Search

We have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (LLyα ≈ 1044 erg s-1) and nearest (z ≈ 2.38) of all Lyα blobs (LABs). The target, known in the literature as object "B1", lies at a redshift where the main optical emission lines are accessible in the observed near-infrared.We detect luminous [O III] λλ4959,5007 and Hα emission with a spatial extent of at least 32 × 40 kpc (4" × 5"). The dominant optical emission line component shows relatively broad lines (600-800 km s-1, FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. The new evidence for AGN photoionization, combined with previously detected C IV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [O II] is relatively weak compared with [O III] (extinction-corrected [O III]/[O II] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the extinction-corrected [O III] luminosity we infer a bolometric AGN luminosity of ~3×1046 erg s-1, and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow-line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Lyα, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Lyα in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment. [ABSTRACT FROM AUTHOR]

With two central galaxies engaged in a major merger and a remarkable chain of 19 young stellar superclusters wound around them in projection, the galaxy cluster SDSS J1531+3414 (z = 0.335) offers an excellent laboratory to study the interplay between mergers, active galactic nucleus (AGN) feedback, and star formation. New Chandra X-ray imaging reveals rapidly cooling hot (T ∼ 106 K) intracluster gas, with two "wings" forming a concave density discontinuity near the edge of the cool core. LOFAR 144 MHz observations uncover diffuse radio emission strikingly aligned with the "wings," suggesting that the "wings" are actually the opening to a giant X-ray supercavity. The steep radio emission is likely an ancient relic of one of the most energetic AGN outbursts observed, with 4 pV > 1061 erg. To the north of the supercavity, GMOS detects warm (T ∼ 104 K) ionized gas that enshrouds the stellar superclusters but is redshifted up to +800 km s−1 with respect to the southern central galaxy. The Atacama Large Millimeter/submillimeter Array detects a similarly redshifted ∼1010 M ⊙ reservoir of cold (T ∼ 102 K) molecular gas, but it is offset from the young stars by ∼1–3 kpc. We propose that the multiphase gas originated from low-entropy gas entrained by the X-ray supercavity, attribute the offset between the young stars and the molecular gas to turbulent intracluster gas motions, and suggest that tidal interactions stimulated the "beads-on-a-string" star formation morphology. [ABSTRACT FROM AUTHOR]

We report ALMA Early Science CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in A1664. The BCG contains 1.1 × 1010M☼ of molecular gas divided roughly equally between two distinct velocity systems: one from –250 to +250 km s–1 centered on the BCG's systemic velocity and a high-velocity system blueshifted by 570 km s–1 with respect to the systemic velocity. The BCG's systemic component shows a smooth velocity gradient across the BCG center, suggestive of rotation about the nucleus. However, the mass and velocity structure are highly asymmetric and there is little star formation coincident with a putative disk. It may be an inflow of gas that will settle into a disk over several 108 yr. The high-velocity system consists of two gas clumps, each ∼2 kpc across, located to the north and southeast of the nucleus. Each has a line of sight velocity spread of 250-300 km s–1. The velocity of the gas in the high-velocity system increases toward the BCG center and may be a massive flow into the nucleus. However, the velocity gradient is not smooth. These structures are also coincident with low optical-ultraviolet surface brightness regions, which could indicate dust extinction associated with each clump. The structure is complex, making a clear interpretation difficult, but if the dusty, molecular gas lies predominantly in front of the BCG, the blueshifted velocities would indicate an outflow. Based on the energy requirements, such a massive outflow would most likely be driven by the active galactic nucleus. A merger origin is unlikely but cannot be ruled out. [ABSTRACT FROM AUTHOR]

We present the correlation between Lyα absorbers and H i galaxies in the nearby universe (0.01 ≤ z ≤ 0.057). We find that Lyα absorbers are strongly correlated to H i galaxies at a projected separation of ≤0.5 Mpc and velocity separation of ≤50 km s−1. Lyα absorbers are 7.6 times more likely to be found near H i galaxies compared to a random distribution. The strength of correlations drops as the projected and/or velocity separation increases. We also find the correlation between Lyα absorbers and H i galaxies to be stronger than those observed between Lyα absorbers and optically selected galaxies. There is an enhancement in the number of absorbers at velocity separations of ≤30 km s−1 from galaxies at distances larger than their viral radius. Combined with the fact that most of our galaxies are not driving strong outflows, we conclude that the absorbers at low-velocity separations are tracing reservoirs of cooler gas around galaxies. This conclusion is consistent with the predictions from cosmological simulations where faint gas from the IGM flows into the disks of galaxies leading to galaxy growth. [ABSTRACT FROM AUTHOR]

We present 0.″14 resolution Atacama Large Millimeter/submillimeter Array (ALMA) CO(2âˆ'1) observations of the circumnuclear gas disk in UGC 2698, a local compact galaxy. The disk exhibits regular rotation with projected velocities rising to 450 km sâˆ'1 near the galaxy center. We fit gas-dynamical models to the ALMA data cube, assuming the CO emission originates from a dynamically cold, thin disk, and measured the mass of the supermassive black hole (BH) in UGC 2698 to be M BH = (2.46 ± 0.07 [1 σ statistical] âˆ' 0.78 + 0.70 [systematic]) Ă— 109 M ⊙. UGC 2698 is part of a sample of nearby early-type galaxies that are plausible z ∼ 2 red nugget relics. Previous stellar-dynamical modeling for three galaxies in the sample found BH masses consistent with the BH massâˆ'stellar velocity dispersion (M BH âˆ' σ ⋆) relation but over-massive relative to the BH massâˆ'bulge luminosity (M BH âˆ' L bul) correlation, suggesting that BHs may gain the majority of their mass before their host galaxies. However, UGC 2698 is consistent with both M BH âˆ' σ ⋆ and M BH âˆ' L bul. As UGC 2698 has the largest stellar mass and effective radius in the local compact galaxy sample, it may have undergone more recent mergers that brought it in line with the BH scaling relations. Alternatively, given that the three previously measured compact galaxies are outliers from M BH âˆ' L bul, while UGC 2698 is not, there may be significant scatter at the poorly sampled high-mass end of the relation. Additional gas-dynamical M BH measurements for the compact galaxy sample will improve our understanding of BHâˆ'galaxy co-evolution. [ABSTRACT FROM AUTHOR]

Intermediate-mass black holes (IMBHs) by definition have masses of MIMBH ∼ 102−5M⊙, a range with few observational constraints. Finding IMBHs in globular star clusters (GCs) would validate a formation channel for massive black-hole seeds in the early universe. Here, we simulate a 60 hr observation with the next-generation Very Large Array (ngVLA) of 728 GC candidates in the Virgo Cluster galaxy NGC 4472. Interpreting the radio detection thresholds as signatures of accretion onto IMBHs, we benchmark IMBH mass thresholds in three scenarios and find the following: (1) radio analogs of ESO 243-49 HLX-1, a strong IMBH candidate with in a star cluster, are easy to access in all 728 GC candidates. (2) For the 30 GC candidates with extant X-ray detections, the empirical fundamental-plane relation involving black-hole mass plus X-ray and radio luminosities suggests access to , with an uncertainty of 0.44 dex. (3) A fiducial Bondi accretion model was applied to all 728 GC candidates and to radio stacks of the GC candidates. This model suggests access to IMBH masses, with a statistical uncertainty of 0.39 dex, of for individual GC candidates, and for radio stacks of about 100–200 GC candidates. The fiducial Bondi model offers initial guidance, but is subject to additional systematic uncertainties and should be superseded by hydrodynamical simulations of gas flows in GCs. [ABSTRACT FROM AUTHOR]

The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys offer an invaluable tracer of high-redshift star formation, as they directly target the faint radio free–free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLDz survey. The deep COSMOS mosaic spans down to σ = 1.3 μJy beam−1, while the wider GOODS-N observations cover to σ = 5.3 μJy beam−1. We detect a total of 18 galaxies at 34 GHz, of which nine show radio emission consistent with being powered by star formation; although for two sources, this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5, and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free–free components, and find typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. We further determine free–free star formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution-fitting and the far-infrared/radio correlation. Our observations place strong constraints on the high-frequency radio emission in typical galaxies at high redshift, and provide some of the first insights into what is set to become a key area of study with future radio facilities, such as the Square Kilometer Array Phase 1 and next-generation VLA. [ABSTRACT FROM AUTHOR]

This paper systematically investigates the comoving megaparsec-scale intergalactic medium (IGM) environment around galaxies traced by the Lyα forest. Using our cosmological hydrodynamic simulations, we investigate the IGM–galaxy connection at z = 2 by two methods: (i) cross-correlation analysis between galaxies and the fluctuation of Lyα forest transmission (δF) and (ii) comparison of the overdensity of neutral hydrogen (H i) and galaxies. Our simulations reproduce observed cross-correlation functions (CCFs) between Lyα forest and Lyman-break galaxies. We further investigate the variation of the CCF using subsamples divided by dark matter halo mass (MDH), galaxy stellar mass (M⋆), and star formation rate (SFR) and find that the CCF signal becomes stronger with increasing MDH, M⋆, and SFR. The CCFs between galaxies and gas density fluctuation are also found to have similar trends. Therefore, the variation of δF–CCF depending on MDH, M⋆, and SFR is due to varying gas densities around galaxies. We find that the correlation between galaxies and the IGM H i distribution strongly depends on MDH as expected from linear theory. Our results support the ΛCDM paradigm, confirming a spatial correlation between galaxies and IGM H i , with more massive galaxies being clustered in higher-density regions. [ABSTRACT FROM AUTHOR]

