Hintze Centre for Astrophysical Surveys

Abstract:

Abstract We investigate the clustering of Lyman-break galaxies at redshifts of 3 ≲ z ≲ 5 within the COSMOS field by measuring the angular two-point correlation function. Our robust sample of ~60,000 bright (mUV ≲ 27) Lyman-break galaxies was selected based on spectral energy distribution fitting across 14 photometric bands spanning optical and near-infrared wavelengths. We constrained both the 1- and 2-halo terms at separations up to 300 arcsec, finding an excess in the correlation function at scales corresponding to <20 kpc, consistent with enhancement due to clumps in the same galaxy or interactions on this scale. We then performed Bayesian model fits on the correlation functions to infer the Halo Occupation Distribution parameters, star formation duty cycle, and galaxy bias in three redshift bins. We examined several cases where different combinations of parameters were varied, showing that our data can constrain the slope of the satellite occupation function, which previous studies have fixed. For an MUV-limited sub-sample, we found galaxy bias values of $b_g=3.18^{+0.14}_{-0.14}$ at z ≃ 3, $b_g=3.58^{+0.27}_{-0.29}$ at z ≃ 4, $b_g=4.27^{+0.25}_{-0.26}$ at z ≃ 5. The duty cycle values are $0.62^{+0.25}_{-0.26}$, $0.40^{+0.34}_{-0.22}$, and $0.39^{+0.31}_{-0.20}$,respectively. These results suggest that, as the redshift increases, there is a slight decrease in the host halo masses and a shorter timescale for star formation in bright galaxies, at a fixed rest-frame UV luminosity threshold.

Abstract:

We present multiband ATLAS and ZTF photometry for SN 2019tsf, a Type Ib stripped-envelope supernova (SESN). The slow spectral evolution could be associated with an uncommon explosion mechanism specific to this SN. Possible explanations include fallback accretion onto a compact remnant or a long-lived central engine, both of which could provide extended energy injection responsible for the late-time rebrightening and unusual spectral features. The rebrightening observations represent the latest photometric measurements of a multipeaked Type Ib SN. As late-time photometry and spectroscopy suggest no hydrogen, the potential circumstellar material (CSM) must be H-poor. The absence of a nebular phase and the lack of narrow emission lines in the late-time spectra (>142 days) of the SNe suggest that any CSM interaction is likely asymmetric and enveloped by the SN ejecta. However, an extended CSM structure is evident through a follow-up radio campaign with the Karl G. Jansky Very Large Array (VLA), indicating a source of bright optically thick radio emission at late times, which is highly unusual among H-poor SESNe. We attribute this phenomenology to an interaction of the supernova ejecta with asymmetric CSM, potentially disk-like, and we present several models that may explain the origin of this rare Type Ib supernova. We propose a warped disk model in which a tertiary companion—commonly present around massive stars—perturbs the progenitor’s CSM, producing density enhancements that may explain the observed multipeaked SN 2019tsf light curve. This SN 2019tsf is a unique SN Type Ib among the recently discovered class of SNe that undergo mass transfer at the moment of explosion.

Abstract:

Abstract Using deep observations across three of the LOFAR Two-metre Sky Survey Deep Fields, this work measures the angular clustering of star forming galaxies (SFGs) and low-excitation radio galaxies (LERGs) to z ≲1.5 for faint sources, S144 MHz ≥200 μJy. We measure the angular auto-correlation of LOFAR sources in redshift bins and their cross-correlation with multi-wavelength sources to measure the evolving galaxy bias for SFGs and LERGs. Our work shows the bias of the radio-selected SFGs increases from $b=0.90^{+0.11}_{-0.10}$ at z ∼0.2 to $b=2.94^{+0.36}_{-0.36}$ at z ∼1.2; faster than the assumed b($z$)∝1/D($z$) models adopted in previous LOFAR cosmology studies (at sensitivities where AGN dominate), but in broad agreement with previous work. We further study the luminosity dependence of bias for SFGs and find little evidence for any luminosity dependence at fixed redshift, although uncertainties remain large for the sample sizes available. The LERG population instead shows a weaker redshift evolution with $b=2.33^{+0.28}_{-0.27}$ at z ∼0.7 to $b=2.65^{+0.57}_{-0.55}$ at z ∼1.2, though it is also consistent with the assumed bias evolution model (b($z$)∝1/D($z$)) within the measured uncertainties. For those LERGs which reside in quiescent galaxies (QLERGs), there is weak evidence that they are more biased than the general LERG population and evolve from b=$2.62^{+0.33}_{-0.33}$ at z ∼0.7 to $b=3.08^{+0.85}_{-0.84}$ at z ∼1.2. This suggests the halo environment of radio sources may be related to their properties. These measurements can help constrain models for the bias evolution of these source populations, and can help inform multi-tracer analyses.

Abstract:

We present new observations of the black hole X-ray binary A0620-00 using the Mid-Infrared (MIR) Instrument on the James Webb Space Telescope, during a state where the X-ray luminosity is 9 orders of magnitude below Eddington, and coordinated with radio, near-infrared, and optical observations. The goal is to understand the nature of the excess MIR emission originally detected by Spitzer redward of 8 μm. The stellar-subtracted MIR spectrum is well modeled by a power law with a spectral index of α = 0.72 ± 0.01, where the flux density scales with frequency as Fν ∝ να. The spectral characteristics, along with rapid variability—a 40% flux flare at 15 μm and 25% achromatic variability in the 5–12 μm range—rule out a circumbinary disk as the source of the MIR excess. The Low Resolution Spectrometer reveals a prominent emission feature at 7.5 μm, resulting from the blend of three hydrogen recombination lines. While the contribution from partially self-absorbed synchrotron radiation cannot be ruled out, we argue that thermal bremsstrahlung from a warm (a few tens of thousands of Kelvin) wind accounts for the MIR excess; the same outflow is responsible for the emission lines. The inferred mass outflow rate indicates that the system’s low luminosity is due to a substantial fraction of the mass supplied by the donor star being expelled through a wind rather than accreted onto the black hole.

Abstract:

Abstract Astrophysical jets signpost the most extreme phenomena in the Universe. Despite a century of study, connections between the physics of black holes and the processes underpinning the formation and launch of these jets remain elusive. Here we present a statistically significant sample of transient jet speeds from stellar-mass black holes and neutron stars. The fastest jets are exclusively from black holes and propagate along a fixed axis across several ejection phases. This provides strong evidence that the most relativistic jets propagate along the spin axis of the black hole that launches them. However, we find no correlation between reported spin estimates and the jet speeds, indicating that some issues remain in connecting the theories of jet formation with spin measurements. By contrast, slower jets can be launched by both black holes and neutron stars and can change in direction or precess, indicating that they are launched from the accretion flow.