Search

Mergers of galaxies are a ubiquitous phenomenon in the universe and represent a natural consequence of the "bottom-up" mass accumulation and galaxy evolution cosmological paradigm. It is generally accepted that the peak of active galactic nucleus (AGN) accretion activity occurs at nuclear separations of ≲10 kpc for major mergers. Here we present new NuSTAR and XMM-Newton observations for a subsample of mid-IR preselected dual AGN candidates in an effort to better constrain the column densities along the line of sight (LOS) for each system. Only one dual AGN candidate, J0841+0101, is detected as a single, unresolved source in the XMM-Newton and NuSTAR imaging, while the remaining three dual AGN candidates, J0122+0100, J1221+1137, and J1306+0735, are not detected with NuSTAR; if these nondetections are due to obscuration alone, these systems are consistent with being absorbed by column densities of log(N H/cm−2) ≥ 24.9, 24.6, and 24.3, which are roughly consistent with previously inferred column densities in these merging systems. In the case of J0841+0101, the analysis of the 0.3–30 keV spectra reveal an LOS column density of N H ≳ 1024 cm−2, significantly larger than the column densities previously reported for this system and demonstrating the importance of the higher signal-to-noise ratio XMM-Newton spectra and access to the >10 keV energies via NuSTAR. Though it is unclear if J0841+0101 truly hosts a dual AGN, these results are in agreement with the high obscuring columns expected in AGNs in late-stage mergers. [ABSTRACT FROM AUTHOR]

We perform X-ray spectral analyses to derive the characteristics (e.g., column density, X-ray luminosity) of ≈10,200 active galactic nuclei (AGNs) in the XMM-Spitzer Extragalactic Representative Volume Survey, which was designed to investigate the growth of supermassive black holes across a wide dynamic range of cosmic environments. Using physical torus models (e.g., Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick (CT; N H > 1.5 × 1024 cm−2) AGN candidates with good signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs. We also find an increasing CT fraction (f CT) from low (z < 0.75) to high (z > 0.75) redshift. Our CT candidates tend to show hard X-ray spectral shapes and dust extinction in their spectral energy distribution fits, which may shed light on the connection between AGN obscuration and host-galaxy evolution. [ABSTRACT FROM AUTHOR]

We present a study of the narrow Fe K α line in seven bright, nearby active galactic nuclei (AGN) that have been observed extensively with the Chandra High Energy Transmission Grating (HETG). The HETG data reveal a wider Fe K α line in the first-order spectrum than in the second- and third-order spectra, which we interpret as the result of spatially extended Fe K α emission. We utilize these differences in narrow Fe K α line widths in the multi-order Chandra HETG spectra to determine the spatial extent and intrinsic velocity width of the emitting material in each object. We find that there is modest evidence for spatially extended emission in each object, corresponding to extension of r ∼ 5â€"100 pc. These distances are significantly larger than those inferred from velocity widths assuming gravitational motions, which give r ∼ 0.01â€"1 pc. This implies either that the gas is emitting at a range of radii, with smaller radii dominating the velocity width and larger radii dominating the spatial extent, or that the gas is exhibiting nongravitational motions, which we suggest would be outflows due to slight excess redshift in the line and velocities that exceed the freefall velocity. We also use the spatial extent information to estimate the mass of the emitting gas by counting fluorescing iron atoms, finding masses on the order of M gas ∼ 105â€"108 M ⊙. Future work with observatories like XRISM will be able to extend this study to a larger number of AGN and decrease uncertainties that arise as a result of the low signal-to-noise ratio of the higher-order HETG data. [ABSTRACT FROM AUTHOR]

This paper is the second in a series aimed at examining the gaseous environments of z ≤ 0.3 quasars and ultraluminous infrared galaxies (ULIRGs) as a function of AGN/host galaxy properties across the merger sequence. This second paper focuses on the Ly α emission and O vi 1032, 1038 and N v 1238, 1243 absorption features, tracers of highly ionized gas outflows, in ULIRGs observed with HST/COS. Ly α emission is detected in 15 out of 19 ULIRGs, and 12 of the 14 clear Ly α detections show emission with blueshifted velocity centroids and/or wings. The equivalent widths of the Ly α emission increase with increasing AGN luminosities and AGN bolometric fractions. The blueshifts of the Ly α emission correlate positively with those of the [O iii ] λ 5007 emission, where the latter traces the ionized gas outflows. The Ly α escape fractions tend to be slightly larger in objects with stronger AGN and larger outflow velocities, but they do not correlate with nebular line reddening. Among the 12 ULIRGs with good continuum signal-to-noise ratios, O vi and/or N v absorption features are robustly detected in six of them, all of which are blueshifted, indicative of outflows. In the combined ULIRG + quasar sample, the outflows are more frequently detected in the X-ray weak or absorbed sources. The absorption equivalent widths, velocities, and velocity dispersions of the outflows are also higher in the X-ray weak sources. No other strong correlations are visible between the properties of the outflows and those of the AGN or host galaxies. [ABSTRACT FROM AUTHOR]

We use combined South Pole Telescope (SPT)+Planck temperature maps to analyze the circumgalactic medium (CGM) encompassing 138,235 massive, quiescent 0.5 ≤ z ≤ 1.5 galaxies selected from data from the Dark Energy Survey (DES) and Wide-Field Infrared Survey Explorer (WISE). Images centered on these galaxies were cut from the 1.85 arcmin resolution maps with frequency bands at 95, 150, and 220 GHz. The images were stacked, filtered, and fit with a graybody dust model to isolate the thermal Sunyaev–Zel'dovich (tSZ) signal, which is proportional to the total energy contained in the CGM of the galaxies. We separated these M⋆ = 1010.9M⊙–1012M⊙ galaxies into 0.1 dex stellar mass bins, detecting tSZ per bin up to 5.6σ and a total signal-to-noise ratio of 10.1σ. We also detect dust with an overall signal-to-noise ratio of 9.8σ, which overwhelms the tSZ at 150 GHz more than in other lower-redshift studies. We corrected for the 0.16 dex uncertainty in the stellar mass measurements by parameter fitting for an unconvolved power-law energy-mass relation, , with the peak stellar mass distribution of our selected galaxies defined as M⋆,peak = 2.3 × 1011M⊙. This yields an erg and. These are consistent with z ≈ 0 observations and within the limits of moderate models of active galactic nucleus feedback. We also computed the radial profile of our full sample, which is similar to that recently measured at lower-redshift by Schaan et al. [ABSTRACT FROM AUTHOR]

We investigate the lowest-mass quiescent galaxies known to exist in isolated environments (; 1.5 Mpc from a more massive galaxy). This population may represent the lowest stellar mass galaxies in which internal feedback quenches galaxy-wide star formation. We present a Keck/Echelle Spectrograph and Imager long-slit spectroscopy for 27 isolated galaxies in this regime (20 quiescent galaxies and 7 star-forming galaxies). We measure emission line strengths as a function of radius and place galaxies on the Baldwin–Phillips–Terlevich (BPT) diagram. Remarkably, 16 of 20 quiescent galaxies in our sample host central active galactic nucleus (AGN)-like line ratios. Only five of these quiescent galaxies were identified as AGN-like in the Sloan Digital Sky Survey due to a lower spatial resolution and signal-to-noise ratio. We find that many of the quiescent galaxies in our sample have spatially extended emission across the non-star-forming regions of BPT-space. While quenched galaxies in denser environments in this mass range often show no evidence for AGN activity, a significant fraction of quiescent galaxies in isolation host AGNs despite their overall passive appearances. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, changing-look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow-line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full Sloan Digital Sky Survey (SDSS) footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude ( mag, mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted signal-to-noise ratio threshold on variability of broad Hβ emission, we find 17 new CLQs, yielding a confirmation rate of ≳20%. These candidates are at lower Eddington ratio relative to the overall quasar population, which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Å increases from 1.5 to 6. We release a catalog of more than 200 highly variable candidates to facilitate future CLQ searches. [ABSTRACT FROM AUTHOR]

We have constructed an all-sky catalog of optical active galactic nuclei (AGNs) with z < 0.09, based on optical spectroscopy, from the parent sample of galaxies in the 2MASS Redshift Survey, a near-complete census of the nearby universe. Our catalog consists of 1929 broad-line AGNs and 6562 narrow-line AGNs that satisfy the Kauffmann et al. criteria, of which 3607 also satisfy the Kewley et al. criteria. We also report emission-line widths, fluxes, flux errors, and signal-to-noise ratios (S/Ns) of all the galaxies in our spectroscopic sample, allowing users to customize the selection criteria. Although we uniformly processed the spectra of galaxies from a homogeneous parent sample, inhomogeneities persist owing to the differences in the quality of the obtained spectra, taken with different instruments, and the unavailability of spectra for ∼20% of the galaxies. We quantify how the differences in spectral quality affect not only the AGN detection rates but also ratios of broad-line to narrow-line AGNs. We find that the inhomogeneities primarily stem from the continuum S/N in the spectra near the emission lines of interest. We fit for the AGN fraction as a function of continuum S/N and assign AGN likelihoods to galaxies that were not identified as AGNs using the available spectra. This correction results in a catalog suitable for statistical studies. This work also paves the way for a truly homogeneous and complete nearby AGN catalog by identifying galaxies whose AGN status needs to be verified with higher-quality spectra, quantifying the spectral quality necessary to do so. [ABSTRACT FROM AUTHOR]

The discovery of an ultrafast outflow has been reported in the z = 0.0658 narrow-line Seyfert galaxy IRAS 13224−3809. The ultrafast outflow was first inferred through the detection of highly blueshifted absorption lines and then confirmed with a principal component analysis. Two of the reported properties of this outflow differed from those typically detected in other AGNs with ultrafast outflows. First, the outflow velocity was found not to vary with v = 0.236c ± 0.006c. Second, the equivalent width of the highly blueshifted absorption line was reported to be anticorrelated with the 3–10 keV flux of this source. We present a reanalysis of the XMM-Newton observations of IRAS 13224−3809 considering the influence of background. We also undertook a different analysis approach in combining the spectra and investigated the change of the properties of the outflow as a function of 3–10 keV flux and time. We confirm the presence of an ultrafast outflow in IRAS 13224−3809; however, we find that the background spectra used in the Parker et al. analyses dominate the source spectra for energies near the blueshifted iron lines. By reducing the source extraction regions to improve the signal-to-noise ratio, we discover larger than previously reported outflow velocities and find that the outflow velocity varies from ∼0.2c to ∼0.3c and increases with 3–10 keV flux. The previously reported anticorrelation between equivalent width of the iron line and 3–10 keV flux disappears when the background spectra are reduced by optimizing the source extraction regions. [ABSTRACT FROM AUTHOR]

We perform a systematic study of outflow in the narrow-line region (NLR) of active galactic nuclei (AGNs) at z ∼ 0.4–0.8 based upon a large sample of ∼900 quasars at z ∼ 0.4–0.8. The sample is extracted from the Sloan Digital Sky Survey by mainly requiring that (1) the g-band magnitude is brighter than 19 mag and (2) the [O iii]λ5007 emission line has a signal-to-noise ratio larger than 30. Profiles of multiple emission lines are modeled by a sum of several Gaussian functions. The spectral analysis allows us to identify (1) a prevalence of both [O iii]λ5007 line blue asymmetry and bulk velocity blueshift of both [Ne iii]λ3869 and [Ne iii]λ3426 lines, when the [O ii]λ3727 line is used as a reference. The velocity offset of the [O iii]λ5007 line is, however, distributed around a value of zero, except for a few outliers. (2) Not only the significant [O iii]λ5007 line asymmetry, but also the large bulk velocity offsets of [Ne iii]λ3869 and [Ne v]λ3426 emission lines tend to occur in the objects with high L/LEdd, which is considerably consistent with the conclusions based on local AGNs. With three MBH estimation methods, the significance level of the trend is found to be better than 2.9σ, 3.2σ, and 1.8σ for [O iii], [Ne iii], and [Ne v], respectively. After excluding the role of radio jets, the revealed dependence of NLR gas outflow on L/LEdd allows us to argue that the pressure caused by the wind/radiation launched/emitted from a central supermassive black hole is the most likely origin of the outflow in these distant quasars, which implies that the outflow in luminous AGNs up to z ∼ 1 have the same origin. [ABSTRACT FROM AUTHOR]