To investigate the growth history of galaxies, we measure the rest-frame radio, ultraviolet (UV), and optical sizes of 98 radio-selected, star-forming galaxies (SFGs) distributed over 0.3 ≲ z ≲ 3 with a median stellar mass of. We compare the size of galaxy stellar disks, traced by rest-frame optical emission, relative to the overall extent of star formation activity that is traced by radio continuum emission. Galaxies in our sample are identified in three Hubble Frontier Fields: MACS J0416.1−2403, MACS J0717.5+3745, and MACS J1149.5+2223. Radio continuum sizes are derived from 3 and 6 GHz radio images (≲0.″6 resolution, ≈0.9 μJy beam−1 noise level) from the Karl G. Jansky Very Large Array. Rest-frame UV and optical sizes are derived using observations from the Hubble Space Telescope and the Advanced Camera for Surveys and Wide Field Camera 3 instruments. We find no clear dependence between the 3 GHz radio size and stellar mass of SFGs, which contrasts with the positive correlation between the UV/optical size and stellar mass of galaxies. Focusing on SFGs with , we find that the radio/UV/optical emission tends to be more compact in galaxies with high star formation rates (≳100 M⊙ yr−1), suggesting that a central, compact starburst (and/or an active galactic nucleus) resides in the most luminous galaxies of our sample. We also find that the physical radio/UV/optical size of radio-selected SFGs with log(M⋆/M⊙) > 10 increases by a factor of 1.5–2 from z ≈ 3 to z ≈ 0.3, yet the radio emission remains two to three times more compact than that from the UV/optical. These findings indicate that these massive, radio-selected SFGs at 0.3 ≲ z ≲ 3 tend to harbor centrally enhanced star formation activity relative to their outer disks. [ABSTRACT FROM AUTHOR]

We present a recent Atacama Large Millimeter/submillimeter Array observation of the CO(1−0) line emission in the central galaxy of the Zw 3146 galaxy cluster (z = 0.2906). We also present updated X-ray cavity measurements from archival Chandra observations. The 5 × 1010M⊙ supply of molecular gas, which is confined to the central 4 kpc, is marginally resolved into three extensions that are reminiscent of the filaments observed in similar systems. No velocity structure that would be indicative of ordered motion is observed. The three molecular extensions all trail X-ray cavities, and are potentially formed from the condensation of intracluster gas lifted in the wakes of the rising bubbles. Many cycles of feedback would be required to account for the entire molecular gas reservoir. The molecular gas and continuum source are mutually offset by 2.6 kpc, with no detected line emission coincident with the continuum source. It is the molecular gas, not the continuum source, that lies at the gravitational center of the brightest cluster galaxy. As the brightest cluster galaxy contains possible tidal features, the displaced continuum source may correspond to the nucleus of a merging galaxy. We also discuss the possibility that a gravitational wave recoil following a black hole merger may account for the displacement. [ABSTRACT FROM AUTHOR]

The polarization properties of radio sources powered by an Active Galactic Nucleus (AGN) have attracted considerable attention because of the significance of magnetic fields in the physics of these sources, their use as probes of plasma along the line of sight, and as a possible contaminant of polarization measurements of the cosmic microwave background. For each of these applications, a better understanding of the statistics of polarization in relation to source characteristics is crucial. In this paper, we derive the median fractional polarization, Π0,med, of large samples of radio sources with 1.4 GHz flux density 6.6 < S1.4 < 70 mJy, by stacking 1.4 GHz NVSS polarized intensity as a function of angular size derived from the FIRST survey. Five samples with deconvolved mean angular size 1.″8 to 8.″2 and two samples of symmetric double sources are analyzed. These samples represent most sources smaller than or near the median angular size of the mJy radio source population We find that the median fractional polarization Π0,med at 1.4 GHz is a strong function of source angular size ≲5″ and a weak function of angular size for larger sources up to ∼8″. We interpret our results as depolarization inside the AGN host galaxy and its circumgalactic medium. The curvature of the low-frequency radio spectrum is found to anticorrelate with Π0,med, a further sign that depolarization is related to the source. [ABSTRACT FROM AUTHOR]

We report the detection of the host galaxy of a damped Lyα system (DLA) with log N(H i) [cm−2] = 21.0 ± 0.10 at z ≈ 3.0091 toward the background quasar SDSS J011852+040644 using the Palomar Cosmic Web Imager at the Hale (P200) telescope. We detect Lyα emission in the dark core of the DLA trough at a 3.3σ confidence level, with Lyα luminosity of LLyα = (3.8 ± 0.8) × 1042 erg s−1, corresponding to a star formation rate of ≳2 M⊙ yr−1 (considering a lower limit on Lyα escape fraction) as typical for Lyman break galaxies at these redshifts. The Lyα emission is blueshifted with respect to the systemic redshift derived from metal absorption lines by 281 ± 43 km s−1. The associated galaxy is at very small impact parameter of ≲12 kpc from the background quasar, which is in line with the observed anticorrelation between column density and impact parameter in spectroscopic searches tracing the large-scale environments of DLA host galaxies. [ABSTRACT FROM AUTHOR]

