A multiwavelength view at the heart of the superwind in NGC253 (original) (raw)
Related papers
The Collimated Wind in NGC 253
The Astrophysical Journal, 2003
Near-infrared Fabry-Perot imaging has revealed H 2 emission extended to about 130 pc from the disk of NGC 253. It is closely related to the hot plasma observed in soft X-rays: filamentary H 2 features are found at the edges of the hot plasma. These are the places of direct interaction between a superwind and its surrounding molecular gas. We suggest that the filamentary features actually trace a more or less conical shell-like structure, whose tangential line of sight to us is intensely observed. The H 2 emission shell is most likely from the molecular gas blown out or swept to the side by the hot plasma outflow. Dust is associated with this molecular gas structure. The outflow is tilted with respect to the disk, possibly suggesting the inhomogeneous nature of the interstellar medium in which the starburst takes place.
The Nuclear Starburst in NGC 253
The Astrophysical Journal, 1998
We have obtained long-slit spectra of NGC 253 in the J, H, K, and N bands, broadband images in the J, H, and K s bands, narrowband images centered at the wavelengths of Brγ and H 2 (1,0)S(1), and imaging spectroscopy centered on [Ne II](12.8µm). We have subtracted a composite stellar spectrum from the galaxy spectrum to measure faint emission lines which otherwise would be buried in the complicated continuum structure.
GALACTIC WIND IN THE NEARBY STARBURST GALAXY NGC 253 OBSERVED WITH THE KYOTO3DII FABRY-PEROT MODE
The Astrophysical Journal, 2009
We have observed the central region of the nearby starburst galaxy NGC 253 with the Kyoto Tridimensional Spectrograph II (Kyoto3DII) Fabry-Perot mode in order to investigate the properties of its galactic wind. Since this galaxy has a large inclination, it is easy to observe its galactic wind. We produced the Hα, [N II]λ6583, and [S II]λλ6716,6731 images, as well as those line ratio maps. The [N II]/Hα ratio in the galactic wind region is larger than those in H II regions in the galactic disk. The [N II]/Hα ratio in the southeastern filament, a part of the galactic wind, is the largest and reaches about 1.5. These large [N II]/Hα ratios are explained by shock ionization/excitation. Using the [S II]/Hα ratio map, we spatially separate the galactic wind region from the starburst region. The kinetic energy of the galactic wind can be sufficiently supplied by supernovae in a starburst region in the galactic center. The shape of the galactic wind and the line ratio maps are non-axisymmetric about the galactic minor axis, which is also seen in M82. In the [N II]λ6583/[S II]λλ6716,6731 map, the positions with large ratios coincide with the positions of star clusters found in the Hubble Space Telescope (HST) observation. This means that intense star formation causes strong nitrogen enrichment in these regions. Our unique data of the line ratio maps including [S II] lines have demonstrated their effectiveness for clearly distinguishing between shocked gas regions and starburst regions, determining the extent of galactic wind and its mass and kinetic energy, and discovering regions with enhanced nitrogen abundance.
A SuperStar Cluster in NGC 253: Mid-Infrared Properties
Astrophysical Journal - ASTROPHYS J, 1999
We observed the nearby starburst galaxy NGC 253 in the mid-infrared to obtain a three-dimensional data set with arcsecond angular resolution and 0.2 km spectral resolution. The observations show the major spectral features in the upper half of the mid-IR window : the 11.3 km polycyclic aromatic hydrocarbon (PAH) line and the 12.8 km [Ne II] line as well as the broad silicate absorption feature at 9.7 km. We use the [Ne II] line to determine the emission measure of the ionized gas, and in combination with radio observations to predict the thermal and nonthermal contributions to the radio continuum. The amount of ionized gas is related to the rate of star formation. Based on the mid-IR spectra, we identify three major components in the nucleus of NGC 243 : an AGN in the center of the galaxy, a superÈstar cluster also seen in optical images, and a larger scale di †use envelope composed of an older population of supernova remnants and lower mass stars.
The Astronomical Journal, 2000
Arcsecond-resolution X-ray imaging of the nucleus of the nearby starburst galaxy NGC 253 with Chandra reveals a well-collimated, strongly limb-brightened, kiloparsec-scale conical outflow from the central starburst region. The outflow is very similar in morphology to the known Hα outflow cone, on scales down to 20 pc. This provides, for the first time, robust evidence that both X-ray and Hα emission come from low volume filling factor regions of interaction between the fast energetic wind of SN-ejecta and the denser ambient interstellar medium (ISM), and not from the wind fluid itself. We provide estimates of the (observationally and theoretically important) filling factor of the X-ray emitting gas, of between ∼ 4 and 40 per cent, consistent with an upper limit of ∼ 40 per cent based directly on the observed limb-brightened morphology of the outflow. Only 20 per cent of the observed X-ray emission can come from the volume-filling, metal-enriched, wind fluid itself. Spatially-resolved spectroscopy of the soft diffuse thermal X-ray emission reveals that the predominant source of spectral variation along the outflow cones is due to strong variation in the absorption, on scales of ∼ 60 pc, there being little change in the characteristic temperature of the emission. We show that these observations are easily explained by, and fully consistent with, the standard model of a superwind driven by a starburst of NGC 253's observed power. If these results are typical of all starburst-driven winds, then we do not directly see all the energy and gas (in particular the hot metal-enriched gas) transported out of galaxies by superwinds, even in X-ray emission.
Possible star formation in the halo of NGC 253
Astronomy and Astrophysics, 2001
We present a deep UBV survey in the direction of the halo of the starburst galaxy NGC 253 aimed at investigating the possible existence of recent star formation far from its disk, as traced by early-type stars. We discuss different classes of objects with blue colors that may contaminate the region of color-color and colormagnitude diagrams occupied by early Population I stars at the distance of NGC 253. Strong upper limits are found on their contribution to the measured object counts by means of models, of surveys of the halo of our Galaxy, and of observations of nearby control fields. A population of objects with (B − V) < 0, V > 23 is identified in the direction of the halo of NGC 253 that has no counterpart in the control fields to a high level of statistical confidence. The absolute magnitudes of these objects at the distance of NGC 253 is consistent with them being main sequence B0-B2 stars. The spatial distribution of the bluest objects in the halo of NGC 253 seems to cluster in two groups: one is closer to the disk of NGC 253, and may contain runaway stars expelled from its disk. The other group has projected distances to the plane of the galaxy ranging between 9 and 15 kpc, and at least its base coincides with a peak in radio continuum due to synchrotron emission of cosmic rays escaping the galactic disk. We hypothesize that the distant group of blue stars in the halo of NGC 253 is a result of the interaction between the superwind produced at its nuclear starburst (and perhaps also in star forming regions in the disk) and cold gas in the halo, in a phenomenon similar to the star formation near Centaurus A induced by the interaction of its jet with a HI cloud. If this is the case, NGC 253 provides an example of the ability of less energetic galactic outflows to trigger star formation in haloes, a phenomenon that may also be responsible for the suspected existence of Population I stars at large distances from the disk of the Milky Way.
The Astrophysical Journal, 2007
We present ∼ 2 ′′ resolution CO (3-2), HCO + (4-3) and 880µm continuum images of the luminous infrared galaxy NGC 6240 obtained at the Submillimeter Array. We find that the spatially resolved CO (3-2), HCO + (4-3) and the 880µm emission peaks between the two nuclear components that are both known to harbor AGNs. Our Large Velocity Gradient (LVG) analysis performed on each velocity channel suggests that the peak of the molecular gas emission traced in our observations is warm (T = 20 -100 K), dense (n H2 = 10 5.0−5.4 cm −3 ) and moderately optically thin (τ = 0.2 -2) in the central 1 kpc. We also find large column densities of ∼ 10 23 cm −2 . Such extreme conditions are observed over ∼ 300 km s −1 centered around the CO derived systemic velocity. The derived molecular gas mass from the CO (3-2) emission and a CO-to-H 2 conversion factor commonly used for ULIRGs is (6.9±1.7)×10 9 M ⊙ , and this is consistent with the mass derived from previous CO (2-1) observations. The gas is highly turbulent in the central kpc (∆v FWZI ∼ 1175 km s −1 ). Furthermore, possible inflow or outflow activity is suggested from the CO (3-2) velocity distribution. We tentatively state that 3.5 × 10 8 M ⊙ of isolated CO (3-2) emission seen west of the northern disk may be associated with outflows from starburst superwinds, but the gas outflow scenario from one of the central AGN is not completely ruled out. Piecing all of the information together, the central region of NGC 6240 harbors 2 AGNs, ∼ 10 10 M ⊙ of molecular gas mass, 5 × 10 7 M ⊙ of dust mass, and has possible evidence of inflow and outflow activity.
