Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Rebecca L. Davies
Emma Ryan-Weber
Valentina D'Odorico
Sarah E. I. Bosman
Romain A. Meyer
George D. Becker
Guido Cupani
Laura C. Keating
Manuela Bischetti
Frederick B. Davies
Anna-Christina Eilers
Emanuele Paolo Farina
Martin G. Haehnelt
Andrea Pallottini
Yongda Zhu
Abstract： Intervening CIV absorbers are key tracers of metal-enriched gas in galaxy halos over cosmic time. Previous studies suggest that the CIV cosmic mass density ($\Omega_{\rm CIV}$) decreases slowly over 1.5 $\lesssim z\lesssim$ 5 before declining rapidly at $z\gtrsim$ 5, but the cause of this downturn is poorly understood. We characterize the $\Omega_{\rm CIV}$ evolution over 4.3 $\lesssim z\lesssim$ 6.3 using 260 absorbers found in 42 XSHOOTER spectra of $z\sim$ 6 quasars, of which 30 come from the ESO Large Program XQR-30. The large sample enables us to robustly constrain the rate and timing of the downturn. We find that $\Omega_{\rm CIV}$ decreases by a factor of 4.8 $\pm$ 2.0 over the ~300 Myr interval between $z\sim$ 4.7 and $z\sim$ 5.8. The slope of the column density (log N) distribution function does not change, suggesting that CIV absorption is suppressed approximately uniformly across 13.2 $\leq$ log N/cm$^{-2}$ < 15.0. Assuming that the carbon content of galaxy halos evolves as the integral of the cosmic star formation rate density (with some delay due to stellar lifetimes and outflow travel times), we show that chemical evolution alone could plausibly explain the fast decline in $\Omega_{\rm CIV}$ over 4.3 $\lesssim z\lesssim$ 6.3. However, the CIV/CII ratio decreases at the highest redshifts, so the accelerated decline in $\Omega_{\rm CIV}$ at $z\gtrsim$ 5 may be more naturally explained by rapid changes in the gas ionization state driven by evolution of the UV background towards the end of hydrogen reionization.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yongda Zhu
George D. Becker
Sarah E. I. Bosman
Laura C. Keating
Valentina D'Odorico
Rebecca L. Davies
Holly M. Christenson
Eduardo Bañados
Fuyan Bian
Manuela Bischetti
Huanqing Chen
Frederick B. Davies
Anna-Christina Eilers
Xiaohui Fan
Prakash Gaikwad
Bradley Greig
Martin G. Haehnelt
Girish Kulkarni
Samuel Lai
Andrea Pallottini
Abstract： We present a new investigation of the intergalactic medium (IGM) near reionization using dark gaps in the Lyman-$\beta$ (Ly$\beta$) forest. With its lower optical depth, Ly$\beta$ offers a potentially more sensitive probe to any remaining neutral gas compared to commonly used Ly$\alpha$ line. We identify dark gaps in the Ly$\beta$ forest using spectra of 42 QSOs at $z_{\rm em}>5.5$, including new data from the XQR-30 VLT Large Programme. Approximately $40\%$ of these QSO spectra exhibit dark gaps longer than $10h^{-1}{\rm Mpc}$ at $z\simeq5.8$. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly$\alpha$ forest are caused solely by ionizing ultraviolet background (UVB) fluctuations and with models that include large neutral hydrogen patches at $z<6$ due to a late end to reionization. Of particular interest is a very long ($L=28h^{-1}{\rm Mpc}$) and dark ($\tau_{\rm eff} \gtrsim 6$) gap persisting down to $z\simeq 5.5$ in the Ly$\beta$ forest of the $z_{\rm}=5.85$ QSO PSO J025$-$11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of $ \langle x_{\rm HI}\rangle \gtrsim 5\%$ by $z=5.6$. Finally, we infer constraints on $\langle x_{\rm HI}\rangle$ over $5.5 \lesssim z \lesssim 6.0$ based on the observed Ly$\beta$ dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find $\langle x_{\rm HI}\rangle \leq 0.05$, 0.17, and 0.29 at $z\simeq 5.55$, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than $z = 6$.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Emanuele Paolo Farina
Jan-Torge Schindler
Fabian Walter
Eduardo Bañados
Frederick B. Davies
Roberto Decarli
Anna-Christina Eilers
Xiaohui Fan
Joseph F. Hennawi
Chiara Mazzucchelli
Romain A. Meyer
Benny Trakhtenbrot
Marta Volonteri
Feige Wang
Gabor Worseck
Jinyi Yang
Thales A. Gutcke
Bram P. Venemans
Sarah E. I. Bosman
Tiago Costa
Abstract： We present measurements of black hole masses and Eddington ratios for a sample of 38 bright (M$_{1450}$ < -24.4 mag) quasars at 5.8 < z < 7.5, derived from VLT/X-shooter near-IR spectroscopy of their broad CIV and MgII emission lines. The black hole masses (on average M$_{BH}$ ~ 4.6 x 10$^9$ M$_{\odot}$) and accretion rates (with Eddington ratios ranging between 0.1 and 1.0) are broadly consistent with that of similarly luminous 0.3 < z < 2.3 quasars, but there is evidence for a mild increase in the median Eddington ratio going towards z > 6. Combined with deep ALMA observations of the [CII] 158 $\mu$m line from the quasar host galaxies and VLT/MUSE investigations of the extended Ly$\alpha$ halos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. Compared to local scaling relations, z > 5.7 black holes appear to be over-massive with respect to their host galaxies, and their accretion properties do not change with host galaxy morphology. Under the assumption that the kinematics of the T ~ 10$^4$ K gas, traced by the extended Ly$\alpha$ halos, are dominated by the gravitational potential of the dark matter halo, we report a similar relation between the black hole mass and circular velocity to the one reported for z ~ 0 galaxies. These results paint a picture where the first supermassive black holes reside in massive halos at z > 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. However, this duty cycle needs to drastically drop towards lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xiangyu Jin
