High redshift X-ray cooling-core cluster associated with the luminous radio loud quasar 3C186 (1008.1739v2)

Abstract: We present the first results from a new, deep (200ks) Chandra observation of the X-ray luminous galaxy cluster surrounding the powerful (L ~10^47 erg/s), high-redshift (z=1.067), compact-steep-spectrum radio-loud quasar 3C186. The diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and extends out to radii of at least ~60 arcsec (~500 kpc). The centroid of the diffuse X-ray emission is offset by 0.68(+/-0.11) arcsec (5.5+/-0.9 kpc) from the position of the quasar. We measure a cluster mass within the radius at which the mean enclosed density is 2500 times the critical density, r_2500=283(+18/-13)kpc, of 1.02 (+0.21/-0.14)x10^14 M_sun. The gas mass fraction within this radius is f_gas=0.129(+0.015/-0.016). This value is consistent with measurements at lower redshifts and implies minimal evolution in the f_gas(z) relation for hot, massive clusters at 0<z\<1.1. The measured metal abundance of 0.42(+0.08/-0.07) Solar is consistent with the abundance observed in other massive, high redshift clusters. The spatially-resolved temperature profile for the cluster shows a drop in temperature, from kT~8 keV to kT~3 keV, in its central regions that is characteristic of cooling core clusters. This is the first spectroscopic identification of a cooling core cluster at z\>1. We measure cooling times for the X-ray emitting gas at radii of 50 kpc and 25 kpc of 1.7(+/-0.2)x10^9 years and 7.5(+/-2.6)x 10^8 years, as well as a nominal cooling rate (in the absence of heating) of 400(+/-190)M_sun/year within the central 100 kpc. In principle, the cooling gas can supply enough fuel to support the growth of the supermassive black hole and to power the luminous quasar. The radiative power of the quasar exceeds by a factor of 10 the kinematic power of the central radio source, suggesting that radiative heating may be important at intermittent intervals in cluster cores.

Insights into the High Redshift X-ray Cooling-Core Cluster 3C186

The paper explores the X-ray properties of a galaxy cluster associated with the powerful quasar 3C186, leveraging deep Chandra observations. The primary focus is on the diffuse X-ray emitting cooling-core cluster surrounding this high-redshift, radio-loud quasar.

Key Findings and Numerical Results

The paper describes the properties of the galaxy cluster identified at redshift $z = 1.067$. The notable findings include:

• Cooling Core Identification: The paper reports the first spectroscopic identification of a cooling core cluster beyond $z > 1$, characterized by a marked drop in the X-ray thermal emission gas temperature from the outer regions to the central core, falling from $kT \sim 8$ keV to $kT \sim 3$ keV.
• Cluster Mass and Gas Fraction: The estimated mass within the cluster is $1.02^{+0.21}_{-0.14} \times 10^{14} M_{\odot}$ within the radius where the mean enclosed density is 2500 times the critical density ($r_{2500} = 283^{+18}_{-13}$ kpc). Importantly, this mass is in accordance with other high-redshift systems, and the cluster exhibits a gas mass fraction ($f_{gas}$) of $0.129^{+0.015}_{-0.016}$, which is consistent with the values observed at lower redshifts.
• Elemental Abundance: The metallicity of the cluster gas is measured at $0.42^{+0.08}_{-0.07}$ Solar, indicating the presence of significant quantities of metals similar to other massive, high-redshift clusters.
• Cooling Times and Rates: Cooling times at radii of 50 kpc and 25 kpc are $1.7 \pm 0.2 \times 10^9$ years and $7.5 \pm 2.6 \times 10^8$ years, respectively. The nominal gas cooling rate in absence of heating mechanisms is $400 \pm 190 M_{\odot}\text{year}^{-1}$ within the inner 100 kpc.

Implications

Fueling the Quasar: The cooling gas supports the possibility of nurturing the supermassive black hole that powers the luminous quasar, suggesting the cooling-core phenomenon as a potential source of sustained accretion fuel for the quasar.

Radiative vs. Kinetic Power: Comparing the radiative power of the quasar against the mechanical power of the radio source reveals that the radiative component exceeds the kinetic power by more than an order of magnitude. This suggests intermittent radiative heating might be a crucial mechanism in the evolution of cluster cores and potentially surpasses traditional kinetic methods represented by radio emissions in controlling cooling and heating cycles.

Theoretical Developments: Findings suggest minimal evolution in the cooling-core properties and gas mass fractions at redshifts up to 1.1, underscoring the relevance of these clusters as cosmological tools in tracing the history and development of structure in the universe.

Future Directions

The paper opens inquiries into whether high-redshift clusters might more frequently host AGNs, offering a direction for future X-ray observational campaigns to dissect the interaction dynamics between core-emission mechanisms and quasar activity. Additionally, further observational efforts could provide rich datasets to understand the role of radio-loud AGNs in the thermal history and X-ray morphology of galaxy clusters.

The refinement in methodologies for disentangling quasar emission from cluster properties enables a more precise understanding of these distant systems, fostering advancements in cosmic epoch explorations where quasars and clusters co-evolve. Continued observations might uncover more high-redshift cooling-core clusters, enriching datasets crucial for constraining cosmological parameters and probing structure formation in the early universe.