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Register a new userFar Ultraviolet Spectroscopic Explorer Spectroscopy of Absorption and Emission Lines from the Narrow-Line Seyfert 1 Galaxy NGC 4051
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We present three Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the Narrow-Line Seyfert 1 galaxy NGC4051. The most prominent features in the far-ultraviolet (FUV) spectrum are the OVI emission and absorption lines and the HI Lyman series absorption lines which are detected up to the Lyman edge. We also identify weak emission from NIII, CIII, and HeII. The CIII line shows absorption while none is detected in the NIII and HeII lines. In HI and CIII we detect two main absorption systems at outflow velocities of -50+/-30 and -240+/-40 km/s, as well as a possible third one at ~ -450 km/s. These systems are consistent in velocity with the 10 absorption systems found previously in CIV, NV, and SiIV, though the individual systems are blended together in the FUV spectrum. We estimate column densities of the two main absorption systems and find that the HI column density is lower for systems with larger outflow velocity. We detect no flux or spectral variations of NGC4051 at FUV wavelengths during three epochs spanning one year. This is consistent with the optical light curve which shows no variations between the three epochs. It is also consistent with the X-ray light curve which shows consistent flux levels at the three epochs of the FUSE observations, although the X-ray light curve shows strong variations on much shorter timescales.
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We derive a distance of $D = 16.6 pm 0.3$~Mpc ($mu=31.10pm0.04$~mag) to the archetypal narrow-line Seyfert 1 galaxy NGC 4051 based on Cepheid Period--Luminosity relations and new Hubble Space Telescope multiband imaging. We identify 419 Cepheid candidates and estimate the distance at both optical and near-infrared wavelengths using subsamples of precisely-photometered variables (123 and 47 in the optical and near-infrared subsamples, respectively). We compare our independent photometric procedures and distance-estimation methods to those used by the SH0ES team and find agreement to 0.01~mag. The distance we obtain suggests an Eddington ratio $dot{m} approx 0.2$ for NGC 4051, typical of narrow-line Seyfert 1 galaxies, unlike the seemingly-odd value implied by previous distance estimates. We derive a peculiar velocity of $-490pm34$~km~s$^{-1}$ for NGC 4051, consistent with the overall motion of the Ursa Major Cluster in which it resides. We also revisit the energetics of the NGC 4051 nucleus, including its outflow and mass accretion rates.
This paper presents the results of a dense and intensive X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051 carried out in 2000. Results of the optical analysis are consistent with previous measurements. The amplitude of optical emission line variability is a factor of two larger than that of the underlying optical continuum, but part or all of the difference can be due to host-galaxy starlight contamination or due to the lines being driven by the unseen UV continuum, which is more variable than the optical continuum. We measured the lag between optical lines and continuum and found a lower, more accurate broad line region size of 3.0+-1.5 light days in this object. The implied black hole mass is M_BH=5(+6,-3)x10^5 M_sun; this is the lowest mass found, so far, for an active nucleus. We find significant evidence for an X-ray-optical (XO) correlation with a peak lag of about <1 day, although the centroid of the asymmetric correlation function reveals that part of the optical flux varies in advance of the X-ray flux by 2.4+-1.0 days. This complex XO correlation is explained as a possible combination of X-ray reprocessing and perturbations propagating from the outer (optically emitting) parts of the accretion disc into its inner (X-ray emitting) region.
We explore the properties of ionized gas in the nuclear and circumnuclear environment of the narrow-line Seyfert 1 galaxy NGC 4051 using spectroscopic and imaging observations from the Hubble Space Telescope (HST) and Apache Point Observatory (APO)s ARC 3.5m Telescope. We identify an unresolved moderate-density intermediate width component and a high-density broad component in the optical emission lines from the active nucleus, as well as spatially-resolved emission extending up to $sim$1 kpc in the AGN ionized narrow-line region (NLR) and $sim$8 kpc in the stellar ionized host galaxy. The HST narrow-band image reveals a distinct conical structure in [O III] emission towards the NE, and the ionized gas kinematics shows up to two blueshifted velocity components, indicating outflows along the edges of a cone. We introduce an improved model of biconical outflow, with our line of sight passing through the wall of the cone, which suggests that the large number of outflowing UV absorbers seen in NGC 4051 are NLR clouds in absorption. Using the de-projection factors from the biconical geometry, we measure true outflow velocities up to 680 km s$^{-1}$ at a distance of $sim$350 pc, however, we do not find any rotational signature inside a projected distance $leq$ 10 ($sim$800 pc) from the nucleus. We compare the gas kinematics with analytical models based on a radiation-gravity formalism, which show that most of the observed NLR outflows are launched within $sim$0.5 pc of the nucleus and can travel up to $sim$1 kpc from this low-luminosity AGN.
Thanks to the execution of extensive spectroscopic surveys that have covered large fractions of the sky down to magnitudes as faint as $i approx 19$, it has been possible to identify several narrow-line Seyfert 1 galaxies (NLS1s) and to investigate their properties over a large range of the electro-magnetic spectrum. The interpretation of their nature, however, is still hampered by the statistical uncertainties related to the way in which NLS1 candidates are selected. In this contribution, we present a study to detect and to model emission lines in optical spectra extracted from the Sloan Digital Sky Survey (SDSS), adopting the most proper strategy to identify the source of line excitation and to produce a detailed model with measurements of several emission-line parameters. We demonstrate the application of this technique to explore fundamental questions, such as the presence of gas and dust around the core of AGNs and the spectral energy distribution of their ionizing radiation. We compare the spectral properties of NLS1s with those of other type 1 active galaxies and we summarize the potential of this approach to identify NLS1s in present day and future spectroscopic surveys. We finally consider the implications of multi-frequency data analysis in the debate concerning the intrinsic nature of NLS1s.
The narrow [O III] 4959, 5007 emission-line fluxes in the spectrum of the well-studied Seyfert 1 galaxy NGC 5548 are shown to vary with time. From this we show that the narrow line-emitting region has a radius of only 1-3 pc and is denser (n ~ 10^5 cm^{-3}) than previously supposed. The [O III] line width is consistent with virial motions at this radius given previous determinations of the black hole mass.Since the [O III] emission-line flux is usually assumed to be constant and is therefore used to calibrate spectroscopic monitoring data, the variability has ramifications for the long-term secular variations of continuum and emission-line fluxes, though it has no effect on shorter-term reverberation studies. We present corrected optical continuum and broad Hbeta emission-line light curves for the period 1988 to 2008.
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