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.
119301028
Quantifying Photometric Redshift Errors in the Absence of Spectroscopic Redshifts
Much of the science that is made possible by multiwavelength redshift surveys requires the use of photometric redshifts. But as these surveys become more ambitious, and as we seek to perform increasingly accurate measurements, it becomes crucial to take proper account of the photometric redshift uncertainties. Ideally the uncertainties can be directly measured using a comparison with spectroscopic redshifts, but this may yield misleading results since spectroscopic samples are frequently small and not representative of the parent photometric samples. We present a simple and powerful empirical method to constrain photometric redshift uncertainties in the absence of spectroscopic redshifts. Close pairs of galaxies on the sky have a significant probability of being physically associated and therefore of lying at nearly the same redshift. The difference in photometric redshifts in close pairs is therefore a measure of the redshift uncertainty. Some observed close pairs will arise from chance projections along the line of sight, but it is straightforward to perform a statistical correction for this effect. We demonstrate the technique using both simulated data and actual observations, and discuss how its usefulness can be limited by the presence of systematic photometric redshift errors. Finally, we use this technique to show how photometric redshift accuracy can depend on galaxy type.
43077834
Lensing effects of misaligned disks in dark matter halos
In this paper we study the observational signatures of the lensing signal produced by dark matter halos with embedded misaligned disks. This issue is of particular interest at present, since several of the observed multiple-lens systems have magnification ratios and image geometries that are not simultaneously well fitted by standard mass models. The presence of substructure exterior to the lens has been invoked by several authors in the context of cold dark matter (CDM) models in order to explain the anomalous magnification ratios. We emphasize that the anomalous magnification ratios may be an artifact of the simple mass models currently in use; the inclusion of a misaligned disk may be able to mimic the effect of substructure. These slight spatial offsets between the dark matter halo and the disk, which are likely to occur as a consequence of interactions or mergers, lead to complex image configurations and nonstandard magnification ratios. We investigate the effects of disk misalignment on two illustrative lenses: a spiral disk embedded within a dark matter halo, and a compact, disklike component within an early-type galaxy. The expected fraction of galaxies with a misaligned disk is estimated to be of the order of the merger fraction, since all mergers are expected to progress via a transiently misaligned phase. We find that there is a significant change in all observed lensing properties due to the added complexity of such mass profiles. In particular cases, the resulting lensing geometries are unusual, with high image multiplicities. The caustic structures—both radial and tangential—are drastically modified, and the magnification ratios differ fromexpectations from standard lens models. The additional parameters required to specify the relative alignment of multiple mass components in the primary lens introduce yet another source of uncertainty in the mass modeling of gravitational lens systems.
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.
18119074
THE AGE SPREAD OF QUIESCENT GALAXIES WITH THE NEWFIRM MEDIUM-BAND SURVEY: IDENTIFICATION OF THE OLDEST GALAXIES OUT TO z ∼ 2
With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey, we study the stellar populations of the oldest and most massive galaxies (>1011 M⊙) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U−V colors out to z = 2.2, with accurate photometric redshifts, σz/(1 + z) ~ 2%, and rest-frame colors, σU−V ~ 0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U−V colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies toward higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000 A and Balmer breaks, respectively. Some of the quiescent galaxies may be up to four times older than the average age and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U−V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies toward higher redshift, red mergers at z ≲ 1, and a frosting of relatively young stars from star formation at later times.
15668832
AN ULTRA-DEEP NEAR-INFRARED SPECTRUM OF A COMPACT QUIESCENT GALAXY AT z = 2.2
Several recent studies have shown that about half of the massive galaxies at z ~ 2 are in a quiescent phase. Moreover, these galaxies are commonly found to be ultra-compact with half-light radii of ~1 kpc. We have obtained a ~29 hr spectrum of a typical quiescent, ultra-dense galaxy at z = 2.1865 with the Gemini Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and several absorption features, which have not previously been detected in z > 2 quiescent galaxies. Comparison of the spectral energy distribution with stellar population synthesis models implies a low star formation rate (SFR) of 1-3 M ☉ yr–1, an age of 1.3-2.2 Gyr, and a stellar mass of ~2 × 1011 M ☉. We detect several faint emission lines, with emission-line ratios of [N II]/Hα, [S II]/Hα, and [O II]/[O III] typical of low-ionization nuclear emission-line regions. Thus, neither the stellar continuum nor the nebular emission implies active star formation. The current SFR is <1% of the past average SFR. If this galaxy is representative of compact quiescent galaxies beyond z = 2, it implies that quenching of star formation is extremely efficient and also indicates that low luminosity active galactic nuclei (AGNs) could be common in these objects. Nuclear emission is a potential concern for the size measurement. However, we show that the AGN contributes 8% to the rest-frame optical emission. A possible post-starburst population may affect size measurements more strongly; although a 0.5 Gyr old stellar population can make up 10% of the total stellar mass, it could account for up to ~40% of the optical light. Nevertheless, this spectrum shows that this compact galaxy is dominated by an evolved stellar population.
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.