The stellar content of the S0 galaxy NGC 5102 is investigated. A modest population of bright main sequence stars and red supergiants (RSGs) is detected throughout the western portion of the disk, and the star formation rate (SFR) during the past ten million years is estimated to have been 0.02 solar masses per year. RGB stars are traced out to galactocentric distances of 10 kpc, which corresponds to ~ 14 disk scale lengths. A large population of bright asymptotic giant branch (AGB) stars are seen throughout the western portion of the disk, and it is concluded that (1) stars that formed within the past Gyr comprise ~ 20% of the total stellar disk mass, and (2) the SFR during intermediate epochs in the disk of NGC 5102 was at least 1.4 solar masses per year. It is suggested that NGC 5102 was a spiral galaxy that experienced a galaxy-wide episode of enhanced star formation that terminated a few hundred Myr in the past, and that much of its interstellar medium was ejected in an outflow.
A renewed attempt to detect radio recombination lines from external galaxies has resulted in the measurement of lines from several bright starburst galaxies. The lines are produced by hydrogen ionized by young, high-mass stars and are diagnostic of the conditions and gas dynamics in the starburst regions without problems of dust obscuration. We present here detections of the lines H91alpha and H92alpha near 8.6 GHz from the starburst nuclei in NGC 3256, NGC 4945, and the Circinus galaxy using the ATCA and VLA. Modelling the line emitting region as a collection of H II regions, we derive the re…
Recently, the CANGAROO-II telescope detected diffuse TeV gamma-ray emission from a nearby edge-on starburst galaxy, NGC 253. The emission mechanism is discussed in this report. We review the emissions of radio-to-TeV gamma-rays from NGC 253, and present a model of the non-thermal emissions due to synchrotron radiations and inverse Compton scatterings. A halo model successfully explains the multiband spectrum of NGC 253.
We present observations of the starburst galaxy NGC 7714 with the Infrared Spectrograph IRS on board the Spitzer Space Telescope. The spectra yield a wealth of ionic and molecular features that allow a detailed characterization of its properties. NGC 7714 has an HII region-like spectrum with strong PAH emission features. We find no evidence for an obscured active galactic nucleus, and with [NeIII]/[NeII]~0.73, NGC7714 lies near the upper end of normal-metallicity starburst galaxies. With very little slicate absorption and a temperature of the hottest dust component of 340K, NGC 7714 is the per…
Detailed modeling of the different regions of NGC 7130 is presented, accounting for its composite nature of AGN and starburst galaxy. Shock waves, created by stellar winds from hot massive stars and by supernova ejecta, are evident in the continuum and line spectra emitted from the clouds. The AGN starburst connection is discussed on the basis of model results, considering in particular the distribution of densities and velocities throughout the galaxy.
(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…
(Abridged) We present deep, Chandra spectral imaging of the dwarf starburst galaxy NGC 1569. The unprecedented spatial resolution allows us to spatially identify the components of the integrated \x spectrum. Fitted spectral models require an intrinsic absorption component and higher metal abundances than previous studies indicated. Our results provide the first direct evidence for metal-enriched winds from dwarf starburst galaxies.
We present high spatial resolution (0.6 arcsec) near-infrared broad-band JHK images and Br_gamma 2.1661 micron and H_2 1-0 S(1) 2.122 micron emission line images of the nuclear regions in the interacting starburst galaxies NGC 520, NGC 1614 and NGC 7714. The near-infrared emission line and radio morphologies are in general agreement, although there are differences in details. In NGC 1614, we detect a nuclear double structure in Br_gamma, in agreement with the radio double structure. We derive average extinctions of A(K) = 0.41 and A(K) = 0.18 toward the nuclear regions of NGC 1614 and NGC 7714…
HST/WFPC2 images resolved NGC 7673 into a large number of star clusters. Among these, 31 fall inside the IUE large aperture, which was used to acquire an integrated ultraviolet spectrum of the galaxy. We have fitted Starburst99 evolutionary synthesis models to the observed colours of these clusters and derived ages, reddenings, and masses of the clusters. Then a simple sum of the clusters synthetic UV spectra has been compared to the observed IUE spectrum, in order to investigate the star formation history of NGC 7673.