Ultra-deep radio surveys are an invaluable probe of dust-obscured star formation, but require a clear understanding of the relative contribution from radio active galactic nuclei (AGNs) to be used to their fullest potential. We study the composition of the μJy radio population detected in the Karl G. Jansky Very Large Array COSMOS-XS survey based on a sample of 1540 sources detected at 3 GHz over an area of ∼350 arcmin2. This ultra-deep survey consists of a single pointing in the well-studied COSMOS field at both 3 and 10 GHz and reaches rms sensitivities of 0.53 and 0.41 μJy beam−1, respectively. We find multiwavelength counterparts for 97% of radio sources, based on a combination of near-UV/optical to sub-millimeter data, and through a stacking analysis at optical/near-IR wavelengths we further show that the sources lacking such counterparts are likely to be high-redshift in nature (typical z ∼ 4−5). Utilizing the multiwavelength data over COSMOS, we identify AGNs through a variety of diagnostics and find these to make up 23.2 ± 1.3% of our sample, with the remainder constituting uncontaminated star-forming galaxies. However, more than half of the AGNs exhibit radio emission consistent with originating from star formation, with only 8.8 ± 0.8% of radio sources showing a clear excess in radio luminosity. At flux densities of ∼30 μJy at 3 GHz, the fraction of star formation-powered sources reaches ∼90%, and this fraction is consistent with unity at even lower flux densities. Overall, our findings imply that ultra-deep radio surveys such as COSMOS-XS constitute a highly effective means of obtaining clean samples of star formation-powered radio sources. [ABSTRACT FROM AUTHOR]

The MAVERIC survey is the first deep radio continuum imaging survey of Milky Way globular clusters, with a central goal of finding and classifying accreting compact binaries, including stellar-mass black holes. Here we present radio source catalogs for 25 clusters with ultra-deep Karl G. Jansky Very Large Array observations. The median observing time was 10 hr per cluster, resulting in typical rms sensitivities of 2.3 and 2.1 μJy per beam at central frequencies of 5.0 and 7.2 GHz, respectively. We detect nearly 1300 sources in our survey at 5σ, and while many of these are likely to be background sources, we also find strong evidence for an excess of radio sources in some clusters. The radio spectral index distribution of sources in the cluster cores differs from the background, and shows a bimodal distribution. We tentatively classify the steep-spectrum sources (those much brighter at 5.0 GHz) as millisecond pulsars and the flat-spectrum sources as compact or other kinds of binaries. These provisional classifications will be solidified with the future addition of X-ray and optical data. The outer regions of our images represent a deep, relatively wide-field (∼0.4 deg2) and high-resolution C band background survey, and we present source counts calculated for this area. We also release radio continuum images for these 25 clusters to the community. [ABSTRACT FROM AUTHOR]

Recent observations provide evidence that some cool-core clusters host quasars in their brightest cluster galaxies (BCGs). Motivated by these findings, we use 3D radiation-hydrodynamic simulations with the code Enzo to explore the joint role of kinetic and radiative feedback from supermassive black holes (SMBHs) in BCGs. We implement kinetic feedback as subrelativistic plasma outflows and model radiative feedback using ray-tracing radiative transfer or thermal energy injection. In our simulations, the central SMBH transitions between the radiatively efficient and radiatively inefficient states on timescales of a few gigayears, as a function of its accretion rate. The timescale for this transition depends primarily on the fraction of power allocated to each feedback mode, and to a lesser degree on the overall feedback luminosity of the active galactic nucleus (AGN). Specifically, we find that (a) kinetic feedback must be present at both low and high accretion rates in order to prevent the cooling catastrophe, and (b) its contribution likely accounts for >10% of the total AGN feedback power, because below this threshold simulated BCGs tend to host radio-loud quasars most of the time, in apparent contrast with observations. We also find a positive correlation between the AGN feedback power and the mass of the cold gas filaments in the cluster core, indicating that observations of Hα filaments can be used as a measure of AGN feedback. [ABSTRACT FROM AUTHOR]

The intergalactic medium (IGM) is the dominant reservoir of baryons, delineates the large-scale structure of the universe at low to moderate overdensities, and provides gas from which galaxies form and evolve. Simulations of a cold-dark-matter- (CDM-) dominated universe predict that the IGM is distributed in a cosmic web of filaments and that galaxies should form along and at the intersections of these filaments. While observations of QSO absorption lines and the large-scale distribution of galaxies have confirmed the CDM paradigm, the cosmic web of IGM has never been confirmed by direct imaging. Here we report our observation of the Lyα blob 2 (LAB2) in SSA22 with the Cosmic Web Imager (CWI). This is an integral field spectrograph optimized for low surface brightness, extended emission. With 22 hr of total on- and off-source exposure, CWI has revealed that LAB2 has extended Lyα emission that is organized into azimuthal zones consistent with filaments. We perform numerous tests with simulations and the data to secure the robustness of this result, which relies on data with modest signal-to-noise ratios. We have developed a smoothing algorithm that permits visualization of data cube slices along image or spectral image planes. With both raw and smoothed data cubes we demonstrate that the filaments are kinematically associated with LAB2 and display double-peaked profiles characteristic of optically thick Lyα emission. The flux is 10-20 times brighter than expected for the average emission from the IGM but is consistent with boosted fluorescence from a buried QSO or gravitation cooling radiation. Using simple emission models, we infer a baryon mass in the filaments of at least 1-4 × 1011M☼, and the dark halo mass is at least 2 × 1012M☼. The spatial-kinematic morphology is more consistent with inflow from the cosmic web than outflow from LAB2, although an outflow feature maybe present at one azimuth. LAB2 and the surrounding gas have significant and coaligned angular momentum, strengthening the case for their association. [ABSTRACT FROM AUTHOR]

