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Register a new userThe Phoenix Deep Survey: the clustering and the environment of Extremely Red Objects
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Added by
Antonis Georgakakis
Publication date
2004
fields
Physics
and research's language is
English
Authors
A. Georgakakis
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In this paper we explore the clustering properties and the environment of the Extremely Red Objects (EROs; I-K>4mag) detected in a ~180arcmin^2 deep (Ks~20mag) Ks-band survey of a region within the Phoenix Deep Survey, an on-going multiwavelength program aiming to investigate the nature and the evolution of faint radio sources. Using our complete sample of 289 EROs brighter than Ks=20mag we estimate a statistically significant (~3.7sigma) angular correlation function signal with amplitude Aw=8.7^{+2.1}_{-1.7}x10^{-3} consistent with earlier work based on smaller samples. This amplitude suggests a clustering length in the range ro=12-17h^{-1}Mpc, implying that EROs trace regions of enhanced density. Using a novel method we further explore the association of EROs with galaxy overdensities by smoothing the K-band galaxy distribution using the matched filter algorithm of Postman et al. (1996) and then cross-correlating the resulting density maps with the ERO positions. Our analysis provides direct evidence that EROs are associated with overdensities at redshifts z>1. We also exploit the deep radio 1.4GHz data (limiting flux 60microJy) available to explore the association of EROs and faint radio sources and whether the two populations trace similar large scale structures. Cross-correlation of the two samples (after excluding 17EROs with radio counterparts) gives a 2sigma signal only for the sub-sample of high-z radio sources (z>0.6). Although the statistics are poor this suggests that it is the high-z radio sub-sample that traces similar structures with EROs.
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The Phoenix Deep Survey (PDS) is a multiwavelength survey based on deep 1.4 GHz radio observations used to identify a large sample of star forming galaxies to z=1. Here we present an exploration of the evolutionary constraints on the star-forming population imposed by the 1.4 GHz source counts, followed by an analysis of the average properties of extremely red galaxies in the PDS, by using the stacking technique.
We present the results of a study of a sample of 375 Extremely Red Galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a subsample which is 80% complete to K_s = 18.5 over an area of 1160 arcmin^2. The angular correlation function for ERGs is estimated, and the association of ERGs with faint radio sources explored. We find tentative evidence that ERGs and faint radio sources are associated at z > 0.5. A new overdensity-mapping algorithm has been used to characterize the ERG distribution, and identify a number of cluster candidates, including a likely cluster containing ERGs at 0.5 < z < 1. Our algorithm is also used in an attempt to probe the environments in which faint radio sources and ERGs are associated. We find limited evidence that the I - K_s > 4 criterion is more efficient than R - K_s > 5 at selecting dusty star-forming galaxies, rather than passively evolving ERGs.
We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM-Newton Deep Field. We find a total of 3715 objects over 2013 sq. arcmin with R-K>5.3 and K<=20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively-evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually-detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that AGNs are more prevalent among the passive ERO population.
We present a catalog of extremely red objects discovered using the NICMOS/HST parallel imaging database and ground-based optical follow-up observations. Within an area of 16 square arc-minutes, we detect 15 objects with $rm R - F160W > 5$ and $rm F160W < 21.5$. We have also obtained K-band photometry for a subset of the 15 EROs. All of the $rm R - F160W$ selected EROs imaged at K-band have $rm R - K > 6$. Our objects have $rm F110W - F160W$ colors in the range of 1.3 - 2.1, redder than the cluster ellipticals at $z sim 0.8$ and nearly 1 magnitude redder than the average population selected from the F160W images at the same depth. In addition, among only 22 NICMOS pointings, we detected two groups or clusters in two fields, each contains 3 or more EROs, suggesting that extremely red galaxies may be strongly clustered. At bright magnitudes with $rm F160W < 19.5$, the ERO surface density is similar to what has been measured by other surveys. At the limit of our sample, F160W = 21.5, our measured surface density is 0.94$pm 0.24$ arcmin^{-2}. Excluding the two possible groups/clusters and the one apparently stellar object, reduces the surface density to 0.38$pm 0.15$ arcmin^{-2}.
We investigate Extremely Red Objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 micron) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the IRAC camera allows us to detect 64 EROs in only 12 minutes of IRAC exposure time, by means of an R-[3.6] color cut (analogous to the traditional red R-K cut). A pure infrared K-[3.6] red cut detects a somewhat different population and may be more effective at selecting z > 1.3 EROs. We find 17% of all galaxies detected by IRAC at 3.6 or 4.5 micron to be EROs. These percentages rise to about 40% at 5.8 micron, and about 60% at 8.0 micron. We utilize the spectral bump at 1.6 micron to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 micron). We conclude that two-thirds of all EROs lie at redshift z > 1.3. Detections at 24 micron imply that at least 11% of 0.6 < z < 1.3 EROs and at least 22% of z > 1.3 EROs are dusty star-forming galaxies.
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