Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLarge-scale shock-ionized and photo-ionized gas in M83: the impact of star formation
248
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 degA)/H{beta} vs. [S II](6716 deg A+6731 deg A)/H{alpha} with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.2 x 0.2) basis and compare it with several photo- and shock-ionization models. For the photo-ionized gas, we observe a gradual increase of the log([O III]/H{beta}) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photo-ionized from the shock-ionized component of the gas. We find that the shock-ionized H{alpha} emission ranges from ~2% to about 15-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is an horizontal distribution around log([O III]/H{beta}) ~ 0. This feature is well fit by a shock-ionization model with 2.0 Zodot metallicity and shock velocities in the range of 250 km/s to 350 km/s. A low velocity shock component, < 200 km/s, is also detected, and is spatially located at the boundary between the outer ring and the spiral arm. The low velocity shock component can be due to : 1) supernova remnants located nearby, 2) dynamical interaction between the outer ring and the spiral arm, 3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.
rate research
Read More
We present the first kinematic study of extraplanar diffuse ionized gas (eDIG) in the nearby, face-on disk galaxy M83 using optical emission-line spectroscopy from the Robert Stobie Spectrograph on the Southern African Large Telescope. We use a Markov Chain Monte Carlo method to decompose the [NII]$lambdalambda$6548, 6583, H$alpha$, and [SII]$lambdalambda$6717, 6731 emission lines into HII region and diffuse ionized gas emission. Extraplanar, diffuse gas is distinguished by its emission-line ratios ([NII]$lambda$6583/H$alpha gtrsim 1.0$) and its rotational velocity lag with respect to the disk ($Delta v = -24$ km/s in projection). With interesting implications for isotropy, the velocity dispersion of the diffuse gas, $sigma = 96$ km/s, is a factor of a few higher in M83 than in the Milky Way and nearby, edge-on disk galaxies. The turbulent pressure gradient is sufficient to support the eDIG layer in dynamical equilibrium at an electron scale height of $h_{z} = 1$ kpc. However, this dynamical equilibrium model must be finely tuned to reproduce the rotational velocity lag. There is evidence of local bulk flows near star-forming regions in the disk, suggesting that the dynamical state of the gas may be intermediate between a dynamical equilibrium and a galactic fountain flow. As one of the first efforts to study eDIG kinematics in a face-on galaxy, this study demonstrates the feasibility of characterizing the radial distribution, bulk velocities, and vertical velocity dispersions in low-inclination systems.
We present Spitzer IRS spectra and MIPS photometry of 12 radio-loud QSOs with FR II morphologies at z ~ 0.3. Six of the sources are surrounded by luminous extended emission-line regions (EELRs), while the other six do not have such extended nebulae. The two subsamples are indistinguishable in their mid-infrared spectra and overall infrared spectral energy distributions (SEDs). For both subsamples, the mid-infrared aromatic features are undetected in either individual sources or their stacked spectra, and the SEDs are consistent with pure quasar emission without significant star formation. The upper limits to the star formation rate are sufficiently low that starburst-driven superwinds can be ruled out as a mechanism for producing the EELRs, which are instead likely the result of the ejection of most of the gas from the system by blast waves accompanying the launching of the radio jets. The FR II quasars deviate systematically from the correlation between host galaxy star formation rate and black hole accretion rate apparently followed by radio-quiet QSOs, implying little or no bulge growth coeval with the current intensive black hole growth. We also present a new Spitzer estimate of the star formation rate for the starburst in the host galaxy of the compact steep-spectrum radio quasar 3C 48.
We considered the regions of triggered star formation inside kpc-sized HI supershells in three dwarf galaxies: IC 1613, IC 2574 and Holmberg II. The ionized and neutral gas morphology and kinematics were studied based on our observations with scanning Fabry-Perot interferometer at the SAO RAS 6-m telescope and 21 cm archival data of THINGS and LITTLE THINGS surveys. The qualitative analysis of the observational data performed in order to highlight the two questions: why the star formation occurred very locally in the supershells, and how the ongoing star formation in HI supershells rims influence its evolution? During the investigation we discovered the phenomenon never observed before in galaxies IC 2574 and Holmberg II: we found faint giant (kpc-sized) ionized shells in H-alpha and [SII]6717,6731 lines inside the supergiant HI shells.
To investigate the connection between radio activity and AGN outflows, we present a study of ionized gas kinematics based on [O III] $lambda$5007 emission line along the large-scale radio jet for six radio AGNs. These AGNs are selected based on the radio activity (i.e., $mathrm{L_{1.4GHz}}$ $geqslant$ 10$^{39.8}$ erg s$^{-1}$) as well as optical emission line properties as type 2 AGNs. Using the Red Channel Cross Dispersed Echellette Spectrograph at the Multiple Mirror Telescope, we investigate in detail the [O III] and stellar kinematics. We spatially resolve and probe the central AGN-photoionization sizes, which is important in understanding the structures and evolutions of galaxies. We find that the typical central AGN-photoionization radius of our targets are in range of 0.9$-$1.6 kpc, consistent with the size-luminosity relation of [O III] in the previous studies. We investigate the [O III] kinematics along the large-scale radio jets to test whether there is a link between gas outflows in the narrow-line region and extended radio jet emissions. Contrary to our expectation, we find no evidence that the gas outflows are directly connected to the large scale radio jets.
We present a simple model that explains the origin of warm diffuse gas seen primarily as highly ionized absorption line systems in the spectra of background sources. We predict the observed column densities of several highly ionized transitions such as OVI, OVIII, NeVIII, NV, and MgX; and present a unified comparison of the model predictions with absorption lines seen in the Milky Way disk, Milky Way halo,starburst galaxies, the circumgalactic medium and the intergalactic medium at low and high redshifts. We show that diffuse gas seen in such diverse environments can be simultaneously explained by a simple model of radiatively cooling gas. We show that most of such absorption line systems are consistent with being collisionally ionized, and estimate the maximum likelihood temperature of the gas in each observation. This model satisfactorily explains why OVI is regularly observed around star-forming low-z L* galaxies, and why NV is rarely seen around the same galaxies. We further present some consequences of this model in quantifying the dynamics of the cooling gas around galaxies and predict the shock velocities associated with such flows. A unique strength of this model is that while it has only one free (but physically well-constrained) parameter, it nevertheless successfully reproduces the available data on O VI absorbers in the interstellar, circumgalactic, intra-group, and intergalactic media, as well as the available data on other absorption-line from highly ionized species.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
