Star forming regions are expected to show linear proper motions due to the relative motion of the Sun with respect to the region. These proper motions appear superposed to the proper motions expected in features associated with mass ejection from the young stellar objects embedded in them. Therefore, it is necessary to have a good knowledge of the proper motions of the region as a whole in order to correctly interpret the motions associated with mass ejection. In this paper we present the first direct measurement of proper motions of the NGC 1333 star forming region. This region harbors one of the most studied Herbig-Haro systems, HH 7-11, whose exciting source remains unclear. Using VLA A configuration data at 3.6 cm taken over 10 years, we have been able to measure the absolute proper motions of four thermal sources embedded in NGC 1333. From our results we have derived the mean proper motions of the NGC 1333 star forming region to be mu(alpha)cos(delta) = 9 +- 1 mas/yr and mu(delta) = -10 +- 2 mas/yr. In this paper, we also discuss the possible implications of our results in the identification of the outflow exciting sources.
We examine the X-ray point source population and 2-10 keV luminosity for two galaxies with high star formation rates (SFRs), NGC 4194 and NGC 7541. The X-ray point source luminosity function (XLF) for these two galaxies is consistent with the XLF found by Grimm et al. (2003) for a sample of star-forming galaxies. Combining our results with a sample of galaxies with SFRs above 1 solar mass/year, we find that the number of X-ray point sources above a luminosity of 2E38 erg/s is N = (1.8 +/- 0.4) SFR/(solar mass/year). This number is lower than previously inferred by Grimm et al. based on a sampl…
We report trigonometric parallaxes for the sources NGC 7538 and Cep A, corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04] kpc, respectively. The distance to NGC 7538 is considerably smaller than its kinematic distance and places it in the Perseus spiral arm. The distance to Cep A is also smaller than its kinematic distance and places it in the Local arm or spur. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star forming regions. We find significant deviations from circular Galactic orbits for t…
We present high resolution (3" - 5") observations of CO(1-0) and HCN(1-0) emission from the circumnuclear star forming ring in the barred spiral galaxy NGC 6951, a host of a type-2 Seyfert, using the Nobeyama Millimeter Array and 45 m telescope. We find that most of the HCN emission is associated with the circumnuclear ring, where vigorous star formation occurs. The HCN to CO integrated intensity ratio is also enhanced in the star forming ring; the peak value of HCN/CO ratio is 0.18, which is comparable to the ratio in the starbursts NGC 253 and M82. The formation mechanism of dense molecular …
A deep 75 ks {\it Chandra} ACIS--I data of NGC 2024 was analyzed, aiming at a search for diffuse X-ray emission in this one of the most nearby (415 pc) massive star-forming regions. After removing point sources, an extended emission was detected in the central circular region with a radius of 0.5 pc. It is spatially associated with the young massive stellar cluster. Its X-ray spectrum exhibits a very hard continuum ($kT>8$ keV) and a sign of He-like Fe K$_α$ line with the 0.5--7 keV absorption corrected luminosity of 2$\times10^{31}$ \ergs. Undetected faint point sources, estimated from the lu…
We present the results of detailed surface photometry of NGC 3808B and NGC 6286 - two spiral galaxies with possibly forming ring-like structures rotating around major axes of the galaxies. The formation of rings in NGC 3808B and NGC 6286 being accompanied by accretion of matter on galactic disk results in some interesting gasdynamical and stellardynamical effects in these galaxies. One can note, for instance, peculiar rotation curve of NGC 3808B gaseous disk; strong infrared and H-alpha emission from the galaxies; bending and flaring stellar disks in both galaxies. Our observations clearly ill…
The magnetic field is believed to play a crucial role in the process of star formation. From the support it provides during the initial collapse of molecular clouds to the creation of strong collimated jets responsible for large mass losses, current theories predict its importance in many different stages during the formation of stars. Here we report on observational evidence which tests one aspect that can be inferred from these theories: the alignment between the local magnetic field and collimated bipolar outflows in such environments. There is good evidence of an alignment in the case of N…
It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. We investigate the population of NGC1893, a young cluster ~3-4 Myr in the outer part of the Galaxy (galactic radius >11 Kpc), to explore the effects of environmental conditions on star forming regions. We present infrared observations acquired using the IRAC camera onboard the Spitzer Space Telescope and analyze the color-color d…
