arXiv subjects

T. Devereaux

Publications and source records attributed to T. Devereaux.

8 recordsLinked to original sources

arXiv2024

Unveiling [CII] clumps in a lensed star-forming galaxy at z ~ 3.4

Observations at UV and optical wavelengths have revealed that galaxies at z~1-4 host star-forming regions, dubbed "clumps", which are believed to form due to the fragmentation of gravitationally unstable, gas-rich disks. However, the detection of the parent molecular clouds that give birth to such clumps is still possible only in a minority of galaxies, mostly at z~1. We investigated the [CII] and dust morphology of a z~3.4 lensed galaxy hosting four clumps detected in the UV continuum. We aimed to observe the [CII] emission of individual clumps that, unlike the UV, is not affected by dust extinction, to probe their nature and cold gas content. We conducted ALMA observations probing scales down to ~300 pc and detected three [CII] clumps. One (dubbed "NE") coincides with the brightest UV clump, while the other two ("SW" and "C") are not detected in the UV continuum. We do not detect the dust continuum. We converted the [CII] luminosity of individual clumps into molecular gas mass and found Mmol~10^8 Msun. By complementing it with the star formation rate (SFR) estimate from the UV continuum, we estimated the gas depletion time (tdep) of clumps and investigated their location in the Schmidt-Kennicutt plane. While the NE clump has a short tdep=0.16 Gyr, comparable with high-redshift starbursts, the SW and C clumps instead have longer tdep>0.65 Gyr and are likely probing the initial phases of star formation. The lack of dust continuum detection is consistent with the blue UV continuum slope estimated for this galaxy (beta~-2.5) and it indicates that dust inhomogeneities do not significantly affect the detection of UV clumps in this target. We pushed the observation of the cold gas content of individual clumps up to z~3.4 and showed that the [C II] line emission is a promising tracer of molecular clouds at high redshift, allowing the detection of clumps with a large range of depletion times.

astro-ph.GA↗

arXiv2023

The ALMA-ALPINE [CII] survey: sub-kpc morphology of 3 main-sequence galaxy systems at z~4.5 revealed by ALMA

Context: From redshift 6 to redshift $\approx$ 4 galaxies grow rapidly from low mass galaxies towards the more mature massive galaxies we see at the cosmic noon. Growth via gas accretion and mergers undoubtedly shape this evolution - however, there currently exists much uncertainty over the contribution of each of these processes to the overall evolution of galaxies. Furthermore, previous characterisations of the morphology of galaxies in the molecular gas phase has been limited by the coarse resolution of previous observations. Aims: The goal of this paper is to derive the morpho-kinematic properties of 3 main-sequence systems at $z\sim4.5$, drawn from the ALPINE survey, using brand new high-resolution ALMA data in band 7. The objects were previously characterised as one merger with three components, and and two dispersion-dominated galaxies. Methods: We use intensity and velocity maps, position-velocity diagrams and radial profiles of [CII], in combination with dust continuum maps, to analyse the morphology and kinematics of the 3 systems.} Results: In general, we find that the high-resolution ALMA data reveal more complex morpho-kinematic properties. We identify in one galaxy interaction-induced clumps, showing the profound effect that mergers have on the molecular gas in galaxies, consistent with what is suggested in recent simulations. A galaxy that was previously classified as dispersion dominated turned out to show two bright [CII] emission regions, that could either be merging galaxies or massive star-forming regions within the galaxy itself. The high resolution data for the other dispersion dominated object also revealed clumps of [CII] that were not previously identified. Within the sample, we might also detect star-formation powered outflows (or outflows from Active Galactic Nuclei) which appear to be fuelling diffuse gas regions and enriching the circumgalactic medium.

astro-ph.GA↗

arXiv2023

The ALMA-ALPINE [CII] survey: Kennicutt-Schmidt relation in four massive main-sequence galaxies at z~4.5

The Kennicutt-Schmidt (KS) relation between the gas and the star formation rate (SFR) surface density ($Σ_{\rm gas}$-$Σ_{\rm SFR}$) is essential to understand star formation processes in galaxies. So far, it has been measured up to z~2.5 in main-sequence galaxies. In this letter, we aim to put constraints at z~4.5 using a sample of four massive main-sequence galaxies observed by ALMA at high resolution. We obtained ~0.3"-resolution [CII] and continuum maps of our objects, which we then converted into gas and obscured SFR surface density maps. In addition, we produced unobscured SFR surface density maps by convolving Hubble ancillary data in the rest-frame UV. We then derived the average $Σ_{\rm SFR}$ in various $Σ_{\rm gas}$ bins, and estimated the uncertainties using a Monte Carlo sampling. Our galaxy sample follows the KS relation measured in main-sequence galaxies at lower redshift and is slightly lower than predictions from simulations. Our data points probe the high end both in terms of $Σ_{\rm gas}$ and $Σ_{\rm gas}$, and gas depletion timescales (285-843 Myr) remain similar to z~2 objects. However, three of our objects are clearly morphologically disturbed, and we could have expected shorter gas depletion timescales (~100 Myr) similar to merger-driven starbursts at lower redshifts. This suggests that the mechanisms triggering starbursts at high redshift may be different than in the low- and intermediate-z Universe.

