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.
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.
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.
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.
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.
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.