arXiv subjects

Steven Gough-Kelly

Publications and source records attributed to Steven Gough-Kelly.

6 recordsLinked to original sources

arXiv2026

A Pilot Study to Verify the RR Lyrae Candidates with Vera C. Rubin Observatory Early Alerts

We present a pilot study using the Vera C. Rubin Observatory early alerts to verify RR Lyrae candidates in the Pan-STARRS1, the Dark Energy Survey, and the Next-Generation Virgo Cluster Survey RR Lyrae catalogs. RR Lyrae candidates fainter than 16 mag in the $g$-band in these catalogs were crossmatched with the alerts observed in several deep drilling fields and the M49 field. After excluding alerts with a low number of detections, there are 40 alerts associated with the RR Lyrae candidates. The multiband Rubin-LSST light curves extracted from the alerts verify 32 variables as genuine RR Lyrae, although several were not classified as variable stars in the ALeRCE and Lasair community alert brokers. While ALeRCE and Lasair provide $\sim70\%$ and $\sim40\%$ true variable classification, respectively, we find that $20\%$ of the alert sample are non-RR Lyrae variables. The remaining eight candidate variables do not show typical RR Lyrae light curves and include two active galactic nuclei and two eclipsing binaries. Additionally, we have also found a small number of known variable candidates with no alerts, which would suggest that they are either not RR Lyrae variables or the template images are not yet available for their difference image analysis.

astro-ph.SR↗

arXiv2026

The edge of the Milky Way's star-forming disc: Evidence from a 'U-shaped' stellar age profile

We leveraged reliable age and distance estimates from LAMOST-DR3 and APOGEE-DR17+AstroNN combined with \gaia\ data to perform a detailed analysis of the stellar age distribution in the Milky Way's (MW) outer disc using giant stars. Selecting stars near the midplane ($|z|<0.3$ kpc) on near-circular orbits ($\lambda_c > 0.9$), we analysed these independent datasets that employed different age-estimation methods. Our stringent kinematic selection criteria effectively exclude halo stars, ensuring that the observed age trends reflect genuine disc properties rather than contamination from older halo populations. Our results reveal a 'U-shaped' stellar age profile, where a negative gradient in the inner disc transitions to a positive gradient in the outer disc region. We identify the minimum in the stellar age profile at $R_{\rm min}=11.28 \pm 0.58$ kpc and $R_{\rm min}=12.15\pm 0.62$ kpc for the APOGEE-DR17 and LAMOST-DR3 samples, respectively. Using N-body+SPH simulations, we demonstrate that $R_{\rm min}$ corresponds to the break radius in the stellar density profile ($R_{\rm br}$), marking the edge of the Galaxy's star-forming disc. This break arises from a sharp decline in the star formation rate, with the outer positive age gradient produced by the radial migration of stars born inside $R_{\rm br}$. The cessation of star formation in the outer disc might be due to several mechanisms, including the dynamical influence of the bar's outer Lindblad resonance, the onset of the Galactic warp, or thermally regulated star formation. Overall, our results support the picture that the MW has a Type II (down-bending) stellar disc with a break at $R_{\rm br} \approx 11.28-12.15$ kpc, where the combination of star-formation cut-off and radial migration produces the observed U-shaped age profile.

astro-ph.GA↗

arXiv2025

The chemical and spatial variations of the bulge's velocity ellipsoids

We study the velocity ellipsoids in an $N$-body$+$SPH simulation of a barred galaxy which forms a bar with a BP bulge. We focus on the 2D kinematics, and quantify the velocity ellipses by the anisotropy, $\beta_{ij}$, the correlation, $\rho_{ij}$, and the vertex deviation, $l_{\rm v}$. We explore the variations in these quantities based on stellar age within the bulge and compare these results with the Milky Way's bulge using data from APOGEE DR16 and {\it Gaia} DR3. We first explore the variation of the model's velocity ellipses in galactocentric velocities, $v_R$ and $v_\phi$, for two bulge populations, a (relatively) young one and an old one. The bar imprints quadrupoles on the distribution of ellipse properties, which are stronger in the young population, as expected from their stronger bar. The quadrupoles are distorted if we use heliocentric velocities $v_r$ and $v_l$. We then project these kinematics along the line of sight onto the $(l,b)$-plane. Along the minor axis $\beta_{rl}$ changes from positive at low $|b|$ to negative at large $|b|$, crossing over at lower $|b|$ in the young stars. Consequently the vertex deviation peaks at lower $|b|$ in the young population, but reaches similar peak values in the old. The $\rho_{rl}$ is much stronger in the young stars, and traces the bar strength. The APOGEE stars split by the median [Fe/H] follow the same trends. Lastly we explore the velocity ellipses across the entire bulge region in $(l,b)$ space, finding good qualitative agreement between the model and observations.

