Search

We present spatially resolved kinematics of the interstellar Na i D λλ5890,5896 doublet absorption and CO (1→0) emission across the inner ∼2× 1 kpc of the disk of M82. These data were obtained with the DensePak IFU on the WIYN telescope and the Caltech Owens Valley Radio Observatory (OVRO) millimetre array. By measuring the Na i and CO (and Hα kinematics from a previous study) at the same spatial resolution, and employing the same line fitting method, we have been able to make meaningful comparisons between the ionized, neutral and molecular gas phases. We detect a component of the Na i line throughout the inner disk with velocities that are forbidden by the known galactic rotation. We interpret this as originating in counterrotating or perhaps inflowing material. In the southern plume, we find clear evidence of entrained CO gas with kinematics consistent with that of Hα. On the northern side, the CO kinematics appear to trace more static clouds in the inner halo that could be pre-existing or tidal in origin. We find no evidence that Na i absorption is kinematically associated with the outflow. We conclude that a combination of lack of velocity resolution and confusion of due to the high inclination of the system is acting to prevent detection. Thus, in the search for neutral outflows from galaxies, the signature high velocity components may easily be missed in observations at low spectral resolution and/or sensitivity, and particularly so in highly inclined systems.

We report the discovery of a ring-like cluster complex in the starburst galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear ring-like distribution of star clusters around a central object. It is located in one of the tidal streams which surround the galaxy. NGC 2146 is part of the Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data has added critical information to the available archival Hubble Space Telescope imaging set of NGC 2146, allowing us to determine ages, masses, and extinctions of the clusters in the Ruby Ring. These properties have then been used to investigate the formation of this extraordinary system. We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring. The latter are about 4 Myr younger than the central cluster, which has an age of 7 Myr. This result is supported by the H alpha emission which is strongly coincident with the ring, and weaker at the position of the central cluster. From the derived total H alpha luminosity of the system we constrain the star formation rate density to be quite high, e.g. ~ 0.47 Msun/yr/kpc^2. The Ruby Ring is the product of an intense and localised burst of star formation, similar to the extended cluster complexes observed in M51 and the Antennae, but more impressive because is quite isolated. The central cluster contains only 5 % of the total stellar mass in the clusters that are determined within the complex. The ring-like morphology, the age spread, and the mass ratio support a triggering formation scenario for this complex. We discuss the formation of the Ruby Ring in a "collect & collapse" framework. The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster, making the Ruby Ring an interesting case of triggered star formation.

We present VLT/VIMOS-IFU emission-line spectroscopy of a volume limited sample of 18 southern ULIRGs selected with z 2000 km/s over spatially extended regions in both the recombination and forbidden lines; in two of these three, they are associated with a known Sy2 nucleus. Eight galaxies have clear rotating gaseous disks, and for these we measure rotation velocities, virial masses, and calculate Toomre Q parameters. We find radial gradients in the emission line ratios in a significant number of systems in our study. We attribute these gradients to changes in ionizing radiation field strength, most likely due to an increasing contribution of shocks with radius. We conclude with a detailed discussion of the results for each individual system, with reference to the existing literature. Our observations demonstrate that the complexity of the kinematics and gas properties in ULIRGs can only be disentangled with high sensitivity, spatially resolved IFU observations. Many of our targets are ideal candidates for future high spatial resolution follow-up observations.

It has long been known that the starburst in M 82 drives a large-scale bipolar superwind, carrying large volumes of material (in the form of hot, warm and cool gas and dust) out of the disk plane. However, what is not known is exactly how the hundreds of catalogued super star clusters power the outflow, and how it becomes so structured and collimated. Here I will present part of the most comprehensive set of spectroscopic integral field observations ever made of the starburst clumps and outflow in M 82. I will describe how we have mapped in detail the spatial variation of Hα kinematics, gas density and excitation from the wind roots out into the halo, and how these compare to features seen in recent high resolution imaging campaigns. These observations will be used to address questions such as: how does the 2D variation of gas kinematics evolve from the core out into the halo? Our spectra indicate evidence for the sites of mass-loading – where is it occurring within the wind?

