We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at ∼25 pc resolution from the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H22.12
We investigate the nature of a Galactic Centre source, G0.17+0.15, lying along the northern extension of the radio arc near l ∼ 0.2°. G0.17+0.15 is an H ii region located towards the eastern edge of the radio bubble, embedded within the highly polarized Galactic Centre eastern lobe where a number of radio filaments appear to cross through the H ii region. We report the detection of hydrogen and helium recombination lines with a radial velocity exceeding 140 km s−1 based on Green Bank Telescope and Very Large Array observations. The morphology of G0.17+0.15, aided by kinematics, and spectral index characteristics, suggests the presence of an external pressure dragging and shredding the ionized gas. We argue that this ionized cloud is interacting with a bundle of radio filaments and is entrained by the ram pressure of the radio bubble, which itself is thought to be produced by cosmic ray driven outflows at the Galactic Centre. In this interpretation, the gas streamers on the western side of G0.17+0.15 are stripped, accelerated from 0 to $\delta v\sim \, 35$ km s−1 over a time-scale roughly 8 × 104 yr, implying that ablating ram pressure is $\sim 700\, \mathrm{eV\, cm^{-3}}$, comparable to the $\sim 10^3\, \mathrm{eV \, cm^{-3}}$ cosmic ray driven wind pressure in the Galactic Centre region.
more » « less- NSF-PAR ID:
- 10499387
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 530
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 235-253
- Size(s):
- ["p. 235-253"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract μ m) to optical ionized gas ([Oiii ], [Nii ], [Sii ], and [Oi ]) and hot plasma (FeXXV ). In the most distinct bubble, we see a clear shock front traced by high [Oiii ]/Hβ and [Oiii ]/[Oi ]. Cool molecular gas (CO(2−1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H2extends at least ∼4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies’ interstellar media are colliding. A ridgeline of high [Oiii ]/Hβ emission along the eastern arm aligns with the southern nucleus’ stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus. -
more » « less
ABSTRACT This paper presents a multiwavelength investigation of the Galactic H ii region IRAS 17149 − 3916. Using the Giant Meterwave Radio Telescope, India, first low-frequency radio continuum observations at 610 and 1280 MHz for this region are presented. The ionized gas emission displays an interesting cometary morphology, which is likely powered by the early-type source, E4 (IRS-1). The origin of the cometary morphology is discussed under the framework of the widely accepted bow shock, champagne flow, and clumpy cloud mechanisms. The mid- and far-infrared data from Spitzer-GLIMPSE and Herschel-Hi-GAL reveal a complex network of pillars, clumps, bubble, filaments, and arcs suggesting the profound influence of massive stars on the surrounding medium. Triggered star formation at the tip of an observed pillar structure is reported. High-resolution ALMA continuum data show a string of cores detected within the identified clumps. The core masses are well explained by thermal Jeans fragmentation and support the hierarchical fragmentation scenario. Four ‘super-Jeans’ cores are identified which, at the resolution of the present data set, are suitable candidates to form high-mass stars.
