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We analyze the rest-optical emission-line ratios of star-forming galaxies at 2.7<=z<6.5 drawn from the Cosmic Evolution Early Release Science (CEERS) Survey, and their relationships with stellar mass (M_*). Our analysis includes both line…
We present a new detailed model of the He I collisional-recombination spectrum based on the most up-to-date atomic data. The model accounts for radiative transfer effects and the influence of a non-zero optical depth in He I lines arising…
We derive new spectral H_gamma index definitions which are robust age indicators for old and relatively old stellar populations and thus have great potential for solving the age-metallicity degeneracy of galaxy spectra. To study H_gamma as…
Recent analyses of nebular spectra have resulted in discrepant abundances from CNO forbidden and recombination lines. We consider independent methods of determining ion abundances for emission nebulae, comparing ion emission measures with…
Ueta & Otsuka (2021) proposed a method, named as the "Proper Plasma Analysis Practice", to analyze spectroscopic data of ionized nebulae. The method is based on a coherent and simultaneous determination of the reddening correction and…
We present new evolutionary synthesis models for Simple Stellar Populations for a wide range of ages and metallicities. The models are based on the Padova isochrones. The core of the spectral library is provided by the medium resolution…
Four IRAS-detected early type galaxies were observed with ISO. With the exception of the 15 micron image of NGC1052, the mid-IR emission from NGC1052, NGC1155, NGC5866 and NGC6958 at 4.5, 7 and 15 microns show extended emission. Mid-IR…
We present ionizing spectra estimated at 13.6--100 eV for ten dwarf galaxies with strong high ionization lines of He {\sc {ii}}$\lambda$4686 and [Ne {\sc{v}}]$\lambda$3426 ([Ne {\sc{iv}}]$\lambda$2424) at $z=0$ ($z=8$) that are identified…
The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Ly$\alpha$ forest in the spectra of quasars. The Ly$\alpha$ forest absorbers have a broad distribution of neutral hydrogen column density $N_{\rm HI}$ and…
With the goal of a thorough investigation of the ionised gas and its origin in early-type group-dominant galaxies, we present archival MUSE data for 18 galaxies from the Complete Local-Volume Groups Sample (CLoGS). This data allowed us to…
We present a self-consistent study of the stellar populations and the ionized gas in a sample of 10 HII galaxies with, at least, four measured electron temperatures and a precise determination of ionic abundances following the "direct…
Nebular spectral lines provide insight into the properties of the interstellar medium (ISM) and the ionizing radiation within galaxies. The presence of high-energy ionization lines such as \heii indicates the existence of ionizing photons…
The rates of SN Ia for double-degenerate and single-degenerate scenario are computed for the models of spiral and elliptical galaxies. The number of nuclearly burning white dwarfs (NBWD) is traced. The data favours double-degenerate…
We constructed diagnostic diagrams using emission line ratios and equivalent widths observed in several samples of HII galaxies. The diagrams are compared to predictions from new photoionization models for evolving starbursts. We find that…
Dust extinction and reddening greatly contribute to type Ia supernovae (SNe Ia) observed color and magnitude variations. The models used to describe the extinction probability density function (PDF) are often simplistic, which can…
We present a detailed study of the rest-optical (3600-7000 Angstrom) nebular spectra of ~380 star-forming galaxies at z~2-3 obtained with Keck/MOSFIRE as part of the Keck Baryonic Structure Survey (KBSS). The KBSS-MOSFIRE sample is…
We present HST/NICMOS images at 0.2" resolution of the HI Paschen Alpha (PaA) emission line in a 70" x 90" region of the Galactic center centered on the non-thermal radio source Sgr A*. The majority of the emission arises from ionized gas…
We analyze several key rest-optical emission-line ratios in a sample of 828 galaxies as well as composite spectra from JADES DR3 in the range $1.4 < z < 7$. These emission-line ratios include: [O III]$\lambda5008$/H$\beta$, [N II]$\lambda…
Analysis of the low resolution UV(IUE) spectra of 15 hot post-AGB candidates is presented. The UV(IUE) spectra of 10 stars suggest partial obscuration of the hot stars due to circumstellar dust. The reddened continua of these 10 stars were…
In systems undergoing starbursts the evolution of the young stellar population is expected to drive changes in the emission line properties. This evolution is usually studied theoretically, with a combination of evolutionary synthesis…