We investigate the relationship between the emission line and the 3000 Å continuum variations using a sample of 68 intermediate-redshift () broad-line quasars spanning a bolometric luminosity range of 44.49 erg erg s−1 (Eddington ratio from ∼0.026 to 0.862). This sample is constructed from SDSS-DR7Q and BOSS-DR12Q, each with at least two spectroscopic epochs in SDSS-I/II/III surveys. In addition, we adopt the following signal-to-noise ratio (S/N) selection criteria: (a) for and the 3000 Å continuum, S/N 10; and (b) for narrow lines, S/N 5. All our quasar spectra are recalibrated based on the assumption of constant narrow emission-line fluxes. In an analysis of spectrum-to-spectrum variations, we find a fairly close correlation (Spearman ) between the variations in broad and in the continuum. This is consistent with the idea that is varying in response to the continuum emission variations. Adopting the modified weighted least squares regression method, we statistically constrain the slopes (i.e., the responsivity α of the broad ) between the variations in both components for the sources in different luminosity bins after eliminating intrinsic biases introduced by the rescaling process itself. It is shown that the responsivity is quite small (average ) and anti-correlates with the quasar luminosity. Our results indicate that high signal-to-noise flux measurements are required to robustly detect the intrinsic variability and the time lag of the line. [ABSTRACT FROM AUTHOR]

Energetic feedback due to active galactic nuclei (AGNs) is likely to play an important role in the observed anti-hierarchical trend in the evolution of galaxies, and yet the energy injected into the circumgalactic medium by this process is largely unknown. One promising approach to constrain this feedback is through measurements of spectral distortions in the cosmic microwave background due to the thermal Sunyaev–Zeldovich (tSZ) effect, whose magnitude is directly proportional to the energy input by AGNs. With current instruments, making such measurements requires stacking large numbers of objects to increase signal-to-noise. While one possible target for such stacks is AGNs themselves, these are relatively scarce sources that contain contaminating emission that complicates tSZ measurements. Here we adopt an alternative approach and co-add South Pole Telescope SZ (SPT-SZ) survey data around a large set of massive quiescent elliptical galaxies at , which are much more numerous and less contaminated than active AGNs, yet are subject to the same feedback processes from the AGNs they hosted in the past. We use data from the Blanco Cosmology Survey and VISTA Hemisphere Survey to create a large catalog of galaxies split up into two redshift bins: one with 3394 galaxies at and one with 924 galaxies at with typical stellar masses of We then co-add the emission around these galaxies, resulting in a measured tSZ signal at significance for the lower redshift bin and a contaminating signal at for the higher redshift bin. To remove contamination due to dust emission, we use SPT-SZ source counts to model a contaminant source population in both the SPT-SZ bands and Planck high-frequency bands for a subset of 937 galaxies in the low-redshift bin and 240 galaxies in the high-redshift bin. This increases our detection to for low redshifts and for high redshifts. We find the mean angularly integrated Compton-y values to be Mpc2 for low redshifts and Mpc2 for high redshifts, corresponding to total thermal energies of erg and erg, respectively. These numbers are higher than expected from simple theoretical models that do not include AGN feedback, and serve as constraints that can be applied to current simulations of massive galaxy formation. [ABSTRACT FROM AUTHOR]

We present the results of recent Chandra, XMM-Newton, and Hubble Space Telescope observations of the radio-loud (RL), broad absorption line (BAL) quasar PG 1004+130. We compare our new observations to archival X-ray and UV data, creating the most comprehensive, high signal-to-noise, multi-epoch, spectral monitoring campaign of a RL BAL quasar to date. We probe for variability of the X-ray absorption, the UV BAL, and the X-ray jet, on month–year timescales. The X-ray absorber has a low column density of when it is assumed to be fully covering the X-ray emitting region, and its properties do not vary significantly between the four observations. This suggests that the observed absorption is not related to the typical “shielding gas” commonly invoked in BAL quasar models, but is likely due to material further from the central black hole. In contrast, the C iv BAL shows strong variability. The equivalent width (EW) in 2014 is , showing a fractional increase of from the 2003 observation, 3183 days earlier in the rest-frame. This places PG 1004+130 among the most highly variable BAL quasars. By combining Chandra observations we create an exposure that is 2.5 times deeper than studied previously, with which to investigate the nature of the X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a synchrotron origin, is detected in the radio jet (30 kpc) from the central X-ray source with a spatial extent of (15 kpc). No similar X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic Microwave Background photons, is also detected. [ABSTRACT FROM AUTHOR]

We present one of the most ultraviolet (UV) luminous Lyman break galaxies (LBGs; J1432+3358) at z = 2.78, discovered in the NOAO Deep Wide-Field Survey Boötes field. The R-band magnitude of J1432+3358 is 22.29 AB, more than two magnitudes brighter than typical L* LBGs at this redshift. The deep z-band image reveals two components of J1432+3358 separated by 1.″0 with a flux ratio of 3:1. The high signal-to-noise ratio rest-frame UV spectrum shows Lyα emission line and interstellar medium absorption lines. The absence of N V and C IV emission lines, and the non-detection in X-ray and radio wavelengths and mid-infrared (MIR) colors indicates weak or no active galactic nuclei (<10%) in this galaxy. The galaxy shows a broader line profile, with a FWHM of about 1000 km s–1 and a larger outflow velocity (≈500 km s–1) than those of typical z ∼ 3 LBGs. The physical properties are derived by fitting the spectral energy distribution (SED) with stellar synthesis models. The dust extinction, E(B – V) = 0.12, is similar to that in normal LBGs. The star formation rates (SFRs) derived from the SED fitting and the dust-corrected UV flux are consistent with each other, ∼300 M☼ yr–1, and the stellar mass is (1.3 ± 0.3) × 1011M☼. The SFR and stellar mass in J1432+3358 are about an order of magnitude higher than those in normal LBGs. The SED-fitting results support that J1432+3358 has a continuous star formation history, with a star formation episode of 6.3 × 108 yr. The morphology of J1432+3358 and its physical properties suggest that J1432+3358 is in an early phase of a 3:1 merger process. The unique properties and the low space number density (∼10–7 Mpc–3) are consistent with the interpretation that such galaxies are either found in a short unobscured phase of the star formation or that a small fraction of intensive star-forming galaxies are unobscured. [ABSTRACT FROM AUTHOR]

We report the discovery of a candidate active galactic nucleus (AGN), 2XMM J123103.2+110648 at z = 0.13, with an X-ray spectrum represented purely by soft thermal emission reminiscent of Galactic black hole (BH) binaries in the disk-dominated state. This object was found in the second XMM-Newton serendipitous source catalog as a highly variable X-ray source. In three separate observations, its X-ray spectrum can be represented either by a multicolor disk blackbody model with an inner temperature of kTin ≈ 0.16-0.21 keV or a Wien spectrum Comptonized by an optically thick plasma with kT ≈ 0.14-0.18 keV. The soft X-ray luminosity in the 0.5-2 keV band is estimated to be (1.6-3.8) × 1042 erg s–1. Hard emission above ∼2 keV is not detected. The ratio of the soft to hard emission is the strongest among AGNs observed thus far. Spectra selected in high/low-flux time intervals are examined in order to study spectral variability. In the second observation with the highest signal-to-noise ratio, the low-energy (below 0.7 keV) spectral regime flattens when the flux is high, while the shape of the high-energy part (1-1.7 keV) remains unchanged. This behavior is qualitatively consistent with being caused by strong Comptonization. Both the strong soft excess and spectral change consistent with Comptonization in the X-ray spectrum imply that the Eddington ratio is large, which requires a small BH mass (smaller than ∼105M☼). [ABSTRACT FROM AUTHOR]