Bright Extremely Red Objects Research Articles

Clustering of extremely red objects in Elais-N1 from the UKIDSS DXS with optical photometry from Pan-STARRS 1 and Subaru

We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg$^{2}$, which cover the redshift range $z=0.8$ to $2$. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 datasets. We confirm the existence of a clear break in the angular correlation function at $\sim 0.02^{\circ}$ corresponding to $1 h^{-1}$ Mpc at $z\sim1$. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo Occupation Distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over $10^{13} h^{-1} M_{\odot}$ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at $z\sim1.1$, at $z\sim1.5$ EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host $10^{11.0} M_{\odot}<M_{*}<10^{11.5} M_{\odot}$ galaxies. We compare our new measurement and HOD fits with the predictions of the GALFORM semi-analytical galaxy formation model. Overall, the clustering predicted by GALFORM gives an encouraging match to our results. However, compared to our deductions from the measurements, GALFORM puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.

THE CLUSTERING OF EXTREMELY RED OBJECTS

We measure the clustering of Extremely Red Objects (EROs) in ~8 deg^2 of the NOAO Deep Wide Field Survey Bo\"otes field in order to establish robust links between ERO z~1.2 and local galaxy z<0.1 populations. Three different color selection criteria from the literature are analyzed to assess the consequences of using different criteria for selecting EROs. Specifically, our samples are (R-K_s)>5.0 (28,724 galaxies), (I-K_s)>4.0 (22,451 galaxies) and (I-[3.6])>5.0 (64,370 galaxies). Magnitude-limited samples show the correlation length (r_0) to increase for more luminous EROs, implying a correlation with stellar mass. We can separate star-forming and passive ERO populations using the (K_s-[24]) and ([3.6]-[24]) colors to K_s=18.4 and [3.6]=17.5, respectively. Star-forming and passive EROs in magnitude limited samples have different clustering properties and host dark halo masses, and cannot be simply understood as a single population. Based on the clustering, we find that bright passive EROs are the likely progenitors of >4L^* elliptical galaxies. Bright EROs with ongoing star formation were found to occupy denser environments than star-forming galaxies in the local Universe, making these the likely progenitors of >L^* local ellipticals. This suggests that the progenitors of massive >4L^* local ellipticals had stopped forming stars by z>1.2, but that the progenitors of less massive ellipticals (down to L^*) can still show significant star formation at this epoch.

Clustering properties of high-redshift red galaxies in SA22 from the UKIDSS Deep eXtragalactic Survey

Deep, wide, near-infrared imaging surveys provide an opportunity to study the clustering of various galaxy populations at high redshift on the largest physical scales. We have selected $1<z<2$ extremely red objects (EROs) and $1<z<3$ distant red galaxies (DRGs) in SA22 from the near-infrared photometric data of the UKIDSS Deep eXtragalactic Survey (DXS) and $gri$ optical data from CTIO covering 3.3~deg$^2$. This is the largest contiguous area studied to sufficient depth to select these distant galaxies to date. The angular two-point correlation functions and the real space correlation lengths of each population are measured and show that both populations are strongly clustered and that the clustering cannot be parameterised with a single power law. The correlation function of EROs shows a double power law with the inflection at $\sim$ 0.6$'$--1.2$'$ (0.6--1.2~h$^{-1}$~Mpc). The bright EROs ($K<18.8$) show stronger clustering on small scales but similar clustering on larger scales, whereas redder EROs show stronger clustering on all scales. Clustering differences between EROs that are old passively evolved galaxies (OGs) and dusty star-forming galaxies (DGs), on the basis of their $J-K$ colour, are also investigated. The clustering of $r-K$ EROs are compared with that of $i-K$ EROs and the differences are consistent with their expected redshift distributions. The correlation function of DRGs is also well described by a double power law and consistent with previous studies once the effects of the broader redshift distribution our selection of DRGs returns are taken into account. We also perform the same analysis on smaller sub-fields to investigate the impact of cosmic variance on the derived clustering properties. Currently this study is the most representative measurement of the clustering of massive galaxies at $z>1$ on large scales.

AnHSTmorphological survey of faint extremely red objects

We present the results from a survey for extremely red objects (EROs) in deep, high-resolution optical images taken from the Hubble Space Telescope (HST) Medium Deep Survey. We have surveyed 35 deep F814W HST/WFPC2 fields in the near-infrared to a typical depth of K 20. From a total area of 206 arcmin 2 and to a limit of K = 20.0, we identify 224 EROs [(1.14 ± 0.08) arcmin −2 ] with (I 814 − K) 4.0 and 83 [(0.41 ± 0.05) arcmin −2 ] with (I 814 − K) 5.0. We find that the slope of the number counts of the (I 814 − K) 4.0 EROs flattens beyond K ∼ 19, in line with results from previous surveys, and the typical colours of the EROs become redder beyond the break magnitude. We morphologically classify our ERO sample using visual and quantitative schemes and find that 35 per cent of our sample exhibit clear disc components, 15 per cent are disturbed or irregular, a further 30 per cent are either spheroidal or compact and the remaining 20 per cent are unclassifiable. Using a quantitative measure of morphology, we find that the ERO morphological distribution evolves across the break in their counts, such that low concentration (disc-like) galaxies decline. We relate the morphological and colour information for our EROs and conclude that those EROs morphologically classified as bulges do indeed possess SEDs consistent with passive stellar populations; while EROs with dusty star-forming SEDs are mostly associated with disc-like and peculiar galaxies. However, ∼30 per cent of disc EROs reside in the passive region of I/J/K colour‐colour space. These could be either genuinely passive systems, lower redshift contaminants to the high-z ERO population, or systems with composite star-forming and passive SEDs. We use photometric redshifts for our high signal-to-noise ratio (S/N) multicolour photometry and derive redshift distributions in good agreement with spectroscopic work of somewhat brighter ERO examples.

The clustering, number counts and morphology of extremely red (R-K &gt; 5) galaxies to K&lt;= 21

Using K- and R-band imaging of the ELAIS N2 field, we investigate the number counts, clustering, morphology and radio/X-ray emission of extremely red objects (EROs), defined as galaxies with R − K > 5.0. This criterion will select old, passive ellipticals at z > 0.9. To K = 21 we identify a total of 158 EROs in 81.5 arcmin 2 . The ERO number counts are lower than predicted by pure luminosity evolution models, but higher than predicted by current cold dark matter-based hierarchical models. The ERO counts are consistent with a non-evolving model and also with a luminosity evolution model incorporating moderate merging and a decrease with redshift in the comoving number density of passive galaxies (‘M-DE’). We investigate the clustering of the EROs by calculating their angular correlation function, ω(θ ), and obtain a >2σ detection of clustering at K =19‐20 limits. The ω(θ ) amplitude of these EROs is much higher than that of full K-limited samples of galaxies, and is best-fitted by models with a comoving correlation radius r 0 � 10‐13 h −1 Mpc. These results, which are in agreement with Daddi et al., suggest that the intrinsic clustering of at least the brighter EROs is even stronger than that of present-day giant ellipticals. We estimate seeing-corrected angular sizes and morphological types for a K 19.5 subsample of EROs (31 galaxies) and find a ∼3:2 mixture of bulge and disc profiles. Of these EROs ∼ 1 appear to be interacting, disturbed or otherwise irregular, and two are visible mergers. We find the angular sizes of the bulge-profile EROs are consistent with passively evolving ellipticals in the M-DE model, at the expected z ∼ 0.9‐2. The ERO mean radii are smaller than the non-evolving prediction, implying surface brightness evolution. Seven of the 31 bright EROs are detected as F(1.4GHz) 30 µJy radio sources in a VLA survey. The strongest, at 5 mJy, is also a Chandra X-ray detection, and lies at the centre of a significant overdensity of EROs ‐ it is probably an FRI radio galaxy in a z ∼ 1 cluster. Of the other, much fainter, sources, five are point-like and may be weak active galactic nuclei, while the sixth is elongated and aligned with the optical axis of an extended, low-surface brightness ERO, suggesting a powerful but dust-reddened starburst. A possible interpretation is discussed in which the EROs are a mixture of (i) ‘pEROs’, strongly clustered passively evolving giant ellipticals, formed at high redshifts, the oldest EROs and (ii) ‘dsfEROs’, dusty post-interaction galaxies, with a few active starbursts (ULIRGs), and less strongly clustered. With time, the younger dsfEROs are continually assimilated into the ERO class, diluting the clustering and increasing the comoving number density. Both types ultimately evolve into present-day early-type galaxies.