The Detectability of AGN Cavities in Cooling-Flow Clusters

Chandra X-ray Observatory has revealed X-ray cavities in many nearby cooling flow clusters. The cavities trace feedback from the central active galactic nulceus (AGN) on the intracluster medium (ICM), an important ingredient in stabilizing cooling flows and in the process of galaxy formation and evolution. But, the prevalence and duty cycle of such AGN outbursts is not well understood. To this end, we study how the cooling is balanced by the cavity heating for a complete sample of clusters (the Brightest 55 clusters of galaxies, hereafter B55). In the B55, we found 33 cooling flow clusters, 20 of which have detected X-ray bubbles in their ICM. Among the remaining 13, all except Ophiuchus could have significant cavity power yet remain undetected in existing images. This implies that the duty cycle of AGN outbursts with significant heating potential in cooling flow clusters is at least 60 % and could approach 100 %, but deeper data is required to constrain this further.Comment: 4 pages, 2 figures; to appear in the proceedings of "The Monsters' Fiery Breath", Madison, Wisconsin 1-5 June 2009, Eds. Sebastian Heinz & Eric Wilcots; added annotation to the figur

Jet Interactions with the Hot Halos of Clusters and Galaxies

X-ray observations of cavities and shock fronts produced by jets streaming through hot halos have significantly advanced our understanding of the energetics and dynamics of extragalactic radio sources. Radio sources at the centers of clusters have dynamical ages between ten and several hundred million years. They liberate between 1E58-1E62 erg per outburst, which is enough energy to regulate cooling of hot halos from galaxies to the richest clusters. Jet power scales approximately with the radio synchrotron luminosity to the one half power. However, the synchrotron efficiency varies widely from nearly unity to one part in 10,000, such that relatively feeble radio source can have quasar-like mechanical power. The synchrotron ages of cluster radio sources are decoupled from their dynamical ages, which tend to be factors of several to orders of magnitude older. Magnetic fields and particles in the lobes tend to be out of equipartition. The lobes may be maintained by heavy particles (e.g., protons), low energy electrons, a hot, diffuse thermal gas, or possibly magnetic (Poynting) stresses. Sensitive X-ray images of shock fronts and cavities can be used to study the dynamics of extragalactic radio sources.Comment: 10 pages, 3 figures, invited review, "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, held in Girdwood, Alaska, U.S.A. 21-24 May, 2007, minor text changes; one added referenc

A Deep Chandra Observation of the AGN Outburst and Merger in Hickson Compact Group 62

We report on an analysis of new Chandra data of the galaxy group HCG 62, well known for possessing cavities in its intragroup medium (IGM) that were inflated by the radio lobes of its central active galactic nucleus (AGN). With the new data, a factor of three deeper than previous Chandra data, we re-examine the energetics of the cavities and determine new constraints on their contents. We confirm that the ratio of radiative to mechanical power of the AGN outburst that created the cavities is less than 10^-4, among the lowest of any known cavity system, implying that the relativistic electrons in the lobes can supply only a tiny fraction of the pressure required to support the cavities. This finding implies additional pressure support in the lobes from heavy particles (e.g., protons) or thermal gas. Using spectral fits to emission in the cavities, we constrain any such volume-filling thermal gas to have a temperature kT > 4.3 keV. For the first time, we detect X-ray emission from the central AGN, with a luminosity of L(2-10 keV) = (1.1 +/- 0.4) x 10^39 erg s^-1 and properties typical of a low-luminosity AGN. Lastly, we report evidence for a recent merger from the surface brightness, temperature, and metallicity structure of the IGM.Comment: Accepted to MNRAS, 14 pages, 9 figure

An Energetic AGN Outburst Powered by a Rapidly Spinning Supermassive Black Hole or an Accreting Ultramassive Black Hole

Powering the 10^62 erg nuclear outburst in the MS0735.6+7421 cluster central galaxy by accretion implies that its supermassive black hole (SMBH) grew by ~6x10^8 solar masses over the past 100 Myr. We place upper limits on the amount of cold gas and star formation near the nucleus of <10^9 solar masses and <2 solar masses per year, respectively. These limits imply that an implausibly large fraction of the preexisting cold gas in the bulge must have been consumed by its SMBH at the rate of ~3-5 solar masses per year while leaving no trace of star formation. Such a high accretion rate would be difficult to maintain by stellar accretion or the Bondi mechanism, unless the black hole mass approaches 10^11 solar masses. Its feeble nuclear luminosities in the UV, I, and X-ray bands compared to its enormous mechanical power are inconsistent with rapid accretion onto a ~5x10^9 solar mass black hole. We suggest instead that the AGN outburst is powered by a rapidly-spinning black hole. A maximally-spinning, 10^9 solar mass black hole contains enough rotational energy, ~10^62 erg, to quench a cooling flow over its lifetime and to contribute significantly to the excess entropy found in the hot atmospheres of groups and clusters. Two modes of AGN feedback may be quenching star formation in elliptical galaxies centered in cooling halos at late times. An accretion mode that operates in gas-rich systems, and a spin mode operating at modest accretion rates. The spin conjecture may be avoided in MS0735 by appealing to Bondi accretion onto a central black hole whose mass greatly exceeds 10^10 solar mass. The host galaxy's unusually large, 3.8 kpc stellar core radius (light deficit) may witness the presence of an ultramassive black hole.Comment: Accepted for publication in ApJ. Modifications: adopted slightly higher black hole mass using Lauer's M_SMBH vs L_bulge relation and adjusted related quantities; considered more seriously the consequences of a ultramassive black hole, motivated by new Kormendy & Bender paper published after our submission; other modifications per referee comments by Ruszkowsk

A Powerful AGN Outburst in RBS 797

Utilizing $\sim 50$ ks of Chandra X-ray Observatory imaging, we present an analysis of the intracluster medium (ICM) and cavity system in the galaxy cluster RBS 797. In addition to the two previously known cavities in the cluster core, the new and deeper X-ray image has revealed additional structure associated with the active galactic nucleus (AGN). The surface brightness decrements of the two cavities are unusually large, and are consistent with elongated cavities lying close to our line-of-sight. We estimate a total AGN outburst energy and mean jet power of $\approx 3 - 6 \times 10^{60}$ erg and $\approx 3 - 6 \times 10^{45}$ erg s$^{-1}$, respectively, depending on the assumed geometrical configuration of the cavities. Thus, RBS 797 is apparently among the the most powerful AGN outbursts known in a cluster. The average mass accretion rate needed to power the AGN by accretion alone is $\sim 1 M_{\odot}$ yr$^{-1}$. We show that accretion of cold gas onto the AGN at this level is plausible, but that Bondi accretion of the hot atmosphere is probably not. The BCG harbors an unresolved, non-thermal nuclear X-ray source with a bolometric luminosity of $\approx 2 \times 10^{44}$ erg s$^{-1}$. The nuclear emission is probably associated with a rapidly-accreting, radiatively inefficient accretion flow. We present tentative evidence that star formation in the BCG is being triggered by the radio jets and suggest that the cavities may be driving weak shocks ($M \sim 1.5$) into the ICM, similar to the process in the galaxy cluster MS 0735.6+7421.Comment: Accepted to ApJ; 20 pages, 11 low-resolution figure

Creative professional users musical relevance criteria

Although known item searching for music can be dealt with by searching metadata using existing text search techniques, human subjectivity and variability within the music itself make it very difficult to search for unknown items. This paper examines these problems within the context of text retrieval and music information retrieval. The focus is on ascertaining a relationship between music relevance criteria and those relating to relevance judgements in text retrieval. A data-rich collection of relevance judgements by creative professionals searching for unknown musical items to accompany moving images using real world queries is analysed. The participants in our observations are found to take a socio-cognitive approach and use a range of content and context based criteria. These criteria correlate strongly with those arising from previous text retrieval studies despite the many differences between music and text in their actual content

Interventions to promote patients and families' involvement in adult intensive care settings: a protocol for a mixed-method systematic review.

