Diagnostic Diagrams Research Articles

The host galaxy of the short GRB 050709

The host of the short gamma-ray burst (GRB) 050709 is a morphologically disturbed low-luminous galaxy. At a redshift of z = 0.16, it belongs to one of the cosmologically nearest short-GRB hosts identified to date. Consequently, it represents a promising target for sensitive, spatially resolved observational studies. We have used the Multi Unit Spectroscopic Explorer (MUSE) mounted at the Very Large Telescope to characterize the GRB host galaxy. In addition, we performed deep radio-continuum observations of the host with the Australia Telescope Compact Array (ATCA) and with ALMA at 1.3 mm. Moreover, we made use of archival Spitzer Space Telescope 24 μm and Hubble Space Telescope/F814W imaging data of this galaxy. The spatially resolved MUSE data reveal that the entire host is a source of strong line emission, in particular from Hα and [O III] λ 5007, superimposed on a rather weak stellar continuum. Using the Balmer decrement, we map the internal host-galaxy reddening and derive an extinction-corrected star formation rate based on the flux in the Hα line of 0.15 ± 0.02 M⊙ yr−1. The galaxy is detected neither by ALMA nor by Spitzer, excluding a substantial amount of optically obscured star formation activity. Using the O3N2 metallicity indicator, we measure an average 12 + log (O/H) = 8.40 ± 0.05 (corresponding to ∼0.5 solar). Diagnostic emission line diagrams show that a substantial fraction of all MUSE spaxels that cover the GRB 050709 host galaxy lie close to the star-formation demarcation line. Some spaxels even suggest line emission by shocked gas. The ATCA observations reveal faint diffuse radio emission at the eastern part of the host in excess to that expected from pure star formation, possibly further evidence for nonthermal processes. The kinematics of the Hα-emitting gas suggests a rotationally supported host-galaxy system, apparently in contrast to its irregular photometric morphology. A comparison with the field-galaxy population reveals, however, that the kinematics of the gas in the 050709 host fits into the ensemble of merging galaxies well. Finally, we use the ATCA radio data to set deep constraints on any late-time flux from the GRB afterglow or a potentially associated kilonova radio flare ∼10 years after the burst.

Optical emission lines in the most massive galaxies: Morphology, kinematics, and ionisation properties

In order to better characterise the upper end of the galaxy stellar mass range, the MUSE Most Massive Galaxies (M3G) Survey targeted the most massive galaxies (M > 1012 M⊙) found in the densest known clusters of galaxies at z ∼ 0.046. The sample is composed of 25 early-type galaxies: 14 brightest cluster galaxies (BCGs), of which 3 are in the densest region of the Shapley super cluster (SSC), and 11 massive satellites in the SSC. In the present work we use MUSE data to derive the spatial distribution and kinematics of the gas and discuss its ionisation mechanism and origin in the optical wavelength range. We fit the continuum of the spectra using an extensive library of single stellar population models and model the emission lines employing up to three Gaussian functions. In the M3G sample, ionised gas was detected in five BCGs, of which one is in the densest region of the SSC, and six massive satellites in the SSC. Among these objects, [O I] and [N I] were detected in three BCGs and one satellite. The gas is centrally concentrated in almost all objects, except for two BCGs that show filaments and two massive satellites with extended emission. Moreover, the emission line profiles of three BCGs present redshifted and/or blueshifted components. The presence of dust was revealed by analysing Balmer line ratios, obtaining a mean E(B − V) of 0.2–0.3. The emission-line diagnostic diagrams show predominately low-ionisation nuclear emission-line regions line ratios with little contamination from star formation. In the M3G sample, the gas was detected in 80% of fast rotators and 35% of slow rotators. The orientations of stellar and gaseous rotations are aligned with respect to each other for 60% of satellites and 25% of BCGs. The presence of misalignments points to an external origin of the gas for three BCGs and two satellites. On the other hand, some of these systems are characterised by triaxial and prolate-like stellar rotation, which could support an internal origin of the gas even in the case of misalignments.

