Physics

Differential photometry of suspected cataclysmic variables

N. Bennert et al. — Tue, 30 Apr 2013 13:12:16 PDT

The cataclysmic variable CW 1045+525: A secondary-dominated dwarf nova?

C. Tappert et al. — Tue, 30 Apr 2013 13:12:13 PDT

We present spectroscopic and photometric observations of the cataclysmic variable CW 1045+525. Both the optical spectrum and the photometric lightcurve show a strong contribution of a K5V-M0V secondary. We derive an orbital period d by measuring the radial velocities of the absorption lines of the secondary. The period and spectral type of the secondary suggest a distance of 350-700 pc. There is evidence for additional sources of line- and continuum emission, but no direct evidence of an accretion disc. We discuss several scenarios for the nature of CW 1045+525 on the basis of our results, finding a dwarf nova classification to be the most probable, although not completely satisfying, explanation for the observed characteristics.

Size and structure of the narrow-line region of quasars

Nicola Bennert et al. — Tue, 30 Apr 2013 13:12:11 PDT

We have observed the narrow-line regions (NLRs) of the seven brightest radio-quiet Palomar-Green (or Bright Quasar Survey) quasars (z < 0.5) with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). Linear-ramp filters were used to image the [O III] λ5007 line emission with 00455-01 pixel resolution. We find that the NLRs are very compact with typical extents of 2''-4''. Two quasars show compact filamentary structures similar to Seyfert NLRs. They may be related to radio outflows. Most interestingly, when including a sample of Seyfert galaxies observed with HST, we tentatively find that the size of the NLR is proportional to the square root of the [O III] luminosity. This is comparable to the scaling found for the size of the broad-line region with continuum luminosity, which has been interpreted in terms of a constant photoionization parameter. The relation determined here connects the NLR of radio-quiet quasars and Seyfert galaxies over 3 orders of magnitude in [O III] luminosity.

Spectral characteristics of water megamaser galaxies. II. ESO103-G035, TXS 2226-184, and IC1481

N. Bennert et al. — Tue, 30 Apr 2013 13:12:10 PDT

Long-slit optical emission-line spectra of the H₂O megamaser galaxies ESO 103-G035, TXS 2226-184, and IC 1481 are evaluated in order to look for characteristics typical for water-megamaser galaxies. We present rotation curves, line ratios, electron densities, temperatures, and H luminosities. The successful line-profile decompositions rest on d-Lorentzians with an additional parameter d to adjust the wings, rather than Gaussians or Lorentzians as basic functions. No significant velocity gradient is found along the major axis in the innermost 2 kpc of TXS 2226-184. IC 1481 reveals a spectrum suggestive of a vigorous starburst in the central kiloparsec 10⁸ years ago. None of the three galaxies shows any hints for outflows nor special features which could give clues to the presence of H₂O megamaser emission. The galaxies are of normal Seyfert-2 (ESO 103-G035) or LINER (TXS 2226-184, IC 1481) type.

Size and properties of the NLR in the Seyfert-2 galaxy NGC1386

N. Bennert et al. — Tue, 30 Apr 2013 13:12:07 PDT

We study the narrow-line region (NLR) of the Seyfert-2 galaxy NGC 1386 by means of long-slit spectroscopy obtained with FORS1 at the VLT. We use the galaxy itself for subtracting the stellar template, applying reddening corrections to fit the stellar template to the spectra of the NLR. The continuum gets steadily redder towards the nucleus. The spatial distribution of the reddening derived from the Balmer decrement differs from the continuum reddening, indicating dust within the NLR with a varying column density along the line of sight. Using spatially resolved spectral diagnostics, we find a transition between central line ratios falling into the AGN regime and outer ones in the H II-region regime, occuring at a radius of 6 (310 pc) in all three diagnostic diagrams. Applying CLOUDY photoionisation models, we show that the observed distinction between H II-like and AGN-like ratios in NGC 1386 represents a true difference in ionisation source and cannot be explained by variations of physical parameters such as ionisation parameter, electron density or metallicity. We interpret it as a real border between the NLR, i.e. the central AGN-photoionised region and surrounding H II regions. We derive surface brightness, electron density, and ionisation parameter as a function of distance from the nucleus. Both the electron density and the ionisation parameter decrease with radius. We discuss the consequences of these observations for the interpretation of the empirical NLR size-luminosity relation. In the outer part of the NLR, we find evidence for shocks, resulting in a secondary peak of the electron-density and ionisation-parameter distribution north of the nucleus. We compare the NLR velocity curve with the stellar one and discuss the differences.

[O III] profile substructure in radio-quiet quasars

C. Leipski et al. — Tue, 30 Apr 2013 13:12:05 PDT

Interactions between the radio jet and the optical emission of the narrow-line region (NLR) are a well known phenomenon in Seyfert galaxies. Here, we present the study of possible jet-NLR interactions in five radio-quiet PG quasars with double or triple radio structure. High spatial and spectral resolution observations were carried out in the H-[O III] 5007 wavelength range. In all cases, there is evidence for [O III] profile substructure (shoulders, subpeaks, blueshifted "broad'' components) with different clarity. To measure the velocity, line width, intensity, and location of these [O III] components, several Gaussians were fitted. Often, the substructures are more pronounced close to the radio lobes, suggestive of jet-NLR interactions. Our observations support the unification scheme in which radio-quiet quasars are assumed to be the luminous cousins of Seyfert galaxies.

