arXiv subjects

Peng Jiang

Publications and source records attributed to Peng Jiang.

375 records · Page 21Linked to original sources

arXiv2012

Rapid Infrared Variability of Three Radio-loud Narrow-line Seyfert 1 Galaxies: A View from the Wide-field Infrared Survey Explorer

Using newly released data from the Wide-field Infrared Survey Explorer, we report the discovery of rapid infrared variability in three radio-loud narrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in the sample of Yuan et al. (2008). J0849+5108 and J0948+0022 clearly show intraday variability, while J1505+0326 has a longer measurable time scale within 180 days. Their variability amplitudes, corrected for measurement errors, are $\sim 0.1-0.2$ mag. The detection of intraday variability restricts the size of the infrared-emitting region to $\sim 10^{-3}$ pc, significantly smaller than the scale of the torus but consistent with the base of a jet. The three variable sources are exceptionally radio-loud, have the highest radio brightness temperature among the whole sample, and all show detected $γ$-ray emission in Fermi/LAT observations. Their spectral energy distributions resemble those of low-energy-peaked blazars, with a synchrotron peak around infrared wavelengths. This result strongly confirms the view that at least some radio-loud NLS1s are blazars with a relativistic jet close to our line of sight. The beamed synchrotron emission from the jet contributes significantly to and probably dominates the spectra in the infrared and even optical bands.

astro-ph.HE↗

arXiv2012

Discovery of six high-redshift quasars with the Lijiang 2.4m telescope and the Multiple Mirror Telescope

Quasars with redshifts greater than 4 are rare, and can be used to probe the structure and evolution of the early universe. Here we report the discovery of six new quasars with $i$-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from the YFOSC spectroscopy of the Lijiang 2.4m telescope in February, 2012. These quasars are in the list of $z>3.6$ quasar candidates selected by using our proposed $J-K/i-Y$ criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as $z>3.6$ quasars. One of the other three objects was identified as a star and the other two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time that $z>4$ quasars have been discovered using a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.

astro-ph.CO↗

arXiv2012

Very Low-mass Stellar and Substellar Companions to Solar-like Stars from MARVELS II: A Short-period Companion Orbiting an F Star with Evidence of a Stellar Tertiary And Significant Mutual Inclination

We report the discovery via radial velocity of a short-period (P = 2.430420 \pm 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1. A long-term trend in the radial velocities indicates the presence of a tertiary stellar companion with $P > 2000$ days. High-resolution spectroscopy of the host star yields T_eff = 6427 +/- 33 K, log(g) = 4.52 +/- 0.14, and [Fe/H]=-0.04 +/- 0.05. These parameters, combined with the broad-band spectral energy distribution and parallax, allow us to infer a mass and radius of the host star of M_1=1.21 +/- 0.08 M_\odot and R_1=1.09_{-0.13}^{+0.15} R_\odot. We are able to exclude transits of the inner companion with high confidence. The host star's spectrum exhibits clear Ca H and K core emission indicating stellar activity, but a lack of photometric variability and small v*sin(I) suggest the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary from an activity-rotation relation matches the orbital period of the inner companion to within 1.5 σ, suggesting they are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis, as expected through tidal evolution, then it has a stellar mass of M_2 ~ 0.3-0.4 M_\odot. Direct imaging limits the existence of stellar companions to projected separations < 30 AU. No set of spectral lines and no significant flux contribution to the spectral energy distribution from either companion are detected, which places individual upper mass limits of M < 1.0 M_\odot, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 M_\odot, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system.

astro-ph.SR↗

arXiv2011

On the X-ray Baldwin Effect in Active Galactic Nuclei Observed by the Chandra High Energy Grating

Using Chandra High Energy Grating (HEG) observations of 32 AGNs, we present a systematic study of the X-ray Baldwin effect (XBE, i.e. the anti-correlation between narrow Fe Kα line EW and X-ray continuum luminosity for AGN samples) with the highest spectral resolution currently available. We have previously reported an anti-correlation with EW\proptoL(2-10 keV)^-0.22 in a HEG sample, and the correlation is much weaker after averaging multiple observations of individual AGNs (EW\proptoL(2-10 keV)^-0.13). This indicates that rapid variation in X-ray continuum plays an important role in producing the XBE, and such an effect should also be visible in individual AGNs. In this paper, by normalizing the line EWs and continuum luminosities to the time-averaged values for each AGN in our sample with multiple HEG observations, we find a strong anti-correlation between EW and Lx (EW/ \propto (L/ )^-0.82+/-0.10), consistent with the XBE expected in an individual AGN if the narrow line flux remains constant while the continuum varies. This is first observational evidence that the Fe Kα line flux in a large sample of AGNs lacks of a corresponding response to the continuum variation, supporting that the narrow Fe-K line emission originates from a region far from the nucleus. We then performed Monte-Carlo simulations to address whether the global XBE can be produced by X-ray continuum variation solely, and found that such interpretation of XBE cannot be ruled out statistically. One thus should be very cautious before reaching any scientific conclusion based on an observed XBE.

