803 research outputs found
A proposed search for a fourth neutrino with a PBq antineutrino source
Several observed anomalies in neutrino oscillation data can be explained by a
hypothetical fourth neutrino separated from the three standard neutrinos by a
squared mass difference of a few eV^2. We show that this hypothesis can be
tested with a PBq (ten kilocurie scale) 144Ce or 106Ru antineutrino beta-source
deployed at the center of a large low background liquid scintillator detector.
In particular, the compact size of such a source could yield an
energy-dependent oscillating pattern in event spatial distribution that would
unabiguously determine neutrino mass differences and mixing angles.Comment: 4 pages ; 1 table ; 4 figures - Add energy spectrum shape only
analysis + referee comments/suggestion
Looking ahead to the sky with the Square Kilometre Array: simulating flux densities & resolved radio morphologies of star-forming galaxies
SKA-MID surveys will be the first in the radio domain to achieve clearly
sub-arcsecond resolution at high sensitivity over large areas, opening new
science applications for galaxy evolution. To investigate the potential of
these surveys, we create simulated SKA-MID images of a 0.04 deg
region of GOODS-North, constructed using multi-band HST imaging of 1723 real
galaxies containing significant substructure at . We create images at
the proposed depths of the band 2 wide, deep and ultradeep reference surveys
(RMS = 1.0 Jy, 0.2 Jy and 0.05 Jy over 1000 deg, 10-30
deg and 1 deg respectively), using the telescope response of
SKA-MID at 0.6" resolution. We quantify the star-formation rate - stellar mass
space the surveys will probe, and asses to which stellar masses they will be
complete. We measure galaxy flux density, half-light radius (),
concentration, Gini (distribution of flux), second-order moment of the
brightest pixels () and asymmetry before and after simulation with the
SKA response, to perform input-output tests as a function of depth, separating
the effects of convolution and noise. We find that the recovery of Gini and
asymmetry is more dependent on survey depth than for , concentration
and . We also assess the relative ranking of parameters before and
after observation with SKA-MID. best retains its ranking, whilst
asymmetries are poorly recovered. We confirm that the wide tier will be suited
to the study of highly star-forming galaxies across different environments,
whilst the ultradeep tier will enable detailed morphological analysis to lower
SFRs.Comment: 25 pages, 14 figures, 1 table. Accepted for publication in MNRA
The IR Compactness of Dusty Galaxies Set Star-formation and Dust Properties at z~0-2
Surface densities of gas, dust and stars provide a window into the physics of
star-formation that, until the advent of high-resolution
far-infrared/sub-millimeter observations, has been historically difficult to
assess amongst dusty galaxies. To study the link between infrared (IR) surface
densities and dust properties, we leverage the Atacama Large
Millimetre/Submillimetre Array (ALMA) archive to measure the extent of cold
dust emission in 15 IR selected galaxies selected on the basis of
having available mid-IR spectroscopy from Spitzer. We use the mid-IR spectra to
constrain the relative balance between dust heating from star-formation and
active galactic nuclei (AGN), and to measure emission from Polycylic Aromatic
Hydrocarbons (PAHs) -- small dust grains that play a key role in the
photoelectric heating of gas. In general, we find that dust-obscured
star-formation at high IR surface densities exhibits similar properties at low-
and high-redshift, namely: local luminous IR galaxies have comparable PAH
luminosity to total dust mass ratios as high- galaxies, and star-formation
at is more efficient at high IR surface densities despite the fact
that our sample of high galaxies are closer to the main-sequence than local
luminous IR galaxies. High star-formation efficiencies are coincident with a
decline in the PAH/IR luminosity ratio reminiscent of the deficit observed in
far-infrared fine-structure lines. Changes in the gas and dust conditions
arising from high star-formation surface densities might help drive the
star-formation efficiency up. This could help explain high efficiencies needed
to reconcile star-formation and gas volume densities in dusty galaxies at
cosmic noon.Comment: 18 pages, 10 figures, accepted to Ap
Broad emission lines in optical spectra of hot dust-obscured galaxies can contribute significantly to JWST/NIRCam photometry
Selecting the first galaxies at z>7-10 from JWST surveys is complicated by
z<6 contaminants with degenerate photometry. For example, strong optical
nebular emission lines at z7-10 Lyman
Break Galaxies (LBGs). Dust-obscured 3<z<6 galaxies in particular are
potentially important contaminants, and their faint rest-optical spectra have
been historically difficult to observe. A lack of optical emission line and
continuum measures for 3<z<6 dusty galaxies now makes it difficult to test
their expected JWST/NIRCam photometry for degenerate solutions with NIRCam
dropouts. Towards this end, we quantify the contribution by strong emission
lines to NIRCam photometry in a physically motivated manner by stacking 21 Keck
II/NIRES spectra of hot, dust-obscured, massive
() and infrared (IR) luminous galaxies at
z~1-4. We derive an average spectrum and measure strong narrow (broad)
[OIII]5007 and H features with equivalent widths of A
( A) and A ( A) respectively. These features can
increase broadband NIRCam fluxes by factors of 1.2-1.7 (0.2-0.6 mag). Due to
significant dust-attenuation (), we find H+[NII] to be
significantly brighter than [OIII]+H, and therefore find that
emission-line dominated contaminants of high-z galaxy searches can only
reproduce moderately blue perceived UV continua of
with and z>4. While there are some
redshifts (z~3.75) where our stack is more degenerate with the photometry of
z>10 LBGs between m, redder filter coverage
beyond m and far-IR/sub-mm follow-up may be useful for
breaking the degeneracy and making a crucial separation between two fairly
unconstrained populations, dust-obscured galaxies at z~3-6 and LBGs at z>10.Comment: 8 pages, 3 figures, 1 table, submitted to ApJ
CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin 2, to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ∼ 9-16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M UV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance (surface density [arcmin −2]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.</p
COSMOS2020: Exploring the dawn of quenching for massive galaxies at 3 < z < 5 with a new colour selection method
We select and characterise a sample of massive
(log(MM) quiescent galaxies (QGs) at in the
latest COSMOS2020 catalogue. QGs are selected using a new rest-frame colour
selection method, based on their probability of belonging to the quiescent
group defined by a Gaussian Mixture Model (GMM) trained on rest-frame colours
() of similarly massive galaxies at . We calculate the
quiescent probability threshold above which a galaxy is classified as quiescent
using simulated galaxies from the SHARK semi-analytical model. We find that at
in SHARK, the GMM/ method out-performs classical rest-frame
selection and is a viable alternative. We select galaxies as quiescent
based on their probability in COSMOS2020 at , and compare the selected
sample to both and selected samples. We find that although the
new selection matches and in number, the overlap between colour
selections is only , implying that rest-frame colour commonly used
at lower redshifts selections cannot be equivalently used at . We compute
median rest-frame SEDs for our sample and find the median quiescent galaxy at
has a strong Balmer/4000 Angstrom break, and residual flux
indicating recent quenching. We find the number densities of the entire
quiescent population (including post-starbursts) more than doubles from
Mpc at to
Mpc at , confirming that the onset of massive galaxy quenching
occurs as early as .Comment: 19 pages, 10 figures + appendix. Accepted for publication in AJ. Both
the GMM model and code to calculate quiescent probabilities from rest frame
flux densities are made available online at
https://github.com/kmlgould/GMM-quiescen
JWST and ALMA discern the assembly of structural and obscured components in a high-redshift starburst galaxy
We present observations and analysis of the starburst, PACS-819, at z=1.45
( M), using high-resolution (;
0.8 kpc) ALMA and multi-wavelength JWST images from the COSMOS-Web program.
Dissimilar to HST/ACS images in the rest-frame UV, the redder NIRCam and MIRI
images reveal a smooth central mass concentration and spiral-like features,
atypical for such an intense starburst. Through dynamical modeling of the CO
J=5--4 emission with ALMA, PACS-819 is rotation-dominated thus has a disk-like
nature. However, kinematic anomalies in CO and asymmetric features in the bluer
JWST bands (e.g., F150W) support a more disturbed nature likely due to
interactions. The JWST imaging further enables us to map the distribution of
stellar mass and dust attenuation, thus clarifying the relationships between
different structural components, not discernable in the previous HST images.
The CO J = 5 -- 4 and FIR dust continuum emission are co-spatial with a
heavily-obscured starbursting core (<1 kpc) which is partially surrounded by
much less obscured star-forming structures including a prominent arc, possibly
a tidally-distorted dwarf galaxy, and a clump, either a sign of an ongoing
violent disk instability or a recently accreted low-mass satellite. With
spatially-resolved maps, we find a high molecular gas fraction in the central
area reaching (/) and short depletion times
( 120 Myrs) across the entire system. These
observations provide insights into the complex nature of starbursts in the
distant universe and underscore the wealth of complementary information from
high-resolution observations with both ALMA and JWST.Comment: 18 pages, 12 figures, Submitted to Ap
A z=1.85 galaxy group in CEERS: evolved, dustless, massive intra-halo light and a brightest group galaxy in the making
We present CEERS JWST/NIRCam imaging of a massive galaxy group at z=1.85, to
explore the early JWST view on massive group formation in the distant Universe.
The group contains >16 members (including 6 spectros. confirmations) down to
log10(Mstar/Msun)=8.5, including the brightest group galaxy (BGG) in the
process of actively assembling at this redshift. The BGG is comprised of
multiple merging components extending ~3.6" (30kpc) across the sky. The BGG
contributes 69% of the group's total galactic stellar mass, with one of the
merging components containing 76% of the total mass of the BGG and a
SFR>1810Msun/yr. Most importantly, we detect intra-halo light (IHL) in several
HST and JWST/NIRCam bands, allowing us to construct a state-of-the-art
rest-frame UV-NIR Spectral Energy Distribution of the IHL for the first time at
this high redshift. This allows stellar population characterisation of both the
IHL and member galaxies, as well as the morphology distribution of group
galaxies vs. their star-formation activity when coupled with Herschel data. We
create a stacked image of the IHL, giving us a sensitivity to extended emission
of 28.5 mag/arcsec2 at rest-frame 1um. We find that the IHL is extremely dust
poor (Av~0), containing an evolved stellar population of log10(t50/yr)=8.8,
corresponding to a formation epoch for 50% of the stellar material 0.63Gyr
before z=1.85. There is no evidence of ongoing star-formation in the IHL. The
IHL in this group at z=1.85 contributes ~10% of the total stellar mass,
comparable with what is observed in local clusters. This suggests that the
evolution of the IHL fraction is more self-similar with redshift than predicted
by some models, challenging our understanding of IHL formation during the
assembly of high-redshift clusters. JWST is unveiling a new side of group
formation at this redshift, which will evolve into Virgo-like structures in the
local Universe.Comment: 14 pages + appendix, 11 figures, 4 tables. Accepted to A&A on 15th
May 202
The Web Epoch of Reionization Lyman- Survey (WERLS) I. MOSFIRE Spectroscopy of Lyman- Emitters
We present the first results from the Web Epoch of Reionization
Lyman- Survey (WERLS), a spectroscopic survey of Lyman-
emission using Keck I/MOSFIRE and LRIS. WERLS targets bright () galaxy
candidates with photometric redshifts of selected
from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three
JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11
Lyman- emitters (LAEs; 3 secure and 8 tentative candidates) detected in
the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield
is %, broadly consistent with expectations assuming some loss from
redshift uncertainty, contamination from sky OH lines, and that the Universe is
approximately half-ionized at this epoch, whereby observable Lyman-
emission is unlikely for galaxies embedded in a neutral intergalactic medium.
Our targets are selected to be UV-bright, and span a range of absolute UV
magnitudes with . With two LAEs detected at
, we also consider the possibility of an ionized bubble at this
redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for
pinpointing beacons of reionization and mapping the large scale distribution of
mass relative to the ionization state of the Universe.Comment: 27 pages, 8 figures; ApJ submitte
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