اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMetal enrichment of the neutral gas of blue compact dwarf galaxies: the compelling case of Pox 36
232
0
0.0
(
0
)
تأليف
V. Lebouteiller
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present the analysis of the interstellar spectrum of Pox 36 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Pox 36 was selected because of the relatively low foreground gas content that makes it possible to detect absorption-lines weak enough that unseen components should not be saturated. Interstellar lines of HI, NI, OI, SiII, PII, ArI, and FeII are detected. Column densities are derived directly from the observed line profiles except for HI, whose lines are contaminated by stellar absorption. We used the TLUSTY models to remove the stellar continuum and isolate the interstellar component. The best fit indicates that the dominant stellar population is B0. The fit of the interstellar HI line gives a column density of 10^{20.3pm0.4} cm-2. Chemical abundances were then computed from the column densities using the dominant ionization stage in the neutral gas. Our abundances are compared to those measured from emission-line spectra in the optical. Our results suggest that the neutral gas of Pox 36 is metal-deficient by a factor ~7 as compared to the ionized gas, and they agree with a metallicity of ~1/35 Z$_odot$. Conclusions: The abundance discontinuity between the neutral and ionized phases implies that most of the metals released by consecutive star-formation episodes mixes with the HI gas. The volume extent of the enrichment is so large that the metallicity of the neutral gas increases only slightly. The star-forming regions could be enriched only by a small fraction (~1%), but it would greatly enhance its metallicity. Our results are compared to those of other BCDs. We confirm the overall underabundance of metals in their neutral gas, with perhaps only the lowest metallicity BCDs showing no discontinuity.
قيم البحث
اقرأ أيضاً
We present the results of high spatial resolution HI observations of five intrinsically compact dwarf galaxies which are currently experiencing a strong burst of star formation. The HI maps indicate that these systems have a complex and clumpy inters
tellar medium. Unlike typical dwarf irregular galaxies, these Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in their neutral gas distributions which may provide a clue to the origin of their strong star-burst activity. Furthermore, while all of the systems do appear to be rotating, based on observed velocity gradients, the kinematics are complex. All systems have non-ordered kinematic structure at some level; some of the extended gas is not necessarily kinematically connected to the main system. The observed gas distributions and kinematics place constraints on evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf irregulars, and dwarf ellipticals have been postulated to explain their high star formation rates and low luminosity, low metallicity nature. The BCDs appear to have higher central mass concentrations in both gas and stellar content than the dwarf irregulars, indicating that evolutionary scenarios connecting these two classes will require mass redistribution. In addition, the fact that BCDs are rotationally supported systems indicates that BCDs are unlikely to evolve into dwarf ellipticals without substantial loss of angular momentum. Thus, while such evolutionary scenarios may still be possible with the aid of mergers or tidal interactions, the isolated nature of BCDs suggests that the majority of BCDs will not fade to become objects similar to the present day dwarf ellipticals.
We have obtained new HI observations with the 100m Green Bank Telescope (GBT) for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf (BCD) galaxies, selected from the Sloan Digital Sky Survey spectral data base to be extremely m
etal-deficient (12+logO/H<7.6). Neutral hydrogen was detected in 28 galaxies, a 97% detection rate. Combining the HI data with SDSS optical spectra for the BCD sample and adding complementary galaxy samples from the literature to extend the metallicity and mass ranges, we have studied how the HI content of a galaxy varies with various global galaxian properties. There is a clear trend of increasing gas mass fraction with decreasing metallicity, mass and luminosity. We obtain the relation M(HI)/L(g)~L(g)^{-0.3}, in agreement with previous studies based on samples with a smaller luminosity range. The median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the mean gas mass fraction is 0.90+/-0.15, with a lower limit of ~0.65. The HI depletion time is independent of metallicity, with a large scatter around the median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of ~0.2. About 65% of the BCDs in our sample have an effective yield larger than the true yield, implying that the neutral gas envelope in BCDs is more metal-deficient by a factor of 1.5-20, as compared to the ionized gas.
We present the results of high spatial resolution HI synthesis observations of six blue compact dwarf (BCD) galaxies. Optically, the selected galaxies have smooth, symmetric isophotes, and thus are the most likely of the BCD class to fade into an obj
ect morphologically similar to a dwarf elliptical when the current starburst ends. The neutral gas in all six galaxies appears to be rotationally supported, however, indicating that true morphological transformation from a BCD to a dE will require significant loss of angular momentum. Based on the observed neutral gas dynamics of these and other BCDs, it is unlikely that present-day BCDs will evolve directly into dwarf ellipticals after a starburst phase. We discuss alternative evolutionary scenarios for BCDs and place them within the larger context of galaxy formation and evolution models.
In a spectroscopic survey of the Fornax cluster to Bj=17.5 using the FLAIR spectrograph on the UK Schmidt Telescope we have discovered seven new compact dwarf cluster members. These were previously thought to be giant background spirals. These new me
mbers are among the most compact, high surface brightness dwarf galaxies known with absolute magnitudes of M_B=-14 and scale lengths of alpha=400 pc. One in particular may be the first high (normal) surface brightness dwarf spiral discovered. Three of the new dwarfs are blue compact dwarfs (BCDs); their inclusion in the cluster increases the faint end of the BCD luminosity function by a factor of 2 or more. We extended the survey 2.5 mag fainter with the 2dF spectrograph and in our first field found 7 bright emission line galaxies beyond the Fornax cluster which were unresolved on the sky survey plates. Galaxies of this type would be missed in most existing galaxy surveys.
The unprecedented sensitivity of the Spitzer Space Telescope has enabled us for the first time to detect a large sample of Blue Compact Dwarf galaxies (BCDs), which are intrinsically faint in the infrared. In the present paper we present a summary of
our findings which providing essential information on the presence/absence of the Polycyclic Aromatic Hydrocarbon features in metal-poor environments. In addition, using Spitzer/IRS high-resolution spectroscopy, we study the elemental abundances of neon and sulfur in BCDs and compare with the results from optical studies. Finally, we present an analysis of the mid- and far-infrared to radio correlation in low luminosity low metallicity galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