We present the most up to date X-ray luminosity function (XLF) and absorption function of active galactic nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5-2 keV) and/or hard (>2 keV) band. We utilize a maximum likelihood method to reproduce the count rate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick (CTK) AGNs, and broadband spectra of AGNs, including reflection components from tori based on the luminosity- and redshift-dependent unified scheme. We find that the shape of the XLF at z ∼ 1-3 is significantly different from that in the local universe, for which the luminosity-dependent density evolution model gives much better description than the luminosity and density evolution model. These results establish the standard population synthesis model of the X-ray background (XRB), which well reproduces the source counts, the observed fractions of CTK AGNs, and the spectrum of the hard XRB. The number ratio of CTK AGNs to the absorbed Compton-thin (CTN) AGNs is constrained to be ≈0.5-1.6 to produce the 20-50 keV XRB intensity within present uncertainties, by assuming that they follow the same evolution as CTN AGNs. The growth history of supermassive black holes is discussed based on the new AGN bolometric luminosity function. [ABSTRACT FROM AUTHOR]

We present IRAM Plateau de Bure Interferometer observations of the CO(3-2) and CO(5-4) line transitions from an Lyα blob at z ∼ 2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emissions are detected at the location of a strong MIPS source that is offset by ∼1.″5 from the Lyα peak. Neither of these emission components is resolved with the 1.″7 beam, showing that the gas and dust are confined to within ∼7 kpc from this galaxy. No millimeter source is found at the location of the Lyα peak, ruling out a central compact source of star formation as the power source for the Lyα emission. Combined with a spatially resolved spectrum of Lyα and He II, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Lyα profile is symmetric, and its line center agrees with that of the CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Lyα emission. In the region near the Lyα peak, the gas is slowly receding (∼100 km s–1) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, ICO(5-4)/ICO(3-2) = 0.97 ± 0.21. This line ratio is lower than the average values found in high-z submillimeter galaxies and QSOs but is consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity. [ABSTRACT FROM AUTHOR]

Feedback heating from active galactic nuclei (AGNs) has been commonly invoked to suppress cooling flows predicted in hot gas in elliptical galaxies, galaxy groups, and clusters. Previous studies have focused on if and how AGN feedback heats the gas but have little paid attention to its triggering mechanism. Using spherically symmetric simulations, we investigate how large-scale cooling flows are accreted by central supermassive black holes (SMBHs) in eight well-observed systems and find an interesting dichotomy. In massive clusters, the gas develops a central cooling catastrophe within about the cooling time (typically ∼100-300 Myr), resulting in cold-mode accretion onto SMBHs. However, in our four simulated systems on group and galaxy scales at a low metallicity Z = 0.3 Z☼, the gas quickly settles into a long-term state that has a cuspy central temperature profile extending to several tens to about 100 pc. At the more realistic solar metallicity, two groups (with Re ∼ 4 kpc) still host the long-term, hot-mode accretion. Both accretion modes naturally appear in our idealized calculations where only cooling, gas inflow, and compressional heating are considered. The long-term, hot-mode accretion is maintained by the quickly established closeness between the timescales of these processes, preferably in systems with low gas densities, low gas metallicities, and importantly, compact central galaxies, which result in strong gravitational acceleration and compressional heating at the intermediate radii. Our calculations predict that central cuspy temperature profiles appear more often in smaller systems than galaxy clusters, which instead often host significant cold gas and star formation. [ABSTRACT FROM AUTHOR]

We present the first systematic search for extended metal-line [O II] λλ3726, 3729 nebulae, or [O II] blobs (O IIBs), at z = 1.2 using deep narrowband imaging with a survey volume of 1.9 × 105 Mpc3 on the 0.62 deg2 sky of Subaru-XMM Deep Survey (SXDS) field. We discover a giant O IIB, called “O IIB 1,” with a spatial extent over ∼75 kpc at a spectroscopic redshift of z = 1.18, and also identify a total of 12 O IIBs with a size of >30 kpc. Our optical spectrum of O IIB 1 presents [Ne V] λ3426 line at the 6σ level, indicating that this object harbors an obscured type-2 active galactic nucleus (AGN). The presence of gas outflows in this object is suggested by two marginal detections of Fe II λ2587 absorption and Fe II* λ2613 emission lines both of which are blueshifted at as large as 500-600 km s–1, indicating that the heating source of O IIB 1 is AGN or associated shock excitation rather than supernovae produced by starbursts. The number density of O IIB 1-type giant blobs is estimated to be ∼5 × 10–6 Mpc–3 at z ∼ 1.2, which is comparable with that of AGNs driving outflow at a similar redshift, suggesting that giant O IIBs are produced only by AGN activity. On the other hand, the number density of small O IIBs, 6 × 10–5 Mpc–3, compared to that of z ∼ 1 galaxies in the blue cloud in the same MB range, may imply that 3% of star-forming galaxies at z ∼ 1 are quenching star formation through outflows involving extended [O II] emission. [ABSTRACT FROM AUTHOR]

We present a new model for the observed Lyα blobs (LABs) within the context of the standard cold dark matter model. In this model, LABs are the most massive halos with the strongest clustering (protoclusters) undergoing extreme starbursts in the high-z universe. Aided by calculations of detailed radiative transfer of Lyα photons through ultrahigh resolution (159 pc), large-scale (⩾30 Mpc) adaptive mesh refinement cosmological hydrodynamic simulations with galaxy formation, this model is shown to be able to, for the first time, reproduce simultaneously the global Lyα luminosity function and the luminosity-size relation of the observed LABs. Physically, a combination of dust attenuation of Lyα photons within galaxies, clustering of galaxies, and the complex propagation of Lyα photons through the circumgalactic and intergalactic medium gives rise to the large sizes and the irregular isophotal shapes of LABs that are frequently observed. A generic and unique prediction of this model is that there should be strong far-infrared (FIR) sources within each LAB with the most luminous FIR source likely representing the gravitational center of the protocluster, not necessarily the apparent center of the Lyα emission of the LAB or the most luminous optical source. Upcoming ALMA observations should unambiguously test this prediction. If verified, LABs will provide very valuable laboratories for studying the formation of galaxies in the most overdense regions of the universe at a time when the global star formation was the most vigorous. [ABSTRACT FROM AUTHOR]

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 < z < 2), low-frequency-selected (and so unbiased in orientation) 3CRR radio sources are reported. The sample includes 21 quasars (=broad-line radio galaxies) and 17 narrow-line radio galaxies (NLRGs) with matched 178 MHz radio luminosity (log LR(5 GHz) ~ 44-45). The quasars have high radio core fraction, high X-ray luminosities (log LX ~ 45-46), and soft X-ray hardness ratios (HR ~ -0.5) indicating low obscuration. The NLRGs have lower core fraction, lower apparent X-ray luminosities (log LX ~43-45), and mostly hard X-ray hardness ratios (HR > 0) indicating obscuration (NH ~ 1022-1024 cm-2). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [OIII] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (1022 cm-2 < NH(int) < 1.5 × 1024 cm-2) to CT (NH(int) > 1.5 × 1024 cm-2) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1-0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is ~60° and the obscuring material covers 30°, ~12° of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10-1000× higher than indicated by their X-ray hardness ratios, and their true LX values are ~10-100× larger than the hardness-ratio absorption corrections would indicate. [ABSTRACT FROM AUTHOR]

We report on an analysis of the Extended Chandra Deep Field South (E-CDFS) region using archival data from the Very Large Array, with the goal of studying radio variability and transients at the sub-milliJansky level. The 49 epochs of E-CDFS observations at 1.4 GHz sample timescales from 1 day to 3 months. We find that only a fraction (1%) of unresolved radio sources above 40μJy are variable at the 4σ level. There is no evidence that the fractional variability changes along with the known transition of radio-source populations below 1 mJy. Optical identifications of the sources show that the variable radio emission is associated with the central regions of an active galactic nucleus or a star-forming galaxy. After a detailed comparison of the efficacy of various source-finding algorithms, we use the best to carry out a transient search. No transients were found. This implies that the areal density of transients with peak flux density greater than 0.21 mJy is less than 0.37 deg-2 (at a confidence level of 95%). This result is approximately an order of magnitude below the transient rate measured at 5 GHz by Bower et al. but it is consistent with more recent upper limits from Frail et al. Our findings suggest that the radio sky at 1.4 GHz is relatively quiet. For multi-wavelength transient searches, such as the electromagnetic counterparts to gravitational waves, this frequency may be optimal for reducing the high background of false positives. [ABSTRACT FROM AUTHOR]

The Very Long Baseline Array was used at 1.6 GHz to observe a target field 50' in diameter including the core of M31. Novel very long baseline interferometry correlation techniques were used to observe 200 sources simultaneously, of which 16 were detected. We classify all 16 as background active galactic nuclei based on their X-ray properties and arcsecond- and mas-scale morphology. The detected sources were then analyzed for evidence of scatter-broadening due to the ionized interstellar medium (ISM) of M31. The detection of a compact background source only 0.25 kpc projected distance from M31" places a constraint on the extent of any extreme scattering region associated with the center of M31. However, the two sources closest to the core show evidence of scatter broadening consistent with that which would be seen for a compact source if it were observed through the inner disk of our Galaxy, at the inclination of M31. We interpret this as a detection of the ionized ISM of M31 along two lines of sight. With the increases in bandwidth and sensitivity envisaged for future long-baseline interferometers, this should prove to be a remarkably powerful technique for understanding the ionized ISM in external galaxies. [ABSTRACT FROM AUTHOR]

