We measure how the properties of star-forming central galaxies correlate with large-scale environment, delta, measured on 10 h(-1) Mpc scales. We use galaxy group catalogues to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disc scale length R-exp, and Sersic index of the galaxy light profile, n(S). We find that, at all stellar masses, there is an inverse correlation between SFR and delta, meaning that above-average star-forming centrals live in underdense regions. For n(S) and R-exp, there is no correlation with delta at M-* less than or similar to 10(10.5) M-circle dot, but at higher masses there are positive correlations; a weak correlation with R-exp and a strong correlation with n(S). These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, (M) over dot(h). In this model, galaxies are assigned to haloes using the abundance-matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but. (M) over dot(h) is used to map onto SFR. The best-fitting model requires some scatter in the (M) over dot(h)-SFR relation. The R-exp and n(S) measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, lambda. Halo spin does not correlate with delta at low halo masses, but for higher mass haloes, high-spin haloes live in higher density environments at fixed M-h. Put together with the earlier instalments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

We measure how the properties of star-forming central galaxies correlate with large-scale environment, delta, measured on 10 h(-1) Mpc scales. We use galaxy group catalogues to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disc scale length R-exp, and Sersic index of the galaxy light profile, n(S). We find that, at all stellar masses, there is an inverse correlation between SFR and delta, meaning that above-average star-forming centrals live in underdense regions. For n(S) and R-exp, there is no correlation with delta at M-* less than or similar to 10(10.5) M-circle dot, but at higher masses there are positive correlations; a weak correlation with R-exp and a strong correlation with n(S). These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, (M) over dot(h). In this model, galaxies are assigned to haloes using the abundance-matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but. (M) over dot(h) is used to map onto SFR. The best-fitting model requires some scatter in the (M) over dot(h)-SFR relation. The R-exp and n(S) measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, lambda. Halo spin does not correlate with delta at low halo masses, but for higher mass haloes, high-spin haloes live in higher density environments at fixed M-h. Put together with the earlier instalments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

We identify subhalos in dark matter-only (DMO) zoom-in simulations that are likely to be disrupted due to baryonic effects by using a random forest classifier trained on two hydrodynamic simulations of Milky Way (MW)-mass host halos from the Latte suite of the Feedback in Realistic Environments (FIRE) project. We train our classifier using five properties of each disrupted and surviving subhalo: pericentric distance and scale factor at first pericentric passage after accretion and scale factor, virial mass, and maximum circular velocity at accretion. Our five-property classifier identifies disrupted subhalos in the FIRE simulations with an 85% out-of-bag classification score. We predict surviving subhalo populations in DMO simulations of the FIRE host halos, finding excellent agreement with the hydrodynamic results; in particular, our classifier outperforms DMO zoom-in simulations that include the gravitational potential of the central galactic disk in each hydrodynamic simulation, indicating that it captures both the dynamical effects of a central disk and additional baryonic physics. We also predict surviving subhalo populations for a suite of DMO zoom-in simulations of MW-mass host halos, finding that baryons impact each system consistently and that the predicted amount of subhalo disruption is larger than the host-to-host scatter among the subhalo populations. Although the small size and specific baryonic physics prescription of our training set limits the generality of our results, our work suggests that machine-learning classification algorithms trained on hydrodynamic zoom-in simulations can efficiently predict realistic subhalo populations.

We identify subhalos in dark matter-only (DMO) zoom-in simulations that are likely to be disrupted due to baryonic effects by using a random forest classifier trained on two hydrodynamic simulations of Milky Way (MW)-mass host halos from the Latte suite of the Feedback in Realistic Environments (FIRE) project. We train our classifier using five properties of each disrupted and surviving subhalo: pericentric distance and scale factor at first pericentric passage after accretion and scale factor, virial mass, and maximum circular velocity at accretion. Our five-property classifier identifies disrupted subhalos in the FIRE simulations with an 85% out-of-bag classification score. We predict surviving subhalo populations in DMO simulations of the FIRE host halos, finding excellent agreement with the hydrodynamic results; in particular, our classifier outperforms DMO zoom-in simulations that include the gravitational potential of the central galactic disk in each hydrodynamic simulation, indicating that it captures both the dynamical effects of a central disk and additional baryonic physics. We also predict surviving subhalo populations for a suite of DMO zoom-in simulations of MW-mass host halos, finding that baryons impact each system consistently and that the predicted amount of subhalo disruption is larger than the host-to-host scatter among the subhalo populations. Although the small size and specific baryonic physics prescription of our training set limits the generality of our results, our work suggests that machine-learning classification algorithms trained on hydrodynamic zoom-in simulations can efficiently predict realistic subhalo populations.

Exploring the structural and physical properties of new vanadium dioxide (VO2) allotropes has attracted considerable interest because of the structure diversity and unique physical properties of VO2. Here, we demonstrate a reversible pressure-induced structural transition and metallization of the novel metastable polymorph VO2(Mx') and a thermally driven structural transition from VO2(Mx') to the monoclinic phase VO2(M1) at relative low temperature based on X-ray diffraction (XRD) and Raman and infrared spectroscopy. It is shown that the metastable phase VO2(Mx') undergoes the structural transitions of VO2(Mx')-(12 GPa) VO2(Mx '')-(30-80 GPa) VO2(X) upon compression, obviously different from the pressure-induced amorphization observed in other metastable phases VO2(A) and VO2(B). Moreover, the IR data demonstrated that the pressure-induced metallization (PIM) occurs in the VO2(Mx '') phase at about 40 GPa, which is mainly associated with electron-electron correlations. Further analysis suggests that all of the sample transforming into the same high-pressure VO2(X) phase with phase could mainly result from the VO6 octahedra and empty spaces between VO6 octahedra in their intermediate high pressure phases VO2(Mx '') and VO2(M1') following similar variations under pressure. These findings present new insight into the differences of structural transitions and physical properties between the stable and metastable phases of transition-metal oxides under pressure.

We introduce the southern stellar stream spectroscopy survey (S-5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S-5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9m Anglo-Australian Telescope's 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S-5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake aMilkyWay halo survey and a low-redshift galaxy survey. This paper presents an overview of the S-5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S-5, including future public data releases, can be found at http://s5collab.github.io.

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of D-circle dot = 116.3(-0.6)(+0.6) kpc, a half-light radius of = r(h) = 2.3(-0.3)(+0.4), an age of tau > 12.85 Gyr, a metallicity of Z = 0.0002(-0.0002)(+0.0001), and an absolute magnitude of M-V = -5.55(-) (+0.11)(0.11). This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus.I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus.I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of D-circle dot = 19.0(-0.6)(+0.5) kpc, a half-light radius of r(h) = 0.97(-0.17)(+0.24) arcmin, an age of tau = 12.5(-0.7)(+1.0) Gyr, a metallicity of Z = 0.0005(-0.0001)(+0.0002), and an absolute magnitude of M-V = -0.2(-0.6)(+0.8) mag, consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy-halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated 6 2 observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last 2 Gyr at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below at 95% confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above, highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.

We perform a comprehensive study of Milky Way (MW) satellite galaxies to constrain the fundamental properties of dark matter (DM). This analysis fully incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and marginalizes over uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk. Our results are consistent with the cold, collisionless DM paradigm and yield the strongest cosmological constraints to date on particle models of warm, interacting, and fuzzy dark matter. At 95% confidence, we report limits on (i) the mass of thermal relic warm DM, m(WDM) > 6.5 keV (free-streaming length, lambda(fs) less than or similar to 10 h(-1) kpc), (ii) the velocity-independent DM-proton scattering cross section, sigma(0) < 8.8 x 10(-29) cm(2) for a 100 MeV DM particle mass [DM-proton coupling, c(p) less than or similar to (0.3 GeV)(-2)], and (iii) the mass of fuzzy DM, m(phi) > 2.9 x 10(-21) eV (de Broglie wavelength, lambda(dB) less than or similar to 0.5 kpc). These constraints are complementary to other observational and laboratory constraints on DM properties.

The DECam Local Volume Exploration survey (DELVE) is a 126-night survey program on the 4 m Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. DELVE seeks to understand the characteristics of faint satellite galaxies and other resolved stellar substructures over a range of environments in the Local Volume. DELVE will combine new DECam observations with archival DECam data to cover similar to 15,000 deg(2) of high Galactic latitude (vertical bar b vertical bar > 10 degrees) southern sky to a 5 sigma depth of g, r, i, z similar to 23.5 mag. In addition, DELVE will cover a region of similar to 2200 deg(2) around the Magellanic Clouds to a depth of g, r, i similar to 24.5 mag and an area of similar to 135 deg(2) around four Magellanic analogs to a depth of g, i similar to 25.5 mag. Here, we present an overview of the DELVE program and progress to date. We also summarize the first DELVE public data release (DELVE DR1), which provides point-source and automatic aperture photometry for similar to 520 million astronomical sources covering similar to 5000 deg(2) of the southern sky to a 5 sigma point-source depth of g = 24.3 mag, r = 23.9 mag, i = 23.3 mag, and z = 22.8 mag. DELVE DR1 is publicly available via the NOIRLab Astro Data Lab science platform.