arXiv subjects

J. E. Steiner

Publications and source records attributed to J. E. Steiner.

At least 37 records · Page 2Linked to original sources

arXiv2016

IFU spectroscopy of 10 early-type galactic nuclei - IV. Properties of the circumnuclear stellar kinematics

The study of stellar kinematic properties may provide hints on the formation and evolution of elliptical and lenticular galaxies. Although most previous studies have focused on the large scale of these galaxies, their central regions (scales of $\sim$ 100 pc) may contain important clues about their structure, such as kinematically decoupled cores. This is the fourth paper on a sample of 10 massive ($σ$ $>$ 200 km s$^{-1}$) and nearby ($d$ $<$ 31 Mpc) early-type galaxies, observed with the integral field unit of the Gemini South Multi Object Spectrograph. Here, we analyse the properties of the stellar kinematics in the circumnuclear region. We fitted the line-of-sight velocity distribution with a Gauss-Hermite function. In seven galaxies of the sample, we detected a rotation pattern in their radial velocity maps that are anti-correlated with $h_3$. We interpret this as stellar structures in rotation embedded in the bulges of the objects. Comparing the stellar kinematic results with the PCA Tomography results and also with the gas kinematic results of IC 5181, it seems that this object may have a non-axisymmetric potential at its centre. The velocity dispersion maps of four objects have a nuclear peak, which must correspond, in part, to unresolved stellar rotation. In NGC 1404, we detected a kinematic decoupled core with an extension of $\sim$ 200 pc. This galaxy also has a $σ$-drop in the centre, which may be related to both stellar components in counterrotation or with a kinematically cold star-forming region.

astro-ph.GA↗

arXiv2016

The off-centered Seyfert-like compact emission in the nuclear region of NGC 3621

We analyze an optical data cube of the nuclear region of NGC 3621, taken with the integral field unit of the Gemini Multi-object Spectrograph. We found that the previously detected central line emission in this galaxy actually comes from a blob, located at a projected distance of 2.14" +/- 0.08" (70.1 +/- 2.6 pc) from the stellar nucleus. Only diffuse emission was detected in the rest of the field of view, with a deficit of emission at the position of the stellar nucleus. Diagnostic diagram analysis reveals that the off-centered emitting blob has a Seyfert 2 spectrum. We propose that the line-emitting blob may be a "fossil" emission-line region or a light "echo" from an active galactic nucleus (AGN), which was significantly brighter in the past. Our estimates indicate that the bolometric luminosity of the AGN must have decreased by a factor of ~13 - 500 during the last ~230 years. A second scenario to explain the morphology of the line-emitting areas in the nuclear region of NGC 3621 involves no decrease of the AGN bolometric luminosity and establishes that the AGN is highly obscured toward the observer but not toward the line-emitting blob. The third scenario proposed here assumes that the off-centered line-emitting blob is a recoiling supermassive black hole, after the coalescence of two black holes. Finally, an additional hypothesis is that the central X-ray source is not an AGN, but an X-ray binary. This idea is consistent with all the scenarios we proposed.

astro-ph.GA↗

arXiv2015

The molecular H2 emission and the stellar kinematics in the nuclear region of the Sombrero galaxy

We analyze the molecular H$_2$ emission and the stellar kinematics in a data cube of the nuclear region of M104, the Sombrero galaxy, obtained with NIFS on the Gemini-north telescope. After a careful subtraction of the stellar continuum, the only emission line we detected in the data cube was H$_2 λ21218$. An analysis of this emission revealed the existence of a rotating molecular torus/disk, aproximately co-planar with a dusty structure detected by us in a previous work. We interpret these two structures as being associated with the same obscuring torus/disk. The kinematic maps provided by the Penalized Pixel Fitting method revealed that the stellar kinematics in the nuclear region of M104 appears to be the result of the superposition of a "cold" rotating disk and a "hot" bulge. Using a model of a thin eccentric disk, we reproduced the main properties of the maps of the stellar radial velocity and of the stellar velocity dispersion, specially within a distance of 0.2" from the kinematic axis (in regions at larger distances, the limitations of a model of a thin rotating disk become more visible). The general behavior of the $h_3$ map, which is significantly noisier than the other maps, was also reproduced by our model (although the discrepancies, in this case, are considerably higher). With our model, we obtained a mass of (9.0 +/- 2.0) x 10^8 Mo for the supermassive black hole of M104, which is compatible, at $1σ$ or $2σ$ levels, with the values obtained by previous studies.

