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Register a new userThe Resolved Distributions of Dust Mass and Temperature in Local Group Galaxies
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We utilize archival far-infrared maps from the Herschel Space Observatory in four Local Group galaxies (Small and Large Magellanic Clouds, M31, and M33). We model their Spectral Energy Distribution (SED) from 100 to 500 $mu$m using a single-temperature modified blackbody emission with a fixed emissivity index of $beta = 1.8$. From the best-fit model, we derive the dust temperature, $T_{rm d}$, and the dust mass surface density, $Sigma_{rm d}$, at 13 parsec resolution for SMC and LMC, and at 167 parsec resolution for all targets. This measurement allows us to build the distribution of dust mass and luminosity as functions of dust temperature and mass surface density. We compare those distribution functions among galaxies and between regions in a galaxy. We find that LMC has the highest mass-weighted average $T_{rm d}$, while M31 and M33 have the lowest mass-weighted average $T_{rm d}$. Within a galaxy, star forming regions have higher $T_{rm d}$ and $Sigma_{rm d}$ relative to the overall distribution function, due to more intense heating by young stars and higher gas mass surface density. When we degrade the resolutions to mimic distant galaxies, the mass-weighted mean temperature gets warmer as the resolution gets coarser, meaning the temperature derived from unresolved observation is systematically higher than that in highly resolved observation. As an implication, the total dust mass is lower (underestimated) in coarser resolutions. This resolution-dependent effect is more prominent in clumpy star-forming galaxies (SMC, LMC, and M33), and less prominent in more quiescent massive spiral (M31).
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We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a stars lifetime on the asymptotic giant branch.
We combine high-resolution ALMA and HST/CANDELS observations of 20 submillimeter galaxies (SMGs) predominantly from the AS2UDS survey at z~2 with bright rest-frame optical counterparts (Ks < 22.9) to investigate the resolved structural properties of their dust and stellar components. We derive two-dimensional stellar-mass distributions that are inferred from spatial mass-to-light ratio (M/L) corrections based on rest-frame optical colors. Due to the high central column densities of dust in our SMGs, our mass distributions likely represent a lower limit to the true central mass density. The centroid positions between the inferred stellar-mass and the dust distributions agree within 1.1 kpc, indicating an overall good spatial agreement between the two components. The majority of our sources exhibit compact dust configurations relative to the stellar component (with a median ratio of effective radii Re,dust/Re,Mstar = 0.6). This ratio does not change with specific star-formation rate (sSFR) over the factor of 30 spanned by our targets, sampling the locus of normal main sequence galaxies up to the starburst regime, log(sSFR/sSFRMS) > 0.5. Our results imply that massive SMGs are experiencing centrally enhanced star formation unlike typical spiral galaxies in the local Universe. The sizes and stellar densities of our SMGs are in agreement with those of the passive population at z=1.5, consistent with these systems being the descendants of z~2 SMGs.
Estimating the temperature and mass of dust in high-$z$ galaxies is essential for discussions of the origin of dust in the early Universe. However, this suffers from limited sampling of the infrared spectral-energy distribution. Here we present an algorithm for deriving the temperature and mass of dust in a galaxy, assuming dust to be in radiative equilibrium. We formulate the algorithm for three geometries: a thin spherical shell, a homogeneous sphere, and a clumpy sphere. We also discuss effects of the mass absorption coefficients of dust at ultraviolet and infrared wavelengths, $kappa_{rm UV}$ and $kappa_{rm IR}$, respectively. As an example, we apply the algorithm to a normal, dusty star-forming galaxy at $z=7.5$, A1689zD1, for which three data points in the dust continuum are available. Using $kappa_{rm UV}=5.0times10^4$ cm$^2$ g$^{-1}$ and $kappa_{rm IR}=30(lambda/100mu m)^{-beta}$ cm$^2$ g$^{-1}$ with $beta=2.0$, we obtain dust temperatures of 38--70~K and masses of $10^{6.5-7.3}$ M$_odot$ for the three geometries considered. We obtain similar temperatures and masses from just a single data point in the dust continuum, suggesting the usefulness of the algorithm for high-$z$ galaxies with limited infrared observations. In the clumpy-sphere case, the temperature becomes equal to that of the usual modified black-body fit, because an additional parameter describing the clumpiness works as an adjuster. The best-fit clumpiness parameter is $xi_{rm cl}=0.1$, corresponding to $sim10$% of the volume filling factor of the clumps in this high-$z$ galaxy if the clump size is $sim10$ pc, similar to that of giant molecular clouds in the local Universe.
We present infrared views of the environmental effects on the dust properties in star-forming (SF) galaxies at z ~ 0, using the AKARI Far-Infrared Surveyor (FIS) all-sky map and the large spectroscopic galaxy sample from Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We restrict the sample to those within the redshift range of 0.05 < z < 0.07 and the stellar mass range of 9.2 < log_10 (M_star/M_solar). We select SF galaxies based on their H_alpha equivalent width (EW_Ha> 4 A) and emission line flux ratios. We perform far-infrared (FIR) stacking analyses by splitting the SDSS SF galaxy sample according to their stellar mass, specific SFR (SSFR_SDSS), and environment. We derive total infrared luminosity (LIR) for each subsample using the average flux densities at WIDE-S (90 micron) and WIDE-L (140 micron) bands, and then compute IR-based SFR (SFR_IR) from L_IR. We find a mild decrease of IR- based SSFR (SSFR_IR) amongst SF galaxies with increasing local density (~0.1-dex level at maximum), which suggests that environmental effects do not instantly shut down the SF activity in galaxies. We also derive average dust temperature (T_dust) using the flux densities at 90 micron and 140 micron bands. We confirm a strong positive correlation between T_dust and SSFR_IR, consistent with recent studies. The most important finding of this study is that we find a marginal trend that T_dust increases with increasing environmental galaxy density. Although the environmental trend is much milder than the SSFR-T_dust correlation, our results suggest that the environmental density may affect the dust temperature in SF galaxies, and that the physical mechanism which is responsible for this phenomenon is not necessarily specific to cluster environments because the environmental dependence of T_dust holds down to relatively low-density environments.
While many tensions between Local Group (LG) satellite galaxies and LCDM cosmology have been alleviated through recent cosmological simulations, the spatial distribution of satellites remains an important test of physical models and physical versus numerical disruption in simulations. Using the FIRE-2 cosmological zoom-in baryonic simulations, we examine the radial distributions of satellites with Mstar > 10^5 Msun around 8 isolated Milky Way- (MW) mass host galaxies and 4 hosts in LG-like pairs. We demonstrate that these simulations resolve the survival and physical destruction of satellites with Mstar >~ 10^5 Msun. The simulations broadly agree with LG observations, spanning the radial profiles around the MW and M31. This agreement does not depend strongly on satellite mass, even at distances <~ 100 kpc. Host-to-host variation dominates the scatter in satellite counts within 300 kpc of the hosts, while time variation dominates scatter within 50 kpc. More massive host galaxies within our sample have fewer satellites at small distances, likely because of enhanced tidal destruction of satellites via the baryonic disks of host galaxies. Furthermore, we quantify and provide fits to the tidal depletion of subhalos in baryonic relative to dark matter-only simulations as a function of distance. Our simulated profiles imply observational incompleteness in the LG even at Mstar >~ 10^5 Msun: we predict 2-10 such satellites to be discovered around the MW and possibly 6-9 around M31. To provide cosmological context, we compare our results with the radial profiles of satellites around MW analogs in the SAGA survey, finding that our simulations are broadly consistent with most SAGA systems.
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