The radio structure of radio-quiet quasars

C. Leipski et al. — Tue, 30 Apr 2013 13:12:02 PDT

Aims. We investigate the radio emitting structures of radio-quiet active galactic nuclei with an emphasis on radio-quiet quasars to study their connection to Seyfert galaxies. Methods. We present and analyse high-sensitivity VLA radio continuum images of 14 radio-quiet quasars and six Seyfert galaxies. Results. Many of the low redshift radio-quiet quasars show radio structures that can be interpreted as jet-like outflows. However, the detection rate of extended radio structures on arcsecond scales among our sample decreases with increasing redshift and luminosity, most likely due to a lack of resolution. The morphologies of the detected radio emission indicate strong interactions of the jets with the surrounding medium. We also compare the radio data of seven quasars with corresponding HST images of the [O III] emitting narrow-line region (NLR). We find that the scenario of interaction between the radio jet and the NLR gas is confirmed in two sources by structures in the NLR gas distribution as previously known for Seyfert galaxies. The extended radio structures of radio-quiet quasars at sub-arcsecond resolution are by no means different from that of Seyferts. Among the luminosities studied here, the morphological features found are similar in both types of objects while the overall size of the radio structures increases with luminosity. This supports the picture where radio-quiet quasars are the scaled-up versions of Seyfert galaxies. In addition to known luminosity relations we find a correlation of the NLR size and the radio size shared by quasars and Seyferts.

Size and properties of the narrow-line region in Seyfert-2 galaxies from spatially-resolved optical spectroscopy

N. Bennert et al. — Tue, 30 Apr 2013 13:12:01 PDT

Context. While [O III] narrow-band imaging is commonly used to measure the size of the narrow-line regions (NLRs) in active galactic nuclei (AGNs), it can be contaminated by emission from surrounding starbursts. Recently, we have shown that long-slit spectroscopy provides a valuable alternative approach to probe the size in terms of AGN photoionisation. Moreover, several parameters of the NLR can be directly accessed. Aims. We here apply the same methods developed and described for the Seyfert-2 galaxy NGC 1386 to study the NLR of five other Seyfert-2 galaxies by using high-sensitivity spatially-resolved optical spectroscopy obtained at the VLT and the NTT. Methods. We probe the AGN-photoionisation of the NLR and thus, its "real'' size using diagnostic line-ratio diagrams. We derive physical properties of the NLR such as reddening, ionisation parameter, electron density, and velocity as a function of distance from the nucleus. Results. For NGC 5643, the diagnostic diagrams unveil a similar transition between line ratios falling in the AGN regime and those typical for H II regions as found for NGC 1386, thus determining the size of the NLR. For the other four objects, all measured line ratios fall in the AGN regime. In almost all cases, both electron density and ionisation parameter decrease with radius. Deviations from this general behaviour (such as a secondary peak) seen in both the ionisation parameter and electron density can be interpreted as signs of shocks from the interaction of a radio jet and the NLR gas. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We compare our results to those of NGC 1386 and show that the latter can be considered as prototypical also for this larger sample. We discuss our findings in detail for each object.

Size and properties of the narrow-line region in Seyfert-1 galaxies from spatially-resolved optical spectroscopy

N. Bennert et al. — Tue, 30 Apr 2013 13:11:59 PDT

Context.Spatially resolved emission-line spectroscopy is a powerful tool for determining the physical conditions in the narrow-line region (NLR) of active galactic nuclei (AGNs). We recently used optical long-slit spectroscopy to study the NLRs of a sample of six Seyfert-2 galaxies. We have shown that such an approach, in comparison to the commonly used [ ] narrow-band imaging alone, allows us to probe the size of the NLR in terms of AGN photoionisation. Moreover, several physical parameters of the NLR can be directly accessed. Aims.We here apply the same methods to study the NLR of six Seyfert-1 galaxies and compare our results to those of Seyfert-2 galaxies. Methods.We employ diagnostically valuable emission-line ratios to determine the physical properties of the NLR, including the core values and radial dependencies of density, ionisation parameter, and reddening. Tracking the radial change of emission-line ratios in diagnostic diagrams allows us to measure the transition between AGN-like and -like line excitation, and thus to measure the size of the NLR. Results.In the diagnostic diagrams, we find a transition between line ratios falling in the AGN regime and those typical of regions in two Seyfert-1 galaxies, thereby determining the size of the NLR. The central electron temperature and ionisation parameter are, in general, higher in type-1 Seyferts than in type 2s. In almost all cases, both electron density and ionisation parameter decrease with radius and the decrease is faster in Seyfert-1 galaxies than in Sy 2s. In several objects, the gaseous velocity distribution is characteristic of rotational motion in an (inclined) emission-line disk in the centre. We give estimates of the black-hole masses and discuss our findings in detail for each object.

