Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946
Yu. N. Efremov, V. L. Afanasiev, E. J. Alfaro, R. Boomsma, N. Bastian, S. Larsen, M. C. Sanchez-Gil, O. K. Silchenko, B. Garcia-Lorenzo, C. Munoz-Tunon, P. W. Hodge
The characteristics of ionized and HI gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) SAO RAS, the Gemini North telescope, and the Westerbork Synthesis Radio Telescope (WSRT), are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, ~300 pc in size, centered 7" east of the supercluster. The Vr of the ionized gas in the dip center is 100 km/s lower than in its surroundings, and emission lines within the dip appear to be shock excited. This dip is near the center of an HI hole and a semi-ring of HII regions. The HI (and less certainly, HII) velocity fields reveal expansion, with the velocity reaching ~30 km/s at a distance about 300 pc from the center of expansion, which is near the deep minimum position. The super star cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the Vr depression origins are discussed, including a HVC/dark mini-halo impact, a BCD galaxy merging, and a gas outflow due to release of energy from the supercluster stars.
We have investigated 1008 objects in the area of five intermediate age open clusters (NGC 2099, NGC 3114, NGC 6204, NGC 6705 and NGC 6756) via the narrow band Delta a-system. The detection limit for photometric peculiarity is very low (always less than 0.009mag) due to the high number of individual frames used (193 in total). We have detected six peculiar objects in NGC 6705 and NGC 6756 from which one in the latter is almost certainly an unreddened late type foreground star. The remaining five stars are probably cluster members and bona fide chemically peculiar objects (two are lambda Bootis …
We present spectroscopic data of ionized gas in the disk--halo regions of three edge-on galaxies, NGC 891, NGC 4631 and NGC 3079, covering a wavelength range from [\ion{O}{2}] $λ$3727Åto [\ion{S}{2}] $λ$6716.4Å. The inclusion of the [\ion{O}{2}] emission provides new constraints on the properties of the diffuse ionized gas (DIG), in particular, the origin of the observed spatial variations in the line intensity ratios. We used three different methods to derive electron temperatures, abundances and ionization fractions along the slit. The increase in the [\ion{O}{2}]/H$α$ line ratio towards the…
Spectroscopic measurements of emission line ratios and velocities are presented for ionized gas across the central plane of NGC 55, a late-type galaxy in the Sculptor group. The low metallicity in NGC 55 leads to relatively low line ratios of [S II]/H$α$ and [N II]/H$α$ for H II regions as well as the diffuse ionized gas. These are the first spectroscopical measurements of line ratios in ionized gas exterior to the stellar disc of NGC 55. Analysis of the line ratios and the relative velocities of different features suggests that photoionization is a plausible explanation for the ionization of …
We present WIYN SparsePak observations of the diffuse ionized gas (DIG) halo of NGC 891. Preliminary results of an analysis of the halo velocity field reveal a clear gradient of the azimuthal velocity with z which agrees with results for the neutral gas. The magnitude of the gradient has been determined, using two independent methods, to be approximately 15 km/s/kpc.
The stellar population, metallicity distribution and ionized gas in the elliptical galaxies NGC 6868 and NGC 5903 are investigated in this paper by means of long-slit spectroscopy and stellar population synthesis. Lick indices in both galaxies present a negative gradient indicating an overabundance of Fe, Mg, Na and TiO in the central parts with respect to the external regions. Concerning the emitting gas conspicuously detected in NGC 6868, we test three hypotheses as ionizing source: an H II region, post-AGB stars and an Active Galactic Nucleus (AGN). Diagnostic diagrams involving the ratios …
In a sample of six young open clusters we investigated 1753 objects using the narrow band, three filter Delta a photometric system resulting in the detection of eleven bona-fide magnetic chemically peculiar (CP) stars and five Be or metal-weak stars. The results for the distant cluster NGC 3105 is most important because of the still unknown influence of the global metallicity gradient of the Milky Way. These findings confirm that CP stars are present in open clusters of very young ages (log t > 6.90) at galactocentric distances up to 11.4 kpc. For all programme clusters the age, reddening, and…
We present new multi-wavelength data for the NGC 4410 galaxy group. This group contains the peculiar radio galaxy NGC 4410A, which has a distorted double-lobed radio structure. NGC 4410A is strongly interacting with three nearby galaxies, and has a peculiar ring-like optical morphology, a number of luminous H II regions, as well as as tidal tails and bridges variously visible in optical, HI, and X-ray light. The gravitational interaction has affected the interstellar matter, the star formation rate, and the radio lobes in this system.
In this work we investigate the stellar population, metallicity distribution and ionized gas in the elliptical galaxy NGC 5044, using long-slit spectroscopy and a stellar population synthesis method. We found differences in the slope of metal-line profiles along the galaxy which suggests an enhancement of alpha elements, particularly towards the central region. The presence of a non-thermal ionization source, such as a low-luminosity AGN and/or shock ionization, is implied by the large values of the ratio (N II])Ha observed in all sampled regions. However, the emission lines observed in the ex…
We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk of NGC 1144, but HI emission is detected over only 1/3 of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is observed. Faint, narrow HI absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes reg…
The planetary nebula NGC 6881 displays in the optical a quadrupolar morphology consisting of two pairs of highly collimated bipolar lobes aligned along different directions. An additional bipolar ejection is revealed by the hydrogen molecular emission, but its wide hourglass morphology is very different from that of the ionized material. To investigate in detail the spatial distribution of molecular hydrogen and ionized material within NGC 6881, and to determine the prevalent excitation mechanism of the H2 emission, we have obtained new near-IR Br-gamma and H2 and optical H-alpha and [N II] im…
I present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC6388 and NGC6441, in order to investigate the nature of the physical mechanism(s) responsible for the existence of an extended blue tail and of a slope in the horizontal branch. Further evidence that the horizontal branch tilt cannot be interpreted as an effect of differential reddening is provided, while I show that a possible solution of the puzzle is to assume that a small fraction of the stellar population in the two clusters is strongly helium enriched.
(Abridged) We investigate the interplay between starbursts and host galaxies by studying the structure and physical characteristics of the ionized gas surrounding the central starbursts in the two nearby galaxies NGC5253 and NGC5236. The two systems represent very different galactic environments, NGC5253 being a metal-poor dwarf, and NGC5236 being a metal-rich, massive spiral. We present images of the starburst regions in these two galaxies in the line emission [OIII], H-alpha, and [SII], and in continuum U, V, R. For NGC5253, line ratio maps [OIII]/H-beta and [SII]/H-alpha show that in the ou…
Studies of the kinematics of gaseous halos in some spiral galaxies have shown that the rotational velocity of the gas decreases with height above the midplane (z). This vertical velocity gradient has been observed in both the neutral and ionized components of halos. We present imaging Fabry-Perot Halpha observations of the edge-on galaxy NGC 5775. These observations allow us to study the variation in the rotation curve (and, to some extent, the radial profile) of the ionized gas component as a function of z. We have used an iterative technique to infer the major axis rotation curve from the io…
The kinematics of stars and ionized gas has been studied near the center of the S0 galaxy NGC 4036. Dynamical models based both on stellar photometry and kinematics have been built in order to derive the gravitational potential in which the gas is expected to orbit. The observed gas rotation curve falls short of the circular velocity curve inferred from these models. Inside 10'' the observed gas velocity dispersion is found to be comparable to the predicted circular velocity, showing that the gas cannot be considered on circular orbits. The understanding of the observed gas kinematics is impro…
Results of an ASCA X-ray observation of NGC 4507 are presented. The spectrum is best parameterized by a double power law (or a partial covering) model plus a narrow FeK$α$ emission line likely due to the line-of-sight absorption matter. The data require also an emission line at $\sim$ 0.9 keV consistent with NeIX, which may indicate that the soft X-ray emission derives from a combination of resonant scattering and fluorescence of the radiation by photoionized gas. Moreover, complex absorption (or other, unresolved, emission lines) is required by the data below 3 keV. Similarities between the X…
Near-infrared H_2 1-0 S(1) and Br_gamma velocity curves along the major axis of NGC 253 have revealed a central velocity gradient that is seven times steeper than that shown by the optical velocity curve. This is interpreted as an optical depth effect due to dust. Approximately 35 mag of visual extinction in the center is required to match the SW side of the optical velocity curve. The spatial variation of the ratio of these lines to the CO (J=1-0) line is compared among starburst galaxies NGC 253, M82, and NGC 4945 to investigate the excitation mechanism responsible for the H_2 1-0 S(1) line.