We have performed high resolution CO(2-1), CO(1-0), HCN(1-0) and HCO+(1-0) observations of a "low star formation efficiency starburst galaxy" NGC 4527 with the Nobeyama Millimeter Array. The integrated intensity ratios, CO(2-1)/CO(1-0) and HCN(1-0)/CO(1-0), are found to be 0.6 +/- 0.05 and 0.06 +/- 0.007, respectively, at the center. These line ratios are smaller than those in prototypical starburst galaxies such as NGC 253 and M82, and we suggest that the fraction of dense molecular gas to the total molecular mass in the central a few kpc region of NGC 4527 is small. This fact may be responsi…
We have conducted a high-resolution ``3D'' imaging survey of the CO(1--0), HCN(1--0), and HCO$^+$(1--0) lines toward the central a few kpc regions of the Seyfert and starburst galaxies in the local universe using the Nobeyama Millimeter Array. We detected luminous HCN(1--0) emissions toward a considerable fraction of these Seyfert galaxies (10 of 12 in our sub-sample), which indicated that some of these Seyfert galaxies, such as NGC 3079, NGC 3227, NGC 4051, NGC 6764, and NGC 7479, are indeed accompanied with compact nuclear starburst, given the tight correlation between the HCN(1--0) luminosi…
We investigate the star cluster system in the starburst galaxy NGC 7673 using archival Hubble Space Telescope WFPC2 broad-band images. For the first time we are able to examine the internal structures of the prominent optical clumps in this galaxy. The clumps are composed of young stars, 16-33 % of which are in bright star clusters. We identify 268 star cluster candidates in both the F555W and F814W images, and 50 clusters with the F255W filter. These data allow us to estimate ages and masses using color-magnitude and two-color diagrams for our sample. We find a population of young, < 6 Myr cl…
Chandra observations of the core of the nearby starburst galaxy NGC 253 reveal a heavily absorbed source of hard X-rays embedded within the nuclear starburst region. The source has an unabsorbed, 2 to 10 keV luminosity of >=10^39 erg/s and photoionizes the surrounding gas. We observe this source through a dusty torus with a neutral absorbing column density of NH ~ 2x10^23 cm^-2. The torus is hundreds of pc across and collimates the starburst-driven nuclear outflow. We suggest that the ionizing source is an intermediate-mass black hole or a weakly accreting supermassive black hole, which may si…
We present NGC 6221 as a case study of ``X-ray loud composite galaxies,'' which appear similar to starbursts at optical wavelengths and resemble traditional active galactic nuclei in X-rays. The net optical spectrum of NGC 6221 is properly characterized as a starburst galaxy, but in X-rays, NGC 6221 is similar to Seyfert 1 galaxies, exhibiting a power-law continuum spectrum, a broad Fe K alpha line, and continuum variability on timescales of days and years. High-resolution images reveal that the detected active nucleus is relatively weak, not only at optical, but also at near-infrared waveleng…
We present and discuss HST (WFPC2 and FOC) images and UV GHRS spectra plus ground-based near UV through to near IR spectra of three Seyfert 2 nuclei (NGC 7130, NGC 5135 and IC 3639). These galaxies, together to Mrk 477, were selected from a bigger sample that comprises the 20 brightest Seyfert 2 nuclei, with the goal to study the origin of the UV-optical-near IR featureless continuum in Seyfert 2 nuclei. These four galaxies have bolometric luminosities, as computed with the four IRAS bands, of 10^11 Lsol. They are close enough to be resolved with HST the nuclear zone. This makes these Seyfert …
The superb spatial resolution of Chandra is utilized to study the X-ray morphology of the dwarf starburst galaxy NGC1800 embedded in a small group of galaxies. Diffuse galactic emission is detected, extending several kpc above the galactic plane, with an overall morphology similar to the galactic winds seen in nearby X-ray bright starburst galaxies. This makes NGC1800 the most distant dwarf starburst with a clear detection of diffuse X-ray emission. The diffuse X-ray luminosity of 1.3+/-0.3 *10^38 erg/s accounts for at least 60 per cent of the total soft X-ray output of the galaxy. A hot gas t…
(ABRIDGED) We have undertaken a programme of 3 micron narrowband imaging of a sample of nearby template galaxies covering a wide range of metallicity, star formation activity, and nuclear activity. In the present paper we present first results: high spatial resolution images of PAH emission and the adjacent continuum emission from the central regions of the nearby starburst galaxies NGC253 and NGC1808. Globally, the PAH emission is seen to peak on the central starburst regions of both sources. On smaller scales, however, we see no general spatial correlation or anti-correlation between the PAH…
In this Work we report, for the extreme starburst in the IR merger NGC 3256: (i) The detection of 4 galactic bubbles, associated with SN explosions.(ii) The first analysis of the spatial distribution of young star clusters (YSC) candidates.(iii) The kinematic study of the ionized gas in the core of of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission line profile could be explained by the presence in the core of YSC with outflow.
As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (HI) in the post-starburst dwarf galaxy NGC 1569. High-resolution measurements with the VLA (B-, C- and D-array) are aimed at identifying morphological and kinematical signatures in the HI caused by the starburst. Our kinematical data suggest a huge hole in the HI distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale HI structure, we con…
Context. Gas ionized by starburst activity radiates radio recombination lines (RRLs), from which one can derive the plasma conditions and the number of massive stars formed in the burst, free of dust obscuration effects. Aims. We aimed to find RRL emission from additional starburst systems and to use the line properties to estimate the properties of the ionized gas. Methods. We conducted a search for RRLs in the nearby extragalactic starburst or Seyfert galaxies NGC 1808, the Circinus galaxy, NGC 4038/9, II Zw 40, NGC 6221, NGC 7552, IRAS 18325-5926, IC 5063, and VV 114. We used the VLA and th…
We present deep HST ACS/WFC photometry of the dwarf irregular galaxy NGC 1569, one of the closest and strongest nearby starburst galaxies. These data allow us, for the first time, to unequivocally detect the tip of the red giant branch and thereby determine the distance to NGC 1569. We find that this galaxy is 3.36 +/- 0.20 Mpc away, considerably farther away than the typically assumed distance of 2.2 +/- 0.6 Mpc. Previously thought to be an isolated galaxy due to its shorter distance, our new distance firmly establishes NGC 1569 as a member of the IC 342 group of galaxies. The higher density …
We present results from Chandra and XMM-Newton X-ray observations of NGC 4214, a nearby dwarf starburst galaxy containing several young regions of very active star-formation. Starburst regions are known to be associated with diffuse X-ray emission, and in this case the X-ray emission from the galaxy shows an interesting morphological structure within the galaxy, clearly associated with the central regions of active star-formation. Of the two main regions of star-formation in this galaxy, X-ray emission associated with the older is identified whereas little is detected from the younger, providi…
The high density medium that characterizes the central regions of starburst galaxies and its power to accelerate particles up to relativistic energies make these objects good candidates as $γ$-rays sources. In this paper, a self-consistent model of the multifrequency emission of the starburst galaxy NGC 253, from radio to gamma-rays, is presented. The model is in agreement with all current measurements and provides predictions for the high energy behavior of the NGC 253 central region. Prospects for observations with the HESS array and GLAST satellite are especially discussed.
Spatial and spectral analysis of deep ROSAT HRI and PSPC observations of the near edge-on starburst galaxy NGC 253 reveal diffuse soft X-ray emission, which contributes 80% to its total X-ray luminosity (L$_{\rm X} = 5 10^{39}$ \ergsec, corrected for foreground absorption). The nuclear area, disk, and halo contribution to the luminosity is about equal. The starburst nucleus itself is highly absorbed and not visible in the ROSAT band. We describe in detail spectra and morphology of the emission from the nuclear area, disk and halo and compare our results to observations at other wavelengths and…
We present our recent spectrophotometric results of the infrared luminous Seyfert 2 galaxy NGC 7679. We find compelling evidence of the presence of a recent nuclear starburst, revealed by the observations of a) the spectral features of high order Balmer absorption lines, b) the weak equivalent widths for CaIIK $λ$3933, CN $λ$4200, G-band $λ$4300 and MgIb $λ$5173, and c) the suggested UV stellar wind resonance lines (N V $λ$1240, Si IV $λ$1400 and C IV $λ$1550) in the IUE spectrum. Using the simple stellar population synthesis model, we find that in the nuclear 2" $\times$ 2" region, the contri…
We report the detection of 22 GHz water vapor emission toward the starburst galaxy NGC2146, made using the Effelsberg 100-m telescope. Interferometric observations with the Very Large Array (VLA) show that a part of the emission originates from two prominent sites of star formation that are associated with compact radio continuum sources, likely ultra-compact HII regions. It is concluded that the emission arises from the most luminous and distant water `kilomasers' detected so far. Our data increase the number of water maser detections in northern galaxies (Dec > -30 deg) with 100 micron IRAS …
We present XMM-Newton EPIC observations of the two nearby starburst merger galaxies NGC 3256 & NGC 3310. The broad-band (0.3-10 keV) integrated X-ray emission from both galaxies shows evidence of multi-phase thermal plasmas plus an underlying hard non-thermal power-law continuum. NGC 3256 is well-fit with a model comprising two MEKAL components (kT=0.6/0.9 keV) plus a hard power-law (Gamma=2), while NGC 3310 has cooler MEKAL components (kT=0.3/0.6 keV) and a harder power-law tail (Gamma=1.8). Chandra observations of these galaxies both reveal the presence of numerous discrete sources embedded …
TeV gamma-rays were recently detected from the nearby normal spiral galaxy NGC 253 (Itoh et al., 2002). Observations to detect the Cherenkov light images initiated by gamma-rays from the direction of NGC 253 were carried out in 2000 and 2001 over a total period of $\sim$150 hours. The orientation of images in gamma-ray--like events is not consistent with emission from a point source, and the emission region corresponds to a size greater than 10 kpc in radius. Here, detailed descriptions of the analysis procedures and techniques are given.
Thanks to the capabilities of modern telescopes and instrumentation, it is now possible to resolve single stars in external dwarf galaxies, provided they are bright enough. For galactic regions with deep enough photometry, detailed colour-magnitude diagrams are constructed, from which the star formation history and the initial mass function can be inferred by comparison with synthetic diagrams. Both the star formation history and the initial mass function are free parameters of galactic chemical evolution models. In this contribution we show how constraining them through high resolution photom…
We report the TeV gamma-ray observations of the nearby normal spiral galaxy NGC 253. At a distance of $\sim$2.5 Mpc, NGC 253 is one of the nearest starburst galaxies. This relative closeness, coupled with the high star formation rate in the galaxy, make it a good candidate TeV gamma-ray source. Observations were carried out in 2000 and 2001 with the CANGAROO-II 10 m imaging atmospheric Cerenkov telescope. TeV gamma-ray emission is detected at the $\sim 11σ$ level with a flux of $(7.8 \pm 2.5)\times 10^{-12} {\rm cm}^{-2} {\rm sec}^{-1}$ at energies $>$0.5 TeV. The data indicate that the emissi…
We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The detected Wolf-Rayet stars' colors and magnitudes are similar to Large Magellanic Cloud late-type WN stars. The physical origin of the other He II sources are discussed. We conclude that the equivalent of 51+/-19 WNL stars have been detected in NGC 1569, and we have estimated the total Wolf-Rayet population in NGC 1569 as 78+/-51. These numbe…
Only two of the twenty highly luminous starburst galaxies analyzed by Smith et al. exhibit circumnuclear rings of star formation. These galaxies provide a link between 10^11 L_sun systems and classical, less-luminous ringed systems. We report the discovery of a near-infrared counterpart to the nuclear ring of radio emission in NGC 7771. A displacement between the ~10 radio bright clumps and the ~10 near-infrared bright clumps indicates the presence of multiple generations of star formation. The estimated thermal emission from each radio source is equivalent to that of ~35000 O6 stars. Each nea…
(abridged) We present new N-body, hydrodynamical simulations of the interaction between the starburst galaxy NGC 7714 and its post-starburst companion NGC 7715, focusing on the formation of the collisional features, including: 1) the gas-rich star forming bridge, 2) the large gaseous loop (and stellar tails) to the west of the system, 3) the very extended HI tail to the west and north of NGC 7714, and 4) the partial stellar ring in NGC 7714. Our simulations confirm the results of earlier work that an off-center inclined collision between two disk galaxies is almost certainly responsible for th…
We have obtained long-slit spectra of NGC 253 in the J, H, K, and N bands, broadband images in the J, H, and Ks bands, narrowband images centered at the wavelengths of BrGamma and H2(1,0)S(1), and imaging spectroscopy centered on [NeII](12.8um). We use these data and data from the literature in a comprehensive re-assessment of the starburst in this galaxy. We derive the supernova rate from the strength of the infrared [FeII] lines. We find that most of the H2 infrared luminosity is excited by fluorescence in low density gas. We derive a strong upper limit of ~37,000K for the stars exciting the…
As part of a research of elusive AGN in a well defined sample of infrared selected galaxies (using BeppoSAX, Chandra, XMM-Newton and INTEGRAL data) we have observed with BeppoSAX the merging starburst system Arp 299. The broad-band (0.1-40 keV) coverage of this observation clearly reveals, for the first time in this system, the presence of a deeply buried AGN having an intrinsic luminosity of L(0.5-100 keV) = 1.9E43 cgs.
