arXiv subjects

Ahmed Shaban

Publications and source records attributed to Ahmed Shaban.

7 recordsLinked to original sources

arXiv2026

The GOLIATH Survey: OVI Absorption Reveals CGM Evolution through the Starburst-to-Quiescent Transition in Massive Galaxies

We present the GOLIATH survey (Galaxies, Outflows, and the Lifecycle of Immense, Active, Transforming Halos), a study of the multiphase circumgalactic medium (CGM) of massive ($\langle\log M_\star/M_\odot\rangle \approx 11$), blue ($u-r < 1.65$) starburst and post-starburst galaxies at $\langle z\rangle \approx$ 0.43. This work characterizes the warm-hot CGM through OVI absorption in the inner halo ($R/R_{\rm vir} \leq 0.6$) of these rare systems. Across the star-forming population, OVI column density rises by nearly 1~dex from $\log M_\star/M_{\odot} \sim 8$ to $\sim 11.5$ and increases with specific star-formation rate (sSFR). Two GOLIATH galaxies with the highest sSFR show the strongest CGM OVI absorption ($\log N_{\rm O\,VI}[\rm cm^{-2}] \gtrsim 15$). In the $\log M_\star/M_{\odot} = [11,12)$ inner-CGM region, massive star-forming galaxies exceed quiescent galaxies on average by a factor of $\sim 3$ in OVI column density and $\sim 1.5$~dex in CGM OVI mass ($\log(M_{\rm O\, VI}/M_\odot) \approx 7.3$ versus $\approx 5.8$), with covering fractions roughly three times higher (62.5% versus 24% at $\log N_{\rm O\,VI}[\rm cm^{-2}] \geq 14$). The OVI line widths and column densities are consistent with feedback-driven radiative cooling, in which outflow shocks heat the CGM and the gas cools back through the OVI window; the short cooling time, $t_{\rm cool} \sim 10$-$100$~Myr, requires continuous replenishment by active feedback to sustain this reservoir. The residual OVI in quiescent systems may arise from ambient gas at the high-temperature end of the cooling curve. OVI thus traces feedback on short timescales and probes the star-forming--quiescent transition at $\log M_\star/M_{\odot} \gtrsim 11$.

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arXiv2025

Spatially Resolved Circumgalactic Medium around a Star-Forming Galaxy Driving a Galactic Outflow at $z\approx 0.8$

We report the small-scale spatial variation in cool ($T\sim 10^4 K$) Mg II absorption detected in the circumgalactic medium (CGM) of a star-forming galaxy at $z\approx 0.8$. The CGM of this galaxy is probed by a spatially extended bright background gravitationally lensed arc at $z = 2.76$. The background arc continuously samples the CGM of the foreground galaxy at a range of impact parameters between 54-66 kpc. The Mg II absorption strengths vary by more than a factor of two within these ranges. A power-law fit to the fractional variation of absorption strengths yields a coherence length of 2.7 kpc within these absorption lines. This suggests a high degree of spatial coherence in the CGM of this galaxy. The host galaxy is driving a strong galactic outflow with a mean outflow velocity $\approx$ -179 km/s and mass outflow rate $\dot{M}_{out}\geq 64_{-27}^{+31} M_{\odot}yr^{-1}$ traced by blueshifted Mg II and Fe II absorption lines. The galaxy itself has a spatially extended emission halo with a maximum spatial extent of $\approx$ 33 kpc traced by [O II], [O III] and $H\beta$ emission lines. The extended emission halo shows kinematic signatures of co-rotating halo-gas with solar metallicity. Taken together, these observations suggest evidence of a baryon cycle that is recycling the outflowing gas to form the next generation of stars.

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arXiv2023

Dissecting a 30 kpc galactic outflow at $z \sim$ 1.7

We present the spatially resolved measurements of a cool galactic outflow in the gravitationally lensed galaxy RCS0327 at $z \approx 1.703$ using VLT/MUSE IFU observations. We probe the cool outflowing gas, traced by blueshifted Mg II and Fe II absorption lines, in 15 distinct regions of the same galaxy in its image-plane. Different physical regions, 5 to 7 kpc apart within the galaxy, drive the outflows at different velocities ($V_{out} \sim $ $-161$ to $-240$ km s$^{-1}$), and mass outflow rates ($\dot{M}_{out} \sim$ 183 to 527 $M_{\odot}\ yr^{-1}$). The outflow velocities from different regions of the same galaxy vary by 80 km s$^{-1}$, which is comparable to the variation seen in a large sample of star-burst galaxies in the local Universe. Using multiply lensed images of RCS0327, we probe the same star-forming region at different spatial scales (0.5 kpc$^2$-25 kpc$^2$), we find that outflow velocities vary between $ \sim $ $-120$ to $-242$ km s$^{-1}$, and the mass outflow rates vary between $\sim$ 37 to 254 $M_{\odot}\ yr^{-1}$. The outflow momentum flux in this galaxy is $\geq$ 100% of the momentum flux provided by star-formation in individual regions, and outflow energy flux is $\approx$ 10% of the total energy flux provided by star-formation. These estimates suggest that the outflow in RCS0327 is energy driven. This work shows the importance of small scale variations of outflow properties due to the variations of local stellar properties of the host galaxy in the context of galaxy evolution.