Spectacular shells in the host galaxy of the QSO MC2 1635+119

Gabriela Canalizo et al. — Tue, 30 Apr 2013 13:11:57 PDT

We present deep HST ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy previously classified as an undisturbed elliptical galaxy. Our new images reveal dramatic shell structure indicative of a merger event in the relatively recent past. The brightest shells in the central regions of the host are distributed alternately in radius, with at least two distinct shells on one side of the nucleus and three on the other, out to a distance of ~13 kpc. The light within the five shells comprises ~6% of the total galaxy light. Lower surface brightness ripples or tails and other debris extend out to a distance of ~65 kpc. A simple N-body model for a merger reproduces the inner shell structure and gives an estimate for the age of the merger of between ~30 Myr and ~1.7 Gyr, depending on a range of reasonable assumptions. While the inner shell structure is suggestive of a minor merger, the total light contribution from the shells and extended structures is more indicative of a major merger. The spectrum of the host galaxy is dominated by a population of intermediate age (~1.4 Gyr), indicating a strong starburst episode that may have occurred at the time of the merger event. We speculate that the current QSO activity may have been triggered in the recent past by either a minor merger, or by debris from an older (~Gyr) major merger that is currently "raining" back into the central regions of the merger remnant.

Evidence for merger remnants in early-type host galaxies of low-redshift QSOs

Nicola Bennert et al. — Tue, 30 Apr 2013 13:11:54 PDT

We present results from a pilot HST ACS deep imaging study in broadband V of five low-redshift QSO host galaxies classified in the literature as ellipticals. The aim of our study is to determine whether these early-type hosts formed at high redshift and have since evolved passively, or whether they have undergone relatively recent mergers that may be related to the triggering of the nuclear activity. We perform two-dimensional modeling of the light distributions to analyze the host galaxies' morphology. We find that, while each host galaxy is reasonably well fitted by a de Vaucouleurs profile, the majority of them (4/5) reveal significant fine structure such as shells and tidal tails. These structures contribute between ~5% and 10% to the total V-band luminosity of each host galaxy within a region of r ~ 3r_eff and are indicative of merger events that occurred between a few hundred Myr and a Gyr ago. These timescales are comparable to starburst ages in the QSO hosts previously inferred from Keck spectroscopy. Our results thus support a consistent scenario in which most of the QSO host galaxies suffered mergers with accompanying starbursts that likely also triggered the QSO activity in some way, but we are also left with considerable uncertainty on physical mechanisms that might have delayed this triggering for several hundred Myr after the merger.

First results from the lick AGN monitoring project: the mass of the black hole in ARP 151

Misty C. Bentz et al. — Tue, 30 Apr 2013 13:11:52 PDT

We have recently completed a 64 night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10⁶-10⁷ M_☉. We present here the first results from this project—the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hβ lag measurement in this object of 4.25_−0.66^+0.68 days in the observed frame. Coupled with the width of the Hβ emission line in the variable spectrum, we determine a black hole mass of (7.1 ± 1.2) × 10⁶ M_☉, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hβ emission line which clearly shows infalling gas in the Hβ-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.

A search for H₂O megamasers in high-z type-2 active galactic nuclei

Vardha N. Bennert et al. — Tue, 30 Apr 2013 13:11:51 PDT

We report a search for H₂O megamasers in 274 SDSS type-2 active galactic nuclei (AGNs; 0.3 <z< 0.83), half of which can be classified as type-2 quasi-stellar objects (QSOs) from their [O III] 5007 luminosity, using the Robert C. Byrd Green Bank Telescope (GBT) and the Effelsberg 100 m radio telescope. Apart from the detection of the extremely luminous water vapor megamaser SDSS J080430.99+360718.1, already reported by Barvainis & Antonucci, we do not find any additional line emission. This high rate of nondetections is compared to the water maser luminosity function created from the 78 water maser galaxies known to date and its extrapolation toward the higher luminosities of "gigamasers" that we would have been able to detect given the sensitivity of our survey. The properties of the known water masers are summarized and discussed with respect to the nature of high-z type-2 AGNs and megamasers in general. In the Appendix, we list 173 additional objects (mainly radio galaxies, but also QSOs and galaxies) that were observed with the GBT, the Effelsberg 100 m radio telescope, or Arecibo Observatory without leading to the detection of water maser emission.

The lick AGN monitoring project: photometric light curves and optical variability characteristics

Jonelle L. Walsh et al. — Tue, 30 Apr 2013 13:11:49 PDT

The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with the intent of measuring the masses of their central black holes using reverberation mapping. The sample includes 12 galaxies selected to have black holes with masses roughly in the range 10⁶-10⁷ M _☉, as well as the well-studied active galactic nucleus (AGN) NGC 5548. In conjunction with a spectroscopic monitoring campaign, we obtained broadband B and V images on most nights from 2008 February through 2008 May. The imaging observations were carried out by four telescopes: the 0.76 m Katzman Automatic Imaging Telescope, the 2 m Multicolor Active Galactic Nuclei Monitoring telescope, the Palomar 60 inch (1.5 m) telescope, and the 0.80 m Tenagra II telescope. Having well-sampled light curves over the course of a few months is useful for obtaining the broad-line reverberation lag and black hole mass, and also allows us to examine the characteristics of the continuum variability. In this paper, we discuss the observational methods and the photometric measurements, and present the AGN continuum light curves. We measure various variability characteristics of each of the light curves. We do not detect any evidence for a time lag between the B- and V-band variations, and we do not find significant color variations for the AGNs in our sample.

