Constraining the size of the narrow line region in distant quasars

We propose a proper method to measure the size of the narrow line region (NLR) in distant quasars. The apparent angular size of the NLR is, in general, too small to resolve technically. However, it is possible to map the NLR if with gravitational lensing. In our method, we directly compare the observed image of the NLR with the expected lensed images of the NLR for various source sizes and lens models. Seeking the best fit image via the comparison procedures, we can obtain the best-fit size and the best-fit lens model. We apply this method to the two-dimensional spectroscopic data of a famous lensed quasar, Q2237+0305. If the lens galaxy resembles the applied lens model, an upper limit to the NLR size can be set 750 pc. Further, we examine how the fitting results will be improved by future observations, taking into account the realistic observational effects, such as seeing. Future observations will provide us more stringent constraints on the size of the NLR and on the density profile of the lens galaxy.Comment: 17 pages including 4 figures, accepted to Ap

VLBI Imaging of Water Maser Emission from the Nuclear Torus of NGC 1068

We have made the first VLBI synthesis images of the H2O maser emission associated with the central engine of the Seyfert galaxy NGC 1068. Emission extends about +/-300 km/s from the systemic velocity. Images with submilliarcsecond angular resolution show that the red-shifted emission lies along an arc to the northwest of the systemic emission. (The blue-shifted emission has not yet been imaged with VLBI.) Based on the maser velocities and the relative orientation of the known radio jet, we propose that the maser emission arises on the surface of a nearly edge-on torus, where physical conditions are conducive to maser action. The visible part of the torus is axially thick, with comparable height and radius. The velocity field indicates sub-Keplerian differential rotation around a central mass of about 1e7 Msun that lies within a cylindrical radius of about 0.65 pc. The estimated luminosity of the central engine is about 0.5 of the Eddington limit. There is no detectable compact radio continuum emission near the proposed center of the torus (T_B< 5e6 K on size scales of about 0.1 pc), so that the observed flat-spectrum core cannot be direct self-absorbed synchrotron radiation.Comment: 12 pages, 4 figures. To appear in ApJ Part 2. Also available at http://www.physics.ucsb.edu/~vlbiweb

The Relationship of Hard X-ray and Optical Line Emission in Low Redshift Active Galactic Nuclei

In this paper we assess the relationship of the population of Active Galactic Nuclei (AGN) selected by hard X-rays to the traditional population of AGN with strong optical emission lines. First, we study the emission-line properties of a new hard X-ray selected sample of 47 local AGN (classified optically as both Type 1 and Type 2 AGN). We find that the hard X- ray (3-20 keV) and [OIII]$\lambda$5007 optical emission-line luminosities are well-correlated over a range of about four orders-of-magnitude in luminosity (mean luminosity ratio 2.15 dex with a standard deviation of $\sigma$ = 0.51 dex). Second, we study the hard X-ray properties of a sample of 55 local AGN selected from the literature on the basis of the flux in the [OIII] line. The correlation between the hard X-ray (2-10 keV) and [OIII] luminosity for the Type 1 AGN is consistent with what is seen in the hard X-ray selected sample. However, the Type 2 AGN have a much larger range in the luminosity ratio, and many are very weak in hard X-rays (as expected for heavily absorbed AGN). We then compare the hard X-ray (3-20 keV) and [OIII] luminosity functions of AGN in the local universe. These have similar faint-end slopes with a luminosity ratio of 1.60 dex (0.55 dex smaller than the mean value for individual hard X-ray selected AGN). We conclude that at low redshift, selection by narrow optical emission- lines will recover most AGN selected by hard X-rays (with the exception of BL Lac objects). However, selection by hard X-rays misses a significant fraction of the local AGN population with strong emission lines

An extreme, blueshifted iron line profile in the Narrow Line Seyfert 1 PG 1402+261; an edge-on accretion disk or highly ionized absorption?