New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps of the NGC7129 star forming region are presented, complemented by C18O J=3-2 spectra at several positions within the mapped region. The maps include the Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and several other pre-stellar sources embedded within the molecular ridge. The SCUBA maps help us understand the nature of the pre-main sequence stars in this actively star forming region. A deeply embedded submillimeter source, SMM2, not clearly seen in any earlier data set, is shown to be a pre-…
We present a preliminary study of the star formation distribution within three Virgo Cluster galaxies using the 24 micron Spitzer observations from the Spitzer Survey of Virgo (SPITSOV) in combination with H-alpha observations. The purpose of our study is to explore the relationship between the star formation distribution within galaxies and the type (and phase) of interactions experienced within the cluster environment. Neither highly-obscured star formation nor strongly enhanced star-forming regions along the leading edges of galaxies experiencing ICM-ISM interactions were found. However, ve…
Deep F555W and F814W Hubble Space Telescope ACS images are the basis for a study of the present day mass function (PDMF) of NGC346, the largest active star forming region in the Small Magellanic Cloud (SMC). We find a PDMF slope of Gamma=-1.43+/-0.18 in the mass range 0.8-60 Mo, in excellent agreement with the Salpeter Initial Mass Function (IMF) in the solar neighborhood. Caveats on the conversion of the PDMF to the IMF are discussed. The PDMF slope changes, as a function of the radial distance from the center of the NGC 346 star cluster, indicating a segregation of the most massive stars. Th…
We present sub-arcsecond (FWHM ~ 0".7), NIR JHKs-band images and a high sensitivity radio continuum image at 1280 MHz, using SIRIUS on UH 88-inch telescope and GMRT. The NIR survey covers an area of ~ 24 arcmin^2 with 10-sigma limiting mags of ~ 19.5, 18.4, and 17.3 in J, H, and Ks-band, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of NGC 7538 star forming region. We construct JHK CC and J-H/J and H-K/K CM diagrams to identify YSOs and to estimate their masses. Based on these CC and CM diagrams, we identified a rich population of YSOs (Class I and Cl…
The problem of star formation within the interacting pair NGC7733/34 has been studied, based on the UBVRI photometry of the source. The distribution of the colors of selected regions within the galaxies is used to infer an estimate for the age distribution of the star forming regions. The results seem to indicate the presence of numerous extended young star-forming regions in the disk of one of the two galaxies, NGC 7733, with ages in the range of $10^6$--$10^8$ yr. However, there exist no evidence for any violent star formation activity, in the past $10^8$ yr, in the nuclei of the two galaxie…
We analyze {\it Spitzer} and Magellan observations of a star forming core near IRS-2 in the young cluster NGC 2264. The submillimeter source IRAS 12 S1, previously believed to be an intermediate mass Class 0 object is shown to be a dense collection of embedded, low mass stars. We argue that this group of stars represents the fragmenting collapse of a dense, turbulent core, based on a number of indicators of extreme youth. With reasonable estimates for the velocity dispersion in the group, we estimate a dynamical lifetime of only a few x 10$^{4}$ years. Spectral energy distributions of stars in…
We present a spectrophotometric study of circumnuclear star forming regions (CNSFR) in the early type spiral galaxies: NGC 2903, NGC 3351 and NGC 3504, all of them of over solar metallicity according to standard empirical calibrations. A detailed determination of their abundances is made after careful subtraction of the very prominent underlying stellar absorption. It is found that most regions show the highest abundances in HII region-like objects. The relative N/O and S/O abundances are discussed. In is also shown that CNSFR, as a class, segregate from the disk HII region family, clustering …
NGC 2264 is a young Galactic cluster and the dominant component of the Mon OB1 association lying approximately 760 pc distant within the local spiral arm. The cluster is hierarchically structured, with subclusters of suspected members spread across several parsecs. Associated with the cluster is an extensive molecular cloud complex spanning more than two degrees on the sky. Star formation is ongoing within the region as evidenced by the presence of numerous embedded clusters of protostars, molecular outflows, and Herbig-Haro objects. The stellar population of NGC 2264 is dominated by the O7 V …
