arXiv subjects

Michael N. Fanelli

Publications and source records attributed to Michael N. Fanelli.

At least 19 recordsLinked to original sources

arXiv2024

A Break In the Size-Stellar Mass Relation: Evidence for Quenching and Feedback in Dwarf Galaxies

Mapping stars and gas in nearby galaxies is fundamental for understanding their growth and the impact of their environment. This issue is addressed by comparing the stellar "edges" of galaxies $D_{\rm stellar}$, defined as the outermost diameter where in situ star formation significantly drops, with the gaseous distribution parameterized by the neutral atomic hydrogen diameter measured at 1 $M_{sun}$/pc$^2$, $D_{HI}$. By sampling a broad HI mass range $10^5 M_{sun} < M_{HI} < 10^{11} M_{sun}$, we find several dwarf galaxies with $M_{HI} < 10^9 M_{sun}$ from the field and Fornax Cluster which are distinguished by $D_{\rm stellar} >> D_{HI}$. For the cluster dwarfs, the average HI surface density near $D_{\rm stellar}$ is $\sim$0.3 $M_{sun}$/pc$^2$, reflecting the impact of quenching and outside-in gas removal from ram pressure and tidal interactions. In comparison, $D_{\rm stellar}/D_{HI}$ ranges between 0.5-2 in dwarf field galaxies, consistent with the expectations from stellar feedback. Only more massive disk galaxies in the field can thus be characterized by the common assumption that $D_{\rm stellar} \lesssim D_{HI}$. We discover a break in the $D_{\rm stellar}-M_{\rm stellar}$ relation at $m_{break} \sim 4\times10^8 M_{sun}$ that potentially differentiates the low mass regime where the influence of stellar feedback and environmental processes more prominently regulates the sizes of nearby galaxies. Our results highlight the importance of combining deep optical and HI imaging for understanding galaxy evolution.

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arXiv2024

SAUNAS II: Discovery of Cross-shaped X-ray Emission and a Rotating Circumnuclear Disk in the Supermassive S0 Galaxy NGC 5084

Combining Chandra, ALMA, EVLA, and Hubble Space Telescope archival data and newly acquired APO/DIS spectroscopy, we detect a double-lobed 17~kpc X-ray emission with plumes oriented approximately perpendicular and parallel to the galactic plane of the massive lenticular galaxy NGC\,5084 at 0.3--2.0~keV. We detect a highly inclined ($i=71.2^{+1.8\circ}_{-1.7}$), molecular circumnuclear disk ($D=304^{+10}_{-11}$ pc) in the core of the galaxy rotating (V$^{\rm (2-1) CO}_{\rm rot}=242.7^{+9.6}_{-6.4}$ km s$^{-1}$) in a direction perpendicular to that of the galactic disk, implying a total mass of $\log_{10}\left( \frac{M_{\rm BH}}{M_{\odot}} \right) = 7.66^{+0.21}_{-0.15}$ for NGC\,5084's supermassive black hole. Archival EVLA radio observations at 6 cm and 20 cm reveal two symmetric radio lobes aligned with the galactic plane, extending to a distance of $\overline{R}=4.6\pm0.6$ kpc from the core, oriented with the polar axis of the circumnuclear disk. The spectral energy distribution lacks strong emission lines in the optical range. Three formation scenarios are considered to explain these multi-wavelength archival observations: 1) AGN re-orientation caused by accretion of surrounding material, 2) AGN-driven hot gas outflow directed along the galactic minor axis, or 3) a starburst / supernovae driven outflow at the core of the galaxy. This discovery is enabled by new imaging analysis tools including \SAUNAS\ (Selective Amplification of Ultra Noisy Astronomical Signal), demonstrating the abundance of information still to be exploited in the vast and growing astronomical archives.

