ترغب بنشر مسار تعليمي؟ اضغط هنا

Stellar X-ray Binary Populations in Elliptical Galaxies

66   0   0.0 ( 0 )
 نشر من قبل Raymond E. White III
 تاريخ النشر 2001
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

Chandras high angular resolution can resolve emission from stellar X-ray binaries out of the diffuse X-ray emission from gaseous atmospheres within elliptical galaxies. Variations in the X-ray binary populations (per unit galaxian optical luminosity) are correlated with variations in the specific frequency of globular clusters in ellipticals. This indicates that X-ray binaries are largely formed in globular clusters, rather than being a primordial field population.



قيم البحث

اقرأ أيضاً

We propose a physically motivated and self-consistent prescription for the modeling of transient neutron star (NS) low-mass X-ray binary (LMXB) properties, such as duty cycle (DC), outburst duration and recurrence time. We apply this prescription to the population synthesis (PS) models of field LMXBs presented by Fragos et al. (2008), and compare the transient LMXB population to the Chandra X-ray survey of the two elliptical galaxies NGC 3379 and NGC 4278, which revealed several transient sources (Brassington et al., 2008, 2009). We are able to exclude models with a constant DC for all transient systems, while models with a variable DC based on the properties of each system are consistent with the observed transient populations. We predict that the majority of the observed transient sources in these two galaxies are LMXBs with red giant donors. Our comparison suggests that LMXBs formed through evolution of primordial field binaries are dominant in globular cluster (GC) poor elliptical galaxies, while they still have a significant contribution in GC rich ones.
We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z~0.2: A115, A655, A963 and A2111. Using the new, high-resolution stellar populations models developed in our group, we obtain ed accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe. We have found that [CN/H] and [Mg/H] are correlated with sigma while [Fe/H] and Log(age) are not. In addition, both abundance ratios [CN/Fe] and [Mg/Fe] increase with sigma. Furthermore, the [CN/H]-sigma and [CN/Fe]-sigma slopes are steeper for galaxies in very rich clusters than those in the less dense Virgo and Coma clusters. On the other hand, [Mg/H]-sigma and [Mg/Fe]-sigma slopes keep constant as functions of the environment. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ~1 Gyr. This result implies that massive elliptical galaxies have evolved passively since, at least, as long ago as z~2. For a given galaxy mass the duration of star formation is shorter in those galaxies belonging to more dense environments; whereas the mass-metallicity relation appears to be also a function of the cluster properties: the denser the environment is, the steeper are the correlations. Finally, we show that the abundance ratios [CN/Fe] and [Mg/Fe] are the key chemical clocks to infer the star formation history timescales in ellipticals. In particular, [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] apperars to be the most suitable parameter to resolve them in elliptical galaxies with sigma<300 km/s.
We are using optical/IR surface brightness fluctuations (SBFs) to validate the latest stellar population synthesis models and to understand the stellar populations of ellipticals. Integrated light and spectra measure only the first moment of the stel lar luminosity function (Sigma n_i * L_i). Since SBFs also depend on the second moment (Sigma n_i * L_i^2), they provide novel information, in particular about the reddest, most luminous RGB and AGB stars, which are the most difficult stars to model. SBFs can also provide useful new constraints on the age/metallicity of unresolved stellar populations in ellipticals. Finally, developing accurate stellar population models benefits several aspects of SBF distance measurements to galaxies.
187 - L. van Zee , 2004
We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the Virgo Cluster with previously measured kinematic properties. The global optical colors are red, with median values for the sample of 0.24 +/- 0.03 in (U-B), 0.77 +/- 0.02 in (B-V), and 1.02 +/- 0.03 in (V-I). We recover the well known color-magnitude relation for cluster galaxies, but find no significant difference in dominant stellar population between rotating and non-rotating dwarf elliptical galaxies; the average age of the dominant stellar population is 5-7 Gyr in all 16 galaxies in this sample. Analysis of optical spectra confirm these age estimates and indicate Fe and Mg abundances in the range of 1/20th to 1/3 of solar, as expected for low luminosity galaxies. Based on Lick indices and simple stellar population models, the derived [alpha/Fe] ratios are sub-solar to solar, indicating a more gradual chemical enrichment history for dEs as compared to giant elliptical galaxies in the Virgo Cluster. These observations confirm the marked difference in stellar population and stellar distribution between dwarf and giant elliptical galaxies and further substantiate the need for alternative evolutionary scenarios for the lowest mass cluster galaxies. We argue that it is likely that several different physical mechanisms played a significant role in the production of the Virgo cluster dE galaxies including in situ formation, infall of dEs that were once part of Local Group analogs, and transformation of dwarf irregular galaxies by the cluster environment. The observations support the hypothesis that a large fraction of the Virgo cluster dEs are formed by ram pressure stripping of gas from infalling dIs.
95 - P. Tzanavaris 2015
We obtain total galaxy X-ray luminosities, $L_X$, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the $pm1sigma$ scatter of the Mineo et al. (2012) $L_X$ - star formation rate (SFR) correlation or have higher $L_X$ than predicted by this correlation for their SFR. We discuss how these excesses may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. (2011) $L_X$ - stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme $L_X$ values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high $L_X$ values can be observed due to strong XRB variability.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا