Abstract
Dust temperature is an important property of the interstellar medium (ISM) of galaxies. It is required when converting (sub)millimetre broad-band flux to total infrared luminosity (LIR), and ...hence star formation rate, in high-redshift galaxies. However, different definitions of dust temperatures have been used in the literature, leading to different physical interpretations of how ISM conditions change with, e.g. redshift and star formation rate. In this paper, we analyse the dust temperatures of massive ($M_{\rm star} \gt 10^{10}\, \mathrm{M}_{\odot }$) $z$ = 2–6 galaxies with the help of high-resolution cosmological simulations from the Feedback in Realistic Environments (fire) project. At $z$ ∼ 2, our simulations successfully predict dust temperatures in good agreement with observations. We find that dust temperatures based on the peak emission wavelength increase with redshift, in line with the higher star formation activity at higher redshift, and are strongly correlated with the specific star formation rate. In contrast, the mass-weighted dust temperature, which is required to accurately estimate the total dust mass, does not strongly evolve with redshift over $z$ = 2–6 at fixed IR luminosity but is tightly correlated with LIR at fixed $z$. We also analyse an ‘equivalent’ dust temperature for converting (sub)millimetre flux density to total IR luminosity, and provide a fitting formula as a function of redshift and dust-to-metal ratio. We find that galaxies of higher equivalent (or higher peak) dust temperature (‘warmer dust’) do not necessarily have higher mass-weighted temperatures. A ‘two-phase’ picture for interstellar dust can explain the different scaling relations of the various dust temperatures.
We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 0.001. This is the highest-redshift unlensed DSFG (and fourth most ...distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 m to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M yr−1 and 220 M yr−1, total molecular hydrogen gas mass of (1.7 0.4) × 1011M , dust mass of (1.3 0.3) × 109M , and stellar mass of ( ) × 109M . The total halo mass, (3.3 0.8) × 1012M , is predicted to exceed 1015M by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τdepl = 40−80 Myr, converting its large molecular gas reservoir (gas fraction of ) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times ( 1 Gyr).
We study the effects of the local environment on the molecular gas content of a large sample of log(M*/M ) 10 star-forming and starburst galaxies with specific star formation rates (sSFRs) on and ...above the main sequence (MS) to z ∼ 3.5. ALMA observations of the dust continuum in the COSMOS field are used to estimate molecular gas masses at z 0.5-3.5. We also use a local universe sample from the ALFALFA H i survey after converting it into molecular masses. The molecular mass (MISM) scaling relation shows a dependence on z, M*, and sSFR relative to the MS, but no dependence on environmental overdensity Δ(MISM ∝ Δ0.03). Similarly, gas mass fraction (fgas) and depletion timescale (τ) show no environmental dependence to z ∼ 3.5. At ∼ 1.8, the average , , and in densest regions is (1.6 0.2) × 1011 M , 55 2%, and 0.8 0.1 Gyr, respectively, similar to those in the lowest density bin. Independent of the environment, fgas decreases and τ increases with increasing cosmic time. Cosmic molecular mass density ( ) in the lowest density bins peaks at z ∼ 1-2, and this peak happens at z < 1 in densest bins. This differential evolution of across environments is likely due to the growth of the large-scale structure with cosmic time. Our results suggest that the molecular gas content and the subsequent star formation activity of log(M*/M ) 10 star-forming and starburst galaxies is primarily driven by internal processes, and not by their local environment since z ∼ 3.5.
Abstract Recent long-wavelength observations on the thermal dust continuum suggest that the Rayleigh–Jeans tail can be used as a time-efficient quantitative probe of the dust and interstellar medium ...(ISM) mass in high-z galaxies. We use high-resolution cosmological simulations from the Feedback in Realistic Environment (FIRE) project to analyse the dust emission of M* ≳ 1010 M⊙ galaxies at z= 2–4. Our simulations (MassiveFIRE) explicitly include various forms of stellar feedback, and they produce the stellar masses and star formation rates of high-z galaxies in agreement with observations. Using radiative transfer modelling, we show that sub-millimetre (sub-mm) luminosity and molecular ISM mass are tightly correlated and that the overall normalization is in quantitative agreement with observations. Notably, sub-mm luminosity traces molecular ISM mass even during starburst episodes as dust mass and mass-weighted temperature evolve only moderately between z = 4 and z = 2, including during starbursts. Our finding supports the empirical approach of using broadband sub-mm flux as a proxy for molecular gas content in high-z galaxies. We thus expect single-band sub-mm observations with ALMA to dramatically increase the sample size of high-z galaxies with reliable ISM masses in the near future.
