Interarm Gas Research Articles

Arm–interarm gas abundance variations explored with MUSE: the role of spiral structure in the chemical enrichment of galaxies

ABSTRACT Spiral arms are the most characteristic features of disc galaxies, easily distinguishable due to their association with ongoing star formation. However, the role of spiral structure in the chemical evolution of galaxies is unclear. Here, we explore gas-phase abundance variations between arm and interarm regions for a sample of 45 spiral galaxies using high spatial resolution VLT/MUSE integral field spectroscopy data. We report the presence of more metal-rich $\rm{H \, \small{II}}$ regions in the spiral arms with respect to the corresponding interarm regions for a large subsample of galaxies ($45\!-\!65{{\ \rm per\ cent}}$ depending on the adopted calibrator for the abundance derivation). A small percentage of the sample is observed to display the opposite trend, i.e. more metal-poor $\rm{H \, \small{II}}$ regions in the spiral arms compared to that of the interarms ($5\!-\!20{{\ \rm per\ cent}}$ depending on the calibrator). We investigate the dependence of the variations with three galaxy properties: the stellar mass, the presence of bars, and the flocculent/grand design appearance of spiral arms. In all cases, we observe that the arm–interarm abundance differences are larger (positive) in more massive and grand-design galaxies. This is confirmed by an analogous spaxel-wise analysis, which also shows a noticeable effect of the presence of galactic bars, with barred systems presenting larger (positive) arm–interarm abundance variations than unbarred systems. The comparison of our results with new predictions from theoretical models exploring the nature of the spirals would highly impact on our knowledge on how these structures form and affect their host galaxies.

Internal structure of spiral arms traced with [C II]: Unraveling the warm ionized medium, H I, and molecular emission lanes

Context. The spiral arm tangencies are ideal lines of sight in which to determine the distribution of interstellar gas components in the spiral arms and study the influence of spiral density waves on the interarm gas in the Milky Way. [C ii] emission in the tangencies delineates the warm ionized component and the photon-dominated regions and is thus an important probe of spiral arm structure and dynamics. Aims. We aim to use [C ii], H i ,a nd 12 CO spectral line maps of the Crux, Norma, and Perseus tangencies to analyze the internal structure of the spiral arms in different gas layers. Methods. We used [C ii] l-V maps along with those for H i and 12 CO to derive the average spectral line intensity profiles over the longitudinal range of each tangency. Using the VLSR of the emission features, we located the [C ii], H i ,a nd 12 CO emissions along a cross cut of the spiral arm. We used the [C ii] velocity profile to identify the compressed warm ionized medium (WIM) in the spiral arm. Results. We present a large-scale (∼15 ◦ ) position-velocity map of the Galactic plane in [C ii] from l = 326. ◦ 6 to 341. 4 observed with Herschel HIFI. In the spectral line profiles at the tangencies, [C ii] has two emission peaks, one associated with the compressed WIM and the other the molecular gas photon-dominated regions. When represented as a cut across the inner to outer edge of the spiral arm, the [C ii]‐WIM peak appears closest to the inner edge while 12 CO and [C ii] associated with molecular gas are at the outermost edge. H i has broader emission with an intermediate peak located nearer to that of 12 CO. Conclusions. The velocity-resolved spectral line data of the spiral arm tangencies unravel the internal structure in the arms locating the emission lanes within them. We interpret the excess [C ii] near the tangent velocities as shock compression of the WIM induced by the spiral density waves and as the innermost edge of spiral arms. For the Norma and Perseus arms, we estimate widths of ∼250 pc in [C ii]‐WIM and ∼400 pc in 12 CO and overall spiral arm widths of ∼500 pc in [C ii ]a nd 12 CO emissions; in H i the widths are ∼400 pc and ∼620 pc for Perseus and Norma, respectively. The electron densities in the WIM are ∼0.5 cm −3 , about an order of magnitude higher than the average for the disk. The enhanced electron density in the WIM is a result of compression of the WIM by the spiral density wave potential.

Ram-Pressure Effects on Dense Molecular Arms in the Central Regions of Spiral Galaxies by Intracluster Medium

We investigated ram-pressure effects by an intracluster wind on an inner disk of spiral galaxies by a hydrodynamical simulation. Even if the wind is mild and not strong enough to strip the gas disk, the ram pressure disturbs orbits of the inter-arm gas significantly. This results in asymmetric dense molecular arms in the inner few kpc region of a galaxy. This mechanism would explain the asymmetric CO gas distributions in the central regions often observed in Virgo spirals.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of the Interacting Galaxies NGC 2207 and IC 2163

