arXiv subjects

Xiaobo Dong

Publications and source records attributed to Xiaobo Dong.

30 records · Page 2Linked to original sources

arXiv2008

The Correlation between X-ray and UV Properties of BAL QSOs

We compile a large sample of broad absorption lines (BAL) quasars with X-ray observations from the \xmm archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for twelve objects. X-ray absorption is detected in all of them. Complementary to that of \citet{gall06} (thereafter G06), our sample spans wide ranges of both BALnicity Index (BI) and maximum outflow velocity (\vmax). Combining our sample with G06's, we find very significant correlations between the intrinsic X-ray weakness with both BALnicity Index (BI) and the maximum velocity of absorption trough. We do not confirm the previous claimed correlation between absorption column density and broad absorption line parameters. We tentatively interpret this as that X-ray absorption is necessary to the production of the BAL outflow, but the properties of the outflow are largely determined by intrinsic SED of the quasars.

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arXiv2008

Difference in Narrow Emission Line Spectra of Seyfert 1 and 2 galaxies

In the unification scheme of Seyfert galaxies, a dusty torus blocks the continuum source and broad line region in Seyfert 2 galaxies. However it is not clear whether or not and to what extent the torus affects the narrow line spectra. In this paper, we show that Seyfert 1 and Seyfert 2 galaxies have different distributions on the [OIII]/H$β$ vs [NII]/H$α$ diagram (BPT diagram) for narrow lines. Seyfert 2 galaxies display a clear left boundary on the BPT diagram and only 7.3% of them lie on the left. By contrast, Seyfert 1 galaxies do not show such a cutoff and 33.0% of them stand on the left side of the boundary. Among Seyfert 1 galaxies, the distribution varies with the extinction to broad lines. As the extinction increases, the distribution on BPT diagram moves to larger [NII]/H$α$ value. We interpret this as an evidence for the obscuration of inner dense narrow line region by the dusty torus. We also demonstrate that the [OIII] and broad line luminosity correlation depends on the extinction of broad lines in the way that high extinction objects have lower uncorrected [OIII] luminosities, suggesting that [OIII] is partially obscured in these objects. Therefore, using [OIII] as an indicator for the nuclear luminosity will systematically under-estimate the nuclear luminosity of Seyfert 2 galaxies.

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arXiv2008

XMM observations of BAL Quasars with polar outflows

We have selected a sample of broad absorption line (BAL) quasars which show significant radio variations, indicating the presence of polar BAL outflows. We obtained snapshot XMM observations of four polar BAL QSOs, to check whether strong X-ray absorption, one of the most prominent characteristics of most BAL QSOs, also exist in polar outflows. Two of the sources are detected in X-ray. Spectral fittings show that they are X-ray normal with no intrinsic X-ray absorption, suggesting the X-ray shielding gas might be absent in polar BAL outflows. Comparing to non-BAL QSOs, one of two X-ray nondetected sources remains consistent with X-ray normal, while the other one, which is an iron low-ionization BAL (FeLoBAL), shows an X-ray weakness factor of > 19, suggesting strong intrinsic X-ray absorption. Alternative explanations to the nondetection of strong X-ray absorption in the two X-ray detected sources are 1) the absorption is more complex than a simple neutral absorber, such as partial covering absorption or ionized absorption; 2) there might be significant jet contribution to the detected X-ray emission. Current data is insufficient to test these possibilities, and further observations are required to understand the X-ray nature of polar BAL outflows.

