A Near-Infrared Study of NGC 7538 IRS 1, 2, and 3 (original) (raw)
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The Optical Structure of the Starburst Galaxy M82. II. Nebular Properties of the Disk and Inner Wind
The Astrophysical Journal, 2009
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 (implying very high thermal pressures), 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 that ultimately power the large-scale superwind.
Monthly Notices of the Royal Astronomical Society, 2010
We report the results of visual spectroscopy, mid-infrared (MIR) mapping and photometry, and near infrared (NIR) photometry of two candidate symbiotic stars (IPHAS J193108.67+164950.5 and IPHAS J193709.65+202655.7) associated with extended MIR emission. Our analysis of the continua of these sources shows that they are likely to represent Class I-II young stellar objects (YSOs) in which most of the IR emission arises from circumstellar disks, and for which the physical characteristics (stellar temperatures, radii, masses and luminosities) are similar. The extended emission is characterised by a substantial increase in fluxes and dimensions to longer MIR wavelengths. This is likely to arise as a result of emission by polycyclic aromatic hydrocarbons (PAHs) within extended photodissociation regimes (PDRs), centred upon more compact ionized regions responsible for much of the shorter wave emission. Such dual emission structures are characteristic of those observed in many compact HII regions. Finally, we note that the clouds have asymmetrical structures and windswept morphologies, conceivably indicative of shock interaction with external winds. Where this is the case, then it is possible that the YSOs are located in regions of triggered star-formation.
The Astrophysical Journal, 2010
We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L > 6 × 10 5 L ⊙ ) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146). Molecular emission was mapped in three lines of CS (J=2→1, 3→2 and 5→4), two lines of SiO (J=2→1 and 3→2), two rotational transitions of CH 3 OH (J k =3 k → 2 k and 2 k → 1 k ), and in the C 34 S(J=3→2) line.
Turbulent Molecular Gas and Star Formation in the Shocked Intergalactic Medium of Stephan's Quintet
The Astrophysical Journal, 2012
We report on single-dish radio CO observations towards the inter-galactic medium (IGM) of the Stephan's Quintet (hereafter SQ) compact group of galaxies. Extremely bright mid-IR H 2 rotational line emission (L(H 2 ) ≈ 10 35 W) from warm (10 2−3 K) molecular gas has been detected by the Spitzer satellite in the kpcscale shock created by a collision between a galaxy, NGC 7318b, and NGC 7319's tidal arm. We detect in the IGM CO(1-0), (2-1) and (3-2) line emission with complex profiles, spanning a velocity range of ≈ 1000 km s −1 . Assuming a Galactic CO(1-0) emission to H 2 mass conversion factor, a total H 2 mass of ≈ 5 × 10 9 M ⊙ is detected in the shock. Note that this mass could be lower by a factor of a few because of the large uncertainties on the CO to H 2 conversion factor. The molecular gas carries a large fraction of the gas kinetic energy involved in the collision, meaning that this energy has not been thermalized yet. The kinetic energy of the H 2 gas derived from CO observations is comparable to that of the warm H 2 gas derived from Spitzer IRS observations. The turbulent kinetic energy of the H 2 gas is at least a factor of 5 greater than the thermal energy of the hot plasma heated by the collision. The spectra exhibit the pre-shock recession velocities of the two colliding gas systems (5700 and 6700 km s −1 ), but also intermediate velocities. This shows that some of the molecular gas originates from the cooling of post-shock gas, which had time to cool and be accelerated by the shock. CO emission is also detected in a bridge feature that connects the shock to the Seyfert member of the group, NGC 7319, and in the northern star forming region, SQ-A, where a new velocity component is identified at 6900 km s −1 , in addition to the two velocity components already known. Spitzer IRS mid-IR spectral mapping is used to estimate the warm H 2 masses and excitation at the positions observed in radio. The ratio between the warm H 2 mass and the H 2 mass derived from CO fluxes is 0.23 ± 0.07 in the IGM of SQ, which is 10 − 100 times higher than in star-forming galaxies. We suggest that the dissipation of turbulent kinetic energy maintain a high heating rate within the H 2 gas. This interpretation implies that the velocity dispersion on the scale of giant molecular clouds in SQ is an order of magnitude larger than the Galactic value. This may explain why this gas is not forming stars efficiently.
