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Register a new userA Redshift Survey of the Submillimeter Galaxy Population
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We have obtained spectroscopic redshifts using the Keck-I telescope for a sample of 73 submillimeter (submm) galaxies for which precise positions are available. The galaxies lie at redshifts out to z=3.6, with a median redshift of 2.2. The dust-corrected ultraviolet (UV) luminosities of the galaxies rarely hint at their huge bolometric luminosities indicated by their radio/submm emission, underestimating the true luminosity by a median factor of ~100 for SMGs with pure starburst spectra. The 850mu, radio, and redshift data is used to estimate the dust temperatures (<Td>=36+-7 K), and characterize photometric redshifts. We calculate total infrared and bolometric luminosities, construct a luminosity function, and quantify the strong evolution of the submm population across z=0.5-3.5, relative to local IRAS galaxies. We conclude that bright submm galaxies contribute a comparable star formation density to Lyman-break galaxies at z=2-3 and including galaxies below our submm flux limit this population may be the dominant site of massive star formation at this epoch. The rapid evolution of submm galaxies and QSO populations contrasts with that seen in bolometrically lower luminosity galaxy samples selected in the restframe UV, and suggests a close link between submm galaxies and the formation and evolution of the galactic halos which host QSOs. [Abridged].
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We have identified 335 galaxy cluster and group candidates spanning 0<z<2, using a 4.5um selected sample of galaxies in a 7.25 deg^2 region in the Spitzer/IRAC Shallow Survey. Using full redshift probability distributions for all galaxies, clusters were identified as 3-dimensional overdensities using a wavelet algorithm. To date 12 clusters at z>1, and over 60 at z < 0.5 have been spectroscopically confirmed. The mean I-[3.6] color for cluster galaxies up to z~1 is well matched by a z_f=3 passively evolving model. At z>1, a wider range of formation histories is needed, but higher formation redshifts (i.e. z_f ge 4-5) are favored for most clusters. The cluster autocorrelation function, measured for the first time out to z=1.5, is found not to have evolved over the last 10 Gyr, in agreement with the prediction from LCDM. The average mass of the IRAC Shallow Cluster Survey sample, inferred from its clustering, is ~ 10^14 Msun.
We have used the Submillimeter Array to image a flux limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890um with 2 resolution. All of the sources - two radio-bright and five radio-dim - are detected as single point-sources at high significance (> 6sigma), with positions accurate to 0.2 that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST/ACS imaging. As compared to the two radio-bright sources in the sample, and those in previous studies, the five radio-dim sources in the sample (1) have systematically higher submillimeter-to-radio flux ratios, (2) have lower IRAC 3.6-8.0um fluxes, and (3) are not detected at 24um. These properties, combined with size constraints at 890um (theta < 1.2), suggest that the radio-dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local ultraluminous infrared galaxies, and an average redshift higher than radio-bright sources.
Using photometric redshifts we determine the galaxy population of the clusters of galaxies Cl0016+16 at z=0.55, Cl1600+41 at z=0.54, Cl1601+42 at z=0.54 and MS1008-1224 at z=0.31. Comparing the clusters, we find no evidence for a universal shape of the total luminosity function (LF) at these redshifts. When dividing the LFs into spectral types, we find that the LF of the early-type galaxies alone can be described by a Gaussian, while the LF of the late-type galaxies is well fitted by a Schechter function, suggesting that the separate LFs for different populations may be universal. The difference in the total LFs can mainly be attributed to the varying relative normalisation of these populations, implying that clusters with an abundant population of late-type galaxies also have steeper faint-end slopes. In MS1008-1224 we detect a faint blue population that dominates over a population with colours consistent with dwarf ellipticals, opposite to clusters at lower redshift. Compared to low redshift clusters, we find that a general fading of the late-type population by ~2 mag and the early-type population by ~1 mag describes the evolution from z=0.55 to z=0 well. As a consequence of the different early-type and late-type LFs and their dependence on cluster radius, the fraction of blue cluster galaxies, as measured by the Butcher-Oemler effect, differs between the clusters and depends on limiting magnitude and radius. We find a correlation between the dwarf-to-giant ratio and the surface density, indicating that the high density environment in the cluster cores is hostile to dwarf galaxies.
We present a study of the luminosity and color properties of galaxies selected from a sample of 57 low-redshift Abell clusters. We utilize the non-parametric dwarf-to-giant ratio (DGR) and the blue galaxy fraction (fb) to investigate the clustercentric radial-dependent changes in the cluster galaxy population. Composite cluster samples are combined by scaling the counting radius by r200 to minimize radius selection bias. The separation of galaxies into a red and blue population was achieved by selecting galaxies relative to the cluster color-magnitude relation. The DGR of the red and blue galaxies is found to be independent of cluster richness (Bgc), although the DGR is larger for the blue population at all measured radii. A decrease in the DGR for the red and red+blue galaxies is detected in the cluster core region, while the blue galaxy DGR is nearly independent of radius. The fb is found not to correlate with Bgc; however, a steady decline toward the inner-cluster region is observed for the giant galaxies. The dwarf galaxy fb is approximately constant with clustercentric radius except for the inner cluster core region where fb decreases. The clustercentric radial dependence of the DGR and the galaxy blue fraction, indicates that it is unlikely that a simple scenario based on either pure disruption or pure fading/reddening can describe the evolution of infalling dwarf galaxies; both outcomes are produced by the cluster environment.
We review theoretical approaches to the study of galaxy formation, with emphasis on the role of hydrodynamic simulations in modeling the high redshift galaxy population. We present new predictions for the abundance of star-forming galaxies in the Lambda + cold dark matter model (Omega_m=0.4, Omega_L=0.6), combining results from several simulations to probe a wide range of redshift. At a threshold density of one object per arcmin^2 per unit z, these simulations predict galaxies with star formation rates of 2 msun/yr (z=10), 5 msun/yr (z=8), 20 msun/yr (z=6), 70-100 msun/yr (z=4-2), and 30 msun/yr (z=0.5). For galaxies selected at a fixed comoving space density n=0.003 h^3 Mpc^{-3], a (50 Mpc/h)^3 simulation predicts a galaxy correlation function (r/5 Mpc/h)^{-1.8} in comoving coordinates, essentially independent of redshift from z=4 to z=0.5. Different cosmological models predict global histories of star formation that reflect their overall histories of mass clustering, but robust numerical predictions of the comoving space density of star formation are difficult because the simulations miss the contribution from galaxies below their resolution limit. The LCDM model appears to predict a star formation history with roughly the shape inferred from observations, but it produces too many stars at low redshift, predicting Omega_* ~ 0.015 at z=0. We conclude with a brief discussion of this discrepancy and three others that suggest gaps in our current theory of galaxy formation: small disks, steep central halo profiles, and an excess of low mass dark halos. While these problems could fade as the simulations or observations improve, they could also guide us towards a new understanding of galactic scale star formation, the spectrum of primordial fluctuations, or the nature of dark matter.
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