3,769 research outputs found
The IRX- relation of high-redshift galaxies
The relation between infrared excess (IRX) and UV spectral slope () is an empirical probe of dust properties of galaxies. The shape, scatter,
and redshift evolution of this relation are not well understood, however,
leading to uncertainties in estimating the dust content and star formation
rates (SFRs) of galaxies at high redshift. In this study, we explore the nature
and properties of the IRX- relation with a sample of
galaxies () extracted from high-resolution
cosmological simulations (MassiveFIRE) of the Feedback in Realistic
Environments (FIRE) project. The galaxies in our sample show an IRX- relation that is in good agreement with the observed relation in nearby
galaxies. IRX is tightly coupled to the UV optical depth, and is mainly
determined by the dust-to-star geometry instead of total dust mass, while
is set both by stellar properties, UV optical depth, and the
dust extinction law. Overall, much of the scatter in the IRX-
relation of our sample is found to be driven by variations of the intrinsic UV
spectral slope. We further assess how the IRX- relation depends
on viewing direction, dust-to-metal ratio, birth-cloud structures, and the dust
extinction law and we present a simple model that encapsulates most of the
found dependencies. Consequently, we argue that the reported `deficit' of the
infrared/sub-millimetre bright objects at does not necessarily imply a
non-standard dust extinction law at those epochs.Comment: 32 pages, 28 figures, 3 tables, submitted to MNRAS (comments are
welcomed
Lyman break and UV-selected galaxies at z ~ 1: II. PACS-100um/160um FIR detections
We report the PACS-100um/160um detections of a sample of 42 GALEX-selected
and FIR-detected Lyman break galaxies (LBGs) at z ~ 1 located in the COSMOS
field and analyze their ultra-violet (UV) to far-infrared (FIR) properties. The
detection of these LBGs in the FIR indicates that they have a dust content high
enough so that its emission can be directly detected. According to a spectral
energy distribution (SED) fitting with stellar population templates to their
UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger, more
massive, dustier, redder in the UV continuum, and UV-brighter than
PACS-undetected LBGs. PACS-detected LBGs at z ~ 1 are mostly disk-like galaxies
and are located over the green-valley and red sequence of the color-magnitude
diagram of galaxies at their redshift. By using their UV and IR emission, we
find that PACS-detected LBGs tend to be less dusty and have slightly higher
total star-formation rates (SFRs) than other PACS-detected UV-selected galaxies
within their same redshift range. As a consequence of the selection effect due
to the depth of the FIR observations employed, all our PACS-detected LBGs are
LIRGs. However, none of them are in the ULIRG regime, where the FIR
observations are complete. The finding of ULIRGs-LBGs at higher redshifts
suggests an evolution of the FIR emission of LBGs with cosmic time. In an
IRX- diagram, PACS-detected LBGs at z ~ 1 tend to be located around the
relation for local starburst similarly to other UV-selected PACS-detected
galaxies at their same redshift. Consequently, the dust-correction factors
obtained with their UV continuum slope allow to determine their total SFR,
unlike at higher redshifts. However, the dust attenuation derived from UV to
NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs
in age-dependent way: the overestimation factor is higher in younger galaxies.Comment: Accepted for publication in MNRA
Dust properties of Lyman break galaxies at
We explore from a statistical point of view the far-infrared (far-IR) and
sub-millimeter (sub-mm) properties of a large sample of LBGs (22,000) at z~3 in
the COSMOS field. The large number of galaxies allows us to split it in several
bins as a function of UV luminosity, UV slope, and stellar mass to better
sample their variety. We perform stacking analysis in PACS (100 and 160 um),
SPIRE (250, 350 and 500 um) and AzTEC (1.1 mm) images. Our stacking procedure
corrects the biases induced by galaxy clustering and incompleteness of our
input catalogue in dense regions. We obtain the full IR spectral energy
distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as
a function of UV luminosity, UV slope, and stellar mass. The average IRX is
roughly constant over the UV luminosity range, with a mean of 7.9 (1.8 mag).
