38 research outputs found
Comparison of Observed Galaxy Properties with Semianalytic Model Predictions using Machine Learning
With current and upcoming experiments such as WFIRST, Euclid and LSST, we can
observe up to billions of galaxies. While such surveys cannot obtain spectra
for all observed galaxies, they produce galaxy magnitudes in color filters.
This data set behaves like a high-dimensional nonlinear surface, an excellent
target for machine learning. In this work, we use a lightcone of semianalytic
galaxies tuned to match CANDELS observations from Lu et al. (2014) to train a
set of neural networks on a set of galaxy physical properties. We add realistic
photometric noise and use trained neural networks to predict stellar masses and
average star formation rates on real CANDELS galaxies, comparing our
predictions to SED fitting results. On semianalytic galaxies, we are nearly
competitive with template-fitting methods, with biases of dex for
stellar mass, dex for star formation rate, and dex for
metallicity. For the observed CANDELS data, our results are consistent with
template fits on the same data at dex bias in and
dex bias in star formation rate. Some of the bias is driven by SED-fitting
limitations, rather than limitations on the training set, and some is intrinsic
to the neural network method. Further errors are likely caused by differences
in noise properties between the semianalytic catalogs and data. Our results
show that galaxy physical properties can in principle be measured with neural
networks at a competitive degree of accuracy and precision to template-fitting
methods.Comment: 19 pages, 10 figures, 6 tables. Accepted for publication in Ap
Dependence of the IRX-β Dust Attenuation Relation on Metallicity and Environment
We use a sample of star-forming field and protocluster galaxies at z = 2.0–2.5 with Keck/MOSFIRE K-band spectra, a wealth of rest-frame ultraviolet (UV) photometry, and Spitzer/MIPS and Herschel/PACS observations, to dissect the relation between the ratio of infrared (IR) to UV luminosity (IRX) versus UV slope (β) as a function of gas-phase metallicity (12+log(O/H) ~ 8.2–8.7). We find no significant dependence of the IRX-β trend on environment. However, we find that at a given β, IRX is highly correlated with metallicity, and less correlated with mass, age, and specific star formation rate (sSFR). We conclude that, of the physical properties tested here, metallicity is the primary physical cause of the IRX-β scatter, and the IRX correlation with mass is presumably due to the mass dependence on metallicity. Our results indicate that the UV attenuation curve steepens with decreasing metallicity, and spans the full range of slope possibilities from a shallow Calzetti-type curve for galaxies with the highest metallicity in our sample (12+log(O/H) ~ 8.6) to a steep Small Magellanic Cloud (SMC)-like curve for those with 12+log(O/H) ~ 8.3. Using a Calzetti (SMC) curve for the low (high) metallicity galaxies can lead to up to a factor of 3 overestimation (underestimation) of the UV attenuation and obscured star formation rate. We speculate that this change is due to different properties of dust grains present in the interstellar medium of low- and high-metallicity galaxies
LATIS: The Stellar Mass-Metallicity Relation of Star-forming Galaxies at
We present the stellar mass - stellar metallicity relation for 3491
star-forming galaxies at using rest-frame
far-ultraviolet (FUV) spectra from the Ly Tomography IMACS Survey
(LATIS). We fit stellar population synthesis models from the Binary Population
And Spectral Synthesis code (BPASS v) to medium resolution (R ) and high signal-to-noise ( per 100 km/s over a wavelength range of
1221 - 1800 \r{A}) composite spectra of galaxies in bins of stellar mass to
determine their stellar metallicity, primarily tracing . We find a
strong correlation between stellar mass and stellar metallicity, with stellar
metallicity monotonically increasing with stellar mass at low masses and
flattening at high masses (). Additionally, we
compare our stellar metallicity measurements with the gas-phase oxygen
abundance of galaxies at similar redshift and estimate the average . Such high -enhancement indicates that
high-redshift galaxies have not yet undergone significant iron enrichment
through Type Ia supernovae. Moreover, we utilize an analytic chemical evolution
model to constrain the mass loading parameter of galactic winds as a function
of stellar mass. We find that as the stellar mass increases, the mass loading
parameter decreases. The parameter then flattens or reaches a turning point at
around . Our findings may signal the onset of black
hole-driven outflows at for galaxies with .Comment: 21 pages, 17 figures, 3 tables, accepted for publication in Ap
Dependence of the IRX- dust attenuation relation on metallicity and environment
We use a sample of star-forming field and protocluster galaxies at z=2.0-2.5
with Keck/MOSFIRE K-band spectra, a wealth of rest-frame UV photometry, and
Spitzer/MIPS and Herschel/PACS observations, to dissect the relation between
the ratio of IR to UV luminosity (IRX) versus UV slope () as a function
of gas-phase metallicity (12+log(O/H)~8.2-8.7). We find no significant
dependence of the IRX- trend on environment. However, we find that at a
given , IRX is highly correlated with metallicity, and less correlated
with mass, age, and sSFR. We conclude that, of the physical properties tested
here, metallicity is the primary physical cause of the IRX- scatter, and
the IRX correlation with mass is presumably due to the mass dependence on
metallicity. Our results indicate that the UV attenuation curve steepens with
decreasing metallicity, and spans the full range of slope possibilities from a
shallow Calzetti-type curve for galaxies with the highest metallicity in our
sample (12+log(O/H)~8.6) to a steep SMC-like curve for those with
12+log(O/H)~8.3. Using a Calzetti (SMC) curve for the low (high) metallicity
galaxies can lead to up to a factor of 3 overestimation (underestimation) of
the UV attenuation and obscured SFR. We speculate that this change is due to
