相关论文: Helium Ionization in the Diffuse Ionized Gas surro…
The first stars and quasars are known sources of hard ionizing radiation in the first billion years of the Universe. We examine the joint effects of X-rays and hard UV radiation from such first-light sources on the hydrogen and helium…
A group of four compact HII regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of ~6 pc. We present a study of ionized…
Hypercompact HII regions (HC) are regions of ionized gas associated with the early stages of high-mass star formation. With the aim of better understanding their characteristics, we studied five candidate HC HII regions. Here, we present…
Helium reionization is the most recent phase change of the intergalactic medium, yet its timing and main drivers remain uncertain. Among the probes to trace its unfolding, the 3.46 cm hyperfine line of singly-ionized helium opens the study…
The dynamics of ionized gas around the W33 Main ultracompact HII region is studied using observations of hydrogen radio recombination lines and a detailed multiwavelength characterization of the massive star-forming region W33 Main is…
From the first published z > 3 survey of 21-cm absorption within the hosts of radio galaxies and quasars, we found an apparent dearth of cool neutral gas at high redshift. From a detailed analysis of the photometry, each object is found to…
We present spectroscopic observations of ionized gas in the disk-halo regions of five edge-on galaxies, covering a wavelength range from [OII] 3727A to [SII] 6716.4A. The inclusion of the [OII] emission provides additional constraints on…
We examine the impact of helium reionization on the structure of the intergalactic medium (IGM). We model the reionization using a radiative transfer (RT) code coupled to the combined gravity hydrodynamics code Enzo. Neutral hydrogen and…
G45.45+0.06 is an ultra-compact HII (UCHII) region extensively studied. It is known that G45.45+0.06 is embedded in a complex of UCHII regions, but up the date, the surrounding ISM in a larger spatial scale has not been analyzed. Using data…
We report on observations of several optical emission lines toward a variety of newly revealed faint, large-scale Halpha-emitting regions in the Galaxy. The lines include [NII] 6583, [NII] 5755, [SII] 6716, [OIII] 5007, and HeI 5876…
We present an analysis combining the simultaneous measurement of intergalactic absorption by hydrogen (H I), helium (He II) and oxygen (O VI) in UV and optical quasar spectra. The combination of the H I and He II Lyman-alpha forests through…
Aims: We systematically explore a plausible subset of the parameter space involving effective temperatures and metallicities of the ionizing stellar sources, the effects of the hardening of their radiation by surrounding leaky HII regions…
The cosmic abundance of hydrides depends critically on high-energy UV, X-ray, and particle irradiation. Here we study hydrides in star-forming regions where irradiation by the young stellar object can be substantial, and density and…
We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15<log N(HI)<19 at z<1 using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity…
We have obtained high resolution FUSE and HST/STIS echelle observations of the quasar PG 1116+215. The semi-continuous coverage of the ultraviolet spectrum over the wavelength range 916-2800 provides detections of Galactic and high velocity…
We investigate the ionization and the opacity of warm, dense helium under conditions found in the atmospheres of cool white dwarf stars. Our particular interest is in densities up to $\rm 3 g/cm^{3}$ and temperatures from 1000K to 10000K.…
The Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) is a fully-sampled radio recombination line (RRL) survey of the inner Galaxy at C-band (4-8 GHz). We average together ~15 Hn$\alpha$ RRLs within the receiver bandpass to…
We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of HII galaxies adequate to the data that can be obtained with the XXI century technology. This methodology requires the…
We present interstellar absorption line measurements of the ions S III and Al III towards six stars using archival Goddard High Resolution Spectrograph data. The ions Al III and S III trace heavily depleted and non-depleted elements,…
Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously…