Engineering topics

Padilla, Nelson

Publications and source records attributed to Padilla, Nelson.

8 records

DOE OSTI2024

SUNBIRD : a simulation-based model for full-shape density-split clustering

Combining galaxy clustering information from regions of different environmental densities can help break cosmological parameter degeneracies and access non-Gaussian information from the density field that is not readily captured by the standard two-point correlation function (2PCF) analyses. However, modelling these density-dependent statistics down to the non-linear regime has so far remained challenging. We present a simulation-based model that is able to capture the cosmological dependence of the full shape of the density-split clustering (DSC) statistics down to intra-halo scales. Our models are based on neural-network emulators that are trained on high-fidelity mock galaxy catalogues within an extended-ΛCDM framework, incorporating the effects of redshift-space, Alcock–Paczynski distortions, and models of the halo–galaxy connection. Our models reach sub-percent level accuracy down to $1 \, h^{-1}\text{Mpc}$ and are robust against different choices of galaxy–halo connection modelling. When combined with the galaxy 2PCF, DSC can tighten the constraints on ω cdm , σ 8 , and n s by factors of 2.9, 1.9, and 2.1, respectively, compared to a 2PCF-only analysis. DSC additionally puts strong constraints on environment-based assembly bias parameters.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Cosmological constraints from density-split clustering in the BOSS CMASS galaxy sample

We present a clustering analysis of the BOSS DR12 CMASS galaxy sample, combining measurements of the galaxy two-point correlation function and density-split clustering down to a scale of $1 \, h^{-1}\, \text{Mpc}$. Our theoretical framework is based on emulators trained on high-fidelity mock galaxy catalogues that forward model the cosmological dependence of the clustering statistics within an extended-ΛCDM framework, including redshift-space and Alcock–Paczynski distortions. Our base-ΛCDM analysis finds ω cdm = 0.1201 ± 0.0022, σ 8 = 0.792 ± 0.034, and n s = 0.970 ± 0.018, corresponding to fσ 8 = 0.462 ± 0.020 at z ≈ 0.525, which is in agreement with Planck 2018 predictions and various clustering studies in the literature. We test single-parameter extensions to base-ΛCDM, varying the running of the spectral index, the dark energy equation of state, and the density of mass-less relic neutrinos, finding no compelling evidence for deviations from the base model. We model the galaxy–halo connection using a halo occupation distribution framework, finding signatures of environment-based assembly bias in the data. We validate our pipeline against mock catalogues that match the clustering and selection properties of CMASS, showing that we can recover unbiased cosmological constraints even with a volume 84 times larger than the one used in this study.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

To stack or not to stack: Spectral energy distribution properties of Lyα-emitting galaxies at z = 2.1

We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Lyα emitting (LAE) galaxies at z = 2.1. We build several types of stacked spectral energy distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage-stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2 × 10{sup 7} M {sub ☉} to 8 × 10{sup 9} M {sub ☉} (median = 3 × 10{sup 8} M {sub ☉}), ages ranging from 4 Myr to 500 Myr (median = 100 Myr), and E(B – V) between 0.02 and 0.24 (median = 0.12). Although still low, this represents significantly more dust reddening than has been reported for LAEs at higher redshifts. We do not observe strong correlations between Lyα equivalent width (EW) and age or E(B – V). The Lyα radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B – V). The absence of strong correlations with EW or q implies that Lyα radiative transfer is highly anisotropic and/or prevents Lyα photons from scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with uncertainties reduced by a factor of two. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods capture the large dispersion of LAE properties.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

EVOLUTION IN THE CONTINUUM MORPHOLOGICAL PROPERTIES OF Ly{alpha}-EMITTING GALAXIES FROM z = 3.1 TO z = 2.1

We present a rest-frame ultraviolet morphological analysis of 108 z {approx_equal} 2.1 Ly{alpha} emitters (LAEs) in the Extended Chandra Deep Field South and compare it to a similar sample of 171 LAEs at z {approx_equal} 3.1. Using Hubble Space Telescope images from the Galaxy Evolution from Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we measure size and photometric component distributions, where photometric components are defined as distinct clumps of UV-continuum emission. At both redshifts, >80% of LAEs have observed half-light radii <2 kpc, but the median half-light radius rises from 0.95 {+-} 0.04 kpc at z 3.1 to 1.41 {+-} 0.14 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of multi-component systems. In the z = 2.1 sample, we see clear correlations between the size of an LAE and other physical properties derived from its spectral energy distribution (SED). LAEs are found to be larger for galaxies with higher stellar mass, star formation rate, and dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at z {approx} 2, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Ly{alpha} emission.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

PRESENT-DAY DESCENDANTS OF z = 3 Ly{alpha}-EMITTING GALAXIES IN THE MILLENNIUM-II HALO MERGER TREES

Using the Millennium-II Simulation dark matter sub-halo merger histories, we created mock catalogs of Ly{alpha}-emitting (LAE) galaxies at z = 3.1 to study the properties of their descendants. Several models were created by selecting the sub-halos to match the number density and typical dark matter mass determined from observations of these galaxies. We used mass-based and age-based selection criteria to study their effects on descendant populations at z {approx_equal} 2, 1, and 0. For the models that best represent LAEs at z = 3.1, the z = 0 descendants have a median dark matter halo mass of 10{sup 12.7} M{sub Sun }, with a wide scatter in masses (50% between 10{sup 11.8} and 10{sup 13.7} M{sub Sun }). Our study differentiated between central and satellite sub-halos and found that {approx}55% of z = 0 descendants are central sub-halos with M{sub Median} {approx} 10{sup 12}. This confirms that central z = 0 descendants of z = 3.1 LAEs have halo masses typical of L*-type galaxies. The satellite sub-halos reside in group/cluster environments with dark matter masses around 10{sup 14} M{sub Sun }. The median descendant mass is robust to various methods of age determination, but it could vary by a factor of five due to current observational uncertainties in the clustering of LAEs used to determine their typical z = 3.1 dark matter mass.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

STACKED REST-FRAME ULTRAVIOLET SPECTRA OF Ly{alpha}-EMITTING AND CONTINUUM-SELECTED GALAXIES AT 2 < z < 3.5

We present properties of individual and composite rest-UV spectra of continuum- and narrowband-selected star-forming galaxies (SFGs) at a redshift of 2 < z < 3.5 discovered by the MUSYC collaboration in the Extended Chandra Deep Field-South. Among our sample of 81 UV-bright SFGs, 59 have R < 25.5, of which 32 have rest-frame equivalent widths of W{sub Ly{alpha}} > 20 A, the canonical limit to be classified as an Ly{alpha}-emitting galaxy. We divide our data set into subsamples based on properties that we are able to measure for each individual galaxy: Ly{alpha} equivalent width, rest-frame UV colors, and redshift. Among our subsample of galaxies with R < 25.5, those with rest frame W{sub Ly{alpha}} > 20 A have bluer UV continua, weaker low-ionization interstellar absorption lines, weaker C IV absorption, and stronger Si II* nebular emission than those with W{sub Ly{alpha}} < 20 A. We measure a velocity offset of {Delta}v {approx} 600 km s{sup -1} between Ly{alpha} emission and low-ionization absorption, which does not vary substantially among any of our subsamples. We find that the interstellar component, as opposed to the stellar component, dominates the high-ionization absorption line profiles. We find that the low- and high-ionization Si ionization states have similar kinematic properties, yet the low-ionization absorption is correlated with Ly{alpha} emission and the high-ionization absorption is not. These trends are consistent with outflowing neutral gas being in the form of neutral clouds embedded in ionized gas as previously suggested by Steidel et al. Moreover, our galaxies with bluer UV colors have stronger Ly{alpha} emission, weaker low-ionization absorption, and more prominent nebular emission line profiles. From a redshift of 2.7 < z < 3.5 to 2.0 < z < 2.7, our subsample of galaxies with W{sub Ly{alpha}} < 20 Angstrom-Sign shows no significant evolution in their physical properties or the nature of their outflows. Among our data set, UV-bright galaxies with W{sub Ly{alpha}} > 20 A exhibit weaker Ly{alpha} emission at lower redshifts, although we caution that this could be caused by spectroscopic confirmation of low Ly{alpha} equivalent width galaxies being harder at z {approx} 3 than z {approx} 2.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2011

The Evolution of Ly-alpha Emitting Galaxies Between z = 2.1 and z = 3.l

We describe the results of a new, wide-field survey for z= 3.1 Ly-alpha emission-line galaxies (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20 Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is dominated by x-ray sources and foreground objects with GALEX detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filter's redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z=3.1 LAE emission-line luminosity function, and show that an apparent anti-correlation between equivalent width and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to LAEs found at z=2.1. We show that in the approximately 1 Gyr after z approximately 3, the LAE luminosity function evolved significantly, with L * fading by approximately 0.4 mag, the number density of sources with L greater than 1.5E42 ergs/s declining by approximately 50%, and the equivalent width scalelength contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms. When combined with literature results, our observations demonstrate that over the redshift range z approximately 0 to z approximately 4, LAEs contain less than approximately 10% of the star-formation rate density of the universe.

Ciardullo, Robin↗

NASA NTRS2011

Evolution in the Continuum Morphological Properties of Ly alpha-Emitting Galaxies from Z=3.1 to Z=2.1

We present a rest-frame ultraviolet morphological analysis of 108 z = 2.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and compare it to a similar sample of 171 LAEs at z = 3.1 . Using Hubble Space Telescope (HST) images taken as part of the Galaxy Evolution From Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field surveys, we measure the size and photometric component distributions, where photo- metric components are defined as distinct clumps of UV-continuum emission. At both redshifts, the majority of LAEs have observed half-light radii < 2 kpc, but the median half-light radius rises from 0.97 kpc at z = 3.1 to 1.41 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of mUlti-component systems. In the z = 2.1 LAE sample, we see clear correlations between the LAE size and other physical properties derived from its SED. LAEs are found to be larger for galaxies with larger stellar mass, larger star formation rate, and larger dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at that redshift, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Lya emission.

Bond, Nicholas A.↗