On the Continuous Formation of Field Spheroidal Galaxies in Hierarchical Models of Structure Formation

We re-examine the assembly history of field spheroidals as a potentially powerful discriminant of galaxy formation models. Whereas monolithic collapse and hierarchical, merger-driven, models suggest radically different histories for these galaxies, neither the theoretical predictions nor the observational data for field galaxies have been sufficiently reliable for precise conclusions to be drawn. A major difficulty in interpreting the observations, reviewed here, concerns the taxonomic definition of spheroidals in merger-based models. Using quantitative measures of recent star formation activity drawn from the internal properties of a sample of distant field galaxies in the Hubble Deep Fields, we undertake a new analysis to assess the continuous formation of spheroidal galaxies. Whereas abundances and redshift distributions of modelled spheroidals are fairly insensitive to their formation path, we demonstrate that the distribution and amount of blue light arising from recent mergers provides a more sensitive approach. With the limited resolved data currently available, the rate of mass assembly implied by the observed colour inhomogeneities is compared to that expected in popular Lambda-dominated cold dark matter models of structure formation. These models produce as many highly inhomogeneous spheroidals as observed, but underpredict the proportion of homogeneous, passive objects. We conclude that colour inhomogeneities, particularly when combined with spectroscopic diagnostics for large, representative samples of field spheroidals, will be a more valuable test of their physical assembly history than basic source counts and redshift distributions. Securing such data should be a high priority for the Advanced Camera for Surveys on Hubble Space Telescope.Comment: 14 pages, 7 figures, submitted to MNRA

Hubble Space Telescope Imaging of the CFRS and LDSS Redshift Surveys---III. Field elliptical galaxies at 0.2 < z < 1.0

Surface photometry has been performed on a sample of 46 field elliptical galaxies. These galaxies are described well by a deVaucouleurs R^{1/4} profile. The sample was selected from the combined Canada-France and LDSS redshift surveys and spans the range 0.20 < z < 1.00. The relationship between galaxy half-light radius and luminosity evolves such that a galaxy of a given size is more luminous by Delta M_B=-0.97 \pm 0.14 mag at z=0.92 and the mean rest-frame color shifts blueward by Delta (U-V) =-0.68 \pm 0.11 at z=0.92 relative to the local cluster relations. Approximately 1/3 of these elliptical galaxies exhibit [OII] 3727 emission lines with equivalent widths > 15 angstroms indicating ongoing star formation. Estimated star-formation rates imply that \le 5% of the stellar mass in the elliptical galaxy population has been formed since z=1. We see no evidence for a decline in the space density of early-type galaxies with look-back time. The statistics and a comparison with local luminosity functions are both consistent with the view that the population of massive early-type galaxies was largely in place by z~1. This implies that merging is not required since that time to produce the present-day space density of elliptical galaxies.Comment: 21 pages plus 8 figures plus 5 tables. Accepted by Astrophysical Journa

Using the local density approximation and the LYP, BLYP, and B3LYP functionals within Reference--State One--Particle Density--Matrix Theory

For closed-shell systems, the local density approximation (LDA) and the LYP, BLYP, and B3LYP functionals are shown to be compatible with reference-state one-particle density-matrix theory, where this recently introduced formalism is based on Brueckner-orbital theory and an energy functional that includes exact exchange and a non-universal correlation-energy functional. The method is demonstrated to reduce to a density functional theory when the exchange-correlation energy-functional has a simplified form, i.e., its integrand contains only the coordinates of two electron, say r1 and r2, and it has a Dirac delta function -- delta(r1 - r2) -- as a factor. Since Brueckner and Hartree--Fock orbitals are often very similar, any local exchange functional that works well with Hartree--Fock theory is a reasonable approximation with reference-state one-particle density-matrix theory. The LDA approximation is also a reasonable approximation. However, the Colle--Salvetti correlation-energy functional, and the LYP variant, are not ideal for the method, since these are universal functionals. Nevertheless, they appear to provide reasonable approximations. The B3LYP functional is derived using a linear combination of two functionals: One is the BLYP functional; the other uses exact exchange and a correlation-energy functional from the LDA.Comment: 26 Pages, 0 figures, RevTeX 4, Submitted to Mol. Phy