Jet‐ and Wind‐driven Ionized Outflows in the Superbubble and Star‐forming Disk of NGC 3079
The Astrophysical Journal, 2001
HST WFPC2 images are presented that span the inner ∼19 kpc diameter of the edge-on galaxy NGC 3079; they are combined with optical, emission-line imaging spectrophotometry and VLA images of radio polarization vectors and rotation measures. Ionized gas filaments within 9-kpc diameter project up to 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 streams with large velocities and velocity dispersions (FWHM ≈450 km s −1 ). The brightest stream emits ≈ 10% of the superbubble Hα flux and extends for 250 pc along the axis of the VLBI radio jet to one corner of the base of the superbubble. The other four streams are not connected to the jet, instead curving up to the vertical ≈ 0.6 kpc above the galaxy disk, then dispersing as a spray of droplets each with ≈ 10 3 √ f M of ionized gas (the volume filling factor f > 3 × 10 −3 ). Shredded clumps of disk gas form a similar structure in hydrodynamical models of a galaxy-scale wind. The pattern of magnetic fields and the gaseous kinematics also suggest that a wind of mechanical luminosity L w ≈ 10 43 ergs s −1 has stagnated in the galaxy disk at a radius of ∼ 800 pc, has flared to larger radii with increasing height as the balancing ISM pressure reduces above the disk, and has entrained dense clouds into a "mushroom vortex" above the disk. Hα emissivity of the filaments limits densities to n e > 4.3 f −1/2 cm −3 , hence kinetic energy and momentum to (0.4 − 5) × 10 55 √ f ergs and (1.6 − 6) × 10 47 √ f dyne s, respectively; the ranges result from uncertain space velocities. A prominent star-forming complex elsewhere in the galaxy shows a striking spray of linear filaments that extend for hundreds of parsecs to end in unresolved "bullets."
Galactic Starburst NGC 3603 from X‐Rays to Radio
The Astrophysical Journal, 2002
NGC 3603 is the most massive and luminous visible starburst region in the Galaxy. We present the first Chandra ACIS-I X-ray image and spectra of this dense, exotic object, accompanied by a deep centimeterwavelength Australia Telescope Compact Array radio image at similar d1 00 spatial resolution and Hubble Space Telescope/ground-based optical data. At the S=N > 3 level, Chandra detects several hundred X-ray point sources (compared to the three distinct sources seen by ROSAT). At least 40 of these sources are definitely associated with optically identified cluster O-and W-R-type members, but most are not. A diffuse Xray component is also seen out to $2 0 (4 pc) from the center, probably arising mainly from the large number of merging/colliding hot stellar winds and/or numerous faint cluster sources. The point-source X-ray fluxes generally increase with increasing bolometric brightnesses of the member O/W-R stars, but with very large scatter. Some exceptionally bright stellar X-ray sources may be colliding wind binaries. The radio image shows (1) two resolved sources, one definitely nonthermal, in the cluster core near where the X-ray/optically brightest stars with the strongest stellar winds are located, (2) emission from all three known proplyd-like objects (with thermal and nonthermal components), and (3) many thermal sources in the peripheral regions of triggered star formation. Overall, NGC 3603 appears to be a somewhat younger and hotter scaled-down version of typical starbursts found in other galaxies.
A 60 kpc Galactic Wind Cone in NGC 3079
The Astrophysical Journal
Galactic winds are associated with intense star formation and AGNs. Depending on their formation mechanism and velocity they may remove a significant fraction of gas from their host galaxies, thus suppressing star formation, enriching the intergalactic medium, and shaping the circumgalactic gas. However, the long-term evolution of these winds remains mostly unknown. We report the detection of a wind from NGC 3079 to at least 60 kpc from the galaxy. We detect the wind in FUV line emission to 60 kpc (as inferred from the broad FUV filter in GALEX) and in X-rays to at least 30 kpc. The morphology, luminosities, temperatures, and densities indicate that the emission comes from shocked material, and the O/Fe ratio implies that the X-ray emitting gas is enriched by Type II supernovae. If so, the speed inferred from simple shock models is about 500 km s −1 , which is sufficient to escape the galaxy. However, the inferred kinetic energy in the wind from visible components is substantially smaller than canonical hot superwind models.