39 research outputs found
Morphology with Light Profile Fitting of Confirmed Cluster Galaxies at z=0.84
We perform a morphological study of 124 spectroscopically confirmed cluster
galaxies in the z=0.84 galaxy cluster RX J0152.7-1357. Our classification
scheme includes color information, visual morphology, and 1-component and
2-component light profile fitting derived from Hubble Space Telescope riz
imaging. We adopt a modified version of a detailed classification scheme
previously used in studies of field galaxies and found to be correlated with
kinematic features of those galaxies. We compare our cluster galaxy
morphologies to those of field galaxies at similar redshift. We also compare
galaxy morphologies in regions of the cluster with different dark-matter
density as determined by weak-lensing maps. We find an early-type fraction for
the cluster population as a whole of 47%, about 2.8 times higher than the
field, and similar to the dynamically young cluster MS 1054 at similar
redshift. We find the most drastic change in morphology distribution between
the low and intermediate dark matter density regions within the cluster, with
the early type fraction doubling and the peculiar fraction dropping by nearly
half. The peculiar fraction drops more drastically than the spiral fraction
going from the outskirts to the intermediate-density regions. This suggests
that many galaxies falling into clusters at z~0.8 may evolve directly from
peculiar, merging, and compact systems into early-type galaxies, without having
the chance to first evolve into a regular spiral galaxy.Comment: 13 pages, 11 figures, accepted for publication in A&
Educators’ Preferences for Professional Learning Formats by Learning Objective
Innovations in information technology have generated an array of options for the professional learning for educators. Face-to-face, remote, and hybrid formats for professional learning each have their advantages and disadvantages for advancing educators’ knowledge and skills in evidence-based practices to promote student achievement. The purpose of this study was to better understand teacher and educational leaders’ preferences for professional learning formats in relation to the intended learning objective. The results indicate that educators preferences for professional learning format varied by the intended learning objective of the session. Remote professional learning was preferred relative to face-to-face and hybrid formats for a session in which the primary objective was to share information uni-directionally from the presenter to the audience (53% versus 25% and 22% preferred hybrid). The respondents were equally split in their preference for either a face-to-face or remote format when the learning objective was to understand new concepts and learn how to apply the concepts to their setting. The results have important implications for designing professional learning
Hubble Space Telescope Photometry of Globular Clusters in M81
We perform aperture photometry and profile fitting on 419 globular cluster
(GC) candidates with mV \leq 23 mag identified in Hubble Space Telescope
Advanced Camera for Surveys BVI imaging, and estimate the effective radii of
the clusters. We identify 85 previously known spectroscopically-confirmed
clusters, and newly identify 136 objects as good cluster candidates within the
3{\sigma} color and size ranges defined by the spectroscopically confirmed
clusters, yielding a total of 221 probable GCs. The luminosity function peak
for the 221 probable GCs with estimated total dereddening applied is V ~(20.26
\pm 0.13) mag, corresponding to a distance of ~3.7\pm0.3 Mpc. The blue and red
GC candidates, and the metal-rich (MR) and metal-poor (MP) spectroscopically
confirmed clusters, are similar in half-light radius, respectively. Red
confirmed clusters are about 6% larger in median half-light radius than blue
confirmed clusters, and red and blue good GC candidates are nearly identical in
half-light radius. The total population of confirmed and "good" candidates
shows an increase in half-light radius as a function of galactocentric
distance.Comment: 42 figures, 14 pages, accepted to A
Star Cluster Candidates in M81
We present a catalog of extended objects in the vicinity of M81 based a set
of 24 Hubble Space Telescope Advanced Camera for Surveys (ACS) Wide Field
Camera (WFC) F814W (I-band) images. We have found 233 good globular cluster
candidates; 92 candidate HII regions, OB associations, or diffuse open
clusters; 489 probable background galaxies; and 1719 unclassified objects. We
have color data from ground-based g- and r-band MMT Megacam images for 79
galaxies, 125 globular cluster candidates, 7 HII regions, and 184 unclassified
objects. The color-color diagram of globular cluster candidates shows that most
fall into the range 0.25 < g-r < 1.25 and 0.5 < r-I < 1.25, similar to the
color range of Milky Way globular clusters. Unclassified objects are often
blue, suggesting that many of them are likely to be HII regions and open
clusters, although a few galaxies and globular clusters may be among them.Comment: 35 pages, 11 figures, submitted to A
Discovery of ram-pressure stripped gas around an elliptical galaxy in Abell 2670
Studies of cluster galaxies are increasingly finding galaxies with
spectacular one-sided tails of gas and young stars, suggestive of intense
ram-pressure stripping. These so-called "jellyfish" galaxies typically have
late-type morphology. In this paper, we present MUSE observations of an
elliptical galaxy in Abell 2670 with long tails of material visible in the
optical spectra, as well as blobs with tadpole-like morphology. The spectra in
the central part of the galaxy reveals a stellar component as well as ionized
gas. The stellar component does not have significant rotation, while the
ionized gas defines a clear star-forming gas disk. We argue, based on deep
optical images of the galaxy, that the gas was most likely acquired during a
past wet merger. It is possible that the star-forming blobs are also remnants
of the merger. In addition, the direction and kinematics of the one-sided
ionized tails, combined with the tadpole morphology of the star-forming blobs,
strongly suggests that the system is undergoing ram pressure from the
intracluster medium. In summary, this paper presents the discovery of a
post-merger elliptical galaxy undergoing ram pressure stripping.Comment: 6 pages, 5 figures, accepted for publication in ApJ
Star-forming fractions and galaxy evolution with redshift in rich X-ray-selected galaxy clusters
