KICC papers

Dark matter-deficient galaxies (DMDGs) discovered in the survey of ultra-diffuse galaxies (UDGs), in apparent conflict with standard CDM, may be produced by high-velocity galaxy-galaxy collisions, the $\textit{Mini-bullet}$ scenario. Recent observations of an aligned trail of $7-11$ UDGs near NGC1052, including DMDGs DF2 and DF4, suggesting a common formation event, $\sim8.9\pm1.5$ Gyr ago, provide a test. Hydro/N-body simulations, supplemented by galaxy orbit integrations, demonstrate that satellite-satellite collisions outside the host-galaxy virial radius can reproduce the observed UDGs in the NGC1052 group. A trail of $\sim10$ DMDGs is shown to form, including two massive ones that replicate the observed motions of DF2 and DF4. The linear relation, $v=Ax+v_{0}$, conjectured previously to relate positions ($x$) and velocities ($v$) of the aligned DMDGs as a signature of the collision event, is approximately obeyed, but individual DMDGs can deviate significantly from it. The progenitors whose collision spawned the trail of DMDGs survive the collision without, themselves, becoming DMDGs. We predict one progenitor is located at the end of the trail, testable by observing the difference between its stars, formed pre-collision, from those of the DMDGs, formed post-collision. By contrast, stellar ages and metallicities of the DMDGs are nearly identical. We further offer a hint that the tidal field of host NGC1052 may contribute to making DMDGs diffuse. $\Lambda$CDM simulation in a 100 cMpc box finds our required initial conditions $\sim10$ times at $z

JWST has recently sparked a new era of Lya spectroscopy, delivering the first measurements of the Lya escape fraction and velocity profile in typical galaxies at z~6-10. These observations offer new prospects for insight into the earliest stages of reionization. But to realize this potential, we need robust intrinsic models of Lya properties in galaxies at z~5-6 when the IGM is mostly ionized. Here we use new JWST observations from the JADES and FRESCO surveys to characterize statistical distributions of Lya velocity offsets, escape fractions, and EWs in z~5-6 galaxies that will be applicable to growing datasets at z>6. We find that galaxies with large Lya escape fractions (>0.2) are common at z~5-6, comprising 30% of Lyman break selected samples. Comparing to literature studies, our census suggests that Lya becomes more prevalent in the galaxy population toward higher redshift from z~3 to z~6, although we find that this evolution slows considerably between z~5 and z~6, consistent with modest attenuation from residual HI in the mostly ionized IGM at z~5-6. We find significant evolution in Lya velocity profiles between z~2-3 and z~5-6. At lower redshifts, the strongest Lya emitters often have line profiles peaking near the systemic redshift, reflecting escape through low HI density channels. At z~5-6, the strongest Lya emitters have profiles with flux emerging at typical redshifted velocities ~230km/s. The rarity of Lya emitters with peak flux near the systemic redshift at z~5-6 may reflect the influence of resonant scattering from residual HI in the IGM. This effect will make it challenging to use Lya peak offsets as a probe of Lyman continuum leakage at z~5-6. We use our z~5-6 Lya distributions to make predictions for typical Lya properties at z>8 and discuss implications of a recently-discovered Lya emitter at z=8.5 with a small peak velocity offset (156km/s).

Dual-field interferometric observations with VLTI/GRAVITY sometimes require the use of a "binary calibrator", a binary star whose individual components remain unresolved by the interferometer, with a separation between 400 and 2000 mas for observations with the Units Telescopes (UTs), or 1200 to 3000 mas for the Auxiliary Telescopes (ATs). The separation vector also needs to be predictable to within 10 mas for proper pointing of the instrument. Up until now, no list of properly vetted calibrators was available for dual-field observations with VLTI/GRAVITY on the UTs. Our objective is to compile such a list, and make it available to the community. We identify a list of candidates from the Washington Double Star (WDS) catalogue, all with appropriate separations and brightness, scattered over the Southern sky. We observe them as part of a dedicated calibration programme, and determine whether these objects are true binaries (excluding higher multiplicities resolved interferometrically but unseen by imaging), and extract measurements of the separation vectors. We combine these new measurements with those available in the WDS to determine updated orbital parameters for all our vetted calibrators. We compile a list of 13 vetted binary calibrators for observations with VLTI/GRAVITY on the UTs, and provide orbital estimates and astrometric predictions for each of them. We show that our list guarantees that there are always at least two binary calibrators at airmass