-
more » « less
ABSTRACT We analyse the internal structure and dynamics of cosmic-web filaments connecting massive high-z haloes. Our analysis is based on a high-resolution arepo cosmological simulation zooming-in on three Mpc-scale filaments feeding three massive haloes of $\sim 10^{12}\, \text{M}_\odot$ at z ∼ 4, embedded in a large-scale sheet. Each filament is surrounded by a cylindrical accretion shock of radius $r_{\rm shock} \sim 50 \, {\rm kpc}$. The post-shock gas is in virial equilibrium within the potential well set by an isothermal dark-matter filament. The filament line-mass is $\sim 9\times 10^8\, \text{M}_\odot \, {\rm kpc}^{-1}$, the gas fraction within rshock is the universal baryon fraction, and the virial temperature is ∼7 × 105 K. These all match expectations from analytical models for filament properties as a function of halo mass and redshift. The filament cross-section has three radial zones. In the outer ‘thermal’ (T) zone, $r \ge 0.65 \, r_{\rm shock}$, inward gravity, and ram-pressure forces are overbalanced by outward thermal pressure forces, decelerating the inflowing gas and expanding the shock outwards. In the intermediate ‘vortex’ (V) zone, 0.25 ≤ r/rshock ≤ 0.65, the velocity field is dominated by a quadrupolar vortex structure due to offset inflow along the sheet through the post-shock gas. The outward force is dominated by centrifugal forces associated with these vortices, with additional contributions from global rotation and thermal pressure. Shear and turbulent forces associated with the vortices act inwards. The inner ‘stream’ (S) zone, $r \lt 0.25 \, r_{\rm shock}$, is a dense isothermal core, $T\sim 3 \times 10^4 \, {\rm K}$ and $n_{\rm H}\sim 0.01 \, {\rm cm^{-3}}$, defining the cold streams that feed galaxies. The core is formed by an isobaric cooling flow and is associated with a decrease in outward forces, though exhibiting both inflows and outflows.
-
more » « less
ABSTRACT G0.253+0.016, commonly referred to as ‘the Brick’ and located within the Central Molecular Zone, is one of the densest (≈103–4 cm−3) molecular clouds in the Galaxy to lack signatures of widespread star formation. We set out to constrain the origins of an arc-shaped molecular line emission feature located within the cloud. We determine that the arc, centred on $\lbrace l_{0},b_{0}\rbrace =\lbrace 0{_{.}^{\circ}} 248,\, 0{_{.}^{\circ}} 018\rbrace$, has a radius of 1.3 pc and kinematics indicative of the presence of a shell expanding at $5.2^{+2.7}_{-1.9}$ $\mathrm{\, km\, s}^{-1}$. Extended radio continuum emission fills the arc cavity and recombination line emission peaks at a similar velocity to the arc, implying that the molecular gas and ionized gas are physically related. The inferred Lyman continuum photon rate is NLyC = 1046.0–1047.9 photons s−1, consistent with a star of spectral type B1-O8.5, corresponding to a mass of ≈12–20 M⊙. We explore two scenarios for the origin of the arc: (i) a partial shell swept up by the wind of an interloper high-mass star and (ii) a partial shell swept up by stellar feedback resulting from in situ star formation. We favour the latter scenario, finding reasonable (factor of a few) agreement between its morphology, dynamics, and energetics and those predicted for an expanding bubble driven by the wind from a high-mass star. The immediate implication is that G0.253+0.016 may not be as quiescent as is commonly accepted. We speculate that the cloud may have produced a ≲103 M⊙ star cluster ≳0.4 Myr ago, and demonstrate that the high-extinction and stellar crowding observed towards G0.253+0.016 may help to obscure such a star cluster from detection.
-
ABSTRACT We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass haloes hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity $\kappa \sim 3\times 10^{29}\, \mathrm{cm^2\ s^{-1}}$ chosen to match γ-ray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MW-mass haloes at z ≲ 1–2. The gas in these ‘CR-dominated’ haloes differs significantly from runs without CRs: the gas is primarily cool (a few ${\sim}10^{4}\,$ K), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. Ionization of the ‘low’ and ‘mid’ ions in this diffuse cool gas is dominated by photoionization, with O vi columns ${\gtrsim}10^{14.5}\, \mathrm{cm^{-2}}$ at distances ${\gtrsim}150\, \mathrm{kpc}$. CR and thermal gas pressure are locally anticorrelated, maintaining total pressure balance, and the CGM gas density profile is determined by the balance of CR pressure gradients and gravity. Neglecting CRs, the same haloes are primarily warm/hot ($T\gtrsim 10^{5}\,$K) with thermal pressure balancing gravity, collisional ionization dominates, O vi columns are lower and Ne viii higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase.more » « less
