Search

The powerful combination of the Chandra X-ray telescope, the SCUBA submillimetre-wave camera and the gravitational lensing effect of the massive galaxy clusters A2390 and A1835 has been used to place stringent X-ray flux limits on six faint submillimetre SCUBA sources and deep submillimetre limits on three Chandra sources which lie in fields common to both instruments. One further source is marginally detected in both the X-ray and submillimetre bands. For all the SCUBA sources our results are consistent with starburst-dominated emission. For two objects, including SMMJ 14011+0252 at z=2.55, the constraints are strong enough that they can only host powerful active galactic nuclei if they are both Compton-thick and any scattered X-ray flux is weak or itself absorbed. The lensing amplification for the sources is in the range 1.5–7, assuming that they lie at z>=1. The brightest detected X-ray source has a faint extended optical counterpart (Iapprox. 22) with colours consistent with a galaxy at z=1. The X-ray spectrum of this galaxy is hard, implying strong intrinsic absorption with a column density of about 10[sup 23] cm[sup -2] and an intrinsic (unabsorbed) 2–10 keV luminosity of 3×10[sup 44] erg s[sup -1]. This source is therefore a Type II quasar. The weakest detected X-ray sources are not detected in Hubble Space Telescope images down to I=26. [ABSTRACT FROM AUTHOR]

Summary. Recent papers dealing with the most controversial aspects of AGNs are reviewed. They suggest interesting conclusions: all Seyferts can be described by a single parameter, the X-ray column density; radio loud AGNs may host a rapidly spinning black hole and radio quiet AGNs a slowly spinning black hole; high-ionization AGNs (Seyfert galaxies and QSOs) contain an optically thick, geometrically thin accretion disk, while low-ionization AGNs (Liners) contain an optically thin, geometrically thick accretion disk; a number of blazars have been classified as BLLs on the basis of insufficient data; most objects with weak broad emission lines are in fact HPQs; many objects have been called Liners although they are not AGNs but rather the result of stellar activity; type 2 QSOs exist, but are quite inconspicuous if radio quiet. [ABSTRACT FROM AUTHOR]

We have used near-infrared and optical Integral Field Spectroscopy along with optical images to study the inner 100 pc of NGC 4111 in a project to investigate the stellar and gas kinematics in the surroundings of Supermassive Black Holes in nearby galaxies. We have compared the inner stellar and gas kinematics with data of the outer regions of the galaxy. We found larger scale hot ionized gas and warm molecular gas within the inner 100 pc that is in counter-rotation relative to the stellar kinematics, a sign of inflowing material that is probably triggering an Active Galactic Nucleus. This is supported by the nuclear X-ray emission which is heating the molecular gas and causing it to emit. The presence of large amounts of dust in a polar ring suggests that this is a fairly recent event probably due to the capture of a dwarf galaxy. [ABSTRACT FROM AUTHOR]

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Lyα blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Lyα emitters with a bright () and spatially extended Lyα emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7–6.6. The z70-1 LAB shows extended Lyα emission with a scale length of 1.4 ± 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N v λ1240 emission, or Lyα line broadening, while z49-1 has a strong C iv λ1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Lyα emission of the LABs. The Lyα scale lengths of the core (star-forming region) and halo components are rc = 0.6–1.2 kpc and rh = 2.0–13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Lyα luminosity LLyα, Lyα rest-frame equivalent width EW0, and UV continuum magnitude MUV) of our LABs are similar to those of Lyα halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs. [ABSTRACT FROM AUTHOR]

We perform a systematic search of quasiperiodic variabilities in γ-ray active galactic nuclei in the third Fermi Large Area Telescope source catalog (3FGL). We employ two techniques, Lomb–Scargle Periodogram and Weighted Wavelet Z-transform, to obtain power spectra of γ-ray light curves covering from 2008 August to 2016 December. The results show that besides several objects that have been reported in previous works, an additional source, the flat spectrum radio quasars PKS 0601-70 has a possible quasiperiodic variability of 450 days in its γ-ray light curves with the significance of >3σ. The physical implications of our findings are discussed. [ABSTRACT FROM AUTHOR]

