The big picture of AGN feedback: Black hole accretion and galaxy evolution in multiwavelength surveys

Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time, and so explore the consequences of AGN feedback on galaxy evolution. Recent studies have found significant links between the accretion states of black holes and galaxy stellar populations, local environments, and obscuration by gas and dust. This article describes some recent results and shows how such studies may provide new constraints on models of the co-evolution of galaxies and their central SMBHs. Finally, I discuss observational prospects for the proposed Wide-Field X-ray Telescope mission.Comment: 4 pages, 1 figure. To appear in proceedings of "The Monster's Fiery Breath", Madison, WI, 1-5 June 2009, Eds. Sebastian Heinz & Eric Wilcot

Can Chandra resolve the remaining cosmic X-ray background?

The deepest extragalactic X-ray observation, the 2 Ms Chandra Deep Field North (CDF-N), resolves ~80% of the total extragalactic cosmic X-ray background (CXB) in the 1-2 keV band. Recent work has shown that 70% of the remaining CXB flux is associated with sources detected by the Hubble Space Telescope (HST). This paper uses the existing CDF-N data to constrain the X-ray flux distribution of these X-ray undetected HST sources, by comparing the number of 0.5-2 keV X-ray counts at the HST positions to those expected for model flux distributions. In the simple case where all the undetected HST X-ray sources have the same 0.5-2 keV flux, the data are best fit by 1.5-3 counts per source in 2 Ms, compared to a detection limit (at 10% completeness) of 9 counts. Assuming a more realistic power-law logN-logS distribution [N(>S) S^-alpha], the data favor a relatively steep flux distribution, with alpha=1.1^+0.5_-0.3 (limits are 99% confidence). This slope is very similar to that previously found for faint normal and starburst galaxies in the CDF-N. These results suggest deeper Chandra observations will detect a new population of faint X-ray sources, but extremely deep exposures are needed to resolve the remainder of the soft CXB. In the most optimistic scenario, when the HST sources have the flattest allowed flux distribution and all the sources without HST counterparts are detected, observations 5 times more sensitive than the existing ones would resolve at most ~60% of the remaining soft CXB.Comment: 9 emulateapj pages, 8 figures, v3: matches version to appear in ApJ (note correction to approximation of Poisson errors

Star Formation and Relaxation in 379 Nearby Galaxy Clusters

We investigate the relationship between star formation (SF) and level of relaxation in a sample of 379 galaxy clusters at z < 0.2. We use data from the Sloan Digital Sky Survey to measure cluster membership and level of relaxation, and to select star-forming galaxies based on mid-infrared emission detected with the Wide-Field Infrared Survey Explorer. For galaxies with absolute magnitudes M_r < -19.5, we find an inverse correlation between SF fraction and cluster relaxation: as a cluster becomes less relaxed, its SF fraction increases. Furthermore, in general, the subtracted SF fraction in all unrelaxed clusters (0.117 +/- 0.003) is higher than that in all relaxed clusters (0.097 +/- 0.005). We verify the validity of our SF calculation methods and membership criteria through analysis of previous work. Our results agree with previous findings that a weak correlation exists between cluster SF and dynamical state, possibly because unrelaxed clusters are less evolved relative to relaxed clusters.Comment: 6 pages, 4 figures, accepted for publication in Ap

Are most low-luminosity active galactic nuclei really obscured?

At low Eddington ratios (ṁ), two effects make it more difficult to detect certain active galactic nuclei (AGN) given a particular set of selection methods. First, even allowing for fixed accretion physics, at low ṁ AGN become less luminous relative to their hosts, diluting their emission; the magnitude of the dilution depends on host properties and, therefore, on luminosity and redshift. Secondly, low-forumla systems are expected and observed to transition to a radiatively inefficient state, which changes the spectral energy distribution (SED) shape and dramatically decreases the luminosity at optical through infrared (IR) wavelengths. The effects of dilution are unavoidable, while the precise changes in accretion physics at low ṁ are somewhat uncertain, but potentially very important for our understanding of AGN. These effects will have different implications for samples with different selection criteria, and generically lead to differences in the AGN populations recovered in observed samples, even at fixed bolometric luminosity and after correction for obscuration. Although the true Eddington ratio distribution may depend strongly on mass/luminosity, this will be seen only in surveys robust to dilution and radiative inefficiency, such as X-ray or narrow-line samples; by contrast, selection effects imply that AGN in optical samples will have uniformly high Eddington ratios, with little dependence on luminosity, even at low L_(bol) where the median ‘true’ ṁ ≲ 0.01. These same selection effects also imply that different selection criteria pick out systems with different hosts: as a result, the clustering of low-luminosity optical/IR sources will be weaker than that of X-ray sources, and optical/IR Seyferts will reside in more disc-dominated galaxies, while X-ray-selected Seyferts will be preferentially in early-type systems. Taken together, these effects can naturally explain longstanding, apparently contradictory claims in the literature regarding AGN Eddington ratio distributions, host populations and clustering. Finally, we show that if current observed Eddington ratio distributions are correct, a large fraction of low-luminosity AGN currently classified as ‘obscured’ are in fact radiatively diluted and/or radiatively inefficient, not obscured by gas or dust. This is equally true if X-ray hardness is used as a proxy for obscuration, since radiatively inefficient SEDs near ṁ ~ 0.01 are characteristically X-ray hard. These effects can explain most of the claimed luminosity/redshift dependence in the ‘obscured’ AGN population, with the true obscured fraction as low as ∼20 per cent

Galaxy pairs in the Sloan Digital Sky Survey - XII: The fuelling mechanism of low excitation radio-loud AGN

We investigate whether the fuelling of low excitation radio galaxies (LERGs) is linked to major galaxy interactions. Our study utilizes a sample of 10,800 spectroscopic galaxy pairs and 97 post-mergers selected from the Sloan Digital Sky Survey with matches to multi-wavelength datasets. The LERG fraction amongst interacting galaxies is a factor of 3.5 higher than that of a control sample matched in local galaxy density, redshift and stellar mass. However, the LERG excess in pairs does not depend on projected separation and remains elevated out to at least 500 kpc, suggesting that major mergers are not their main fuelling channel. In order to identify the primary fuelling mechanism of LERGs, we compile samples of control galaxies that are matched in various host galaxy and environmental properties. The LERG excess is reduced, but not completely removed, when halo mass or D4000 are included in the matching parameters. However, when BOTH M_halo and D4000 are matched, there is no LERG excess and the 1.4 GHz luminosities (which trace jet mechanical power) are consistent between the pairs and control. In contrast, the excess of optical and mid-IR selected AGN in galaxy pairs is unchanged when the additional matching parameters are implemented. Our results suggest that whilst major interactions may trigger optically and mid-IR selected AGN, the gas which fuels the LERGs has two secular origins: one associated with the large scale environment, such as accretion from the surrounding medium or minor mergers, plus an internal stellar mechanism, such as winds from evolved stars.Comment: Accepted for publication in MNRAS Letters; 5 page

Students with Disabilities: Fundamentals to Determine the Best Academic Environment

Since the inception of Public Law 94-142 (the Education for All Handicapped Children Act of 1975), students with disabilities have gained access to regular education classrooms. Educating students with disabilities has changed significantly. Much discussion continues to find the basic fundamentals necessary to determine the best learning environment for students with disabilities. This descriptive paper identifies and examines the four fundamentals within the academic community that are responsible for determining and maintaining the best educational environments for students with disabilities: the parental role, the administrators’ support, the teachers’ attitude and aptitude, and the students’ evaluations. Past research studies are synthesized in this paper to show when children with disabilities will learn best. Research shows that in order to have successful educational environments for students with disabilities, the service delivery team of the Individualized Education Plan must include a school community that works together to provide a full continuum of educational options as required by law. This paper applies research of the four education fundamentals to the Christian school setting. Appendices include the continuum of services and four holistic rubrics that clarify the expectations and assess the four fundamentals of successful educational environments