[abridged] We present optical integral field unit observations (VLT/VIMOS-IFU and WIYN/SparsePak), and associated archival deep Halpha imaging (ESO 2.2m WFI), of the nearby starburst galaxy NGC253. With VIMOS we observed the nuclear region and southern superwind outflow in detail with five pointings, and with SparsePak we observed two partially overlapping regions covering the central disk and northern halo. The high signal-to-noise of the data and spectral resolution (80-90 km/s) enable us to accurately decompose the emission line profiles into multiple components. The combination of these datasets, together with information available in the literature, has allowed us to study the starburst-driven superwind in great detail. We investigate the known minor axis outflow cone, which is well-defined in the Halpha imaging and kinematics between r=280-660 pc from the nucleus. Kinematic modelling indicates a wide opening angle (~60 deg), an inclination consistent with the disk, and deprojected outflow speeds of a few 100 km/s that increase with distance above the plane. The [NII]/Halpha and [SII]/Halpha line ratio maps imply that a significant fraction of the wind optical emission lines arise from shocked gas. From the kinematics, the cone appears partially closed in at least one place, and very broad Halpha line widths (>400 km/s FWHM) suggest there is material filling the cone in some regions. Extrapolation of the cone to its apex shows it is not centred on the starburst nucleus, suggesting the wind is deflected and collimated by the dense circumnuclear material. We discuss the implications of these findings on our understanding of the origins and evolution of the superwind. The lack of an obvious connection between the inner (r

It has been claimed in the past that in low-metallicity Blue Compact Dwarf (BCDs) galaxies, the N/O value is independent of metallicity (O/H ratio), implying the need to invoke a primary production of nitrogen in intermediate-mass stars, in addition to the secondary nitrogen produced from the CNO cycle in high-mass stars. In order to better understand this controversial issue we undertook an integral field spectroscopic study of the nebular gas within a sample of BCDs previously thought to have anomalously high N/O values. Here we present the results of this study for 3 BCDs: two with anomalous N/O values (Mrk 996 and UM 420) and one with more normal N/O values (UM 462). We describe in detail how we derived the physical conditions (Te, Ne) as a function of position within the galaxy, and as a consequence, how this revealed both revised metallicities and normal N/O ratios and uncovered one of the first clear evidences of nitrogen self-enrichment of an H ii region from WR stars.

We present optical/near-IR IFU observations of a gas pillar in the Galactic HII region NGC 6357 containing the young open star cluster Pismis 24. These observations have allowed us to examined in detail the gas conditions of the strong wind-clump interactions taking place on its surface. We identify the presence of a narrow (~20 km/s) and broad (50-150 km/s) component to the H_alpha emission line, where the broadest broad component widths are found in a region that follows the shape of the eastern pillar edge. These connections have allowed us to firmly associate the broad component with emission from ionized gas within turbulent mixing layers on the pillar's surface set up by the shear flows of the O-star winds from the cluster. We discuss the implications of our findings in terms of the broad emission line component that is increasingly found in extragalactic starburst environments. Although the broad line widths found here are narrower, we conclude that the mechanisms producing both must be the same. The difference in line widths may result from the lower total mechanical wind energy produced by the O stars in Pismis 24 compared to that from a typical young massive star cluster found in a starburst galaxy. The pillar's edge is also clearly defined by dense ( 20000 K), and excited (via [NII]/H_a and [SII]/H_a ratios) gas conditions, implying the presence of a D-type ionization front propagating into the pillar surface. Although there must be both photoevaporation outflows produced by the ionization front, and mass-loss through mechanical ablation, we see no evidence for any significant bulk gas motions on or around the pillar. We postulate that the evaporated/ablated gas must be rapidly heated before being entrained.

(Abridged) In this second paper of the series, we present the results from optical Gemini-North GMOS-IFU and WIYN DensePak IFU spectroscopic observations of the starburst and inner wind zones of M82, with a focus on the state of the T~10^4 K ionized interstellar medium. Our electron density maps show peaks of a few 1000 cm-3, local small spatial-scale variations, and a fall-off in the minor axis direction. We discuss the implications of these results with regards to the conditions/locations that may favour the escape of individual cluster winds. Our findings imply that the starburst environment is highly fragmented into a range of clouds from small/dense clumps with low filling factors (10^4 cm-3) to larger filling factor, less dense gas. The near-constant state of the ionization state of the ~10^4 K gas throughout the starburst can be explained as a consequence of the small cloud sizes, which allow the gas conditions to respond quickly to any changes. We have examined in more detail both the broad (FWHM 150-350 km/s) line component found in Paper I that we associated with emission from turbulent mixing layers on the gas clouds, and the discrete outflow channel identified within the inner wind. The channel appears as a coherent, expanding cylindrical structure of length >120 pc and and width 35-50 pc and the walls maintain an approximately constant (but subsonic) expansion velocity of ~60 km/s. We use the channel to examine further the relationship between the narrow and broad component emitting gas within the inner wind. Within the starburst energy injection zone, we find that turbulent motions (as traced by the broad component) appear to play an increasing role with height., 27 pages, 18 figures (13 in colour), accepted for publication in ApJ

The exact nature of the interaction between hot, fast-flowing star-cluster winds and the surrounding clumpy interstellar medium (ISM) in starburst galaxies has very few observational constraints. Besides furthering our knowledge of ISM dynamics, detailed observations of ionised gas at the very roots of large-scale outflows are required to place limits on the current generation of high-resolution galactic wind models. To this end, we conduct a detailed investigation of the ionised gas environment surrounding the young star clusters in the starburst galaxy NGC1569. Using high spatial and spectral-resolution Gemini/GMOS integral-field unit observations, we accurately characterise the line-profile shapes of the optical nebular emission lines and find a ubiquitous broad (∼300 km s−1) component underlying a bright narrower component. By mapping the properties of the individual line components, we find correlations that suggest that the broad component results from powerful cluster wind–gas clump interactions. We propose a model to explain the properties of the line components and the general turbulent state of the ISM.

A study of the blue compact dwarf (BCD) galaxy Mrk 996 based on high resolution optical VLT VIMOS integral field unit spectroscopy is presented. Mrk 996 displays multi-component line emission, with most line profiles consisting of a narrow, central Gaussian with an underlying broad component. The broad HI Balmer component splits into two separate broad components inside a 1".5 radius from the nucleus; these are attributed to a two-armed mini-spiral. The rotation curve of Mrk 996 derived from the H\alpha narrow component yields a total mass of 5x10^8 Msol within a radius of 3 kpc. The high excitation energy, high critical density [O III] 4363 and [N II] 5755 lines are only detected from the inner region and exist purely in broad component form, implying unusual excitation conditions. Surface brightness, radial velocity, and FWHM maps for several emission components are presented. A separate physical analysis of the broad and narrow emission line regions is undertaken. We derive an upper limit of 10,000 K for the electron temperature of the narrow line gas, together with an electron density of 170 cm^-3, typical of normal H II regions. For the broad line component, we estimate a temperature of 11,000 K and an electron density of 10^7 cm^-3. The broad line emission regions show a N/H enrichment factor of ~20 relative to the narrow line regions, but no He/H, O/H, S/H, or Ar/H enrichment is inferred. The dominant line excitation mechanism is photoionisation by the ~3000 WR stars and ~150,000 O-type stars estimated to be present in the core. This is indeed a peculiar BCD, with extremely dense zones of gas in the core, through which stellar outflows and possible shock fronts permeate contributing to the excitation of the broad line emission. [Abridged], Comment: Accepted for publication in MNRAS main journal. Minor corrections made and additional discussion. 23 pages, 23 figures

We present deep WIYN H-alpha imaging of the dwarf irregular starburst galaxy NGC 1569, together with WIYN SparsePak spatially-resolved optical spectroscopy of the galactic outflow. This leads on from our previous detailed analyses of the state of the ISM in the central regions of this galaxy. Our deep imaging reveals previously undetected ionized filaments in the outer halo. Through combining these results with our spectroscopy we have been able to re-define the spatial extent of the previously catalogued superbubbles, and derive estimates for their expansion velocities, which we find to be in the range 50-100 km/s. The implied dynamical ages of

[Abridged] We present high-resolution optical HST/STIS observations made with two slits crossing four of the brightest starburst clumps in the vicinity of the nucleus of M82. These provide H_alpha kinematics, extinction, electron density and emission measures. From the radial velocity curves we confirm the presence of a stellar bar, and find that the super star cluster M82-A1 has a position and radial velocity consistent with it being at the end of one of the unique x2 bar orbits formed by an inner Lindblad resonance. We derive a new model for the orientation of the bar and disc with respect to the main starburst clumps, and propose that clump A has formed within the bar region as a result of gas interactions between the bar orbits, whereas region C lies at the edge of the bar and regions D and E are located further out from the nucleus but heavily obscured. We derive extremely high interstellar densities, corresponding to ISM pressures of P/k ~ 0.5-1.0 x 10^7 cm^-3 K, and discuss the implications of the measured gas properties surrounding the nuclear star clusters on the production and evolution of the galactic wind. Despite varying pressures, the ionization parameter is uniform down to parsec-scales, and we discuss why this might be so. Where the S/N of our spectra are high enough, we identify multiple emission-line components. Through detailed Gaussian line-fitting, we identify a ubiquitous broad (200-300 km/s) underlying component to the bright H_alpha line, and discuss the physical mechanism(s) that could be responsible for such widths. We conclude that the evaporation and/or ablation of material from interstellar gas clouds caused by the impact of the high-energy photons and fast-flowing cluster winds produces a highly turbulent layer on the surface of the clouds from which the emission arises.

