Massive early-type galaxies represent the modern day remnants of the earliest major star formation episodes in the history of the universe. These galaxies are central to our understanding of the evolution of cosmic structure, stellar populations, and supermassive black holes, but the details of their complex formation histories remain uncertain. To address this situation, we have initiated the MASSIVE Survey, a volume-limited, multi-wavelength, integral-field spectroscopic (IFS) and photometric survey of the structure and dynamics of the ∼100 most massive early-type galaxies within a distance of 108 Mpc. This survey probes a stellar mass range M * 10 11.5 M and diverse galaxy environments that have not been systematically studied to date. Our wide-field IFS data cover about two effective radii of individual galaxies, and for a subset of them, we are acquiring additional IFS observations on sub-arcsecond scales with adaptive optics. We are also acquiring deep K-band imaging to trace the extended halos of the galaxies and measure accurate total magnitudes. Dynamical orbit modeling of the combined data will allow us to simultaneously determine the stellar, black hole, and dark matter halo masses. The primary goals of the project are to constrain the black hole scaling relations at high masses, investigate systematically the stellar initial mass function and dark matter distribution in massive galaxies, and probe the late-time assembly of ellipticals through stellar population and kinematical gradients. In this paper, we describe the MASSIVE sample selection, discuss the distinct demographics and structural and environmental properties of the selected galaxies, and provide an overview of our basic observational program, science goals and early survey results.

We examine stellar population gradients in ∼100 massive early-type galaxies spanning 180 * 370 s << km s −1 and M K of −22.5 to −26.5 mag, observed as part of the MASSIVE survey. Using integral-field spectroscopy from the Mitchell Spectrograph on the 2.7 m telescope at McDonald Observatory, we create stacked spectra as a function of radius for galaxies binned by their stellar velocity dispersion, stellar mass, and group richness. With excellent sampling at the highest stellar mass, we examine radial trends in stellar population properties extending to beyond twice the effective radius (R 2.5 ẽ). Specifically, we examine trends in age, metallicity, and abundance ratios of Mg, C, N, and Ca, and discuss the implications for star formation histories and elemental yields. At a fixed physical radius of 3-6 kpc (the likely size of the galaxy cores formed at high redshift), stellar age and [α/Fe] increase with increasing * s and depend only weakly on stellar mass, as we might expect if denser galaxies form their central cores earlier and faster. If we instead focus on R 1-1 .5 e , the trends in abundance and abundance ratio are washed out, as might be expected if the stars at large radius were accreted by smaller galaxies. Finally, we show that when controlling for * s , there are only very subtle differences in stellar population properties or gradients as a function of group richness; even at large radius, internal properties matter more than environment in determining star formation history.

Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago 1 . Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found 2 in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall 3 -the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe 4,5 ; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600-a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.We observed NGC 1600 ( Fig. 1) as part of the MASSIVE Survey 6 , the aim of which is to study the structure, dynamics, and formation history of the 100 most massive early-type galaxies within 108 megaparsecs (Mpc) of Earth. This volume-limited survey probes galaxies with stellar masses above 5 × 10 11 M ( (where M ( is the mass of the Sun) in diverse, large-scale environments that have not been systematically studied before. The stellar mass (8.3 × 10 11 M ( ), halo mass (∼ 1.5 × 10 14 M ( ), and distance (64 Mpc) of NGC 1600 are fairly typical of the galaxies in the survey. We obtained stellar spectra covering the central 5-arcsec-by-7-arcsec region of NGC 1600 with roughly 0.6-arcsec spatial resolution, using the Gemini multi-object spectrograph (GMOS) at the Gemini North Telescope. We further obtained large-area (107-arcsec-by-107-arcsec) stellar spectra of NGC 1600 using the Mitchell integral field spectrograph (IFS) at the McDonald Observatory. The stellar luminosity distribution of the galaxy is provided by surface photometry from the Hubble Space Telescope (HST) and the Kitt Peak National Observatory 7 .We measured the distribution of the line-of-sight stellar velocities at 86 locations in NGC 1600 by modelling the deep calcium triplet absorption lines in our GMOS IFS spectra and several optical absorption features in our Mitchell IFS spectra. The galaxy shows little rotation (less than 30 km s −1 ), and the line-of-sight velocity dispersion rises from 235-275 km s −1 at large radii to a maximum value of 359 km s −1 near the centre, consistent with previous long-slit measure...

We present spatially-resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (M K −25.7 mag, stellar mass M * 10 11.8 M ) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain highquality spectra in the wavelength range of 3650 to 5850Å from the 246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory, covering a 107 × 107 field of view (often reaching 2 to 3 effective radii). We measure the 2-D spatial distribution of each galaxy's angular momentum (λ and fast or slow rotator status), velocity dispersion (σ), and higher-order non-Gaussian velocity features (Gauss-Hermite moments h 3 to h 6 ). Our sample contains a high fraction (∼ 80%) of slow and non-rotators with λ 0.2. When combined with the lower-mass ETGs in the ATLAS 3D survey, we find the fraction of slow-rotators to increase dramatically with galaxy mass, reaching ∼ 50% at M K ∼ −25.5 mag and ∼ 90% at M K −26 mag. All of our fast rotators show a clear anti-correlation between h 3 and V /σ, and the slope of the anti-correlation is steeper in more round galaxies. The radial profiles of σ show a clear luminosity and environmental dependence: the 12 most luminous galaxies in our sample (M K −26 mag) are all brightest cluster/group galaxies (except NGC 4874) and all have rising or nearly flat σ profiles, whereas five of the seven "isolated" galaxies are all fainter than M K = −25.8 mag and have falling σ. All of our galaxies have positive average h 4 ; the most luminous galaxies have average h 4 ∼ 0.05 while less luminous galaxies have a range of values between 0 and 0.05. Most of our galaxies show positive radial gradients in h 4 , and those galaxies also tend to have rising σ profiles. We discuss the implications for the relationship among dynamical mass, σ, h 4 , and velocity anisotropy for these massive galaxies.

Dark matter that is capable of sufficiently heating a local region in a white dwarf will trigger runaway fusion and ignite a type Ia supernova. This was originally proposed by Graham et al. and used to constrain primordial black holes which transit and heat a white dwarf via dynamical friction. In this paper, we consider dark matter (DM) candidates that heat through the production of highenergy standard model (SM) particles, and show that such particles will efficiently thermalize the white dwarf medium and ignite supernovae. Based on the existence of long-lived white dwarfs and the observed supernovae rate, we derive new constraints on ultra-heavy DM with masses greater than 10 16 GeV which produce SM particles through DM-DM annihilations, DM decays, and DM-SM scattering interactions in the stellar medium. As a concrete example, we place bounds on supersymmetric Q-ball DM in parameter space complementary to terrestrial bounds. We put further constraints on DM that is captured by white dwarfs, considering the formation and self-gravitational collapse of a DM core which heats the star via decays and annihilations within the core. It is also intriguing that the DM-induced ignition discussed in this work provide an alternative mechanism of triggering supernovae from sub-Chandrasekhar, non-binary progenitors.