We explore the large to moderate scale anisotropy in distant radio sources using the TIFR GMRT Sky Survey (TGSS) ADR1 catalog. We use different measures, i.e., number counts, sky brightness, and flux per source, for this study. In agreement with earlier results, we report a significant excess of clustering signal above the angular scale of roughly 10° (i.e., l ⪅ 20–30). We find that some survey areas have a systematically low/high flux and argue this may be the cause of the observed signal of excess power at low multipoles. With mocks we demonstrate the effect of such large-scale flux systematics and recover a TGSS-like excess clustering signal by assuming 20% flux uncertainties over ∼10° × 10° sized patches. We argue that that TGSS at this stage, i.e., TGSS ADR1, is not suitable for large-scale clustering measurements. We find that the measure, flux per source, shows evidence of isotropy for all multipoles l > 2 despite the presence of systematics in the data. [ABSTRACT FROM AUTHOR]

We analyze Chandra observations of the hot atmospheres of 40 early spiral and elliptical galaxies. Using new temperature, density, cooling time, and mass profiles, we explore relationships between their hot atmospheres and cold molecular gas. Molecular gas mass correlates with atmospheric gas mass and density over four decades from central galaxies in clusters to normal giant ellipticals and early spirals. The mass and density relations follow power laws: and , respectively, at 10 kpc. The ratio of molecular gas to atmospheric gas within a 10 kpc radius lies between 3% and 10% for early-type galaxies and between 3% and 50% for central galaxies in clusters. Early-type galaxies have detectable levels of molecular gas when their atmospheric cooling times fall below ∼1 Gyr at a radius of 10 kpc. A similar trend is found in central cluster galaxies. We find no relationship between the ratio of the cooling time to free-fall time, tc/tff, and the presence or absence of molecular clouds in early-type galaxies. The data are consistent with much of the molecular gas in early-type galaxies having condensed from their hot atmospheres. [ABSTRACT FROM AUTHOR]

We examine the new Galactic supernova remnant (SNR) candidate, G23.11+0.18, as seen by the Murchison Widefield Array radio telescope. We describe the morphology of the candidate and find a spectral index of −0.63 ± 0.05 in the 70–170 MHz domain. Coincident TeV gamma-ray detection in High Energy Stereoscopic System (HESS) data supports the SNR nature of G23.11+0.18 and suggests that G23.11+0.18 is accelerating particles beyond TeV energies, thus making this object a promising new cosmic-ray hadron source candidate. The remnant cannot be seen in current optical, infrared and X-ray data sets. We do find, however, a dip in CO-traced molecular gas at a line-of-sight velocity of ∼85 km s−1, suggesting the existence of a G23.11+0.18 progenitor wind-blown bubble. Furthermore, the discovery of molecular gas clumps at a neighboring velocity toward HESS J1832−085 adheres to the notion that a hadronic gamma-ray production mechanism is plausible toward the north of the remnant. Based on these morphological arguments, we propose an interstellar medium association for G23.11+0.18 at a kinematic distance of 4.6 ± 0.8 kpc. [ABSTRACT FROM AUTHOR]

The overwhelming foreground contamination is one of the primary impediments to probing the Epoch of Reionization (EoR) through measuring the redshifted 21 cm signal. Among various foreground components, radio halos are less studied and their impacts on the EoR observations are still poorly understood. In this work, we employ the Press–Schechter formalism, merger-induced turbulent reacceleration model, and the latest SKA1-Low layout configuration to simulate the SKA “observed” images of radio halos. We calculate the one-dimensional power spectra from simulated images and find that radio halos can be about 104, 103, and 102.5 times more luminous than the EoR signal on scales of in the 120–128, 154–162, and 192–200 MHz bands, respectively. By examining the two-dimensional power spectra inside properly defined EoR windows, we find that the power leaked by radio halos can still be significant, as the power ratios of radio halos to the EoR signal on scales of can be up to about 230%–800%, 18%–95%, and 7%–40% in the three bands when the 68% uncertainties caused by the variation of the number density of bright radio halos are considered. Furthermore, we find that radio halos located inside the far side lobes of the station beam can also impose strong contamination within the EoR window. In conclusion, we argue that radio halos are severe foreground sources and need serious treatments in future EoR experiments. [ABSTRACT FROM AUTHOR]

We prepare the full sky radio galaxy map (), using the north NRAO VLA Sky Survey and south Sydney University Molonglo Sky Survey galaxy catalogs, and study the large-scale multipole anomalies. These galaxies are roughly at redshift z ∼ 0.8 and are therefore tracing the matter distribution at very large scales. The quadruple and octopole from the radio galaxy catalog are consistent with ΛCDM for a reasonable value of galaxy bias and we do not find dipole–quadruple–octopole alignment as seen in cosmic microwave background (CMB) temperature maps. The quadrupole direction is roughly 46° away from dipole, and the octopole direction is approximately 33° from dipole. The angle between quadrupole and octopole is around 70°. We have large errors in multipole directions due to shot noise. However, with the data that is currently available we do not find any significant alignment between the l = 1, 2, 3 modes. The magnitude of all multipoles, except dipole, are roughly consistent with ΛCDM for reasonable galaxy bias. The dipole magnitude remains inconsistent with CMB as reported in previous studies. Our findings may impose stringent constraints on cosmological models with large-scale anisotropy features. [ABSTRACT FROM AUTHOR]

Highlights from the article: Finally, a deep Ly image reveals a diffuse Ly nebula along a filamentary structure with Extended Ly emissions, or Ly blobs (LABs; Steidel et al. A close-up smoothed Ly image around the HLQSO is An enormous Ly nebula around the QSO High are ionized by the QSO and emit Ly photons which.

We present a measurement of the spatial clustering of rest-frame UV-selected massive galaxies at 0.5 ≤ z ≤ 2.5 in the COSMOS/UltraVISTA field. Considering four separate redshift bins with Δz = 0.5, we construct three galaxy populations, i.e., red sequence (RS), blue cloud (BC), and green valley (GV) galaxies, according to their rest-frame extinction-corrected UV colors. The correlation lengths of these populations are confirmed to be dependent on their rest-frame UV color and redshift: UV redder galaxies are found to be more clustered. In all redshift bins, the GV galaxies generally have medium clustering amplitudes and are hosted within dark matter halos whose masses are more or less between those of RS and BC galaxies; and the clustering amplitude of GV galaxies is close to that of active galactic nuclei (AGNs) in the same redshift bin, suggesting that AGN activity may be responsible for transforming galaxy colors. After carefully examining their stellar masses, we find that the clustering amplitudes of galaxy samples with different colors are all similar once they have a similar median stellar mass and that the median stellar mass alone may be a good predictor of galaxy clustering. [ABSTRACT FROM AUTHOR]

A primary aim of the (NuSTAR) mission is to find and characterize heavily obscured Active Galactic Nuclei (AGNs). Based on mid-infrared photometry from the Wide-Field Infrared Survey Explorer (WISE) and optical photometry from the Sloan Digital Sky Surveys, we have selected a large population of luminous obscured AGNs (i.e., “obscured quasars”). Here we report NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy from the Southern African Large Telescope and W. M. Keck Observatory. Optical diagnostics confirm that all four targets are AGNs. With NuSTAR hard X-ray observations, three of the four objects are undetected, while the fourth has a marginal detection. We confirm that these objects have observed hard X-ray (10–40 keV) luminosities at or below ∼1043 erg s−1. We compare X-ray and IR luminosities to obtain estimates of the hydrogen column densities (NH) based on the suppression of the hard X-ray emission. We estimate NH of these quasars to be at or larger than 1025 cm−2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys, and they do not contribute significantly to the cosmic X-ray background. From the optical Balmer decrements, we found that our three extreme obscured targets lie in highly reddened host environments. This galactic extinction cannot adequately explain the more obscured AGNs, but it may imply a different scale of obscuration in the galaxy. [ABSTRACT FROM AUTHOR]

