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Martin Elvis

Publications and source records attributed to Martin Elvis.

At least 37 records · Page 2Linked to original sources
arXiv2021

The Chandra view of the relation between X-ray and UV emission in quasars

We present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey DR14 with the latest Chandra Source Catalog 2.0 (2,332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500 A, $L_{O}$) and the X-ray (at 2 keV, $L_{X}$) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of Chandra, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3,430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the $L_{X}-L_{O}$ relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, $z \simeq 0.5-4$. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of $0.6$ over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are `standardisable candles', that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available.

astro-ph.GA↗
arXiv2021

The most luminous blue quasars at 3.0<z<3.3. II. CIV/X-ray emission and accretion disc physics

We analyse the properties of the CIV broad emission line in connection with the X-ray emission of 30 bright SDSS quasars at z~3.0-3.3 with pointed XMM-Newton observations, which were selected to test the suitability of AGN as cosmological tools. In our previous work, we found that a large fraction (~25%) of the quasars in this sample are X-ray underluminous by factors of >3-10. As absorbing columns of >10$^{23}$ cm$^{-2}$ can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness. We fit their UV SDSS spectra and analyse their CIV properties (e.g., equivalent width, EW; line peak velocity, $\upsilon_{\rm peak}$) as a function of the X-ray photon index and 2-10 keV flux. We confirm the trends of CIV $\upsilon_{\rm peak}$ and EW with UV luminosity at 2500 angstrom for both X-ray weak and X-ray normal quasars, as well as the correlation between X-ray weakness and CIV EW. In contrast to some recent work, we do not observe any clear relation between the 2-10 keV luminosity and $\upsilon_{\rm peak}$. We find a correlation between the hard X-ray flux and the integrated CIV flux for X-ray normal quasars, whilst X-ray weak quasars deviate from the main trend by more than 0.5 dex. We argue that X-ray weakness might be interpreted in a starved X-ray corona picture associated with an ongoing disc-wind phase. If the wind is ejected in the vicinity of the black hole, the extreme-UV radiation that reaches the corona will be depleted, depriving the corona of seeds photons and generating an X-ray weak quasar. Yet, at the largest UV luminosities (>10$^{47}$ erg s$^{-1}$), there will still be an ample reservoir of ionising photons that can explain the excess CIV emission observed in the X-ray weak quasars with respect to normal sources of similar X-ray luminosities.

astro-ph.GA↗
arXiv2021

A Giant Loop of Ionized Gas Emerging from the Tumultuous Central Region of IC 5063

The biconical radiation pattern extending from an active galactic nucleus (AGN) may strongly photoionize the circumnuclear interstellar medium (ISM) and stimulate emission from the narrow line region (NLR). Observations of the NLR may provide clues to the structure of dense material that preferentially obscures the bicone at certain angles, and may reveal the presence of processes in the ISM tied to AGN accretion and feedback. Ground-based integral field units (IFUs) may study these processes via well-understood forbidden diagnostic lines such as [O III] and [S II], but scales of $\sim10$s of pc remain challenging to spatially resolve at these wavelengths for all but the nearest AGN. We present recent narrow filter Hubble Space Telescope (HST) observations of diagnostic forbidden ([O III], [S II]) and Balmer (H$α$, H$β$) lines in the NLR of IC 5063. This AGN's jet inclination into the plane of the galaxy provides an important laboratory for strong AGN-host interactions. We find evidence for a low-ionization loop which emits brightly in [S II] and [N II], and which may arise from plume-like hot outflows that ablate ISM from the galactic plane before escaping laterally. We also present spatially resolved Baldwin-Phillips-Terlevich diagnostic maps of the IC 5063 NLR. These maps suggest a sharp transition to lower-ionization states outside the jet path, and that such emission is dominated by $\sim10-40$ pc clumps and filamentary structure at large (>>25°) angles from the bicone axis. Such emission may arise from precursorless shocks when AGN outflows impact low-density hot plasma in the cross-cone.

