Search

We analyze the physical properties of 8 X-ray selected active galactic nuclei (AGN) and one candidate protoquasar system (ADF22A1) in the $z = 3.09$ SSA22 protocluster by fitting their X-ray-to-IR spectral energy distributions (SEDs) using our SED fitting code, Lightning. We recover star formation histories (SFH) for 7 of these systems which are well-fit by composite stellar population plus AGN models. We find indications that 4/9 of the SSA22 AGN systems we study have host galaxies below the main sequence, with $\rm SFR/SFR_{MS} \leq -0.4$. The remaining SSA22 systems, including ADF22A1, are consistent with obscured supermassive black hole (SMBH) growth in star forming galaxies. We estimate the SMBH accretion rates and masses, and compare the properties and SFH of the 9 protocluster AGN systems with X-ray detected AGN candidates in the Chandra Deep Fields (CDF), finding that the distributions of SMBH growth rates, star formation rates, SMBH masses, and stellar masses for the protocluster AGN are consistent with field AGN. We constrain the ratio between the sample-averaged SSA22 SMBH mass and CDF SMBH mass to $<1.41$. While the AGN are located near the density peaks of the protocluster, we find no statistically significant trends between the AGN or host galaxy properties and their location in the protocluster. We interpret the similarity of the protocluster and field AGN populations together with existing results as suggesting that the protocluster and field AGN co-evolve with their hosts in the same ways, while AGN-triggering events are more likely in the protocluster., Comment: 27 pages, 14 figures, 8 tables. Updated with published version

We present an updated version of Lightning, a galaxy spectral energy distribution (SED) fitting code that can model X-ray to submillimeter observations. The models in Lightning include the options to contain contributions from stellar populations, dust attenuation and emission, and active galactic nuclei (AGN). X-ray emission, when utilized, can be modeled as originating from stellar compact binary populations with the option to include emission from AGN. We have also included a variety of algorithms to fit the models to observations and sample parameter posteriors; these include an adaptive Markov-Chain Monte-Carlo (MCMC), affine-invariant MCMC, and Levenberg-Marquardt gradient decent (MPFIT) algorithms. To demonstrate some of the capabilities of Lightning, we present several examples using a variety of observational data. These examples include (1) deriving the spatially resolved stellar properties of the nearby galaxy M81, (2) demonstrating how X-ray emission can provide constrains on the properties of the supermassive black hole of a distant AGN, (3) exploring how to rectify the attenuation effects of inclination on the derived the star formation rate of the edge-on galaxy NGC 4631, (4) comparing the performance of Lightning to similar Bayesian SED fitting codes when deriving physical properties of the star-forming galaxy NGC 628, and (5) comparing the derived X-ray and UV-to-IR AGN properties from Lightning and CIGALE for a distant AGN. Lightning is an open-source application developed in the Interactive Data Language (IDL) and is available at https://github.com/rafaeleufrasio/lightning., Comment: 34 pages, 17 figures. Updated with published version

We examine and quantify how hybrid (e.g., UV+IR) star formation rate (SFR) estimators and the $A_{\rm FUV}$-$\beta$ relation depend on inclination for disk-dominated galaxies using spectral energy distribution modeling that utilizes the inclination-dependent attenuation curves described in Doore et al. We perform this analysis on a sample of 133 disk-dominated galaxies from the CANDELS fields and 18 disk galaxies from the Spitzer Infrared Nearby Galaxies Survey and Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel samples. We find that both the hybrid SFR estimators and the $A_{\rm FUV}$-$\beta$ relation present clear dependencies on inclination. To quantify this dependence in the hybrid SFR estimators, we derive an inclination and a far-UV and near-IR color-dependent parametric relation for converting observed UV and IR luminosities into SFRs. For the $A_{\rm FUV}$-$\beta$ relation, we introduce an inclination-dependent component that accounts for the majority of the inclination dependence with the scatter of the relation increasing with inclination. We then compare both of these inclination-dependent relations to similar inclination-independent relations found in the literature. From this comparison, we find that the UV+IR correction factor and $A_{\rm FUV}$ for our hybrid and $A_{\rm FUV}$-$\beta$ relations, respectively, result in a reduction in the residual scatter of our sample by approximately a factor of 2. Therefore, we demonstrate that inclination must be considered in hybrid SFR estimators and the $A_{\rm FUV}$-$\beta$ relation to produce more accurate SFR estimates in disk-dominated galaxies., Comment: 24 pages, 15 figures. 23 page body and 1 page appendix. Updated with published version

