Clustering of Lyα Absorbing Clouds at High Redshift

ABSTRACT One of the main challenges in using high-redshift active galactic nuclei (AGNs) to study the correlations between the mass of a supermassive black hole ($\mathcal {M}_{\rm BH}$) and the properties of its active host galaxy is instrumental resolution. Strong lensing magnification effectively increases instrumental resolution and thus helps to address this challenge. In this work, we study eight strongly lensed AGNs with deep Hubble Space Telescope imaging, using the lens modelling code lenstronomy to reconstruct the image of the source. Using the reconstructed brightness of the host galaxy, we infer the host galaxy stellar mass based on stellar population models. $\mathcal {M}_{\rm BH}$ are estimated from broad emission lines using standard methods. Our results are in good agreement with recent work based on non-lensed AGNs, demonstrating the potential of using strongly lensed AGNs to extend the study of the correlations to higher redshifts. At the moment, the sample size of lensed AGNs is small and thus they provide mostly a consistency check on systematic errors related to resolution for non-lensed AGNs. However, the number of known lensed AGNs is expected to increase dramatically in the next few years, through dedicated searches in ground- and space-based wide-field surveys, and they may become a key diagnostic of black holes and galaxy co-evolution.

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Transit cosmological models coupled with zero-mass scalar field with high redshift in higher derivative theory

New Astronomy ◽

10.1016/j.newast.2021.101587 ◽

2021 ◽

pp. 101587

Author(s):

Archana Dixit ◽

Dinesh Chandra Maurya ◽

Anirudh Pradhan

Keyword(s):

Scalar Field ◽

High Redshift ◽

Cosmological Models ◽

Zero Mass ◽

Higher Derivative

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A complete search for redshift z ≳ 6.5 quasars in the VIKING survey

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3808 ◽

2020 ◽

Vol 501 (2) ◽

pp. 1663-1676

Author(s):

R Barnett ◽

S J Warren ◽

N J G Cross ◽

D J Mortlock ◽

X Fan ◽

...

Keyword(s):

Model Comparison ◽

High Redshift ◽

Detailed Comparison ◽

Selection Function ◽

Data Set ◽

Bayesian Model Comparison ◽

Fitting Method ◽

Complete Search ◽

Potential Contaminant ◽

Ranked List

ABSTRACT We present the results of a new, deeper, and complete search for high-redshift 6.5 < z < 9.3 quasars over 977 deg2 of the VISTA Kilo-Degree Infrared Galaxy (VIKING) survey. This exploits a new list-driven data set providing photometry in all bands Z, Y, J, H, Ks, for all sources detected by VIKING in J. We use the Bayesian model comparison (BMC) selection method of Mortlock et al., producing a ranked list of just 21 candidates. The sources ranked 1, 2, 3, and 5 are the four known z > 6.5 quasars in this field. Additional observations of the other 17 candidates, primarily DESI Legacy Survey photometry and ESO FORS2 spectroscopy, confirm that none is a quasar. This is the first complete sample from the VIKING survey, and we provide the computed selection function. We include a detailed comparison of the BMC method against two other selection methods: colour cuts and minimum-χ2 SED fitting. We find that: (i) BMC produces eight times fewer false positives than colour cuts, while also reaching 0.3 mag deeper, (ii) the minimum-χ2 SED-fitting method is extremely efficient but reaches 0.7 mag less deep than the BMC method, and selects only one of the four known quasars. We show that BMC candidates, rejected because their photometric SEDs have high χ2 values, include bright examples of galaxies with very strong [O iii] λλ4959,5007 emission in the Y band, identified in fainter surveys by Matsuoka et al. This is a potential contaminant population in Euclid searches for faint z > 7 quasars, not previously accounted for, and that requires better characterization.

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Cold gas studies of a z = 2.5 protocluster

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320004226 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 136-140

Author(s):

Minju M. Lee ◽

Ichi Tanaka ◽

Rohei Kawabe

Keyword(s):

Galaxy Evolution ◽

High Redshift ◽

Kinematic Model ◽

Molecular Gas ◽

General View ◽

Massive Galaxies ◽

Star Forming ◽

Gas Kinematics ◽

Narrow Band Filter ◽

Stellar Masses

AbstractWe present studies of a protocluster at z =2.5, an overdense region found close to a radio galaxy, 4C 23.56, using ALMA. We observed 1.1 mm continuum, two CO lines (CO (4–3) and CO (3–2)) and the lower atomic carbon line transition ([CI](3P1-3P0)) at a few kpc (0″.3-0″.9) resolution. The primary targets are 25 star-forming galaxies selected as Hα emitters (HAEs) that are identified with a narrow band filter. These are massive galaxies with stellar masses of > 1010Mʘ that are mostly on the galaxy main sequence at z =2.5. We measure the molecular gas mass from the independent gas tracers of 1.1 mm, CO (3–2) and [CI], and investigate the gas kinematics of galaxies from CO (4–3). Molecular gas masses from the different measurements are consistent with each other for detection, with a gas fraction (fgas = Mgas/(Mgas+ Mstar)) of ≃ 0.5 on average but with a caveat. On the other hand, the CO line widths of the protocluster galaxies are typically broader by ˜50% compared to field galaxies, which can be attributed to more frequent, unresolved gas-rich mergers and/or smaller sizes than field galaxies, supported by our high-resolution images and a kinematic model fit of one of the galaxies. We discuss the expected scenario of galaxy evolution in protoclusters at high redshift but future large surveys are needed to get a more general view.

