ABSTRACT We study the effects of the local environment and stellar mass on galaxy properties using a mass complete sample of quiescent and star-forming systems in the COSMOS field at . We show that ...at the median star formation rate (SFR) and specific SFR (sSFR) of all galaxies depend on the environment, but they become independent of the environment at z 1. However, we find that only for star-forming galaxies, the median SFR and sSFR are similar in different environments regardless of redshift and stellar mass. We find that the quiescent fraction depends on the environment at z 1 and on stellar mass out to z ∼ 3. We show that at z 1 galaxies become quiescent faster in denser environments and that the overall environmental quenching efficiency increases with cosmic time. Environmental and mass quenching processes depend on each other. At z 1 denser environments more efficiently quench galaxies with higher masses (log( ) 10.7), possibly due to a higher merger rate of massive galaxies in denser environments. We also show that mass quenching is more efficient in denser regions. We show that the overall mass quenching efficiency ( ) for more massive galaxies (log( ) 10.2) rises with cosmic time until z ∼ 1 and then flattens out. However, for less massive galaxies, the rise in continues to the present time. Our results suggest that environmental quenching is only relevant at z 1 and is likely a fast process, whereas mass quenching is the dominant mechanism at z 1 with a possible stellar feedback physics.
On the dust temperatures of high-redshift galaxies Liang, Lichen; Feldmann, Robert; Kereš, Dušan ...
Monthly notices of the Royal Astronomical Society,
10/2019, Letnik:
489, Številka:
1
Journal Article
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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.
ABSTRACT We analyze radial and azimuthal variations of the phase balance between the molecular and atomic interstellar medium (ISM) in the Milky Way (MW) using archival CO(J = 1-0) and HI 21 cm data. ...In particular, the azimuthal variations-between the spiral arm and interarm regions-are analyzed without any explicit definition of the spiral arm locations. We show that the molecular gas mass fraction, i.e., , varies predominantly in the radial direction: starting from at the center, remaining to and decreasing to ∼10%-20% at when averaged over the whole disk thickness (from ∼100% to 60%, then to ∼50% in the midplane). Azimuthal, arm-interarm variations are secondary: only in the globally molecule-dominated inner MW, but becoming larger, ∼40%-50%, in the atom-dominated outskirts. This suggests that in the inner MW the gas remains highly molecular ( ) as it moves from an interarm region into a spiral arm and back into the next interarm region. Stellar feedback does not dissociate molecules much, and the coagulation and fragmentation of molecular clouds dominate the evolution of the ISM at these radii. The trend differs in the outskirts where the gas phase is globally atomic ( ). The HI and H2 phases cycle through spiral arm passage there. These different regimes of ISM evolution are also seen in external galaxies (e.g., the LMC, M33, and M51). We explain the radial gradient of using a simple flow continuity model. The effects of spiral arms on this analysis are illustrated in the Appendix.
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.
We use a mass complete (log( ) ) sample of galaxies with accurate photometric redshifts in the COSMOS field to construct the density field and the cosmic web to z = 1.2. The comic web extraction ...relies on the density field Hessian matrix and breaks the density field into clusters, filaments, and the field. We provide the density field and cosmic web measures to the community. We show that at z 0.8, the median star formation rate (SFR) in the cosmic web gradually declines from the field to clusters and this decline is especially sharp for satellites (∼1 dex versus ∼0.5 dex for centrals). However, at z 0.8, the trend flattens out for the overall galaxy population and satellites. For star-forming (SF) galaxies only, the median SFR is constant at z 0.5 but declines by ∼0.3-0.4 dex from the field to clusters for satellites and centrals at z 0.5. We argue that for satellites, the main role of the cosmic web environment is to control their SF fraction, whereas for centrals, it is mainly to control their overall SFR at z 0.5 and to set their fraction at z 0.5. We suggest that most satellites experience a rapid quenching mechanism as they fall from the field into clusters through filaments, whereas centrals mostly undergo a slow environmental quenching at z 0.5 and a fast mechanism at higher redshifts. Our preliminary results highlight the importance of the large-scale cosmic web on galaxy evolution.
ABSTRACT
The infrared (IR) spectral energy distributions (SEDs) of main-sequence galaxies in the early Universe (z > 4) is currently unconstrained as IR continuum observations are time-consuming and ...not feasible for large samples. We present Atacama Large Millimetre Array Band 8 observations of four main-sequence galaxies at z ∼ 5.5 to study their IR SED shape in detail. Our continuum data (rest-frame 110 $\rm \mu m$, close to the peak of IR emission) allows us to constrain luminosity-weighted dust temperatures and total IR luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame $100\, {\rm \mu m}$. The derived dust peak temperatures at z ∼ 5.5 ($30\!-\!43\, {\rm K}$) are elevated compared to average local galaxies, however, $\sim 10\, {\rm K}$ below what would be predicted from an extrapolation of the trend at z < 4. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the IR SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the $850{\hbox{-}}{\rm \mu m}$ dust continuum, we derive molecular gas masses between 1010 and $10^{11}\, {\rm M_{\odot }}$ and gas fractions (gas over total mass) of $30\!-\!80{{\ \rm per\ cent}}$ (gas depletion times of $100\!-\!220\, {\rm Myr}$). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe.
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 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.
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