The lick AGN monitoring project: broad-line region radii and black hole masses from reverberation mapping of Hß

Misty C. Bentz et al. — Tue, 30 Apr 2013 13:11:46 PDT

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10⁶-10⁷ M _☉ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission. We present here the light curves for all the objects in this sample and the subsequent Hβ time lags for the nine objects where these measurements were possible. The Hβ lag time is directly related to the size of the broad-line region (BLR) in AGNs, and by combining the Hβ lag time with the measured width of the Hβ emission line in the variable part of the spectrum, we determine the virial mass of the central supermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al., which brings the masses determined by reverberation mapping into agreement with the local M _BH-σrelationship for quiescent galaxies. We also examine the time lag response as a function of velocity across the Hβ line profile for six of the AGNs. The analysis of four leads to rather ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting BLR clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple gravitational infall model. Further investigation will be necessary to fully understand the constraints placed on the physical models of the BLR by the velocity-resolved response in these objects.

Cosmic evolution of black holes and spheroids. IV. The M_BH - L_sph relation

Vardha N. Bennert et al. — Tue, 30 Apr 2013 13:11:43 PDT

From high-resolution images of 23 Seyfert-1 galaxies at z = 0.36 and z = 0.57 obtained with the Near-Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope (HST), we determine host-galaxy morphology, nuclear luminosity, total host-galaxy luminosity, and spheroid luminosity. Keck spectroscopy is used to estimate black hole mass (M _BH). We study the cosmic evolution of the M _BH-spheroid luminosity (L _sph) relation. In combination with our previous work, totaling 40 Seyfert-1 galaxies, the covered range in BH mass is substantially increased, allowing us to determine for the first time intrinsic scatter and correct evolutionary trends for selection effects. We re-analyze archival HST images of 19 local reverberation-mapped active galaxies to match the procedure adopted at intermediate redshift. Correcting spheroid luminosity for passive luminosity evolution and taking into account selection effects, we determine that at fixed present-day V-band spheroid luminosity, M _BH/L _sph (1 + z)^{2.8± 1.2}. When including a sample of 44 quasars out to z = 4.5 taken from the literature, with luminosity and BH mass corrected to a self-consistent calibration, we extend the BH mass range to over 2 orders of magnitude, resulting in M _BH/L _sph (1 + z)^{1.4± 0.2}. The intrinsic scatter of the relation, assumed constant with redshift, is 0.3 ± 0.1 dex (M _BH-total-host-galaxy-luminosity relation is apparently non-evolving. It hints at either a more fundamental relation or that the spheroid grows by a redistribution of stars. However, the high-z sample does not follow this relation, indicating that major mergers may play the dominant role in growing spheroids above z 1.

SDSS J1254+0846: a binary quasar caught in the act of merging

Paul J. Green et al. — Tue, 30 Apr 2013 13:11:39 PDT

We present the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z = 0.44 radio-quiet quasars, with a radial velocity difference of just 215 km s^–1, separated on the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal tails. The pair was targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry. We present follow-up optical imaging which shows broad, symmetrical tidal arm features spanning some 75 kpc at the quasars' redshift. Previously, the triggering of two quasars during a merger had only been hypothesized but our observations provide strong evidence of such an event. SDSS J1254+0846, as a face-on, pre-coalescence merger hosting two luminous quasars separated by a few dozen kpc, provides a unique opportunity to probe quasar activity in an ongoing gas-rich merger. Numerical modeling suggests that the system consists of two massive disk galaxies prograde to their mutual orbit, caught during the first passage of an active merger. This demonstrates rapid black hole growth during the early stages of a merger between galaxies with pre-existing bulges. Neither of the two luminous nuclei show significant intrinsic absorption by gas or dust in our optical or X-ray observations, illustrating that not all merging quasars will be in an obscured, ultraluminous phase. We find that the Eddington ratio for the fainter component B is rather normal, while for the A component L/L _Edd is quite (>3σ) high compared to quasars of similar luminosity and redshift, possibly evidence for strong merger-triggered accretion. More such mergers should be identifiable at higher redshifts using binary quasars as tracers.

