164 research outputs found
An Online Tutor for Astronomy: The GEAS Self-Review Library
We introduce an interactive online resource for use by students and college
instructors in introductory astronomy courses. The General Education Astronomy
Source (GEAS) online tutor guides students developing mastery of core
astronomical concepts and mathematical applications of general astronomy
material. It contains over 12,000 questions, with linked hints and solutions.
Students who master the material quickly can advance through the topics, while
under-prepared or hesitant students can focus on questions on a certain topic
for as long as needed, with minimal repetition. Students receive individual
accounts for study and course instructors are provided with overview tracking
information, by time and by topic, for entire cohorts of students. Diagnostic
tools support self-evaluation and close collaboration between instructor and
student, even for distance learners. An initial usage study shows clear trends
in performance which increase with study time, and indicates that distance
learners using these materials perform as well as or better than a comparison
cohort of on-campus astronomy students. We are actively seeking new
collaborators to use this resource in astronomy courses and other educational
venues.Comment: 15 pages, 9 figures; Vogt, N. P., and A. S. Muise. 2015. An online
tutor for general astronomy: The GEAS self-review library. Cogent Education,
2 (1
The Rotation Curves of Galaxies at Intermediate Redshift
We have undertaken a pilot project to measure the rotation velocities of
spiral galaxies in the redshift range 0.18 < z < 0.4 using high dispersion long
slit spectroscopy obtained with the Palomar 5m telescope. One field galaxy and
three cluster objects known to have strong emission lines were observed over
wavelength ranges covering the redshifted lines of [OII], CaII K, H beta, and
[OIII]. Two of the objects show extended line emission that allows the tracing
of the rotation curve in one or more lines. A line width similar to that
obtained with single dish telescopes for the 21-cm HI line observed in lower
redshift galaxies can be derived from the observed H beta, [OII], and [OIII]
emission by measuring a characteristic width from the velocity histogram. These
moderately distant galaxies have much stronger emission lines than typical
low-redshift spirals but they appear to be kinematically similar. Application
of the Tully-Fisher relation suggests that the two galaxies with rotation
curves are intrinsically brighter at R-band than nearby galaxies.Comment: Text is 15 pages (18 with figures). Full text and postscript figures
are also available at http://www.ucolick.org/~nicole/pubs/pubs.html#highz
Evolution of the Near-Infrared Tully-Fisher Relation: Constraints on the Relationship Between the Stellar and Total Masses of Disk Galaxies since z=1
Using a combination of Keck spectroscopy and near-infrared imaging, we
investigate the K-band and stellar mass Tully-Fisher relation for 101 disk
galaxies at 0.2 < z < 1.2, with the goal of placing the first observational
constraints on the assembly history of halo and stellar mass. Our main result
is a lack of evolution in either the K-band or stellar mass Tully-Fisher
relation from z = 0 - 1.2. Furthermore, although our sample is not
statistically complete, we consider it suitable for an initial investigation of
how the fraction of total mass that has condensed into stars is distributed
with both redshift and total halo mass. We calculate stellar masses from
optical and near-infrared photometry and total masses from maximum rotational
velocities and disk scale lengths, utilizing a range of model relationships
derived analytically and from simulations. We find that the stellar/total mass
distribution and stellar-mass Tully-Fisher relation for z > 0.7 disks is
similar to that at lower redshift, suggesting that baryonic mass is accreted by
disks along with dark matter at z < 1, and that disk galaxy formation at z < 1
is hierarchical in nature. We briefly discuss the evolutionary trends expected
in conventional structure formation models and the implications of extending
such a study to much larger samples.Comment: ApJ, in press, 9 page
The Magnitude-Size Relation of Galaxies out to z ~ 1
As part of the Deep Extragalactic Evolutionary Probe (DEEP) survey, a sample
of 190 field galaxies (I_{814} <= 23.5) in the ``Groth Survey Strip'' has been
used to analyze the magnitude-size relation over the range 0.1 < z < 1.1. The
survey is statistically complete to this magnitude limit. All galaxies have
photometric structural parameters, including bulge fractions (B/T), from Hubble
Space Telescope images, and spectroscopic redshifts from the Keck Telescope.