BACKGROUND: There has been an identified need for greater patient and family member involvement in healthcare. This is particularly relevant in an intensive care unit (ICU), as the family provides a key communicative and practical link between patient and clinician. Family members have been deemed a positive beneficial influence on ICU care and recovery processes, yet they themselves are often emotionally affected after discharge. There has been no standardised evidenced-based approach which explores research on family member involvement and the range and quality of contributions remain unclear. This project will undertake a systematic review to assess the evidence base for interventions designed to promote patient and family member involvement in adult intensive care settings and develop a comprehensive typology of interventions for use by clinicians, patients and carers. METHODS: The following databases will be searched without date restriction: MEDLINE, EMBASE and CINAHL, as well as the Cochrane Central Register of Controlled Trials, Joanna Briggs and Cochrane Libraries. Manual searches of recent back issues of leading ICU and patient experience journals will also be undertaken, as will the reference lists of included studies. Unpublished literature will be sought through grey literature databases, including GreyLit and OpenGrey. All evaluation studies that consider intervention activities to promote patient and family member involvement in adult ICUs will be included; all research designs will be eligible. We will seek to include studies that report on a mixture of relevant outcomes for patients and family members. Abstracts and papers will be independently screened by at least two members of the team to determine their inclusion. Included papers will be assessed for methodological rigour using a standard rating approach, which assesses 'quality of study' and 'quality of information'. Quality assessment will be completed by at least two members of the team. Data on interventions, evaluation methods and outcomes will be collated using a predetermined extraction table. These are likely to be heterogeneous in nature, which will mean that the review will follow a narrative approach to synthesis. DISCUSSION: The review will provide valuable and rigorous insight into the range and quality of interventions available to promote patient and family member involvement in ICU. This is the first step towards addressing the absence of a synthesis of research for this context, and will, in addition, develop a typology of available interventions that will help service users and clinicians make informed decisions about the approaches to patient and family member involvement which they might want to adopt. SYSTEMATIC REVIEW REGISTRATION: PROSPERO (CRD42018086325)

Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

9 figures, 6 tables and 17 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density ($\Sigma_{\rm SFR}$) at 1 kpc scale. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio $\Sigma_{\rm SFR}$ maps using the Condon relation. We compared these maps with hybrid $\Sigma_{\rm SFR}$ maps from a combination of GALEX far-ultraviolet and Spitzer 24 $\mu\rm m$ data using plots tracing the relation at $1.2\times 1.2$-kpc$^2$ resolution. The RC emission is smoothed with respect to the hybrid $\Sigma_{\rm SFR}$ owing to the transport of cosmic-ray electrons (CREs). This results in a sublinear relation $(\Sigma_{\rm SFR})_{\rm RC} \propto [(\Sigma_{\rm SFR})_{\rm hyb}]^{a}$, where $a=0.59\pm 0.13$ (140 MHz) and $a=0.75\pm 0.10$ (1365 MHz). Both relations have a scatter of $\sigma = 0.3~\rm dex$. If we restrict ourselves to areas of young CREs ($\alpha > -0.65$; $I_\nu \propto \nu^\alpha$), the relation becomes almost linear at both frequencies with $a\approx 0.9$ and a reduced scatter of $\sigma = 0.2~\rm dex$. We then simulate the effect of CRE transport by convolving the hybrid $\Sigma_{\rm SFR}$ maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are $l=1$-5 kpc. Solving the CRE diffusion equation, we find diffusion coefficients of $D=(0.13$-$1.5) \times 10^{28} \rm cm^2\,s^{-1}$ at 1 GeV. A RC-SFR relation at $1.4$ GHz can be exploited to measure SFRs at redshift $z \approx 10$ using $140$ MHz observations.Peer reviewe