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arXiv2007

Broad-line Balmer Decrements in Blue Active Galactic Nuclei

We have investigated the broad-line Balmer decrements (Halpha/Hbeta) for a large, homogeneous sample of Seyfert 1 galaxies and QSOs using spectroscopic data obtained in the Sloan Digital Sky Survey. The sample, drawn from the Fourth Data Release, comprises 446 low redshift (z < 0.35) active galactic nuclei (AGN) that have blue optical continua as indicated by the spectral slopes in order to minimize the effect of dust extinction. We find that (i) the distribution of the intrinsic broad-line Halpha/Hbeta ratio can be well described by log-Gaussian, with a peak at Halpha/Hbeta=3.06 and a standard deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate with AGN properties such as luminosity, accretion rate, and continuum slope, etc.; (iii) on average, the Balmer decrements are found to be only slightly larger in radio-loud sources (3.37) and sources having double-peaked emission-line profiles (3.27) compared to the rest of the sample. We therefore suggest that the broad-line Halpha/Hbeta ratio can be used as a good indicator for dust extinction in the AGN broad-line region; this is especially true for radio-quiet AGN with regular emission-line profiles, which constitute the vast majority of the AGN population.

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arXiv2007

Metal Enriched Outflows and Dusty starburst in the type II quasar Q 1321+058

We present an analysis of the emission line property and the broad band spectral energy distribution of the ultra-luminous infrared Type II quasar Q132+058. The optical and ultraviolet emission lines show four distinct components: a LINER-like component at the systematic velocity, a heavily reddened HII-like component blueshifted by about 400 km/s, and two broad components blueshifted by about 400 km/s and 1900 km/s, respectively. The emission line ratios suggest that broad components are produced in dense and alpha-enriched outflows with a metalicity of 3-5 Zsun and a density of n_H ~ 10^7 cm^-3. The optical--UV continuum is dominated by stellar light and can be modeled with a young (<1 Myr) plus an intermediate age (0.5-0.8Gyr) stellar populations. The near to mid-infrared light is dominated by hot and warm dust heated by the hidden quasar. We derive a star formation rate (SFR) of 300-500 M\sun yr$^{-1}$ from the UV spectrum and far-infrared luminosity, which is two orders of magnitude larger than that indicated by reddening uncorrected [OII] luminosity.

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arXiv2006

Systematic study of a large sample of NLS1 galaxies from SDSS: first results

This proceedings contribution summarizes first results obtained from a systematic study of 2011 NLS1 galaxies, as presented in Zhou et al. (2006, ApJS 166, 128). The sample was compiled by examining the spectral parameters of galaxies and QSOs derived from SDSS DR3 data. We discuss some preliminary results on the statistic properties of the sample, such as the fraction of NLS1, the properties of broad and narrow emission lines, and emission in other wavebands. The black hole mass--velocity dispersion relation for NLS1s was re-examined using the velocity dispersion values estimated from the stellar absorption spectra of the host galaxies. Preliminary result from an X-ray study for a small subset using data obtained by XMM-Newton is briefly discussed.

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arXiv2006

Broad-line AGNs with Candidate Intermediate-mass Black holes in the Sloan Digital Sky Survey

We have conducted a systematic search of AGNs with IMBHs from the SDSS DR4. As results we found 245 candidates of broad-line AGN with M_{BH}<10^6 \Msun estimated from the luminosity and width of the broad Halpha component. Compared to the pioneer Greene & Ho (2004) sample of 19 IMBH AGNs, our sample has improved in covering a larger range of the Eddington ratio, as well as black hole mass and redshift, taking the advantage of our AGN-galaxy spectral decomposition algorithm. Among these, thirty-six have L_{bol}/L_{Edd} < 0.1, hinting that a significant fraction of IMBHs might exist with weak or no nuclear activity.

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arXiv2006

SDSS J160531.84+174826.1: A Dwarf Disk Galaxy With An Intermediate-Mass Black Hole

We report the discovery of a dwarf Seyfert 1 active galactic nucleus (AGN) with a candidate intermediate-mass black hole hosted by the dwarf galaxy SDSS J160531.84+174826.1 at z=0.032. A broad component of the H-alpha line with FWHM=781 km/s is detected in its optical spectrum, and a bright, point-like nucleus is evident from a HST imaging observation. Non-thermal X-ray emission is also detected from the nucleus. The black hole mass, as estimated from the luminosity and width of the broad H-alpha component, is about 7x10^4 \msun. The host galaxy appears to be a disk galaxy with a boxy bulge or nuclear bar; with an absolute magnitude of M_R = -17.8 (M_B = -16.4), it is among the least luminous host galaxies ever identified for a Seyfert 1.