We estimate the 21 cm radio background from accretion onto the first intermediate-mass black holes between z ≈ 30 and z ≈ 16. Combining potentially optimistic, but plausible, scenarios for black hole formation and growth with empirical correlations between luminosity and radio emission observed in low-redshift active galactic nuclei, we find that a model of black holes forming in molecular cooling halos is able to produce a 21 cm background that exceeds the cosmic microwave background (CMB) at z ≈ 17, though models involving larger halo masses are not entirely excluded. Such a background could explain the surprisingly large amplitude of the 21 cm absorption feature recently reported by the EDGES collaboration. Such black holes would also produce significant X-ray emission and contribute to the 0.5–2 keV soft X-ray background at the level of ≈10−13–10−12 erg s−1 cm−2 deg−2, consistent with existing constraints. In order to avoid heating the intergalactic medium (IGM) over the EDGES trough, these black holes would need to be obscured by hydrogen column depths of NH ∼ 5 × 1023 cm−2. Such black holes would avoid violating constraints on the CMB optical depth from Planck if their UV photon escape fractions were below fesc ≲ 0.1, which would be a natural result of NH ∼ 5 × 1023 cm−2 being imposed by an unheated IGM. [ABSTRACT FROM AUTHOR]

We explore the gas morphology and excitation mechanisms of the ionization cones of the Type II Seyfert galaxy NGC 5728. Near-IR and optical data from the SINFONI and MUSE integral field units on the Very Large Telescope are combined with Hubble Space Telescope optical images, Chandra X-ray data, and Very Large Array radio observations. The complex nuclear structure has a star-forming (SF) ring with a diameter of 2 kpc. A radio jet impacts on the interstellar medium at about 200 pc from the nucleus, with the supernova remnants in the SF ring also present. Emission-line ratios of [Fe ii] and H ii show heavy extinction toward the nucleus, moderate extinction in the SF ring, and reduced extinction in the ionization cones. The active galactic nucleus (AGN) is hidden by a dust bar with up to 19 mag of visual extinction; the dust temperature at the nuclear position is ∼870 K. An X-ray jet is aligned with the ionization cones and associated with high-excitation emission lines of [Si vi] in a coronal line region extending 300 pc from the nucleus. Molecular hydrogen is spatially independent of the cones, concentrated in a disk equatorial to the SF ring, but also showing entrainment along the sides of the bicone. Gas masses for warm and cold H2, H i, and H ii are estimated, and the excitation mechanisms for ionized and molecular gas are elucidated, from both optical (which shows a clean SF–AGN mixing sequence) and infrared diagnostics (which show more complicated, multicomponent excitation regimes). [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/submillimeter Array and Multi-Unit Spectroscopic Explorer observations of the brightest cluster galaxy in Abell 2597, a nearby (z = 0.0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy’s core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning “fountain,” wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales. [ABSTRACT FROM AUTHOR]

In the unified scheme, FR I type radio galaxies are identified with the blazar type active galaxies for which jets are aligned at large angles to the line of sight. A few radio galaxies of this type have been discovered to emit GeV–TeV gamma-rays. We consider a scenario that naturally explains the very high energy gamma-ray emission at large angles to the jet axis. It is proposed that two emission regions are present in the jet at this same moment. The inner region (blob I) moves with the large Lorentz factor, producing radiation strongly collimated along the jet axis, as observed in BL Lac type blazars. On the other hand, the outer region (blob II), which moves with the mild Lorentz factor, contains isotropically distributed relativistic electrons in the blob reference frame. These electrons upscatter monodirectional soft radiation from blob I preferentially in the direction opposite to the jet motion. Therefore, gamma-rays, produced in blob II, can be emitted at relatively large angles to the jet axis in the observer’s reference frame. We analyze the basic emission features of such an external blob radiation model. The example modeling of the emission from the FR I type radio galaxy, NGC 1275, is presented. [ABSTRACT FROM AUTHOR]