We report on a short XMM-Newton observation of the radio-quiet Narrow Line Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong excess of counts between 6-9 keV in the rest frame. This feature can be modeled by an unusually strong (equivalent width 2 keV) and very broad (FWHM velocity of 110000 km/s) iron K-shell emission line. The line centroid energy at 7.3 keV appears blue-shifted with respect to the iron Kalpha emission band between 6.4-6.97 keV, while the blue-wing of the line extends to 9 keV in the quasar rest frame. The line profile can be fitted by reflection from the inner accretion disk, but an inclination angle of >60 deg is required to model the extreme blue-wing of the line. Furthermore the extreme strength of the line requires a geometry whereby the hard X-ray emission from PG 1402+261 above 2 keV is dominated by the pure-reflection component from the disk, while little or none of the direct hard power-law is observed. Alternatively the spectrum above 2 keV may instead be explained by an ionized absorber, if the column density is sufficiently high (N_H > 3 x 10^23 cm^-2) and if the matter is ionized enough to produce a deep (tau~1) iron K-shell absorption edge at 9 keV. This absorber could originate in a large column density, high velocity outflow, perhaps similar to those which appear to be observed in several other high accretion rate AGN. Further observations, especially at higher spectral resolution, are required to distinguish between the accretion disk reflection or outflow scenarios.Comment: Accepted for publication in ApJ (18 pages, 5 figures, 1 table

Chandra Snapshot Observations of Low-Luminosity AGNs with a Compact Radio Source

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness (RO = L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2, AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert galaxies, quasars and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio loud.Comment: 15 pages, accepted for publication in Ap

VLTI/VINCI observations of the nucleus of NGC 1068 using the adaptive optics system MACAO

We present the first near-infrared K-band long-baseline interferometric measurement of the prototype Seyfert 2 galaxy NGC 1068 with resolution lambda/B \~ 10 mas obtained with the Very Large Telescope Interferometer (VLTI) and the two 8.2m Unit Telescopes UT2 and UT3. The adaptive optics system MACAO was employed to deliver wavefront-corrected beams to the K-band commissioning instrument VINCI. A squared visibility amplitude of 16.3 +/- 4.3 % was measured for NGC 1068 at a sky-projected baseline length of 45.8 m and azimuth angle 44.9 deg. This value corresponds to a FWHM of the K-band intensity distribution of 5.0 +/- 0.5 mas (0.4 +/- 0.04 pc) at the distance of NGC 1068) if it consists of a single Gaussian component. Taking into account K-band speckle interferometry observations (Wittkowski et al. 1998; Weinberger et al. 1999; Weigelt et al. 2004), we favor a multi-component model for the intensity distribution where a part of the flux originates from scales clearly smaller than about 5 mas (<0.4 pc), and another part of the flux from larger scales. The K-band emission from the small (< 5 mas) scales might arise from substructure of the dusty nuclear torus, or directly from the central accretion flow viewed through only moderate extinction.Comment: Accepted for publication in Astronomy and Astrophysics Letter

Polarized Broad-Line Emission from Low-Luminosity Active Galactic Nuclei

In order to determine whether unified models of active galactic nuclei apply to low-luminosity objects, we have undertaken a spectropolarimetric survey of of LINERs and Seyfert nuclei at the Keck Observatory. The 14 objects observed have a median H-alpha luminosity of 8x10^{39} erg/s, well below the typical value of ~10^{41} erg/s for Markarian Seyfert nuclei. Polarized broad H-alpha emission is detected in three LINERs: NGC 315, NGC 1052, and NGC 4261. Each of these is an elliptical galaxy with a double-sided radio jet, and the emission-line polarization in each case is oriented roughly perpendicular to the jet axis, as expected for the obscuring torus model. NGC 4261 and NGC 315 are known to contain dusty circumnuclear disks, which may be the outer extensions of the obscuring tori. The detection of polarized broad-line emission suggests that these objects are nearby, low-luminosity analogs of obscured quasars residing in narrow-line radio galaxies. The nuclear continuum of the low-luminosity Seyfert 1 galaxy NGC 4395 is polarized at p = 0.67%, possibly the result of an electron scattering region near the nucleus. Continuum polarization is detected in other objects, with a median level of p = 0.36% over 5100-6100 A, but in most cases this is likely to be the result of transmission through foreground dust. The lack of significant broad-line polarization in most type 1 LINERs is consistent with the hypothesis that we view the broad-line regions of these objects directly, rather than in scattered light.Comment: 28 pages, including 3 tables and 16 figures. Uses the emulateapj latex style file. Accepted for publication in The Astrophysical Journa

