Publications (7)0 Total impact
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ABSTRACT: Recent work has suggested that the stellar initial mass function (IMF) is not
universal, but rather is correlated with galaxy stellar mass, stellar velocity
dispersion, or morphological type. In this paper, we investigate variations of
the IMF within individual galaxies. For this purpose, we use strong lensing and
gas kinematics to measure independently the normalisation of the IMF of the
bulge and disk components of a sample of 5 massive spiral galaxies with
substantial bulge components taken from the SWELLS survey. We find that the
stellar mass of the bulges are tightly constrained by the lensing and kinematic
data. A comparison with masses based on stellar population synthesis models
fitted to optical and near infrared photometry favors a Salpeter-like
normalisation of the IMF. Conversely, the disk masses are less well constrained
due to degeneracies with the dark matter halo, but are consistent with Milky
Way type IMFs in agreement with previous studies. The disks are submaximal at
2.2 disk scale lengths, but due to the contribution of the bulges, the galaxies
are baryon dominated at 2.2 disk scale lengths. Globally, our inferred IMF
normalisation is consistent with that found for early-type galaxies of
comparable stellar mass (> 10^11 M_sun). Our results suggest a non-universal
IMF within the different components of spiral galaxies, adding to the
well-known differences in stellar populations between disks and bulges.
06/2012;
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ABSTRACT: We present dynamical modeling of the broad line region (BLR) in the
Seyfert 1 galaxy Mrk 50, using reverberation mapping data taken as part
of the Lick AGN Monitoring Project 2011. We model the reverberation
mapping data directly, constraining the geometry and kinematics of the
BLR, as well as deriving a black hole mass estimate that does not depend
on a normalizing factor or virial coefficient. We find that the geometry
of the BLR in Mrk 50 is a nearly face-on thick disk, with a mean radius
of 10 light days. We also constrain the inclination angle to be 80
degrees, closer to face-on. Finally, we measure the black hole mass to a
precision of 0.4 dex. We compare our inferred black hole mass to the
virial black hole mass, Mvir = (f v2 c tau)/G, measured from
traditional reverberation mapping analysis, also constraining the
normalizing coefficient, f, to within 0.4 dex. While our dynamical model
includes the possibility of a net inflow or outflow in the BLR, we find
a slight preference for outflow.
12/2011; 219.
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A. J. Barth,
A. Pancoast,
S. J. Thorman,
V. N. Bennert,
D. J. Sand,
W Li,
G. Canalizo,
A. V. Filippenko,
E. L. Gates,
J. E. Greene, [......],
C. E. Harris,
E. Y. Hsiao,
J Lee,
L. Lopez,
J. Rex,
N Suzuki,
J. R. Trump,
D. Tytler,
G. Worseck,
H. M. Yesuf
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ABSTRACT: The Lick AGN Monitoring Project 2011 observing campaign was carried out over
the course of 11 weeks in Spring 2011. Here we present the first results from
this program, a measurement of the broad-line reverberation lag in the Seyfert
1 galaxy Mrk 50. Combining our data with supplemental observations obtained
prior to the start of the main observing campaign, our dataset covers a total
duration of 4.5 months. During this time, Mrk 50 was highly variable,
exhibiting a maximum variability amplitude of a factor of 4 in the U-band
continuum and a factor of 2 in the H-beta line. Using standard
cross-correlation techniques, we find that H-beta and H-gamma lag the V-band
continuum by tau_cen = 10.64(-0.93,+0.82) and 8.43(-1.28,+1.30) days,
respectively, while the lag of He II 4686 is unresolved. The H-beta line
exhibits a symmetric velocity-resolved reverberation signature with shorter
lags in the high-velocity wings than in the line core, consistent with an
origin in a broad-line region dominated by orbital motion rather than infall or
outflow. Assuming a virial normalization factor of f=5.25, the virial estimate
of the black hole mass is (3.2+-0.5)*10^7 solar masses. These observations
demonstrate that Mrk 50 is among the most promising nearby active galaxies for
detailed investigations of broad-line region structure and dynamics.
10/2011;
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ABSTRACT: The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.
