46 research outputs found
Spectroscopic detection of CIV in a galaxy at z=7.045: Implications for the ionizing spectra of reionization-era galaxies
We present Keck/MOSFIRE observations of UV metal lines in four bright
gravitationally-lensed z~6-8 galaxies behind the cluster Abell 1703. The
spectrum of A1703-zd6, a highly-magnified star forming galaxy with a
Lyman-alpha redshift of z=7.045, reveals a confident detection of the nebular
CIV emission line (unresolved with FWHM < 125 km/s). UV metal lines are not
detected in the three other galaxies. At z~2-3, nebular CIV emission is
observed in just 1% of UV-selected galaxies. The presence of strong CIV
emission in one of the small sample of galaxies targeted in this paper may
indicate hard ionizing spectra are more common at z~7. The total estimated
equivalent width of the CIV doublet (38 A) and CIV/Lyman-alpha flux ratio (0.3)
are comparable to measurements of narrow-lined AGNs. Photoionization models
show that the nebular CIV line can also be reproduced by a young stellar
population, with very hot metal poor stars dominating the photon flux
responsible for triply ionizing carbon. Regardless of the origin of the CIV, we
show that the ionizing spectrum of A1703-zd6 is different from that of typical
galaxies at z~2, producing more H ionizing photons per unit 1500A luminosity
and a larger flux density at 30-50 eV. If such extreme radiation fields are
typical in UV-selected systems at z>7, it would indicate that reionization-era
galaxies are more efficient ionizing agents than previously thought.
Alternatively, we suggest that the small sample of Lyman-alpha emitters at z>7
may trace a rare population with intense radiation fields capable of ionizing
their surrounding hydrogen distribution. Additional constraints on high
ionization emission lines in galaxies with and without Lyman-alpha detections
will help clarify whether hard ionizing spectra are common in the reionization
era.Comment: 11 pages, 6 figures, submitted to MNRA
Hierarchical Triggering of Star Formation by Superbubbles in W3/W4
It is generally believed that expanding superbubbles and mechanical feedback
from massive stars trigger star formation, because there are numerous examples
of superbubbles showing secondary star formation at their edges. However, while
these systems show an age sequence, they do not provide strong evidence of a
causal relationship. The W3/W4 Galactic star-forming complex suggests a
three-generation hierarchy: the supergiant shell structures correspond to the
oldest generation; these triggered the formation of IC 1795 in W3, the
progenitor of a molecular superbubble; which in turn triggered the current
star-forming episodes in the embedded regions W3-North, W3-Main, and W3-OH. We
present UBV photometry and spectroscopic classifications for IC 1795, which
show an age of 3 - 5 Myr. This age is intermediate between the reported 6 - 20
Myr age of the supergiant shell system, and the extremely young ages (10^4 -
10^5 yr) for the embedded knots of ultracompact HII regions, W3-North, W3-Main,
and W3-OH. Thus, an age sequence is indeed confirmed for the entire W3/W4
hierarchical system. This therefore provides some of the first convincing
evidence that superbubble action and mechanical feedback are indeed a
triggering mechanism for star formation.Comment: 10 pages, 6 figures; accepted to the Astronomical Journal. Figure 2
included in this submission as JPE
Keck Spectroscopy of Lyman-break Galaxies and its Implications for the UV-continuum and Ly_alpha Luminosity Functions at z>6
We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG)
candidates in the Subaru Deep Field (SDF). The candidates were selected as
i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band
image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly_alpha
emission lines at 6< z < 6.4. The median value of the Ly_alpha rest-frame
equivalent widths (EWs) is ~50 A, with four EWs >100 A. This well-defined
spectroscopic sample spans a UV-continuum luminosity range of -21.8<
M_{UV}<-19.5 (0.6~5 L*_{UV}) and a Ly_alpha luminosity range of (0.3~3) x
10^{43} erg s^{-1} (0.3~3 L*_ {Ly_alpha}). We derive the UV and Ly_alpha
luminosity functions (LFs) from our sample at ~6.2 after we correct for
sample incompleteness. We find that our measurement of the UV LF is consistent
with the results of previous studies based on photometric LBG samples at 5<z<7.
