arXiv subjects

Rashid Yaaqib

Publications and source records attributed to Rashid Yaaqib.

6 recordsLinked to original sources

arXiv2025

Inclinations and Position Angles for Disc Galaxies in the SGA sample

We present a data-driven method for determining the inclination and position angle (PA) of disc galaxies using a Fourier-Laguerre basis decomposition of imaging data. We define a dimensionless metric, $η$, that characterises the ratio of the quadrupole and monopole coefficients in the Fourier-Laguerre basis function expansion. This metric serves as a robust measure which is related to the inclination of a galaxy. We find an empirical relationship between $η$ and inclination which is agnostic to the galaxy morphology. The PA is derived directly from the phase of the quadrupolar Fourier-Laguerre functions. Across a benchmark sample of galaxies, the method reproduces published inclination and PA values to within a median of 10$^\circ$ and 5$^\circ$, respectively, while also demonstrating essentially zero catastrophic failures. Applying this pipeline to galaxies from the Siena Galaxy Atlas (SGA), we report measurements of $η$, scale length and PA for three different bands of 133,942 disc galaxies. Our computationally inexpensive technique automates parametrisation analysis and returns reproducible results for large surveys. We release a Python package ready for application to next generation surveys.

astro-ph.GA↗

arXiv2025

Constraining the Milky Way dark matter halo with LMC-induced reflex motion

Modelling perturbations of the Milky Way (MW) halo induced by the infall of the Large Magellanic Cloud (LMC) offers new avenues to constrain the dark matter (DM) distribution in our Galaxy. A key observable is the reflex motion of the MW disc with respect to the halo induced by the LMC's infall, which imprints a velocity dipole on kinematics of halo stars. Here we investigate how the dipole varies with Galactocentric radius, and study the sensitivity of the reflex motion signal to different DM outer-halo profiles. Using a suite of basis function expansion (BFE) simulations with truncated NFW profiles ($ρ\propto r^{-β}$ beyond $r=50$ kpc), our $N$-body models show that (i) The reflex motion amplitude varies with Galactocentric radius but is largely insensitive to the outer DM slope, implying that the MW-LMC mass ratio alone does not set the dipole strength. (ii) In contrast, the direction of the disc motion is very sensitive to the density distribution of the outer DM halo. (iii) The contraction of the MW halo induced by the LMC's gravitational pull also depends strongly on the outer DM halo profile. (iv) We find a halo instability whose oscillation frequency increases with $β$ producing a potentially observable signature - a sinusoidal pattern of the mean radial velocity of halo stars. Finally, using BFE coefficients we find that steeper truncations produce smaller dipole distortions, while amplifying the quadrupole distortion. These results highlight the limited constraining power of the reflex motion amplitude alone for outer MW profile parameters.

astro-ph.GA↗

arXiv2025

Disc asymmetry characterisation in JWST-observed galaxies at 1 < z < 4

We present a novel technique using Fourier series and Laguerre polynomials to represent morphological features of disc galaxies. To demonstrate the utility of this technique, we study the evolution of disc asymmetry in a sample of disc galaxies drawn from the Extended Groth Strip and imaged by the JWST Cosmic Evolution Early Release Science Survey as well as archival HST observations. We measure disc asymmetry as the amplitude of the of the m = 1 Fourier harmonic for galaxies within redshift ranges of 1 < z < 4 relative to the amplitude of m = 0 harmonic. We show that when viewed in shorter rest frame wavelengths, disc galaxies have a higher asymmetry as the flux is dominated by star forming regions. We find generally low asymmetry at rest frame infrared wavelengths, where our metric tracks asymmetry in morphological features such as bars and spiral arms. We show that higher mass galaxies have lower asymmetry and vice versa. Higher asymmetry in lower mass galaxies comes from lower mass galaxies (typically) having higher star formation rates. We measure the relation between disc galaxy asymmetry and redshift and find no conclusive relationship between them. We demonstrate the utility of the Fourier-Laguerre technique for recovering physically informative asymmetry measurements as compared to rotational asymmetry measurements. We also release the software pipeline and quantitative analysis for each galaxy.

astro-ph.GA↗

arXiv2025

The angular momentum spiral of the Milky Way disc in Gaia

Data from the Gaia mission shows prominent phase-space spirals that are the signatures of disequilibrium in the Milky Way (MW) disc. In this work, we present a novel perspective on the phase-space spiral in angular momentum (AM) space. Using Gaia DR3, we detect a prominent AM spiral in the solar neighbourhood. We demonstrate the relation of AM to the $z-v_z$ spiral and show that we can map to this space from angular momentum through simplifying assumptions. By modelling the orbit of stars in AM, we develop a generative model for the spiral where the disc is perturbed by a bulk tilt at an earlier time. Our model successfully describes the salient features of the AM spiral in the data. Modelling the phase spiral in AM is a promising method to constrain both perturbation and MW potential parameters. Our AM framework simplifies the interpretation of the spiral and offers a robust approach to modelling disequilibrium in the MW disc using all six dimensions of phase space simultaneously.

astro-ph.GA↗

arXiv2024

The radial variation of the LMC-induced reflex motion of the Milky Way disc observed in the stellar halo

We measure the kinematic signature arising from the Milky Way (MW) disc moving with respect to the outer stellar halo, which is observed as a dipole signal in the kinematics of stellar halo tracers. We quantify how the reflex motion varies as a function of Galactocentric distance, finding that (i) the amplitude of the dipole signal increases as a function of radius, and (ii) the direction moves across the sky. We compare the reflex motion signal against a compilation of published models that follow the MW--LMC interaction. These models show a similar trend of increasing amplitude of the reflex motion as a function of distance, but they do not reproduce the direction of the disc motion with respect to the stellar halo well. We also report mean motions for the stellar halo as a function of distance, finding radial compression in the outer halo and nonzero prograde rotation at all radii. The observed compression signal is also present in MW--LMC models, but the rotation is not, which suggests that the latter is not induced by the LMC. We extensively validate our technique to measure reflex motion against idealised tests. We discuss prospects for directly constraining the mass and orbital history of the LMC through the impact on the motion of the MW stellar disc, and how the modelling of the reflex motion can be improved as more and better data become available.

astro-ph.GA↗

arXiv2017

Mass models of NGC 6624 without an intermediate-mass black hole

An intermediate-mass black hole (IMBH) was recently reported to reside in the centre of the Galactic globular cluster (GC) NGC 6624, based on timing observations of a millisecond pulsar (MSP) located near the cluster centre in projection. We present dynamical models with multiple mass components of NGC 6624 - without an IMBH - which successfully describe the surface brightness profile and proper motion kinematics from the Hubble Space Telescope (HST) and the stellar mass function at different distances from the cluster centre. The maximum line-of-sight acceleration at the position of the MSP accommodates the inferred acceleration of the MSP, as derived from its first period derivative. With discrete realizations of the models we show that the higher-order period derivatives - which were previously used to derive the IMBH mass - are due to passing stars and stellar remnants, as previously shown analytically in literature. We conclude that there is no need for an IMBH to explain the timing observations of this MSP.

astro-ph.GA↗