Flux excesses in the early time light curves of Type Ia supernovae (SNe\,Ia) are predicted by multiple theoretical models and have been observed in a number of nearby SNe\,Ia over the last decade. However, the astrophysical processes that cause these excesses may affect their use as standardizable candles for cosmological parameter measurements. In this paper, we perform a systematic search for early-time excesses in SNe\,Ia observed by the Zwicky Transient Facility (ZTF) to study whether SNe\,Ia with these excesses yield systematically different Hubble residuals. We analyze two compilations of ZTF SN\,Ia light curves from its first year of operations: 127 high-cadence light curves from \citet{Yao19} and 305 light curves from the ZTF cosmology data release of \citet{Dhawan22}. We detect significant early-time excesses for 17 SNe\,Ia in these samples and find that the excesses have an average $g-r$ color of $0.06\pm0.09$~mag; we do not find a clear preference for blue excesses as predicted by several models. Using the SALT3 model, we measure Hubble residuals for these two samples and find that excess-having SNe\,Ia may have lower Hubble residuals (HR) after correcting for shape, color, and host-galaxy mass, at $\sim$2-3$\sigma$ significance; our baseline result is $\Delta HR = -0.056 \pm 0.026$~mag ($2.2 \sigma$). We compare the host-galaxy masses of excess-having and no-excess SNe\,Ia and find they are consistent, though at marginal significance excess-having SNe\,Ia may prefer lower-mass hosts. Additional discoveries of early excess SNe\,Ia will be a powerful way to understand potential biases in SN\,Ia cosmology and probe the physics of SN\,Ia progenitors.

We study the H$\alpha$ equivalent width, EW(H$\alpha$), maps of 19 galaxies at $0.6

Several Lyman Continuum (LyC) emitters have been detected so far, but their observed ionising spectra sometimes differ from attenuated stellar spectra predicted by stellar population synthesis modelling. This discrepancy may be due to a significant contribution of LyC nebular emission. We aim to quantify the importance this emission in LyC leakers: its contribution to the ionising photons budget, and to measurements of LyC escape. To estimate the nebular contribution to the LyC spectra of galaxies, we run photoionisation models with Cloudy for a range of BPASS templates, varying the column density of the surrounding gas, from density-bounded (log(NH$_{\rm{stop}}$/cm$^{-2}$)=16) to ionisation-bounded (log(NH$_{\rm{stop}}$/cm$^{-2}$)=19) regimes. In the limits of very optically thin (f$_{\rm{esc}}$ = 1), or thick configurations (f$_{\rm{esc}}$ = 0), there is no nebular contribution to the emergent LyC spectra. This contribution matters only at intermediate LyC opacities ($0

The Cosmic Dawn marks the first star formations and preceded the Epoch-of-Reionization, when the Universe underwent a fundamental transformation propelled by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA-LOW instrument of the Square Kilometre Array telescope is envisaged to be the largest and most sensitive radio telescope at m and cm wavelengths. The latest Aperture Array Verification Systems feature 7m coaxial transmission lines connecting the Low Noise Amplifiers to optical transmitters at the front of the analogue-receiving chain. An impedance mismatch between these components results in a partially reflected electromagnetic signal, which introduces chromatic aberrations in the instrument bandpass. This causes power from the foreground signals to appear at higher delays, potentially contaminating the EoR window, a region at which the 21-cm signal should be detectable. We present an end-to-end simulation pipeline for SKA-LOW using a composite sky model combining radio foregrounds from The GLEAM Survey, Haslam $408$MHz, and a $1.5$cGpc 21-cm brightness temperature cube generated with the 21cmSPACE simulator. Iterating a parametric approach, we derive a model for the scattering parameters of a coaxial transmission line in terms of its specifications and bulk material properties. Assuming identical cables of length $\leq 15.0$m with impedance mismatch $\leq 10\Omega$ confines the reflection to k-modes below the EoR window. However, we demonstrate that even a $0.1$% length tolerance introduces contamination with an RMSE of $\sim 10$% across all accessible k-modes.