The Chandra Deep Field-South and North surveys (CDFs) provide unique windows into the cosmic history of X-ray emission from normal (non-active) galaxies. Scaling relations of normal galaxy X-ray luminosity (L_X) with star formation rate (SFR) and stellar mass (M_star) have been used to show that the formation rates of low-mass and high-mass X-ray binaries (LMXBs and HMXBs, respectively) evolve with redshift across z = 0-2 following L_HMXB/SFR ~ 1 + z and L_LMXB/M_star ~ (1 + z)^{2-3}. However, these measurements alone do not directly reveal the physical mechanisms behind the redshift evolution of X-ray binaries (XRBs). We derive star-formation histories for a sample of 344 normal galaxies in the CDFs, using spectral energy distribution (SED) fitting of FUV-to-FIR photometric data, and construct a self-consistent, age-dependent model of the X-ray emission from the galaxies. Our model quantifies how X-ray emission from hot gas and XRB populations vary as functions of host stellar-population age. We find that (1) the ratio L_X/M_star declines by a factor of ~1000 from 0-10 Gyr and (2) the X-ray SED becomes harder with increasing age, consistent with a scenario in which the hot gas contribution to the X-ray SED declines quickly for ages above 10 Myr. When dividing our sample into subsets based on metallicity, we find some indication that L_X/M_star is elevated for low-metallicity galaxies, consistent with recent studies of X-ray scaling relations. However, additional statistical constraints are required to quantify both the age and metallicity dependence of X-ray emission from star-forming galaxies.

We develop and implement an inclination-dependent attenuation prescription for spectral energy distribution (SED) fitting and study its impact on derived star-formation histories. We apply our prescription within the SED fitting code Lightning to a clean sample of 82, z=0.21-1.35 disk-dominated galaxies in the Great Observatories Origins Deep Survey North and South fields. To compare our inclination-dependent attenuation prescription with more traditional fitting prescriptions, we also fit the SEDs with the inclination-independent Calzetti et al. (2000) attenuation curve. From this comparison, we find that fits to a subset of 58, z < 0.7 galaxies in our sample, utilizing the Calzetti et al. (2000) prescription, recover similar trends with inclination as the inclination-dependent fits for the far-UV-band attenuation and recent star-formation rates. However, we find a difference between prescriptions in the optical attenuation (AV) that is strongly correlated with inclination (p-value < 10^-11). For more face-on galaxies, with i < 50 deg, (edge-on, i = 90 deg), the average derived AV is 0.31 +\- 0.11 magnitudes lower (0.56 +\- 0.16 magnitudes higher) for the inclination-dependent model compared to traditional methods. Further, the ratio of stellar masses between prescriptions also has a significant (p-value < 10^-2) trend with inclination. For i = 0-65 deg, stellar masses are systematically consistent between fits, with log(Mstar_inc/Mstar_Calzetti) = -0.05 +/- 0.03 dex and scatter of 0.11 dex. However, for i = 80-90 deg, derived stellar masses are lower for the Calzetti et al. (2000) fits by an average factor of 0.17 +\- 0.03 dex and scatter of 0.13 dex. Therefore, these results suggest that SED fitting assuming the Calzetti et al. (2000) attenuation law potentially underestimates stellar masses in highly inclined disk-dominated galaxies., Comment: 38 pages, 22 figures. 30 page body and 8 page appendix. Updated with published version

We examine possible environmental sources of the enhanced star formation and active galactic nucleus (AGN) activity in the $z = 3.09$ SSA22 protocluster using Hubble WFC3 F160W ($\sim1.6\ \rm \mu m$) observations of the SSA22 field, including new observations centered on eight X-ray selected protocluster AGN. To investigate the role of mergers in the observed AGN and star formation enhancement, we apply both quantitative (S\'ersic-fit and Gini-$M_{20}$) and visual morphological classifications to F160W images of protocluster Lyman break galaxies (LBGs) in the fields of the X-ray AGN and $z \sim 3$ field LBGs in SSA22 and GOODS-N. We find no statistically significant differences between the morphologies and merger fractions of protocluster and field LBGs, though we are limited by small number statistics in the protocluster. We also fit the UV-to-near-IR spectral energy distributions (SED) of F160W-detected protocluster and field LBGs to characterize their stellar masses and star formation histories (SFH). We find that the mean protocluster LBG is by a factor of $\sim2$ times more massive and more attenuated than the mean $z \sim 3$ field LBG. We take our results to suggest that ongoing mergers are not more common among protocluster LBGs than field LBGs, though protocluster LBGs appear to be more massive. We speculate that the larger mass of the protocluster LBGs contributes to the enhancement of SMBH mass and accretion rate in the protocluster, which in turn drives the observed protocluster AGN enhancement., Comment: 43 pages, 18 figures. 32 page body and 11 page appendix. Updated with published version

We present detailed constraints on the metallicity dependence of the high mass X-ray binary (HMXB) X-ray luminosity function (XLF). We analyze ~5 Ms of Chandra data for 55 actively star-forming galaxies at D < 30 Mpc with gas-phase metallicities spanning 12 + log(O/H) = 7-9.2. Within the galactic footprints, our sample contains a total of 1311 X-ray point sources, of which ~49% are expected to be HMXBs, with the remaining sources likely to be low-mass X-ray binaries (LMXBs; ~22%) and unrelated background sources (~29%). We construct a model that successfully characterizes the average HMXB XLF over the full metallicity range. We demonstrate that the SFR-normalized HMXB XLF shows clear trends with metallicity, with steadily increasing numbers of luminous and ultraluminous X-ray sources (logL(erg/s) = 38-40.5) with declining metallicity. However, we find that the low-luminosity (logL(erg/s) = 36-38) HMXB XLF appears to show a nearly constant SFR scaling and slope with metallicity. Our model provides a revised scaling relation of integrated LX/SFR versus 12 + log(O/H) and a new characterization of its the SFR-dependent stochastic scatter. The general trend of this relation is broadly consistent with past studies based on integrated galaxy emission; however, our model suggests that this relation is driven primarily by the high-luminosity end of the HMXB XLF. Our results have implications for binary population synthesis models, the nature of super-Eddington accreting objects (e.g., ultraluminous X-ray sources), recent efforts to identify active galactic nucleus candidates in dwarf galaxies, and the X-ray radiation fields in the early Universe during the epoch of cosmic heating at z > 10., Comment: Accepted for publication in ApJ

We investigate X-ray binary (XRB) luminosity function (XLF) scaling relations for Chandra detected populations of low-mass XRBs (LMXBs) within the footprints of 24 early-type galaxies. Our sample includes Chandra and HST observed galaxies at D < 25 Mpc that have estimates of the globular cluster (GC) specific frequency (SN) reported in the literature. As such, we are able to directly classify X-ray-detected sources as being either coincident with unrelated background/foreground objects, GCs, or sources that are within the fields of the galaxy targets. We model the GC and field LMXB population XLFs for all galaxies separately, and then construct global models characterizing how the LMXB XLFs vary with galaxy stellar mass and SN. We find that our field LMXB XLF models require a component that scales with SN, and has a shape consistent with that found for the GC LMXB XLF. We take this to indicate that GCs are "seeding" the galactic field LMXB population, through the ejection of GC-LMXBs and/or the diffusion of the GCs in the galactic fields themselves. However, we also find that an important LMXB XLF component is required for all galaxies that scales with stellar mass, implying that a substantial population of LMXBs are formed "in situ," which dominates the LMXB population emission for galaxies with SN < 2. For the first time, we provide a framework quantifying how directly-associated GC LMXBs, GC-seeded LMXBs, and in-situ LMXBs contribute to LMXB XLFs in the broader early-type galaxy population., Comment: Accepted for publication in ApJS. Data products and catalogs available at https://lehmer.uark.edu/downloads/

Ultrasonic agitation is a proven method for breaking down layered materials such as MoS2 into single or few layer nanoparticles. In this experiment, MoS2 powder is sonicated in isopropanol for an extended period of time in an attempt to create particles of the smallest possible size. As expected, the process yielded a significant quantity of nanoscale MoS2 in the form of finite layer sheets with lateral dimensions as small as a few tens of nanometers. Although no evidence was found to indicate a larger the longer sonication times resulted in a significant increase in yield of single layer MoS2, the increased sonication did result in the formation of several types of carbon allotropes in addition to the sheets of MoS2. These carbon structures appear to originate from the breakdown of the isopropanol and consist of finite layer graphite platelets as well as a large number of multi-walled fullerenes, also known as carbon onions. Both the finite layer graphite and MoS2 nanoplatelets were both found to be heavily decorated with carbon onions. However, isolated clusters of carbon onions could also be found. Our results show that liquid exfoliation of MoS2 is not only useful for forming finite layer MoS2, but also creating carbon onions at room temperature as well.