astro-ph.GA↗
arXiv2021

Towers on the Peaks of Eternal Light: Quantifying the Available Solar Power

The Peaks of Eternal Light (PELs), that are largely unshaded regions mostly at the lunar south pole, have been suggested as a source of solar power for mining the water and other volatiles in the nearby permanently dark regions. As mining is a power-intensive activity, it is interesting to estimate the maximum solar power that could be generated at the PELs. Here we use average percentage illumination maps for a range of heights above the local topography from 2 m to 2 km to determine the total power available as a function of time of lunar day. Overshadowing of highly illuminated areas by towers placed in sunward locations (at a given time of day) limits the total power to much smaller values than the highly illuminated area would suggest. We find that for near-term realizable towers (up to 20 m), the upper limit to the time-averaged power available is ~55 MW at >70% illumination, and ~6 MW at >90% illumination. For the more distant future a maximum time-averaged power of order 21000 MW at >70% illumination could be realizable for towers up to 2 km in height, and ~5270 MW, respectively, at 90% illumination. Towers 1 km high provide about a factor 2.7 times less power. The variation with lunar time of day ranges from a factor of 1.1 to ~ 3.

astro-ph.EP↗
arXiv2021

Concentrated Lunar Resources: Imminent Implications for Governance and Justice

Numerous missions planned for the next decade are likely to target a handful of smal sites of interest on the Moon's surface, creating risks of crowding and interference at these locations. The Moon presents finite and scarce areas with rare topography or concentrations of resources of special value. Locations of interest to science, notably for astronomy, include the Peaks of Eternal Light, the coldest of the cold traps and smooth areas on the far side. Regions richest in physical resources could also be uniquely suited to settlement and commerce. Such sites of interest are both few and small. Typically, there are fewer than ten key sites of each type, each site spanning a few kilometres across. We survey the implications for different kins of mission and find that the diverse actors pursuing incomptible ends at these sites could soon crowd and interfere with each other, leaving almost all actors worse off. Without proactive measures to prevent these outcomes, lunar actors are likely to experience significant losses of opportunity. We highlight the legal, policy, and ethical ramifications. Insights from research on comparable sites on Earth present a path toward managing lunar crowding and interference grounded in ethical and practical near-term considerations. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades'.

physics.pop-ph↗
arXiv2020

Spatially resolved BPT mapping of nearby Seyfert 2 galaxies

We present spatially resolved BPT mapping of the extended narrow line regions (ENLRs) of seven nearby Seyfert 2 galaxies, using HST narrow band filter imaging. We construct the BPT diagrams using $\leq$ 0.1" resolution emission line images of [O III]$λ$5007, H$α$, [S II]$λ$$λ$6717,6731, and H$β$. By mapping these diagnostic lines according to the BPT classification, we dissect the ENLR into Seyfert, LINER, and star-forming regions. The nucleus and ionization cones are dominated by Seyfert-type emission, which can be interpreted as predominantly photoionization by the active galactic nucleus (AGN). The Seyfert nucleus and ionization cones transition to and are surrounded by a LINER cocoon, extending up to $\sim$ 250 pc in thickness. The ubiquity of the LINER cocoon in Seyfert 2 galaxies suggests that the circumnuclear regions are not necessarily Seyfert-type, and LINER activity plays an important role in Seyfert 2 galaxies. We demonstrate that spatially resolved diagnostics are crucial to understanding the excitation mechanisms in different regions and the AGN-host galaxy interactions.

astro-ph.GA↗
arXiv2020

The future of astronomy with small satellites

The number of small satellites has grown dramatically in the past decade from tens of satellites per year in the mid-2010s to a projection of tens of thousands in orbit by the mid-2020s. This presents both problems and opportunities for observational astronomy. Small satellites offer complementary cost-effective capabilities to both ground-based astronomy and larger space missions. Compared to ground-based astronomy, these advantages are not just in the accessibility of wavelength ranges where the Earth's atmosphere is opaque, but also in stable, high precision photometry, long-term monitoring and improved areal coverage. Astronomy has a long history of new observational parameter spaces leading to major discoveries. Here we discuss the potential for small satellites to explore new parameter spaces in astrophysics, drawing on examples from current and proposed missions, and spanning a wide range of science goals from binary stars, exoplanets and solar system science to the early Universe and fundamental physics.

astro-ph.IM↗
arXiv2020

Crepuscular Rays from the Highly Inclined Active Galactic Nucleus in IC 5063

On Earth near sunset, the sun may cast "crepuscular rays" such that clouds near the horizon obscure the origin of light scattered in bright rays. In principle, AGN should be able to produce similar effects. Using new Hubble Space Telescope (HST) near-infrared and optical observations, we show that the active galaxy IC 5063 contains broad radial rays extending to $\gtrsim$11 kpc from the nucleus. We argue that the bright rays may arise from dusty scattering of continuum emission from the active nucleus, while the dark rays are due to shadowing near the nucleus, possibly by a warped torus. We also consider alternative AGN-related and stellar origins for the extended light.

astro-ph.GA↗
arXiv2020

Reconstructing EUV spectrum of star forming regions from millimeter recombination lines of HI, HeI, and HeII

The extreme ultraviolet (EUV) spectra of distant star-forming regions cannot be probed directly using either ground- or space-based telescopes due to the high cross-section for interaction of EUV photons with the interstellar medium. This makes EUV spectra poorly constrained. The mm/submm recombination lines of H and He, which can be observed from the ground, can serve as a reliable probe of the EUV. Here we present a study based on ALMA observations of three Galactic ultra-compact HII regions and the starburst region Sgr B2(M), in which we reconstruct the key parameters of the EUV spectra using mm recombination lines of HI, HeI and HeII. We find that in all cases the EUV spectra between 13.6 and 54.4 eV have similar frequency dependence: L_ν~ ν^{-4.5 +/- 0.4}. We compare the inferred values of the EUV spectral slopes with the values expected for a purely single stellar evolution model (Starburst99) and the Binary Population and Spectral Synthesis code (BPASS). We find that the observed spectral slope differs from the model predictions. This may imply that the fraction of interacting binaries in HII regions is substantially lower than assumed in BPASS. The technique demonstrated here allows one to deduce the EUV spectra of star forming regions providing critical insight into photon production rates at λ< 912 A and can serve as calibration to starburst synthesis models, improving our understanding of star formation in distant universe and the properties of ionizing flux during reionization.

astro-ph.GA↗
arXiv2020

X-ray Studies of Planetary Systems: A 2020 Decadal Survey White Paper

Whether it is fluorescence emission from asteroids and moons, solar wind charge exchange from comets, exospheric escape from Mars, pion reactions on Venus, sprite lighting on Saturn, or the Io plasma torus in the Jovian magnetosphere, the Solar System is surprisingly rich and diverse in X-ray emitting objects. The compositions of diverse planetary bodies are of fundamental interest to planetary science, providing clues to the formation and evolutionary history of the target bodies and the solar system as a whole. X-ray fluorescence (XRF) lines, triggered either by solar X-rays or energetic ions, are intrinsic to atomic energy levels and carry an unambiguous signature of the elemental composition of the emitting bodies. All remote-sensing XRF spectrometers used so far on planetary orbiters have been collimated instruments, with limited achievable spatial resolution, and many have used archaic X-ray detectors with poor energy resolution. Focusing X-ray optics provide true spectroscopic imaging and are used widely in astrophysics missions, but until now their mass and volume have been too large for resource-limited in-situ planetary missions. Recent advances in X-ray instrumentation such as the Micro-Pore Optics used on the BepiColombo X-ray instrument (Fraser et al., 2010), Miniature X-ray Optics (Hong et al., 2016) and highly radiation tolerant CMOS X-ray sensors (e.g., Kenter et al., 2012) enable compact, yet powerful, truly focusing X-ray Imaging Spectrometers. Such instruments will enable compositional measurements of planetary bodies with much better spatial resolution and thus open a large new discovery space in planetary science, greatly enhancing our understanding of the nature and origin of diverse planetary bodies. Here, we discuss many examples of the power of XRF to address key science questions across the solar system.

astro-ph.IM↗
arXiv2020

Is extended hard X-ray emission ubiquitous in Compton-thick AGN?

The recent Chandra discovery of extended $\sim$kpc-scale hard ($>$ 3 keV) X-ray emission in nearby Compton-thick (CT) active galactic nuclei (AGN) opens a new window to improving AGN torus modeling and investigating how the central super massive black hole interacts with and impacts the host galaxy. Since there are only a handful of detections so far, we need to establish a statistical sample to determine the ubiquity of the extended hard X-ray emission in CT AGN, and quantify the amount and extent of this component. In this paper, we present the spatial analysis results of a pilot Chandra imaging survey of 7 nearby ($0.006 < z < 0.013$) CT AGN selected from the Swift-BAT spectroscopic AGN survey. We find that five out of the seven CT AGN show extended emission in the 3-7 keV band detected at $>$ 3$σ$ above the Chandra PSF with $\sim$12% to 22% of the total emission in the extended components. ESO 137-G034 and NGC 3281 display biconical ionization structures with extended hard X-ray emission reaching kpc-scales ($\sim$ 1.9 kpc and 3.5 kpc in diameter). The other three show extended hard X-ray emission above the PSF out to at least $\sim$360 pc in radius. We find a trend that a minimum 3-7 keV count rate of 0.01 cts/s and total excess fraction $>$20% is required to detect a prominent extended hard X-ray component. Given that this extended hard X-ray component appears to be relatively common in this uniformly selected CT AGN sample, we further discuss the implications for torus modeling and AGN feedback.

