Cool gas in brightest cluster galaxies

This thesis deals with the cool gas, i.e. less than 10000 degrees Kelvin, at the centres of relaxed, rich galaxy clusters. We find that a significant amount of this gas exists within a 50 kiloparsec nebula centered on the Brightest Cluster Galaxy. The cool gas is locked up in long, thin filaments and exists in three phases, i.e. ionised, atomic and molecular, that share the same extent and dynamics. The bright line emission of this gas implies rapid cooling. However, the inferred cooling rates are not in line with observations and therefore this gas requires continues reheating. The total reheating necessary rivals that of the hot X-ray emitting phase. Several sources of reheating are investigated with heating by X-rays or Cosmic rays being the most promising candidatesUBL - phd migration 201

Discovery of five low-luminosity active galactic nuclei at the centre of the Perseus cluster

Galaxie

ALMA observation of the disruption of molecular gas in M87

We present the results from Atacama Large Millimeter Array (ALMA) observations centred 40 arcsec (3 kpc in projection) south-east of the nucleus of M87. We report the detection of extended CO (2-1) line emission with a total flux of (5.5 ± 0.6) × 10-18 erg s-1 cm-2 and corresponding molecular gas mass M_{H_2}=(4.7 ± 0.4) × 10^5 M_{⊙}, assuming a Galactic CO to H2 conversion factor. ALMA data indicate a line-of-sight velocity of -129 ± 3 km s-1, in good agreement with measurements based on the [C II] and H α+[N II] lines, and a velocity dispersion of σ = 27 ± 3 km s-1. The CO (2-1) emission originates only outside the radio lobe of the active galactic nucleus (AGN) seen in the 6 cm Very Large Array image, while the filament prolongs further inwards at other wavelengths. The molecular gas in M87 appears to be destroyed or excited by AGN activity, either by direct interaction with the radio plasma, or by the shock driven by the lobe into the X-ray emitting atmosphere. This is an important piece of the puzzle in understanding the impact of the central AGN on the amount of the coldest gas from which star formation can proceed

Spatially resolved studies of extragalactic jets in high redshift radio galaxies

High Energy Astrophysic

Taking snapshots of the jet-ISM interplay: the case of PKS 0023-26

High Energy Astrophysic

ALMA observations of PKS 1549-79: a case of feeding and feedback in a young radio quasar

Large scale structure and cosmolog

Arecibo-green bank-LOFAR carbon radio recombination line observations toward cold H I clouds

Interstellar matter and star formatio

Mapping low-frequency carbon radio recombination lines towards Cassiopeia A at 340, 148, 54, and 43 MHz

Quantitative understanding of the interstellar medium requires knowledge of its physical conditions. Low-frequency carbon radio recombination lines (CRRLs) trace cold interstellar gas and can be used to determine its physical conditions (e.g. electron temperature and density). In this work, we present spatially resolved observations of the low-frequency (≤390 MHz) CRRLs centred around C268α, C357α, C494α, and C539α towards Cassiopeia A on scales of ≤1.2 pc. We compare the spatial distribution of CRRLs with other interstellar medium tracers. This comparison reveals a spatial offset between the peak of the CRRLs and other tracers, which is very characteristic for photodissociation regions and that we take as evidence for CRRLs being preferentially detected from the surfaces of molecular clouds. Using the CRRLs, we constrain the gas electron temperature and density. These constraints on the gas conditions suggest variations of less than a factor of 2 in pressure over ˜1 pc scales, and an average hydrogen density of 200-470 cm-3. From the electron temperature and density maps, we also constrain the ionized carbon emission measure, column density, and path length. Based on these, the hydrogen column density is larger than 1022 cm-2, with a peak of ˜4 × 1022 cm-2 towards the south of Cassiopeia A. Towards the southern peak, the line-of-sight length is ˜40 pc over a ˜2 pc wide structure, which implies that the gas is a thin surface layer on a large (molecular) cloud that is only partially intersected by Cassiopeia A. These observations highlight the utility of CRRLs as tracers of low-density extended H I and CO-dark gas halo's around molecular clouds.Interstellar matter and star formatio

Deep study of A399-401: application of a wide-field facet calibration

Galaxie