Mass AGN Research Articles

First detection of the outer edge of an AGN accretion disc: very fast multiband optical variability of NGC 4395 with GTC/HiPERCAM and LT/IO:O

ABSTRACT We present fast (∼200 s sampling) $\it ugriz$ photometry of the low -mass AGN NGC 4395 with the Liverpool Telescope, followed by very fast (3 s sampling) us, gs, rs, is, and zs simultaneous monitoring with HiPERCAM on the 10.4m GTC. These observations provide the fastest ever AGN multiband photometry and very precise lag measurements. Unlike in all other AGN, gs lags us by a large amount, consistent with disc reprocessing but not with reprocessing in the broad-line region (BLR). There is very little increase in lag with wavelength at long wavelengths, indicating an outer edge (Rout) to the reprocessor. We have compared truncated disc reprocessing models to the combined HiPERCAM and previous X-ray/UV lags. For the normally accepted mass of 3.6 × 105M⊙, we obtain reasonable agreement with zero spin, Rout ∼ 1700Rg and the done physically motivated temperature-dependent disc colour-correction factor (f$\rm _{col}$). A smaller mass of 4 × 104M⊙ can only be accommodated if f$\rm _{col}=2.4$, which is probably unrealistically high. Disc self gravity is probably unimportant in this low-mass AGN but an obscuring wind may provide an edge. For the small mass, the dust sublimation radius is similar to Rout so the wind could be dusty. However, for the more likely large mass, the sublimation radius is further out so the optically thick base of a line-driven gaseous wind is more likely. The inner edge of the BLR is close to Rout in both cases. These observations provide the first good evidence for a truncated AGN disc and caution that truncation should be included in reverberation lag modelling.

The miniJPAS survey

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a photometric survey that is poised to scan several thousands of square degrees of the sky. It will use 54 narrow-band filters, combining the benefits of low-resolution spectra and photometry. Its offshoot, miniJPAS, is a 1 deg2 survey that uses J-PAS filter system with the Pathfinder camera. In this work, we study mJPC2470-1771, the most massive cluster detected in miniJPAS. We survey the stellar population properties of the members, their star formation rates (SFR), star formation histories (SFH), the emission line galaxy (ELG) population, spatial distribution of these properties, and the ensuing effects of the environment. This work shows the power of J-PAS to study the role of environment in galaxy evolution. We used a spectral energy distribution (SED) fitting code to derive the stellar population properties of the galaxy members: stellar mass, extinction, metallicity, (u − r)res and (u − r)int colours, mass-weighted age, the SFH that is parametrised by a delayed-τ model (τ, t0), and SFRs. We used artificial neural networks for the identification of the ELG population via the detection of the Hα, [NII], Hβ, and [OIII] nebular emission. We used the Ew(Hα)-[NII] (WHAN) and [OIII]/Hα-[NII]/Hα (BPT) diagrams to separate them into individual star-forming galaxies and AGNs. We find that the fraction of red galaxies increases with the cluster-centric radius; and at 0.5R200 the red and blue fractions are both equal. The redder, more metallic, and more massive galaxies tend to be inside the central part of the cluster, whereas blue, less metallic, and less massive galaxies are mainly located outside of the inner 0.5R200. We selected 49 ELG, with 65.3% of them likely to be star-forming galaxies, dominated by blue galaxies, and 24% likely to have an AGN (Seyfert or LINER galaxies). The rest are difficult to classify and are most likely composite galaxies. These latter galaxies are red, and their abundance decreases with the cluster-centric radius; in contrast, the fraction of star-forming galaxies increases outwards up to R200. Our results are compatible with an scenario in which galaxy members were formed roughly at the same epoch, but blue galaxies have had more recent star formation episodes, and they are quenching out from within the cluster centre. The spatial distribution of red galaxies and their properties suggest that they were quenched prior to the cluster accretion or an earlier cluster accretion epoch. AGN feedback or mass might also stand as an obstacle in the quenching of these galaxies.

A Comparison of Supermassive Black Hole Mass of NGC 4151 Using Different Methods

We found a new value of supermassive black hole (SMBH) mass in the middle of type 1 Seyfert, NGC 4151 galaxy. In this Study, the image of NGC 4151 galaxy was deprojected to face-on, using spiral galaxy of face-on, and applied IRAF to calculate the ellipticity and position angle of major-axis. A two-dimensional (2D) Fast Fourier Transform (FFT) applied to the deprojected image to calculate the spiral arm of NGC 4151 galaxy, and, in that way, find a central mass AGN 4151 galaxy. We compared our results of the mass of SMBH in in the center of NGC 4151 galaxy with the mass of SMBH calculated using different methods ((direct method: stellar dynamics, gas dynamics, reverberation mapping), and indirect method: MBH-σ*, MBH-Vrot, MBH-n, MBH-Lbulge, and MBH-P correlations). We concluded that the results of mass for these methods are in agreement with the estimated ones, i.e. using direct methods.

AGN mass estimates in large spectroscopic surveys: the effect of host galaxy light

Virial–based methods for estimating active supermassive black hole masses are now commonly used on extremely large spectroscopic quasar catalogs. Most spectral analyses, though, do not pay enough attention to the detailed continuum decomposition. To understand how this affects virial mass estimates, we test the influence of host galaxy light on them, along with a Balmer continuum component. A detailed fit with the new spectroscopic analysis software QSFIT demonstrates that the presence or absence of continuum components does not significantly affect the virial-based results for our sample. Taking a host galaxy component into consideration or not, instead, affects the emission line fitting in a more pronounced way at lower redshifts, where in fact we observe dimmer quasars and more visible host galaxies.

Doppler disc tomography applied to low-mass AGN spin

Doppler tomography can provide a powerful means of determining black hole spin when our view to the central regions are revealed and obscured by optically thick orbiting material, and can provide an independent estimate that does not suffer as many degeneracies as traditional methods. For low mass AGN, time-dependent obscuration is expected to leave a signature in the changing spectrum of the disc emission which extends into the soft X-ray bandpass. We create a spectral model incorporating Doppler tomography and apply it to the case of the low mass (8 $\times$ 10$^{5}$ M$_{\odot}$) AGN, RX J1301.9+2747 which shows unusual timing properties in the form of short-lived flares that we argue are best explained by the orbit of a window through an optically thick wind. Modelling the phase-resolved spectrum over the course of the highest data quality flare indicates a very low spin even when we relax our constraints. This is the lowest mass AGN for which a spin has been measured and the first via this technique. We note that, as the mass and spin are very low, this appears to favour supermassive black hole (SMBH) growth by chaotic rather than constant accretion.

DISCOVERY OF A ∼5 DAY CHARACTERISTIC TIMESCALE IN THEKEPLERPOWER SPECTRUM OF Zw 229–15

We present time series analyses of the full Kepler dataset of Zw 229-15. This Kepler light curve --- with a baseline greater than three years, composed of virtually continuous, evenly sampled 30-minute measurements --- is unprecedented in its quality and precision. We utilize two methods of power spectral analysis to investigate the optical variability and search for evidence of a bend frequency associated with a characteristic optical variability timescale. Each method yields similar results. The first interpolates across data gaps to use the standard Fourier periodogram. The second, using the CARMA-based time-domain modeling technique of Kelly et al. (2014), does not need evenly-sampled data. Both methods find excess power at high frequencies that may be due to Kepler instrumental effects. More importantly both also show strong bends ({\Delta}{\alpha} ~ 2) at timescales of ~5 days, a feature similar to those seen in the X-ray PSDs of AGN but never before in the optical. This observed ~5 day timescale may be associated with one of several physical processes potentially responsible for the variability. A plausible association could be made with light-crossing, dynamical or thermal timescales, depending on the assumed value of the accretion disk size and on unobserved disk parameters such as {\alpha} and H/R. This timescale is not consistent with the viscous timescale, which would be years in a ~10^7 Solar mass AGN such as Zw 229-15. However there must be a second bend on long (>~1 year) timescales, and that feature could be associated with the viscous timescale.

Reverberation time lags in the high luminosity quasar PG 1247+267

Virial estimates of the black hole mass in the center of AGNs, derived from single-epoch observations of luminosity and emission line widths, are now available for several thousands of objects at all redshifts and luminosities, so that studies of the cosmological evolution of the AGN mass function are becoming possible. These estimates are based on the empirical luminosity-size relation measured through reverberation mapping at low redshifts and luminosities. For this reason the spectrophotometric monitoring of 4 luminous quasars was started in 2003, with the 1.8m telescope of the Asiago Observatory. To measure the reverberation time lag we adopt a method, recently introduced by Zu et al. (2011), which takes advantage of the available statistical information on variability autocorrelation and makes simple assumptions on the continuum-emission line transfer function. We present the estimate of the broad line region size for the quasar PG 1247+267, which is the most luminous object with reverberation measures to date. Virial products computed for C iv and C iii] emission lines provide consistent results. A possible flattening of the size-luminosity relation for C iv at high luminosity is suggested.

A transition mass for black holes to show broad emission lines

Although the super-massive (AGN) and stellar mass (XRBs) black holes have many properties in common, the broad emission lines (BELs) are exclusively signatures of the AGN. Based on the detection of these lines from SDSS data bases, there seems to be no AGN with mass M_BH \lesssim 10^5 M_sun. In this paper we investigate if such low mass black holes are really non-existent or they are undetected because the BELs in them are not produced efficiently. Using the ionizing spectral energy distribution for a wide range of black hole mass, 10 - 10^9 M_sun, spanning XRBs to AGN, we calculate the equivalent widths (EWs) of ultraviolet and optical lines Ly\alpha 1216 \AA, H\beta 4861 \AA, CIV 1549 \AA and MgII 2798 \AA. The LOC (locally optimally emitting cloud) model has been used to describe the broad emission line region (BELR) for the calculations. We find that the hardening of the SED shape with decreasing mass do not decrease the BEL EWs. However, finite size of the BELR, as measured by the line widths, which is controlled by the mass of the black hole, regulates the production of these emission lines. There seems to be a peak in the EWs of the emission lines for typical AGN black holes of ~ 10^8 M_sun, below which the lines become intrinsically fainter with a sharp fall-off below ~ 10^6 M_sun. This may be the cause of the absence of low mass AGN in SDSS.

Feeding versus feedback in AGNs from near-infrared IFU observations: the case of Mrk 79

We have mapped the gaseous kinematics and the emission-line flux distributions and ratios from the inner ~680pc radius of the Seyfert 1 galaxy Mrk79, using two-dimensional (2D) near-IR J- and Kl-band spectra obtained with the Gemini instrument NIFS at a spatial resolution of ~100pc and velocity resolution of ~40km/s. The molecular hydrogen flux distribution presents two spiral arms extending by ~700pc, one to the north and another to the south of the nucleus, with an excitation indicating heating by X-rays from the central source. The low velocity dispersion (sigma~50km/s) and rotation pattern supports a location of the H2 gas in the disk of the galaxy. Blueshifts observed along the spiral arm in the far side of the galaxy and redshifts in the spiral arm in the near side, suggest that the spiral arms are feeding channels of H2 to the inner 200pc. From channel maps along the H2 l2.1218um emission-line profile we estimate a mass inflow rate of ~4E-3 M_Sun/year, which is one order of magnitude smaller than the mass accretion rate necessary to power the AGN of Mrk79. The emission from the ionized gas (traced by Pabeta and [FeII]l1.2570um emission lines) is correlated with the radio jet and with the narrow-band [OIII] flux distribution. Its kinematics shows both rotation and outflows to the north and south of the nucleus. The ionized gas mass outflow rate through a cross section with radius ~320pc located at a distance of ~455pc from the nucleus is 3.5 MSun/year, which is much larger than the AGN mass accretion rate, indicating that most of the outflowing gas originates in the interstellar medium surrounding the galaxy nucleus, which is pushed away by a nuclear jet.

Correlated X-ray/ultraviolet/optical variability in the very low mass AGN NGC 4395

We report the results of a one year Swift X-ray/UV/optical programme monitoring the dwarf Seyfert nucleus in NGC 4395 in 2008-2009. The UV/optical flux from the nucleus was found to vary dramatically over the monitoring period, with a similar pattern of variation in each of the observed UV/optical bands (spanning 1900 - 5500 {\AA}). In particular, the luminosity of NGC 4395 in the 1900 {\AA} band changed by more than a factor of eight over the monitoring period. The fractional variability was smaller in the UV/optical bands than that seen in the X-rays, with the X-ray/optical ratio increasing with increasing flux. Pseudo-instantaneous flux measurements in the X-ray and each UV/optical band were well correlated, with cross correlation coefficients of >0.7, significant at 99.9 per cent confidence. Archival Swift observations from 2006 sample the intra-day X-ray/optical variability on NGC 4395. These archival data show a very strong correlation between the X-ray and b bands, with a cross-correlation coefficient of 0.84 (significant at >99 per cent confidence). The peak in the cross correlation function is marginally resolved and asymmetric, suggesting that X-rays lead the b band, but by 1 hour. In response to recent (August 2011) very high X-ray flux levels from NGC4395 we triggered Swift ToO observations, which sample the intra-hour X-ray/UV variability. These observations indicate, albeit with large uncertainties, a lag of the 1900 {\AA} band behind the X-ray flux of ~400 s. The tight correlation between the X-ray and UV/optical lightcurves, together with the constraints we place on lag time-scale are consistent with the UV/optical variability of NGC 4395 being primarily due to reprocessing of X-ray photons by the accretion disc.

Determining the zero-point calibration for AGN black hole mass estimates

By fitting to the quiescent galaxy MBH-σ∗ relation, we calculate the average shift required to scale reverberation-mapped AGN masses to the same zero-point. We use reanalyzed virial products ( rV 2 /G ) and both new and published velocity dispersions to find the offset in the AGN calibration. This scaling factor, f, accounts for the detailed dynamics and geom- etry of the broad-line region (BLR). Finally, we confirm the rough correlation between σ∗ and FWHM((O III)) for these 16 AGNs.

Determination of NGC 4151 Nucleus Mass from Parameters of Narrow Satellites of Broad Lines

The paper considers the possibility of AGN mass estimation from observations of spectral lines emitted by jets. Jets are a typical for AGNs.Similar to SS433 the inner parts of AGN jets may emit spectral lines. 88433 spectra show that jet lines are week in comparison with those of slowly outflowing gas. Consequently the proper time for AGNs jet lines observations is the deep brightness minima (so-called transition from Sy1 type to Sy2 type of spectra). It is possibly the only chance for jet lines observations, because on the Sy1 stage gas surrounding the central object can. be optically thick in the broad lines wings or at least light up the week jet lines. The only well studied case of A(;N transition from Sy1 to Sy2 with evidence of jets is NGC 4151 when this galaxy was in a deep minimum of brightness during the 1984-1987.