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Register a new userMCSED: A flexible spectral energy distribution fitting code and its application to $z sim 2$ emission-line galaxies
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We present MCSED, a new spectral energy distribution (SED)-fitting code, which mates flexible stellar evolution calculations with the Markov Chain Monte Carlo algorithms of the software package emcee. MCSED takes broad, intermediate, and narrow-band photometry, emission-line fluxes, and/or absorption line spectral indices, and returns probability distributions and co-variance plots for all model parameters. MCSED includes a variety of dust attenuation curves with parameters for varying the UV slopes and bump strengths, a prescription for continuum and PAH emission from dust, models for continuum and line emission from ionized gas, options for fixed and variable stellar metallicity, and a selection of star formation rate (SFR) histories. The code is well-suited for exploring parameter inter-dependencies in sets of galaxies with known redshifts, for which there is multi-band photometry and/or spectroscopy. We apply MCSED to a sample of $sim2000$ $1.90<z<2.35$ galaxies in the five CANDELS fields, which were selected via their strong [O III] $lambda5007$ emission, and explore the systematic behavior of their SEDs. We find the galaxies become redder with stellar mass, due to both increasing internal attenuation and a greater population of older stars. The slope of the UV extinction curve also changes with stellar mass, and at least some galaxies exhibit an extinction excess at 2175 Angstroms. Finally, we demonstrate that below $Mlesssim10^9,M_{odot}$), the shape of the star-forming galaxy main sequence is highly dependent on the galaxies assumed SFR history, as calculations which assume a constant SFR produce stellar masses that are $sim1$ dex smaller than those found using more realistic SFR histories.
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We perform SED fitting analysis on a COSMOS sample covering UV-to-FIR wavelengths with emission lines from the FMOS survey. The sample of 182 objects with H$alpha$ and [OIII]$lambda5007$ emission spans over a range of $1.40<rm{z}<1.68$. We obtain robust estimates of stellar mass ($10^{9.5}-10^{11.5}~rm{M_odot}$) and SFR ($10^1-10^3~rm{M_odot}~rm{yr}^{-1}$) from the Bayesian analysis with CIGALE fitting continuum photometry and H$alpha$. We obtain a median attenuation of A$_rm{Halpha}=1.16pm0.19$ mag and A$_rm{[OIII]}=1.41pm0.22$ mag. H$alpha$ and [OIII]$lambda5007$ attenuations are found to increase with stellar mass, confirming previous findings. A difference of $57$% in the attenuation experienced by emission lines and continuum is found in agreement with the lines being more attenuated than the continuum. New CLOUDY HII-region models in CIGALE enable good fits of H$alpha$, H$beta$, [OIII]$lambda5007$ emission lines with differences smaller than $0.2$ dex. Fitting [NII]$lambda6584$ line is challenging due to well-known discrepancies in the locus of galaxies in the BPT diagram at intermediate redshifts. We find a positive correlation for SFR and dust-corrected L$_rm{[OIII]lambda5007}$ and we derive the linear relation $log_{10}rm{(SFR/rm{M}_odot~rm{yr}^{-1})}=log_{10} (rm{L}_{[rm{OIII]}}/rm{ergs~s^{-1}})-(41.20pm0.02)$. Leaving the slope as a free parameter leads to $log_{10}rm{(SFR/rm{M}_odot~rm{yr}^{-1})}=(0.83pm0.06)log_{10}(rm{L}_{[rm{OIII]}}/rm{ergs~s^{-1}})-(34.01pm2.63)$. Gas-phase metallicity and ionization parameter variations account for a $0.24$ dex and $1.1$ dex of the dispersion, respectively. An average value of $logrm{U}approx-2.85$ is measured for this sample. Including HII-region models to fit simultaneously photometry and emission line fluxes are paramount to analyze future data from surveys such as MOONS and PFS.
We present piXedfit, pixelized spectral energy distribution (SED) fitting, a Python package that provides tools for analyzing spatially resolved properties of galaxies using multiband imaging data alone or in combination with integral field spectroscopy (IFS) data. piXedfit has six modules that can handle all tasks in the spatially resolved SED fitting. The SED fitting module uses the Bayesian inference technique with two kinds of posteriors sampling methods: Markov Chain Monte Carlo (MCMC) and random densely-sampling of parameter space (RDSPS). We test the performance of the SED fitting module using mock SEDs of simulated galaxies from IllustrisTNG. The SED fitting with both posteriors sampling methods can recover physical properties and star formation histories of the IllustrisTNG galaxies well. We further test the performance of piXedfit modules by analyzing 20 galaxies observed by the CALIFA and MaNGA surveys. The data comprises of 12-band imaging data from GALEX, SDSS, 2MASS, and WISE, and the IFS data from CALIFA or MaNGA. piXedfit can spatially match (in resolution and sampling) of the imaging and IFS data. By fitting only the photometric SEDs, piXedfit can predict the spectral continuum, $text{D}_{rm n}4000$, $H_{alpha}$, and $H_{beta}$ well. The star formation rate (SFR) derived by piXedfit is consistent with that derived from $H_{alpha}$ emission. The RDSPS method gives equally good fitting results as the MCMC and it is much faster than the MCMC. piXedfit is a versatile tool equipped with a parallel computing module for efficient analysis of large datasets, and will be made publicly available (https://github.com/aabdurrouf/piXedfit).
Euclid, WFIRST, and HETDEX will make emission-line selected galaxies the largest observed constituent in the $z > 1$ universe. However, we only have a limited understanding of the physical properties of galaxies selected via their Ly$alpha$ or rest-frame optical emission lines. To begin addressing this problem, we present the basic properties of $sim 2,000$ AEGIS, COSMOS, GOODS-N, GOODS-S, and UDS galaxies identified in the redshift range $1.90 < z < 2.35$ via their [O II], H$beta$, and [O III] emission lines. For these $z sim 2$ galaxies, [O III] is generally much brighter than [O II] and H$beta$, with typical rest-frame equivalent widths of several hundred Angstroms. Moreover, these strong emission-line systems span an extremely wide range of stellar mass ($sim 3$ dex), star-formation rate ($sim 2$ dex), and [O III] luminosity ($sim 2$ dex). Comparing the distributions of these properties to those of continuum selected galaxies, we find that emission-line galaxies have systematically lower stellar masses and lower optical/UV dust attenuations. These measurements lay the groundwork for an extensive comparison between these rest-frame optical emission-line galaxies and Ly$alpha$ emitters identified in the HETDEX survey.
Upcoming missions such as Euclid and the Nancy Grace Roman Space Telescope (Roman) will use emission-line selected galaxies to address a variety of questions in cosmology and galaxy evolution in the $z>1$ universe. The optimal observing strategy for these programs relies upon knowing the number of galaxies that will be found and the bias of the galaxy population. Here we measure the $rm{[O III]} lambda 5007$ luminosity function for a vetted sample of 1951 $m_{rm J+JH+H} < 26$ galaxies with unambiguous redshifts between $1.90 < z < 2.35$, which were selected using HST/WFC3 G141 grism frames made available by the 3D-HST program. These systems are directly analogous to the galaxies that will be identified by the Euclid and Roman missions, which will utilize grism spectroscopy to find $rm{[O III]} lambda 5007$-emitting galaxies at $0.8 lesssim z lesssim 2.7$ and $1.7 lesssim z lesssim 2.8$, respectively. We interpret our results in the context of the expected number counts for these upcoming missions. Finally, we combine our dust-corrected $rm{[O III]}$ luminosities with rest-frame ultraviolet star formation rates to present the first estimate of the SFR density associated with $1.90 < z < 2.35$ $rm{[O III]}$-emitting galaxies. We find that these grism-selected galaxies contain roughly half of the total star formation activity at $zsim2$.
We measure the Ly$alpha$ escape fraction of 935 [OIII]-emitting galaxies between $1.9 < z < 2.35$ by comparing stacked spectra from the Hubble Space Telescope/WFC3s near-IR grism to corresponding stacks from the Hobby Eberly Telescope Dark Energy Experiments Internal Data Release 2. By measuring the stacks H$beta$ to Ly$alpha$ ratios, we determine the Ly$alpha$ escape fraction as a function of stellar mass, star formation rate, internal reddening, size, and [OIII]/H$beta$ ratio. We show that the escape fraction of Ly$alpha$ correlates with a number of parameters, such as galaxy size, star formation rate, and nebular excitation. However, we also demonstrate that most of these relations are indirect, and the primary variables that control the escape of Ly$alpha$ are likely stellar mass and internal extinction. Overall, the escape of Ly$alpha$ declines from $gtrsim 18%$ in galaxies with $log M/M_{odot} lesssim 9$ to $lesssim 1%$ for systems with $log M/M_{odot} gtrsim 10$, with the samples mean escape fraction being $6.0^{+0.6%}_{-0.5%}$.
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