118372419
The number density and mass density of star-forming and quiescent galaxies at 0.4 ≤ z ≤ 2.2
We study the buildup of the bimodal galaxy population using the NEWFIRM Medium-Band Survey, which provides excellent redshifts and well-sampled spectral energy distributions of {approx}27, 000 galaxies with K 3 x 10{sup 10} M{sub sun} increases by a factor of {approx}10 from z {approx} 2 to the present day, whereas the mass density in star-forming galaxies is flat or decreases over the same time period. Modest mass growth by a factor of {approx}2 of individual quiescent galaxies can explain roughly half of the strong density evolution at masses >10{sup 11} M{sub sun}, due to the steepness of the exponential tail of the mass function. The rest of the density evolution of massive, quiescent galaxies is likely due to transformation (e.g., quenching) of the massive star-forming population, a conclusion which ismore » consistent with the density evolution we observe for the star-forming galaxies themselves, which is flat or decreasing with cosmic time. Modest mass growth does not explain the evolution of less massive quiescent galaxies ({approx}10{sup 10.5} M{sub sun}), which show a similarly steep increase in their number densities. The less massive quiescent galaxies are therefore continuously formed by transforming galaxies from the star-forming population.« less
15420113
The NEWFIRM Medium-Band Survey : Filter Definitions and First Results
Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-frame optical, and have transformed our understanding of the early Universe. As the vast majority of K- or IRAC-selected galaxies are too faint for spectroscopy, the interpretation of these surveys relies almost exclusively on photometric redshifts determined from fitting templates to the broadband photometry. The best-achieved accuracy of these redshifts, Δz/(1 + z) 0.06 at z > 1.5, is sufficient for determining the broad characteristics of the galaxy population but not for measuring accurate rest-frame colors, stellar population parameters, or the local galaxy density. We have started a near-infrared imaging survey with the NEWFIRM camera on the Kitt Peak 4-m telescope to greatly improve the accuracy of photometric redshifts in the range 1.5 z 3.5. The survey uses five medium-bandwidth filters, which provide crude "spectra" over the wavelength range 1-1.8 μm for all objects in the 27.6' × 27.6' NEWFIRM field. In this first paper, we illustrate the technique by showing medium-band NEWFIRM photometry of several galaxies at 1.7 1.5 in the COSMOS and AEGIS fields. The filter set also enables efficient selection of exotic objects such as high-redshift quasars, galaxies dominated by emission lines, and very cool brown dwarfs; we show that late T and candidate Y dwarfs could be identified using only two of the filters.
18936230
Galaxy Evolution and Environment
The properties of galaxies are strongly correlated with their environment, with red galaxies dominating galaxy clusters and blue galaxies dominating the general field. However, not all field galaxies are young: studies of the colors, line strengths, and M/L ratios of massive early-type galaxies at 0<z<1.3 show that the most massive galaxies do not seem to care about their surroundings, and have very similar ages irrespective of their environment. There is good evidence that the growth of these galaxies does continue longer in the field than in clusters, via (nearly) dissipationless mergers of already old galaxies. These results are consistent with predictions of recent galaxy formation models, which incorporate AGN feedback to suppress star formation in the most massive halos. Systematic studies of the relation of galaxies with their environment beyond z=1 are difficult, and still somewhat contradictory. Intriguingly both the DEEP2 and VVDS surveys find that the color-density relation disappears at z~1.3, unfortunately just at the point where both surveys become highly incomplete. On the other hand, clustering studies at z~2.5 have shown that red galaxies cluster more strongly than blue galaxies, implying that the color-density relation was already in place at that redshift.