We present Gemini/IFU observations that sample the roots of the galactic wind outflows in the starburst galaxies NGC 1569 and M82. The good spatial and spectral resolutions of these observations allow us to probe the interactions of cluster winds with their environments on small scales. For both galaxies, we find a ubiquitous broad (200–300 km s−1) Hα component underlying a brighter narrower component. By mapping the properties of the individual line components, we find correlations that suggest that the broad component results from powerful cluster wind-gas clump interactions. For NGC 1569, there is little evidence for organised gas flows within the central zone and we suggest that the flow-dominated wind must form well beyond the region containing the massive star clusters. For M82, we find that the kinematics of the wind base are very complex; the width of the broad component reaches values of > 350 km s−1 at the base of the wind, and the outflow itself rapidly becomes chaotic in the inner wind region.

We present a set of four Gemini-North GMOS/IFU observations of the central disturbed regions of the dwarf irregular starburst galaxy NGC 1569, surrounding the well-known super star clusters A and B. This continues on directly from a companion paper, in which we describe the data reduction and analysis techniques employed and present the analysis of one of the IFU pointings. By decomposing the emission line profiles across the IFU fields, we map out the properties of each individual component identified and identify a number of relationships and correlations that allow us to investigate in detail the state of the ionized ISM. Our observations support and expand on the main findings from the analysis of the first IFU position, where we conclude that a broad (< 400 km/s) component underlying the bright nebular emission lines is produced in a turbulent mixing layer on the surface of cool gas knots, set up by the impact of the fast-flowing cluster winds. We discuss the kinematic, electron density and excitation maps of each region in detail and compare our results to previous studies. Our analysis reveals a very complex environment with many overlapping and superimposed components, including dissolving gas knots, rapidly expanding shocked shells and embedded ionizing sources, but no evidence for organised bulk motions. We conclude that the four IFU positions presented here lie well within the starburst region where energy is injected, and, from the lack of substantial ordered gas flows, within the quasi-hydrostatic zone of the wind interior to the sonic point. The net outflow occurs at radii beyond 100-200 pc, but our data imply that mass-loading of the hot ISM is active even at the roots of the wind.

[Abridged] We present Gemini-North GMOS/IFU observations of a young star cluster (cluster 10) and its environment near the centre of the dwarf irregular starburst galaxy NGC 1569. This forms part of a larger and on-going study of the formation and collimation mechanisms of galactic winds, including three additional IFU pointings in NGC 1569 covering the base of the galactic wind which are analysed in a companion paper. The good spatial- and spectral-resolution of these GMOS/IFU observations, covering 4740-6860 A, allow us to probe the interactions between clusters and their environments on small scales. Combining our GMOS spectrum with HST imaging, we find that cluster 10 is composed of two very close components with ages of 5-7 Myr and

We present observations obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope of the "fossil" starburst region B in the nearby starburst galaxy M82. By comparing UBVI photometry with models, we derive ages and extinctions for 35 U-band selected star clusters. We find that the peak epoch of cluster formation occurred ~ 150 Myr ago, in contrast to earlier work that found a peak formation age of 1.1 Gyr. The difference is most likely due to our inclusion of U-band data, which are essential for accurate age determinations of young cluster populations. We further show that the previously reported turnover in the cluster luminosity function is probably due to the neglect of the effect of extended sources on the detection limit. The much younger cluster ages we derive clarifies the evolution of the M82 starburst. The M82-B age distribution now overlaps with the ages of: the nuclear starburst; clusters formed on the opposite side of the disk; and the last encounter with M81, some 220 Myr ago., Comment: 11 pages, 4 figures, accepted for publication in ApJ Letters