Radio jets in active galaxies have been expected to interact with circumnuclear environments in their early phase evolutions. By performing the multi-epoch monitoring observation with the KVN and VERA Array at 43 GHz, we investigate the kinematics of the notable newborn bright component C3 located at the tip of the recurrent jet of 3C 84. During 2015 August–September, we discover the flip of C3 and the amount of the flip is about 0.4 mas in angular scale, which corresponds to 0.14 parsec in physical scale. After the flip of C3, it wobbled at the same location for a few months and then it restarted to propagate toward the southern direction. The flux density of C3 coherently showed the monotonic increase during the observation period. The flip is in good agreement with hydrodynamical simulations of jets in clumpy ambient medium. We estimate the number density of the putative clump based on the momentum balance between the jet thrust and the ram pressure from the clump and it is about 103–5 cm−3. We briefly discuss possible origins of the clump. [ABSTRACT FROM AUTHOR]

We present recent ALMA observations of the CO (1–0) and CO (3–2) emission lines in the brightest cluster galaxy of RXC J1504.1−0248, which is one of the most extreme cool core clusters known. The central galaxy contains of molecular gas. The molecular gas morphology is complex and disturbed, showing no evidence for a rotationally supported structure in equilibrium. A total of 80% of the gas is situated within the central 5 kpc of the galactic center, while the remaining gas is located in a 20 kpc long filament. The cold gas has likely condensed out of the hot atmosphere. The filament is oriented along the edge of a putative X-ray cavity, suggesting that active galactic nucleus activity has stimulated condensation. This is energetically feasible, although the morphology is not as conclusive as systems whose molecular filaments trail directly behind buoyant radio bubbles. The velocity gradient along the filament is smooth and shallow. It is only consistent with freefall if it lies within 20° of the plane of the sky. The abundance of clusters with comparably low velocities suggests that the filament is not freefalling. Both the central gas and filamentary gas are coincident with bright UV emission from ongoing star formation. Star formation near the cluster core is consistent with the Kennicutt–Schmidt law. The filament exhibits increased star formation surface densities, possibly resulting from either the consumption of a finite molecular gas supply or spatial variations in the CO-to-H2 conversion factor. [ABSTRACT FROM AUTHOR]

We conduct a stacking analysis using the combination of 1.4 GHz detections in the NRAO VLA Sky Survey (NVSS) and Planck all-sky maps to estimate the differential source counts down to the few 100 μJy level at 30, 44, 70, and 100 GHz. Using these source count estimates, we are able to measure the integrated extragalactic background light from discrete sources at these frequencies for comparison with the fit to the total radio sky measurements from ARCADE 2. By integrating down to a 1.4 GHz flux density of ≈2 μJy, we measure integrated, extragalactic brightness temperatures from discrete sources of 105.63 ± 10.56 mK, 21.76 ± 3.09 μK, 8.80 ± 0.95 μK, 2.59 ± 0.27 μK, and 1.15 ± 0.10 μk at 1.4, 30, 44, 70, and 100 GHz, respectively. Our measurement at 1.4 GHz is slightly larger than previous measurements, most likely due to using NVSS data compared with older interferometric data in the literature, but it still remains a factor of ≈4.5 below that required to account for the excess extragalactic sky brightness measured at 1.4 GHz by ARCADE 2. The fit to ARCADE 2 total extragalactic sky brightness measurements is also a factor of ≈8.6, 6.6, 6.2, and 4.9 times brighter than what we estimate from discrete sources at 30, 44, 70, and 100 GHz, respectively. The extragalactic sky spectrum (i.e., Tb ∝ νβ) from discrete sources appears to flatten with increasing frequency, having a spectral index of β = −2.82 ± 0.06 between 1.4 and 30 GHz, flattening to β = −2.39 ± 0.12 between 30 and 100 GHz. We estimate that the spectral flattening most likely arises from a combination of gigahertz-peaked sources and the hardening of the spectra of radio-detected sources at higher frequencies, particularly at faint flux densities. However, the precise origin of a hard component of energetic electrons responsible for the emission remains unclear. [ABSTRACT FROM AUTHOR]

We present a study of 107 galaxies, groups, and clusters spanning ∼3 orders of magnitude in mass, ∼5 orders of magnitude in central galaxy star formation rate (SFR), ∼4 orders of magnitude in the classical cooling rate () of the intracluster medium (ICM), and ∼5 orders of magnitude in the central black hole accretion rate. For each system in this sample, we measure the ICM cooling rate, , using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding % for systems with M⊙ yr−1. For these systems, we measure a slope in the SFR– relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical versus radiative) of feedback. For systems with M⊙ yr−1, we find that the SFR and are uncorrelated and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at a fixed of 0.52 ± 0.06 dex (1σ rms), suggesting that cooling is tightly self-regulated over very long timescales but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (∼0.4 dex) for systems for which the mechanical feedback power is within a factor of two of the cooling luminosity. [ABSTRACT FROM AUTHOR]

We made two new sensitive (rms noise μJy beam−1) high-resolution (θ = 3.″0 and θ = 0.″66 FWHM) S-band (2 < ν < 4 GHz) images covering a single JVLA primary beam (FWHM ≈ 14′) centered on J2000 , δ = +59°01′ in the Lockman Hole. These images yielded a catalog of 792 radio sources, 97.7 ± 0.8% of which have infrared counterparts stronger than S ≈ 2 μJy at λ = 4.5 μm. About 91% of the radio sources found in our previously published, comparably sensitive low-resolution (θ = 8″ FWHM) image covering the same area were also detected at 0.″66 resolution, so most radio sources with S(3 GHz) ≳ 5 μJy have angular structure ϕ ≲ 0.″66. The ratios of peak brightness in the 0.″66 and 3″ images have a distribution indicating that most μJy radio sources are quite compact, with a median Gaussian angular diameter FWHM and an rms scatter σϕ ≲ 0.″3 of individual sizes. Most of our μJy radio sources obey the tight far-infrared/radio correlation, indicating that they are powered by star formation. The median effective angular radius enclosing half the light emitted by an exponential disk is , so the median effective radius of star-forming galaxies at redshifts z ∼ 1 is . [ABSTRACT FROM AUTHOR]

Forward modeling of the full galaxy SED is a powerful technique, providing self-consistent constraints on stellar ages, dust properties, and metallicities. However, the accuracy of these results is contingent on the accuracy of the model. One significant source of uncertainty is the contribution of obscured AGN, as they are relatively common and can produce substantial mid-IR (MIR) emission. Here we include emission from dusty AGN torii in the Prospector SED-fitting framework, and fit the UV–IR broadband photometry of 129 nearby galaxies. We find that 10% of the fitted galaxies host an AGN contributing >10% of the observed galaxy MIR luminosity. We demonstrate the necessity of this AGN component in the following ways. First, we compare observed spectral features to spectral features predicted from our model fit to the photometry. We find that the AGN component greatly improves predictions for observed Hα and Hβ luminosities, as well as mid-infrared Akari and Spitzer/IRS spectra. Second, we show that inclusion of the AGN component changes stellar ages and SFRs by up to a factor of 10, and dust attenuations by up to a factor of 2.5. Finally, we show that the strength of our model AGN component correlates with independent AGN indicators, suggesting that these galaxies truly host AGN. Notably, only 46% of the SED-detected AGN would be detected with a simple MIR color selection. Based on these results, we conclude that SED models which fit MIR data without AGN components are vulnerable to substantial bias in their derived parameters. [ABSTRACT FROM AUTHOR]

We present an analysis of 55 central galaxies in clusters and groups with molecular gas masses and star formation rates lying between and 0.5 and 270 , respectively. Molecular gas mass is correlated with star formation rate, Hα line luminosity, and central atmospheric gas density. Molecular gas is detected only when the central cooling time or entropy index of the hot atmosphere falls below ∼1 Gyr or ∼35 keV cm2, respectively, at a (resolved) radius of 10 kpc. These correlations indicate that the molecular gas condensed from hot atmospheres surrounding the central galaxies. We explore the origins of thermally unstable cooling by evaluating whether molecular gas becomes prevalent when the minimum of the cooling to free-fall time ratio () falls below ∼10. We find that (1) molecular gas-rich systems instead lie between , where corresponds approximately to cooling time and entropy thresholds of 1 Gyr and , respectively; (2) ) is uncorrelated with molecular gas mass and jet power; and (3) the narrow range can be explained by an observational selection effect, although a real physical effect cannot be excluded. These results and the absence of isentropic cores in cluster atmospheres are in tension with models that assume thermal instability ensues from linear density perturbations in hot atmospheres when . Some of the molecular gas may instead have condensed from atmospheric gas lifted outward by buoyantly rising X-ray bubbles or by dynamically induced uplift (e.g., mergers, sloshing). [ABSTRACT FROM AUTHOR]