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arXiv2024

SAUNAS I: Searching for Low Surface Brightness X-ray Emission with Chandra/ACIS

We present SAUNAS (Selective Amplification of Ultra Noisy Astronomical Signal), a pipeline designed for detecting diffuse X-ray emission in the data obtained with the Advanced CCD Imaging Spectrometer (ACIS) of the Chandra X-ray Observatory. SAUNAS queries the available observations in the Chandra archive, performs photometric calibration, PSF (point spread function) modeling, and deconvolution, point-source removal, adaptive smoothing, and background correction. This pipeline builds on existing and well-tested software including CIAO, VorBin, and LIRA. We characterize the performance of SAUNAS through several quality performance tests, and demonstrate the broad applications and capabilities of SAUNAS using two galaxies already known to show X-ray emitting structures. SAUNAS successfully detects the 30 kpc X-ray super-wind of NGC 3079 using Chandra/ACIS datasets, matching the spatial distribution detected with more sensitive XMM-Newton observations. The analysis performed by SAUNAS reveals an extended low surface brightness source in the field of UGC 5101 in the 0.3-1.0 keV and 1.0-2.0 keV bands. This source is potentially a background galaxy cluster or a hot gas plume associated with UGC 5101. SAUNAS demonstrates its ability to recover previously undetected structures in archival data, expanding exploration into the low surface brightness X-ray universe with Chandra/ACIS.

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arXiv2023

Flares, Warps, Truncations, and Satellite: The Ultra-thin Galaxy UGC 11859

The structure of the outskrits of galaxies provides valuable information about their past and evolution. Due to their projected orientation, edge-on isolated galaxies effectively serve as test labs in which to study the three-dimensional structures of galaxies including warps and flares, and to explore the possible sources of souch distortions. We analyzed the structure of the apparently isolated edge-on ultra-thin galaxy UGC11859 to look for the presence of disortions. The deep optical imaging observations we acquired with the GTC (Gran Telescopio Canarias) are used to derive the radial and vertical surface brightness profiles and g-r color radial profile. We find that the galaxy disk display a significant gravitational distortion. A warp is clearly detected on one side of the disk, and the galactic plane on both sides of the centre shows increasing scale height with increasing galactocentric radius, indicating the presence of a flare in the stellar distribution. The surface brightness profile of the disk shows a sharp break at 24 kiloparsecs galactocentric radius, and a steep decline to larger radii, and edge-on truncation, which we associate with the presence of the flare. The present study is the first observational support for a connection between truncations and flares. Just beyond the warped side of the disk a faint galaxy is observed within a small angular distance, identified as a potential interacting companion. Bases on ultra-deep g and r photometry we estimate that if the potential companion is at the same distance as UGC11859, the stellar mas of the satellite galaxy is approximately 6.33 log(MSol)

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arXiv2019

The Neutral Gas Properties of Extremely Isolated Early-Type Galaxies III

We report on the neutral hydrogen gas content (21-cm emission) of eight extremely isolated early-type galaxies (IEGs) using the Green Bank Telescope. Emission is detected in seven of the eight objects. This paper is the third in a series that collectively present new HI observations for 20 IEGs. Among the 14 HI detections in our observations, eight exhibit a Gaussian-like HI line profile shape, four are double-peaked, one is triple-peaked, and another has a plateaued rectangular shape. Five additional IEGs observed in previous surveys were added to our analysis, bringing the total number of IEGs with HI observations to 25. Of these objects, emission is detected in 19 (76%). The 25 IEGs in our combined study have gas masses that are systematically larger than their luminosity-matched comparison galaxy counterparts. The isolated early-type galaxies presented here follow a trend of increasing gas-richness with bluer B-V colors. This correlation is also observed in a comparison sample drawn from the literature composed of loose group and field early-type galaxies. Two IEGs, KIG164 and KIG870, exhibit properties highly anomalous for spheroidal systems: luminous (M_B = -20.5, -20.1) and blue (B-V = 0.47, 0.48) respectively, with substantial neutral gas, M_HI = 4.1 & 5.5x10^9 M_(sun). Other IEG systems may represent early-type galaxies continuing to assemble via quiescent HI accretion from the cosmic web or relaxed merged systems.

