38 research outputs found
The Spin of M87 as measured from the Rotation of its Globular Clusters
We revisit the kinematical data for 204 globular clusters in the halo of M87.
Beyond 3 r_eff along the major axis of the galaxy light, these globular
clusters exhibit substantial rotation (~ 300 +/- 70 km/s) that translates into
an equally substantial spin (lambda ~ 0.18). The present appearance of M87 is
most likely the product of a single major merger, since this event is best able
to account for so sizable a spin. A rotation this large makes improbable any
significant accretion of material after this merger, since that would have
diluted the rotation signature. We see weak evidence for a difference between
the kinematics of the metal-poor and metal-rich population, in the sense that
the metal-poor globular clusters appear to dominate the rotation. If, as we
suspect, the last major merger event of M87 was mainly dissipationless and did
not trigger the formation of a large number of globular clusters, the kinematic
difference between the two could reflect their orbital properties in the
progenitor galaxies; these differences would be compatible with these
progenitors having formed in dissipational mergers. However, to put strong
kinematic constraints on the origin of the globular clusters themselves is
difficult, given the complex history of the galaxy and its last dominant merger
event.Comment: 20 pages (AAS two column style, including 1 table and 7 figures)
accepted in the AJ (November issue), also available at
http://www.ucolick.org/~mkissler
Bureau of Land Management
The authors wish to thank Steve Leonard and George Staidle, who authored Technical Reference 1737-5, Riparian and Wetland Classification Review, which provided the basis for this document. We also thank those who reviewed and commented on Technical Reference 1737-5: Paul Hansen, Bill Platts, Bud Kovalchik
Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: II. Kinematical Analysis and Dynamical Modeling
We analyze HST/STIS spectra (see Paper I) of the central region of the dense
globular cluster M15. We infer the velocities of 64 individual stars,
two-thirds of which have their velocity measured for the first time. This
triples the number of stars with measured velocities in the central 1 arcsec of
M15 and doubles the number in the central 2 arcsec. Combined with existing
ground-based data we obtain the radial profiles of the projected kinematical
quantities. The RMS velocity sigma_RMS rises to 14 km/s in the central few
arcsec, somewhat higher than the values of 10-12 km/s inferred previously from
ground-based data. To interpret the results we construct dynamical models based
on the Jeans equation, which imply that M15 must have a central concentration
of non-luminous material. If this is due to a single black hole, then its mass
is M_BH = (3.9 +/- 2.2) x 10^3 solar masses. This is consistent with the
relation between M_BH and sigma_RMS that has been established for galaxies.
Also, the existence of intermediate-mass black holes in globular clusters is
consistent with several scenarios for globular cluster evolution proposed in
the literature. Therefore, these results may have important implications for
our understanding of the evolution of globular clusters, the growth of black
holes, the connection between globular cluster and galaxy formation, and the
nature of the recently discovered `ultra-luminous' X-ray sources in nearby
galaxies. Instead of a single black hole, M15 could have a central
concentration of dark remnants (e.g., neutron stars) due to mass segregation.
However, the best-fitting Fokker-Planck models that have previously been
constructed for M15 do not predict a central mass concentration that is
sufficient to explain the observed kinematics.[ABRIDGED]Comment: 43 pages, LaTeX, with 14 PostScript figures. Astronomical Journal, in
press (Dec 2002). Please note that the results reported here are modified by
the Addendum available at astro-ph/0210158 (Astronomical Journal, in press,
Jan 2003). This second version submitted to astro-ph is identical to first,
with the exception of the preceeding remar
External Mass Accumulation onto Core Potentials: Implications for Star Clusters, Galaxies and Galaxy Clusters
Accretion studies have been focused on the flow around bodies with point mass
gravitational potentials, but few general results are available for non-point
mass distributions. Here, we study the accretion flow onto non-divergent, core
potentials moving through a background medium. We use Plummer and Hernquist
potentials as examples to study gas accretion onto star clusters, dwarf and
large galaxy halos and galaxy clusters in a variety of astrophysical
environments. The general conditions required for a core potential to
collectively accrete large quantities of gas from the external medium are
derived using both simulations and analytic results. The consequences of large
mass accumulation in galaxy nuclei, dwarf galaxies and star clusters are
twofold. First, if the gas cools effectively star formation can be triggered,
generating new stellar members in the system. Second, if the collective
potential of the system is able to alter the ambient gas properties before the
gas is accreted onto the individual core members, the augmented mass supply
rates could significantly alter the state of the various accreting stellar
populations and result in an enhanced central black hole accretion luminosity.Comment: 24 pages, 15 figures, accepted to Ap
Are There Blue, Massive E/S0s at z < 1 ?: Kinematics of Blue Spheroidal Galaxy Candidates
Several recent studies find that 10 - 50% of morphologically selected field
early-type galaxies at redshifts z <= 1 have blue colors indicative of recent
star formation. Such ``blue spheroids''might be massive early-type galaxies
with active star formation, perhaps induced by recent merger events.
