Broad Hα Line Research Articles

Hitomi observation of radio galaxy NGC 1275: The first X-ray microcalorimeter spectroscopy of Fe-Kα line emission from an active galactic nucleus

Abstract The origin of the narrow Fe-Kα fluorescence line at 6.4 keV from active galactic nuclei has long been under debate; some of the possible sites are the outer accretion disk, the broad line region, a molecular torus, or interstellar/intracluster media. In 2016 February–March, we performed the first X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS) on board the Hitomi satellite of the Fanaroff–Riley type I radio galaxy NGC 1275 at the center of the Perseus cluster of galaxies. With the high-energy resolution of ∼5 eV at 6 keV achieved by Hitomi/SXS, we detected the Fe-Kα line with ∼5.4 σ significance. The velocity width is constrained to be 500–1600 km s−1 (FWHM for Gaussian models) at 90% confidence. The SXS also constrains the continuum level from the NGC 1275 nucleus up to ∼20 keV, giving an equivalent width of ∼20 eV for the 6.4 keV line. Because the velocity width is narrower than that of the broad Hα line of ∼2750 km s−1, we can exclude a large contribution to the line flux from the accretion disk and the broad line region. Furthermore, we performed pixel map analyses on the Hitomi/SXS data and image analyses on the Chandra archival data, and revealed that the Fe-Kα line comes from a region within ∼1.6 kpc of the NGC 1275 core, where an active galactic nucleus emission dominates, rather than that from intracluster media. Therefore, we suggest that the source of the Fe-Kα line from NGC 1275 is likely a low-covering-fraction molecular torus or a rotating molecular disk which probably extends from a parsec to hundreds of parsecs scale in the active galactic nucleus system.

Investigating the Evolution of the Dual AGN System ESO 509-IG066

Abstract We analyze the evolution of the dual active galactic nucleus (AGN) in ESO 509-IG066, a galaxy pair located at z = 0.034 whose nuclei are separated by 11 kpc. Previous observations with XMM-Newton on this dual AGN found evidence for two moderately obscured ( ∼ 1022 cm−2) X-ray luminous ( ∼ 1043 erg s−1) nuclear sources. We present an analysis of subsequent Chandra, NuSTAR, and Swift/XRT observations that show one source has dropped in flux by a factor of 10 between 2004 and 2011, which could be explained by either an increase in the absorbing column or an intrinsic fading of the central engine, possibly due to a decrease in mass accretion. Both of these scenarios are predicted by galaxy merger simulations. The source that has dropped in flux is not detected by NuSTAR, which argues against absorption, unless it is extreme. However, new Keck/LRIS optical spectroscopy reveals a previously unreported broad Hα line that is highly unlikely to be visible under the extreme absorption scenario. We therefore conclude that the black hole in this nucleus has undergone a dramatic drop in its accretion rate. From AO-assisted near-infrared integral-field spectroscopy of the other nucleus, we find evidence that the galaxy merger is having a direct effect on the kinematics of the gas close to the nucleus of the galaxy, providing a direct observational link between the galaxy merger and the mass accretion rate onto the black hole.

Near-IR Spectroscopy of Luminous LoBAL Quasars at 1 < z < 2.5

Abstract We present near-IR spectroscopy of 22 luminous low-ionization broad absorption line quasars (LoBAL QSOs) at redshift , with 12 objects at z ∼ 1.5 and 10 at z ∼ 2.3. The spectra cover the rest-frame Hα and Hβ line regions, allowing us to obtain robust black hole mass estimates based on the broad Hα line. We use these data, augmented by a lower-redshift sample from the Sloan Digital Sky Survey, to test the proposed youth scenario for LoBALs, which suggests that LoBALs constitute an early short-lived evolutionary stage of quasar activity, by probing for any difference in their masses, Eddington ratios, or rest-frame optical spectroscopic properties compared to normal quasars. In addition, we construct the UV to mid-IR spectral energy distributions (SEDs) for the LoBAL sample and a matched non-BAL quasar sample. We do not find any statistically significant difference between LoBAL QSOs and non-BAL QSOs in their black hole mass or Eddington ratio distributions. The mean UV to mid-IR SED of the LoBAL QSOs is consistent with non-BAL QSOs, apart from their stronger reddening. At there is no clear difference in their optical emission line properties. We do not see particularly weak [O iii] or strong Fe ii emission. The LoBAL QSOs do not show a stronger prevalence of ionized gas outflows as traced by the [O iii] line, compared to normal QSOs of similar luminosity. We conclude that the optical–MIR properties of LoBAL QSOs are consistent with the general quasar population and do not support them to constitute a special phase of active galactic nucleus evolution.