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arXiv2012

Transit Timing Observations from Kepler: IV. Confirmation of 4 Multiple Planet Systems by Simple Physical Models

Eighty planetary systems of two or more planets are known to orbit stars other than the Sun. For most, the data can be sufficiently explained by non-interacting Keplerian orbits, so the dynamical interactions of these systems have not been observed. Here we present 4 sets of lightcurves from the Kepler spacecraft, which each show multiple planets transiting the same star. Departure of the timing of these transits from strict periodicity indicates the planets are perturbing each other: the observed timing variations match the forcing frequency of the other planet. This confirms that these objects are in the same system. Next we limit their masses to the planetary regime by requiring the system remain stable for astronomical timescales. Finally, we report dynamical fits to the transit times, yielding possible values for the planets' masses and eccentricities. As the timespan of timing data increases, dynamical fits may allow detailed constraints on the systems' architectures, even in cases for which high-precision Doppler follow-up is impractical.

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arXiv2012

Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction

With the unprecedented photometric precision of the Kepler Spacecraft, significant systematic and stochastic errors on transit signal levels are observable in the Kepler photometric data. These errors, which include discontinuities, outliers, systematic trends and other instrumental signatures, obscure astrophysical signals. The Presearch Data Conditioning (PDC) module of the Kepler data analysis pipeline tries to remove these errors while preserving planet transits and other astrophysically interesting signals. The completely new noise and stellar variability regime observed in Kepler data poses a significant problem to standard cotrending methods such as SYSREM and TFA. Variable stars are often of particular astrophysical interest so the preservation of their signals is of significant importance to the astrophysical community. We present a Bayesian Maximum A Posteriori (MAP) approach where a subset of highly correlated and quiet stars is used to generate a cotrending basis vector set which is in turn used to establish a range of "reasonable" robust fit parameters. These robust fit parameters are then used to generate a Bayesian Prior and a Bayesian Posterior Probability Distribution Function (PDF) which when maximized finds the best fit that simultaneously removes systematic effects while reducing the signal distortion and noise injection which commonly afflicts simple least-squares (LS) fitting. A numerical and empirical approach is taken where the Bayesian Prior PDFs are generated from fits to the light curve distributions themselves.

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arXiv2012

Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves

Kepler provides light curves of 156,000 stars with unprecedented precision. However, the raw data as they come from the spacecraft contain significant systematic and stochastic errors. These errors, which include discontinuities, systematic trends, and outliers, obscure the astrophysical signals in the light curves. To correct these errors is the task of the Presearch Data Conditioning (PDC) module of the Kepler data analysis pipeline. The original version of PDC in Kepler did not meet the extremely high performance requirements for the detection of miniscule planet transits or highly accurate analysis of stellar activity and rotation. One particular deficiency was that astrophysical features were often removed as a side-effect to removal of errors. In this paper we introduce the completely new and significantly improved version of PDC which was implemented in Kepler SOC 8.0. This new PDC version, which utilizes a Bayesian approach for removal of systematics, reliably corrects errors in the light curves while at the same time preserving planet transits and other astrophysically interesting signals. We describe the architecture and the algorithms of this new PDC module, show typical errors encountered in Kepler data, and illustrate the corrections using real light curve examples.

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arXiv2011

Kepler-21b: A 1.6REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070

We present Kepler observations of the bright (V=8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequencypower spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ} respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3σ) that the transit event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ~10 M_Earth (2-σ). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.

