Dynamics and Interactions of High-Redshift Galaxies

A large number of high redshift galaxies observed with the Hubble Space Telescope (HST) show anomalous morphology and photometric properties, which may be an indication of evolutionary process in young galaxies. We show here by means of numerical simulations that the copious interstellar gas existing in the disks of rapidly collapsing protogalaxies can bring about these peculiarities. Gravitational instability in a gas-rich disk leads to the formation of massive gas clumps with a typical mass of 109M⊙. These subgalactic clumps make disk galaxy evolution a dynamically energetic and chaotic process, and give a natural explanation for peculiar morphology of high redshift galaxies. Moreover, the present model provides a new picture on the causal relationship between the emergence of quasar activities and the dynamical evolution of host galaxies. The clump-driven evolution model is also capable of explaining the correlations observed among present-day galaxies. Namely, the relative bulge dominance, existence of a thick disk, and a mass of the super-massive black hole situated at the galactic center should all be correlated positively. In contrast to their vigorous evolution in isolated state, primeval disk galaxies do not show any dramatic enhancement of activity or remarkable dynamical response in interaction with another galaxies.

Download Full-text

Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa870 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2312-2326 ◽

Cited By ~ 3

Author(s):

Cristiana Spingola ◽

Anna Barnacka

Keyword(s):

Gravitational Lensing ◽

Angular Resolution ◽

Hubble Space Telescope ◽

High Redshift ◽

Monte Carlo Sampling ◽

High Angular Resolution ◽

Radio Emissions ◽

High Redshift Galaxies ◽

Long Baseline ◽

Redshift Galaxies

ABSTRACT We present a multiwavelength analysis of two highly magnified strong gravitationally lensed galaxies, CLASS B0712+472 and CLASS B1608+656, at redshifts 1.34 and 1.394, respectively, using new VLBI (very long baseline interferometry) and archival Hubble Space Telescope observations. We reconstruct the positions of the radio and optical emissions with their uncertainties using Monte Carlo sampling. We find that in CLASS B0712+472 the optical and radio emissions are co-spatial within 2 ± 5 mas (17 ± 42 pc at redshift of 1.34). But, in CLASS B1608+656, we reconstruct an optical–radio offset of 25 ± 16 mas (214 ± 137 pc at redshift of 1.394), among the smallest offsets measured for an AGN (active galactic nucleus) at such high redshift. The spectral features indicate that CLASS B1608+656 is a post-merger galaxy, which, in combination with the optical–VLBI offset reported here, makes CLASS B1608+656 a promising candidate for a high- z offset–AGN. Furthermore, the milliarcsecond angular resolution of the VLBI observations combined with the precise lens models allow us to spatially locate the radio emission at 0.05 mas precision (0.4 pc) in CLASS B0712+472, and 0.009 mas precision (0.08 pc) in CLASS B1608+656. The search for optical–radio offsets in high redshift galaxies will be eased by the upcoming synoptic all-sky surveys, including Extremely Large Telescope and Square Kilometre Array, which are expected to find ∼105 strongly lensed galaxies, opening an era of large strong lensing samples observed at high angular resolution.

Download Full-text

Dark-ages reionization and galaxy formation simulation – XVII. Sizes, angular momenta, and morphologies of high-redshift galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1810 ◽

2019 ◽

Vol 488 (2) ◽

pp. 1941-1959 ◽

Cited By ~ 2

Author(s):

Madeline A Marshall ◽

Simon J Mutch ◽

Yuxiang Qin ◽

Gregory B Poole ◽

J Stuart B Wyithe

Keyword(s):