astro-ph.GA↗
arXiv2020

Hyper-massive Black Holes have Faint Broad and Narrow Emission Lines

The EUV provides most of the ionization that creates the high equivalent width (EW) broad and narrow emission lines (BELs, NELs) of quasars. Spectra of Hypermassive Schwarzschild black holes (HMBHs, $M_{BH} \geq 10^{10} M_{\odot}$) with $α$-discs, decline rapidly in the EUV suggesting much lower EWs. Model spectra for black holes of mass $10^{6}-10^{12} M_{\odot}$ and accretion rates $0.03 \leq L_{bol}/L_{edd} \leq 1.0$ were input to the CLOUDY photoionization code. BELs become $\sim$100 times weaker in EW from $M_{BH} \sim 10^8 M_{\odot}$ to $M_{BH} \sim 10^{10} M_{\odot}$. The high ionization BELs (O VI 1034 $\overset{\circ}{\mathrm {A}}$, C IV 1549 $\overset{\circ}{\mathrm {A}}$, He II 1640 $\overset{\circ}{\mathrm {A}}$) decline in EW from ($M_{BH} \geq 10^6 M_{\odot}$, reproducing the Baldwin effect, but regain EW for $M_{BH} \geq 10^{10} M_{\odot}$). The low ionization lines (MgII 2798 $\overset{\circ}{\mathrm {A}}$, H$β$ 4861 $\overset{\circ}{\mathrm {A}}$ and H$α$ 6563 $\overset{\circ}{\mathrm {A}}$) remain weak. Lines for maximally spinning HMBHs behave similarly. Line ratio diagrams for the BELs show that high OVI/H$β$ and low CIV/H$α$ may pick out HMBH, although OVI is often hard to observe. In NEL BPT diagrams HMBHs lie among star-forming regions, except for highly spinning, high accretion rate HMBHs. In summary, the BELs expected from HMBHs would be hard to detect using the current optical facilities. From 100 to $10^{12} M_{\odot}$, the emission lines used to detect AGN only have high EW in the $10^6 - 10^9 M_{\odot}$ window, where most AGN are found. This selection effect may be distorting reported distributions of $M_{BH}$.

astro-ph.GA↗
arXiv2020

Qwind code release: a non-hydrodynamical approach to modelling line-driven winds in active galactic nuclei

Ultraviolet (UV) line driven winds may be an important part of the active galactic nucleus (AGN) feedback process, but understanding their impact is hindered by the complex nature of the radiation hydrodynamics. Instead, we have taken the approach pioneered by Risaliti & Elvis, calculating only ballistic trajectories from radiation forces and gravity, but neglecting gas pressure. We have completely re-written their QWIND code using more robust algorithms, and can now quickly model the acceleration phase of these winds for any AGN spectral energy distribution spanning UV and X-ray wavebands. We demonstrate the code using an AGN with black hole mass $10^8\, M_\odot$ emitting at half the Eddington rate and show that this can effectively eject a wind with velocities $\simeq (0.1-0.2)\, c$. The mass loss rates can be up to $\simeq 0.3 M_\odot$ per year, consistent with more computationally expensive hydrodynamical simulations, though we highlight the importance of future improvements in radiation transfer along the multiple different lines of sight illuminating the wind. The code is fully public, and can be used to quickly explore the conditions under which AGN feedback can be dominated by accretion disc winds.

astro-ph.HE↗
arXiv2020

Chandra Observations of NGC 7212: Large-scale Extended Hard X-ray Emission

Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (>3 keV) X-ray emission extending out from the central supermassive black hole to kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ~parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ~150 ks. We find ~20 percent of the observed emission is found outside of the central ~kiloparsec, with ~17 percent associated with the soft X-rays, and ~3 percent with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ~3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428-G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales.

