اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641
123
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present a search for metal absorption line systems at the highest redshifts to date using a deep (30h) VLT/X-Shooter spectrum of the z = 7.084 quasi-stellar object (QSO) ULAS J1120+0641. We detect seven intervening systems at z > 5.5, with the highest-redshift system being a C IV absorber at z = 6.51. We find tentative evidence that the mass density of C IV remains flat or declines with redshift at z < 6, while the number density of C II systems remains relatively flat over 5 < z < 7. These trends are broadly consistent with models of chemical enrichment by star formation-driven winds that include a softening of the ultraviolet background towards higher redshifts. We find a larger number of weak ( W_rest < 0.3A ) Mg II systems over 5.9 < z < 7.0 than predicted by a power-law fit to the number density of stronger systems. This is consistent with trends in the number density of weak Mg II systems at z = 2.5, and suggests that the mechanisms that create these absorbers are already in place at z = 7. Finally, we investigate the associated narrow Si IV, C IV, and N V absorbers located near the QSO redshift, and find that at least one component shows evidence of partial covering of the continuum source.
قيم البحث
اقرأ أيضاً
We present new observations of the highest-redshift quasar known, ULAS J1120+0641, redshift $z=7.084$, obtained in the optical, at near-, mid-, and far-infrared wavelengths, and in the sub-mm. We combine these results with published X-ray and radio o
bservations to create the multiwavelength spectral energy distribution (SED), with the goals of measuring the bolometric luminosity $L_{rm bol}$, and quantifying the respective contributions from the AGN and star formation. We find three components are needed to fit the data over the wavelength range $0.12-1000,mu$m: the unobscured quasar accretion disk and broad-line region, a dusty clumpy AGN torus, and a cool 47K modified black body to characterise star formation. Despite the low signal-to-noise ratio of the new long-wavelength data, the normalisation of any dusty torus model is constrained within $pm40%$. We measure a bolometric luminosity $L_{rm bol}=2.6pm0.6times10^{47},$erg$,$s$^{-1}=6.7 pm 1.6times10^{13}L_{odot}$, to which the three components contribute $31%,32%,3%$, respectively, with the remainder provided by the extreme UV $<0.12,mu$m. We tabulate the best-fit model SED. We use local scaling relations to estimate a star formation rate (SFR) in the range $60-270,{rm M}_odot$/yr from the [C$,{scriptsize rm II}$] line luminosity and the $158,mu$m continuum luminosity. An analysis of the equivalent widths of the [C$,{scriptsize rm II}$] line in a sample of $z>5.7$ quasars suggests that these indicators are promising tools for estimating the SFR in high-redshift quasars in general. At the time observed the black hole was growing in mass more than 100 times faster than the stellar bulge, relative to the mass ratio measured in the local universe, i.e. compared to ${M_{rm BH}}/{M_{rm bulge}} simeq 1.4times10^{-3}$, for ULAS J1120+0641 we measure ${dot{M}_{rm BH}}/{dot{M}_{rm bulge}} simeq 0.2$.
We present X-ray imaging and spectroscopy of the redshift z=7.084 radio-quiet quasar ULAS J112001.48+064124.3 obtained with Chandra and XMM-Newton. The quasar is detected as a point source with both observatories. The Chandra observation provides a p
recise position, confirming the association of the X-ray source and the quasar, while a sufficient number of photons is detected in the XMM-Newton observation to yield a meaningful X-ray spectrum. In the XMM-Newton observation the quasar has a 2-10 keV luminosity of 4.7+-0.9 times 10^44 erg/s and a spectral slope alpha = 1.6+0.4/-0.3 (where f_nu is proportional to nu^-alpha). The quasar appears to have dimmed in the 15 months between the two observations, with a 2-10 keV luminosity of $1.8+1.0/-0.7 times 10^45 erg/s during the Chandra observation. We derive optical to X-ray spectral slopes alpha_OX of 1.76+-0.07 and 1.54+0.09/-0.08 at the times of the XMM-Newton and Chandra observations respectively, consistent with the range of alpha_OX found in other quasars of comparable ultraviolet luminosity. The very soft X-ray spectrum suggests that the quasar is accreting above the Eddington rate, L/L_Edd = 5+15/-4, compared to L/L_Edd = 1.2+0.6/-0.5 derived from the rest-frame ultraviolet. Super-Eddington accretion would help to reduce the discrepancy between the age of the quasar implied by the small size of the ionized near zone in which it sits (<10^7 years), and the characteristic e-folding time (2.5 times 10^7 years if L/L_Edd=2). Such super-Eddington accretion would also alleviate the challenging constraints on the seed black hole mass provided that the quasar has been rapidly accreting throughout its history. The remnant of an individual population III star is a plausible progenitor if an average L/L_Edd>1.46 has been maintained over the quasars lifetime.