Jinyi Yang
Xiaohui Fan
Feige Wang
Eduardo Bañados
Fuyan Bian
Frederick B. Davies
Anna-Christina Eilers
Emanuele Paolo Farina
Joseph F. Hennawi
Fabio Pacucci
Bram Venemans
Fabian Walter
Abstract： Cosmic reionization was the last major phase transition of hydrogen from
neutral to highly ionized in the intergalactic medium (IGM). Current
observations show that the IGM is significantly neutral at $z>7$, and largely
ionized by $z\sim5.5$. However, most methods to measure the IGM neutral
fraction are highly model-dependent, and are limited to when the
volume-averaged neutral fraction of the IGM is either relatively low
($\bar{x}_{\rm HI} \lesssim 10^{-3}$) or close to unity ($\bar{x}_{\rm HI}\sim
1$). In particular, the neutral fraction evolution of the IGM at the critical
redshift range of $z=6-7$ is poorly constrained. We present new constraints on
$\bar{x}_{\rm HI}$ at $z\sim5.1-6.8$, by analyzing deep optical spectra of $53$
quasars at $5.73
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yongda Zhu
George D. Becker
Sarah E. I. Bosman
Laura C. Keating
Holly M. Christenson
Eduardo Bañados
Fuyan Bian
Frederick B. Davies
Valentina D'Odorico
Anna-Christina Eilers
Xiaohui Fan
Martin G. Haehnelt
Girish Kulkarni
Andrea Pallottini
Yuxiang Qin
Feige Wang
Jinyi Yang
Abstract： We present a new investigation of the intergalactic medium (IGM) near the end of reionization using "dark gaps" in the Lyman-alpha (Ly$\alpha$) forest. Using spectra of 55 QSOs at $z_{\rm em}>5.5$, including new data from the XQR-30 VLT Large Programme, we identify gaps in the Ly$\alpha$ forest where the transmission averaged over 1 comoving $h^{-1}\,{\rm Mpc}$ bins falls below 5%. Nine ultra-long ($L > 80~h^{-1}\,{\rm Mpc}$) dark gaps are identified at $z<6$. In addition, we quantify the fraction of QSO spectra exhibiting gaps longer than $30~h^{-1}\,{\rm Mpc}$, $F_{30}$, as a function of redshift. We measure $F_{30} \simeq 0.9$, 0.6, and 0.15 at $z = 6.0$, 5.8, and 5.6, respectively, with the last of these long dark gaps persisting down to $z \simeq 5.3$. Comparing our results with predictions from hydrodynamical simulations, we find that the data are consistent with models wherein reionization extends significantly below redshift six. Models wherein the IGM is essentially fully reionized that retain large-scale fluctuations in the ionizing UV background at $z \lesssim 6$ are also potentially consistent with the data. Overall, our results suggest that signature of reionization in the form of islands of neutral hydrogen and/or large-scale fluctuations in the ionizing background remain present in the IGM until at least $z \simeq 5.3$.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jinyi Yang
Feige Wang
Xiaohui Fan
Aaron J. Barth
Joseph F. Hennawi
Riccardo Nanni
Fuyan Bian
Frederick B. Davies
Emanuele P. Farina
Jan-Torge Schindler
Eduardo Banados
Roberto Decarli
Anna-Christina Eilers
Richard Green
Hengxiao Guo
Linhua Jiang
Jiang-Tao Li
Bram Venemans
Fabian Walter
Xue-Bing Wu
Abstract： We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range $6.3< z\le7.64$, including 32 quasars at $z>6.5$, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the MgII emission lines are in the range $(0.3-3.6)\times10^{9}\,M_{\odot}$, which requires massive seed black holes with masses $\gtrsim10^{3-4}\,M_{\odot}$, assuming Eddington accretion since $z=30$. The Eddington ratio distribution peaks at $\lambda_{\rm Edd}\sim0.8$ and has a mean of 1.08, suggesting high accretion rates for these quasars. The CIV - MgII emission line velocity differences in our sample show an increase of CIV blueshift towards higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The FeII/MgII flux ratios derived for these quasars up to $z=7.6$, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for $z>6.5$ quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the CIV line. Our sample yields a strong broad absorption line quasar fraction of $\sim$24%, higher than the fractions in lower redshift quasar samples, although this could be affected by small sample statistics and selection effects.
Peer Review Status:Awaiting Review
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