We present an imaging survey of the CO(1--0), HCN(1--0), and HCO$^+$(1--0) lines in the nearby Seyfert galaxies using the Nobeyama Millimeter Array and RAINBOW Interferometer. Some of the observed Seyfert galaxies including NGC 1068, NGC 1097, NGC 5033, and NGC 5194 exhibit strong HCN(1--0) emission on a few 100 pc scales. The observed HCN(1--0)/CO(1--0) and HCN(1--0)/HCO$^+$(1--0) line ratios in the Seyfert nuclei ($>$0.2 and $>$1.8, respectively) have never been observed in the central regions of nuclear starburst galaxies. On the other hand, the molecular line ratios in the nuclei of NGC 30…
We present an X-ray spectral study of the prototype far-infrared galaxy NGC6240 from ASCA. The soft X-ray spectrum (below 2 keV) shows clear signatures of thermal emission well described with a multi-temperature optically-thin plasma, which probably originates in a powerful starburst. Strong hard X-ray emission is also detected with ASCA and its spectrum above 3 keV is extremely flat with a prominent iron K line complex, very similar to that seen in the Seyfert 2 galaxy NGC1068 but about an order of magnitude more luminous [L(3-10keV)=1.4E42 erg/s]. The hard X-ray spectrum indicates that only …
We present high resolution H I 21 cm line, 20 cm radio continuum, and CO(1-0) line observations of the luminous infrared galaxy NGC 6670. NGC 6670 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear separation of ~16 kpc. While there are no optically identified tidal features and the molecular disks are not distorted much, we have detected a 90 kpc long H I tail which suggests that the galaxies are interacting and have already experienced at least one close encounter. Our observations suggest that the previous encounter between the galaxies had a large impa…
[ABRIDGED] We analyse near-infrared integral field spectroscopy of the central starburst region of NGC 1140, obtained at the Gemini-South telescope equipped with CIRPASS. Our ~1.45-1.67 um wavelength coverage includes the bright [Fe II] emission line, as well as high-order Brackett (hydrogen) lines. While strong [Fe II] emission, thought to originate in the thermal shocks associated with supernova remnants, is found throughout the galaxy, both Br 12-4 and Br 14-4 emission, and weak CO(6,3) absorption, is predominantly associated with the northern starburst region. The Brackett lines originate …
The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesis CO(1-0) observations of the post-starburst galaxy NGC 5195. CO(1-0) and HCN(1-0) observations of NGC 5195 using the Nobeyama 45 m telescope are also presented. High-resolution (1".9 x 1".8 or 86 pc x 81 pc at D = 9.3 Mpc) NMA maps show a strong concentration of CO emission toward the central a few 100 pc region of NGC 5195, despite the fact that the current massive star formation is suppressed there. The HCN-to-CO integrated intensity ratio on the brightness temperature scale, R_{HCN/CO}, is about 0.02 within the cent…
We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field and Planetary Camera 2 in both broadband (F300W, F547M and F814W) and narrowband (F487N and F656N) filters. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each star cluster, which provides constraints on the recent star formation histories of the host galaxies. We compare the star cluster populations in these dwarf starburst galaxies to those of the nuclear starbu…
We analyze extensive data on NGC1377 from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Within the category of nascent starbursts, that we previously selected by their infrared to radio continuum ratios in large excess of the average and their hot dust, NGC1377 has the largest infrared excess yet measured. Optical imaging reveals a morphological distortion suggestive of a recent accretion event. Infrared spectroscopy reveals a compact and opaque source dominated by a hot, self-absorbed continuum (tau ~ 20 in the 10 micron silicate band). We provide physical evidence against non-stellar …
We report the detection of 13CO(J=6-5) emission from the nucleus of the starburst galaxy NGC 253 with the redshift (z) and Early Universe Spectrometer (ZEUS), a new submillimeter grating spectrometer. This is the first extragalactic detection of the 13CO(J=6-5) transition, which traces warm, dense molecular gas. We employ a multi-line LVG analysis and find ~ 35% - 60% of the molecular ISM is both warm (T ~ 110 K) and dense (n(H2) ~ 10^4 cm^-3). We analyze the potential heat sources, and conclude that UV and X-ray photons are unlikely to be energetically important. Instead, the molecular gas is…