astro-ph.GA↗

arXiv2024

Synergies between Roman Galactic Plane Survey and other major surveys

Nancy Grace Roman Space Telescope will revolutionize our understanding of the Galactic Bulge with its Galactic Bulge Time Domain survey. At the same time, Rubin Observatories's Legacy Survey of Space and Time (LSST) will monitor billions of stars in the Milky Way. The proposed Roman survey of the Galactic Plane, with its NIR passbands and exquisite spacial resolution, promises groundbreaking insights for a wide range of time-domain galactic astrophysics. In this white paper, we describe the scientific returns possible from the combination of the Roman Galactic Plane Survey with the data from LSST.

astro-ph.GA↗

arXiv2023

The interplay between accretion, galaxy downsizing and the formation of box/peanut bulges in TNG50

From the TNG50 cosmological simulation we build a sample of 191 well-resolved barred galaxies with a stellar mass $\log M_\star > 10$ at $z=0$. We search for box/peanut bulges (BPs) in this sample, finding them in 55 per cent of cases. We compute $f_\mathrm{BP}$, the BP probability for barred galaxies as a function of $M_\star$, and find that this rises to a plateau, as found in observations of nearby galaxies. The transition mass where $f_\mathrm{BP}$ reaches half the plateau value is $\log M_\star = 10.14$, consistent with the observational value within measurement errors. We show that this transition in $f_\mathrm{BP}$ can be attributed to the youth of the bars at low $M_\star$, which is a consequence of downsizing of galaxies. Young bars, being generally shorter and weaker, have not yet had time to form BPs. At high mass, while we find a plateau, the value is at $\sim 60$ per cent, whereas observations saturate at 100 per cent. We attribute this difference to excessive heating in TNG50, due to merger activity and to numerical resolution effects. BPs in TNG50 tend to occur in galaxies with more quiescent merger histories. As a result, the main driver of whether a bar hosts a BP in TNG50 is not the galaxy mass, but how long and strong the bar is. Separating the BP sample into those that have visibly buckled and those that have not, we find that fully half of BP galaxies show clear signs of buckling, despite the excessive heating and limited vertical resolution of TNG50.

astro-ph.GA↗

arXiv2021

Predicted Trends in Milky Way Bulge Proper Motion Rotation Curves: future Prospects for HST and LSST

We use an $N$-body+smoothed particle hydrodynamics simulation of an isolated barred galaxy to study the age dependence of bulge longitudinal proper motion ($μ_l$) rotation curves. We show that close to the minor axis ($|l| \sim 0^\circ$) the relatively young stars rotate more rapidly than the old stars, as found by Hubble Space Telescope in the Milky Way's (MW's) bulge. This behaviour would be expected also if the MW were unbarred. At larger $|l|$ a different behaviour emerges. Because younger stars trace a strong bar, their galactocentric radial motions dominate their $μ_l$ at $|l| \sim 6^\circ$, leading to a reversal in the sign of $\left< μ_l \right>$. This results in a rotation curve with forbidden velocities (negative $\left< μ_l \right>$ at positive longitudes, and positive $\left< μ_l \right>$ at negative longitudes). The old stars, instead, trace a much weaker bar and thus their kinematics are more axisymmetric, resulting in no forbidden velocities. We develop metrics of the difference in the $\left< μ_l \right>$ rotation curves of young and old stars, and forbidden velocities. We use these to predict the locations where rotation curve reversals can be observed by HST and the Vera Rubin Telescope. Such measurements would represent support for the amplitude of the bar being a continuous function of age, as predicted by kinematic fractionation, in which the bar strength variations are produced purely by differences in the random motions of stellar populations at bar formation.

astro-ph.GA↗