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Register a new userA Large Population of High Redshift Galaxy Clusters in the IRAC Shallow Cluster Survey
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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.
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We present the galaxy cluster autocorrelation function of 277 galaxy cluster candidates with 0.25 le z le 1.5 in a 7 deg^2 area of the IRAC Shallow Cluster Survey. We find strong clustering throughout our galaxy cluster sample, as expected for these massive structures. Specifically, at <z> = 0.5 we find a correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent agreement with the Las Campanas Distant Cluster Survey, the only other non-local measurement. At higher redshift, <z> = 1, we find that strong clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56} h^-1 Mpc. A comparison with high resolution cosmological simulations indicates these are clusters with halo masses of sim 10^{14} Msun, a result supported by estimates of dynamical mass for a subset of the sample. In a stable clustering picture, these clusters will evolve into massive (10^{15} Msun) clusters by the present day.
The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions.
We report the X-ray detection of two z>1.4 infrared-selected galaxy clusters from the IRAC Shallow Cluster Survey (ISCS). We present new data from the Hubble Space Telescope and the W. M. Keck Observatory that spectroscopically confirm cluster ISCS J1432.4+3250 at z=1.49, the most distant of 18 confirmed z>1 clusters in the ISCS to date. We also present new spectroscopy for ISCS J1438.1+3414, previously reported at z = 1.41, and measure its dynamical mass. Clusters ISCS J1432.4+3250 and ISCS J1438.1+3414 are detected in 36ks and 143ks Chandra exposures at significances of 5.2 sigma and 9.7 sigma, from which we measure total masses of log(M_{200,Lx}/Msun) = 14.4 +/- 0.2 and 14.35^{+0.14}_{-0.11}, respectively. The consistency of the X-ray and dynamical properties of these high redshift clusters further demonstrates that the ISCS is robustly detecting massive clusters to at least z = 1.5.
Accurate photometric redshifts are calculated for nearly 200,000 galaxies to a 4.5 micron flux limit of ~13 uJy in the 8.5 deg^2 Spitzer/IRAC Shallow survey. Using a hybrid photometric redshift algorithm incorporating both neural-net and template-fitting techniques, calibrated with over 15,000 spectroscopic redshifts, a redshift accuracy of sigma = 0.06(1+z) is achieved for 95% of galaxies at 0<z<1.5. The accuracy is sigma = 0.12(1+z) for 95% of AGN at 0<z<3. Redshift probability functions, central to several ongoing studies of the galaxy population, are computed for the full sample. We demonstrate that these functions accurately represent the true redshift probability density, allowing the calculation of valid confidence intervals for all objects. These probability functions have already been used to successfully identify a population of Spitzer-selected high redshift (z>1) galaxy clusters. We present one such spectroscopically confirmed cluster at <z>=1.24, ISCS J1434.5+3427. Finally, we present a measurement of the 4.5 micron-selected galaxy redshift distribution.
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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