The Fossils of the First Galaxies in the Local Universe

We argue that, at least a fraction of the newly discovered population of ultra-faint dwarfs in the Local Group constitute the fossil relics of a once ubiquitous population of dwarf galaxies formed before reionization with maximum circular velocities, vmax &#8722;1, where vmax = M1/3. To follow the evolution and distribution of the fossils of the first galaxies on Local Volume, 5 &#8722; 10 Mpc, scales, we have developed a new method for generating initial conditions for &#923;CDM N-body simulations which provides the necessary dynamic range. The initial distribution of particles represents the position, velocity and mass distribution of the dark and luminous ha- los extracted from pre-reionization simulations. We find that ultra-faint dwarfs have properties compatible with well preserved fossils of the first galaxies and are able to reproduce the observed luminosity-metallicity relation. However, because the brightest pre-reionization dwarfs form preferentially in overdense regions, they have merged into non-fossil halos with vmax > 20&#8722;30 km s&#8722;1. Hence, we find a luminosity threshold of true-fossils of 6 Lsolar, casting doubts on the classification of some clas- sical dSphs as fossils. We also argue that the ultra-faints at R V ) < &#8722;1.4. Next, we show that fossils of the first galaxies have galactocentric distributions and cumulative luminosity func- tions consistent with observations. We predict there are &#8764; 300 luminous satellites orbiting within Rvir of the Milky Way, &#8764; 50 &#8722; 70% of which are fossils. Despite our multidimensional agreement at low luminosities, our primordial model produces an overabundance of bright dwarf satellites (LV > 105 Lsolar), with this "bright satellite problem" most evident in the outer parts of the Milky Way. We estimate that, although relatively bright (LV > 105 Lsolar), these ghostly primordial populations are very diffuse, producing primordial populations with surface brightnesses below survey detection limits. Although we cannot yet present unmistakable evidence for the existence of the fossils of first galaxies in the Local Group, we suggest observational strategies to prove their existence. (i) The detection of "ghost halos" of primordial stars around isolated dwarfs. (ii) The existence of a yet unknown popu- lation of &#8764; 150 Milky Way ultra-faints with half-light radii rhl &#8776; 100 &#8722; 1000 pc and luminosities LV 4 Lsolar, detectable by future deep surveys

Devouring the Milky Way Satellites: Modeling Dwarf Galaxies with Galacticus

Dwarf galaxies are ubiquitous throughout the universe and are extremely sensitive to various forms of internal and external feedback. Over the last two decades, the census of dwarf galaxies in the Local Group and beyond has increased markedly. While hydrodynamic simulations (e.g., FIRE II, Mint Justice League) have reproduced the observed dwarf properties down to the ultrafaints, such simulations require extensive computational resources to run. In this work, we constrain the standard physical implementations in the semianalytic model Galacticus to reproduce the observed properties of the Milky Way satellites down to the ultrafaint dwarfs found in the Sloan Digital Sky Survey. We run Galacticus on merger trees from our high-resolution N-body simulation of a Milky Way analog. We determine the best-fit parameters by matching the cumulative luminosity function and luminosity-metallicity relation from both observations and hydrodynamic simulations. With the correct parameters, the standard physics in Galacticus can reproduce the observed luminosity function and luminosity-metallicity relation of the Milky Way dwarfs. In addition, we find a multidimensional match with half-light radii, velocity dispersions, and mass to light ratios at z = 0 down to M V ≤ −6 (L ≥ 104 L ⊙). In addition to successfully reproducing the properties of the z = 0 Milky Way satellite population, our modeled dwarfs have star formation histories that are consistent with those of the Local Group dwarfs

The Survey of Centaurus A's Baryonic Structures (SCABS) – II. The extended globular cluster system of NGC 5128 and its nearby environment

International audienceNew wide-field u^΄g^΄r^΄i^΄z^΄Dark Energy Camera observations centred on the nearby giant elliptical galaxy NGC 5128 covering ∼21 deg^2 are used to compile a new catalogue of ∼3200 globular clusters (GCs). We report 2404 newly identified candidates, including the vast majority within ∼140 kpc of NGC 5128. We find evidence for a transition at a galactocentric radius of R_gc ≈ 55 kpc from GCs ‘intrinsic’ to NGC 5128 to those likely to have been accreted from dwarf galaxies or that may transition to the intragroup medium of the Centaurus A galaxy group. We fit power-law surface number density profiles of the form $$\Sigma _{N, R_{\rm gc}}\propto R_{\rm gc}^\Gamma$$ and find that inside the transition radius, the red GCs are more centrally concentrated than the blue, with Γ_inner, red ≈ −1.78 and Γ_inner, blue ≈ −1.40, respectively. Outside this region both profiles flatten, more dramatically for the red GCs (Γ_outer, red ≈ −0.33) compared to the blue (Γ_outer, blue ≈ −0.61), although the former is more likely to suffer contamination by background sources. The median (g^΄ − z^΄)_0 = 1.27 mag colour of the inner red population is consistent with arising from the amalgamation of two giant galaxies each less luminous than present-day NGC 5128. Both inwards and outwards of the transition radius, we find the fraction of blue GCs to dominate over the red GCs, indicating a lively history of minor mergers. Assuming the blue GCs to originate primarily in dwarf galaxies, we model the population required to explain them, while remaining consistent with NGC 5128’s present-day spheroid luminosity. We find that several dozen dwarfs of luminosities Ldw, V ≃ 10^6–9.3 LV, ⊙, following a Schechter luminosity function with a faint-end slope of −1.50 ≲ α ≲ −1.25 is favoured, many of which may have already been disrupted in NGC 5128’s tidal field

Accessible Astronomy: Policies, Practices, and Strategies to Increase Participation of Astronomers with Disabilities

One outcome of the 2015 Inclusive Astronomy conference was the establishment of an accessibility/disability advocacy group within professional, US-based astronomy, organized by a coalition of disabled astronomers and allies and is supported by the American Astronomical Society (AAS). While the Working Group on Accessibility and Disability (WGAD) has focused on AAS-led initiatives to increase the accessibility of publications, databases, and professional meetings, there is an urgent need to expand these accessibility efforts beyond the professional society and into the wider astronomical community. Our long-term goals include proactively designing learning and working environments to be as accessible as possible, the removal of existing physical, technological, and pedagogical barriers to access, and provision of greater support for the career progress, promotion, and retention of disabled astronomers and educators. Progress toward these goals can be made by establishing and then sustaining a culture of inclusion in which all identities and intersections of identity are equally represented, while recognizing that progress which liberates one identity group may not liberate another in the same way. In the decades since the passage of the Americans with Disabilities Act (ADA), it has become clear that academic departments and research institutions will only undertake the necessary cultural and infrastructure changes if motivated by clear guidelines from funding organizations or ADA non-compliance lawsuits. In this white paper, we outline the major barriers to access within the educational and professional practice of astronomy. We present current best practices for inclusivity and accessibility, including classroom practices, institutional culture, support for infrastructure creation, hiring processes, and outreach initiatives. We present specific ways—beyond simple compliance with the ADA—that funding agencies, astronomers, and institutions can work together to make astronomy as a field more accessible, inclusive, and equitable. In particular, funding agencies should include the accessibility of institutions during proposal evaluation, hold institutions accountable for inaccessibility, and support efforts to gather data on the status and progress of astronomers and astronomy students with disabilities