04/2011;
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ABSTRACT: The degeneracy among the disk, bulge and halo contributions to galaxy
rotation curves prevents an understanding of the distribution of baryons and
dark matter in disk galaxies. In an attempt to break this degeneracy, we
present an analysis of the spiral galaxy strong gravitational lens SDSS
J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space
Telescope multicolor imaging, gas and stellar kinematics data derived from
long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the
Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bulge,
disk and halo components and infer the contribution of each component, using
information from gravitational lensing and gas kinematics. This analysis yields
a best-fitting total (disk plus bulge) stellar mass of log_{10}(Mstar/Msun) =
10.99(+0.11,-0.25). The photometric data combined with stellar population
synthesis models yield log_{10}(Mstar/Msun) = 10.97\pm0.07, and 11.21\pm0.07
for the Chabrier and Salpeter IMFs, respectively. Accounting for the expected
gas fraction of \simeq 20% reduces the lensing plus kinematics stellar mass by
0.10\pm0.05 dex, resulting in a Bayes factor of 11.9 in favor of a Chabrier
IMF. The dark matter halo is roughly spherical, with minor to major axis ratio
q_{halo}=0.91(+0.15,-0.13). The dark matter halo has a maximum circular
velocity of V_{max}=276(+17,-18) km/s, and a central density parameter of
log_{10}\Delta_{V/2}=5.9(+0.9,-0.5). This is higher than predicted for
uncontracted dark matter haloes in LCDM cosmologies, log_{10}\Delta_{V/2}=5.2,
suggesting that either the halo has contracted in response to galaxy formation,
or that the halo has a higher than average concentration. At 2.2 disk scale
lengths the dark matter fraction is f_{DM}=0.55(+0.20,-0.15), suggesting that
SDSS J2141-0001 is sub-maximal.
01/2011;
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ABSTRACT: We use Keck laser guide star adaptive optics imaging and exploit the magnifying effects of strong gravitational lensing (the effective resolution is FWHM ~ 200 pc) to investigate the sub-kpc scale of an intermediate-redshift (z = 0.63) massive early-type galaxy being lensed by a foreground early-type galaxy; we dub this class of strong gravitational lens systems EELs, e.g., early-type/early-type lenses. We find that the background source is massive (M* = 10^{10.9} M_sun) and compact (r_e = 1.1 kpc), and a two-component fit is required to model accurately the surface brightness distribution, including an extended low-surface-brightness component. This extended component may arise from the evolution of higher-redshift `red nuggets' or may already be in place at z ~ 2 but is unobservable due to cosmological surface brightness dimming. Comment: 5 pages, 4 figures; accepted to MNRAS
11/2010;
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P. J. Marshall,
N. Bennert,
E. S. Rykoff,
K. J. Shen,
J. D. R. Steinfadt,
J. Fregeau,
R. -R. Chary,
K. Sheth,
B. Weiner,
K. B. Henisey, [......],
S. McHugh,
M. Elvis, B. J. Brewer,
T. Urrutia,
F Guo,
W. Hovest,
R. Nakajima,
B. -Q. For,
D. Erb,
D. Paneque
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ABSTRACT: In this paper we address the consumption of energy by astronomers while performing their professional duties. Although we find that astronomy uses a negligible fraction of the US energy budget, the rate at which energy is consumed by an average astronomer is similar to that of a typical high-flying businessperson. We review some of the ways in which astronomers are already acting to reduce their energy consumption. In the coming decades, all citizens will have to reduce their energy consumption to conserve fossil fuel reserves and to help avert a potentially catastrophic change in the Earth's climate. The challenges are the same for astronomers as they are for everyone: decreasing the distances we travel and investing in energy-efficient infrastructure. The high profile of astronomy in the media, and the great public interest in our field, can play a role in promoting energy-awareness to the wider population. Our specific recommendations are therefore to 1) reduce travel when possible, through efficient meeting organization, and by investing in high-bandwidth video conference facilities and virtual-world software, 2) create energy-efficient observatories, computing centers and workplaces, powered by sustainable energy resources, and 3) actively publicize these pursuits.
04/2009;
