relation and M {sub *}-M {sub dyn} all match well to those of compact quiescent galaxies at z ∼ 2, as measured from stellar absorption lines. Since log(M {sub *}/M {sub dyn}) =–0.06 ± 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13{sub −13}{sup +17}%), and present larger σ{sub int} than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than ∼300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z ≳ 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z ∼ 2.
The 'Eagle' galaxy at a redshift of 0.77 is studied with the Oxford Short Wavelength Integral Field Spectrograph (SWIFT) and multiwavelength data from the All-wavelength Extended Groth strip ...International Survey (AEGIS). It was chosen from AEGIS because of the bright and extended emission in its slit spectrum. 3D kinematic maps of the Eagle reveal a gradient in velocity dispersion which spans 35-75 ± 10 km s−1 and a rotation velocity of 25 ± 5 km s−1 uncorrected for inclination. Hubble Space Telescope images suggest it is close to face-on. In comparison with galaxies from AEGIS at similar redshifts, the Eagle is extremely bright and blue in the rest-frame optical, highly star forming, dominated by unobscured star formation and has a low metallicity for its size. This is consistent with its selection. The Eagle is likely undergoing a major merger and is caught in the early stage of a starburst when it has not yet experienced metal enrichment or formed the mass of dust typically found in star-forming galaxies.
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