arXiv subjects

Brandon Coleman

Publications and source records attributed to Brandon Coleman.

6 recordsLinked to original sources

arXiv2026

The Need for Ultra High Resolution X-ray Imaging

This paper discusses the broad science case for obtaining milliarcsecond to microarcsecond astronomical imaging resolution in the soft to medium-energy X-ray band (~0.5 to ~8 keV). Astronomy across much of the electromagnetic spectrum has been fundamentally transformed with a rapid increase in ground-based and space-based capabilities to examine celestial objects on small scales that relate directly to their relevant physical processes. X-ray imaging capabilities, however, have fallen far behind observations at longer wavelengths. As such, without decisive advances in X-ray imaging, we will be unable to uncover key phenomena on the smallest astrophysical scales, leaving entire classes of high-energy discoveries beyond our reach. Here we describe several science goals for which high quality X-ray imaging is crucial and the status of some current technologies or mission concepts that would be required for these advances. In particular, we discuss the Accretion Explorer, a mission architecture under current study for a dispersed aperture X-ray interferometer.

astro-ph.HE↗

arXiv2024

Cold Quasar Investigation: Comparing Star Formation Rates to Black Hole Growth

Cold quasars are a rare population of luminous, unobscured quasars associated with host galaxies that have a high star formation rate. We aimed to study the host galaxies of sixty four of these cold quasars in order to probe how the supermassive black holes and host galaxies were coevolving. We compiled data from the XXL survey and crossmatched with the VHS, WISE, and HerMES surveys to obtain multiwavelength photometry spanning the Xray to the infrared and including optical spectroscopy. From the data, we calculated the supermassive black hole masses using broad emission from the magnesium II and hydrogen beta lines. We compared this with the stellar mass of the entire galaxy and find that the black holes are significantly more massive than would be predicted by local relations, indicating that the majority of black hole growth precedes the bulk of the the stellar mass formation. In addition to this, we created a spectral energy distribution for each galaxy to calculate the star formation rate. We compared the star formation rate with the black hole accretion rate and find that the stellar mass is rapidly increasing at a relative rate faster than the black hole growth, supporting the picture where the black hole grows first.

astro-ph.GA↗

arXiv2023

The Accretion History of AGN: The Spectral Energy Distributions of X-ray Luminous AGN

Spectral energy distributions (SEDs) from X-ray to far-infrared (FIR) wavelengths are presented for a sample of 1246 X-ray luminous active galactic nuclei (AGN; $L_{0.5-10\rm{keV}}>10^{43}$ erg s$^{-1}$), with $z_{\rm{spec}}<1.2$, selected from Stripe 82X, COSMOS, and GOODS-N/S. The rest-frame SEDs show a wide spread ($\sim2.5$ dex) in the relative strengths of broad continuum features at X-ray, ultraviolet (UV), mid-infrared (MIR), and FIR wavelengths. A linear correlation (log-log slope of 0.7$\pm0.04$) is found between $L_{\rm{MIR}}$ and $L_{\rm{X}}$. There is significant scatter in the relation between the $L_{\rm{UV}}$ and $L_{\rm{X}}$ due to heavy obscuration, however the most luminous and unobscured AGN show a linear correlation (log-log slope of 0.8$\pm0.06$) in the relation above this scatter. The relation between $L_{\rm{FIR}}$ and $L_{\rm{X}}$ is predominantly flat, but with decreasing dispersion at $L_{\rm{X}}>10^{44}$ erg s$^{-1}$. The ratio between the "galaxy subtracted" bolometric luminosity and the intrinsic $L_{\rm{X}}$ increases from a factor of $\sim$$10-70$ from log $L_{\rm{bol}}/{\rm(erg\; s}^{-1})=44.5-46.5$. Characteristic SED shapes have been determined by grouping AGN based on relative strengths of the UV and MIR emission. The average $L_{1\mu\rm{m}}$ is constant for the majority of these SED shapes, while AGN with the strongest UV and MIR emission have elevated $L_{1\mu\rm{m}}$, consistent with the AGN emission dominating their SEDs at optical and NIR wavelengths. A strong correlation is found between the SED shape and both the $L_{\rm{X}}$ and $L_{\rm{bol}}$, such that $L_{\rm{bol}}/L_{\rm{X}}=20.4\pm1.8$, independent of the SED shape. This is consistent with an evolutionary scenario of increasing $L_{\rm{bol}}$ with decreasing obscuration as the AGN blows away circumnuclear gas.