We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z ≈ 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 M⊙ yr−1. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submillimeter dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submillimeter/radio-detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3% among the submillimeter-detected LABs, which is lower than a lower limit of 11% for the submillimeter-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data. [ABSTRACT FROM AUTHOR]

We present observations in CO (3–2) that, combined with previous observations in CO (2–1), constrain the physical properties of the filamentary molecular gas in the central ∼6.5 kpc of NGC 1275, the central giant elliptical galaxy of the Perseus Cluster. We find this molecular gas to have a temperature K and a density , typically warmer and denser than the bulk of Giant Molecular Clouds (GMCs) in the Galaxy. Bathed in the harsh radiation and particle field of the surrounding intracluster X-ray gas, the molecular gas likely has a much higher ionization fraction than that of GMCs. For an ionization fraction of ∼10−4, similar to that of Galactic diffuse () partially molecular clouds that emit in HCN (1–0) and HCO+ (1–0), we show that the same gas traced in CO can produce the previously reported emissions in HCN (3–2), HCO+ (3–2), and CN (2–1) from NGC 1275; the dominant source of excitation for all the latter molecules is collisions with electrons. For the molecular filaments to not collapse, as evidenced by their lack of star formation, they must consist of thin strands that have cross-sectional radii ≲0.2–2 pc if supported solely by thermal gas pressure; larger radii are permissible if turbulence or poloidal magnetic fields provide additional pressure support. We point out that the conditions required to relate CO luminosities to molecular gas masses in our Galaxy are unlikely to apply in cluster central elliptical galaxies. Rather than being virialized structures analogous to GMCs, we propose that the molecular gas in NGC 1275 comprises pressure-confined structures created by turbulent flows. [ABSTRACT FROM AUTHOR]

We analyze heating and cooling processes in an idealized simulation of a cool-core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense. We find that, on average, energy dissipation via shock waves is almost an order of magnitude higher than via turbulence. Most of the shock waves in the simulation are very weak shocks with Mach numbers smaller than 1.5, but the stronger shocks, although rare, dissipate energy more effectively. We find that shock dissipation is a steep function of radius, with most of the energy dissipated within 30 kpc, more spatially concentrated than radiative cooling loss. However, adiabatic processes and mixing (of post-shock materials and the surrounding gas) are able to redistribute the heat throughout the core. A considerable fraction of the AGN energy also escapes the core region. The cluster goes through cycles of AGN outbursts accompanied by periods of enhanced precipitation and star formation, over gigayear timescales. The cluster core is under-heated at the end of each cycle, but over-heated at the peak of the AGN outburst. During the heating-dominant phase, turbulent dissipation alone is often able to balance radiative cooling at every radius but, when this is occurs, shock waves inevitably dissipate even more energy. Our simulation explains why some clusters, such as Abell 2029, are cooling dominated, while in some other clusters, such as Perseus, various heating mechanisms including shock heating, turbulent dissipation and bubble mixing can all individually balance cooling, and together, over-heat the core. [ABSTRACT FROM AUTHOR]

We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates (SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far-IR. By comparing these quantities to intracluster medium (ICM) cooling times and freefall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR and the ICM cooling time to freefall time ratio, , with an upper limit on the intrinsic scatter of 0.15 dex. Furthermore, starburst durations may correlate with ICM cooling times at a radius of , and the two quantities converge upon reaching the gigayear regime. Our results provide a direct observational link between the thermodynamical state of the ICM and the intensity and duration of BCG star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable ICM overdensities that fuel long-duration (>1 Gyr) BCG starbursts. This scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between SFR and . We also find that the scaling relation between SFR and dust mass in BCGs with SFRs yr−1 is similar to that in star-forming field galaxies; BCGs with large ( yr−1) SFRs have dust masses comparable to extreme starbursts. [ABSTRACT FROM AUTHOR]