astro-ph.CO↗

arXiv2011

Activated dissociation of O2 on Pb(111) surfaces by Pb adatoms

We investigate the dissociation of O2 on Pb(111) surface using first-principles calculations. It is found that in a practical high-vacuum environment, the adsorption of molecular O2 takes place on clean Pb surfaces only at low temperatures such as 100 K, but the O2 easily desorbs at (elevated) room temperatures. It is further found that the Pb adatoms enhance the molecular adsorption and activate the adsorbed O2 to dissociate during subsequent room-temperature annealing. Our theory explains the observation of a two-step oxidation process on the Pb surfaces by the unique role of Pb adatoms.

physics.chem-ph↗

arXiv2011

SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems

Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2, which is now completed, measured medium-resolution (R=1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)

astro-ph.IM↗

arXiv2011

Fundamental Performance of a Dispersed Fixed Delay Interferometer In Searching For Planets Around M Dwarfs

We present a new method to calculate fundamental Doppler measurement limits with a dispersed fixed-delay interferometer (DFDI) in the near infrared wavelength region for searching for exoplanets around M dwarfs in the coming decade. It is based on calculating the Q factor, a measure of flux-normalized Doppler sensitivity in the fringing spectra created with DFDI. We calculate the Q factor as a function of spectral resolution R, stellar projected rotational velocity V sini, stellar effective temperature T_eff and optical path difference (OPD) of the interferometer. We also compare the DFDI Q factor to that for the popular cross-dispersed echelle spectrograph method (the direct echelle (DE) method). Given the IR Doppler measurement is likely to be detector-limited for a while, we introduce new merit functions, which is directly related to photon-limited RV uncertainty, to evaluate Doppler performance with the DFDI and DE methods. We find that DFDI has strength in wavelength coverage and multi-object capability over the DE for a limited detector resource. We simulate the performance of the InfraRed Exoplanet Tracker (IRET) based on the DFDI design, being considered for the next generation IR Doppler measurements. The predicted photon-limited RV uncertainty suggests that IRET is capable of detecting Earth-like exoplanets in habitable zone around nearby bright M dwarfs if they exist. A new method is developed to quantitatively estimate the influence of telluric lines on RV uncertainty. Our study shows that photon-limited RV uncertainty can be reached if 99% of the strength of telluric lines can be removed from the measured stellar spectra. At low to moderate levels of telluric line strength removal (50% to 90%), the optimal RV uncertainty is typically a factor of 2-3 times larger than photon-limited RV uncertainty.

astro-ph.EP↗

arXiv2011

Weighing Super-Massive Black Holes with Narrow Fe K$α$ Line

It has been suggested that the narrow cores of the Fe K$α$ emission lines in Active Galactic Nuclei (AGNs) are likely produced in the torus, the inner radius of which can be measured by observing the lag time between the $V$ and $K$ band flux variations. In this paper we compare the virial products of the infrared time lags and the narrow Fe K$α$ widths for 10 type 1 AGNs with the black hole masses from other techniques. We find the narrow Fe K$α$ line width is in average 2.6$^{+0.9}_{-0.4}$ times broader than expected assuming an isotropic velocity distribution of the torus at the distance measured by the infrared lags. We propose the thick disk model of the torus could explain the observed larger line width. Another possibility is the contamination by emission from the broad line region or the outer accretion disk. Alternatively, the narrow iron line might originate from the inner most part of the obscuring torus within the sublimation radius, while the infrared emission from outer cooler part. We note the correlation between the black hole masses based on this new technique and those based on other known techniques is statistically insignificant. We argue that this could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths. The next generation of X-ray observatories could help verify the origin of the narrow iron K$α$ line and the reliability of this new technique.

astro-ph.HE↗

arXiv2011

Towards Detecting The 2175-Å Dust Feature Associated With Strong High Redshift Mg ßII Absorption Lines