We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick H I gas associated with the foreground quasar. These unique sightlines allow us to study the quasar circumgalactic medium (CGM) in absorption and emission simultaneously, because the background quasar pinpoints large concentrations of gas where Lyα emission, resulting from quasar-powered fluorescence, resonant Lyα scattering, and/or cooling radiation, is expected. A sensitive search (1σ surface-brightness limits of SBLyα ≃ 3 × 10-18 erg s-1 cm-2 arcsec-2) for diffuse Lyα emission in the environments of the foreground (predominantly radio-quiet) quasars is conducted using Gemini/GMOS and Keck/LRIS slit spectroscopy. We fail to detect large-scale ∼100 kpc Lyα emission, either at the location of the optically thick absorbers or in the foreground quasar halos, in all cases except a single system. We interpret these non-detections as evidence that the gas detected in absorption is shadowed from the quasar UV radiation due to obscuration effects, which are frequently invoked in unified models of active galactic nuclei. Small-scale R⊥ ≲ 50 kpc extended Lyα nebulosities are detected in 34% of our sample, which are likely the high-redshift analogs of the extended emission-line regions (EELRs) commonly observed around low-redshift (z < 0.5) quasars. This may be fluorescent recombination radiation from a population of very dense clouds with a low covering fraction illuminated by the quasar. We also detect a compact high rest-frame equivalent width (WLyα > 50 Å) Lyα-emitter with luminosity LLyα = 2.1 ± 0.32 × 1041 erg s-1 at small impact parameter R⊥ = 134 kpc from one foreground quasar, and argue that it is more likely to result from quasar-powered fluorescence, than simply be a star-forming galaxy clustered around the quasar. Our observations imply that much deeper integrations with upcoming integral-field spectrometers such as MUSE and KCWI will be able to routinely detect a diffuse Lyα glow around bright quasars on scales R ∼ 100 kpc and thus directly image the CGM. [ABSTRACT FROM AUTHOR]

The usefulness of Hi Lyα photons for characterizing star formation in the distant universe is limited by our understanding of the astrophysical processes that regulate their escape from galaxies. These processes can only be observed in detail out to a few ×100 Mpc. Past nearby (z < 0.3) spectroscopic studies are based on small samples and/or kinematically unresolved data. Taking advantage of the high sensitivity of Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we observed the Lyα lines of 20 Hα-selected galaxies located at (z) = 0.03. The galaxies cover a broad range of luminosity, oxygen abundance, and reddening. In this paper, we characterize the observed Lyα lines and establish correlations with fundamental galaxy properties.We find seven emitters. These host young (⩽10 Myr) stellar populations have rest-frame equivalent widths in the range 1-12 Å, and have Lyα escape fractions within the COS aperture in the range 1%-12%. One emitter has a double-peaked Lyα with peaks 370 km s-1 apart and a stronger blue peak. Excluding this object, the emitters have Lyα and Oi λ1302 offsets from Hα in agreement with expanding-shell models and Lyman break galaxies observations. The absorbers have offsets that are almost consistent with a static medium. We find no one-to-one correspondence between Lyα emission and age, metallicity, or reddening. Thus, we confirm that Lyα is enhanced by outflows and is regulated by the dust and Hi column density surrounding the hot stars. [ABSTRACT FROM AUTHOR]

The discovery of very high energy (VHE; E > 100GeV) γ-ray emission from intermediate- and low-frequency- peaked blazars suggests that γγ absorption and pair cascading might occur in these objects. In previous papers, we investigated the Compton emission from VHE γ-ray-induced pair cascades, deflected by moderate magnetic fields, in a largely model-independent way, and demonstrated that this emission can explain the Fermi fluxes and spectra of the radio galaxies Cen A and NGC 1275. In this paper, we describe a generalization of our Monte Carlo cascade code to include the angle-dependent synchrotron output from the cascades, allowing for the application to situations with non-negligible magnetic fields, leading to potentially observable synchrotron signatures, but still not dominating the radiative energy loss of cascade particles. We confirm that the synchrotron radiation from the cascades in NGC 1275 and Cen A is negligible for the parameters used in our previous works. We demonstrate that the magnetic field cannot be determined from a fit of the cascade emission to the γ-ray spectrum alone, and the degeneracy can only be lifted if the synchrotron emission from the cascades is observed as well. We illustrate this fact with the example of NGC 1275. We point out that the cascade synchrotron emission may produce spectral features in the same energy range in which the big blue bump is observed in the spectral energy distributions of several blazars, and may make a non-negligible contribution to this feature. We illustrate this idea with the example of 3C 279. [ABSTRACT FROM AUTHOR]

We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500μm), we calculate the obscured star formation rate (SFR). 22-5.3+6.2% of the BCGs are detected in the far-infrared, with SFR = 1-150 M ⊙ yr-1. The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing Hα emission is also correlated with obscured star formation. For all but the most luminous BCGs (LTIR > 2 x 1011 L ⊙), only a small (≾ 0.4 mag) reddening correction is required for SFR(Hα) to agree with SFRFIR. The relatively low Hα extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss. [ABSTRACT FROM AUTHOR]

The cores of massive galaxy clusters, where hot gas is cooling rapidly, appear to undergo cycles of self-regulating energy feedback, in which active galactic nucleus (AGN) outbursts in the central galaxies episodically provide sufficient heating to offset much of the gas cooling. We use deep integral-field spectroscopy to study the optical line emission from the extended nebulae of three nearby brightest cluster galaxies and investigate how they are related to the processes of heating and cooling in the cluster cores. Two of these systems, A3581 and Sersic 159-03, appear to be experiencing phases of feedback that are dominated by the activity and output of a central AGN. A3581 shows evidence for significant interaction between the radio outflows and the optical nebula, in addition to accretion flows into the nucleus of the galaxy. X-ray and radio data show that Sersic 159-03 is dominated by the feedback of energy from the central AGN, but the kinematics of the optical nebula are consistent with infall or outflow of material along its bright filaments. The third system, 2A 0335+096, is dominated by mass accretion and cooling, and so we suggest that it is in an accumulation phase of the feedback cycle. The outer nebula forms a disk-like structure, ~14 kpc in radius, that rotates about the central galaxy with a velocity amplitude of ~200 km s-1. Overall, our data are consistent with ongoing AGN-driven feedback cycles occurring in these systems. [ABSTRACT FROM AUTHOR]