different properties of dust grains present in the ISM of low- and
high-metallicity galaxies.Comment: Accepted for publication in ApJ
Bridging between the integrated and resolved main sequence of star formation
The position of galaxies on the stellar mass, star formation rate (SFR) plane with respect to the star-forming main sequence at each redshift is a convenient way to infer where the galaxy is in its evolution compared to the rest of the population. We use Hubble Space Telescope high-resolution images in the GOODS-S field from the the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) and fit multiwavelength lights in resolution elements of galaxies with stellar population synthesis models. We then construct resolved kpc-scale stellar mass, SFR surface density curves for galaxies at z ~ 1. Fitting these resolved main sequence curves with Schechter functions, we parameterize and explain the multiwavelength structure of galaxies with three variables: φ*, α, and M*. For quenched galaxies below the main sequence, we find an average high-mass slope (α) of the resolved main sequence curves to be ~−0.4. The scatter of this slope is higher among the lower mass star-forming galaxies and those above the main sequence compared to quenched galaxies, due to lack of an evolved bulge. Our findings agree well with an inside-out quenching of star formation. We find that the knee of the Schechter fits (M*) for galaxies below the main sequence occurs at lower stellar mass surface densities compared to star-forming galaxies, which hints at how far quenching has proceeded outward
Bridging between the integrated and resolved main sequence of star formation
The position of galaxies on the stellar mass, star formation rate (SFR) plane with respect to the star-forming main sequence at each redshift is a convenient way to infer where the galaxy is in its evolution compared to the rest of the population. We use Hubble Space Telescope high-resolution images in the GOODS-S field from the the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) and fit multiwavelength lights in resolution elements of galaxies with stellar population synthesis models. We then construct resolved kpc-scale stellar mass, SFR surface density curves for galaxies at z ~ 1. Fitting these resolved main sequence curves with Schechter functions, we parameterize and explain the multiwavelength structure of galaxies with three variables: φ*, α, and M*. For quenched galaxies below the main sequence, we find an average high-mass slope (α) of the resolved main sequence curves to be ~−0.4. The scatter of this slope is higher among the lower mass star-forming galaxies and those above the main sequence compared to quenched galaxies, due to lack of an evolved bulge. Our findings agree well with an inside-out quenching of star formation. We find that the knee of the Schechter fits (M*) for galaxies below the main sequence occurs at lower stellar mass surface densities compared to star-forming galaxies, which hints at how far quenching has proceeded outward
Exploring the Correlation between -to-UV Ratio and Burstiness for Typical Star-forming Galaxies at
The -to-UV luminosity ratio () is
often used to probe SFHs of star-forming galaxies and it is important to
validate it against other proxies for burstiness. To address this issue, we
present a statistical analysis of the resolved distribution of
as well as stellar age and their correlations with the
globally measured for a sample of 310 star-forming
galaxies in two redshift bins of and
observed by the MOSDEF survey. We use the multi-waveband CANDELS/3D-HST imaging
of MOSDEF galaxies to construct and stellar age maps. We
analyze the composite rest-frame far-UV spectra of a subsample of MOSDEF
targets obtained by the Keck/LRIS, which includes 124 star-forming galaxies
(MOSDEF-LRIS) at redshifts , to examine the average stellar
population properties, and the strength of age-sensitive FUV spectral features
in bins of . Our results show no significant evidence
that individual galaxies with higher are undergoing
a burst of star formation based on the resolved distribution of
of individual star-forming galaxies. We segregate the
sample into subsets with low and high . The
high- subset exhibits, on average, an age of
= 8.0, compared to = 8.4 for the
low- galaxies, though the difference in age is
significant at only the level. Furthermore, we find no variation in
the strengths of Siiv and Civ P-Cygni features from massive stars between the two subsamples.Comment: 16 pages, 10 figures, published by the Monthly Notices of the Royal
Astronomical Societ
The clustering of typical Ly emitters from : host halo masses depend on Ly and UV luminosities
We investigate the clustering and halo properties of Ly-selected emission line galaxies (LAEs) from the Slicing COSMOS 4K (SC4K) and from archival NB497 imaging of SA22 split in 15 discrete redshift slices between . We measure clustering lengths of Mpc and typical halo masses of M for our narrowband-selected LAEs with typical erg s. The intermediate band-selected LAEs are observed to have Mpc with typical halo masses of M and typical erg s. We find a strong, redshift-independent correlation between halo mass and Ly luminosity normalized by the characteristic Ly luminosity, . The faintest LAEs () typically identified by deep narrowband surveys are found in M halos and the brightest LAEs () are found in M halos. A dependency on the rest-frame 1500 \AA~UV luminosity, M_\rm{UV}, is also observed where the halo masses increase from to M for M_\rm{UV} \sim -19 to mag. Halo mass is also observed to increase from to M for dust-corrected UV star formation rates from to M yr and continues to increase up to M in halo mass, where the majority of those sources are AGN. All the trends we observe are found to be redshift-independent. Our results reveal that LAEs are the likely progenitors of a wide range of galaxies depending on their luminosity, from dwarf-like, to Milky Way-type, to bright cluster galaxies. LAEs therefore provide unique insight into the early formation and evolution of the galaxies we observe in the local Universe