Recent studies have found a significant evolution and scatter in the relationship between the UV spectral slope (βUV) and the infrared excess (IRX; LIR/LUV) at z > 4, suggesting different dust ...properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis, but it is poorly constrained in normal (main-sequence) star-forming z > 5 galaxies, where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogues of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) spectral energy distribution (SED) compared to average z < 4 galaxies that are used as priors in these studies. The blueshifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of metal-poor interstellar medium being optically thin to ultraviolet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests a 0.6 dex increase in total FIR luminosities, which removes some tension between the dust attenuation models and observations of the IRX−β relation at z > 5. Despite this, some galaxies still fall below the minimum IRX−β relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX−β diagram.
Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological ...simulations using the current cold dark matter model predict that these systems should descend from 'protoclusters'-early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 10(11) solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.
ABSTRACT
Although photometric redshifts (photo-z’s) are crucial ingredients for current and upcoming large-scale surveys, the high-quality spectroscopic redshifts currently available to train, ...validate, and test them are substantially non-representative in both magnitude and colour. We investigate the nature and structure of this bias by tracking how objects from a heterogeneous training sample contribute to photo-z predictions as a function of magnitude and colour, and illustrate that the underlying redshift distribution at fixed colour can evolve strongly as a function of magnitude. We then test the robustness of the galaxy–galaxy lensing signal in 120 deg2 of HSC–SSP DR1 data to spectroscopic completeness and photo-z biases, and find that their impacts are sub-dominant to current statistical uncertainties. Our methodology provides a framework to investigate how spectroscopic incompleteness can impact photo-z-based weak lensing predictions in future surveys such as LSST and WFIRST.
We report interferometric imaging of C II({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) and OH({sup 2}Π{sub 1/2} J = 3/2→1/2) emission toward the center of the galaxy protocluster associated with the z = ...5.3 submillimeter galaxy (SMG) AzTEC-3, using the Atacama Large (sub)Millimeter Array (ALMA). We detect strong C II, OH, and rest-frame 157.7 μm continuum emission toward the SMG. The C II({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of 9.7 × 10{sup 10} M {sub ☉}, and a star formation rate (SFR) surface density of Σ{sub SFR} = 530 M {sub ☉} yr{sup –1} kpc{sup –2}. This suggests that AzTEC-3 forms stars at Σ{sub SFR} approaching the Eddington limit for radiation pressure supported disks. We find that the OH emission is slightly blueshifted relative to the C II line, which may indicate a molecular outflow associated with the peak phase of the starburst. We also detect and dynamically resolve C II({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) emission over a scale of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs in the protocluster at ∼95 kpc projected distance from the SMG. These galaxies are not detected in the continuum, suggesting far-infrared SFRs of <18-54 M {sub ☉} yr{sup –1}, consistent with a UV-based estimate of 22 M {sub ☉} yr{sup –1}. The spectral energy distribution of these galaxies is inconsistent with nearby spiral and starburst galaxies, but resembles those of dwarf galaxies. This is consistent with expectations for young starbursts without significant older stellar populations. This suggests that these galaxies are significantly metal-enriched, but not heavily dust-obscured, 'normal' star-forming galaxies at z > 5, showing that ALMA can detect the interstellar medium in 'typical' galaxies in the very early universe.
We describe the CO Luminosity Density at High-z (COLDz) survey, the first spectral line deep field targeting CO(1-0) emission from galaxies at z = 1.95-2.85 and CO(2-1) at z = 4.91-6.70. The main ...goal of COLDz is to constrain the cosmic density of molecular gas at the peak epoch of cosmic star formation. By targeting both a wide (∼51 arcmin2) and a deep (∼9 arcmin2) area, the survey is designed to robustly constrain the bright end and the characteristic luminosity of the CO(1-0) luminosity function. An extensive analysis of the reliability of our line candidates and new techniques provide detailed completeness and statistical corrections as necessary to determine the best constraints to date on the CO luminosity function. Our blind search for CO(1-0) uniformly selects starbursts and massive main-sequence galaxies based on their cold molecular gas masses. Our search also detects CO(2-1) line emission from optically dark, dusty star-forming galaxies at z > 5. We find a range of spatial sizes for the CO-traced gas reservoirs up to ∼40 kpc, suggesting that spatially extended cold molecular gas reservoirs may be common in massive, gas-rich galaxies at z ∼ 2. Through CO line stacking, we constrain the gas mass fraction in previously known typical star-forming galaxies at z = 2-3. The stacked CO detection suggests lower molecular gas mass fractions than expected for massive main-sequence galaxies by a factor of ∼3-6. We find total CO line brightness at ∼34 GHz of 0.45 0.2 K, which constrains future line intensity mapping and CMB experiments.
Abstract
We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, ...using ≃ 1250 objects ($\mathit {NB387}\le 25.5$) in four separate fields of ≃ 1 deg2 in total. With an average stellar mass of 10.2 ± 1.8 × 108 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr−1, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} \times 10^{10}{\,\,}M_{\odot }$ with an effective bias of $1.22^{+0.16}_{-0.18}$, which is lower than that of z ∼ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H i gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press–Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself.
Machine-learning (ML) algorithms will play a crucial role in studying the large data sets delivered by new facilities over the next decade and beyond. Here, we investigate the capabilities and limits ...of such methods in finding galaxies with brightness-variable active galactic nuclei (AGNs). Specifically, we focus on an unsupervised method based on self-organizing maps (SOM) that we apply to a set of nonparametric variability estimators. This technique allows us to maintain domain knowledge and systematics control while using all the advantages of ML. Using simulated light curves that match the noise properties of observations, we verify the potential of this algorithm in identifying variable light curves. We then apply our method to a sample of ∼8300 WISE color-selected AGN candidates in Stripe 82, in which we have identified variable light curves by visual inspection. We find that with ML we can identify these variable classified AGN with a purity of 86% and a completeness of 66%, a performance that is comparable to that of more commonly used supervised deep-learning neural networks. The advantage of the SOM framework is that it enables not only a robust identification of variable light curves in a given data set, but it is also a tool to investigate correlations between physical parameters in multidimensional space-such as the link between AGN variability and the properties of their host galaxies. Finally, we note that our method can be applied to any time-sampled light curve (e.g., supernovae, exoplanets, pulsars, and other transient events).
LARGE-SCALE STRUCTURE AROUND A z = 2.1 CLUSTER Hung (洪肇伶), Chao-Ling; Casey, Caitlin M.; Chiang, Yi-Kuan ...
Astrophysical journal/The Astrophysical journal,
08/2016, Letnik:
826, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with large-scale environments is less clear at . We present a search of large-scale ...structure around a galaxy cluster core at z = 2.095 using a set of spectroscopically confirmed galaxies. We find that both color-selected star-forming galaxies (SFGs) and dusty star-forming galaxies (DSFGs) show significant overdensities around the z = 2.095 cluster. A total of eight DSFGs (including three X-ray luminous active galactic nuclei, AGNs) and 34 SFGs are found within a 10′ radius (corresponds to ∼15 cMpc at ) from the cluster center and within a redshift range of , which leads to galaxy overdensities of and . The cluster core and the extended DSFG- and SFG-rich structures together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large-scale structure while the more mature core may begin to virialize. Our finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare sources indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 m images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.
Abstract To study the role of environment in galaxy evolution, we reconstruct the underlying density field of galaxies based on COSMOS2020 (The Farmer catalog) and provide the density catalog for a ...magnitude-limited ( K s < 24.5) sample of ∼210,000 galaxies at 0.4 < z < 5 within the COSMOS field. The environmental densities are calculated using a weighted kernel density estimation approach with the choice of a von Mises–Fisher kernel, an analog of the Gaussian kernel for periodic data. Additionally, we make corrections for the edge effect and masked regions in the field. We utilize physical properties extracted by LePhare to investigate the connection between star formation activity and the environmental density of galaxies in six mass-complete subsamples at different cosmic epochs within 0.4 < z < 4. Our findings confirm a strong anticorrelation between star formation rate (SFR)/specific SFR (sSFR) and environmental density out to z ∼ 1.1. At 1.1 < z < 2, there is no significant correlation between SFR/sSFR and density. At 2 < z < 4, we observe a reversal of the SFR/sSFR–density relation such that both SFR and sSFR increase by a factor of ∼10 with increasing density contrast, δ , from −0.4 to 5. This observed reversal at higher redshifts supports the scenario where an increased availability of gas supply, along with tidal interactions and a generally higher star formation efficiency in dense environments, could potentially enhance star formation activity in galaxies located in rich environments at z > 2.
Abstract
We present a new method based on information theory to find the optimal number of bands required to measure the physical properties of galaxies with desired accuracy. As a proof of concept, ...using the recently updated COSMOS catalog (COSMOS2020), we identify the most relevant wave bands for measuring the physical properties of galaxies in a Hawaii Two-0- (H20) and UVISTA-like survey for a sample of
i
< 25 AB mag galaxies. We find that with the available
i
-band fluxes,
r
,
u
, IRAC/
ch
2, and
z
bands provide most of the information regarding the redshift with importance decreasing from
r
band to
z
band. We also find that for the same sample, IRAC/
ch
2,
Y
,
r
, and
u
bands are the most relevant bands in stellar-mass measurements with decreasing order of importance. Investigating the intercorrelation between the bands, we train a model to predict UVISTA observations in near-IR from H20-like observations. We find that magnitudes in the
YJH
bands can be simulated/predicted with an accuracy of 1
σ
mag scatter ≲0.2 for galaxies brighter than 24 AB mag in near-IR bands. One should note that these conclusions depend on the selection criteria of the sample. For any new sample of galaxies with a different selection, these results should be remeasured. Our results suggest that in the presence of a limited number of bands, a machine-learning model trained over the population of observed galaxies with extensive spectral coverage outperforms template fitting. Such a machine-learning model maximally comprises the information acquired over available extensive surveys and breaks degeneracies in the parameter space of template fitting inevitable in the presence of a few bands.
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