We present velocity-channel maps and analysis of the warm ionized medium (WIM) throughout the Sagittarius- Carina arm at Galactic longitudes 20 1000 pc along the far Carina arm. Physical conditions of the ionized gas are analyzed using the [S II]/H-alpha line ratio, which more closely traces H-alpha intensity than height above the plane, z, suggesting a stronger relationship with the in-situ electron density. We interpret this result as further evidence for the majority of the observed diffuse emission originating from in-situ ionized gas as opposed to scattered light from classical H II regions in the plane.
Two giant plasma lobes, known as the Fermi Bubbles, extend 10 kpc above and below the Galactic Center. Since their discovery in X-rays in 2003 (and in gamma-rays in 2010), the Bubbles have been recognized as a new morphological feature of our Galaxy and a striking example of energetic feedback from the nuclear region. They remain the subject of intense research and their origin via AGN activity or nuclear star formation is still debated. While imaging at gamma-ray, X-ray, microwave, and radio wavelengths has revealed their morphology and energetics, spectroscopy at radio and UV wavelengths has recently been used to study the kinematics and chemical abundances of outflowing gas clouds embedded in the Bubbles (the nuclear wind). Here we identify the scientific themes that have emerged from the spectroscopic studies, determine key open questions, and describe further observations needed in the next ten years to characterize the basic physical conditions in the nuclear wind and its impact on the rest of the Galaxy. Nuclear winds are ubiquitous in galaxies, and the Galactic Center represents the best opportunity to study the constitution and structure of a nuclear wind in close detail.
Wisconsin H-Alpha Mapper (WHAM) observations reveal high-velocity and [NII]$\lambda6584$ emission lines in the same direction and velocity as ultraviolet absorption-line features that have been previously associated with the biconical gamma-ray lobes known as the Fermi Bubbles. We measure an extinction-corrected intensity of $I_{\textrm{H}\alpha}=0.84^{+0.10}_{-0.09}$ Rayleigh for emission with line center $v_\textrm{LSR}=-221\pm3~\textrm{km}~\textrm{s}^{-1}$, corresponding to an emission measure of $EM = 2.00^{+0.64}_{-0.63}~\textrm{cm}^{-6}~\textrm{pc}$. This emission arises at the same velocity as Hubble Space Telescope/Cosmic Origins Spectrograph observations of ultraviolet absorption features detected in the PDS 456 quasar sight line that passes through the northern Bubble near $l = 10^\circ.4, b = +11^\circ.2$. We estimate the total column density of ionized gas in this velocity component to be $N(H^{+}) = \left(3.28 \pm 0.33\right) \times 10^{18}~\textrm{cm}^{-2}$. The comparison of ionized gas emission and absorption yields an estimate for the characteristic density of $n_{e,c} = 1.8 \pm 0.6~\textrm{cm}^{-3}$ and a characteristic length of $L_{c} =0.56 \pm 0.21~\textrm{pc}$ assuming $30\%$ solar metallicity. For a temperature of $T_{e}=8500^{+2700}_{-2600}$ K---consistent with the measured line widths and [NII]/H$\alpha$ line ratio---the gas has a thermal pressure of $p/k = 32,000^{+15,000}_{-14,000}~\textrm{cm}^{-3}~\textrm{K}$. Assuming the gas is $\sim 6.5$ kpc distant, the derived density and pressure appear to be anomalously high for gas $\sim 1.3$ kpc above the Galactic midplane. The large thermal pressure is comparable to both a hot halo or Fermi Bubble model, but suggest that the H$\alpha$ arises in an overpressurized zone.
We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane. However, our earlier models reproduce the peak but not the width of the observed emission measure distribution. Here, we examine whether inclusion of magnetic fields and a greater vertical extent to the simulation domain produce a gas distribution that better matches the observations. We further study the change of magnetic energy over time in our models, showing that it appears to reach a steady state after a few hundred megayears, presumably supported by a turbulent dynamo driven by the supernova explosions.