Alternatively, they could be starbursting, low-mass spheroids. To distinguish
between these two choices, we have selected 10 ``Blue Spheroid Candidates''
(hereafter, BSCs) from a quantitatively selected E/S0 sample and studied
their properties, including kinematics from Keck spectra obtained as part of
the DEEP Groth Strip Survey (GSS). Most BSCs (70%) turn out to belong to two
broad categories, while the remaining objects are likely to be misclassified
objects. Type-1 BSCs have underlying red stellar components with bluer inner
components. Type-2 BSCs do not show an obvious sign of the underlying red
stellar component, and their overall colors are quite blue ((U-B)_rest < 0).
Both Type-1 and Type-2 BSCs have internal velocity dispersions measured from
emission lines sigma < 80$ km/sec and estimated dynamical masses of only a few
times 10^10 M_sun or less. For Type-1 BSCs, we estimate sigma of the red
component using the fundamental plane relation of distant field absorption-line
galaxies and find that these sigma estimates are similar to the sigma measured
from emission lines. Overall, we conclude that our Type-1 and Type-2 BSCs are
more likely to be star-forming low mass spheroids than star-forming, massive,
early-type galaxies.Comment: Accepted for publication in the Astronomical Journa
The DEEP Groth Strip Galaxy Redshift Survey. III. Redshift Catalog and Properties of Galaxies
The Deep Extragalactic Evolutionary Probe (DEEP) is a series of spectroscopic
surveys of faint galaxies, targeted at the properties and clustering of
galaxies at redshifts z ~ 1. We present the redshift catalog of the DEEP 1 GSS
pilot phase of this project, a Keck/LRIS survey in the HST/WFPC2 Groth Survey
Strip. The redshift catalog and data, including reduced spectra, are publicly
available through a Web-accessible database. The catalog contains 658 secure
galaxy redshifts with a median z=0.65, and shows large-scale structure walls to
z = 1. We find a bimodal distribution in the galaxy color-magnitude diagram
which persists to z = 1. A similar color division has been seen locally by the
SDSS and to z ~ 1 by COMBO-17. For red galaxies, we find a reddening of only
0.11 mag from z ~ 0.8 to now, about half the color evolution measured by
COMBO-17. We measure structural properties of the galaxies from the HST
imaging, and find that the color division corresponds generally to a structural
division. Most red galaxies, ~ 75%, are centrally concentrated, with a red
bulge or spheroid, while blue galaxies usually have exponential profiles.
However, there are two subclasses of red galaxies that are not bulge-dominated:
edge-on disks and a second category which we term diffuse red galaxies
(DIFRGs). The distant edge-on disks are similar in appearance and frequency to
those at low redshift, but analogs of DIFRGs are rare among local red galaxies.
DIFRGs have significant emission lines, indicating that they are reddened
mainly by dust rather than age. The DIFRGs in our sample are all at z>0.64,
suggesting that DIFRGs are more prevalent at high redshifts; they may be
related to the dusty or irregular extremely red objects (EROs) beyond z>1.2
that have been found in deep K-selected surveys. (abridged)Comment: ApJ in press. 24 pages, 17 figures (12 color). The DEEP public
database is available at http://saci.ucolick.org
Ages and Metallicities of Extragalactic Globular Clusters from Spectral and Photometric Fits of Stellar Population Synthesis Models
Spectra of galaxies contain an enormous amount of information about the
relative mixture of ages and metallicities of constituent stars. We present a
comprehensive study designed to extract the maximum information from spectra of
data quality typical in large galaxy surveys. We test fitting techniques using
the Bruzual-Charlot 2003 high resolution simple stellar population synthesis
models to simultaneously estimate the ages and metallicities of 101 globular
clusters in M31 and the Magellanic Clouds. The clusters cover a wide range of
ages and metallicities, 4 Myr to 20 Gyr and -1.6 < [Fe/H] < +0.3, estimated by
other methods in the literature. We compare results from model fits to both the
spectra and photometry and find that fits to continuum-normalized (CN) spectra
over the entire range available, typically 350-1000 nm for this sample,
provides the best results. For clusters older than 1 Gyr we agree with
literature ages to 0.16 dex (35%) and [Fe/H] to 0.12 dex. For younger clusters
we agree with literature ages to 0.3 dex (63%), but cannot constrain the
metallicity. It is particularly important to use the entire CN spectrum to
avoid problems with model continua for young objects and to break
age-metallicity degeneracies of broadband photometry. Our required S/N = 15-30
for 20% age uncertainties and 30-55 for 10% uncertainties over spectral
resolutions of 5-25 Angstroms. This technique should work well for the
age-metallicity parameter space expected for early-type galaxies at z~1,
although individual galaxy spectral S/N may require the coaddition of a few
like objects.Comment: 70 pages, 18 figures, ApJ, in pres
CFHT Adaptive Optics Observations of the Central Kinematics in M15
We have used an Imaging Fabry-Perot Spectrophotometer with the Adaptive
Optics Bonnette on the Canada-France-Hawaii Telescope to measure stellar radial
velocities in the globular cluster M15. An average seeing of 0.15" full-width
at half maximum, with the best-seeing image having 0.09", allowed us to measure
accurately the velocities for five stars within 1" of the center of M15. Our
estimate of the second moment of the velocity distribution inside a radius of
2" is 11.5 km/s, the same value we find out to a radius of about 6". However,
the projected net rotation does increase dramatically at small radii, as our
previous observations led us to suspect. The rotation amplitude inside a radius
of 3.4" is v = 10.4 +- 2.7 km/s and the dispersion after removing the rotation
is sigma = 10.3 +- 1.4 km/s, so v/sigma = 1 in this region. In addition, the
position angle (PA) of the projected rotation axis differs by 100 degrees from
that of the net cluster rotation at larger radii. Current theoretical models do
not predict either this large an increase in the rotation amplitude or such a
change in the PA. However, a central mass concentration, such as a black hole,
could possibly sustain such a configuration. The rotation increase is
consistent with the existence of a central dark mass concentration equal to
2500 M_solar.Comment: 23 pages, emulateapj style, accepted for publication in The
Astronomical Journal, Marc
The Stars of the HETDEX Survey. I. Radial Velocities and Metal-Poor Stars from Low-Resolution Stellar Spectra
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution (RâŒ750) spectra of Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also observe a few 105 stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between 10â) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for âŒ42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1Ï precision of 28.0 km/s and bias of 3.5 km/s with respect to the LAMOST surveys and 1Ï precision of 27.5 km/s and bias of 14.0 km/s compared to the SEGUE survey. Since these RVs are for faint (Gâ„16) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (t-SNE), we also demonstrate that the HETDEX spectra can be used to determine a star's Teff, and log g and its [Fe/H]. With the t-SNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] <â1~dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys
The Centers of Early-Type Galaxies with HST. V. New WFPC2 Photometry
We analyze HST+WFPC2 images of 77 early-type galaxies. Brightness profiles
are classed into "core" or "power-law" forms. Cores are typically rounder than
power-law galaxies. Nearly all power-laws with central ellipticity >=0.3 have
stellar disks, implying that disks are present in power-laws with epsilon <0.3,
but are not visible due to unfavorable geometry. A few low-luminosity core
galaxies also have disks; these may be transition forms from power-laws. Cores
and power-laws both have twisting isophotes at small radii. Core galaxies have
somewhat weaker color gradients than power-laws. Nuclei are found in 29% of the
cores and 60% of the power-laws. Nuclei are typically bluer than the
surrounding galaxy. NGC 4073 and 4382 have central minima in their intrinsic
starlight distributions; NGC 4382 resembles the double nucleus of M31. In
general, the peak brightness location is coincident with the photocenter of the
core to <1 pc. Five galaxies, however, have centers significantly displaced
from their cores; these may be unresolved asymmetric double nuclei. Central
dust is visible in half of the galaxies. The presence and strength of dust
correlates with nuclear emission. The prevalence of dust and its morphology
suggests that dust clouds form, settle to the center, and disappear repeatedly
on ~10^8 yr timescales. We discuss the hypothesis that cores are created by the
decay of a massive black hole binary. Apart from their brightness profiles,
there are no strong differences between cores and power-laws that demand this
scenario; however, the rounder shapes of cores, their lack of disks, and their
reduced color gradients may be consistent with it.Comment: 76 pages, 40 figures, submitted to the Astronomical Journal. The
complete postscript version of the paper is available at
http://www.noao.edu/noao/staff/lauer/nuker.html (the Nuker Team page