On the Impact of Inclination-Dependent Attenuation on the Derived Star Formation Histories of Disk Galaxies

The physical properties of a galaxy (e.g., its star-formation history and dust content) regulate the distribution of light that is emitted by stars and attenuated by the interstellar gas and dust. This attenuation by dust can have a significant impact on the observed spectral energy distribution (SED) of a disk galaxy, especially when taking into account its viewing angle (i.e., inclination). For example, as the inclination angle of a galactic disk changes from face-on to edge-on (i.e., i = 0 deg to i = 90 deg), the proportion of light that is attenuated along the line of sight increases, due to an increasing column density of dust. Therefore, additional care must be taken when modeling the SED of a disk galaxy to account for any inclination dependence. In this work, we develop and implement an inclination-dependent attenuation prescription into our SED fitting code, Lightning, to more accurately derive the physical properties of disk galaxies. First, we present the details of our SED fitting code, Lightning, as it is the cornerstone of our inclination-dependent analyses. We discuss all of the models in Lightning, which can include contributions from a variety of sources, along with the available algorithms to fit the models to observations. Then, to show the future potential of Lightning, we present several examples using a variety of observational data. Next, to better understand how inclination affects the physical properties of disk galaxies, we apply our prescription on two respective galactic samples to (1) study the impact of inclination-dependent attenuation on derived stellar properties and (2) examine and quantify how commonly used star formation rate (SFR) estimators depend on inclination. For the first application, we compare our inclination-dependent attenuation prescription with a more traditional inclination-independent attenuation prescription. Our results indicate stark statistical differences in the derived optical attenuation and stellar masses, with the traditional attenuation prescription resulting in these properties being underestimated compared to the inclination-dependent attenuation prescription at high inclinations. Therefore, the results from this application suggest that SED fitting assuming inclination-independent attenuation potentially underestimates these properties in highly inclined disk galaxies. For the second application, We find that two commonly used SFR estimators (the hybrid UV+IR and AFUV-beta relations) present clear dependencies on inclination. To quantify these dependencies, we expand the parametric form of the estimators to include an inclination-dependence. We then compare both of these new inclination-dependent estimators to similar inclination-independent relations found in the literature. From this comparison, we find that our inclination-dependent relations result in a reduction in the residual scatter of the derived SFRs of our sample by approximately a factor of two. Therefore, this second application demonstrates that inclination must be considered in SFR estimators to produce more accurate SFR estimates in disk galaxies. Overall, this work provides the crucial steps towards understanding and incorporating the impact of inclination-dependence on the derived star-formation histories of disk galaxies. It additionally presents a novel tool (Lightning) which can be used in future studies to more accurately account for this inclination-dependence

On the Impact of Inclination-Dependent Attenuation on the Derived Star Formation Histories of Disk Galaxies

The physical properties of a galaxy (e.g., its star-formation history and dust content) regulate the distribution of light that is emitted by stars and attenuated by the interstellar gas and dust. This attenuation by dust can have a significant impact on the observed spectral energy distribution (SED) of a disk galaxy, especially when taking into account its viewing angle (i.e., inclination). For example, as the inclination angle of a galactic disk changes from face-on to edge-on (i.e., i = 0 deg to i = 90 deg), the proportion of light that is attenuated along the line of sight increases, due to an increasing column density of dust. Therefore, additional care must be taken when modeling the SED of a disk galaxy to account for any inclination dependence. In this work, we develop and implement an inclination-dependent attenuation prescription into our SED fitting code, Lightning, to more accurately derive the physical properties of disk galaxies. First, we present the details of our SED fitting code, Lightning, as it is the cornerstone of our inclination-dependent analyses. We discuss all of the models in Lightning, which can include contributions from a variety of sources, along with the available algorithms to fit the models to observations. Then, to show the future potential of Lightning, we present several examples using a variety of observational data. Next, to better understand how inclination affects the physical properties of disk galaxies, we apply our prescription on two respective galactic samples to (1) study the impact of inclination-dependent attenuation on derived stellar properties and (2) examine and quantify how commonly used star formation rate (SFR) estimators depend on inclination. For the first application, we compare our inclination-dependent attenuation prescription with a more traditional inclination-independent attenuation prescription. Our results indicate stark statistical differences in the derived optical attenuation and stellar masses, with the traditional attenuation prescription resulting in these properties being underestimated compared to the inclination-dependent attenuation prescription at high inclinations. Therefore, the results from this application suggest that SED fitting assuming inclination-independent attenuation potentially underestimates these properties in highly inclined disk galaxies. For the second application, We find that two commonly used SFR estimators (the hybrid UV+IR and AFUV-beta relations) present clear dependencies on inclination. To quantify these dependencies, we expand the parametric form of the estimators to include an inclination-dependence. We then compare both of these new inclination-dependent estimators to similar inclination-independent relations found in the literature. From this comparison, we find that our inclination-dependent relations result in a reduction in the residual scatter of the derived SFRs of our sample by approximately a factor of two. Therefore, this second application demonstrates that inclination must be considered in SFR estimators to produce more accurate SFR estimates in disk galaxies. Overall, this work provides the crucial steps towards understanding and incorporating the impact of inclination-dependence on the derived star-formation histories of disk galaxies. It additionally presents a novel tool (Lightning) which can be used in future studies to more accurately account for this inclination-dependence

