اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPhotoionization models of CALIFA HII regions. Genetic method
80
0
0.0
(
0
)
تأليف
Christophe Morisset
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
I present recent and forthcoming works to model the CALIFA HII region using photoionization models. The first results are obtained with ad-hoc models (combining parameter determination by model fitting and strong line methods) while the next ones will use a Genetic Algorithm to fit the observations in a multi-dimensional space.
قيم البحث
اقرأ أيضاً
Photoionization models of HII regions require as input a description of the ionizing SED and of the gas distribution, in terms of ionization parameter U and chemical abundances (e.g. O/H and N/O). A strong degeneracy exists between the hardness of th
e SED and U, which in turn leads to high uncertainties in the determination of the other parameters, including abundances. One way to resolve the degeneracy is to fix one of the parameters using additional information. For each of the ~ 20000 sources of the CALIFA HII regions catalog, a grid of photoionization models is computed assuming the ionizing SED being described by the underlying stellar population obtained from spectral synthesis modeling. The ionizing SED is then defined as the sum of various stellar bursts of different ages and metallicities. This solves the degeneracy between the shape of the ionizing SED and U. The nebular metallicity (associated to O/H) is defined using the classical strong line method O3N2 (which gives to our models the status of hybrids). The remaining free parameters are the abundance ratio N/O and the ionization parameter U, which are determined by looking for the model fitting [NII]/Ha and [OIII]/Hb. The models are also selected to fit [OII]/Hb. This process leads to a set of ~ 3200 models that reproduce simultaneously the three observations. We find that the regions associated to young stellar bursts suffer leaking of the ionizing photons, the proportion of escaping photons having a median of 80%. The set of photoionization models satisfactorily reproduces the electron temperature derived from the [OIII]4363/5007 line ratio. We determine new relations between the ionization parameter U and the [OII]/[OIII] or [SII]/[SIII] line ratios. New relations between N/O and O/H and between U and O/H are also determined. All the models are publicly available on the 3MdB database.
We present a new catalog of HII regions based on the integral field spectroscopy (IFS) data of the extended CALIFA and PISCO samples. The selection of HII regions was based on two assumptions: a clumpy structure with high contrast of H$alpha$ emissio
n and an underlying stellar population comprising young stars. The catalog provides the spectroscopic information of 26,408 individual regions corresponding to 924 galaxies, including the flux intensities and equivalent widths of 51 emission lines covering the wavelength range between 3745-7200A. To our knowledge, this is the largest catalog of spectroscopic properties of HII regions. We explore a new approach to decontaminate the emission lines from diffuse ionized gas contribution. This diffuse gas correction was estimated to correct every emission line within the considered spectral range. With the catalog of HII regions corrected, new demarcation lines are proposed for the classical diagnostic diagrams. Finally, we study the properties of the underlying stellar populations of the HII regions. It was found that there is a direct relationship between the ionization conditions on the nebulae and the properties of stellar populations besides the physicals condition on the ionized regions.
Context. The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young HII regions such as hyper-compact HII(HCHII) and ultra-co
mpact HII(UCHII) regions and leads to the underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Aims. The two primary goals of this study are (1) to determine the physical properties of young HII regions from radio SEDs in the search for potential HCHII regions, and (2) to use these physical properties to investigate their evolution. Method. We used the Karl G. Jansky Very Large Array (VLA) to observe the X-band and K-band with angular resolutions of ~1.7 and ~0.7, respectively, toward 114 HII regions with rising-spectra between 1-5 GHz. We complement our observations with VLA archival data and construct SEDs in the range of 1-26 GHz and model them assuming an ionization-bounded HII region with uniform density. Results. Our sample has a mean electron density of ne=1.6E4cm^{-3}, diameter diam=0.14pc, and emission measure EM = 1.9E7pc*cm^{-6}. We identify 16 HCHII region candidates and 8 intermediate objects between the classes of HCHII and UCHII regions. The ne, diam, and EM change as expected, but the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman-continuum photons are absorbed by dust within these HII regions and the dust absorption fraction tends to be more significant for more compact and younger HII regions. Conclusion. Young HII regions are commonly located in dusty clumps; HCHII regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
We calculate the effective temperature ($T_{rm eff}$) of ionizing star(s), oxygen abundance of the gas phase $(rm O/H)$, and the ionization parameter $U$ for a sample of H,{sc ii} regions located in the disks of 59 spiral galaxies in the 0.005 < z <
0.03 redshift range. We use spectroscopic data taken from the CALIFA data release 3 (DR3) and theoretical (for $T_{rm eff}$ and $U$) and empirical (for O/H) calibrations based on strong emission-lines. We consider spatial distribution and radial gradients of those parameters in each galactic disk for the objects in our sample. Most of the galaxies in our sample ($sim70$ %) shows positive $T_{rm eff}$ radial gradients even though some them exhibit negative or flat ones. The median value of the $T_{rm eff}$ radial gradient is 0.762 kK/$R_{25}$. We find that radial gradients of both $log U$ and $T_{rm eff}$ depend on the oxygen abundance gradient, in the sense that the gradient of $log U$ increases as $log(rm O/H)$ gradient increases while there is an anti-correlation between the gradient of $T_{rm eff}$ and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat $log U$ and $T_{rm eff}$ gradients as well. Although our results are in agreement with the idea of the existence of positive $T_{rm eff}$ gradients along the disk of the majority of spiral galaxies, this seems not to be an universal property for these objects.
Helium is the second most common chemical species in the Universe. The study of helium abundance has the potential to unravel the chemical evolution of and within galaxies. In this study, we provide an empirical calibration for the singly ionized hel
ium abundance: $12+log_{10}({rm He}^+/{rm H}^+)$, based on the emission line flux ratio He$_{lambda5876}$/H$alpha$ from Galactic and extragalactic HII regions compiled from the literature. Based on this calibrator, we explore for the first time the helium abundance in a large sample of HII regions located in galaxies representative of the nearby Universe from the CALIFA survey. Furthermore, this calibrator allows us to explore the variations of the helium abundance with respect to the oxygen abundance. The observed trends are in agreement with a change in the chemical enrichment with mass/oxygen abundance similar to the one observed due to the inside-out model in a MW-galaxy (highlighting the connection between resolved and global trends in galaxies). Our calibrator provides an empirical proxy to estimate the helium abundance at kpc scales as well as to constrain chemical evolutionary models.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