Molecules, dust, and protostars in NGC 3503
Astronomy & Astrophysics, 2014
Aims. We are presenting here a follow-up study of the molecular gas and dust in the environs of the star forming region NGC 3503. This study aims at dealing with the interaction of the Hii region NGC 3503 with its parental molecular cloud, and also with the star formation in the region, that was possibly triggered by the expansion of the ionization front against the parental cloud. Methods. To analyze the molecular gas we use CO(J=2→1), 13 CO(J=2→1), C 18 O(J=2→1), and HCN(J=3→2) line data obtained with the on-the-fly technique from the APEX telescope. To study the distribution of the dust, we make use of unpublished images at 870 µm from the ATLASGAL survey and IRAC-GLIMPSE archival images. We use public 2MASS and WISE data to search for infrared candidate YSOs in the region. Results. The new APEX observations allowed the substructure of the molecular gas in the velocity range from ∼ −28 to −23 km s −1 to be imaged in detail. The morphology of the molecular gas close to the nebula, the location of the PDR, and the shape of radio continuum emission suggest that the ionized gas is expanding against its parental cloud, and confirm the "champagne flow" scenario. We have identified several molecular clumps and determined some of their physical and dynamical properties such as density, excitation temperature, mass, and line width. Clumps adjacent to the ionization front are expected to be affected by the Hii region, unlike those that are distant to it. We have compared the physical properties of the two kind of clumps to investigate how the molecular gas has been affected by the Hii region. Clumps adjacent to the ionization fronts of NGC 3503 and/or the bright rimmed cloud SFO 62 have been heated and compressed by the ionized gas, but their line width is not different to those that are too distant to the ionization fronts. We identified several candidate YSOs in the region. Their spatial distribution suggests that stellar formation might have been boosted by the expansion of the nebula. We discard the "collect and collapse" scenario and propose alternative mechanisms such as radiatively driven implosion on pre-existing molecular clumps or small-scale Jeans gravitational instabilities.
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.
Astronomy and Astrophysics, 2010
Context. Starbursts are one of the main contributors to the chemical enrichment of the interstellar medium. However, mechanisms governing the interaction between the recent star formation and the surrounding gas are not fully understood. Because of their a priori simplicity, the subgroup of H ii galaxies constitute an ideal sample to study these mechanisms. Aims. A detailed 2D study of the central region of NGC 5253 has been performed to characterize the stellar and ionized gas structure as well as the extinction distribution, physical properties and kinematics of the ionized gas in the central ∼210 pc×130 pc. Methods. We utilized optical integral field spectroscopy (IFS) data obtained with FLAMES. Results. A detailed extinction map for the ionized gas in NGC 5253 shows that the largest extinction is associated with the prominent Giant H ii region. There is an offset of ∼0. ′′ 5 between the peak of the optical continuum and the extinction peak in agreement with findings in the infrared. We found that stars suffer less extinction than gas by a factor of ∼0.33. The [S ii]λ6717/[S ii]λ6731 map shows an electron density (N e ) gradient declining from the peak of emission in Hα (790 cm −3 ) outwards, while the argon line ratio traces areas with N e ∼ 4200 − 6200 cm −3 . The area polluted with extra nitrogen, as deduced from the excess [N ii]λ6584/Hα, extends up to distances of 3. ′′ 3 (∼60 pc) from the maximum pollution, which is offset by ∼1. ′′ 5 from the peak of continuum emission. Wolf-Rayet features are distributed in an irregular pattern over a larger area (∼ 100 pc×100 pc) and associated with young stellar clusters. We measured He + abundances over most of the field of view and values of He ++ /H + ∼ < 0.0005 in localized areas which do not coincide, in general, with the areas presenting W-R emission or extra nitrogen. The line profiles are complex. Up to three emission components were needed to reproduce them. One of them, associated with the giant H ii region, presents supersonic widths and [N ii]λ6584 and [S ii]λλ6717,6731 emission lines shifted up to 40 km s −1 with respect to Hα. Similarly, one of the narrow components presents offsets in the [N ii]λ6584 line of ∼ < 20 km s −1 . This is the first time that maps with such velocity offsets for a starburst galaxy have been presented. The observables in the giant H ii region fit with a scenario where the two super stellar clusters (SSCs) produce an outflow that encounters the previously quiescent gas. The south-west part of the FLAMES IFU field is consistent with a more evolved stage where the star clusters have already cleared out their local environment.