The detection of magnetic chemically peculiar (CP2) stars in open clusters of the Milky Way can be used to study the influence of different galactic environments on the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Furthermore it is still unknown if the CP2 phenomenon evolves, i.e. does the strength of the peculiarity feature at 5200A, increase or decrease with age. We have observed eight young to intermediate age open clusters in the Delta a photometric system. This intermediate band photometric system samples the depth of the 5200A, flux dep…
We present $V$ and $I$ continuum images and H$α$+[N II] maps of nine early-type galaxies observed with the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. Dust and ionized gas are detected in all galaxies. The optical nebulae are primarily concentrated on the nuclei and extend out to radii of a few hundred parsecs, in compact clumps, filaments, or disks. Two galaxies, NGC 6166 and NGC 6338, also possess diffuse, ionized filaments on kiloparsec scales. The ionized gas is entirely contained within the nuclear disks of ESO 208-G021, NGC 3078, and NGC 7720. In …
The millisecond pulsars discovered in globular clusters are diagnostic tools for studying the dynamics of the clusters, the intracluster ionized gas and the evolution of the binaries embedded in the cluster. In the first two years of a search at 1.4 GHz in progress at the Parkes radio telescope 12 new millisecond pulsars have been discovered in 6 globular clusters in which no pulsars were previously known. The scientific fall-back of these discoveries is here discussed for the case of two globular clusters: NGC 6397 and NGC 6752.
Existing long-slit spectral data for edge-on spiral galaxies suggesting that their Diffuse Ionized Gas (DIG) halos rotate slower than their underlying disks are summarized. An attempt to characterize lagging halos using a model of purely ballistic disk-halo flow is discussed, with the result that the model fails badly for the lagging halo of NGC 891, but is somewhat more successful for NGC 5775. New two-dimensional kinematic data on the DIG halo of NGC 4302 are presented, along with a preliminary analysis of its rotation. Two-dimensional data on NGC 5775 and a preliminary analysis of its halo …
We present FUSE spectra of the giant HII region NGC604 in the spiral galaxy M33. Chemical abundances are derived from far-UV absorption lines and are compared to those derived from optical emission lines. We derived the column densities of HI, NI, OI, SiII, PII, ArI, and FeII, fitting the line profiles with either a single component or several components. Our net results, assuming a single component, show that N, O, Si, and Ar are apparently underabundant in the neutral phase by a factor of 10 or more with respect to the ionized phase, while Fe is the same. However, we discuss the possibility …
We present the results of the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies. The stellar velocity field are mostly consistent with a rotation pattern, but some of them shows interesting features such as; S-shaped stellar isovelocity contours in NGC 4064, and signatures of kinematical distinct components in NGC 4429, and NGC 4698. This latter galaxy and NGC 4424 exhibit extremely low (V/sigma)* values suggesting that these galaxies are the result of mergers. The ionized gas velocity fields are more disturbed than the stellar velocity fields, displaying non-circ…
We have detected the H92alpha radio recombination line from two dwarf starburst galaxies, NGC 5253 and He 2-10, using the Very Large Array. Both the line data as well as the radio continuum data are used to model the properties of the ionized gas in the centers of these galaxies. We consider a multi-density model for radio recombination lines and show why previous models, which were based on the assumption of gas at a single density, are valid in many situations. The models show that the ionized gas has a density of ~10^4 /cc in both galaxies, with an effective size of 2-10 pc and a total mass…
We have studied the differences between the diffuse ionized gas (DIG) and the HII regions along a slit position in the local dwarf irregular galaxy NGC 6822. The slit position passes through the two most prominent HII regions: Hubble V and Hubble X. Important differences have been found in the excitation, ionization, and [NII]6584/Ha and [SII]6717/Ha line ratios between the DIG and the HII locations. Moreover, the values of all the line ratios are not similar to those in the DIG locations of spiral galaxies but are very similar to the values in other irregular galaxies, such as IC 10. We also …
We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects. NGC 772 and NGC 7782 have apparently normal kinematics with the ionized g…
We continue our survey for magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open clusters ages and metallicities can help to find a correlation of these parameters with the (non-)presence of peculiarities which has to be taken into account in stellar evolution models. The intermediate band Delta a photometric system samples the depth of the 5200A flux depression …
(Abridged) We present H-alpha images of five edge-on galaxies: NGC 891, NGC 4631, NGC 4244, NGC 3003, and UGC 9242. We also analyze [SII] 6717+6731A and [OIII] 5007A images of NGC 4631. We analyze the ionized gas content, with particular attention to the diffuse ionized gas (DIG). The DIG layer in NGC 891 is traced out to at least 5 kpc from the midplane, confirming an earlier spectroscopic detection. The DIG in four of these galaxies contributes 40 to 50% of the total H-alpha luminosity, similar to face-on galaxies, but in NGC 891 the DIG contributes 80 to 90%. This is likely due to the highe…
We present and discuss the high energy (E>4 keV) XMM-Newton spectrum of the Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5 years before is found. Several Fe and Ni emission lines, from both neutral and highly ionized material, are detected. The intensity of the iron K$α$ Compton shoulder implies that the neutral reflector is Compton--thick, likely the visible inner wall of the $N_H > 10^{25}$ cm$^{-2}$ absorber. From the equivalent width of the ionized iron lines a column density of …
We present a detailed study of the peculiar HI-deficient Virgo cluster spiral galaxies NGC 4064 and NGC 4424, using $^{12}$CO 1-0 interferometry, optical imaging and integral-field spectroscopic observations, in order to learn what type of environmental interactions have afected these galaxies. Optical imaging reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses a relatively undisturbed outer stellar disk and a central bar. In both galaxies H-alpha emission is confined to the central kilop…
The excellent quality of the Chandra observation of NGC 5846 reveals a complex X-ray morphology of the central regions of this galaxy. An intriguing morphological similarity between the X-ray and the optical line emission, discovered before using ROSAT HRI images (Trinchieri, Noris & Di Serego Alighieri 1997), is confirmed here in unprecedented detail. Complex spectral characteristics are associated with the morphological peculiarities, indicating a possibly turbulent gas in this object. A population of ~ 40 individual sources is also observed, with Lx in the range ~ 3 x 10**{38}- 2 x 10**{39}…
We present the discovery of four absorption lines in the X-ray spectrum of the Seyfert Galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are detected with high statistical confidence (from >20sigma for the strongest to \~4sigma for the weakest) in two XMM-Newton observations 60 ksec long. We also detect the same lines, with lower signal-to-noise (but still >2sigma for each line) in two previous shorter (~10 ksec) XMM observations. The spectral analysis identifies these features as FeXXV and FeXXVI Kalpha and Kbeta lines, outflowing with velocities varying between ~1000 to ~5000 k…
We present a new approach for calculating the physical properties of highly ionized X-ray flows in active galactic nuclei (AGN). Our method relies on a detailed treatment of the structure, dynamics and spectrum of the gas. A quantitative comparison of our model predictions with the 900 ksec Chandra/HETG X-ray spectrum of NGC 3783 shows that: (1) The highly ionized outflow is driven by thermal pressure gradients and radiation pressure force is less important. (2) A full featured dynamical model that provides a very good fit to the high resolution X-ray spectrum requires a multi-phased flow with…
The nearly face-on spiral galaxy NGC 3938 has been observed in the $H_α$ line with the TAURUS II Fabry-Perot interferometer at the William Herschel Telescope in order to study the kinematics of the ionized gas. We are able to construct intensity, velocity and velocity dispersion maps for this galaxy. The rotation curve of the galaxy is calculated up to 4.5 radial scale lengths from the galactic centre. The residual velocity field shows very small values with no systematic pattern. The mean velocity dispersion is approximately constant with radius at about 11 km/s as previously reported for the…
The blue star reported in the field of the young LMC cluster NGC1818 by Elson et al. (1998) has the wrong luminosity and radius to be a "luminous white dwarf" member of the cluster. In addition, unless the effective temperature quoted by the authors is a drastic underestimate, the luminosity is much too low for it to be a cluster member in the post-AGB phase. Other possibilities, including that of binary evolution, are briefly discussed. However, the implication that the massive main sequence turnoff stars in this cluster can produce white dwarfs (instead of neutron stars) from single-star evo…
