13569282
Identifying high redshift AGNs from X-ray colors
The X-ray color (hardness ratio) of optically undetected X-ray sources can be used to distinguish obscured active galactic nuclei (AGNs) at low and intermediate redshift from viable high-redshift (i.e., z > 5) AGN candidates, and thus to better determine the space density, ionizing photon production, and X-ray background contribution of the earliest detectable AGNs. High redshift AGNs should appear soft in X-ray with hardness ratio HR ∼ -0.5, even if there is strong absorption with hydrogen column density NH up to 10 cm, simply because the absorption redshift out of the soft X-ray band in the observed frame. Here the X-ray hardness ratio is defined as HR= (H-S)/(H+S), where S and H are the soft and hard band net counts detected by Chandra. High redshift AGNs that are Compton thick (NH & 10 cm) could have HR ∼ 0.0, however, these should be rare in deep Chandra images, since they have to be & 10 times brighter intrinsically, which implies & 100 times drop in their space density. Applying the hardness criterion (HR < 0.0) can filter out about 50% of the candidate high redshift AGNs selected from deep Chandra images. Subject headings: galaxies: active — galaxies: high-redshift — X-rays: galaxies
119329374
Polarization of Quasars: Rotated and Funnel-shaped Outflow
Polarization is a useful probe to investigate the geometries and dynamics of outflow in BAL QSOs. We perform a Monte-Carlo simulation to calculate the polarization produced by resonant and electron scattering in BALR. We find: 1)A rotated and funnel-shaped outflow is preferred to explain many observed polarization features. 2)The resonant scattering can contribute a significant part of NV emission line in some QSOs.
16103411
Partially obscured quasars in the Sloan Digital Sky Survey Early Data Release
We have compiled a sample of 21 low redshift (z . 0.3), luminous active galactic nuclei (AGN) with large Balmer decrements (Hα/Hβ > 7) using the galaxy and QSO catalogs of the Sloan Digital Sky Survey Early Data Release. Using this sample we attempt to determine the fraction of quasars with large internal absorption. We find that these AGN have Strong [O III] λ5007 and broad Hα emission, and that starlight dominates the spectra in the blue band, suggesting that these objects are heavily reddened. Their narrow emission line ratios are similar to those of Seyfert 2 galaxies, yet the average [O III] λ5007 emission is ∼10 times more luminous. Applying the empirical relation between the optical continuum and the Balmer line luminosity for blue quasars, we find that the intrinsic luminosities of these 21 objects are in the range for quasars. We propose that they are obscured, intermediate type quasars analogous to type 1.8 and 1.9 Seyfert galaxies. The ratio of these optically selected, intermediate type quasars to type 1 quasars are found to be around 1, similar to that for local Seyfert galaxies. Preliminary study indicates that most of these quasars are hosted in early type galaxies. Subject headings: galaxies: active — quasars: general — galaxies: nuclei
13062064
Polar outflows in six broad absorption line quasars
Using radio observations by FIRST and NVSS, we build a sample of 151 radio-variable quasars selected from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Six (and probably another two) of these objects are classified as broad absorption line (BAL) quasars and show radio flux variations of a few tens of percent within 1.5-5 yr. Such large amplitudes of variations imply brightness temperatures much higher than the inverse Compton limits (10(12) K) in all these BAL quasars, suggesting the presence of relativistic jets beaming toward the observer. The angles between the outflow and the jet are constrained to be less than similar to 20 degrees. Such BAL quasars with polar outflows are beyond the simple unification models of BAL and non-BAL quasars, which hypothesize BAL quasars as otherwise normal quasars seen nearly edge-on.
