196,065 research outputs found
Deep into the structure of the first galaxies: SERRA views
No full textWe study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations
The mass-metallicity relation as a ruler for galaxy evolution: Insights from the James Webb Space Telescope
No full textContext. Galaxy evolution emerges from the balance between cosmic gas accretion, fueling star formation, and supernova feedback, regulating metal enrichment of the interstellar medium. Hence, the relation between stellar mass (M⋆) and gas metallicity (Zg) is fundamental to understanding the physics of galaxies. High-quality spectroscopic JWST data enable accurate measurements of both M⋆ and Zg up to redshift z ≃ 10.
Aims. Our aims are to understand (i) the nature of the observed mass-metallicity relation (MZR), (ii) its connection with the star formation rate (SFR), (iii) the role played by SFR stochasticity (flickering), and (iv) how it is regulated by stellar feedback.
Methods. We compared the MZR obtained by the JADES, CEERS, and UNCOVER surveys, which comprise about 180 galaxies at z ≃ 3 − 10 with 106 M⊙ ≲ M⋆ ≲ 1010 M⊙, with ≃200 simulated galaxies in the same mass range from the SERR
[C ii] halos in ALPINE galaxies: Smoking-gun of galactic outflows?
No full textALMA observations have revealed that many high-redshift galaxies are surrounded by extended (10–15 kpc) [C ii]-emitting haloes that are not predicted by even the most advanced zoom-in simulations. Using a semi-analytical model, in a previous work we suggested that such haloes are produced by starburst-driven, catastrophically cooling outflows. Here, we further improve the model and compare its predictions with data from seven star-forming (10≲SFR/M⊙yr−1≲100) galaxies at z = 4–6, observed in the ALPINE survey. We find that (a) detected [C ii] haloes are a natural by-product of starburst-driven outflows; (b) the outflow mass loading factors are in the range 4 ≲ η ≲ 7, with higher η values for lower mass, lower star formation rate systems, and scale with stellar mass as η∝M−0.43∗, consistently with the momentum-driven hypothesis. Our model suggests that outflows are widespread phenomena in high-z galaxies. However, in low-mass systems the halo extended [C ii] emission is likely too faint to be detected with the current levels of sensitivity.ALMA observations have revealed that many high-redshift galaxies are surrounded by extended (10.15 kpc) [C II] -emitting haloes that are not predicted by even the most advanced zoom-in simulations. Using a semi-analytical model, in a previous work we suggested that such haloes are produced by starburst-driven, catastrophically cooling outflows. Here, we further improve the model and compare its predictions with data from seven star-forming (10 ≲ SFR /M⊙yr-1 ≲ 100) galaxies at z = 4.6, observed in the ALPINE survey. We find that (a) detected [C II] haloes are a natural by-product of starburst-driven outflows; (b) the outflow mass loading factors are in the range 4 ≲ η ≲ 7, with higher η values for lower mass, lower star formation rate systems, and scale with stellar mass as η ∝ M∗-0.43, consistently with the momentum-driven hypothesis. Our model suggests that outflows are widespread phenomena in high- z galaxies. However, in low-mass systems the halo extended [C II] emission is likely t..
Blue monsters : why are JWST super-early, massive galaxies so blue?
No full textThe recent James Webb Space Telescope tentative discovery of a population of super-early (redshift z > 10), relatively massive (stellar mass M* = 108-109M⊙) and evolved (metallicity Z ≈ 0.1 Z⊙) galaxies, which nevertheless show blue (β ≃ -2.6) spectra, and very small dust attenuation (AV ≲ 0.02), challenges our interpretation of these systems. To solve the puzzle, we propose two solutions in which dust is either (a) ejected by radiation pressure, or (b) segregated with respect to UV-emitting regions. We clarify the conditions for which the two scenarios apply, and show that they can be discriminated by ALMA observations, such as the recent non-detection of the 88μm dust continuum in GHZ2 (z ≃ 12) favouring dust ejection
Velocity dispersion in the interstellar medium of early galaxies
No full textWe study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by [C II] 158 mu m line emission. Our laboratory is a simulated prototypical Lyman-break galaxy, 'Freesia, part of the SERRA suite'. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disc at z = 7.4, Merger at z = 8.0, and Disturbed Disc at z = 6.5) using [C II] hyperspectral data cubes. We find that, at a high spatial resolution of 0.005 arcsec (similar or equal to 30 pc), the luminosity-weighted average velocity dispersion is sigma(CII) similar or equal to 23-38 km s(-1) with the highest value belonging to the highly structured Disturbed Disc stage. Low-resolution observations tend to overestimate sigma(CII) values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02 arcsec (0.1 arcsec), the average velocity dispersion is 16-34 per cent (52-115 per cent) larger than the actual one. The [C II] emitting gas in Freesia has a Toomre parameter Q similar or equal to 0.2 and rotational-to-dispersion ratio of v(c)/sigma similar or equal to 7 similar to that observed in z = 2-3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally sub-dominant (< 10 per cent). Finally, we find that the resolved sigma(CII) - Sigma(SFR) relation is relatively flat for 0.02 < Sigma(SFR)/M-circle dot yr(-1)kpc(-2) < 30, with the majority of data lying on the derived analytical relation sigma proportional to Sigma(5/7)(SFR). At high SFR, the increased contribution from stellar feedback steepens the relation, and sigma(CII) rises slightly
Missing [C ii ] emission from early galaxies
No full textABSTRACT
ALMA observations have revealed that [C ii] 158 μm line emission in high-z galaxies is ≈2–3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming (SBD) of the [C ii] line is responsible for the reported [C ii] deficit, and the large luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z > 6 galaxies observed in both [C ii] and [O iii]. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect [C ii] emission in the whole sample, with an extent systematically larger than the [O iii] emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40 per cent of the extended [C ii] component might be missed at an angular resolution of 0.8 arcsec, implying that is underestimated by a factor ≈2 in data at low ( 6 galaxies lies, on average, slightly below the local relation (Δz = 6–9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields , i.e. more in line with current hydrodynamical simulations
Early galaxy growth: mergers or gravitational instability?