The Seyfert 1 galaxy NGC4151 is characterized by complex X-ray absorption, well described by a dual absorber, composed of a uniform mildly ionized gas and a cold system that partially covers the central source. However, in one of the 5 BeppoSAX observations, the spectrum shows two peculiar features. An absorption feature is detected around 8.5-9 keV with a statistical significance of 99.96%. This feature can be fitted either with an absorption edge at E=8.62^{+0.34}_{-0.52} keV with optical depth τ=0.06\pm0.03 or with an absorption line with 9.5^{+1.3}_{-0.6} keV, width σ=0.95^{+1.2}_{-0.7} ke…
NGC 1427A is a LMC-like irregular galaxy in the Fornax cluster with an extended pattern of strong star formation around one of its edges, which is probably due to some kind of interaction with the cluster environment. We present H-alpha velocities within NGC 1427A, obtained through long-slit spectroscopy at seven different positions, chosen to fall on the brightest HII regions of the galaxy. Due to its location very near the center of the cluster this object is an excellent candidate to study the effects that the cluster environment has on gas-rich galaxies embedded in it. The rotation of NGC …
We present deep Halpha+[NII], [SII] (6716,6731A) and [OII] (3726,3729A) images of the highly inclined, actively star--forming SBm galaxy NGC 55, located in the nearby Sculptor Group. Due to its proximity, NGC 55 provides a unique opportunity to study the disk--halo interface in a late--type galaxy with unprecedented spatial resolution. Our images reveal a spectacular variety of ionized gas features, ranging from giant HII region complexes, to supergiant filamentary and shell features, to patches of very faint diffuse emission. Many of these features protrude well above the plane of the galaxy,…
We present new H alpha and [O III] 5007 narrow band images of the starbursting dwarf galaxy NGC 4214, obtained with the WFPC2 onboard HST, together with VLA observations of the same galaxy. The HST images resolve features down to physical scales of 2-5 pc, revealing several young (<10 Myr) star forming complexes of various ionized gas morphologies (compact knots, complete or fragmentary shells) and sizes (10-200 pc). Our results are consistent with a uniform set of evolutionary trends: The youngest, smaller, filled regions that presumably are those just emerging from dense star forming clouds,…
We present improved values of the three components of the absolute space velocity of the open cluster NGC6791. One HST ACS/WFC field with two-epoch observations provides astrometric measurements of objects in a field containing the cluster center. Identification of 60 background galaxies with sharp nuclei allows us to determine an absolute reference point, and measure the absolute proper motion of the cluster. We find (mu_alpha cos(delta), mu_delta)_J2000.0 = (-0.57+/-0.13, -2.45+/-0.12)mas/yr, and adopt V_rad = -47.1+/-0.7km/s from the average of the published values. Assuming a Galactic pote…
We present Australia Telescope Compact Array (ATCA) HI imaging of the edge-on galaxy NGC 1596, which was recently found to have counter-rotating ionized gas in its center (<15"). We find a large HI envelope associated with a nearby companion, the dwarf irregular galaxy NGC 1602. The HI covers a region \~11.9'x13.4' (62x70 kpc^2) and the total HI mass detected is 2.5+/-0.1x10^9 Msun (assuming an 18 Mpc distance). The HI is centered on NGC 1602 but appears to have two tidal tails, one of which crosses over NGC 1596. The HI located at the position of NGC 1596 has a velocity gradient in the same s…
We present high resolution radio continuum maps of the Galactic nebula Simeis 57 (= HS 191 = G 80.3+4.7) made with the WSRT and the DRAObservatory at frequencies of 609, 1412 and 1420 MHz. At optical and at radio wavelengths, the nebula has a peculiar ``S'' shape, crossed by long, thin and straight filaments. The radio maps, combined with other maps from existing databases, show essentially all radio emission from the peculiar and complex nebula to be thermal and optically thin. Although neither the distance nor the source of excitation of Simeis 57 are known, the nebula can only have a modera…
We present the chemical composition of the bright companion to the millisecond pulsar J1740-5340 in NGC 6397, based on high resolution spectra. Though the large rotation velocity of the star broadens the lines and complicates the analysis, the derived abundances are found fully compatible with those of normal unperturbed stars in NGC 6397, with the exception of a few elements (Li, Ca, and C). The lack of C suggests that the star has been peeled down to regions where incomplete CNO burning occurs, favouring a scenario where the companion is a turn-off star which has lost most of its mass. In ad…
We present key results from deep spectra of the Diffuse Ionized Gas (DIG) halo of the edge-on galaxy NGC 5775. [NII]6583 has been detected up to about z=13 kpc above the plane in one of two vertically oriented long slits -- making this the spiral galaxy with the greatest spectroscopically detected halo extent in emission. Key diagnostic line ratios have been measured up to about z=8 kpc, allowing the source of ionization and physical state to be probed. Ionization by a dilute radiation field from massive stars in the disk can explain some of the line ratio behavior, but departures from this pi…
