* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> Extremely Red Objects
Post Info TOPIC: Extremely Red Objects
Blobrana


L

Posts: 131433
Date:
RE: Extremely Red Objects
Permalink  
 

Title: The Clustering of Extremely Red Objects
Authors: David P. Palamara, Michael J. I. Brown, Buell T. Jannuzi, Arjun Dey, Daniel Stern, Kevin A. Pimbblet, Benjamin J. Weiner, Matthew L. N. Ashby, C. S. Kochanek, Anthony Gonzalez, Mark Brodwin, Emeric Le Floc'h, Marcia Rieke

We measure the clustering of Extremely Red Objects (EROs) in ~8 deg^2 of the NOAO Deep Wide Field Survey Boötes field in order to establish robust links between ERO z~1.2 and local galaxy z<0.1 populations. Three different colour selection criteria from the literature are analysed 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]) colours 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.

Read more (2958kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Extremely red galaxies
Permalink  
 

Strange New "Species" of Ultra-Red Galaxy Discovered

In the distant reaches of the universe, almost 13 billion light-years from Earth, a strange species of galaxy lay hidden. Cloaked in dust and dimmed by the intervening distance, even the Hubble Space Telescope couldn't spy it. It took the revealing power of NASA's Spitzer Space Telescope to uncover not one, but four remarkably red galaxies. And while astronomers can describe the members of this new "species," they can't explain what makes them so ruddy.
Spitzer succeeded where Hubble failed because Spitzer is sensitive to infrared light - light so red that it lies beyond the visible part of the spectrum. The newfound galaxies are more than 60 times brighter in the infrared than they are at the reddest colours Hubble can detect.
Read more 



__________________
Blobrana


L

Posts: 131433
Date:
Red galaxies
Permalink  
 

Title: On the nature of red galaxies: the Chandra perspective
Authors: M.A. Campisi, C. Vignali, M. Brusa, E. Daddi, A. Comastri, L. Pozzetti, D.M. Alexander, A. Renzini, N. Arimoto, X. Kong

We present the X-ray properties of the extremely red objects (ERO) population observed by Chandra with three partially overlapping pointings (up to ~90 ks) over an area of ~500 arcmin^2, down to a 0.5-8 keV flux limit of ~10-15 erg cm-2 s-1. We selected EROs using a multi-band photometric catalogue down to a KS-band magnitude of ~19.3 (Vega system); 14 EROs were detected in X-rays, corresponding to ~9% of the overall X-ray source population (149 X-ray sources) and to ~5% of the ERO population (288). The X-ray emission of all X-ray detected EROs is consistent with that of an active galactic nucleus (AGN) (>=3.5x10^{42} erg s-1 at photometric redshifts z > 1), in agreement with previous X-ray observations, with an indication of increasing absorption between the three X-ray brightest EROs and the 11 X-ray faintest EROs. We take advantage of the good spatial resolution and limited background provided by Chandra to place constraints on the population of the X-ray undetected EROs by a stacking analysis. Their stacked emission, whose statistical significance is 5.7sigma in the observed 0.5-8 keV band, provides an upper limit to the average intrinsic absorption at z=1 of 2.5x10^{22} cm^{-2} and corresponds to a rest-frame 0.5-8 keV luminosity of 8.9x10^{41} erg s^{-1} . We estimate that any accretion-related X-ray emission to the stacked signal is likely "diluted" by emission due to hot gas in normal galaxies and star-formation activity in dust-enshrouded galaxies at high redshift.

Read more  (166kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
RE: Extremely Red Objects
Permalink  
 

Title: EROs found behind lensing clusters: II.Empirical properties, classification, and SED modelling based on multi-wavelength observations
Authors: A. Hempel (1), D. Schaerer (1 and 3), E. Egami (2), R. Pelló (3), M. Wise (4), J. Richard (5 and 3), J.-F. Le Borgne (3), J.-P. Kneib (6) ((1) Observatoire de Gené ve, (2) Steward Observatory, (3) Observatoire Midi-Pyrénées, (4) Astronomical Institute Anton Pannekoek, (5) Caltech Astronomy, (6) OAMP)

We study the properties and nature of extremely red galaxies (ERO, R-K>5.6) found behind two lensing clusters and compare them with other known galaxy populations. New HST/ACS observations, Spitzer IRAC and MIPS, and Chandra/ACIS observations of the two lensing clusters Abell 1835 and AC114 contemplate our earlier optical and near-IR observations and have been used to study extremely red objects (EROs) in these deep fields. We have found 6 and 9 EROs in Abell 1835 and AC114. Several (7) of these objects are undetected up to the I and/or z band, and are hence ``optical'' drop-out sources. The photometric redshifts of most of our sources (80%) are z~0.7-1.5. According to simple colour-colour diagrams the majority of our objects would be classified as hosting old stellar populations. However, there are clear signs of dusty starbursts for several among them. These objects correspond to the most extreme ones in R-K colour. We estimate a surface density of (0.97+-0.31) arcmin-2 for EROs with (R-K>5.6) at K<20.5. Among our 15 EROs 6 (40 %) also classify as distant red galaxies (DRGs). 11 of 13 EROs with available IRAC photometry also fulfil the selection criteria for IRAC selected EROs (IEROs) of Yan et al. (2004). SED modelling shows that ~ 36 % of the IEROs in our sample are luminous or ultra-luminous infrared galaxies ((U)LIRG). Some very red DRGs are found to be very dusty starbursts, even (U)LIRGs, as also supported by their mid-IR photometry. No indication for AGNs is found, although faint activity cannot be excluded for all objects. From mid-IR and X-ray data 5 objects are clearly classified as starbursts. The derived properties are quite similar to those of DRGs and IEROs, except for 5 extreme objects in terms of colours, for which a very high extinction (Av>3) is found.

Read more (2579kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Extremely Red Objects in Two Quasar Fields at z ~ 1.5
Authors: Alan Stockton (IfA, U. Hawaii), Elizabeth McGrath (IfA, U. Hawaii), Gabriela Canalizo (IGPP & Physics Dept, UCR)

We present an investigation of the properties and environments of bright extremely red objects (EROs) found in the fields of the quasars TXS 0145+386 and 4C 15.55, both at z ~ 1.4. There is marginal evidence from Chandra ACIS imaging for hot cluster gas with a luminosity of a few 10^44 ergs/s in the field of 4C 15.55. The TXS 0145+386 field has an upper limit at a similar value, but it also clearly shows an overdensity of faint galaxies. None of the EROs are detected as X-ray sources. For two of the EROs that have spectral-energy distributions and rest-frame near-UV spectra that show that they are strongly dominated by old stellar populations, we determine radial-surface-brightness profiles from adaptive-optics images. Both of these galaxies are best fit by profiles close to exponentials, plus a compact nucleus comprising ~30% of the total light in one case and 8% in the other. Neither is well fit by an r^1/4-law profile. This apparent evidence for the formation of massive ~2 X 10^11 disks of old stars in the early universe indicates that at least some galaxies formed essentially monolithically, with high star-formation rates sustained over a few 10^8 years, and without the aid of major mergers.

Read more (834kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Spitzer Observations of the Prototypical Extremely Red Objects HR10 and LBDS53W091: Separating Dusty Starbursts from Old Elliptical Galaxies
Authors: Daniel Stern (1), Ranga-Ram Chary (2), Peter Eisenhardt (1), Leonidas Moustakas (1) ((1) JPL/Caltech, (2) SSC/Caltech)

Researchers present Spitzer Space Telescope observations of the well-studied extremely red objects (EROs) HR10 and LBDS53W091 from 3.6 to 160 microns. These galaxies are the prototypes of the two primary classes of EROs: dusty starbursts and old, evolved galaxies, respectively. Both galaxies, as well as LBDS53W069, another example of an old, quiescent galaxy, are well-detected out to 8 microns. However, only the dusty starburst HR10 is detected in the far-infrared. All three EROs have stellar masses of a few times 10^11 M(sun). Using evolutionary model fits to their multiband photometry, the researchers predict the infrared colours of similar EROs at 1<z<2. They find that blueward of observed 10 microns, the two ERO classes are virtually indistinguishable photometrically. Deep spectroscopy and 24 micron data allow the classes to be separated.

Read more (278kb, PDF)

-- Edited by Blobrana at 13:12, 2006-07-24

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> Extremely Red Objects


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard