arXiv subjects

G. R. Tremblay

Publications and source records attributed to G. R. Tremblay.

40 records · Page 3Linked to original sources

arXiv2012

Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: High Excitation and Broad Line Galaxies

We analyze Chandra observations of diffuse soft X-ray emission associated with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus on the properties of the spectroscopic sub-classes of high excitation galaxies (HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or possibly extended) emission in about 40% of the sources; the fraction is even higher (8/10) restricting the analysis to the objects with exposure times larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects; this lower detection rate can be ascribed to the presence of their bright X-ray nuclei that easily outshine any genuine diffuse emission. A very close correspondence between the soft X-ray and optical line morphology emerges. We also find that the ratio between [O III] and extended soft X-ray luminosity is confined within a factor of 2 around a median value of 5. Both results are similar to what is seen in Seyfert galaxies. We discuss different processes that could explain the soft X-ray emission and conclude that the photoionization of extended gas, coincident with the narrow line region, is the favored mechanism.

astro-ph.CO↗

arXiv2012

Residual Cooling and Persistent Star Formation amid AGN Feedback in Abell 2597

New Chandra X-ray and Herschel FIR observations enable a multiwavelength study of active galactic nucleus (AGN) heating and intracluster medium (ICM) cooling in the brightest cluster galaxy of Abell 2597. The new Chandra observations reveal the central < 30 kiloparsec X-ray cavity network to be more extensive than previously thought, and associated with enough enthalpy to theoretically inhibit the inferred classical cooling flow. Nevertheless, we present new evidence, consistent with previous results, that a moderately strong residual cooling flow is persisting at 4%-8% of the classically predicted rates in a spatially structured manner amid the feedback-driven excavation of the X-ray cavity network. New Herschel observations are used to estimate warm and cold dust masses, a lower-limit gas-to-dust ratio, and a star formation rate consistent with previous measurements. The cooling time profile of the ambient X-ray atmosphere is used to map the locations of the observational star formation entropy threshold as well as the theoretical thermal instability threshold. Both lie just outside the < 30 kpc central region permeated by X-ray cavities, and star formation as well as ionized and molecular gas lie interior to both. The young stars are distributed in an elongated region that is aligned with the radio lobes, and their estimated ages are both younger and older than the X-ray cavity network, suggesting both jet-triggered as well as persistent star formation over the current AGN feedback episode. Bright X-ray knots that are coincident with extended Ly-alpha and FUV continuum filaments motivate a discussion of structured cooling from the ambient hot atmosphere along a projected axis that is perpendicular to X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant contributor of the cold gas reservoir fueling star formation and AGN activity in the Abell 2597 BCG.

astro-ph.CO↗

arXiv2012

Multiphase Signatures of AGN Feedback in Abell 2597

We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the cool core cluster Abell 2597. The data reveal an extensive kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas exhibiting strong spatial correlation with archival VLA radio data. In addition to several possible scenarios, multiwavelength evidence may suggest that the filament is associated with multiphase (10^3 - 10^7 K) gas that has been entrained and dredged-up by the propagating radio source. Stemming from a full spectral analysis, we also present profiles and 2D spectral maps of modeled X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an arc of hot gas which in projection borders the inner edge of a large X-ray cavity. Although limited by strong caveats, we suggest that the hot arc may be (a) due to a compressed rim of cold gas pushed outward by the radio bubble or (b) morphologically and energetically consistent with cavity-driven active galactic nucleus (AGN) heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas rushes to refill its wake. If confirmed, this would be the first observational evidence for this model.

astro-ph.CO↗

arXiv2010

Three candidate clusters of galaxies at redshift ~1.8: the "missing link" between protoclusters and local clusters?

We present three candidate clusters of galaxies at redshifts most likely between 1.7 and 2.0, which corresponds to a fundamentally unexplored epoch of clusters evolution. The candidates were found by studying the environment around our newly selected sample of "beacons" low-luminosity (FRI) radio galaxies in the COSMOS field. In this way we intend to use the fact that FRI at low z are almost invariably located in clusters of galaxies. We use the most accurate photometric redshifts available to date, derived by the COSMOS collaboration using photometry with a set of 30 filters, to look for three-dimensional space over-densities around our objects. Three out of the five FRIs in our sample which possess reliable photometric redshifts between z_phot = 1.7 and 2.0 display overdensities that together are statistically significant at the 4-sigma level, compared to field counts, arguing for the presence of rich clusters of galaxies in their Mpc environment. These first results show that the new method for finding high-z clusters we recently proposed, which makes use of low power FRI radio galaxies instead of the more powerful FRII sources often used in the literature to date, is returning very promising candidates.

astro-ph.CO↗