Balmer Filaments in Tycho’s Supernova Remnant: An Interplay between Cosmic-ray and Broad-neutral Precursors

Abstract We present Hα spectroscopic observations and detailed modeling of the Balmer filaments in the supernova remnant (SNR) Tycho (SN 1572). We used GH α FaS (Galaxy Hα Fabry–Pérot Spectrometer) on the William Herschel Telescope with a 3.′4 × 3.′4 field of view, 0.″2 pixel scale, and σ instr = 8.1 km s−1 resolution at 1″ seeing for ∼10 hr, resulting in 82 spatial−spectral bins that resolve the narrow Hα line in the entire SN 1572 northeastern rim. For the first time, we can therefore mitigate artificial line broadening from unresolved differential motion and probe Hα emission parameters in varying shock and ambient medium conditions. Broad Hα line remains unresolved within spectral coverage of 392 km s−1. We employed Bayesian inference to obtain reliable parameter confidence intervals and to quantify the evidence for models with multiple line components. The median Hα narrow-line (NL) FWHM of all bins and models is W NL = ( 54.8 ± 1.8 ) km s−1 at the 95% confidence level, varying within [35, 72] km s−1 between bins and clearly broadened compared to the intrinsic (thermal) ≈20 km s−1. Possible line splits are accounted for, significant in ≈ 18 % of the filament, and presumably due to remaining projection effects. We also find widespread evidence for intermediate-line emission of a broad-neutral precursor, with a median W IL = ( 180 ± 14 ) km s−1 (95% confidence). Finally, we present a measurement of the remnant’s systemic velocity, V LSR = − 34 km s−1, and map differential line-of-sight motions. Our results confirm the existence and interplay of shock precursors in Tycho’s remnant. In particular, we show that suprathermal NL emission is near-universal in SN 1572, and that, in the absence of an alternative explanation, collisionless SNR shocks constitute a viable acceleration source for Galactic TeV cosmic-ray protons.

Balmer-dominated shocks in Tycho’s SNR: omnipresence of CRs

AbstractWe present wide-field, spatially and highly resolved spectroscopic observations of Balmer filaments in the northeastern rim of Tycho’s supernova remnant in order to investigate the signal of cosmic-ray (CR) acceleration. The spectra of Balmer-dominated shocks (BDSs) have characteristic narrow (FWHM ~ 10 km s−1) and broad (FWHM ~ 1000 km s−1) Hα components. CRs affect the Hα-line parameters: heating the cold neutrals in the interstellar medium results in broadening of the narrow Hα-line width beyond 20 km s−1, but also in reduction of the broad Hα-line width due to energy being removed from the protons in the post-shock region. For the first time we show that the width of the narrow Hα line, much larger than 20 km s−1, is not a resolution or geometric effect nor a spurious result of a neglected intermediate (FWHM ~ 100 km s−1) component resulting from hydrogen atoms undergoing charge exchange with warm protons in the broad-neutral precursor. Moreover, we show that a narrow line width ≫ 20 km s−1extends across the entire NE rim, implying CR acceleration is ubiquitous, and making it possible to relate its strength to locally varying shock conditions. Finally, we find several locations along the rim, where spectra are significantly better explained (based on Bayesian evidence) by inclusion of the intermediate component, with a width of 180 km s−1on average.

Determination of magnetic fields in broad line region of active galactic nuclei from polarimetric observations

Magnetic fields play an important role in confining gas clouds in the broad line region (BLR) of active galactic nuclei (AGN) and in maintaining the stability of these clouds. Without magnetic fields the clouds would not be stable, and soon after their formation they would expand and disperse. We show that the strength of the magnetic field can be derived from the polarimetric observations. Estimates of magnetic fields for a number of AGNs are based on the observed polarization degrees of broad Hα lines and nearby continuum. The difference between their values allows us to estimate the magnetic field strength in the BLR using the method developed by Silant’ev et al. (2013). Values of magnetic fields in BLR for a number of AGNs have been derived.