Megamaser detection and nuclear obscuration in Seyfert galaxies

M. Ramolla et al. — Tue, 30 Apr 2013 13:11:36 PDT

We revisit the relation between H₂O maser detection rate and nuclear obscuration for a sample of 114 Seyfert galaxies drawn from the CfA, 12 μm, and IRAS F25/F60 catalogs. These sources have mid-infrared spectra from the Spitzer Space Telescope and we search for accompanying X-ray and [O III] 5007 Å fluxes from the literature. We use the strength of the [O IV] 25.9 μm emission line as a tracer of the intrinsic AGN strength. After the normalization by [O IV], the observed X-ray flux provides information about X-ray absorption. The distribution of X-ray/[O IV] flux ratios is significantly different for masers and non-masers: The maser detected Seyfert-2s (Sy 1.8–2.0) populate a distinct X-ray/[O IV] range, which is, on average, about a factor of four lower than the range of Seyfert-2 non-masers and about a factor of ten lower than the range of Seyfert-1s (Sy 1.0–1.5). Non-masers are almost equally distributed over the entire X-ray/[O IV] range. This provides evidence that high nuclear obscuration plays a crucial role in determining the probability of maser detection. Furthermore, after normalization with [O IV], we find a similar but weaker trend for the distribution of the maser detection rate with the absorption of the 7 μm dust continuum. This suggests that the obscuration of the 7 μm continuum occurs on larger spatial scales than that of the X-rays. Hence, in the AGN unified model, at moderate inclinations away from edge-on, the 7 μm dust absorption may occur without any proportionate X-ray absorption. The absorption of [O III] appears unrelated to maser detections. The failure to detect masers in obscured AGN is most likely due to insufficient observational sensitivity.

The lick AGN monitoring project: the M _BH-σ* relation for reverberation-mapped active galaxies

Jong-Hak Woo et al. — Tue, 30 Apr 2013 13:11:34 PDT

To investigate the black hole mass versus stellar velocity dispersion (M _BH-σ_*) relation of active galaxies, we measured the velocity dispersions of a sample of local Seyfert 1 galaxies, for which we have recently determined black hole masses using reverberation mapping. For most objects, stellar velocity dispersions were measured from high signal-to-noise ratio optical spectra centered on the Ca II triplet region (~8500 Å), obtained at the Keck, Palomar, and Lick Observatories. For two objects, in which the Ca II triplet region was contaminated by nuclear emission, the measurement was based on high-quality H-band spectra obtained with the OH-Suppressing Infrared Imaging Spectrograph at the Keck-II telescope. Combining our new measurements with data from the literature, we assemble a sample of 24 active galaxies with stellar velocity dispersions and reverberation-based black hole mass measurements in the range of black hole mass 10⁶ < M _BH/M _☉ < 10⁹. We use this sample to obtain reverberation-mapping constraints on the slope and intrinsic scatter of the M _BH-σ_* relation of active galaxies. Assuming a constant virial coefficient f for the reverberation-mapping black hole masses, we find a slope β = 3.55 ± 0.60 and the intrinsic scatter σ_int = 0.43 ± 0.08 dex in the relation log(M _BH/M _☉) = α + β log(σ_*/200 km s^–1), which are consistent with those found for quiescent galaxies. We derive an updated value of the virial coefficient f by finding the value which places the reverberation masses in best agreement with the M _BH-σ_* relation of quiescent galaxies; using the quiescent M _BH-σ_* relation determined by Gültekin et al., we find log f = 0.72^+0.09 _–0.10 with an intrinsic scatter of 0.44 ± 0.07 dex. No strong correlations between f and parameters connected to the physics of accretion (such as the Eddington ratio or line-shape measurements) are found. The uncertainty of the virial coefficient remains one of the main sources of the uncertainty in black hole mass determinations using reverberation mapping, and therefore also in single-epoch spectroscopic estimates of black hole masses in active galaxies.

The lick AGN monitoring project: Reverberation mapping of optical hydrogen and helium recombination lines

Misty C. Bentz et al. — Tue, 30 Apr 2013 13:11:31 PDT

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10⁶-10⁷ M _☉ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission, which we have previously reported. We present here the light curves for the Hα, Hγ, He II λ4686, and He I λ5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux. Combining each emission-line time lag with the measured width of the line in the variable part of the spectrum, we determine a virial mass of the central supermassive black hole from several independent emission lines. We find that the masses are generally consistent within the uncertainties. The time-lag response as a function of velocity across the Balmer line profiles is examined for six of the AGNs. We find similar responses across all three Balmer lines for Arp 151, which shows a strongly asymmetric profile, and for SBS 1116+583A and NGC 6814, which show a symmetric response about zero velocity. For the other three AGNs, the data quality is somewhat lower and the velocity-resolved time-lag response is less clear. Finally, we compare several trends seen in the data set against the predictions from photoionization calculations as presented by Korista & Goad. We confirm several of their predictions, including an increase in responsivity and a decrease in the mean time lag as the excitation and ionization level for the species increases. Specifically, we find the time lags of the optical recombination lines to have weighted mean ratios of τ(Hα):τ(Hβ):τ(Hγ):τ(He I):τ(He II) = 1.54:1.00:0.61:0.36:0.25. Further confirmation of photoionization predictions for broad-line gas behavior will require additional monitoring programs for these AGNs while they are in different luminosity states.