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arXiv2006

A Comprehensive Study of 2 000 Narrow Line Seyfert 1 Galaxies from the Sloan Digital Sky Survey: I. The Sample

This is the first paper in a series dedicated to the study of the emission-line and continuum properties of narrow line Seyfert 1 galaxies (NLS1s). We carried out a systematic search for NLS1s from objects assigned as ``QSOs'' or ``galaxies'' in the spectroscopic sample of the Sloan Digital Sky Survey Data Release 3 (SDSS DR3) by a careful modeling of their emission lines and continua. The result is a uniform sample comprising $\sim 2~000$ NLS1. This sample dramatically increases the number of known NLS1 by a factor of $\sim 10$ over previous compilations. This paper presents the parameters of the prominent emission lines and continua, which were measured accurately with typical uncertainties $<10%$. Taking advantage of such an unprecedented large and uniform sample with accurately measured spectral parameters, we carried out various statistical analysis, some of which were only possible for the first time (abbreviated).

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arXiv2005

Ensemble Learning Independent Component Analysis of Normal Galaxy Spectra

In this paper, we employe a new statistical analysis technique, Ensemble Learning for Independent Component Analysis (EL-ICA), on the synthetic galaxy spectra from a newly released high resolution evolutionary model by Bruzual & Charlot. We find that EL-ICA can sufficiently compress the synthetic galaxy spectral library to 6 non-negative Independent Components (ICs), which are good templates to model huge amount of normal galaxy spectra, such as the galaxy spectra in the Sloan Digital Sky Survey (SDSS). Important spectral parameters, such as starlight reddening, stellar velocity dispersion, stellar mass and star formation histories, can be given simultaneously by the fit. Extensive tests show that the fit and the derived parameters are reliable for galaxy spectra with the typical quality of the SDSS.

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arXiv2005

Strong CaII absorption lines in the reddened quasar SDSS J2339$-$0912: Evidence of the collision/merger in the host galaxy?

We report the detection of strong CaII/MgII absorption lines at the quasar redshift in the narrow line quasar SDSS J2339-0912 (z=0.6604). The quasar exhibits strong FeII, small Balmer emission line width and a very red B-Ks color. Both the optical continuum and broad emission lines are reddened by SMC-like dust of E(B-V)~1.0 mag, while its near-infrared color (J-Ks=1.60) shows little reddening. The CaII absorption lines are saturated and resolved with an FWHM of 362 km/s and an equivalent width of W_{CaII K}=4.2Å(in the source rest frame). MgII absorption lines are also saturated and have a similar line width. The line profile and the fact that there is no evidence for starlight from the host galaxy suggest that these absorption lines are not of a stellar origin. The ratio of column density of CaII to that of dust is consistent with that of the ISM in our Galaxy. We suggest that both the heavy reddening and the large absorption line width are due to the highly disturbed ISM on the line of sight toward the quasar, and that the disturbance is caused by a galaxy collision or even merger in the quasar host galaxy.

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arXiv2004

Obscured Binary Quasar Cores in SDSS J104807.74+005543.5?

We report the discovery of a possible close binary system of quasars in SDSS J1048+0055. The [OIII]4959,5007 emission lines are clearly double-peaked, and two discrete radio sources with a projected physical separation of ~20 pc are found in the VLBA milliarcsec resolution image at 8.4 GHz. Each of the [O III]4959,5007 doublets and Hbeta can be well modelled by two Gaussians and the line ratio, [O III]5007/Hbeta ~7, is typical of Seyfert 2 galaxies. No broad component of Hbeta was detected and its [O III]5007 luminosity, L_[OIII] ~ 9.2 times 10^42 erg s^-1, is comparable to luminous quasars and is a few ten times more luminous than typical Seyfert galaxies. One natural interpretation is that SDSS J1048+0055 contains two close quasar-like nuclei and the BLR around them are obscured. Other possible models are also discussed. We suggest that double-peaked narrow emission line profile may be an effective way of selecting candidates of binary black holes with intermediate separation.

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