We present a detailed study of the stellar cluster M82F, using multi-band high resolution HST imaging and deep ground based optical slit and integral field spectroscopy. Using the imaging we create colour maps of the cluster and surrounding region in order to search for substructure. We find a large amount of substructure, which we interpret as the result of differential extinction across the projected face of the cluster. With this interpretation, we are able to construct a spatially resolved extinction map across the cluster which is used to derive the intrinsic flux distribution. Fitting cluster profiles (King and EFF) to the intrinsic images we find that the cluster is 15-30% larger than previous estimates, and that no strong evidence of mass segregation in this cluster exists. Using the optical spectra, we find that the age of M82F is 60-80 Myr and from its velocity conclude that the cluster is not physically associated with a large HII region that it is projected upon, both in agreement with previous studies. The reconstructed integral field maps show that that majority of the line emission comes from a nearby HII region. The spatial dependence of the line widths (implying the presence of multiple components)measured corresponds to the extinction map derived from photometry, indicating that the gas/dust clouds responsible for the extinction are also partially ionised. Even with the wealth of observations presented here, we do not find a conclusive solution to the problem of the high light-to-mass ratio previously found for this cluster and its possible top-heavy stellar IMF., Comment: 12 pages, 7 figures, accepted MNRAS

We present HST/STIS optical and Gemini/NIFS near-IR IFU spectroscopy, and archival HST imaging of the triplet of super star clusters (A1, A2 and A3) in the core of the M82 starburst. Using model fits to the STIS spectra, and the weakness of red supergiant CO absorption features (appearing at ~6 Myr) in the NIFS H-band spectra, the ages of A2 and A3 are $4.5\pm1.0$~Myr. A1 has strong CO bands, consistent with our previously determined age of $6.4\pm0.5$~Myr. The photometric masses of the three clusters are 4--$7\times10^5$~\Msol, and their sizes are $R_{\rm eff}=159$, 104, 59~mas ($\sim$2.8, 1.8, 1.0~pc) for A1,2 and 3. The STIS spectra yielded radial velocities of $320\pm2$, $330\pm6$, and $336\pm5$~\kms\ for A1,2, and 3, placing them at the eastern end of the $x_2$ orbits of M82's bar. Clusters A2 and A3 are in high density (800--1000~\cmt) environments, and like A1, are surrounded by compact H\two\ regions. We suggest the winds from A2 and A3 have stalled, as in A1, due to the high ISM ambient pressure. We propose that the 3 clusters were formed \textit{in-situ} on the outer $x_2$ orbits in regions of dense molecular gas subsequently ionized by the rapidly evolving starburst. The similar radial velocities of the 3 clusters and their small projected separation of $\sim 25$~pc suggest that they may merge in the near future unless this is prevented by velocity shearing., 15 pages, 9 figures, ApJ in press

We report on our observations of the 79 and 119um doublet transitions of OH for 24 local (z, 23 pages, 12 figures, 4 tables

We present optical integral field unit (IFU) observations of two gas pillars surrounding the Galactic young massive star cluster NGC 3603. The high S/N and spectral resolution of these data have allowed us to accurately quantify the H-alpha, [NII] and [SII] emission line shapes, and we find a mixture of broad (FWHM~70-100 km/s) and narrow (10000 cm-3. In one pillar we found that these high densities are only found in the narrow component, implying it must originate from deeper within the pillar than the broad component. From this, together with our kinematical data, we conclude that the narrow component traces a photoevaporation flow, and that the TML forms at the interface with the hot wind. On the pillar surfaces we find a consistent offset in radial velocity between the narrow (brighter) components of H-alpha and [NII] of ~5-8 km/s, for which we were unable to find a satisfactory explanation. We urge the theoretical community to simulate mechanical and radiative cloud interactions in more detail to address the many unanswered questions raised by this study., 17 pages, 19 figures, accepted to MNRAS

Using VLT/FLAMES optical integral field unit observations, we present the first spatially resolved spectroscopic study of the well known blue compact galaxy Haro11, thought to be a local analogue to high redshift Lyman Break Galaxies. Haro11 displays complex emission line profiles, consisting of narrow (FWHM, 18 pages, 12 figures, accepted for publication in MNRAS

We present Gemini-S/GMOS-IFU optical spectroscopy of four regions near the centre of the nearby (3.8 Mpc) dwarf starburst galaxy NGC 5253. This galaxy is famous for hosting a radio supernebula containing two deeply embedded massive super star clusters, surrounded by a region of enhanced nitrogen abundance that has been linked to the presence of WR stars. We detected 11 distinct sources of red WR bump (CIV) emission over a 20" (~350 pc) area, each consistent with the presence of ~1 WCE-type star. WC stars are not found coincident with the supernebula, although WN stars have previously been detected here. We performed a multi-component decomposition of the H\alpha\ line across all four fields and mapped the kinematics of the narrow and broad (FWHM = 100-250 km/s) components. These maps paint a picture of localised gas flows, as part of multiple overlapping bubbles and filaments driven by the star clusters throughout the starburst. We confirm the presence of a strong H\alpha\ velocity gradient over ~4.5" (~80 pc) coincident with the region of N/O enhancement, and high gas density known from previous study, and interpret this as an accelerating ionized gas outflow from the supernebula clusters. We measure the ionized gas abundances in a number of regions in the outer IFU positions and combine these with measurements from the literature to assess the radial abundance distribution. We find that the O/H and N/H profiles are consistent with being flat. Only the central 50 pc exhibits the well-known N/O enhancement, and we propose that the unusually high densities/pressures in the supernebula region have acted to impede the escape of metal-enriched hot winds from the star clusters and allow them to mix with the cooler phases, thus allowing these freshly processed chemicals to be seen in the optical., Comment: 16 pages, accepted to A&A

Using VLT/FLAMES optical IFU observations, we present a detailed study of UM 448, a nearby Blue Compact Galaxy (BCG) previously reported to have an anomalously high N/O abundance ratio. NTT/SuSI2 images reveal a morphology suggestive of a merger of two systems of contrasting colour, whilst our H-alpha emission maps resolve UM 448 into three separate regions that do not coincide with the stellar continuum peaks. UM 448 exhibits complex emission line profiles, with lines consisting of a narrow, central component, an underlying broad component and a third, narrow blue-shifted component. Radial velocity maps show signs of solid body rotation across UM 448, with a projected rotation axis that correlates with the continuum morphology of the galaxy. A spatially-resolved, chemodynamical analysis is presented. Whilst the eastern tail of UM 448 has electron temperatures (Te) that are typical of BCGs, we find a region within the main body of the galaxy where the narrow and broad [O III] 4363 line components trace temperatures differing by 5000K and oxygen abundances differing by 0.4 dex. We measure spatially resolved and integrated ionic and elemental abundances for O, N, S and Ne throughout UM 448, and find they do not agree, possibly due the flux-weighting of Te from the integrated spectrum. This has significant implications for abundances derived from long-slit and integrated spectra of star-forming galaxies in the nearby and distant universe. A region of enhanced N/O ratio is indeed found, extended over a ~0.6 kpc^2 region within the main body of the galaxy. Contrary to previous studies, however, we do not find evidence for a large Wolf-Rayet population, and conclude that WR stars alone cannot be responsible for producing the observed N/O excess. Instead, the location and disturbed morphology of the N-enriched region suggests that interaction-induced inflow of metal-poor gas may be responsible., 18 pages, 14 figures, to appear in MNRAS (revised version following referee report)

We present deep WIYN H_alpha SparsePak and DensePak spatially-resolved optical spectroscopy of the dwarf irregular starburst galaxy NGC 1140. The different spatial resolutions and coverage of the two sets of observations have allowed us to investigate the properties and kinematics of the warm ionized gas within both the central regions of the galaxy and the inner halo. We find that the position angle of the H_alpha rotation axis for the main body of the galaxy is consistent with the HI rotation axis at PA = 39 deg, but that the ionized gas in the central 20x20 arcsecs (~2x2 kpc) is kinematically decoupled from the rest of the system, and rotates at a PA approximately perpendicular to that of the main body of the galaxy at +40 deg. We find no evidence of coherent large-scale galactic outflows. Instead multiple narrow emission line components seen within a radius of ~1-1.5 kpc, and high [SII]/H_alpha ratios found beyond ~2 kpc implying a strong contribution from shocks, suggest that the intense star formation is driving material outwards from the main star forming zone in the form of a series of interacting superbubbles/shells. A broad component (1002 kpc. Based on recent work, we conclude that it is produced in turbulent mixing layers on the surfaces of cool gas knots embedded within the ISM, set up by the feedback from young massive star clusters. Our data suggest a physical limit to the radius where the broad emission line component is significant, and we propose that this limit marks a significant transition point in the development of the galactic outflow, where turbulent motion becomes less dominant. This mirrors what has recently been found in another similar irregular starburst galaxy NGC 1569., Comment: 13 pages, 9 figures (6 colour). Accepted for publication in MNRAS