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Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab402 ◽

2021 ◽

Author(s):

Arpan Das ◽

Dominik R G Schleicher ◽

Nathan W C Leigh ◽

Tjarda C N Boekholt

Keyword(s):

Black Holes ◽

Initial Conditions ◽

High Redshift ◽

Star Clusters ◽

Gas Reservoir ◽

Highly Sensitive ◽

Stellar Collisions ◽

Key Variables ◽

Chaotic Nature ◽

Gas Accretion

Abstract More than two hundred supermassive black holes (SMBHs) of masses ≳ 109 M⊙ have been discovered at z ≳ 6. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses ∼103 − 5 M⊙ into seed black holes which could grow upto few times 109 M⊙ SMBHs observed at z ∼ 7. In this paper, we explore how SMSs with masses ∼103 − 5 M⊙ could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs) using idealised N-body simulations. We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, SMSs of masses ∼103 − 5 M⊙ can form for all three accretion scenarios considered in this work.

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The nature of giant clumps in high-z discs: a deep-learning comparison of simulations and observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3778 ◽

2020 ◽

Vol 501 (1) ◽

pp. 730-746

Author(s):

Omri Ginzburg ◽

Marc Huertas-Company ◽

Avishai Dekel ◽

Nir Mandelker ◽

Gregory Snyder ◽

...

Keyword(s):

Neural Network ◽

Deep Learning ◽

Main Sequence ◽

High Redshift ◽

High Mass ◽

Galactic Centre ◽

Preferential Formation ◽

Maximum Resolution ◽

Supernova Feedback ◽

Disc Galaxies

ABSTRACT We use deep learning to explore the nature of observed giant clumps in high-redshift disc galaxies, based on their identification and classification in cosmological simulations. Simulated clumps are detected using the 3D gas and stellar densities in the VELA zoom-in cosmological simulation suite, with ${\sim}25\ \rm {pc}$ maximum resolution, targeting main-sequence galaxies at 1 < z < 3. The clumps are classified as long-lived clumps (LLCs) or short-lived clumps (SLCs) based on their longevity in the simulations. We then train neural networks to detect and classify the simulated clumps in mock, multicolour, dusty, and noisy HST-like images. The clumps are detected using an encoder–decoder convolutional neural network (CNN), and are classified according to their longevity using a vanilla CNN. Tests using the simulations show our detector and classifier to be ${\sim}80{{\ \rm per\ cent}}$ complete and ${\sim}80{{\ \rm per\ cent}}$ pure for clumps more massive than ∼107.5 M⊙. When applied to observed galaxies in the CANDELS/GOODS S+N fields, we find both types of clumps to appear in similar abundances in the simulations and the observations. LLCs are, on average, more massive than SLCs by ∼0.5 dex, and they dominate the clump population above Mc ≳ 107.6 M⊙. LLCs tend to be found closer to the galactic centre, indicating clump migration to the centre or preferential formation at smaller radii. The LLCs are found to reside in high-mass galaxies, indicating better clump survivability under supernova feedback there, due to clumps being more massive in these galaxies. We find the clump masses and radial positions in the simulations and the observations to agree within a factor of 2.

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Mapping large-scale-structure evolution over cosmic times

Experimental Astronomy ◽

10.1007/s10686-021-09755-3 ◽

2021 ◽

Author(s):

Marta B. Silva ◽

Ely D. Kovetz ◽

Garrett K. Keating ◽

Azadeh Moradinezhad Dizgah ◽

Matthieu Bethermin ◽

...

Keyword(s):

Galaxy Formation ◽

Large Scale ◽

High Redshift ◽

Formation Rate ◽

Far Infrared ◽

Large Scale Structure ◽

Scale Structure ◽

Structure Evolution ◽

Intensity Mapping ◽

Wide Range

AbstractThis paper outlines the science case for line-intensity mapping with a space-borne instrument targeting the sub-millimeter (microwaves) to the far-infrared (FIR) wavelength range. Our goal is to observe and characterize the large-scale structure in the Universe from present times to the high redshift Epoch of Reionization. This is essential to constrain the cosmology of our Universe and form a better understanding of various mechanisms that drive galaxy formation and evolution. The proposed frequency range would make it possible to probe important metal cooling lines such as [CII] up to very high redshift as well as a large number of rotational lines of the CO molecule. These can be used to trace molecular gas and dust evolution and constrain the buildup in both the cosmic star formation rate density and the cosmic infrared background (CIB). Moreover, surveys at the highest frequencies will detect FIR lines which are used as diagnostics of galaxies and AGN. Tomography of these lines over a wide redshift range will enable invaluable measurements of the cosmic expansion history at epochs inaccessible to other methods, competitive constraints on the parameters of the standard model of cosmology, and numerous tests of dark matter, dark energy, modified gravity and inflation. To reach these goals, large-scale structure must be mapped over a wide range in frequency to trace its time evolution and the surveyed area needs to be very large to beat cosmic variance. Only a space-borne mission can properly meet these requirements.

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