astro-ph.GA↗

arXiv2015

IFU spectroscopy of 10 early-type galactic nuclei - III. Properties of the circumnuclear gas emission

Many Early-type galaxies (ETG) have ionized gas emission in their centres that extends to scales of ~ 1kpc. The majority of such objects are classified as LINERs, but the nature of their ionizing source is still not clear. The kinematics associated with these gaseous structures usually shows deviations from a pure rotational motion due to non-gravitational effects or to non-axisymmetric potentials. This is the third of a series of papers that describes a sample of 10 nearby and massive ETG observed with the Gemini Multi-Object Spectrograph in Integral Field mode installed on the Gemini-South telescope. In paper II, we performed spectral synthesis to subtract the stellar components from the data cubes of the sample galaxies in order to study their nuclear spectra. Here, we analyse the circumnuclear gas emission (scales of ~ 100 pc) of the sample galaxies. Circumnuclear gas emission was detected in seven galaxies, all of them classified as LINERs. Pure gaseous discs are found in three galaxies. In two objects, gaseous discs are probably present, but their kinematics are affected by non-Keplerian motions. In IC 5181, we detected a spiral structure of gas that may be caused either by a non-axisymmetric potential or by an outflow together with a gaseous disc. In NGC 3136, an ionization bicone is present in addition to five compact structures with LINER-like emission. In galaxies with a gaseous disc, we found that ionizing photons emitted by an AGN are not enough to explain the observed Ha flux along this structure. On the other hand, the Ha flux distribution and equivalent width along the direction perpendicular the gaseous disc suggest the presence of low-velocity ionized gas emission which seem to be related to the nuclear activity. We propose a scenario for LINER-like circumnuclear regions where a low-velocity ionization cone is formed by a collimating agent aligned with the gaseous disc.

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arXiv2015

A treatment procedure for VLT/SINFONI data cubes: application to NGC 5643

In this second paper of a series, we present a treatment procedure for data cubes obtained with the Spectrograph for Integral Field Observations in the Near Infrared of the Very Large Telescope. We verified that the treatment procedure improves significantly the quality of the images of the data cubes, allowing a more detailed analysis. The images of the Br$γ$ and H$_2 λ21218$ emission lines from the treated data cube of the nuclear region of NGC 5643 reveal the existence of ionized and molecular-gas clouds around the nucleus, which cannot be seen clearly in the images from the non-treated data cube of this galaxy. The ionized-gas clouds represent the narrow-line region, in the form of a bicone. We observe a good correspondence between the positions of the ionized-gas clouds in the Br$γ$ image and in an [O III] image, obtained with the Hubble Space Telescope, of the nuclear region of this galaxy convolved with an estimate of the point-spread function of the data cube of NGC 5643. The morphologies of the ionized and molecular gas seem to be compatible with the existence of a molecular torus/disc that collimates the active galactic nucleus (AGN) emission. The molecular gas may also flow along this torus/disc, feeding the AGN. This scenario is compatible with the unified model for AGNs.

astro-ph.IM↗

arXiv2015

A hot bubble at the centre of M81

Context. Messier 81 has the nearest active nucleus with broad H$α$ emission. A detailed study of this galaxy's centre is important for understanding the innermost structure of the AGN phenomenon. Aims. Our goal is to seek previously undetected structures using additional techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the Gemini North telescope (Schnorr Müller et al. 2011). Method. We analysed the data cube using techniques of noise reduction, spatial deconvolution, starlight subtraction, PCA tomography, and comparison with HST images. Results. We identified a hot bubble with T $>$ 43500 K that is associated with strong emission of [N II]$λ$5755Å and a high [O I]$λ$6300/H$α$ ratio; the bubble displays a bluish continuum, surrounded by a thin shell of H$α$ + [N II] emission. We also reinterpret the outflow found by Schnorr Müller et al. (2011) showing that the blueshifted cone nearly coincides with the radio jet, as expected. Conclusions. We interpret the hot bubble as having been caused by post starburst events that left one or more clusters of young stars, similar to the ones found at the centre of the Milky Way, such as the Arches and the IRS 16 clusters. Shocked structures from combined young stellar winds or supernova remnants are probably the cause of this hot gas and the low ionization emission.