We present a spectroscopic study of the stellar cluster population of M82, the archetype starburst galaxy, based primarily on new Gemini-North multi-object spectroscopy of 49 star clusters. These observations constitute the largest to date spectroscopic dataset of extragalactic young clusters, giving virtually continuous coverage across the galaxy; we use these data to deduce information about the clusters as well as the M82 post-starburst disk and nuclear starburst environments. Spectroscopic age-dating places clusters in the nucleus and disk between (7, 15) and (30, 270) Myr, with distribution peaks at ~10 and ~140 Myr respectively. We find cluster radial velocities in the range (-160, 220) km/s (wrt the galaxy centre) and line of sight Na I D interstellar absorption line velocities in (-75, 200) km/s, in many cases entirely decoupled from the clusters. As the disk cluster radial velocities lie on the flat part of the galaxy rotation curve, we conclude that they comprise a regularly orbiting system. Our observations suggest that the largest part of the population was created as a result of the close encounter with M81 ~220 Myr ago. Clusters in the nucleus are found in solid body rotation on the bar. The possible detection of WR features in their spectra indicates that cluster formation continues in the central starburst zone. We also report the potential discovery of two old populous clusters in the halo of M82, aged >8 Gyr. Using these measurements and simple dynamical considerations, we derive a toy model for the invisible physical structure of the galaxy, and confirm the existence of two dominant spiral arms., Accepted for publication in the Astrophysical Journal

We present Gemini North GMOS/IFU observations of the roots of the NGC 1569 super-galactic wind. This forms part of a larger and on-going study of the formation and collimation mechanisms of galactic winds. Four IFU pointings cover the base of the outflows originating from the central super-star clusters; we present a preliminary analysis for two positions. The choice of single-slit mode and the R831 grating (dispersion = 0.34 A pix−) allowed us to cover the spectral range 4740-6860A through 500 object fibres. We observe the nebular diagnostic lines of Hα, Hβ, [OIII]λλ4959,5007, [NII]λλ6548,6583, [SII]λλ6716, 6731. The data were reduced using the standard Gemini pipeline included with IRAF, and corrected for differential atmospheric refraction. We find emission lines clearly composed of multiple components—in most cases a bright narrow feature (intrinsic FWHM = 50 kms−1) superimposed on a fainter broad component (FWHM ≤ 300 kms−1). We discuss the origin of these components, in the context of the wind/interstellar medium interaction.

[Abridged] We present Gemini-N GMOS-IFU observations of the central starburst clumps and inner wind of M82, together with WIYN DensePak IFU observations of the inner 2x0.9kpc of the disk. These cover the emission lines of H$\alpha$, [NII], [SII], and [SIII]. We were able to accurately decompose the emission line profiles into multiple narrow components (FWHM~30-130kms) superimposed on a broad (FWHM 150-350kms) feature. This paper is the first of a series examining the optical structure of M82's disk and inner wind; here we focus on the ionized gaseous and stellar dynamics and present maps of the relevant emission line properties. Our observations show that ionized gas in the starburst core of M82 is dynamically complex. Localised line splitting of up to 100kms in the narrow component is associated with expanding shells of compressed, cool, photoionized gas. We have been able to associate some of this inner-wind gas with a distinct outflow channel characterised by its dynamics and gas density patterns, and we discuss the consequences of this discovery in terms of the developing wind outflow. The broad optical emission line component is observed to become increasingly important moving outward along the outflow channel, and in general with increasing height above/below the plane. Following our recent work on the origins of this component, we associate it with turbulent gas in wind-clump interface layers and hence sites of mass loading, meaning that the turbulent mixing of cooler gas into the outflowing hot gas must become increasingly important with height, and provides powerful direct evidence for the existence of mass-loading over a large, spatially extended area., Comment: 36 pages, 21 figures, accepted for publication in ApJ