astro-ph.GA↗

arXiv2023

AGN's Deadness Over Cosmic Time: UVJ Diagrams of X-Ray-Selected AGN

Active Galactic Nuclei (AGN) are intensely accreting supermassive black holes at the centers of massive galaxies. Though these objects occupy little spatial extent of the galaxy itself, they are thought to have far reaching affects, impacting the galaxy's star formation, and possibly it's lifespan until it becomes 'red and dead'. Typical galaxies demonstrate that, over cosmic time, they tend to separate into a bimodal distribution of 'red and dead' or blue and star forming. We examine whether active galaxies evolve over cosmic time in a similar way, and whether this can reveal anything about the complexities of the relationship between an AGN and the host galaxy. We use the Stripe82X survey to identify 3940 X-ray AGN spanning z=0-2.5, and we measure the rest-frame UVJ colors of each galaxy. We classify AGN as star-forming or quiescent based on their location in a UVJ color diagram. We find that there is not a clear bimodal distribution between AGN in star forming and quiescent galaxies. Furthermore, the most luminous X-ray sources tend to lie in the star forming region, which may indicate a correlation between central engine activity and increased rates of star formation.

astro-ph.GA↗

arXiv2022

Accretion History of AGN: Estimating the Host Galaxy Properties in X-ray Luminous AGN from z=0-3

We aim to determine the intrinsic far-Infrared (far-IR) emission of X-ray-luminous quasars over cosmic time. Using a 16 deg^2 region of the Stripe 82 field surveyed by XMM-Newton and Herschel Space Observatory, we identify 2905 X-ray luminous (LX > 10^42 erg/s) Active Galactic Nuclei (AGN) in the range z ~ 0-3. The IR is necessary to constrain host galaxy properties such as star formation rate (SFR) and gas mass. However, only 10% of our AGN are detected both in the X-ray and IR. Because 90% of the sample is undetected in the far-IR by Herschel, we explore the mean IR emission of these undetected sources by stacking their Herschel/SPIRE images in bins of X-ray luminosity and redshift. We create stacked spectral energy distributions from the optical to the far-IR, and estimate the median star formation rate, dust mass, stellar mass, and infrared luminosity using a fitting routine. We find that the stacked sources on average have similar SFR/L_bol ratios as IR detected sources. The majority of our sources fall on or above the main sequence line suggesting that X-ray selection alone does not predict the location of a galaxy on the main sequence. We also find that the gas depletion timescales of our AGN are similar to those of dusty star forming galaxies. This suggests that X-ray selected AGN host high star formation and that there are no signs of declining star formation.

astro-ph.GA↗

arXiv2019

The Accretion History of AGN: A Newly Defined Population of Cold Quasars

Quasars are the most luminous of active galactic nuclei (AGN), and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg$^2$ of the Stripe 82 field, of which the 15.6 deg$^2$ covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multi-wavelength counterparts, and 30% of these are unobscured quasars, with $L_X > 10^{44}\,$erg/s and $M_B < -23$. We define a new population of quasars which are unobscured, have X-ray luminosities in excess of $10^{44}\,$erg/s, have broad emission lines, and yet are also bright in the far-infrared, with a 250$\mu$m flux density of $S_{\rm 250}>30$mJy. We refer to these Herschel-detected, unobscured quasars as "Cold Quasars". A mere 4% (21) of the X-ray- and optically-selected unobscured quasars in Stripe 82X are detected at 250$\mu$m. These Cold Quasars lie at $z\sim1-3$, have $L_{\rm IR}>10^{12}\,L_\odot$, and have star formation rates of $\sim200-1400\,M_\odot$/yr. Cold Quasars are bluer in the mid-IR than the full quasar population, and 72% of our Cold Quasars have WISE W3 $<$ 11.5 [Vega], while only 19% of the full quasar sample meets this criteria. Crucially, Cold Quasars have on average $\sim9\times$ as much star formation as the main sequence of star forming galaxies at similar redshifts. Although dust-rich, unobscured quasars have occasionally been noted in the literature before, we argue that they should be considered as a separate class of quasars due to their high star formation rates. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold Quasars are type-1 blue quasars that reside in starburst galaxies.

astro-ph.GA↗