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Register a new userRevealing the Stellar Mass and Dust Distributions of Submillimeter Galaxies at Redshift 2
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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.
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We derive the mean wavelength dependence of stellar attenuation in a sample of 239 high redshift (1.90 < z < 2.35) galaxies selected via Hubble Space Telescope (HST) WFC3 IR grism observations of their rest-frame optical emission lines. Our analysis indicates that the average reddening law follows a form similar to that derived by Calzetti et al. for local starburst galaxies. However, over the mass range 7.2 < log M/Msolar < 10.2, the slope of the attenuation law in the UV is shallower than that seen locally, and the UV slope steepens as the mass increases. These trends are in qualitative agreement with Kriek & Conroy, who found that the wavelength dependence of attenuation varies with galaxy spectral type. However, we find no evidence of an extinction bump at 2175 A in any of the three stellar mass bins, or in the sample as a whole. We quantify the relation between the attenuation curve and stellar mass and discuss its implications.
We study the history from $zsim2$ to $zsim0$ of the stellar mass assembly of quiescent and star-forming galaxies in a spatially resolved fashion. For this purpose we use multi-wavelength imaging data from the Hubble Space Telescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS) for the local population. We present the radial stellar mass surface density profiles of galaxies with $M_{ast}>10^{10} M_{odot}$, corrected for mass-to-light ratio ($M_{ast}/L$) variations, and derive the half-mass radius ($R_{m}$), central stellar mass surface density within 1 kpc ($Sigma_{1}$) and surface density at $R_{m}$ ($Sigma_{m}$) for star-forming and quiescent galaxies and study their evolution with redshift. At fixed stellar mass, the half-mass sizes of quiescent galaxies increase from $zsim2$ to $zsim0$ by a factor of $sim3-5$, whereas the half-mass sizes of star-forming galaxies increase only slightly, by a factor of $sim2$. The central densities $Sigma_{1}$ of quiescent galaxies decline slightly (by a factor of $lesssim1.7$) from $zsim2$ to $zsim0$, while for star-forming galaxies $Sigma_{1}$ increases with time, at fixed mass. We show that the central density $Sigma_{1}$ has a tighter correlation with specific star-formation rate (sSFR) than $Sigma_{m}$ and for all masses and redshifts galaxies with higher central density are more prone to be quenched. Reaching a high central density ($Sigma_{1} gtrsim 10^{10} M_{odot} mathrm{kpc}^2$) seems to be a prerequisite for the cessation of star formation, though a causal link between high $Sigma_{1}$ and quenching is difficult to prove and their correlation can have a different origin.
We present high-resolution (0.16$$) 870um Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous (L_IR ~ 4 x 10^12 L_sun) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z~2.5 galaxies on ~1.3 kpc scales. The emission has a median effective radius of $R_e=0.24 pm 0.02$, corresponding to a typical physical size of $R_{e}=1.8pm$0.2 kpc. We derive a median Sersic index of $n=0.9pm0.2$, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.12$$ (~1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate S/N interferometric data. We compare our maps to comparable-resolution HST H$_{160}$-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the $zsim0$ descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive (M_* ~ 1-2 x 10^11 M_sun) early-type galaxies observed locally.
The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6$mu m$ IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6$mu m$ and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G). This survey consists of images in two infrared bands (3.6 and 4.5$mu m$), and we use the Independent Component Analysis (ICA) method presented in Meidt et al. (2012) to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6$mu m$ flux. We exclude from our ICA analysis galaxies with low signal-to-noise ratio (S/N < 10) and those with original [3.6]-[4.5] colors compatible with an old stellar population, indicative of little dust emission (mostly early Hubble types, which can directly provide good mass maps). For the remaining 1251 galaxies to which ICA was successfully applied, we find that as much as 10-30% of the total light at 3.6$mu m$ typically originates from dust, and locally it can reach even higher values. This contamination fraction shows a correlation with specific star formation rates, confirming that the dust emission that we detect is related to star formation. Additionally, we have used our large sample of mass estimates to calibrate a relationship of effective mass-to-light ratio ($M/L$) as a function of observed [3.6]-[4.5] color: $log(M/L)=-0.339 (pm 0.057) times ([3.6]-[4.5]) -0.336 (pm 0.002)$. Our final pipeline products have been made public through IRSA, providing the astronomical community with an unprecedentedly large set of stellar mass maps ready to use for scientific applications.
We report the bivariate HI- and H$_2$-stellar mass distributions of local galaxies in addition of an inventory of galaxy mass functions, MFs, for HI, H$_2$, cold gas, and baryonic mass, separately into early- and late-type galaxies. The MFs are determined using the HI and H$_2$ conditional distributions and the galaxy stellar mass function, GSMF. For the conditional distributions we use the compilation presented in Calette et al. 2018. For determining the GSMF from $M_{ast}sim3times10^{7}$ to $3times10^{12}$ $M_{odot}$, we combine two spectroscopic samples from the SDSS at the redshift range $0.0033<z<0.2$. We find that the low-mass end slope of the GSMF, after correcting from surface brightness incompleteness, is $alphaapprox-1.4$, consistent with previous determinations. The obtained HI MFs agree with radio blind surveys. Similarly, the H$_2$ MFs are consistent with CO follow-up optically-selected samples. We estimate the impact of systematics due to mass-to-light ratios and find that our MFs are robust against systematic errors. We deconvolve our MFs from random errors to obtain the intrinsic MFs. Using the MFs, we calculate cosmic density parameters of all the baryonic components. Baryons locked inside galaxies represent 5.4% of the universal baryon content, while $sim96$% of the HI and H$_2$ mass inside galaxies reside in late-type morphologies. Our results imply cosmic depletion times of H$_2$ and total neutral H in late-type galaxies of $sim 1.3$ and 7.2 Gyr, respectively, which shows that late type galaxies are on average inefficient in converting H$_2$ into stars and in transforming HI gas into H$_2$. Our results provide a fully self-consistent empirical description of galaxy demographics in terms of the bivariate gas--stellar mass distribution and their projections, the MFs. This description is ideal to compare and/or to constrain galaxy formation models.
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