One of the key questions in understanding galaxy formation and evolution is how starbursts affect the assembly of stellar populations in galaxies over time. We define a burst indicator ( ) that ...compares a galaxy's star formation rates (SFRs) on short (∼10 Myr) and long (∼100 Myr) timescales. To estimate , we apply the detailed time-luminosity relationship for H and near-ultraviolet emission to simulated star formation histories (SFHs) from semi-analytic models and the Mufasa hydrodynamical cosmological simulations. The average of is not a good indicator of star formation stochasticity (burstiness); indeed, we show that this average should be close to zero unless the galaxy population has an average SFH that is rising or falling rapidly. Instead, the width of the distribution characterizes the burstiness of a galaxy population's recent star formation. We find this width to be robust to variations in stellar initial mass function and metallicity. We apply realistic noise and selection effects to the models to generate mock Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) galaxy catalogs and compare these catalogs with 3D-HST observations of 956 galaxies at 0.65 < z < 1.5 detected in H . Measurements of are unaffected by dust measurement errors under the assumption that E(B − V)stars = 0.44 E(B − V)gas (i.e., Qsg = 0.44). However, setting removes an unexpected dependence of the average value of upon dust attenuation and stellar mass in the 3D-HST sample while also resolving disagreements in the distribution of SFRs. However, even varying the dust law cannot resolve all discrepancies between the simulated and the observed galaxies.
To achieve a fuller understanding of galaxy evolution, SED fitting can be used to recover quantities beyond stellar masses (M*) and star formation rates (SFRs). We use star formation histories (SFHs) ...reconstructed via the Dense Basis method of Iyer & Gawiser for a sample of 17,873 galaxies at 0.5 < z < 6 in the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey GOODS-S field to study the nature and evolution of the SFR-M* correlation. The reconstructed SFHs represent trajectories in SFR-M* space, enabling us to study galaxies at epochs earlier than observed by propagating them backward in time along these trajectories. We study the SFR-M* correlation at z = 1, 2, 3, 4, 5, 6 using both direct fits to galaxies observed at those epochs and SFR-M* trajectories of galaxies observed at lower redshifts. The SFR-M* correlations obtained using the two approaches are found to be consistent with each other through a K-S test. Validation tests using SFHs from semi-analytic models and cosmological hydrodynamical simulations confirm the sensitivity of the method to changes in the slope, normalization, and shape of the SFR-M* correlation. This technique allows us to further probe the low-mass regime of the correlation at high z by ∼1 dex and over an effective volume of ∼10× larger than possible with just direct fits. We find that the SFR-M* correlation is consistent with being linear down to M* ∼ 106 M at z > 4. The evolution of the correlation is well described by , where tuniv is the age of the universe in Gyr.
We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, ...F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ∼4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
We study the correlation of galaxy structural properties with their location relative to the SFR-M* correlation, also known as the star formation 'star-forming main sequence' (SFMS), in the Cosmic ...Assembly Near-infrared Deep Extragalactic Legacy Survey and Galaxy and Mass Assembly Survey and in a semi-analytic model (SAM) of galaxy formation. We first study the distribution of median Sersic index, effective radius, star formation rate (SFR) density and stellar mass density in the SFR-M* plane. We then define a redshift-dependent main sequence and examine the medians of these quantities as a function of distance from this main sequence, both above (higher SFRs) and below (lower SFRs). Finally, we examine the distributions of distance from the main sequence in bins of these quantities. We find strong correlations between all of these galaxy structural properties and the distance from the SFMS, such that as we move from galaxies above the SFMS to those below it, we see a nearly monotonic trend towards higher median Sersic index, smaller radius, lower SFR density, and higher stellar density. In the SAM, bulge growth is driven by mergers and disc instabilities, and is accompanied by the growth of a supermassive black hole which can regulate or quench star formation via active galactic nucleus feedback. We find that our model qualitatively reproduces the trends described above, supporting a picture in which black holes and bulges co-evolve, and active galactic nucleus feedback plays a critical role in moving galaxies off of the SFMS.