astro-ph.GA↗

arXiv2023

UV-continuum $β$ slopes of individual $z \sim 2-6$ clumps and their evolution

We study the ultraviolet (UV) continuum $β$ slope of a sample of 166 clumps, individual star-forming regions observed in high redshift galaxies. They are hosted by 67 galaxies with redshift between 2 and 6.2, strongly lensed by the Hubble Frontier Fields cluster of galaxies MACS J0416.1-2403. The $β$ slope is sensitive to a variety of physical properties, such as the metallicity, the age of the stellar population, the dust attenuation throughout the galaxy, the stellar initial mass function (IMF), and the star-formation history (SFH). The aim of this study is to compare the $β$ values of individual clumps with those measured on the entire galaxy, to investigate possible physical differences between these regions and their hosts. We found a median value of $β\sim -2.4$, lower than that of integrated galaxies. This result confirms that clumps are sites of intense star formation, populated by young, massive stars, whose spectrum strongly emits in the UV. This is also consistent with the assumption that the dust extinction at the location of the clumps is lower than the average extinction of the galaxy, or that clumps have a different IMF or SFH. We made use of the correlations, discovered for high-redshift galaxies, of the $β$ value with those of redshift and UV magnitude, $M_{UV}$, finding that clumps follow the same relations, extended to much fainter magnitudes ($M_{UV}<-13$). We also find evidence of eight clumps with extremely blue ($β\lesssim -2.7$) slopes, which could be the signpost of low-metallicity stars and constrain the emissivity of ionizing photons at high redshift.

astro-ph.GA↗

arXiv2017

Holon Wigner Crystal in a Lightly Doped Kagome Quantum Spin Liquid

We address the problem of a lightly doped spin-liquid through a large-scale density-matrix renormalization group (DMRG) study of the $t$-$J$ model on a Kagome lattice with a small but non-zero concentration, $δ$, of doped holes. It is now widely accepted that the undoped ($δ=0$) spin 1/2 Heisenberg antiferromagnet has a spin-liquid groundstate. Theoretical arguments have been presented that light doping of such a spin-liquid could give rise to a high temperature superconductor or an exotic topological Fermi liquid metal (FL$^\ast$). Instead, we infer that the doped holes form an insulating charge-density wave state with one doped-hole per unit cell - i.e. a Wigner crystal (WC). Spin correlations remain short-ranged, as in the spin-liquid parent state, from which we infer that the state is a crystal of spinless holons (WC$^\ast$), rather than of holes. Our results may be relevant to Kagome lattice Herbertsmithite $\rm ZnCu_3(OH)_6Cl_2$ upon doping.

cond-mat.str-el↗

arXiv2009

High resolution angle resolved photoemission studies on quasi-particle dynamics in graphite

We obtained the spectral function of the graphite H point using high resolution angle resolved photoelectron spectroscopy (ARPES). The extracted width of the spectral function (inverse of the photo-hole lifetime) near the H point is approximately proportional to the energy as expected from the linearly increasing density of states (DOS) near the Fermi energy. This is well accounted by our electron-phonon coupling theory considering the peculiar electronic DOS near the Fermi level. And we also investigated the temperature dependence of the peak widths both experimentally and theoretically. The upper bound for the electron-phonon coupling parameter is ~0.23, nearly the same value as previously reported at the K point. Our analysis of temperature dependent ARPES data at K shows that the energy of phonon mode of graphite has much higher energy scale than 125K which is dominant in electron-phonon coupling.

cond-mat.mtrl-sci↗

arXiv2006

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

This treatise reviews latest results obtained from angle-resolved photoemission spectroscopy (ARPES) on cuprate superconductors, with a special focus on the electron-phonon interaction. What has emerged is rich information about the anomalous electron-phonon interaction well beyond the traditional views of the subject. It exhibits strong doping, momentum and phonon symmetry dependence, and shows complex interplay with the strong electron-electron interaction in these materials.

cond-mat.str-el↗

arXiv1997

Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)

In a recent paper Kendziora et al concluded that the superconducting gap in overdoped Bi-2212 is isotropic. From data obtained from electronic Raman scattering measurements, their conclusion was based on the observation that pair breaking peaks occured at approximately the same frequency in different scattering geometries and that the normalized scattering intensity at low energies was strongly depleted. We discuss a different interpretation of the raw data and present new data which is consistent with a strongly anisotropic gap with nodes. The spectra can be successfully described by a model for Raman scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and impurity scattering included.

cond-mat.supr-con↗