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Most stars are born in the crowded environments of gradually forming star clusters. Dynamical interactions between close-passing stars and the evolving UV radiation fields from proximate massive stars are expected to sculpt the protoplanetary discs in these clusters, potentially contributing to the diversity of planetary systems that we observe. Here, we investigate the impact of cluster environment on disc demographics by implementing simple protoplanetary disc evolution models within $N$-body simulations of gradual star cluster formation. We consider a range of star formation efficiency per free-fall time, $\epsilon_{\rm ff}$, and mass surface density of the natal cloud environment, $\Sigma_{\rm cl}$, both of which affect the overall duration of cluster formation. We track the interaction history of all stars to estimate the dynamical truncation of the discs around stars involved in close encounters. We also track external photoevaporation of the discs due to the ionizing radiation field of the nearby high- and intermediate-mass ($> 5 M_\odot$) stars. We find that $\epsilon_{\rm ff}$, $\Sigma_{\rm cl}$, and the degree of primordial binarity have major influences on the masses and radii of the disc population. In particular, external photo-evaporation has a greater impact than dynamical interactions in determining the fate of discs in our clusters., Comment: Submitted to MNRAS. 16 pages, 9 figures. Comments welcome

Determining the physical processes that control galactic-scale star formation rates is essential for an improved understanding of galaxy evolution. The role of orbital shear is currently unclear, with some models expecting reduced star formation rates (SFRs) and efficiencies (SFEs) with increasing shear, e.g., if shear stabilizes gas against gravitational collapse, while others predicting enhanced rates, e.g., if shear-driven collisions between giant molecular clouds (GMCs) trigger star formation. Expanding on the analysis of 16 galaxies by Suwannajak, Tan, & Leroy (2014), we assess the shear dependence of SFE per orbital time ($\epsilon_\mathrm{orb}$) in 49 galaxies selected from the PHANGS-ALMA survey. In particular, we test a prediction of the shear-driven GMC collision model that $\epsilon_\mathrm{orb}\propto(1-0.7\beta)$, where $\beta\equiv{d}\:\mathrm{ln}\:v_\mathrm{circ}/d\:\mathrm{ln}\:r$, i.e., SFE per orbital time declines with decreasing shear. We fit the function $\epsilon_\mathrm{orb}=\epsilon_\mathrm{orb,\,0}(1-\alpha_\mathrm{CC}\beta)$ finding $\alpha_\mathrm{CC}\simeq0.76\pm0.16$; an alternative fit with $\epsilon_\mathrm{orb}$ normalized by the median value in each galaxy yields $\alpha_\mathrm{CC}^*=0.80\pm0.15$. These results are in good agreement with the prediction of the shear-driven GMC collision theory. We also examine the impact of a galactic bar on $\epsilon_\mathrm{orb}$ finding a modest decrease in SFE in the presence of bar, which can be attributed to lower rates of shear in these regions. We discuss the implications of our results for the GMC life cycle and environmental dependence of star formation activity., Comment: Submitted to ApJL, 9 pages, 4 figures, Comments welcome

Context. Most stars form in clusters or associations but only a small number of these groups are expected to remain bound for longer than a few Myr. Once star formation has ended and the molecular gas around young stellar objects has been expelled via feedback processes, most initially bound young clusters lose the majority of their binding mass and begin to disperse into the Galactic field. Aims. This process can be investigated by analysing the structure and kinematic trends in nearby young clusters, particularly expansion, the tell-tale sign that a cluster is no longer gravitationally bound but is dispersing into the field. Methods. We combine Gaia DR3 5-parameter astrometry with calibrated radial velocities for members of the nearby young cluster {\lambda} Ori (Collinder 69). Results. We characterise the plane-of-sky substructure of the cluster using the Q-parameter and Angular Dispersion parameter. We find evidence that the cluster contains significant substructure, but that this is preferentially located away from the central cluster core, which is smooth and likely remains bound. We find strong evidence for expansion in {\lambda} Ori in the plane-of-sky using a number of metrics, but also that the trends are asymmetric at the 5{\sigma} significance level. with the maximum rate of expansion being directed nearly parallel to the Galactic plane. We then invert the maximum rate of expansion of 0.144^{+0.003}_{-0.003} kms^{-1}pc^{-1} to give an expansion timescale of 6.944^{+0.148}_{-0.142} Myr, which is slightly larger than typical literature age estimates for the cluster. We also find asymmetry in the velocity dispersion, potential signatures of cluster rotation, and calculate kinematic ages for individual cluster members by tracing their motion back in time to their closest approach to the cluster center., Comment: 20 pages, 17 figures, submitted to A&A

We present an implementation of Pop III.1 seeding of supermassive black holes (SMBHs) in a theoretical model of galaxy formation and evolution to assess the growth the SMBH population and the properties of the host galaxies. The model of Pop III.1 seeding involves SMBH formation at redshifts $z\gtrsim 20$ in dark matter minihalos that are isolated from external radiative feedback, parameterized by isolation distance $d_{\rm iso}$. Within a standard $\Lambda$CDM cosmology, we generate dark matter halos using the code \textsc{pinocchio} and seed them according to the Pop III.1 scenario, exploring values of $d_{\rm iso}$ from 50 to 100~kpc (proper distance). We consider two alternative cases of SMBH seeding: a Halo Mass Threshold (HMT) model in which all halos $>7\times10^{10}\:M_\odot$ are seeded with $\sim 10^5\:M_\odot$ black holes; an All Light Seed (ALS) model in which all halos are seeded with low, stellar-mass black holes. We follow the redshift evolution of the halos, populating them with galaxies using the GAlaxy Evolution and Assembly theoretical model of galaxy formation, including accretion on SMBHs and related feedback processes. Here we present predictions for the properties of galaxy populations, focusing on stellar masses, star formation rates, and black hole masses. The local, $z\sim0$ metrics of occupation fraction as a function of the galaxy stellar mass, galaxy stellar mass function (GSMF), and black hole mass function (BHMF) all suggest a constraint of $d_{\rm iso}<75\:$kpc. We discuss the implications of this result for the Pop III.1 seeding mechanism., Comment: Submitted to MNRAS, comments welcome

We report first results from a deep near infrared campaign with the Hubble Space Telescope to obtain late-epoch images of the Hubble Ultra-Deep Field (HUDF), 10-15 years after the first epoch data were obtained. The main objectives are to search for faint active galactic nuclei (AGN) at high redshifts by virtue of their photometric variability, and measure (or constrain) the comoving number density of supermassive black holes (SMBHs), n_{SMBH}, at early times. In this Letter we present an overview of the program and preliminary results concerning eight objects. Three variables are supernovae, two of which are apparently hostless with indeterminable redshifts, although one has previously been recorded at a z\approx 6 object precisely because of its transient nature. Two further objects are clear AGN at z= 2.0 and 3.2, based on morphology and/or infrared spectroscopy from JWST. Three variable targets are identified at z = 6-7, which are also likely AGN candidates. These sources provide a first measure of n_{SMBH} in the reionization epoch by photometric variability, which places a firm lower limit of 3 \times 10^{-4} cMpc^{-3}. After accounting for variability and luminosity incompleteness, we estimate n_{SMBH} \gtrsim 8 \times 10{-3} cMpc{-3}, which is the largest value so far reported at these redshifts. This SMBH abundance is also strikingly similar to estimates of n_{SMBH} in the local Universe. We discuss how these results test various theories for SMBH formation., Comment: In press at ApJL

The origin of the stellar Initial Mass Function (IMF) and how it may vary with galactic environment is a matter of debate. Certain star formation theories involve a close connection between the IMF and the Core Mass Function (CMF) and so it is important to measure this CMF in a range of locations in the Milky Way. Here we study the CMF of three Galactic Center clouds: G0.253+0.016 ("The Brick"), Sgr B2 (Deep South field) and Sgr C. We use ALMA 1 mm continuum images and identify cores as peaks in thermal dust emission via the dendrogram algorithm. We develop a completeness correction method via synthetic core insertion, where a realistic mass-dependent size distribution is used for the synthetic cores. After corrections, a power law of the form $\text{d}N/\text{d}\log M \propto M^{-\alpha}$ is fit to the CMFs above 2 M$_\odot$. The three regions show disparate CMFs, with the Brick showing a Salpeter-like power law index $\alpha=1.21\pm0.11$ and the other two regions showing shallower indices ($\alpha=0.92\pm0.09$ for Sgr C and $\alpha=0.66\pm0.05$ for Sgr B2-DS). Furthermore, we analyze the spatial distribution and mass segregation of cores in each region. Sgr C and Sgr B2-DS show signs of mass segregation, but the Brick does not. We compare our results to several other CMFs from different Galactic regions derived with the same methods. Finally, we discuss how these results may help define an evolutionary sequence of star cluster formation and can be used to test star formation theories., Comment: Submitted to ApJ, comments welcome. 26 pages, 14 figures

In their early, formative stages star clusters can undergo rapid dynamical evolution leading to strong gravitational interactions and ejection of ``runaway'' stars at high velocities. While O/B runaway stars have been well studied, lower-mass runaways are so far very poorly characterised, even though they are expected to be much more common. We carried out spectroscopic observations with MAG2-MIKE to follow-up 27 high priority candidate runaways consistent with having been ejected from the Orion Nebula Cluster (ONC) $>2.5$ Myr ago, based on Gaia astrometry. We derive spectroscopic youth indicators (Li \& H$\alpha$) and radial velocities, enabling detection of bona fide runaway stars via signatures of youth and 3D traceback. We successfully confirmed 10 of the candidates as low-mass Young Stellar Objects (YSOs) on the basis of our spectroscopic criteria and derived radial velocities (RVs) with which we performed 3D traceback analysis. Three of these confirmed YSOs have kinematic ejection ages $>4\:$Myr, with the oldest being 4.7~Myr. This yields an estimate for the overall formation time of the ONC to be at least $\sim 5\:$Myr, i.e., about 10 free-fall times, and with a mean star formation efficiency per free-fall time of $\bar{\epsilon}_{\rm ff}\lesssim0.05$. These results favor a scenario of slow, quasi-equilibrium star cluster formation, regulated by magnetic fields and/or protostellar outflow feedback., Comment: submitted to MNRAS, comments welcome

Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ $214\:\mu$m observations of polarized thermal dust emission and high-resolution GBT-Argus C$^{18}$O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of $B$-field orientations, we produce a map of $B$-field strength of the IRDC, which exhibits values between $\sim0.03 - 1\:$mG based on a refined Davis-Chandrasekhar-Fermi (r-DCF) method proposed by Skalidis \& Tassis. Comparing to a map of inferred density, the IRDC exhibits a $B-n$ relation with a power law index of $0.51\pm0.02$, which is consistent with a scenario of magnetically-regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfv\'enic conditions and a dominant role for $B-$fields in regulating collapse. A clear alignment of magnetic field morphology with direction of steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the $B-$field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation and so need to be accounted for in theoretical models of these processes., Comment: Submitted to ApJ, comments welcome