We report evidence for a recent burst of star formation located within 9 pc of the active nucleus of NGC 1097. The observational signatures of the starburst include UV absorption lines and continuum emission from young stars observed in a small-aperture HST spectrum. The burst is a few times 10^6 yr old, has a mass of approximately 10^6 solar masses, an observed luminosity of 1.5 x 10^7 solar luminosities and is obscured by approximately 3 visual magnitudes. The importance of this finding is two-fold: (1) the proximity of the starburst to the active nucleus and thus possible association with i…
We present preliminary results from a Hubble Space Telescope (HST) WFPC2 investigation of spatial and temporal distributions of star clusters in the clumpy irregular galaxy NGC 7673 and the starburst spirals NGC 3310 and Haro 1. We compare the spectral energy distributions of star clusters in the large clumps in NGC 7673 to model calculations of stellar clusters of various ages. We also propose that the presence of super star clusters in clumps seems to be a feature of intense starbursts.
Deep ROSAT PSPC and HRI observations of the nuclear starburst, UV flat spectrum spiral NGC6217 reveal a jet-like X-ray filament extending out 2.7' (18.8 kpc) to the SW of the galaxy. Radio images of NGC6217 show an extent in the same direction, giving further evidence for a one-sided X-ray jet interpretation of this feature. It's X-ray spectrum is harder than that of NGC6217 and the luminosity in the 0.5-2.0 keV band ~1.7 E39 erg\s. We compare our findings to parameters of other X-ray jets from other active galaxies. We also give positions of a total of 91 X-ray sources detected in the field t…
We present 5.2" x 2.6" resolution interferometry of CO J=1-0 emission from the starburst galaxy NGC 253. The high spatial resolution of these new data, in combination with recent high resolution maps of 13CO, HCN and near-infrared emission, allow us for the first time to link unambiguously the gas properties in the central starburst of NGC 253 with its bar dynamics. We confirm that the star formation results from bar-driven gas flows as seen in "twin peaks" galaxies. Two distinct kinematic features are evident from the CO map and position-velocity diagram: a group of clouds rotating as a solid…
We present high spatial resolution X-ray Chandra HRC and HST WFPC2 Halpha observations of the prototypical infrared luminous galaxy NGC6240. The central region of this system shows a remarkably complex morphology, with filaments and loops observed in the optical and X-rays. The total X-ray luminosity is dominated by the extended emission. Both nuclei are clearly detected in the HRC image and both appear to be extended. The energetics of the nuclei imply that the southern nucleus is the more plausible counterpart to the obscured AGN. The overall SED of the galaxy is in good agreement with a ble…
A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945 has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The study covers the frequency range from 82 GHz to 354 GHz and includes 80 transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are also presented. A large number of molecular species indicate the presence of a prominent high density interstellar gas component characterized by $n_{\rm H_2}\sim10^5$ cm$^{-3}$. Abundances of molecular species are calculated and compared with abundances observed toward the starburst galaxies NGC…
We present a comparison of X-ray point source luminosity functions of 3 starburst galaxies (the Antennae, M82, and NGC 253) and 4 non-starburst spiral galaxies (NGC 3184, NGC 1291, M83, and IC 5332). We find that the luminosity functions of the starbursts are flatter than those of the spiral galaxies; the starbursts have relatively more sources at high luminosities. This trend extends to early-type galaxies which have steeper luminosity functions than spirals. We show that the luminosity function slope is correlated with 60 micron luminosity, a measure of star formation. We suggest that the di…
The results of a 0.4-10.0 keV ASCA spectral analysis of a sample of low-luminosity AGN (LLAGN; M51, NGC 3147, NGC 4258), low-ionization nuclear emission line regions (LINERs; NGC 3079, NGC 3310, NGC 3998, NGC 4579, NGC 4594) and starburst galaxies (M82, NGC 253, NGC 3628 and NGC 6946) are presented. In spite of the heterogeneous optical classifications of these galaxies, the X-ray spectra are fit well by a ``canonical'' model consisting of an optically-thin Raymond-Smith plasma ``soft'' component with T ~ 7 x 10^6 K and a ``hard'' component that can be modeled by either a power-law with a phot…