Heavy quark flavour dependence of multiparticle production in QCD jets

After inserting the heavy quark mass dependence into QCD partonic evolution equations, we determine the mean charged hadron multiplicity and second multiplicity correlators of jets produced in high energy collisions. We thereby extend the so-called dead cone effect to the phenomenology of multiparticle production in QCD jets and find that the average multiplicity of heavy-quark initiated jets decreases significantly as compared to the massless case, even taking into account the weak decay products of the leading primary quark. We emphasize the relevance of our study as a complementary check of $b$-tagging techniques at hadron colliders like the Tevatron and the LHC.Comment: Version revised, accepted for publication in JHEP, 21 pages and 7 figure

The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features -- I. Optical properties

We present a comprehensive study of the nature of the SDSS galaxies divided into various classes based on their morphology, colour, and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, HII, Seyfert, and LINER, returning a total of 16 fine classes of galaxies. We examine the luminosity dependence of seven physical parameters of galaxies in each class. We find that more than half of red early-type galaxies (REGs) have star formation or AGN activity, and that these active REGs have smaller axis ratio and bluer outside compared to the passive REGs. Blue early-type galaxies (BEGs) show structural features similar to those of REGs, but their centres are bluer than REGs. HII BEGs are found to have bluer centres than passive BEGs, but HII REGs have bluer outside than passive REGs. Bulge-dominated late-type galaxies have red colours. Passive red late-types are similar to REGs in several aspects. Most blue late-type galaxies (BLGs) have forming stars, but a small fraction of BLGs do not show evidence for current star formation activity. Differences of other physical parameters among different classes are inspected, and their implication on galaxy evolution is discussed.Comment: 16 pages, 10 tables, 16 figures; accepted for publication in MNRA

The Cosmic Lens All-Sky Survey: statistical strong lensing, cosmological parameters, and global properties of galaxy populations

Extensive analyses of statistical strong gravitational lensing are performed based on the final Cosmic Lens All Sky Survey (CLASS) well-defined statistical sample of flat spectrum radio sources and current estimates of galaxy luminosity functions per morphological type. The analyses are done under the assumption that galactic lenses are well-approximated by singular isothermal ellipsoids and early-type galaxies evolved passively since redshift $z \sim 1$. Depending on how the late-type galaxy population is treated (i.e., whether its characteristic velocity dispersion is constrained or not), we find for a flat universe with a cosmological constant that the present matter fraction of the present critical density $\Omega_{\rm m} = 0.31^{+0.27}_{-0.14}$ (68%) for the unconstrained case or $0.40^{+0.28}_{-0.16}$ (68%) for the constrained case, with an additional systematic uncertainty of $\approx 0.11$ arising from the present uncertainty in the distribution of CLASS sources in redshift and flux density. For a flat universe with a constant equation of state for dark energy w = $p_x$(pressure)/$\rho_x$(energy density), we find that $w < -0.55^{+0.18}_{-0.11}$ (68%) for the unconstrained case or $w < -0.41^{+0.28}_{-0.16}$ (68%) for the constrained case. For the equal frequencies of oblates and prolates, we find that $\sigma_{*}^{(e)} = 198^{+22}_{-18}$ km s$^{-1}$ (68%) for a `steep' $\alpha^{(e)}=-1$ or $\sigma_{*}^{(e)} = 181^{+18}_{-15}$ km s$^{-1}$ (68%) for a `shallow' $\alpha^{(e)}=-0.54$. Finally, from the relative frequencies of doubly-imaged sources and quadruply-imaged sources, we find that a mean projected mass ellipticity of early-type galaxies $\bar{\epsilon}_{\rm mass} = 0.42$ with a 68% lower limit of 0.28. (Abridged)Comment: 31 pages, 12figures, 6 tables, to appear in MNRAS (referee comments incorporated, a section on future prospects added