The analysis includes a determination of the survey selection function in the
magnitude-size plane as a function of redshift, which mainly drops faint
galaxies at large distances. Our results suggest that selection effects play a
very important role. A first analysis treats disk-dominated galaxies with B/T <
0.5. If selection effects are ignored, the mean disk surface brightness
(averaged over all galaxies) increases by ~1.3 mag from z = 0.1 to 0.9.
However, most of this change is plausibly due to comparing low luminosity
galaxies in nearby redshift bins to high luminosity galaxies in distant bins.
If this effect is allowed for, no discernible evolution remains in the disk
surface brightness of bright (M_B < -19) disk-dominated galaxies. A second
analysis treats all galaxies by substituting half-light radius for disk scale
length, with similar conclusions. Indeed, at all redshifts, the bulk of
galaxies is consistent with the magnitude-size envelope of local galaxies,
i.e., with little or no evolution in surface brightness. In the two highest
redshift bins (z > 0.7), a handful of luminous, high surface brightness
galaxies appears that occupies a region of the magnitude-size plane rarely
populated by local galaxies. Their wide range of colors and bulge fractions
points to a variety of possible origins.Comment: 19 pages, 12 figures. Accepted for publication in the Astrophysical
Journa
The I Band Tully-Fisher Relation for Cluster Galaxies: Data Presentation.
Observational parameters which can be used for redshift-independent distance determination using the Tully-Fisher (TF) technique are given for 782 spiral galaxies in the fields of 24 clusters or groups. I band photometry for the full sample was either obtained by us or compiled from published literature. Rotational velocities are derived either from 21 cm spectra or optical emission line long--slit spectra, and converted to a homogeneous scale. In addition to presenting the data, a discussion of the various sources of error on TF parameters is introduced, and the criteria for the assignment of membership to each cluster are given
M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: II. Evidence for Galaxy Infall
We have conducted a study of optical and HI properties of spiral galaxies
(size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass)
to explore the role of gas stripping as a driver of morphological evolution in
clusters. We find a strong correlation between the spiral and S0 fractions
within clusters, and the spiral fraction scales tightly with cluster X-ray gas
luminosity. We explore young star formation and identify spirals that are (1)
asymmetric, with truncated H-alpha emission and HI gas reservoirs on the
leading edge of the disk, on a first pass through the dense intracluster medium
in the cores of rich clusters; (2) strongly HI deficient and stripped, with
star formation confined to the inner 5 kpc/h and 3 disk scale lengths; (3)
reddened, extremely HI deficient and quenched, where star formation has been
halted across the entire disk. We propose that these spirals are in successive
stages of morphological transformation, between infalling field spirals and
cluster S0s, and that the process which acts to remove the HI gas reservoir
suppresses new star formation on a similarly fast timescale. These data suggest
that gas stripping plays a significant role in morphological transformation and
rapid truncation of star formation across the disk.Comment: 24 pages, 12 figures; accepted for publication in AJ;
higher-resolution figures available at http://astronomy.nmsu.edu/nicol
Keck Spectroscopy of Redshift z ⌠3 Galaxies in the Hubble Deep Field
We have obtained spectra with the 10 m Keck telescope of a sample of 24 galaxies having colors consistent with star-forming galaxies at redshifts 2 âČ z âČ 4.5 in the Hubble deep field (HDF). Eleven of these galaxies are confirmed to be at high redshift (z = 3.0), one is at z = 0.5, and the other 12 have uncertain redshifts but have spectra consistent with their being at z \u3e 2. The spectra of the confirmed high-redshift galaxies show a diversity of features, including weak Lyα emission, strong Lyα breaks or damped Lyα absorption profiles, and the stellar and interstellar rest-UV absorption lines common to local starburst galaxies and high-redshift star-forming galaxies reported recently by others. The narrow profiles and low equivalent widths of C IV, Si IV, and N V absorption lines may imply low stellar metallicities. Combined with the five high-redshift galaxies in the HDF previously confirmed with Keck spectra by Steidel et al. (1996a), the 16 confirmed sources yield a comoving volume density of n â„ 2.4 Ă 10 h Mpc for q = 0.05, or n â„ 1.1 Ă 10 h Mpc for q = 0.5. These densities are 3-4 times higher than the recent estimates of Steidel et al. (1996b) based on ground-based photometry with slightly brighter limits and are comparable to estimates of the local volume density of galaxies brighter than L*. The high-redshift density measurement is only a lower limit and could be almost 3 times higher still if all 29 of the unconfirmed candidates in our original sample, including those not observed, are indeed also at high redshift. The galaxies are small but luminous, with half-light radii 1.8 \u3c r \u3c 6.5 h kpc and absolute magnitudes -21.5 \u3e M \u3e -23. The HST images show a wide range of morphologies, including several with very close, small knots of emission embedded in wispy extended structures. Using rest-frame UV continuum fluxes with no dust correction, we calculate star formation rates in the range 7-24 or 3-9 h M yr for q = 0.05 and q = 0.5, respectively. These rates overlap those for local spiral and H II galaxies today, although they could be more than twice as high if dust extinction in the UV is significant. If the objects at z = 3 were simply to fade by 5 mag (assuming a 10 yr burst and passive evolution) without mergers in the 14 Gyr between then and now (for q = 0.05, h = 1.0), they would resemble average dwarf elliptical/spheroidal galaxies in both luminosity and size. However, the variety of morphologies and the high number density of z = 3 galaxies in the HDF suggest that they represent a range of physical processes and stages of galaxy formation and evolution, rather than any one class of object, such as massive ellipticals. A key issue remains the measurement of masses. These high-redshift objects are likely to be the low-mass, starbursting building blocks of more massive galaxies seen today
Keck Spectroscopy of Redshift z~3 Galaxies in the Hubble Deep Field
We have obtained spectra with the 10-m Keck telescope of a sample of 24
galaxies having colors consistent with star-forming galaxies at redshifts
2<z<4.5 in the Hubble Deep Field (HDF). Eleven of these galaxies are confirmed
to be at high redshift (median z=3.0), one is at z=0.5, and the other 12 have
uncertain redshifts but have spectra consistent with their being at z>2.
Combined with 5 previously confirmed high-redshift galaxies in the HDF, the 16
confirmed sources yield a comoving volume density of n>2.5^-4 h50^3 Mpc^-3 for
q0=0.05, or n>1.2^-3 h50^3 Mpc^-3 for q0=0.5. These densities are comparable to
estimates of the local volume density of galaxies brighter than L*, and could
be almost three times higher still if all 29 of the unconfirmed candidates in
our original sample are indeed also at high redshift. The galaxies are small
but luminous, with half-light radii 1.8 < r(1/2) < 6.5 h50^-1 kpc and absolute
magnitudes -21.5 > M_B > -23. The HST images show a wide range of morphologies,
including several with very close, small knots of emission embedded in wispy
extended structures. Using rest-frame UV continuum fluxes with no dust
correction, we calculate star formation rates in the range 7 - 24 or 3 - 9
h50^-2 Msun/yr for q0=0.05 and q0=0.5, respectively. The variety of
morphologies and the high number density of z=3 galaxies in the HDF suggest
that they represent a range of physical processes and stages of galaxy
formation and evolution, rather than any one class of object, such as massive
ellipticals. A key issue remains the measurement of masses. These high-redshift
objects are likely to be the low-mass, starbursting building blocks of more
massive galaxies seen today.Comment: 45 pages, AASLaTeX, 3 postscript tables, 2 JPG + 3 GIF + 5
encapsulated postscript figures. To appear in The Astrophysical Journal. Also
available at http://www.ucolick.org/~deep/papers/papers.html and
http://www.ucolick.org/~james/papers/hdf/hdf.htm
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
M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: I. Data
A survey of 329 nearby galaxies (redshift z < 0.045) has been conducted to
study the distribution of mass and light within spiral galaxies over a range of
environments. The 18 observed clusters and groups span a range of richness,
density, and X-ray temperature, and are supplemented by a set of 30 isolated
field galaxies. Optical spectroscopy taken with the 200-inch Hale Telescope
provides separately resolved H-alpha and [NII] major axis rotation curves for
the complete set of galaxies, which are analyzed to yield velocity widths and
profile shapes, extents and gradients. HI line profiles provide an independent
velocity width measurement and a measure of HI gas mass and distribution.
I-band images are used to deconvolve profiles into disk and bulge components,
to determine global luminosities and ellipticities, and to check morphological
classification. These data are combined to form a unified data set ideal for
the study of the effects of environment upon galaxy evolution.Comment: 23 pages, 16 figures.; accepted for publication in AJ;
higher-resolution figures available at http://astronomy.nmsu.edu/nicole; typo
corrected in figure captions 14 - 16 (x-axes units are kpc/h, not arcseconds
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