13331517
THE GROWTH OF MASSIVE GALAXIES SINCE z = 2
We study the growth of massive galaxies from z = 2 to the present using data from the NOAO/Yale NEWFIRM Medium Band Survey. The sample is selected at a constant number density of n = 2 ? 10?4?Mpc?3, so that galaxies at different epochs can be compared in a meaningful way. We show that the stellar mass of galaxies at this number density has increased by a factor of 2 since z = 2, following the relation log Mn (z) = 11.45 ? 0.15z. In order to determine at what physical radii this mass growth occurred, we construct very deep stacked rest-frame R-band images of galaxies with masses near Mn (z), at redshifts z = 0.6, 1.1, 1.6, and 2.0. These image stacks of typically 70-80 galaxies enable us to characterize the stellar distribution to surface brightness limits of ~28.5 mag?arcsec?2. We find that massive galaxies gradually built up their outer regions over the past 10 Gyr. The mass within a radius of r = 5?kpc is nearly constant with redshift, whereas the mass at 5 kpc < r < 75?kpc has increased by a factor of ~4 since z = 2. Parameterizing the surface brightness profiles, we find that the effective radius and Sersic n parameter evolve as re (1 + z)?1.3 and n (1 + z)?1.0, respectively. The data demonstrate that massive galaxies have grown mostly inside-out, assembling their extended stellar halos around compact, dense cores with possibly exponential radial density distributions. Comparing the observed mass evolution to the average star formation rates of the galaxies we find that the growth is likely dominated by mergers, as in situ star formation can only account for ~20% of the mass buildup from z = 2 to z = 0. A direct consequence of these results is that massive galaxies do not evolve in a self-similar way: their structural profiles change as a function of redshift, complicating analyses which (often implicitly) assume self-similarity. The main uncertainties in this study are possible redshift-dependent systematic errors in the total stellar masses and the conversion from light-weighted to mass-weighted radial profiles.
3447277
THE MOST MASSIVE GALAXIES AT 3.0 ≤ z < 4.0 IN THE NEWFIRM MEDIUM-BAND SURVEY: PROPERTIES AND IMPROVED CONSTRAINTS ON THE STELLAR MASS FUNCTION
We use the optical to mid-infrared coverage of the NEWFIRM Medium-Band Survey (NMBS) to characterize, for the first time, the properties of a mass-complete sample of 14 galaxies at 3.0 ≤ z 2.5 × 1011 M ☉, and to derive significantly more accurate measurements of the high-mass end of the stellar mass function (SMF) of galaxies at 3.0 ≤ z 25.5. We find that ~30% of the sample has star formation rates (SFRs) from SED modeling consistent with zero, although SFRs of up to ~1-18 M ☉ yr–1 are also allowed within 1σ. However, >80% of the sample is detected at 24 μm, resulting in total infrared luminosities in the range (0.5-4.0) × 1013 L ☉. This implies the presence of either dust-enshrouded starburst activity (with SFRs of 600-4300 M ☉ yr–1) and/or highly obscured active galactic nuclei (AGNs). The contribution of galaxies with M star>2.5 × 1011 M ☉ to the total stellar mass budget at 3.0 ≤ z < 4.0 is ~8+13 –3%. Compared to recent estimates of the stellar mass density in galaxies with M star 109-1011 M ☉ at z ~ 5 and z ~ 6, we find an evolution by a factor of 2-7 and 3-22 from z ~ 5 and z ~ 6, respectively, to z = 3.5. The previously found disagreement at the high-mass end between observed and model-predicted SMFs is now significant at the 3σ level when only random uncertainties are considered. However, systematic uncertainties dominate the total error budget, with errors up to a factor of ~8 in the densities at the high-mass end, bringing the observed SMF in marginal agreement with the predicted SMF. Additional systematic uncertainties on the high-mass end could be potentially introduced by either (1) the intense star formation and/or the very common AGN activities as inferred from the MIPS 24 μm detections, and/or (2) contamination by a significant population of massive, old, and dusty galaxies at z ~ 2.6.
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.
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
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.
119234516
The Spectral Energy Distribution of Post-starburst Galaxies in the NEWFIRM Medium-band Survey: A Low Contribution from TP-AGB Stars
Stellar population synthesis (SPS) models are a key ingredient of many galaxy evolution studies. Unfortunately, the models are still poorly calibrated for certain stellar evolution stages. Of particular concern is the treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase, as different implementations lead to systematic differences in derived galaxy properties. Post-starburst galaxies are a promising calibration sample, as TP-AGB stars are thought to be most prominently visible during this phase. Here, we use post-starburst galaxies in the NEWFIRM medium-band survey to assess different SPS models. The available photometry allows the selection of a homogeneous and well-defined sample of 62 post-starburst galaxies at 0.7 {approx_lt} z {approx_lt} 2.0, from which we construct a well-sampled composite spectral energy distribution (SED) over the range 1200-40000 A. The SED is well fit by the Bruzual and Charlot SPS models, while the Maraston models do not reproduce the rest-frame optical and near-infrared parts of the SED simultaneously. When the fitting is restricted to {lambda} < 6000 A, the Maraston models overpredict the near-infrared luminosity, implying that these models give too much weight to TP-AGB stars. Using the flexible SPS models by Conroy et al. and assuming solar metallicity, we find that the contributionmore » of TP-AGB stars to the integrated SED is a factor of {approx}3 lower than predicted by the latest Padova TP-AGB models. Whether this is due to lower bolometric luminosities, shorter lifetimes, and/or heavy dust obscuration of TP-AGB stars remains to be addressed. Altogether, our data demand a low contribution from TP-AGB stars to the SED of post-starburst galaxies.« less
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.