20 research outputs found
Discovery of Massive, Mostly Star-formation Quenched Galaxies with Extremely Large Lyman-alpha Equivalent Widths at z ~ 3
We report a discovery of 6 massive galaxies with both extremely large Lya
equivalent width and evolved stellar population at z ~ 3. These MAssive
Extremely STrong Lya emitting Objects (MAESTLOs) have been discovered in our
large-volume systematic survey for strong Lya emitters (LAEs) with twelve
optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS
field. Based on the SED fitting analysis for these LAEs, it is found that these
MAESTLOs have (1) large rest-frame equivalent width of EW_0(Lya) ~ 100--300 A,
(2) M_star ~ 10^10.5--10^11.1 M_sun, and (3) relatively low specific star
formation rates of SFR/M_star ~ 0.03--1 Gyr^-1. Three of the 6 MAESTLOs have
extended Ly emission with a radius of several kpc although they show
very compact morphology in the HST/ACS images, which correspond to the
rest-frame UV continuum. Since the MAESTLOs do not show any evidence for AGNs,
the observed extended Lya emission is likely to be caused by star formation
process including the superwind activity. We suggest that this new class of
LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving
galaxies at the peak era of the cosmic star-formation history.Comment: Accepted for publication in ApJ Letters on 15th July, 2015. 6 pages
including 3 figures and 2 table
An ALMA survey of submillimetre galaxies in the COSMOS field: The extent of the radio-emitting region revealed by 3 GHz imaging with the Very Large Array
We determine the radio size distribution of a large sample of 152 SMGs in
COSMOS that were detected with ALMA at 1.3 mm. For this purpose, we used the
observations taken by the VLA-COSMOS 3 GHz Large Project. One hundred and
fifteen of the 152 target SMGs were found to have a 3 GHz counterpart. The
median value of the major axis FWHM at 3 GHz is derived to be kpc.
The radio sizes show no evolutionary trend with redshift, or difference between
different galaxy morphologies. We also derived the spectral indices between 1.4
and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median
values were found to be and K. Three of the
target SMGs, which are also detected with the VLBA, show clearly higher
brightness temperatures than the typical values. Although the observed radio
emission appears to be predominantly powered by star formation and supernova
activity, our results provide a strong indication of the presence of an AGN in
the VLBA and X-ray-detected SMG AzTEC/C61. The median radio-emitting size we
have derived is 1.5-3 times larger than the typical FIR dust-emitting sizes of
SMGs, but similar to that of the SMGs' molecular gas component traced through
mid- line emission of CO. The physical conditions of SMGs probably render
the diffusion of cosmic-ray electrons inefficient, and hence an unlikely
process to lead to the observed extended radio sizes. Instead, our results
point towards a scenario where SMGs are driven by galaxy interactions and
mergers. Besides triggering vigorous starbursts, galaxy collisions can also
pull out the magnetised fluids from the interacting disks, and give rise to a
taffy-like synchrotron-emitting bridge. This provides an explanation for the
spatially extended radio emission of SMGs, and can also cause a deviation from
the well-known IR-radio correlation.Comment: 32 pages (incl. 5 appendices), 17 figures, 7 tables; accepted for
publication in A&A; abstract abridged for arXi
Identification and Characterization of Six Spectroscopically Confirmed Massive Protostructures at
We present six spectroscopically confirmed massive protostructures, spanning
a redshift range of in the Extended Chandra Deep Field South
(ECDFS) field discovered as part of the Charting Cluster Construction in VUDS
and ORELSE (C3VO) survey. We identify and characterize these remarkable systems
by applying an overdensity measurement technique on an extensive data
compilation of public and proprietary spectroscopic and photometric
observations in this highly studied extragalactic field. Each of these six
protostructures, i.e., a large scale overdensity (volume \thinspace
cMpc) of more than above the field density levels at
these redshifts, have a total mass and one or more
highly overdense (overdensity) peaks. One of the
most complex protostructures discovered is a massive
() system at that contains six peaks and
55 spectroscopic members. We also discover protostructures at and
that appear to at least partially overlap on sky with the
protostructure at , suggesting a possible connection. We
additionally report on the discovery of three massive protostructures at
, 2.80, and 4.14 and discuss their properties. Finally, we discuss the
relationship between star formation rate and environment in the richest of
these protostructures, finding an enhancement of star formation activity in the
densest regions. The diversity of the protostructures reported here provide an
opportunity to study the complex effects of dense environments on galaxy
evolution over a large redshift range in the early universe.Comment: 10 pages, 4 figures, 1 tabl
Lyman-alpha Forest Tomography from Background Galaxies: The First Megaparsec-Resolution Large-Scale Structure Map at z>2
We present the first observations of foreground Lyman- forest
absorption from high-redshift galaxies, targeting 24 star-forming galaxies
(SFGs) with within a region of the COSMOS
field. The transverse sightline separation is
comoving, allowing us to create a tomographic reconstruction of the 3D
Ly forest absorption field over the redshift range . The resulting map covers in the transverse plane and
along the line-of-sight with a spatial resolution of , and is the first high-fidelity map of large-scale
structure on scales at . Our map reveals significant
structures with extent, including several
spanning the entire transverse breadth, providing qualitative evidence for the
filamentary structures predicted to exist in the high-redshift cosmic web.
Simulated reconstructions with the same sightline sampling, spectral
resolution, and signal-to-noise ratio recover the salient structures present in
the underlying 3D absorption fields. Using data from other surveys, we
identified 18 galaxies with known redshifts coeval with our map volume enabling
a direct comparison to our tomographic map. This shows that galaxies
preferentially occupy high-density regions, in qualitative agreement with the
same comparison applied to simulations. Our results establishes the feasibility
of the CLAMATO survey, which aims to obtain Ly forest spectra for SFGs over of the COSMOS field, in order to map
out IGM large-scale structure at over a large
volume .Comment: Accepted for publication in Astrophysical Journal Letters; 8 pages
and 5 figure
The First Data Release of the Sloan Digital Sky Survey
The Sloan Digital Sky Survey has validated and made publicly available its
First Data Release. This consists of 2099 square degrees of five-band (u, g, r,
i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating
blank sky patches selected over 1360 square degrees of this area, and tables of
measured parameters from these data. The imaging data go to a depth of r ~ 22.6
and are photometrically and astrometrically calibrated to 2% rms and 100
milli-arcsec rms per coordinate, respectively. The spectra cover the range
3800--9200 A, with a resolution of 1800--2100. Further characteristics of the
data are described, as are the data products themselves.Comment: Submitted to The Astronomical Journal. 16 pages. For associated
documentation, see http://www.sdss.org/dr
Identification and characterization of six spectroscopically confirmed massive protostructures at 2.5 < z < 4.5
International audienceWe present six spectroscopically confirmed massive protostructures, spanning a redshift range of 2.5 9000 cMpc3) of more than 2.5ÏÎŽ above the field density levels at these redshifts, have a total mass Mtot â„ 1014.8Mâ and one or more highly overdense (overdensity > 5ÏÎŽ) peaks. One of the most complex protostructures discovered is a massive (Mtot = 1015.1Mâ) system at z ~ 3.47 that contains six peaks and 55 spectroscopic members. We also discover protostructures at z ~ 3.30 and z ~ 3.70 that appear to at least partially overlap on sky with the protostructure at z ~ 3.47, suggesting a possible connection. We additionally report on the discovery of three massive protostructures at z = 2.67, 2.80, and 4.14 and discuss their properties. Finally, we discuss the relationship between star formation rate and environment in the richest of these protostructures, finding an enhancement of star formation activity in the densest regions. The diversity of the protostructures reported here provide an opportunity to study the complex effects of dense environments on galaxy evolution over a large redshift range in the early universe
Analogues of primeval galaxies two billion years after the Big Bang
Deep observations are revealing a growing number of young galaxies in the first billion years of cosmic time 1. Compared to typical galaxies at later times, they show more extreme emission-line properties 2, higher star formation rates 3, lower masses 4, and smaller sizes 5. However, their faintness precludes studies of their chemical abundances and ionization conditions, strongly limiting our understanding of the physics driving early galaxy build-up and metal enrichment. Here we study a rare population of ultraviolet-selected, low-luminosity galaxies at redshift 2.4 < z < 3.5 that exhibit all the rest-frame properties expected from primeval galaxies. These low-mass, highly compact systems are rapidly forming galaxies able to double their stellar mass in only a few tens of millions of years. They are characterized by very blue ultraviolet spectra with weak absorption features and bright nebular emission lines, which imply hard radiation fields from young hot massive stars 6,7. Their highly ionized gas phase has strongly sub-solar carbon and oxygen abundances, with metallicities more than a factor of two lower than that found in typical galaxies of similar mass and star formation rate at z\ue2\u89\ua42.5 8. These young galaxies reveal an early and short stage in the assembly of their galactic structures and their chemical evolution, a vigorous phase that is likely to be dominated by the effects of gas-rich mergers, accretion of metal-poor gas and strong outflows