Our Ly_alpha LF is also generally in agreement with the results of
Ly_alpha-emitter surveys at z~5.7 and 6.6. This study shows that deep
spectroscopic observations of LBGs can provide unique constraints on both the
UV and Ly_alpha LFs at z>6.Comment: 14 pages, 7 figures, accepted for publication in Ap
Cold Mode Gas Accretion on Two Galaxy Groups at z2
We present Keck Cosmic Web Imager (KCWI) integral field spectroscopy (IFS)
observations of rest-frame UV emission lines , C IV 1548 \AA, 1550\AA and He II 1640 \AA observed in the circumgalactic
medium (CGM) of two radio-loud quasar host galaxies. We detect extended
emission on 80-90 kpc scale in in both systems with C IV, and He
II emission also detected out to 30-50 kpc. All emission lines show kinematics
with a blue and redshifted gradient pattern consistent with velocities seen in
massive dark matter halos and similar to kinematic patterns of inflowing gas
seen in hydrodynamical simulations. Using the kinematics of both resolved emission and absorption, we can confirm that both kinematic
structures are associated with accretion. Combining the KCWI data with
molecular gas observations with Atacama Large Millimeter/submillimeter Array
(ALMA) and high spatial resolution of ionized gas with Keck OSIRIS, we find
that both quasar host galaxies reside in proto-group environments at . We
estimate M of warm-ionized gas within 30-50 kpc from
the quasar that is likely accreting onto the galaxy group. We estimate inflow
rates of 60-200 Myr, within an order of magnitude of the outflow
rates in these systems. In the 4C 09.17 system, we detect narrow gas streams
associated with satellite galaxies, potentially reminiscent of ram-pressure
stripping seen in local galaxy groups and clusters. We find that the quasar
host galaxies reside in dynamically complex environments, with ongoing mergers,
gas accretion, ISM stripping, and outflows likely playing an important role in
shaping the assembly and evolution of massive galaxies at cosmic noon.Comment: 24 pages, 11 figures, 6 tabes. Accepted for publication in MNRA
Infrared Galaxies in the Field of the Massive Cluster Abell S1063: Discovery of a Luminous Kiloparsec-Sized HII Region in a Gravitationally Lensed IR-Luminous Galaxy at
Using the Spitzer Space Telescope and Herschel Space Observatory, we have
conducted a survey of infrared galaxies in the field of the galaxy cluster
Abell S1063 (AS1063) at , which is one of the most massive clusters
known and a target of the HST CLASH and Frontier-Field surveys. The
Spitzer/MIPS 24 m and Herschel/PACS & SPIRE images revealed that the core
of AS1063 is surprisingly devoid of infrared sources, showing only a few
detectable sources within the central r. There is, however, one
particularly bright source (2.3 mJy at 24 m; 106 mJy at 160 m), which
corresponds to a background galaxy at . The modest magnification factor
(4.0) implies that this galaxy is intrinsically IR-luminous (L). What is particularly interesting about
this galaxy is that HST optical/near-infrared images show a remarkably bright
and large (1 kpc) clump at one edge of the disk. Our follow-up
optical/near-infrared spectroscopy shows Balmer (H-H8) and forbidden
emission from this clump ([OII] 3727, [OIII]
4959,5007, [NII] 6548,6583), indicating that it
is a HII region. The HII region appears to have formed in-situ, as
kinematically it is part of a rotating disk, and there is no evidence of nearby
interacting galaxies. With an extinction correction of A mag, the
star formation rate of this giant HII region is 10 M yr,
which is exceptionally large, even for high redshift HII regions. Such a large
and luminous HII region is often seen at but quite rare in the nearby
Universe.Comment: Accepted for publication in the Astrophysical Journal. 29 pages, 15
figure
The InfraRed Imaging Spectrograph (IRIS) for TMT: photometric precision and ghost analysis
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the
Thirty Meter Telescope (TMT) that will be used to sample the corrected adaptive
optics field by NFIRAOS with a near-infrared (0.8 - 2.4 m) imaging camera
and Integral Field Spectrograph (IFS). In order to understand the science case
specifications of the IRIS instrument, we use the IRIS data simulator to
characterize photometric precision and accuracy of the IRIS imager. We present
the results of investigation into the effects of potential ghosting in the IRIS
optical design. Each source in the IRIS imager field of view results in ghost
images on the detector from IRIS's wedge filters, entrance window, and
Atmospheric Dispersion Corrector (ADC) prism. We incorporated each of these
ghosts into the IRIS simulator by simulating an appropriate magnitude point
source at a specified pixel distance, and for the case of the extended ghosts
redistributing flux evenly over the area specified by IRIS's optical design. We
simulate the ghosting impact on the photometric capabilities, and found that
ghosts generally contribute negligible effects on the flux counts for point
sources except for extreme cases where ghosts coalign with a star of
m2 fainter than the ghost source. Lastly, we explore the photometric
precision and accuracy for single sources and crowded field photometry on the
IRIS imager.Comment: SPIE 2018, 14 pages, 14 figures, 4 tables, Proceedings of SPIE
10702-373, Ground-based and Airborne Instrumentation for Astronomy VII,
10702A7 (16 July 2018