We study the initial mass function (IMF) of one of the most massive Galactic star-forming regions NGC 3603 to answer a fundamental question in current astrophysics: is the IMF universal, or does it vary? Using our very deep, high angular resolution JHKsL' images obtained with NAOS-CONICA at the VLT at ESO, we have successfully revealed the stellar population down to the subsolar mass range in the core of the starburst cluster. The derived IMF of NGC 3603 is reasonably fitted by a single power law with index Gamma ~ -0.74 within a mass range of 0.4 - 20 Msun, substantially flatter than the Salp…
The northern Milky Way in the constellation of Cepheus (100 deg < l < 120 deg; 0 deg < b < 20 deg) contains several star forming regions. The molecular clouds of the Cepheus Flare region at b > 10 deg, are sites of low and intermediate mass star formation located between 200 and 450 pc from the Sun. Three nearby OB associations, Cep OB2, Cep OB3, Cep OB4, located at 600-800 pc, are each involved in forming stars, like the well known high mass star forming region S140 at 900 pc. The reflection nebula NGC 7129 around 1 kpc harbors young, compact clusters of low and intermediate mass stars. The g…
We report observations of dust continuum emission at 1.2 mm toward the star forming region NGC 6334 made with the SEST SIMBA bolometer array. The observations cover an area of $\sim 2$ square degrees with approximately uniform noise. We detected 181 clumps spanning almost three orders of magnitude in mass (3\Msun$-6\times10^3$ \Msun) and with sizes in the range 0.1--1.0 pc. We find that the clump mass function $dN/d\log M$ is well fit with a power law of the mass with exponent -0.6 (or equivalently $dN/dM \propto M^{-1.6}$). The derived exponent is similar to those obtained from molecular line…
We have studied the unbarred Sb galaxy with a nuclear star-forming ring, NGC 7742, by means of 2D spectroscopy, long-slit spectroscopy, and imaging, and have compared the results with the properties of another galaxy of this type, NGC 7217, which is studied by us earlier. Both galaxies have many peculiar features in common: each has two global exponential stellar disks with different scalelengths, each possesses a circumnuclear inclined gaseous disk with a radius of 300 pc, and each has a global counterrotating subsystem, gaseous one in NGC 7742 and stellar one in NGC 7217. We suggest that pas…
(Context) When a galaxy acquires material from the outside, it is likely that the resulting angular momentum of the accreted material is decoupled from that of the pre-existing galaxy. The presence of stars counter-rotating with respect to other stars and/or gas represents an extreme case of decoupling. (Aims) NGC5719, an almost edge-on Sab galaxy with a prominent skewed dust lane, shows a spectacular on-going interaction with its face-on Sbc companion NGC5713. Observations of such interacting systems provide insight into the processes at work in assembling and reshaping galaxies. (Methods) St…
We present submillimeter polarimetry at 850 micron toward the filamentary star-forming region associated with the reflection nebulosity NGC 2068 in Orion B. These data were obtained using the James Clerk Maxwell Telescope's SCUBA polarimeter. The polarization pattern observed is not consistent with that expected for a field geometry defined by a single mean field direction. There are three distinct distributions of polarization angle, which could represent regions of differing inclination and/or field geometry within the filamentary gas. In general, the polarization pattern does not correlate …
We present results from the cross-correlation of the spectroscopic atlas of Ho etal (1995) with the ROSAT All-Sky Survey Bright Source Catalogue, in an attempt to understand the X-ray emission mechanisms in nearby galaxies. The resulting sample of 45 galaxies consists predominantly of AGN. However, there are several starforming galaxies spanning a wide range of X-ray luminosities (~10^{38} - 10^{42} erg s^{-1}). We have analyzed ROSAT and ASCA data for the two most luminous star-forming galaxies, namely NGC3310 and NGC3690. We find that their 0.1-10 keV X-ray spectra can be fitted by a soft th…
We discuss BeppoSAX observations and archive ASCA data of NGC 7679, a nearby, nearly face-on SB0 galaxy in which starburst and AGN activities coexist. The X-ray observations reveal a bright (L_{0.1-50 keV} \sim 2.9 \times 10^{43} erg s^{-1}) and variable source having a minimum observed doubling/halving time scale of \sim 10 - 20 ksec. A simple power law with photon index of Γ\sim 1.75 and small absorption (N_H < 4\times 10^{20} cm^{-2}) can reproduce the NGC 7679 spectrum from 0.1 up to 50 keV. These X-ray properties are unambiguous signs of Seyfert 1 activity in the nucleus of NGC 7679. The …
We present a photometric study of the star-forming region NGC 346 and its surrounding field in the Small Magellanic Cloud, using data taken with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). The data set contains both short and long exposures for increased dynamic range, and photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected almost 100,000 stars over a magnitude range of V ~ 11 to V ~ 28 mag, including all stellar types from the most massive young stars to faint lower main sequence and pre-main sequence stars.…
Context: The earliest phases of massive star formation are currently much debated. Aims. In an effort to make progress, we took a census of Class0-like protostellar dense cores in the NGC 3576 region, one of the nearest and most luminous embedded sites of high-mass star formation in the Galaxy. Methods: We used the P-ArTeMiS bolometer camera on the APEX telescope to produce the first 450-micron dust continuum map of the filamentary dense clump associated with NGC 3576. Results: Combining our 450-micron observations with existing data at other wavelengths, we have identified seven massive proto…
Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria,to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the Li I 6707.8 Angstroms line to derive radial and rotational velocities, bina…
V,R,I continuum bands and Halpha + [NII] photometry for circumnuclear star forming regions (CNSFR) is presented, for galaxies with different kinds of nuclear activity: NGC 7469 (Sy 1), NGC 1068 (Sy 2), NGC 7177 (LINER) and NGC 3310 (Starburst). Their Halpha luminosities (0.02 - 7x10**40 erg/s; uncorrected for internal extinction), are comparable to those observed in other galaxies. No systematic differences in the broad band colours are found for the CNSFR in the different galaxies, except for those in NGC 3310 which are considerably bluer, partially due to a younger stellar population. Using …
We present the first interferometric polarization maps of the NGC2024 FIR5 molecular core obtained with the BIMA array at approximately 2 arcsec resolution. We measure an average position angle of -60+-6 degrees in the main core of FIR5 and 54+-9 degrees in the eastern wing of FIR5. The morphology of the polarization angles in the main core of FIR5 suggests that the field lines are parabolic with a symmetry axis approximately parallel to the major axis of the putative disk in FIR5, which is consistent with the theoretical scenario that the gravitational collapse pulled the field lines into an …
We have conducted deep JHKs imaging polarimetry of a ~8' x 8' area of the NGC 2071 star forming region. Our polarization data have revealed various infrared reflection nebulae (IRNe) associated with the central IR young star cluster NGC2071IR and identified their illuminating sources. There are at least 4 IRNe in NGC2071IR and several additional IRNe are identified around nearby young stars in the same field-of-view. Each illuminating source coincides with a known near-IR source except for IRS3, which is only a part of IRN2 and is illuminated by the radio source 1c. Aperture polarimetry of eac…
High-mass star-forming regions are known to have a rich molecular spectrum from many species. Some of the very highly excited lines are emitted from very hot and dense gas close to the central object(s). The physics and chemistry of the inner cores of two high mass star forming regions, NGC6334(I) and G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX telescope provide spectra which sample many molecular lines at high excitation stages. Partial spectral surveys were obtained, the lines were identified, physical parameters were determined through fitting of the spectra…
We present Spitzer/IRAC photometry on the star-forming HII region N 90, related to the young stellar association NGC 602 in the Small Magellanic Cloud. Our photometry revealed bright mid-infrared sources, which we classify with the use of a scheme based on templates and models of red sources in the Milky Way, and criteria recently developed from the Spitzer Survey of the SMC for the selection of candidate Young Stellar Objects (YSOs). We detected 57 sources in all four IRAC channels in a 6.2' x 4.8' field-of-view centered on N 90; 22 of these sources are classified as candidate YSOs. We compar…
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 conducted wide-field JHKs imaging polarimetry toward NGC 2024. We found a prominent and extended polarized nebula over NGC 2024, and constrained the location of illuminating source of the nebula through the analysis of polarization vectors. A massive star, IRS 2b, is located in the center of the symmetric vector pattern. Five small polarized nebulae associated with YSOs are discovered on our polarization images. These nebulae are responsible for the structures of circumstellar matter that produce strongly polarized light through dust scattering. For the point-like sources, we performed soft…