We present optical and near-infrared imaging of the field of the z=7.0842 quasar ULAS J112001.48+064124.3 taken with the Hubble Space Telescope. We use these data to search for galaxies that may be physically associated with the quasar, using the Lym
an break technique, and find three such objects, although the detection of one in Spitzer Space Telescope imaging strongly suggests it lies at z~2. This is consistent with the field luminosity function and indicates that there is no excess of >L* galaxies within 1 Mpc of the quasar. A detection of the quasar shortward of the Ly-alpha line is consistent with the previously observed evolution of the intergalactic medium at z>5.5.
The quasar ULAS J1120+0641 at redshift z=7.085 has a highly ionised near zone which is smaller than those around quasars of similar luminosity at z~6. The spectrum also exhibits evidence for a damping wing extending redward of the systemic Lya redshi
ft. We use radiative transfer simulations in a cosmological context to investigate the implications for the ionisation state of the inhomogeneous IGM surrounding this quasar. Our simulations show that the transmission profile is consistent with an IGM in the vicinity of the quasar with a volume averaged HI fraction of f_HI>0.1 and that ULAS J1120+0641 has been bright for 10^6--10^7 yr. The observed spectrum is also consistent with smaller IGM neutral fractions, f_HI ~ 10^-3--10-4, if a damped Lya system in an otherwise highly ionised IGM lies within 5 proper Mpc of the quasar. This is, however, predicted to occur in only ~5 per cent of our simulated sight-lines for a bright phase of 10^6--10^7 yr. Unless ULAS J1120+0641 grows during a previous optically obscured phase, the low age inferred for the quasar adds to the theoretical challenge of forming a 2x10^9 M_sol black hole at this high redshift.
To establish the connection between galaxies and UV-detected absorption systems in the local universe, a deep ($gleq20$) and wide ($sim20^{prime}$ radius) galaxy redshift survey is presented around 47 sight lines to UV-bright AGN observed by the Cosm
ic Origins Spectrograph (COS). Specific COS science team papers have used this survey to connect absorbers to galaxies, groups of galaxies, and large-scale structures, including voids. Here we present the technical details of the survey and the basic measurements required for its use, including redshifts for individual galaxies and uncertainties determined collectively by spectral class (emission-line, absorption-line, and composite spectra) and completeness for each sight line as a function of impact parameter and magnitude. For most of these sight lines the design criteria of $>90$% completeness over a $>1$ Mpc region down to $lesssim0.1,L^*$ luminosities at $zleq0.1$ allows a plausible association between low-$z$ absorbers and individual galaxies. Ly$alpha$ covering fractions are computed to approximate the star-forming and passive galaxy populations using the spectral classes above. In agreement with previous results, the covering fraction of star-forming galaxies with $Lgeq0.3,L^*$ is consistent with unity inside one virial radius and declines slowly to $>50$% at 4 virial radii. On the other hand, passive galaxies have lower covering fractions ($sim60$%) and a shallower decline with impact parameter, suggesting that their gaseous halos are patchy but have a larger scale-length than star-forming galaxies. All spectra obtained by this project are made available electronically for individual measurement and use.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