We have measured the fraction of bars in nearby spiral galaxies using near-infrared J, H, and K sub(S) images of 151 spiral galaxies from 2MASS. This local sample provides an anchor for the study of ...the evolution of the bar fraction and bar properties with redshift. We identify bars by analyzing the full two-dimensional light distribution and requiring a combined ellipticity and position angle signature. The combined "bar signature" is found in 59% of the galaxies. The bar fraction increases to 67% when we include "candidate" bars, where only the ellipticity signature is present. We also measure the change in the bar fraction as a function of bar size; the bar fraction drops to 31% for bars with a semimajor axis larger than 4 kpc. We find that infrared bars typically extend to one-third of the galactic disk, with a deprojected relative size of (a sub(bar)/R sub(25)) 6 0.3 c 0.2. Early-type spirals host significantly larger bars, consistent with earlier studies. The (a sub(bar)/R sub(25)) is 2 times larger in early types man in late types. The typical bar axial ratio (b/a) is 60.5, with a weak trend of higher axial ratios for larger bars.
We report the spectroscopic confirmation of a new protocluster in the COSMOS field at z ∼ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as an overdensity of narrowband selected H emitting ...candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both H (∼1.47-1.81 m) and K (∼1.92-2.40 m) bands (∼1.5 hr each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N > 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift and a line-of-sight velocity dispersion of zmean = 2.23224 0.00101 and los = 645 69 km s−1 for this protocluster, respectively. Assuming virialization and spherical symmetry for the system, we estimate a total mass of Mvir ∼ (1-2) ×1014M for the structure. We evaluate a number density enhancement of δg ∼ 7 for this system and we argue that the structure is likely not fully virialized at z ∼ 2.2. However, in a spherical collapse model, δg is expected to grow to a linear matter enhancement of ∼1.9 by z = 0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of Mdyn(z = 0) ∼ 9.2 × 1014M by now. This observationally efficient confirmation suggests that large narrowband emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies.
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.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The underlying distribution of galaxies’ dust spectral energy distributions (SEDs) (i.e., their spectra reradiated by dust from rest-frame ∼3
μ
m to 3 mm) remains relatively unconstrained ...owing to a dearth of far-IR/(sub)millimeter data for large samples of galaxies. It has been claimed in the literature that a galaxy’s dust temperature—observed as the wavelength where the dust SED peaks (
λ
peak
)—is traced most closely by its specific star formation rate (sSFR) or parameterized “distance” to the SFR–
M
⋆
relation (the galaxy “main sequence”). We present 024 resolved 870
μ
m ALMA dust continuum observations of seven
z
= 1.4–4.6 dusty star-forming galaxies chosen to have a large range of well-constrained luminosity-weighted dust temperatures. We also draw on similar-resolution dust continuum maps from a sample of ALESS submillimeter galaxies from Hodge et al (2016). We constrain the physical scales over which the dust radiates and compare those measurements to characteristics of the integrated SED. We confirm significant correlations of
λ
peak
with both
L
IR
(or SFR) and Σ
IR
(∝SFR surface density). We investigate the correlation between log
10
(
λ
peak
) and log
10
(Σ
IR
) and find the relation to hold as would be expected from the Stefan–Boltzmann law, or the effective size of an equivalent blackbody. The correlations of
λ
peak
with sSFR and distance from the SFR–
M
⋆
relation are less significant than those for Σ
IR
or
L
IR
; therefore, we conclude that the more fundamental tracer of galaxies’ luminosity-weighted integrated dust temperatures are indeed their star formation surface densities in line with local universe results, which relate closely to the underlying geometry of dust in the interstellar medium.
We present 90 cm Very Large Array imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0arcsec × 6.0arcsec angular resolution with an average rms of 0.5 mJy beam−1. The ...extracted catalogue contains 182 sources (down to 5.5σ), 30 of which are multicomponent sources. Using Monte Carlo artificial source simulations, we derive the completeness of the catalogue, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV–NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei. The average 90–20 cm spectral index (S
ν ∝ να, where S
ν is the flux density at frequency ν and α the spectral index) of our 90 cm selected sources is −0.70, with an interquartile range from −0.90 to −0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than −1 all lie at z ≳ 1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z ≳ 1).
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