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arXiv2011

Modeling Kepler Observations of Solar-like Oscillations in the Red-giant Star HD 186355

We have analysed oscillations of the red giant star HD 186355 observed by the NASA Kepler satellite. The data consist of the first five quarters of science operations of Kepler, which cover about 13 months. The high-precision time-series data allow us to accurately extract the oscillation frequencies from the power spectrum. We find the frequency of the maximum oscillation power, ν_max, and the mean large frequency separation, Δν, are around 106 and 9.4 μHz respectively. A regular pattern of radial and non-radial oscillation modes is identified by stacking the power spectra in an echelle diagram. We use the scaling relations of Δν and ν_max to estimate the preliminary asteroseismic mass, which is confirmed with the modelling result (M = 1.45 \pm 0.05 M_sun) using the Yale Rotating stellar Evolution Code (YREC7). In addition, we constrain the effective temperature, luminosity and radius from comparisons between observational constraints and models. A number of mixed l = 1 modes are also detected and taken into account in our model comparisons. We find a mean observational period spacing for these mixed modes of about 58 s, suggesting that this red giant branch star is in the shell hydrogen-burning phase.

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arXiv2011

Kepler-16: A Transiting Circumbinary Planet

We report the detection of a planet whose orbit surrounds a pair of low-mass stars. Data from the Kepler spacecraft reveal transits of the planet across both stars, in addition to the mutual eclipses of the stars, giving precise constraints on the absolute dimensions of all three bodies. The planet is comparable to Saturn in mass and size, and is on a nearly circular 229-day orbit around its two parent stars. The eclipsing stars are 20% and 69% as massive as the sun, and have an eccentric 41-day orbit. The motions of all three bodies are confined to within 0.5 degree of a single plane, suggesting that the planet formed within a circumbinary disk.

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arXiv2011

A Closely-Packed System of Low-Mass, Low-Density Planets Transiting Kepler-11

When an extrasolar planet passes in front of its star (transits), its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star that reveal six transiting planets, five with orbital periods between 10 and 47 days plus a sixth one with a longer period. The five inner planets are among the smallest whose masses and sizes have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation.

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arXiv2000

Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)

M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along with spectra from the International Ultraviolet Explorer and Lick 1-m telescopes. The wide-field UIT image shows FUV emission from (a) an elongated nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c) a bright inner ring of H II regions at the perimeter of the inner disk (R = 48 arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc). The HST/FOC image resolves the NUV emission from the nuclear region into a bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30 deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk indicates an approximately 10^7 or 10^8 yr-old stellar population from low-level starbirth activity blended with some LINER activity. Analysis of the H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers of stars and gas in M94 indicates that most of the star formation is being orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring, oval disk, and outer ring. The inner starburst ring and bi-symmetric knots at intermediate radius, in particular, argue for bar-mediated resonances as the primary drivers of evolution in M94 at the present epoch. Similar processes may be governing the evolution of the ``core-dominated'' galaxies that have been observed at high redshift. The gravitationally-lensed ``Pretzel Galaxy'' (0024+1654) at a redshift of approximately 1.5 provides an important precedent in this regard.

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arXiv2000

Far Ultraviolet Imagery of the Edge-On Spiral Galaxy NGC 4631

Far ultraviolet FUV imagery of the edge-on, Sc/SBd galaxy, NGC 4631 reveals very strong FUV emission, resulting from active star formation, uniformly distributed along the galactic mid- plane. Multi-band imagery, HI and HII position-velocity curves and extinction considerations all imply that the emission is from the outer edges of the visible galaxy. The overall FUV morphology of this edge-on disk system is remarkably similar to those of the so-called "chain galaxies" evident at high redshift, thus suggesting a similar interpretation for at least some of those distant objects. FUV, U, B and V magnitudes, measured for 48 star forming regions, along with corresponding H-alpha and H-beta measurements are used to construct diagnostic color-color diagrams. Although there are significant exceptions, most of the star forming regions are less massive and older than 30 Doradus. Comparison with the expectations from two star formation models yields ages of 2.7 to 10 Myr for the instantaneous burst (IB) model and star formation cut-off ages of 0 to 9 Myr for the continuous star formation (CSF) model. Interpreted in terms of the IB model the photometry implies a total created mass in the 48 star forming regions of 25 million solar-masses. When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33 solar-masses/yr. These results are compared to those derived from FIR and radio observations. Corrections for FUV emission reprocessed by interstellar grains are estimated.