We report detections of 39 2175-Å dust extinction bump candidates associated with strong Mg II absorption lines at z$\sim$ 1--1.8 on quasar spectra in Sloan Digital Sky Survey (SDSS) DR3. These strong Mg II absorption line systems are detected among 2,951 strong Mg II absorbers with the rest equivalent width $W_r\lambda2796 >$ 1.0Å at $1.0 < z < 1.86$, which is part of a full sample of 7,421 strong Mg II absorbers compiled by Prochter et al. (2006). The redshift range of the absorbers is chosen to allow the 2175-Å extinction features to be completely covered within the SDSS spectrograph operation wavelength range. An upper limit of the background quasar emission redshift at z$=$2.1 is set to prevent the Ly$α$ forest lines from contaminating the sensitive spectral region for the 2175-Å bump measurements. The FM90 (Fitzpatrick & Massa 1990) parameterization is applied to model the Optical/UV extinction curve in the rest frame of Mg II absorbers of the 2175-Å bump candidates. The simulation technique developed by Jiang et al. (2010a, b) is used to derive the statistical significance of the candidate 2175-Å bumps. A total of 12 absorbers are detected with 2175-Å bumps at a 5$σ$ level of statistical significance, 10 are detected at a 4$σ$ level and 17 are detected at a 3$σ$ level. Most of the candidate bumps in this work are similar to the relatively weak 2175-Å bumps observed in the Large Magellanic Clouds (LMC) LMC2 supershell rather than the strong ones observed in the Milky Way (MW). This sample has greatly increased the total number of 2175-Å extinction bumps measured on SDSS quasar spectra. Follow-up observations may rule out some of possible false detections and reveal the physical and chemical natures of 2175-Å quasar absorbers.

astro-ph.CO↗

arXiv2010

MARVELS-1b: A Short-Period, Brown Dwarf Desert Candidate from the SDSS-III MARVELS Planet Search

We present a new short-period brown dwarf candidate around the star TYC 1240-00945-1. This candidate was discovered in the first year of the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the third phase of the Sloan Digital Sky Survey (SDSS-III), and we designate the brown dwarf as MARVELS-1b. MARVELS uses the technique of dispersed fixed-delay interferometery to simultaneously obtain radial velocity measurements for 60 objects per field using a single, custom-built instrument that is fiber fed from the SDSS 2.5-m telescope. From our 20 radial velocity measurements spread over a ~370 d time baseline, we derive a Keplerian orbital fit with semi-amplitude K=2.533+/-0.025 km/s, period P=5.8953+/-0.0004 d, and eccentricity consistent with circular. Independent follow-up radial velocity data confirm the orbit. Adopting a mass of 1.37+/-0.11 M_Sun for the slightly evolved F9 host star, we infer that the companion has a minimum mass of 28.0+/-1.5 M_Jup, a semimajor axis 0.071+/-0.002 AU assuming an edge-on orbit, and is probably tidally synchronized. We find no evidence for coherent instrinsic variability of the host star at the period of the companion at levels greater than a few millimagnitudes. The companion has an a priori transit probability of ~14%. Although we find no evidence for transits, we cannot definitively rule them out for companion radii ~<1 R_Jup.

astro-ph.EP↗

arXiv2010

High Dust Depletion in Two Intervening Quasar Absorption Line Systems with the 2175-Å Extinction Bump at $z\sim1.4$

We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-Å dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-Å absorber at $z$=1.64 toward the quasar SDSS J160457.50+220300.5, Noterdaeme et al. (2009) reported a similar dust depletion measurement ([Fe/Zn]=$-1.47$ and [Si/Zn]=$-1.07$) and detected C~I and CO absorption lineson its VLT/UVES spectrum. We conclude that heavy dust depletion (i.e. a characteristic of cold dense clouds in MW) is required to produce a pronounced 2175-Å extinction bump.

astro-ph.CO↗

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.

astro-ph↗

arXiv2007

On the fraction of X-ray obscured quasars

Various studies have claimed that the fraction of obscured AGN drops with luminosity, but contrary results are also reported. We present our recent studies on the fraction of X-ray obscured quasars in Chandra Deep Fields and in the local universe showing that most quasars in CDFs (at redshift of 1 ~ 4) are obscured and a consistent pattern in the local universe.

astro-ph↗

arXiv2006

The statistical properties of galaxy morphological types in compact groups of Main galaxies from the SDSS Data Release 4

In order to explore the statistical properties of galaxy morphological types in compact groups (CGs), we construct a random group sample which has the same distributions of redshift and number of member galaxies as those of the CG sample. It turns out that the proportion of early-type galaxies in different redshift bins for the CG sample is statistically higher than that for random group sample, and with growing redshift z this kind of difference becomes more significant. This may be due to the existence of interactions and mergers within a significant fraction of SDSS CGs. We also compare statistical results of CGs with those of more compact groups and pairs, but do not observe as large statistical difference as Hickson (1982)'results.

astro-ph↗

arXiv2006

The local environmental dependence of galaxy properties in the volume-limited sample of Main Galaxies from the SDSS Data Release 5

Using a volume-limited sample of Main Galaxies from the SDSS Data Release 5, we investigate the dependence of galaxy properties on local environment. For each galaxy, the local three-dimensional density is calculated. We find that galaxy morphologies strongly depend on local environment: galaxies in dense environments have predominantly early type morphologies, but other galaxy properties do not present significant dependence on local environment. Clearly, this puts a important constraint on proposed physical mechanisms.

astro-ph↗