AGNs in small galaxy systems: comparing the main properties of active objects in pairs, triplets, and groups

ABSTRACT We perform a comparative study of active galactic nuclei (AGNs) in pairs, triplets, and groups. To this end, we use the Duplancic et al. catalogue of small galaxy systems and consider BPT and WHAN diagnostic diagrams to select optical AGNs. Also, we identify mid-IR AGNs by using WISE data. We performed a comparison between the different AGN classification methodologies and study the AGN fraction in pairs, triplets, and groups with four to six members. We also analyse the main properties of Optical and mid-IR AGN hosts and the influence of environment on the active nuclei phenomena in these small galaxy systems. Our results show that, regardless the specifically adopted classification scheme, the fraction of AGN in pairs and triplets is always higher than the corresponding fraction in groups. Moreover, the fraction of powerful AGNs in pair and triplets is about twice the fraction of regular AGNs. We also find a remarkable difference between Optical and mid-IR AGNs in groups, where host galaxies of WISE AGNs are less massive and concentrated, with young stellar populations and blue colours. Also, all WISE AGNs in groups have a very close companions and reside in an intermediate global density environment. Galaxy triplets show a larger AGN fraction for galaxies with a close nearest neighbours, while pairs present a nearly constant AGN fraction regardless the distance to the nearest companion. Our studies highlight the important role of interactions, besides the global environment dependence, in the activation of the AGN phenomenon in small galaxy systems.

Star formation quenching stages of active and non-active galaxies

The mechanisms that bring galaxies to strongly reduce their star formation activity (star-formation quenching) remain poorly understood. To better study galaxy evolution, we propose a classification based on maps of ionised hydrogen distribution traced by the kiloparsec-resolved, equivalent width of Hα maps, and the nuclear activity of the galaxies using information from the Baldwin-Philips-Terlevich diagnostic diagrams. Using these tools, we group a sample of 238 galaxies from the Calar Alto Legacy Integral Field spectroscopy Area survey in six quenching stages (QSs): (i) objects dominated by recent star formation; (ii) systems that present a quiescent-nuclear-ring structure in their centre; (iii) galaxies that are centrally quiescent; (iv) galaxies with no clear pattern in their ionisation gas distribution (mixed); (v) systems that posses only a few star-forming regions (nearly retired), or (vi) galaxies that are completely quiescent (fully retired). Regarding their nuclear activity, we further divide the galaxies into two groups: active systems that host a weak or strong active galactic nucleus (AGN) at their centre, and non-active objects. Galaxies grouped into quenching-stage classes occupy specific locations on the star-formation-rate versus stellar mass diagram. The ‘blue cloud’ is populated by the star-forming and the quiescent-nuclear-ring galaxies, the ‘green valley’ is populated by centrally quiescent and mixed systems, and the ‘red sequence’ by the nearly- and fully retired objects. Generally, galaxies that host a weak or strong AGN show properties comparable to those of their non-active counterparts at the same QSs, except for the AGN-hosting star-forming systems. The degree of star-formation quenching increases along the present emission-line pattern sequence from star-forming to fully retired. The proposed emission-line classes reinforce the ‘inside-out’ quenching scenario, which foresees that the suppression of star formation begins from the central regions of the galaxies.

Gemini NIFS survey of feeding and feedback in nearby active galaxies – IV. Excitation

ABSTRACT The near-infrared spectra of active galactic nuclei (AGN) present emission lines of different atomic and molecular species. The mechanisms involved in the origin of these emission lines in AGN are still not fully understood. We use J- and K-band integral field spectra of six luminous ($43.1\lt \log L_{\rm bol}/({\rm erg\, s^{-1}})\lt 44.4$) Seyfert galaxies (NGC 788, Mrk 607, NGC 3227, NGC 3516, NGC 5506, and NGC 5899) in the local Universe (0.0039 < z < 0.0136) to investigate the gas excitation within the inner 100–300 pc radius of the galaxies at spatial resolutions of a few tens of parsecs. In all galaxies, the H2 emission originates from thermal processes with excitation temperatures in the range 2400–5200 K. In the high-line ratio (HLR) region of the H2/Brγ versus [Fe ii]/Paβ diagnostic diagram, which includes 29 per cent of the spaxels, shocks are the main excitation mechanism, as indicated by the correlation between the line widths and line ratios. In the AGN region of the diagram (64 per cent of the spaxels) the H2 emission is due to the AGN radiation. The [Fe ii] emission is produced by a combination of photoionization by the AGN radiation and shocks in five galaxies and is dominated by photoionization in NGC 788. The [S ix]1.2523 μm coronal emission line is present in all galaxies, and its flux distributions are extended from 80 to 185 pc from the galaxy nuclei, except for NGC 5899, in which this line is detected only in the integrated spectrum.

Feedback from Ionized Outflows Traced Across the Nearly Edge-on Disk of the Nearby Seyfert 2 Galaxy NGC 4945*

The aim of this work is to understand the impact of ionized outflows from H II regions in the nearby Seyfert 2 galaxy NGC4945. The study is based on long-slit optical spectra obtained at the Southern African large Telescope (SALT). The analysis focussed on recombination lines (Hα and Hβ) and forbidden lines ([N II]λλ6549,6583, [S II]λλ 6717,6731 and [O III] λλ4959,5007). The physical properties of 26 emission-line objects were determined from a diagnostic diagram. They are found to represent different physical environments normally encountered in supernova remnants, planetary nebulae (PNe) and classical HII regions, with electron densities varying between 16–3000 cm-3. Apart from tracing the galactic rotation, in some cases the line profiles show broadening or even line splitting – we take this as evidence that these regions will have an impact (feedback) onto the surrounding interstellar medium. The presentday chemical abundances were determined using the strong lines method (O3N2 and N2 indices). The oxygen abundances are constant between galactocentric distances of ~ 1–5 kpc, while the nitrogen abundance increases outwards. Taken together with a tentative positive correlation between oxygen and nitrogen abundance, a generally high metallicity but lower in the nucleus than expected from a comparison with the Milky Way, we explain this in terms of the inside–out build-up of the disk and present-day nuclear activity triggered by the accretion of relatively metal-poor gas.

On the influence of magnetic topology on the propagation of internal gravity waves in the solar atmosphere.

The solar surface is a continuous source of internal gravity waves (IGWs). IGWs are believed to supply the bulk of the wave energy for the lower solar atmosphere, but their existence and role for the energy balance of the upper layers is still unclear, largely due to the lack of knowledge about the influence of the Sun's magnetic fields on their propagation. In this work, we look at naturally excited IGWs in realistic models of the solar atmosphere and study the effect of different magnetic field topographies on their propagation. We carry out radiation-magnetohydrodynamic simulations of a magnetic field free and two magnetic models-one with an initial, homogeneous, vertical field of 100 G magnetic flux density and one with an initial horizontal field of 100 G flux density. The propagation properties of IGWs are studied by examining the phase-difference and coherence spectra in the kh - ω diagnostic diagram. We find that IGWs in the upper solar atmosphere show upward propagation in the model with predominantly horizontal field similar to the model without magnetic field. In contrast to that the model with predominantly vertical fields show downward propagation. This crucial difference in the propagation direction is also revealed in the difference in energy transported by waves for heights below 0.8 Mm. Higher up, the propagation properties show a peculiar behaviour, which require further study. Our analysis suggests that IGWs may play a significant role in the heating of the chromospheric layers of the internetwork region where horizontal fields are thought to be prevalent. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

Determining star formation rates in active galactic nuclei hosts via stellar population synthesis

ABSTRACT The effect of active galactic nuclei (AGNs) feedback on the host galaxy, and its role in quenching or enhancing star formation, is still uncertain due to the fact that usual star formation rate (SFR) indicators – emission-line luminosities based on the assumption of photoionization by young stars – cannot be used for active galaxies as the ionizing source is the AGN. We thus investigate the use of SFR derived from the stellar population and its relation with that derived from the gas for a sample of 170 AGN hosts and a matched control sample of 291 galaxies. We compare the values of SFR densities obtained via the H α emission line ($\rm \Sigma SFR_{Gas}$) for regions ionized by hot stars according to diagnostic diagrams with those obtained from stellar population synthesis ($\rm \Sigma SFR_\star$) over the last 1 to 100 Myr. We find that the $\rm \Sigma SFR_\star$ over the last 20 Myr closely reproduces the $\rm \Sigma SFR_{Gas}$, although a better match is obtained via the transformation: $\mbox{log($ \rm \Sigma SFR_\star $)} = (0.872\pm 0.004)\mbox{log($\rm \Sigma SFR_{Gas}$)} -(0.075\pm 0.006)$ (or $\mbox{log($\rm \Sigma SFR_{Gas}$)} = (1.147\pm 0.005)\mbox{log($ \rm \Sigma SFR_\star $)} +(0.086\pm 0.080)$), which is valid for both AGN hosts and non-active galaxies. We also compare the reddening obtained via the gas H α/H β ratio with that derived via the full spectral fitting in the stellar population synthesis. We find that the ratio between the gas and stellar extinction is in the range 2.64 ≤AVg/AV⋆ ≤ 2.85, in approximate agreement with previous results from the literature, obtained for smaller samples. We interpret the difference as being due to the fact that the reddening of the stars is dominated by that affecting the less obscured underlying older population, while the reddening of the gas is larger as it is associated with a younger stellar population buried deeper in the dust.

GLACE survey: Galaxy activity in ZwCl0024+1652 cluster from strong optical emission lines

ABSTRACT Although ZwCl0024+1652 galaxy cluster at z ∼ 0.4 has been thoroughly analysed, it lacks a comprehensive study of star formation and nuclear activity of its members. With GaLAxy Cluster Evolution (GLACE) survey, a total of 174 H α emission-line galaxies (ELGs) were detected, most of them having [N ii]. We reduced and analysed a set of [O iii] and H β tunable filter (TF) observations within GLACE survey. Using H α priors, we identified [O iii] and H β in 35 (∼20 per cent) and 59 (∼34 per cent) sources, respectively, with 21 of them having both emission lines, and 20 having in addition [N ii]. Applying BPT-NII diagnostic diagram, we classified these ELGs into 40 per cent star-forming (SF), 55 per cent composites, and 5 per cent LINERs. Star formation rate (SFR) measured through extinction corrected H α fluxes increases with stellar mass (M*), attaining its peak at $\mathrm{\mathit{ M}}_{*}\sim 10^{9.8}\, \mathrm{M}_\odot$. We observed that the cluster centre to ∼ 1.3 Mpc is devoid of SF galaxies and AGN. Our results suggest that the star formation efficiency declines as the local density increases in the cluster medium. Moreover, the SF and AGN fractions drop sharply towards high-density environments. We observed a strong decline in SF fraction in high M*, confirming that star formation is highly suppressed in high-mass cluster galaxies. Finally, we determined that SFR correlates with M* while specific SFR (sSFR) anticorrelates with M*, both for cluster and field. This work shows the importance and strength of TF observations when studying ELGs in clusters at higher redshifts. We provide with this paper a catalogue of ELGs with H β and/or [O iii] lines in ZwCl0024+1652 cluster.

Dual AGN Candidates with Double-peaked [O iii] Lines Matching that of Confirmed Dual AGNs

Abstract We have performed a spectral decomposition to search for dual active galactic nuclei (DAGNs) in the Sloan Digital Sky Survey (SDSS) quasars with z < 0.25. Potential DAGN candidates are searched by referencing velocity offsets and spectral shapes of double-peaked [O iii] lines of known DAGNs. Out of 1271 SDSS quasars, we have identified 77 DAGN candidates. Optical and mid-infrared (MIR) diagnostic diagrams are used to investigate the ionizing source in the DAGN candidates. The optical diagnostic analysis suggests 93% of them are powered by AGNs, and MIR diagnostic analysis suggests 97% are powered by AGNs. About one-third of the SDSS images of the DAGN candidates show signs of tidal interaction, but we are unable to identify double nuclei in most of them due to the low spatial resolution of the archival imaging data available for most of the sample. The radio-loud fraction of the DAGN candidates (∼10%) is similar to that of typical AGNs.

Constraining photoionization models with a reprojected optical diagnostic diagram

ABSTRACT Optical diagnostic diagrams are powerful tools to separate different ionizing sources in galaxies. However, the model-constraining power of the most widely used diagrams is very limited and challenging to visualize. In addition, there have always been classification inconsistencies between diagrams based on different line ratios, and ambiguities between regions purely ionized by active galactic nuclei (AGNs) and composite regions. We present a simple reprojection of the 3D line ratio space composed of [N ii]λ6583/H α, [S ii]λλ6716, 6731/H α, and [O iii]λ5007/H β, which reveals its model-constraining power and removes the ambiguity for the true composite objects. It highlights the discrepancy between many theoretical models and the data loci. With this reprojection, we can put strong constraints on the photoionization models and the secondary nitrogen abundance prescription. We find that a single nitrogen prescription cannot fit both the star-forming locus and AGN locus simultaneously, with the latter requiring higher N/O ratios. The true composite regions stand separately from both models. We can compute the fractional AGN contributions for the composite regions, and define demarcations with specific upper limits on contamination from AGN or star formation. When the discrepancy about nitrogen prescriptions gets resolved in the future, it would also be possible to make robust metallicity measurements for composite regions and AGNs.

Ionized Gas in the NGC 3077 Galaxy

The nearby dwarf galaxy NGC 3077 is known for its peculiar morphology, which includes numerous dust lanes and emission-line regions. The interstellar medium in this galaxy is subject to several perturbing factors. These are primarily the central starburst and tidal structures in the M 81 group. We present a comprehensive study of the state of ionization, kinematics, and chemical composition of ionized gas in NGC 3077, including both star-forming regions and diffuse ionized gas (DIG) at the periphery. We study gas motions in the H$\alpha$ line via high-resolution ($R\approx15\,000$) 3D spectroscopy with the scanning Fabry-Perot interferometer installed into SCORPIO-2 instrument attached to the 6-m telescope of the SAO RAS. Images in the main optical emission lines were acquired with MaNGaL photometer with a tunable filter at the 2.5-m telescope of the Caucasian Mountain Observatory of SAI MSU. We also used SCORPIO-2 to perform long-slit spectroscopy of the galaxy with a resolution of $R\approx1\,000$. Our estimate of the gas metallicity, $Z=0.6Z_\odot$, is significantly lower than the earlier determination, but agrees with the "luminosity--metallicity" dependence. Spatially resolved diagnostic diagrams of the emission-line ratios do not show correlations between the gas ionization state and its velocity dispersion, and this is most likely due to strong ionization by young stars, whereas the contribution of shocks to the excitation of emission lines is less important. We also studied the locations of multicomponent H$\alpha$ profiles and provide arguments suggesting that they are mostly associated with individual kinematic components along the line of sight and not with expanding shells as it was believed earlier. We also observe there a combination of wind outflow from star-forming regions and accretion from interstellar gas clouds in the M 81 group.

Classification by Activity Type of a Sample of Active Galaxies with Radio Emission

This is a detailed spectral classification of 96 active galaxies from the Veron-Cetty and Veron catalog (2010, Version 13, VCV-13) of active galaxies and quasars. These objects were identified as radio sources using standard radio catalogs. Those galaxies which had radio sources in at least 6 different radio bands and had been identified spectrally in the SDSS catalog were selected. The types of activity of these were determined using their SDSS spectra. Three diagnostic diagrams and a direct study of the spectra were used for more certain classification. As a result, the classifications of 85% of the objects were changed. The radio sources in different radio bands make it possible to construct the spectral distribution of the energy in the radio range and to compare it with the optical activity types.

Hidden AGNs in Dwarf Galaxies Revealed by MaNGA: Light Echoes, Off-nuclear Wanderers, and a New Broad-line AGN

Abstract Active galactic nuclei (AGNs) in dwarf galaxies could host the relics of those early universe seed black holes that did not grow into supermassive black holes. Using MaNGA integral field unit (IFU) spectroscopy we have found a sample of 37 dwarf galaxies that show AGN ionization signatures in spatially resolved emission line diagnostic diagrams. The AGN signatures are largely missed by integrated emission line diagnostics for 23 of them. The bolometric luminosity of these 23 new AGN candidates is ≲1040 erg s−1, fainter than that of single-fiber SDSS AGNs, X-ray AGNs, and radio AGNs in dwarf galaxies, which supports IFU spectroscopy as a powerful tool for identifying hidden and faint AGNs in dwarf galaxies. The AGN emission is in most cases offset from the optical center of the dwarf galaxy and shows a symmetric morphology, which indicates that either the AGNs are off-nuclear, that the central emission of the galaxy is dominated by star formation, or that the AGNs are turned off and we are observing a past ionization burst. One of the new AGNs shows a broad Hα emission line component, from which we derive a black hole mass in the realm of intermediate-mass black holes. This constitutes the first hidden type 1 AGN discovered in a dwarf galaxy based on IFU spectroscopy. The finding of this sample of hidden and faint AGNs has important implications for population studies of AGNs in dwarf galaxies and for seed black hole formation models.

Interactions among intermediate redshift galaxies

We present the properties of the central supermassive black holes and the host galaxies of the interacting object SDSS J134420.86+663717.8. We obtained optical long slit spectroscopy data from the Large Binocular Telescope using the Multi Object Double Spectrograph. Analysing the spectra revealed several strong broad and narrow emission lines of ionised gas in the nuclear region of one galaxy, whereas only narrow emission lines were visible for the second galaxy. The optical spectra were used to plot diagnostic diagrams, deduce rotation curves of the two galaxies, and calculate the masses of the central supermassive black holes. We find that the galaxy with broad emission line features has Seyfert 1 properties, while the galaxy with only narrow emission line features seems to be star-forming in nature. Furthermore, we find that the masses of the central supermassive black holes are almost equal at a few times 107 M⊙. Additionally, we present a simple N-body simulation to shed some light on the initial conditions of the progenitor galaxies. We find that for an almost orthogonal approach of the two interacting galaxies, the model resembles the optical image of the system.

Chemical abundances in active galaxies

ABSTRACT The Sloan Digital Sky Survey (SDSS) has proved to be a powerful resource for understanding the physical properties and chemical composition of star-forming galaxies in the local Universe. The SDSS population of active galactic nuclei (AGNs) remains as of yet less explored in this capacity. To extend the rigorous study of H ii regions in the SDSS to AGNs, we adapt methods for computing direct-method chemical abundances for application to the narrow-line regions (NLR) of AGNs. By accounting for triply ionized oxygen, we are able to more completely estimate the total oxygen abundance. We find a strong correlation between electron temperature and oxygen abundance due to collisional cooling by metals. Furthermore, we find that nitrogen and oxygen abundances in AGNs are strongly correlated. From the metal–temperature relation and the coupling of nitrogen and oxygen abundances, we develop a new, empirically and physically motivated method for determining chemical abundances from the strong emission lines commonly employed in flux-ratio diagnostic diagrams (BPT diagrams). Our approach, which for AGNs reduces to a single equation based on the BPT line ratios, consistently recovers direct-method abundances over a 1.5 dex range in oxygen abundance with an rms uncertainty of 0.18 dex. We have determined metallicities for thousands of AGNs in the SDSS, and in the process have discovered an ionization-related discriminator for Seyfert and LINER galaxies.

Upper boundaries of active galactic nucleus regions in optical diagnostic diagrams

ABSTRACT The distribution of galaxies in optical diagnostic diagrams can provide information about their physical parameters when compared with ionization models under proper assumptions. By using a sample of central emitting regions from the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA), we find evidence of the existence of upper boundaries for narrow-line regions (NLRs) of active galactic nuclei (AGNs) in optical Baldwin, Phillips & Terlevich (BPT) diagrams, especially in diagrams involving [S ii]λλ6716, 6731/Hα. Photoionization models can reproduce the boundaries well, as a consequence of the decrease of [S ii]λλ6716, 6731/Hα and [O iii]λ5007/Hβ ratios at very high metallicity. Whilst the exact location of the upper boundary in the [S ii] BPT diagram depends only weakly on the electron density of the ionized cloud and the secondary nitrogen prescription, its dependence on the shapes of the input spectral energy distributions (SEDs) is much stronger. This allows us to constrain the power-law index of the AGN SED between 1 Ryd and ∼100 Ryd to be less than or equal to −1.40 ± 0.05. The coverage of photoionization models in the [N ii] BPT diagram has a stronger dependence on the electron density and the secondary nitrogen prescription. With the density constrained by the [S ii] doublet ratio and the input SED constrained by the [S ii] BPT diagram, we find that the extent of the data in the [N ii] BPT diagram favours those prescriptions with high N/O ratios. Although shock-ionized clouds can produce line ratios similar to those from photoionization, the resulting shapes of the upper boundaries, if they exist, would likely be different from those of photoionizing origin.

Activity Types of Galaxies Selected from an HRC/BHRC Sample. II

This is a detailed spectral classification of 198 candidate active galactic nuclei (AGN) from a joint HRC/BHRC sample consisting of a combination of the HRC (Hamburg-ROSAT) and BHRC (Byurakan-ROSAT) catalogs. These objects have been identified as optical counterparts of ROSAT x-ray sources, but spectra for 198 of them are given in the SDSS without determinations of their spectral classification. They are studied using the SDSS spectra and detailed types of activity are found for them. For a more reliable classification, three diagnostic diagrams have been used, along with direct studies of the spectra. These sources were also identified in other wavelength ranges and their physical parameters have also been calculated.

Star formation in outer rings of S0 galaxies

Aims. Even though S0 galaxies are usually thought to be ‘red and dead’, they often demonstrate star formation organised in ring structures. We try to clarify the nature of this phenomenon and the difference between this occurrence and star formation in spiral galaxies. The luminous S0 galaxy with a large ring, UGC 5936, is studied in this work. Methods. We measured gas and star kinematics by applying long-slit spectroscopy along the major axis of UGC 5936, as well as Lick indices for the main body of the galaxy and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using line ratio diagnostic diagrams and having ensured that it is ionised mostly by young stars, we determined the gas oxygen abundance with popular strong-line methods. We also proved the spatial proximity of the south-eastern dwarf satellite to UGC 5936 and measured its gas metallicity. Results. The ionised gas of the ring is excited by young stars and has solar metallicity. Star formation in the ring is rather prolonged and its intensity corresponds to the current HI content of UGC 5936 (to the Kennicutt-Schmidt relation). The whole morphology of the HI distribution implies current accretion of the cold gas from the satellite onto the outer disc of UGC 5936. The accretion being smooth and laminar provides a favourable condition for star formation ignition; this is a consequence of the satellite location and rotation in the plane of the stellar disc of the host galaxy.

The AMUSING++ Nearby Galaxy Compilation. I. Full Sample Characterization and Galactic-scale Outflow Selection

Abstract We present here AMUSING++: the largest compilation of nearby galaxies observed with the MUSE integral-field spectrograph so far. This collection consists of 635 galaxies from different MUSE projects covering the redshift interval 0.0002 < z < 0.1. The sample and its main properties are characterized and described here. It includes galaxies of almost all morphological types, with a good coverage in its color–magnitude diagram, within the stellar mass range between 108 and 1012 M ⊙, and with properties resembling those of a diameter-selected sample. The AMUSING++ sample is, therefore, suitable for studying, with unprecendented detail, the properties of nearby galaxies at global and local scales, providing us with more than 50 million individual spectra. We use this compilation to investigate the presence of galactic outflows. We exploit the use of combined emission-line images to explore the shape of the different ionized components and the distribution along classical diagnostic diagrams to disentangle the different ionizing sources across the optical extension of each galaxy. We use the cross-correlation function to estimate the level of symmetry of the emission lines as an indication of the presence of shocks and/or active galactic nuclei. We uncovered a total of 54 outflows, comprising ∼8% of the sample. A large number of the discovered outflows correspond to those driven by active galactic nuclei (∼60%), suggesting some bias in the selection of our sample. No clear evidence was found that outflow host galaxies are highly star-forming, and outflows appear to be found within all galaxies around the star-formation sequence.