اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدObservational selection effects and the M-sigma relation
93
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We examine the possibility that the observed relation between black-hole mass and host-galaxy stellar velocity dispersion (the M-sigma relation) is biased by an observational selection effect, the difficulty of detecting a black hole whose sphere of influence is smaller than the telescope resolution. In particular, we critically investigate recent claims that the M-sigma relation only represents the upper limit to a broad distribution of black-hole masses in galaxies of a given velocity dispersion. We find that this hypothesis can be rejected at a high confidence level, at least for the early-type galaxies with relatively high velocity dispersions (median 268 km/s) that comprise most of our sample. We also describe a general procedure for incorporating observational selection effects in estimates of the properties of the M-sigma relation. Applying this procedure we find results that are consistent with earlier estimates that did not account for selection effects, although with larger error bars. In particular, (i) the width of the M-sigma relation is not significantly increased; (ii) the slope and normalization of the M-sigma relation are not significantly changed; (iii) most or all luminous early-type galaxies contain central black holes at zero redshift. Our results may not apply to late-type or small galaxies, which are not well-represented in our sample.
قيم البحث
اقرأ أيضاً
We report on recently derived improv
We describe a method to measure the M-sigma relation in the non-local universe using dust-obscured QSOs. We present results from a pilot sample of nine 2MASS red QSOs with redshifts 0.14<z<0.37. We find that there is an offset (0.8 dex, on average) b
etween the position of our objects and the local relation for AGN, in the sense that the majority of red QSO hosts have lower velocity dispersions and/or more massive BHs than local galaxies. These results are in agreement with recent studies of AGN at similar and higher redshifts. This could indicate an unusually rapid growth in the host galaxies since z~0.2, if these objects were to land in the local relation at present time. However, the z>0.1 AGN (including our sample and those of previous studies) have significantly higher BH mass than those of local AGN, so a direct comparison is not straightforward. Further, using several samples of local and higher-z AGN, we find a striking trend of an increasing offset with respect to the local M-sigma relation as a function of AGN luminosity, with virtually all objects with log(L_5100/erg s^-1) > 43.6 falling above the relation. Given the relatively small number of AGN at z>0.1 for which there are direct measurements of stellar velocity dispersions, it is impossible at present to determine whether there truly is evolution in M-sigma with redshift. Larger, carefully selected samples of AGN are necessary to disentangle the dependence of M-sigma on mass, luminosity, accretion rates, and redshift.
(Abridged) We examine the evolution of the black hole mass - stellar velocity dispersion (M-sigma) relation over cosmic time using simulations of galaxy mergers that include feedback from supermassive black hole growth. We consider mergers of galaxie
s varying the properties of the progenitors to match those expected at redshifts z=0-6. We find that the slope of the resulting M-sigma relation is the same at all redshifts considered. For the same feedback efficiency that reproduces the observed amplitude of the M-sigma relation at z=0, there is a weak redshift-dependence to the normalization that results from an increasing velocity dispersion for a given galactic stellar mass. We develop a formalism to connect redshift evolution in the M-sigma relation to the scatter in the local relation at z=0. We show that the scatter in the local relation places severe constraints on the redshift evolution of both the normalization and slope of the M-sigma relation. Furthermore, we demonstrate that cosmic downsizing introduces a black hole mass-dependent dispersion in the M-sigma relation and that the skewness of the distribution about the locally observed M-sigma relation is sensitive to redshift evolution in the normalization and slope. In principle, these various diagnostics provide a method for differentiating between theories for producing the M-sigma relation. In agreement with existing constraints, our simulations imply that hierarchical structure formation should produce the relation with small intrinsic scatter.
The relation between the mass of supermassive black holes located in the center of the host galaxies and the kinetic energy of random motions of the corresponding bulges can be reinterpreted as an age-temperature diagram for galaxies. This relation f
its the experimental data better than the M_bh-M_G, M_bh-L_G, and M_bh-sigma laws. The validity of this statement has been confirmed by using three samples extracted from different catalogues of galaxies. In the framework of the LambdaCDM cosmology our relation has been compared with the predictions of two galaxy formation models based on the Millennium Simulation.
We examine the present-day total stellar-to-halo mass (SHM) ratio as a function of halo mass for a new sample of simulated field galaxies using fully cosmological, LCDM, high resolution SPH + N-Body simulations.These simulations include an explicit t
reatment of metal line cooling, dust and self-shielding, H2 based star formation and supernova driven gas outflows. The 18 simulated halos have masses ranging from a few times 10^8 to nearly 10^12 solar masses. At z=0 our simulated galaxies have a baryon content and morphology typical of field galaxies. Over a stellar mass range of 2.2 x 10^3 to 4.5 x 10^10 solar masses, we find extremely good agreement between the SHM ratio in simulations and the present-day predictions from the statistical Abundance Matching Technique presented in Moster et al. (2012). This improvement over past simulations is due to a number systematic factors, each decreasing the SHM ratios: 1) gas outflows that reduce the overall SF efficiency but allow for the formation of a cold gas component 2) estimating the stellar masses of simulated galaxies using artificial observations and photometric techniques similar to those used in observations and 3) accounting for a systematic, up to 30 percent overestimate in total halo masses in DM-only simulations, due to the neglect of baryon loss over cosmic times. Our analysis suggests that stellar mass estimates based on photometric magnitudes can underestimate the contribution of old stellar populations to the total stellar mass, leading to stellar mass errors of up to 50 percent for individual galaxies. These results highlight the importance of using proper techniques to compare simulations with observations and reduce the perceived tension between the star formation efficiency in galaxy formation models and in real galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
