Prof Chris Lintott

Abstract:

Abstract We present morphological classifications of over 41 000 galaxies out to zphot ∼ 2.5 across six square degrees of the Euclid Deep Field North (EDFN) from the Hawaii Twenty Square Degree (H20) survey, a part of the wider Cosmic Dawn survey. Galaxy Zoo citizen scientists play a crucial role in the examination of large astronomical data sets through crowdsourced data mining of extragalactic imaging. This iteration, Galaxy Zoo: Cosmic Dawn (GZCD), saw tens of thousands of volunteers and the deep learning foundation model Zoobot collectively classify objects in ultra-deep multiband Hyper Suprime-Cam (HSC) imaging down to a depth of mHSC − i = 21.5. Here, we present the details and general analysis of this iteration, including the use of Zoobot in an active learning cycle to improve both model performance and volunteer experience, as well as the discovery of 51 new gravitational lenses in the EDFN. We also announce the public data release of the classifications for over 45 000 subjects, including more than 41 000 galaxies (median zphot of 0.42 ± 0.23), along with their associated image cutouts. This data set provides a valuable opportunity for follow-up imaging of objects in the EDFN as well as acting as a truth set for training deep learning models for application to ground-based surveys like that of the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) collaboration and the newly operational Vera C. Rubin Observatory.

Abstract:

Stellar bars are elongated structures in disk galaxies that can torque and funnel gas inward, influencing galaxy evolution. While strong bars are known to induce rapid inflow, the impact of weaker bars remains less certain. We collected spectroscopic data using the Isaac Newton Telescope to analyze 18 nearby galaxies (strongly barred, weakly barred, and unbarred) drawn from Galaxy Zoo DESI. We obtained spatial profiles of equivalent width (EW) and ionized gas velocity dispersion by fitting Gaussian profiles to the Hα emission line. Strongly barred galaxies exhibit a distinctive three-peaked EW[Hα] structure, consistent with inward funneling of gas. Weakly barred systems lack this pattern, which suggests limited inflow. Velocity dispersion distributions further distinguish the bar types, with strongly barred galaxies showing significantly higher values than weakly barred and unbarred systems. These results suggest that strong bars drive gas inflow, while weak bars exert a limited dynamical influence.

Abstract:

We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be MA=0.250−0.004+0.005 M⊙, MB=0.208−0.004+0.005 M⊙, and RA=0.255−0.005+0.004 R⊙, RB=0.233−0.005+0.006 R⊙, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (≲0.35 M⊙); therefore, they can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging, and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries.

Abstract:

Stars in galactic centres are occasionally scattered so close to the central supermassive black hole that they are completely disrupted by tidal forces, initiating a transient accretion event. The aftermath of such a tidal disruption event (TDE) produces a bright-and-blue accretion flow that is known to persist for at least a decade (observationally) and can in principle produce ionizing radiation for hundreds of years. TDEs are known (observationally) to be overrepresented in galaxies that show extended emission-line regions (EELRs), with no pre-TDE classical active galactic nucleus activity, and to produce transient ‘coronal lines’, such as [Fe x] and [Fe xiv]. Using coupled cloudy-TDE disc simulations we show that TDE discs produce a sufficient ionizing radiation flux over their lifetimes to power both EELR of radial extents of light years, and coronal lines. EELRs are produced when the ionizing radiation interacts with low-density () clouds on galactic scales, while coronal lines are produced by high-density () clouds near the galactic centre. High-density gas in galactic centres will also result in the rapid switching on of narrow-line features in post-TDE galaxies, and also various high-ionization lines, which may be observed throughout the infrared with James Webb Space Telescope. Galaxies with a higher intrinsic rate of TDEs will be more likely to show macroscopic EELRs, which can be traced to originate from the previous TDE in that galaxy.

Abstract:

The first JWST deep surveys have expanded our understanding of the morphological evolution of galaxies across cosmic time. The improved spatial resolution and near-infrared (NIR) coverage have revealed a population of morphologically evolved galaxies at very early epochs. However, all previous works are based on relatively small samples; this has prevented accurate probing of the morphological diversity at cosmic dawn. Leveraging the wide area coverage of the COSMOS-Web survey, we quantified the abundance of different morphological types from z∼7 with unprecedented statistics and established robust constraints on the epoch of emergence of the Hubble sequence. We measured the global morphologies (spheroids, disk-dominated, bulge-dominated, peculiar) and resolved morphologies (stellar bars) for about 400,000 galaxies down to F150W=27 using deep learning; this represents an increase of two orders of magnitude over previous studies. We provide reference stellar mass functions (SMFs) of different morphologies between z∼0.2 and z∼7 as well as best-fit parameters to inform models of galaxy formation. All catalogs and data are made publicly available. At redshift ( z > 4.5 ), the massive galaxy population (łog M_*/M_⊙>10) is dominated by disturbed morphologies (( ∼70% )), even in the optical rest frame, and very compact objects (( ∼30% )) with effective radii smaller than ( ∼500 pc ). This confirms that a significant fraction of the star formation at cosmic dawn occurs in very dense regions, although the stellar mass for these systems could be overestimated. Galaxies with Hubble-type morphologies, including bulge- and disk-dominated galaxies, arose rapidly around ( z ∼ 4 ) and dominate the morphological diversity of massive galaxies as early as ( z ∼ 3 ). Using stellar bars as a proxy, we speculate that stellar disks in massive galaxies might have been common ($>50%$) among the star-forming population since cosmic noon (( z ∼ 2 2.5 )) and formed as early as z∼7. Massive quenched galaxies are predominantly bulge-dominated from ( z ∼ 4 ) onward, suggesting that morphological transformations briefly precede or are simultaneous to quenching mechanisms at the high-mass end. Low-mass (łog M_*/M_⊙<10) quenched galaxies are typically disk-dominated, which points to different quenching routes at the two ends of the stellar mass spectrum from cosmic dawn.