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Title: CLASSIFICATION OF EXTREMELY RED OBJECTS IN THE COSMOS FIELD

Abstract

We present a study of the classification of z {approx} 1 extremely red objects (EROs), using a combination of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), Spitzer Infrared Array Camera (IRAC), and ground-based images of the COSMOS field. Our sample includes {approx}5300 EROs with i - K{sub s} {>=} 2.45 (AB, equivalently I - K{sub s} = 4 in Vega) and K{sub s} {<=} 21.1 (AB). For EROs in our sample, we compute, using the ACS F814W images, their concentration, asymmetry, as well as their Gini coefficient and the second moment of the brightest 20% of their light. Using those morphology parameters and the Spitzer IRAC [3.6] - [8.0] color, the spectral energy distribution (SED) fitting method, we classify EROs into two classes: old galaxies (OGs) and young, dusty starburst galaxies (DGs). We found that the fraction of OGs and DGs in our sample is similar, about 48% of EROs in our sample are OGs, and 52% of them are DGs. To reduce the redundancy of these three different classification methods, we performed a principal component analysis on the measurements of EROs, and find that morphology parameters and SEDs are efficient in segregating OGs and DGs. The [3.6]more » - [8.0] color, which depends on reddening, redshift, and photometric accuracy, is difficult to separate EROs around the discriminating line between starburst and elliptical. We investigate the dependence of the fraction of EROs on their observational properties, and the results suggest that DGs become increasingly important at fainter magnitudes, redder colors, and higher redshifts. The clustering of the entire EROs, DGs, and OGs was estimated by calculating their correlation function, and we find that the clustering of EROs is much stronger than that of full K-limited samples of galaxies; the clustering amplitude of OGs is a factor of {approx}2 larger than that of DGs.« less

Authors:
 [1]; ;  [2];  [3]
  1. Key Laboratory for Research in Galaxies and Cosmology, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)
  2. Center for Astrophysics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
  3. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan), E-mail: xkong@ustc.edu.cn
Publication Date:
OSTI Identifier:
21336003
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 702; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/702/2/1458; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASYMMETRY; CAMERAS; CLASSIFICATION; COLOR; CORRELATION FUNCTIONS; COSMOLOGY; ENERGY SPECTRA; GALAXIES; IMAGES; MORPHOLOGY; PHOTOMETRY; RED SHIFT; TELESCOPES; UNIVERSE; VISIBLE RADIATION

