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Register a new userEstimating dust attenuation from galactic spectra. I. methodology and tests
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We develop a method to estimate the dust attenuation curve of galaxies from full spectral fitting of their optical spectra. Motivated from previous studies, we separate the small-scale features from the large-scale spectral shape, by performing a moving average method to both the observed spectrum and the simple stellar population model spectra. The intrinsic dust-free model spectrum is then derived by fitting the observed ratio of the small-scale to large-scale (S/L) components with the S/L ratios of the SSP models. The selective dust attenuation curve is then determined by comparing the observed spectrum with the dust-free model spectrum. One important advantage of this method is that the estimated dust attenuation curve is independent of the shape of theoretical dust attenuation curves. We have done a series of tests on a set of mock spectra covering wide ranges of stellar age and metallicity. We show that our method is able to recover the input dust attenuation curve accurately, although the accuracy depends slightly on signal-to-noise ratio of the spectra. We have applied our method to a number of edge-on galaxies with obvious dust lanes from the ongoing MaNGA survey, deriving their dust attenuation curves and $E(B-V)$ maps, as well as dust-free images in $g$, $r$, and $i$ bands. These galaxies show obvious dust lane features in their original images, which largely disappear after we have corrected the effect of dust attenuation. The vertical brightness profiles of these galaxies become axis-symmetric and can well be fitted by a simple model proposed for the disk vertical structure. Comparing the estimated dust attenuation curve with the three commonly-adopted model curves, we find that the Calzetti curve provides the best description of the estimated curves for the inner region of galaxies, while the Milky Way and SMC curves work better for the outer region.
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We investigate the dust attenuation in both stellar populations and ionized gas in kpc-scale regions in nearby galaxies, using integral field spectroscopy data from MaNGA MPL-9. We identify star-forming (HII) and diffuse ionized gas (DIG) regions from MaNGA datacubes. From the stacked spectrum of each region, we measure the stellar attenuation, $E(B-V)_{rm star}$, using the technique developed by Li et al.(2020), as well as the gas attenuation, $E(B-V)_{rm gas}$, from the Balmer decrement. We then examine the correlation of $E(B-V)_{rm star}$, $E(B-V)_{rm gas}$, $E(B-V)_{rm gas}-E(B-V)_{rm star}$ and $E(B-V)_{rm star}/E(B-V)_{rm gas}$ with 16 regional/global properties, and for regions with different $rm H{alpha}$ surface brightnesses ($Sigma_{rm Halpha}$). We find a stronger correlation between $E(B-V)_{rm star}$ and $E(B-V)_{rm gas}$ in regions of higher $Sigma_{rm Halpha}$. Luminosity-weighted age ($t_L$) is found to be the property that is the most strongly correlated with $E(B-V)_{rm star}$, and consequently with $E(B-V)_{rm gas}-E(B-V)_{rm star}$ and $E(B-V)_{rm star}/E(B-V)_{rm gas}$. At fixed $Sigma_{rm Halpha}$, $log_{10}t_L$ is linearly and negatively correlated with $E(B-V)_{rm star}/E(B-V)_{rm gas}$ at all ages. Gas-phase metallicity and ionization level are important for the attenuation in the gas. Our results indicate that the ionizing source for DIG regions is likely distributed in the outer-skirt of galaxies, while for HII regions our results can be well explained by the two-component dust model of Charlot & Fall (2000).