astro-ph.GA↗
arXiv2020

The Case for Probe-class NASA Astrophysics Missions

Astrophysics spans an enormous range of questions on scales from individual planets to the entire cosmos. To address the richness of 21st century astrophysics requires a corresponding richness of telescopes spanning all bands and all messengers. Much scientific benefit comes from having the multi-wavelength capability available at the same time. Most of these bands,or measurement sensitivities, require space-based missions. Historically, NASA has addressed this need for breadth with a small number of flagship-class missions and a larger number of Explorer missions. While the Explorer program continues to flourish, there is a large gap between Explorers and strategic missions. A fortunate combination of new astrophysics technologies with new, high capacity, low dollar-per-kg to orbit launchers, and new satellite buses allow for cheaper missions with capabilities approaching strategic mission levels. NASA has recognized these developments by calling for Probe-class mission ideas for mission studies, spanning most of the electromagnetic spectrum from GeV gamma-rays to the far infrared, and the new messengers of neutrinos and ultra-high energy cosmic rays. The key insight from the Probes exercise is that order-of-magnitude advances in science performance metrics are possible across the board for initial total cost estimates in the range 500M-1B dollars.

astro-ph.IM↗
arXiv2019

How much of the Solar System should we leave as Wilderness?

"How much of the Solar System should we reserve as wilderness, off-limits to human development?" We argue that, as a matter of policy, development should be limited to one eighth, with the remainder set aside. We argue that adopting a "1/8 principle" is far less restrictive, overall, than it might seem. One eighth of the iron in the asteroid belt is more than a million times greater than all of the Earth's estimated iron reserves and may suffice for centuries. A limit of some sort is needed because of the problems associated with exponential growth. Humans are poor at estimating the pace of such growth, so the limitations of a resource are hard to recognize before the final three doubling times which take utilization successively from 1/8 to 1/4 to 1/2, and then to the point of exhaustion. Population growth and climate change are instances of unchecked exponential growth. Each places strains upon ouru available resources. Each is a problem we would like to control but attempts to do so at this comparatively late stage have not been encouraging. Our limited ability to see ahead suggests that we should set ourselves a 'tripwire' that gives us at least 3 doubling times as leeway, i.e. when 1/8 of Solar System resources are close to being exploited. At a 3.5 percent growth rate for the space economy, comparable to that of the iron use from the beginning of the Industrial Revolution until now, the 1/8 point would be reached after 400 years. At that point the 20 year doubling time of a 3.5 percent growth rate means that only 60 years would remain to transition the economic system to new "steady state" conditions. The rationale for adopting the 1/8 principle now is that it may be far easier to implement in principle restrictions at an early stage, rather than later, when vested and competing interests have come into existence.

physics.pop-ph↗
arXiv2019

ASIME 2018 White Paper. In-Space Utilisation of Asteroids: Asteroid Composition -- Answers to Questions from the Asteroid Miners

In keeping with the Luxembourg government's initiative to support the future use of space resources, ASIME 2018 was held in Belval, Luxembourg on April 16-17, 2018. The goal of ASIME 2018: Asteroid Intersections with Mine Engineering, was to focus on asteroid composition for advancing the asteroid in-space resource utilisation domain. What do we know about asteroid composition from remote-sensing observations? What are the potential caveats in the interpretation of Earth-based spectral observations? What are the next steps to improve our knowledge on asteroid composition by means of ground-based and space-based observations and asteroid rendez-vous and sample return missions? How can asteroid mining companies use this knowledge? ASIME 2018 was a two-day workshop of almost 70 scientists and engineers in the context of the engineering needs of space missions with in-space asteroid utilisation. The 21 Questions from the asteroid mining companies were sorted into the four asteroid science themes: 1) Potential Targets, 2) Asteroid-Meteorite Links, 3) In-Situ Measurements and 4) Laboratory Measurements. The Answers to those Questions were provided by the scientists with their conference presentations and collected by A. Graps or edited directly into an open-access collaborative Google document or inserted by A. Graps using additional reference materials. During the ASIME 2018, first day and second day Wrap-Ups, the answers to the questions were discussed further. New readers to the asteroid mining topic may find the Conversation boxes and the Mission Design discussions especially interesting.

astro-ph.EP↗