Our sensitive (), high-resolution (FWHM ), 10 GHz image covering a single Karl G. Jansky Very Large Array (VLA) primary beam (FWHM ) in the GOODS-N field contains 32 sources with and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is , with rms scatter . In units of the effective radius that encloses half their flux, these radio sizes are , with rms scatter . These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected Hα sizes. We made a low-resolution () image with better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices . It contains six new sources with and OIR counterparts. The median redshift of all 38 sources is . The 19 sources with 1.4 GHz counterparts have a median spectral index of , with rms scatter . Including upper limits on α for sources not detected at 1.4 GHz flattens the median to , suggesting that the μJy radio sources at higher redshifts—and hence those selected at higher rest-frame frequencies—may have flatter spectra. If the non-thermal spectral index is , the median thermal fraction of sources selected at median rest-frame frequency is ≳48%. [ABSTRACT FROM AUTHOR]

The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at ∼65 and west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium (ICM) was recently disturbed. We analyze the properties of the ICM using multiple Chandra observations of Abell 2204. We find a density ratio of and a temperature ratio of (projected, or 1.87 ± 0.56 deprojected) across the western edge, and correspondingly and (projected, or 1.25 ± 0.26 deprojected) across the eastern edge. These values are typical of cold fronts in galaxy clusters. This, together with the spiral pattern observed in the cluster core, supports the sloshing scenario for Abell 2204. No Kelvin–Helmholtz eddies are observed along the cold front surfaces, indicating that they are effectively suppressed by some physical mechanism. We argue that the suppression is likely facilitated by the magnetic fields amplified in the sloshing motion and deduce from the measured gas properties that the magnetic field strength should be greater than 24 ± 6 μG and 32 ± 8 μG along the west and east cold fronts, respectively. [ABSTRACT FROM AUTHOR]

We study the long-term ( years) radio variability of 43 radio-bright active galactic nuclei (AGNs) by exploiting the database of the University of Michigan Radio Astronomy Observatory monitoring program. We model the periodograms (temporal power spectra) of the observed light curves as simple power-law noise (red noise, spectral power ) using Monte Carlo simulations, taking into account windowing effects (red-noise leak, aliasing). The power spectra of 39 (out of 43) sources are in good agreement with the models, yielding a range in power spectral index (β) from ≈1 to ≈3. We fit a Gaussian function to each flare in a given light curve to obtain the flare duration. We discover a correlation between β and the median duration of the flares. We use the derivative of a light curve to obtain a characteristic variability timescale, which does not depend on the assumed functional form of the flares, incomplete fitting, and so on. We find that, once the effects of relativistic Doppler boosting are corrected for, the variability timescales of our sources are proportional to the accretion rate to the power of 0.25 ± 0.03 over five orders of magnitude in accretion rate, regardless of source type. We further find that modeling the periodograms of four of our sources requires the assumption of broken power-law spectra. From simulating light curves as superpositions of exponential flares, we conclude that strong overlap of flares leads to featureless simple power-law periodograms of AGNs at radio wavelengths in most cases. [ABSTRACT FROM AUTHOR]

During a systematic search for supermassive black holes (SMBHs) not in galactic nuclei, we identified the compact, symmetric radio source B3 1715+425 with an emission-line galaxy offset from the nucleus of the brightest cluster galaxy (BCG) in the redshift z = 0.1754 cluster ZwCl 8193. B3 1715+425 is too bright (brightness temperature at observing frequency ) and too luminous (1.4 GHz luminosity ) to be powered by anything but an SMBH, but its host galaxy is much smaller ( full width between half-maximum points) and optically fainter (R-band absolute magnitude ) than any other radio galaxy. Its high radial velocity relative to the BCG, continuous ionized wake extending back to the BCG nucleus, and surrounding debris indicate that the radio galaxy was tidally shredded passing through the BCG core, leaving a nearly naked SMBH fleeing from the BCG with space velocity . The radio galaxy has mass and infrared luminosity close to its dust Eddington limit, so it is vulnerable to further mass loss from radiative feedback. [ABSTRACT FROM AUTHOR]