view Abstract Citations (33) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Mid-Infrared Evolution of Nova V1974 Cygni Hayward, T. L. ; Saizar, P. ; Gehrz, R. D. ; Benjamin, R. A. ; Mason, C. G. ; Houck, J. R. ; Miles, J. W. ; Gull, G. E. ; Schoenwald, J. Abstract We observed nova V1974 Cygni (1992) at mid-infrared wavelengths λ = 7.5-13 μm nine times between 1992 April (54 days after the outburst) and 1994 July (day 882). Low- and medium-resolution spectra recorded the evolution of hydrogen recombination lines, free-free continuum emission, and the [Ne II] 12.8 μm, [Ne VI] 7.6 μm, and [Mg VII] 9.0 μm forbidden lines through the nebular and coronal line phases of this event. We interpret the spectra in terms of a series of CLOUDY models that evolve in a physically realistic way throughout the period of observation. The models indicate the presence in the ejecta of three major components of differing densities, but with masses, geometries, and expansion velocities that are consistent with values indicated by optical and UV observations of the nova. In our models the abundances of neon and magnesium relative to hydrogen are 50 and 5 times their solar values, respectively, and significant overabundances of other metals are also implied. We discuss many effects such as the increase of line widths with ionization and the origin of coronal line emission as they are represented by our modeling. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177833 Bibcode: 1996ApJ...469..854H Keywords: INFRARED: STARS; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: ABUNDANCES; STARS: INDIVIDUAL CONSTELLATION NAME: NOVA V1974 CYGNI full text sources ADS | data products SIMBAD (5)
view Abstract Citations (32) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Spectroscopy of Classical Novae in the Coronal Phase Benjamin, Robert A. ; Dinerstein, Harriet L. Abstract Spectroscopic observations of V1819 Cyg, V827 Her, and V2214 Oph, obtained at 1-2.5 microns using a 32-channel InSb array detector at the Cassegrain focus of the 2.7-m telescope at McDonald Observatory during 1986-1989, are reported. The data are presented in extensive tables and graphs and characterized in detail, with a focus on the nature of the 'coronal' emission. The ratios of Br-gamma (2.167 microns) and forbidden Si VI (1.960 microns) are found to be consistent with coronal gas temperatures of about 10,000 K and with photoionization as the primary mechanism of origin for the coronal species. Severe constraints on theoretical models involving shock heating and collisional ionization are inferred. Publication: The Astronomical Journal Pub Date: November 1990 DOI: 10.1086/115619 Bibcode: 1990AJ....100.1588B Keywords: Astronomical Spectroscopy; Line Spectra; Near Infrared Radiation; Novae; Stellar Coronas; Forbidden Transitions; Stellar Evolution; Stellar Mass Ejection; Stellar Temperature; Astrophysics; STARS: NOVAE full text sources ADS | data products SIMBAD (22)
The Radcliffe wave (RW) is a recently discovered sinusoidal vertical feature of dense gas in the proximity of the Sun. In the disk plane, it is aligned with the Local Arm. However, the origin of its vertical undulation is still unknown. This study constrains the kinematics of the RW, using young stars and open clusters as tracers, and explores the possibility of this oscillation being part of a more extended vertical mode. We study the median vertical velocity trends of the young stars and clusters along with the RW and extend it further to the region beyond it. We discovered a kinematic wave in the Galaxy, distinct from the warp, with the amplitude of oscillation depending on the age of the stellar population. We performed a similar analysis in the N -body simulation of a satellite as massive as the Sagittarius dwarf galaxy impacting the galactic disk. When projected in the plane, the spiral density wave induced by the satellite impact is aligned with the RW, suggesting that both may be the response of the disk to an external perturbation. However, the observed kinematic wave is misaligned. It appears as a kinematic wave travelling radially, winding up faster than the density wave matched by the RW, setting its origins into question. If a satellite galaxy is indeed responsible for the presence of this kinematic wave, we predict the existence of a vertical velocity dipole that would be expected to form across the disk. The reality of this prediction may be measurable with the upcoming Gaia DR3 and DR4.
We present models of turbulent mixing at the boundaries between hot (T~10^{6-7} K) and warm material (T~10^4 K) in the interstellar medium, using a three-dimensional magnetohydrodynamical code, with radiative cooling. The source of turbulence in our simulations is a Kelvin-Helmholtz instability, produced by shear between the two media. We found, that because the growth rate of the large scale modes in the instability is rather slow, it takes a significant amount of time (~1 Myr) for turbulence to produce effective mixing. We find that the total column densities of the highly ionized species (C IV, N V, and O VI) per interface (assuming ionization equilibrium) are similar to previous steady-state non-equilibrium ionization models, but grow slowly from log N ~10^{11} to a few 10^{12} cm^{-2} as the interface evolves. However, the column density ratios can differ significantly from previous estimates, with an order of magnitude variation in N(C IV)/N(O VI) as the mixing develops.