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arXiv1998

Ultraviolet Imaging of the Irregular Galaxy NGC 4449 with UIT: Photometry and Recent Star-Formation History

The bright Magellanic irregular galaxy NGC 4449 was observed during the Astro-2 Space Shuttle mission by the Ultraviolet Imaging Telescope (UIT), which obtained images of a ~40 arcmin field centered on the galaxy in two broad far-ultraviolet (FUV) bands centered at 1520 A and 1620 A, with 3 arcsec - 5 arcsec spatial resolution. Together with H-alpha and H-beta fluxes from ground-based Fabry-Perot images, these data are analyzed in order to explore the recent star formation history of NGC 4449. Maps of the flux ratios H-alpha/FUV and FUV/blue continuum are presented and interpreted using evolutionary synthesis models. Photometry is presented both for 22 apertures containing large OB complexes and for 57 small apertures containing compact FUV-emitting knots. The OB complexes along the northern edge of the visible system have high H-alpha/FUV ratios, and thus appear to be more dominated by the current generation of stars than are other parts of the galaxy. However, young sources do exist elsewhere and are particularly conspicuous along the bar. The small aperture analysis shows three candidate regions for sequential star formation. Surface brightness profiles are consistent with an exponential disk in both the FUV and the optical continuum.

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arXiv1997

The Ultraviolet Imaging Telescope: Instrument and Data Characteristics

The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro observatory on the Space Shuttle Columbia in December 1990 and again on the Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images of a variety of astronomical objects, with a 40 arcmin field of view and a resolution of about 3 arcsec, were recorded on photographic film. The data recorded during the first flight are available to the astronomical community through the National Space Science Data Center (NSSDC); the data recorded during the second flight will soon be available as well. This paper discusses in detail the design, operation, data reduction, and calibration of UIT, providing the user of the data with information for understanding and using the data. It also provides guidelines for analyzing other astronomical imagery made with image intensifiers and photographic film.

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arXiv1996

UIT Astro-2 Observations of NGC 4449

The bright Magellanic irregular galaxy NGC 4449 was observed by the Ultraviolet Imaging Telescope (UIT) during the Astro-2 Spacelab mission in March, 1995. Far ultraviolet (FUV) images at a spatial resolution of ~3 arcsec show bright star-forming knots that are consistent with the general optical morphology of the galaxy and are often coincident with bright H II regions. Comparison of FUV with H-alpha shows that in a few regions, sequential star formation may have occurred over the last few Myr. The bright star forming complexes in NGC 4449 are superposed on a smooth, diffuse FUV background that may be associated with the H-alpha "froth."

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arXiv1996

Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy, M101

We present new evidence for tidal interactions having occurred in the disk of M101 in the last 10^8 - 10^9 years. Recent imaging of the far-ultraviolet emission from M101 by the Shuttle-borne Ultraviolet Imaging Telescope (UIT) reveals with unprecedented clarity a disk-wide pattern of multiple linear arm segments (``crooked arms''). The deep FUV image also shows a faint outer spiral arm with a (``curly tail'') feature that appears to loop around the supergiant HII region NGC 5471 - linking this outlying starburst with the rest of the galaxy. These FUV-bright features most likely trace hot O & B-type stars along with scattered light from associated nebular dust. Counterparts of the outermost ``crooked arms'' are evident in maps at visible wavelengths and in the 21-cm line of HI. The inner-disk FUV arms are most closely associated with H$α$ knots and the outer (downstream) sides of CO arms. Comparisons of the ``crooked arm'' and ``curly tail'' morphologies with dynamical simulations yield the greatest similitude, when the non- axisymmetric forcing comes from a combination of ``external interactions'' with one or more companion galaxies and ``internal perturbations'' from massive objects orbiting within the disk. We speculate that NGC 5471 represents one of these ``massive disturbers'' within the disk, whose formation followed from a tidal interaction between M101 and a smaller galaxy.

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