Executive functions and attention processes in adolescents and young adults with intellectual disability

(1) Background: We made a comprehensive evaluation of executive functions (EFs) and attention processes in a group of adolescents and young adults with mild intellectual disability (ID). (2) Methods: 27 adolescents and young adults (14 females and 13 males) with ID, aged between 15.1 and 23 years (M = 17.4; SD = 2.04), were compared to a control group free of cognitive problems and individually matched for gender and age. (3) Results: As for EFs, individuals with ID were severely impaired on all subtests of the Behavioral Assessment of Dysexecutive Syndrome (BADS) battery. However, we also found appreciable individual differences, with eight individuals (approximately 30%) scoring within normal limits. On the attention tests, individuals with ID were not generally slower but presented specific deficits only on some attention tests (i.e., Choice Reaction Times, Color Naming and Color–Word Interference, and Shifting of Attention for Verbal and for Visual Targets). The role of a global factor (i.e., cognitive speed) was modest in contributing to the group differences; i.e., when present, group differences were selectively associated with specific task manipulations, not global differences in cognitive speed. (4) Conclusions: The study confirmed large group differences in EFs; deficits in attentional processing were more specific and occurred primarily in tasks taxing the selective dimension of attention, with performance on intensive tasks almost entirely spared

Transient and Highly Polarized Double-Peaked H-alpha Emission in the Seyfert 2 Nucleus of NGC 2110

We have discovered an extremely broad, double-peaked H-alpha emission line in the polarized flux spectrum of NGC 2110, establishing that this well-studied Seyfert 2 galaxy contains a disk-like hidden broad-line region (BLR). Several properties of NGC 2110 suggest that it is an obscured twin of Arp 102B, the prototypical double-peaked emission-line active galactic nucleus (AGN). A comparison between our data and previous spectra of NGC 2110 indicates that the double-peaked H-alpha feature is transient. The presence of a disk-like BLR in NGC 2110 has important implications for AGNs: it expands the range of properties exhibited by Seyfert 2 galaxies, and the fact that the BLR is obscured by a torus-like structure provides the first evidence that double-peaked emitters and classical Seyfert nuclei may have the same basic parsec-scale geometry.Comment: 5 pages, including 3 postscript figures. Uses emulateapj. Accepted for publication in ApJ Letter

Variable Iron K-alpha Lines in Seyfert 1 Galaxies

We find that variability of the iron K-alpha line is common in Seyfert 1 galaxies. Using data from the ASCA archive for objects that have been observed more than once during the mission, we study the time-averaged spectra from individual observations, thereby probing variability on timescales that range from days to years. Since the statistics of the data do not warrant searches for line variability in terms of a complex physical model, we use a a simple Gaussian to model the gross shape of the line, and then use the centroid energy, intensity and equivalent width as robust indicators of changes in the line profile. We find that ~70% of Seyfert 1s (ten out of fifteen) show variability in at least one of these parameters: the centroid energy, intensity, and equivalent width vary in six, four, and eight sources respectively. Due to the low S/N, limited sampling and time averaging, we consider these results to represent lower limits to the rate of incidence of variability. In most cases changes in the line do not appear to track changes in the continuum. In particular, we find no evidence for variability of the line intensity in NGC 4151, suggesting an origin in a region larger than the putative accretion disk, where most of the iron line has been thought to originate. Mkn 279 is investigated on short timescales. The time-averaged effective line energy is 6.5 keV in the galaxy rest frame. As the continuum flux increases by 20% in a few hours, the Fe K line responds with the effective line energy increasing by 0.22 keV (~10,500 km s^-1). Problems with the ASCA and Rosat calibration that affect simultaneous spectral fits are discussed in an appendix.Comment: 26 pages, 30 figures, accepted for publication in the Astrophysical Journa