اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Impact of Dust in Host Galaxies on Quasar Luminosity Functions
125
0
0.0
(
0
)
تأليف
Hikari Shirakata
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We have investigated effects of dust attenuation on quasar luminosity functions using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, about 2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fueling to a central black hole starts some time after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical timescale of their host bulges or the dust covering factor is as small as 0.1.
قيم البحث
اقرأ أيضاً
We investigate quasar outflows at $z geq 6$ by performing zoom-in cosmological hydrodynamical simulations. By employing the SPH code GADGET-3, we zoom in the $2 R_{200}$ region around a $2 times 10^{12} M_{odot}$ halo at $z = 6$, inside a $(500 ~ {rm
Mpc})^3$ comoving volume. We compare the results of our AGN runs with a control simulation in which only stellar/SN feedback is considered. Seeding $10^5 M_{odot}$ BHs at the centers of $10^{9} M_{odot}$ halos, we find the following results. BHs accrete gas at the Eddington rate over $z = 9 - 6$. At $z = 6$, our most-massive BH has grown to $M_{rm BH} = 4 times 10^9 M_{odot}$. Fast ($v_{r} > 1000$ km/s), powerful ($dot{M}_{rm out} sim 2000 M_{odot}$/yr) outflows of shock-heated low-density gas form at $z sim 7$, and propagate up to hundreds kpc. Star-formation is quenched over $z = 8 - 6$, and the total SFR (SFR surface density near the galaxy center) is reduced by a factor of $5$ ($1000$). We analyse the relative contribution of multiple physical process: (i) disrupting cosmic filamentary cold gas inflows, (ii) reducing central gas density, (iii) ejecting gas outside the galaxy; and find that AGN feedback has the following effects at $z = 6$. The inflowing gas mass fraction is reduced by $sim 12 %$, the high-density gas fraction is lowered by $sim 13 %$, and $sim 20 %$ of the gas outflows at a speed larger than the escape velocity ($500$ km/s). We conclude that quasar-host galaxies at $z geq 6$ are accreting non-negligible amount of cosmic gas, nevertheless AGN feedback quenches their star formation dominantly by powerful outflows ejecting gas out of the host galaxy halo.
We present the results from a MUSE survey of twelve $zsimeq3.15$ quasars, which were selected to be much fainter (20<i<23) than in previous studies of Giant Ly$alpha$ Nebulae around the brightest quasars (16.6<i<18.7). We detect HI Ly$alpha$ nebulae
around 100% of our target quasars, with emission extending to scales of at least 60 physical kpc, and up to 190 pkpc. We explore correlations between properties of the nebulae and their host quasars, with the goal of connecting variations in the properties of the illuminating QSO to the response in nebular emission. We show that the surface brightness profiles of the nebulae are similar to those of nebulae around bright quasars, but with a lower normalization. Our targeted quasars are on average 3.7 magnitudes (~30 times) fainter in UV continuum than our bright reference sample, and yet the nebulae around them are only 4.3 times fainter in mean Ly$alpha$ surface brightness, measured between 20 and 50 pkpc. We find significant correlations between the surface brightness of the nebula and the luminosity of the quasar in both UV continuum and Ly$alpha$. The latter can be interpreted as evidence for a substantial contribution from unresolved inner parts of the nebulae to the narrow components seen in the Ly$alpha$ lines of some of our faint quasars, possibly from the inner CGM or from the host galaxys ISM.
We explore the kinematics of 27 z~6 quasar host galaxies observed in [CII]-158 micron ([CII]) emission with the Atacama Large Millimeter/sub-millimeter Array at a resolution of ~0.25. We find that nine of the galaxies show disturbed [CII] emission, e
ither due to a close companion galaxy or recent merger. Ten galaxies have smooth velocity gradients consistent with the emission arising from a gaseous disk. The remaining eight quasar host galaxies show no velocity gradient, suggesting that the gas in these systems is dispersion-dominated. All galaxies show high velocity dispersions with a mean of 129+-10 km/s. To provide an estimate of the dynamical mass within twice the half-light radius of the quasar host galaxy, we model the kinematics of the [CII] emission line using our publicly available kinematic fitting code, qubefit. This results in a mean dynamical mass of 5.0+-0.8(+-3.5) x 10^10 Msun. Comparison between the dynamical mass and the mass of the supermassive black hole reveals that the sample falls above the locally derived bulge mass--black hole mass relation at 2.4sigma significance. This result is robust even if we account for the large systematic uncertainties. Using several different estimators for the molecular mass, we estimate a gas mass fraction of >10%, indicating gas makes up a large fraction of the baryonic mass of z~6 quasar host galaxies. Finally, we speculate that the large variety in [CII] kinematics is an indication that gas accretion onto z~6 super massive black holes is not caused by a single precipitating factor.
During five decades astronomers have been puzzled by the presence of strong absorption features including metal lines, observed in the optical and ultraviolet spectra of quasars, signalling in- and outflowing gas winds with relative velocities up to
several thousands of km/sec. In particular the location of these winds - close to the quasar, further out in its host galaxy, or in its direct environment - and the possible impact on their surroundings have been issues of intense discussion and uncertainty. Using our Herschel Space Observatory data, we report a tendency for this so-called associated metal absorption to occur along with prodigious star formation in the quasar host galaxy, indicating that the two phenomena are likely to be interrelated, that the gas winds likely occur on the kiloparsec scale and would then have a strong impact on the interstellar medium of the galaxy. This correlation moreover would imply that the unusually high cold dust luminosities in these quasars are connected with ongoing star formation. Given that we find no correlation with the AGN strength, the wind feedback which we establish in these radio-loud objects is most likely associated with their host star formation rather than with their black hole accretion.
Long-Duration Gamma-Ray Bursts (GRBs) are powerful probes of the Universe star formation history, but correlation between the two depends on the highly debated presence/strength of a metallicity bias. To investigate this correlation, we use a phenome
nological model that successfully describes star formation rates, luminosities and stellar masses of star forming galaxies, applying it to GRB production. We predict luminosities, stellar masses, and metallicities of host galaxies depending on the metallicity bias. Our best-fitting model includes a moderate metallicity bias, broadly consistent with the large majority of long-duration GRBs in metal-poor environments originating from collapsars (probability ~83%), but with a secondary contribution (~17%) from metal-independent production channels, such as binary evolution. Because of the mass-metallicity relation of galaxies, the maximum likelihood model predicts that the metal-independent channel becomes dominant at z<2, where hosts have higher metallicities and collapsars are suppressed. This possibly explains why some studies find no clear evidence of a metal-bias based on low-z samples. However, while metallicity predictions match observations well at high redshift, there is tension with low redshift observations, since a significant fraction of GRB hosts are predicted to have (near-)solar metallicity. This is in contrast to observations, unless obscured, metal-rich hosts are preferentially missed in current datasets, and suggests that lower efficiencies of the metal-independent GRB channel might be preferred following a comprehensive fit from complete samples. Overall, we are able to establish the presence of a metallicity bias for GRB production, but continued characterization of GRB host galaxies is needed to quantify its strength.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
