69 research outputs found
The Violent Youth of Bright and Massive Cluster Galaxies and their Maturation over 7 Billion Years
In this study we investigate the formation and evolution mechanisms of the
brightest cluster galaxies (BCGs) over cosmic time. At high redshift
(), we selected BCGs and most massive cluster galaxies (MMCGs) from
the Cl1604 supercluster and compared them to low-redshift ()
counterparts drawn from the MCXC meta-catalog, supplemented by SDSS imaging and
spectroscopy. We observed striking differences in the morphological, color,
spectral, and stellar mass properties of the BCGs/MMCGs in the two samples.
High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies,
with blue broadband colors, properties largely absent amongst the low-redshift
BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor
of from to . Through this and other
comparisons we conclude that a combination of major merging (mainly wet or
mixed) and \emph{in situ} star formation are the main mechanisms which build
stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also
appears to grow in lockstep with both the stellar baryonic and total mass of
the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a
factor of , while their average S\'ersic index increased by 0.45
from to , also supporting a scenario involving major
merging, though some adiabatic expansion is required. These observational
results are compared to both models and simulations to further explore the
implications on processes which shape and evolve BCGs/MMCGs over the past
7 Gyr.Comment: Accepted for publication in MNRA
MC: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9
The second most significant detection of the Planck Sunyaev Zel'dovich
survey, PLCK~G287.0+32.9 () boasts two similarly bright radio relics
and a radio halo. One radio relic is located kpc northwest of the
X-ray peak and the other Mpc to the southeast. This large difference
suggests that a complex merging scenario is required. A key missing puzzle for
the merging scenario reconstruction is the underlying dark matter distribution
in high resolution. We present a joint Subaru Telescope and {\it Hubble Space
Telescope} weak-lensing analysis of the cluster. Our analysis shows that the
mass distribution features four significant substructures. Of the
substructures, a primary cluster of mass
$M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \
\text{M}_{\odot}M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}\sim 400\sim 2M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times
10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio
relic.Comment: 19 pages, 14 figures; Accepted to Ap
The DEEP2 Redshift Survey: Lyman Alpha Emitters in the Spectroscopic Database
We present the first results of a search for Lyman-alpha emitters (LAEs) in
the DEEP2 spectroscopic database that uses a search technique that is different
from but complementary to traditional narrowband imaging surveys. We have
visually inspected ~20% of the available DEEP2 spectroscopic data and have
found nine high-quality LAEs with clearly asymmetric line profiles and an
additional ten objects of lower quality, some of which may also be LAEs. Our
survey is most sensitive to LAEs at z=4.4-4.9 and that is indeed where all but
one of our high-quality objects are found. We find the number density of our
spectroscopically-discovered LAEs to be consistent with those found in
narrowband imaging searches. The combined, averaged spectrum of our nine
high-quality objects is well fit by a two-component model, with a second,
lower-amplitude component redshifted by ~420 km/s with respect to the primary
Lyman-alpha line, consistent with large-scale outflows from these objects. We
conclude by discussing the advantages and future prospects of blank-sky
spectroscopic surveys for high-z LAEs.Comment: Accepted for publication in Ap
An Optical/NIR Exploration of Forming Cluster Environments at High Redshift with VLT, Keck, and HST
The past decade has been witness to immense progress in the understanding of the early stages of cluster formation both from a theoretical and observational perspective. During this time, samples of forming clusters at higher redshift, termed "protoclusters", once comprised of heterogeneous mix of serendipitous detections or detections arising from dedicated searches around rare galaxy populations, have begun to compete with lower-redshift samples both in terms of numbers and in the homogeneity of the detection methods. Much of this progress has come from optical/near-infrared (NIR) imaging and spectroscopic campaigns designed to target large numbers of typical galaxies to exquisite depth.
In this poster talk I will focus on observations from VIMOS on VLT, MOSFIRE/DEIMOS on Keck, and a 50-orbit cycle 29 HST WFC3/G141 grism campaign taken as part of the Charting Cluster Construction with VUDS and ORELSE (C3VO) survey. These observations, combined with novel mapping and search techniques, have uncovered a large number of "protostructures" at 2 < z < 5 that appear to resemble clusters and groups forming in the early universe. I will discuss the development of the methods for finding, confirming, and characterizing proto-clusters and proto-groups in our sample, as well as groups and clusters at intermediate redshifts. Several case studies of spectroscopically-confirmed massive proto-clusters with a diverse set of properties will be presented. I will finally discuss constraints on the relationship between star formation rate, stellar mass, and galaxy density at these redshift
The Properties of Radio Galaxies and the Effect of Environment in Large Scale Structures at
In this study we investigate 89 radio galaxies that are
spectroscopically-confirmed to be members of five large scale structures in the
redshift range of . Based on a two-stage classification
scheme, the radio galaxies are classified into three sub-classes: active
galactic nucleus (AGN), hybrid, and star-forming galaxy (SFG). We study the
properties of the three radio sub-classes and their global and local
environmental preferences. We find AGN hosts are the most massive population
and exhibit quiescence in their star-formation activity. The SFG population has
a comparable stellar mass to those hosting a radio AGN but are unequivocally
powered by star formation. Hybrids, though selected as an intermediate
population in our classification scheme, were found in almost all analyses to
be a unique type of radio galaxies rather than a mixture of AGN and SFGs. They
are dominated by a high-excitation radio galaxy (HERG) population. We discuss
environmental effects and scenarios for each sub-class. AGN tend to be
preferentially located in locally dense environments and in the cores of
clusters/groups, with these preferences persisting when comparing to galaxies
of similar colour and stellar mass, suggesting that their activity may be
ignited in the cluster/group virialized core regions. Conversely, SFGs exhibit
a strong preference for intermediate-density global environments, suggesting
that dusty starbursting activity in LSSs is largely driven by galaxy-galaxy
interactions and merging.Comment: 28 pages, 10 figures, accepted to MNRA
Star Formation Quenching in High-redshift Large-scale Structure: Post-starburst Galaxies in the Cl1604 Supercluster at
The Cl1604 supercluster at is one of the most extensively
studied high redshift large scale structures, with more than 500
spectroscopically confirmed members. It consists of 8 clusters and groups, with
members numbering from a dozen to nearly a hundred, providing a broad range of
environments for investigating the large scale environmental effects on galaxy
evolution. Here we examine the properties of 48 post-starburst galaxies in
Cl1604, comparing them to other galaxy populations in the same supercluster.
Incorporating photometry from ground-based optical and near-infrared imaging,
along with mid-infrared observations, we derive stellar masses for
all Cl1604 members. The colors and stellar masses of the K+A galaxies support
the idea that they are progenitors of red sequence galaxies. Their
morphologies, residual star-formation rates, and spatial distributions suggest
galaxy mergers may be the principal mechanism producing post-starburst
galaxies. Interaction between galaxies and the dense intra-cluster medium is
also effective, but only in the cores of dynamically evolved clusters. The
prevalence of post-starburst galaxies in clusters correlates with the dynamical
state of the host cluster, as both galaxy mergers and the dense intra-cluster
medium produce post-starburst galaxies. We also investigate the incompleteness
and contamination of K+A samples selected by means of H and [OII]
equivalent widths. K+A samples may be up to incomplete due to the
presence of LINER/Seyferts and up to of K+A galaxies could have
substantial star formation activity.Comment: 19 pages, 13 figures, accepted by Ap
Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization
Within one billion years of the Big Bang, intergalactic hydrogen was ionized
by sources emitting ultraviolet and higher energy photons. This was the final
phenomenon to globally affect all the baryons (visible matter) in the Universe.
It is referred to as cosmic reionization and is an integral component of
cosmology. It is broadly expected that intrinsically faint galaxies were the
primary ionizing sources due to their abundance in this epoch. However, at the
highest redshifts (; lookback time 13.1 Gyr), all galaxies with
spectroscopic confirmations to date are intrinsically bright and, therefore,
not necessarily representative of the general population. Here, we report the
unequivocal spectroscopic detection of a low luminosity galaxy at . We
detected the Lyman- emission line at {\AA} in two separate
observations with MOSFIRE on the Keck I Telescope and independently with the
Hubble Space Telescope's slit-less grism spectrograph, implying a source
redshift of . The galaxy is gravitationally magnified by
the massive galaxy cluster MACS J1423.8+2404 (), with an estimated
intrinsic luminosity of mag and a stellar mass of
solar masses. Both are an order of
magnitude lower than the four other Lyman- emitters currently known at
, making it probably the most distant representative source of
reionization found to date
Detection of Lyman-Alpha Emission From a Triple Imaged z=6.85 Galaxy Behind MACS J2129.4-0741
We report the detection of Ly emission at \AA{} in the
Keck/DEIMOS and \HST WFC3 G102 grism data from a triply-imaged galaxy at
behind galaxy cluster MACS J2129.40741. Combining the
emission line wavelength with broadband photometry, line ratio upper limits,
and lens modeling, we rule out the scenario that this emission line is \oii at
. After accounting for magnification, we calculate the weighted average
of the intrinsic Ly luminosity to be
and Ly equivalent
width to be \AA{}. Its intrinsic UV absolute magnitude at 1600\AA{} is
mag and stellar mass , making
it one of the faintest (intrinsic ) galaxies with
Ly detection at to date. Its stellar mass is in the typical
range for the galaxies thought to dominate the reionization photon budget at
; the inferred Ly escape fraction is high (\%),
which could be common for sub- galaxies with Ly
emission. This galaxy offers a glimpse of the galaxy population that is thought
to drive reionization, and it shows that gravitational lensing is an important
avenue to probe the sub- galaxy population.Comment: Accepted by ApJ Letter
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