NGC 1705 is one of the optically brightest and best studied dwarf galaxies. It appears to be in the late stage of a major starburst and contains a young super star cluster. Type II supernovae are therefore likely to have been a major effect in the recent evolution of this galaxy and are likely to have produced a superbubble whose affects on the low-density ambient interstellar medium can be ideally studied. ROSAT PSPC observations of this galaxy reveal two striking blobs of X-ray emission embedded in \Ha loops which can be interpreted as both sides of the upper plumes of the same superbubble. …
We present the result of 28 hours of observations of the nearby starburst galaxy NGC 253 with the H.E.S.S. detector in 2003. We find no evidence for very high energy gamma-ray emission from this object. Gamma-ray emission above 400 GeV from NGC 253 had been reported by the CANGAROO collaboration in 2002. From the H.E.S.S. data we derive upper limits on the flux above 300 GeV of 1.9 * 10^-12 photons cm^-2 s^-1 for a point-like source and 6.3 * 10^-12 photons cm^-2 s^-1 for a source of radius 0.5 degrees as reported by CANGAROO, both at a confidence level of 99%. These upper limits are inconsist…
We present 21cm HI line observations of the blue compact dwarf galaxy NGC1705. Previous optical observations show a strong outflow powered by an ongoing starburst dominating the HII morphology and kinematics. In contrast, most of the HI lies in a rotating disk. An extraplanar HI spur accounts for ~ 8% of the total HI mass, and is possibly associated with the HII outflow. The inferred mass loss rate out of the galaxy's core is significant ~ 0.2 - 2 M_sun/yr, but does not dominate the HI dynamics. Mass model fits to the rotation curve show that the dark matter (DM) halo is dominant at nearly all…
In order to examine the relative importance of powerful starbursts and Compton-thick AGNs in NGC 6240, we have obtained mid-infrared images and low-resolution spectra of the galaxy with sub-arcsecond spatial resolution using the Keck Telescopes. Despite the high spatial resolution (~200 pc) of our data, no signature of the hidden AGNs has been detected in the mid-infrared. The southern nucleus, which we show provides 80-90% of the total 8-25 um luminosity of the system, has a mid-infrared spectrum and a mid-/far-infrared spectral energy distribution consistent with starbursts. At the same time…
Earlier observations of NGC 1808 in various wavebands (X-ray, optical, near-infrared, radio) provided evidence for the existence of either a starburst or a Seyfert 2 nucleus. We here present the results of multiwavelength XMM-Newton and Chandra observations, which directly prove the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). The broad bandwidth of XMM-Newton allows us to show that the unresolved nuclear source in …
We have studied the physical conditions in the central 300 pc of the proto-typical starburst galaxy NGC 7714. Our analysis is based on ultraviolet spectroscopy with the HST+GHRS and ground-based optical observations.The data are interpreted using evolutionary models optimized for young starburst regions. The massive stellar population is derived in a self-consistent way using the continuum and stellar absorption lines in the ultraviolet and the nebular emission line optical spectrum. The central starburst has an age of about 4.5 Myr, with little evidence for an age spread. Wolf-Rayet features …
We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an optical spectrum, far-IR, Xray and radio fluxes) with new HST/WFPC2 images, near-IR photometry and K band spectroscopy. We use these data to constrain the young, the intermediate age and the old stellar populations in the central 330 pc of the starburst galaxy NGC 7714. [...] We find that the young burst responsible for the UV light is only a small part of an extended episode of enhanced star formation (SF) [...]. The mass of young and intermediate age stars thus formed equals at least 10% of the mass locked in pre-exi…
The modest extinction and reasonably face-on viewing geometry make the luminous IR galaxy NGC1614 an ideal laboratory for study of a powerful starburst. HST/NICMOS observations show: 1.) deep CO stellar absorption, tracing a starburst nucleus about 45 pc in diameter; 2.) surrounded by a ~600 pc diameter ring of supergiant HII regions revealed in Pa$α$ line emission; 3.) lying within a molecular ring indicated by its extinction shadow in H-K; 4.) all at the center of a disturbed spiral galaxy. The luminosities of the giant HII regions in the ring are extremely high, an order of magnitude bright…