We carry out high-resolution adaptive mesh refinement simulations of a cool core cluster, resolving the flow from Mpc scales down to pc scales. We do not (yet) include any active galactic nucleus (AGN) heating, focusing instead on cooling in order to understand how gas reaches the supermassive black hole at the center of the cluster. We find that, as the gas cools, the cluster develops a very flat temperature profile, undergoing a cooling catastrophe only in the central 10-100 pc of the cluster. Outside of this region, the flow is smooth, with no local cooling instabilities, and naturally produces very little low-temperature gas (below a few keV), in agreement with observations. The gas cooling in the center of the cluster rapidly forms a thin accretion disk. The amount of cold gas produced at the very center grows rapidly until a reasonable estimate of the resulting AGN heating rate (assuming even a moderate accretion efficiency) would overwhelm cooling. We argue that this naturally produces a thermostat which links the cooling of gas out to 100 kpc with the cold gas accretion in the central 100 pc, potentially closing the loop between cooling and heating. Isotropic heat conduction does not affect the result significantly, but we show that including the potential well of the brightest cluster galaxy is necessary to obtain the correct result. Also, we found that the outcome is sensitive to resolution, requiring very high mass resolution to correctly reproduce the small transition radius. [ABSTRACT FROM AUTHOR]

We investigate how environmental effects by gas stripping alter the growth ofa supermassive black hole (SMBH) and its host galaxy evolution, by means of one-dimensional hydrodynamical simulations that include both mechanical and radiative active galactic nucleus (AGN) feedback effects. By changing the truncation radius of the gas distribution (Rt), beyond which gas stripping is assumed to be effective, we simulate possible environments for satellite and central galaxies in galaxy clusters and groups. The continuous escape of gas outside the truncation radius strongly suppresses star formation, while the growth of the SMBH is less affected by gas stripping because the SMBH accretion is primarily ruled by the density of the central region. As we allow for increasing environmental effects—the truncation radius decreasing from about 410 to 50 kpc— we find that the final SMBH mass declines from about 109 to 8 x 108 Mʘ, but the outflowing mass is roughly constant at about 2 x 1010 Mʘ. There are larger changes in the mass of stars formed, which declines from about 2 x 1010 to 2 x 109 Mʘ, and the final thermal X-ray gas, which declines from about 109 to 5 x 108 M&#x 0298;, with increasing environmental stripping. Most dramatic is the decline in the total time that the objects would be seen as quasars, which declines from 52 Myr (for Rt = 377 kpc) to 7.9 Myr (for Rt = 51 kpc). The typical case might be interpreted as a red and dead galaxy having episodic cooling flows followed by AGN feedback effects resulting in temporary transitions of the overall galaxy color from red to green or to blue, with (cluster) central galaxies spending a much larger fraction of their time in the elevated state than do satellite galaxies. Our results imply that various scaling relations for elliptical galaxies, in particular, the mass ratio between the SMBH and its host galaxy, can have dispersions due to environmental effects such as gas stripping. In addition, the simulations also suggest that the increase in AGN fraction in high-redshift galaxy clusters might be related to environmental effects which shut down the SMBH mass accretion in satellite galaxies and reduce their AGN activity. [ABSTRACT FROM AUTHOR]

We report narrowband imaging of the 1-0 S(1) ro-vibrational transition of molecular hydrogen (H2) from NGC 1275, the central cD galaxy of the Perseus Cluster. We find that the H2 gas has a spatial morphology identical to the optical emission-line nebula associated with this galaxy, a total luminosity in H2 1-0 S(1) only an order of magnitude less than in Hα, and if the line-emitting gas is thermalized a mass (at ~2000 K) that is over two orders of magnitude smaller than that of the optical emission-line nebula (at ~ 10,000 K). The ratio in H2 1-0 S(1) to Hα + [N II] line intensities spans a characteristic range of ~0.02-0.08 throughout the nebula; the brighter inner nebula exhibits patches with (nearly) constant line ratios unrelated to individual filaments. Recent models proposed to explain the peculiar nebular spectrum from the optical to infrared invoke thermalized along with non-thermalized injection of energy from ionizing particles. The energy density of highly relativistic electrons inferred to cause inverse-Compton scattering of hard X-ray emission from the core of the Perseus Cluster decreases steeply beyond a central radius of ~20 kpc, yet we do not find any changes in the average or range spanned by the H2 1-0 S(1) to Hα + [N II] line ratio between the inner (≲20 kpc) and outer (~20-50 kpc) nebulae. On the other hand, saturated conduction from the surrounding X-ray gas produces, in the absence of magnetic fields, a heat flux that is approximately constant throughout the nebula: the change in the line ratio with position would then reflect the ability of the X-ray gas to penetrate presumably magnetically threaded filaments at different locations. [ABSTRACT FROM AUTHOR]