An effective selection method for low-mass active black holes and first spectroscopic identification

Abstract We present a new method for effectively selecting objects which may be low-mass active black holes (BHs) at galaxy centers using high-cadence optical imaging data, and our first spectroscopic identification of an active 2.7 × 106 M⊙ BH at z = 0.164. This active BH was originally selected due to its rapid optical variability, from a few hours to a day, based on Subaru Hyper Suprime-Cam g-band imaging data taken with a 1 hr cadence. Broad and narrow Hα lines and many other emission ones are detected in our optical spectra taken with Subaru FOCAS, and the BH mass is measured via the broad Hα emission line width (1880 km s−1) and luminosity (4.2 × 1040 erg s−1) after careful correction to the atmospheric absorption around 7580–7720 Å. We measure the Eddington ratio and find it to be as low as 0.05, considerably smaller than those in a previous SDSS sample with similar BH mass and redshift, which indicates one of the special potentials of our Subaru survey. The g − r color and morphology of the extended component indicate that the host galaxy is a star-forming galaxy. We also show the effectiveness of our variability selection for low-mass active BHs.

Red QSOs in the MBH-M∗ plane

AbstractWe present new results on the the MBH-M∗ relation of X-ray obscured, red QSOs at high redshift (1.2<z<2.6). The sample is made of 21 red QSOs, nine of them are new sources for which near-infrared spectra have been obtained with SINFONI and XShooter observations at ESO VLT, and show a broad Hα component. The rest of the sample (12 sources) is made of sources taken from the literature with similar properties. From the broad Hα line we have computed the BH masses through the virial formula while stellar masses have been obtained through multi-component SED fitting.We find that red QSOs preferentially lie on the local relation up to z ~ 2.6 with the most massive objects mainly located above it. We also studied the evolution of these sources on the MBH-M∗ plane compared to a sample of optically blue type–1 QSOs and we find that obscured red QSOs show a constant MBH/M∗ ratio consistent/slightly higher than the local one but lower than what has been found for blue QSOs. These sources may represent the intermediate phase (blow-out phase) between the major-merger induced starbursts which appear as ULIRGs and SMGs and the optical type–1 blue QSOs which are revealed once the dust and nuclear gas is cleared up.

An Integral View of Balmer-dominated Shocks in Supernova Remnants

AbstractWe present integral-field spectroscopic observations with the VIMOS-IFU at the VLT of fast (2000-3000 kms−1) Balmer-dominated shocks surrounding the northwestern rim of the remnant of supernova 1006. The high spatial and spectral resolution of the instrument enable us to show that the physical characteristics of the shocks exhibit a strong spatial variation over few atomic scale lengths across 133 sky locations. Our results point to the presence of a population of non-thermal protons (10-100 keV) which might well be the seed particles for generating high-energy cosmic rays. We also present observations of Tycho's supernova remnant taken with the narrow-band tunable filter imager OSIRIS at the GTC and the Fabry-Perot interferometer GHaFaS at the WHT to resolve respectively the broad and narrow Hα lines across a large part of the remnant.

Magnetic fields of active galactic nuclei and quasars with regions of polarized broad Hα lines

We present estimates of magnetic field in a number of AGNs from the Spectropolarimetric atlas of Smith, Young & Robinson (2002) from the observed degrees of linear polarization and the positional angles of spectral lines (H-alpha) (broad line regions of AGNs) and nearby continuum. The observed polarization is lower than the Milne value in a non-magnetized atmosphere. We hypothesize that the polarized radiation escapes from optically thick magnetized accretion discs and is weakened by the Faraday rotation effect. This effect is able to explain both the value of the polarization and the position angle. We estimate the required magnetic field in the broad line region by using simple asymptotic analytical formulas for Milne's problem in magnetized atmosphere, which take into account the last scattering of radiation before escaping from the accretion disc. The polarization of a broad spectral line escaping from disc is described by the same mechanism. The characteristic features of polarization of a broad line is the minimum of the degree of polarization in the center of the line and continuous rotation of the position angle from one wing to another. These effects can be explained by existence of clouds in the left (velocity is directed to an observer) and the right (velocity is directed from an observer) parts of the orbit in a rotating keplerian magnetized accretion disc. The base of explanation is existence of azimuthal magnetic field in the orbit. The existence of normal component of magnetic field makes the picture of polarization asymmetric. The existence of clouds in left and right parts of the orbit with different emissions also give the contribution in asymmetry effect. Assuming a power-law dependence of the magnetic field inside the disc, we obtain the estimate of the magnetic field strength at first stable orbit near the central SMBH for a number of AGNs.