Angular Momentum ◽

Galaxy Evolution ◽

Galaxy Formation ◽

High Redshift ◽

Stellar Mass ◽

Galaxy Mergers ◽

High Redshift Galaxies ◽

Massive Galaxies ◽

Angular Momenta ◽

Redshift Galaxies

Abstract We study the sizes, angular momenta, and morphologies of high-redshift galaxies, using an update of the meraxes semi-analytic galaxy evolution model. Our model successfully reproduces a range of observations from redshifts z = 0–10. We find that the effective radius of a galaxy disc scales with ultraviolet (UV) luminosity as $R_\mathrm{ e}\propto L_{\textrm{UV}}^{0.33}$ at z = 5–10, and with stellar mass as $R_e\propto M_\ast ^{0.24}$ at z = 5 but with a slope that increases at higher redshifts. Our model predicts that the median galaxy size scales with redshift as Re ∝ (1 + z)−m, where m = 1.98 ± 0.07 for galaxies with (0.3–1)$L^\ast _{z=3}$ and m = 2.15 ± 0.05 for galaxies with (0.12–0.3)$L^\ast _{z=3}$. We find that the ratio between stellar and halo specific angular momentum is typically less than 1 and decreases with halo and stellar mass. This relation shows no redshift dependence, while the relation between specific angular momentum and stellar mass decreases by ∼0.5 dex from z = 7 to z = 2. Our model reproduces the distribution of local galaxy morphologies, with bulges formed predominantly through galaxy mergers for low-mass galaxies, disc-instabilities for galaxies with M* ≃ 1010–$10^{11.5}\, \mathrm{M}_\odot$, and major mergers for the most massive galaxies. At high redshifts, we find galaxy morphologies that are predominantly bulge-dominated.

Download Full-text

Shedding light on high-redshift galaxies with the 21cm signal

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320001118 ◽

2019 ◽

Vol 15 (S352) ◽

pp. 69-69

Author(s):

Anne Hutter

Keyword(s):

Galaxy Evolution ◽

High Redshift ◽

Neutral Hydrogen ◽

First Stars ◽

High Redshift Galaxies ◽

Redshift Galaxy ◽

First Galaxies ◽

Galaxy Population ◽

The Impact ◽

Redshift Galaxies

AbstractReionization represents an important epoch in the history in the Universe, when the first stars and galaxies gradually ionize the neutral hydrogen in the intergalactic medium (IGM). Understanding the nature of the ionizing sources, the associated ionization of the IGM, and its impact on subsequent structure formation and galaxy evolution by means of radiative feedback effects, represent key outstanding questions in current astrophysics. High-redshift galaxy observations and simulations have significantly extended our knowledge on the nature of high-redshift galaxies. However, essential properties such as the escape fraction of ionizing photons from galaxies into the IGM and their dependency on galactic properties remain essentially unknown, but determine significantly the distribution and time evolution of the ionized regions during reionization. Analyzing this ionization topology by means of the neutral hydrogen sensitive 21cm signal with radio interferometers such as SKA offers a complementary and unique opportunity to determine the nature of these first galaxies. I will show results from a self-consistent semi-numerical model of galaxy evolution and reionization, and discuss the potential of inferring galactic properties with the 21cm signal as well as the impact of reionization on the high-redshift galaxy population and its evolution.

Download Full-text

Hierarchical fragmentation in high redshift galaxies revealed by hydrodynamical simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab272 ◽

2021 ◽

Author(s):

Baptiste Faure ◽

Frédéric Bournaud ◽

Jérémy Fensch ◽

Emanuele Daddi ◽

Manuel Behrendt ◽

...

Keyword(s):

Gravitational Lensing ◽

Hubble Space Telescope ◽

High Redshift ◽

High Redshift Galaxies ◽

Star Forming ◽

Low Mass ◽

Hydrodynamical Simulations ◽

Gas Clusters ◽

Very High ◽

Redshift Galaxies

Abstract High-redshift star-forming galaxies have very different morphologies compared to nearby ones. Indeed, they are often dominated by bright star-forming structures of masses up to 108 − 9 M⊙ dubbed Â«giant clumpsÂ». However, recent observations questioned this result by showing only low-mass structures or no structure at all. We use Adaptative Mesh Refinement hydrodynamical simulations of galaxies with parsec-scale resolution to study the formation of structures inside clumpy high-redshift galaxies. We show that in very gas-rich galaxies star formation occurs in small gas clusters with masses below 107 − 8 M⊙ that are themselves located inside giant complexes with masses up to 108 and sometimes 109 M⊙ . Those massive structures are similar in mass and size to the giant clumps observed in imaging surveys, in particular with the Hubble Space Telescope. Using mock observations of simulated galaxies, we show that at very high resolution with instruments like the Atacama Large Millimeter Array or through gravitational lensing, only low-mass structures are likely to be detected, and their gathering into giant complexes might be missed. This leads to the non-detection of the giant clumps and therefore introduces a bias in the detection of these structures. We show that the simulated giant clumps can be gravitationally bound even when undetected in mocks representative for ALMA observations and HST observations of lensed galaxies. We then compare the top-down fragmentation of an initially warm disc and the bottom-up fragmentation of an initially cold disc to show that the process of formation of the clumps does not impact their physical properties.

