124 research outputs found
The MASSIVE Survey - III. Molecular gas and a broken Tully-Fisher relation in the most massive early-type galaxies
In this work we present CO(1-0) and CO(2-1) observations of a pilot sample of
15 early-type galaxies (ETGs) drawn from the MASSIVE galaxy survey, a
volume-limited integral-field spectroscopic study of the most massive ETGs
() within 108 Mpc. These objects were selected because
they showed signs of an interstellar medium and/or star formation. A large
amount of gas (210 M) is present in 10 out of 15
objects, and these galaxies have gas fractions higher than expected based on
extrapolation from lower mass samples. We tentatively interpret this as
evidence that stellar mass loss and hot halo cooling may be starting to play a
role in fuelling the most massive galaxies. These MASSIVE ETGs seem to have
lower star-formation efficiencies (SFE=SFR/M) than spiral galaxies,
but the SFEs derived are consistent with being drawn from the same distribution
found in other lower mass ETG samples. This suggests that the SFE is not simply
a function of stellar mass, but that local, internal processes are more
important for regulating star formation. Finally we used the CO line profiles
to investigate the high-mass end of the Tully-Fisher relation (TFR). We find
that there is a break in the slope of the TFR for ETGs at high masses
(consistent with previous studies). The strength of this break correlates with
the stellar velocity dispersion of the host galaxies, suggesting it is caused
by additional baryonic mass being present in the centre of massive ETGs. We
speculate on the root cause of this change and its implications for galaxy
formation theories.Comment: 13 pages, 7 figures, accepted by MNRA
The Effect of Spatial Gradients in Stellar Mass-to-Light Ratio on Black Hole Mass Measurements
We have tested the effect of spatial gradients in stellar mass-to-light ratio
(Y) on measurements of black hole masses (MBH) derived from stellar orbit
superposition models. Such models construct a static gravitational potential
for a galaxy and its central black hole, but typically assume spatially uniform
Y. We have modeled three giant elliptical galaxies with gradients alpha = d(log
Y)/d(log r) from -0.2 to +0.1. Color and line strength gradients suggest mildly
negative alpha in these galaxies. Introducing a negative (positive) gradient in
Y increases (decreases) the enclosed stellar mass near the center of the galaxy
and leads to systematically smaller (larger) MBH measurements. For models with
alpha = -0.2, the best-fit values of MBH are 28%, 27%, and 17% lower than the
constant-Y case, in NGC 3842, NGC 6086, and NGC 7768, respectively. For alpha =
+0.1, MBH are 14%, 22%, and 17% higher than the constant-Y case for the three
respective galaxies. For NGC 3842 and NGC 6086, this bias is comparable to the
statistical errors from individual modeling trials. At larger radii, negative
(positive) gradients in Y cause the total stellar mass to decrease (increase)
and the dark matter fraction within one effective radius to increase
(decrease).Comment: 6 pages, 4 figures, 1 table. To appear in ApJ
The MASSIVE Survey - I. A Volume-Limited Integral-Field Spectroscopic Study of the Most Massive Early-Type Galaxies within 108 Mpc
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} Msun 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.Comment: 19 pages, 14 figures. ApJ (2014) vol. 795, in pres
The MASSIVE Survey II: Stellar Population Trends Out to Large Radius in Massive Early Type Galaxies
We examine stellar population gradients in ~100 massive early type galaxies
spanning 180 < sigma* < 370 km/s and M_K of -22.5 to -26.5 mag, observed as
part of the MASSIVE survey (Ma et al. 2014). Using integral-field spectroscopy
from the Mitchell Spectrograph on the 2.7m 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 (~2.5
R_e). 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 [alpha/Fe] increase
with increasing sigma* 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 1-1.5 R_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 \sigmastar, 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.Comment: 17 pages, 9 figures, accepted by ApJ; resubmitted with updated
reference
The MASSIVE Survey - VII. The Relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies
We analyse the environmental properties of 370 local early-type galaxies
(ETGs) in the MASSIVE and ATLAS3D surveys, two complementary volume-limited
integral-field spectroscopic (IFS) galaxy surveys spanning absolute -band
magnitude , or stellar mass . We find these galaxies to reside in a diverse range of