The Stellar-age Dependence of X-Ray Emission from Normal Star-forming Galaxies in the GOODS Fields

The Chandra Deep Field-South and North surveys (CDFs) provide unique windows into the cosmic history of X-ray emission from normal (nonactive) galaxies. Scaling relations of normal-galaxy X-ray luminosity (L X) with star formation rate (SFR) and stellar mass (M ∗) 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 α(1 + z) and L LMXB/M ∗ α(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 ∗ declines by a factor of ∼1000 from 0 to 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 ∗ 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

thodson-usgs/ratingcurve: v1.0.0

<h2>What's Changed</h2> <ul> <li>Fixed ModelBuilder Doc Action by @kjdoore in https://github.com/thodson-usgs/ratingcurve/pull/52</li> <li>Modelbuilder API doc fix by @kjdoore in https://github.com/thodson-usgs/ratingcurve/pull/53</li> <li>Update deploy-book.yml by @thodson-usgs in https://github.com/thodson-usgs/ratingcurve/pull/54</li> <li>Add datasets by @thodson-usgs in https://github.com/thodson-usgs/ratingcurve/pull/56</li> <li>Fixed skajalfandafljot example typo by @kjdoore in https://github.com/thodson-usgs/ratingcurve/pull/57</li> <li>Typo fix in Nordura Description by @kjdoore in https://github.com/thodson-usgs/ratingcurve/pull/58</li> </ul> <p><strong>Full Changelog</strong>: https://github.com/thodson-usgs/ratingcurve/compare/v0.4.0...v1.0.0</p&gt

Ratingcurve: A Python Package for Fitting Streamflow Rating Curves

Streamflow is one of the most important variables in hydrology, but it is difficult to measure continuously. As a result, nearly all streamflow time series are estimated from rating curves that define a mathematical relationship between streamflow and some easy-to-measure proxy like water surface elevation (stage). Despite the existence of automated methods, most rating curves are still fit manually, which can be time-consuming and subjective. Although several automated methods exist, they vary greatly in performance because of the non-convex nature of the problem. In this work, we develop a parameterization of the segmented power law that works reliably with minimal data, which could serve operationally or as a benchmark for evaluating other methods. The model, along with test data and tutorials, is available as an open-source Python package called ratingcurve. The implementation uses a modern probabilistic machine-learning framework, which is relatively easy to modify so that others can improve upon it

Revisiting the Properties of X-ray AGN in the SSA22 Protocluster: Normal SMBH and Host-Galaxy Growth for AGN in a z=3.09z=3.09 Overdensity

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. Accepted in Ap

On the Nature of AGN and Star Formation Enhancement in the z = 3.1 SSA22 Protocluster: The HST WFC3 IR View

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 (∼1.6 μm) 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 (Sérsic-fit and Gini–M20) and visual morphological classifications to F160W images of protocluster Lyman-break galaxies (LBGs) in the fields of the X-ray AGN and z ∼ 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 of F160W-detected protocluster and field LBGs to characterize their stellar masses and star formation histories. We find that the mean protocluster LBG is a factor of ∼2 times more massive and more attenuated than the mean z ∼ 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

X-Ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-mass X-Ray Binaries in Galactic Fields

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 Hubble Space Telescope observed galaxies at $D\lesssim 25$ Mpc that have estimates of the globular cluster (GC) specific frequency (S N ) reported in the literature. As such, we are able to directly classify X-ray-detected sources as being 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 S N . We find that our field LMXB XLF models require a component that scales with S N 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 S N lesssim 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