The morphologies and masses of extremely red galaxies in the Groth Strip survey

We present a new cataloge of EROs from the Groth strip and study the relation between their morphology and mass. We find 102 EROs (F814W-K=>4, K<=21.0), over a survey area of 155 arcmin^2. The photometric data include U,B,F606W,F814W,J,K bands. Morphologies are based on a by eye classification and we distinguish between 3 basic classes: compact objects, targets with a disc and/or a bulge component and irregular or merger candidates. The majority of our targets has either a very compact morphology (33+-6%), or show more or less distinct disc components (41+-6%). 14+-4% are merger or irregulars and 7 objects could not be classified. We also study the dependence of structural parameters on morphological appearance. EROs that are either compact or show a distinct bulge component have smaller median effective radii (1.22+-0.14 kpc and 3.31+-0.53 kpc) than disc dominated (5.50+-0.51 kpc) or possible irregular galaxies or merger candidates (4.92+-0.14 kpc). The Sersic index changes from 2.30+-0.34 and 3.24+-0.55, to 1.03+-0.24 and 1.54+-0.40 respectively. Most the EROs in our sample have redshifts between z=1 and z=2; however, compact EROs in our sample are found at redshifts as low as z=0.4 and as high as z=2.8; the latter qualify as well as DRGs. Disc-like EROs are also found up to z=2.8; however those with a bulge-disc structure are only seen at z<1.5. For each of these EROs we determined the stellar mass and mean population age by fitting synthetic Bruzual (2007) spectra to the SED. Mass estimates were obtained by assuming an exponentially declining star formation rate. Total stellar masses are in the range 9.1<log(M/M_sun)<11.6. We cannot detect significant differences between the stellar mass distribution of the morphological classes. EROs with masses of log(M/M_sun)>11.0 dominantly show compact morphologies, but also include a significant number of sources with a disc morphology.Comment: 21 pages, 17 figures, accepted for publication in MNRA

Witnessing the active assembly phase of massive galaxies since z = 1

We present an analysis of ~60 000 massive (stellar mass M_star > 10^{11} M_sun) galaxies out to z = 1 drawn from 55.2 deg2 of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) and the Sloan Digital Sky Survey (SDSS) II Supernova Survey. This is by far the largest survey of massive galaxies with robust mass estimates, based on infrared (K-band) photometry, reaching to the Universe at about half its present age. We find that the most massive (M_star > 10^{11.5} M_sun) galaxies have experienced rapid growth in number since z = 1, while the number densities of the less massive systems show rather mild evolution. Such a hierarchical trend of evolution is consistent with the predictions of the current semi-analytic galaxy formation model based on Lambda CDM theory. While the majority of massive galaxies are red-sequence populations, we find that a considerable fraction of galaxies are blue star-forming galaxies. The blue fraction is smaller in more massive systems and decreases toward the local Universe, leaving the red, most massive galaxies at low redshifts, which would support the idea of active 'bottom-up' formation of these populations during 0 < z < 1.Comment: Accepted for publication in MNRAS; replaced with revised version (minor changes in results and wordings); MNRAS online early version availabl

Galaxy evolution by color-log(n) type since redshift unity in the Hubble Ultra Deep Field

We explore the use of the color-log(n) plane (where n is the global Sersic index) as a tool for subdividing the high redshift galaxy population in a physically-motivated manner. Using a series of volume-limited samples out to z=1.5 in the Hubble Ultra Deep Field (UDF) we confirm the correlation between color-log(n) plane position and visual morphology observed locally and in other high redshift studies in the color and/or structure domain. Via comparison to a low redshift sample from the Millennium Galaxy Catalogue we quantify evolution by color-log(n) type, accounting separately for the specific selection and measurement biases against each. Specifically, we measure decreases in B-band surface brightness of 1.57 +/- 0.22 mag/sq.arcsec and 1.65 +/- 0.22 mag/sq.arcsec for `blue, diffuse' and `red, compact' galaxies respectively between redshift unity and the present day.Comment: 12 pages, 6 figures, to be published in A&A (accepted 29/10/08

Cosmic Star Formation: Constraints on the Galaxy Formation Models

We study the evolution of the cosmic star formation by computing the luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass density (MD) of galaxies in two reference models of galaxy evolution: the pure luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al. (2002). The former includes a detailed description of the chemical evolution of galaxies of different morphological types with no density evolution; the latter includes the merging histories of the galactic DM haloes, as predicted by the hierarchical clustering scenario, but it does not contain morphological classification nor chemical evolution. We find that at z< 1.5 both models are consistent with the available data on the LD of galaxies in all the considered bands. At high z, the LDs predicted in the PLE model show a peak due to the formation of ellipticals, whereas the SAM predicts a gradual decrease of the star formation and of the LD for z> 2.5. At such redshifts the PLE predictions tend to overestimate the present data in the B band whereas the SAM tends to underestimate the observed UV LD. As for the stellar MD, the PLE picture predicts that nearly 50% and 85% of the present stellar mass are in place at z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit the observed MD up to z=1. At z>1, the PLE model and the SAM tend to overestimate and underestimate the observed values, respectively. We discuss the origin of the above model results, and the role of observational uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA