Oligomer formation within secondary organic aerosols: equilibrium and dynamic considerations

We present a model based on the volatility basis set to consider the potential influence of oligomer content on volatility driven secondary organic aerosol (SOA) yields. The implications for aerosol evaporation studies, including dilution, chamber thermo-equilibration, and thermodenuder studies, are also considered. A simplified description of oligomer formation reproduces essentially all of the broad classes of equilibrium and dynamical observations related to SOA formation and evaporation: significant oligomer content may be consistent with mass yields that increase with organic aerosol mass concentration; reversible oligomerization can explain the hysteresis between the rate of SOA formation and its evaporation rate upon dilution; and the model is consistent with both chamber thermo-equilibration studies and thermodenuder studies of SOA evaporation

C IV BAL disappearance in a large SDSS QSO sample

Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) originate from outflowing winds along our line of sight; winds are thought to originate from the inner regions of the QSO accretion disk, close to the central supermassive black hole (SMBH). Winds likely play a role in galaxy evolution and aid the accretion mechanism onto the SMBH. BAL equivalent widths can change on typical timescales from months to years; such variability is generally attributed to changes in the covering factor and/or in the ionization level of the gas. We investigate BAL variability, focusing on BAL disappearance. We analyze multi-epoch spectra of more than 1500 QSOs -the largest sample ever used for such a study- observed by different programs from the Sloan Digital Sky Survey-I/II/III (SDSS), and search for disappearing C IV BALs. The spectra rest-frame time baseline ranges from 0.28 to 4.9 yr; the source redshifts range from 1.68 to 4.27. We detect 73 disappearing BALs in the spectra of 67 sources. This corresponds to 3.9% of disappearing BALs, and 5.1% of our BAL QSOs exhibit at least one disappearing BAL. We estimate the average lifetime of a BAL along our line of sight (~ 80-100 yr), which appears consistent with the accretion disk orbital time at distances where winds are thought to originate. We inspect properties of the disappearing BALs and compare them to the properties of our main sample. We also investigate the existence of a correlation in the variability of multiple troughs in the same spectrum, and find it persistent at large velocity offsets between BAL pairs, suggesting that a mechanism extending on a global scale is necessary to explain the phenomenon. We select a more reliable sample of disappearing BALs following Filiz Ak et al. (2012), where a subset of our sample was analyzed, and compare the findings from the two works, obtaining generally consistent results.Comment: 22 pages, 9 figures. Accepted for publication in A&

Ballistic magnon heat conduction and possible Poiseuille flow in the helimagnetic insulator Cu2_2OSeO3_3

We report on the observation of magnon thermal conductivity $\kappa_m\sim$ 70 W/mK near 5 K in the helimagnetic insulator Cu$_2$OSeO$_3$, exceeding that measured in any other ferromagnet by almost two orders of magnitude. Ballistic, boundary-limited transport for both magnons and phonons is established below 1 K, and Poiseuille flow of magnons is proposed to explain a magnon mean-free path substantially exceeding the specimen width for the least defective specimens in the range 2 K $<T<$ 10 K. These observations establish Cu$_2$OSeO$_3$ as a model system for studying long-wavelength magnon dynamics.Comment: 10pp, 9 figures, accepted PRB (Editor's Suggestion

The Sloan Digital Sky Survey Reverberation Mapping Project: Post-Starburst Signatures in Quasar Host Galaxies at z < 1

Quasar host galaxies are key for understanding the relation between galaxies and the supermassive black holes (SMBHs) at their centers. We present a study of 191 broad-line quasars and their host galaxies at z < 1, using high signal-to-noise ratio (SNR) spectra produced by the Sloan Digital Sky Survey Reverberation Mapping project. Clear detection of stellar absorption lines allows a reliable decomposition of the observed spectra into nuclear and host components, using spectral models of quasar and stellar radiations as well as emission lines from the interstellar medium. We estimate age, mass (M*), and velocity dispersion (sigma*) of the host stars, the star formation rate (SFR), quasar luminosity, and SMBH mass (Mbh), for each object. The quasars are preferentially hosted by massive galaxies with M* ~ 10^{11} Msun characterized by stellar ages around a billion years, which coincides with the transition phase of normal galaxies from the blue cloud to the red sequence. The host galaxies have relatively low SFRs and fall below the main sequence of star-forming galaxies at similar redshifts. These facts suggest that the hosts have experienced an episode of major star formation sometime in the past billion years, which was subsequently quenched or suppressed. The derived Mbh - sigma* and Mbh - M* relations agree with our past measurements and are consistent with no evolution from the local Universe. The present analysis demonstrates that reliable measurements of stellar properties of quasar host galaxies are possible with high-SNR fiber spectra, which will be acquired in large numbers with future powerful instruments such as the Subaru Prime Focus Spectrograph.Comment: ApJ in pres

The XMM-Newton wide-field survey in the COSMOS field. IV: X-ray spectral properties of Active Galactic Nuclei

We present a detailed spectral analysis of point-like X-ray sources in the XMM-COSMOS field. Our sample of 135 sources only includes those that have more than 100 net counts in the 0.3-10 keV energy band and have been identified through optical spectroscopy. The majority of the sources are well described by a simple power-law model with either no absorption (76%) or a significant intrinsic, absorbing column (20%).As expected, the distribution of intrinsic absorbing column densities is markedly different between AGN with or without broad optical emission lines. We find within our sample four Type-2 QSOs candidates (L_X > 10^44 erg/s, N_H > 10^22 cm^-2), with a spectral energy distribution well reproduced by a composite Seyfert-2 spectrum, that demonstrates the strength of the wide field XMM/COSMOS survey to detect these rare and underrepresented sources.Comment: 16 pages, ApJS COSMOS Special Issue, 2007 in press. The full-resolution version is available at http://www.mpe.mpg.de/XMMCosmos/PAPERS/mainieri_cosmos.ps.g

The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of 1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this paper we report the i, K and 3.6micron identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only 2 sources are truly empty fields. Making use of the large number of X-ray sources, we update the "classic locus" of AGN and define a new locus containing 90% of the AGN in the survey with full band luminosity >10^42 erg/s. We present the linear fit between the total i band magnitude and the X-ray flux in the soft and hard band, drawn over 2 orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between C and X/O, computed in the hard band, and that 90% of the obscured AGN in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the BH growth at X-ray luminosities of 10^43- 10^44.5 erg/s.Comment: 21 pages, 17 figures, 4 tables; accepted for publication in ApJS. The catalog is available at the urls listed in the pape

Linking black-hole growth with host galaxies: The accretion-stellar mass relation and its cosmic evolution

Previous studies suggest that the growth of supermassive black holes (SMBHs) may be fundamentally related to host-galaxy stellar mass ($M_\star$). To investigate this SMBH growth-$M_\star$ relation in detail, we calculate long-term SMBH accretion rate as a function of $M_\star$ and redshift [$\overline{\rm BHAR}(M_\star, z)$] over ranges of $\log(M_\star/M_\odot)=\text{9.5--12}$ and $z=\text{0.4--4}$. Our $\overline{\rm BHAR}(M_\star, z)$ is constrained by high-quality survey data (GOODS-South, GOODS-North, and COSMOS), and by the stellar mass function and the X-ray luminosity function. At a given $M_\star$, $\overline{\rm BHAR}$ is higher at high redshift. This redshift dependence is stronger in more massive systems (for $\log(M_\star/M_\odot)\approx 11.5$, $\overline{\rm BHAR}$ is three decades higher at $z=4$ than at $z=0.5$), possibly due to AGN feedback. Our results indicate that the ratio between $\overline{\rm BHAR}$ and average star formation rate ($\overline{\rm SFR}$) rises toward high $M_\star$ at a given redshift. This $\overline{\rm BHAR}/\overline{\rm SFR}$ dependence on $M_\star$ does not support the scenario that SMBH and galaxy growth are in lockstep. We calculate SMBH mass history [$M_{\rm BH}(z)$] based on our $\overline{\rm BHAR}(M_\star, z)$ and the $M_\star(z)$ from the literature, and find that the $M_{\rm BH}$-$M_\star$ relation has weak redshift evolution since $z\approx 2$. The $M_{\rm BH}/M_\star$ ratio is higher toward massive galaxies: it rises from $\approx 1/5000$ at $\log M_\star\lesssim 10.5$ to $\approx 1/500$ at $\log M_\star \gtrsim 11.2$. Our predicted $M_{\rm BH}/M_\star$ ratio at high $M_\star$ is similar to that observed in local giant ellipticals, suggesting that SMBH growth from mergers is unlikely to dominate over growth from accretion.Comment: 27 pages, 21 figures, 2 tables; MNRAS accepte

Bayesian High-Redshift Quasar Classification from Optical and Mid-IR Photometry

We identify 885,503 type 1 quasar candidates to i<22 using the combination of optical and mid-IR photometry. Optical photometry is taken from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III/BOSS), while mid-IR photometry comes from a combination of data from the Wide-Field Infrared Survey Explorer (WISE) "ALLWISE" data release and several large-area Spitzer Space Telescope fields. Selection is based on a Bayesian kernel density algorithm with a training sample of 157,701 spectroscopically-confirmed type-1 quasars with both optical and mid-IR data. Of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623 are objects that we have not previously classified as photometric quasar candidates). These candidates include 7874 objects targeted as high probability potential quasars with 3.5<z<5 (of which 6779 are new photometric candidates). Our algorithm is more complete to z>3.5 than the traditional mid-IR selection "wedges" and to 2.2<z<3.5 quasars than the SDSS-III/BOSS project. Number counts and luminosity function analysis suggests that the resulting catalog is relatively complete to known quasars and is identifying new high-z quasars at z>3. This catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars and for further machine learning quasar selection using Spitzer and WISE data combined with other large-area optical imaging surveys.Comment: 54 pages, 17 figures; accepted by ApJS Data for tables 1 and 2 available at http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/master_quasar_catalogs.011414.fits.bz2 and http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/optical_ir_quasar_candidates.052015.fits.bz

GABRB3 mutations: a new and emerging cause of early infantile epileptic encephalopathy

The gamma-aminobutyric acid type A receptor β3 gene (GABRB3) encodes the β3-subunit of the gamma-aminobutyric acid type A (GABAA ) receptor, which mediates inhibitory signalling within the central nervous system. Recently, GABRB3 mutations have been identified in a few patients with infantile spasms and Lennox-Gastaut syndrome. We report the clinical and electrographic features of a novel case of GABRB3-related early-onset epileptic encephalopathy. Our patient presented with neonatal hypotonia and feeding difficulties, then developed pharmacoresistant epileptic encephalopathy, characterized by multiple seizure types from 3 months of age. Electroencephalography demonstrated ictal generalized and interictal multifocal epileptiform abnormalities. Using a SureSelectXT custom multiple gene panel covering 48 early infantile epileptic encephalopathy/developmental delay genes, a novel de novo GABRB3 heterozygous missense mutation, c.860C>T (p.Thr287Ile), was identified and confirmed on Sanger sequencing. GABRB3 is an emerging cause of early-onset epilepsy. Novel genetic technologies, such as whole-exome/genome sequencing and multiple gene panels, will undoubtedly identify further cases, allowing more detailed electroclinical delineation of the GABRB3-related genotypic and phenotypic spectra