Gas Phase Metallicities of Local Ultra-Luminous Infrared Galaxies Follow Normal Star-Forming Galaxies

Despite advances in observational data, theoretical models, and computational techniques to simulate key physical processes in the formation and evolution of galaxies, the stellar mass assembly of galaxies still remains an unsolved problem today. Optical spectroscopic measurements appears to show that the gas-phase metallicities of local ultra-luminous infrared galaxies (ULIRGs) are significantly lower than those of normal star-forming galaxies1–3. This difference has resulted in the claim that ULIRGs are fueled by metal-poor gas accretion from the outskirts4. Here we report on a new set of gas-phase metallicity measurements making use of the far-infrared spectral lines of [Oiii]52 μm, [Oiii]88 μm, and [Niii]57 μm instead of the usual optical lines. Photoionization models have resulted in a metallicity diagnostic based on these three lines that break the electron density degeneracy and reduces the scatter of the correlation significantly5. Using new data from SOFIA and archival data from Herschel Space Observatory, we find that local ULIRGs lie on the mass-metallicity relation of star-forming galaxies and have metallicities comparable to other galaxies with similar stellar masses and star formation rates. The lack of a departure suggests that ULIRGs follow the same mass assembly mechanism as luminous star-forming galaxies and ∼ 0.3 dex under-abundance in metallicities derived from optical lines is a result of heavily obscured metal-rich gas which has a negligible effect when using the FIR line diagnostics.

A stripped-companion origin for Be stars: clues from the putative black holes HR 6819 and LB-1

ABSTRACT HR 6819 is a bright (V = 5.36), blue star recently proposed to be a triple containing a detached black hole (BH). We show that the system is a binary and does not contain a BH. Using spectral decomposition, we disentangle the observed composite spectra into two components: a rapidly rotating Be star and a slowly rotating B star with low surface gravity (log g ≈ 2.75). Both stars show periodic radial velocity (RV) variability, but the RV semi-amplitude of the B star’s orbit is $K_{\rm B}= (62.7 \pm 1)\, \rm km\, s^{-1}$, while that of the Be star is only $K_{\rm Be} = (4.5\pm 2)\, \rm km\, s^{-1}$. This implies that the B star is less massive by at least a factor of 10. The surface abundances of the B star bear imprints of CNO burning. We argue that the B star is a bloated, recently stripped helium star with mass ${\approx}0.5\, \mathrm{ M}_{\odot }$ that is currently contracting to become a hot subdwarf. The orbital motion of the Be star obviates the need for a BH to explain the B star’s motion. A stripped-star model reproduces the observed luminosity of the system, while a normal star with the B star’s temperature and gravity would be more than 10 times too luminous. HR 6819 and the binary LB-1 probably formed through similar channels. We use MESA (Modules for Experiments in Stellar Astrophysics) models to investigate their evolutionary history, finding that they likely formed from intermediate-mass ($3\!-\!7\, \mathrm{ M}_{\odot }$) primaries stripped by slightly lower-mass secondaries and are progenitors to Be + sdOB binaries such as ϕ Persei. The lifetime of their current evolutionary phase is on average 2 × 105 yr, of the order of half a per cent of the total lifetime of the Be phase. This implies that many Be stars have hot subdwarf and white dwarf companions, and that a substantial fraction ($20\!-\!100{{\ \rm per\ cent}}$) of field Be stars form through accretion of material from a binary companion.

ALMA detects molecular gas in the halo of the powerful radio galaxy TXS 0828+193

Both theoretical and observational results suggest that high-redshift radio galaxies (HzRGs) inhabit overdense regions of the universe and might be the progenitors of local, massive galaxies residing in the centre of galaxy clusters. In this paper we present CO(3–2) line observations of the HzRG TXS 0828+193 (z = 2.57) and its environment using the Atacama Large Millimeter/submillimeter Array. In contrast to previous observations, we detect CO emission associated with the HzRG and derive a molecular gas mass of $(0.9\pm 0.3)\times 10^{10}\, \rm M_{\odot }$. Moreover, we confirm the presence of a previously detected off-source CO emitting region (companion #1), and detect three new potential companions. The molecular gas mass of each companion is comparable to that of the HzRG. Companion #1 is aligned with the axis of the radio jet and has stellar emission detected by Spitzer. Thus this source might be a normal star-forming galaxy or alternatively a result of jet-induced star formation. The newly found CO sources do not have counterparts in any other observing band and could be high-density clouds in the halo of TXS 0828+193 and thus potentially linked to the large-scale filamentary structure of the cosmic web.