Dense molecular globulettes and the dust arc toward the runaway O star AE Aurigae (HD 34078)
Astronomy & Astrophysics, 2014
Context. Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. Aims. We aim to understand the physical mechanisms that shape the dust arc observed near the runaway O-star AE Aur (HD 34078). Methods. We obtained and analyzed a high spatial resolution (4.4 ) map of the 12 CO(1−0) emission that is centered on HD 34078, and that combines data from both the IRAM interferometer and 30 m single-dish antenna. Results. One third of the 30 m flux mainly originates from two small (no larger than 5 × 10 or 0.013 × 0.026 pc), and bright (1 and 3 K peak temperatures) CO globulettes. The line of sight toward HD 34078 intersects the outer part of one of the globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD 34078's spectra, including those from highly excited H 2 . Their modeled distance from the star (0.2 pc) is compatible with the fact that they lie on the 3D paraboloid, which fits the arc detected in the 24 μm Spitzer image. Four other compact CO globulettes are detected in the mapped area, all lying close to the rim of this paraboloid. These globulettes have a high density and linewidth, and are strongly pressure-confined or transient. Conclusions. The presence of molecular globulettes at such a close distance from an O star is unexpected, and probably related to the high proper motion of HD 34078. Indeed, the good spatial correlation between the CO globulettes and the IR arc suggests that they result from the interaction of the radiation and wind emitted by HD 34078 with the ambient gas. However, the details of this interaction remain unclear. A wind mass-loss rate significantly larger than the value inferred from UV lines is favored by the large IR arc size, but does not easily explain the low velocity of the CO globulettes. The effect of radiation pressure on dust grains also meets several issues in explaining the observations. Further observational and theoretical work is needed to fully elucidate the processes shaping the gas and dust in bow shocks around runaway O stars.
The Astrophysical Journal, 2011
We have studied the X-ray emission within the inner ∼150 pc radius of NGC 4151 by constructing high spatial resolution emission line images of blended OVII, OVIII, and NeIX. These maps show extended structures that are spatially correlated with the radio outflow and optical [OIII] emission. We find strong evidence for jet-gas cloud interaction, including morphological correspondences with regions of X-ray enhancement, peaks of near-infrared [FeII] emission, and optical clouds. In these regions, moreover, we find evidence of elevated NeIX/OVII ratios; the X-ray emission of these regions also exceeds that expected from nuclear photoionization. Spectral fitting reveals the presence of a collisionally ionized component. The thermal energy of the hot gas suggests that 0.1% of the estimated jet power is deposited into the host interstellar medium through interaction between the radio jet and the dense medium of the circum-nuclear region. We find possible pressure equilibrium between the collisionally ionized hot gas and the photoionized line-emitting cool clouds. We also obtain constraints on the extended iron and silicon fluorescent emission. Both lines are spatially unresolved. The upper limit on the contribution of an extended emission region to the Fe Kα emission is 5% of the total, in disagreement with a previous claim that 65% of the Fe Kα emission originates in the extended narrow line region.