119360994
The 172 ks Chandra Exposure of the LALA Bootes Field: X-Ray Source Catalog
We present an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha survey (LALA) Bootes field, obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on board the Chandra X-Ray Observatory. This is one of the deepest Chandra images of the extragalactic sky; only the 2 Ms Chandra Deep Field North (CDF-N) and 1 Ms Chandra Deep Field South (CDF-S) are substantially deeper. In this paper we present the X-ray source catalog obtained from this image, along with an analysis of source counts and optical identifications. The X-ray image is composed of two individual observations obtained in 2002 and reaches 0.5–2.0 and 2.0–10.0 keV flux limits of 1.5 × 10-16 and 1.0 × 10-15 ergs cm-2 s-1, respectively, for point sources near the aim point. A total of 168 X-ray sources were detected: 160 in the 0.5–7.0 keV band, 132 in the 0.5–2.0 keV band, and 111 in the 2.0–7.0 keV band. The X-ray source counts were derived and compared with those from other Chandra deep surveys; the hard X-ray source density of the LALA Bootes field is 33% higher than that of CDF-S at the flux level of 2.0 × 10-15 ergs cm-2 s-1, confirming the field-to-field variances of the hard-band source counts reported by previous studies. The deep exposure resolves 72% of the 2.0–10.0 keV X-ray background. Our primary optical data are R-band imaging from the NOAO Deep Wide-Field Survey (NDWFS), with a limiting magnitude of R = 25.7 (Vega, 3 σ, and 4'' diameter aperture). We have found optical counterparts for 152 of the 168 Chandra sources (90%); 144 of these are detected in the R-band image, and eight have optical counterparts in other bands (either BW, V, I, or z'). Among the R-band nondetected sources, not more than 11 of them can possibly be at z > 5, based on the hardness ratios of their X-ray emission and nondetections in bluer bands (BW, V). The majority (~76%) of the X-ray sources are found to have log(fX/fR) within 0.0 ± 1; these are believed to be AGNs. Most of the X-ray–faint/optically bright sources [log(fX/fR) 1.0], which are harder in X-ray and are probably obscured AGNs.
121240830
Relation between Starlight and Nebular Emission Lines of Star-Forming Galaxies
We present an exercise that intends to establish a relationship between the strength of nebular emission lines and optical stellar features in the spectrum of a galaxy. After accurately subtracting the stellar continuum and the underlying stellar absorption, we made reliable measurements of the emission lines of all the galaxies in the Sloan Digital Sky Survey Data Release 2 (SDSS DR2). More than 4000 star-forming galaxies with high S/N ratio of both the stellar spectrum and the emission lines are selected. These galaxy spectra are fitted with the 10 PCs of Yip et al., after all the emission line regions have been filtered out. We find that the flux of hydrogen Balmer emission lines, H α and H β can be well recovered from the PCs, while the metal lines are not well reproduced. The fluxes of H α and H β measured from the PC-reconstructed spectra and from the observed spectra agree well with an rms scatter of only ~0.1 dex. This result suggests that, with moderate spectral resolution and S/N ratio, the optical stellar spectrum of a galaxy can serve as an indicator of star formation rate.
119332033
Photometric redshift of X-ray sources in the Chandra Deep Field-South
Based on the photometry of 10 near-ultraviolet, optical, and near-infrared bands of the Chandra Deep Field-South, we estimate the photometric redshifts for 342 X-ray sources, which constitute ~99% of all the detected X-ray sources in the field. The models of spectral energy distribution are based on galaxies and a combination of power-law continuum and emission lines. Color information is useful for source classifications: type I active galactic nuclei (AGNs) show nonthermal spectral features that are distinct from galaxies and type II AGNs. The hardness ratio in X-ray and the X-ray-to-optical flux ratio are also useful discriminators. Using rudimentary color separation techniques, we are able to further refine our photometric redshift estimations. Among these sources, 173 have reliable spectroscopic redshifts, which we use to verify the accuracy of photometric redshifts and to modify the model inputs. The average relative dispersion in redshift distribution is ~8%, among the most accurate for photometric surveys. The high reliability of our results is attributable to the high quality and broad coverage of data as well as the applications of several independent methods and a careful evaluation of every source. We apply our redshift estimations to study the effect of redshift on broadband colors and to study the redshift distribution of AGNs. Our results show that both the hardness ratio and U - K color decline with redshift, which may be the result of a K-correction. The number of type II AGNs declines significantly at z > 2 and that of galaxies declines at z > 1. However, the distribution of type I AGNs exhibits less redshift dependence. As well, we observe a significant peak in the redshift distribution at z = 0.6. We demonstrate that our photometric redshift estimation produces a reliable database for the study of X-ray luminosity of galaxies and AGNs.