The properties of the gas in halos of galaxies constrain global models of the interstellar medium. Kinematical information is of particular interest since it is a clue to the origin of the gas. Here we report observations of the kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to determine the rotation curve of the halo gas. We have obtained a Fabry-Pérot data cube in Halpha to measure the kinematics of the halo gas with angular resolution much higher than obtained from HI 21 cm observations. The data cube was obtained with the TAURUS II spectrograph at the WHT on L…
This study presents first results from an X-ray mini-survey carried out with XMM-Newton to investigate the diffuse Hot Ionized Medium in the halos of nine nearby star-forming edge-on spiral galaxies. Diffuse gaseous X-ray halos are detected in eight of our targets, covering a wide range of star formation rates from quiescent to starburst cases. For four edge-on spiral galaxies, namely NGC3044, NGC3221, NGC4634, and NGC5775, we present the first published high resolution/sensitivity detections of extended soft X-ray halos. EPIC X-ray contour maps overlaid onto Halpha imaging data reveals that i…
We present the LTE abundance analysis of high resolution spectra for red giant stars in the peculiar bulge globular cluster NGC 6388. Spectra of seven members were taken using the UVES spectrograph at the ESO VLT2 and the multiobject FLAMES facility. We exclude any intrinsic metallicity spread in this cluster: on average, [Fe/H]=-0.44+/-0.01+/-0.03 dex on the scale of the present series of papers, where the first error bar refers to individual star-to-star errors and the second is systematic, relative to the cluster. Elements involved in H-burning at high temperatures show large spreads, excee…
In this paper we study new infrared spectra of the evolved planetary nebula NGC 6445 obtained with ISO. These data show that the thermal emission from the grains is very cool and has a low flux compared to H beta. A model of the ionized region is constructed, using the photo-ionization code CLOUDY 90.05. Based on this model, we show from depletions in the gas phase elements that little grain destruction can have occurred in the ionized region of NGC 6445. We also argue that dust-gas separation in the nebula is not plausible. The most likely conclusion is that grains are residing inside the ion…
The bright Narrow Emission Line Galaxy, NGC 5506, has been observed simultaneously by XMM-Newton and BeppoSAX. The iron line is complex, with at least two components: one narrow and corresponding to neutral iron, the second one broad and corresponding to ionized iron. The latter line is equally well fitted by a truly broad line or by a blend of He- and H-like narrow lines. The bulk of the Compton reflection continuum originates in neutral matter, and is therefore associated with the narrow line: they are most likely emitted in distant matter. The origin of the ionized line(s) is less certain, …
Two long-slit spectra of the diffuse ionized gas in NGC 891 are presented. The first reveals variations parallel to the major axis in emission line ratios in the halo gas at z=700 pc. It is found that filaments of Halpha emission show lower values of [NII]/Halpha, [SII]/Halpha and [OI]/Halpha. Although this result is expected if the filaments represent the walls of evacuated chimneys, it merely reflects a more general correlation of these ratios with Halpha surface brightness along the slit, and may simply arise from radiation dilution effects. Much more interesting information on the nature o…
We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the ionized gas component of the interstellar medium. Covering the galaxy out to a radius larger than 12 kpc, and with a spatial sampling of 1.6 arcsec, we investigate the large-scale dynamics as well as feedback from individual HII regions into their surrounding medium. We study the role of gravitational perturbations along with that of external triggers which can disturb the kinematics and morphology of NGC 628. We verify the presence of an inner rapid…
We report a result of our near-infrared repeated observations of Mira variables in the globular clusters NGC 6388 and 6441. These two clusters are known as peculiar clusters with blue horizontal branch stars and RR Lyr variables which are unexpected for their relatively high metallicities. We derive their distance moduli by fitting the Mira variables in the period-luminosity relation. They are the first distance estimates, for these clusters, which were observationally obtained in an independent way from the horizontal branch stars. The obtained distances revealed that the absolute magnitudes …