Using the imaging polarimeter for the Submillimeter Common User Bolometric Array at the James Clerk Maxwell Telescope, we have detected polarized thermal emission at 850 micron from dust toward three star-forming core systems in the Orion B molecular cloud: NGC 2071, NGC 2024 and LBS 23N (HH 24). The polarization patterns are not indicative of those expected for magnetic fields dominated by a single field direction, and all exhibit diminished polarization percentages toward the highest intensity peaks. NGC 2024 has the most organized polarization pattern which is centered consistently along th…
We present XMM-Newton observations of NCG891, a nearby edge-on spiral galaxy. We analyse the extent of the diffuse emission emitted from the disk of the galaxy, and find that it has a single temperature profile with best fitting temperature of 0.26 keV, though the fit of a dual-temperature plasma with temperatures of 0.08 and 0.30 keV is also an acceptable fit. There is a considerable amount of diffuse X-ray emission protruding from the disk in the NW direction out to approximately 6 kpc. We analyse the point source population using a Chandra observation, using a maximum likelihood method to f…
(Abridged) We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC 2403, NGC 3031, NGC 5194, and NGC 6946). Using Spitzer MIPS imaging and WSRT radio continuum data, observed as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS), we are able to probe variations in the logarithmic 24mu/22cm (q_24) and 70mu/22cm (q_70) surface brightness ratios across each disk at sub-kpc scales. We find general trends of decreasing q_24 and q_70 with declining surface brightness and with increasing radius. The residual …
We have mapped the water maser emission associated with the infrared centers IRS1 and IRS3 of the NGC 2071IR star forming region at four epochs over ~4 months with the Very Long Baseline Array (VLBA). We detected 269 maser features with ~1 km/sec linewidths and measured 30 proper motions. In each infrared center, the water maser emission appears to trace parts of a protostellar disk and collimated outflow. The disk components are ~9 and ~17 AU long, in IRS3 and IRS1 respectively, and ~2 AU wide. They are identified as disks by their compact size, elongation parallel to the direction of known I…
Broad-band near-infrared images are used to probe the photometric properties of the brightest asymptotic giant branch (AGB) stars within 2 arcminutes of the centers of the dwarf elliptical galaxies NGC 147, NGC 185, and NGC 205. Based on the peak brightness and color of the M giant sequences, ages of 1 Gyr and 0.1 Gyr are predicted for the most recent significant star forming events in NGC 185 and NGC 205, respectively. The brightest AGB stars in NGC 147 indicate that the most recent significant star-forming activity in that galaxy occured \~3 Gyr in the past. The specific frequency of C stars…
(abridged)We present the observations of the pair of interacting galaxies NGC6285/86 carried out with the 6m SAO RAS telescope by using 1D and 2D spectroscopy. The observations of NGC6286 with a long-slit spectrograph (UAGS) near the H-alpha line revealed the rotation of the gaseous disk around an axis offset by 5''-7'' from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this gala…
The bright Magellanic irregular galaxy NGC 4449 was observed by the Ultraviolet Imaging Telescope (UIT) during the Astro-2 Spacelab mission in March, 1995. Far ultraviolet (FUV) images at a spatial resolution of ~3 arcsec show bright star-forming knots that are consistent with the general optical morphology of the galaxy and are often coincident with bright H II regions. Comparison of FUV with H-alpha shows that in a few regions, sequential star formation may have occurred over the last few Myr. The bright star forming complexes in NGC 4449 are superposed on a smooth, diffuse FUV background th…
The prominent interacting galaxy pair NGC 4038/9 contains many active star-forming regions and is continuously forming new star clusters. We present a self-consistent n-body model for this system which includes an SPH gas component. The model qualitatively explains the apparent concentration of gas in the so-called overlap region between the two nuclei as a bridge of gas connecting the two galaxies. Projected on the sky, the bridge appears as a dense spot of gas. We discuss some implications for the evolution of Ultra-luminous infrared galaxies.
We present ISOCAM images (1.5"/px) in the LW2 (6.75 microns) and LW3 (15 microns) broad band filters of the circumnuclear starburst of NGC 4321 (M 100). A detailed comparison with the emission at other wavelengths (U, B, Halpha, and CO) is also presented. The nature and intensity of the mid-infrared emission is shown to be remarkably different from one star forming region to the next. For instance, star forming regions at the ends of the nuclear bar may contain enshrouded Wolf-Rayet stars.