17021242
Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual AGNs?
Double-peaked [OIII ] profiles in active galactic nuclei (AGNs) may provide evide nc for the existence of dual AGNs, but a good diagnostic for selecting them is currently l acking. Starting from∼ 7000 active galaxies in SDSS DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III ] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galax ies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted re lativ to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. Th e correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [OIII ] double-peaked sources are dual AGNs and disfavors other ex planations, such as rotating disk and outflows. These dual AGNs have a separation distance at ∼ 1 kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about ∼ 10−2, impacting on the current observational deficit of binary supermassive black holes with a probability of ∼ 10−4 (Boroson & Lauer). Subject headings: black hole physics — galaxies: evolution
118403124
How Close Are We To Detecting Earth-like Planets in the Habitable Zone Using the Radial Velocity Technique?
Discovering an Earth-like exoplanet in habitable zone is an important milestone for astronomers in search of extra-terrestrial life. While the radial velocity (RV) technique remains one the most powerful tools in detecting and characterizing exo-planetary sys- tems, we calculate the uncertainties in precision RV measurements considering stellar spectral quality factors, RV calibration sources, stellar noise and telluric contamination in different observational bandpasses and for different spectral types. We predict the optimal observational bandpass for different spectral types using the RV technique un- der a variety of conditions. We compare the RV signal of an Earth-like planet in the habitable zone (HZ) to the near future state of the art RV precision and attempt to answer the question: How close are we to detecting Earth-like planet in the HZ using the RV technique?
116966286
Search for a $W^\prime$ or Techni-$\rho$ Decaying into $WZ$ in $pp$ Collisions at $\sqrt{s}=7$ TeV
A search is performed in pp collisions at √s=7  TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5  fb^(-1). No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W′ boson described by the sequential standard model and on the W′ WZ coupling. W′ bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters.
2353414
AGN/starburst connection in action: the half million second RGS spectrum of NGC 1365
Context. High-resolution X-ray observations in the imaging and spectral domain have recently opened a new window on active galactic nuclei (AGN) feedback onto the circumnuclear gas. Spectral diagnostics, as well as the remarkable morphological coincidence between [O iii] and X-rays, point to AGN photoionisation as the dominant ionisation mechanism on scales as large as a few kpc. Aims. In this paper we extend these studies to the nearby Seyfert 2 galaxy NGC 1365, known to host a circumnuclear ring of intense star formation at � 1.3 kpc from the nucleus. The main scope of this investigation is to study the connection between nuclear activity and star formation in nearby AGN. Methods. We present a deep (� 5.8 days) 0.3–2 keV high-resolution spectrum of NGC 1365, collected with the reflection grating spectrometer (RGS) on board XMM-Newton. Results. The spectrum is dominated by strong recombination lines of He- and H-like transitions from carbon to silicon, as well as by L transitions from Fexvii. The continuum is strong, especially in the 10 to 20 A range. Formal fits require two optically thin, collisionally ionised plasma components, with temperatures � 300 and � 640 eV. However, they leave the bulk of the forbidden components of the He-α Ovii and Nvi triplets unaccounted for. These features can be explained as being produced by photoionised gas. NGC 1365 is therefore the first obscured AGN, whose high-resolution X-ray spectrum requires both collisional ionisation and photoionisation. Conclusions. The relative weakness of photoionisation does not stem from the intrinsic weakness of its AGN, whose X-ray luminosity is ∼ >10 42 erg s −1 . We suggest that it may instead come from the line-of-sight from the active nucleus to the NLR being blocked by optically thick matter in the broad line region, at the same time responsible for the large observed variation of the column density obscuring the X-ray active nucleus. Alternatively, NGC 1365 could host a remarkably luminous nuclear starburst when compared to the AGN accretion power.