分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Some studies suggest that the dust temperatures ($T_\mathrm{d}$) in high-redshift ($z\gtrsim 5$) Lyman break galaxies (LBGs) are high. However, possible observational bias in $T_\mathrm{d}$ is yet to be understood. Thus, we perform a simple test using random realizations of LBGs with various stellar masses, dust temperatures, and dust-to-stellar mass ratios, and examine how the sample detected by ALMA is biased in terms of $T_\mathrm{d}$. We show that ALMA tends to miss high-$T_\mathrm{d}$ objects even at total dust luminosity. LBGs are, however, basically selected by the stellar UV luminosity. The dust-temperature bias in a UV-selected sample is complicated because of the competing effects between high $T_\mathrm{d}$ and low dust abundance. For ALMA Band 6, there is no tendency of high-$T_\mathrm{d}$ LBGs being more easily detected in our experiment. Thus, we suggest that the observed trend of high $T_\mathrm{d}$ in $z\gtrsim 5$ LBGs is real. We also propose that the 450 $\mu$m band is useful in further clarifying the dust temperatures. To overcome the current shallowness of 450 $\mu$m observations, we examine a future Antarctic 30-m class telescope with a suitable atmospheric condition for wavelengths $\lesssim 450~\mu$m, where the detection is not confusion-limited. We find that, with this telescope, an $L_\mathrm{IR}$-selected sample with $\log(L_\mathrm{IR}/\mathrm{L}_{\odot})>11$ is constructed for $z\gtrsim 5$, and detection in the intermediate-$M_\star$ (stellar mass) range [$9<\log (M_\star /M_{\odot})<9.5$] is much improved, especially at high $T_\mathrm{d}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： To understand how the evolution of grain size distribution in galaxies affects observed dust properties, we apply a post-processing dust evolution model to galaxy merger trees from the IllustrisTNG cosmological hydrodynamical simulation. Our dust model includes stellar dust production, sputtering in hot gas, dust growth by accretion and coagulation in the dense interstellar medium (ISM), and shattering in the diffuse ISM. We decompose the grain size distribution into different dust species depending on the elemental abundances and the dense ISM fraction given by the simulation. In our previous work, we focused on Milky Way (MW) analogs and reproduced the observed MW extinction curve. In this study, we compute dust spectral energy distributions (SEDs) for the MW analogues. Our simulated SEDs broadly reproduce the observed MW SED within their dispersion and so does the observational data of nearby galaxies, although they tend to underpredict the MW SED at short wavelengths where emission is dominated by polycyclic aromatic hydrocarbons (PAHs). We find that metallicity and dense gas fraction are the most critical factors for the SED shape, through their influence on coagulation and shattering.The overall success of our models in reproducing the MW SED further justifies the dust evolution processes included in the model and predicts the dispersion in the SEDs caused by the variety in the assembly history. We also show that the most significant increase in the dust SED occurs between redshifts $z\sim 3$ and 2 in the progenitors of the simulated MW-like galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dust emission from high-redshift galaxies gives us a clue to the origin and evolution of dust in the early Universe. Previous studies have shown that different sources of dust (stellar dust production and dust growth in dense clouds) predict different ultraviolet (UV) extinction curves for galaxies at $z\sim 7$ but that the observed attenuation curves depend strongly on the geometry of dust and star distributions. Thus, we perform radiative transfer calculations under the dust-stars geometries computed by a cosmological hydrodynamic simulation (IllustrisTNG). This serves to investigate the dust attenuation curves predicted from `realistic' geometries. We choose objects with stellar mass and star formation rate appropriate for Lyman break galaxies at $z\sim 7$. We find that the attenuation curves are very different from the original extinction curves in most of the galaxies. This makes it difficult to constrain the dominant dust sources from the observed attenuation curves. We further include infrared dust emission in the analysis and plot the infrared excess (IRX)-UV spectral slope ($\beta$) diagram. We find that different sources of dust cause different IRX-$\beta$ relations for the simulated galaxies. In particular, if dust growth is the main source of dust, a variation of dust-to-metal ratio causes a more extended sequence with smaller IRX in the IRX-$\beta$ diagram. Thus, the comprehensive analysis of the abundances of dust and metals, the UV slope, and the dust emission could provide a clue to the dominant dust sources in the Universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
I-Da Chiang
Hiroyuki Hirashita
Jeremy Chastenet
Eric W. Koch
Adam K. Leroy
Erik Rosolowsky
Karin M. Sandstrom
Amy Sardone
Jiayi Sun
Thomas G. Williams
摘要： We investigate how the dust temperature is affected by local environmental quantities, especially dust surface density ($\Sigma_\mathrm{dust}$), dust-to-gas ratio (D/G) and interstellar radiation field. We compile multi-wavelength observations in 46 nearby galaxies, uniformly processed with a common physical resolution of $2~$kpc. A physical dust model is used to fit the infrared dust emission spectral energy distribution (SED) observed with WISE and Herschel. The star formation rate (SFR) is traced with GALEX ultraviolet data corrected by WISE infrared. We find that the dust temperature correlates well with the SFR surface density ($\Sigma_{\rm SFR}$), which traces the radiation from young stars. The dust temperature decreases with increasing D/G at fixed $\Sigma_{\rm SFR}$ as expected from stronger dust shielding at high D/G, when $\Sigma_\mathrm{SFR}$ is higher than $\sim 2\times 10^{-3}~\rm M_\odot~yr^{-1}~kpc^{-2}$. These measurements are in good agreement with the dust temperature predicted by our proposed analytical model. Below this range of $\Sigma_\mathrm{SFR}$, the observed dust temperature is higher than the model prediction and is only weakly dependent on D/G, which is possibly due to the dust heating from old stellar population or the variation of SFR within the past $10^{10}~$yr. Overall, the dust temperature as a function of $\Sigma_\mathrm{SFR}$ and $\Sigma_\mathrm{dust}$ predicted by our analytical model is consistent with observations. We also notice that at fixed gas surface density, $\Sigma_{\rm SFR}$ tends to increase with D/G, i.e. we can empirically modify the Kennicutt-Schmidt law with a dependence on D/G to better match observations.
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