14432445
Detection of quiescent galaxies in a bicolor sequence from z=0-2
We investigate the properties of quiescent and star-forming galaxy populations to z ~ 2 with purely photometric data, employing a novel rest-frame color-selection technique. From the UKIDSS Ultra-Deep Survey Data Release 1, with matched optical and mid-infrared photometry taken from the Subaru-XMM Deep Survey and Spitzer Wide-Area Infrared Extragalactic Survey, respectively, we construct a K-selected galaxy catalog and calculate photometric redshifts. Excluding stars, objects with uncertain z phot solutions, those that fall in bad or incomplete survey regions, and those for which reliable rest-frame colors could not be derived, 30,108 galaxies with K 2 for this sample, but we show that MIPS 24 μm data suggest that a significant population of quiescent galaxies exists even at these higher redshifts. At z = 1-2, the most luminous objects in the sample are divided roughly equally between star-forming and quiescent galaxies, while at lower redshifts most of the brightest galaxies are quiescent. Moreover, quiescent galaxies at these redshifts are clustered more strongly than those actively forming stars, indicating that galaxies with early-quenched star formation may occupy more massive host dark matter halos. This suggests that the end of star formation is associated with, and perhaps brought about by, a mechanism related to halo mass.
17850887
A Near-Infrared Spectroscopic Survey of K-Selected Galaxies at z ~ 2.3: Redshifts and Implications for Broadband Photometric Studies
Using the Gemini Near-Infrared Spectrograph (GNIRS), we have completed a near-infrared spectroscopic survey for -->K-bright galaxies at -->z ~ 2.3 selected from the MUSYC survey. We derived spectroscopic redshifts from emission lines or from continuum features and shapes for all 36 observed galaxies. The continuum redshifts are driven by the Balmer/4000 A break and have an uncertainty in -->Δ z/(1 + z) of Δ z/(1 + z) . The systematic error can be reduced by using optimal templates and deep photometry; the random error, however, will be hard to reduce below 5%. The spectra lead to significantly improved constraints for stellar population parameters. For most quantities this improvement is about equally driven by the higher spectral resolution and by the much reduced redshift uncertainty. Properties such as the age, -->AV, current star formation rate, and the star formation history are generally very poorly constrained with broadband data alone. Interestingly, stellar masses and mass-to-light ratios are among the most stable parameters from broadband data. Nevertheless, photometric studies may overestimate the number of massive galaxies at -->2 z = 2-3.
119110006
The Diminishing Importance of Major Galaxy Mergers at Higher Redshifts
Using mass-selected galaxy samples from deep multiwavelength data we investigate the incidence of close galaxy pairs between z = 0.4 and 2. Many such close pairs will eventually merge, and the pair fraction is therefore related to the merger rate. Over this redshift range the mean pair fraction is essentially constant (evolving as f pair ~ (1 + z)–0.4 ± 0.6) with about 6% ± 1% of massive galaxies having a 1: 4 or greater companion within 30 h –1 kpc. Assuming the timescale over which pairs merge is not a strong function of redshift, this implies a similarly constant merger rate (per unit time) out to z = 2. Since about three times as much cosmic time passes at z < 1 as between z = 1 and 2, this implies that correspondingly more mergers occur in the low-redshift universe. When minor companions (1:10 mass ratio or greater) are included, the pair fraction increases to ~20% and still does not evolve strongly with redshift. We also use a rest-frame color criterion to select pairs containing only quiescent galaxies (major "dry merger" progenitors), and find them to be similarly rare and constant with 4%-7% of massive quiescent galaxies exhibiting a nearby companion. Thus, even though other studies find major mergers to be relatively uncommon since z = 1, our results suggest that few additional mergers occur in the 1 < z < 2 range and other mechanisms may be required to explain the mass and size growth of galaxies over this epoch.
15847137
Physical unitarity for massive non-Abelian gauge theories in the Landau gauge: Stueckelberg and Higgs
We discuss the problem of unitarity for Yang-Mills theory in the Landau gauge with a mass term a la Stuckelberg. We assume that the theory (non-renormalizable) makes sense in some subtraction scheme (in particular the Slavnov-Taylor identities should be respected!) and we devote the paper to the study of the space of the unphysical modes. We find that the theory is unitary only under the hypothesis that the 1-PI two-point function of the vector mesons has no poles (at p2 = 0). This normalization condition might be rather crucial in the very definition of the theory. With all these provisos the theory is unitary. The proof of unitarity is given both in a form that allows a direct transcription in terms of Feynman amplitudes (cutting rules) and in the operatorial form. The same arguments and conclusions apply verbatim to the case of non-abelian gauge theories where the mass of the vector meson is generated via Higgs mechanism. To the best of our knowledge, there is no mention in the literature on the necessary condition implied by physical unitarity.