No full textWe investigate the spatially resolved morphology of galaxies in the early Universe. We consider a typical redshift z = 6 Lyman break galaxy, ‘Althæa’, from the SERRA hydrodynamical simulations. We create mock rest-frame ultraviolet (UV), optical, and far-infrared observations, and perform a two-dimensional morphological analysis to deblend the galaxy disc from substructures (merging satellites or star-forming regions). We find that the [C II]158 μm emitting region has an effective radius 1.5–2.5 times larger than the optical one, consistent with recent observations. This [C II] halo in our simulated galaxy arises as the joint effect of stellar outflows and carbon photoionization by the galaxy UV field, rather than from the emission of unresolved nearby satellites. At the typical angular resolution of current observations (≳ 0.15 arcsec) only merging satellites can be detected; detection of star-forming regions requires resolutions of ≲ 0.05 arcsec. The [C II]-detected satellite has a 2.5-kpc projected distance from the galaxy disc, whereas the star-forming regions are embedded in the disc itself (distance ≲ 1 kpc). This suggests that multicomponent systems reported in the literature, which have separations ≳ 2 kpc, are merging satellites, rather than galactic substructures. Finally, the star-forming regions found in our mock maps follow the local L[C II]–SFRUV relation of galaxy discs, although sampling the low-luminosity, low-SFR tail of the distribution. We show that future James Webb Space Telescope observations, bridging UV and [C II] data sets, will be exceptionally suited to characterize galaxy substructures, thanks to their exquisite spatial resolution and sensitivity to both low-metallicity and dust-obscured regions that are bright at infrared wavelengths
A physical model for [C II] line emission from galaxies
No full textA tight relation between the [C II] 158 μm line luminosity and star formation rate is measured in local galaxies. At high redshift (z > 5), though, a much larger scatter is observed, with a considerable (15–20 per cent) fraction of the outliers being [C II]-deficient. Moreover, the [C II] surface brightness ([C II]) of these sources is systematically lower than expected from the local relation. To clarify the origin of such [C II]-deficiency, we have developed an analytical model that fits local [C II] data and has been validated against radiative transfer simulations performed with CLOUDY. The model predicts an overall increase of [C II] with SFR. However, for SFR 1 M yr−1 kpc−2[C II] saturates. We conclude that underluminous [C II] systems can result from a combination of three factors: (a) large upward deviations from the Kennicutt–Schmidt relation (κs 1), parametrized by the ‘burstiness’ parameter κs; (b) low metallicity; (c) low gas density, at least for the most extreme sources (e.g. CR7). Observations of [C II] emission alone cannot break the degeneracy among the above three parameters; this requires additional information coming from other emission lines (e.g. [O III]88 μm, C III]1909 Å, CO lines). Simple formulae are given to interpret available data for low- and high-z galaxies
Dynamically cold disks in the early Universe: myth or reality?
No full textTheoretical models struggle to reproduce dynamically cold disks with
significant rotation-to-dispersion support() observed in
star-forming galaxies in the early Universe, at redshift . We aim to
explore the possible emergence of dynamically cold disks in cosmological
simulations and to understand if different kinematic tracers can help reconcile
the tension between theory and observations. We use 3218 galaxies from the
SERRA suite of zoom-in simulations, with and
SFR, within range. We generate hyper-spectral
data cubes for 6436 synthetic observations of H and [CII]. We find that
the choice of kinematic tracer strongly influences gas velocity dispersion
estimates. When using H ([CII]) synthetic observations, we observe a
strong (mild) correlation between and . Such a difference arises
mostly for galaxies, for which
for a significant fraction of the sample.
Regardless of the tracer, our predictions suggest the existence of massive
() galaxies with at ,
maintaining cold disks for >10 orbital periods (200Myr). Furthermore, we do not
find any significant redshift dependence for ratio in our
sample. Our simulations predict the existence of dynamically cold disks in the
early Universe. However, different tracers are sensitive to different kinematic
properties. While [CII] effectively traces the thin, gaseous disk of galaxies,
H includes the contribution from ionized gas beyond the disk,
characterized by prevalent vertical or radial motions that may be associated
with outflows. The presence of H halos could be a signature of such
galactic outflows. This emphasizes the importance of combining ALMA and
JWST/NIRspec studies of high-z galaxies.Comment: submitted to A&
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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