The Structure of the BLR in 3C 390.3

AbstractVelocity-dependent flux ratios of the broad Lyα, Civ, Hβ, and Hα lines are used to investigate conditions in the archetypical displaced BLR peak emitter 3C 390.3. Our results suggest that gas producing the the UV emission lines has a lower density than the higher-velocity gas producing broad disk-like profile and is less flattened.

The Transition Zone in Balmer‐dominated Shocks

We examine the structure of the postshock region in supernova remnants (SNRs). The transition zone is set up by charge transfer and ionization events between atoms and ions and has a width ~(1015 cm-2)n, where n0 is the total preshock density (including both atoms and ions). For Balmer-dominated SNRs with shock velocity vs 1000 km s-1, the Rankine-Hugoniot conditions for ion velocity and temperature are obeyed instantly, leaving the full width at half-maximum (FWHM) of the broad Hα line versus vs relation intact. However, the spatial variation in the postshock densities is relevant to the problem of Lyα resonant scattering in young, core-collapse SNRs. Both two- (preshock atoms and ions) and three-component (preshock atoms, broad neutrals, and ions) models are considered. We compute the spatial emissivities of the broad (ξb) and narrow (ξn) Hα lines; a calculation of these emissivities in SN 1006 is in general agreement with the computed ones of Raymond and coworkers. The (dimensionless) spatial shift, Θshift, between the centroids of ξb and ξn is unique for a given shock velocity and fion, the preshock ion fraction. Measurements of Θshift can be used to constrain n0.

Discovery of a very cool object with extraordinarily strong H$\mathsf{\alpha}$ emission

We report on the finding of the strongest Hα emission – pseudoequivalent width of 705 Å – known so far in a young, late type dwarf. This object, named as S Ori 71, is a substellar candidate member of the 1–8 Myr star cluster σ Orionis. Due to its overluminous location in color-magnitude diagrams, S Ori 71 might be younger than other cluster members, or a binary of similar components. Its mass is in the range 0.021–0.012 , depending on evolutionary models and possible binarity. The broad Hα line of S Ori 71 appears asymmetric, indicative of high velocity mass motions in the Hα forming region. The origin of this emission is unclear at the present time. We discuss three possible scenarios: accretion from a disk, mass exchange between the components of a binary system, and emission from a chromosphere.

Spectropolarimetry of broad Hα lines in radio galaxies: constraints on the geometry of the broad-line and scattering regions

We present optical spectropolarimetric observations of three radio-loud broad-line active galactic nuclei: 3C 332, 3C 351 and 4C 73.18, together with new observations of 3C 390.3, which we observed previously. Intrinsically polarized broad Hα emission was detected in 3C 332 and 3C 390.3 at levels of ∼3 per cent and ∼1 per cent, respectively. Significant polarization was not detected in 3C 351, while the polarization measured in 4C 73.18 (∼1 per cent) is consistent with foreground contamination by the galactic interstellar medium. Although 3C 332 and 3C 390.3 both exhibit ‘double-peaked’ broad Hα line profiles, their polarization properties differ significantly. The polarized Hα emission in 3C 332 has a similar profile to that seen in total flux and the continuum and line emission is polarized at 70° to the axis of the radio source. In 3C 390.3, however, the double peaks seen in total flux are suppressed in polarized flux and the Hα line and continuum are polarized at ∼5° to the axis of the radio emission. Comparison of these new observations of 3C 390.3 with data obtained 2 years previously reveals significant variations in both total and polarized flux. The implications of these observations for the relationship between the geometry of the broad-line region and that of the scattering medium are discussed. We argue that models in which the Hα emission arises in a relativistically rotating disc cannot easily explain the observed polarization properties of 3C 332 and, in particular, 3C 390.3. We consider instead a model in which the line emission originates in a bipolar outflow and present calculations showing that the observed polarization properties of 3C 390.3 can be broadly explained by scattering from the inner wall of an obscuring torus, while those of 3C 332 are consistent with scattering by particles situated above the poles of the torus. We outline a scheme in which either toroidal or polar scattering dominates in a given object, depending on the orientation of its radio jet axis to our line of sight.