The post-starburst region B in M82 and its massive star cluster component have been the focus of multiple studies, with reports that there is a large population of coeval clusters of age ~1 Gyr, which were created with a Gaussian initial mass distribution. This is in disagreement with other studies of young star clusters, which invariably find a featureless power-law mass distribution. Here, we present Gemini-North optical spectra of seven star clusters in M82-B and show that their ages are all between 10 and 300 Myr (a factor of 3-100 younger than previous photometric results) and that their extinctions range between near-zero and 4 mag (Av). Using new HST ACS-HRC U-band observations we age date an additional ~30 clusters whose ages/extinctions agree well with those determined from spectroscopy. Completeness tests show that the reported `turn-over' in the luminosity/mass distributions is most likely an artefact, due to the resolved nature of the clusters. We also show that the radial velocities of the clusters are inconsistent with them belonging to a bound region., Comment: To appear in Perez, de Grijs and Gonzalez Delgado (eds.), `Young Massive Star Clusters: Initial Conditions and Environments', 2008, Astrophysics & Space Science

We present new spectroscopic observations of the stellar cluster population of region B in the prototype starburst galaxy M82 obtained with the Gillett Gemini-North 8.1-metre telescope. By coupling the spectroscopy with UBVI photometry acquired with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST), we derive ages, extinctions and radial velocities for seven young massive clusters (YMCs) in region B. We find the clusters to have ages between 70 and 200 Myr and velocities in the range 230 to 350 km/s, while extinctions Av vary between ~1-2.5 mag. We also find evidence of differential extinction across the faces of some clusters which hinders the photometric determination of ages and extinctions in these cases. The cluster radial velocities indicate that the clusters are located at different depths within the disk, and are on regular disk orbits. Our results overall contradict the findings of previous studies, where region B was thought to be a bound region populated by intermediate-age clusters that formed in an independent, offset starburst episode that commenced 600 Myr-1 Gyr ago. Our findings instead suggest that region B is optically bright because of low extinction patches, and this allows us to view the cluster population of the inner M82 disk, which probably formed as a result of the last encounter with M81. This study forms part of a series of papers aimed at studying the cluster population of M82 using deep optical spectroscopy and multi-band photometry., 12 pages, 8 figures; accepted for publication in The Astrophysical Journal

We present HST/STIS spectroscopy for one slit position crossing the starburst core of M82, sampling both clusters and ionized gas at optical wavelengths. The spectra have a spatial resolution of 2 pc at the distance of M82, allowing us to probe the conditions within a starburst environment in unprecedented detail. We find that the ionized gas has high turbulent and thermal pressures (P/κ ∼ 107), reflecting the intense energy input from supernovae concentrated in super star clusters. The data also provide new insights into young clusters and their immediate environments. We identify a 6–7 Myr old cluster, M82-A1, which is still embedded in a compact Hii region.

Observations obtained by the Atacama Large Millimeter Array in Chile's Atacama Desert have revealed properties of the cold molecular phase of the wind that is being blown out of a nearby starburst galaxy. See Letter p.450 New interferometric observations from the ALMA radio telescope reveal the central two kiloparsec region of the nearby starburst galaxy NGC 253 in unprecedented detail. Using the new data it is now possible to measure the mass-outflow rate of the starburst system for the first time. By ejecting around nine solar masses per year (three times the mass converted to stars in the same period), the starburst-driven 'superwind' limits the star-formation rate and the number of stars produced in this galaxy.

ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst galaxies. We present for the first time in a starburst galaxy a 2D study of the spatial behavior of collisional and radiative transfer effects in He^+. The HeI lines are analysed based on data obtained with FLAMES and GMOS. Collisional effects are negligible for transitions in the singlet cascade while relatively important for those in the triplet cascade. In particular, they can contribute up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are important over an extended and circular area of 30pc in diameter centered at the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the stellar absorption equivalent width as well as the most recent emissivities. We found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the excitation and the total helium abundance, y_tot, is consistent with no abundance gradient. Uncertainties in the derivation of He abundances are dominated by the adopted assumptions. We illustrated the difficulty of detecting a putative He enrichment due to the presence of Wolf-Rayet stars in the main GHIIR. Data are marginally consistent with an excess in the N/He ratio in the N enriched area of the order of both, the atmospheric N/He ratios in WR stars and the uncertainties estimated for the N/He ratios., Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been included

We present the Snapshot Hubble U-band Cluster Survey (SHUCS), a project aimed at characterizing the star cluster populations of ten nearby galaxies (d, Accepted for publication in the Astronomical Journal. 31 pages, 18 figures. Paper I in a series