The lick AGN monitoring project: Velocity-delay maps from the maximum-entropy method for Arp 151

Misty C. Bentz et al. — Tue, 30 Apr 2013 13:11:28 PDT

We present velocity-delay maps for optical H I, He I, and He II recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. H I response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similar morphologies but exhibit radial stratification, with progressively longer delays for Hγ to Hβ to Hα. The He I and He II response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: free-falling gas and a half-illuminated disk with a hot spot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial outflows are also largely ruled out by the observed asymmetry. A warped-disk geometry provides a physically plausible mechanism for the asymmetric illumination and hot spot features. Simple estimates show that a disk in the broad-line region of Arp 151 could be unstable to warping induced by radiation pressure. Our results demonstrate the potential power of detailed modeling combined with monitoring campaigns at higher cadence to characterize the gas kinematics and physical processes that give rise to the broad emission lines in active galactic nuclei.

The lick AGN monitoring project: alternate routes to a broad-line region radius

Jenny E. Greene et al. — Tue, 30 Apr 2013 13:11:25 PDT

It is now possible to estimate black hole (BH) masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central BHs coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region (BLR). Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the BLR scales as the square root of the X-ray and Hβ luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the BLR correlates most tightly with Hβ luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of 2. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua.

A local baseline of the black hole mass scaling relations for active galaxies. I. Methodology and results of pilot study

Vardha Nicola Bennert et al. — Tue, 30 Apr 2013 13:11:22 PDT

We present high-quality Keck/LRIS long-slit spectroscopy of a pilot sample of 25 local active galaxies selected from the SDSS (0.02 ≤z ≤ 0.1; M _BH>10⁷ M _☉) to study the relations between black hole mass (M _BH) and host-galaxy properties. We determine stellar kinematics of the host galaxy, deriving stellar-velocity dispersion profiles and rotation curves from three spectral regions (including CaH&K, MgIb triplet, and Ca II triplet). In addition, we perform surface photometry on SDSS images, using a newly developed code for joint multi-band analysis. BH masses are estimated from the width of the Hβ emission line and the host-galaxy free 5100 Å active galactic nucleus (AGN) luminosity. Combining results from spectroscopy and imaging allows us to study four M _BH scaling relations: M _BH-σ, M _BH-L _sph, M _BH-M _sph,, and M _BH-M _sph,dyn. We find the following results. First, stellar-velocity dispersions determined from aperture spectra (e.g., SDSS fiber spectra or unresolved data from distant galaxies) can be biased, depending on aperture size, AGN contamination, and host-galaxy morphology. However, such a bias cannot explain the offset seen in the M _BH-σ relation at higher redshifts. Second, while the CaT region is the cleanest to determine stellar-velocity dispersions, both the MgIb region, corrected for Fe II emission, and the CaHK region, although often swamped by the AGN power-law continuum and emission lines, can give results accurate to within a few percent. Third, the M _BH scaling relations of our pilot sample agree in slope and scatter with those of other local active and inactive galaxies. In the next papers of the series we will quantify the scaling relations, exploiting the full sample of ~100 objects.

The mass of the black hole in Arp 151 from bayesian modeling of reverberation mapping data

Brendon J. Brewer et al. — Tue, 30 Apr 2013 13:11:19 PDT

Supermassive black holes are believed to be ubiquitous at the centers of galaxies. Measuring their masses is extremely challenging yet essential for understanding their role in the formation and evolution of cosmic structure. We present a direct measurement of the mass of a black hole in an active galactic nucleus (Arp 151) based on the motion of the gas responsible for the broad emission lines. By analyzing and modeling spectroscopic and photometric time series, we find that the gas is well described by a disk or torus with an average radius of 3.99 ± 1.25 light days and an opening angle of 68.9^+21.4 _{– 17.2} deg, viewed at an inclination angle of 67.8 ± 7.8 deg (that is, closer to face-on than edge-on). The black hole mass is inferred to be 10^{6.51 ± 0.28} M _☉. The method is fully general and can be used to determine the masses of black holes at arbitrary distances, enabling studies of their evolution over cosmic time.

Hubble space telescope imaging of post-starburst quasars

S. L. Cales et al. — Tue, 30 Apr 2013 13:11:17 PDT

We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (M _burst ~ 10¹⁰ M _☉), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN-starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the remaining three hosts having indeterminate classifications. AGNs hosted by early-type galaxies have on average greater luminosity than those hosted by spiral galaxies. Disturbances such as tidal tails, shells, star-forming knots, and asymmetries are seen as signposts of interaction/merger activity. Disturbances like these were found in 17 of the 29 objects and are evenly distributed among early-type and spiral galaxies. Two of these systems are clearly merging with their companions. Compared to other AGNs of similar luminosity and redshift, these PSQs have a higher fraction of early-type hosts and disturbances. Our most luminous objects with disturbed early-type host galaxies appear to be consistent with merger products. Thus, these luminous galaxies may represent a phase in an evolutionary scenario for merger-driven activity. Our less luminous objects appear to be consistent with Seyfert galaxies not requiring triggering by major mergers. Many of these Seyferts are barred spiral galaxies.