Coherent representation of fields and deformation quantization

Motivated by some well-known results in the phase space description of quantum optics and quantum information theory, we aim to describe the formalism of quantum field theory by explicitly considering the holomorphic representation for a scalar field within the deformation quantization program. Notably, the symbol of a symmetric ordered operator in terms of holomorphic variables may be straightforwardly obtained by the quantum field analogue of the Husimi distribution associated with a normal ordered operator. This relation also allows to establish a [Formula: see text]-equivalence between the Moyal and the normal star-products. In addition, by writing the density operator in terms of coherent states we are able to directly introduce a series representation of the Wigner functional distribution, which may be convenient in order to calculate probability distributions of quantum field observables without performing formal phase space integrals at all.

VLA imaging of the XMM-LSS/VIDEO deep field at 1–2 GHz

ABSTRACT Modern radio telescopes are routinely reaching depths where normal star-forming galaxies are the dominant observed population. Realizing the potential of radio as a tracer of star formation and black hole activity over cosmic time involves achieving such depths over representative volumes, with radio forming part of a larger multiwavelength campaign. In pursuit of this, we used the Karl G. Jansky Very Large Array (VLA) to image ∼5 deg2 of the VIDEO/XMM-LSS extragalactic deep field at 1–2 GHz. We achieve a median depth of 16 µJy beam−1 with an angular resolution of 4.5 arcsec. Comparisons with existing radio observations of XMM-LSS showcase the improved survey speed of the upgraded VLA: we cover 2.5 times the area and increase the depth by ∼20 per cent in 40 per cent of the time. Direction-dependent calibration and wide-field imaging were required to suppress the error patterns from off-axis sources of even modest brightness. We derive a catalogue containing 5762 sources from the final mosaic. Sub-band imaging provides in-band spectral indices for 3458 (60 per cent) sources, with the average spectrum becoming flatter than the canonical synchrotron slope below 1 mJy. Positional and flux density accuracy of the observations, and the differential source counts are in excellent agreement with those of existing measurements. A public release of the images and catalogue accompanies this article.

Spatially resolved molecular gas properties of host galaxy of Type I superluminous supernova SN 2017egm

We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is Mgas = (4.8 ± 0.3) × 109 M⊙, placing it on the sequence of normal star-forming galaxies in an Mgas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies.

Ram pressure stripping candidates in the coma cluster: evidence for enhanced star formation

ABSTRACT The Coma cluster is the nearest massive ($M \gtrsim 10^{15}\, \mathrm{M_\odot }$) galaxy cluster, making it an excellent laboratory to probe the influence of the cluster environment on galaxy star formation. Here, we present a sample of 41 galaxies with disturbed morphologies consistent with ram pressure stripping. These galaxies are identified visually using high-quality, multiband imaging from the Canada–France–Hawaii telescope covering ${\sim}9\, \mathrm{deg^2}$ of the Coma cluster. These ‘stripping candidates’ are clear outliers in common quantitative morphological measures, such as concentration-asymmetry and Gini-M20, confirming their disturbed nature. Based on the orientations of observed asymmetries, as well as the galaxy positions in projected phase space, these candidates are consistent with galaxies being stripped shortly after infall on to the Coma cluster. Finally, the stripping candidates show enhanced star formation rates, both relative to ‘normal’ star-forming Coma galaxies and isolated galaxies in the field. Ram pressure is likely driving an enhancement in star formation during the stripping phase, prior to quenching. On the whole, ram pressure stripping appears to be ubiquitous across all regions of the Coma cluster.

The ALPINE-ALMA [C II] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe

We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 μm emission in a large sample of normal star-forming galaxies at 4 < z < 6 from the ALMA Large Program to INvestigate [C II] at Early times (ALPINE) survey. Searching for typical signatures of outflows in the high-velocity tails of the stacked [C II] profile, we observe (i) deviations from a single-component Gaussian model in the combined residuals and (ii) broad emission in the stacked [C II] spectrum, with velocities of |v|≲500 km s−1. The significance of these features increases when stacking the subset of galaxies with star formation rates (SFRs) higher than the median (SFRmed = 25 M⊙ yr−1), thus confirming their star-formation-driven nature. The estimated mass outflow rates are comparable to the SFRs, yielding mass-loading factors of the order of unity (similarly to local star-forming galaxies), suggesting that star-formation-driven feedback may play a lesser role in quenching galaxies at z > 4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km s−1) of the higher-SFR galaxies is extended on physical sizes of ∼30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs.