On the nature of red galaxies: the Chandra perspective

Abstract

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 catalog down to a K S -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) ( > ∼ 3.5 × 10 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 5.7σ in the observed 0.5-8 keV band, provides an upper limit to the average intrinsic absorption at z = 1 of 2.5 × 10 22 cm −2 and corresponds to a rest-frame 0.5-8 keV luminosity of 8.9 × 10 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.

A mature cluster with X-ray emission atz= 2.07

“…The B, R, I and z-band data have already been described in a previous paper (Kong et al 2006). The XMM and Chandra data have also been described in other papers (Brusa et al 2005, Campisi et al 2009). The raw IRAC and MIPS data were taken from the archive and reduced using MOPEX and custom scripts.…”

“…The unambiguous signature of an evolved cluster is the X-ray emission from the ICM, as it implies a deep and established potential well. To check for emission from a diffuse atmosphere, we looked for extended emission in deep X-ray observations available in the field with both the XMM-Newton and Chandra telescopes totalling 80 ks each (Brusa et al 2005, Campisi et al 2009). A detection was found in both soft-band (0.5-2 keV) images: the Chandra observation Fig.…”

A contribution of star-forming clumps and accreting satellites to the mass assembly of z ∼ 2 galaxies

“…We checked for the presence of AGN in our sample galaxies by analysing our XMM (80 ks, Brusa et al 2005;Gobat et al 2011) and Chandra (94 ks, Campisi et al 2009;Valentino et al 2016) data centred on the cluster Cl J1449+0856, covering a total field of view of ∼500 arcmin 2 . Only one galaxy (ID607) was detected (L 2−10 keV = 5.2 +3.4 −1.8 × 10 43 erg s −1 ), suggesting the presence of one X-ray AGN, and we excluded it from our final sample.…”

A GIANT LYα NEBULA IN THE CORE OF AN X-Ray CLUSTER AT Z = 1.99: IMPLICATIONS FOR EARLY ENERGY INJECTION

“…These three observations (5032, 5033, and 5034) were performed in 2004 June by the Advanced CCD Imaging Spectrometer (ACIS) with the I0 CCD at the aimpoint and all ACIS-I CCDs in use. Faint mode was used for the event telemetry, and ASCA grade 0, 2, 3, 4, and 6 events were used in the analysis (full details are reported in Campisi et al 2009). In Cycle16, we followed-up the field with the ACIS-S camera (aimpoint at CCD=7) for a nominal exposure of 94.81 ks in very faint mode.…”