The nucleus of the nearby galaxy, NGC 1097, is known to host a young, compact (r < 9 parsec) nuclear star cluster as well as a low-luminosity active galactic nucleus (AGN). It has been suggested both that the nuclear stellar cluster is associated with a dusty torus, and that low-luminosity AGN like NGC 1097 do not have the torus predicted by the unified model of AGN. To investigate these contradictory possibilities we have acquired Gemini/T-ReCS 11.7 micron and 18.3 micron images of the central few hundred parsecs of this galaxy at < 45 parsec angular resolution, in which the nucleus and spect…
We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC~2403, NGC~3031, NGC~5194, and NGC~6946). Using {\it Spitzer} MIPS imaging and WSRT radio continuum data, we are able to probe variations in the logarithmic 70~$μ$m/22~cm ($q_{70}$) flux density ratios across each disk at sub-kpc scales. We find general trends of decreasing $q_{70}$ with declining surface brightness and with increasing radius. We also find that the dispersion in $q_{70}$ within galaxies is comparable to what is measured {\it globally} among…
We present large-area maps of the CO J=3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J=1-0, 24 micron, and Halpha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC4321, and NGC 4569), we obtain molecular gas masses of 7E8-3E9 Msun and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J=3-2 line is a better tracer of the dense star forming molecular gas than the CO J…
J, H, and K' images obtained with the Canada-France-Hawaii Telescope adaptive optics system are used to investigate the star-forming histories of the central regions of the Sc galaxies NGC 247 and NGC 2403. The brightest resolved red stars within 15 arcsec of the nucleus of each galaxy are red supergiants, indicating that the central few hundred parsecs of these galaxies experienced star formation within the last ~ 0.1 Gyr. However, when averaged over Gyr time scales, the star-forming histories of the inner disks of these galaxies have been remarkably similar, as expected if the long-term evol…
We present the first high spatial resolution X-ray study of the massive star forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large HII region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and Initial Mass Function and detect ~800 X-ray sources with a limiting sensitivity of 10^{30} ergs s^{-1}; this provides the first reliable probe of the r…
We report single-dish multi-transition measurements of the 12^CO, HCN, and HCO^+ molecular line emission as well as HNC J=1-0 and HNCO in the two ultraluminous infra-red galaxies Arp220 and NGC6240. Using this new molecular line inventory, in conjunction with existing data in the literature, we compiled the most extensive molecular line data sets to date for such galaxies. The many rotational transitions, with their different excitation requirements, allow the study of the molecular gas over a wide range of different densities and temperatures with significant redundancy, and thus allow good c…
HST WFPC2 images are presented that span the inner 19 kpc diameter of the edge-on spiral galaxy NGC 3079; they are combined with ground-based Halpha+[N II] Fabry-Perot spectra and VLA images of radio polarization vectors and rotation measures. Ionized gas filaments within 9 kpc diameter project ~3 kpc above the disk, with the brightest forming the 1 kpc diameter superbubble. They are often resolved into strands ~0."3 (25 pc) wide which emerge from the nuclear CO ring as five distinct gas streams with velocity gradients and dispersions of hundreds of km/s. One stream flows for 250 pc and aligns…
We report the detection of water maser emission from four nearby galaxies hosting ultradense HII (UDHII) regions, He 2-10, the Antennae galaxies (NGC 4038/4039), NGC 4214, and NGC 5253, with the Green Bank Telescope. Our detection rate is 100%, and all of these H2O "kilomasers" (L(H2O) < 10 L_sun) are located toward regions of known star formation as traced by UDHII regions and bright 24 micron emission. Some of the newly discovered H2O masers have luminosities 1-2 orders of magnitude less than previous extragalactic studies and the same order of magnitude as those typical of Galactic massive …
We have studied the candidate optical counterparts and the stellar population in the star-forming complex around a bright ULX in NGC4559, using HST/WFPC2, XMM-Newton/OM, and ground-based data. We find that the ULX is located near a small group of OB stars. The brightest point source in the Chandra error circle is consistent with a single blue supergiant of mass ~ 20 M_sun and age ~ 10 Myr. A few other stars are resolved inside the error circle: mostly blue and red supergiants with masses ~ 10-15 M_sun and ages ~ 20 Myr. This is consistent with the interpretation of this ULX as a black hole (BH…
