The Cluster and Field Galaxy Active Galactic Nucleus Fraction at Z = 1-1.5: Evidence for a Reversal of the Local Anticorrelation between Environment and AGN Fraction

The fraction of cluster galaxies that host luminous active galactic nuclei (AGNs) is an important probe of AGN fueling processes, the cold interstellar medium at the centers of galaxies, and how tightly black holes and galaxies co-evolve. We present a new measurement of the AGN fraction in a sample of 13 clusters of galaxies (M \u3e= 1014 M ⊙) at 1 \u3c z \u3c 1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the field fraction in the immediate vicinity of these clusters, and combine these data with measurements from the literature to quantify the relative evolution of cluster and field AGN from the present to z ~ 3. We estimate that the cluster AGN fraction at 1 \u3c z \u3c 1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGNs with a rest-frame, hard X-ray luminosity greater than L X, H \u3e= 1044 erg s-1. This fraction is measured relative to all cluster galaxies more luminous than M^*_{3.6}(z) + 1, where M^*_{3.6}(z) is the absolute magnitude of the break in the galaxy luminosity function at the cluster redshift in the IRAC 3.6 μm bandpass. The cluster AGN fraction is 30 times greater than the 3σ upper limit on the value for AGNs of similar luminosity at z ~ 0.25, as well as more than an order of magnitude greater than the AGN fraction at z ~ 0.75. AGNs with L X, H \u3e= 1043 erg s-1 exhibit similarly pronounced evolution with redshift. In contrast to the local universe, where the luminous AGN fraction is higher in the field than in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters are consistent at 1 \u3c z \u3c 1.5. This is evidence that the cluster AGN population has evolved more rapidly than the field population from z ~ 1.5 to the present. This environment-dependent AGN evolution mimics the more rapid evolution of star-forming galaxies in clusters relative to the field

The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction

The fraction of cluster galaxies that host luminous AGN is an important probe of AGN fueling processes, the cold ISM at the centers of galaxies, and how tightly black holes and galaxies co-evolve. We present a new measurement of the AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at 1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the field fraction in the immediate vicinity of these clusters, and combine these data with measurements from the literature to quantify the relative evolution of cluster and field AGN from the present to z~3. We estimate that the cluster AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame, hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1, where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The cluster AGN fraction is 30 times greater than the 3sigma upper limit on the value for AGN of similar luminosity at z~0.25, as well as more than an order of magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43} erg/s exhibit similarly pronounced evolution with redshift. In contrast with the local universe, where the luminous AGN fraction is higher in the field than in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters are consistent at 1<z<1.5. This is evidence that the cluster AGN population has evolved more rapidly than the field population from z~1.5 to the present. This environment-dependent AGN evolution mimics the more rapid evolution of star-forming galaxies in clusters relative to the field.Comment: ApJ Accepted. 16 pages, 8 figures in emulateapj forma

The Impact of Cluster Structure and Dynamical State on Scatter in the Sunyaev-Zel'dovich Flux-Mass Relation

Cosmological constraints from cluster surveys rely on accurate mass estimates from the mass-observable relations. In order to avoid systematic biases and reduce uncertainties, we study the form and physical origin of the intrinsic scatter about the mean Sunyaev-Zel'dovich (SZ) flux-mass relation using a hydrodynamical simulation of galaxy cluster formation. We examine the assumption of lognormal scatter and detect non-negligible positive skewness and kurtosis (> 0.5) for a wide range of limiting masses and redshifts. These higher-order moments should be included in the parametrization of scatter in order not to bias cosmological constraints. We investigate the sources of the scatter by correlating it with measures of cluster morphology, halo concentration, and dynamical state, and we quantify the individual contribution from each source. We find that statistically the impact of dynamical state is weak, so the selection bias due to mergers is negligible. On the other hand, there is a strong correlation between the scatter and halo concentration, which can be used to reduce the scatter significantly (from 12.07% to 7.34% or by ~40% for clusters at z = 0). We also show that a cross-calibration by combining information from X-ray followups can be used to reduce the scatter in the flux-mass relation and also identify outliers in both X-ray and SZ cluster surveys.Comment: 14 pages, 12 figures; accepted for publication in Ap

A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization

(Brief Summary) What is the total radiative content of the Universe since the epoch of recombination? The extragalactic background light (EBL) spectrum captures the redshifted energy released from the first stellar objects, protogalaxies, and galaxies throughout cosmic history. Yet, we have not determined the brightness of the extragalactic sky from UV/optical to far-infrared wavelengths with sufficient accuracy to establish the radiative content of the Universe to better than an order of magnitude. Among many science topics, an accurate measurement of the EBL spectrum from optical to far-IR wavelengths, will address: What is the total energy released by stellar nucleosynthesis over cosmic history? Was significant energy released by non-stellar processes? Is there a diffuse component to the EBL anywhere from optical to sub-millimeter? When did first stars appear and how luminous was the reionization epoch? Absolute optical to mid-IR EBL spectrum to an astrophysically interesting accuracy can be established by wide field imagingat a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is reduced by more than two orders of magnitude.Comment: 7 pages; Science White Paper for the US Astro 2010-2020 Decadal Survey. If interested in further community-wide efforts on this topic please contact the first autho

Mid-Infrared Selection of Active Galaxies

Mid-infrared photometry provides a robust technique for identifying active galaxies. While the ultraviolet to mid-infrared continuum of normal galaxies is dominated by the composite stellar black body curve and peaks at approximately 1.6 microns, the ultraviolet to mid-infrared continuum of active galaxies is dominated by a power law. Consequently, with sufficient wavelength baseline, one can easily distinguish AGN from stellar populations. Mirroring the tendency of AGN to be bluer than galaxies in the ultraviolet, where galaxies (and stars) sample the blue, rising portion of stellar spectra, AGN tend to be redder than galaxies in the mid-infrared, where galaxies sample the red, falling portion of the stellar spectra. We report on Spitzer Space Telescope mid-infrared colors, derived from the IRAC Shallow Survey, of nearly 10,000 spectroscopically identified sources from the AGN and Galaxy Evolution Survey. Based on this spectroscopic sample, we find that simple mid-infrared color criteria provide remarkably robust separation of active galaxies from normal galaxies and Galactic stars, with over 80% completeness and less than 20% contamination. Considering only broad-lined AGN, these mid-infrared color criteria identify over 90% of spectroscopically identified quasars and Seyfert 1s. Applying these color criteria to the full imaging data set, we discuss the implied surface density of AGN and find evidence for a large population of optically obscured active galaxies.Comment: 13 pages, 3 figures; submitted to the Astrophysical Journal Letter

Giving an Account of One’s Pain in the Anthropological Interview

In this paper, I analyze the illness stories narrated by a mother and her 13-year-old son as part of an ethnographic study of child chronic pain sufferers and their families. In examining some of the moral, relational and communicative challenges of giving an account of one’s pain, I focus on what is left out of some accounts of illness and suffering and explore some possible reasons for these elisions. Drawing on recent work by Judith Butler (Giving an Account of Oneself, 2005), I investigate how the pragmatic context of interviews can introduce a form of symbolic violence to narrative accounts. Specifically, I use the term “genre of complaint” to highlight how anthropological research interviews in biomedical settings invoke certain typified forms of suffering that call for the rectification of perceived injustices. Interview narratives articulated in the genre of complaint privilege specific types of pain and suffering and cast others into the background. Giving an account of one’s pain is thus a strategic and selective process, creating interruptions and silences as much as moments of clarity. Therefore, I argue that medical anthropologists ought to attend more closely to the institutional structures and relations that shape the production of illness narratives in interview encounters