However, it is correlated with UV slope, and stellar mass. We investigate using
a statistically-controlled stacking analysis as a function of (stellar mass, UV
slope) the dispersion of the IRX-UVslope and IRX-M* plane. Our results enable
us to study the average relation between star-formation rate (SFR) and stellar
mass, and we show that our LBG sample lies on the main sequence of star
formation at z~3.Comment: Accepted to A&A, 17 Pages, 14 Figures, 2 Table
New Young Star Candidates in BRC 27 and BRC 34
We used archival Spitzer Space Telescope mid-infrared data to search for
young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed
clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These
regions both appear to be actively forming young stars, perhaps triggered by
the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of
the 26 YSOs or YSO candidates identified in the literature, and identify 16 new
YSO candidates that appear to have IR excesses. In BRC 34, the one
literature-identified YSO has an IR excess, and we suggest 13 new YSO
candidates in this region, including a new Class I object. Considering the
entire ensemble, both BRCs are likely of comparable ages, within the
uncertainties of small number statistics and without spectroscopy to confirm or
refute the YSO candidates. Similarly, no clear conclusions can yet be drawn
about any possible age gradients that may be present across the BRCs.Comment: 54 pages, 19 figures, accepted by A
An Analysis of ALMA Deep Fields and the Perceived Dearth of High-z Galaxies
Deep, pencil-beam surveys from ALMA at 1.1-1.3mm have uncovered an apparent
absence of high-redshift dusty galaxies, with existing redshift distributions
peaking around . This has led to a perceived dearth of dusty
systems at , and the conclusion, according to some models, that the early
Universe was relatively dust-poor. In this paper, we extend the backward
evolution galaxy model described by Casey et al. (2018) to the ALMA regime (in
depth and area) and determine that the measured number counts and redshift
distributions from ALMA deep field surveys are fully consistent with
constraints of the infrared luminosity function (IRLF) at determined by
single-dish submillimeter and millimeter surveys conducted on much larger
angular scales (deg). We find that measured 1.1-1.3mm number
counts are most constraining for the measurement of the faint-end slope of the
IRLF at . Recent
studies have suggested that UV-selected galaxies at may be particularly
dust-poor, but we find their millimeter-wave emission cannot rule out
consistency with the Calzetti dust attenuation law even by assuming relatively
typical, cold-dust (K) SEDs. Our models suggest that
the design of ALMA deep fields requires substantial revision to constrain the
prevalence of early Universe obscured starbursts. The most promising
avenue for detection and characterization of such early dusty galaxies will
come from future ALMA 2mm blank field surveys covering a few hundred
arcmin and the combination of existing and future dual-purpose 3mm
datasets.Comment: 21 pages, 12 figures, accepted for publication in Ap
Large Population of ALMA Galaxies at z>6 with Very High [OIII]88um to [CII]158um Flux Ratios: Evidence of Extremely High Ionization Parameter or PDR Deficit?
We present our new ALMA observations targeting [OIII]88um, [CII]158um,
[NII]122um, and dust continuum emission for three Lyman break galaxies at
z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly
detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels,
and identify multi-band dust continuum emission in two of the three galaxies,
allowing us to estimate infrared luminosities and dust temperatures
simultaneously. In conjunction with previous ALMA observations for six galaxies
at z>6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[CII]
ratios of L[OIII]/L[CII]~3-20, ~10 times higher than z~0 galaxies. We also find
a positive correlation between the [OIII]/[CII] ratio and the Lya equivalent
width (EW) at the ~90% confidence level. We carefully investigate physical
origins of the high [OIII]/[CII] ratios at z=6-9 using Cloudy, and find that
high density of the interstellar medium, low C/O abundance ratio, and the
cosmic microwave background attenuation are responsible to only a part of the
z=6-9 galaxies. Instead, the observed high [OIII]/[CII] ratios are explained by
10-100 times higher ionization parameters or low photodissociation region (PDR)
covering fractions of 0-10%, both of which are consistent with our [NII]
observations. The latter scenario can be reproduced with a density bounded
nebula with PDR deficit, which would enhance the Lya, Lyman continuum, and C+
ionizing photons escape from galaxies, consistent with the [OIII]/[CII]-Lya EW
correlation we find.Comment: 20 pages, 18 figures, Accepted for publication in Ap
The IRX- relation: Insights from simulations
We study the relationship between the UV continuum slope and infrared excess
(IRX) predicted by performing dust radiative
transfer on a suite of hydrodynamical simulations of galaxies. Our suite
includes both isolated disk galaxies and mergers intended to be representative
of galaxies at both and . Our low-redshift isolated
disks and mergers often populate a region around the the locally calibrated
\citet[][M99]{M99} relation but move well above the relation during
merger-induced starbursts. Our high-redshift simulated galaxies are blue and
IR-luminous, which makes them lie above the M99 relation. The value of UV
continuum slope strongly depends on the dust type used in the radiative
transfer calculations: Milky Way-type dust leads to significantly more negative
(bluer) slopes compared with Small Magellanic Cloud-type dust. The effect on
due to variations in the dust composition with galaxy properties or
redshift can dominate over other sources of variations and is the
dominant model uncertainty. The dispersion in is anticorrelated with
specific star formation rate and tends to be higher for the
simulations. In the actively star-forming simulated galaxies, dust
attenuation dominates the dispersion in , whereas in the
simulations, the contributions of SFH variations and dust are similar. For
low-SSFR systems at both redshifts, SFH variations dominate the dispersion.
Finally, the simulated isolated disks and mergers both occupy a
region in the \irxbeta\ plane consistent with observed dusty
star-forming galaxies (DSFGs). Thus, contrary to some claims in the literature,
the blue colors of high-z DSFGs do not imply that they are short-lived
starbursts.Comment: 20 pages+a 4-page appendix, Accepted for publication at Ap
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