We have compared stacked spectra of galaxies, grouped by environment and stellar mass, among 58 members of the redshift z = 1.24 galaxy cluster RDCS J1252.9-2927 (J1252.9) and 134 galaxies in the z = 0.84 cluster RX J0152.7-1357 (J0152.7). These two clusters are excellent laboratories to study how galaxies evolve from star-forming to passive at z ~ 1. We measured spectral indices and star-forming fractions for our density- and mass-based stacked spectra. The star-forming fraction among low-mass galaxies (<7 × 10^(10)M_⊙) is higher in J1252.9 than in J0152.7, at about 4σ significance. Thus star formation is being quenched between z = 1.24 and z = 0.84 for a substantial fraction of low-mass galaxies. Star-forming fractions were also found to be higher in J1252.9 in all environments, including the core. Passive galaxies in J1252.9 have systematically lower D_n4000 values than in J0152.7 in all density and mass groups, consistent with passive evolution at modestly super-solar metallicities
Discovery of a Rich Cluster at z = 1.63 Using the Rest-frame 1.6 μm "Stellar Bump Sequence" Method
We present a new two-color algorithm, the "Stellar Bump Sequence" (SBS), that is optimized for robustly identifying candidate high-redshift galaxy clusters in combined wide-field optical and mid-infrared (MIR) data. The SBS algorithm is a fusion of the well-tested cluster red-sequence method of Gladders & Yee with the MIR 3.6 μm-4.5 μm cluster detection method developed by Papovich. As with the cluster red-sequence method, the SBS identifies candidate overdensities within 3.6 μm-4.5 μm color slices, which are the equivalent of a rest-frame 1.6 μm stellar bump "red-sequence." In addition to employing the MIR colors of galaxies, the SBS algorithm incorporates an optical/MIR (z'-3.6 μm) color cut. This cut effectively eliminates foreground 0.2 1.0 galaxies and add noise when searching for high-redshift galaxy overdensities. We demonstrate using the z ~ 1 GCLASS cluster sample that similar to the red sequence, the stellar bump sequence appears to be a ubiquitous feature of high-redshift clusters, and that within that sample the color of the stellar bump sequence increases monotonically with redshift and provides photometric redshifts accurate to Δz = 0.05. We apply the SBS method in the XMM-LSS SWIRE field and show that it robustly recovers the majority of confirmed optical, MIR, and X-ray-selected clusters at z > 1.0 in that field. Lastly, we present confirmation of SpARCS J022427-032354 at z = 1.63, a new cluster detected with the method and confirmed with 12 high-confidence spectroscopic redshifts obtained using FORS2 on the Very Large Telescope. We conclude with a discussion of future prospects for using the algorithm
Evidence for the Universality of Properties of Red-sequence Galaxies in X-Ray- and Red-Sequence-Selected Clusters at z ~ 1
We study the slope, intercept, and scatter of the color–magnitude and color–mass relations for a sample of 10 infrared red-sequence-selected clusters at z ~ 1. The quiescent galaxies in these clusters formed the bulk of their stars above z ≳ 3 with an age spread Δt ≳ 1 Gyr. We compare UVJ color–color and spectroscopic-based galaxy selection techniques, and find a 15% difference in the galaxy populations classified as quiescent by these methods. We compare the color–magnitude relations from our red-sequence selected sample with X-ray- and photometric-redshift-selected cluster samples of similar mass and redshift. Within uncertainties, we are unable to detect any difference in the ages and star formation histories of quiescent cluster members in clusters selected by different methods, suggesting that the dominant quenching mechanism is insensitive to cluster baryon partitioning at z ~ 1
Hα star formation main sequence in cluster and field galaxies at z ∼ 1.6
We calculate Hα-based star formation rates and determine the star formation rate–stellar mass relation for members of three Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) clusters at z ∼ 1.6 and serendipitously identified field galaxies at similar redshifts to the clusters. We find similar star formation rates in cluster and field galaxies throughout our range of stellar masses. The results are comparable to those seen in other clusters at similar redshifts, and consistent with our previous photometric evidence for little quenching activity in clusters. One possible explanation for our results is that galaxies in our z ∼ 1.6 clusters have been accreted too recently to show signs of environmental quenching. It is also possible that the clusters are not yet dynamically mature enough to produce important environmental quenching effects shown to be important at low redshift, such as ram-pressure stripping or harassment
The GOGREEN Survey: Evidence of an excess of quiescent disks in clusters at
We present results on the measured shapes of 832 galaxies in 11 galaxy
clusters at 1.0 < z <1.4 from the GOGREEN survey. We measure the axis ratio
(), the ratio of the minor to the major axis, of the cluster galaxies from
near-infrared Hubble Space Telescope imaging using S\'ersic profile fitting and
compare them with a field sample. We find that the median of both
star-forming and quiescent galaxies in clusters increases with stellar mass,
similar to the field. Comparing the axis ratio distributions between clusters
and the field in four mass bins, the distributions for star-forming galaxies in
clusters are consistent with those in the field. Conversely, the distributions
for quiescent galaxies in the two environments are distinct, most remarkably in
where clusters show a flatter
distribution, with an excess at low . Modelling the distribution with oblate
and triaxial components, we find that the cluster and field sample difference
is consistent with an excess of flattened oblate quiescent galaxies in
clusters. The oblate population contribution drops at high masses, resulting in
a narrower distribution in the massive population than at lower masses.
Using a simple accretion model, we show that the observed distributions and
quenched fractions are consistent with a scenario where no morphological
transformation occurs for the environmentally quenched population in the two
intermediate mass bins. Our results suggest that environmental quenching
mechanism(s) likely produce a population that has a different morphological mix
than those resulting from the dominant quenching mechanism in the field.Comment: Accepted for publication in ApJ. 25 pages, 15 figure