The circumstellar material around SN IIn 1997eg: another detection of a very narrow P Cygni profile

We report the detection of a very narrow P Cygni profile on top of the broad emission Hα and Hβ lines of the Type IIn Supernova 1997eg. A similar feature has been detected in SN 1997ab, SN 1998S and SN 1995G. The detection of the narrow P Cygni profile indicates the existence of a dense circumstellar material (CSM), into which the ejecta of the supernova is expanding. From the analysis of the spectra of SN 1997eg we deduce (i) that such CSM is very dense (n ≳ 5 × 107 cm−3), (ii) that it has a low expanding velocity of about 160 km s−1. The origin of such dense CSM can be either a very dense progenitor wind (Ṁ ∼ 10−2 M⊙ yr−1) or a circumstellar shell product of the progenitor wind expanding into a highpressure environment.

A Candidate of a Type 2 Quasi‐stellar Object atz = 0.9: Large X‐Ray Absorption with a Strong Broad Hα Emission Line

Deep hard X-ray and near-infrared observations of a type 2 radio-quiet quasi-stellar object (QSO) candidate at z = 0.9, AX J08494+4454, are reported. The 0.5-10 keV Chandra X-Ray Observatory spectrum of AX J08494+4454 is hard and is explained well with a power-law continuum absorbed by a hydrogen column density of (2.3 ± 1.1) × 1023 cm-2. The 2-10 keV luminosity of the object is estimated to be 7.2 × 1044 ergs s-1, after correcting the absorption, and reaches hard X-ray luminosities of QSOs. The large X-ray absorption and the large intrinsic luminosity support the original identification of AX J08494+4454 as a type 2 radio-quiet QSO. Nevertheless, the deep Subaru/IRCS J-band spectroscopic observation suggests the presence of a strong broad Hα emission line from AX J08494+4454. If real, the broad Hα emission line has a velocity width of 9400 ± 1000 km s-1, which corresponds to a typical broad Balmer line velocity width of a luminous QSO. The existence of the strong broad Hα line means that the object is not a type 2 QSO but a luminous cousin of a Seyfert 1.9 galaxy in the source-frame optical spectrum. The Balmer decrement of broad lines and the broad Hα emission to the hard X-ray luminosity ratio suggest that the nucleus is affected by dust extinction with an AV of 1-3 mag in the optical wavelength. Optical colors and faint optical magnitudes of AX J08494+4454 are consistent with the model. The estimated amount of dust extinction is much smaller than that expected from the X-ray column density (AV = 130 ± 60 mag).

The 1 October 2001 Eruptive Prominence: Observed and Modeled Structures

Using TRACE 171 A image observations and Hα spectra and images observed at the Ondřejov Observatory, the October 1, 2001, eruptive prominence is studied. The evolution of this prominence is described and velocities of specific parts of the prominence are determined. It was found that, after the rising phase of the cold loop-like prominence, its upper part expanded and below this expanding part, around one of its legs a `ring' structure, visible in the TRACE images, was formed. Then, at the same place, a tearing of the prominence leg was recognized. Simultaneous spectral observations of this structure reveal a very broad Hα line, which indicates strong turbulent motion at these positions. These processes were accompanied by an expanding Hα envelope. Due to the similarity of the observed `ring' and tearing structures with those modeled by Lau and Finn (1996), the prominence leg tearing is interpreted as a reconnection process between two parallel magnetic ropes having parallel electric currents, but anti-parallel axial magnetic fields.

Rapid Profile Variations in the Broad Hα Line of the Seyfert Galaxy Markarian 6: Possible Evidence for Turbulence in the Accretion Disk

We report on implications for the geometrical and kinematic parameters of BLR gas on the basis of short timescale variability in the broad Hα profile shape. Data on rapid variations have been obtained at the 2.6−m telescope of the BAO (Asatrian, Khachikian & Notni, 1999). To search for variations in the profile, difference spectra (second minus first epoch) were examined. We believe that the structure of the underlying stellar continuum and the atmospheric features do not affect significantly the Hα difference profiles of Mark 6. Variations occurred simultaneously on the blue and red sides of Hα on a time scale of ≃ 50.7 minutes and take the form of three narrow, positive small bumps on each side in the difference spectrum. The positions of the bumps are −4400, −3100, −1700 and +1900, +4200 and +6600 kms−1. These changes may indicate the response of circularly rotating emitting gas at three orbits to a light pulse from a central source. In this case the pairs of blue and red bumps observed at −4400 and +6600, −3100 and +4200, and −1700 and 1900 km s−1 are formed in two opposite zones of gas close to the line of nodes. On the assumption that these orbits lie around a central massive object, orbital parameters (radii, velocities and inclination angles of orbital planes) of the clouds and the central mass can be found. The shift of each bump is defined by the combination of the relativistic Doppler effect due to the Keplerian orbital motion and the gravitational redshift. The six observed radial velocities are determined by six parameters: the orbital radii, R1, R2, R3 (or velocities, Vi, V2, V3) and the inclination angles i1, i2, i3 of the rotation planes. Thus, the expressions for the radial velocities form a system of six algebraic equations with six unknowns and can be solved. Using the difference of the orbital radii in absolute units (R3 − R1 = Δt C, where ΔtC, ≃ 50.7 minutes and C is the speed of light) we can derive the central mass M. Analytical solution gives: Error limits for the results are determined by the uncertainty of the input radial velocities, 300 km s−1. However, the value of the mass obtained is smaller by two orders of magnitude than the estimate for the dynamical mass of the nucleus of Mark 6 (M = 1 × 107M⊙ Dibai 1984). Such a low mass is excluded, therefore.

The Broad‐Line and Narrow‐Line Regions of the LINER NGC 4579

We report the discovery of an extremely broad Hα emission line in the LINER nucleus of NGC 4579. From ground-based observations, the galaxy was previously known to contain a type 1 nucleus with a broad Hα line of FWHM ≈ 2300 km s-1 and FWZI ≈ 5000 km s-1. New spectra obtained with the Hubble Space Telescope (HST) and a 02 wide slit reveal an Hα component with an FWZI of ~18,000 km s-1. The line is not obviously double peaked, but it does possess shoulders on the red and blue sides which resemble the profiles seen in double-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggests that the very broad Hα profile in NGC 4579 may represent emission from an accretion disk. Three such objects have been found recently in two HST programs which have targeted a total of 30 galaxies, demonstrating that double-peaked or extremely broad-line emission in LINERs must be much more common than would be inferred from ground-based surveys. The ratio of the narrow [S II] λλ6716, 6731 lines shows a pronounced gradient indicating a steep rise in density toward the nucleus. The direct detection of a density gradient within the inner arcsecond of the narrow-line region confirms expectations from previous observations of line width-critical density correlations in several LINERs.

A Seyfert-like nucleus concealed in BL Lacertae?

We present a series of new spectroscopic observations of BL Lacertae. The observations were obtained over a period of 30 months and sample the violent continuum flare of 1997 June–August. The equivalent width of the recently discovered broad Hα line varies approximately inversely with the optical continuum flux, implying that the broad-line-emitting gas does not respond significantly to large variations in the beamed synchrotron continuum which dominates the spectrum at optical wavelengths. The simplest and most plausible interpretation of this result is that the broad-line region in BL Lacertae is ‘unaware’ of the synchrotron beam and is photoionized by another source, a likely candidate being a hot accretion disc. Alternatively, similar behaviour would be observed if the broad-line region is indeed photoionized by the synchrotron beam but is predominantly matter-bounded so that it absorbs only a small fraction of the incident ionizing photon flux.