The red clump stars in the open cluster NGC 752 present a peculiar distribution in the colour-magnitude diagran (CMD): the clump is observed to present a faint extension, slightly to the blue of the main concentration of clump stars. We point out that a similar structure is present in the CMD of NGC 7789, and discuss their possible origins. This feature may be understood as the result of having, at the same time, stars of low-mass which undergo the helium-flash, and those just massive enough for avoiding it. The ages of both clusters are compatible with this interpretation. Similar features ca…
In order to examine the excitation and ionization mechanism of extraplanar diffuse ionized gas (DIG) we have obtained optical longslit spectra of seven edge-on spiral galaxies. In four objects the brightest emission lines can be traced out to distances of typically 1.5 kpc above the disk. For NGC1963 and NGC3044 line ratios such as [NII]6583/Ha or [SII]6717/Ha as well as [OIII]5007/Hb could be measured for the halo DIG. This allows us to discuss the DIG in the halo of these objects in the framework of diagnostic diagrams. For these two objects, the line ratios of [OIII]5007/Hb decrease with in…
We present in this paper a detailed study of the kinematical properties of the ionized gas around the young massive star clusters in the nucleus of NGC 4214. The analysis is based on bidimensional spectroscopical data, allowing to derive the spatial variation of different properties (intensity, velocity and width / line splitting) of the emission lines Hαand [O III] λ5007 along the nuclear region. We have found that the Giant H II region around the two most massive clusters in NGC 4214 (A and B) is resolved into two clearly separated regions. We have not detected superbubbles with the properti…
The ASCA and BeppoSAX spectra of the Circinus Galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy. In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus, and the low ionized one in NGC1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2 pc for Circinus an…
We present moderate resolution spectroscopy of extraplanar diffuse ionized gas (EDIG) emission in the edge-on spiral galaxy NGC 4302. The spectra were obtained with the SparsePak integral field unit (IFU) at the WIYN Observatory. The spectra are used to construct position-velocity (PV) diagrams at several ranges of heights above the midplane. Azimuthal velocities are directly extracted from the PV diagrams using the envelope tracing method, and indicate an extremely steep dropoff in rotational velocity with increasing height, with magnitude ~30 km/s/kpc. We find evidence for a radial variation…
Nearly simultaneous VLBA observations of 3C 84, the radio source associated with NGC 1275, have been made at multiple frequencies to study the free-free absorption of the northern, or "counterjet", feature found by Walker, Romney, and Benson (1994, Ap.J. 430, L45) and by Vermeulen, Readhead, and Backer (1994, Ap.J. 430, L41). Our observations confirm that the spectra are consistent with free-free absorption and eliminate the possibility that the earlier result was an effect of variability. The northern feature is well resolved spatially, so images have been made showing the distribution of the…
In this paper we present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC 6388 and NGC 6441. We have obtained the first UV color-magnitude diagrams for NGC 6388 and NGC 6441. These diagrams confirm previous results, obtained in optical bands, about the presence of a sizeable stellar population of extremely hot horizontal branch stars. At least in NGC 6388, we find a clear indication that at the hot end of the horizontal branch the distribution of stars forms a hook-like feature, closely resembling those observed in NGC 2808 and Omega Centauri…
We present the kinematics and photometry of the stars and of the ionized gas near the centre of the S0 galaxy NGC4036. Dynamical models based on the Jeans Equation have been constructed from the stellar data to determine the gravitational potential in which the ionized gas is expected to orbit. Inside 10'', the observed gas rotation curve falls well short of the predicted circular velocity. Over a comparable radial region the observed gas velocity dispersion is far higher than the one expected from thermal motions or small scale turbulence, corroborating that the gas cannot be following the st…
We observed the Seyfert 1 galaxy NGC 4593 with the Chandra high energy transmission gratings and present a detailed analysis of the soft X-ray spectrum. We measure strong absorption lines from He-like O, Ne, Mg, Si, H-like N, O, Ne, Mg, Si and highly ionized Fe XIX-XXV. Only the NLya, OLya and MgLya lines appear to be marginally resolved. We identify a spectral feature at $\sim 0.707$ keV with a neutral Fe L edge, which might suggest that there is dust along the line-of-sight to \ngc. Neutral Si absorption, which might also be expected from absorption due to dust is present (though not signifi…
