arXiv subjects

Stephen Molyneux

Publications and source records attributed to Stephen Molyneux.

5 recordsLinked to original sources

arXiv2026

The Atacama Large Aperture Submillimeter Telescope (AtLAST): enabling large-scale sub-mm science beyond 2030

AtLAST is designed to be the largest (sub-)mm single-dish astronomical observatory and the first climate-neutral modern research infrastructure. It offers a unique combination of large aperture (50 m), large field of view (>1 deg), fast scanning speed (up to 3 deg/s), and high surface accuracy (20micron nighttime half wavefront error) that allows >=50% Ruze efficiency up to 1 THz. The design features a rocking chair mount with an active main reflector surface, a high precision closed-loop metrology system, and the space to house six major instruments. Instruments will be periodically updated as spectroscopic focal plane array, detector, coherent amplifier, and semiconductor technologies used in readout and backend electronics will advance over the next decades. AtLAST will be a multi-purpose facility that will produce transformational results in nearly all fields of Astrophysics, such as Astrochemistry, Galactic and Extragalactic Astronomy, Cosmology, Planetary science, Stellar and Solar Physics, High energy astrophysics, and Time domain astronomy. Its unrivalled throughput of 6170 m^2 deg^2 will enable wide-field unbiased surveys. These will overcome extragalactic confusion noise and enable the detection of normal galaxy populations out to z=7. AtLAST will reveal and characterise the missing baryons in the Universe, by mapping the elusive, low surface brightness gas within and around galaxies across cosmic time. AtLAST will be the first green off-grid observatory, powered by a bespoke renewable energy system and reusing its braking energy thanks to a cutting-edge energy recovery system. By sharing surplus power and technological know-how with local communities, AtLAST will contribute to energy justice in Chile. AtLAST's new bold vision of a sustainable pursuit of breakthrough astronomy is an exceptional opportunity to shape the future of scientific research infrastructures. [abridged]

astro-ph.IM↗

arXiv2026

The Quasar Feedback Survey: Revealing the importance of sensitive radio imaging for AGN identification deeper into the radio-quiet regime

We present new sub-arcsecond ($\sim$0.3-1 arcsec; $\sim$1--3\,kpc) VLA imaging at 1.4\,GHz and 6\,GHz of 29 optically-selected, [O~{\sc iii}] luminous ($L_{\rm [O III]}$ > 10$^{42.1}$\,erg\,s$^{-1}$), $z<0.2$ quasars drawn from the expanded Quasar Feedback Survey (QFeedS; with $L_\mathrm{1.4\,GHz} = 10^{22.6}$--10$^{26.3}$\,W\,Hz$^{-1}$). These 29 new objects occupy the low end of the radio-power distribution ($L_\mathrm{1.4\,GHz}$=$10^{22.63}$--10$^{23.45}$\,W\,Hz$^{-1}$) in the QFeedS sample and are nominally `radio quiet'. Despite this, we find widespread evidence of AGN-driven synchrotron activity. Nearly $\sim 31\,$per\,cent exhibit resolved radio structures on $\sim$0.1--20\,kpc scales consistent with compact jets or wind-driven outflows, and $\sim 90\,$per\,cent display steep spectra ($\alpha \lesssim -1$) indicative of optically thin synchrotron emission. Combining morphology, spectral index and brightness-temperature diagnostics, at least $\sim38\,$per\,cent of the sample show clear AGN signatures that cannot be explained by star formation alone. These constitute the first results from the expanded QFeedS (now 71 quasars spanning $\approx 4$ dex in radio power) and demonstrate that compact, low-power jets and AGN shocks are common deep inside the radio-quiet regime. A thorough understanding of feedback processes from quasars, deep into the `radio-quiet' regime, will be obtained by connecting these high resolution radio observations with multi-wavelength observations.

astro-ph.GA↗

arXiv2025

The Quasar Feedback Survey: zooming into the origin of radio emission with e-MERLIN

We present 6 GHz e-MERLIN observations of 42 $z<0.2$ type 1 and type 2 mostly radio-quiet quasars ($L_{\rm[OIII]}\gtrsim10^{42}$ erg s$^{-1}$; $L_{\rm AGN}\gtrsim10^{45}$ erg s$^{-1}$) from the Quasar Feedback Survey. The nature and origin of radio emission in these types of sources is typically ambiguous based on all-sky, low-resolution surveys. With e-MERLIN, we investigate radio emission on sub-kiloparsec scales ($\sim$10s-100s pc). We find 37/42 quasars are detected, with a diversity of radio morphologies, including compact cores, knots and extended jet-like structures, with sizes of 30-540 pc. Based on morphology and brightness temperature, we classify 76 per cent of the quasars as radio-AGN, compared to the $\sim$57 per cent identified as radio-AGN at the $\sim$1-60 kpc scales probed in prior studies. Combining results from e-MERLIN and the Very Large Array, 86 per cent reveal a radio-AGN. On average, $\sim$60 per cent of the total radio flux is resolved away in the e-MERLIN maps, and is likely dominated by jet-driven lobes and outflow-driven shocks. We find no significant differences in measured radio properties between type 1 and type 2 quasars, and estimate sub-relativistic jet speeds of $\sim$0.2-0.3c and modest jet powers of $P_\mathrm{jet} \approx \times$10$^{43}$ erg s$^{-1}$ for the few targets, where these measurements were possible. These quasars share characteristics with compact radio-selected populations, and the global radio emission likely traces strong interactions between the AGN (jets/outflows) and their host galaxy ISM from 10s parsec to 10s kiloparsec scales.

astro-ph.GA↗

arXiv2024

Deep rest-UV JWST/NIRSpec spectroscopy of early galaxies: the demographics of CIV and N-emitters in the reionization era

JWST has recently discovered a subset of reionization era galaxies with ionized gas that is metal poor in oxygen and carbon but heavily-enriched in nitrogen. This abundance pattern is almost never seen in lower redshift galaxies but is commonly observed in globular cluster stars. We have recently demonstrated that this peculiar abundance pattern appears in a compact ($\simeq 20$ pc) metal-poor galaxy undergoing a strong burst of star formation. This galaxy was originally selected based on strong CIV emission, indicating a hard radiation field rarely seen locally. In this paper, we present JWST/NIRSpec observations of another reionization-era galaxy known to power strong CIV emission, the $z=7.04$ gravitationally-lensed galaxy A1703-zd6. The emission line spectrum reveals this is a metal poor galaxy ($12+\log(\rm O/H) = 7.47\pm0.19$) dominated by a young stellar population ($1.6^{+0.5}_{-0.4}$ Myr) that powers a very hard ionizing spectrum (CIV EW = 19.4 $\unicode{x212B}$, He II EW = 2.2 $\unicode{x212B}$). The ISM is highly-enriched in nitrogen ($\log(\rm N/O)=-0.6$) with very high electron densities ($8-19\times10^4$ cm$^{-3}$) and extreme ionization conditions rarely seen at lower redshift. We also find intense CIV emission (EW$\gtrsim20$ $\unicode{x212B}$) in two new $z\gtrsim 6$ metal poor galaxies. To put these results in context, we search for UV line emission in a sample of 737 $z\gtrsim 4$ galaxies with NIRSpec spectra, establishing that 40(30)% of systems with [OIII]+H$\beta$ EW $>2000\unicode{x212B}$ have NIV] (CIV) detections with EW$>5$ $\unicode{x212B}$ ($>10$ $\unicode{x212B}$). These results suggest high N/O ratios and hard ionizing sources appear in a brief phase following a burst of star formation in compact high density stellar complexes.

astro-ph.GA↗

arXiv2024

Metal-poor star formation at $z>6$ with JWST: new insight into hard radiation fields and nitrogen enrichment on 20 pc scales

Nearly a decade ago, we began to see indications that reionization-era galaxies power hard radiation fields rarely seen at lower redshift. Most striking were detections of nebular CIV emission in what appeared to be typical low mass galaxies, requiring an ample supply of 48 eV photons to triply ionize carbon. The nature of this population has long remained unclear owing to limitations of ground-based spectroscopy. We have obtained deep JWST/NIRSpec R=1000 spectroscopy of the two z>6 CIV-emitting galaxies known prior to JWST. Here we present a rest-UV to optical spectrum of one of these two systems, the multiply-imaged z=6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals two compact (<22pc) clumps separated by 220pc, with one comprising a dense concentration of massive stars ($>10,400M_{\odot}$/yr/kpc$^2$) formed in a recent burst. We stack spectra of 3 images of the galaxy (J=24.8-25.9), yielding a very deep spectrum providing a high S/N template of strong emission line sources at z>6. The spectrum reveals narrow high ionization lines (HeII, CIV, NIV]) with line ratios consistent with powering by massive stars. The rest-optical spectrum is dominated by very strong emission lines ([OIII] EW=2800Å), albeit with weak emission from low-ionization transitions ([OIII]/[OII]=184). The electron density is found to be very high($6.4-31\times10^4$cm$^{-3}$) based on three UV transitions. The ionized gas is metal poor ($12+\log(\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highly enriched in nitrogen ($\log(\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrum appears broadly similar to that of GNz11 at z=10.6, without showing the same AGN signatures. We suggest that the hard radiation field and rapid nitrogen enrichment may be a short-lived phase that many z>6 galaxies go through as they undergo strong bursts of star formation. We comment on the potential link of such spectra to globular cluster formation.

astro-ph.GA↗