ABSTRACT We present estimates of intrinsic scatter in the star formation rate (SFR)-stellar mass (M*) correlation in the redshift range and in the mass range M . We utilize photometry in the Hubble ...Ultradeep Field (HUDF12) and Ultraviolet Ultra Deep Field (UVUDF) campaigns and CANDELS/GOODS-S and estimate SFR, M* from broadband spectral energy distributions and the best-available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 depth) probes the SFR-M* correlation down to 107M , a factor of 10-100× lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. We find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. We find a moderate increase in intrinsic scatter with cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic star formation. None of our redshift bins show a statistically significant increase in intrinsic scatter at low mass. However, it remains possible that intrinsic scatter increases at low mass on timescales shorter than ∼100 Myr. Our results are consistent with a picture of gradual and self-similar assembly of galaxies across more than three orders of magnitude in stellar mass from as low as 107M .
We present the rest-1500 UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon-the peak of cosmic star formation rate at . We use deep NUV imaging data obtained as part ...of the Hubble Ultra-Violet Ultra Deep Field (UVUDF) program, along with existing deep optical and NIR coverage on the HUDF. We select F225W, F275W, and F336W dropout samples using the Lyman break technique, along with samples in the corresponding redshift ranges selected using photometric redshifts, and measure the rest-frame UV LF at , respectively, using the modified maximum likelihood estimator. We perform simulations to quantify the survey and sample incompleteness for the UVUDF samples to correct the effective volume calculations for the LF. We select galaxies down to and fit a faint-end slope of at , , and , respectively. We compare the star formation properties of galaxies from these UV observations with results from H and UV+IR observations. We find a lack of high-SFR sources in the UV LF compared to the H and UV+IR, likely due to dusty SFGs not being properly accounted for by the generic relation used to correct for dust. We compute a volume-averaged UV-to-H ratio by abundance matching the rest-frame UV LF and H LF. We find an increasing UV-to-H ratio toward low-mass galaxies ( ). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end.
We investigate the environmental quenching of galaxies, especially those with stellar masses (M*) < 109.5 M , beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are ...believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z 1.5. For each low-mass galaxy, we measure the projected distance (dproj) to its nearest massive neighbor (M* > 1010.5 M ) within a redshift range. At a given z and M*, the environmental quenching effect is considered to be observed if the dproj distribution of QGs ( ) is significantly skewed toward lower values than that of star-forming galaxies ( ). For galaxies with 108 M < M* < 1010 M , such a difference between and is detected up to z ∼ 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (RVir) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, , decreases with satellite M* at M* 109.5 M , but increases with satellite M* at M* 109.5 M . This trend suggests a smooth, if any, transition of the quenching timescale around M* ∼ 109.5 M at 0.5 < z < 1.0.
Stacking analysis is a means of detecting faint sources using a priori position information to estimate an aggregate signal from individually undetected objects. Confusion severely limits the ...effectiveness of stacking in deep surveys with limited angular resolution, particularly at far-infrared to submillimeter wavelengths, and causes a bias in stacking results. Deblending corrects measured fluxes for confusion from adjacent sources; however, we find that standard deblending methods only reduce the bias by roughly a factor of 2 while tripling the variance. We present an improved algorithm for simultaneous stacking and deblending that greatly reduces bias in the flux estimate with nearly minimum variance. When confusion from neighboring sources is the dominant error, our method improves upon rms error by at least a factor of 3 and as much as an order of magnitude compared to other algorithms. This improvement will be useful for Herschel and other telescopes working in a source confused, low signal-to-noise regime.
ABSTRACT Dust attenuation affects nearly all observational aspects of galaxy evolution, yet very little is known about the form of the dust-attenuation law in the distant universe. Here, we model the ...spectral energy distributions of galaxies at z ∼ 1.5-3 from CANDELS with rest-frame UV to near-IR imaging under different assumptions about the dust law, and compare the amount of inferred attenuated light with the observed infrared (IR) luminosities. Some individual galaxies show strong Bayesian evidence in preference of one dust law over another, and this preference agrees with their observed location on the plane of infrared excess (IRX, / ) and UV slope (β). We generalize the shape of the dust law with an empirical model, where kλ is the dust law of Calzetti et al., and show that there exists a correlation between the color excess and tilt δ with . Galaxies with high color excess have a shallower, starburst-like law, and those with low color excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample show no correlation between the shape of the dust law and stellar mass, star formation rate, or β. The change in the dust law with color excess is consistent with a model where attenuation is caused by scattering, a mixed star-dust geometry, and/or trends with stellar population age, metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows potential to constrain the dust law at even higher redshifts ( ).
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