The relation between black hole mass and host spheroid stellar mass out to z~2

Vardha N. Bennert et al. — Tue, 30 Apr 2013 13:11:12 PDT

We combine Hubble Space Telescope images from the Great Observatories Origins Deep Survey with archival Very Large Telescope and Keck spectra of a sample of 11 X-ray-selected broad-line active galactic nuclei in the redshift range 1 < z < 2 to study the black-hole-mass-stellar-mass relation out to a look-back time of 10 Gyr. Stellar masses of the spheroidal component (M _sph,) are derived from multi-filter surface photometry. Black hole masses (M _BH) are estimated from the width of the broad Mg II emission line and the 3000 Å nuclear luminosity. Comparing with a uniformly measured local sample and taking into account selection effects, we find evolution in the form M _BH/M _sph,(1 + z)^{1.96 ± 0.55}, in agreement with our earlier studies based on spheroid luminosity. However, this result is more accurate because it does not require a correction for luminosity evolution and therefore avoids the related and dominant systematic uncertainty. We also measure total stellar masses (M _host,). Combining our sample with data from the literature, we find M _BH/M _host,(1 + z)^{1.15 ± 0.15}, consistent with the hypothesis that black holes (in the range M _BH ~ 10^8-9 M _☉) pre-date the formation of their host galaxies. Roughly, one-third of our objects reside in spiral galaxies; none of the host galaxies reveal signs of interaction or major merger activity. Combined with the slower evolution in host stellar masses compared to spheroid stellar masses, our results indicate that secular evolution or minor mergers play a non-negligible role in growing both BHs and spheroids.

The lick AGN monitoring project 2011: recalibrating single-epoch virial black hole mass estimates

Daeseong Park et al. — Tue, 30 Apr 2013 13:11:10 PDT

We investigate the calibration and uncertainties of black hole (BH) mass estimates based on the single-epoch (SE) method, using homogeneous and high-quality multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN) Monitoring Project for nine local Seyfert 1 galaxies with BH masses <10⁸ M _☉. By decomposing the spectra into their AGNs and stellar components, we study the variability of the SE Hβ line width (full width at half-maximum intensity, FWHM_Hβ or dispersion, σ_Hβ) and of the AGN continuum luminosity at 5100 Å (L ₅₁₀₀). From the distribution of the "virial products" ( FWHM_Hβ ² L ^0.5 ₅₁₀₀ or σ_Hβ ² L ^0.5 ₅₁₀₀) measured from SE spectra, we estimate the uncertainty due to the combined variability as ~0.05 dex (12%). This is subdominant with respect to the total uncertainty in SE mass estimates, which is dominated by uncertainties in the size-luminosity relation and virial coefficient, and is estimated to be ~0.46 dex (factor of ~3). By comparing the Hβ line profile of the SE, mean, and root-mean-square (rms) spectra, we find that the Hβ line is broader in the mean (and SE) spectra than in the rms spectra by ~0.1 dex (25%) for our sample with FWHM_Hβ <3000 km s^-1. This result is at variance with larger mass BHs where the difference is typically found to be much less than 0.1 dex. To correct for this systematic difference of the Hβ line profile, we introduce a line-width dependent virial factor, resulting in a recalibration of SE BH mass estimators for low-mass AGNs.

The lick AGN monitoring project 2011: reverberation mapping of markarian 50

Aaron J. Barth et al. — Tue, 30 Apr 2013 13:11:07 PDT

The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our data set covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of ~4 in the U-band continuum and a factor of ~2 in the Hβ line. Using standard cross-correlation techniques, we find that Hβ and Hγ lag the V-band continuum by τ_cen = 10.64^+0.82 _{– 0.93} and 8.43^+1.30 _{– 1.28} days, respectively, while the lag of He II λ4686 is unresolved. The Hβ line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region (BLR) dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f = 5.25, the virial estimate of the black hole mass is (3.2 ± 0.5) × 10⁷ M _☉. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of BLR structure and dynamics.

Very early ultraviolet and optical observations of the type Ia supernova 2009ig

Ryan J. Foley et al. — Tue, 30 Apr 2013 13:11:03 PDT

Supernova (SN) 2009ig was discovered 17 hr after explosion by the Lick Observatory Supernova Search, promptly classified as a normal Type Ia SN (SN Ia), peaked at V = 13.5 mag, and was equatorial, making it one of the foremost SNe for intensive study in the last decade. Here, we present ultraviolet (UV) and optical observations of SN 2009ig, starting about 1 day after explosion until around maximum brightness. Our data include excellent UV and optical light curves, 25 premaximum optical spectra, and 8 UV spectra, including the earliest UV spectrum ever obtained of an SN Ia. SN 2009ig is a relatively normal SN Ia, but does display high-velocity ejecta—the ejecta velocity measured in our earliest spectra (v –23, 000 km s^–1 for Si II λ6355) is the highest yet measured in an SN Ia. The spectral evolution is very dramatic at times earlier than 12 days before maximum brightness, but slows after that time. The early-time data provide a precise measurement of 17.13 ± 0.07 days for the SN rise time. The optical color curves and early-time spectra are significantly different from template light curves and spectra used for light-curve fitting and K-corrections, indicating that the template light curves and spectra do not properly represent all SNe Ia at very early times. In the age of wide-angle sky surveys, SNe like SN 2009ig that are nearby, bright, well positioned, and promptly discovered will still be rare. As shown with SN 2009ig, detailed studies of single events can provide significantly more information for testing systematic uncertainties related to SN Ia distance estimates and constraining progenitor and explosion models than large samples of more distant SNe.

The lick AGN monitoring project 2011: Dynamical modeling of the broad-line region in Mrk 50

Anna Pancoast et al. — Tue, 30 Apr 2013 13:11:00 PDT

We present dynamical modeling of the broad-line region (BLR) in the Seyfert 1 galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN Monitoring Project (LAMP) 2011. We model the reverberation mapping data directly, constraining the geometry and kinematics of the BLR, as well as deriving a black hole mass estimate that does not depend on a normalizing factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is a nearly face-on thick disk, with a mean radius of 9.6^+1.2 _–0.9 light days, a width of the BLR of 6.9^+1.2 _–1.1 light days, and a disk opening angle of 25 ± 10 deg above the plane. We also constrain the inclination angle to be 9⁺⁷ _–5 deg, close to face-on. Finally, the black hole mass of Mrk 50 is inferred to be log₁₀(M _BH/M _☉) = 7.57^+0.44 _–0.27. By comparison to the virial black hole mass estimate from traditional reverberation mapping analysis, we find the normalizing constant (virial coefficient) to be log₁₀ f = 0.78^+0.44 _–0.27, consistent with the commonly adopted mean value of 0.74 based on aligning the M _BH-σ* relation for active galactic nuclei and quiescent galaxies. While our dynamical model includes the possibility of a net inflow or outflow in the BLR, we cannot distinguish between these two scenarios.

A local baseline of the black hole mass scaling relations for active galaxies. II. Measuring stellar velocity dispersion in active galaxies

Chelsea E. Harris et al. — Tue, 30 Apr 2013 13:10:55 PDT

We derive spatially resolved stellar kinematics for a sample of 84 out of 104 observed local (0.02 < z < 0.09) galaxies hosting type-1 active galactic nuclei (AGNs), based on long-slit spectra obtained at the 10 m W. M. Keck-1 Telescope. In addition to providing central stellar velocity dispersions, we measure major axis rotation curves and velocity dispersion profiles using three separate wavelength regions, including the prominent Ca H&K, Mg Ib, and Ca II NIR stellar features. In this paper, we compare kinematic measurements of stellar velocity dispersion obtained for different apertures, wavelength regions, and signal-to-noise ratios, and provide recipes to cross-calibrate the measurements reducing systematic effects to the level of a few percent. We also provide simple recipes based on readily observable quantities such as global colors and Ca H&K equivalent width that will allow observers of high-redshift AGN hosts to increase the probability of obtaining reliable stellar kinematic measurements from unresolved spectra in the region surrounding the Ca H&K lines. In subsequent papers in this series, we will combine this unprecedented spectroscopic data set with surface photometry and black hole mass measurements to study in detail the scaling relations between host galaxy properties and black hole mass.

Accretion properties of high- and low-excitation young radio galaxies

Donghoon Son et al. — Tue, 30 Apr 2013 13:10:52 PDT

Young radio galaxies (YRGs) provide an ideal laboratory to explore the connection between the accretion disk and radio jet thanks to their recent jet formation. We investigate the relationship between the emission-line properties, the black hole accretion rate, and the radio properties using a sample of 34 low-redshift (z < 0.4) YRGs. We classify YRGs as high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of high-ionization to low-ionization emission lines. Using the Hα luminosities as a proxy of accretion rate, we find that HEGs in YRGs have ~1 dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have a higher mass accretion rate or higher radiative efficiency than LEGs. In agreement with previous studies, we find that the luminosities of emission lines, in particular Hα, are correlated with radio core luminosity, suggesting that accretion and young radio activities are fundamentally connected.

The properties of post-starburst quasars based on optical spectroscopy

Sabrina L. Cales et al. — Tue, 30 Apr 2013 13:10:49 PDT

We present optical spectroscopy of a sample of 38 post-starburst quasars (PSQs) at z ~ 0.3, 29 of which have morphological classifications based on Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs) possess the spectral signatures of massive intermediate-aged stellar populations, making them potentially useful for studying connections between nuclear activity and host galaxy evolution. We model the spectra in order to determine the ages and masses of the host stellar populations, and the black hole masses and Eddington fractions of the AGNs. Our model components include an instantaneous starburst, a power law, and emission lines. We find that the PSQs have M _BH ~ 10⁸ M _☉ accreting at a few percent of Eddington luminosity and host ~10^10.5 M _☉ stellar populations which are several hundred Myr to a few Gyr old. We investigate relationships among these derived properties, spectral properties, and morphologies. We find that PSQs hosted in spiral galaxies have significantly weaker AGN luminosities, older starburst ages, and narrow emission-line ratios diagnostic of ongoing star formation when compared to their early-type counterparts. We conclude that the early-type PSQs are likely the result of major mergers and were likely luminous infrared galaxies in the past, while spiral PSQs with more complex star formation histories are triggered by less dramatic events (e.g., harassment, bars). We provide diagnostics to distinguish the early-type and spiral hosts when high spatial resolution imaging is not available.