environments measured by four methods: group membership (whether a galaxy is a
brightest group/cluster galaxy, satellite, or isolated), halo mass, large-scale
mass density (measured over a few Mpc), and local mass density (measured within
the th neighbour). The spatially resolved IFS stellar kinematics provide
robust measurements of the spin parameter and enable us to examine
the relationship among , , and galaxy environment. We find a
strong correlation between and , where the average
decreases from to below 0.1 with increasing mass, and the fraction
of slow rotators increases from % to 90%. We show for
the first time that at fixed , there are almost no trends between galaxy
spin and environment; the apparent kinematic morphology-density relation for
ETGs is therefore primarily driven by and is accounted for by the joint
correlations between and spin, and between and environment. A
possible exception is that the increased at high local density
is slightly more than expected based only on these joint correlations. Our
results suggest that the physical processes responsible for building up the
present-day stellar masses of massive galaxies are also very efficient at
reducing their spin, in any environment.Comment: Accepted to MNRA
The MASSIVE Survey XIII -- Spatially Resolved Stellar Kinematics in the Central 1 kpc of 20 Massive Elliptical Galaxies with the GMOS-North Integral-Field Spectrograph
We use observations from the GEMINI-N/GMOS integral-field spectrograph (IFS)
to obtain spatially resolved stellar kinematics of the central kpc of
20 early-type galaxies (ETGs) with stellar masses greater than in the MASSIVE survey. Together with observations from the wide-field
Mitchell IFS at McDonald Observatory in our earlier work, we obtain
unprecedentedly detailed kinematic maps of local massive ETGs, covering a scale
of kpc. The high () signal-to-noise of the GMOS spectra
enable us to obtain two-dimensional maps of the line-of-sight velocity,
velocity dispersion , as well as the skewness and kurtosis
of the stellar velocity distributions. All but one galaxy in the sample have
profiles that increase towards the center, whereas the slope of
at one effective radius () can be of either sign. The is
generally positive, with 14 of the 20 galaxies having positive within the
GMOS aperture and 18 having positive within . The positive
and rising towards small radii are indicative of a central black
hole and velocity anisotropy. We demonstrate the constraining power of the data
on the mass distributions in ETGs by applying Jeans anisotropic modeling (JAM)
to NGC~1453, the most regular fast rotator in the sample. Despite the
limitations of JAM, we obtain a clear minimum in black hole mass,
stellar mass-to-light ratio, velocity anisotropy parameters, and the circular
velocity of the dark matter halo.Comment: Accepted to Ap
Indigenous Rural Entrepreneurialism and Social Venturing Within Native Alaskan and Canadian Aboriginal Communities: An Empirical Analysis of Critical Success Factors and Socio-Economic Benefits of Alaska Native Corporations
This research examines the correlation between Alaskan Native Corporations’ corporate social responsibility investment strategies and their impact on effectively creating entrepreneurial opportunities for Alaskan Native communities. Our analysis begins by examining factors affecting the alignment of Alaska Native Corporation values with indigenous cultural values (Anders &amp; Anders, 1987). It then builds off further from previous research into social entrepreneurship and indigenous people (Curry, Donker, & Michel, 2016). We reviewed existing literature addressing connections between indigenous culture and entrepreneurial opportunities (Bardy, Drew, & Kennedy, 2011) and then adapted Donker, et. al.’s (2008) research model for assessing the relationship between corporate values and firm performance to establish a method for data collection and analysis.
We hypothesize that there is a significantly positive and strong correlation between economic community development and corporate financial performance when Alaska Native cultural values are integrated into Alaska Native Corporations, when gender diversity is promoted in leadership roles within the corporations and within entrepreneurial businesses within Alaska Native communities, and when serious reasonable efforts are made to promote social well-being, economic, and educational development. In our assessment of cultural values and their impact on firm performance in Alaska Native Corporations, we used H. Donker, et. al.’s (2008) research model for assessing the relationship between corporate values and firm performance to provide a method for data collection and analysis.
We also examined publicly available data regarding socio-economic factors to gauge labor participation including unemployment rates, high school Indigenous Rural Entrepreneurialism and Social Venturing in Alaska graduation rates, and student performance. This data was correlated with Alaska Native Corporation community investment programs to evaluate connections and test our hypothesis. We examined the gender diversity of Alaska Native Corporations Board of Directors to identify any impacts on firm performance, specifically how the gender diversity of corporate executive boards impacts investments in communities. Our data sample focused on the twelve regional Alaska Native Corporations, their respective non-profit foundations, and their affiliated communities
The MASSIVE Survey - V. Spatially-Resolved Stellar Angular Momentum, Velocity Dispersion, and Higher Moments of the 41 Most Massive Local Early-Type Galaxies
We present spatially-resolved two-dimensional stellar kinematics for the 41
most massive early-type galaxies (MK ~ 10^11.8
Msun) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we
obtain high-quality spectra in the wavelength range of 3650 to 5850 A from the
246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory,
covering a 107" x 107" field of view (often reaching 2 to 3 effective radii).
We measure the 2-D spatial distribution of each galaxy's angular momentum
(lambda and fast or slow rotator status), velocity dispersion (sigma), and
higher-order non-Gaussian velocity features (Gauss-Hermite moments h3 to h6).
Our sample contains a high fraction (~80% ) of slow and non-rotators with
lambda <~ 0.2. When combined with the lower-mass ETGs in the ATLAS3D survey, we
find the fraction of slow-rotators to increase dramatically with galaxy mass,
reaching ~50% at MK ~ -25.5 mag and ~90% at MK <~ -26 mag. All of our fast
rotators show a clear anti-correlation between h3 and V/sigma, and the slope of
the anti-correlation is steeper in more round galaxies. The radial profiles of
sigma show a clear luminosity and environmental dependence: the 12 most
luminous galaxies in our sample (MK <~ -26 mag) are all brightest cluster/group
galaxies (except NGC 4874) and all have rising or nearly flat sigma profiles,
whereas five of the seven "isolated" galaxies are all fainter than MK = -25.8
mag and have falling sigma. All of our galaxies have positive average h4; the
most luminous galaxies have average h4 ~ 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 h4, and those galaxies also tend to have rising sigma profiles. We
discuss the implications for the relationship among dynamical mass, sigma, h4,
and velocity anisotropy for these massive galaxies.Comment: 32 pages, 14 figures, 16 appendix figures. Accepted to MNRA
The MASSIVE Survey. VI. The spatial sistribution and kinematics of warm ionized gas in the most massive local early-type galaxies
We present the first systematic investigation of the existence, spatial distribution, and kinematics of warm ionized gas as traced by the [O ii] 3727 Å emission line in 74 of the most massive galaxies in the local universe. All of our galaxies have deep integral-field spectroscopy from the volume- and magnitude-limited MASSIVE survey of early-type galaxies with stellar mass (M K < −25.3 mag) and distance D < 108 Mpc. Of the 74 galaxies in our sample, we detect warm ionized gas in 28, which yields a global detection fraction of 38 ± 6% down to a typical [O ii] equivalent width limit of 2 Å. MASSIVE fast rotators are more likely to have gas than MASSIVE slow rotators with detection fractions of 80 ± 10% and 28 ± 6%, respectively. The spatial extents span a wide range of radii (0.6–18.2 kpc; 0.1–4R e ), and the gas morphologies are diverse, with 17/28 ≈ 61 ± 9% being centrally concentrated, 8/28 ≈ 29 ± 9% exhibiting clear rotation out to several kiloparsecs, and 3/28 ≈ 11 ± 6% being extended but patchy. Three out of four fast rotators show kinematic alignment between the stars and gas, whereas the two slow rotators with robust kinematic measurements available exhibit kinematic misalignment. Our inferred warm ionized gas masses are roughly ~105 M ⊙. The emission line ratios and radial equivalent width profiles are generally consistent with excitation of the gas by the old underlying stellar population. We explore different gas origin scenarios for MASSIVE galaxies and find that a variety of physical processes are likely at play, including internal gas recycling, cooling out of the hot gaseous halo, and gas acquired via mergers
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