Emission Line Region Research Articles

Near-infrared Hydrogen and Helium QSO Emission Lines

Abstract We present 14 near-infrared (NIR) quasar spectra observed with the Flamingos-2 NIR spectrometer instrument at the Gemini South Observatory. The targets were selected with redshifts of (0.58 ≤ z ≤ 0.63) to ensure the spectral wavelength range included specifically identified hydrogen and helium broad emission lines. We present measurements of their FWHM, equivalent widths, and flux ratios relative to H α. The quasars are all within the Sloan Digital Sky Survey (SDSS) Stripe 82 region which, then also provides multi-epoch rest-frame UV and optical spectroscopic observations of our targets. In future work, these data and those from Galaxy Evolution Explorer and NUV spectra will be utilized to constrain photoionization models to determine physical conditions within the broad emission line regions, such as the incident ionizing photon flux and gas density.

Constraining the geometry and kinematics of the quasar broad emission line region using gravitational microlensing

The quadruply lensed quasar HE0435−1223 shows a clear microlensing effect that affects differently the blue and red wings of the Hα line profile in its image D. To interpret these observations, and constrain the broad emission line region (BLR) properties, the effect of gravitational microlensing on quasar broad emission line profiles and their underlying continuum has been simulated considering representative BLR models and microlensing magnification maps. The amplification and distortion of the Hα line profile, characterized by a set of four indices, can be reproduced by the simulations. Although the constraints on the BLR models set by the observed single-epoch microlensing signal are not very robust, we found that flattened geometries (Keplerian disk and equatorial wind) can more easily reproduce the observed line profile deformations than a biconical polar wind. With an additional independent constraint on the size of the continuum source, the Keplerian disk model of the Hα BLR is slightly favored.

A young and obscured AGN embedded in the giant radio galaxy Mrk 1498

Abstract Mrk 1498 is part of a sample of galaxies with extended emission line regions (extended outwards up to a distance of ∼7 kpc) suggested to be photo-ionized by an AGN that has faded away or that is still active but heavily absorbed. Interestingly, the nucleus of Mrk 1498 is at the center of two giant radio lobes with a projected linear size of 1.1 Mpc. Our multi-wavelength analysis reveals a complex nuclear structure, with a young radio source (Giga-hertz Peaked Spectrum) surrounded by a strong X-ray nuclear absorption, a mid-infrared spectrum that is dominated by the torus emission, plus a circum-nuclear extended emission in the [OIII] image (with radius of ∼ 1 kpc), most likely related to the ionization of the AGN, aligned with the small and large scale radio jet and extended also at X-rays. In addition a large-scale extended emission (up to ∼ 10 kpc) is only visible in [OIII]. These data show conclusive evidence of a heavily absorbed nucleus and has recently restarted its nuclear activity. To explain its complexity, we propose that Mrk 1498 is the result of a merging event or secular processes, such as a minor interaction, that has triggered the nuclear activity and produced tidal streams. The large-scale extended emission that gives place to the actual morphology could either be explained by star formation or outflowing material from the AGN.

X-Ray Reprocessing: Through the Eclipse Spectra of High-mass X-Ray Binaries with XMM-Newton

Abstract The study of X-ray reprocessing is one of the key diagnostic tools to probe the environment in X-ray binary systems. One difficult aspect of studying X-ray reprocessing is the presence of much brighter primary radiation from the compact star together with the reprocessed radiation. In contrast, for eclipsing systems, the X-rays we receive during eclipse are only those produced by the reprocessing of the emission from the compact star by the surrounding medium. We report results from a spectral study of the X-ray emission during eclipse and outside eclipse in nine high-mass X-ray binaries (HMXBs) with the XMM-Newton European Photon Imaging Camera (EPIC) pn to investigate different aspects of the stellar wind in these HMXBs. During eclipse the continuum component of the spectrum is reduced by a factor of ∼8–237, but the count rate for the 6.4 keV iron emission line or the complex of iron emission lines in HMXBs is reduced by a smaller factor, leading to large equivalent widths of the iron emission lines. This indicates a large size for the line emission region, comparable to or larger than the companion star in these HMXB systems. However, there are significant system to system differences. 4U 1538−522, despite having a large absorption column density, shows a soft emission component with comparable flux during the eclipse and out-of-eclipse phases. Emission from hydrogen-like iron has been observed in LMC X-4 for the first time, in the out-of-eclipse phase in one of the observations.. Overall, we find significant differences in the eclipse spectrum of different HMXBs and also in their eclipse spectra against out-of-eclipse spectra.

A Novel Approach to Study the Variability of NGC 5548

Abstract Understanding the properties of the continuum radiation and broad emission lines of active galactic nuclei provides significant information not only to model the radiation mechanism and constrain the geometry and kinematics of the broad-line region (BLR) but also to probe the central engine of the sources. Here we investigate the multifractal behavior of the Hβ emission line and the 5100 Å continuum flux light curves of NGC 5548. The aim is to search for multiscaling signatures in the light curves and check if there is a possible nonlinear relationship between them. To this end, we use a multifractality analysis technique called the Multifractal Detrended Moving Average analysis. We detect multifractal (nonlinear) signatures in the full monitoring and densely sampled period of the Hβ line and 5100 Å continuum light curves of NGC 5548, possibly indicating the presence of complex and nonlinear interaction in the 5100 Å continuum and Hβ emission line regions. Moreover, the degree of multifractality of the Hβ line is found to be about twice that of the 5100 Å continuum. The nonlinearity of both emissions could be generated when the BLR reprocesses the radiation from the central compact source. Finally, we found that antipersistent long-range temporal correlation is the main source of the multifractality detected in both light curves.

The Evolution of the Interstellar Medium in Post-starburst Galaxies

Abstract We derive dust masses (M dust) from the spectral energy distributions of 58 post-starburst galaxies (PSBs). There is an anticorrelation between specific dust mass (M dust/M ⋆) and the time elapsed since the starburst ended, indicating that dust was either destroyed, expelled, or rendered undetectable over the ∼1 Gyr after the burst. The M dust/M ⋆ depletion timescale, , is consistent with that of the CO-traced , suggesting that dust and gas are altered via the same process. Extrapolating these trends leads to the M dust/M ⋆ and values of early-type galaxies (ETGs) within 1–2 Gyr, a timescale consistent with the evolution of other PSB properties into ETGs. Comparing M dust and for PSBs yields a calibration, log , that allows us to place 33 PSBs on the Kennicutt–Schmidt (KS) plane, . Over the first ∼200–300 Myr, the PSBs evolve down and off of the KS relation, as their star formation rate (SFR) decreases more rapidly than . Afterwards, continues to decline whereas the SFR levels off. These trends suggest that the star formation efficiency bottoms out at 10−11 yr−1 and will rise to ETG levels within 0.5–1.1 Gyr afterwards. The SFR decline after the burst is likely due to the absence of gas denser than the CO-traced H2. The mechanism of the M dust/M ⋆ and decline, whose timescale suggests active galactic nucleus/low-ionization nuclear emission-line region feedback, may also be preventing the large CO-traced molecular gas reservoirs from collapsing and forming denser star-forming clouds.

Optical long-slit spectroscopy in the cluster Abell S0805

ABSTRACT This contribution aims to study the nature (kinematic, nuclear activity, and stellar population) of a sample of 10 galaxies in the poor cluster Abell S0805. As no detailed optical spectroscopy for some members has been published yet, the selected sample makes this study ideal for investigating the properties of the following objects: ESO 104- G(002, 006, 007, 008, 009, 010, 013), Fairall 0187, and PGC (062384, 062391). Our main results were obtained after subtraction of the underlying stellar population with the spectral synthesis code starlight. The residual spectra reveal seven galaxies with only absorption lines [ESO 104- G(002, 007, 008, 009), Fairall 0187 and PGC (062384, 062391)], and three galaxies with emission lines [ESO 104- G(006, 010, 013)]. According to the boundaries in the diagnostic diagrams, the intensities of H α and the low-ionization lines ([N ii] λ6584 Å and [S ii] λλ6716,6731 Å) suggest the following results: (i) the brightest cluster galaxy (ESO 104- G006, an elliptical cD galaxy) shows low-ionization nuclear emission-line region (LINER)-like excitation, quite common in ‘cool core clusters’; (ii) the ESO 104- G010 (‘X-Galaxy’ or ‘Crystal Frog’) shows an excess of the nitrogen emission-line [N ii] λ6584 Å not yet reported. We also suggest this object as a LINER; (iii) the spiral ESO 104- G013 is a star-forming galaxy with typical emission lines. No obvious signs of interaction were observed in this study. The heliocentric velocities agree within 1σ with the most recent values. The stellar population, rotation curves, and velocity dispersions are also discussed for the first time for some objects.

3D optical spectroscopic study of NGC 3344 with SITELLE: I. Identification and confirmation of supernova remnants

ABSTRACT We present the first optical identification and confirmation of a sample of supernova remnants (SNRs) in the nearby galaxy NGC 3344. Using high spectral and spatial resolution data, obtained with the CFHT imaging Fourier transform spectrograph SITELLE, we identified about 2200 emission line regions, many of which are H ii regions, diffuse ionized gas regions, and also SNRs. Considering the stellar population and diffuse ionized gas background, which are quite important in NGC 3344, we have selected 129 SNR candidates based on four criteria for regions where the emission lines flux ratio [S ii]/H α ≥ 0.4. Emission lines of [O ii] λ3727, H β, [O iii] λλ4959,5007, H α, [N ii] λλ6548,6583, and [S ii] λλ6716,6731 have been measured to study the ionized gas properties of the SNR candidates. We adopted a self-consistent spectroscopic analysis, based on Sabbadin plots and Baldwin, Phillips & Terlevich diagrams, to confirm the shock-heated nature of the ionization mechanism in the candidates sample. With this analysis, we end up with 42 Confirmed SNRs, 45 Probable SNRs, and 42 Less likely SNRs. Using shock models, the confirmed SNRs seem to have a metallicity ranging between Large Magellanic Cloud and 2×solar. We looked for correlations between the size of the confirmed SNRs and their emission lines ratios, their galaxy environment, and their galactocentric distance: We see a trend for a metallicity gradient among the SNR population, along with some evolutionary effects.

Inquiring into the nature of the Abell 2667 brightest cluster galaxy: physical properties from MUSE

ABSTRACT Based on HST and MUSE data, we probe the stellar and gas properties (i.e. kinematics, stellar mass, star formation rate) of the radio-loud brightest cluster galaxy (BCG) located at the centre of the X-ray-luminous cool-core cluster Abell 2667 (z = 0.2343). The bi-dimensional modelling of the BCG surface brightness profile reveals the presence of a complex system of substructures extending all around the galaxy. Clumps of different size and shape plunged into a more diffuse component constitute these substructures, whose intense ‘blue’ optical colour hints at the presence of a young stellar population. Our results depict the BCG as a massive (M⋆ ≃ 1.38 × 1011 M⊙) dispersion-supported spheroid (Δv⋆ ≤ 150 km s−1, σ0 ∼ 216 km s−1) hosting an active supermassive black hole (MSMBH ≃ 3.8 × 109 M⊙) whose optical features are typical of low-ionization nuclear emission line regions. Although the velocity pattern of the stars in the BCG is irregular, the stellar kinematics in the regions of the clumps show a positive velocity of ∼100 km s−1, similarly to the gas component. An analysis of the mechanism giving rise to the observed lines in the clumps through empirical diagnostic diagrams points out that the emission is composite, suggesting contribution from both star formation and an active galactic nucleus. We conclude our analysis describing how scenarios of both chaotic cold accretion and merging with a gas-rich disc galaxy can efficaciously explain the phenomena the BCG is undergoing.

On the emergence of thousands of absorption lines in the quasar PG 1411+442: a clumpy high-column density outflow from the broad emission-line region?

Abstract Quasar outflows are fundamental components of quasar environments that might play an important role in feedback to galaxy evolution. We report on the emergence of a remarkable new outflow absorption-line system in the quasar PG1411+442 (redshift ∼0.089) detected in the UV and visible with the Hubble Space Telescope Cosmic Origins Spectrograph and the Gemini Multi-Object Spectrograph, respectively. This new ‘transient’ system contains thousands of lines, including Fe ii and Fe ii∗ from excited states up to 3.89 eV, H i∗ Balmer lines, Na i D λλ5890, 5896, and the first detection of He i∗ λ5876 in a quasar. The transient absorber is spatially inhomogeneous and compact, with sizes ≲0.003 pc, based on covering fractions on the quasar continuum source ranging from ∼0.45 in strong UV lines to ∼0.04 in Na i D. cloudy photoionization simulations show that large total column densities log NH(cm−2) ≳ 23.4 and an intense radiation field ≲0.4 pc from the quasar are needed to produce the observed lines in thick zones of both fully ionized and partially ionized gas. The densities are conservatively log nH(cm−3) ≳ 7 based on Fe ii∗, H i∗, and He i∗ but they might reach log nH(cm−3) ≳ 10 based on Na i D. The transient lines appear at roughly the same velocity shift, v ∼ −1900 km s−1, as a ‘mini-BAL’ outflow detected previously, but with narrower Doppler widths, b ∼ 100 km s−1, and larger column densities in more compact outflow structures. We propose that the transient lines identify a clumpy outflow from the broad emission-line region that, at its current speed and location, is still gravitationally bound to the central black hole.

Effects of dust evolution on protoplanetary disks in the mid-infrared

In this paper, we couple the dust evolution code two-pop-py with the thermochemical disk modelling code ProDiMo. We create a series of thermochemical disk models that simulate the evolution of dust over time from 0.018 to 10 Myr, including the radial drift, growth, and settling of dust grains. We examine the effects of this dust evolution on mid-infrared gas emission, focusing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3, OH, and H2O, which are readily observable with Spitzer and the upcoming E-ELT and JWST. The addition of dust evolution acts to increase line fluxes by reducing the population of small dust grains. We find that the spectral lines of all species except C2H2 respond strongly to dust evolution; line fluxes increase by more than an order of magnitude across the model series as the density of small dust grains decreases over time. The C2H2 line fluxes are extremely low because of a low abundance in the infrared line-emitting regions, even though C2H2 is commonly detected with Spitzer, suggesting that warm chemistry in the inner disk may need further investigation. Finally, we find that the CO2 flux densities increase more rapidly than the other species as the dust disk evolves. This suggests that the flux ratios of CO2 to other species may be lower in disks with less-evolved dust populations.

SDSS J153636.22+044127.0 and Its Analogs: Shocked Outflows, Not Active Binary Black Holes

Abstract The binary emission-line system, particularly the binary broad-line emission system, is considered the most effective indicator of the black hole binary. A plausible example of such a system, SDSS J153636.22+044127.0, was reported as the first known object with two hydrogen Balmer broad-line systems, which are interpreted to be the result of broad-line regions around a pair of black holes. Here, we show the follow-up optical and near-infrared spectral observations of SDSS J153636.22+044127.0 and its analogs. In these objects, the broad hydrogen Balmer and Paschen, He i, and Mg ii lines share the same peculiar emission-line profile (including a blue system, a red system, and a double-peaked disk-line component); however, the invariance in the large time interval, the absence of the blue system in He i λ10830 profile, and the abnormally strong emission of the hydrogen Paβ blue system oppose the binary proposal. We suggest that these unique broad lines arise from the active galactic nucleus emission-line region and the shock-heated outflowing gases rather than a binary system of two active black holes.

Polarization of changing-look quasars

If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.

CLOUDY View of the Warm Corona

Abstract Bright active galaxies show a range of properties, but many of these properties are correlated, which has led to the concept of the quasar main sequence. We test whether our current understanding of the quasar structure allows the pattern observed in the optical plane formed by the kinematic line width of Hβ and the relative importance of the Fe ii optical emission to be reproduced. We performed simulations of the Hβ and Fe ii production using the code CLOUDY and well-justified assumptions about the broadband spectra, distance to the emission line region, and the cloud properties. We show that the presence of the warm corona is an important element of the broadband spectrum, which decreases the dependence of the relative Fe ii emissivity on the Eddington ratio and allows the rare cases of particularly strong Fe ii emitters to be reproduced. Results are sensitive to the adopted cloud distance, and strong Fe ii emission can be obtained either by adopting strongly supersolar metallicity or a much shorter distance than traditionally obtained from reverberation mapping. We modeled in a similar way the UV plane defined by the Mg ii line and Fe ii UV pseudo-continuum, but here our approach is less successful, in general overproducing the Fe ii strength. We found that the Fe ii optical and UV emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the broad-line region clouds.

Dust Continuum Emission and the Upper Limit Fluxes of Submillimeter Water Lines of the Protoplanetary Disk around HD 163296 Observed by ALMA

Abstract In this paper, we analyze the upper limit fluxes of submillimeter ortho-H2 16O 321 GHz, para-H2 18O 322 GHz, and HDO 335 GHz lines from the protoplanetary disk around the Herbig Ae star HD 163296, using the Atacama Large Millimeter/Submillimeter Array. These water lines are considered to be the best candidate submillimeter lines to locate the position of the H2O snowline, on the basis of our previous model calculations. We compare the upper limit fluxes with the values calculated by our models with dust emission included, and we constrain the line-emitting region and the dust opacity from the observations. We conclude that, if the outer edge of the region with a high water abundance and the position of the water snowline are both beyond 8 au, then themillimeter dust opacity κ mm will have a value larger than 2.0 cm2 g−1. In addition, the position of the water snowline must lie inside 20 au if the millimeter dust opacity κ mm is 2.0 cm2 g−1. Future observations of the dust continuum emission at higher angular resolution and submillimeter water lines with a longer observation time are required to clarify the detailed structures and the position of the H2O snowline in the disk midplane.

Detection of a double-peaked H α component from the accretion disc of NGC 4958

Abstract Active Galactic Nuclei are objects associated with the presence of an accretion disc around supermassive black holes found in the very central region of galaxies with a well-defined bulge. In the optical range of the spectrum, a possible signature of the accretion disc is the presence of a broad double-peaked component that is mostly seen in H α. In this paper, we report the detection of a double-peaked feature in the H α line in the nucleus of the galaxy NGC 4958. The narrow-line region of this object has an emission that is typical of a low-ionization nuclear emission-line region galaxy, which is the usual classification for double-peaked emitters. A central broad component, related to the broad-line region of this object, is seen in H α and also in H β. We concluded that the double-peaked emission is emitted by a circular relativistic Keplerian disc with an inner radius ξi = 570 ± 83, an outer radius ξo = 860 ± 170 (both in units of GMSMBH/c2), an inclination to the line of sight i = 27.2 ± 0.7° and a local broadening parameter σ = 1310 ± 70 km s−1.

GASP – XIX. AGN and their outflows at the centre of jellyfish galaxies

The GASP survey, based on MUSE data, is unveiling the properties of the gas in the so-called "jellyfish" galaxies: these are cluster galaxies with spectacular evidence of gas stripping by ram pressure. In a previous paper, we selected the seven GASP galaxies with the most extended tentacles of ionized gas, and based on individual diagnostic diagrams concluded that at least five of them present clear evidence for an Active Galactic Nucleus. Here we present a more detailed analysis of the emission lines properties in these galaxies. Our comparison of several emission line ratios with both AGN and shock models show that photoionization by the AGN is the dominant ionization mechanism. This conclusion is strengthened by the analysis of $\rm H\beta$ luminosities, the presence of nuclear iron coronal lines and extended ($>10$ kpc) emission line regions ionized by the AGN in some of these galaxies. From emission line profiles, we find the presence of outflows in four galaxies, and derive mass outflow rates, timescales and kinetic energy of the outflows.

Radio–infrared correlation for local dusty galaxies and dusty AGNs from the AKARI All-Sky Survey

Abstract We use the new release of the AKARI Far-Infrared All-Sky Survey (FIS) matched with the NVSS radio database to investigate the local ($z$ < 0.25) far-infrared–radio correlation (FIRC) of different types of extragalactic sources. To obtain the redshift information for the AKARI FIS sources we cross-match the catalogue with the SDSS DR8. This also allows us to use emission line properties to divide sources into four categories: (i) star-forming galaxies (SFGs), (ii) composite galaxies (displaying both star formation and active nucleus components), (iii) Seyfert galaxies, and (iv) low-ionization nuclear emission-line region (LINER) galaxies. We find that the Seyfert galaxies have the lowest far-infrared/radio flux ratios and display excess radio emission when compared to the SFGs. We conclude that the FIRC can be used to separate SFGs and AGNs only for the most radio-loud objects.

H i galaxies with little star formation: an abundance of LIERs

Abstract We present a sample of 91 H i galaxies with little or no star formation, and discuss the analysis of the integral field unit (IFU) spectra of 28 of these galaxies. We identified H i galaxies from the H i Parkes All-Sky Survey Catalog (HICAT) with Wide-field Infrared Survey Explorer (WISE) colours consistent with low specific star formation (<10−10.4 yr−1), and obtained optical IFU spectra with the Wide-Field Spectrograph (WiFeS). Visual inspection of the PanSTARRS, Dark Energy Survey, and Carnegie-Irvine imaging of 62 galaxies reveals that at least 32 galaxies in the sample have low levels of star formation, primarily in arms/rings. New IFU spectra of 28 of these galaxies reveals 3 galaxies with central star formation, 1 galaxy with low-ionization nuclear emission-line regions (LINERs), 20 with extended low-ionization emission-line regions (LIERs), and 4 with high excitation Seyfert (Sy) emission. From the spectroscopic analysis of H i selected galaxies with little star formation, we conclude that 75 per cent of this population are LINERs/LIERs.

An Extended Emission Line Region around Mrk 1172

AbstractWe serendipitously found an intriguing Extended Emission Line Region (EELR) near the quiescent and massive early-type Mrk 1172, with a projected extension of approximately 14 × 14 kpc. Its irregular shape, high gas content, strong emission lines and proximity to an isolated possible faded quasar raise questions about the ionization of this gas and the nature of this object. Analyzing the stellar population in both objects we observe that the EELR has a dominance of young-intermediate and intermediate stellar populations (200 Myr < t < 1 Gyr) with significant star formation activity, while Mrk 1172 is dominated by old stellar population (t > 5 Gyr). BPT diagnostic diagrams indicate that the gas in the EELR is photoionized by hot massive stars rather than by a hard radiation field or by shocks. Further analysis on abundances of the gas and its kinematics shall be performed to better comprehend the nature of this object and how it is interacting with Mrk 1172.