HD 142527 A is a young and massive Herbig Ae/Be star surrounded by a highly structured disc. The disc shows numerous morphological structures, such as spiral arms, a horseshoe region of dust emission, a set of shadows cast by an inner disc on the outer disc, and a large cavity extending from $\simeq{}$30 au to $\simeq{}$130 au. HD 142527 A also has a lower mass companion, HD 142527 B (M = 0.13 $\pm$ 0.03 $M_\odot{}$), which is thought to be responsible for most of the structures observed in the surrounding disc. We gathered VLTI/GRAVITY observations of HD 142527, either from our own programmes or from the ESO archive. We used this inhomogeneous set of data to extract a total of seven high-precision measurements of the relative astrometry between HD 142527 A and B, spread from mid-2017 to early 2021. Combined with what is available in the literature, we now have 9 yr of astrometric monitoring on HD 142527. We used orbit fitting tools to determine the orbital parameters of HD 142527 B, and used them as inputs for a 3D hydrodynamical model of the disc to determine whether or not the binary is able to create the structures observed in the disc. Our VLTI/GRAVITY astrometry gives excellent constraints on the orbit of HD 142527 B. We show that the secondary is following an orbit of semi-major axis a = 10.80 $\pm$ 0.22 au, with moderate eccentricity (e = 0.47 $\pm$ 0.01). With such a compact orbit, we show that HD 142527 B can only generate a gap and spiral arms of $\sim$30 au in the disc, which is much smaller than what is revealed by observations. Even from a theoretical standpoint, the observed cavity size of $\sim$100 au far exceeds even the most generous predictions for a companion like HD 142527 B on such a compact orbit. Thus, we conclude that the low-mass companion cannot be solely responsible for the observed morphology of the disc surrounding the system.

Aims. As part of the ongoing GRAVITY+ upgrade of the Very Large Telescope Interferometer infrastructure, we aim to improve the performance of the GRAVITY Fringe-Tracker, and to enable its use by other instruments. Methods. We modify the group delay controller to consistently maintain tracking in the white light fringe, characterised by a minimum group delay. Additionally, we introduce a novel approach in which fringe-tracking is performed in the non-observable Optical Path Length state-space, using a covariance-weighted Kalman filter and an auto-regressive model of the disturbance. We outline this new state-space representation, and the formalism we use to propagate the state-vector and generate the control signal. While our approach is presented specifically in the context of GRAVITY/GRAVITY+, it can easily be adapted to other instruments or interferometric facilities. Results. We successfully demonstrate phase delay tracking within a single fringe, with any spurious phase jumps detected and corrected in less than 100 ms. We also report a significant performance improvement, as evidenced by a reduction of about 30 to 40% in phase residuals, and a much better behaviour under sub-optimal atmospheric conditions. Compared to what was observed in 2019, the median residuals have decreased from 150 nm to 100 nm on the Auxiliary Telescopes and from 250 nm to 150 nm on the Unit Telescopes. Conclusions. The improved phase-delay tracking combined with whit light fringe tracking means that from now-on, the GRAVITY Fringe-Tracker can be used by other instruments operating in different wavebands. The only limitation remains the need for an optical path dispersion adjustment.

Extreme emission line galaxies (EELGs) exhibit large equivalent widths (EW) in their rest-optical emission lines ([OIII]$\lambda5007$ or H$\alpha$ rest-frame EW$ > 750\r{A}$) which can be tied to a recent upturn in star formation rate, due to the sensitivity of the nebular line emission and the rest-optical continuum to young ($<10$Myr) and evolved stellar populations, respectively. By studying a sample of 85 star forming galaxies (SFGs), spanning the redshift and magnitude interval $3 <z<9.5$ and $-16>$ M$_{UV}>-21$, in the JWST Advanced Deep Extragalactic Survey (JADES) with NIRSpec/prism spectroscopy, we determine that SFGs initiate an EELG phase when entering a significant burst of star formation, with the highest EWs observed in EELGs with the youngest mass-weighted ages ($<5$ Myr old) and the highest burst intensity (those with the highest proportion of their total stellar mass formed in the last 10 Myr). We spectroscopically confirm that a greater proportion of SFGs are in an EELG phase at high redshift in our UV-selected sample ($61\pm4\%$ in our $z>5.7$ high-redshift bin, compared to $23^{+4}_{-1}\%$ in our lowest-redshift bin $3<z<4.1$) due to the combined evolution of metallicity, ionisation parameter and star formation histories (SFH) with redshift. We report that the EELGs within our sample exhibit a higher average ionisation efficiency ($\log_{10}(\xi_{ion}^{HII}/$erg$^{-1}$Hz)$=25.5\pm0.2$) than the non-EELGs. High-redshift EELGs therefore comprise a population of efficient ionising photon producers. Additionally, we report that $53\%$ (9/17) of EELGs at $z>5.7$ have observed Lyman-$\alpha$ emission, potentially lying within large ionised regions. The high detection rate of Lyman-$\alpha$ emitters in our EELG selection suggests that the physical conditions associated with entering an EELG phase also promote the escape of Lyman-$\alpha$ photons.

Extreme emission line galaxies (EELGs) exhibit large equivalent widths (EW) in their rest-optical emission lines ([OIII]$\lambda5007$ or H$\alpha$ rest-frame EW$ > 750\r{A}$) which can be tied to a recent upturn in star formation rate, due to the sensitivity of the nebular line emission and the rest-optical continuum to young ($$ M$_{UV}>-21$, in the JWST Advanced Deep Extragalactic Survey (JADES) with NIRSpec/prism spectroscopy, we determine that SFGs initiate an EELG phase when entering a significant burst of star formation, with the highest EWs observed in EELGs with the youngest mass-weighted ages ($5.7$ high-redshift bin, compared to $23^{+4}_{-1}\%$ in our lowest-redshift bin $35.7$ have observed Lyman-$\alpha$ emission, potentially lying within large ionised regions. The high detection rate of Lyman-$\alpha$ emitters in our EELG selection suggests that the physical conditions associated with entering an EELG phase also promote the escape of Lyman-$\alpha$ photons.

We use deep JWST/NIRSpec R~1000 slit spectra of 113 galaxies at 1.7 $ 10), with similar incidence rates in star-forming and quenching systems. Half of the absorption profiles are blueshifted by at least 100 km/s, providing unambiguous evidence for neutral gas outflows. Galaxies with strong Na I D absorption are distinguished by enhanced emission line ratios consistent with AGN ionization. We conservatively measure mass outflow rates of 3 - 100 $M_\odot$ yr$^{-1}$; comparable to or exceeding ionized gas outflow rates measured for galaxies at similar stellar mass and redshift. The outflows from the quenching systems (log(sSFR)[yr$^{-1}$] $\lesssim$ -10) have mass loading factors of 4 - 360, and the energy and momentum outflow rates exceed the expected injection rates from supernova explosions, suggesting that these galaxies could possibly be caught in a rapid blowout phase powered by the AGN. Our findings suggest that AGN-driven ejection of cold gas may be a dominant mechanism for fast quenching of star formation at z~2.

Dust-obscured star formation has dominated the cosmic history of star formation since z = 4. However, the recent finding of significant amount of dust in galaxies out to z = 8 has opened the new frontier of investigating the origin of dust also in the earliest phases of galaxy formation, within the first 1.5 billion years from the Big Bang. This is a key and rapid transition phase for the evolution of dust, as galaxy evolutionary timescales become comparable with the formation timescales of dust. Our aim is to provide an overview of the several findings on dust formation and evolution at z > 4, and of the theoretical efforts to explain the observational results. We have organized the review in two parts. In the first part, presented here, we focus on dust sources, primarily supernovae and asymptotic giant branch stars, and the subsequent reprocessing of dust in the interstellar medium, through grain destruction and growth. We also discuss other dust production mechanisms, such as Red Super Giants, Wolf--Rayet stars, Classical Novae, Type Ia Supernovae, and dust formation in quasar winds. The focus of this first part is on theoretical models of dust production sources, although we also discuss the comparison with observations in the nearby Universe, which are key to put constraints on individual sources and processes. While the description has a general applicability at any redshift, we emphasize the relative role of different sources in the dust build-up in the early Universe. In the second part, which will be published later on, we will focus on the recent observational results at z > 4, discussing the theoretical models that have been proposed to interpret those results, as well as the profound implications for galaxy formation.

Blue Horizontal Branch (BHB) stars, excellent distant tracers for probing the Milky Way's halo density profile, are distinguished in the $(g-r)_0$ vs $(i-z)_0$ color space from another class of stars, blue straggler stars (BSs). We develop a Bayesian mixture model to classify BHB stars using high-precision photometry data from the Dark Energy Survey Data Release 2 (DES DR2). We select $\sim2100$ highly-probable BHBs based on their $griz$ photometry and the associated uncertainties, and use these stars to map the stellar halo over the Galactocentric radial range $20 \lesssim R \lesssim 70$ kpc. After excluding known stellar overdensities, we find that the number density $n_\star$ of BHBs can be represented by a power law density profile $n_\star \propto R^{-\alpha}$ with an index of $\alpha=4.28_{-0.12}^{+0.13}$, consistent with existing literature values. In addition, we examine the impact of systematic errors and the spatial inhomogeneity on the fitted density profile. Our work demonstrates the effectiveness of high-precision $griz$ photometry in selecting BHB stars. The upcoming photometric survey from the Rubin Observatory, expected to reach depths 2-3 magnitudes greater than DES during its 10-year mission, will enable us to investigate the density profile of the Milky Way's halo out to the virial radius, unravelling the complex processes of formation and evolution in our Galaxy.