Hubble Space Telescope (HST) images of the galaxies NGC 2207 and IC 2163 show star formation and dust structures in a system that has experienced a recent grazing encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC 2163, forming an oval ridge of star formation along a caustic where the perturbed gas rebounded after its inward excursion. Gas flowing away from this ridge has a peculiar structure characterized by thin parallel dust filaments transverse to the direction of motion. The filaments become thicker and longer as the gas approaches the tidal arm. Star formation that occurs in the filaments consistently lags behind, as if the exponential disk pressure gradient pushes outward on the gas but not on the young stars. Numerical models suggest that the filaments come from flocculent spiral arms that were present before the interaction. The arms stretch out into parallel filaments as the tidal tail forms. A dust lane at the outer edge of the tidal tail is a shock front where the flow abruptly changes direction. Gas at small-to-intermediate radii along this edge flows back toward the galaxy, while elsewhere in the tidal arm, the gas flows outward. A spiral arm of NGC 2207 that is backlit by IC 2163 is seen with HST to contain several parallel, knotty filaments spanning the full width of the arm. These filaments are probably shock fronts in a density wave. The parallel structure suggests that the shocks occur in several places throughout the arm, or that the interarm gas is composed of spiral-like wisps that merge together in the arms. Blue clusters of star formation inside the clumps of these dust lanes show density-wave triggering in unprecedented detail. The star formation process seems to be one of local gravitational collapse, rather than cloud collisions. Spiral arms inside the oval of IC 2163 have a familiar geometry reminiscent of a bar, although there is no obvious stellar bar. The shape and orientation of these arms suggest they could be the result of inner Lindblad resonance–related orbits in the cos 2θ tidal potential that formed the oval. Their presence suggests that tidal forces alone may initiate a temporary nuclear gas flow and eventual starburst without first forming a stellar bar. Several emission structures resembling jets or conical flows that are 100–1000 pc long appear in these galaxies. In the western arm of NGC 2207, there is a dense dark cloud with a conical shape 400 pc long and a bright compact cluster at the tip, and there is a conical emission nebula of the same length that points away from the cluster in the other direction. This region also coincides with a nonthermal radio continuum source that is ~1000 times the luminosity of Cas A at λ = 20 cm. Surrounding clusters in arclike patterns may have been triggered by enormous explosions.

Are Flocculent Spirals Devoid of Density Waves? Gas Morphology and Kinematics in NGC 5055

We present interferometric observations of CO and H I in the prototypical flocculent spiral NGC 5055, which has recently been shown to exhibit weak, two-arm spiral structure in the near-infrared. The morphology and kinematics described by VLA observations of H I emission and FCRAO and Berkeley-Illinois-Maryland Association (BIMA) Array observations of CO emission provide evidence for the presence of low-amplitude density waves in NGC 5055. The distribution of CO and H I emission suggests enhanced gas surface densities along the NIR spiral arms, and structures similar to the giant molecular associations found in the grand design spirals M51 and M100 are detected. An analysis of H I and Hα velocity fields shows the kinematic signature of streaming motions similar in magnitude to those of M100 in both tracers. The lesser degree of organization along the spiral arms of NGC 5055 may be due to the lower overall gas surface density, which in the arms of NGC 5055 is a factor of 2 lower than in M100 and a factor of 6 lower than in M51; an analysis of gravitational instability shows the gas in the arms is only marginally unstable and the interarm gas is marginally stable. The limited extent of the spiral arm pattern is consistent with an isolated density wave with a relatively high pattern speed; other possible formation mechanisms are also discussed.

Detection of H II regions and ionized interarm gas in the Sombrero Galaxy /NGC 4594/

view Abstract Citations (43) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of H II regions and ionized interarm gas in the Sombrero Galaxy (NGC 4594). Schweizer, F. Abstract Spectroscopic observations of NGC 4594 unambiguously show the presence of H II regions and ionized interarm gas in that galaxy. The brightest H II regions appear to be excited by early O-type stars, giving evidence for the formation of high-mass stars. Ionized gas of low density pervades the visible disk of the galaxy and apparently corotates with the stars. The unusually high rotational velocities reveal a very massive galaxy. When combined with available photometric data, these velocities also indicate a large radial increase of the mass-to-light ratio similar to that observed in M31. Publication: The Astrophysical Journal Pub Date: February 1978 DOI: 10.1086/155884 Bibcode: 1978ApJ...220...98S Keywords: Galactic Structure; H Ii Regions; H Lines; Interstellar Gas; Ionized Gases; Spiral Galaxies; Early Stars; Nebulae; Radial Velocity; Spectroscopy; Stellar Evolution; Astrophysics; Galaxies:H II Regions full text sources ADS | data products SIMBAD (2) NED (1)

Cassiopeia A Absorption Spectrum and the Interarm Medium

A MEASUREMENT of the neutral hydrogen absorption spectrum of the Cassiopeia A radio source can in principle give information about the interarm regions of the Milky Way because this source lies in (and probably on the far side of) the Perseus arm. Neutral hydrogen lying in the region between the local arm and the Perseus arm may therefore be detectable in absorption as well as in emission. A combination of the emission and absorption data can give the spin temperature of the interarm gas (for example, see ref. 1). During the Conference of Young European Radio Astronomers at Jodrell Bank in June 1969, I was encouraged to make these measurements in discussions with Dr U. Mebold. This report describes measurements of the Cassiopeia A spectrum made with higher precision than those already published2–4.