The [O III ] 5007 Planetary Nebula Luminosity Function (PNLF) is an established distance indicator that has been used for more than 30 years to measure the distances of galaxies out to ~15 Mpc. With the advent of the Multi-Unit Spectroscopic Explorer on the Very Large Telescope (MUSE) as an efficient wide-field integral field spectrograph, the PNLF method is due for a renaissance, as the spatial and spectral information contained in the instruments datacubes provides many advantages over classical narrow-band imaging. Here we use archival MUSE data to explore the potential of a novel differential emission-line filter (DELF) technique to produce spectrophotometry that is more accurate and more sensitive than other methods. We show that DELF analyses are superior to classical techniques in high surface brightness regions of galaxies and we validate the method both through simulations and via the analysis of data from two early-type galaxies (NGC 1380 and NGC 474) and one late-type spiral (NGC 628). We demonstrate that with adaptive optics support or under excellent seeing conditions, the technique is capable of producing precision (< 0.05 mag) [O III ] photometry out to distances of 40 Mpc while providing discrimination between planetary nebulae and other emission-line objects such as H II regions, supernova remnants, and background galaxies. These capabilities enable us to use MUSE to measure precise PNLF distances beyond the reach of Cepheids and the tip of the red giant branch method, and become an additional tool for constraining the local value of the Hubble constant.
Measuring the physical properties of galaxies such as redshift frequently requires the use of Spectral Energy Distributions (SEDs). SED template sets are, however, often small in number and cover limited portions of photometric color space. Here we present a new method to estimate SEDs as a function of color from a small training set of template SEDs. We first cover the mathematical background behind the technique before demonstrating our ability to reconstruct spectra based upon colors and then compare to other common interpolation and extrapolation methods. When the photometric filters and spectra overlap we show reduction of error in the estimated spectra of over 65% compared to the more commonly used techniques. We also show an expansion of the method to wavelengths beyond the range of the photometric filters. Finally, we demonstrate the usefulness of our technique by generating 50 additional SED templates from an original set of 10 and applying the new set to photometric redshift estimation. We are able to reduce the photometric redshifts standard deviation by at least 22.0% and the outlier rejected bias by over 86.2% compared to original set for z $leq$ 3.
We present a suite of 34 high-resolution cosmological zoom-in simulations consisting of thousands of halos up to M_halo~10^12 M_sun (M_star~10^10.5 M_sun) at z>=5 from the Feedback in Realistic Environments project. We post-process our simulations with a three-dimensional Monte Carlo dust radiative transfer code to study dust extinction, dust emission, and dust temperature within these simulated z>=5 galaxies. Our sample forms a tight correlation between infrared excess (IRX=F_IR/F_UV) and ultraviolet (UV)-continuum slope (beta_UV), despite the patchy, clumpy dust geometry shown in our simulations. We find that the IRX-beta_UV relation is mainly determined by the shape of the extinction curve and is independent of its normalization (set by the dust-to-gas ratio). The bolometric IR luminosity (L_IR) correlates with the intrinsic UV luminosity and the star formation rate (SFR) averaged over the past 10 Myr. We predict that at a given L_IR, the peak wavelength of the dust spectral energy distributions for z>=5 galaxies is smaller by a factor of 2 (due to higher dust temperatures on average) than at z=0. The higher dust temperatures are driven by higher specific SFRs and SFR surface densities with increasing redshift. We derive the galaxy UV luminosity functions (LFs) at z=5-10 from our simulations and confirm that a heavy attenuation is required to reproduce the observed bright-end UVLFs. We also predict the IRLFs and UV luminosity densities at z=5-10. We discuss the implications of our results on current and future observations probing dust attenuation and emission in z>=5 galaxies.
Galaxies rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates. While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-$z$, here we investigate attenuation in dusty, star-forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15--500,$mu$m in the COSMOS field, in particular making use of {it Herschel} imaging, and a rich dataset on local galaxies, we find a empirical variation in the relationship between rest-frame UV slope ($beta$) and ratio of infrared-to-ultraviolet emission ($L_{rm IR}/L_{rm UV}equiv,IRX$) as a function of infrared luminosity, or total star formation rate, SFR. Both locally and at high-$z$, galaxies above SFR$gt$50,M$_odot$,yr$^{-1}$ deviate from the nominal $IRX-beta$ relation towards bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-$z$ dropout searches of $ll1$% at $zlt4-10$, providing independent verification that contamination from very dusty foreground galaxies is low in LBG searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g. galaxies with $>50$,M$_odot$,yr$^{-1}$, are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at $zsim2$ exhibit steady-state star formation in secular disks.
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