M. Smith

The Luminosity Function of X-Ray-selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift

We present a measure of the hard (2Y8 keV) X-ray luminosity function (XLF) of AGNs up to z � 5. At high redshifts, the wide area coverage of the Chandra Multiwavength Project is crucial to detect rare and luminous (LX > 10 44 ergs s � 1 ) AGNs. The inclusion of samples from deeper published surveys, such as the Chandra Deep Fields, allows us to span the lower LX range of the XLF. Our sample is selected from both the hard (z 6:3 ; 10 � 16 ergs cm � 2 s � 1 ) and soft (z > 3, f0:5Y2:0 keV > 1:0 ; 10 � 16 ergs cm � 2 s � 1 ) energy band detections. Within our optical magnitude limits (r 0 ; i 0 50%) regarding X-ray source identification (i.e., redshift). Wefind that the luminosity function is similar to that found in previous X-ray surveys up to z � 3 with an evolution dependent on both luminosity and redshift. At z > 3, there is a significant decline in the numbers of AGNs with an evolution rate similar to that found by studies of optically selected QSOs. Based on our XLF, we assess the resolved fraction of the cosmic X-ray background, the cumulative mass density of SMBHs, and the comparison of the mean accretion rate onto SMBHs and the star formation history of galaxies as a function of redshift. A coevolution scenario up to z � 2 is plausible, although at higher redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we highlight the need for better statistics of high-redshift AGNs at zk3, which is achievable with the upcoming Chandra surveys. Subject headingg galaxies: active — quasars: general — surveys — X-rays: galaxies

H-alpha emission lines in high-redshift quasars

Infrared spectra have been obtained of the H-alpha lines in 18 medium- to high-redshift QSOs and optical spectra taken nearly simultaneously to measure the strong UV line. It is found that the H-alpha line is redshifted by an average of 1000 km/s with respect to the lines from high ionization species such as C IV. Low ionization lines from ions like O I and Mg II are shifted by similar, or slightly smaller, amounts with respect to the high ionization lines. These results are difficult to reconcile with any simple models currently available, including those where dust obscuration is solely responsible for the observed velocity shifts. The similarity between the velocities of H-alpha and Mg II, O I provides some support for models in which the Balmer lines are produced predominantly in a warm H I region, while the Lyman lines arise mainly in a population of optically thin clouds. A velocity separation between the two cloud populations, along with some obscuration, could explain the main features. 25 refs.

ChaMP Serendipitous Galaxy Cluster Survey

We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg 2 , we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about � 10 � 14 ergs cm � 2 s � 1 , with a median cluster core radius of 21 00 . For 56 of the 130 X-ray fields, we use the ChaMP’s deep NOAO 4 m MOSAIC g 0 , r 0 , and i 0 imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z � 0:7. From the overlapping 6.1 deg 2 X-ray/optical imaging, wefind115opticalclusters (ofwhich11%areintheX-raycatalog)and28X-rayclusters(ofwhich46%are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5‐2 keV) is LX ¼ 2:65 � 0:19 ðÞ ; 10 43 ergs s � 1 . The clusters in our sample that are only detected in our optical data are poorer on average (� 4 � ) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions. Subject headingg galaxies: clusters: general — surveys — X-rays: galaxies: clusters

The rapid decay of the optical emission from GRB 980326 and its possible implications

We report the discovery of the optical counterpart to GRB 980326. Its rapid optical decay can be characterized by a power law with exponent - 2.10+/-0.13 and a constant underlying source at R_{{c}}=25.5+/-0.5 . Its optical colors 2.1 days after the burst imply a spectral slope of - 0.66+/-0.70 . The gamma -ray spectrum as observed with BATSE shows that it is among the 4% softest bursts ever recorded. We argue that the rapid optical decay may be a reason for the nondetection of some low-energy afterglows of GRBs

Multifrequency observations of blazars. III - The spectral shape of the radio to X-ray continuum

Multifrequency, quasi-simultaneous spectra for a sample of 11 blazars are presented. The spectral shape of the violently variable millimeter to ultraviolet flux is consistent with emission from a very compact single component which becomes self-absorbed at wavelengths longer than about 3 mm. The centimeter emission can be attributed to a separate, more slowly varying component. Three out of four optically violent variable quasars also exhibit evidence of a UV excess component. Values for the size of the flaring regions of 0.001-0.1 pc and magnetic fields of order 1 G are deduced. It is found that photon energy densities may dominate over magnetic field energy densities, in which case inverse Compton scattering may be the dominant energy loss mechanism in flaring components.

Multifrequency observations of blazars. IV - The variability of the radio to ultraviolet continuum

The results of analysis of the variability properties of the high-frequency radio to UV continua of a sample of nine blazars are presented. The IR and optical variations of the three sources for which detailed comparisons can be made between the light curves obtained at the various wavebands are found to be well correlated. A strong correlation is observed beween the near-IR flux levels and the near-IR spectral slopes of the BL Lac objects, in the sense that the spectra are steeper when the sources are fainter. A similar correlation is observed to hold in optically violent variable (OVV) quasars during large-amplitude flare events; in general, however, the spectra of the OVV quasars exhibit no significant correlation between flux level and spectral slope. An additional nonvariable 1-5 micron component may be present in the near-IR spectra of OVV quasars.

The Chandra Multi-wavelength Project: Optical Spectroscopy and the Broadband Spectral Energy Distributions of X-Ray-selected AGNs.

From optical spectroscopy of X-ray sources observed as part of the Chandra Multi-wavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-up using the FLWO/1.5 m, SAAO/1.9 m, WIYN 3.5 m, CTIO/4 m, KPNO/4 m, Magellan/6.5 m, MMT/6.5 m, and Gemini/8 m telescopes, and from archival Sloan Digital Sky Survey (SDSS) spectroscopy. We classify the optical counterparts as 50% broad-line active galactic nuclei (AGNs), 16% emission line galaxies, 14% absorption line galaxies, and 20% stars. We detect QSOs out to z ~ 5.5 and galaxies out to z ~ 3. We have compiled extensive photometry, including X-ray (ChaMP), ultraviolet (GALEX), optical (SDSS and ChaMP-NOAO/MOSAIC follow-up), near-infrared (UKIDSS, Two Micron All Sky Survey, and ChaMP-CTIO/ISPI follow-up), mid-infrared (WISE), and radio (FIRST and NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGNs and starburst components where both are present. While ~58% of X-ray Seyferts (1042 erg s–1 5% starburst contribution to bolometric luminosity) to fit observed photometry only 26% of the X-ray QSO (L 2 – 10 keV >1044 erg s–1) population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z > 1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 X-ray Bright Optically inactive Galaxies, 78 z > 3 X-ray sources, and eight Type-2 QSO candidates. Also, we have identified the highest redshift (z = 5.4135) X-ray-selected QSO with optical spectroscopy.

Emission-line galaxies and quasars in the southern hemisphere. I. Description and applications of an objective-prism survey

A selection of objects from the first plates of a low-dispersion, objective-prism survey for emission-line galaxies and quasars is used to illustrate the application of the survey to the following lines of research in extragalactic astronomy: quasi-stellar objects, Seyfert galaxies, instabilities in galaxies produced by tidal interaction or explosive events, and rates of star formation and the general chemical evolution of galaxies. Included in the discussion is a description of how the survey provides a new, purely optical, color-independent method for the direct isolation of bright, high-redshift QSOs with strong emission lines (L

Near-infrared spectra of Seyfert nuclei. I. The reddening problem

alpha

Multifrequency observations of blazars. II - The variability of the 1 micron to 2 MM continuum

is often directly visible on the Schmidt- survey plates). The newly discovered objects used for illustration are a radio- quiet QSO of redshift 2.07, a luminous, class 2 Seyfert galaxy, a compact blue emission-line galaxy with a jet or streamer, yet with no obvious interacting companion, and a blue galaxy with H