Citation Formats

Kong Xu, Fang Guanwen, Wang Min, and Arimoto, Nobuo. CLASSIFICATION OF EXTREMELY RED OBJECTS IN THE COSMOS FIELD. United States: N. p., 2009. Web. doi:10.1088/0004-637X/702/2/1458; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Kong Xu, Fang Guanwen, Wang Min, & Arimoto, Nobuo. CLASSIFICATION OF EXTREMELY RED OBJECTS IN THE COSMOS FIELD. United States. doi:10.1088/0004-637X/702/2/1458; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Kong Xu, Fang Guanwen, Wang Min, and Arimoto, Nobuo. Thu . "CLASSIFICATION OF EXTREMELY RED OBJECTS IN THE COSMOS FIELD". United States. doi:10.1088/0004-637X/702/2/1458; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21336003,
title = {CLASSIFICATION OF EXTREMELY RED OBJECTS IN THE COSMOS FIELD},
author = {Kong Xu and Fang Guanwen and Wang Min and Arimoto, Nobuo},
abstractNote = {We present a study of the classification of z {approx} 1 extremely red objects (EROs), using a combination of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), Spitzer Infrared Array Camera (IRAC), and ground-based images of the COSMOS field. Our sample includes {approx}5300 EROs with i - K{sub s} {>=} 2.45 (AB, equivalently I - K{sub s} = 4 in Vega) and K{sub s} {<=} 21.1 (AB). For EROs in our sample, we compute, using the ACS F814W images, their concentration, asymmetry, as well as their Gini coefficient and the second moment of the brightest 20% of their light. Using those morphology parameters and the Spitzer IRAC [3.6] - [8.0] color, the spectral energy distribution (SED) fitting method, we classify EROs into two classes: old galaxies (OGs) and young, dusty starburst galaxies (DGs). We found that the fraction of OGs and DGs in our sample is similar, about 48% of EROs in our sample are OGs, and 52% of them are DGs. To reduce the redundancy of these three different classification methods, we performed a principal component analysis on the measurements of EROs, and find that morphology parameters and SEDs are efficient in segregating OGs and DGs. The [3.6] - [8.0] color, which depends on reddening, redshift, and photometric accuracy, is difficult to separate EROs around the discriminating line between starburst and elliptical. We investigate the dependence of the fraction of EROs on their observational properties, and the results suggest that DGs become increasingly important at fainter magnitudes, redder colors, and higher redshifts. The clustering of the entire EROs, DGs, and OGs was estimated by calculating their correlation function, and we find that the clustering of EROs is much stronger than that of full K-limited samples of galaxies; the clustering amplitude of OGs is a factor of {approx}2 larger than that of DGs.},
doi = {10.1088/0004-637X/702/2/1458; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
number = 2,
volume = 702,
place = {United States},
year = {Thu Sep 10 00:00:00 EDT 2009},
month = {Thu Sep 10 00:00:00 EDT 2009}
}
  • 10 ..mu..m radiation has been detected from 1413+135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 ..mu..m. Upper limits are also given for the 10 ..mu..m emission from 2255+14, 0026+34, and 0406+121. Photometry between 1.25 and 2.2 ..mu..m confirms the variability of 1413+135, 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+121 between 1.5 and 2.4 ..mu..m show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths andmore » a redshift 1.3>z>4. The lack of features of the 1.5--2.4 ..mu..m spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributions are consistent with BL Lac nature for these objects.« less
  • In order to find the most extreme dust-hidden high-redshift galaxies, we select 196 extremely red objects in the K{sub S} and Infrared Array Camera (IRAC) bands (KIEROs, [K{sub s} - 4.5 {mu}m]{sub AB} > 1.6) in the 0.06 deg{sup 2} Great Observatories Origins Deep Surveys-North (GOODS-N) region. This selection avoids the Balmer breaks of galactic spectra at z < 4 and picks up red galaxies with strong dust extinction. The photometric redshifts of KIEROs are between 1.5 and 5, with {approx}70% at z {approx} 2-4. KIEROs are very massive, with M{sub *} {approx} 10{sup 10}-10{sup 12} M{sub Sun }. Theymore » are optically faint and usually cannot be picked out by the Lyman break selection. On the other hand, the KIERO selection includes approximately half of the known millimeter and submillimeter galaxies in the GOODS-N. Stacking analyses in the radio, millimeter, and submillimeter all show that KIEROs are much more luminous than average 4.5 {mu}m-selected galaxies. Interestingly, the stacked fluxes for Advanced Camera for Surveys (ACS)-undetected KIEROs in these wave bands are 2.5-5 times larger than those for ACS-detected KIEROs. With the stacked radio fluxes and the local radio-FIR correlation, we derive mean infrared luminosities of (2-7) Multiplication-Sign 10{sup 12} L{sub Sun} and mean star formation rates (SFRs) of 400-1200 M{sub Sun} yr{sup -1} for KIEROs with redshifts. We do not find evidence of a significant subpopulation of passive KIEROs. The large stellar masses and SFRs imply that KIEROs are z > 2 massive galaxies in rapid formation. Our results show that a large sample of dusty ultraluminous sources can be selected in this way and that a large fraction of high-redshift star formation is hidden by dust.« less
  • We measure the clustering of extremely red objects (EROs) in Almost-Equal-To 8 deg{sup 2} of the NOAO Deep Wide Field Survey Booetes field in order to establish robust links between ERO (z Almost-Equal-To 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{sub s} ) > 5.0 (28, 724 galaxies), (I - K{sub s} ) > 4.0 (22, 451 galaxies), and (I - [3.6]) > 5.0 (64, 370 galaxies). Magnitude-limited samples show the correlationmore » length (r {sub 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{sub s} - [24]) and ([3.6] - [24]) colors to K{sub 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 {approx}> 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 {approx}> L* local ellipticals. This suggests that the progenitors of massive {approx}> 4L* local ellipticals had stopped forming stars by z {approx}> 1.2, but that the progenitors of less massive ellipticals (down to L*) can still show significant star formation at this epoch.« less