Aims: NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its HII regions, to elucidate the conditions under which HII regions form and their spatial relation to the principal dynamical features of the bar. Methods: We obtained BVRKs and Halpha photometry of the HII regions of the bar in NGC 1530. Broad-band integrated colours and Halpha equivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar. Resu…
We performed a high-sensitivity search for galaxy-scale magnetic fields by radio polarimetry at 10.45GHz and 4.85GHz with the Effelsberg 100m radio telescope, accompanied by Halpha imaging, for the two Local Group irregular galaxies IC10 and NGC6822. Their star-forming bodies are small and rotate slowly. IC10 is known to have a very high star-forming activity, resembling blue compact dwarfs, while NGC6822 has a low overall star-formation level. Despite very different current star formation rates, our Halpha imaging revealed a large web of diffuse Halpha filaments and shells in both IC10 and NG…
We present new high spatial resolution HST/ACS imaging of NGC 1140 and high spectral resolution VLT/UVES spectroscopy of its central star-forming region. The central region contains several clusters, the two brightest of which are clusters 1 and 6 from Hunter, O'Connell & Gallagher, located within star-forming knots A and B, respectively. Nebular analysis indicates that the knots have an LMC-like metallicity of 12 + log(O/H) = 8.29 +/- 0.09. According to continuum subtracted H alpha ACS imaging, cluster 1 dominates the nebular emission of the brighter knot A. Conversely, negligible nebular emi…
Images obtained with the CFHTIR camera on the Canada-France-Hawaii Telescope are used to investigate the near-infrared photometric properties of the star-forming M81 group galaxy NGC 3077. The spectral-energy distribution (SED) of the near-infrared light within 10 arcsec of the nucleus is consistent with the 2um light being dominated by hot young (log(t_{yr}) < 6.8) stars reddened by A_V = 3 - 4, with A_V < 8 mag in some regions. A population like that near the center of NGC 205 likely contributes only a modest fraction of the light near 2um. A number of candidate star clusters are detected in…
Chandra ACIS-I data of the molecular cloud and HII region complex NGC 6334 were analyzed. The hard X-ray clumps detected with ASCA (Sekimoto et al. 2000) were resolved into 792 point sources. After removing the point sources, an extended X-ray emission component was detected over a 5x9 pc2 region, with the 0.5-8 keV absorption-corrected luminosity of 2x10^33 erg/s. The contribution from faint point sources to this extended emission was estimated as at most ~20 %, suggesting that most of the emission is diffuse in nature. The X-ray spectrum of the diffuse emission was observed to vary from plac…
We present FUSE spectroscopy and supporting data for star-forming regions in nearby galaxies, to examine their massive-star content and explore the use of abundance and population indicators in this spectral range for high-redshift galaxies. New far-ultraviolet spectra are shown for four bright H II regions in M33 (NGC 588, 592, 595, and 604), the H II region NGC 5461 in M101, and the starburst nucleus of NGC 7714, supplemented by the very-low-metallicity galaxy I Zw 18. In each case, we see strong Milky Way absorption systems from H2, but intrinsic absorption within each galaxy is weak or und…
We have studied an ultraluminous X-ray source (ULX) in NGC 4559 with XMM-Newton, and its peculiar star-forming environment with HST/WFPC2. The X-ray source is one of the brightest in its class (L_x ~ 2 x 10^{40} erg/s). Luminosity and timing arguments suggest a mass >~ 50 M_sun for the accreting black hole. The ULX is located near the rim of a young (age < 30 Myr), large (diameter ~ 700 pc) ring-like star forming complex possibly triggered by the impact of a dwarf satellite galaxy through the gas-rich outer disk of NGC 4559. We speculate that galaxy interactions (including the infall of high-v…
NGC 6611 is the massive young cluster (2-3 Myr) that ionises the Eagle Nebula. We present very deep photometric observations of the central region of NGC 6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down to I ~ 26 mag. We construct the Initial Mass Function (IMF) from ~ 1.5 Msun well into the brown dwarf regime (down to ~ 0.02 Msun). We have detected 30-35 brown dwarf candidates in this sample. The low-mass IMF is combined with a higher-mass IMF co…
We report results of a Chandra observation of the X-ray luminous star-forming galaxy Arp299 (NGC3690/IC694). We detect 18 discrete X-ray sources with luminosities above ~10^39 erg\s (0.5-8.0 keV band), which contribute ~40% of the total galactic emission in this band. The remaining emission is associated with a diffuse component spatially coincident with regions of widespread star-formation. We detect X-ray emission from both nuclei. One of the discrete sources within the complex nuclear region of NGC 3690 is found to have a very hard spectrum and therefore we associate it with the origin of t…