Download Full-text

Galaxies Unveiled: Rest-frame UV Clumps at 0.5 < z < 1.5

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316009248 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 364-365

Author(s):

Emmaris Soto ◽

Duilia F. de Mello ◽

Marc A. Rafelski ◽

Jonathan P. Gardner ◽

Anton M. Koekemoer

Keyword(s):

Star Formation ◽

High Resolution ◽

Galaxy Evolution ◽

Time Scales ◽

Rest Frame ◽

Large Time ◽

Hubble Space Telescope ◽

High Redshift ◽

High Redshift Galaxies ◽

Intermediate Redshifts

AbstractStudies of high redshift galaxies reveal compact sub-galactic regions of star formation, known as ‘clumps’. These ‘clumpy’ galaxies are useful for the study of galactic outskirts by enabling us to examine the radial progression of clumps over large time scales. We use the first deep high resolution NUV image from the Hubble Space Telescope covering intermediate redshifts to explore the implications this radial progression may have on galaxy evolution. From the analysis of 209 clumpy galaxies, we find that higher redshift clumps dominate the outer regions of galactic outskirts. This indicates that clumps may be migrating from the outskirts inward toward their galactic centers.

Download Full-text

Disentangling the Physical Origin of Emission Line Ratio Offsets at High Redshift with Spatially Resolved Spectroscopy

The Astrophysical Journal ◽

10.3847/1538-4357/ac1d52 ◽

2021 ◽

Vol 922 (1) ◽

pp. 12

Author(s):

Jessie Hirtenstein ◽

Tucker Jones ◽

Ryan L. Sanders ◽

Crystal L. Martin ◽

M. C. Cooper ◽

...

Keyword(s):

Emission Line ◽

Hubble Space Telescope ◽

High Redshift ◽

Emission Spectra ◽

High Redshift Galaxies ◽

Star Forming ◽

Spatially Resolved ◽

Resolution Element ◽

Spatially Resolved Spectroscopy ◽

Redshift Galaxies

Abstract We present spatially resolved Hubble Space Telescope grism spectroscopy of 15 galaxies at z ∼ 0.8 drawn from the DEEP2 survey. We analyze Hα+[N ii], [S ii], and [S iii] emission on kiloparsec scales to explore which mechanisms are powering emission lines at high redshifts, testing which processes may be responsible for the well-known offset of high-redshift galaxies from the z ∼ 0 locus in the [O iii]/Hβ versus [N ii]/Hα Baldwin—Phillips—Terlevich (BPT) excitation diagram. We study spatially resolved emission-line maps to examine evidence for active galactic nuclei (AGN), shocks, diffuse ionized gas (DIG), or escaping ionizing radiation, all of which may contribute to the BPT offsets observed in our sample. We do not find significant evidence of AGN in our sample and quantify that, on average, AGN would need to contribute ∼25% of the Hα flux in the central resolution element in order to cause the observed BPT offsets. We find weak (2σ) evidence of DIG emission at low surface brightnesses, yielding an implied total DIG emission fraction of ∼20%, which is not significant enough to be the dominant emission line driver in our sample. In general we find that the observed emission is dominated by star-forming H ii regions. We discuss trends with demographic properties and the possible role of α-enhanced abundance patterns in the emission spectra of high-redshift galaxies. Our results indicate that photoionization modeling with stellar population synthesis inputs is a valid tool to explore the specific star formation properties which may cause BPT offsets, to be explored in future work.

Download Full-text

Surveys of High-Redshift Galaxies

The First Galaxies in the Universe ◽

10.23943/princeton/9780691144917.003.0010 ◽

2013 ◽

Author(s):

Abraham Loeb ◽

Steven R. Furlanetto

Keyword(s):

Hubble Space Telescope ◽

High Redshift ◽

Spatial Correlations ◽

Space Telescope ◽

High Redshift Galaxies ◽

James Webb Space Telescope ◽

Observational Techniques ◽

Mass Functions ◽

Lower Redshift ◽

Redshift Galaxies

This chapter details the study of high-redshift galaxies. It first outlines the telescopes used for observing these galaxies: the Hubble Space Telescope (HST) and its follow ups, as well as the next-generation telescopes such as the James Webb Space Telescope (JWST). Next, the chapter discusses the methods for isolating candidate high-redshift galaxies from the foreground population of feeble lower-redshift galaxies. After outlining the observational techniques for identifying high-redshift galaxies, the chapter turns to the luminosity and mass functions, before enumerating strategies to constrain the statistical properties of galaxies, including “one point functions” like the luminosity or stellar mass functions as well as spatial correlations.

Download Full-text

The e-MERGE Survey (e-MERLIN Galaxy Evolution Survey): overview and survey description

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1279 ◽

2020 ◽

Vol 495 (1) ◽

pp. 1188-1208 ◽

Cited By ~ 3

Author(s):

T W B Muxlow ◽

A P Thomson ◽

J F Radcliffe ◽

N H Wrigley ◽

R J Beswick ◽

...

Keyword(s):

Galaxy Evolution ◽

Angular Resolution ◽

Hubble Space Telescope ◽

High Redshift ◽

Continuum Emission ◽

High Angular Resolution ◽

Very Large Array ◽

High Redshift Galaxies ◽

Star Forming ◽

Large Program

ABSTRACT We present an overview and description of the e-MERGE Survey (e-MERLIN Galaxy Evolution Survey) Data Release 1 (DR1), a large program of high-resolution 1.5-GHz radio observations of the GOODS-N field comprising ∼140 h of observations with enhanced-Multi-Element Remotely Linked Interferometer Network (e-MERLIN) and ∼40 h with the Very Large Array (VLA). We combine the long baselines of e-MERLIN (providing high angular resolution) with the relatively closely packed antennas of the VLA (providing excellent surface brightness sensitivity) to produce a deep 1.5-GHz radio survey with the sensitivity (${\sim}1.5\, \mu$ Jy beam−1), angular resolution (0.2–0.7 arcsec) and field-of-view (∼15 × 15 arcmin2) to detect and spatially resolve star-forming galaxies and active galactic nucleus (AGN) at $z$ ≳ 1. The goal of e-MERGE is to provide new constraints on the deep, sub-arcsecond radio sky which will be surveyed by SKA1-mid. In this initial publication, we discuss our data analysis techniques, including steps taken to model in-beam source variability over an ∼20-yr baseline and the development of new point spread function/primary beam models to seamlessly merge e-MERLIN and VLA data in the uv plane. We present early science results, including measurements of the luminosities and/or linear sizes of ∼500 galaxies selected at 1.5 GHz. In combination with deep Hubble Space Telescope observations, we measure a mean radio-to-optical size ratio of re-MERGE/rHST ∼ 1.02 ± 0.03, suggesting that in most high-redshift galaxies, the ∼GHz continuum emission traces the stellar light seen in optical imaging. This is the first in a series of papers that will explore the ∼kpc-scale radio properties of star-forming galaxies and AGN in the GOODS-N field observed by e-MERGE DR1.

Download Full-text

The [CII] 158 μm line emission in high-redshift galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732019 ◽

2018 ◽

Vol 609 ◽

pp. A130 ◽

Cited By ~ 52

Author(s):

G. Lagache ◽

M. Cousin ◽

M. Chatzikos

Keyword(s):

Galaxy Evolution ◽

High Redshift ◽

Formation Rate ◽

Line Emission ◽

Interstellar Gas ◽

Structure Transition ◽

High Redshift Galaxies ◽

Star Forming ◽

Crucial Component ◽

Redshift Galaxies

Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z ≃ 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII ]–SFR and L[ CII ]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[ CII ]–SFR and L[ CII ]–Zg, respectively. Our model reproduces the L[ CII ]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[ CII ]–SFR relations. Accordingly, the local observed L[ CII ]–SFR relation does not apply at high-z (z ≳ 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[ CII ]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[ CII] probed by the model (1 × 107–2 × 109 L⊙ at z = 6) with a slope α = −1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.

Download Full-text