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arXiv2022

A 30 kpc Spatially Extended Clumpy and Asymmetric Galactic Outflow at z $\sim$ 1.7

We image the spatial extent of a cool galactic outflow with fine structure Fe II$^*$ emission and resonant Mg II emission in a gravitationally lensed star-forming galaxy at $z = 1.70347$. The Fe II$^*$ and Mg II (continuum-subtracted) emissions span out to radial distances of $\sim$14.33 kpc and 26.5 kpc, respectively, with maximum spatial extents of $\sim$21 kpc for Fe II$^*$ emission and $\sim$30 kpc for Mg II emission. Mg II residual emission is patchy and covers a total area of $\sim$184 kpc$^2$, constraining the minimum area covered by the outflowing gas to be $\sim$13% of the total area. Mg II emission is asymmetric and shows $\sim$21% more extended emission along the declination direction. We constrain the covering fractions of the Fe II$^*$ and Mg II emission as a function of radial distance and characterize them with a power law model. The Mg II 2803 emission line shows two kinematically distinct emission components, and may correspond to two distinct shells of outflowing gas with a velocity separation of $Δv \sim$ 400 km/s. By using multiple images with different magnifications of the galaxy in the image plane, we trace the Fe II$^*$, Mg II emissions around three individual star-forming regions. In all cases, both the Fe II$^*$ and Mg II emissions are more spatially extended compared to the star forming regions traced by the [O II] emission. These findings provide robust constraints on the spatial extent of the outflowing gas, and combined with outflow velocity and column density measurements will give stringent constraints on mass outflow rates of the galaxy.

astro-ph.GA↗

arXiv2022

Low Power Neuromorphic EMG Gesture Classification

EMG (Electromyograph) signal based gesture recognition can prove vital for applications such as smart wearables and bio-medical neuro-prosthetic control. Spiking Neural Networks (SNNs) are promising for low-power, real-time EMG gesture recognition, owing to their inherent spike/event driven spatio-temporal dynamics. In literature, there are limited demonstrations of neuromorphic hardware implementation (at full chip/board/system scale) for EMG gesture classification. Moreover, most literature attempts exploit primitive SNNs based on LIF (Leaky Integrate and Fire) neurons. In this work, we address the aforementioned gaps with following key contributions: (1) Low-power, high accuracy demonstration of EMG-signal based gesture recognition using neuromorphic Recurrent Spiking Neural Networks (RSNN). In particular, we propose a multi-time scale recurrent neuromorphic system based on special double-exponential adaptive threshold (DEXAT) neurons. Our network achieves state-of-the-art classification accuracy (90%) while using ~53% lesser neurons than best reported prior art on Roshambo EMG dataset. (2) A new multi-channel spike encoder scheme for efficient processing of real-valued EMG data on neuromorphic systems. (3) Unique multi-compartment methodology to implement complex adaptive neurons on Intel's dedicated neuromorphic Loihi chip is shown. (4) RSNN implementation on Loihi (Nahuku 32) achieves significant energy/latency benefits of ~983X/19X compared to GPU for batch size as 50.

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arXiv2022

A Statistical Primer on Classical Period-Finding Techniques in Astronomy

The aim of our paper is to investigate the properties of the classical phase-dispersion minimization (PDM), analysis of variance (AOV), string-length (SL), and Lomb-Scargle (LS) power statistics from a statistician's perspective. We confirm that when the data are perturbations of a constant function, i.e. under the null hypothesis of no period in the data, a scaled version of the PDM statistic follows a beta distribution, the AOV statistic follows an F distribution, and the LS power follows a chi-squared distribution with two degrees of freedom. However, the SL statistic does not have a closed-form distribution. We further verify these theoretical distributions through simulations and demonstrate that the extreme values of these statistics (over a range of trial periods), often used for period estimation and determination of the false alarm probability (FAP), follow different distributions than those derived for a single period. We emphasize that multiple-testing considerations are needed to correctly derive FAP bounds. Though, in fact, multiple-testing controls are built into the FAP bound for these extreme-value statistics, e.g. the FAP bound derived specifically for the maximum LS power statistic over a range of trial periods. Additionally, we find that all of these methods are robust to heteroscedastic noise aimed to mimic the degradation or miscalibration of an instrument over time. Finally, we examine the ability of these statistics to detect a non-constant periodic function via simulating data that mimics a well-detached binary system, and we find that the AOV statistic has the most power to detect the correct period, which agrees with what has been observed in practice.

astro-ph.EP↗

arXiv2022

Resolving the HI in Damped Lyman-α systems that power star-formation

Reservoirs of dense atomic gas (primarily hydrogen), contain approximately 90 percent of the neutral gas at a redshift of 3, and contribute to 2-3 percent of the total baryons in the Universe. These damped Lyman-$α$ systems (so called because they absorb Lyman-$α$ photons from within and from background sources) have been studied for decades, but only through absorption lines present in the spectra of background quasars and gamma-ray bursts. Such pencil beams do not constrain the physical extent of the systems. Here, we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman-$α$ systems. These systems are $>$ 238 $kpc^2$ in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on $<$ 3 kpc-scales. The mean column densities are $10^{20.46}$ - $10^{20.84} cm^{-2}$ and the total masses are $> 5.5 \times 10^{8}$ - $1.4 \times 10^{9} M_{\odot}$, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts $>$ 2.

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