astro-ph.GA↗

arXiv2014

An off-centered active galactic nucleus in NGC 3115

NGC 3115 is an S0 galaxy that has always been considered to have a pure absorption-line spectrum. Some recent studies have detected a compact radio-emitting nucleus in this object, coinciding with the photometric center and with a candidate for the X-ray nucleus. This is evidence of the existence of a low-luminosity active galactic nucleus (AGN) in the galaxy, although no emission line has ever been observed. We report the detection of an emission-line spectrum of a type 1 AGN in NGC 3115, with an H$α$ luminosity of $L_{Hα} = (4.2 \pm 0.4) \times 10^{37}$ erg s$^{-1}$. Our analysis revealed that this AGN is located at a projected distance of $\sim 0.29" \pm 0.05"$ (corresponding to $\sim 14.3 \pm 2.5$ pc) from the stellar bulge center, which is coincident with the kinematic center of this object's stellar velocity map. The black hole corresponding to the observed off-centered AGN may form a binary system with a black hole located at the stellar bulge center. However, it is also possible that the displaced black hole is the merged remnant of the binary system coalescence, after the "kick" caused by the asymmetric emission of gravitational waves. We propose that certain features in the stellar velocity dispersion map are the result of perturbations caused by the off-centered AGN.

astro-ph.GA↗

arXiv2014

The orbital period of the V Sge star candidate QU Carinae

Close Binary Supersoft X-ray Sources (CBSS) are considered strong candidates to SN Ia progenitors, but very few CBSS are known in our Galaxy. The galactic counterparts of the CBSS may be the V Sge stars, not detected in X-rays due to the strong absorption by the interstellar gas. Nevertheless, the number of members in the V Sge class is still small. In order to find new members we selected QU Car for photometric and spectroscopic observations. The orbital period of this system was published in the literature as 10.9 h, determined from radial velocity data taken in 1979-1980, but posterior analysis of data taken in 2006-2007 did not confirm this period. We analysed the high variability of its emission line profiles with the Temporal Variance Spectrum (TVS) technique. Besides, we recovered the 10.9 h orbital period from the radial velocities of the He II 4686 A emission line and, for the first time, detected what may be the orbital modulation in the photometric data. This photometric modulation is present only in the lower brightness state data, when the flickering is attenuated. The inclusion of QU Car in the V Sge class is supported by many features like high/low states, strong winds, nebular lines and He II 4686 A/Hbeta line ratios. However, the non-detection of the characteristic O VI 3811-34 A lines in its spectrum claims against this classification. These lines, though, may be highly variable so additional spectra analysed with the TVS technique can, possibly, solve this question.

astro-ph.SR↗

arXiv2014

Integral field unit spectroscopy of 10 early type galactic nuclei: I - Principal component analysis Tomography and nuclear activity

Most massive galaxies show emission lines that can be characterized as LINERs. To what extent this emission is related to AGNs or to stellar processes is still an open question. In this paper, we analysed a sample of such galaxies to study the central region in terms of nuclear and circumnuclear emission lines, as well as the stellar component properties. For this reason, we selected 10 massive ($σ$ > 200 km/s) nearby (d < 31 Mpc) galaxies and observed them with the IFU/GMOS (integral field unit/Gemini Multi-Object Spectrograph) spectrograph on the Gemini South Telescope. The data were analysed with principal component analysis (PCA) Tomography to assess the main properties of the objects. Two spectral regions were analysed: a yellow region (5100-5800 A), adequate to show the properties of the stellar component, and a red region (6250-6800 A), adequate to analyse the gaseous component. We found that all objects previously known to present emission lines have a central AGN-type emitting source. They also show gaseous and stellar kinematics typical of discs. Such discs may be co-aligned (NGC 1380 and ESO 208 G-21), in counter-rotation (IC 1459 and NGC 7097) or misaligned (IC 5181 and NGC 4546). We also found one object with a gaseous disc but no stellar disc (NGC 2663), one with a stellar disc but no gaseous disc (NGC 1404), one with neither stellar nor gaseous disc (NGC 1399) and one with probably ionization cones (NGC 3136). PCA Tomography is an efficient method for detecting both the central AGN and gaseous and stellar discs. In the two cases (NGC 1399 and NGC 1404) in which no lines were previously reported, we found no evidence of either nuclear or circumnuclear emission, using PCA Tomography only.

astro-ph.GA↗

arXiv2014

IFU spectroscopy of 10 early type galactic nuclei: II - Nuclear emission line properties

Although it is well known that massive galaxies have central black holes, most of them accreting at low Eddington ratios, many important questions still remain open. Among them, are the nature of the ionizing source, the characteristics and frequencies of the broad line region and of the dusty torus. We report observations of 10 early-type galactic nuclei, observed with the IFU/GMOS spectrograph on the Gemini South telescope, analysed with standard techniques for spectral treatment and compared with results obtained with principal component analysis Tomography (Paper I). We performed spectral synthesis of each spaxel of the data cubes and subtracted the stellar component from the original cube, leaving a data cube with emission lines only. The emission lines were decomposed in multi-Gaussian components. We show here that, for eight galaxies previously known to have emission lines, the narrow line region can be decomposed in two components with distinct line widths. In addition to this, broad H$α$ emission was detected in six galaxies. The two galaxies not previously known to have emission lines show weak H$α$+[N II] lines. All 10 galaxies may be classified as low-ionization nuclear emission regions in diagnostic diagrams and seven of them have bona fide active galactic nuclei with luminosities between 10$^{40}$ and 10$^{43}$ erg s$^{-1}$. Eddington ratios are always < 10$^{-3}$.

astro-ph.GA↗

arXiv2014

A treatment procedure for Gemini North/NIFS data cubes: application to NGC 4151

We present a detailed procedure for treating data cubes obtained with the Near-Infrared Integral Field Spectrograph (NIFS) of the Gemini North telescope. This process includes the following steps: correction of the differential atmospheric refraction, spatial re-sampling, Butterworth spatial filtering, 'instrumental fingerprint' removal and Richardson-Lucy deconvolution. The clearer contours of the structures obtained with the spatial re-sampling, the high spatial-frequency noise removed with the Butterworth spatial filtering, the removed 'instrumental fingerprints' (which take the form of vertical stripes along the images) and the improvement of the spatial resolution obtained with the Richardson-Lucy deconvolution result in images with a considerably higher quality. An image of the Brγ emission line from the treated data cube of NGC 4151 allows the detection of individual ionized-gas clouds (almost undetectable without the treatment procedure) of the narrow-line region of this galaxy, which are also seen in an [O III] image obtained with the Hubble Space Telescope. The radial velocities determined for each one of these clouds seem to be compatible with models of biconical outflows proposed by previous studies. Considering the observed improvements, we believe that the procedure we describe in this work may result in more reliable analysis of data obtained with this instrument.

astro-ph.IM↗

arXiv2013

Identification of a high-velocity compact nebular filament 2.2 arcsec south of the Galactic Centre

The central parsec of the Milky Way is a very special region of our Galaxy; it contains the supermassive black hole associated with Sgr A* as well as a significant number of early-type stars and a complex structure of streamers of neutral and ionized gas, within two parsecs from the centre, representing a unique laboratory. We report the identification of a high velocity compact nebular filament 2.2 arcsec south of Sgr A*. The structure extends over ~1 arcsec and presents a strong velocity gradient of ~200 km s^{-1} arcsec^{-1}. The peak of maximum emission, seen in [Fe III] and He I lines, is located at dα = +0.20 +/- 0.06 arcsec and dδ = -2.20 +/- 0.06 arcsec with respect to Sgr A*. This position is near the star IRS 33N. The velocity at the emission peak is Vr = -267 km s^{-1}. The filament has a position angle of PA = 115{\degr} +/- 10{\degr}, similar to that of the Bar and of the Eastern Arm at that position. The peak position is located 0.7 arcsec north of the binary X-ray and radio transient CXOGX J174540.0-290031, a low-mass X-ray binary with an orbital period of 7.9 hr. The [Fe III] line emission is strong in the filament and its vicinity. These lines are probably produced by shock heating but we cannot exclude some X-ray photoionization from the low-mass X-ray binary. Although we cannot rule out the idea of a compact nebular jet, we interpret this filament as a possible shock between the Northern and the Eastern Arm or between the Northern Arm and the mini-spiral "Bar".

astro-ph.GA↗

arXiv2013

Collimation and scattering of the active galactic nucleus emission in the Sombrero galaxy

We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the Hα emission line. The collimation and scattering of this broad Hα component was also revealed by fitting the [NII] λλ6548,6583 and Hα emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18° +/- 13° and P.A. = 162° +/- 13°) along a direction perpendicular to the torus/disk (P.A. = 72° +/- 14°) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the Unified Model and explains why only a weak broad component of the Hα emission line is visible and also why many previous studies detected no broad Hα. The technique used here proved to be an efficient method not only for detecting scattered light but also for testing the Unified Model in low luminosity AGNs.

astro-ph.CO↗

arXiv2012

Discovery of an Halpha emitting disk around the supermassive black hole of M31

Due to its proximity, the mass of the supermassive black hole in the nucleus of Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk that surrounds it. We report here the discovery of an eccentric Halpha emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0_{-1.0}^{+0.8} x 10^7 Mo for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1-sigma level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-sigma relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Halpha emitting disk. This result suggests that the stellar and the Halpha emitting disks are intrinsically different from each other. A plausible explanation is that the Halpha emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Halpha emission is, at least partially, generated by stars.

astro-ph.CO↗

arXiv2011

He II 4686 in eta Carinae: collapse of the wind-wind collision region during periastron passage

The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of eta Carinae with 5 Southern telescopes during the 2009 low excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II 4686 emission line (L~310 Lsun) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II 4686 light-curves. After a short-lived minimum, He II 4686 emission rises again to a ne

astro-ph.SR↗

arXiv2011

NGC 7097: the AGN and its mirror, revealed by PCA Tomography

Three-dimensional (3D) spectroscopy techniques are becoming more and more popular, producing an increasing number of large data cubes. The challenge of extracting information from these cubes requires the development of new techniques for data processing and analysis. We apply the recently developed technique of Principal Component Analysis (PCA) Tomography to a data cube from the center of the elliptical galaxy NGC 7097 and show that this technique is effective in decomposing the data into physically interpretable information. We find that the first five principal components of our data are associated with distinct physical characteristics. In particular, we detect a LINER with a weak broad component in the Balmer lines. Two images of the LINER are present in our data, one seen through a disk of gas and dust, and the other after scattering by free electrons and/or dust particles in the ionization cone. Furthermore, we extract the spectrum of the LINER, decontaminated from stellar and extended nebular emission, using only the technique of PCA Tomography. We anticipate that the scattered image has polarized light, due to its scattered nature.

astro-ph.CO↗

arXiv2010

Gas Streaming Motions towards the Nucleus of M81

We present stellar and gaseous kinematics of the inner 120x250pc^2 of the Liner/Seyfert 1 galaxy M81, from optical spectra obtained with the GMOS integral field spectrograph on the Gemini North telescope at a spatial resolution of 10pc. The stellar velocity field shows circular rotation but deviations are observed close to the minor axis which can be attributed to stellar motions possibly associated to a nuclear bar. The stellar velocity dispersion of the bulge is 162km/s leading to a black hole mass of M_BH=5.5x10^7M_sun based on the M_BH-sigma relationship. The gas kinematics is dominated by non-circular motions and the subtraction of the stellar velocity field reveals blueshifts of ~-100km/s on the far side of the galaxy and a few redshifts on the near side. These characteristics can be interpreted in terms of streaming towards the center if the gas is in the plane. On the basis of the observed velocities and geometry of the flow, we estimate a mass inflow rate in ionized gas of ~4.0x10^-3M_sun/year, which is of the order of the accretion rate necessary to power the LINER nucleus of M81. We have also applied the technique of Principal Component Analysis (PCA) to our data, which reveals the presence of a rotating nuclear gas disk within ~50pc from the nucleus and a compact outflow, approximately perpendicular to the disk. The PCA combined with the observed gas velocity field shows that the nuclear disk is being fed by gas circulating in the galaxy plane. The presence of the outflow is supported by a compact jet seen in radio observations at a similar orientation, as well as by an enhancement of the [OI]\Halpha line ratio, probably resulting from shock excitation of the circumnuclear gas by the radio jet. With these observations we are thus resolving both the feeding -- via the nuclear disk and observed gas inflow, and the feedback -- via the outflow, around the nucleus of M81.

astro-ph.CO↗

arXiv2010

Optical identification of the transient supersoft X-ray source RX J0527.8-6954, in the LMC

Context. Close binary supersoft X-ray sources (CBSS) are binary systems that contain a white dwarf with stable nuclear burning on its surface. These sources, first discovered in the Magellanic Clouds, have high accretion rates and near-Eddington luminosities (10^37 - 10^38 erg/s) with high temperatures (T = 2 - 7 x 10^5 K). Aims. The total number of known objects in the MC is still small and, in our galaxy, even smaller. We observed the field of the unidentified transient supersoft X-ray source RX J0527.8-6954 in order to identify its optical counterpart. Methods. The observation was made with the IFU-GMOS on the Gemini South telescope with the purpose of identifying stars with possible He II or Balmer emission or else of observing nebular extended jets or ionization cones, features that may be expected in CBSS. Results. The X-ray source is identified with a B5e V star that is associated with subarcsecond extended Halpha emission, possibly bipolar. Conclusions. If the primary star is a white dwarf, as suggested by the supersoft X-ray spectrum, the expected orbital period exceeds 21 h; therefore, we believe that the 9.4 h period found so far is not associated to this system.

astro-ph.SR↗